U.S. patent application number 11/343893 was filed with the patent office on 2006-06-15 for method and apparatus for reducing decomposition byproducts in a methanol to olefin reactor system.
Invention is credited to Kenneth Ray Clem, Stephen N. Vaughn, Jeffrey L. White, Teng Xu.
Application Number | 20060129011 11/343893 |
Document ID | / |
Family ID | 29733822 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060129011 |
Kind Code |
A1 |
Clem; Kenneth Ray ; et
al. |
June 15, 2006 |
Method and apparatus for reducing decomposition byproducts in a
methanol to olefin reactor system
Abstract
Disclosed is a method and apparatus for reducing the amount of
metal catalyzed side-reaction byproducts formed in the feed
vaporization and introduction system of a methanol to olefin
reactor system by monitoring and/or maintaining the temperature of
at least a portion of the feed vaporization and introduction system
and/or of the feedstock contained therein below about 400.degree.
C., 350.degree. C., 300.degree. C., 250.degree. C., 200.degree. C.
or below about 150.degree. C. The temperature can be maintained in
the desired range by jacketing at least a portion of the feed
vaporization and introduction system, such as at least a portion of
the feed introduction nozzle, with a thermally insulating material
or by implementing a cooling system.
Inventors: |
Clem; Kenneth Ray; (Humble,
TX) ; Vaughn; Stephen N.; (Kingwood, TX) ; Xu;
Teng; (Houston, TX) ; White; Jeffrey L.;
(Cary, NC) |
Correspondence
Address: |
ExxonMobil Chemical Company;Law Technology
P.O. Box 2149
Baytown
TX
77522-2149
US
|
Family ID: |
29733822 |
Appl. No.: |
11/343893 |
Filed: |
January 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10175285 |
Jun 19, 2002 |
7034196 |
|
|
11343893 |
Jan 31, 2006 |
|
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|
Current U.S.
Class: |
585/639 ;
422/131; 422/138 |
Current CPC
Class: |
Y02P 30/40 20151101;
Y10S 585/92 20130101; B01J 2219/00119 20130101; B01J 2208/00274
20130101; B01J 2219/00155 20130101; B01J 2208/00176 20130101; B01J
19/26 20130101; Y02P 30/20 20151101; B01J 2219/00254 20130101; C07C
1/20 20130101; B01J 8/1827 20130101; Y02P 30/42 20151101; Y10S
585/923 20130101 |
Class at
Publication: |
585/639 ;
422/131; 422/138 |
International
Class: |
C07C 1/00 20060101
C07C001/00; B01J 19/00 20060101 B01J019/00 |
Claims
1-30. (canceled)
31. A feed introduction nozzle for an MTO reactor, comprising: a
generally tubular member including an exterior portion oriented
externally to the MTO reactor and adapted to receive an
oxygenate-containing feedstock, and an interior portion oriented
within the MTO reactor and adapted to deliver the feedstock to the
MTO reactor; and a jacket formed at least in part of a thermally
insulating material covering at least a portion of the generally
tubular member.
32. The nozzle of claim 31, wherein the thermally insulating
material is selected from the group consisting of fire brick,
alumina bricks, silica bricks, magnesite bricks, chrome bricks,
silicon carbide bricks, zircon, zirconia, forsterite, high
temperature calcium silicate, alumina and silica-alumina ceramics,
diatomaceous silica, cements, fillers, calcium carbonate, calcium
sulfate, concrete, glass, granite, marble, mineral wool, porcelain,
portland cement, Pumice stone, and gunnite.
33. The nozzle of claim 32, wherein the jacket covers at least a
portion of the interior portion of the generally tubular
member.
34. The nozzle of claim 33, wherein the jacket covers at least a
portion of the exterior portion of the generally tubular
member.
35. A feed introduction nozzle for an MTO reactor, comprising: a
first generally tubular member adapted to receive a feedstock from
a heating device and to deliver the feedstock to the MTO reactor;
and a cooling system covering at least a portion of the first
generally tubular member and adapted to cool the nozzle to a
temperature effective to substantially eliminate the production of
metal catalyzed side-reaction byproducts.
36. The nozzle of claim 35, wherein the cooling system includes a
second generally tubular member of larger diameter than the first
generally tubular member, the first and second members being
coaxially oriented about a central axis thereby defining inner and
outer conduits, and wherein the inner conduit is adapted to receive
the feedstock and the outer conduit is adapted to receive the
cooling medium.
37. The nozzle of claim 36, wherein the nozzle includes an outlet
inside the MTO reactor adapted to direct the cooling medium into
the MTO reactor.
38. The nozzle of claim 35, further comprising: a jacket layer
formed at least in part of a thermally insulating material.
39. The nozzle of claim 38, wherein the jacket layer covers at
least a portion of the cooling system.
40. The nozzle of claim 38, wherein the thermally insulating
material is selected from the group consisting of fire brick,
alumina bricks, silica bricks, magnesite bricks, chrome bricks,
silicon carbide bricks, zircon, zirconia, forsterite, high
temperature calcium silicate, alumina and silica-alumina ceramics,
diatomaceous silica, cements, fillers, calcium carbonate, calcium
sulfate, concrete, glass, granite, marble, mineral wool, porcelain,
portland cement, Pumice stone, and gunnite.
Description
FIELD OF THE INVENTION
[0001] This invention is to an apparatus and method for reducing
methanol decomposition byproducts in a methanol to olefin reactor
system.
BACKGROUND OF THE INVENTION
[0002] Light olefins, defined herein as ethylene and propylene,
serve as feeds for the production of numerous important chemicals
and polymers. Light olefins traditionally are produced by cracking
petroleum feeds. Because of the limited supply and escalating cost
of petroleum feeds, the cost of producing olefins from petroleum
sources has increased steadily. Efforts to develop and improve
olefin production technologies, particularly light olefins
production technologies, have increased.
[0003] The petrochemical industry has known for some time that
oxygenates, especially alcohols, are convertible into light
olefin(s). There are numerous technologies available for producing
oxygenates including fermentation or reaction of synthesis gas
derived from natural gas, petroleum liquids, carbonaceous materials
including coal, recycled plastics, municipal waste or any other
organic material. Generally, the production of synthesis gas
involves a combustion reaction of natural gas, mostly methane, and
an oxygen source into hydrogen, carbon monoxide and/or carbon
dioxide. Syngas production processes are well known, and include
conventional steam reforming, autothermal reforming, or a
combination thereof.
[0004] Methanol, the preferred alcohol for light olefin production,
is typically synthesized from the catalytic reaction of hydrogen,
carbon monoxide and/or carbon dioxide in a methanol reactor in the
presence of a heterogeneous catalyst. For example, in one synthesis
process methanol is produced using a copper/zinc oxide catalyst in
a water-cooled tubular methanol reactor. The preferred methanol
conversion process is generally referred to as a
methanol-to-olefin(s) process, where methanol is converted to
primarily ethylene and/or propylene in the presence of a molecular
sieve.
[0005] In an oxygenate to olefin (OTO) reaction system, a feedstock
containing an oxygenate is vaporized and introduced into a reactor.
Exemplary oxygenates include alcohols such as methanol and ethanol,
dimethyl ether, methyl ethyl ether, methyl formate, and dimethyl
carbonate. In a methanol to olefin (MTO) reaction system, the
oxygenate-containing feedstock includes methanol. In the reactor,
the methanol contacts a catalyst under conditions effective to
create desirable light olefins. Typically, molecular sieve
catalysts have been used to convert oxygenate compounds to olefins.
Silicoaluminophosphate (SAPO) molecular sieve catalysts are
particularly desirable in such conversion processes because they
are highly selective in the formation of ethylene and
propylene.
[0006] In a typical MTO reactor system, undesirable byproducts may
be formed through side reactions. For example, the metals in
conventional reactor walls may act as catalysts in one or more side
reactions. If the methanol contacts the metal reactor wall at
sufficient temperature and pressure, the methanol may be converted
to undesirable methane and/or other byproducts.
[0007] Byproduct formation in an MTO reactor is undesirable for
several reasons. First, increased investment is required to
separate and recover the byproducts from the desired light olefins.
Additionally, as more byproducts are formed, less light olefins are
synthesized. In other words, the production of byproducts is
undesirable because methanol feed is consumed to produce the
byproducts. Further, although the relative concentrations of metal
catalyzed side reaction byproducts are generally quite low, the
total amount of byproducts produced on an industrial scale can be
enormous. Thus, it is desirable to decrease or eliminate the
synthesis of byproducts in an MTO reactor system.
[0008] Sulfur-containing chemicals have proven effective for
deactivating or passivating the metal surface of a reactor thereby
reducing the formation of undesirable byproducts in the reactor.
For example, Japanese Laid Open Patent Application JP 01090136 to
Yoshinari et al. is directed to a method for preventing
decomposition of methanol or dimethyl ether and coking by sulfiding
the metal surface of a reactor. More particularly, the method
includes reacting methanol and/or dimethyl ether in the presence of
a catalyst at above 450.degree. C. in a tubular reactor made of
Iron and/or Nickel or stainless steel. The inside wall of the
reactor is sulfided with a compound such as carbon disulfide,
hydrogen disulfide or dimethyl sulfide. Additionally, a sulphur
compound may be added to the feed.
[0009] Although passivating chemicals have proven effective in
reducing metal catalyzed side reactions, the introduction of
deactivating or passivating chemicals increases production costs
because these chemicals or their products must be separated from
the desired product. Thus, a need exists for a method and apparatus
for reducing the formation of metal catalyzed side reaction
byproducts in an MTO reactor system while minimizing the use of
deactivating or passivating chemicals.
SUMMARY OF THE INVENTION
[0010] The present invention includes a method for making an olefin
product from an oxygenate-containing feedstock including directing
the feedstock through a feed introduction nozzle having an inner
surface and being attached to an MTO reactor. The inner surface of
the nozzle is maintained at a temperature below about 400.degree.
C., 350.degree. C., 300.degree. C., 250.degree. C., 200.degree. C.
or below about 150.degree. C. The method also includes contacting,
in the reactor, the feedstock with a catalyst under conditions
effective to form an effluent comprising light olefins. The present
invention provides the ability to produce light olefins while
reducing or eliminating the production of metal catalyzed side
reaction byproducts in the feed vaporization and introduction (FVI)
system. The FVI system is the region of the reactor system
beginning at the point that at least a portion of the feedstock is
in a vaporized state and extending to the point that the feedstock
exits the feed introduction nozzle and enters the MTO reactor where
the feedstock contacts the catalyst. As the resulting light olefin
stream contains less metal catalyzed side reaction byproducts than
is produced in conventional MTO reactor systems, olefin separation
and purification costs can be reduced. The resulting purified
olefin stream is particularly suitable for use as a feed in the
manufacture of polyolefins.
[0011] Additionally, the inventive method, optionally, includes
cooling at least a portion of the inner surface of the nozzle with
a cooling system. The nozzle of one embodiment is additionally or
alternatively be jacketed with a thermally insulating material,
which is selected from the group consisting of fire brick, alumina
bricks, silica bricks, magnesite bricks, chrome bricks, silicon
carbide bricks, zircon, zirconia, forsterite, high temperature
calcium silicate, alumina and silica-alumina ceramics, diatomaceous
silica, cements, fillers, calcium carbonate, calcium sulfate,
concrete, glass, granite, marble, mineral wool, porcelain, portland
cement, Pumice stone, gunnite, and other refractory materials with
insulating properties. For additional insulating materials which
are incorporated in one embodiment of the present invention, see
Petroleum Processing Handbook, ed. W. F. Bland and R. L. Davidson,
McGraw Hill Publishers, 1967, p 4-137 to 4-147, and Robert H.
Perry, Perry's Chemical Engineers' Handbook, 7.sup.th Ed., 1997, p.
11-68 to 11-74, both of which are incorporated herein by reference.
Optionally, he thermally insulating material covers at least a
portion of an interior portion of the nozzle extending inside the
MTO reactor and/or at least a portion of the exterior portion of
the nozzle extending outside the MTO reactor.
[0012] The invention is also directed to a method for making an
olefin product from an oxygenate-containing feedstock including
directing the feedstock through a feed nozzle having a nozzle
temperature and being attached to a MTO reactor, wherein at least a
portion of the nozzle is covered by a thermally insulating material
as described above. The method also includes contacting, in the
reactor, the feedstock with a catalyst under conditions effective
to form an effluent comprising light olefins. Optionally, the
thermally insulating material may cover at least a portion of an
interior portion of the nozzle extending inside the MTO reactor
and/or at least a portion of the exterior portion of the nozzle
extending outside the MTO reactor.
[0013] Another embodiment of the present invention is a method for
making an olefin product from an oxygenate-containing feedstock
including heating the feedstock in a heating device to form a
heated feedstock. The heated feedstock is directed through a feed
nozzle having a nozzle temperature and being attached to a MTO
reactor. At least a portion of the nozzle is cooled with a cooling
system. The method also includes contacting, in the reactor, the
feedstock with a catalyst under conditions effective to form an
effluent comprising light olefins. Optionally, a cooling medium
cools the nozzle, which is directed into the MTO reactor wherein
the cooling medium mixes with the feedstock.
[0014] A further embodiment is a method for making an olefin
product from an oxygenate-containing feedstock including directing
the feedstock through a feed introduction nozzle having an inner
surface and being attached to an MTO reactor. The feedstock is
maintained below about 400.degree. C., 350.degree. C., 300.degree.
C., 250.degree. C., 200.degree. C. or below about 150.degree. C.
while the feedstock is in the nozzle. In the reactor, the feedstock
contacts a catalyst under conditions effective to form an effluent
comprising light olefins. This embodiment may include insulating at
least a portion of the nozzle with a thermally insulating material
and/or cooling at least a portion of the nozzle with a cooling
medium.
[0015] The invention is also directed to a method for making an
olefin product from an oxygenate-containing feedstock including
directing the feedstock through a feed introduction nozzle having
an inner surface and being attached to an MTO reactor. The nozzle
is maintained at conditions effective to produce less than 0.8 or
0.4 weight percent of metal catalyzed side reaction byproducts
excluding CO, CO.sub.2 and H.sub.2. Optionally, the conditions are
effective to substantially eliminate the formation of metal
catalyzed side reaction byproducts. In the reactor, the feedstock
contacts a catalyst under conditions effective to form an effluent
comprising light olefins.
[0016] The invention is also directed to a feed introduction nozzle
for an MTO reactor including a generally tubular member including
an exterior portion oriented externally to the MTO reactor and
adapted to receive an oxygenate-containing feedstock, and an
interior portion oriented within the MTO reactor and adapted to
deliver the feedstock to the MTO reactor. The nozzle includes a
jacket formed at least in part of a thermally insulating material,
as described above, covering at least a portion of the generally
tubular member. The jacket may cover at least a portion of the
interior portion and/or at least a portion of the exterior portion
of the generally tubular member.
[0017] The invention is also directed to a feed introduction nozzle
for an MTO reactor including a first generally tubular member
adapted to receive a feedstock from a heating device and to deliver
the feedstock to the MTO reactor. A cooling system covers at least
a portion of the first generally tubular member and is adapted to
cool the nozzle to a temperature effective to substantially
eliminate the production of metal catalyzed side-reaction
byproducts. The nozzle can include a cooling system having a second
generally tubular member of larger diameter than the first
generally tubular member, the first and second members being
coaxially oriented about a central axis thereby defining inner and
outer conduits, and wherein the inner conduit is adapted to receive
the feedstock and the outer conduit is adapted to receive the
cooling medium. The nozzle may include an outlet inside the MTO
reactor adapted to direct the cooling medium into the MTO reactor.
Also, the nozzle can include a jacket layer formed at least in part
of a thermally insulating material as described above. The jacket
layer may cover at least a portion of the cooling system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] This invention will be better understood by reference to the
Detailed Description of the Invention when taken together with-the
attached drawings, wherein:
[0019] FIG. 1 illustrates a flow diagram of a methanol to olefin
reactor system including the FVI system and the MTO reactor;
[0020] FIG. 2 illustrates a nozzle jacketing configuration in
accordance with one embodiment of the present invention; and
[0021] FIG. 3 illustrates a nozzle jacketing and cooling system in
accordance with another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention is directed to reducing or eliminating
the formation of metal catalyzed side reaction byproducts in
reactor systems, and in particular, in methanol to olefin (MTO)
reactor systems. When a feedstock including an oxygenate such as
methanol contacts a metal surface, e.g., the reactor walls, at
relatively high temperatures and pressures, the oxygenate
decomposes to form the undesirable byproducts. The inventors have
discovered that in addition to metal catalyzed side reactions
occurring on reactor walls, metal catalyzed side reactions may
occur before the feedstock enters the reactor. Before entering the
reactor, the feedstock passes through a FVI system wherein the
feedstock is at least partially vaporized by one or more heating
device(s), is passed through feed line(s) to a feed introduction
nozzle, and is introduced into the reactor. The inner surface of at
least a portion of the FVI system may be formed of metal which
absorbs heat from the reactor volume thereby creating conditions in
the FVI system which are conducive to the formation of metal
catalyzed side reaction byproducts. As used herein, the term "inner
surface" is defined to mean a portion of the FVI system, e.g., the
feed introduction nozzle, which contacts the feedstock prior to its
introduction into the reaction unit.
[0023] The present invention provides a method for making an olefin
product from an oxygenate-containing feedstock while reducing the
amount of reaction byproducts formed in the FVI system. The method
includes maintaining at least a portion of the FVI system, e.g.,
the inner surface of the feed introduction nozzle, and/or the
feedstock contained therein at a temperature effective to reduce or
eliminate the formation of metal catalyzed side reaction byproducts
in the FVI system. Preferably, the temperature of at least a
portion of the inner walls of the FVI system will be less than the
temperature of the MTO reactor. In one embodiment of the present
invention, the temperature of the inner walls of at least a portion
of the FVI system, and/or the feedstock contained therein, may be
maintained below about 400.degree. C., 350.degree. C., 300.degree.
C., 250.degree. C., 200.degree. C. or below about 150.degree.
C.
[0024] As the feedstock passes through the FVI system, the
oxygenate contacts the inner metal surface of one or more of the
heating device(s), the feed introduction nozzle, and/or the lines
connecting the heat exchanger(s) to the feed introduction nozzle.
In one side reaction in the FVI system, the metal surface of the
heat exchanger(s), line(s) and/or feed introduction nozzle acts as
a catalyst at high temperatures and converts some of the methanol
in the feedstock to hydrogen, carbon monoxide, carbon dioxide,
methane and/or graphite. This side reaction may be illustrated as
follows: Metal, Heat 29 CH.sub.3OH.fwdarw.54 H.sub.2+15 CO+7
CO.sub.2+2 CH.sub.4+5C
[0025] The tendency of the FVI system to form undesirable metal
catalyzed side-reaction byproducts is especially favorable because
the ratio of metal surface area to quantity of feedstock is much
higher in the FVI system than in the MTO reactor itself.
Additionally, in conventional MTO reactor systems, the temperature
in the FVI system is conducive to the formation of metal catalyzed
side-reaction byproducts because heat is transferred from hot
material in the MTO reactor to the FVI system.
[0026] A portion of the feed introduction nozzle may extend into
the reactor volume of the reactor further increasing the formation
of metal catalyzed side reaction byproducts. The temperature within
the reactor volume is generally much higher than the minimum
temperatures that are conducive to the formation of metal catalyzed
side reaction byproducts. Heat from the MTO reactor is transferred
to the nozzle which may extend into the reactor volume. This heat
transfer may be significantly increased if the nozzle includes an
"interior portion" which is defined herein to mean a portion of the
feed introduction nozzle, which extends into the reactor volume. In
one embodiment, the interior portion protrudes into a dense phase
zone of the reactor wherein heated solid particles continuously
collide with the outer surface of the nozzle. Accordingly, with
conventional nozzle designs, the temperature of the
metal-containing nozzle will increase to temperatures conducive to
promote undesirable side reactions which are catalyzed by the
heated inner metal surface of the nozzle.
[0027] One method of keeping the inner wall of at least a portion
of the FVI system and/or of the feedstock contained therein at a
temperature effective to reduce or eliminate the formation of metal
catalyzed side reaction byproducts is to thermally insulate at
least a portion of the FVI system, e.g., a portion or all of the
feed introduction nozzle, with an insulating material. Non-limiting
examples of insulating materials include: fire brick, alumina
bricks, silica bricks, magnesite bricks, chrome bricks, silicon
carbide bricks, zircon, zirconia, forsterite, high temperature
calcium silicate, alumina and silica-alumina ceramics, diatomaceous
silica, cements, fillers, calcium carbonate, calcium sulfate,
concrete, glass, granite, marble, mineral wool, porcelain, portland
cement, Pumice stone, gunnite, and other refractory materials with
insulating properties. For additional insulating materials which
may be incorporated in the present invention, see Petroleum
Processing Handbook, ed. W. F. Bland and R. L. Davidson, McGraw
Hill Publishers, 1967, p 4-137 to 4-147, and Robert H. Perry,
Perry's Chemical Engineers' Handbook, 7.sup.th Ed., 1997, p. 11-68
to 11-74, both of which are incorporated herein by reference. The
specific characteristics of the insulation, e.g., density, material
and thickness, implemented in accordance with the present invention
may be selected based on the specific reaction conditions inside
the reactor, the composition and physical properties of the
feedstock, and the composition and physical properties of the
heating device, lines, and/or feed introduction nozzle.
[0028] in another embodiment of the present invention, the
temperature of the feed introduction nozzle, and/or of the inner
metal-containing nozzle surface thereof and/or the feedstock
itself, may be controlled with a cooling system. Many types of
cooling systems could be implemented in the present invention. For
example, the cooling system may include a cooling tube helically
wrapped around the feed introduction nozzle. As cooling medium
flows through the tube and around the feed introduction nozzle, the
metal in the feed introduction nozzle as well as the feedstock
flowing therethrough can be maintained at a temperature effective
to minimize or eliminate the formation of metal catalyzed
side-reaction byproducts.
[0029] Referring now to the drawings, FIG. 1 illustrates an MTO
reactor system in accordance with one embodiment of the present
invention. The MTO reactor system includes a feedstock vaporization
and introduction system, or FVI system, which is generally
designated by numeral 102, and an MTO reactor, which is generally
designated by numeral 104. As defined herein, the FVI system 102 is
a region of the reactor system beginning at the point that at least
a portion of the feedstock is in a vaporized state and extending to
the point that the feedstock exits the feed introduction nozzle and
enters the MTO reactor, as illustrated in FIG. 1. At least a
portion of the FVI system may be formed of one or more metals, or
an alloy of metals, e.g., steel, to accommodate the temperature and
pressure of the feedstock as it is transported to the reactor.
[0030] In FIG. 1, a liquid oxygenate feedstock or feed stream 108
containing an oxygenate such as methanol is shown being directed to
heating device(s) 106 which heats the feedstock to a temperature
just below, at or above the feedstock bubble point. Optionally, a
series of heating devices may be implemented in the present
invention to gradually heat the feedstock in steps as indicated in
U.S. Pat. No. 6,121,504 to Kuechler et al., the entirety of which
is incorporated herein by reference. If a series of heating devices
is implemented in the present invention, a series of lines will
transfer the feedstock between the heating devices to the feed
introduction nozzle. The lines may be formed of a metal or alloy
such as steel to accommodate the temperature and pressure of the
feedstock. These metal lines or pipes may catalyze side reactions
of the vaporized methanol thereby increasing separation costs by
introducing impurities and reducing reaction efficiency by
decreasing the production of desired light olefins.
[0031] One of ordinary skill in the art would recognize the various
heating devices known in the art. Preferably, the heating device is
a shell and tube heat exchanger wherein the heating medium may be
product effluent 118, as shown in FIG. 1, a heat integration
stream, e.g., from a water stripper or quench tower, or any other
material having a higher temperature than the feedstock.
Preferably, the heating device(s) 106 will cause at least a portion
of the feedstock stream to vaporize. The point at which at least a
portion of the feedstock vaporizes is defined herein as the FVI
system inlet 114. The FVI inlet may be within the heating device
106, the feed introduction nozzle 112 or anywhere between.
[0032] After being heated in the heating device(s) 106, the heated
feedstock is directed through line or lines 110 to a feed
introduction nozzle 112. The feed introduction nozzle may be formed
of a metal or alloy such as steel and may protrude into the MTO
reactor volume, as illustrated in FIGS. 1-3. Alternatively, the
portion of the nozzle adjacent the reactor may be oriented flush
with the interior surface of the reactor wall. The metal in the
feed introduction nozzle 112 can act as a catalyst in side
reactions at high temperatures to form undesirable byproducts. The
heated feedstock passes through the feed introduction nozzle 112
and enters the MTO reactor 104.
[0033] The pressure in the MTO reactor may be less than the
pressure of the feedstock within the FVI system, and the
temperature within the MTO reactor may be much higher than the
temperature in the FVI system. Accordingly, a portion or the
entirety of any liquid contained in the heated feedstock may
vaporize as it exits the feed introduction nozzle and enters the
MTO reactor. The point that the feedstock exits the feed
introduction nozzle 112 and enters the MTO reactor 104 is defined
herein as the FVI system outlet 116.
[0034] In the MTO reactor 104, the methanol in the feed stream
contacts a catalyst under conditions effective to form an olefin
product which exits the reactor in product effluent 118. As
indicated above, the product effluent 118 from the MTO reactor 104
may be directed to the heat exchanger(s) 106 in order to heat the
feed stream 108. As shown in FIG. 1, after the product effluent 118
has heated the feed stream 108, it may be directed in line 120 to a
product separation and purification system (not shown).
Alternatively, the product effluent may be directed to the product
separation and purification system without first being directed to
a heat exchanger.
[0035] In one embodiment of the present invention, the feedstock is
maintained at a temperature effective to reduce, minimize or
eliminate the formation of metal catalyzed side reaction
byproducts. In this embodiment, the feedstock may act as a cooling
agent for cooling the inner metal surface of one or more of the
following portions of the FVI system: at least a portion of the
heating device(s), at least a portion of the line(s), and/or at
least a portion of the feed introduction nozzle. The desired
temperature of the feedstock throughout the FVI system is
preferably below about 400.degree. C., 350.degree. C., 300.degree.
C., 250.degree. C., 200.degree. C. or below about 150.degree. C.
These relatively low temperatures may be maintained by controlling
the heating characteristics and number of the feedstock heating
device(s), and/or by insulating and/or cooling one or more of the
following portions of the FVI system: at least a portion of the
heating device(s), at least a portion of the line(s), and/or at
least a portion of the feed introduction nozzle, as discussed in
more detail below. One effective FVI system produces vapor feed at
its saturation, or dew point. In such an FVI system the pressure at
which vaporization occurs will determine the temperature.
Superheating of the vapor can then be introduced by reducing the
pressure of the saturated vapor feedstock either within or prior to
entering the feed nozzle. Surprisingly and unexpectedly, the
inventors have found that the introduction of a low temperature
feedstock into a hot MTO reactor does not substantially affect the
formation of light olefins in the MTO reactor.
[0036] Additionally or alternatively, the inventive method includes
maintaining at least a portion of the inner surfaces of the feed
vaporization and introduction system, e.g., the inner surface of
the feed introduction nozzle, at a temperature effective to reduce
or eliminate the formation of metal catalyzed side reaction
byproducts. In accordance with the present invention, the
temperature of the metal-containing inner surface(s) of the FVI
system may be maintained at the desired temperature in a variety of
ways. For example, one or more of the heating device(s), the
line(s) between the feed heating device(s) and the feed
introduction nozzle, and/or the feed introduction nozzle itself may
be jacketed with a thermally insulating material. Additionally or
alternatively, one or more of the heating device(s), the line(s)
between the feed heating device(s) and the feed introduction
nozzle, and/or the feed introduction nozzle itself may include a
cooling device for controlling the temperature of all or a portion
of the FVI system. The invention is also directed to an FVI system
having a temperature monitoring and controlling feature, and to
feed introduction nozzles incorporating a jacket formed of a
thermally insulating material and/or incorporating a cooling
system.
[0037] As a non-limiting example, FIG. 2 illustrates one embodiment
of the present invention which reduces or eliminates metal
catalyzed side reaction byproduct formation caused by heat transfer
from the MTO reactor to the inner surface of the feed introduction
nozzle. A feed introduction nozzle 112 is shown in FIG. 2
penetrating the reactor wall 204. The portion of the feed
introduction nozzle which is inside the reactor volume 208 is
identified as the interior portion 210. Methanol stream 206 from
the heating device (not shown) travels through a line or pipe (not
shown) and enters the feed introduction nozzle 112. The methanol
stream 206 passes through the feed introduction nozzle 112 and
enters the inner reactor volume 208 wherein the methanol contacts a
catalyst under conditions effective to convert the methanol to
light olefins. An insulating material 212 covers at least a portion
of the outer nozzle surface 218 of the interior portion 210 of the
feed introduction nozzle 112. The insulating material reduces the
quantity of heat that is transferred from the reactor volume 208 to
the interior portion 210 of the feed introduction nozzle 112. As a
result, the metal on the inner nozzle surface 216 of the feed
introduction nozzle can be maintained at a temperature effective to
reduce, minimize or eliminate the formation of metal-catalyzed side
reaction byproducts.
[0038] Although a portion of the feed introduction nozzle 112
adjacent the FVI system outlet 116 may be exposed to the reactor
volume 208, the amount of heat transferred from the reactor volume
to the portion of the inner nozzle surface 216 of the feed
introduction nozzle that is adjacent the FVI system outlet 116 is
minimal because the feedstock may tend to cool the inner nozzle
surface 216 adjacent the FVI system outlet. Beneficially, only a
relatively small amount of hot material in the reactor will contact
the FVI system outlet 116 because the flow characteristics of the
feedstock as it enters the reactor volume 208 will tend to direct
the hot material away from the FVI system outlet 116. Accordingly,
even the portion of the inner nozzle surface 216 that is adjacent
the FVI system outlet 116 can be maintained at temperatures
effective to reduce, minimize or eliminate the formation of metal
catalyzed side reaction byproducts. In other words, to the extent
that heat is transferred from the hot material in the reactor to
the portion of the feed introduction nozzle that is adjacent the
FVI system outlet 116, the amount of metal catalyzed side reaction
byproducts formed in that region is negligible.
[0039] FIG. 2 illustrates the insulating material 212 covering the
entire interior portion 210 of the feed introduction nozzle 112.
Optionally, the insulating material 212 may cover a portion of the
interior portion 210 of the feed introduction nozzle 112.
Additionally or alternatively, the insulating material may cover a
portion of the FVI outlet 116. Similarly, the insulating material
may additionally or alternatively provide increased thermal
protection for the metal contained in the feed introduction nozzle
and the feedstock contained in the FVI system by extending the
insulating material into and/or through the reactor wall 204. In
this embodiment, the opening in the reactor wall through which the
feed introduction nozzle extends must be increased in size in order
to allow the insulating material to traverse the reactor wall.
Optionally, the insulating material 212 may also extend to cover
all or a portion of the external portion 214 of the feed
introduction nozzle 112. The insulating material may extend to
cover additional areas of the FVI system. For-example, the
insulating material may cover all or a portion of the heating
device(s) and/or the line(s) directing the feedstock from the
heating device(s) to the feed introduction nozzle.
[0040] In another non-limiting example, FIG. 3 illustrates another
embodiment of the present invention wherein the feed introduction
nozzle 112 includes a cooling system generally designated by
numeral 302. As shown in FIG. 3, the feed introduction nozzle 112
is a generally cylindrical tube defining a feedstock pathway 308. A
second larger diameter cylindrical tube is oriented coaxially to
the feed introduction nozzle 112 thereby forming an outer cooling
pathway 306 around the feedstock pathway 308. A cooling medium 304,
such as water or a cooling steam, e.g., from a water stripper or
quench tower, or any other material having a lower temperature than
the feedstock in the feed introduction nozzle, is introduced into
cooling pathway 306 at cooling inlet 310 and is circulated in the
cooling pathway 306 around the feedstock in the feedstock pathway
308. Preferably, exterior nozzle end 314 of the cooling pathway 306
is closed-off so that the cooling medium flows toward the reactor.
As feedstock passes through the feedstock pathway 306 toward the
MTO reactor, the cooling medium 304 is passed through the cooling
pathway 306 and withdraws heat from the feed introduction nozzle
and/or the feedstock. By cooling the feedstock and the inner nozzle
surface 216 of the feed introduction nozzle, the feed introduction
nozzle 112 and/or the feedstock can be maintained at a temperature
effective to minimize or eliminate the formation of metal catalyzed
side reaction byproducts.
[0041] This embodiment of the present invention has the additional
advantage of providing the ability to control and vary the
temperature of the feedstock and of the feed introduction nozzle.
For example, the temperature of the feedstock/feed introduction
nozzle can be modified by varying the flow rate and/or temperature
of the cooling medium which passes over the nozzle and feedstock
pathway.
[0042] The cooling medium 304 may exit the feed introduction nozzle
within the reactor through diluent outlet 312, as shown in FIG. 3,
or outside of the reactor through a cooling medium outlet (not
shown). If the cooling medium 304 exits the feed introduction
nozzle within the reactor through diluent outlet 312, the cooling
medium will mix with the oxygenate feedstock inside the reactor. In
this manner, the invention provides an additional advantage in that
the partial pressure of the oxygenate introduced into the MTO
reactor may be carefully controlled in order to obtain a desired
product selectivity and/or oxygenate conversion as discussed, for
example, in U.S. patent application Ser. No. 09/506,843 to Fung et
al., the entirety of which is incorporated herein by reference.
Thus, the cooling medium may be selected from one or more of the
diluents more fully discussed below.
[0043] FIG. 3 illustrates the cooling system 302 traversing the
reactor wall 204 and covering the entire surface of the feed
introduction nozzle. Optionally, the cooling system 302 may provide
thermal protection for a portion of the feed introduction nozzle
rather than the entire feed introduction nozzle. For example, the
cooling system 302 may cover the entirety or only a portion of the
interior portion 210 of the feed introduction nozzle 112. In this
embodiment, the cooling system may, or may not, extend partially or
entirely through the reactor wall 204. Similarly, the cooling
system 302 may cover all or a portion of the external portion 214.
The cooling system may extend to cover additional areas of the FVI
system. For example, the cooling system may cover all or a portion
of the heating device(s) and/or the line(s) directing the feedstock
from the heating device(s) to the feed introduction nozzle.
[0044] In accordance with the present invention, the jacketing and
cooling embodiments, discussed above, may be combined. For example,
the nozzle may include a feedstock pathway, a cooling system and a
jacket formed of one or more of the thermally insulating materials
discussed above. Either the jacket or the cooling system may be the
outermost layer depending on the MTO reactor conditions, the
cooling medium used, the physical properties of the nozzle, the
physical properties of the heating device(s) and the physical
properties of the line(s) connecting the heating device(s) to the
feed introduction nozzle. Additionally or alternatively, a
plurality of the same or different jacketing layers and/or the same
or different cooling systems may be implemented in the present
invention.
[0045] Additionally or alternatively, the jacketing and/or cooling
embodiments may be combined with the low temperature feedstock
embodiment. By coupling the low temperature feedstock throughout
the FVI system, e.g., below about 400.degree. C., 350.degree. C.,
300.degree. C., 250.degree. C., 200.degree. C., or below about
150.degree. C., with the insulating and/or cooling system
embodiments, the temperature of the metal-containing inner surface
of at least a portion of the FVI system can be maintained at a
temperature effective to reduce or eliminate the formation of metal
catalyzed side reaction byproducts, e.g., below about 400.degree.
C., 350.degree. C., 300.degree. C., 250.degree. C., 200.degree. C.,
or below about 150.degree. C.
[0046] In one embodiment, the inner metal-containing surface(s) of
the FVI system may be maintained at a temperature effective to
maintain the feedstock at liquid-vapor equilibrium throughout the
FVI system. Because the feedstock is maintained at a temperature
effective to maintain the feedstock in a liquid-vapor equilibrium
throughout the FVI system, superheating of the vapor is minimized
or eliminated thereby reducing the formation of reaction byproducts
through metal-catalyzed side reactions. Alternatively, the
feedstock may be entirely vaporized prior to entering the reactor.
For example, the feedstock may pass through a valve 122 in line
110, as shown in FIG. 1, wherein the feed is subjected to a
pressure drop and the feedstock is further vaporized. The feedstock
may be superheated so long as the temperature of the superheated
feedstock is maintained below temperatures conducive to the
formation of metal catalyzed side reaction byproducts.
[0047] The invention also provides for the ability to monitor the
temperature of any point along the FVI system including one or more
of the heating device, the line(s), and/or the feed introduction
nozzle. For example, a thermocouple may be implemented on the inner
and/or outer surface of the feed introduction nozzle and/or on the
inner and/or outer surface of the cooling system or insulating
material. By incorporating a thermocouple in the present invention,
the temperature of the feedstock and/or of the metal in the feed
introduction nozzle may be monitored to determine whether
conditions are conducive to the formation of metal catalyzed
side-reaction byproducts. Moreover, with the cooling system
embodiment of the present invention, the characteristics of the
cooling medium may be modified responsive to variations in
temperature of any inner or outer nozzle surfaces. For example, as
the monitored temperature of the inner surface of the nozzle
approaches temperatures conducive to the formation of metal
catalyzed side reaction byproducts, the characteristics of the
cooling medium, e.g., flow rate and/or temperature, may be modified
to lower the temperature of the inner nozzle surface to
non-reactive temperatures.
[0048] Preferably, the conditions in the MTO reactor including the
pressure, temperature, weight hourly space velocity (WHSV), etc.,
are conducive to converting the methanol to light olefins, as
discussed in more detail below. In accordance with the present
invention, at least a portion of the FVI system, especially the
feed introduction nozzle, is monitored and/or maintained at
conditions, e.g., temperatures, effective to reduce, minimize or
substantially eliminate the formation of metal catalyzed
side-reaction byproducts irrespective of the conditions within the
MTO reactor. That is, the conditions within the MTO reactor may or
may not be conducive to the formation of metal catalyzed
side-reaction byproducts. Thus, the present invention may be
implemented with a deactivated or passivated reactor.
[0049] Typically, molecular sieve catalysts have been used to
convert oxygenate compounds to light olefins.
Silicoaluminophosphate (SAPO) molecular sieve catalysts are
particularly desirable in such a conversion process, because they
are highly selective in the formation of ethylene and
propylene.
[0050] The feedstock preferably contains one or more
aliphatic-containing compounds that include alcohols, amines,
carbonyl compounds for example aldehydes, ketones and carboxylic
acids, ethers, halides, mercaptans, sulfides, and the like, and
mixtures thereof. The aliphatic moiety of the aliphatic-containing
compounds typically contains from 1 to about 50 carbon atoms,
preferably from 1 to 20 carbon atoms, more preferably from 1 to 10
carbon atoms, and most preferably from 1 to 4 carbon atoms.
[0051] Non-limiting examples of aliphatic-containing compounds
include: alcohols such as methanol and ethanol, alkyl-mercaptans
such as methyl mercaptan and ethyl mercaptan, alkyl-sulfides such
as methyl sulfide, alkyl-amines such as methyl amine, alkyl-ethers
such as dimethyl ether, diethyl ether and methylethyl ether,
alkyl-halides such as methyl chloride and ethyl chloride, alkyl
ketones such as dimethyl ketone, formaldehydes, and various acids
such as acetic acid.
[0052] In a preferred embodiment of the process of the invention,
the feedstock contains one or more oxygenates, more specifically,
one or more organic compound(s) containing at least one oxygen
atom. In the most preferred embodiment of the process of invention,
the oxygenate in the feedstock is one or more alcohol(s),
preferably aliphatic alcohol(s) where the aliphatic moiety of the
alcohol(s) has from 1 to 20 carbon atoms, preferably from 1 to 10
carbon atoms, and most preferably from 1 to 4 carbon atoms. The
alcohols useful as feedstock in the process of the invention
include lower straight and branched chain aliphatic alcohols and
their unsaturated counterparts. Non-limiting examples of oxygenates
include methanol, ethanol, n-propanol, isopropanol, methyl ethyl
ether, dimethyl ether, diethyl ether, di-isopropyl ether,
formaldehyde, dimethyl carbonate, dimethyl ketone, acetic acid, and
mixtures thereof. In the most preferred embodiment, the feedstock
is selected from one or more of methanol, ethanol, dimethyl ether,
diethyl ether or a combination thereof, more preferably methanol
and dimethyl ether, and most preferably methanol.
[0053] The various feedstocks discussed above, particularly a
feedstock containing an oxygenate, more particularly a feedstock
containing an alcohol, is converted primarily into one or more
olefin(s). The olefin(s) or olefin, monomer(s) produced from the
feedstock typically have from 2 to 30 carbon atoms, preferably 2 to
8 carbon atoms, more preferably 2 to 6 carbon atoms, still more
preferably 2 to 4 carbons atoms, and most preferably ethylene an/or
propylene.
[0054] Non-limiting examples of olefin monomer(s) include ethylene,
propylene, butene-1, pentene-1, 4-methyl-pentene-1, hexene-1,
octene-1 and decene-1, preferably ethylene, propylene, butene-1,
pentene-1, 4-methyl-pentene-1, hexene-1, octene-1 and isomers
thereof. Other olefin monomer(s) include unsaturated monomers,
diolefins having 4 to 18 carbon atoms, conjugated or nonconjugated
dienes, polyenes, vinyl monomers and cyclic olefins.
[0055] In the most preferred embodiment, the feedstock, preferably
of one or more oxygenates, is converted in the presence of a
molecular sieve catalyst composition into olefin(s) having 2 to 6
carbons atoms, preferably 2 to 4 carbon atoms. Most preferably, the
olefin(s), alone or combination, are converted from a feedstock
containing an oxygenate, preferably an alcohol, most preferably
methanol, to the preferred olefin(s) ethylene and/or propylene.
[0056] The most preferred process is generally referred to as
gas-to-olefins (GTO) or alternatively, methanol-to-olefins (MTO).
In a MTO process, typically an oxygenated feedstock, most
preferably a methanol containing feedstock, is converted in the
presence of a molecular sieve catalyst composition into one or more
olefin(s), preferably and predominantly, ethylene and/or propylene,
often referred to as light olefin(s).
[0057] The feedstock, in one embodiment, contains one or more
diluent(s), typically used to reduce the concentration of the
feedstock. The diluents are generally non-reactive to the feedstock
or molecular sieve catalyst composition. Non-limiting examples of
diluents include helium, argon, nitrogen, carbon monoxide, carbon
dioxide, water, essentially non-reactive paraffins (especially
alkanes such as methane, ethane, and propane), essentially
non-reactive aromatic compounds, and mixtures thereof. The most
preferred diluents are water and nitrogen, with water being
particularly preferred. In other embodiments, the feedstock does
not contain any diluent.
[0058] The diluent may be used either in a liquid or a vapor form,
or a combination thereof. The diluent is either added directly to a
feedstock entering into a reactor or added directly into a reactor,
or added with a molecular sieve catalyst composition. In one
embodiment, the amount of diluent in the feedstock is in the range
of from about 1 to about 99 mole percent based on the total number
of moles of the feedstock and diluent, preferably from about 1 to
80 mole percent, more preferably from about 5 to about 50, most
preferably from about 5 to about 25. In one embodiment, other
hydrocarbons are added to a feedstock either directly or
indirectly, and include olefin(s), paraffin(s), aromatic(s) (see
for example U.S. Pat. No. 4,677,242, addition of aromatics) or
mixtures thereof, preferably propylene, butylene, pentylene, and
other hydrocarbons having 4 or more carbon atoms, or mixtures
thereof.
[0059] The process for converting a feedstock, especially a
feedstock containing one or more oxygenates, in the presence of a
molecular sieve catalyst composition of the invention, is carried
out in a reaction process in a reactor, where the process is a
fixed bed process, a fluidized bed process (includes a turbulent
bed process), preferably a continuous fluidized bed process, and
most preferably a continuous high velocity fluidized bed
process.
[0060] The reaction processes can take place in a variety of
catalytic reactors such as hybrid reactors that have a dense bed or
fixed bed reaction zones and/or fast fluidized bed reaction zones
coupled together, circulating fluidized bed reactors, riser
reactors, and the like. Suitable conventional reactor types are
described in for example U.S. Pat. No. 4,076,796, U.S. Pat. No.
6,287,522 (dual riser), and Fluidization Engineering, D. Kunii and
O. Levenspiel, Robert E. Krieger Publishing Company, New York, N.Y.
1977, which are all herein fully incorporated by reference.
[0061] The preferred reactor type are riser reactors generally
described in Riser Reactor, Fluidization and Fluid-Particle
Systems, pages 48 to 59, F. A. Zenz and D. F. Othmo, Reinhold
Publishing Corporation, New York, 1960, and U.S. Pat. No. 6,166,282
(fast-fluidized bed reactor), and U.S. patent application Ser. No.
09/564,613 filed May 4, 2000 (multiple riser reactor), which are
all herein fully incorporated by reference.
[0062] In an embodiment, the amount of fresh feedstock fed
separately or jointly with a vapor feedstock, to a reactor system
is in the range of from 0.1 weight percent to about 85 weight
percent, preferably from about 1 weight percent to about 75 weight
percent, more preferably from about 5 weight percent to about 65
weight percent based on the total weight of the feedstock including
any diluent contained therein. The liquid and vapor feedstocks are
preferably the same composition, or contain varying proportions of
the same or different feedstock with the same or different
diluent.
[0063] The conversion temperature employed in the conversion
process, specifically within the reactor system, is in the range of
from about 200.degree. C. to about 1000.degree. C., preferably from
about 250.degree. C. to about 800.degree. C., more preferably from
about 250.degree. C. to about 750.degree. C., yet more preferably
from about 300.degree. C. to about 650.degree. C., yet even more
preferably from about 350.degree. C. to about 600.degree. C. most
preferably from about 350.degree. C. to about 550.degree. C.
[0064] The conversion pressure employed in the conversion process,
specifically within the reactor system, varies over a wide range
including autogenous pressure. The conversion pressure is based on
the partial pressure of the feedstock exclusive of any diluent
therein. Typically the conversion pressure employed in the process
is in the range of from about 0.1 kPaa to about 5 MPaa, preferably
from about 5 kPaa to about 1 MPaa, and most preferably from about
20 kPaa to about 500 kPaa.
[0065] The weight hourly space velocity (WHSV), particularly in a
process for converting a feedstock containing one or more
oxygenates in the presence of a molecular sieve catalyst
composition within a reaction zone, is defined as the total weight
of the feedstock excluding any diluents to the reaction zone per
hour per weight of molecular sieve in the molecular sieve catalyst
composition in the reaction zone. The WHSV is maintained at a level
sufficient to keep the catalyst composition in a fluidized state
within a reactor.
[0066] Typically, the WHSV ranges from about 1 hr.sup.-1 to about
5000 hr.sup.-1, preferably from about 2 hr.sup.-1 to about 3000
hr.sup.-1, more preferably from about 5 hr.sup.-1 to about 1500
hr.sup.-1, and most preferably from about 10 hr.sup.-1 to about
1000 hr.sup.-1. In one preferred embodiment, the WHSV is greater
than 20 hr.sup.-1, preferably the WHSV for conversion of a
feedstock containing methanol, dimethyl ether, or both, is in the
range of from about 20 hr.sup.-1 to about 300 hr.sup.-1.
[0067] The superficial gas velocity (SGV) of the feedstock
including diluent and reaction products within the reactor system
is preferably sufficient to fluidize the molecular sieve catalyst
composition within a reaction zone in the reactor. The SGV in the
process, particularly within the reactor system, more particularly
within the riser reactor(s), is at least 0.1 meter per second
(m/sec), preferably greater than 0.5 m/sec, more preferably greater
than 1 m/sec, even more preferably greater than 2 m/sec, yet even
more preferably greater than 3 m/sec, and most preferably greater
than 4 m/sec. See for example U.S. patent application Ser. No.
09/708,753 filed Nov. 8, 2000, which is herein incorporated by
reference.
EXAMPLE
[0068] provide a better understanding of the present invention
including representative advantages thereof, the following example
is offered. The Example compares the reactivity of a methanol
feedstock in a stainless steel reactor with a methanol feedstock in
a coated reactor at various temperatures.
[0069] All data presented was obtained using a microflow reactor.
The microflow reactor used was a No. 316 stainless steel reactor
(1/4 inch outer diameter) located in a furnace to which vaporized
methanol was fed. The vaporized methanol was maintained at
120.degree. C. The methanol conversion reactions were performed at
25 psig (172 kPag) methanol pressure and at a methanol feed rate of
80 .mu.l/min. The control experiment was performed under identical
reaction conditions except that a coated reactor was used. The
coated reactor was 1/16 inch in water and was made of steel coated
with a thin layer of fused silica.
[0070] The effluent from the reactor was collected in a 15-sample
loop Valco valve. The collected samples were analyzed by on-line
gas chromatography (Hewlett Packard 6890) equipped with a flame
ionization detector. CO, CO.sub.2 and H.sub.2 were not analyzed.
The measured conversions of methanol, which were calculated on the
carbon basis, would have been higher if CO. CO.sub.2 and H.sub.2
were included in the calculations. The chromatographic column used
was a Q-column.
[0071] Table 1 summarizes the results of the conversions (wt %) of
methanol. reacting on the lab reactor. TABLE-US-00001 TABLE 1
Methanol conversions (wt %) from Methanol Reacting on Stainless
Steel Reactor Wall Methanol Conversion (Wt. %) Temperature
(.degree. C.) Stainless Steel Reactor Coated Reactor 200 0.02 0.00
300 0.04 0.00 350 0.15 0.00 400 0.34 0.01 450 0.91 0.04 500 3.46
0.06 550 5.79 0.16
[0072] According to the results indicated above, a negligible
amount of metal catalyzed side reaction byproducts were detected
below 350.degree. C. in a No. 316 stainless steel reactor. At
350.degree. C., 0.15 wt % methanol conversion was observed in an
untreated stainless steel reactor. The conversion was much higher
at 500.degree. C. and 550.degree. C. The conversion of methanol on
the coated reactor was essentially zero even at 500.degree. C. This
experimental data indicates that the metal in the reactor is active
for decomposing methanol under effective MTO conditions. Moreover,
this data indicates that undesirable reaction byproducts can be
minimized by maintaining the methanol feedstock at a temperature
lower than the MTO reactor temperature.
[0073] In another embodiment of the present invention, the percent
conversion of oxygenate over the surface of a metal reactor,
preferably in the absence of a MTO catalyst, is less than 1.0
percent, preferably less than 0.8 percent, more preferably less
than 0.4 or 0.1 percent, and most preferably less than 0.05 or 0.01
percent, or below detection limits. In other words, the invention
includes maintaining the feedstock while it is in the FVI system,
especially the feed introduction nozzle, at conditions, e.g.,
temperature, effective to substantially eliminate the formation of
metal catalyzed side reaction byproducts. "Substantially eliminate"
is defined herein as less than 0.05 percent conversion to
byproducts excluding CO, CO.sub.2 and H.sub.2.
[0074] Having now fully described the invention, it will be
appreciated by those skilled in the art that the invention can be
performed within a wide range of parameters within what is claimed,
without departing from the spirit and scope of the invention.
* * * * *