U.S. patent application number 13/750089 was filed with the patent office on 2014-07-31 for hybrid fischer-tropsch catalysts and processes for use.
This patent application is currently assigned to Chevron U.S.A. Inc.. The applicant listed for this patent is Kandaswamy Jothimurugesan, Robert James Saxton. Invention is credited to Kandaswamy Jothimurugesan, Robert James Saxton.
Application Number | 20140213670 13/750089 |
Document ID | / |
Family ID | 49684080 |
Filed Date | 2014-07-31 |
United States Patent
Application |
20140213670 |
Kind Code |
A1 |
Jothimurugesan; Kandaswamy ;
et al. |
July 31, 2014 |
HYBRID FISCHER-TROPSCH CATALYSTS AND PROCESSES FOR USE
Abstract
Disclosed are hybrid Fischer-Tropsch catalysts containing cobalt
and ZSM-48 zeolite. The hybrid Fischer-Tropsch catalysts can
contain cobalt deposited on ZSM-48 extrudate supports.
Alternatively, the Fischer-Tropsch catalysts can contain cobalt
deposited on supports mixed with ZSM-48 particles. It has
surprisingly been found that the use of hybrid Fischer-Tropsch
catalysts containing ZSM-48 zeolite in synthesis gas conversion
reactions results in improved C.sub.5+ productivity and catalyst
activity, as well as a desirable product distribution including low
formation of methane and C.sub.21+.
Inventors: |
Jothimurugesan; Kandaswamy;
(Hercules, CA) ; Saxton; Robert James;
(Pleasanton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jothimurugesan; Kandaswamy
Saxton; Robert James |
Hercules
Pleasanton |
CA
CA |
US
US |
|
|
Assignee: |
Chevron U.S.A. Inc.
San Ramon
CA
|
Family ID: |
49684080 |
Appl. No.: |
13/750089 |
Filed: |
January 25, 2013 |
Current U.S.
Class: |
518/721 ; 502/66;
502/74; 518/715 |
Current CPC
Class: |
C10G 2/333 20130101;
B01J 2229/20 20130101; C10G 2/334 20130101; C10G 2300/1022
20130101; B01J 37/0009 20130101; C07C 1/0435 20130101; B01J 37/0203
20130101; C10G 2/332 20130101; C10G 2/332 20130101; C07C 9/00
20130101; C10G 2/334 20130101; C07C 9/00 20130101; C10G 2300/1022
20130101; B01J 2229/42 20130101; B01J 29/7661 20130101 |
Class at
Publication: |
518/721 ;
518/715; 502/74; 502/66 |
International
Class: |
C07C 1/04 20060101
C07C001/04; B01J 29/76 20060101 B01J029/76 |
Claims
1. A method of performing a Fischer-Tropsch synthesis gas
conversion reaction, the method comprising: a. contacting a hybrid
Fischer-Tropsch catalyst comprising a Fischer-Tropsch metal
component selected from cobalt, iron and ruthenium and a ZSM-48
zeolite component with synthesis gas comprising hydrogen and carbon
monoxide at a ratio of hydrogen to carbon monoxide of from 1 to 3
at a temperature of from 180 to 280.degree. C. and a pressure of
from 5 to 30 atmospheres to yield a hydrocarbon product containing
less than 8 weight % C.sub.21+ and at least 60 weight % C.sub.5+ at
a C.sub.5+ productivity of at least 0.25
mLC.sub.5+/g.sub.cat/h.
2. A method of performing a Fischer-Tropsch synthesis gas
conversion reaction, the method comprising: a. contacting a hybrid
Fischer-Tropsch catalyst comprising a Fischer-Tropsch metal
component selected from cobalt, iron and ruthenium and a ZSM-48
zeolite component with synthesis gas comprising hydrogen and carbon
monoxide at a ratio of hydrogen to carbon monoxide of from 1 to 3
at a temperature of from 180 to 280.degree. C. and a pressure of
from 5 to 30 atmospheres to yield a hydrocarbon product containing
less than 8 weight % C.sub.21+ and at least 60 weight % C.sub.5+ at
a C.sub.5+ productivity of at least 50% greater than an equivalent
hybrid Fischer-Tropsch catalyst containing ZSM-5 zeolite rather
than ZSM-48.
3. The method of claim 2, wherein the C.sub.5+ productivity is at
least 80% greater than an equivalent hybrid Fischer-Tropsch
catalyst containing ZSM-5 zeolite rather than ZSM-48.
4. A method of performing a Fischer-Tropsch synthesis gas
conversion reaction, the method comprising: a. contacting a hybrid
Fischer-Tropsch catalyst comprising a Fischer-Tropsch metal
component selected from cobalt, iron and ruthenium and a ZSM-48
zeolite component with synthesis gas comprising hydrogen and carbon
monoxide at a ratio of hydrogen to carbon monoxide of from 1 to 3
at a temperature of from 180 to 280.degree. C. and a pressure of
from 5 to 30 atmospheres to yield a hydrocarbon product containing
less than 8 weight % C.sub.21+ and at least 60 weight % C.sub.5+ at
a C.sub.5+ productivity of at least 40% greater than an equivalent
hybrid Fischer-Tropsch catalyst containing ZSM-12 zeolite rather
than ZSM-48.
5. The method of claim 4, wherein the C.sub.5+ productivity of at
least 55% greater than an equivalent hybrid Fischer-Tropsch
catalyst containing ZSM-12 zeolite rather than ZSM-48.
6. The method of any of claim 1, 2 or 4, wherein the hybrid
Fischer-Tropsch catalyst comprises an extrudate comprising a
support containing ZSM-48 impregnated with cobalt.
7. The method of any of claim 1, 2 or 4, wherein the hybrid
Fischer-Tropsch catalyst comprises a mixture of cobalt deposited
onto a support and ZSM-48 particles.
8. The method of claim 1, wherein the hydrocarbon product further
contains: a. less than 20 weight % methane; and b. less than 16
weight % C.sub.2-C.sub.4.
9. The method of claim 1, wherein the C.sub.5+ productivity is at
least 0.30 mL.sub.c5+/g.sub.cat/h.
10. The method of claim 1, wherein the C.sub.5+ productivity is at
least 0.35 mL.sub.c5+/g.sub.cat/h.
11. The method of claim 1, wherein the hybrid Fischer-Tropsch
catalyst comprises from 55 to 95 weight % ZSM-48 zeolite and from 5
to 45 weight % cobalt.
12. The method of claim 1, wherein the hybrid Fischer-Tropsch
catalyst comprises from 70 to 90 weight % ZSM-48 zeolite and from
10 to 30 weight % cobalt.
13. The method of claim 1, wherein the ZSM-48 zeolite has a
SiO.sub.2/Al.sub.2O.sub.3 ratio of from 60 to 190.
14. A hybrid Fischer-Tropsch catalyst comprising from 5 to 45
weight % cobalt and from 55 to 95 weight % ZSM-48 zeolite.
15. The hybrid Fischer-Tropsch catalyst of claim 14, wherein the
hybrid Fischer-Tropsch catalyst comprises an extrudate comprising a
support containing ZSM-48 impregnated with cobalt.
16. The hybrid Fischer-Tropsch catalyst of claim 14, wherein the
hybrid Fischer-Tropsch catalyst comprises a mixture of cobalt
deposited onto a support and ZSM-48 particles.
17. The hybrid Fischer-Tropsch catalyst of claim 14, wherein the
hybrid Fischer-Tropsch catalyst has a BET surface area of greater
than 90 m.sup.2/g.
18. The hybrid Fischer-Tropsch catalyst of claim 14, wherein the
hybrid Fischer-Tropsch catalyst has a BET surface area of from 100
to 300 m.sup.2/g.
19. The hybrid Fischer-Tropsch catalyst of claim 14, wherein the
ZSM-48 zeolite extrudate includes a binder.
20. The hybrid Fischer-Tropsch catalyst of claim 19, wherein the
binder represents less than 40 weight % of the hybrid
Fischer-Tropsch catalyst.
21. The hybrid Fischer-Tropsch catalyst of claim 19, wherein the
binder is selected from the group consisting of alumina, silica,
titania, zirconia and combinations thereof.
22. The hybrid Fischer-Tropsch catalyst of claim 14, further
comprising a cobalt reduction promoter selected from the group
consisting of platinum, ruthenium, rhenium, silver and combinations
thereof.
23. The hybrid Fischer-Tropsch catalyst of claim 14, wherein the
ZSM-48 zeolite has a SiO.sub.2/Al.sub.2O.sub.3 ratio of from 60 to
120.
Description
FIELD
[0001] The present disclosure relates to improved hybrid synthesis
gas conversion catalysts containing a Fischer-Tropsch component and
an acidic zeolite component. The present disclosure further relates
to the use of the catalysts in synthesis gas conversion processes
to produce liquid hydrocarbon fuels.
BACKGROUND
[0002] Fischer-Tropsch synthesis is an effective process for
converting synthesis gas containing hydrogen and carbon monoxide,
also referred to as syngas, to liquid hydrocarbon fuels. It is well
known that Fischer-Tropsch synthesis involves a polymerization
reaction beginning with a methylene intermediate to produce a wide
distribution of hydrocarbons ranging from light gases to solid wax.
Hybrid Fischer-Tropsch catalysts, also referred to interchangeably
as "hybrid FT catalysts" or "HFT catalysts," have been developed
containing both a Fischer-Tropsch synthesis component, e.g. cobalt,
and an acidic zeolite component which have been found to be capable
of limiting chain growth in the polymerization reaction to provide
a more desirable product distribution.
[0003] Challenges have been encountered in hybrid Fischer-Tropsch
catalysts containing cobalt as a result of the strong interaction
between the cobalt and the zeolite. These may include lower than
desired catalytic activity, lower than desired degree of cobalt
reduction and undesirably high methane selectivity. For example,
the activity of some hybrid Fischer-Tropsch synthesis catalysts
which have been reported is about 0.2 g of C.sub.5+/g.sub.cat/h
(U.S. Pat. Nos. 7,973,087; 7,973,086; 7,943,674; and 7,825,164).
Generally, it is preferred that the activity of a catalyst be
higher.
[0004] Another challenge in the development of improved hybrid
Fischer-Tropsch catalysts is the development of catalysts which are
active, stable and provide high C.sub.5+ productivity. There
remains a need for hybrid Fischer-Tropsch catalysts with improved
catalytic activity which provides improved productivity in a
desired range of product distribution, i.e., C.sub.5+.
SUMMARY
[0005] In one aspect, a method is provided for performing a
Fischer-Tropsch synthesis gas conversion reaction. The method
includes contacting a hybrid Fischer-Tropsch catalyst comprising a
Fischer-Tropsch metal component selected from cobalt, iron and
ruthenium and a ZSM-48 zeolite component with synthesis gas
comprising hydrogen and carbon monoxide at a ratio of hydrogen to
carbon monoxide of from 1 to 3 at a temperature of from 180 to
280.degree. C. and a pressure of from 5 to 30 atmospheres to yield
a hydrocarbon product containing less than 8 weight % C.sub.21+ and
at least 60 weight % C.sub.5+ at a C.sub.5+ productivity of at
least 0.25 mLC.sub.5+/g.sub.cat/h.
[0006] In another aspect, a method is provided for performing a
Fischer-Tropsch synthesis gas conversion reaction, including
contacting a hybrid Fischer-Tropsch catalyst comprising a
Fischer-Tropsch metal component selected from cobalt, iron and
ruthenium and a ZSM-48 zeolite component with synthesis gas
comprising hydrogen and carbon monoxide at a ratio of hydrogen to
carbon monoxide of from 1 to 3 at a temperature of from 180 to
280.degree. C. and a pressure of from 5 to 30 atmospheres to yield
a hydrocarbon product containing less than 8 weight % C.sub.21+ and
at least 60 weight % C.sub.5+ at a C.sub.5+ productivity of at
least 50% greater than an equivalent hybrid Fischer-Tropsch
catalyst containing ZSM-5 zeolite rather than ZSM-48.
[0007] In another aspect, a method is provided for performing a
Fischer-Tropsch synthesis gas conversion reaction, including
contacting a hybrid Fischer-Tropsch catalyst comprising a
Fischer-Tropsch metal component selected from cobalt, iron and
ruthenium and a ZSM-48 zeolite component with synthesis gas
comprising hydrogen and carbon monoxide at a ratio of hydrogen to
carbon monoxide of from 1 to 3 at a temperature of from 180 to
280.degree. C. and a pressure of from 5 to 30 atmospheres to yield
a hydrocarbon product containing less than 8 weight % C.sub.21+ and
at least 60 weight % C.sub.5+ at a C.sub.5+ productivity of at
least 40% greater than an equivalent hybrid Fischer-Tropsch
catalyst containing ZSM-12 zeolite rather than ZSM-48.
[0008] In another aspect, a hybrid Fischer-Tropsch catalyst is
provided which includes from 5 to 45 weight % cobalt and from 55 to
95 weight % ZSM-48 zeolite.
DETAILED DESCRIPTION
[0009] Hybrid Fischer-Tropsch catalysts include at least one
Fischer-Tropsch component and at least one acidic component. As is
known, the presence of an acidic component such as a zeolite
enables the hybrid Fischer-Tropsch catalyst to limit the formation
of undesirable heavy hydrocarbon components, such as C.sub.21+ wax.
In one embodiment, the Fischer-Tropsch component can be deposited
onto a support containing the zeolite. In another embodiment, the
Fischer-Tropsch component and the zeolite component can be separate
mixed particles.
[0010] The Fischer-Tropsch component may also be referred to herein
as the "Fischer-Tropsch metal," "synthesis gas conversion
component" or "syngas conversion component." The Fischer-Tropsch
component includes a Group VIII of the Periodic Table metal
component, preferably cobalt, iron and/or ruthenium. References to
the Periodic Table and groups thereof used herein refer to the
IUPAC version of the Periodic Table of Elements described in the
68th Edition of the Handbook of Chemistry and Physics (CPC Press).
The optimum amount of catalytically active metal present depends
inter alia on the specific catalytically active metal. Typically,
the amount of cobalt present in the catalyst may range from 1 to
100 parts by weight per 100 parts by weight of support material,
preferably from 10 to 50 parts by weight per 100 parts by weight of
support material.
[0011] The catalytically active Fischer-Tropsch component may be
present in the catalyst together with one or more metal promoters
or co-catalysts. The promoters may be present as metals or as metal
oxide, depending upon the particular promoter concerned. Suitable
promoters include metals or oxides of metals from Groups IA, IB,
IVB, VB, VIIB and/or VIIB of the Periodic Table, lanthanides and/or
the actinides or oxides of the lanthanides and/or the actinides. As
an alternative or in addition to the metal oxide promoter, the
catalyst may comprise a metal promoter selected from Groups VIIB
and/or VIII of the Periodic Table. In some embodiments, the
Fischer-Tropsch component further comprises a cobalt reduction
promoter selected from the group consisting of platinum, ruthenium,
rhenium, silver and combinations thereof.
[0012] According to the present disclosure, the acidic zeolite
component of the hybrid Fischer-Tropsch catalyst is advantageously
ZSM-48. The use of ZSM-48 has been found to provide a surprisingly
high level of activity and productivity. ZSM-48 has a chemical
formula of Si48O96 and a framework structure of *MRE designated by
the Structure Commission of the International Zeolite Association
(IZA-SC) wherein the *indicates that the structure is disordered.
It has a framework density of 19.9 T/1000 .ANG.3. ZSM-48 has
one-dimensional channels. The ZSM-48 zeolite advantageously is
characterized by having a SiO2/Al2O3 ratio of from 60 to 190, even
from 60 to 120. Further details on the structure of ZSM-48 can be
found at Ch. Baerlocher and L. B. McCusker, Database of Zeolite
Structures: http://www.iza-structure.org/databases/ and Schlenker,
J. L. Rohrbaugh, W. J., Chu, P., Valyocsik, E. W. and Kokotailo, G.
T. Zeolites, 5, 355-358 (1985).
[0013] The amount of acidic component used in the catalyst can be
suitably varied to obtain the desired product. For instance, if the
amount of acidic component is too low, there may be insufficient
cracking to remove a desired amount of wax; whereas if too much
acidic component is used, there may be excessive cracking and the
resulting product may be lighter than desired.
[0014] In one embodiment, the hybrid Fischer-Tropsch catalyst can
contain from 55 to 95 weight % ZSM-48 zeolite extrudate impregnated
with from 5 to 45 weight % cobalt. In another embodiment, the
hybrid Fischer-Tropsch catalyst can contain from 70 to 90 weight %
ZSM-48 zeolite extrudate impregnated with from 10 to 30 wt %
cobalt.
[0015] In one embodiment, the hybrid Fischer-Tropsch catalyst
extrudate has a BET surface area of greater than 90 m.sup.2/g. In
another embodiment, the hybrid Fischer-Tropsch catalyst extrudate
has a BET surface area of from 100 to 300 m.sup.2/g.
[0016] The ZSM-48 zeolite component may further contain a promoter
such as platinum, ruthenium, rhenium, silver, palladium, nickel,
rhodium, iridium or combinations thereof.
[0017] In addition to the zeolite component, the supports of the
hybrid Fischer-Tropsch catalysts can further include a binder
material. Suitable binder materials for use in the support include
alumina, silica, titania, zirconia and combinations thereof. The
binder can represent less than 40 weight % of the hybrid
Fischer-Tropsch catalyst. The supports are advantageously formed by
mixing the zeolite component with the binder material and extruding
the mixture to form ZSM-48 extrudates. In embodiments in which the
Fischer-Tropsch component and the zeolite component are separate
mixed particles, the cobalt can be deposited onto one of the above
listed binder materials.
[0018] The method employed to deposit the Fischer-Tropsch component
on an extrudate support involves an impregnation technique using
aqueous or non-aqueous solution containing a soluble cobalt salt in
a suitable solvent and, if desired, a soluble promoter metal salt,
e.g., platinum salt, in order to achieve the necessary metal
loading and distribution required to provide a highly selective and
active hybrid synthesis gas conversion catalyst.
[0019] Initially, the support can be treated by oxidative
calcination at a temperature in the range of from 450.degree. to
900.degree. C., for example, from 600.degree. to 750.degree. C., to
remove water and any organics from the support.
[0020] Suitable solvents include, for example, water, ketones, such
as acetone, butanone (methyl ethyl ketone); the lower alcohols,
e.g., methanol, ethanol, propanol and the like; amides, such as
dimethyl formamide; amines, such as butylamine; ethers, such as
diethylether and tetrahydrofuran; hydrocarbons, such as pentane and
hexane; and mixtures of the foregoing solvents. In one embodiment,
the solvent is ethanol, for use with cobalt nitrate.
[0021] Suitable cobalt salts include, for example, cobalt nitrate,
cobalt acetate, cobalt carbonyl, cobalt acetylacetonate, and the
like. Likewise, any suitable platinum salt, such as chloroplatinic
acid hexahydrate, tetraammineplatinum nitrate, tetraamminoplatinum
hydroxide or the like can be used. In one embodiment,
tetraammineplatinum nitrate is used. In general, any metal salt
which is soluble in the suitable solvent and will not have a
poisonous effect on the metal catalyst or on the acid sites of the
ZSM-48 can be used.
[0022] The calcined support is then impregnated in a dehydrated
state with the aqueous or non-aqueous solvent solution of the metal
salts. Care should be taken so that the calcined support is not
unduly exposed to atmospheric humidity so as to become
rehydrated.
[0023] Any suitable impregnation technique can be employed
including techniques well known to those skilled in the art so as
to distend the catalytic metals in a uniform thin layer on the
catalyst support. For example, the cobalt along with the oxide
promoter can be deposited on the support material by the "incipient
wetness" technique. Such technique is well known and requires that
the volume of aqueous or non-aqueous solution be predetermined so
as to provide the minimum volume which will just wet the entire
surface of the support, with no excess liquid. Alternatively, the
excess solution technique can be used if desired. If the excess
solution technique is used, then the excess solvent present, e.g.,
ethanol is merely removed by evaporation.
[0024] Next, the aqueous or non-aqueous solution and support are
stirred while evaporating the solvent at a temperature of from
25.degree. to 50.degree. C. until "dryness."
[0025] The impregnated catalyst is slowly dried at a temperature of
from 110.degree. to 120.degree. C. for a period of about 1 hour to
spread the metals over the entire support. The drying step is
conducted at a very slow rate in air.
[0026] The dried catalyst may be reduced directly in hydrogen or it
may be calcined first. In the case of impregnation with cobalt
nitrate, direct reduction can yield a higher cobalt metal
dispersion and synthesis activity, but reduction of nitrates is
difficult to control; calcination before reduction may be preferred
for large scale preparations. A single calcination step to
decompose nitrates may be preferred if multiple impregnations are
needed to provide the desired metal loading. Reduction in hydrogen
requires a prior purge with inert gas, a subsequent purge with
inert gas and a passivation step in addition to the reduction
itself, as described later as part of the
reduction-oxidation-reduction (ROR) activation. However,
impregnation of cobalt carbonyl is preferably carried out in a dry,
oxygen-free atmosphere and decomposed directly, then
passivated.
[0027] The dried catalyst is calcined by heating slowly in flowing
air, for example 10 cc/gram/minute, to a temperature in the range
of from 200.degree. to 350.degree. C., for example, from
250.degree. to 300.degree. C., that is sufficient to decompose the
metal salts and fix the metals. The aforesaid drying and
calcination steps can be done separately or can be combined.
Calcination should be conducted by using a slow heating rate of,
for example, 0.5.degree. to 3.degree. C. per minute or from
0.5.degree. to 1.degree. C. per minute and the catalyst should be
held at the maximum temperature for a period of from 1 to 20 hours,
for example, for 2 hours.
[0028] The foregoing impregnation steps are repeated with
additional solutions in order to obtain the desired metal loading.
Platinum and other promoter metal oxides are conveniently added
together with cobalt, but they may be added in other impregnation
steps, separately or in combination, either before, after, or
between impregnations of cobalt.
[0029] The hybrid FT catalyst prepared according to any of the
foregoing methods can optionally be further activated prior to use
in a synthesis gas conversion process by either reduction in
hydrogen or a reduction-oxidation-reduction (ROR) treatment. The
reduction or ROR activation treatment is conducted at a temperature
considerably below 500.degree. C. in order to achieve the desired
increase in activity and selectivity of the hybrid FT catalyst.
Temperatures of 500.degree. C. or above reduce activity and liquid
hydrocarbon selectivity of the catalyst. Suitable reduction or ROR
activation temperatures are below 500.degree. C., even below
450.degree. C. and even at or below 400.degree. C. Thus, ranges of
from 100.degree. C. or 150.degree. C. to 450.degree. C., for
example, from 250.degree. C. to 400.degree. C., are suitable for
the reduction steps. The oxidation step should be limited to from
200.degree. C. to 300.degree. C. These activation steps are
conducted while heating at a rate of from 0.1.degree. C. to
5.degree. C., for example, from 0.10.degree. C. to 2.degree. C.
[0030] The catalyst can be slowly reduced in the presence of
hydrogen. If the catalyst has been calcined after each
impregnation, to decompose nitrates or other salts, then the
reduction may be performed in one step, after an inert gas purge,
with heating in a single temperature ramp (e.g., 1.degree. C./min.)
to the maximum temperature and held at that temperature, from
250.degree. C. or 300.degree. C. to 450.degree. C., for example,
from 350.degree. C. to 400.degree. C., for a hold time of from 6 to
65 hours, for example, from 16 to 24 hours. Pure hydrogen is
preferred in the first reduction step. If nitrates are still
present, the reduction is best conducted in two steps wherein the
first reduction heating step is carried out at a slow heating rate
of no more than 5.degree. C. per minute, for example, from
0.1.degree. C. to 1.degree. C. per minute up to a maximum hold
temperature of from 200.degree. C. to 300.degree. C., for example,
from 200.degree. C. to 250.degree. C., for a hold time of from 6 to
24 hours, for example, from 16 to 24 hours under ambient pressure
conditions. In the second treating step of the first reduction, the
catalyst can be heated at from 0.5.degree. C. to 3.degree. C. per
minute, for example, from 0.1.degree. C. to 1.degree. C. per minute
to a maximum hold temperature of from 250.degree. C. or 300.degree.
C. up to 450.degree. C., for example, from 350.degree. C. to
400.degree. C. for a hold time of from 6 hours to 65 hours, for
example, from 16 to 24 hours. Although pure hydrogen is preferred
for these reduction steps, a mixture of hydrogen and nitrogen can
be used.
[0031] Thus, the reduction may involve the use of a mixture of
hydrogen and nitrogen at 100.degree. C. for one hour; increasing
the temperature 0.5.degree. C. per minute until a temperature of
200.degree. C.; holding that temperature for approximately 30
minutes; and then increasing the temperature 1.degree.C. per minute
until a temperature of 350.degree. C. is reached and then
continuing the reduction for approximately 16 hours. Reduction can
be conducted sufficiently slowly and the flow of the reducing gas
maintained sufficiently high to maintain the partial pressure of
water in the offgas below 1%, to avoid excessive steaming of the
outlet end of the catalyst bed. Before and after all reductions,
the catalyst can be purged in an inert gas such as nitrogen, argon
or helium.
[0032] The reduced catalyst can be passivated at ambient
temperature (25.degree. C. to 35.degree. C.) by flowing diluted air
over the catalyst sufficiently slowly so that a controlled exotherm
of no larger than +50.degree. C. passes through the catalyst bed.
After passivation, the catalyst is heated slowly in diluted air to
a temperature of from 300.degree. C. to 350.degree. C. in the same
manner as previously described in connection with calcination of
the catalyst.
[0033] The temperature of the exotherm during the oxidation step
can be less than 100.degree. C., and will be 50.degree. C. to
60.degree. C. if the flow rate and/or the oxygen concentration are
dilute enough.
[0034] Next, the reoxidized catalyst is slowly reduced again in the
presence of hydrogen, in the same manner as previously described in
connection with the initial reduction of the catalyst. Since
nitrates are no longer present, this reduction may be accomplished
in a single temperature ramp and held, as described above for the
reduction of the calcined catalysts.
[0035] The hybrid Fischer-Tropsch catalyst of the present
disclosure can be utilized in a process the synthesis gas
conversion in which a synthesis gas feed containing hydrogen and
carbon monoxide is contacted in a reactor with the hybrid
Fischer-Tropsch catalyst to produce a hydrocarbon product
containing at least 60 wt % C.sub.5+ hydrocarbons. The synthesis
gas feed can have a H.sub.2/CO ratio between 1 and 3. The reaction
can occur at a temperature from 180 to 280.degree. C., a pressure
from 5 to 30 atmospheres, and a gaseous hourly space velocity less
than 20,000 volumes of gas per volume of catalyst per hour. In one
embodiment, the C.sub.5+ productivity of the process is
advantageously at least 0.25 mLC.sub.5+/g.sub.cat/h (milliliters of
C.sub.5+ per grams of catalyst per hour), even at least 0.30
mLC.sub.5+/g.sub.cat/h, and even at least 0.35
mLC.sub.5+/g.sub.cat/h. It has been found that the C.sub.5+
productivity of the process is at least 50% greater, even at least
80% greater, than an equivalent hybrid Fischer-Tropsch catalyst
containing ZSM-5 zeolite rather than ZSM-48. It has further been
found that the C.sub.5+ productivity of the process is at least 40%
greater, even at least 55% greater, than an equivalent hybrid
Fischer-Tropsch catalyst containing ZSM-12 zeolite rather than
ZSM-48.
[0036] In one embodiment, the resulting hydrocarbon product further
contains:
[0037] 0-20 wt % CH.sub.4;
[0038] 0-16 wt % C.sub.2-C.sub.4;
[0039] 60-80 wt % C.sub.5+; and
[0040] 0-8 wt % C.sub.21+.
[0041] The reactor type can be selected from any reactor type known
for use in a Fischer-Tropsch synthesis process, including, but not
limited to, multi-tubular fixed bed reactors, circulating fluidized
bed reactors, fixed fluidized bed reactors, compact heat exchange
reactors and microchannel reactors. When a multi-tubular fixed bed
reactor is used, the particle size of the hybrid Fischer-Tropsch
catalyst can be between 1 and 3 mm. When a circulating or fixed
fluidized bed reactor is used, the particle size can be between 35
and 175 .mu.m. When a compact heat exchange reactor or microchannel
reactor is used, the particle size can be between 10 and 250
.mu.m.
Analytical Methods
[0042] BET surface area and pore volume of catalyst samples were
determined from nitrogen adsorption/desorption isotherms measured
at -196.degree. C. using a Tristar analyzer available from
Micromeritics Instrument Corporation (Norcross, Ga.). Prior to gas
adsorption measurements, the catalyst samples were degassed at
190.degree. C. for 4 hours. The total pore volume (TPV) was
calculated at a relative pressure of approximately 0.99.
[0043] Metal dispersion and average particle diameter were measured
by hydrogen chemisorption using an AutoChem 2900 analyzer available
from Micromeritics Instrument Corporation (Norcross, Ga.). The
fraction of surface cobalt on the catalysts was measured using
H.sub.2 temperature programmed desorption (TPD). Samples (0.25 g)
were heated to 350.degree. C. in H.sub.2 at 1.degree. C. min.sup.-1
and held for 3 hours then cooled to 30.degree. C. Then a flow of
argon was used to purge the samples before heating to 350.degree.
C. at 20.degree. C. min.sup.-1. Hydrogen desorption was monitored
using a thermal conductivity detector. TPD were repeated after
oxidizing samples in 10% O.sub.2/He and a second reduction in pure
hydrogen. Dispersions were calculated relative to the cobalt
concentration in each sample.
[0044] Average crystallite size (diameter) of cobalt in nanometers
was estimated by assuming a spherical geometry of reduced cobalt.
The fraction of reduced cobalt was measured by dehydrating
as-prepared materials, prior to reduction, at 350.degree. C., then
cooling to room temperature and reducing in 5% H.sub.2/Ar at a
heating rate of 5.degree. C. min.sup.-1 to 350.degree. C. Catalyst
reducibility during H.sub.2 TPR was measured using TGA, and weight
losses were assumed to be from cobalt oxide reduction in order to
calculate O/Co stoichiometric ratios. The fractional reducibility
was calculated by assuming the complete reduction of
Co.sub.3O.sub.4 to Co metal, calculated using the equation
below:
d=96.2*(Co Fractional Reduction)% Dispersion
EXAMPLES
Example 1
Preparation of catalyst extrudates comprising 10 weight % Co-0.25
weight % Ru supported on 80 weight % ZSM-48 and 20 weight %
alumina
[0045] ZSM-48 zeolite powder having a SiO.sub.2/Al.sub.2O.sub.3
ratio of 120 was obtained from Sud-Chemie, Inc. (Munich, Germany).
96 g of the ZSM-48 powder and 24 g of catapal B alumina powder were
added to a mixer and mixed for 10 minutes. 60 g of deionized water
and 4.5 g of nitric acid were added to the mixed powder and mixed
for 10 minutes. The mixture was then transferred to a 1 inch (2.54
cm) BB gun extruder available from The Bonnot Company (Uniontown,
Ohio) and extruded through a dieplate containing thirty 1/16 inch
(0.16 cm) holes. The ZSM-48 extrudates were dried first at
70.degree. C. for 2 h, then at 120.degree. C. for 2 h and finally
calcined in flowing air at 600.degree. C. for 2 h.
[0046] A catalyst containing 10% Co-0.25% Ru on 1/16 inch (0.16 cm)
alumina-bound ZSM-48 extrudates was prepared in a single step using
non-aqueous impregnation. The ZSM-48 extrudates prepared as above
were used. First, 0.3396 g of ruthenium acetylacetonate (available
from Alfa Aesar, Ward Hill, Mass.) was dissolved in 40 g of
acetone. Second, 16.59 g of cobalt(II) nitrate hexahydrate
(available from Sigma-Aldrich, St. Louis, Mo.) was dissolved in 80
g of acetone. The two solutions were then mixed together and added
to the 30 g of dry alumina-bound ZSM-48 extrudates. The solvent was
removed in a rotary evaporator under vacuum by heating slowly to
45.degree. C. The vacuum-dried material was then further dried in
air in an oven at 120.degree. C. overnight. The dried catalyst
extrudates were then calcined at 300.degree. C. for 2 hours in a
muffle furnace. The properties of the ZSM-48 zeolite powder and the
catalyst extrudates are shown in Table 1.
TABLE-US-00001 TABLE 1 External BET Micro Average Micropore Surface
Surface Pore pore Particle Catalyst Area, Area, Area, Volume volume
Diameter, Composition m.sup.2/g m.sup.2/g m.sup.2/g cc/g cc/g
Dispersion, % nm ZSM-48 136.56 120.66 257.22 0.4192 0.0635 na na
10% Co--0.25Ru/ 43.57 98.27 141.8 0.2670 0.0200 16.1 6.2 (80% ZSM-
48 + 20% Al.sub.2O.sub.3)
Catalyst Activation
[0047] Ten grams of catalyst prepared as described above was
charged to a glass tube reactor. The reactor was placed in a muffle
furnace with upward gas flow. The tube was purged first with
nitrogen gas at ambient temperature, after which time the gas feed
was changed to pure hydrogen with a flow rate of 750 sccm. The
temperature to the reactor was increased to 350.degree. C. at a
rate of 1.degree. C./minute and then held at that temperature for
six hours. After this time, the gas feed was switched to nitrogen
to purge the system and the unit was then cooled to ambient
temperature. Then a gas mixture of 1 volume % O.sub.2/N.sub.2 was
passed up through the catalyst bed at 750 sccm for 10 hours to
passivate the catalyst. No heating was applied, but the oxygen
chemisorption and partial oxidation exotherm caused a momentary
temperature rise. After 10 hours, the gas feed was changed to pure
air, the flow rate was lowered to 200 sccm and the temperature was
raised to 300.degree. C. at a rate of 1.degree. C./minute and then
kept at 300.degree. C. for two hours. At this point, the catalyst
was cooled to ambient temperature and discharged from the glass
tube reactor. It was transferred to a 316-SS tube reactor of 0.51
in (1.3 cm) inner diameter and placed in a clam-shell furnace. The
catalyst bed was flushed with a downward flow of helium for a
period of two hours, after which time the gas feed was switched to
pure hydrogen at a flow rate of 500 sccm. The temperature was
slowly raised to 120.degree. C. at a temperature interval of
1.degree. C./minute, held there for a period of one hour, then
raised to 250.degree. C. at a temperature interval of 1.degree.
C./minute and held at that temperature for 10 hours. After this
time, the catalyst bed was cooled to 180.degree. C. while remaining
under a flow of pure hydrogen gas. All flows were directed
downward.
Fischer-Tropsch Activity
[0048] Catalysts prepared and activated as described above were
subjected to a synthesis run in which the catalyst was contacted
with syngas containing hydrogen and carbon monoxide. Experimental
conditions and results are given in Table 2.
TABLE-US-00002 TABLE 2 Experiment No. 1 2 3 TOS, h 77 116 146 Yield
Time, h 25.5 39.3 30.5 Temperature, .degree. C. 220.0 220.0 220.0
Pressure, atm 20 20 20 H.sub.2/CO Fresh Feed 2.00 2.00 2.00 H.sub.2
Conv (mol %). 45.2% 44.1% 43.3% CO Conv (mol %). 39.10% 37.90%
37.60% Rate, gCH.sub.2/g/h 0.41 0.40 0.39 Rate, mLC.sub.5.sup.+/g/h
0.35 0.35 0.34 CO.sub.2, wt % 1.10% 0.90% 1.00% CH.sub.4, wt %
18.8% 18.6% 18.8% C.sub.2, wt % 2.1% 2.0% 2.0% C.sub.3, wt % 7.9%
7.8% 7.8% C.sub.4, wt % 5.2% 5.2% 4.9% C.sub.5.sup.+, wt % 64.8%
65.5% 65.5% C.sub.21.sup.+, wt % 5.1% 7.2% 7.4% C1-C3, wt % 28.8%
28.4% 28.6% C.sub.2.sup.=/C.sub.2, mol % 2.9% 2.1% 3.1%
C.sub.3.sup.=/C.sub.3, mol % 29.2% 28.4% 27.7%
C.sub.4.sup.=/C.sub.4, mol % 31.4% 31.9% 30.4% DOB, mol % 5.1% 5.7%
5.1%
[0049] It can be seen from the results in Table 2 that the hybrid
Fischer-Tropsch catalyst of the present invention prepared using
ZSM-48 zeolite is effective for the conversion of synthesis gas to
give a liquid hydrocarbon product substantially free of solid wax
under commercially viable process conditions. Further, the yield of
C5+ hydrocarbons is above 60%.
Comparative Example 1
Hybrid Catalyst Prepared with ZSM-48 and Hybrid Catalyst Prepared
with ZSM-5
[0050] A catalyst comprising 10.0% weight Co/0.25% weight Ru on 80%
weight ZSM-Sand 20% weight alumina was prepared according to the
following procedure. First, ruthenium acetylacetonate was dissolved
in acetone. Second, cobalt nitrate was dissolved in acetone. The
two solutions were mixed together and then added to 1/16''
extrudates of alumina (20 weight % alumina) bound ZSM-5 zeolite
(Si/Al=15, obtained from Zeolyst International, Conshohocken, Pa.).
After the mixture was stirred for 1 hour at ambient temperature,
the solvent was eliminated by rotavaporation. Then the catalyst was
dried in an oven at 120.degree. C. overnight and finally calcined
at 300.degree. C. for 2 hours in a muffle furnace.
[0051] The data presented in Tables 2 and 3 provide a comparison of
hybrid, integral catalysts prepared with ZSM-48 and ZSM-5 zeolites.
It can be seen from Tables 2 and 3 that a hybrid, integral catalyst
prepared with ZSM-48 surprisingly results in a higher yield of
desired C.sub.5+ product while producing lower yields of undesired
light gases with good conversion of synthesis gas. In fact, the
C.sub.5+ productivity of the process using the hybrid catalyst
prepared with ZSM-48 (Example 1) is shown to be at least 80%
greater than the equivalent hybrid Fischer-Tropsch catalyst
containing a ZSM-5 zeolite rather than ZSM-48 (Comparative Example
1). By "equivalent hybrid Fischer-Tropsch catalyst containing ZSM-5
zeolite rather than ZSM-48" is meant that the catalysts are
prepared in the same manner using the same weight percentages of
the catalyst components and using all identical components other
than the zeolite type.
[0052] No solid wax was seen for either catalyst under these
reaction conditions.
TABLE-US-00003 TABLE 3 Hybrid catalyst Hybrid catalyst Prepared
with ZSM-48 Prepared with ZSM-5 TOS, h 77 168 Yield Time, h 25.5 41
Temperature, .degree. C. 220.0 220 Pressure, atm 20 20 H.sub.2/CO
Fresh Feed 2.00 2 H.sub.2 Conv (mol %). % 45.2 27.0 CO 39.10 33.1
Conv (mol %). % Rate, gCH.sub.2/g/h 0.41 0.23 Rate,
mLC.sub.5.sup.+/g/h 0.35 0.19 CO.sub.2, wt % 1.10 0.6 CH.sub.4, wt
% 18.8 21.9 C.sub.2, wt % 2.1 2.2 C.sub.3, wt % 7.9 8.9 C.sub.4, wt
% 5.2 5.4 C.sub.5.sup.+, wt % 64.8 61.3 C.sub.21.sup.+, wt % 5.1
5.1 C1-C3, wt % 28.8 33.0 C.sub.2.sup.=/C.sub.2, mol % 2.9% 2.5
C.sub.3.sup.=/C.sub.3, mol % 29.2% 28.3 C.sub.4.sup.=/C.sub.4, mol
% 31.4% 36.9 DOB, mol % 5.1% 7.7
Comparative Example 2
Hybrid Catalyst Extrudates Prepared with ZSM-48 and Hybrid Catalyst
Extrudates Prepared with ZSM-12
[0053] A catalyst comprising 10.0% weight Co/0.25% weight Ru on 80%
weight ZSM-12 and 20% weight alumina was prepared according to the
following procedure. First, ruthenium nitrosyl nitrate was
dissolved in acetone. Second, cobalt nitrate was dissolved in
acetone. The two solutions were mixed together and then added to
1/16 in (0.16 cm) extrudates of alumina (20 weight % alumina) bound
ZSM-12 zeolite (Si/Al=45, obtained from Zeolyst International,
Conshohocken, Pa.). After the mixture was stirred for 1 hour at
ambient temperature, the solvent was eliminated by rotavaporation.
Then the catalyst extrudates were dried in an oven at 120.degree.
C. overnight and finally calcined at 300.degree. C. for 2 hours in
a muffle furnace.
[0054] The data presented in Tables 2 and 4 provide a comparison of
hybrid, integral catalysts prepared with ZSM-48 and ZSM-12 zeolite
extrudates. It can be seen from Tables 2 and 3 that a hybrid,
integral catalyst extrudates prepared with ZSM-48 surprisingly
result in a higher yield of desired C5+ product while producing
lower yields of undesired light gases with good conversion of
synthesis gas. The C.sub.5+ productivity of the process using the
hybrid catalyst prepared with ZSM-48 (Example 1) is shown to be at
least 55% greater than the equivalent hybrid Fischer-Tropsch
catalyst comprising a ZSM-12 zeolite extrudate impregnated with
cobalt (Comparative Example 2). No solid wax was seen for either
catalyst under these reaction conditions.
TABLE-US-00004 TABLE 4 Hybrid catalyst Hybrid catalyst Prepared
Prepared with ZSM-48 with ZSM-12 TOS, h 77 96 Yield Time, h 25.5
25.5 Temperature, .degree. C. 220.0 220.0 Pressure, atm 20 20
H.sub.2/CO Fresh Feed 2.00 2.0 H.sub.2 Conv (mol %). 45.2 32.9 CO
Conv (mol %). 39.10 26.3 Rate, gCH.sub.2/g/h 0.41 0.28 Rate,
mLC.sub.5.sup.+/g/h 0.35 0.22 CO.sub.2, wt % 1.10 0.5 CH.sub.4, wt
% 18.8 24.6 C.sub.2, wt % 2.1 2.1 C.sub.3, wt % 7.9 8.0 C.sub.4, wt
% 5.2 5.0 C.sub.5.sup.+, wt % 64.8 59.8 C.sub.21.sup.+, wt % 5.1
5.2 C1-C3, wt % 28.8 34.7 C.sub.2.sup.=/C.sub.2, mol % 2.9% 3.9%
C.sub.3.sup.=/C.sub.3, mol % 29.2% 28.4% C.sub.4.sup.=/C.sub.4, mol
% 31.4% 29.6% DOB, mol % 5.1% 6.4%
* * * * *
References