U.S. patent application number 09/992371 was filed with the patent office on 2003-05-08 for slurry hydrocarbon synthesis with external hydroisomerization in downcomer reactor loop.
Invention is credited to Clark, Janet Renee, Feeley, Jennifer Schaefer, Mart, Charles John, Wittenbrink, Robert Jay.
Application Number | 20030088137 09/992371 |
Document ID | / |
Family ID | 25538257 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030088137 |
Kind Code |
A1 |
Mart, Charles John ; et
al. |
May 8, 2003 |
SLURRY HYDROCARBON SYNTHESIS WITH EXTERNAL HYDROISOMERIZATION IN
DOWNCOMER REACTOR LOOP
Abstract
A slurry Fischer-Tropsch hydrocarbon synthesis process for
synthesizing liquid hydrocarbons from synthesis gas, in a
hydrocarbon synthesis reactor, also hydroisomerizes the synthesized
hydrocarbons in one or more external downcomer reactor
hydroisomerizing loops outside of the reactor, but which are a part
of the synthesis reactor. A monolithic catalyst is used for the
hydroisomerization, and slurry circulation between the synthesis
reactor and the one or more hydroisomerization loops is achieved,
at least in part, by density-difference driven hydraulics created
by removing gas bubbles from the slurry passed into the loop.
Preferably, catalyst particles are also removed before the slurry
contacts the monolithic hydroisomerization catalyst.
Inventors: |
Mart, Charles John; (Baton
Rouge, LA) ; Wittenbrink, Robert Jay; (Kingwood,
TX) ; Clark, Janet Renee; (Baton Rouge, LA) ;
Feeley, Jennifer Schaefer; (Lebanon, NJ) |
Correspondence
Address: |
EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
P.O. BOX 900
1545 ROUTE 22 EAST
ANNANDALE
NJ
08801-0900
US
|
Family ID: |
25538257 |
Appl. No.: |
09/992371 |
Filed: |
November 6, 2001 |
Current U.S.
Class: |
585/734 ;
518/702; 585/921; 585/922 |
Current CPC
Class: |
Y10S 208/95 20130101;
C10G 45/66 20130101; B01J 8/006 20130101; B01J 8/226 20130101; C10G
2/32 20130101; C10K 3/04 20130101; B01J 8/228 20130101 |
Class at
Publication: |
585/734 ;
585/921; 585/922; 518/702 |
International
Class: |
C07C 005/22 |
Claims
What is claimed is:
1. A process for hydroisomerizing the slurry hydrocarbon liquid
produced in a slurry Fischer-Tropsch hydrocarbon synthesis reactor,
while said reactor is producing said liquid from a synthesis gas
and wherein said slurry in said synthesis reactor comprises gas
bubbles and catalyst particles in said liquid, said process
comprising: (a) contacting a portion of said slurry with means for
removing gas bubbles, to produce a gas bubble reduced slurry having
a density greater than that of said slurry in said synthesis
reactor; (b) passing a hydrogen treat gas and said densified, gas
bubble reduced slurry into and down through a hydroisomerization
zone in one or more downcomer reactors external of said synthesis
reactor and, in fluid communication with said slurry therein, each
said downcomer reactor containing a hydroisomerization catalyst
therein which defines a hydroisomerization zone; (c) reacting said
gas bubble reduced slurry and hydrogen in the presence of said
hydroisomerization catalyst, at reaction conditions effective to
hydroisomerize at least a portion of said liquid and produce a
hydroisomerized liquid, and (d) passing all or a portion of said
hydroisomerized hydrocarbon liquid back into said synthesis reactor
in which it mixes with said slurry therein and forms part of said
slurry liquid.
2. A process according to claim 1 wherein there is more than one
downcomer reactor.
3. A process according to claim 2 wherein at least one downcomer
contains noble metal containing hydroisomerization catalyst and
wherein at least one other downcomer contains non-noble metal
hydroisomerization catalyst.
4. A process according to claim 1 wherein circulation of said gas
bubble reduced slurry down through said downcomer reactor and back
into said synthesis reactor is produced at least in part by
density-driven hydraulics due to said slurry density
differences.
5. A process a cording to claim 4 wherein said slurry hydrocarbon
liquid is intermittently or continuously withdrawn as product
liquid from said synthesis reactor, while it is producing said
hydrocarbon slurry liquid.
6. A process according to claim 5 wherein, in addition to gas
bubble removal, at least a portion of said catalyst particles are
also removed from said slurry, before it is passed down into said
hydroisomerization zone.
7. A process according to claim 6 wherein said hydroisomerization
catalyst comprises a monolithic catalyst.
8. A process according to claim 7 wherein said hydroisomerization
catalyst is in the form of a monolith.
9. A process according to claim 7 wherein said monolithic catalyst
comprises a plurality of monolithic catalyst bodies vertically
arrayed in said zone.
10. A process according to claim 9 wherein at least a portion of
said slurry liquid removed from said synthesis reactor is passed to
at least one upgrading operation comprising at least fractionation
and/or one or more conversion operations.
11. A process according to claim 10 wherein said one or more
downcomer reactors are connected to and depend from said synthesis
reactor.
12. A process according to claim 11 wherein at least a portion of
said monolithic bodies are vertically spaced apart in said
hydroisomerization zone.
13. A process according to claim 12 wherein said hydrogen treat gas
is passed into said zone through at least two separate gas
injection means vertically spaced apart along said zone, each
upstream of a monolithic catalyst body.
14. A process according to claim 13 wherein a static mixing means
is located in at least a portion of said spaces between said
monolithic bodies.
15. A process according to claim 14 wherein at least a portion of
said hydrogen is injected into said hydroisomerization zone
upstream of at least one of said mixing means.
16. A process according to claim 15 wherein said gas bubbles and
particulate solids are removed from said slurry by gas bubble and
solids removing means immersed in said slurry in said synthesis
reactor.
17. A process according to claim 16 wherein said gas bubbles and
particulate solids are removed from said slurry liquid upstream of
said hydroisomerizing zone by density difference.
18. A process according to claim 17 wherein said gas bubble reduced
slurry liquid is fed into said one or more lift reactors by
downcomer means immersed in said slurry in said synthesis
reactor.
19. A slurry hydrocarbon synthesis process which includes
hydroisomerizing hydrocarbon liquid produced by the synthesis
reaction while said hydrocarbon liquid is being produced from a
synthesis gas comprises the steps of: (a) passing said synthesis
gas comprising a mixture of H2 and CO into a slurry body comprising
a three-phase main slurry body in a slurry Fischer-Tropsch
hydrocarbon synthesis reactor, in which said slurry body comprises
gas bubbles and a particulate hydrocarbon synthesis catalyst in a
slurry hydrocarbon liquid; (b) reacting said H.sub.2 and CO in the
presence of said catalyst at reaction conditions effective to form
hydrocarbons, a portion of which are liquid at said reaction
conditions and comprise said slurry liquid; (c) contacting a
portion of said slurry from said slurry body with means for
removing gas bubbles, to form a gas bubble reduced slurry densified
to a density greater than that of said slurry comprising said
slurry body; (d) passing a hydrogen treat gas and said densified
slurry into and down through a hydroisomerization zone in one or
more downcomer reactors external of, in fluid contact with and
depending from, said synthesis reactor, in which they react in the
presence of a monolithic hydroisomerization catalyst to form a
hydroisomerized hydrocarbon liquid of reduced pour point, and
wherein circulation of said densified slurry down through said one
or more downcomer reactors and back into said synthesis reactor, is
produced at least in part by density-driven hydraulics due to said
slurry density differences; (e) passing at least a portion of said
hydroisomerized hydrocarbon liquid back into said synthesis reactor
in which it mixes with said slurry body therein.
20. A process according to claim 19 wherein said slurry hydrocarbon
liquid is intermittently or continuously withdrawn as product
liquid from said synthesis reactor, while it is producing said
hydrocarbon slurry liquid and wherein at least a portion of said
product liquid is passed to at least one upgrading operation
comprising at least fractionation and/or one or more conversion
operations.
21. A process according to claim 20 wherein said gas bubble reduced
slurry is passed through heat exchange means to change its
temperature to a value different than that in said slurry reactor,
before it reacts with said hydrogen in said hydroisomerization
zone.
22. A process according to claim 21 wherein said monolithic
hydroisomerization catalyst comprises a plurality of vertically
arrayed monolithic catalyst bodies, at least a portion of which are
vertically spaced apart.
23. A process according to claim 22 wherein said hydrogen treat gas
is passed into said zone by at least two separate gas injection
means vertically spaced apart along said zone, each upstream of a
monolithic catalyst body.
24. A process according to claim 23 wherein solid particles are
also removed from said slurry, before said slurry liquid contacts
said hydroisomerization catalyst and wherein said gas bubbles and
particulate solids are removed from said slurry by gas bubble and
solids removing means immersed in said slurry body.
25. A process according to claim 24 wherein a static mixing means
is located in at least a portion of said spaces between said
catalyst bodies.
26. A process according to claim 25 wherein at least a portion of
slurry liquid produced in said reactor and hydroisomerized is
passed to at least one upgrading operation.
27. A process according to claim 26 wherein said upgrading
comprises fractionation and/or one or more conversion operations.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Invention
[0002] The invention relates to a slurry hydrocarbon synthesis
process which includes liquid isomerization in an external
downcomer reaction loop. More particularly the invention relates to
a slurry Fischer-Tropsch type of hydrocarbon synthesis process, in
which the synthesized hydrocarbon slurry liquid in the synthesis
reactor is circulated through at least one external downcomer
reactor, in which it reacts with hydrogen in the presence of a
hydroisomerization catalyst, and preferably a monolithic catalyst,
to hydroisomerize the liquid and reduce its pour point. The liquid
then passes back into the synthesis reactor.
[0003] 2. Background of the Invention
[0004] The slurry Fischer-Tropsch hydrocarbon synthesis process is
now well known and documented, both in patents and in the technical
literature. This process comprises passing a synthesis gas, which
comprises a mixture of H.sub.2 and CO, up into a hot reactive
slurry in a hydrocarbon synthesis reactor. The slurry comprises
synthesized hydrocarbons which are liquid at the synthesis reaction
conditions and in which is dispersed a particulate Fischer-Tropsch
type of catalyst. The H.sub.2 and CO react in the presence of the
catalyst and form hydrocarbons. The hydrocarbon liquid is
continuously or intermittently withdrawn from the reactor and
pipelined to one or more downstream upgrading operations. The
upgraded products may include, for example, a syncrude, various
fuels and lubricating oil fractions and wax. The downstream
upgrading includes fractionation and conversion operations,
typically comprising hydroisomerization, in which a portion of the
molecular structure of at least some the hydrocarbon molecules is
changed. It would be an improvement if the synthesized hydrocarbon
slurry liquid could be hydroisomerized to reduce its pour and melt
points, which make it more transportable by pipeline, before it is
transferred to downstream operations.
SUMMARY OF THE INVENTION
[0005] The invention relates to a slurry Fischer-Tropsch type of
hydrocarbon synthesis process, in which a portion of the
synthesized hydrocarbon slurry liquid is passed out of the
synthesis reactor and into at least one external downcomer reactor,
in which it reacts with hydrogen in the presence of a
hydroisomerization catalyst, and preferably a monolithic
hydroisomerization catalyst, to hydroisomerize the liquid, which is
then passed back into the three-phase slurry (main slurry body) in
the synthesis reactor. The slurry liquid, which comprises
synthesized hydrocarbons that are liquid at the synthesis reaction
conditions, comprises mostly normal paraffins and the
hydroisomerization reduces its pour and melt points, thereby making
it more pumpable and pipelineable. By downcomer reactor is meant
that all or most of the slurry circulation between it and the
synthesis reactor is achieved by density-driven hydraulics, in
which the density of the downflowing slurry is greater than in the
synthesis reactor. Slurry densification is achieved by removing at
least a portion of the gas bubbles from the slurry, thereby
densifying the slurry, before it is passed into the downcomer
reactor. The one or more downflow reactors may each be a simple,
substantially vertical, hollow fluid conduit or pipe. The process
comprises contacting hot slurry from the main slurry body, with
means for removing gas bubbles, and preferably both gas bubbles and
at least a portion of the particulate solids from the slurry liquid
which, along with a hydrogen treat gas, is then passed out of the
synthesis reactor and down into the one or more external downcomer
reactors. The hydroisomerization catalyst is located in the
interior of the downcomer reactor and comprises the
hydroisomerization reaction zone. This hydroisomerized hydrocarbon
liquid of reduced pour point is then passed back into the main
slurry body in the synthesis reactor. Thus, the synthesized
hydrocarbon liquid is passed out of the synthesis reactor, down
into and through the interior of the one or more external downcomer
reactors and back into the synthesis reactor. The downcomer reactor
is in fluid communication with the main slurry body inside the
synthesis reactor, via upper and lower conduit portions opening
into respective upper and lower portions of the synthesis reactor.
This enables hydroisomerization of the slurry liquid (i) in an
external reaction loop which depends from, and is therefore part
of, the synthesis reactor and (ii) while the synthesis reactor is
producing hydrocarbons, but without interfering with the
hydrocarbon synthesis reaction. The concentration of
hydroisomerized hydrocarbon liquid in the synthesis reactor
continues to increase until equilibrium conditions are reached.
When the reactor reaches equilibrium, it is possible for the slurry
liquid being removed from it to comprise mostly hydroisomerized
hydrocarbons of reduced pour point. In some cases, no further
hydroisomerization of the liquid hydrocarbon product withdrawn from
the hydrocarbon synthesis reactor is necessary. Thus, the process
of the invention will reduce and in some cases even eliminate the
need for a separate, stand-alone hydroisomerization reactor and
associated equipment, downstream of the synthesis reactor. If a
downstream hydroisomerization reactor is needed, it will be smaller
than it would be if the synthesized hydrocarbon liquid passed into
it was not at least partially hydroisomerized. While all of the
hydroisomerized hydrocarbon liquid is typically returned back into
the main slurry body with which it mixes, in some embodiments a
portion of the hydroisomerized liquid will be passed from the
downcomer reactor directly to downstream operations.
[0006] Hydroisomerizing the slurry liquid in one or more external
loops permits the use of heat exchange means associated therewith
to adjust the hydroisomerization temperature to be different (e.g.,
higher) from that in the synthesis reactor. A higher
hydroisomerization temperature enables the use of a less expensive,
non-noble metal hydroisomerization catalyst. The gas bubble and
preferably the slurry gas bubble and particulate solids removal
means is preferably located in the main slurry body and may
comprise the same or separate means. While various filtration means
may be used to separate the slurry liquid from at least a portion
of the catalyst and any other particles, before the slurry is
passed down into the hydroisomerization zone, in the practice of
the invention the use of filtration means may be avoided by using
known slurry solids reducing means that do not employ filtration.
Gas bubble and solids removal means suitable for use with the
present invention are known and disclosed in, for example, U.S.
Pat. Nos. 5,866,621 and 5,962,537, the disclosures of which are
incorporated herein by reference. Simple gas bubble removing means
are disclosed in U.S. Pat. Nos. 5,382,748; 5,811,468 and 5,817,702,
the disclosures of which are also incorporated herein by reference.
Removing gas bubbles from the slurry densifies it and, if properly
employed in connection with feeding the densified slurry down into
and through the downcomer reactor (e.g., the slurry is densified
sufficiently vertically above the external hydroisomerization
zone), provides a density-difference driven hydraulic head to
circulate the slurry from inside the synthesis reactor, down into
and through the external downcomer reactor and back into the
synthesis reactor. Removing gas bubbles from the slurry prior to
hydroisomerization also reduces the CO and water vapor content of
the flowing fluid, which could otherwise react with the
hydroisomerization hydrogen and also adversely effect the
hydroisomerization catalyst. A monolithic hydroisomerization
catalyst having a minimal solid cross-sectional area perpendicular
to the flow direction of the fluid, minimizes the pressure drop of
the fluid flowing down and across the catalyst surface. Removing
catalyst and other solid particles, such as inert heat transfer
particles, from the slurry upstream of the hydroisomerization zone,
reduces scouring of the monolithic catalyst and plugging of the
hydroisomerization reaction zone.
[0007] In a broad sense, the process of the invention comprises a
slurry Fischer-Tropsch hydrocarbon synthesis process, in which a
portion of the hydrocarbon slurry liquid is removed from the main
slurry body in the hydrocarbon synthesis reactor, reduced in gas
bubble content and passed down into and through a
hydroisomerization zone in a downcomer reactor external of, and in
fluid communication with, the synthesis reactor, in which it reacts
with hydrogen in the presence of a hydroisomerization catalyst, at
reaction conditions effective to hydroisomerize at least a portion
of the hydrocarbon liquid and produce a hydroisomerized hydrocarbon
liquid of reduced pour point, with at least a portion of the
hydroisomerized passed back into the synthesis reactor. Preferably
at least a portion of both gas bubbles and particulate solids are
removed from the slurry before it contacts the hydroisomerization
catalyst. In a still further embodiment, the invention comprises a
hydrocarbon synthesis process which includes hydroisomerizing
hydrocarbon liquid produced by the synthesis reaction while the
hydrocarbon liquid is being produced from a synthesis gas, the
process comprising the steps of:
[0008] (a) passing a synthesis gas comprising a mixture of H.sub.2
and CO into a slurry body comprising a three-phase slurry in a
slurry Fischer-Tropsch hydrocarbon synthesis reactor, in which the
slurry comprises gas bubbles and a particulate hydrocarbon
synthesis catalyst in a slurry hydrocarbon liquid;
[0009] (b) reacting the H.sub.2 and CO in the presence of the
catalyst at reaction conditions effective to form hydrocarbons, a
portion of which are liquid at the reaction conditions and comprise
the slurry hydrocarbon liquid;
[0010] (c) contacting a portion of the slurry from the slurry body
with means for removing gas bubbles, to form a densified slurry
hydrocarbon liquid reduced in gas bubbles whose density is greater
than that of the slurry comprising the slurry body in the synthesis
reactor;
[0011] (d) passing a hydrogen treat gas and the densified
hydrocarbon liquid formed in (iii) into a hydroisomerizing zone in
one or more downcomer reactors external of, in fluid contact with
and depending from the synthesis reactor, in which they react in
the presence of a preferably monolithic hydroisomerization catalyst
to form a hydrocarbon liquid of reduced pour point, and
[0012] (e) passing all or a portion of the pour point reduced
liquid back into the synthesis reactor, wherein it mixes with the
main slurry body therein.
[0013] While the liquid is being synthesized and hydroisomerized in
the synthesis reactor, a portion is continuously or intermittently
withdrawn and sent to downstream operations.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 is a simple schematic flow diagram of a hydrocarbon
synthesis reactor containing a hydroisomerization zone within,
according to one embodiment of the invention.
[0015] FIG. 2 is a brief schematic showing static mixers in the
hydroisomerization zone.
[0016] FIGS. 3(a) and 3(b) are respective top plan and a side
schematic views of a monolithic catalyst body.
[0017] FIG. 4 is a plot of hexadecane conversion as a function of
temperature in the presence of a monolithic hydroisomerization
catalyst in a pilot plant tubular reactor.
[0018] FIG. 5 is a graph illustrating hexadecane hydroisomerization
selectivity over a monolithic hydroisomerization catalyst in a
pilot plant tubular reactor.
DETAILED DESCRIPTION
[0019] The waxy slurry liquid synthesized in the hydrocarbon
synthesis reactor will typically comprise 500.degree. F.+
hydrocarbons, with most having an initial boiling point in the
650-750.degree. F.+ range. The end boiling point will be at least
850.degree. F., preferably at least 1050.degree. F. and even higher
(1050.degree. F.+). This liquid also comprises mostly (more than 50
wt. %), typically more than 90%, preferably more than 95% and more
preferably more than 98 wt. % paraffinic hydrocarbons, most of
which are normal paraffins, and this is what is meant by
"paraffinic" in the context of the invention, particularly when the
hydrocarbon synthesis catalyst comprises a cobalt catalytic
component. The exact boiling range, hydrocarbon composition, etc,
are determined by the catalyst and process variables used for the
synthesis. It has negligible amounts of sulfur and nitrogen
compounds (e.g., less than 1 wppm). Slurry liquids having these
properties and useful in the process of the invention have been
made using a slurry Fischer-Tropsch process with a catalyst having
a catalytic cobalt component. In the practice of the invention, it
is preferred that the slurry Fischer-Tropsch hydrocarbon synthesis
catalyst comprise a catalytic cobalt or iron component. It is also
preferred that the synthesis reaction have a Schulz-Flory alpha of
at least 0.90, as higher molecular weight hydrocarbons are
preferred in most cases. The gas bubbles in the slurry comprise
synthesis gas, vapor and gaseous products of the synthesis
reaction, such as C.sub.1-C.sub.4 hydrocarbons, and especially
methane, CO.sub.2 and water vapor. The hydroisomerization catalyst
is adversely effected by water vapor. Therefore, in addition to
densifying the slurry, gas bubble removal is also beneficial to the
downstream hydroisomerizing catalyst. The flow rate of a gas
bubble-reduced slurry down through a vertical downcomer can be
substantial and a high flow rate is desired to offset the lift
action of the hydrogen treat gas injected into the hydroisomerizing
zone in the downcomer reactor. A high liquid flow rate prevents the
hydrogen treat gas from pushing the downflowing slurry back up and
out of the downcomer reactor, it also prevents the gas from rising
up and out of the hydroisomerization zone, before
hydroisomerization can take place. In an experiment with a 30 foot
tall slurry hydrocarbon synthesis reactor, using a simple gas
disengaging cup on top of a vertical downcomer pipe of the type
disclosed in U.S. Pat. No. 5,382,748, resulted in a 12 ft/sec
liquid flow rate down a 3 inch downcomer pipe, from which only half
of the 60 vol. % of gas bubbles had been removed.
[0020] The hydroisomerization catalyst will have a both a
hydrogenation/dehydrogenation function and an acid hydrocracking
function for hydroisomerizing the normal paraffinic hydrocarbons in
the slurry hydrocarbon liquid. The hydrocracking functionality of
the catalyst results in the conversion of some of the waxy slurry
liquid to lower boiling material. The use of an external
hydroisomerization reaction zone connected to the synthesis
reactor, means that the hydroisomerization reaction temperature is
not limited to that in the hydrocarbon synthesis reactor to the
extent that an internal hydroisomerization zone is. Therefore, the
hydroisomerization reaction temperature may range from
300-900.degree. F. and preferably 550-750.degree. F., compared to a
typically 320-600.degree. F. temperature range in the slurry
hydrocarbon synthesis reactor. However, the pressure in the
hydroisomerization reaction zone will be about the same as that in
the hydrocarbon synthesis reactor and will typically range from
80-600 psig. The hydrogen treat gas rate will be from 500-5000
SCF/B, with a preferred range of 2000-4000 SCF/B. By hydrogen treat
gas is meant all hydrogen or preferably at least about 60 vol. %
hydrogen and an inert diluent gas, such as argon or methane. Excess
hydrogen is employed during the hydroisomerization to insure an
adequate hydrogen partial pressure and to prevent any CO remaining
in the downflowing slurry from adversely effecting the
hydroisomerization reaction and catalyst. he hydroisomerization
catalyst comprises one or more Group VIII catalytic metal
components supported on an acidic metal oxide support to give the
catalyst both a hydrogenation function and an acid function for
hydroisomerizing the hydrocarbons. At relatively low
hydroisomerizing temperatures, such as those in a hydrocarbon
synthesis reactor, the catalytic metal component may comprise a
Group VIII noble metal, such as Pt or Pd, and preferably Pt.
However, at the higher temperatures which can be employed with the
process of the invention, it is preferred that the catalytic metal
component comprise one or more less expensive non-noble Group VIII
metals, such as Co, Ni and Fe, which will typically also include a
Group VIB metal (e.g., Mo or W) oxide promoter. The catalyst may
also have a Group IB metal, such as copper, as a hydrogenolysis
suppressant. The Groups referred to herein refer to Groups as found
in the Sargent-Welch Periodic Table of the Elements copyrighted in
1968 by the Sargent-Welch Scientific Company. The cracking and
hydrogenating activity of the catalyst is determined by its
specific composition, as is known. In a preferred embodiment the
catalytically active metal comprises cobalt and molybdenum. The
acidic oxide support or carrier may include silica, alumina,
silica-alumina, silica-alumina-phosphates, titania, zirconia,
vanadia, and other Group II, IV, V or VI oxides, as well as Y
sieves, such as ultra stable Y sieves. Preferred supports include
silica, alumina and silica-alumina and, more preferably
silica-alumina in which the silica concentration in the bulk
support (as opposed to surface silica) is less than about 50 wt. %,
preferably less than 35 wt. % and more preferably 15-30 wt. %. As
is known, if the support is alumina, small amounts of fluorine or
chlorine are often be incorporated into it to increase the acid
functionality. However, in the process of the invention, the use of
halogens in the catalyst is to be avoided, to prevent impairing the
hydrocarbon synthesis catalyst.
[0021] Hydroisomerization can be enhanced by using noble metal
containing catalysts in at least one hydroisomerization zone within
the downcomer reactor and non-noble metal containing catalysts in
at least one other hydroisomerization zone within the downcomer
reactor.
[0022] A hydroisomerization catalyst that is particularly preferred
in the practice of the invention comprises both cobalt and
molybdenum catalytic components supported on an amorphous, low
silica alumina-silica support, and most preferably one in which the
cobalt component is deposited on the support and calcined before
the molybdenum component is added. This catalyst will contain from
10-20 wt. % MoO.sub.3 and 2-5 wt. % CoO on an amorphous
alumina-silica support in which the silica content ranges from
20-30 wt. % of the support. This catalyst has been found to have
good selectivity retention and resistance to deactivation by
oxygenates typically found in Fischer-Tropsch produced waxy feeds.
The addition of a copper component suppresses hydrogenolysis. The
preparation of this catalyst is disclosed in, for example, U.S.
Pat. Nos. 5,757, 920 and 5,750,819, the disclosures of which are
incorporated herein by reference.
[0023] Monolithic catalysts are known for automotive exhausts and
for chemical reactions as is shown, for example, in an article by
Crynes, et al., "Monolithic Froth Reactor: Development of a novel
three-Phase Catalytic System", AIChE 1, v. 41, n. 2, p. 337-345
(February 1995). A corrugated type of monolithic catalyst has even
been suggested for Fischer-Tropsch hydrocarbon synthesis (GB
2,322,633 A). Basically monolithic catalysts comprise a ceramic or
metal support structure of a desired shape, with a catalyst applied
to its surface. The monolith may be a metal foam or may be prepared
from the catalyst composition itself or from the catalyst support,
e.g., molecular sieves, with the catalytic metal(s) deposited onto
the monolith support. In this latter case, monolith attrition will
still leave catalyst available for the hydroisomerization reaction.
Preferred channel sizes for monoliths are in the range >300
.mu.m and less than 600 .mu.m. Very high strength monolithic
catalysts may be fabricated from a metal foundation, over which is
applied a suitable ceramic and then the catalyst. The catalytic
material may be a finished catalyst which has been ground to a
small particle size, slurried in an appropriate liquid, such as
water or an organic liquid, with the slurry then applied to the
monolithic support surface as a wash coat and calcined. It is also
possible to apply one or more applications of catalytic precursor
materials to the ceramic support by impregnation or incipient
wetness, followed by drying and calcining. In the practice of the
invention, a monolithic catalyst having a minimal solid
cross-sectional area perpendicular to the fluid flow direction is
preferred, to minimize the pressure drop of the fluid flowing
across the catalytic surface. Such catalysts will not be limited to
containing substantially longitudinal and parallel fluid flow
channels. However, since pressure drop across the catalyst is
important, this must be taken into consideration. Micron size
channel openings or openings on the order of a few microns will not
be large enough for this application but openings generally
exceeding 300 microns would be acceptable. Suitable catalyst shapes
for providing a low pressure drop include an open cell foam
structure, and configurations having a low cross-sectional area
perpendicular to the fluid flow direction may also be used. Such
shapes will include, for example, elongated star shapes, with and
without an outer peripheral wall, corrugated constructions, with
longitudinal channels parallel to the fluid flow direction, a
honeycomb containing a plurality of open-ended flow channels
substantially parallel to the fluid flow direction and the like.
Many of these shapes may be extruded from a preceramic paste, dried
and then fired to the green or fully fired to the final state, to
provide the foundation for the catalyst material. Still further,
all or some of the monolithic catalysts used in the
hydroisomerization zone may be shaped in the form of a low pressure
drop static mixer, such as a Kenics.RTM. static mixer in the form
of slightly twisted or spiral-shaped metal strips. A monolithic
catalyst having this shape may be prepared by applying a ceramic
over a twisted metal strip and then applying or forming the
catalyst on the ceramic. The advantage of this is to provide more
intimate mixing of hydrogen and liquid and to prevent
stratification of the gas and liquid flows as they flow down
through the hydroisomerizing zone.
[0024] In the practice of the invention, the hydroisomerization
zone in the downcomer reactor will preferably comprise a plurality
of monoliths vertically arrayed on top of each other in the
hydroisomerization zone. For example, in the case of a vertical,
elongated and substantially vertical downcomer conduit, a plurality
of cylindrical monoliths may be vertically arranged or arrayed
along the vertical axis inside the downcomer conduit to form the
hyroisomerization zone. The cross-sectional area of the catalyst
monoliths perpendicular to the direction of fluid flow will
typically proximate that of the interior of the conduit. It is
preferred that there be vertical spaces between at least some of
the monoliths, to prevent stratification of the gas and liquid as
they flown down through the zone. More preferably, a low pressure
drop static mixer, such as a Kenics.RTM. static mixer will be
placed in the space between at least some of the arrays, to insure
adequate mixing and remixing of the hydrogen treat gas and slurry
liquid, as they flow down through the zone. Some or all of the
catalyst monoliths themselves may be in the form of a low pressure
drop static mixer, to insure good mixing and low pressure drop. It
is preferred to inject the hydrogen or hydrogen treat gas into the
hydroisomerization zone via a plurality of gas injection means,
vertically spaced apart along the hydroisomerization zone. This
will help to reduce the lifting action of the gas and
stratification, as well as insuring good mixing of the downflowing
fluid and the hydrogen. It is more preferred that the hydrogen be
injected into such spaces upstream of one or more low pressure drop
static mixers in the hydroisomerization zone, to mix the injected
gas into the downflowing liquid at each gas injection point. The
invention will be further understood with reference to the
Figures.
[0025] Referring to FIG. 1, a slurry hydrocarbon synthesis reactor
10 is shown as comprising a cylindrical vessel 12 with a synthesis
gas feed line 14 at the bottom and a gas product line 16 at the
top. A synthesis gas comprising a mixture of H.sub.2 and CO is
introduced into the plenum space 22 at the bottom of the vessel via
feed line 14 and then injected up through a gas injection means
briefly illustrated by dashed line 18, and into the slurry body 20,
which is a three-phase slurry comprising bubbles of the uprising
synthesis gas, and gas and vapor products of the synthesis
reaction, along with solid particles of a Fischer-Tropsch catalyst
in a hydrocarbon slurry liquid which comprises synthesized
hydrocarbons that are liquid at the temperature and pressure in the
reactor. Suitable gas injection means comprises a plurality of gas
injectors horizontally arrayed across and extending through an
otherwise gas and liquid impermeable, horizontal tray or plate, as
is disclosed for example, in U.S. Pat. No. 5,908,094 the disclosure
of which is incorporated herein by reference. The H.sub.2 and CO in
the slurry react in the presence of the particulate catalyst to
form predominantly paraffinic hydrocarbons, most of which are
liquid at the reaction conditions, particularly when the catalyst
includes a catalytic cobalt component. Unreacted synthesis gas and
gas products of the hydrocarbon synthesis reaction rise up and out
the top of the slurry and into the gas collection space 24 in the
top of the reactor, from where they are removed from the
hydrocarbon synthesis reactor as tail gas, via line 16. A filter
means immersed in the slurry, which is simply indicated by box 26,
separates the hydrocarbon liquids in the reactor from the catalyst
particles and passes the synthesized and hydroisomerized
hydrocarbon liquid out of the reactor via line 28. Filter 26 may be
fabricated of sintered metal, wound wire and the like to separate
the liquid product from the particulate solids in the slurry, and
the hydroisomerized slurry liquid removed via line 28 is typically
sent to further processing or sold as a highly refined syncrude of
reduced pour point. Not shown is means for overhead removal and
replacement of the filter. An external reactor loop 30 is shown as
a hollow liquid conduit comprising a vertical downcomer 32, with
its slurry entrance and exit conduits 34 and 35 in open fluid
communication with the three-phase slurry 20 inside the synthesis
reactor, as shown. While only one such hydroisomerization loop is
shown for convenience, a plurality of such loops may be employed.
The fluid entrance to conduit 34 comprises a gas disengaging means
36, in the form of an upwardly opening cup, which opens upward near
to the top of the slurry body 20. This could be a simple gas bubble
disengaging cup as is disclosed in U.S. Pat. No. 5,382,748. Means
36 is wholly immersed in the slurry and is located in the upper
portion of the slurry, to maximize the hydraulic head of the gas
bubble reduced slurry entering into 34 and also because the
catalyst concentration in the slurry 20 is typically lowest at the
top. While only a simple gas bubble removing means is illustrated
for the sake of simplicity, it is preferred that a means be
employed which removes both gas bubbles and particulate solids,
either proximate to or comprising the fluid entrance to conduit 34.
Conduit 34 is shown as comprising a downwardly angled downcomer
and, when combined with a gas bubble and/or gas bubble removing
means such as 36, is similar to those disclosed in the '748, '621
and '537 patents, except for the off-vertical angle. While only a
simple degassing means is illustrated for the sake of simplicity,
it is preferred that the means 36 both degas and reduce the solids
content of the slurry, before it passes down through 34 and into
38. Simple gas, and preferably gas and solids disengaging means,
such as those disclosed in the '621 and '537 patents referred to
above are preferred to means such as conventional filters, magnetic
or centrifugal solids separating means, because they do not require
pumps or expensive equipment. They also provide a
density-difference hydraulic head to circulate the slurry from the
synthesis reactor down into and out of hydroisomerization loop 30.
The gas reduced, and preferably the gas and solids reduced slurry
formed in means 36, passes down through conduit 34 and through a
heat exchanger shown as box 38, in which it is either cooled or
heated (more typically heated) by indirect heat exchange means. The
use of heat exchange means to heat or cool the hydrocarbon liquid
for hydroisomerization is optional, and depends on the
hydroisomerization catalyst, and the temperature and pressure of
the slurry in the synthesis reactor, relative to the desired
temperature for the hydroisomerization. Not shown is another heat
exchanger between the hydroisomerization zone and the fluid exit 46
of the downcomer, to heat or cool the hydroisomerized slurry, if
necessary, as the hydroisomerized hydrocarbon liquid exits the
downcomer and passes, via conduit 35 into the synthesis reactor and
enters the main slurry body 20, with which it mixes. The interior
of the vertical portion 32 of loop 30 comprises the
hydroisomerization zone and contains one or more sections
comprising one or more monolithic hydroisomerization catalyst
sections 40. Typically and preferably, the hydroisomerization zone
comprises a plurality of monolithic catalyst sections 40, each
comprising one or more discrete bodies and each vertically spaced
apart to permit the hydroisomerization hydrogen gas injected
upstream of each stage, to mix with the downflowing liquid prior to
contact with the downstream catalyst section. The hydrogen treat
gas is injected into the hydroisomerization zone by a plurality of
gas injection lines 42. This multiple injection of the hydrogen
treat gas provides more efficient and thorough mixing of the
hydrogen with the downflowing liquid, before each of the five
hydroisomerization section stages or zones shown, reduces
gas/liquid stratification and also reduces the lifting effect of
the injected gas, which tends to oppose the hydraulic circulation
between the external loop 30 and the synthesis reactor 10, to be
less than would be encountered if all of the hydrogen was injected
into the downcomer at one point. During the hydroisomerization, a
portion of the hydrogen is consumed. Thus, multiple hydrogen
injection points vertically spaced apart along the vertical axis of
the hydroisomerization zone minimizes the lifting effect of the gas
and provides more efficient mixing of the gas and liquid. Not shown
in FIG. 1 is a low pressure drop static mixer, such as a
Kenics.RTM. static mixer which comprises twisted strips of sheet
metal, located in the vertical space between each catalyst section.
One or more such static mixers is located downstream of each
hydrogen injection point and upstream of the next, successive
catalyst section, to mix and remix the hydrogen gas with the
downflowing slurry before it enters the next catalyst section. The
extent of the hydrocarbon liquid hydroisomerization per pass
through the loop, will vary with the type of catalyst, the amount
of catalytic surface area, reaction conditions, hydrogen gas and
hydrocarbon liquid flow rate, the amount of residual water and CO,
if any, remaining in the liquid, the concentration of normal
paraffinic components in the hydrocarbon liquid, etc. The
hydrocarbon liquid flowing out of the hydroisomerization reaction
zone comprises a mixture of normal paraffins and hydroisomerized
components of reduced pour point. These flow down into the
synthesis reactor via conduit 35 and mix with the slurry in it. If
desired, a portion of this mixture may be withdrawn from the
external loop as hydroisomerized synthesis reactor product liquid,
by means not shown, with the remainder passing back into the
synthesis reactor. A simple baffle plate 44, proximate the fluid
exit end 46 of exit conduit 35, prevents bubbles of synthesis gas
and synthesis reaction water from entering into the external loop.
If desired, another simple baffle 48, may be placed above baffle
44, to impart a horizontal flow component shown by the arrow, to
the liquid mixture entering the synthesis reactor from loop 30.
That is, baffle 44, in addition to preventing gas bubbles from
entering up into loop 30, may impart an upward flow component to
the liquid, which then is redirected more horizontally by baffle
plate 48, for more thorough and efficient fluid mixing, nearer to
the bottom of the synthesis reactor. Also, the hydroisomerized
liquid will have bubbles of gas in it which will make it tend to
rise, irrespective of baffle 44. A space is left between the end of
baffle 44 and the interior wall of the synthesis reactor, to permit
any disengaged catalyst particles to fall down into the main slurry
body, in which the uprising synthesis gas feed redisperses them in
the slurry liquid. Also shown in synthesis reactor 10 is a gas
bubble disengaging downcomer 50 having an upwardly opening gas
disengaging cup 52 at the top immersed in the slurry. This is
similar to that disclosed in U.S. Pat. No. 5,382,748 which is
intended to produce a more uniform catalyst particle distribution
between the top and bottom of the slurry 20. A plurality of such
downcomers may be employed. A plurality of hydroisomerization loops
may be circumferentially arranged around the exterior of synthesis
reactor, laterally spaced apart from the outer wall of the
synthesis reactor and from each other. Not shown in the synthesis
reactor are heat exchange means for removing some of the heat of
the exothermic hydrocarbon synthesis reaction, in order to maintain
the reactor temperature at the desired synthesis reaction
temperature. Also not shown is means, such as a rod and a catalyst
removal port above the hydroisomerization zone, for removing and
replacing the monolithic catalyst
[0026] FIG. 2 is a brief schematic side view of a portion of the
hydroisomerizing zone containing two monolithic catalyst bodies 40,
with a very low pressure drop static mixer 90, just upstream of
each monolith. Hydrogen or a hydrogen treat gas is injected into a
space 41, above each monolith, via lines 42 above each static
mixer, for insuring intimate mixing of the hydrogen and downflowing
liquid, with the mixture then passed into the monolithic catalyst
below. Only two monolithic bodies and static mixers are shown, for
the sake of convenience. While each of the monolithic catalyst
bodies is illustrated as a single body, each could, and typically
will be made up of a plurality of bodies stacked on top of each
other. The static mixers also reduce stratification of the
downflowing gas and liquid mixture. Thus, even if hydrogen was not
introduced above each static mixer, the static mixer will
reestablish an intimate gas and liquid mixture, before it is passed
through the monolithic catalyst body below. FIGS. 4(a) and 4(b) are
a top plan view and a side schematic view of a monolithic catalyst
body form suitable for use with the invention, which comprises a
hexagonal close packed honeycomb 92. A plurality of vertical,
hexagonal channels 94 extend down through the monolith, each of an
equivalent diameter of about 1/2 inch. The outer, circumferential
periphery 96 of the monolith is fluted to increase the outer
catalytic surface area. Hexagonal close packing maximizes the area
to mass ratio. However, there are many other shapes that can be
used.
[0027] It is known that in a Fischer-Tropsch hydrocarbon synthesis
process, liquid and gaseous hydrocarbon products are formed by
contacting a synthesis gas comprising a mixture of H.sub.2 and CO
with a Fischer-Tropsch catalyst, in which the H.sub.2 and CO react
to form hydrocarbons under shifting or non-shifting conditions and
preferably under non-shifting conditions in which little or no
water gas shift reaction occurs, particularly when the catalytic
metal comprises Co, Ru or mixture thereof Suitable Fischer-Tropsch
reaction types of catalyst comprise, for example, one or more Group
VIII catalytic metals such as Fe, Ni, Co, and Ru. In one embodiment
the catalyst comprises catalytically effective amounts of Co and
one or more of Ru, Fe, Nit Th, Zr, Hf, U, Mg and La on a suitable
inorganic support material, preferably one which comprises one or
more refractory metal oxides. Preferred supports for Co containing
catalysts comprise titania, particularly when employing a slurry
hydrocarbon synthesis process in which higher molecular weight,
primarily paraffinic liquid hydrocarbon products are desired.
Useful catalysts and their preparation are known and illustrative,
but nonlimiting examples may be found, for example, in U.S. Pat.
Nos. 4,568,663; 4,663,305; 4,542,122; 4,621,072 and 5,545,674.
Fixed bed, fluid bed and slurry hydrocarbon synthesis processes are
well known and documented in the literature. In all of these
processes the synthesis gas is reacted in the presence of a
suitable Fischer-Tropsch type of hydrocarbon synthesis catalyst, at
reaction conditions effective to form hydrocarbons. Some of these
hydrocarbons will be liquid, some solid (e.g., wax) and some gas at
standard room temperature conditions of temperature and pressure of
25.degree. C. and one atmosphere, particularly if a catalyst having
a catalytic cobalt component is used. Slurry Fischer-Tropsch
hydrocarbon synthesis processes are often preferred because they
are able to produce relatively high molecular weight paraffinic
hydrocarbons when using a catalyst having a catalytic cobalt
component. In a slurry hydrocarbon synthesis process and preferably
one conducted under nonshifting conditions, which is used in the
practice of the invention, a synthesis gas comprising a mixture of
H.sub.2 and CO is bubbled up into a slurry in the hydrocarbon
synthesis reactor. The slurry comprises a particulate
Fischer-Tropsch type hydrocarbon synthesis catalyst in a
hydrocarbon slurry liquid comprising hydrocarbon products of the
synthesis reaction which are liquid at the reaction conditions. The
mole ratio of the hydrogen to the carbon monoxide may broadly range
from about 0.5 to 4, but is more typically within the range of from
about 0.7 to 2.75 and preferably from about 0.7 to 2.5. The
stoichiometric mole ratio for a Fischer-Tropsch reaction is 2.0,
but in the practice of the present invention it may be increased to
obtain the amount of hydrogen desired from the synthesis gas for
other than the hydrocarbon synthesis reaction. In the slurry
process, the mole ratio of the H.sub.2 to CO is typically about
2.1/1, particularly when using a synthesis catalyst comprising a
catalytic cobalt component. Slurry hydrocarbon synthesis process
conditions vary somewhat depending on the catalyst and desired
products. Typical conditions effective to form hydrocarbons
comprising mostly C.sub.5+ paraffins, (e.g., C.sub.5+-C.sub.200)
and preferably C.sub.10+ paraffins in a slurry process employing a
catalyst comprising a supported cobalt component include, for
example, temperatures, pressures and hourly gas space velocities in
the range of from about 320-600.degree. F., 80-600 psi and
100-40,000 V/hr/V, expressed as standard volumes of the gaseous CO
and H.sub.2 mixture (60.degree. F., 1 atm) per hour per volume of
catalyst, respectively.
[0028] The hydrocarbons which are liquid at the synthesis reaction
conditions and which comprise the slurry liquid which is
hydroisomerized by the practice of the invention, are typically
fractionated, with one or more of the resulting fractions receiving
one or more additional conversion operations. By conversion is
meant one or more operations in which the molecular structure of at
least a portion of the hydrocarbon is changed and includes both
noncatalytic processing (e.g., steam cracking), and catalytic
processing in which a fraction is contacted with a suitable
catalyst, with or without the presence of hydrogen or other
coreactants. If hydrogen is present as a reactant, such process
steps are typically referred to as hydroconversion and include, for
example, further hydroisomerization, hydrocracking, hydrorefining
and the more severe hydrorefining referred to as hydrotreating.
Illustrative, but nonlimiting examples of suitable products formed
by upgrading include one or more of a synthetic crude oil, liquid
fuel, olefins, solvents, lubricating, industrial or medicinal oil,
waxy hydrocarbons, nitrogen and oxygen containing compounds, and
the like. Liquid fuel includes one or more of motor gasoline,
diesel fuel, jet fuel, and kerosene, while lubricating oil
includes, for example, automotive, jet, turbine and metal working
oils. Industrial oil includes well drilling fluids, agricultural
oils, heat transfer fluids and the like.
[0029] The invention will be further understood with reference to
the Examples below.
EXAMPLES
Example 1
[0030] Four bifunctional monolithic hydroisomerization catalysts,
each consisting of an acidic cracking component and a
hydrogenation/dehydrogen- ation metal component, were prepared
using cylindrically shaped and commercially available, open cell
alpha alumina foam as the monolith support. The alumina foam
cylinders were each 0.5 inches in diameter and 1 inch long. Two
different cell sizes were used, one having 20 pores per inch (ppi)
and the other having 65 ppi. The average pore sizes were about 1000
.mu.m and 300 .mu.m. Two different zeolites were used as the acidic
components, to make two different hydroisomerization catalysts.
These zeolites were LZY-82 and zeolite beta. Each zeolite was first
impregnated with 0.5 wt. % Pt using standard incipient wetness
techniques, dried, and calcined at 400.degree. C. for 4 hours. The
zeolite materials were slurried in water/acetic acid (5%) and then
applied onto the alpha alumina foam as washcoats using multiple
dips followed by calcination (600.degree. C. for 2 hours). The four
finished monolithic catalysts are summarized in Table 1.
1 TABLE 1 Catalyst Monolith Volume Average Loading Description
in..sup.3 g/in..sup.3 Pt/beta (20 ppi) 0.196 1.82 Pt/beta (65 ppi)
0.196 1.78 Pt/LZY-82 (20 ppi) 0.196 1.35 Pt/LZY-82 (65 ppi) 0.196
1.67
Example 2
[0031] These four catalysts were evaluated for their
hydroconversion effectiveness for heavy, waxy, paraffinic
hydrocarbons using hexadecane (n-C.sub.16H.sub.38) as a
representative feed for a Fischer-Tropsch synthesized hydrocarbon
liquid. The hydroconversion runs were carried out in a small,
up-flow pilot plant running at a hydrogen pressure and nominal
treat rate of 750 psig and 2500 SCF/B with weight hourly space
velocity (WHSV) ranging from 2.3 to 3.1. The degree of conversion
was varied by adjusting the temperature from 400-550.degree. F.
Each reactor was charged with 5 of the cylindrical catalytic
monoliths in series with alpha alumina foams of similar ppi rating
and at the front and back of the reaction zone. The reactor
conditions for each run are summarized in Table 2.
2TABLE 2 Feedstock Hexadecane Hexadecane Hexadecane Hexadecane
Catalyst 0.5 wt. % 0.5 wt. % 0.5 wt. % 0.5 wt. % Description
Pt/Beta (20 Pt/Beta (65 Pt/LZY (20 Pt/LZY ppi) ppi) ppi) (20 ppi)
Conditions WHSV, g/hr/g 2.3 2.4 3.1 2.5 Temp., .degree. F. 400-500
H.sub.2 rate, SCF 2500 Feed, grs/hr 4.1
[0032] The results of the runs are shown in FIGS. 3 and 4. FIG. 3
is a plot of hexadecane conversion as a function of temperature,
using the Pt/Beta catalysts. FIG. 4 is a plot of the selectivity of
the hexadecane conversion to C.sub.16 isoparaffins, determined by
gas chromatography, as a function of the reactor temperature for
the Pt/Beta catalysts. The results for the Pt/LZY-82 catalysts are
not shown, because this catalyst was essentially inactive, even at
the relatively high temperature of 550.degree. F. The results for
the Pt/Beta catalysts shown in FIG. 4 clearly demonstrate the
conversion of the hexadecane to isoparaffin. While the cracking
activity of the catalysts was greater than desired, the results
nevertheless demonstrate the efficacy of hydroisomerizing
n-paraffins to isoparaffins, using a monolithic hydroisomerization
catalyst.
* * * * *