U.S. patent application number 15/271252 was filed with the patent office on 2017-01-12 for process for making styrene using microchannel process technology.
The applicant listed for this patent is Velocys, Inc.. Invention is credited to Francis P. Daly, Thomas P. Hickey, Kai Tod Paul Jarosch, Timothy J. LaPlante, Richard Q. Long, Jeffrey Marco, Anna Lee Tonkovich, Bin Yang.
Application Number | 20170007978 15/271252 |
Document ID | / |
Family ID | 38329597 |
Filed Date | 2017-01-12 |
United States Patent
Application |
20170007978 |
Kind Code |
A1 |
Tonkovich; Anna Lee ; et
al. |
January 12, 2017 |
PROCESS FOR MAKING STYRENE USING MICROCHANNEL PROCESS
TECHNOLOGY
Abstract
The disclosed invention relates to a process for converting
ethylbenzene to styrene, comprising: flowing a feed composition
comprising ethylbenzene in at least one process microchannel in
contact with at least one catalyst to dehydrogenate the
ethylbenzene and form a product comprising styrene; exchanging heat
between the process microchannel and at least one heat exchange
channel in thermal contact with the process microchannel; and
removing product from the process microchannel. Also disclosed is
an apparatus comprising a process microchannel, a heat exchange
channel, and a heat transfer wall positioned between the process
microchannel and heat exchange channel wherein the heat transfer
wall comprises a thermal resistance layer.
Inventors: |
Tonkovich; Anna Lee;
(Gilbert, AZ) ; Jarosch; Kai Tod Paul; (Bexley,
OH) ; Yang; Bin; (Dublin, OH) ; Daly; Francis
P.; (Waldoboro, ME) ; Hickey; Thomas P.;
(Dublin, OH) ; Marco; Jeffrey; (London, OH)
; LaPlante; Timothy J.; (Powell, OH) ; Long;
Richard Q.; (New Albany, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Velocys, Inc. |
Plain City |
OH |
US |
|
|
Family ID: |
38329597 |
Appl. No.: |
15/271252 |
Filed: |
September 21, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12958461 |
Dec 2, 2010 |
|
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15271252 |
|
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|
11690319 |
Mar 23, 2007 |
7847138 |
|
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12958461 |
|
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60785131 |
Mar 23, 2006 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 2219/00826
20130101; B01J 2219/00831 20130101; C07C 5/48 20130101; C07C
2523/28 20130101; C07C 2523/46 20130101; B01J 2219/00876 20130101;
C07C 2523/745 20130101; F28F 3/086 20130101; B01J 2219/00835
20130101; B01J 2219/00873 20130101; B01F 5/0646 20130101; C07C
15/46 20130101; C07C 5/3332 20130101; C07C 2521/02 20130101; F28F
2260/02 20130101; C07C 2523/847 20130101; B01J 2219/00869 20130101;
F28F 3/048 20130101; F28F 2270/00 20130101; B01J 2219/00828
20130101; B01F 2005/0621 20130101; C07C 2523/04 20130101; B01F
5/0483 20130101; C07C 5/48 20130101; B01J 2219/00833 20130101; B01J
2219/00891 20130101; B01J 2219/00824 20130101; C07C 2/66 20130101;
B01F 5/061 20130101; C07C 5/277 20130101; C07C 2521/06 20130101;
C07C 2523/22 20130101; F28D 9/00 20130101; F28F 21/081 20130101;
B01J 2219/00804 20130101; Y02P 20/52 20151101; C07C 2523/883
20130101; Y02P 20/582 20151101; B01J 2219/0086 20130101; C07C
2523/18 20130101; B01F 5/0475 20130101; C07C 2523/44 20130101; B01F
5/0655 20130101; B01F 13/0059 20130101; C07C 2521/10 20130101; C07C
2527/167 20130101; B01J 2219/00783 20130101; C07C 2523/30 20130101;
C07C 2523/02 20130101; B01J 2219/00844 20130101; B01J 2219/0081
20130101; C07C 2523/42 20130101; B01J 2219/00889 20130101; C07C
2/66 20130101; C07C 2523/26 20130101; C07C 2523/881 20130101; F28F
21/04 20130101; Y10S 585/921 20130101; B01F 2215/0036 20130101;
C07C 5/48 20130101; B01F 2005/0636 20130101; C07C 5/3332 20130101;
C07C 2521/08 20130101; F28F 13/12 20130101; B01J 2219/00822
20130101; C07C 2523/10 20130101; B01F 5/0478 20130101; B01J 19/0093
20130101; B01J 2219/00878 20130101; C07C 2523/888 20130101; C07C
15/073 20130101; C07C 15/46 20130101; C07C 11/04 20130101; C07C
15/46 20130101 |
International
Class: |
B01J 19/00 20060101
B01J019/00; B01F 5/04 20060101 B01F005/04; B01F 13/00 20060101
B01F013/00; F28F 21/08 20060101 F28F021/08; F28F 3/04 20060101
F28F003/04; F28F 13/12 20060101 F28F013/12; F28F 21/04 20060101
F28F021/04; C07C 5/27 20060101 C07C005/27; F28F 3/08 20060101
F28F003/08 |
Claims
1-178. (canceled)
179. An apparatus, comprising: a process microchannel; a heat
exchange channel; and a heat transfer wall positioned between the
process microchannel and the heat exchange channel, the heat
transfer wall comprising at least one thermal resistance layer.
180. The apparatus of claim 179 wherein the thermal resistance
layer is positioned on the heat transfer wall and/or embedded
within the heat transfer wall.
181. The apparatus of claim 179 wherein the thermal resistance
layer comprises a vacuum, a gaseous material, a liquid and/or a
solid material.
182. The apparatus of claim 179 wherein the thermal resistance
layer comprises a solid material which contains void spaces,
openings and/or through holes.
183. The apparatus of claim 179 wherein the thermal resistance
layer comprises one or more strips or shims which contain void
spaces, openings and/or through holes.
184. The apparatus of claim 179 wherein the thermal resistance
layer comprises one or more strips with grooves formed in the
strip.
185. The apparatus of claim 179 wherein the thermal resistance
layer comprises one or more shims, each of the shims having a first
surface and a second surface, and grooves formed in the first
surface and/or the second surface.
186. The apparatus of claim 179 wherein the process microchannel
comprises at least one structured wall.
187. The apparatus of claim 179 wherein the heat transfer wall
forms an interior wall of the process microchannel and one or more
shims are positioned on said interior wall, the one or more shims
containing void spaces, openings and/or through holes.
188. The apparatus of claim 187 wherein a catalyst is supported by
the one or more shims.
189. The apparatus of claim 179 wherein the process microchannel
has an internal dimension of width or height of up to 10 mm.
190. The apparatus of claim 179 wherein the process microchannel
has a length in the range up to 10 meters.
191. The apparatus of claim 179 wherein the process microchannel is
made of a material comprising: steel; monel; inconel; aluminum;
titanium; nickel; copper; brass; an alloy of any of the foregoing
metals; ceramics; glass; quartz; silicon; or a combination of two
or more thereof.
192. The apparatus of claim 179 wherein the process microchannel
and/or heat exchange channel contain internal surface features for
imparting a disruptive flow to fluid flowing in the process
microchannels and/or heat exchange channels.
193. The apparatus of claim 179 wherein the heat exchange channel
is a microchannel.
194. The apparatus of claim 179 wherein the heat exchange channel
is made of a material comprising: steel; monel; inconel; aluminum;
titanium; nickel; copper; brass; an alloy of any of the foregoing
metals; ceramics; glass; quartz; silicon; or a combination of two
or more thereof.
195. The apparatus of claim 179 wherein the heat transfer wall is
made of a material comprising: steel; monel; inconel; aluminum;
titanium; nickel; copper; brass; an alloy of any of the foregoing
metals; ceramics; glass; quartz; silicon; or a combination of two
or more thereof.
196. The apparatus of claim 179 wherein the heat transfer wall
and/or thermal resistance layer comprise one or more
sub-assemblies, each sub-assembly comprising two or more shims
stacked one above another with one or more void spaces positioned
between the shims.
197. The apparatus of claim 179 wherein one or more staged addition
channels are adjacent the process microchannel.
198. A microchannel reactor comprising the apparatus of claim
179.
199. An apparatus, comprising: a plurality of the microchannel
reactors of claim 198 positioned in a vessel, each microchannel
reactor comprises a plurality of process microchannels, a plurality
of heat exchange channels, and optionally a plurality of staged
addition channels, the vessel being equipped with a manifold for
flowing a feed to the process microchannels, a manifold for flowing
product from the process microchannels, a manifold for flowing heat
exchange fluid to the heat exchange channels, optionally a manifold
for flowing oxygen or a source of oxygen to the staged addition
channels, and a manifold for flowing heat exchange fluid from the
heat exchange channels.
200. The apparatus of claim 199 wherein each microchannel reactor
comprises from 1 to 50,000 process microchannels, and the vessel
comprises 1 to 1000 microchannel reactors.
Description
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Application Ser. No. 60/785,131
filed Mar. 23, 2006. The disclosure in this provisional application
is incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention relates to a process for making styrene using
microchannel process technology.
BACKGROUND
[0003] Styrene is typically produced commercially by
dehydrogenating ethylbenzene in the presence of an iron-based
catalyst. This reaction is endothermic and equilibrium limited. The
process is usually operated at temperatures between about
600-850.degree. C. and at atmospheric or sub-atmospheric pressure.
Steam is often co-fed to the reactor with the ethylbenzene. A
problem with the process is that it consumes a high level of
energy. The conversion of ethylbenzene is typically below 65% to
maintain selectivity to styrene in excess of 95%. As a result,
reactant recycles are often needed. However, the separation of
unreacted ethylbenzene from styrene is costly due to the close
boiling points of ethylbenzene (136.degree. C.) and styrene
(145.degree. C.).
[0004] The use of oxidative dehydrogenation of ethylbenzene has
been suggested as a substitute for the dehydrogenation of
ethylbenzene. Thus far this process has not been commercialized.
This reaction is exothermic. Although high styrene selectivities
may be achieved, ethylbenzene conversions less than 60% are
typically obtained in order to provide for such high selectivities.
An increase in the reaction temperature may increase the
ethylbenzene conversion, but styrene selectivity tends to decrease
significantly due to combustion of styrene and ethylbenzene. The
presence of hot spots in the catalyst bed tends to sinter the
catalyst resulting in catalyst deactivation.
[0005] This invention, in at least one embodiment, provides a
solution to these problems.
SUMMARY
[0006] This invention relates to a process for converting
ethylbenzene to styrene, comprising: flowing a feed composition
comprising ethylbenzene in at least one process microchannel in
contact with at least one catalyst to dehydrogenate the
ethylbenzene and form a product comprising styrene; exchanging heat
between the process microchannel and at least one heat exchange
channel in thermal contact with the process microchannel; and
removing product from the process microchannel.
[0007] In one embodiment, the gas hourly space velocity for the
flow of the feed composition in the process microchannel may be at
least about 1000 normal liters of feed per hour per liter of
volume. The conversion of ethylbenzene may be at least about 50%
per cycle or per pass through the process microchannel. The
selectivity to styrene may be at least about 70%.
[0008] In one embodiment, the catalyst may comprise at least one
dehydrogenation catalyst.
[0009] In one embodiment, the feed composition may be combined with
oxygen and the catalyst may comprise at least one oxidative
dehydrogenation catalyst.
[0010] In one embodiment, a staged addition feed stream comprising
the oxygen may flow in a staged addition channel, the staged
addition channel being adjacent to the process microchannel, the
process microchannel having an entrance for the feed composition,
the feed composition entering the process microchannel through the
entrance for the feed composition, the staged addition feed stream
flowing from the staged addition channel into the process
microchannel, the staged addition feed stream entering the process
microchannel downstream of the entrance for the feed composition
and contacting the feed composition in the process
microchannel.
[0011] In one embodiment, the process may be conducted in a
microchannel reactor comprising a plurality of the process
microchannels and a plurality of the heat exchange channels.
[0012] In one embodiment, the invention relates to a process for
converting ethylbenzene to styrene, comprising: flowing a feed
composition comprising ethylbenzene in at least one process
microchannel in contact with at least one catalyst to dehydrogenate
the ethylbenzene and form a product comprising styrene; exchanging
heat between the process microchannel and at least one heat
exchange channel in thermal contact with the process microchannel;
and removing product from the process microchannel; wherein the
catalyst comprises at least one dehydrogenation catalyst; the
catalyst being supported on a support, the support comprising a
microgrooved support strip with a support strip having a length
with a center axis extending along the length, a first surface, a
first side edge, a second side edge, a front edge extending from
the first side edge to the second side edge, a back edge extending
from the first side edge to the second side edge, a plurality of
parallel microgrooves in the first surface extending between the
first side edge and the second side edge at an angle relative to
the center axis sufficient to permit fluid flowing in the
microgrooves to flow in a direction from the front edge to the back
edge of the microgrooved strip. In one embodiment, the microgrooves
project part way through the support strip from the first surface
to the second surface. In one embodiment, the microgrooves project
all the way through the support strip thereby providing open
microgrooves that may be suitable for permitting fluid to flow
through the support strip. In one embodiment, process fluids may
flow over or by the microgrooves in a flow-by manner. In one
embodiment, the microgrooves may extend across the entire width of
the process microchannel, and in one embodiment they may extend
over only part of the width of the process microchannel.
[0013] In one embodiment, the invention relates to a process for
converting ethylbenzene to styrene, comprising: flowing a feed
composition comprising ethylbenzene in at least one process
microchannel in contact with at least one catalyst to dehydrogenate
the ethylbenzene and form a product comprising styrene; exchanging
heat between the process microchannel and at least one heat
exchange channel in thermal contact with the process microchannel;
and removing product from the process microchannel; wherein the
catalyst comprises at least one dehydrogenation catalyst; the
catalyst being supported by a composite support structure, the
composite support structure being a flow through structure, the
feed composition contacting the catalyst in the composite support
structure and reacting to form the product, the composite support
structure comprising: at least one first support strip comprising a
first surface, a second surface, a length with a center axis
extending along the length, a front edge, a back edge, a first side
edge, a second side edge, the front edge and the back edge
extending from the first side edge and to the second side edge, a
plurality of parallel microgrooves in the first surface extending
from the front edge to the second side edge, and a plurality of
parallel microgrooves in the first surface extending from first
side edge to the back edge; at least one second support strip
comprising a first surface, a second surface, a length with a
center axis extending along the length, a front edge, a back edge,
a first side edge, a second side edge, the front edge and the back
edge extending from the first side edge to the second side edge, a
plurality of parallel microgrooves in the first surface extending
from the front edge to the first side edge, and a plurality of
parallel microgrooves in the first surface extending from second
side edge to the back edge; the first support strip being adjacent
to the second support strip with the second surface of the first
support strip contacting the first surface of the second support
strip; the front and back edges of each of the support strips being
open to permit fluid to flow through the front and back edges; the
side edges of each of the support strips being closed to prevent
fluid from flowing through the side edges; each of the microgrooves
penetrating through the support strips sufficiently to permit fluid
to flow through the support strips from one support strip to
another; the microgrooves in the first surface of the first support
strip being oriented toward the front edge and the first side edge
of the first support strip and forming an angle with the center
axis of more than about 0.degree. and less than 90.degree.; and the
microgrooves in the first surface of the second support strip being
oriented toward the front edge and the first side edge of the
second support strip and forming an angle with the center axis of
more than 90.degree. and less than about 180.degree..
[0014] In one embodiment, the invention relates to a process for
converting ethylbenzene to styrene, comprising: flowing a feed
composition comprising ethylbenzene in at least one process
microchannel in contact with at least one catalyst to dehydrogenate
the ethylbenzene and form a product comprising styrene; exchanging
heat between the process microchannel and at least one heat
exchange channel in thermal contact with the process microchannel;
and removing product from the process microchannel; wherein the
feed composition is combined with oxygen and the catalyst comprises
at least one oxidative dehydrogenation catalyst; wherein the
catalyst is supported on a support, the support comprising a
microgrooved support strip with a support strip having a length
with a center axis extending along the length, a first surface, a
first side edge, a second side edge, a front edge extending from
the first side edge to the second side edge, a back edge extending
from the first side edge to the second side edge, a plurality of
parallel microgrooves in the first surface extending between the
first side edge and the second side edge at an angle relative to
the center axis sufficient to permit fluid flowing in the
microgrooves to flow in a direction from the front edge to the back
edge of the microgrooved support strip.
[0015] In one embodiment, the invention relates to a process for
converting ethylbenzene to styrene, comprising: flowing a feed
composition comprising ethylbenzene in at least one process
microchannel in contact with at least one catalyst to dehydrogenate
the ethylbenzene and form a product comprising styrene; exchanging
heat between the process microchannel and at least one heat
exchange channel in thermal contact with the process microchannel;
and removing product from the process microchannel; wherein the
feed composition is combined with oxygen and the catalyst comprises
at least one oxidative dehydrogenation catalyst; and wherein the
catalyst is supported by a composite support structure, the
composite support structure being a flow through structure, the
feed composition and oxygen contacting the catalyst in the
composite support structure and reacting to form the product, the
composite support structure comprising: at least one first support
strip comprising a first surface, a second surface, a length with a
center axis extending along the length, a front edge, a back edge,
a first side edge, a second side edge, the front edge and the back
edge extending from the first side edge and to the second side
edge, a plurality of parallel microgrooves in the first surface
extending from the front edge to the second side edge, and a
plurality of parallel microgrooves in the first surface extending
from first side edge to the back edge; at least one second support
strip comprising a first surface, a second surface, a length with a
center axis extending along the length, a front edge, a back edge,
a first side edge, a second side edge, the front edge and the back
edge extending from the first side edge to the second side edge, a
plurality of parallel microgrooves in the first surface extending
from the front edge to the first side edge, and a plurality of
parallel microgrooves in the first surface extending from second
side edge to the back edge; the first support strip being adjacent
to the second support strip with the second surface of the first
support strip contacting the first surface of the second support
strip; the front and back edges of each of the support strips being
open to permit fluid to flow through the front and back edges; the
side edges of each of the support strips being closed to prevent
fluid from flowing through the side edges; each of the microgrooves
penetrating through the support strips sufficiently to permit fluid
to flow through the support strips from one support strip to
another; the microgrooves in the first surface of the first support
strip being oriented toward the front edge and the first side edge
of the first support strip and forming an angle with the center
axis of more than about 0.degree. and less than 90.degree.; and the
microgrooves in the first surface of the second support strip being
oriented toward the front edge and the first side edge of the
second support strip and forming an angle with the center axis of
more than 90.degree. and less than about 180.degree..
[0016] In one embodiment, the invention relates to a process for
converting ethylbenzene to styrene, comprising: flowing a feed
composition comprising ethylbenzene in at least one process
microchannel in contact with at least one catalyst to dehydrogenate
the ethylbenzene and form a product comprising styrene; exchanging
heat between the process microchannel and at least one heat
exchange channel in thermal contact with the process microchannel;
and removing product from the process microchannel; wherein the
feed composition is combined with oxygen and the catalyst comprises
at least one oxidative dehydrogenation catalyst; wherein a staged
addition feed stream comprising the oxygen flows in a staged
addition channel, the staged addition channel being adjacent to the
process microchannel, the process microchannel having an entrance
for the feed composition, the feed composition entering the process
microchannel through the entrance for the feed composition, the
staged addition feed stream flowing from the staged addition
channel into the process microchannel, the staged addition feed
stream entering the process microchannel downstream of the entrance
for the feed composition and contacting the feed composition in the
process microchannel.
[0017] In one embodiment, the invention relates to an apparatus,
comprising: a process microchannel; a heat exchange channel; and a
heat transfer wall positioned between the process microchannel and
the heat exchange channel, the heat transfer wall comprising at
least one thermal resistance layer. This apparatus may be used as a
repeating unit in a microchannel reactor.
[0018] In one embodiment, the invention relates to a microchannel
reactor comprising the foregoing apparatus.
[0019] In one embodiment, the invention relates to an apparatus,
comprising: a plurality of the foregoing microchannel reactors
positioned in a vessel, each microchannel reactor comprises a
plurality of process microchannels, a plurality of heat exchange
channels, and optionally a plurality of staged addition channels;
the vessel being equipped with a manifold for flowing a feed to the
process microchannels, a manifold for flowing product from the
process microchannels, a manifold for flowing heat exchange fluid
to the heat exchange channels, optionally a manifold for flowing
oxygen or a source of oxygen to the staged addition channels, and a
manifold for flowing heat exchange fluid from the heat exchange
channels. In one embodiment, each microchannel reactor may comprise
from about 1 to about 50,000 process microchannels, and the vessel
may comprise from 1 to about 1000 microchannel reactors.
[0020] This invention, in at least one embodiment, provides the
advantage of increasing product yield and energy efficiency by
improving heat and mass transfer performance. With this invention
it is possible to reduce capital costs by reducing the size of
processing equipment and the number of downstream separation units.
Catalyst productivity may be enhanced by allowing the catalyst to
operate in its peak performance window and by avoiding hot spots.
With this invention it is possible to provide cost-effective plant
expansion by adding incremental capacity with favorable
economics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the annexed drawings, like parts and features have like
designations. A number of the annexed drawings are schematic
illustrations which are not necessarily proportioned accurately or
drawn to scale.
[0022] FIG. 1 is a schematic illustration of a microchannel which
may be used in accordance with the invention.
[0023] FIG. 2 is a flow sheet illustrating one embodiment of a
process for making styrene in accordance with the invention.
[0024] FIG. 3 is a flow sheet illustrating an alternate embodiment
of a process for making styrene in accordance with the
invention.
[0025] FIG. 4 is a flow sheet illustrating another alternate
embodiment of a process for making styrene in accordance with the
invention.
[0026] FIG. 5 is a flow sheet illustrating another alternate
embodiment of a process for making styrene in accordance with the
invention.
[0027] FIG. 6 is a schematic illustration of a microchannel reactor
that may be used in accordance with the invention, the microchannel
reactor comprising a plurality of repeating units comprising one or
more process microchannels containing a catalyst, and heat exchange
channels for exchanging heat with the process microchannels.
[0028] FIG. 7 is a schematic illustration of a layer of process
microchannels and a layer of heat exchange channels that may be
used in the microchannel reactor illustrated in FIG. 6. Each of the
process microchannels may contain a catalyst.
[0029] FIG. 8 is a schematic illustration of a repeating unit
comprising a process microchannel that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel contains a reaction zone comprising a catalyst. The
catalyst illustrated in FIG. 8 is in the form of a bed of
particulate solids. However, any of the catalyst forms discussed in
the specification may be used in the process microchannel
illustrated in FIG. 8.
[0030] FIG. 9 is a schematic illustration of an alternate
embodiment of a repeating unit that may be used in the microchannel
reactor illustrated in FIG. 6. This repeating unit comprises a
process microchannel and two adjacent staged addition channels.
Each of the staged addition channels has a common wall with the
process microchannel and an apertured section positioned in each of
the common walls. The process microchannel contains a reaction zone
comprising a catalyst. The catalyst illustrated in FIG. 9 is in the
form of particulate solids. However, a catalyst having any of the
forms discussed in the specification may be used in the reaction
zone. This repeating unit may be used for oxidative dehydrogenation
processes wherein a staged addition feed stream comprising oxygen
flows from the staged addition channel through the apertured
section into the process microchannel where it contacts and mixes
with a feed composition comprising ethylbenzene and reacts to form
styrene.
[0031] FIG. 10 is a schematic illustration of another alternate
embodiment of a repeating unit that may be used in the microchannel
reactor illustrated in FIG. 6. The repeating unit comprises a
process microchannel which contains a reaction zone. A catalyst is
positioned in the reaction zone. The repeating unit also includes a
staged addition channel adjacent to the process microchannel and an
apertured section positioned between the process microchannel and
the staged addition channel. This repeating unit may be used for
oxidative dehydrogenation processes wherein a staged addition feed
stream comprising oxygen flows from the staged addition channel
through the apertured section into the process microchannel where
it contacts and mixes with a feed composition comprising
ethylbenzene and reacts to form styrene. The staged addition feed
stream and the feed composition contact each other in a mixing zone
upstream of the reaction zone.
[0032] FIG. 11 is a schematic illustration of an alternate
embodiment of the repeating unit illustrated in FIG. 10 wherein the
staged addition feed stream and the feed composition contact and
mix with each other in the reaction zone.
[0033] FIG. 12 is a schematic illustration of another alternate
embodiment of the repeating unit illustrated in FIG. 10 wherein
part of the staged addition feed stream contacts and mixes with the
feed composition in a mixing zone upstream of a reaction zone, and
part of the staged feed stream contacts and mixes with the feed
composition in the reaction zone.
[0034] FIG. 13 is a scanning electron microscopic (SEM) image of a
porous stainless steel substrate before being heat treated. This
substrate may be used for making an apertured section for a process
microchannel used with the inventive process.
[0035] FIG. 14 is an SEM image of the substrate illustrated in FIG.
13 after being heat treated. This substrate may be used for making
an apertured section for a process microchannel used with the
inventive process.
[0036] FIG. 15 is an SEM image of a tailored porous substrate which
may be used for making an apertured section for a process
microchannel used with the inventive process.
[0037] FIG. 16 is a plan view of an apertured sheet which may be
used in making an apertured section for a process microchannel used
with the inventive process.
[0038] FIG. 17 is a plan view of an apertured sheet or plate which
may be used in making an apertured section for a process
microchannel used with the inventive process.
[0039] FIG. 18 is an illustration of a relatively thin apertured
sheet overlying a relatively thick apertured sheet or plate which
may be used in making an apertured section for a process
microchannel used with the inventive process.
[0040] FIG. 19 is an illustration of a relatively thin apertured
sheet overlying a relatively thick apertured sheet or plate which
may be used in making an apertured section for a process
microchannel used with the inventive process.
[0041] FIG. 20 is an illustration of an alternate embodiment of an
aperture that may be used in the apertured section of a process
microchannel used with the inventive process, the aperture having a
coating partially filling it and overlying its sidewalls.
[0042] FIG. 21 is a schematic illustration of the reaction zone of
a process microchannel that may be used with the inventive process,
the reaction zone comprising a catalyst having a packed bed
configuration.
[0043] FIG. 22 is a schematic illustration of the reaction zone of
a process microchannel that may be used with the inventive process,
the reaction zone comprising a catalyst having a flow-by
configuration.
[0044] FIG. 23 is a schematic illustration of the reaction zone of
a process microchannel that may be used with the inventive process,
the reaction zone comprising a catalyst having a flow-through
configuration.
[0045] FIG. 24 is a schematic illustration of a process
microchannel that may be used in the inventive process, the process
microchannel containing a fin assembly comprising a plurality of
fins, a catalyst being supported by the fins.
[0046] FIG. 25 is a schematic illustration of an alternate
embodiment of the process microchannel and fin assembly illustrated
in FIG. 24.
[0047] FIG. 26 is a schematic illustration of an another alternate
embodiment of the process microchannel and fin assembly illustrated
in FIG. 24.
[0048] FIG. 27 is a schematic illustration of a microgrooved
support strip that may be used to support a catalyst for use with
the inventive process, the support strip comprising a top surface,
a bottom surface, a front edge, back edge and side edges. The edges
may be sufficiently open to permit fluid to flow through the
edges.
[0049] FIG. 28 is a schematic illustration of a microgrooved
support strip similar to the support strip illustrated in FIG. 27
with the exception that the front edge and the back edge of the
microgrooved support strip illustrated in FIG. 28 are closed and
thus do not permit fluid to flow through the front and back
edges.
[0050] FIG. 29 is a schematic illustration of a microgrooved
support strip similar to the support strip illustrated in FIG. 28
with the exception that the side edges of the microgrooved support
strip illustrated in FIG. 29 are closed and thus do not permit
fluid to flow through the side edges. The microgrooves may
penetrate part way or all the way through the support strip.
Penetration of the microgrooves all the way through the support
strip may permit fluid to flow through the microgrooves in the
direction from the top surface to the bottom surface, or vice
versa.
[0051] FIG. 30 is a schematic illustration showing a plurality of
microgrooved support strips stacked one above another forming a
composite support structure, the front and back edges of each of
the microgrooved support strips being open sufficiently to permit
fluid to flow through such edges. The microgrooves in each of the
support strips project through the support strips sufficiently to
permit fluid to flow through the support strips from one support
strip to another.
[0052] FIG. 31 is a schematic illustration of an exploded view of
the composite support structure illustrated in FIG. 30. The support
structure illustrated in FIG. 31 comprises four (4) first
microgrooved support strips and four (4) second microgrooved
support strips positioned side by side in alternating sequence. The
microgrooves in each of the support strips project through the
support strips sufficiently to permit fluid to flow through the
support strips from one support strip to another. The first
microgrooved support strips employ microgrooves that form angles
with the center axis of the support strips that are oriented toward
the front edges and first side edges of the support strips and are
more than about 0.degree. and less than 90.degree., for example, in
the range from about 60.degree. to about 80.degree.. The second
microgrooved support strips employ microgrooves that form angles
with the center axis of the support strips that are oriented toward
the front edges and first side edges of the support strips and are
more than 90.degree. and less than about 180.degree., for example,
in the range from about 100.degree. to about 120.degree..
[0053] FIG. 32(a) is a schematic illustration of a repeating unit
comprising a process microchannel that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel contains a microgrooved support strip as illustrated
in FIG. 28, the microgrooved support strip supporting a catalyst.
FIG. 32(b) is a cross-sectional view of the process microchannel
illustrated in FIG. 32(a) taken along line (b)-(b) in FIG.
32(a).
[0054] FIG. 33 is a schematic illustration of a repeating unit
comprising a process microchannel that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel is similar to the process microchannel illustrated in
FIG. 32(a) with the exception that the process microchannel
illustrated in FIG. 33(a) contains opposite interior walls and a
catalyst supporting microgrooved support strip positioned on each
of the opposite interior walls. FIG. 33(b) is a cross-sectional
view of the process microchannel illustrated in FIG. 33(a) taken
along line (b)-(b) of FIG. 33(a).
[0055] FIG. 34(a) is a schematic illustration of a repeating unit
comprising a process microchannel that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel contains a catalyst supporting composite support
structure of the type illustrated in FIGS. 30 and 31. FIG. 34(b) is
a cross-sectional view of the process microchannel illustrated in
FIG. 34(a) taken along line (b)-(b).
[0056] FIG. 35 is a photograph of a microgrooved support structure
suitable for supporting a catalyst for use with the inventive
process, the support structure being made of an alloy of iron,
chromium, aluminum and yttrium, the thickness of the support
structure being 0.002 inch (50.8 microns), the ribs dividing the
microgrooves having a thickness of 0.007 inch (178 microns), and
the microgrooves having a width of 0.007 inch (178 microns).
[0057] FIG. 36 is a photograph of a microgrooved support structure
similar to the support structure illustrated in FIG. 35 with the
exception that the microgrooved support structure illustrated in
FIG. 36 is made of stainless steel.
[0058] FIG. 37 is a microphotograph enlarged 50.times. showing a
microgrooved support structure with catalyst particles deposited in
the microgrooves of the microgrooved support structure, the
microgrooved support structure being made of stainless steel 304,
the catalyst comprising 0.7% K.sub.2O-15%
MoO.sub.3/SiO.sub.2--TiO.sub.2.
[0059] FIG. 38 is a photograph of a process microchannel containing
two catalyst supporting microgrooved support structures of the type
illustrated in FIG. 28. The process microchannel has a length of
2.5 inches (6.35 cm), a width of 0.5 inch (12.7 mm), and a height
of 0.002 inch (50.8 microns). A top plate for the process
microchannel is shown on the right side of FIG. 38.
[0060] FIG. 39 is a schematic illustration of a repeating unit
comprising a process microchannel that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel contains a catalyst supporting microgrooved support
strip on one interior wall of the process microchannel and surface
features for modifying the flow of process fluid in the process
microchannel on an opposite interior wall. The microgrooved support
strip corresponds to the microgrooved support strip illustrated in
FIG. 28. The surface features are in the form of spherical
depressions in the interior wall of the process microchannel. The
flow of process fluid through the process microchannel is indicated
by the arrows in FIG. 39.
[0061] FIG. 40 is a schematic illustration of a repeating unit
comprising a process microchannel that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel contains a catalyst supporting microgrooved support
strip on one interior wall of the process microchannel and surface
features for modifying the flow of process fluid in the process
microchannel on an opposite interior wall. The microgrooved support
strip corresponds to the microgrooved support strip illustrated in
FIG. 28. The surface features are in the form of frustrum
depressions in the interior wall of the process microchannel. The
flow of process fluid through the process microchannel is indicated
by the arrows in FIG. 40.
[0062] FIG. 41 is a schematic illustration of a repeating unit
comprising a process microchannel that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel contains a catalyst supporting microgrooved support
strip on one wall of the process microchannel and surface features
for modifying the flow of process fluid in the process microchannel
on an opposite interior wall. The microgrooved support strip
corresponds to the microgrooved support strip illustrated in FIG.
28. The surface features are in the form of angled rectangular
depressions in the interior wall of the process microchannel. The
flow of process fluid through the process microchannel is indicated
by the arrows in FIG. 41.
[0063] FIG. 42 is a schematic illustration of a modified version of
the surface features illustrated in FIG. 39, 40 or 41 that may be
used in combination with the catalyst supporting microgrooved
support strip illustrated in FIG. 39, 40 or 41. The surface
features illustrated in FIG. 42 comprise depressions in or
projections from the microchannel wall which are in the form of
vanes.
[0064] FIG. 43 is a schematic illustration of a modified version of
the surface features illustrated in FIG. 39, 40 or 41 that may be
used in combination with the catalyst supporting microgrooved
support strip illustrated in FIG. 39, 40 or 41. The surface
features illustrated in FIG. 43 comprise depressions in or
projections from the microchannel wall which are in the form of air
foils.
[0065] FIG. 44 is a schematic illustration of a modified version of
the surface features illustrated in FIG. 39, 40 or 41 that may be
used in combination with the catalyst supporting microgrooved
support strip illustrated in FIG. 39, 40 or 41. The surface
features illustrated in FIG. 44 comprise angular rectangular
depressions in or projections from the microchannel wall.
[0066] FIG. 45 is a schematic illustration of various surface
feature designs that may be used in the process microchannels
illustrated in FIG. 39, 40 or 41 in combination with a catalyst
supporting microgrooved support strip. Each of the configurations
illustrated in FIG. 45 comprise depressions in or projections from
the process microchannel wall.
[0067] FIG. 46 is a schematic illustration of a microchannel
reactor that may be used in accordance with the inventive process,
the microchannel reactor being used in combination with an adjacent
preheat section and a downstream cool down section.
[0068] FIG. 47 is a schematic illustration that is identical to
FIG. 46 with the exception that a styrene knockout drum for
collecting styrene is provided downstream of the cool-down
section.
[0069] FIG. 48 is a schematic illustration of a repeating unit
comprising a process microchannel and a heat exchange channel that
may be used in the microchannel reactor illustrated in FIG. 6. The
process microchannel contains a reaction zone comprising a catalyst
supporting microgrooved support strip corresponding to the support
strip illustrated in FIG. 28. The flow of heat exchange fluid in
the heat exchange channel may be co-current or counter-current
relative to the flow of process fluid in the process
microchannel.
[0070] FIG. 49 is a schematic illustration of a repeating unit
comprising a process microchannel and a plurality of heat exchange
channels that may be used in the microchannel reactor illustrated
in FIG. 6. The process microchannel contains a reaction zone
comprising a catalyst supporting microgrooved support strip
corresponding to the support strip illustrated in FIG. 28. The flow
of heat exchange fluid in the heat exchange channels is
cross-current relative to the flow of process fluid in the process
microchannel.
[0071] FIG. 50 is a schematic illustration of a repeating unit
comprising two adjacent process microchannels, and a plurality of
heat exchange channels that may be used in the microchannel reactor
illustrated in FIG. 6. The process microchannels contain reaction
zones comprising catalyst supporting microgrooved support strips
corresponding to the support strip illustrated in FIG. 28. The heat
exchange channels are adjacent to one of the process microchannel
and in thermal contact with the other process microchannel. The
flow of heat exchange fluid in the heat exchange channels is
cross-current relative to the flow of process fluid in the process
microchannels.
[0072] FIG. 51 is a schematic illustration of a repeating unit
similar to the repeating unit illustrated in FIG. 49 with the
exception that the repeating unit illustrated in FIG. 51 includes
additional heat exchange channels near the exit of the process
microchannel. These additional heat exchange channels may be used
to provide for additional heating or cooling.
[0073] FIG. 52 is a schematic illustration of a repeating unit
comprising a process microchannel, a staged addition channel, and a
plurality of heat exchange channels that may be used in the
microchannel reactor illustrated in FIG. 6. The process
microchannel contains a reaction zone comprising a catalyst
supporting microgrooved support strip corresponding to the support
strip illustrated in FIG. 28. The staged addition channel and the
process microchannel have a common wall with an apertured section
positioned in the common wall. A feed composition comprising
ethylbenzene flows in the process microchannel. A staged addition
feed stream comprising oxygen flows from the staged addition
channel through the apertured section into the process microchannel
where it contacts and mixes with the feed composition. The oxygen
and ethylbenzene react in the presence of the catalyst to form
styrene. Heat exchange fluid flows in the heat exchange channels in
a direction that is cross-current relative to the direction of flow
of process fluids in the process microchannel.
[0074] FIG. 53 is a schematic illustration of a repeating unit that
is similar to the repeating unit illustrated in FIG. 52 with the
exception that the repeating unit illustrated in FIG. 53 contains
two adjacent sets of process microchannels, staged addition
channels and apertured sections. One of these sets is adjacent to
the heat exchange channels while the other set is in thermal
contact with the heat exchange channels.
[0075] FIG. 54 is a schematic illustration of a test set up for the
test runs reported in Examples 7 and 8.
[0076] FIG. 55 is a chart showing conversion of ethylbenzene and
selectivity to styrene for tests reported in Examples 1-5, 7 and
8.
[0077] FIG. 56 consists of drawings of the body backing plate used
in the microchannel reactor disclosed in Example 7.
[0078] FIG. 57 consists of drawings of the body cover plate used in
the microchannel reactor disclosed in Example 7.
[0079] FIG. 58 is a schematic illustration of the microchannel
reactor disclosed in Example 7.
[0080] FIG. 59 is a schematic illustration of a shim which has a
front or first surface and a back or second surface, and grooves or
microgrooves formed in each surface, the grooves or microgrooves in
the front or first surface intersecting the grooves or microgrooves
in the back or second surface with the result being the formation
of a plurality of voids, through holes or openings in the shim.
[0081] FIG. 60 is a schematic illustration of a composite structure
comprising a plurality of the shims illustrated in FIG. 59.
[0082] FIG. 61 is a schematic illustration of an apparatus which
comprises a process microchannel, a heat exchange channel and a
heat transfer wall positioned between the process microchannel and
heat exchange channel, the heat transfer wall comprising a thermal
resistance layer.
[0083] FIG. 62 is a schematic illustration of the process
microchannel illustrated in FIG. 61.
[0084] FIG. 63 is a plot of heat flux for the flow of heat through
the heat transfer wall for the process reported in Example 9.
[0085] FIG. 64 is a plot of temperature profile for the process
reported in Example 9.
[0086] FIG. 65 is a schematic illustration of the process
microchannel and heat transfer wall shown in FIG. 61.
[0087] FIG. 66 is a schematic illustration of a thermal resistance
layer and a formula for calculating heat flux.
[0088] FIG. 67 is a plot showing temperature profiles at three
locations within the microchannel reactor discussed in Example 9
wherein the contact time is 200 ms.
[0089] FIG. 68 is a plot showing temperature profiles at three
locations within the microchannel reactor discussed in Example 9
wherein the contact time is 2,000 ms.
[0090] FIG. 69 is a plot showing heat flux through the heat
transfer wall of the microchannel reactor discussed in Example 9
wherein the contact time is 2,000 ms.
[0091] FIG. 70 is a plot showing heat flux through the heat
transfer wall of the microchannel reactor discussed in Example 9
wherein the contact time is 200 ms.
[0092] FIG. 71 is a plot showing three temperature profiles within
a microchannel reactor for the process reported in Example 10.
[0093] FIG. 72 is a plot showing heat flux for heat flowing through
the heat transfer wall for the process reported in Example 10.
[0094] FIG. 73 is a plot showing three temperature profiles within
a microchannel reactor for the process reported in Example 11.
[0095] FIG. 74 is a plot showing heat flux for heat flowing through
the heat transfer wall for the process reported in Example 11.
[0096] FIG. 75 is a schematic illustration of the process
microchannel and heat transfer wall for the process reported in
Example 12.
[0097] FIG. 76 is a plot of temperature profiles for the positions
P1 through P5 in the microchannel reactor discussed in Example
12.
[0098] FIGS. 77 and 78 are schematic illustrations of a
pressurizable vessel that may be used for housing microchannel
reactors provided for in accordance with the invention.
DETAILED DESCRIPTION
[0099] All ranges and ratio limits disclosed in the specification
may be combined. It is to be understood that unless specifically
stated otherwise, references to "a," "an," and/or "the" may include
one or more than one and that reference to an item in the singular
may also include the item in the plural.
[0100] The term "microchannel" may refer to a channel having at
least one internal dimension of height or width of up to about 10
millimeters (mm), and in one embodiment up to about 5 mm, and in
one embodiment up to about 2 mm, and in one embodiment up to about
1 mm. The microchannel may comprise at least one inlet and at least
one outlet wherein the at least one inlet is distinct from the at
least one outlet. The microchannel may not be merely an orifice.
The microchannel may not be merely a channel through a zeolite or a
mesoporous material. An example of a microchannel that may be used
with the inventive process as a process microchannel and/or a heat
exchange microchannel is illustrated in FIG. 1. Referring to FIG.
1, the illustrated microchannel has a height (h), width (w) and
length (l). Fluid may flow through the microchannel in the
direction indicated by the arrows. Both the height (h) and width
(w) are perpendicular to the flow of fluid through the
microchannel. The height (h) or width (w) of the microchannel may
be in the range of about 0.05 to about 10 mm, and in one embodiment
from about 0.05 to about 5 mm, and in one embodiment from about
0.05 to about 2 mm, and in one embodiment from about 0.05 to about
1.5 mm, and in one embodiment from about 0.05 to about 1 mm, and in
one embodiment from about 0.05 to about 0.75 mm, and in one
embodiment from about 0.05 to about 0.5 mm. The other dimension of
height (h) or width (w) may be of any dimension, for example, up to
about 3 meters, and in one embodiment about 0.01 to about 3 meters,
and in one embodiment about 0.1 to about 3 meters. The length (l)
of the microchannel may be of any dimension, for example, up to
about 10 meters, and in one embodiment from about 0.1 to about 10
meters, and in one embodiment from about 0.2 to about 10 meters,
and in one embodiment from about 0.2 to about 6 meters, and in one
embodiment from 0.2 to about 3 meters. Although the microchannel
illustrated in FIG. 1 has a cross section that is rectangular, it
is to be understood that the microchannel may have a cross section
having any shape, for example, a square, circle, semi-circle,
trapezoid, etc. The shape and/or size of the cross section of the
microchannel may vary over its length. For example, the height or
width may taper from a relatively large dimension to a relatively
small dimension, or vice versa, over the length of the
microchannel.
[0101] The term "process microchannel" may refer to a microchannel
wherein a process is conducted. The process may relate to
converting ethylbenzene (EB) to styrene. The process microchannel
may contain one or more catalysts.
[0102] The term "microchannel reactor" may refer to an apparatus
comprising at least one process microchannel for conducting a
reaction. The reactor may be used for converting ethylbenzene to
styrene. The microchannel reactor may comprise a plurality of the
process microchannels that may be operated in parallel, a header or
manifold assembly for providing for the flow of fluid into the
process microchannels, and a footer or manifold assembly providing
for the flow of fluid out of the process microchannels. The
microchannel reactor may comprise one or more heat exchange
channels, for example heat exchange microchannels, adjacent to
and/or in thermal contact with the process microchannels for
cooling and/or heating the contents of the process
microchannels.
[0103] The term "structured wall" or "SW" may refer to an interior
channel wall, for example, a microchannel wall, with one or more
strips or shims positioned or mounted on its surface. The strips or
shims may contain one or more void spaces, openings or through
holes. Two or more layers of the strips or shims may be stacked one
above another or positioned side by side to provide a porous
structure positioned or mounted on the channel wall. A catalyst may
be supported by the structured wall. An open bulk flow region or
gap may be positioned in the process microchannel adjacent the
structured wall.
[0104] The term "structured wall reactor" may refer to a
microchannel reactor comprising at least one process microchannel
wherein the process microchannel contains one or more structured
walls. A catalyst may be supported by the one or more structured
walls. An open bulk flow region or gap may be positioned in the
process microchannel adjacent the structured wall.
[0105] The term "volume" with respect to volume within a process
microchannel may include all volume in the process microchannel a
process fluid may flow through or flow by. This volume may include
the volume within the void spaces, openings or holes in a
structured wall within the process microchannel. This volume may
include volume within surface features that may be positioned in
the process microchannel and adapted for the flow of fluid in a
flow-through manner or in a flow-by manner.
[0106] The term "shim" may refer to a planar or substantially
planar sheet or plate. The thickness of the shim may be the
smallest dimension of the shim and may be up to about 2 mm, and in
one embodiment in the range from about 0.05 to about 2 mm, and in
one embodiment in the range of about 0.05 to about 1 mm, and in one
embodiment in the range from about 0.05 to about 0.5 mm. The shim
may have any length and width.
[0107] The term "surface feature" may refer to a depression in a
microchannel wall and/or a projection from a microchannel wall that
modifies flow and/or mixing within the microchannel. The surface
features may be in the form of circles, spheres, frustrums,
oblongs, squares, rectangles, angled rectangles, checks, chevrons,
vanes, air foils, wavy shapes, and the like. The surface features
may contain subfeatures where the major walls of the surface
features further contain smaller surface features that may take the
form of notches, waves, indents, holes, burrs, checks, scallops,
and the like. The surface features may have a depth, a width, and
for non-circular surface features a length. Examples are
illustrated in FIGS. 39-45. The surface features may be formed on
or in one or more of the interior walls of the process
microchannels. The surface features may be positioned in or on one
or more strips or shims used to form one or more structured walls
within a microchannel. The surface features may be formed on or in
one or more of the apertured sections that may be used with the
process microchannels. The surface features may be formed on or in
one or more of the interior walls of the heat exchange channels
employed herein. The surface features may be referred to as passive
surface features or passive mixing features. The surface features
may be used to disrupt laminar flow streamlines and create
advective flow at an angle to the bulk flow direction. The surface
features may be used to enhance contact between reactants and
catalyst, or enhance heat transfer.
[0108] The term "microgroove" may refer to a groove in a substrate
having a depth of up to about 1000 microns, and in one embodiment
in the range from about 1 to about 1000 microns, and in one
embodiment in the range from about 1 to about 500 microns, and in
one embodiment from about 1 to about 100 microns. The substrate may
be a strip or shim used as a support structure for a catalyst
and/or to form a structured wall. The microgrooves may penetrate
all the way through the substrate over part or all of the length of
the microgrooves. The microgrooves may penetrate only partially
through the substrate. The depth of the microgrooves may be
measured at the deepest point of penetration into the substrate.
The microgrooves may have a width up to about 1000 microns, and in
one embodiment in the range from about 0.1 to about 1000 microns,
and in one embodiment in the range from about 1 to about 500
microns. The width may be the width measured at the widest point of
the microgroove. The microgroove may have any length, for example,
up to about 100 cm, and in one embodiment from about 0.1 to about
100 cm, and in one embodiment from about 0.1 to about 10 cm. The
microgroove may have a cross section of any shape. Examples include
square, rectangle, vee, semi-circle, dovetail, trapezoid, and the
like. The shape and/or size of the cross section of the microgroove
may vary over the length of the microgroove.
[0109] The term "heat exchange channel" may refer to a channel
having a heat exchange fluid in it that may give off heat and/or
absorb heat. The heat exchange channel may be a microchannel.
[0110] The term "heat transfer wall" may refer to a common wall
between a process microchannel and an adjacent heat exchange
channel where heat transfers from one channel to the other through
the common wall.
[0111] The term "thermal resistance layer" may refer to a layer on
either or both sides of a heat transfer wall or embedded within a
heat transfer wall that reduces the flow of heat through the heat
transfer wall. In one embodiment, the thermal resistance layer is
embedded within the heat transfer wall and may not directly contact
the interior of the process microchannel and/or the interior of the
heat exchange channel. The thermal resistance layer may comprise a
vacuum, a gaseous material (e.g., air or an inert gas), a liquid
material (e.g., a high boiling liquid) and/or a solid material. The
solid material may contain void spaces, openings or through holes.
The thermal resistance layer may be made of the same or
substantially the same material as the heat transfer wall except
that it may have a lower density than the heat transfer wall. The
thermal resistance layer and/or heat transfer wall may comprise one
or more sub-assemblies of a thermal resistant construction. Each
sub-assembly may comprise two or more shims stacked one above
another with one or more void spaces positioned between the shims.
The void spaces may comprise a vacuum or a gas such as air or an
inert gas. The thermal resistance layer may comprise any desired
number of these sub-assemblies stacked one above another, for
example, from 1 to about 100 sub-assemblies. The thermal resistance
layer may comprise one or more strips or shims containing void
spaces, openings and/or through holes. The strips or shims may
contain grooves (e.g., microgrooves) in either or both sides of the
strips or shims. The thermal resistance layer may comprise a
plurality of strips or shims containing void spaces, openings
and/or through holes, the strips or shims being stacked one above
another resulting in the formation of a porous structure. The
thermal resistance layer may be constructed of any suitable
material that provides desired properties of thermal resistance
(e.g., metal, metal alloy, ceramics, glass, quartz, silicon,
polymer, or combinations of two or more thereof, etc.). The thermal
resistance layer may have a void volume in the range from about 1%
to about 99%, and in one embodiment from about 10% to about 90%.
Alternatively, the thermal resistance layer may have a non-solid
volume in the range from about 1% to about 99%, and in one
embodiment from about 10% to about 90%. The thermal resistance
layer may have a varying solid to void ratio or solid to non-solid
ratio over the length and/or width of the heat transfer wall. The
thermal resistance layer may have physical properties and/or a form
that varies as a function of distance over the length of the heat
transfer wall. For example, the thermal resistance layer may
exhibit heat transfer characteristics that are relatively low at
the entrance to a process microchannel and increase gradually or
abruptly to a higher level near the exit of the process
microchannel, or vice versa. The thermal resistance layer may
change in composition gradually or abruptly as a function of
distance from one location to another along the length of the heat
transfer wall. The thickness of the thermal resistance layer may
comprise from about 1 to about 99% of the thickness of the heat
transfer wall, and in one embodiment from about 10 to about
90%.
[0112] The term "heat exchange fluid" may refer to a fluid that may
give off heat and/or absorb heat.
[0113] The term "adjacent" when referring to the position of one
channel relative to the position of another channel may mean
directly adjacent such that a wall separates the two channels. This
wall may vary in thickness. However, "adjacent" channels may not be
separated by an intervening channel that would interfere with heat
transfer between the channels.
[0114] The term "thermal contact" may refer to two bodies, for
example channels, that are not necessarily in contact with each
other or adjacent to each other but still may exchange heat with
each other. Thus, for example, one body in thermal contact with
another body may heat or cool the other body.
[0115] The term "fluid" may refer to a gas, a liquid, or a gas or a
liquid containing dispersed solids, or a mixture thereof. The fluid
may be in the form of a gas containing dispersed liquid
droplets.
[0116] The term "bulk flow region" may refer to open areas within a
process microchannel. A contiguous bulk flow region may allow rapid
fluid flow through a process microchannel without significant
pressure drops. In one embodiment there may be laminar flow in the
bulk flow region. A bulk flow region may comprise at least about
5%, and in one embodiment from about 30 to about 80% of the
internal volume of a process microchannel or the cross-sectional
area of the process microchannel.
[0117] The term "residence time," which may also be referred to as
the "average residence time," may be the internal volume of a
channel occupied by a fluid flowing through the channel divided by
the average volumetric flowrate for the fluid flowing through the
channel at the temperature and pressure being used.
[0118] The terms "upstream" and "downstream" may refer to positions
within a channel (e.g., a process microchannel) that is relative to
the direction of flow of a fluid stream in the channel. For
example, a position within the channel not yet reached by a portion
of a fluid stream flowing toward that position would be downstream
of that portion of the fluid stream. A position within the channel
already passed by a portion of a fluid stream flowing away from
that position would be upstream of that portion of the fluid
stream. The terms "upstream" and "downstream" do not necessarily
refer to a vertical position since the channels used herein may be
oriented horizontally, vertically or at an inclined angle.
[0119] The terms "standard cubic feet" or "standard cubic meters"
refer to volumes measured at a temperature of 20 EC and atmospheric
pressure.
[0120] The term "normal liters" refers to volumes measured at a
temperature of 20.degree. C. and atmospheric pressure.
[0121] The term "gauge pressure" refers to absolute pressure, less
atmospheric pressure. For example, a gauge pressure of zero
atmospheres corresponds to atmospheric pressure. However,
throughout the text and in the appended claims, unless otherwise
indicated, all pressures are absolute pressures.
[0122] The term "graded catalyst" may refer to a catalyst with one
or more gradients of catalytic activity. The graded catalyst may
have a varying concentration or surface area of a catalytically
active metal. The graded catalyst may have a varying turnover rate
of catalytically active sites. The graded catalyst may have
physical properties and/or a form that varies as a function of
distance. For example, the graded catalyst may have an active metal
concentration that is relatively low at the entrance to a process
microchannel and increases to a higher concentration near the exit
of the process microchannel, or vice versa; or a lower
concentration of catalytically active metal nearer the center
(i.e., midpoint) of a process microchannel and a higher
concentration nearer a process microchannel wall, or vice versa,
etc. The thermal conductivity of a graded catalyst may vary from
one location to another within a process microchannel. The surface
area of a graded catalyst may be varied by varying size of
catalytically active metal sites on a constant surface area
support, or by varying the surface area of the support such as by
varying support type or particle size. A graded catalyst may have a
porous support where the surface area to volume ratio of the
support is higher or lower in different parts of the process
microchannel followed by the application of the same catalyst
coating everywhere. A combination of two or more of the preceding
embodiments may be used. The graded catalyst may have a single
catalytic component or multiple catalytic components (for example,
a bimetallic or trimetallic catalyst). The graded catalyst may
change its properties and/or composition gradually as a function of
distance from one location to another within a process
microchannel. The graded catalyst may comprise rimmed particles
that have "eggshell" distributions of catalytically active metal
within each particle. The graded catalyst may be graded in the
axial direction along the length of a process microchannel or in
the lateral direction. The graded catalyst may have different
catalyst compositions, different loadings and/or numbers of active
catalytic sites that may vary from one position to another position
within a process microchannel. The number of catalytically active
sites may be changed by altering the porosity of the catalyst
structure. This may be accomplished using a washcoating process
that deposits varying amounts of catalytic material. An example may
be the use of different porous catalyst thicknesses along the
process microchannel length, whereby a thicker porous structure may
be left where more activity is required. A change in porosity for a
fixed or variable porous catalyst thickness may also be used. A
first pore size may be used adjacent to an open area or gap for
flow and at least one second pore size may be used adjacent to the
process microchannel wall.
[0123] The term "conversion of oxygen" refers to the oxygen mole
change between reactant (including all oxygen added using staged
addition) and product divided by the moles of oxygen in the
reactant.
[0124] The term "conversion of ethylbenzene" refers to the
ethylbenzene mole change between reactant and product divided by
the moles of ethylbenzene in the reactant.
[0125] The term "selectivity to styrene" refers to the moles of
styrene produced divided by the moles of styrene produced plus
moles of ethylbenzene in the product.
[0126] The term "cycle" refers to a single pass of the reactants
through the process microchannels.
[0127] The term "ml (milliliter) per gram of catalyst per hour"
refers to a volume (ml) of product produced per gram of catalyst
per hour wherein the gram of catalyst refers to catalytic material
in the catalyst but not any support that may be present.
[0128] The term "yield" refers to moles of reactant converted to a
specific product (for example, styrene) divided by the number of
moles of reactant converted. The yield may be calculated by
[0129] The term "mm" may refer to millimeter. The term "nm" may
refer to nanometer. The term "ms" may refer to millisecond. The
term ".mu.m" may refer to micron or micrometer. The terms "micron"
and "micrometer" have the same meaning and may be used
interchangeably.
[0130] The inventive process for converting ethylbenzene (EB) to
styrene may be a dehydrogenation (DH) process or an oxidative
dehydrogenation (ODH) process. The dehydrogenation reaction is an
endothermic reaction, while the oxidative dehydrogenation reaction
is an exothermic reaction. Although both processes may be conducted
in a microchannel reactor in accordance with the invention, heat
management with the oxidative dehydrogenation process may be easier
and therefore advantageous. The inventive process for making
styrene may be employed in a process where ethylene is formed in a
microchannel reactor upstream of the styrene forming microchannel
reactor. Also, the ethylbenzene may be formed upstream of the
styrene forming microchannel reactor in an alkylation reactor. The
alkylation reactor may be a microchannel reactor or a conventional
alkylation reactor. When the process is an oxidative
dehydrogenation process, oxygen or a source of oxygen may be used.
The source of oxygen may be air or oxygen enriched air. The
ethylbenzene may be mixed with air and/or steam. Flow sheets
illustrating a number of these processes are provided in FIGS.
2-5.
[0131] Referring to FIG. 2, ethane (C2) is dehydrogenated (DH) in a
first microchannel reactor to form ethylene (C2=). The ethylene is
fed with benzene (BZ) to an alkylation reactor where ethylbenzene
(EB) is formed. The ethylbenzene is then dehydrogenated to form
styrene in a second microchannel reactor. Styrene and ethylbenzene
are separated and the unreacted ethylbenzene may be recycled.
[0132] In the process illustrated in FIG. 3, ethane is oxidatively
dehydrogenated (ODH) in a first microchannel reactor to form
ethylene. The ethylene is fed together with benzene to an
alkylation reactor to produce ethylbenzene. Ethylbenzene is then
dehydrogenated to form styrene in a second microchannel reactor.
Styrene and ethylbenzene are separated and the unreacted
ethylbenzene may be recycled.
[0133] In the process illustrated in FIG. 4, ethane is oxidatively
dehydrogenated in a first microchannel reactor to form ethylene.
The ethylene is fed together with benzene to an alkylation reactor
to form ethylbenzene. Ethylbenzene is then oxidatively
dehydrogenated in a second microchannel reactor to form styrene.
Styrene and ethylbenzene are separated and the unreacted
ethylbenzene may be recycled.
[0134] In the process illustrated in FIG. 5, benzene and recycled
ethylene are fed to an alkylation reactor to produce ethylbenzene.
Ethane, ethylbenzene, oxygen and recouped hydrogen are fed to a
microchannel reactor to be simultaneously oxidatively
dehydrogenated to for styrene. Styrene, unreacted ethylene and
hydrogen are separated. The ethylene may be recycled to the
alkylation unit. The recouped hydrogen may be totally or partially
co-fed to the microchannel oxidative dehydrogenation reactor.
[0135] The following description of the microchannel reactor used
to make styrene in accordance with the inventive process is also
applicable to the microchannel reactors used upstream for making
ethylene and ethylbenzene. In one embodiment, the microchannel
reactor may be in the form illustrated in FIG. 6. Referring to FIG.
6, microchannel reactor 100 comprises microchannel reactor core
110, feed inlet 120, product outlet 130, heat exchange fluid inlet
140, and heat exchange fluid outlet 150. The microchannel reactor
core 110 may comprise a plurality of repeating units, each of the
repeating units comprising one or more process microchannels. The
process microchannels may be operated in parallel in combination
with a header or manifold assembly for providing for the flow of
reactants into the process microchannels, and a footer or manifold
assembly providing for the flow of product out of the process
microchannels. The microchannel reactor core 110 may further
comprise one or more heat exchange channels adjacent to and/or in
thermal contact with the process microchannels. The heat exchange
channels may be microchannels. When the reaction that is conducted
in the process microchannels is an exothermic reaction, the heat
exchange channels may be used to cool the process microchannels.
When the reaction that is conducted in the process microchannels is
an endothermic reaction, the heat exchange channels may be used to
heat the process microchannels. The heat exchange change channels
may be used to preheat one or more reactants and/or cool down the
product. Various combinations of heating and/or cooling may be
employed to provide for desired temperature profiles along the
lengths of the process microchannels. Each of the process
microchannels may contain a catalyst. The catalyst may be in any of
the forms discussed below and is positioned in reaction zones in
the process microchannels. In operation, a feed composition
comprising ethylbenzene flows into the microchannel reactor core
110 as indicated by arrow 120. Optionally, oxygen may be combined
with the feed composition when the reaction is an oxidative
dehydrogenation reaction. When oxygen is employed in the reaction,
the ethylbenzene and oxygen may be mixed upstream of the
microchannel reactor 100, in the header or manifold assembly of the
microchannel reactor core 110, or in the process microchannels
within the microchannel reactor core 110. Within each process
microchannel, the ethylbenzene and oxygen may be mixed with each
other in a mixing zone upstream of the reaction zone or in the
reaction zone. Part of the oxygen may be mixed with the
ethylbenzene in a mixing zone upstream of the reaction zone, and
part of the oxygen may be mixed with the ethylbenzene in the
reaction zone. When the oxygen and ethylbenzene are mixed with each
other in the process microchannels, the oxygen may enter the
process microchannels as a staged addition feed stream. The
ethylbenzene, or the ethylbenzene in combination with oxygen, may
undergo reaction in the process microchannels to form a product
comprising styrene. The product flows through the footer or
manifold assembly in the microchannel reactor core 110 and out of
the microchannel reactor core 110 as indicated by arrow 130. Heat
exchange fluid enters the microchannel reactor core 110 as
indicated by arrow 140, circulates through heat exchange channels
in the microchannel reactor core 110, heats or cools the process
microchannels, and flows out of the microchannel reactor core 110
as indicated by arrow 150.
[0136] The microchannel reactor core 110 may be positioned adjacent
to or in thermal contact with a preheat section and/or upstream
from a cool down section. The preheat section may be positioned
adjacent to or in thermal contact with the cool down section. The
preheat section and cool down section may each comprise a plurality
of process microchannels that are the same as or similar to the
process microchannels in the microchannel core 110 except that the
process microchannels in the preheat and cool down sections do not
contain catalyst. This is illustrated in FIGS. 46 and 47. Referring
to FIG. 46, microchannel reactor 100A is the same as microchannel
reactor 100 illustrated in FIG. 6 except that the microchannel
reactor 100A further comprises preheat section 112 and cool down
section 114. The microchannel reactor core 110 may be operated at a
temperature in the range from about 220.degree. C. to about
850.degree. C., and in one embodiment about 300.degree. C. to about
550.degree. C. for a dehydrogenation process. For an oxidative
dehydrogenation process the microchannel core 110 may be operated
at a temperature in the range from about 300.degree. C. to about
550.degree. C., and in one embodiment from about 350.degree. C. to
about 500.degree. C. Heat from the microchannel reactor core 110
may be used to heat reactants flowing into the microchannel reactor
core 110 through preheat section 112. The reactants may be heated
in the preheat section 112 from room temperature or ambient
temperature up to the temperature in the microchannel reactor core
110. In one embodiment, the reactants may be heated in the preheat
section 112 from room temperature or ambient temperature to a
temperature in the range from about 50.degree. C. to about
500.degree. C., and in one embodiment in the range from about
150.degree. C. to about 400.degree. C. Similarly, the relatively
cool reactants entering the preheat section 112, as indicated by
arrow 120, may be used to cool the relatively hot product flowing
out of the microchannel reactor core 110 through the cool-down
section 114, as indicated by arrow 130. In the cool down section
114 the product may be cooled to a temperature in the range from
about 550.degree. C. to about 250.degree. C., and in one embodiment
from about 450.degree. C. to about 300.degree. C. Additional
cooling may be employed in the cool down using a relatively cool
heat exchange fluid flowing in heat exchange channels, which may be
microchannels, in the cool down section 114. This process may be
conducted in an apparatus having a box-like construction wherein
the microchannel reactor and cool-down sections 114 are adjacent to
the preheat section 112 as illustrated in FIG. 46.
[0137] The process illustrated in FIG. 47 is the same as the
process illustrated in FIG. 46 with the exception that the
microchannel reactor 100B illustrated in FIG. 47 also includes
styrene knockout drum 134 which cools the product flowing from the
cool-down section 114 as indicated by arrow 130. The temperature of
the product stream entering the styrene knockout drum 134 may be in
the range from about 350.degree. C. to about 50.degree. C., and in
one embodiment about 250.degree. C. The product flowing out of the
styrene knockout drum 134 may be at a temperature in the range from
about 100.degree. C. to about -20.degree. C., and in one embodiment
about 5.degree. C. The residence time of the product in the styrene
knockout drum 134 may be in the range from about 0.01 to about 1000
seconds, and in one embodiment from about 10 to about 100 seconds.
The product stream flows out of the knockout drum as indicated by
arrow 136. The knockout drums 134 may be in the form of any vessel
or container suitable for receiving the product flowing out of the
cool down section 114. The internal volume of the knockout drum 134
may be relatively large compared to the internal volume of the
process microchannels in the microchannel reactor core 110. For
example, the internal volume of the knockout drum 134 may be up to
about 10000 times the internal volume of the process microchannels,
and in one embodiment from about 4 to about 10000 times the
internal volume of the process microchannels in the microchannel
reactor core 110. The knockout drum 134 may be useful in preventing
or reducing the tendency of the product styrene to polymerize.
[0138] In one embodiment, the microchannel reactor core 110 may
contain layers 200 of process microchannels and layers 250 of heat
exchange channels (e.g., microchannels) aligned side by side as
illustrated in FIG. 7. Alternately, the layers 200 and 250 may be
stacked one above the other. For each heat exchange layer 250, one
or more process microchannel layers 200 may be used. Thus, for
example, two, three, four, five, six or more process microchannel
layers 200 may be employed with a single heat exchange layer 250.
Alternatively, two or more heat exchange layers 250 may be employed
with each process microchannel layer 200. Process microchannel
layer 200 comprises a plurality of process microchannels 210 which
provide for the flow of process fluid. Heat exchange microchannel
layer 250 comprises a plurality of heat exchange microchannels 260
which provide for the flow of heat exchange fluid. The heat
exchange layers 250 may be used for heating or cooling. In one
embodiment, each process microchannel layer 200 may be positioned
between adjacent heat exchange microchannel layers 250 on each side
of the process microchannel layer 200. In one embodiment, two or
more process microchannel layers 200 may be positioned adjacent to
each other to form a vertically or horizontally oriented stack of
process microchannel layers, and a heat exchange layer 250 may be
positioned on one or both sides of the stack. In various
embodiments of the invention, layers of staged addition channels,
which may be microchannels, may be used in combination with the
process microchannels, and for these embodiments one or more layers
of the staged addition channels may be positioned adjacent to each
of the process microchannel layers. Each combination of one or more
process microchannel layers 200, heat exchange channel layers 250
and optional staged addition channels layers may be referred to as
a repeating unit.
[0139] The process microchannels 210 in process microchannel layer
200 may be aligned in parallel. Each process microchannel 210 may
extend along the length of microchannel layer 200 from end 212 to
end 214. The process microchannels 210 may extend along the width
of the process microchannel layer 200 from end 216 to end 218. The
catalyst may be positioned in the process microchannels 210. The
flow of process fluid through the process microchannels 210 may be
in the direction indicated by arrows 220 and 222. The staged
addition channels, when used, may be configured in the same way as
the process microchannels 210 except that the staged addition
channels do not contain a catalyst. For each process microchannel
210, one or more adjacent staged addition channels may be used. The
process microchannels and staged addition channels may have at
least one common wall with an opening to permit flow of fluid from
the staged addition channel into the process microchannel at
various or numerous points along the length of the process
microchannel.
[0140] The heat exchange microchannels 260 may be aligned in
parallel in heat exchange microchannel layer 250. Each heat
exchange microchannel 260 may extend along the width of
microchannel layer 250 from end 266 to end 268. The heat exchange
microchannels 260 may extend along the length of microchannel layer
250 from end 262 to end 264 of microchannel layer 250. The heat
exchange fluid may flow through the heat exchange microchannels 260
in the direction indicated by arrows 270 and 272. The flow of heat
exchange fluid in the direction indicated by arrows 270 and 272 may
be cross-current to the flow of process fluid flowing through
process microchannels 210, as indicated by arrows 220 and 222.
Alternatively, the heat exchange microchannels 260 may be oriented
to provide for flow of the heat exchange fluid along the length of
the microchannel layer 250 from end 262 to end 264 or from end 264
to end 262. This would result in the flow of heat exchange fluid in
a direction that would be cocurrent or counter-current to the flow
of process fluid through the process microchannels 210.
[0141] The number of microchannels 210 and 260 in each of the
microchannel layers 200 and 250, as well as the number of channels
in the optional staged addition layers, may be any desired number,
for example, one, two, three, four, five, six, eight, ten,
hundreds, thousands, tens of thousands, hundreds of thousands,
millions, etc. The number of repeating units containing process
microchannel layers, heat exchange channel layers and optionally
staged addition channel layers that may be used in the microchannel
reactor core 110 may be any number, for example, one, two, three,
four, five, six, eight, ten, hundreds, thousands, etc.
[0142] A number of repeating units that may be used in the
microchannel reactor core 110 are illustrated in FIGS. 8-12. The
microchannel reactor core 110 may contain any number of these
repeating units, for example, one, two, three, four, five, six,
eight, ten, hundreds, thousands, etc. The repeating unit 201
illustrated in FIG. 8 comprises process microchannel 210 which
includes reaction zone 212 wherein catalyst 215 is situated. The
catalyst 215 illustrated in FIG. 8 is in the form of a bed of
particulate solids. However, any of the catalyst forms discussed in
the specification may be used in the process microchannel
illustrated in FIG. 8. One or more heat exchange channels may be
positioned adjacent to one or both sides of the process
microchannel 210. Alternatively, one or more heat exchange channels
may be positioned remotely from, but in thermal contact with, the
process microchannel 210.
[0143] The repeating unit 202 illustrated in FIG. 9 comprises
process microchannel 210 and adjacent staged addition channels 280
and 280A. The staged addition channels may be microchannels
although alternatively they may be larger channels. Each of the
staged addition channels 280 and 280A has a common wall 281 and
281A with the process microchannel 210 and an apertured section 290
and 290A positioned in each of the common walls 281 and 281A. Each
of the apertured sections 290 and 290A contain a plurality of
apertures 293 and 293A for permitting the flow of the staged
addition feed stream through the apertured sections. The process
microchannel 210 contains a reaction zone 212 wherein catalyst 215
is situated. The catalyst illustrated in FIG. 9 is in the form of
particulate solids. However, a catalyst having any of the forms
discussed in the specification may be used in the reaction
zone.
[0144] Repeating unit 202A, which may be used in the microchannel
reactor core 110, is illustrated in FIG. 10. Repeating unit 202A
comprises process microchannel 210, staged addition channel 280,
and apertured section 290. A common wall 281 separates process
microchannel 210 and staged addition channel 280. The apertured
section 290 is positioned in common wall 281. The apertured section
290 contains a plurality of apertures 293 for permitting the flow
of staged addition feed stream through the apertured section. The
process microchannel 210 has a mixing zone 211, and a reaction zone
212. Microgrooved support strip 400A, which supports a catalyst, is
positioned in the reaction zone 212. The support strip 400A is
described below. The mixing zone 211 is upstream from the reaction
zone 212. A feed composition comprising ethylbenzene flows into
process microchannel 210, as indicated by the arrow 220, and into
the mixing zone 211. A staged addition feed stream comprising
oxygen flows into staged addition channel 280, as indicated by
arrow 282, and from the staged addition channel 280 through the
apertured section 290 into mixing zone 211, as indicated by arrows
292. The direction of flow of the staged addition feed stream in
the staged addition channel 280, as indicated by arrow 282, is
cocurrent with the direction of flow of the feed composition in the
process microchannel 210, as indicated by arrow 220. Alternatively,
the flow of staged addition feed stream in the staged addition
channel 280 may be counter-current or cross-current relative to the
flow of the feed composition in the process microchannel 210. The
feed composition and staged addition contact each other in the
mixing zone 211 and form a reactant mixture. The reactant mixture
flows from the mixing zone 211 into the reaction zone 212, contacts
the catalyst, and reacts to form the product comprising styrene.
The product exits the process microchannel 210, as indicated by
arrow 222. A heat exchange channel may be positioned adjacent to
the staged addition channel 280 or the process microchannel 210.
Alternatively, one or more heat exchange channels may be positioned
remotely from, but in thermal contact with, the staged addition
channel 280 and/or the process microchannel 210. In either case the
heat exchange channels may exchange heat with the process fluids in
the staged addition channel 280 and the process microchannel
210.
[0145] In an alternate embodiment of the repeating unit 202
illustrated in FIG. 10, a supplemental mixing zone may be provided
in the process microchannel 210 between the mixing zone 211 and the
reaction zone 212.
[0146] The repeating unit 202B illustrated in FIG. 11 is identical
to the repeating unit 202A illustrated in FIG. 10 with the
exception that the repeating unit 202B does not contain the
separate mixing zone 211. With repeating unit 202B, the staged
addition feed stream flows through the apertured section 290 into
the reaction zone 212 where it contacts the feed composition and
reacts in the presence of the catalyst to form the product
comprising styrene. The product then flows out of the process
microchannel 210, as indicated by arrow 222.
[0147] The repeating unit 202C illustrated in FIG. 12 is identical
to the repeating unit 202A illustrated in FIG. 10 with the
exception that part of the staged addition feed stream mixes with
the feed composition in the mixing zone 211, and part of the staged
addition feed stream mixes with the feed composition in the
reaction zone 212. The amount of the staged addition feed stream
that mixes with the feed composition in the mixing zone 211 may be
from about 1% to about 99% by volume of the staged addition feed
stream, and in one embodiment from about 5% to about 95% by volume,
and in one embodiment from about 10% to about 90% by volume, and in
one embodiment from about 20% to about 80% by volume, and in one
embodiment from about 30% to about 70% by volume, and in one
embodiment from about 40% to about 60% by volume of the staged
addition feed stream. The remainder of the staged addition feed
stream mixes with the feed composition in the reaction zone
212.
[0148] The apertures 293 and 293A may be of sufficient size to
permit the flow of the staged addition feed stream through the
apertured sections 290 and 290A, respectively. The apertures may be
referred to as pores. The apertured sections 290 and 290A
containing the foregoing apertures may have thicknesses in the
range from about 0.01 to about 50 mm, and in one embodiment about
0.05 to about 10 mm, and in one embodiment about 0.1 to about 2 mm.
The apertures may have average diameters in the range up to about
250 microns, and in one embodiment up to about 100 microns, and in
one embodiment up to about 50 microns, and in one embodiment in the
range from about 0.001 to about 50 microns, and in one embodiment
from about 0.05 to about 50 microns, and in one embodiment from
about 0.1 to about 50 microns. In one embodiment, the apertures may
have average diameters in the range from about 0.5 to about 10
nanometers (nm), and in one embodiment about 1 to about 10 nm, and
in one embodiment about 5 to about 10 nm. The number of apertures
in the apertured sections may be in the range from about 1 to about
5.times.10.sup.8 apertures per square centimeter, and in one
embodiment about 1 to about 1.times.10.sup.6 apertures per square
centimeter. The apertures may or may not be isolated from each
other. A portion or all of the apertures may be in fluid
communication with other apertures within the apertured section.
That is, a fluid may flow from one aperture to another aperture.
The ratio of the thickness of the apertured sections 290 and 290A
to the length of the apertured sections along the flow path of the
fluids flowing through the process microchannels 210 may be in the
range from about 0.001 to about 1, and in one embodiment about 0.01
to about 1, and in one embodiment about 0.03 to about 1, and in one
embodiment about 0.05 to about 1, and in one embodiment about 0.08
to about 1, and in one embodiment about 0.1 to about 1.
[0149] In one embodiment, the apertured sections 290 and 290A may
comprise an interior portion that forms part of one or more of the
interior walls of each process microchannel 210. A surface feature
sheet may overlie this interior portion of the apertured section.
Surface features may be formed in and/or on the surface feature
sheet. The staged addition feed stream may flow through the
apertured section and the surface feature sheet into the process
microchannel. Part of the staged addition feed stream may be
detached from the surface of the surface feature sheet while part
may flow within the surface features of the surface feature sheet.
The surface feature sheet may contain angled surface features that
have relatively small widths or spans relative to the overall flow
length. The surface feature sheet may provide mechanical support
for the apertured section. The surface features may impart a
vortical flow pattern to the staged addition feed stream. The
vortical flow pattern may impart shear to the staged addition feed
stream flowing through the apertured section and thus reduce the
size of the staged addition feed stream bubbles or droplets in the
bulk flow path.
[0150] The apertured sections 290 and 290A may be constructed of
any material that provides sufficient strength and dimensional
stability to permit the operation of the inventive process. These
materials include: steel (e.g., stainless steel, carbon steel, and
the like); monel; inconel; aluminum; titanium; nickel; platinum;
rhodium; copper; chromium; brass; alloys of any of the foregoing
metals; polymers (e.g., thermoset resins); ceramics; glass;
composites comprising one or more polymers (e.g., thermoset resins)
and fiberglass; quartz; silicon; microporous carbon, including
carbon nanotubes or carbon molecular sieves; zeolites; or a
combination of two or more thereof. The apertures may be formed
using known techniques such as laser drilling, microelectro
machining system (MEMS), lithography electrodeposition and molding
(LIGA), electrical sparkling, photochemical machining (PCM),
electrochemical machining (ECM), electrochemical etching, and the
like. The apertures may be formed using techniques used for making
structured plastics, such as extrusion, or membranes, such as
aligned carbon nanotube (CNT) membranes. The apertures may be
formed using techniques such as sintering or compressing metallic
powder or particles to form tortuous interconnected capillary
channels and the techniques of membrane fabrication. The apertures
may be reduced in size from the size provided by any of these
methods by the application of coatings over the apertures internal
side walls to partially fill the apertures. The selective coatings
may also form a thin layer exterior to the porous body that
provides the smallest pore size adjacent to the continuous flow
path. The smallest average pore opening may be in the range from
about one nanometer to about several hundred microns depending upon
the desired droplet size for the emulsion. The apertures may be
reduced in size by heat treating as well as by methods that form an
oxide scale or coating on the internal side walls of the apertures.
These techniques may be used to partially occlude the apertures to
reduce the size of the openings for flow. FIGS. 13 and 14 show a
comparison of SEM surface structures of a stainless steel porous
substrate before and after heat treatment at the same magnification
and the same location. FIG. 13 shows the surface before heat
treating and FIG. 14 shows the surface after heat treating. The
surface of the porous material after the heat treatment has a
significantly smaller gap and opening size. The average distance
between the openings is correspondingly increased.
[0151] The apertured sections 290 and 290A may be made from a
metallic or nonmetallic porous material having interconnected
channels or pores of an average pore size in the range from about
0.01 to about 1000 microns, and in one embodiment in the range from
about 0.01 to about 200 microns. These pores may function as the
apertures 293 and 293A. The porous material may be made from powder
or particulates so that the average inter-pore distance is similar
to the average pore size. The porous material may be tailored by
oxidization at a high temperature in the range from about
300.degree. C. to about 1000.degree. C. for a duration of about 1
hour to about 20 days, or by coating a thin layer of another
material such as alumina by sol coating or nickel using chemical
vapor deposition over the surface and the inside of pores to block
the smaller pores, decrease pore size of larger pores, and in turn
increase the inter-pore distance. An SEM image of a tailored
substrate or apertured section is shown in FIG. 15.
[0152] The making of substrates for use as apertured sections 290
and 290A with sufficiently small micro-scale apertures or pores 293
and 293A to provide a staged addition feed stream having bubble or
droplet sizes smaller than about one micron can be problematic. One
of the reasons for this lies in the fact that relatively high
surface roughness occurs with untreated regular porous materials
such as a metallic porous substrates made from powder/particles by
compression and/or sintering. These metallic porous substrates
typically do not have the required pore size in the surface region
when a given nominal pore size is lower than a certain value. While
the bulk of the porous material may have the specified nominal pore
size, the surface region is often characterized by merged pores and
cavities of much larger sizes. This problem can be overcome by
tailoring these substrates to provide for the desired pore size and
inter-pore distance in the surface region. This may be done by
removing a surface layer from the porous substrate and adding a
smooth new surface with smaller openings. The droplet size or
bubble size of staged addition feed stream that may be formed using
these tailored substrates may be reduced without increasing the
pressure drop across the substrate. Since direct grinding or
machining of the porous surface may cause smearing of the surface
structure and blockage of the pores, the porous structure may be
filled with a liquid filler, followed by solidification and
mechanical grinding/polishing. The filler is then removed to regain
the porous structure of the material. The filler may be a metal
with a low melting point such as zinc or tin or the precursor of a
polymer such as an epoxy. The liquid filling and removing steps may
be assisted by the use of a vacuum. Grinding/polishing may be
effected using a grinding machine and a grinding powder. Metal
filler removal may be effected by melting and vacuum suction, or by
acid etching. Epoxies or other polymers may be removed by solvent
dissolution or by burn-off in air.
[0153] Referring to FIGS. 16-19, the apertured sections 290 and
290A, in one embodiment, may be constructed of a relatively thin
sheet 300 containing relatively small apertures 302, and a
relatively thick sheet or plate 310 containing relatively large
apertures 312. The apertures 312 may be aligned with or connected
to the apertures 302. The relatively thin sheet 300 overlies and is
bonded to the relatively thick sheet or plate 310, the relatively
thin sheet 300 facing the interior of process microchannel 210 and
the relatively thick sheet 310 facing the interior of the staged
addition channel 280 or 280A. The relatively thin sheet 300 may be
bonded to the relatively thick sheet 310 using any suitable
procedure (e.g., diffusion bonding) to provide a composite
construction 320 with enhanced mechanical strength. The relatively
thin sheet 300 may have a thickness in the range from about 0.001
to about 0.5 mm, and in one embodiment about 0.05 to about 0.2 mm.
The relatively small apertures 302 may have any shape, for example,
circular, triangular or rectangular. The relatively small apertures
302 may have an average diameter in the range from about 0.05 to
about 50 microns, and in one embodiment about 0.05 to about 20
microns. The relatively thick sheet or plate 310 may have a
thickness in the range from about 0.01 to about 5 mm, and in one
embodiment about 0.1 to about 2 mm. The relatively large apertures
312 may have any shape, for example, circular, triangular or
rectangular. The relatively large apertures 312 may have an average
diameter in the range from about 0.01 to about 4000 microns, and in
one embodiment about 1 to about 2000 microns, and in one embodiment
about 10 to about 1000 micron. The total number of apertures 302 in
sheet 300 and the total number of apertures 312 in sheet or plate
310 may be in the range from about 1 to about 10000 apertures per
square centimeter, and in one embodiment from about 1 to about 1000
apertures per square centimeter. The sheet 300 and the sheet or
plate 310 may be constructed of any of the materials described
above as being useful for constructing the apertured sections 290
and 290A. The apertures 302 and 312 may be aligned or connected in
such a manner that fluid flowing through the apertured sections 290
and 290A flows initially through the apertures 312 then through the
apertures 302. The relatively short passageway for the fluid to
flow through the relatively small apertures 302 enables the fluid
to flow through the apertures 302 with a relatively low pressure
drop as compared to the pressure drop that would occur if the
passageway in the apertures had a depth equal to the combined depth
of apertures 302 and 312.
[0154] In the embodiment illustrated in FIG. 19, the composite
construction 320a has the same design as illustrated in FIG. 18
with the exception that convex portion 304 of the relatively thin
sheet 300 covering the aperture 312 is provided. Convex portion 304
provides increased local shear force in the adjacent channel. The
staged addition feed stream flows through the apertures 312 and 302
in the direction indicated by arrow 323. The directional arrows 322
in FIG. 19 show the flow of the feed composition in the process
microchannel adjacent to the aperture 302. The increased local
shear force leads to a smaller droplet size or gas bubble for the
fluid flowing through the aperture 302.
[0155] In the embodiment illustrated in FIG. 20, a surface coating
330 is deposited on the surface of sheet or plate 332 and on the
internal sidewalls 334 of aperture 336. This coating provides a
facilitated way of reducing the diameter of the apertures 293 and
293A. The coating material used to form coating 330 may be alumina,
nickel, gold, or a polymeric material (e.g., Teflon). The coating
330 may be applied to the sheet or plate 332 using known techniques
including chemical vapor deposition, metal sputtering, metal
plating, sintering, sol coating, and the like. The diameter of the
apertures may be controlled by controlling the thickness of the
coating 330.
[0156] In one embodiment, the apertured sections 290 and 290A may
be formed from an asymmetric porous material, for example, a porous
material having multiple layers of sintered particles. The number
of layers may be two, three, or more. An advantage of these
multilayered substrates is that they provide enhanced durability
and adhesion. Examples include sintered ceramics that have
relatively large pores on one side and relatively small pores on
the other side. The relatively small pores may have diameters in
the range of about 2 to about 10 nm. The relatively small pores may
be positioned in a relatively thin layer of the multilayered
substrate. The relatively thin layer may have a thickness in the
range of about 1 to about 10 microns. The side with the relatively
small pores may be placed facing the interior of the process
microchannel 210 to take advantage of relatively high shear forces
to remove the relatively small droplets of reactant and/or liquid
catalyst as they are formed.
[0157] During the inventive process the staged addition feed stream
may flow through the apertured sections 290 and 290A into the
process microchannel 210. In one embodiment, the apertured section
may extend along at least about 5% of the axial length of the
process microchannel, and in one embodiment at least about 20% of
the axial length of the process microchannel, and in one embodiment
at least about 35% of the axial length of the process microchannel,
and in one embodiment at least about 50% of the axial length of the
process microchannel, and in one embodiment at least about 65% of
the axial length of the process microchannel, and in one embodiment
at least about 80% of the axial length of the process microchannel,
and in one embodiment at least about 95% of the axial length of the
process microchannel, and in one embodiment from about 5% to about
100% of the axial length of the process microchannel, and in one
embodiment from about 10% to about 95% of the axial length of the
process microchannel, and in one embodiment from about 25% to about
75% of the axial length of the process microchannel, and in one
embodiment from about 40% to about 60% of the axial length of the
process microchannel.
[0158] The dehydrogenation catalyst may comprise at least one oxide
of iron, chromium or a combination thereof. In one embodiment, the
catalyst may comprise iron oxide and one or more of potassium
oxide, molybdenum oxide, cerium oxide, and calcium carbonate. In
one embodiment, the catalyst may comprise one or more Group VII
nobel metals (e.g., platinum, iridium, rhodium, palladium). The
catalytic metals may be combined with a carrier such as a
refractory inorganic oxide. Alumina may be used as the carrier.
[0159] The oxidative dehydrogenation catalyst may comprise any
vanadium-containing, molybdenum-containing or tungsten-containing
oxidative dehydrogenation catalyst. Catalysts containing
combinations of two or more of V, Mo and W may be used. The
catalyst may comprise one or more of V.sub.2O.sub.5, MoO.sub.3 or
WO.sub.3 catalysts. The catalyst may be supported. The support may
comprise Al.sub.2O.sub.3, MgO, MgAl.sub.2O.sub.4, CaO, TiO.sub.2,
ZrO.sub.2, SiO.sub.2, Ga.sub.2O.sub.3, rare earth oxide, active
carbon, carbon fibers, molecular sieves, or a combination of two or
more thereof. The catalyst may comprise any vanadate, molybdate,
tungstate, or a combination of two or more thereof. Examples may
include FeVO.sub.4, CrVO.sub.4, NaVO.sub.3, BiVO.sub.4, AlVO.sub.4,
CeVO.sub.4, VOPO.sub.4, LaVO.sub.4, SmVO.sub.4, NiMoO.sub.4,
MgMoO.sub.4, CaMoO.sub.4, FeMoO.sub.4, Fe.sub.2(MoO.sub.4).sub.3,
MgWO.sub.4, CaWO.sub.4, NiWO.sub.4, FeWO.sub.4, or a combination of
two or more thereof. The catalyst may be promoted by alkali,
alkaline earth, rare earth, transition metal oxides, Group VB
elements (P, As, Sb and Bi), or a combination of two or more
thereof. The catalyst may be prepared by impregnation, sol-gel,
co-precipitation, ion-exchange, solution evaporation or
deposition-precipitation. The catalyst may be coated on a
substrate. The substrate may have a flat surface or a structured
surface. Examples of the substrates may include flat coupons,
shims, honeycombs, gauze, foams, fins, felts, and/or
surface-featured coupons. The materials of the substrates may be
made of a material comprising metal, alloys, super alloys,
ceramics, or a combination of two or more thereof. The metallic
substrates may be heat treated prior to catalyst coating. The
catalyst coating may be performed by slurry-coating, sol-coating or
solution-coating.
[0160] The catalyst may have any size and geometric configuration
that fits within the process microchannels. The catalyst may be in
the form of particulate solids (e.g., pellets, powder, fibers, and
the like) having a median particle diameter of about 1 to about
1000 microns, and in one embodiment about 10 to about 500 microns,
and in one embodiment about 25 to about 250 microns.
[0161] The catalyst may comprise a graded catalyst.
[0162] The catalyst may be in the form of a mesoporous material
wherein the average pore size may be at or above about 1 nanometer
(nm), for example, in the range from about 1 to about 100 nm, and
in one embodiment from about 1 to about 20 nm. In one embodiment,
mesoporous catalysts may be surprisingly active and selective for
forming styrene.
[0163] The catalyst may be in the form of a fixed bed of
particulate solids such as illustrated in FIG. 21. Referring to
FIG. 21, the catalyst 350 is contained within process microchannel
352. The reactants flow through the catalyst bed as indicated by
arrows 354 and 356.
[0164] The catalyst may be supported on a porous support structure
such as a foam, felt, wad or a combination thereof. The term "foam"
is used herein to refer to a structure with continuous walls
defining pores throughout the structure. The term "felt" is used
herein to refer to a structure of fibers with interstitial spaces
therebetween. The term "wad" is used herein to refer to a support
having a structure of tangled strands, like steel wool. The
catalyst may be supported on a support having a honeycomb structure
or a serpentine configuration.
[0165] The catalyst may be supported on a flow-by support structure
such as a felt with an adjacent gap, a foam with an adjacent gap, a
fin structure with gaps, a washcoat on any inserted substrate, or a
gauze that is parallel to the flow direction with a corresponding
gap for flow. An example of a flow-by structure is illustrated in
FIG. 22. In FIG. 22 the catalyst 360 is contained within process
microchannel 362. An open passage way 364 permits the flow of the
reactants through the process microchannel 362 in contact with the
catalyst 360 as indicated by arrows 366 and 368.
[0166] The catalyst may be supported on a flow-through support
structure such as a foam, wad, pellet, powder, or gauze. An example
of a flow-through structure is illustrated in FIG. 23. In FIG. 23,
the flow-through catalyst 370 is contained within process
microchannel 372 and the reactants flow through the catalyst 370 as
indicated by arrows 374 and 376.
[0167] The support may be formed from a material comprising silica
gel, foamed copper, sintered stainless steel fiber, steel wool,
alumina, poly(methyl methacrylate), polysulfonate,
poly(tetrafluoroethylene), iron, nickel sponge, nylon,
polyvinylidene difluoride, polypropylene, polyethylene,
polyethylene ethylketone, polyvinyl alcohol, polyvinyl acetate,
polyacrylate, polymethylmethacrylate, polystyrene, polyphenylene
sulfide, polysulfone, polybutylene, or a combination of two or more
thereof. In one embodiment, the support structure may be made of a
heat conducting material, such as a metal, to enhance the transfer
of heat away from the catalyst.
[0168] The catalyst may be directly washcoated on the interior
walls of the process microchannels, grown on the walls from
solution, or coated in situ on a fin structure. The catalyst may be
in the form of a single piece of porous contiguous material, or
many pieces in physical contact. In one embodiment, the catalyst
may comprise a contiguous material and have a contiguous porosity
such that molecules can diffuse through the catalyst. In this
embodiment, the fluids may flow through the catalyst rather than
around it. In one embodiment, the cross-sectional area of the
catalyst may occupy from about 1 to about 99%, and in one
embodiment from about 10 to about 95% of the cross-sectional area
of the process microchannels. The catalyst may have a surface area,
as measured by BET, of greater than about 0.5 m.sup.2/g, and in one
embodiment greater than about 2 m.sup.2/g, and in one embodiment
greater than about 5 m.sup.2/g, and in one embodiment greater than
about 10 m.sup.2/g, and in one embodiment greater than about 25
m.sup.2/g, and in one embodiment greater than about 50
m.sup.2/g.
[0169] The catalyst may comprise a porous support, an interfacial
layer overlying the porous support, and a catalyst material
dispersed or deposited on the interfacial layer. The interfacial
layer may be solution deposited on the support or it may be
deposited by chemical vapor deposition or physical vapor
deposition. In one embodiment the catalyst comprises a porous
support, optionally a buffer layer overlying the support, an
interfacial layer overlying the support or the optional buffer
layer, and a catalyst material dispersed or deposited on the
interfacial layer. Any of the foregoing layers may be continuous or
discontinuous as in the form of spots or dots, or in the form of a
layer with gaps or holes.
[0170] The porous support may have a porosity of at least about 5%
as measured by mercury porosimetry and an average pore size (sum of
pore diameters divided by number of pores) of about 1 to about 1000
microns. The porous support may be made of any of the above
indicated materials identified as being useful in making a support
structure. The porous support may comprise a porous ceramic support
or a metal foam. Other porous supports that may be used include
carbides, nitrides, and composite materials. The porous support may
have a porosity of about 30% to about 99%, and in one embodiment
about 60% to about 98%. The porous support may be in the form of a
foam, felt, wad, or a combination thereof. The open cells of the
metal foam may range from about 20 pores per inch (ppi) to about
3000 ppi, and in one embodiment about 20 to about 1000 ppi, and in
one embodiment about 40 to about 120 ppi. The term "ppi" refers to
the largest number of pores per inch (in isotropic materials the
direction of the measurement is irrelevant; however, in anisotropic
materials, the measurement is done in the direction that maximizes
pore number).
[0171] The buffer layer, when present, may have a different
composition and/or density than both the porous support and the
interfacial layers, and in one embodiment has a coefficient of
thermal expansion that is intermediate the thermal expansion
coefficients of the porous support and the interfacial layer. The
buffer layer may be a metal oxide or metal carbide. The buffer
layer may be comprised of Al.sub.2O.sub.3, TiO.sub.2, SiO.sub.2,
ZrO.sub.2, or combination thereof. The Al.sub.2O.sub.3 may be
.alpha.-Al.sub.2O.sub.3, .gamma.-Al.sub.2O.sub.3 or a combination
thereof. .alpha.-Al.sub.2O.sub.3 provides the advantage of
excellent resistance to oxygen diffusion. The buffer layer may be
formed of two or more compositionally different sublayers. For
example, when the porous support is metal, for example a stainless
steel foam, a buffer layer formed of two compositionally different
sub-layers may be used. The first sublayer (in contact with the
porous support) may be TiO.sub.2. The second sublayer may be
.alpha.-Al.sub.2O.sub.3 which is placed upon the TiO.sub.2. In one
embodiment, the .alpha.-Al.sub.2O.sub.3 sublayer is a dense layer
that provides protection of the underlying metal surface. A less
dense, high surface area interfacial layer such as alumina may then
be deposited as support for a catalytically active layer.
[0172] The porous support may have a thermal coefficient of
expansion different from that of the interfacial layer. In such a
case a buffer layer may be needed to transition between the two
coefficients of thermal expansion. The thermal expansion
coefficient of the buffer layer can be tailored by controlling its
composition to obtain an expansion coefficient that is compatible
with the expansion coefficients of the porous support and
interfacial layers. The buffer layer should be free of openings and
pin holes to provide superior protection of the underlying support.
The buffer layer may be nonporous. The buffer layer may have a
thickness that is less than one half of the average pore size of
the porous support. The buffer layer may have a thickness of about
0.05 to about 10 .mu.m, and in one embodiment about 0.05 to about 5
.mu.m.
[0173] In one embodiment of the invention, adequate adhesion and
chemical stability may be obtained without a buffer layer. In this
embodiment the buffer layer may be omitted.
[0174] The interfacial layer may comprise nitrides, carbides,
sulfides, halides, metal oxides, carbon, or a combination thereof.
The interfacial layer provides high surface area and/or provides a
desirable catalyst-support interaction for supported catalysts. The
interfacial layer may be comprised of any material that is
conventionally used as a catalyst support. The interfacial layer
may be comprised of a metal oxide. Examples of metal oxides that
may be used include .gamma.-Al.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2,
TiO.sub.2, tungsten oxide, magnesium oxide, vanadium oxide,
chromium oxide, manganese oxide, iron oxide, nickel oxide, cobalt
oxide, copper oxide, zinc oxide, molybdenum oxide, tin oxide,
calcium oxide, aluminum oxide, lanthanum series oxide(s),
zeolite(s) and combinations thereof. The interfacial layer may
serve as a catalytically active layer without any further
catalytically active material deposited thereon. Usually, however,
the interfacial layer is used in combination with a catalytically
active layer. The interfacial layer may also be formed of two or
more compositionally different sublayers. The interfacial layer may
have a thickness that is less than one half of the average pore
size of the porous support. The interfacial layer thickness may
range from about 0.5 to about 100 .mu.m, and in one embodiment from
about 1 to about 50 .mu.m. The interfacial layer may be either
crystalline or amorphous. The interfacial layer may have a BET
surface area of at least about 1 m.sup.2/g.
[0175] The catalyst may be deposited on the interfacial layer.
Alternatively, the catalyst material may be simultaneously
deposited with the interfacial layer. The catalyst layer may be
intimately dispersed on the interfacial layer. That the catalyst
layer is "dispersed on" or "deposited on" the interfacial layer
includes the conventional understanding that microscopic catalyst
particles are dispersed: on the support layer (i. e., interfacial
layer) surface, in crevices in the support layer, and in open pores
in the support layer.
[0176] The catalyst may be supported on an assembly of one or more
fins positioned within the process microchannels. Examples are
illustrated in FIGS. 24-26. Referring to FIG. 24, fin assembly 380
includes fins 382 which are mounted on fin support 384 which
overlies base wall 386 of process microchannel 388. The fins 382
project from the fin support 384 into the interior of the process
microchannel 388. The fins 382 extend to the interior surface of
upper wall 390 of process microchannel 388. Fin channels 392
between the fins 392 provide passage ways for fluid to flow through
the process microchannel 388 parallel to its length. Each of the
fins 382 has an exterior surface on each of its sides, this
exterior surface provides a support base for the catalyst. With the
inventive process, the reactants flow through the fin channels 392,
contact the catalyst supported on the exterior surface of the fins
382, and react to form the product. The fin assembly 380a
illustrated in FIG. 25 is similar to the fin assembly 380
illustrated in FIG. 24 except that the fins 382a do not extend all
the way to the interior surface of the upper wall 390 of the
microchannel 388. The fin assembly 380b illustrated in FIG. 26 is
similar to the fin assembly 380 illustrated in FIG. 24 except that
the fins 382b in the fin assembly 380b have cross sectional shapes
in the form of trapezoids. Each of the fins (382, 382a, 382b) may
have a height ranging from about 0.02 mm up to the height of the
process microchannel 838, and in one embodiment from about 0.02 to
about 10 mm, and in one embodiment from about 0.02 to about 5 mm,
and in one embodiment from about 0.02 to about 2 mm. The width of
each fin (382, 382a, 382b) may range from about 0.02 to about 5 mm,
and in one embodiment from about 0.02 to about 2 mm and in one
embodiment about 0.02 to about 1 mm. The length of each fin (382,
382a, 382b) may be of any length up to the length of the process
microchannel 838, and in one embodiment up to about 10 m, and in
one embodiment about 1 cm to about 10 m, and in one embodiment
about 1 cm to about 5 m, and in one embodiment about 1 cm to about
2.5 m. The gap between each of the fins (382, 382a, 382b) may be of
any value and may range from about 0.02 to about 5 mm, and in one
embodiment from about 0.02 to about 2 mm, and in one embodiment
from about 0.02 to about 1 mm. The number of fins (382, 382a, 382b)
in the process microchannel 388 may range from about 1 to about 50
fins per centimeter of width of the process microchannel 388, and
in one embodiment from about 1 to about 30 fins per centimeter, and
in one embodiment from about 1 to about 10 fins per centimeter, and
in one embodiment from about 1 to about 5 fins per centimeter, and
in one embodiment from about 1 to about 3 fins per centimeter. As
indicated above, each of the fins may have a cross-section in the
form of a rectangle or square as illustrated in FIG. 24 or 25, or a
trapezoid as illustrated in FIG. 26. When viewed along its length,
each fin (382, 382a, 382b) may be straight, tapered or have a
serpentine configuration. The fin assembly (380, 380a, 380b) may be
made of any material that provides sufficient strength, dimensional
stability and heat transfer characteristics to permit operation for
which the process microchannel is intended. These materials
include: steel (e.g., stainless steel, carbon steel, and the like);
monel; inconel; aluminum; titanium; nickel; platinum; rhodium;
copper; chromium; brass; alloys of any of the foregoing metals;
polymers (e.g., thermoset resins); ceramics; glass; composites
comprising one or more polymers (e.g., thermoset resins) and
fiberglass; quartz; silicon; or a combination of two or more
thereof. The fin assembly (380, 380a, 380b) may be made of an
Al.sub.2O.sub.3 forming material such as an alloy comprising Fe,
Cr, Al and Y, or a Cr.sub.2O.sub.3 forming material such as an
alloy of Ni, Cr and Fe.
[0177] The catalyst may be supported by the microgrooved support
strip illustrated in FIG. 27, 28 or 29. Referring to FIG. 27,
microgrooved support strip 400 comprises support strip 410 which is
rectangular in shape and has a length (l), width (w) and thickness
(t). The support strip 410 has a first or top surface 412, a second
or bottom surface 414, a first side edge 416, a second side edge
418, a front edge 420 and a back edge 422. The support strip 410
has a center axis 424 extending along the length (l) of the support
strip. A plurality of parallel microgrooves 430 are formed in the
first surface 412. A first group 432 of parallel microgrooves
extends from the first side edge 416 of the support strip 410 to
the second side edge 418. A second group 434 of the microgrooves
430 extends from the front edge 420 to the second side edge 418. A
third group 436 of the microgrooves 430 extends from the first side
edge 416 of the support strip 410 to the back edge 422. The
microgrooves 430 are oriented at an angle 425 relative to the
center axis 420 that is sufficient to permit fluid to flow in the
microgrooves 430 in a general direction from the front edge 420
toward the back edge 422. That is, the microgrooves 430 do not
extend straight across the top surface 412 at an angle of
90.degree. with the center axis 424. The front edge 420, back edge
422 and side edges 416 and 418 of the microgrooved support strip
400 are open. That is, the microgrooves 430 have open ends that
project through the front edge 420, back edge 422 and side edges
416 and 418. These open ends may permit the flow of fluid through
the front edge, back edge and side edges.
[0178] The microgrooves 430 illustrated in FIG. 27 have
cross-sections in the form of squares. Alternatively, each of the
microgrooves 430 may have a rectangular cross-section, a vee shaped
cross-section, a semi-circular cross-section, a dovetail shaped
cross-section, or a trapezoid shaped cross-section. Those skilled
in the art will recognize that microgrooves with other
cross-sectional shapes may be used. Each of the microgrooves 430
has a depth, width and length. The depth of each of the
microgrooves 430 may be in the range from about 0.1 to about 1000
microns, and in one embodiment from about 1 to about 100 microns.
The width, which would be the width at its widest dimension, for
each of the microgrooves 430 may be in the range of about 0.1 to
about 1000 microns, and in one embodiment from about 1 to about 500
microns. The length of each of the microgrooves 430 may be of any
dimension which depends upon the width (w) of the support strip
410. The length of each microgroove 430 may be in the range of
about 0.1 to about 100 cm, and in one embodiment from about 0.1 to
about 10 cm. The spacing between the microgrooves 430 may be in the
range up to about 1000 microns, and in one embodiment from about
0.1 to about 1000 microns, and in one embodiment from about 1 to
about 1000 microns. Each of the microgrooves 430 may be oriented
toward the front edge 420 and the first side edge 416 and forms an
angle 425 with the center axis 424 that is sufficient to permit
fluid to flow in the microgrooves in a general direction toward the
second side edge 418 and back edge 422. The angle 425 may be more
than about 0.degree. and less than 90.degree.. The angle 125 may be
in the range from about 50.degree. to about 80.degree., and in one
embodiment from about 60.degree. to about 75.degree.. The
microgrooves 430 may be formed in the first surface 412 of the
support strip 410 by any suitable technique, including
photochemical machining, laser etching, water jet machining, and
the like.
[0179] The support strip 410 may have a thickness (t) in the range
from about 0.1 to about 5000 microns, and in one embodiment from
about 1 to about 1000 microns. The support strip 410 may have any
width (w) and any length (l), the width and length depending upon
the dimensions of the microchannel for which the support strip 410
is to be used. The support strip 410 may have a width (w) in the
range from about 0.01 to about 100 cm, and in one embodiment from
about 0.1 to about 10 cm. The length (l) of the support strip 110
may be in the range of about 0.01 to about 100 cm, and in one
embodiment from about 0.1 to about 10 cm. The support strip 410 as
illustrated in FIG. 27 is in the form of a rectangle. However, it
is to be understood that the support strip 410 may have any
configuration, for example, square, circle, oval, etc., to conform
to the design of the microchannel for which it is to be used.
[0180] The support strip 410 may be made of any material that
provides sufficient strength, dimensional stability and heat
transfer characteristics to permit the use of the microgrooved
support strip 400 in a microchannel for supporting a catalyst. The
support strip 410 may be made of metal, silicon carbide, graphite
or a combination of two or more thereof. The metal may comprise
steel, aluminum, titanium, nickel, platinum, rhodium, copper,
chromium, brass, or an alloy of any of the foregoing metals. The
support structure 410 may be made of stainless steel or an alloy
comprising iron, chromium, aluminum and yttrium.
[0181] The microgrooved support strip 400A illustrated in FIG. 28
is the same as the microgrooved support strip 400 illustrated in
FIG. 27 with the exception that the second group 434 of
microgrooves 430 and third group 436 of microgrooves 430 that are
present in the microgroove support strip 400 are not present in the
microgrooved support strip 400A. The microgrooved support strip
400A includes non-grooved sections 434a and 436a which provide the
microgrooved support strip 100A with a front edge 420 and a back
edge 422 that are closed. That is, the front edge 420 and the back
edge 422 of the microgrooved support strip 400A are sufficiently
blocked to prevent fluid from flowing through the front edge 420
and back edge 422.
[0182] The microgrooved support strip 400A is also shown in FIGS.
35 and 36. FIG. 35 is a photograph of a microgrooved support
structure made of an alloy of iron, chromium, aluminum and yttrium,
the thickness of the support structure being 0.002 inch (50.8
microns), the ribs dividing the microgrooves having a thickness of
0.007 inch (178 microns), and the microgrooves having a width of
0.007 inch (178 microns). FIG. 36 is a photograph of a microgrooved
support structure similar to the support structure illustrated in
FIG. 35 with the exception that the microgrooved support structure
illustrated in FIG. 36 is made of stainless steel.
[0183] The microgrooved support strip 400B illustrated in FIG. 29
is the same as the microgrooved support strip 400A illustrated in
FIG. 28 with the exception that the side edges 416 and 418 in the
microgrooved support strip 400B are closed. The microgrooves 430
extend between the side edges 416 and 418 but not through the side
edges. Thus, the flow of fluid through the side edges 416 and 418
may be blocked. Also, the microgrooves 430 may penetrate part way
or all the way through the support strip 410. Penetration of the
microgrooves 430 all the way through the support strip 410 may be
sufficient to permit fluid to flow through the support strip 410
from the top surface 412 to the bottom surface 414, or vice
versa.
[0184] The microgrooves 430 may be aligned at an angle of about
90.degree. or a right angle with the center axis 424, and in one
embodiment extend from the first side edge 416 to the second side
edge 418.
[0185] The microgrooves 430 may be aligned parallel to the center
axis 424, and in one embodiment extend from the front edge 420 to
the back edge 422.
[0186] The microgrooved support strips 400 and 400B may be used as
flow-through and/or flow-by support structures in a microchannel.
Microgrooved support strip 400A may be used as a flow by support
structure in a microchannel.
[0187] In one embodiment, a plurality of the microgrooved support
strips may be stacked one above another or positioned side by side
to form a composite support structure which may be used to support
a catalyst for use in the inventive process. The composite support
structure, in one embodiment, is illustrated in FIGS. 30 and 31.
The support strips 400C and 400D illustrated in FIGS. 30 and 31
have open front 420 and back edges 422, closed side edges 416 and
418, and microgrooves 430 that penetrate all the way through the
support strip 410 from the top surface 412 to the bottom surface
414. The open front edges 420, back edges 422 and microgrooves 430
permit fluid to flow through the microgrooved support strips from
one support strip to another support strip within the composite
support structure as the fluid flows through the composite support
structure. The number of microgrooved support strips employed in
such a composite support structure may be of any number, for
example up to about 50, and in one embodiment up to about 30, and
in one embodiment up to about 15, and in one embodiment up to about
10. The composite support structure also includes end plates to
prevent fluid from flowing out of the sides of the composite
construction.
[0188] The composite support structure 402 illustrated in FIGS. 30
and 31 comprises eight (8) microgrooved support strips, four each
of microgrooved support strips 400C and 400D positioned side by
side in alternating sequence and two end plates 405 (only one end
plate is shown in FIG. 5). The microgrooved support strips 400C and
400D each comprise support strip 410 which is rectangular in shape
and has a length, width and thickness. The support strip 410 has a
center axis extending along the length of the support strip. A
plurality of parallel microgrooves 430 are formed in the support
strip 410 and project through the support strip from the top
surface 412 to the bottom surface 414. The open front 420 and back
edges 422 and the open microgrooves 430 permit fluid to flow from
one microgrooved support strip to another within the composite
support structure 402. A first group of parallel microgrooves
extends from the first side edge 416 of the support strip 410 to
the second side edge 418. A second group of the microgrooves 430
extends from the front edge 420 to the second side edge 418. A
third group of the microgrooves 430 extends from the first side
edge 416 of the support strip 410 to the back edge 422. The
microgrooves 430 extend to the side edges 416 and 418 but do not
project through these side edges. The end plates 405 prevent fluid
from flowing out of the sides of the composite support structure
402. The second end plate 405 that is not shown in the drawings
would be positioned adjacent to the first microgrooved support
strip 400C on the left side in FIGS. 30 and 31. The microgrooves
430 in the support strips 400C are oriented at an angle relative to
the center axis of the support strip and the side edge 416 that is
more than 90.degree. and less than 180.degree., and in one
embodiment in the range from about 100.degree. to about
150.degree.. The microgrooves 430 in the support strip 400D are
oriented at an angle relative to the center axis of the support
strip and the side edge 116 that is more than 0.degree. and less
than 90.degree., and in one embodiment in the range from about
50.degree. to about 80.degree.. Fluid flows through the composite
structure 402 by entering the front edge 420 of the support strips
400C and 400D, flowing in and through the microgrooves 430 and
transferring from the microgrooves 430 in one support strip (400C
or 400D) to the microgrooves 430 in another support strip (400C or
400D) until the fluid reaches the back edge 422 of the support
strips and then flows out of composite support structure 402. FIG.
31 shows an example of a flow path through the composite support
structure 402 for a fluid entering opening `A` of the composite
support structure illustrated in FIG. 20. The flow of fluid through
the composite support structure 402 may be described as permeating,
diffusing and advecting from one layer to another until the fluid
passes from the front end of the composite support structure to the
back end.
[0189] The catalyst may be supported by a composite support
structure, comprising: at least one first support strip comprising
a first surface, a second surface, a length with a center axis
extending along the length, a front edge, a back edge, a first side
edge, a second side edge, the front edge and the back edge
extending from the first side edge and to the second side edge, a
plurality of parallel microgrooves in the first surface aligned at
an angle of about 90.degree. with the center axis; and at least one
second support strip comprising a first surface, a second surface,
a length with a center axis extending along the length, a front
edge, a back edge, a first side edge, a second side edge, the front
edge and the back edge extending from the first side edge to the
second side edge, a plurality of parallel microgrooves in the first
surface aligned parallel with the center axis; the first support
strip being adjacent to the second support strip with the second
surface of the first support strip contacting the first surface of
the second support strip; the microgrooves penetrating through the
support strips sufficiently to permit fluid to flow through the
support strips from one support strip to another support strip.
[0190] The catalyst may be supported by a composite support
structure, comprising: at least one first support strip comprising
a first surface, a second surface, a length with a center axis
extending along the length, a front edge, a back edge, a first side
edge, a second side edge, the front edge and the back edge
extending from the first side edge and to the second side edge, and
a plurality of parallel microgrooves in the first surface; at least
one second support strip comprising a first surface, a second
surface, a length with a center axis extending along the length, a
front edge, a back edge, a first side edge, a second side edge, the
front edge and the back edge extending from the first side edge to
the second side edge, and a plurality of parallel microgrooves in
the first surface; the first support strip being adjacent to the
second support strip with the second surface of the first support
strip contacting the first surface of the second support strip; the
microgrooves penetrating through the support strips sufficiently to
permit fluid to flow through the support strips from one support
strip to another; microgrooves in the first surface of the first
support strip intersecting microgrooves in the first surface of the
second support strip to provide through holes extending through the
first support strip and through the second support strip. In one
embodiment, the through holes may be of sufficient dimension to
permit reactants and/or product to flow from the first surface of
the first support strip to the first surface of the second support
strip and/or from the first surface of the second support strip to
the first surface of the first support strip. In one embodiment,
the first support strip and the second support strip are made of
thermally conductive materials and the contacting between the
second surface of the first support strip and the first surface of
the second support strip is sufficient to permit heat to be
conducted between the first support strip and the second support
strip.
[0191] An advantage of the microgrooved support strips and
composite structures relates to the fact that microsized particles
of catalyst may be positioned in and anchored to the microgrooves
thus reducing the tendency of the particulates being swept away by
the flow of process fluids through the microchannels.
[0192] The support strips 400, 400A or 400B, or the composite
support structure 402 may be positioned or mounted on one or more
walls within a microchannel to form one or more structured walls
within the microchannel.
[0193] The catalyst may be supported by one or more structured
walls within the process microchannels wherein the one or more
structured walls may be formed from one or more shims. One or more
of the shims may contain one or more void spaces, openings or
through holes. The shims may contain grooves or microgrooves that
are formed in one surface of the shims or in both the front or
first surface and the back or second surface of the shims. The
grooves or microgrooves from the first surface may intersect the
grooves or microgrooves from the second surface to form a plurality
of voids, through holes or openings in the shim. Examples are
illustrated in FIGS. 59 and 60. FIG. 59 illustrates a shim 510
which has a front or first surface 512 and a back or second surface
514, and a plurality of grooves or microgrooves 530 formed in each
surface. The grooves or microgrooves 530 formed in the front
surface 512 are parallel to each other and are positioned in an
array of block patterns 550 wherein in a first block pattern 550
the grooves or microgrooves are aligned in a first or horizontal
direction and then in an adjacent second block pattern 550 the
grooves or microgrooves are aligned in a second or vertical
direction. The array of block patterns 550 comprises a plurality of
block patterns 550 arranged in successive rows positioned one above
another, the successive rows forming a plurality of columns
positioned side by side one another. The grooves or microgrooves
530 formed in the back surface 514 are also parallel to each other
and are positioned in an array of block patterns 550 similar to the
block patterns 550 in the front surface 512 with the exception that
where the front surface 512 has grooves or microgrooves that are
aligned in a first or horizontal direction the back surface 514 has
grooves or microgrooves 530 that are aligned in a second or
vertical direction. Similarly, where the front surface 512 has
grooves or microgrooves 530 that are aligned in a second or
vertical direction the back surface 514 has grooves or microgrooves
that are aligned in a first or horizontal direction. The grooves or
microgrooves 530 in the front surface 512 and the grooves or
microgrooves 530 in the back surface 514 partially penetrate the
shim 510. The penetration of the grooves or microgrooves 530 in the
front surface and back surface is sufficient for the grooves or
microgrooves 530 in the front surface 512 to intersect the grooves
or microgrooves 530 in the back surface 514 with the result being
the formation of an array of voids, through holes or openings 552
in the shim 510 at the points where the grooves or microgrooves
intersect. The openings 552 may be of sufficient size to permit a
fluid to flow or diffuse through the openings 552. The number of
openings may range from about 1 to about 200,000 openings per
cm.sup.2, and in one embodiment from about 10 to about 100,000
openings per cm.sup.2. The openings 552 may have average dimensions
(e.g., diameter) in the range from about 1 to about 2000 microns,
and in one embodiment from about 10 to about 1000 microns. The
block patterns 550 may have the dimensions of about 0.01 by about
500 mm, and in one embodiment about 0.5 by about 20 mm. The
separation between each block pattern 550 and the next adjacent
block pattern may be in the range from about 0.01 to about 10 mm,
and in one embodiment about 0.1 to about 1 mm. In this embodiment,
the pattern is alternated in an A, B, A, B fashion. In an alternate
embodiment the geometry may be varied such that the surface area to
volume of the structure may be different along the length of the
reactor or in different zones of the reactor. By this manner a
reaction with a very high rate of heat release near the top of the
reactor may be advantaged by the use of a structure with a higher
surface area to volume near the middle or end of the reactor where
the kinetics are slower and the rate of heat transfer lower. The
resulting heat generation rate along the reactor length or heat
flux profile along the reactor length may be made more even or
uniform. The pattern may be further optimized to maximize
selectivity to the desired reaction products. The pattern may also
be optimized to create a tailored gradient within the catalyst
structure, along the length of the catalyst structure, or both.
[0194] The grooves or microgrooves 530 in the front or first
surface 512 intersect the grooves or microgrooves in the back or
second surface 514 at right angles in the illustrated embodiment,
however, it is to be understood that the angles of intersection may
be of any value (e.g., from about 30.degree. to about 120.degree.)
and are therefore not limited to being only right angles.
[0195] FIG. 60 illustrates a composite structure 502 comprising a
plurality of the shims 510 illustrated in FIG. 59 which may be
stacked one above another or positioned side by side. Any number of
shims 510 may be stacked one above the other or positioned side by
side in the composite support structure 502. For example, 2, 3, 4,
6, 8, 10, 20, 30, 50, 100, etc., shims 510 may be stacked one above
another.
[0196] The catalyst may be deposited on the support strips 400,
400A, 400B, 400C or 400D, or shims 510, using conventional
techniques. These may include washcoating the catalyst on the
support strips or shims, growing the catalyst on the support strips
or shims, or depositing the catalyst on the support strips or shims
using vapor deposition. The vapor deposition may be chemical vapor
deposition or physical vapor deposition. The catalyst may be
deposited by slurry-coating, sol-coating or solution-coating. In
one embodiment, the catalyst may be in the form of microsized
particulates deposited in and adhered to the grooves or
microgrooves of the support strips or shims. The catalyst loading
may be in the range from about 0.1 to about 100 milligrams (mg) per
square centimeter of support strip or shim, and in one embodiment
in the range from about 1 to about 10 mg of catalyst per square
centimeter of support strip or shim. The microsized particulates
may have average particle sizes in the range from about 0.01 to
about 100 microns, and in one embodiment in the range from about
0.1 to about 50 microns, and in one embodiment in the range from
about 0.1 to about 10 microns, and in one embodiment from about 0.1
to about 7 microns, and in one embodiment from about 0.1 to about 5
microns, and in one embodiment from about 0.1 to about 3 microns,
and in one embodiment from about 0.1 to about 2 microns, and in one
embodiment from about 0.1 to about 1 micron, and in one embodiment
from about 0.1 to about 0.5 micron.
[0197] Repeating units for use in microchannel reactor core 110
employing support strip 400A for supporting a catalyst are
illustrated in FIGS. 32, 33 and 48-53. The number of these
repeating units that may be used in the microchannel reactor core
110 may be any number, for example, one, two, three, four, five,
six, eight, ten, hundreds, thousands, etc. Referring to FIG. 32,
repeating unit 201A includes process microchannel 210 with support
strip 400A mounted on interior wall 230 of the process microchannel
210. Bulk flow region 234 is defined by the space within the
process microchannel 210 above the support strip 400A. Process
fluid flows through the process microchannel 210 as indicated by
arrows 220 and 222. In flowing through the process microchannel
210, the process fluid flows through the bulk flow region 234 in
contact with the catalyst support strip 400A. The catalyst may be
in the form of microsized particulates positioned in the
microgrooves 430. The support strip 400A is a flow-by support
strip. However, some of the process fluid may flow in the
microgrooves 430 in contact with the catalyst. The flow of the
process fluid through the microgrooves 430 may be in the general
direction from the first side edge 416 toward the second side edge
418 and the back edge 422. FIG. 38 is a photograph of a process
microchannel 210 corresponding to the process microchannel 210
schematically illustrated in FIG. 32.
[0198] The repeating unit 201B illustrated in FIG. 33 is similar to
the repeating unit 201A illustrated in FIG. 32 with the exception
that the process microchannel 210 illustrated in FIG. 33 contains
opposite interior walls 230 and 232 and a catalyst supporting
support strip 400A mounted on each of the opposite interior
walls.
[0199] The repeating unit 201C illustrated in FIG. 34 contains
composite support structure 402 in its reaction zone. The process
fluids flow through the process microchannel 210 in the direction
indicated by arrows 220 and 222. The composite support structure
402 is a flow-through device. In the composite support structure
402, the openings in the microgrooves 430 in each of the support
strips 400C and 400D are sufficient to permit flow to permeate,
defuse and/or weakly advect from layer to layer to fully access the
catalytic sites.
[0200] The repeating unit 201D illustrated in FIG. 39 includes
process microchannel 210 which has support strip 400A mounted on
interior wall 230 and surface features 235 formed in the opposite
interior wall 232. Process fluid flows through the process
microchannel 210 as indicated by arrows 220. The flow of the
process fluid is modified as the process fluid flows through
surface features 235. The surface features 235 illustrated in FIG.
39 are in the form of spherical depressions in the microchannel
wall 232. The modification of the flow of the process fluids by the
surface features 235 enhances contact between the process fluid and
the catalyst supported by the support structure 400A.
[0201] The repeating unit 201E illustrated in FIG. 40 is similar to
the repeating unit 201D illustrated in FIG. 39 with the exception
that the surface features 235 are in the form of frustrum
depressions in the microchannel wall 232.
[0202] The repeating unit 201F illustrated in FIG. 41 is similar to
the repeating unit 201D illustrated in FIG. 39 with the exception
that the surface features 235 in FIG. 41 are in the form of
rectangular depressions in the microchannel wall 232.
[0203] The interior wall 232 of process microchannel 210 is
illustrated in FIGS. 42, 43 and 44 wherein surface features of
different forms are provided. The surface features in FIG. 42 are
in the form of depressions in or projections from the microchannel
wall 232 which are in the form of vanes. The surface features
illustrated in FIG. 43 are in the form of depressions in or
projections from the microchannel wall 232 which are in the form of
air foils. The surface features illustrated in FIG. 44 are in the
form of angular rectangular depressions in or projections from the
microchannel wall 232.
[0204] Surface features 235 of various designs are illustrated in
FIG. 45. Each of the surface features 235 illustrated in FIG. 45
may be in the form of a depressions in or a projections from
microchannel wall 232.
[0205] The repeating unit 201G illustrated in FIG. 48 comprises
process microchannel 210 and heat exchange channel 295. This
repeating unit is similar to repeating unit 210A illustrated in
FIG. 32 except that repeating unit 201G includes heat exchange
channel 295. The flow of heat exchange fluid in the heat exchange
channel 295 may be co-current or counter-current relative to the
flow of process fluid in the process microchannel 210.
[0206] FIG. 49 is a schematic illustration of repeating unit 201H
which comprises process microchannel 210 and a plurality of heat
exchange channels 296. The process microchannel 210 contains a
reaction zone comprising a catalyst supporting support 400A. The
flow of heat exchange fluid in the heat exchange channels 296 is
cross-current relative to the flow of process fluid in the process
microchannel.
[0207] FIG. 50 is a schematic illustration of a repeating unit
comprising two adjacent process microchannels 210 and 210a, and a
plurality of heat exchange channels 296. The process microchannels
210 contain reaction zones comprising catalyst supporting support
strips 400A. The heat exchange channels 296 are adjacent to
microchannel 210 and in thermal contact with process microchannel
210a. The flow of heat exchange fluid in the heat exchange channels
296 is cross-current relative to the flow of process fluid in the
process microchannels 210 and 210a.
[0208] FIG. 51 is a schematic illustration of repeating unit 201J
which is similar to repeating unit 201H illustrated in FIG. 49 with
the exception that the repeating unit 201J includes additional heat
exchange channels 296a near the exit of the process microchannel.
These additional heat exchange channels may be used to provide for
additional heating or cooling.
[0209] FIG. 52 is a schematic illustration of repeating unit 202D
which comprises process microchannel 210, staged addition channel
280, and a plurality of heat exchange channels 296. The process
microchannel 210 contains a reaction zone 210 containing a catalyst
supporting support strip 400A. The staged addition channel 280 and
the process microchannel 210 have a common wall 281 with an
apertured section 290 positioned in the common wall. A feed
composition comprising ethylbenzene flows in the process
microchannel as indicated by arrow 220. A staged addition feed
stream comprising oxygen flows from the staged addition channel 280
through the apertured section 290 into the process microchannel 210
where it contacts and mixes with the feed composition. The oxygen
and ethylbenzene react in the presence of the catalyst to form
styrene. Heat exchange fluid flows in the heat exchange channels
296 in a direction that is cross-current relative to the direction
of flow of process fluids in the process microchannel 210.
[0210] FIG. 53 is a schematic illustration of repeating unit 202E
that is similar to the repeating unit 202D illustrated in FIG. 52
with the exception that the repeating unit 202E contains two
adjacent sets of process microchannels, staged addition channels
and apertured sections. One of these sets is adjacent to the heat
exchange channels 296 while the other set is in thermal contact
with the heat exchange channels 296.
[0211] The microchannel reactor core 110 including the process
microchannels, optional staged addition channels, and heat exchange
channels, as well as any process headers, process footers, heat
exchange headers or heat exchange footers, and structured wall
strips or shims, may be made of any material that provides
sufficient strength, dimensional stability and heat transfer
characteristics to permit operation of the inventive process. These
materials include steel; aluminum, titanium; nickel, platinum;
rhodium; copper; chromium; brass; alloys of any of the foregoing
metals; polymers (e.g., thermoset resins); ceramics; glass;
composites comprising one or more polymers (e.g., thermoset resins)
and fiberglass; quartz; silicon; or a combination of two or more
thereof.
[0212] The microchannel reactor core 110 may be fabricated using
known techniques including wire electrodischarge machining,
conventional machining, laser cutting, photochemical machining,
electrochemical machining, molding, water jet, stamping, etching
(for example, chemical, photochemical or plasma etching) and
combinations thereof.
[0213] The microchannel reactor core 110 may be constructed by
forming layers or sheets with portions removed that allow flow
passage. A stack of sheets may be assembled via diffusion bonding,
laser welding, diffusion brazing, and similar methods to form an
integrated device. The microchannel reactor core 110 may be
assembled using a combination of sheets or laminae and partial
sheets or strips. In this method, the channels or void areas may be
formed by assembling strips or partial sheets to reduce the amount
of material required.
[0214] In one embodiment, subsections or modular units of the
microchannel reactor core 110 may be fabricated using the following
components: a substrate piece with a hermetically sealed perimeter
and open top/bottom for process flow; and a heat exchange piece.
The substrate piece and heat exchange piece may be joined (welded,
glued, soldered, etc.) to form a leak-free operating unit. The heat
exchange piece may be extruded. The substrate piece and the heat
exchange piece may be made from plastic, metal, or other materials
as discussed above.
[0215] In one embodiment, the microchannel reactor core 110 may be
made by a process that comprises laminating or diffusion bonding
shims made of any of the above-indicated materials (e.g., metal,
plastic or ceramic) so that each layer has a defined geometry of
channels and openings through which to convey fluids. After the
individual layers have been created, the microgrooved support
strips and/or composite support structures may be inserted and the
desired catalyst or sorption medium may be applied to the
microgrooved support strips and/or composite support structures.
The catalyst or sorption medium may be applied to the microgrooved
support strips and/or composite support structures prior to
inserting the support strips into the desired process
microchannels. The layers may then be stacked in a prescribed order
to build up the lamination. The layers may be stacked side-by-side
or one above the other. The completed stack may then be diffusion
bonded to prevent fluids from leaking into or out of the
microchannel reactor or microchannel separator. After bonding, the
device may be trimmed to its final size and prepared for attachment
of pipes and manifolds.
[0216] Feature creation methods include photochemical etching,
milling, drilling, electrical discharge machining, laser cutting,
and stamping. A useful method for mass manufacturing is stamping.
In stamping, care should be taken to minimize distortion of the
material and maintain tight tolerances of channel geometries.
Preventing distortion, maintaining shim alignment and ensuring that
layers are stacked in the proper order are factors that should be
controlled during the stacking process.
[0217] The stack may be bonded through a diffusion process. In this
process, the stack may be subjected to elevated temperatures and
pressures for a precise time period to achieve the desired bond
quality. Selection of these parameters may require modeling and
experimental validation to find bonding conditions that enable
sufficient grain growth between metal layers.
[0218] The next step, after bonding, may be to machine the device.
A number of processes may be used, including conventional milling
with high-speed cutters, as well as highly modified electrical
discharge machining techniques. A full-sized bonded microchannel
reactor or microchannel separator unit or sub-unit that has
undergone post-bonding machining operations may comprise, for
example, tens, hundreds or thousands of shims.
[0219] The microchannel reactor 100 may have appropriate manifolds,
valves, conduit lines, etc. to control flow of the process fluid,
and the flow of the heat exchange fluid. These are not shown in the
drawings, but can be readily provided by those skilled in the
art.
[0220] The staged addition channels 280 and 280A may be
microchannels or they may have larger dimensions. The process
microchannels 210 and the staged addition channels 280 and 280A may
have cross sections with any shape, for example, a square,
rectangle, circle, semi-circle, etc. Each process microchannel 210
and staged addition channel 280 and 280A may have an internal
height or gap of up to about 10 mm, and in one embodiment up to
about 6 mm, and in one embodiment up to about 4 mm, and in one
embodiment up to about 2 mm. In one embodiment, the height or gap
may be in the range of about 0.05 to about 10 mm, and in one
embodiment about 0.05 to about 6 mm, and in one embodiment about
0.05 to about 4 mm, and in one embodiment about 0.05 to about 2 mm.
The width of each process microchannel 210 and staged addition
channel 280 and 280A may be of any dimension, for example, up to
about 3 meters, and in one embodiment about 0.01 to about 3 meters,
and in one embodiment about 0.1 to about 3 meters. The length of
each process microchannel 210 and staged addition channel 280 and
280A may be of any dimension, for example, up to about 10 meters,
and in one embodiment from about 0.1 to about 10 meters, and in one
embodiment from about 0.2 to about 10 meters, and in one embodiment
from about 0.2 to about 6 meters, and in one embodiment from 0.2 to
about 3 meters.
[0221] The heat exchange channels 260, 295 and 296 may be
microchannels or they may have larger dimensions. Each of the heat
exchange channels 260, 295 and 296 may have a cross section having
any shape, for example, a square, rectangle, circle, semi-circle,
etc. Each of the heat exchange channels 260, 295 and 296 may have
an internal height or gap of up to about 10 mm, and in one
embodiment in the range of about 0.05 to about 10 mm, and in one
embodiment from about 0.05 to about 5 mm, and in one embodiment
from about 0.05 to about 2 mm. The width of each of these channels
may be of any dimension, for example, up to about 3 meters, and in
one embodiment from about 0.01 to about 3 meters, and in one
embodiment about 0.1 to about 3 meters. The length of each of the
heat exchange channels 260, 295 and 296 may be of any dimension,
for example, up to about 10 meters, and in one embodiment from
about 0.1 to about 10 meters, and in one embodiment from about 0.2
to about 6 meters, and in one embodiment from 0.2 to about 3
meters.
[0222] In one embodiment, the process microchannels and heat
exchange channels used in the microchannel reactor core 110 may
have rectangular cross sections and be aligned in side-by-side
vertically oriented planes or horizontally oriented stacked planes.
These planes may be tilted at an inclined angle from the
horizontal. These configurations may be referred to as parallel
plate configurations. Various combinations of two or more process
microchannels with a single heat exchange channel, or two or more
heat exchange channels in combination with a single process
microchannel may be employed. An array of these rectangular
channels may be arranged in a modularized compact unit for
scale-up.
[0223] The cross-sectioned shape and size of the process
microchannels may vary along their axial length to accommodate
changing hydrodynamics of the reaction. For example, if the
reaction is an oxidative dehydrogenation reaction and one of the
reactants is in excess, the fluidic properties of the reaction
mixture may change over the course of the reaction. Surface
features may be used to provide a different geometry, pattern,
angle, depth, or ratio of size relative to the cross-section of the
microchannel along its axial length to accommodate these
hydrodynamic changes.
[0224] The separation between each process microchannel or staged
addition channel and the next adjacent heat exchange channel may be
in the range from about 0.05 mm to about 50 mm, and in one
embodiment about 0.1 to about 10 mm, and in one embodiment about
0.2 mm to about 2 mm.
[0225] The invention may relate to an apparatus, comprising: a
process microchannel; a heat exchange channel; and a heat transfer
wall positioned between the process microchannel and the heat
exchange channel, the heat transfer wall comprising at least one
thermal resistance layer. The thermal resistance layer may be
positioned on either or both sides of the heat transfer wall and/or
embedded in the heat transfer wall. The apparatus, which is
illustrated in FIG. 61, may be used as a repeating unit within the
microchannel reactor 100. Referring to FIG. 61, the apparatus,
which may be referred to as repeating unit 600, comprises process
microchannel 602 and heat exchange channel 604. Heat transfer wall
605 is positioned between the process microchannel 602 and heat
exchange channel 604. The process microchannel 602 includes bulk
flow region 603 and structured wall 606 which may be used to
support a catalyst. Thermal resistance layer 608 may be embedded
within the heat transfer wall 605 as illustrated in FIG. 61.
Alternatively or additionally, the thermal resistance layer 608 may
be positioned on the process microchannel side of the heat transfer
wall 605 and/or on the heat exchange channel side of the heat
transfer wall 605. The thermal resistance layer 608 may have the
same construction as the structured wall 606 (except that no
catalyst is present). The thermal resistance layer 608 may be
separated from the interior of the process microchannel 602 by wall
609 and from the interior of the heat exchange channel 604 by wall
610. In FIG. 61 only half the process microchannel 602 is shown.
The other half of the process microchannel may comprise a second
structured wall for supporting a catalyst. The second half of the
process microchannel may comprise a second heat transfer wall 605
including a second thermal resistance layer 608. A second heat
exchange channel may be provided on the other side of the process
microchannel 602. A staged addition channel may be positioned
adjacent the process microchannel 602.
[0226] The heat exchange channel 604 may be a microchannel or it
may have a larger dimension. The process microchannel 602 and the
heat exchange channel 604 may each have an internal height or gap
of up to about 10 mm, and in one embodiment in the range of about
0.05 to about 10 mm, and in one embodiment from about 0.05 to about
5 mm, and in one embodiment from about 0.05 to about 2 mm. The
width of each of these channels may be of any dimension, for
example, up to about 3 meters, and in one embodiment from about
0.01 to about 3 meters, and in one embodiment about 0.1 to about 3
meters. The length of each of the these channels may be of any
dimension, for example, up to about 10 meters, and in one
embodiment from about 0.1 to about 10 meters, and in one embodiment
from about 0.2 to about 6 meters, and in one embodiment from 0.2 to
about 3 meters. The heat transfer wall may have a thickness in the
range from about 0.05 to about 5 mm, and in one embodiment from
about 0.05 to about 4 mm, and in one embodiment from about 0.05 to
about 3 mm, and in one embodiment from about 0.05 to about 2 mm,
and in one embodiment from about 0.05 to about 1.5 mm, and in one
embodiment from about 0 to about 1 mm. The thermal resistance layer
608 may have a thickness in the range from about 1 to about 99% of
the thickness of the heat transfer wall 605, and in one embodiment
from about 1 to about 80%, and in one embodiment from about 1 to
about 50%, and in one embodiment from about 1 to about 30%, and in
one embodiment from about 1 to about 20%, and in one embodiment
from about 1 to about 10%.
[0227] The process microchannel 602, heat exchange channel 604,
heat transfer wall 605, and thermal resistance layer 608 may
independently be made of a material comprising: steel; monel;
inconel; aluminum; titanium; nickel; copper; brass; an alloy of any
of the foregoing metals; ceramics; glass; quartz; silicon; or a
combination of two or more thereof.
[0228] The construction and/or material of construction of the
thermal resistance layer 608 may comprise any construction and/or
material of construction having a different thermal conductivity
than the thermal conductivity of the heat transfer wall 605. The
thermal resistance layer 608 may comprise a vacuum, a gaseous
material, a liquid and/or a solid material embedded in the heat
transfer wall 605. The solid material may contain void spaces,
openings and/or through holes. The thermal resistance layer may
comprise one or more strips or shims which may contain void spaces,
openings and/or through holes. The thermal resistance layer may
comprise one or more strips with grooves or microgrooves formed in
the strip. The thermal resistance layer may comprise one or more
shims, each of the shims having a first surface and a second
surface, and grooves or microgrooves formed in the first surface
and/or the second surface.
[0229] The thermal resistance layer 608 and/or heat transfer wall
605 may comprise one or more sub-assemblies of a thermal resistant
construction. Each sub-assembly may comprise two or more shims
stacked one above another with one or more void spaces positioned
between the shims. The void spaces may comprise a vacuum, air or an
inert gas. The thermal resistance layer 608 and/or heat transfer
wall 605 may comprise any desired number of these sub-assemblies
stacked one above another, for example, from 1 to about 100
sub-assemblies, and in one embodiment from 1 to about 50
sub-assemblies, and in one embodiment from 1 to about 20
sub-assemblies, and in one embodiment from 1 to about 10
sub-assemblies, and in one embodiment from 1 to about 5
sub-assemblies, and in one embodiment from 1 to about 3
sub-assemblies, and in one embodiment 1 or 2 sub-assemblies.
[0230] The structured wall 606 and the thermal resistance layer 608
may be constructed by stacking a plurality of the shims illustrated
in FIGS. 59 and 60 one above another. The shims used to form the
structured wall 606 and thermal resistance layer 608 may
independently have alternating patterns such that a porous
structure may be created when the shims are stacked together to
form the structured wall 606 and/or thermal resistance layer 608.
The openings in the alternating shims may be arranged to create
solid metal connections through the stack of shims along with
completely open large pores through the stack to facilitate rapid
diffusion. There may be cross members that extend from the solid
metal connections through some of the open porous area to further
increase the internal surface area. The openings in the structured
wall 606 and/or thermal resistance layer 608 may vary from about 25
microns to about 500 microns, and in one embodiment from about 50
to about 250 microns.
[0231] The mass of reactants may diffuse and to some extent flow
within the open porous structure of the structured wall 606. The
catalyst may coat part of or the entire surface area of the
structured wall 606.
[0232] The bulk flow region 603 in the process microchannel may
reduce the impediment to flow resistance and allow the reactants to
diffuse into the open structured walls 606 to access the
catalyst.
[0233] In one embodiment, the heat transfer wall 605 may form an
interior wall of the process microchannel 602 and one or more shims
may be positioned on said interior wall to form structured wall
606, the one or more shims containing void spaces, openings or
through holes. A catalyst may be supported by the one or more
shims.
[0234] The microchannel reactor 100 may comprise one or more of the
repeating units 600. In one embodiment, the microchannel reactor
may comprise from 1 to about 50,000 of the repeating units 600, and
in one embodiment from about 10 to about 50,000 of the repeating
units 600, and in one embodiment from about 10 to about 30,000
repeating units, and in one embodiment from about 10 to about
10,000 of the repeating units 600, and in one embodiment from about
10 to about 5000 repeating units 600, and in one embodiment from
about 10 to about 2000 repeating units 600, and in one embodiment
from about 10 to about 1000 repeating units 600, and in one
embodiment from about 10 to about 500 repeating units 600, and in
one embodiment from about 10 to about 100 repeating units 600.
[0235] A plurality of the microchannel reactors 100 may be housed
in vessel 700 which is illustrated in FIGS. 77 and 78. Referring to
FIGS. 77 and 78, the vessel 700 contains five microchannel reactors
100. These are identified in FIGS. 77 and 78 as microchannel
reactors 100-1, 100-2, 100-3, 100-4 and 100-5. Although five
microchannel reactors 100 are disclosed in the drawings, it will be
understood that the vessel 700 may contain any desired number of
microchannel reactors. For example, the vessel 700 may contain from
1 to about 1000 microchannel reactors 100, and in one embodiment
from about 3 to about 500 microchannels reactors 100, and in one
embodiment from about 3 to about 250 microchannel reactors 100, and
in one embodiment from about 3 to about 150 microchannel reactors
100, and in one embodiment from about 5 to about 50 microchannel
reactors 100, and in one embodiment from about 5 to about 12
microchannel reactors 100. In one embodiment, the vessel 700 may
contain from 1 to about 50 microchannel reactors 100, and in one
embodiment from 1 to about 20 microchannel reactors 100. Each
microchannel reactor 100 may comprise from about 1 to about 50,000
process microchannels, and in one embodiment from about 10 to about
50,000 process microchannels, and in one embodiment from about 10
to about 30,000, and in one embodiment from about 10 to about
10,000 process microchannels. The vessel 700 may be a pressurizable
vessel. The vessel 700 includes inlets 702 and 704, and outlets 706
and 708. The inlet 702 is connected to a manifold which may be
provided for flowing the ethylbenzene feed to the process
microchannels in the microchannel reactors 100-1, 100-2, 100-3,
100-4 and 100-5. The inlet 704 is connected to a manifold which may
be provided for flowing heat exchange fluid to the heat exchange
channels in the microchannel reactors 100-1, 100-2, 100-3, 100-4
and 100-5. The outlet 706 is connected to a manifold which may be
provided for flowing product from the microchannel reactors 100-1,
100-2, 100-3, 100-4 and 100-5 out of the vessel 700. The inlet 708
is connected to a manifold which may provide for the flow of the
oxygen or source of oxygen (e.g., air) to staged addition channels
that may be in the microchannel reactors 100-1, 100-2, 100-3, 100-4
and 100-5. The vessel 700 also includes an outlet (not shown in the
drawings) providing for the flow of heat exchange fluid from the
microchannel reactors 100-1, 100-2, 100-3, 100-4 and 100-5.
[0236] The vessel 700 may be constructed from any suitable material
sufficient for operating under the pressures and temperatures
required for operating the microchannel reactors. For example, the
shell and heads of the vessels 700 may be constructed of cast
steel. The flanges, couplings and pipes may be constructed of
stainless steel or other suitable alloys. The vessel 700 may have
any desired diameter, for example, from about 30 to about 500 cm,
and in one embodiment from about 100 to about 300 cm. The axial
length of the vessel 700 may be of any desired value, for example,
from about 0.5 to about 50 meters, and in one embodiment from about
0.5 to about 15 meters, and in one embodiment from about 1 to about
10 meters.
[0237] As indicated above, the microchannel reactors 100 may
comprise a plurality of process microchannels, heat exchange
channels and optionally staged addition channels stacked one above
the other or positioned side-by-side. The microchannel reactors 100
may be in the form of cubic blocks as illustrated in FIGS. 77 and
78. Each of these cubic blocks may have a length, width and height.
The length may be in the range from about 10 to about 1000 cm, and
in one embodiment in the range from about 50 to about 200 cm. The
width may be in the range from about 10 to about 1000 cm, and in
one embodiment in the range from about 50 to about 200 cm. The
height may be in the range from about 10 to about 1000 cm, and in
one embodiment in the range from about 50 to about 200 cm.
[0238] In one embodiment, the reaction zone 212 in the process
microchannel 210 may be characterized by having a bulk flow path.
The term "bulk flow path" refers to an open path (contiguous bulk
flow region) within the process microchannels. A contiguous bulk
flow region allows rapid fluid flow through the microchannels
without large pressure drops. In one embodiment, the flow of fluid
in the bulk flow region is laminar. Bulk flow regions within each
process microchannel 210 may have a cross-sectional area of about
0.05 to about 10,000 mm.sup.2, and in one embodiment about 0.05 to
about 5000 mm.sup.2, and in one embodiment about 0.1 to about 2500
mm.sup.2. The bulk flow regions may comprise from about 5% to about
95%, and in one embodiment about 30% to about 80% of the
cross-section of the process microchannels.
[0239] In one embodiment of the invention relatively short contact
times, high selectivity to the desired product and relatively low
rates of deactivation of the catalyst may be achieved by limiting
the diffusion path required for the catalyst. For example, this may
be achieved when the catalyst is in the form of a thin layer on an
engineered support such as a metallic foam or on the wall of the
process microchannel. This allows for increased space velocities.
In one embodiment, the thin layer of catalyst can be produced using
chemical vapor deposition. This thin layer may have a thickness in
the range up to about 1 micron, and in one embodiment from about
0.1 to about 1 micron, and in one embodiment about 0.25 micron.
These thin layers may reduce the time the reactants are within the
active catalyst structure by reducing the diffusional path. This
decreases the time the reactants spend in the active portion of the
catalyst. The result may be increased selectivity to the product
and reduced unwanted by-products. An advantage of this mode of
catalyst deployment is that, unlike conventional catalysts in which
the active portion of the catalyst may be bound up in an inert low
thermal conductivity binder, the active catalyst film is in
intimate contact with either the engineered structure or the wall
of the process microchannel. This may leverage high heat transfer
rates attainable in the microchannel reactor and allows for close
control of temperature. The result is the ability to operate at
increased temperature (faster kinetics) without promoting the
formation of undesired by-products, thus producing higher
productivity and yield and prolonging catalyst life.
[0240] In one embodiment, the catalyst may be regenerated. This may
be done by flowing a regenerating fluid through the process
microchannels in contact with the catalyst. The regenerating fluid
may comprise hydrogen or a diluted hydrogen stream. The diluent may
comprise nitrogen, argon, steam, methane, carbon dioxide, or a
mixture of two or more thereof. The concentration of H.sub.2 in the
regenerating fluid may range up to about 100% by volume, and in one
embodiment from about 1 to about 100% by volume, and in one
embodiment about 1 to about 50% volume. The regenerating fluid may
flow from the header through the process microchannels to the
footer, or in the opposite direction from the footer through the
process microchannels to the header. The temperature of the
regenerating fluid may be from about 20 to about 600.degree. C.,
and in one embodiment about 20 to about 400.degree. C., and in one
embodiment about 80 to about 200.degree. C. The pressure within the
process microchannels during this regeneration step may range from
about 1 to about 100 atmospheres absolute pressure, and in one
embodiment about 1 to about 10 atmospheres. The residence time for
the regenerating fluid in the process microchannels may range from
about 0.001 to about 10 seconds, and in one embodiment about 0.01
second to about 1 second.
[0241] The contact time of the process fluids with the catalyst
within the process microchannels may be in the range up to about
100 seconds, and in one embodiment in the range from about 1
millisecond (ms) to about 100 seconds, and in one embodiment in the
range from about 1 ms to about 50 seconds, and in one embodiment in
the range from about 1 ms to about 25 seconds, and in one
embodiment in the range from about 1 ms to about 10 seconds, and in
one embodiment from about 1 ms to about 1 second, and in one
embodiment from about 1 ms to about 500 ms, and in one embodiment
about 1 ms to about 200 ms, and in one embodiment about 1 ms to
about 100 ms, and in one embodiment about 1 ms to about 50 ms, and
in one embodiment about 1 ms to about 20 ms, and in one embodiment
about 1 ms to about 10 ms. In one embodiment, the reactants may be
combined with up to about 50% by volume diluent (e.g., nitrogen
gas) and the contact time may be up to about 25 seconds, and in one
embodiment up to about 10 seconds, and in one embodiment up to
about 1 second. In one embodiment, the reactants may be combined
with up to about 25% by volume diluent and the contact time may be
up to about 50 seconds, and in one embodiment up to about 25
seconds, and in one embodiment up to about 5 seconds. In one
embodiment, the reactants may be combined with up to about 10% by
volume diluent and the contact time may be up to about 100 seconds,
and in one embodiment up to about 50 seconds, and in one embodiment
up to about 10 seconds.
[0242] The flow rate of process fluid flowing in the process
microchannels may be in the range from about 0.001 to about 500
lpm, and in one embodiment about 0.001 to about 250 lpm, and in one
embodiment about 0.001 to about 100 lpm, and in one embodiment
about 0.001 to about 50 lpm, and in one embodiment about 0.001 to
about 25 lpm, and in one embodiment about 0.01 to about 10 lpm. The
velocity of fluid flowing in the process microchannels may be in
the range from about 0.01 to about 200 m/s, and in one embodiment
about 0.01 to about 75 m/s, and in one embodiment about 0.01 to
about 50 m/s, and in one embodiment about 0.01 to about 30 m/s, and
in one embodiment about 0.02 to about 20 m/s. The Reynolds Number
for the fluid flowing in the process microchannels may be in the
range from about 0.0001 to about 100000, and in one embodiment
about 0.001 to about 10000.
[0243] The space velocity (or gas hourly space velocity (GHSV)) for
the flow of the process fluids in the process microchannels may be
at least about 1000 hr.sup.-1 (normal liters of feed per hour per
liter of volume within the process microchannels), and in one
embodiment at least about 2000 hr.sup.-1, and in one embodiment at
least about 4000 hr.sup.-1, and in one embodiment at least about
7000 hr.sup.-1, and in one embodiment at least about 10000
hr.sup.-1. The space velocity may be in the range from about 1000
to about 500000 hr.sup.-1, and in one embodiment in the range from
about 4000 to about 40000 hr.sup.-1. The volume within the process
microchannels may include all volume in the process microchannels
in which a process fluid may flow in a flow-through manner or a
flow-by manner. The volume may include the volume within any
microgrooved supports positioned in the microchannels as well as
the volume within any surface features that may be present in the
process microchannels.
[0244] The management of heat exchange with the inventive process
may provide advantageous control of the conversion of ethylbenzene
and the selectivity to styrene. The heat exchange channels may be
adapted for heat exchange fluid to flow in the heat exchange
channels in a direction that is co-current with the flow of fluid
in process microchannels and/or staged addition channels that are
adjacent to or in thermal contact with the heat exchange channels.
Alternatively, the heat exchange fluid may flow through the heat
exchange channels in a direction that is countercurrent to the flow
of fluid through the process microchannels and/or staged addition
channels. Alternatively, the heat exchange channels may be oriented
relative to the process microchannels and/or staged addition
channels to provide for the flow of heat exchange fluid in a
direction that is cross-current relative to the flow of fluid
through the process microchannels and/or staged addition channels.
The heat exchange channels may have a serpentine configuration to
provide a combination of cross-flow and co-current or
counter-current flow.
[0245] The heat exchange fluid may be any fluid. These include air,
steam, liquid water, gaseous nitrogen, liquid nitrogen, other gases
including inert gases, carbon monoxide, carbon dioxide, oils such
as mineral oil, gaseous hydrocarbons, liquid hydrocarbons, and heat
exchange fluids such as Dowtherm A and Therminol which are
available from Dow-Union Carbide. The heat exchange fluid may
comprise one or more organic compounds containing 1 to about 5
carbon atoms per molecule such as methylenechloride,
fluorochloromethanes (e.g., dichlordiflouromethane), hydrocarbons
containing 1 to about 5 carbon atoms per molecule (e.g., methane,
ethane, ethylene, propanes, butanes, pentanes, etc.), or a mixture
of two or more thereof.
[0246] The heat exchange fluid may comprise the feed composition,
staged addition feed stream and/or product. This can provide
process pre-heat, cool-down and/or an increase in overall thermal
efficiency of the process.
[0247] In one embodiment, the heat exchange channels may comprise
process channels wherein an endothermic or exothermic process is
conducted. These heat exchange process channels may be
microchannels. Examples of endothermic processes that may be
conducted in the heat exchange channels include steam reforming and
dehydrogenation reactions. Examples of exothermic processes that
may be conducted in the heat exchange channels include water-gas
shift reactions, methanol synthesis reactions and ammonia synthesis
reactions.
[0248] In one embodiment, the heat exchange fluid undergoes a phase
change in the heat exchange channels. This phase change provides
additional heat addition to or removal from the process
microchannels and/or second reactant stream channels beyond that
provided by convective heating or cooling. An example of such a
phase change would be an oil or water that undergoes boiling. In
one embodiment, the vapor mass fraction quantity of the boiling of
the phase change fluid may be up to about 100%, and in one
embodiment up to about 75%, and in one embodiment up to about 50%,
and in one embodiment in the range from about of 1% to about
50%.
[0249] The pressure within each individual heat exchange channel
may be controlled using passive structures (e.g., obstructions),
orifices and/or mechanisms upstream of the heat exchange channels
or in the channels. By controlling the pressure within each heat
exchange channel, the temperature within each heat exchange channel
can be controlled. A higher inlet pressure for each heat exchange
fluid may be used where the passive structures, orifices and/or
mechanisms let down the pressure to the desired heat exchange
microchannel pressure. By controlling the temperature within each
heat exchange channel, the temperature in the process microchannels
in thermal contact with the heat exchange microchannel can be
controlled. Thus, for example, each process microchannel may be
operated at a desired temperature by employing a specific pressure
in the heat exchange channel in thermal contact with the process
microchannel. This may provide the advantage of precisely
controlled temperatures for each process microchannel. The use of
precisely controlled temperatures for each process microchannel may
provide the advantage of a tailored temperature profile and an
overall reduction in the energy requirements for the reaction
process.
[0250] The heat flux for heat exchange in the microchannel reactor
may be in the range from about 0.01 to about 500 watts per square
centimeter (W/cm.sup.2) of the surface area of the heat transfer
walls in the microchannel reactor, and in one embodiment from about
0.01 to about 250 W/cm.sup.2. The heat flux may be in the range
from about 0.01 to about 125 W/cm.sup.2, and in one embodiment
about 0.1 to about 50 W/cm.sup.2, and in one embodiment from about
0.1 to about 10 W/cm.sup.2. The heat flux may be in the range from
about 1 to about 500 W/cm.sup.2, and in one embodiment from about 1
to about 250 W/cm.sup.2, and in one embodiment, from about 1 to
about 100 W/cm.sup.2, and in one embodiment from about 1 to about
50 W/cm.sup.2, and in one embodiment from about 1 to about 25
W/cm.sup.2, and in one embodiment from about 1 to about 10
W/cm.sup.2.
[0251] In one embodiment, the temperature of the reactant streams
entering the microchannel reactor may be within about 200.degree.
C., and in one embodiment within about 100.degree. C., and in one
embodiment within about 50.degree. C., and in one embodiment within
about 20.degree. C., of the temperature of the product exiting the
microchannel reactor.
[0252] The use of controlled heat exchange between heat exchange
channels in thermal contact with or adjacent to the process
microchannels and/or staged addition channels may allow for uniform
temperature profiles for the process microchannels and/or staged
addition channels. This provides for the possibility of a more
uniform heat exchange at more rapid rates than can be obtained with
conventional processing equipment such as mixing tanks. For a
microchannel reactor employing multiple process microchannels and
staged addition channels, the temperature difference between the
process microchannels and/or staged addition channels at at least
one common position along the lengths of the process microchannels
may be less than about 5.degree. C., and in one embodiment less
than about 2.degree. C., and in one embodiment less than about
1.degree. C.
[0253] The heat exchange channels in thermal contact with or
adjacent to either the process microchannels and/or staged addition
channels may employ separate temperature zones along the length of
such channels. For example, in one embodiment, the temperature in a
first zone near the entrance to the process microchannel may be
maintained at a temperature above or below a second temperature in
a second zone near the end of the process microchannel. A cool down
or quench zone may be incorporated into the process microchannels
to cool the product. Numerous combinations of thermal profiles are
possible, allowing for a tailored thermal profile along the length
of the process microchannels and/or staged addition channels,
including the possibility of heating or cooling zones before and/or
after the reaction zone in the process microchannels to heat or
cool the reactants and/or product.
[0254] The heat exchange fluid entering the heat exchange channels
may be at a temperature in the range from about 50.degree. C. to
about 650.degree. C., and in one embodiment in the range from about
150.degree. C. to about 600.degree. C., and in one embodiment in
the range from about 250.degree. C. to about 500.degree. C. The
heat exchange fluid exiting the heat exchange channels may be at a
temperature in the range from about 100.degree. C. to about
700.degree. C., and in one embodiment in the range from about
200.degree. C. to about 650.degree. C., and in one embodiment in
the range from about 300.degree. C. to about 550.degree. C. The
residence time of the heat exchange fluid in the heat exchange
channels may be in the range from about 5 ms to about 1 minute, and
in one embodiment from about 20 ms to about 1 minute, and in one
embodiment from about 50 ms to about 1 minute, and in one
embodiment about 100 ms to about 1 minute. The pressure drop for
the heat exchange fluid as it flows through the heat exchange
channels may be in the range up to about 1 atm/m, and in one
embodiment up to about 0.5 atm/m, and in one embodiment up to about
0.1 atm/m, and in one embodiment from about 0.01 to about 1 atm/m.
The heat exchange fluid may be in the form of a vapor, a liquid, or
a mixture of vapor and liquid. The Reynolds Number for the flow of
vapor through the heat exchange channels may be in the range from
about 10 to about 5000, and in one embodiment about 100 to about
3000. The Reynolds Number for the flow of liquid through heat
exchange channels may be in the range from about 10 to about 10000,
and in one embodiment about 100 to about 5000.
[0255] The temperature of the reactants entering the microchannel
reactor reactor core 110 may be in the range up to about
600.degree. C., and in one embodiment in the range from about
150.degree. C. to about 600.degree. C., and in one embodiment from
about 250.degree. C. to about 550.degree. C.
[0256] The temperature within the process microchannels for a
dehydrogenation reaction process may be in the range from about
650.degree. C. to about 900.degree. C., and in one embodiment from
about 700.degree. C. to about 850.degree. C. The temperature within
the process microchannels for an oxidative dehydrogenation reaction
process may be in the range from about 250.degree. C. to about
650.degree. C., and in one embodiment from about 350.degree. C. to
about 550.degree. C., and in one embodiment from about 400.degree.
C. to about 500.degree. C.
[0257] The temperature of the product exiting the microchannel
reactor core 110 may be in the range up to about 650.degree. C.,
and in one embodiment in the range from about 150.degree. C. to
about 650.degree. C., and in one embodiment from about 200.degree.
C. to about 600.degree. C., and in one embodiment from about
250.degree. C. to about 550.degree. C.
[0258] The pressure within the process microchannels may be in the
range up to about 50 atmospheres absolute pressure, and in one
embodiment up to about 40 atmospheres, and in one embodiment up to
about 30 atmospheres. In one embodiment the pressure may be in the
range from about 1 to about 50 atmospheres absolute pressure, and
in one embodiment from about 10 to about 40 atmospheres, and in one
embodiment from about 20 to about 30 atmospheres.
[0259] The pressure drop of the process fluids as they flow in the
process microchannels may be in the range up to about 5 atmospheres
per meter of length of the process microchannel (atm/m), and in one
embodiment up to about 1 atm/m, and in one embodiment up to about
0.1 atm/m.
[0260] The pressure drop for the stage addition feed stream flowing
through the apertured sections may be in the range up to about 0.1
atm, and in one embodiment from about 0.001 to about 0.1 atm, and
in one embodiment from about 0.001 to about 0.05 atm, and in one
embodiment about 0.001 to about 0.005 atm. The reactants and
products flowing through the process microchannels may be in the
form of a vapor, a liquid, or a mixture of vapor and liquid. The
Reynolds Number for the flow of vapor through the process
microchannels may be in the range from about 10 to about 10000, and
in one embodiment about 100 to about 3000. The Reynolds Number for
the flow of liquid through the process microchannels may be about
10 to about 10000, and in one embodiment about 100 to about
3000.
[0261] The conversion of the ethylbenzene may be in the range from
about 25% or higher per cycle, and in one embodiment about 50% or
higher per cycle, and in one embodiment from about 25 to about
100%, and in one embodiment from about 50% to about 100% per cycle.
In one embodiment, the conversion may be at least about 70%.
[0262] The conversion of the oxygen, when used, may be in the range
from about 40% or higher per cycle, and in one embodiment from
about 40% to about 100% per cycle.
[0263] The yield of styrene may be in the range from about 20% or
higher, and in one embodiment about 50% or higher, and in one
embodiment from about 50% to about 99%.
[0264] The selectivity to styrene may be at least about 50%, and in
one embodiment at least about 80%, and in one embodiment at least
about 90%, and in one embodiment at least about 95%, and in one
embodiment in the range from about 50% to about 99%, and in one
embodiment in the range from about 80% to about 99%, and in one
embodiment from about 95% to about 99%.
[0265] It may be possible to achieve a yield of styrene that is at
least about 20% with less than about 20% change in the yield of
styrene for a period of at least about 24 hours with a contact time
of less than about 10 seconds and a feed composition containing
less than about 50% by volume diluent (e.g., nitrogen gas). It may
be possible to achieve a yield of styrene that is at least about
35%, and in one embodiment at least about 50%, and in one
embodiment at least about 75% with less than about 20% change in
the yield of styrene for at least about 24 hours with a contact
time of less than about 10 seconds and a feed composition
containing less than about 50% by volume diluent (e.g., nitrogen
gas). In one of these embodiments, the contact time may be less
than about 5 seconds, and in one embodiment less than about 2
seconds, and in one embodiment less than about 1 second. In one of
these embodiments, the feed composition may contain less than about
25% by volume diluent, and in one embodiment less than about 10% by
volume diluent.
[0266] It may be possible to produce styrene at a rate of at least
about 500 ml per gram of catalyst per hour using the inventive
process, and in one embodiment at least about 750 ml per gram of
catalyst per hour, and in one embodiment at least about 900 ml per
gram of catalyst per hour, and in one embodiment at least about
1000 ml per gram of catalyst per hour.
[0267] It may be possible to achieve a styrene yield that is at
least about 20% with less than about 20% change in the styrene
yield for at least about 24 hours wherein the styrene is produced
at a rate of at least about 500 ml per gram of catalyst per hour.
In one of these embodiments, the styrene yield may be at least
about 35%, and in one embodiment at least about 50%, and in one
embodiment at least about 75%. In one of these embodiments, the
styrene may be produced at a rate of at least about 750 ml per gram
of catalyst per hour, and in one embodiment at least about 900 ml
per gram of catalyst per hour, and in one embodiment at least about
1000 ml per gram of catalyst per hour.
Example 1
[0268] 0.7% K.sub.2O-15% MoO.sub.3/SiO.sub.2--TiO.sub.2 catalyst is
prepared by the sol-gel method. 20.0 g tetraethylorthosilicate and
27.29 g titanium isopropoxide are dissolved in 200 ml isopropyl
alcohol solution with stirring. In another beaker, 2.93 g ammonium
paramolybdate are dissolved in 13.65 g H.sub.2O and then 0.30 g 45%
KOH solution are added. The aqueous solution is added dropwise to
the alcohol solution (1 ml/min). After all of the aqueous solution
is added, the resulting gel is stirred for additional 15 min. The
gel is dried at 110.degree. C. overnight and calcined at
550.degree. C. for 5 hours. The catalyst is crushed and sieved to
60-100 mesh.
[0269] The catalyst (0.4 g) is loaded in a quartz tube reactor
having a 0.2 inch O.D. (0.635 cm). The reactor volume is 0.3 ml. A
feed gas composition containing 9.9% by volume ethylbenzene, 5% by
volume O.sub.2 and 85.1% by volume N.sub.2 flows into the reactor.
The feed gas flow rate is 180 ml/min. The contact time based on
reactor volume is 0.1 second. The process operates for 3 hours with
no evidence of catalyst deactivation. The process is operated at
atmospheric pressure. The GHSV based on reactor volume is 36000
hr.sup.-1. The GHSV based on the catalyst is 27000 ml/g-cat/hour.
The GHSV for ethylbenzene based on catalyst is 2670 ml/g-cat/hour.
The products are analyzed by GC. At 500.degree. C., 43%
ethylbenzene conversion and 91% styrene selectivity are achieved.
The styrene yield is 39%. The styrene yield is 1041 ml/g-cat/hour.
O.sub.2 conversion is 98%.
Example 2
[0270] 0.7% K.sub.2O-18% V.sub.2O.sub.5/SiO.sub.2--ZrO.sub.2
catalyst is prepared by the sol-gel method. 7.05 g vanadium (III)
2,4-pentanedionate are dissolved in 200 ml iso-butanol with
stirring at 60.degree. C. After cooling, 19.97 g zirconium
n-butoxide are added at room temperature with stirring, followed by
15.0 g n-butoxysilane. In another beaker, 0.19 g 45% KOH solution
are mixed with 6.63 g H.sub.2O. The aqueous solution is added
dropwise to the alcohol solution (1 ml./min). After all of the
aqueous solution is added, the resulting mixture is stirred for an
additional 15 min. The gel is then dried at 110.degree. C.
overnight and calcined at 550.degree. C. for 5 hours. The catalyst
is crushed and sieved to 60-100 mesh.
[0271] The catalyst (0.5 g) is loaded in the quartz tube reactor
identified in Example 1. The feed gas composition contains 9.9% by
volume ethylbenzene, 5% by volume O.sub.2 and 85.1% by volume
N.sub.2. The contact time is 0.1 second. The process operates for 3
hours with no evidence of catalyst deactivation. The process is
operated at atmospheric pressure. The products are analyzed by GC.
At 450.degree. C., 36% ethylbenzene conversion and 89% styrene
selectivity are achieved. The styrene yield is 32%. O.sub.2
conversion is 96%.
Example 3
[0272] Mg.sub.0.99MoO.sub.3.99 catalyst is prepared by the sol-gel
method. 16.00 g molybdenum (VI) oxide bis (2,4-pentanedionate) is
dissolved in 200 ml methoxyethanol. 5.56 g magnesium ethoxide are
then added with stirring. Subsequently, 14.13 g 2.5 mol/L
NH.sub.4OH solution are added dropwise to the mixture. The
resulting gel is dried at 110.degree. C. for 5 hours and then
calcined at 550.degree. C. for 12 hours. The catalyst is crushed
and sieved to 60-100 mesh.
[0273] The catalyst (0.3 g) is loaded in the quartz tube reactor
identified in Example 1. The feed gas composition contains 9.9% by
volume ethylbenzene, 5% by volume O.sub.2 and 85.1% by volume
N.sub.2. The contact time is 0.1 second. The process operates for 4
hours with no evidence of catalyst deactivation. The process is
conducted at atmospheric pressure. The products are analyzed by GC.
At 500.degree. C., 29% ethylbenzene conversion and 88% styrene
selectivity are achieved. The styrene yield is 26%. O.sub.2
conversion is 78%.
Example 4
[0274] Mesoporous V--Mg--Ox (18% V.sub.2O.sub.5) catalyst is
prepared by the co-precipitation method. 6.97 g vanadium (III)
2,4-pentanedionate are dissolved in 200 ml ethanol solution with
stirring at 70.degree. C. In another beaker, 19.59 g MgCl.sub.2 and
9.03 g hexadecyltrimethylammonium chloride are dissolved in 200 ml
H.sub.2O. The vanadium solution is added into the MgCl.sub.2
solution. The mixture is heated to 92-95.degree. C. The pH is
adjusted to 9 by 5 mol/L NH.sub.3.H.sub.2O and then to 10 by 45 wt
% KOH solution. The temperature is kept at 92-95.degree. C. for 2
h. Subsequently, the slurry is cooled to room temperature and aged
overnight. The mixture is filtered and the solid is washed with
H.sub.2O three times. After drying at 110.degree. C. overnight, the
sample is calcined at 550.degree. C. for 4 hours. The catalyst is
crushed and sieved to 60-100 mesh.
[0275] The catalyst (0.2 g) is loaded in the quartz tube reactor
identified in Example 1. The feed gas composition contains 9.9% by
volume ethylbenzene, 5% by volume O.sub.2 and 85.1% by volume
N.sub.2. The contact time is 0.1 second. The process operates for 4
hours with no evidence of catalyst deactivation. The process is
conducted at atmospheric pressure. The products are analyzed by GC.
At 550.degree. C., 36% ethylbenzene conversion and 89% styrene
selectivity are achieved. The styrene yield is 32%. O.sub.2
conversion is 98%.
Example 5
[0276] V.sub.2Mo.sub.6O.sub.26/MgO catalyst is prepared by the
ion-exchange method. 1.66 g KVO.sub.3 and 8.57 g K.sub.2MoO.sub.4
are dissolved in 300 ml H.sub.2O. The pH of the solution is
adjusted to 5.5 by HCl solution. After storing for 5 days, 1.45 g
MgO powder are added into the solution and stirred for one day at
room temperature. The mixture is filtered and the solid is washed
with H.sub.2O three times. After drying at 110.degree. C.
overnight, the sample is calcined at 500.degree. C. for 5 hours.
The catalyst is sieved to 60-100 mesh.
[0277] The catalyst (0.16 g) is loaded in the quartz tube reactor
identified in Example 1. The feed gas composition contains 9.9% by
volume ethylbenzene, 5% by volume O.sub.2 and 85.1% by volume
N.sub.2. The contact time is 0.1 second. The process operates for 5
hours with no evidence of catalyst deactivation. The process is
conducted at atmospheric pressure. The products are analyzed by GC.
At 550.degree. C., 25% ethylbenzene conversion and 82% styrene
selectivity are achieved. The styrene yield is 21%. O.sub.2
conversion is 97%.
Example 6
[0278] 0.7% K.sub.2O-15% MoO.sub.3/SiO.sub.2--TiO.sub.2 catalyst is
prepared by the sol-gel method. 20.0 g tetraethylorthosilicate and
27.29 g titanium isopropoxide are dissolved in 200 ml isopropyl
alcohol solution with stirring. In another beaker, 2.93 g ammonium
paramolybdate are dissolved in 13.65 g H.sub.2O and then 0.30 g 45%
KOH solution are added. The aqueous solution is dropped slowly into
the alcohol solution (1 ml/min). After all of the aqueous solution
is added, the resulting gel is stirred for additional 15 min. The
gel is dried at 110.degree. C. overnight and calcined at
550.degree. C. for 5 hours. The catalyst is crushed and sieved to
60-100 mesh.
[0279] The catalyst (5 g) is mixed with 45 g H.sub.2O and 95 g 6-mm
ZrO.sub.2 beads in a jar. The mixture is ball-milled for three
days. The resulting slurry (10 wt %) is then diluted to 2.5 wt % by
H.sub.2O. The average particle size in the slurry is about 1
micron. The slurry is dropped onto the microgrooved support strip
illustrated in FIG. 36 by pipette and then dried at 120.degree. C.
for 1 hour. The microgrooved support strip is made of stainless
steel 304. The microgrooved support strip has a length of 2.500
inches (6.350 cm), a width of 0.500 inch (1.27 cm), and a thickness
of 0.002 inch (50.8 microns). The microgrooves in the microgrooved
support have a width of 0.007 inch (178 microns). The spacing
between the microgrooves is 0.007 inch (178 microns). This
washcoating procedure is repeated twelve times. The catalyst-coated
microgrooved support strip is then calcined at 500.degree. C. for 1
hour. The catalyst loading is 28.8 mg. A microphotograph
(50.times.) of the catalyst coated microgrooved support strip is
shown in FIG. 37.
[0280] The catalyst coated microgrooved support strip is welded in
the microchannel device shown in FIG. 38. The microchannel device,
which is fabricated with FeCrAlY, has internal volume of 0.039
ml.
[0281] A feed gas composition, which contains 18.8% ethylbenzene
and 81.2% air, flows into the microchannel device. The feed gas
flow rate is 2.93 ml/min. The ethylbenzene to oxygen molar ratio is
1.1. The contact time based on reactor volume is 0.8 second. The
process is operated for 96 hours with no evidence of catalyst
deactivation. The process is conducted at atmospheric pressure. The
GHSV based on reactor volume is 4508 hr.sup.-1. The GHSV based on
the catalyst is 6104 ml/g-cat/hour. The GHSV for the ethylbenzene
is 1148 ml/g-cat/hour. The products are analyzed by GC. At an
average temperature of 412.degree. C., 86% ethylbenzene conversion
and 94% styrene selectivity are achieved. The styrene yield is 81%.
The styrene yield is 930 ml/g-cat/hour. O.sub.2 conversion is
98%.
[0282] The results of Examples 1-6 are summarized in Table I. For
each of Examples 1-5, the feed stream contains 9.9% by volume
ethylbenzene, 5% by volume oxygen, and 85.1% by volume nitrogen.
For Example 6, the feed stream contains 18.8% by volume
ethylbenzene, 17.1% by volume oxygen, and 64.1% by volume
nitrogen.
TABLE-US-00001 TABLE 1 Sty- Time Ex- EB O.sub.2 rene on am- T conv.
conv. Styrene Yield steam ple Catalyst (.degree. C.) (%) (%) Sel.
(%) (%) (h) 1 0.7% K.sub.2O--15% 450 38 91 90 34 3 MoO.sub.3/ 500
43 98 91 39 SiO.sub.2--TiO.sub.2 2 0.7% K.sub.2O--18% 450 36 96 89
32 3 V.sub.2O.sub.5/SiO.sub.2--ZrO.sub.2 3 Mg.sub.0.99MoO.sub.3.99
500 29 78 88 26 4 4 Mesoporous 550 36 98 89 32 4 V--Mg--Ox (18%
V.sub.2O.sub.5) 5 V.sub.2Mo.sub.6O.sub.26/ 550 25 97 82 21 5 MgO 6.
0.7% K.sub.2O--15% 412 86 98 94 81 96
MoO.sub.3/SiO.sub.2--TiO.sub.2 coated on microgrooved support
[0283] A comparison between the results for Examples 1 and 6 is
provided in Table II:
TABLE-US-00002 TABLE II Example 1 Example 6 Catalyst weight (g) 0.4
0.0288 Reactor volume (ml) 0.3 0.039 Total feed gas flow rate
(ml/min) 180 2.93 EB concentration (%) 9.89 18.80 Contact time
based on reactor volume(s) 0.10 0.80 GHSV based on reactor volume
(1/h) 36000 4508 GHSV based on catalyst amount (ml,/g-cat/h) 27000
6104 EB GHSV based on catalyst amount 2670 1148 (ml/g-cat/hour)
Styrene yield (%) 39 81 Styrene yield (ml/g-cat/hour) 1041 930
Ratio (microgrooved catalyst/powder catalyst) 0.9
[0284] Examples 1 and 6 suggest that at a lower temperature
(412.degree. C. versus 450-500.degree. C.) higher conversions of
ethylbenzene may be achieved. A comparison between Examples 1 and 6
suggests that a higher single pass yield of styrene (81% versus
39%) may be achieved when the catalyst supported microgrooved
support strip of Example 6 is used.
Example 7
[0285] Microgrooved Test Reactors #1 and #2 are fabricated. The
reactors contain inlet and outlet tubing, headers and footers, a
body cover plate, a body backing plate and a microgrooved assembly.
The inlet and outlet tubing is welded to the header and footer of
each device. Each is a 3 inch (7.62 cm) length of 1/8 inch (0.318
cm) OD SS316 tube with a tubular wall thickness of 0.035 inch
(0.089 cm). The headers and footers are fabricated from SS316 bar
stock via conventional machining and have outer dimensions of 0.820
inch.times.0.375 inch.times.0.375 inch
(2.08.times.0.953.times.0.953 cm). One of the 0.375
inch.times.0.820 inch (0.953.times.2.08 cm) faces is given a
45.degree. 0.020 inch (0.0508 cm) chamfer on each of the 0.375 inch
(0.953 cm) long edges. This face is the "top" of the piece. A 0.180
inch (0.457 cm) deep by 0.520 inch (1.32 cm) long by 0.069 inch
(0.175 cm) wide slot is cut in one of the 0.820 inch.times.0.375
inch (2.08.times.0.953 cm) faces (orthogonal to the top face) such
that the long axis of the slot is located 0.227 inch (0.577 cm)
from the bottom face of the piece and the short axis of the slot is
located 0.410 inch (1.04 cm) from the 0.375 inch (0.953 cm) long
edge of the face. The slot is flat bottomed and terminated in a
full round. On the face opposite the slot is drilled a 0.069 inch
(0.175 cm) through hole with a 0.125 inch (0.318) counter bore to a
depth of 0.125 inch (0.318 cm). The through hole is centered on the
location of the slot.
[0286] The process microchannel is in the form depicted in FIG. 38
and is assembled using a body cover plate (right side of FIG. 38),
a body backing plate and a microgrooved assembly. The microgrooved
assembly contains two microgrooved support strips depicted in FIGS.
35-38. The microgrooved support strips are stacked one on top of
the other. The microgrooved assembly is attached to the body
backing plate. The body cover plate and body backing plate are
fabricated from FeCrAlY plate. The body backing plate has overall
dimensions of 3.900 inches (9.91 cm) by 0.750 inch (1.91 cm) and is
0.190 inch (0.483 cm) thick. In cross section the part has a raised
central tenon 0.502 inch (1.275 cm) wide that runs the length of
the device.
[0287] The tenon is formed by removing material 0.124 inch (0.315
cm) from either side of the tenon to a depth of 0.074 inch (0.188
cm). The lip of the step so formed is given a 0.030 inch (0.076 cm)
45.degree. chamfer on either side as shown in the lower left of
FIG. 56. The body cover plate has overall dimensions of 3.900
inches (9.91 cm) by 0.750 inch (1.91 cm) and is 0.190 inch (0.483
cm) thick. A deep slot is cut down the center of the part 0.505
inch (1.283 cm) wide and 0.080 inch (0.203 cm) deep extending the
entire length of the part as shown in FIG. 57. A 0.030 inch (0.076
cm) wide 0.002 inch (50.8 microns) rib of material is left running
down the center of the deep slot as shown in FIG. 38. The outside
edges of the part adjacent to the slot is given a 0.030 inch (0.076
cm) 45.degree. chamfer. The chamfers on the body cover plate and
body backing plate mate after assembling to provide a groove
suitable for seal welding. The body backing plate and body cover
plate are toleranced and fabricated to provide a friction fit to
minimize by pass.
[0288] The microgrooved support strips are fabricated via
photochemical machining from 0.002 inch (50.8 microns) thick
stainless steel 304. Each strip is 2.500 inches (6.35 cm) long and
0.500 inch (1.27 cm) wide. The microgrooves are parallel to each
other, 0.007 inch (178 microns) wide and separated from adjacent
grooves by 0.007 inch (178 microns) of the base material. The
microgrooves form a 20.degree. angle from the center line (long
axis of the microgrooved support strip). The microgrooves start
approximately 0.030 inch (0.076 cm) from the edge of the strip
measuring 0.500 inch (1.27 cm) and each individual microgroove
stops approximately 0.007 inch (178 microns) from the long (2.5
inches, 6.35 cm) edge of the strip (see FIGS. 35 and 36). A large
central rib (0.064 inch, 1.63 cm wide) is located half way down the
length of the microgrooved support strip. The microgrooved assembly
is made by stacking two microgrooved support strips, one on top of
the other. The angled direction of the microgrooves is alternated
to produce a lattice like structure as shown in FIGS. 30 and 31.
The microgrooved assembly is then saturated with isopropyl alcohol
(to aid in positioning and to maintain flatness) and tack welded to
the body backing plate tack welds being placed at the front and
back edges and on the middle of the large central rib to produce an
assembly as depicted on the left hand side in FIG. 38. The
microgrooved assembly is centered on the body backing plate in both
the axial and side to side dimensions. Any overhang of the
microgrooved support strips is removed with a fine diamond hone.
Once completely assembled, the device is in the form of a
microchannel with an inlet and outlet gap of 0.006 inch (152
microns) that is approximately 0.503 inch (1.28 cm) wide and 3.900
inches (9.91 cm) long. In the portion of the channel containing the
microgrooved support strips the gap is reduced to 0.002 inch (50.8
microns) the balance of the channel being occupied by the
microgrooved support strips. The main flow path is through the
0.002 inch (50.8 microns) channel that sits above the 0.004 inch
(102 microns) assembly of two microgrooved support strips.
[0289] The microgrooved assembly and the body cover plates are
cleaned first in an ultrasonic bath containing isopropanol, then a
20% nitric acid solution, and then deionized water. Each cleaning
step has a duration of 30 minutes at 90% power output. The bath
temperature is 25.degree. C. The cleaned parts are then heated in
stagnant air while increasing the temperature at a rate of
3.5.degree. C. per minute to 650.degree. C. and held at that
temperature for 10 hours.
[0290] The catalyst described in Example 6 is prepared and
washcoated on the microgrooved assembly using the procedure
described in Example 6. The resulting microchannel reactor is
designated as Microgroove Test Reactor #2.
[0291] The body cover plate is placed on the body backing plate and
a seam weld is applied to close the device forming the microchannel
reactor body assembly. The header and footer, after having their
respective inlet and outlet tubing welded to them are also welded
to the body assembly such that the slot on the header or footer is
aligned with the channel formed by the body assembly which is shown
in FIG. 58. A test set-up for the microchannel reactor is shown in
FIG. 54.
[0292] Referring to FIG. 54, ethylbenzene (EB) is pumped into a
microchannel vaporizer at a rate of 0.10 ml/min via a HPLC piston
pump outfitted with pulse dampeners. The ethylbenzene is heated,
vaporized, and superheated to 200.degree. C. before mixing with an
air stream. The air is fed into the system with a mass flow
controller. The air is preheated before mixing with the
ethylbenzene stream by an electrical heating tape that is wrapped
around the outside of the feed tube. The surface of the tube is
held at held at 200.degree. C. The total feed rate of the air
stream ranges from 42-87 SCCM giving an ethylbenzene:oxygen mole
ratio ranging from 2.1 to 1.0.
[0293] The mixed feed stream of ethylbenzene and oxygen flows
through a 200 mesh screen before reaching the orifice and split
section. All of the lines and the orifice are heated with and
electrical heating tape holding the outside surface of the tubing
at 200.degree. C. An orifice with a diameter of 0.0007 inch (17.8
microns) is placed immediately upstream of the reactor. The orifice
has a pressure drop that is significantly larger than the pressure
drop across the reactor. The feed rate to the reactor is controlled
by varying the back pressure of the split stream. The pressures
upstream and downstream of the orifice are controlled in order to
maintain the total flow to the reactor from 2 to 6 SCCM. The split
stream is condensed via a microchannel heat exchanger and collected
in two chilled product collection drums. The gasses exit through
the back pressure regulator, septa sampling point, and bubble flow
meter, before going to a vent. Samples of this exit gas stream are
collected by a gas tight syringe and the liquid is collected and
analyzed.
[0294] The microchannel reactor is installed inside an electrically
powered ceramic heating element. This heater provides a temperature
ranging from 350.degree. C. to 500.degree. C.
[0295] The product of the reactor is mixed with room temperature
nitrogen flow of 15 SCCM from a second mass flow controller to help
increase the total flow rate through the downstream components. The
diluted product is condensed in a chilled, 2 mm glass bead packed
sample collection drum. The product is collected in a chilled, open
volume knock-out drum before the gas stream is sent through a
bubble flow meter and to the on-line GC system. The flow rates of
both the split and product gas streams are recorded.
[0296] There are two GCs that provide the analysis for the system.
The product gas stream is analyzed by an Agilent 5890 GC equipped
with two TCD detectors, three sample valves, and a sample pump.
H.sub.2, O.sub.2, N.sub.2, CH.sub.4, CO, CO.sub.2, ethane and
ethylene are quantified in the 5890GC with an analysis time of
approximately 20 min. The liquid feed, liquid collected from the
split stream knockout drum, split stream gas, liquid product and
product stream gas are analyzed by an Agilent 6890GC with a FID
detector. Benzene, toluene, ethylbenzene and styrene are quantified
in approximately 20 min.
[0297] The system is started-up as follows. N.sub.2 flow at 200
SCCM purges the system as the devices begin to heat. The back
pressure is increased on the split stream in order to push flow
through the reactor. The reactor flow is established at 5 SCCM. The
vaporizer is heated to 200.degree. C. while the heat tracing is
heated to 200.degree. C. The reactor is heated to an average
temperature of 380.degree. C. at a rate of 3.degree. C./min in the
ceramic heater (clam shell furnace). Once the temperatures are
steady ethylbenzene and air flows are stepped in, while the N.sub.2
flow is stepped out until an ethylbenzene:oxygen mole ratio of 2:1
and reactor inlet flow 4 SCCM is reached. The system is left until
steady state and a full sample is recorded. The temperature is then
increased at a rate of 2.degree. C./min in 10.degree. C. increments
while taking product GC samples. The temperature ramp stops once
full oxygen conversion has been reached. The temperature is held
constant and a sample is taken at 412.degree. C. average
temperature. Next the ethylbenzene:oxygen mole ratio is decreased
to 1.8:1, 1.5:1, and 1.1:1 consecutively. This increases conversion
of the ethylbenzene and selectivity to styrene.
[0298] Conversion of the ethylbenzene and selectivity to styrene is
determined using a methodology based on oxygen balance. This method
involves determining the conversion of ethylbenzene based on
performing an oxygen balance and assumes the following
stoichiometry to dominate.
C.sub.8H.sub.10+0.5O.sub.2.fwdarw.C.sub.8H.sub.8+H.sub.2O Equation
1
C.sub.8H.sub.10+6.5O.sub.2.fwdarw.8CO+5H.sub.2O Equation 2
C.sub.8H.sub.10+10.5O.sub.2.fwdarw.8CO.sub.2+5H.sub.2O Equation
3
The conversion of ethylbenzene is approximated as shown in the
equations below:
x EB = 1 - n ST , out + 1 8 ( n CO , out + n CO 2 , out ) n EB , in
Equation 4 ##EQU00001##
where n.sub.CO,out, n.sub.CO2,out, and n.sub.ST,out are calculated
as follows:
n CO , out = n dry gas , out f CO , out , dry Equation 5 n CO 2 ,
out = n dry gas , out f CO 2 , out , dry Equation 6 n ST , out = n
O , m - n O , out - 5 8 ( n CO , out + n CO 2 , out ) Equation 7
##EQU00002##
In the above equations, n.sub.dry gas,out is the measured molar
outlet dry flow rate, f.sub.i,out,dry is the mole fraction of
component i (CO, CO.sub.2, or O.sub.2) in the dry outlet flow as
measured by gas chromatograph, 5/8 is the assumed stoichiometric
ratio of H.sub.2O to CO or CO.sub.2 formed during combustion,
and
n.sub.O,in=2n.sub.O.sub.2.sub.,in+20.21n.sub.air,in Equation 8
n.sub.O,out=n.sub.dry
gas,out(f.sub.CO,out,dry+2f.sub.CO.sub.2.sub.,out,dry+2f.sub.O.sub.2.sub.-
,out,dry) Equation 9
where n.sub.i,in is the inlet molar flow rate of component i
(O.sub.2 or air). The above calculations assume a perfect oxygen
balance wherein the molar flow rate of water out of the system is
equal to the molar flow rate of missing oxygen atoms. It is further
assumed that one mole of water is formed for every mole of styrene
produced, and five moles of water are formed for every eight moles
of CO or CO.sub.2 produced.
[0299] The weight selectivity to styrene is calculated as
follows:
Sel ST = n ST , out MW ST n EB , in x EB MW EB Equation 10
##EQU00003##
Furthermore, the carbon selectivity to CO, and CO.sub.2 is
calculated as shown below.
Sel CO = n CO , out ( n CO , out + n CO 2 , out + 8 n ST , out )
Equation 11 Sel CO 2 = n CO 2 , out ( n CO , out + n CO 2 , out + 8
n ST , out ) Equation 12 ##EQU00004##
[0300] The selectivity to non-COx (taken to approximate the carbon
selectivity to styrene) is calculated by subtracting the sum of the
selectivity to CO and the selectivity to CO.sub.2 from 100%.
[0301] The results of testing the device are summarized in Table
III where comparison is given between similar catalysts tested in a
powdered state using a quartz tube reactor (inner diameter 4 mm).
The catalyst is online under reactive conditions for 96.5 hours in
the Microgroove Test Reactor #2 (see, Table IV).
TABLE-US-00003 TABLE III Test conditions and reactor performance
for Microgroove Test Reactor #2. Contact time is based on reactor
volume including volume within microgrooved support strips.
Catalyst 0.7% K.sub.2O--15% MoO.sub.3/SiO.sub.2--TiO.sub.2 Oxygen
Source Air Device (Type) Quartz Tube Microgroove Test Reactor #2
Condition (#) 1 2 3 4 5 6 7 8 9 10 M.sub.cat (mg) 400 400 28.8 28.8
28.8 28.8 28.8 28.8 28.8 28.8 WHSV (hr.sup.-1) 13 13 8.8 7.8 9 7.4
5.5 6.4 6.2 6.3 CT (ms) 100 100 2228 2514 1902 2071 2439 2096 2163
2433 GHSV (I.sub.feed/(hr I.sub.channel)) 36000 36000 1616 1432
1892 1738 1476 1718 1664 1480 T (.degree. C.) 450 495 401 415 417
416 418 420 410 416 EB:O.sub.2 (mol/mol) 2 2 1.8 1.8 1.5 1.3 1.1
1.1 1.1 1.3 Dilution (N.sub.2: Reactants) 2 2 0 0 0 0 0 0 0 0
Conversion EB (%) 37.6 43.1 42.1 40.9 59.0 74.8 86.7 77.7 74.0 76.2
O.sub.2 (%) 91.3 98.8 83.6 97 95.4 97.8 99.1 96.9 90.2 99.7
Selectivity Styrene (mol %) 91.8 92.5 93.3 90.6 93.7 94.4 94 92.9
93.3 94.4 CO (mol %) 2.7 2.5 1.7 2.3 1.4 1.5 1.5 1.9 1.5 1.2 CO2
(mol %) 5.5 4.9 5.1 7.1 4.9 4.2 4.5 5.2 5.2 4.4 Yield Styrene Yield
mol (%) 34.5 39.9 39.3 37.1 55.3 70.6 81.5 72.2 69.0 71.9
TABLE-US-00004 TABLE IV Time on stream under reactive conditions
for Microgroove Test Reactor #2 Condition (#) 10 MG 3 5 8 9 Test MG
Test MG Test MG Test MG Test Reacor Reacor #2 Reacor #2 Reacor #2
Reacor #2 #2 Time on (h:m) 1:45 6:15 13:20 15:00 22:30 stream
TABLE-US-00005 TABLE V Temperature profiles for Microgroove Test
Reactor #2 Data Point 4 6 7 1 2 MG Test MG Test MG Test Quartz
Quart Reactor Reactor Reactor Reactor Type Tube Tube #2 #2 #2 WHSV
(hr.sup.-1) 13 13 7.8 7.4 5.5 T (.degree. C.) 450 495 415 416 418
EB:O2 (mol/mol) 2 2 1.8 1.3 1.1 Time on stream (h:m) 1:40 3:40 3:49
26:09 47:49 pressure drop (psid) 3.95 6.71 0.03 0.1* 0.06 Top of
catalyst bed (.degree. C.) 450 495 N/A N/A N/A 3/4'' from top of
cat bed (.degree. C.) 385 399 N/A N/A N/A 0.3 inchs from start of
coupon (.degree. C.) N/A N/A 415 416 418 0.8 inches from start of
coupon (.degree. C.) N/A N/A 418 418 419 1.3 inches from start of
coupon (.degree. C.) N/A N/A 414 415 413 1.8 inches from start of
coupon (.degree. C.) N/A N/A 408 408 403 2.3 inches from start of
coupon (.degree. C.) N/A N/A 397 398 388
[0302] The yield increases are achieved at lower WHSV in the
Microgroove Test Reactor #2 but also at significantly reduced
temperatures thus productivity may be increased markedly by
increasing temperature. As the selectivity is not dramatically
reduced by operation at 495.degree. C. (condition 2 in Table III)
it is anticipated that the WHSV may be increased in the
microchannel reactor employing the microgrooved catalyst
support.
Example 8
[0303] Microgroove Test Reactor #1 is prepared in a manner similar
to that described in Example 7 using the catalyst described in
Examples 1, 6 and 7. Testing is conducted in a manner analogous to
that described in Example 7 with several exceptions. One of these
is that the flow of nitrogen used to aid in the down stream purge
is 25 SCCM for conditions 3 through 7 and 0 SCCM for conditions 8
through 13. In addition the microgroove test device described in
Example 7 is placed in a clam shell furnace such that the bottom
(outlet of the microchannel) of the body assembly even with the
bottom of the 3 inches long heating zone of the clam shell furnace
thus approximately 0.9 inch (2.29 cm) sticks out above the heated
zone. In this example the device is placed in the clam shell
furnace such that the top (inlet of the microchannel) is even with
the top of the heating zone thus approximately 0.9 inch (2.29 cm)
sticks out below the heated zone. This leads to a more pronounced
temperature profile (15.degree. C. from inlet to outlet for Example
7 vs. 50.degree. C. for Example 8) as can be seen by comparing
Tables VII and V.
TABLE-US-00006 TABLE VI Test conditions and reactor performance for
Microgroove Test Reactor #1. Contact time is based on reactor
volume including volume within microgrooved support strips.
Catalyst 0.7% K.sub.2O--15% MoO.sub.3/SiO.sub.2--TiO.sub.2 Oxygen
Source Air Device (Type) Quartz Tube Microgroove Test Reactor #1
Condition (#) 1 2 3 4 5 6 7 8 9 10 11 12 13 M.sub.cat (mg) 400 400
24.3 24.3 24.3 24.3 24.3 24.3 24.3 24.3 24.3 24.3 24.3 WHSV
(hr.sup.-1) 13 13 16 14 18 13 13 14 11 11 11 10 6 CT (ms) 100 100
1620 1852 1440 1994 1787 1660 2112 2112 2112 2324 2450 GHSV
(I.sub.feed/ 36000 36000 2222 1944 2500 1805 2014 2169 1704 1704
1704 1549 1469 (hr I.sub.channel)) T (.degree. C.) 450 495 395 454
415 423 423 416 415 425 426 426 426 EB:O.sub.2 (mol/mol) 2 2 2.1
2.1 2.1 2.1 1.8 1.8 1.8 1.8 1.8 1.8 1 Dilution (N.sub.2: Reac- 2 2
0 0 0 0 0 0 0 0 0 0 0 tants) Conversion EB (%) 37.6 43.1 30.9 32.1
39.1 52.7 73.2 43.1 42.9 40.4 37.0 37.6 53.7 O.sub.2 (%) 91.3 98.8
59.2 95.7 82.8 95.1 97.4 79.9 84.9 88.1 92.1 91.4 89 Selectivity
Styrene (mol %) 91.8 92.5 95.7 89.2 94.2 96.0 97.4 93.9 93.2 91.7
87.4 90.3 85.1 CO (mol %) 2.7 2.5 0.0 2.8 1.0 0.6 0.4 1.8 2.1 2.5
3.4 2.7 4.1 CO2 (mol %) 5.5 4.9 4.3 7.9 4.7 3.4 2.1 4.3 4.8 5.7 9.2
7.0 10.9 Yield Styrene Yield mol (%) 34.5 39.9 29.6 28.6 36.8 50.6
71.3 40.5 40.0 37.0 32.3 34.0 45.7
TABLE-US-00007 TABLE VII Temperature profiles for Microgroove Test
Reactor #1 Condition # 4 6 7 1 2 MG Test MG Test MG Test Quartz
Quart Reactor Reactor Reactor Reactor Type Tube Tube #1 #1 #1 WHSV
(hr.sup.-1) 13 13 14 13 13 T (.degree. C.) 450 495 454 423 423
EB:O2 (mol/mol) 2 2 2.1 2.1 1.8 Time on stream (h:m) 1:40 3:40 3:30
25:10 26:30 pressure drop (psid) 3.95 6.71 2.06 1.25 0.99 Top of
catalyst bed (.degree. C.) 450 495 N/A N/A N/A 3/4'' from top of
cat bed (.degree. C.) 385 399 N/A N/A N/A 0.3 inchs from start of
coupon (.degree. C.) N/A N/A 454 423 423 0.8 inches from start of
coupon (.degree. C.) N/A N/A N/A N/A N/A 1.3 inches from start of
coupon (.degree. C.) N/A N/A 437 405 406 1.8 inches from start of
coupon (.degree. C.) N/A N/A N/A N/A N/A 2.3 inches from start of
coupon (.degree. C.) N/A N/A 404 374 375
TABLE-US-00008 TABLE VIII Time on stream under reactive conditions
for Microgroove Test Reactor #1 Conditon (#) 3 5 8 9 10 11 12 13 MG
Test MG Test MG Test MG Test MG Test MG Test MG Test MG Test Reacor
#1 Reacor #1 Reacor #1 Reacor #1 Reacor #1 Reacor #1 Reacor #1
Reacor #1 Time on stream (h:m) 1:30 6:20 18:20 20:35 22:15 41:20
65:35 73:00
[0304] In Example 8 the advantages of the microgrooved support
structure are apparent when the same catalyst is run in both a
packed bed in a quartz tube (4 mm inner diameter) and the
microgrooved reactor. In this case when condition 2 and condition 7
in Table VI are compared the microgrooved reactor allows for
improve conversion and selectivity at a similar weight hourly space
velocity (WHSV) and lower temperature. The term WHSV is used herein
to refer to the mass of reactant (for example, ethylbenzene) per
unit of time contacting a given mass of catalyst. The enhanced
productivity of Microgroove Test Reactor #1 vs. Microgroove Test
Reactor #2, where Microgroove Test Reactor #1 has a higher
conversion at greater WHSV, may be due to the larger pressure drop
experienced by Microgroove Test Reactor #1, a on possible outcome
of which may be that part of the bulk flow is diverted from the
flow by channel into the microgrooved structure.
[0305] The results for two microgrooved test reactors (Examples 7
and 8) are compared to results collected for the catalysts reported
in Examples 1 through 5. The comparison is shown in FIG. 55. These
results show that beyond approximately 40% conversion in the quartz
tube reactor selectivity falls off step wise while the enhanced
ability of the microgrooved reactor to remove heat allows for
conversion to be increased beyond 40% while at the same time
maintaining high selectivity.
Example 9
[0306] A computational fluid dynamics (CFD) study on thermal
management for the formation of styrene via oxidative
dehydrogenation of ethylbenzene is conducted. The production of
styrene in a microchannel reactor may be particularly advantaged by
the incorporation of a structured wall to increase the surface area
for coating a highly active and selective ethylbenzene oxidative
dehydrogenation (ODH) catalyst. The reactor may be further
advantaged by incorporating a thermal resistance layer in the heat
transfer wall between the heat exchange transfer channel and the
process microchannel to create a controlled temperature gradient
such that a lower temperature heat exchange fluid, such as an oil,
may be used to remove heat for higher temperature oxidation
reactions. Typical hot oils may be rated to a maximum of about
400.degree. C. A desirable operating temperature window for styrene
production via oxidative dehydrogenation of ethylbenzene may be in
the range from about 300.degree. to about 500.degree. C., and in
one embodiment from about 400.degree. to about 450.degree.. In one
embodiment, the oxidant may be added by staged into the process
microchannel to reduce the local partial pressure of oxygen and
enhance the resulting reaction selectivity to styrene.
[0307] A microchannel reactor may be designed to maintain a heat
exchange fluid temperature at 380.degree. while running the process
microchannel at 420.degree. C. by positioning a thermal resistance
layer between the process microchannel and heat exchange channel.
The thermal resistance layer may not be open to flow of heat
exchange fluid or process reactants. The thermal resistance layer
may be formed using techniques and constructions similar to those
used for making structured walls. The pattern selected for the
thermal resistance layer may be the same as or different than the
structured wall in the process microchannel for supporting the
catalyst.
[0308] The temperature rise in the catalyst may be controlled by
varying the thermal resistance in thermal resistance layer. The
thermal resistance may be varied along the length of the process
microchannel. It may be desirable to have a higher thermal lag at
one end of the process microchannel or a varying function down the
process microchannel length either digitally or in an analog
fashion.
[0309] The structured walls that support the catalyst may vary
along the length of the process microchannel to reduce or enhance
the heat release such that isothermal or an axially varying
temperature profile may be obtained.
[0310] Transient simulation shows that the thermal resistance layer
may not create an unpredictable thermal response or thermal lag to
the change of flow variables. Temperature overshoot may not occur
at high temperature locations. This may be an important
consideration to keep the catalyst temperature under control to
avoid hot spots, sintering, deactivation, or otherwise unwanted
thermal excursions.
[0311] Microchannel apparatus 600 illustrated in FIG. 61 is used to
convert ethylbenzene (EB) to styrene in the presence of an
oxidative dehydrogenation (ODH) catalyst. The apparatus includes
process microchannel 602 and heat exchange channel 604. Heat
transfer wall 605 is positioned between the process microchannel
602 and heat exchange channel 604. The process microchannel 602
includes bulk flow region 603 and structured wall 606 which is used
to support the ODH catalyst. Thermal resistance layer 608 is
positioned between the process microchannel 602 and heat exchange
channel 604. In FIG. 61 only half the process microchannel 602 is
shown. The other half of the process microchannel has a second
structured wall for supporting the ODH catalyst opposite the
structured wall 606, and a second thermal resistance layer 608. The
structured wall 606 and the thermal resistance layer 608 are
constructed by stacking a plurality of the microgrooved shims
illustrated in FIGS. 59 and 60 one above another. Each of the
microgrooved shims has a thickness of 50 microns.
[0312] The shims have alternating patterns such that a porous
structure having a thickness of 1.5 mm is created when 30 shims are
stacked together to form the structured wall 606. The openings in
the alternating shims are arranged to create solid metal
connections through the stack of 30 shims along with completely
open large pores through the stack to facilitate rapid diffusion.
There are cross members that extend from the solid metal
connections through some of the open porous area to further
increase the internal surface area. The mass of reactants diffuse
and to some extent slightly flow within the open porous structure.
The openings of the structured wall vary from about 25 microns to
about 500 microns. The ODH catalyst may coat the entire surface
area of the structured wall 606.
[0313] The bulk flow region 603 in the process microchannel 602 has
a height of 0.75 mm. The bulk flow region 603 reduces the
impediment to flow resistance and allows the reactants to diffuse
into the open structured walls 606 to access the catalyst. The
length of the process microchannel 602 is 56 inches (142.2 cm). The
channel width is 0.25 inches (0.64 cm).
[0314] The thermal resistance layer 608 has the same construction
as the structured wall 606 (except that no catalyst is present).
The thermal resistance layer 608 has a thickness of is 0.5 mm thick
and is separated by wall 609 from the structured wall 606 and by
wall 610 from the heat exchange channel 604.
[0315] The following chemical reactions are conducted:
C.sub.6H.sub.5CH.sub.2CH.sub.3+0.5O.sub.2.fwdarw.C.sub.6H.sub.5CH.dbd.CH-
.sub.2+H.sub.2O 1.
C.sub.6H.sub.5CH.dbd.CH.sub.2+6O.sub.2.fwdarw.8CO+4H.sub.2O 2.
C.sub.6H.sub.5CH.dbd.CH.sub.2+10O.sub.2.fwdarw.8CO.sub.2+4H.sub.2O
3.
[0316] Reaction 1 is the main reaction.
[0317] The catalyst kinetics are shown below:
1. r EB = k o 1 exp [ - E a 1 RT ] C EB C O 2 0.5 ##EQU00005## 2. r
ST = k o 2 exp [ - E a 2 RT ] C ST C O 2 ##EQU00005.2## 3. r st = k
o 3 exp [ - E a 3 RT ] C ST C O 2 ##EQU00005.3##
[0318] The parameters are given in the following Table.
TABLE-US-00009 Reaction Parameter Value Units 1 k.sub.01 8.66E-02
(m.sup.9/2 a-1 Kmol.sup.-1/2mg.sup.-1) E.sub.a1 71063 (J/mol) 2
k.sub.02 2.38E+05 (m.sup.6kgmol.sup.-1s.sup.-1mg.sup.-1) E.sub.a2
165542 (J/mol) 3 k.sub.03 2.48E+03
(m.sup.6kgmol.sup.-1s.sup.-1mg.sup.-1) E.sub.a3 130195 (J/mol)
[0319] The reaction rates are in kmol/mg-cat. The catalyst loading
in the structured wall 606 is 1.365E+05 g-cat/m.sup.3 as
experimentally demonstrated. Simulations to evaluate the impact of
the thermal resistance layer 608 are based on the following
assumptions:
[0320] The reaction contact time is based on the volume defined by
the total internal reactor volume inclusive of the structured walls
606 and bulk flow region 603 for process flow. [0321] Wall
temperature 380.degree. C.--as maintained by the boiling of a hot
oil such as Therminol or Dowtherm, or the convective heat transfer
of a fluid [0322] Reaction nominal temperature of 420.degree. C.
[0323] Ethylbenzene (EB) to O.sub.2 ratio=1.8 (O.sub.2 fed as air)
[0324] Outlet pressure set to 1 atm
[0325] The concentration of the feed is given in the table
below:
TABLE-US-00010 mole mass fraction fraction EB 0.2743 0.5819 O.sub.2
0.1524 0.0974 N.sub.2 0.5733 0.3207
[0326] The heat removal rate is first estimated using a
two-dimensional model of the process microchannel only. The
structured wall catalyst has an effective thermal conductivity of 4
W/m-K. The wall temperature is maintained at a constant 420.degree.
C. and the feed inlet is also 420.degree. C. The channel geometry
is shown in FIG. 62. The table below shows the reactor performance
when the catalyst activity is at the reported level (1.times.). The
impact of increasing and decreasing the catalyst activity is also
shown in the table below.
Reactor Performance Summary
Contact Time: 200 ms
TABLE-US-00011 [0327] 0.5X 1X 2X Kinetics Kinetics Kinetics
Conversion EB 33.7% 47.4% 51.2% Conversion O.sub.2 30.9% 93.5%
92.9% Selectivity Styrene 99.2% 94.5% 91.7% Selectivity CO 0.1%
5.4% 4.8% Selectivity CO.sub.2 0.7% 3.9% 3.6% T, max C. 437 444
761
[0328] The heat flux profile for the flow of heat through the heat
transfer wall wherein the catalyst structure is for a catalyst with
1.times. kinetics and a contact time of 200 ms is shown in FIG. 63.
The negative sign means the heat is removed from the domain through
the wall. The heat flux reaches peak value at about 13 inches (33.0
cm) into the reactor length (of the total 56 inch (142.2 cm)
reactor length) and the peak value is about 14 W/cm.sup.2.
[0329] FIG. 64 shows the temperature profile in the catalyst
structure at a location of 0.01 inch (0.254 mm) deep in the
structure at 1.times. kinetics and a contact time of 200 ms. The
temperature reaches a peak value 15 inches (38.1 cm) from the front
edge of the catalyst structure, roughly the same axial location of
maximum heat flux. The maximum temperature for this case is
444.degree. C., which is 24.degree. C. above the targeted operating
temperature.
[0330] In the next step of the design, the thermal resistance or
heat resistance layer 608 is added between the process microchannel
602 and the heat exchange channel 604. This is shown in FIGS. 65
and 66. The thermal resistance layer is modeled as a porous medium
with adjustable properties. The coolant wall is maintained at
380.degree. C. with a reaction feed temperature of 420.degree. C.
as shown in FIG. 66.
[0331] The required features of the heat resistance layer are
estimated by one-dimensional heat conduction calculations. It is
assumed that the effective thermal conductivity of the heat
resistance layer 608 is constant k. The actual value may be
calculated if the structure of the layer is known. The thickness of
heat resistance layer 608 is assigned as H. The heat flux is
determined from the temperature difference using the equation in
FIG. 66.
[0332] If the required heat flux Q is known, the value of the
effective thermal conductivity of the heat resistance layer 608 can
be determined given the thickness of the thermal resistance layer
608. The range of the heat flux may be from about 1.0E5 to about
1.0E6 W/m.sup.2. The thickness of the heat resistance layer 608 may
be in the range from about 0.02 to about 0.08 inches (about 0.508
to about 2.032 mm). The effective thermal conductivities of the
thermal resistance layer are reported in the following table. This
table shows that if higher level of heat removal is desired, the
thermal resistance layer should be either more conductive or
fabricated using a material with a higher thermal conductivity.
This may be accomplished by creating fewer voids in the strips or
shims that may be used to form the thermal resistance layer 608. If
the desired heat removal rate is 1.0E5 W/m.sup.2, the thermal
conductivity may be from 1.27 to 5.08 W/m-K for a thermal
resistance layer having a thickness from about 0.02 to about 0.08
inch (about 0.508 to about 2.032 mm). If the openness of the shim
is 0.5 (that is 50% metal and 50% void), the effective thermal
conductivity of the thermal resistance layer may be about
one-fourth of that of the base material, which in this case is
steel. The effective thermal conductivity may be about 4 W/m-K.
TABLE-US-00012 Effective thermal conductivity, W/m-K Heat Flux, Q
k/H 0.02 0.04 0.06 0.08 W/m.sup.2 W/m.sup.2-K inch inch inch inch
1.00E+05 2.50E+03 1.27 2.54 3.81 5.08 4.00E+05 1.00E+04 5.08 10.16
15.24 20.32 8.00E+05 2.00E+04 10.16 20.32 30.48 40.64 1.00E+06
2.50E+04 12.70 25.40 38.10 50.80 1.50E+06 3.75E+04 19.05 38.10
57.15 76.20
[0333] The table below shows reactor performance at four contact
times. The catalyst activity in these models is 50% (or 0.5.times.)
of the reported level. The thermal resistance layer is 0.02 inch
(0.508 mm) thick and the thermal conductivity is 2.23 W/m-K.
Reactor Performance
0.5.times. Kinetics Over Reported
Thermal Resistance Layer has a k of 2.23 W/m-K and is 0.02 Inch
Thick
TABLE-US-00013 [0334] Contact ms 1000 500 2000 200 time Conversion
EB 33.7% 28.8% 34.7% 15.3% Conversion O.sub.2 30.9% 30.1% 31.5%
22.3% Selectivity Styrene 99.2% 98.8% 99.2% 98.1% Selectivity CO
0.1% 0.2% 0.1% 0.4% Selectivity CO.sub.2 0.7% 1.0% 0.7% 1.5% T, max
.degree. C. 437 434 420 444
[0335] Trends identified from these results may include: [0336]
There exists a range of flow rates within which the reactor
performance is stable. [0337] The maximum temperate increases as
the contact time gets shorter. [0338] The location of maximum
temperature shifts downstream as the contact time gets shorter.
[0339] Ethylene conversion is low at short contact time, but the
maximum temperature remains high. This trend shows the importance
of further increases to the effective thermal conductivity of the
structured wall 606 for supporting the catalyst.
[0340] FIG. 67 shows the temperature profiles at three locations
for a 200 ms contact time. The curve labeled "A" is for the profile
in the catalyst structure at a depth 0.01 inch (0.254 mm) from the
interface with the bulk flow region 603. The curve labeled "B" is
for the profile at the middle of the thermal resistance layer 608,
and the line labeled "C" is along the center open flow area of the
bulk flow region 603. The fluid temperature is at almost a constant
level. The temperature in the resistance layer is relatively flat.
The only significant temperature variation along the reactor length
is in the structured wall for supporting the catalyst. This
temperature is above the target level. The maximum temperature rise
is 24.degree. C. This implies that the thermal resistance of the
thermal resistance layer should be lowered to bring down the
maximum temperature.
[0341] The temperature predictions for a 2000 ms contact time are
plotted in FIG. 68. Temperatures at three locations are shown. The
curve labeled "A" is in the structured wall for supporting the
catalyst as indicated above. The curve labeled "B" is in the
thermal resistance layer. The curve labeled "C" is in the center of
the bulk flow region 603. For this case, although the temperature
is controlled below the target temperature near the inlet of the
reactor, at other axial locations, the temperature is below the
target level. This shows that the heat resistance layer for the
reactor is overly conductive or that the thermal resistance is
higher than it should be. This low average catalyst temperature
contributes to a relatively low ethylbenzene conversion.
[0342] The heat flux through the heat transfer wall at a contact
time of 2000 ms is shown in FIG. 69. The heat flux through the heat
transfer wall at a contact time of 200 ms is shown in FIG. 70.
[0343] Even at modest levels of ethylbenzene conversion, the
temperature in catalyst structure is significant. The temperature
rises with more active catalysts. As such it may be advantageous to
tailor the catalyst loading density along the reactor length to
reduce the temperature rise. This may be achieved by using
different patterns of the structured walls at different axial
positions so that the surface area to volume is lower in the front
of the reactor and higher near the end of the reactor. Another way
to boost the ethylbenzene conversion while controlling temperature
rise may be to tailor the thermal resistance of the thermal
resistance layer along the reactor length. Based on the temperature
profile for the 1000 ms contact time case, the reaction temperature
in most of the reactor may be lower than the target level. As such,
the thermal resistance in the second half of the reactor may be
lowered in order to raise the reaction temperature to a temperature
near the desired level.
Example 10
[0344] This example shows that reactor performance may be improved
by varying thermal resistance along the length of the process
microchannel. The catalyst structure is divided into several
sections along the process microchannel. The thermal resistance
layer is also divided into the same number of sections. The details
of catalyst activity and thermal resistance in each section are
given in the following table.
Sectional Catalyst Activity and Thermal Resistance
Baseline Thermal Conductivity: 2.23 W/m-K (1y)
Thermal Resistance Layer Thickness: 0.02 Inch (0.508 mm)
TABLE-US-00014 [0345] Kinetics scale Thermal Location factor (1x is
conductivity scale Section (inches) reported) factor 1 0-18 0.8x 1y
2 18-22 Linear from 1y 0.8x to 1.2x 3 22-40 1.2x 1y 4 40-44 Linear
from Linear from 1y to 1.2x to 1.5x 0.5y 5 44-56 1.5x 0.5y
Reactor Performance
TABLE-US-00015 [0346] Contact time ms 200 Conversion EB 49.0%
Conversion O.sub.2 64.4% Selectivity Styrene 97.2% Selectivity CO
1.0% Selectivity CO.sub.2 1.7% T, max .degree. C. 451
[0347] The results show improvement in reactor performance by
grading both the catalyst to reduce the activity near the front and
by increasing the amount of thermal resistance (i.e., reducing the
thermal conductivity of the thermal resistance layer) in the
thermal resistance layer near the end of the reactor. The
conversion increases with only a modest reduction to selectivity
and minor increase in the maximum temperature. The temperature
profiles are shown in FIG. 71. The curve labeled "A" is for in the
structured wall for supporting the catalyst. The curve labeled "B"
is in the thermal resistance layer. The line labeled "C" is in the
center of the open bulk flow region of the process microchannel.
The heat flux at 200 ms through the heat transfer wall is shown in
FIG. 72.
Example 11
[0348] The catalyst structure is divided into several sections
along the length of the process microchannel. The thermal
resistance layer is also divided into the same number of sections.
The details of catalyst activity and thermal resistance in each
section are given in the following table.
Sectional Catalyst Activity and Thermal Resistance
Baseline Thermal Conductivity: 2.23 W/m-K (1y)
Thermal Resistance Layer Thickness: 0.02 Inch (0.508 mm)
TABLE-US-00016 [0349] Kinetics scale factor (1x is as Thermal
reported conductivity scale Section Location previously) factor 1
0-18 0.5x 1y 2 18-22 Linear from 1y 0.5x to 1.2x 3 22-40 1.2x 1y 4
40-44 Linear from Linear from 1y to 1.2x to 1.5x 0.5y 5 44-56 1.5x
0.5y
Reactor Performance
TABLE-US-00017 [0350] Contact time ms 200 Conversion EB 50.6%
Conversion O2 64.4% Selectivity ST 97.5% Selectivity CO 0.5%
Selectivity CO2 2.0% T, max C. 462
[0351] The modest change in the catalyst loading in the first
section shifts the maximum hot spot downstream. The temperature
profiles for the contact time of 200 ms are shown in FIG. 73. The
curve labeled "A" is for the structured wall for supporting the
catalyst as indicated above. The curve labeled "B" is for the
thermal resistance layer. The line labeled "C" is for the center of
the open bulk flow region of the process microchannel. The heat
flux through the heat transfer wall at 200 ms contact time is shown
in FIG. 74.
Example 12
[0352] CFD simulations are carried out to examine how reactor
temperature responds to changes of operating parameters. The
operating parameter reviewed for this study is the feed
temperature. At time zero, the reactor is at steady state with the
process feed stream temperature at 410.degree. C. Then, the feed
temperature is raised to 420.degree. C. This temperature change
leads to subsequent changes in reactor performance, temperature and
other variables until a new steady state, if any, is reached. In
order to obtain details of how the reactor responds to this change,
catalyst temperature is monitored at five locations as illustrated
in the following FIG. 75. These five locations are distributed
along the process microchannel length with more points in the first
half of the process microchannel. P1 is 5 inches (12.7 cm) from the
inlet. P2 is 8 inches (20.3 cm) from the inlet. P3 is 10 inches
(25.4 cm) from the inlet. P4 is 15 inches (38.1 cm) from the inlet.
P5 is 40 inches (101.6 cm) from the inlet. All locations are 0.01
inch (0.254 mm) from the surface of the structure facing the bulk
flow region.
[0353] Other conditions include: [0354] Catalyst activity is 50% of
the original [0355] Contact time: 1000 ms [0356] Heat resistance
layer thickness: 0.02 inch (0.508 mm) [0357] Effective thermal
conductivity of heat resistance layer: 1 W/m-K [0358] Uniform
catalyst activity and thermal resistance of the heat resistance
layer along the reactor length
[0359] The temperatures at the five locations on the catalyst are
plotted in FIG. 76. The overall trends are temperature increase due
to higher ethylbenzene conversion under 10 degree higher feed
temperature condition. Temperature overshoot is observed only for
point P-5 and P-4 at very small magnitude. This small transient
effect away from the hot spot is not expected to create problems
for reactor operation since the temperature levels are low at P5
and P4 locations. FIG. 76 also reveals that the elapsed time before
the stable temperature is reached depends on the location. At 95
second after the temperature change in the feed, the temperature
reaches stable values at all locations monitored. At 50 seconds,
the temperature at P1 reaches a stable level, but not at P2 and P3
at where the temperatures still climbs higher.
[0360] The table below compares the performance of three CFD cases.
First case is steady state model with feed temperature at
410.degree. C., and the second case is also steady state case with
feed temperature at 420.degree. C. The third case is transient
simulation wherein the feed temperature is changed from 410.degree.
C. to 420.degree. C. at time zero at 95 seconds after the
temperature change of the process feed stream. The reactor almost
reaches steady state after 95 seconds. The maximum temperature
overshoots one degree and the oxygen conversion is a few percent
higher. The reactor operation is robust to the perturbation with
the use of the thermal resistance layer to create a lower coolant
temperature (380.degree. C. for the reported simulations) and a
warmer and stable reaction operating temperature.
Reactor Performance Comparison
TABLE-US-00018 [0361] CFD cases Steady Steady Transient T, C feed
410 420 420 Conversion EB 30.8% 33.3% 33.5% Conversion O.sub.2
33.0% 37.6% 40.5% Selectivity Styrene 98.5% 98.3% 98.1% Selectivity
CO 0.3% 0.3% 0.4% Selectivity CO.sub.2 1.2% 1.4% 1.5% T, max C. 453
479 480
[0362] While the invention has been explained in relation to
various embodiments, it is to be understood that various
modifications thereof will become apparent to those skilled in the
art upon reading the specification. Therefore, it is to be
understood that the invention disclosed herein is intended to cover
such modifications as fall within the scope of the appended
claims.
* * * * *