U.S. patent application number 10/706880 was filed with the patent office on 2004-07-15 for supports for high surface area catalysts.
This patent application is currently assigned to ConocoPhillips Company. Invention is credited to Coy, Kevin L., Espinoza, Rafael L., Minahan, David M., Niu, Tianyan, Wolf, Mary E., Wright, Harold A., Xie, Shuibo.
Application Number | 20040138317 10/706880 |
Document ID | / |
Family ID | 32314887 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040138317 |
Kind Code |
A1 |
Xie, Shuibo ; et
al. |
July 15, 2004 |
Supports for high surface area catalysts
Abstract
The present invention relates to thermally stable, high surface
area alumina supports and method of preparing such supports with at
least one modifying agent. The method includes adding the modifying
agent to the alumina prior to calcining. More particularly, the
invention relates to the use of such catalysts for the catalytic
partial oxidation of light hydrocarbons (e.g., methane or natural
gas) to produce primarily synthesis gas. The present invention
further relates to gas-to-liquids conversion processes, more
specifically for producing C.sub.5+ hydrocarbons.
Inventors: |
Xie, Shuibo; (Ponca City,
OK) ; Wolf, Mary E.; (Ponca City, OK) ;
Wright, Harold A.; (Ponca City, OK) ; Espinoza,
Rafael L.; (Ponca City, OK) ; Niu, Tianyan;
(Ponca City, OK) ; Minahan, David M.; (Stillwater,
OK) ; Coy, Kevin L.; (Ponca City, OK) |
Correspondence
Address: |
DAVID W. WESTPHAL
CONOCOPHILLIPS COMPANY
P.O. BOX 1267
PONCA CITY
OK
74602-1267
US
|
Assignee: |
ConocoPhillips Company
Houston
TX
|
Family ID: |
32314887 |
Appl. No.: |
10/706880 |
Filed: |
November 12, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60425383 |
Nov 11, 2002 |
|
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|
60425381 |
Nov 11, 2002 |
|
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60501185 |
Sep 8, 2003 |
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Current U.S.
Class: |
518/703 ;
423/651 |
Current CPC
Class: |
C01B 2203/1082 20130101;
B01J 37/06 20130101; B01J 2523/00 20130101; B01J 2523/00 20130101;
B01J 2523/00 20130101; C01B 3/386 20130101; C01B 2203/1017
20130101; B01J 35/0053 20130101; B01J 2523/00 20130101; C01B 3/40
20130101; C01B 2203/0261 20130101; B01J 23/40 20130101; B01J
35/1019 20130101; C01B 2203/1052 20130101; B01J 23/63 20130101;
B01J 21/04 20130101; B01J 2523/00 20130101; B01J 37/08 20130101;
C01B 2203/1241 20130101; B01J 23/10 20130101; B01J 2523/00
20130101; C01B 2203/1633 20130101; C01B 2203/1011 20130101; B01J
23/468 20130101; B01J 35/1014 20130101; C01B 2203/1041 20130101;
Y02P 20/52 20151101; B01J 35/0026 20130101; B01J 37/0201 20130101;
C01B 2203/1064 20130101; C01B 2203/1094 20130101; B01J 23/464
20130101; B01J 2523/00 20130101; B01J 21/12 20130101; B01J 23/75
20130101; B01J 35/002 20130101; B01J 21/10 20130101; B01J 23/56
20130101; B01J 23/6567 20130101; B01J 23/002 20130101; C01B
2203/062 20130101; B01J 23/8913 20130101; B01J 2523/00 20130101;
B01J 2523/3706 20130101; C01B 2203/1047 20130101; B01J 2523/00
20130101; C10G 2/30 20130101; B01J 2523/822 20130101; B01J 2523/822
20130101; B01J 2523/31 20130101; B01J 2523/3737 20130101; B01J
2523/22 20130101; B01J 2523/31 20130101; B01J 2523/845 20130101;
B01J 2523/31 20130101; B01J 2523/31 20130101; B01J 2523/41
20130101; B01J 2523/3706 20130101; B01J 2523/31 20130101; B01J
2523/3737 20130101; B01J 2523/31 20130101; B01J 2523/3737 20130101;
B01J 2523/3706 20130101; B01J 2523/821 20130101; B01J 2523/822
20130101; B01J 2523/822 20130101; B01J 2523/822 20130101; B01J
2523/3706 20130101; B01J 2523/31 20130101; B01J 2523/3737 20130101;
B01J 2523/3737 20130101; B01J 2523/31 20130101; B01J 2523/822
20130101; B01J 2523/3706 20130101 |
Class at
Publication: |
518/703 ;
423/651 |
International
Class: |
C01B 003/26; C07C
027/06 |
Claims
What is claimed is:
1. A process for producing synthesis gas comprising passing a
hydrocarbon containing gas and an oxygen containing gas over a
catalyst, under conditions effective to produce a gas stream
comprising hydrogen and carbon monoxide, wherein the catalyst
comprises: (a) an alumina support comprising at least one modifying
agent; and (b) at least one catalytically active metal deposited on
said alumina support, and wherein the alumina support has undergone
a high temperature calcination in the presence of a precursor of
the at least one modifying agent at a temperature equal to or
greater than about 1000.degree. C.
2. The process according to claim 1 wherein the high temperature
calcination is performed at a temperature greater than 1000.degree.
C.
3. The process according to claim 1 wherein the alumina support has
a surface area of greater than or equal to about 10 m.sup.2/g after
said high temperature calcination.
4. The process according to claim 1 wherein the catalyst comprises
a metal surface area greater than 0.35 m.sup.2/g of the
catalyst.
5. The process according to claim 1 wherein the catalytically
active metal is selected from the group consisting of Group VIII
metals, rhenium, tungsten, zirconia, molybdenum and mixtures
thereof.
6. The process according to claim 1 wherein the catalytically
active metal comprises a metal selected from the group consisting
of Rh, Ru, Ir, Re or mixtures thereof.
7. The process according to claim 1 wherein the catalytically
active metal comprises rhodium.
8. The process according to claim 1 wherein the catalytically
active metal comprises a rhodium alloy.
9. The process according to claim 1 wherein the modifying agent
comprises at least one element selected from the group consisting
of aluminum, boron, silicon, gallium, selenium, rare earth metals,
alkali earth metals and transition metals, and their corresponding
oxides and ions.
10. The process according to claim 1 wherein the modifying agent
comprises at least one element selected from the group consisting
of La, Al, Sm, Pr, Ce, Eu, Yb, Si, Mg, Co, their corresponding
oxides, their corresponding ions, and combinations thereof.
11. The process according to claim 1 wherein the modifying agent
comprises one element selected from the group consisting of
aluminum, lanthanum, samarium, cobalt, magnesium, silicon, their
corresponding oxides, their corresponding ions, and combinations
thereof.
12. The process according to claim 1 wherein the process exhibits a
hydrocarbon conversion equal to or greater than 80%, and a hydrogen
selectivity equal to or greater than 80%, under operating
conditions of at least greater than or equal to 2 atmospheres.
13. The process according to claim 1 wherein the process exhibits a
hydrocarbon conversion equal to or greater than 85%, and a hydrogen
selectivity equal to or greater than 85%, under operating
conditions of at least greater than or equal to 2 atmospheres.
14. The process according to claim 1 wherein the process exhibits a
loss in hydrocarbon conversion no greater than about 3% per
day.
15. The process according to claim 1 wherein the process exhibits a
loss in hydrogen selectivity no greater than about 1% per day.
16. A process for producing liquid hydrocarbons comprising: (a)
converting at least a portion of a feedstream comprising a
hydrocarbon containing gas and an oxygen containing gas over a
catalyst comprising an alumina support having at least one
modifying agent and at least one catalytically active metal, under
conditions effective to produce a gas stream comprising hydrogen
and carbon monoxide, wherein the alumina support has undergone a
high temperature calcination with a temperature equal to or greater
than about 1000.degree. C. in the presence of a precursor of the at
least one modifying agent; and (b) reacting at least a portion of
the gas stream from step (a) in a hydrocarbon synthesis reactor
under conditions effective to produce C.sub.5+ hydrocarbons.
17. The process according to claim 16 wherein the high temperature
treatment is greater than 1100.degree. C.
18. The process according to claim 16 wherein the catalyst
comprises a metal surface area greater than 0.35 m.sup.2/g of the
catalyst.
19. The process according to claim 16 wherein the catalytically
active metal is selected from the group consisting of Group VIII
metals, rhenium, tungsten, zirconia, molybdenum and mixtures
thereof.
20. The process according to claim 16 wherein the catalytically
active metal comprises a metal selected from the group consisting
of Rh, Ru, Ir, Re or mixtures thereof.
21. The process according to claim 16 wherein the catalytically
active metal comprises rhodium.
22. The process according to claim 16 wherein the catalytically
active metal comprises a Rh alloy.
23. The process according to claim 16 wherein Step (a) exhibits a
hydrocarbon conversion equal to or greater than 80%, and a hydrogen
selectivity equal to or greater than 80%, under operating
conditions of at least greater than or equal to 2 atmospheres.
24. The process according to claim 16 wherein Step (a) exhibits a
loss in hydrocarbon conversion no greater than about 3% per
day.
25. The process according to claim 16 wherein Step (a) exhibits a
loss in hydrogen selectivity no greater than about 1% per day.
26. The process according to claim 16 wherein the alumina support
has a surface area of greater than or equal to about 10 m.sup.2/g
after said high temperature treatment.
27. The process according to claim 16 wherein the modifying agent
comprises at least one element selected from the group consisting
of aluminum, boron, silicon, gallium, selenium, rare earth metals,
alkali earth metals and transition metals, and their corresponding
oxides and ions.
28. The process according to claim 16 wherein the modifying agent
comprises one element selected from the group consisting of
aluminum, lanthanum, samarium, cobalt, magnesium, silicon, their
corresponding oxides, their corresponding ions, and combinations
thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of 35 U.S.C.
111(b) Provisional Application Serial No. 60/425,383 filed Nov. 11,
2002, and U.S. Provisional Application Serial No. 60/425,381 filed
Nov. 11, 2002, entitled "Novel Syngas Catalysts and Their Method of
Use" which are hereby incorporated by reference herein for all
purposes. This application is related to the concurrently filed,
commonly owned, co-pending U.S. Provisional Application Serial No.
60/501,185 filed Sep. 8, 2003, entitled "Stabilized Alumina
Supports, Catalysts Made Therefrom, And Their Use in Partial
Oxidation."
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
TECHNICAL FIELD OF THE INVENTION
[0003] The present invention generally relates to catalyst supports
having high surface area and stability in ultra high temperature
conditions. This invention more particularly relates to modified
alumina supports and catalysts made therefrom that maintain high
surface areas at high temperature reaction conditions. The present
invention also relates to processes employing these catalysts for
the catalytic conversion of light hydrocarbons (e.g., natural gas)
to produce carbon monoxide and hydrogen (synthesis gas), and
conversion of synthesis gas to hydrocarbons. This invention also
discloses methods of making such supports and catalysts.
BACKGROUND OF THE INVENTION
[0004] It is well known that the efficiency of catalyst systems is
often related to the surface area on the support. This is
especially true for systems using precious metal catalysts or other
expensive catalysts. The greater the surface area, the more
catalytic material is exposed to the reactants and the less time
and catalytic material is needed to maintain a high rate of
productivity.
[0005] Alumina (Al.sub.2O.sub.3) is a well known support for many
catalyst systems. It is also well known that alumina has a number
of crystalline phases such as alpha alumina (often noted as
.alpha.-alumina or .alpha.-Al.sub.2O.sub.3), gamma alumina (often
noted as .gamma.-alumina or .gamma.-Al.sub.2O.sub.3) as well as a
myriad of others. One of the properties of gamma alumina is that it
has a very high surface area. This is commonly believed to be
because the aluminum and oxygen molecules are in a crystalline
structure or form that is not very densely packed. Unfortunately,
when gamma alumina is heated to high temperatures, the structure of
the atoms collapses such that the surface area decreases
substantially. The most dense crystalline form of alumina is alpha
alumina. Thus, alpha alumina has the lowest surface area, but is
the most stable at high temperatures.
[0006] Alumina is ubiquitous as supports and/or catalysts for many
heterogeneous catalytic processes. Some of these catalytic
processes occur under conditions of high temperature, high pressure
and/or high water vapor pressure.
[0007] It has long been a desire of those skilled in the catalyst
support arts to create a form of alumina that has high surface area
like gamma alumina and stability at high temperature like alpha
alumina.
[0008] Such a catalyst support would have many uses. One such use
is in the production of synthesis gas in a catalytic partial
oxidation reactor. Synthesis gas is primarily a mixture of hydrogen
and carbon monoxide and can be made from the partial burning of
light hydrocarbons with oxygen. The hydrocarbons, such as methane
or ethane are mixed with oxygen or oxygen containing gas and
heated. When the mixture comes in contact with an active catalyst
material at a temperature above an initiation temperature, the
reactants quickly react generating synthesis gas and a lot of heat.
Catalytic partial oxidation is a very fast reaction requiring only
milliseconds of contact of reactant gases with the catalyst. As a
result, it is quite exothermic causing reactor temperatures to
exceed 800.degree. C., often going above 1000.degree. C. and even
sometimes going above 1200.degree. C. Since catalysts used in the
partial oxidation of hydrocarbons is typically supported, the
support should be able to sustain this high thermal condition
during long-term operation. In other words, a stable catalyst
support which retains most of its surface area is desirable for
long catalyst life.
[0009] The selectivity of catalytic partial oxidation of light
hydrocarbons to the desired products, carbon monoxide and hydrogen,
are influenced by several factors, but one of the most important of
these factors is the catalyst composition. Noble metals typically
serve as the best catalysts for the partial oxidation of methane.
Noble metals are however scarce and expensive, making their use
economically challenging especially when the stability of the
catalyst is questionable. One of the better known noble metal
catalysts for catalytic partial oxidation is Rhodium. Rhodium-based
syngas catalysts deactivate very fast due to sintering of both
catalyst support and/or metal particles. Prevention of any of these
undesirable phenomena is well-sought after in the art of catalytic
partial oxidation process, particularly for successful and
economical operation at commercial scale.
[0010] Another use for a highly stabilized, high surface area
catalyst support would be in catalytic reactions that produce high
temperature water vapor at high partial pressures. Such an
environment challenges the hydrothermal stability of alumina
supports making the supports more prone to degradation,
fragmentation, or other processes that compromise the ability to
support catalytic metals. For purposes of the present discussion,
hydrothermal stability is defined as the property of resisting
morphological and/or structural change in the face of elevated heat
and water vapor pressure.
[0011] The Fischer-Tropsch process (also called the Fischer-Tropsch
reaction or Fischer-Tropsch synthesis) is an example of a process
that can generate water vapor of high partial pressure at high
temperatures. The Fischer-Tropsch process comprises contacting a
feed stream comprising syngas with a catalyst comprising typically
a Group VIII metal at conditions of elevated pressure and
temperature to produce mixtures of hydrocarbons and by-products
comprising water and oxides of carbon. Syngas can be provided to a
Fischer-Tropsch process from several sources such as the
gasification of coal; from natural gas reserves using a partial
oxidation process with an oxygen source; or by reaction of natural
gas with steam (steam reforming).
[0012] It would therefore be highly desirable to create a
thermally-stable high surface area support with a Group VIII metal
loaded onto the support for highly productive long lifetime
catalysts for the syngas production and/or its conversion to
hydrocarbons.
SUMMARY OF THE INVENTION
[0013] The present invention is a thermally stable, high surface
area alumina support with at least one modifying agent. The
modifying agent is at least one element selected from the group
consisting of aluminum, boron, silicon, gallium, selenium, rare
earth metals, alkali earth metals and transition metals, and their
corresponding oxides and ions. The inventive support has thermal
stability at temperatures above 800.degree. C.
[0014] The present invention also includes the process for
stabilizing a high surface area alumina support. The process for
stabilizing the support includes adding at least one modifying
agent to the alumina prior to calcining. The modifying agents
include aluminum, boron, silicon, gallium, selenium, rare earth
metals, alkali earth metals and transition metals.
[0015] The invention further includes a catalyst comprising a
catalytically active metal on alumina support wherein the support
includes at least one modifying agent. The modifying agent
comprises at least one element selected from the group consisting
of aluminum, boron, silicon, gallium, selenium, a rare earth metal,
an alkali earth metal or a transition metal, their corresponding
oxides or ions.
[0016] The present invention can be more specifically seen as a
support, process and catalyst wherein the preferred modifying
agents are lanthanide metals, aluminum, silicon, magnesium,
calcium, manganese, cobalt, iron, zirconia, their oxides, their
ions, or combinations thereof. The supported catalyst comprises at
least one group VIII metal or rhenium with an optional
promoter.
[0017] A more specific embodiment of the invention is a catalyst
having a high surface area thermally stable alumina support with at
least one group VIII metal or rhenium and an optional promoter
loaded onto the support. Another specific embodiment of the
invention is a catalyst having a high surface area hydro-thermally
stable alumina support modified with aluminum with at least one
group VIII metal and an optional promoter loaded onto the
support.
[0018] More particularly, the invention relates to processes for
the catalytic partial oxidation of light hydrocarbons (e.g.,
methane or natural gas) to produce primarily synthesis gas and the
use of such supported catalysts to make carbon monoxide and
hydrogen under conditions of high gas hourly space velocity,
elevated pressure and high temperature.
[0019] The present invention further relates to Fischer-Tropsch
catalysts and processes for the conversion of syngas for producing
C.sub.5+ hydrocarbons.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] For a more detailed understanding of the preferred
embodiments, reference is made to the accompanying drawings,
wherein:
[0021] FIG. 1 represents the pore distribution of unmodified
Al.sub.2O.sub.3 and several examples of modified
Al.sub.2O.sub.3;
[0022] FIG. 2 represents X-ray diffraction traces of the unmodified
Al.sub.2O.sub.3 and several modified Al.sub.2O.sub.3 after
calcinations at 1100.degree. C.; and
[0023] FIG. 3 represents the performance data for syngas production
from a catalyst made according to a preferred embodiment of the
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] Herein will be described in detail, specific embodiments of
the present invention, with the understanding that the present
disclosure is to be considered an exemplification of the principles
of the invention, and is not intended to limit the invention to
that illustrated and described herein. The present invention is
susceptible to embodiments of different forms or order and should
not be interpreted to be limited to the specifically expressed
methods or compositions contained herein. In particular, various
embodiments of the present invention provide a number of different
configurations of the overall gas to liquid conversion process.
[0025] The present invention provides a modified alumina support
with enhanced thermal stability and with a high BET surface area
greater than 5 m.sup.2/g, preferably greater than 10 m.sup.2/g, and
preferably greater than 15 m.sup.2/g. The modified alumina support
is obtained by deposition of at least one modifying agent. The
modifying agent comprises at least one element selected from the
group consisting of aluminum, boron, silicon, gallium, selenium,
rare earth metals, transition metals, alkali earth metals, and
their corresponding oxides or ions, preferably selected from the
group consisting of alumina (Al), boron (B), silicon (Si), gallium
(Ga), selenium (Se), calcium (Ca), lanthanum (La), cerium (Ce),
praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm),
europium (Eu), gadolinium (Gd), terbium (Th), dysprosium (Dy),
holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium
(Lu), zirconium (Zr), iron, (Fe), cobalt (Co), manganese (Mn),
magnesium (Mg), and their corresponding oxides or ions. More
preferably the modifying agent comprises La, Al, Sm, Pr, Ce, Eu,
Yb, Si, Ce, Mg, Ca, Mn, Co, Fe, Zr, their corresponding oxides or
ions, or any combinations thereof. Most preferably the modifying
agent comprises La, Al, Sm, Pr, Ce, Eu, Yb, Si, Mg, Co, their
corresponding oxides or ions, or any combinations thereof.
[0026] The present invention provides a method of making a modified
alumina support with a modifying agent. The method comprises the
deposition of the modifying agent followed by a high temperature
treatment. The high temperature treatment is a calcination at a
temperature greater than 400.degree. C. The calcination temperature
is selected based on the highest temperature the catalyst would
likely experience in operation, i.e. the catalytic reactor. Thus,
if the catalytic system is anticipated to operate at a temperature
above 800.degree. C., the calcination temperature would be greater
than 600.degree. C., preferably between 800.degree. C. and
1400.degree. C., more preferably between 900.degree. C. and
1300.degree. C. If the catalytic system is anticipated to operate
at less 800.degree. C., the calcination range would preferably be
between about 400.degree. C. and 800.degree. C., more preferably
between 450.degree. C. and 750.degree. C.
[0027] In preferred embodiments the stabilized support is made by a
method that comprises combining the modifying agent or a precursor
thereof with an alumina material or a precursor of an alumina
material in an amount sufficient to deter disintegration or
structural deterioration of the alumina material during the partial
oxidization process. In certain embodiments the combined modifying
agent and alumina material form a solid solution between the
modifying agent and at least a portion of the support material. As
a result, a modifier-support intermediate structure is obtained. In
certain preferred embodiments the stabilized support comprises, at
least in part, a crystalline structure that is capable of resisting
a phase change at temperatures up to at least 1,200.degree. C. The
modifying agent may comprise, for example, La, Al, Sm, Pr, Ce, Eu,
Yb, Si, Mg, Co, Ca, Mn, Fe or Zr.
[0028] In certain embodiments the syngas catalyst is prepared by a
method that comprises calcining the modifier-support intermediate
at a temperature in the operating temperature range of the catalyst
when the catalyst is used in a reactor for catalyzing the partial
oxidation of the light hydrocarbon to form carbon monoxide and
hydrogen. After the catalytic material is deposited on the
stabilized support, it may be reduced by subjecting the catalyst to
reducing conditions. In some embodiments, the catalytic material
comprises rhodium, and in certain embodiments comprises a rhodium
alloy such as Rh--Ru or Rh--Ir, for example.
[0029] In certain embodiments the modifying agent comprises 0.1-10
wt % of the catalyst, and in some embodiments it comprises 1-5 wt %
of the catalyst. In some embodiments, the modifying agent comprises
cobalt, magnesium, or silicon, and in some embodiments the
modifying agent comprises lanthanum.
[0030] Modifying alumina (Al.sub.2O.sub.3) with some rare earth
metals has been proven to be effective in stabilizing the surface
area of modified Al.sub.2O.sub.3. It was discovered by the
Applicants that doping a .gamma.-Al.sub.2O.sub.3 with lanthanum
oxide (La.sub.2O.sub.3) inhibits or retards the phase
transformation of .gamma. phase to .theta. phase and eventually to
a phase and thus stabilizes the surface area and pore structure of
the alumina material even at high calcination temperatures above
1000.degree. C.
[0031] The support can have different forms such as monolith or
particulate or have discrete or distinct structures. The term
"monolith" as used herein is any singular piece of material of
continuous manufacture such as solid pieces of metal or metal oxide
or foam materials or honeycomb structures. The terms "distinct" or
"discrete" structures or units, as used herein, refer to supports
in the form of divided materials such as granules, beads, pills,
pastilles, pellets, cylinders, trilobes, extrudates, spheres or
other rounded shapes, or another manufactured configuration.
Alternatively, the divided material may be in the form of
irregularly shaped particles. Preferably at least a majority (i.e.,
>50%) of the particles or distinct structures have a maximum
characteristic length (i.e., longest dimension) of less than six
millimeters, preferably less than three millimeters. An especially
preferred particle size range is about 0.18 millimeters (80 mesh)
to about 3 millimeters, more preferably about 0.3-1.4 millimeters
(about 14-50 mesh). The term "mesh" refers to a standard sieve
opening in a screen through which the material will pass, as
described in the Tyler Standard Screen Scale (C. J. Geankoplis,
TRANSPORT PROCESSES AND UNIT OPERATIONS, Allyn and Bacon, Inc.,
Boston, Mass., p. 837), hereby incorporated herein by reference.
Mesh size of the particles or distinct structures can be measured
by the ASTM E-11-61 method.
[0032] The present invention also relates to improved catalyst
compositions using a modified alumina support, as well as methods
of making and using them. In particular, some embodiments of the
present invention comprise high melting point catalysts comprising
metal alloys.
[0033] The catalyst is supported on a modified alumina with a
minimum BET surface area of 5 m.sup.2/g, preferably greater than 10
m.sup.2/g, more preferably greater than 15 m.sup.2/g after high
heat treatment. Preferably the modified alumina is modified with
aluminum, cobalt, magnesium, silicon, a lanthanide metal, their
respective oxide or ion such as for example, aluminum, lanthanum,
samarium, cobalt, magnesium, silicon, or their respective oxide or
ion. Without wishing to be bound to a particular theory, the
Applicants believe that the metal-support interaction in catalysts
supported on for example La.sub.2O.sub.3-modifie- d Al.sub.2O.sub.3
is stronger than that in the catalyst supported on unmodified
Al.sub.2O.sub.3, and that this strong metal-support interaction in
La.sub.2O.sub.3-modified Al.sub.2O.sub.3 supported catalysts might
be responsible for the unusually high catalyst stability.
[0034] The catalyst used for producing synthesis gas comprises an
active metal selected from the group consisting of Group VIII
metals, rhenium, tungsten, zirconium, molybdenum, and any mixtures
thereof. Preferably the catalyst used for producing synthesis gas
comprises rhodium (Rh), ruthenium (Ru), iridium (fr), rhenium (Re)
or any combination thereof. In some embodiments, the active metal
is comprised in an alloy form, preferably a rhodium alloy. Although
not wishing the scope of this application to be limited to this
particular theory, the Applicants believed that alloying rhodium
with other metals appears to sustain the resistance of rhodium
catalysts to sintering, and therefore to allow the Rh alloy
catalysts to deactivate at a slower rate than syngas catalysts
containing only rhodium. Suitable metals for the rhodium alloy
generally include but are not limited to Group VIII metals, as well
as rhenium, tantalum, niobium, molybdenum, tungsten, zirconium and
mixtures thereof. The preferred metals for alloying with rhodium
are ruthenium, iridium, platinum, palladium, tantalum, niobium,
molybdenum, rhenium, tungsten, cobalt, and zirconium, more
preferably ruthenium, rhenium, and iridium.
[0035] The catalyst used for converting synthesis gas comprises an
active metal selected from Group VIII. Preferably the catalyst used
for converting synthesis gas comprises cobalt, iron, ruthenium,
nickel or any combination thereof. In preferred embodiments, the
modifying agent is aluminum or an oxide or ion of aluminum.
[0036] In accordance with the present invention, the loading of the
active metal is preferably between 0.1 and 50 weight percent of the
total catalyst weight (herein wt %).
[0037] In one embodiment of the invention the active metal is
rhodium, which comprises from about 0.1 to about 20 wt % of the
catalyst material, preferably from about 0.5 to about 10 wt %, and
more preferably from about 0.5 to about 5 wt %. When a rhodium
alloy is used, the other metal in the rhodium alloy preferably
comprises from about 0.1 to about 20 wt % of the catalyst material,
preferably from about 0.5 to about 10 wt %, and more preferably
from about 0.5 to about 5 wt %.
[0038] When the active metal is cobalt, nickel, or iron, the metal
comprises from about 0.1 to 50 wt % of the catalyst material,
preferably from about 5 to about 40 wt %, and more preferably from
about 10 to about 35 wt %.
[0039] In another embodiment of the invention the active metal is
ruthenium which comprises from about 0.1 to 15 wt % of the catalyst
material, preferably from about 1 to about 8 wt %, and more
preferably from about 2 to about 5 wt %.
[0040] The catalyst structure employed is characterized by having a
high metal surface area, i.e., at least 0.8 square meters of metal
per gram of catalyst structure, preferably at least 1 m.sup.2/g.
Preferably the metal is rhodium and the rhodium surface area at
least 0.8 square meters of rhodium per gram of supported catalyst,
preferably at least 1 m.sup.2/g.
[0041] Catalyst compositions may also contain one or more
promoters. In some embodiments when one active metal is rhodium,
rhenium, ruthenium, or iridium, the promoter comprises an element
selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Th, Dy, Ho, Er, Tm, Yb and Lu, preferably Sm, Eu, Pr and Yb.
The Applicants discovered that the introduction of a lanthanide
oxide, especially Sm.sub.2O.sub.3, on the modified alumina support
surface before deposition of active metal(s) seems to further
enhance the metal-support interaction, and that the active metal(s)
also disperses better on the surface of Al.sub.2O.sub.3 modified
with La.sub.2O.sub.3 and/or Sm.sub.2O.sub.3. According to some
embodiments with the use of a rhodium alloy, the presence of a
promoter metal can be omitted without detriment to the catalyst
activity and/or selectivity. It is foreseeable however that, in
some alternate embodiments, a promoter could be added to a catalyst
material comprising a rhodium alloy. In other embodiments the
active metal is cobalt, ruthenium, iron, or nickel, and the
promoter is selected from the group consisting of the alkali
metals, the alkaline earths, the lanthanides, Group IIIB, IVB, VB,
VIB and VIIB metals. Promoters, when used, preferably comprise
about 1-15 wt % of the catalyst composition.
[0042] In one embodiment of the present invention is more
preferably directed towards syngas catalysts used in partial
oxidation reactions and even more preferably used in syngas
catalysts that contain solely rhodium or rhodium alloys. However,
it should be appreciated that the catalyst compositions according
to the present invention are useful for other partial oxidation
reactions, which are intended to be within the scope of the present
invention.
[0043] In another embodiment of the present invention the catalyst
support is used for hydrogenation catalysts in conversion of syngas
to alcohols or C.sub.5+ hydrocarbons via the Fischer-Tropsch
reaction. In addition, the present invention contemplates an
improved method for converting hydrocarbon gas to liquid
hydrocarbons using the novel syngas catalyst compositions described
herein. Thus, the invention also relates to processes for
converting hydrocarbon-containing gas to liquid products via an
integrated syngas to Fischer-Tropsch, methanol or other
process.
[0044] Method of Reparation of Catalyst Support
[0045] The present invention further presents a method of making a
syngas catalyst support wherein said method comprises depositing a
compound or precursor of a modifying agent onto an alumina
precursor; calcining the deposited alumina precursor at
temperatures temperature greater than 600.degree. C., preferably
between 800.degree. C. and 1400.degree. C., more preferably between
900.degree. C. and 1300.degree. C. to form a modified alumina.
[0046] The present invention further presents a method of making a
Fischer-Tropsch catalyst support wherein said method comprises
depositing a compound or precursor of a modifying agent onto an
alumina precursor; calcining the deposited alumina precursor at
temperatures temperature between 300.degree. C. and 1000.degree.
C., and more preferably at a temperature between 400.degree. C. and
800.degree. C. to form a modified alumina.
[0047] The alumina precursor can comprise one or more alumina
phases such as, but not limited to, gamma, delta, kappa, theta,
alpha that are known in the art. The alumina precursor can also
comprise Boehmite alumina or pseudoboehmite. An alumina precursor
comprising mainly .gamma.-alumina is preferred. It should be
understood that the alumina precursor could be pre-treated prior to
deposition of the modifying agent. The pre-treatment could be
heating, spraydrying (to e.g., adjust particle sizes) dehydrating,
drying, steaming or calcining. Steaming the alumina precursor can
be done at conditions sufficient to transform the alumina precursor
into a hydrated from of aluminum oxide, such as boehmite or
pseudoboehmite.
[0048] The present process for preparing a modified alumina may
further comprise steaming the deposited alumina precursor at
conditions sufficient to transform the deposited alumina precursor
into a modified boehmite alumina wherein steaming is defined as
subjecting a given material, within the confines of an autoclave or
other suitable device, to an atmosphere comprising a saturated or
under-saturated water vapor at conditions of elevated temperature
and elevated water partial pressure.
[0049] In one aspect, the steaming of the deposited alumina
precursor is preferably performed at a temperature ranging from
150.degree. C. to 500.degree. C., more preferably ranging from
180.degree. C. to 300.degree. C., and most preferably ranging from
200.degree. C. to 250.degree. C.; a water vapor partial pressure
preferably ranging from 1 bar to 40 bars, more preferably ranging
from 4 bars to 20 bars, and most preferably from 10 bars to 20
bars; and an interval of time preferably from 0.5 hour to 10 hours,
and most preferably 0.5 hour to 4 hours. Preferably, under these
steaming conditions, the deposited alumina precursor is at least
partially transformed to at least one phase selected from the group
boehmite, pseudoboehmite and the combination thereof. A
pseudoboehmite alumina refers to a monohydrate of alumina having a
crystal structure corresponding to that of boehmite but having low
crystallinity or ultrafine particle size. Alternatively, the
optional steaming of the deposited alumina precursor may comprise
same conditions of temperature and time as above, but with a
reduced water vapor partial pressure preferably ranging from 1 bar
to 5 bar, and more preferably ranging from 2 bars to 4 bars.
[0050] The compound or precursor of a modifying agent can be in the
form of salt, acid, oxide, hydroxide, oxyhydroxide, carbide, and
the like. Preferably the compound or precursor of a modifying agent
is an oxide or a salt (such as carbonate, acetate, nitrate,
chloride, or oxalate). The modifying agent comprises at least one
element selected from the group consisting of aluminum, boron,
silicon, gallium, selenium, rare earth metals, transition metals,
alkali earth metals, their corresponding oxides or ions, preferably
at least one element selected from the group consisting of Al, B,
Si, Ga, Se, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb,
Lu, and their corresponding oxides or ions. More preferably, the
modifying agent comprises either La, Al, Pr, Ce, Eu, Yb, or Sm, or
their corresponding oxides or ions, or any combinations thereof.
Preferably the compound or precursor of a modifying agent is a
nitrate salt or a chloride salt, as for example only
La(NO.sub.3).sub.3, or Al(NO.sub.3). It should be understood that
more than one modifying agent or more than one compound or
precursor of a modifying agent can be used.
[0051] The modifying agent can be deposited into the alumina
precursor by means of different techniques. For example only,
deposition methods can be spraydrying, impregnation,
co-precipitation, chemical vapor deposition, and the like. It
should also be understood that any combination of techniques or
multiple steps of the same technique can be used to deposit a
modifying agent. One preferred technique for depositing the
modifying agent is impregnation, particularly incipient wetness
impregnation.
[0052] When the deposition is done via impregnation, optionally a
drying step at temperatures between 75.degree. C. and 150.degree.
C. is performed on the deposited alumina prior to calcination. In
another embodiment, the modified support is derived from the
alumina precursor by contacting the alumina precursor with the
modifying agent so as to form a support material and treating the
support material so as to form a hydrothermally stable support.
Contacting the alumina precursor with the structural stabilizer
preferably includes dispersing the alumina precursor in a solvent
so as to form a sol, adding a compound of the modifying agent to
the sol, and spraydrying the sol so as to form the support
material. It should be understood that more than one modifying
agents or more than one compound or precursors of a modifying agent
can be added to the sol. Alternatively, one modifying agent can be
incorporated into the support by means of the aforementioned
techniques. Alternatively, two or more modifying agents can be
incorporated into the support by means of the aforementioned
techniques.
[0053] Method of Catalyst Preparation
[0054] The present invention further presents a method of making a
syngas catalyst wherein said method comprises optionally depositing
a compound or precursor of one or more promoters to the modified
alumina and calcining the (deposited) modified alumina at
temperatures greater than 600.degree. C., preferably between about
800.degree. C. and about 1400.degree. C., more preferably between
about 900.degree. C. and about 1300.degree. C. to form a catalyst
precursor; depositing a compound or precursor of one or more active
metals to the catalyst precursor; calcining the deposited catalyst
precursor at temperatures between about 300.degree. C. and about
1200.degree. C., preferably between about 500.degree. C. and about
1100.degree. C.
[0055] The compound or precursor of the promoter can be in the form
of salt, acid, oxide, hydroxide, oxyhydroxide, carbide, and the
like. Preferably the compound or precursor of a promoter is a salt.
The promoter comprises at least one element selected from the group
consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm,
Yb, Lu, and their corresponding oxides or ions. Preferably the
promoter comprises either Pr, Yb, Eu, Sm, their corresponding
oxides or ions, or any combinations thereof. Preferably the
compound or precursor of a promoter is a nitrate salt, as for
example only Sm(NO.sub.3).sub.3 or La(NO.sub.3). It should be
understood that more than one promoter or more than one compound or
precursor of a promoter can be used.
[0056] The present invention further includes a method of making a
FT catalyst wherein said method comprises optionally depositing a
compound or precursor of one or more promoters to the modified
alumina and calcining the (deposited) modified alumina at
temperatures greater than 250.degree. C., preferably between about
300.degree. C. and about 800.degree. C. to form a catalyst
precursor; depositing a compound or precursor of one or more active
metals to the catalyst precursor; calcining the deposited catalyst
precursor at temperatures between about 250.degree. C. and about
800.degree. C., preferably between about 300.degree. C. and about
800.degree. C. The promoter comprises at least one element selected
from the group consisting of alkali metals, the alkaline earths,
the lanthanides, Group IIIB, IVB, VB, VIB and VIIB metals, their
corresponding oxides or ions, or any mixtures thereof. Preferably,
the promoter comprises either Pt, Pd, Re, Ru, Ag, B, Au, Cu, their
corresponding oxides or ions, or any combinations thereof. The
compound or precursor of the promoter can be in the form of salt,
acid, oxide, hydroxide, oxyhydroxide, carbide, and the like.
Preferably the compound or precursor of a promoter is a salt, for
example only Co(NO.sub.3).sub.3.
[0057] The promoter can be deposited into the modified alumina by
means of different techniques. For example only, deposition methods
can be impregnation, co-precipitation, chemical vapor deposition,
and the like. The preferred technique for depositing the promoter
is impregnation.
[0058] When the deposition of the promoter is done via
impregnation, optionally a drying step at temperatures between
75.degree. C. and 150.degree. C. is performed on the deposited
modified alumina prior to calcination.
[0059] The compound or precursor of the active metal can be in the
form of salt, acid, oxide, hydroxide, oxyhydroxide, carbide, and
the like. Preferably the compound or precursor of the active metal
is a salt. The active metal comprises one element selected from the
group consisting of Group VIII metals, rhenium, tungsten,
zirconium, their corresponding oxides or ions, and any combinations
thereof. Preferably the active metal for syngas catalyst comprises
either rhodium, iridium, ruthenium, their corresponding oxides or
ions, or any combinations thereof. Preferably the compound or
precursor of the active metal is a nitrate or a chloride salt, as
for example only Rh(NO.sub.3).sub.3 or RhCl.sub.3. Preferably the
active metal for FT catalyst comprises either cobalt, ruthenium,
iron, nickel, their corresponding oxides or ions, or any
combinations thereof. It should be understood that more than one
active metal or more than one compound or precursor of an active
metal can be used. When two active metals are used in the syngas
catalyst, it is preferred that at least rhodium is selected as one
metal, that the other metal is selected from the active metal list
above for syngas catalyst, and that the loading of both metals is
such so as to form a rhodium alloy.
[0060] The active metal can be deposited on the catalyst precursor
(promoted or unpromoted modified alumina) by means of different
techniques. For example only, deposition methods can be
impregnation, co-precipitation, chemical vapor deposition, and the
like. The preferred technique for depositing the active metal is
impregnation.
[0061] When the deposition of the active metal is done via
impregnation, optionally a drying step at temperatures between
75.degree. C. and 150.degree. C. is performed on the deposited
catalyst precursor prior to calcination.
[0062] Process of Producing Syngas
[0063] According to the present invention, a syngas reactor can
comprise any of the synthesis gas technology and/or methods known
in the art. The hydrocarbon-containing feed is almost exclusively
obtained as natural gas. However, the most important component is
generally methane. Natural gas comprise at least 50% methane and as
much as 10% or more ethane. Methane or other suitable hydrocarbon
feedstocks (hydrocarbons with four carbons or less) are also
readily available from a variety of other sources such as higher
chain hydrocarbon liquids, coal, coke, hydrocarbon gases, etc., all
of which are clearly known in the art. Preferably, the feed
comprises at least about 50% by volume methane, more preferably at
least 80% by volume, and most preferably at least 90% by volume
methane. The feed can also comprise as much as 10% ethane.
Similarly, the oxygen-containing gas may come from a variety of
sources and will be somewhat dependent upon the nature of the
reaction being used. For example, a partial oxidation reaction
requires diatomic oxygen as a feedstock, while steam reforming
requires only steam. According to the preferred embodiment of the
present invention, partial oxidation is assumed for at least part
of the syngas production reaction.
[0064] Regardless of the source, the hydrocarbon-containing feed
and the oxygen-containing feed are reacted under catalytic
conditions. Improved catalyst compositions in accordance with the
present invention are described herein. They generally are
comprised of a catalytic metal, some alloyed, that has been reduced
to its active form and with one or more optional promoters on a
modified alumina support structure.
[0065] It has been discovered that the modification of alumina by a
modifying agent selected from the lanthanide metals group
particularly, results in a catalytic support suitable for
high-temperature reactions such as syngas production via partial
oxidation.
[0066] The syngas catalyst compositions according to the present
invention comprise an active metal selected from the group
consisting of Group VIII metals, rhenium, tungsten, zirconium,
their corresponding oxides or ions, and any combinations thereof,
preferably a group VII metal or rhenium, more preferably rhodium,
indium, ruthenium, rhenium, or combinations thereof.
[0067] In some embodiments when the active metal is rhodium,
rhodium is comprised in a high melting point alloy with another
metal. It has been discovered that in addition to the enhanced
thermal stability of the support, the high melting point rhodium
alloys used in some of these syngas catalysts confer additional
thermally stability than non-alloy rhodium catalysts, which leads
to enhanced ability of the catalyst to resist various deactivation
phenomena.
[0068] It is well known that during syngas reactions, several
undesired processes, such as coking (carbon deposition), metal
migration, and sintering of metal and/or the support, can occur and
severely deteriorate catalytic performance. The catalyst
compositions of the present invention are better able to resist at
least one of these phenomena over longer periods of time than prior
art catalysts. As a consequence, these novel rhodium containing
catalysts on modified alumina can maintain high methane conversion
as well as high CO and H.sub.2 selectivity over extended periods of
time with little to no deactivation of the syngas catalyst.
[0069] The support structure of these catalysts can be in the form
of a monolith or can be in the form of divided or discrete
structures or particulates. Particulates are preferred. Small
support particles tend to be more useful in fluidized beds.
Preferably at least a majority (i.e., >50%) of the particles or
distinct structures have a maximum characteristic length (i.e.,
longest dimension) of less than six millimeters, preferably less
than three millimeters. According to some embodiments, the divided
catalyst structures have a diameter or longest characteristic
dimension of about 0.25 mm to about 6.4 mm (about {fraction
(1/100)}" to about 1/4"), preferably between about 0.5 mm and about
4.0 mm. In other embodiments they are in the range of about 50
microns to 6 mm.
[0070] The hydrocarbon feedstock and the oxygen-containing gas may
be passed over the catalyst at any of a variety of space
velocities. Space velocities for the process, stated as gas hourly
space velocity (GHSV), are in the range of about 20,000 to about
100,000,000 hr.sup.-1, more preferably of about 100,000 to about
800,000 hr.sup.-1, most preferably of about 400,000 to about
700,000 hr.sup.-1. Although for ease in comparison with prior art
systems space velocities at standard conditions have been used to
describe the present invention, it is well recognized in the art
that residence time is the inverse of space velocity and that the
disclosure of high space velocities corresponds to low residence
times on the catalyst. "Space velocity," as that term is
customarily used in chemical process descriptions, is typically
expressed as volumetric gas hourly space velocity in units of
hr.sup.-1. Under these operating conditions a flow rate of reactant
gases is maintained sufficient to ensure a residence or dwell time
of each portion of reactant gas mixture in contact with the
catalyst of no more than 200 milliseconds, preferably less than 50
milliseconds, and still more preferably less than 20 milliseconds.
A contact time less than 10 milliseconds is highly preferred. The
duration or degree of contact is preferably regulated so as to
produce a favorable balance between competing reactions and to
produce sufficient heat to maintain the catalyst at the desired
temperature.
[0071] In order to obtain the desired high space velocities, the
process is operated at atmospheric or superatmospheric pressures.
The pressures may be in the range of about 100 kPa to about 32,000
kPa (about 1-320 atm), preferably from about 200 kPa to about
10,000 kPa (about 2-100 atm).
[0072] The process is preferably operated at a temperature in the
range of about 350.degree. C. to about 2,000.degree. C. More
preferably, the temperature is maintained in the range 400.degree.
C.-2,000.degree. C., as measured at the reactor outlet.
[0073] The catalysts of the present invention should maintain
hydrocarbon conversion of equal to or greater than about 85%,
preferably equal to or greater than about 90% after 100 hours of
operation when operating at pressures of greater than 2
atmospheres. Likewise, the catalysts of the present invention
should maintain CO and H2 selectivity of equal to or greater than
about 85%, preferably equal to or greater than about 90% after 100
hours of operation when operating at pressures of greater than 2
atmospheres.
[0074] The synthesis gas product contains primarily hydrogen and
carbon monoxide, however, many other minor components may be
present including steam, nitrogen, carbon dioxide, ammonia,
hydrogen cyanide, etc., as well as unreacted feedstock, such as
methane and/or oxygen. The synthesis gas product, i.e., syngas, is
then ready to be used, treated, or directed to its intended
purpose. The product gas mixture emerging from the syngas reactor
may be routed directly into any of a variety of applications,
preferably at pressure. For example, in the instant case some or
all of the syngas can be used as a feedstock in subsequent
synthesis processes, such as Fischer-Tropsch synthesis, alcohol
(particularly methanol) synthesis, hydrogen production,
hydroformylation, or any other use for syngas. One preferred such
application for the CO and H.sub.2 product stream is for producing,
via the Fischer-Tropsch synthesis, higher molecular weight
hydrocarbons, such as C.sub.5+ hydrocarbons.
[0075] Syngas is typically at a temperature of about
600-1500.degree. C. when leaving a syngas reactor. The syngas must
be transitioned to be useable in a Fischer-Tropsch or other
synthesis reactors, which operate at lower temperatures of about
200.degree. C. to 400.degree. C. The syngas is typically cooled,
dehydrated (i.e., taken below 100.degree. C. to knock out water)
and compressed during the transition phase. Thus, in the transition
of syngas from the syngas reactor to for example a Fischer-Tropsch
reactor, the syngas stream may experience a temperature window of
50.degree. C. to 1500.degree. C.
[0076] Fischer-Tropsch Synthesis
[0077] The synthesis reactor using synthesis gas as feedstock is
preferably a Fischer-Tropsch reactor. The Fischer-Tropsch reactor
can comprise any of the Fischer-Tropsch technology and/or methods
known in the art. The Fischer-Tropsch feedstock is hydrogen and
carbon monoxide, i.e., syngas. The hydrogen to carbon monoxide
molar ratio is generally deliberately adjusted to a desired ratio
of approximately 2:1, but can vary between 0.5 and 4. The syngas is
then contacted with a Fischer-Tropsch catalyst. Fischer-Tropsch
catalysts are well known in the art and generally comprise a
catalytically active metal, a promoter and a support structure. The
most common catalytic metals are Group VIII metals, such as cobalt,
nickel, ruthenium, and iron or mixtures thereof. The support is
generally alumina, titania, zirconia, silica, or mixtures thereof.
In some embodiments, the catalyst is supported on a modified
alumina as described in this invention. The preferred modifying
agent is aluminum. Fischer-Tropsch reactors use fixed and fluid
type conventional catalyst beds as well as slurry bubble columns.
The literature is replete with particular embodiments of
Fischer-Tropsch reactors and Fischer-Tropsch catalyst compositions.
As the syngas feedstock contacts the catalyst, the hydrocarbon
synthesis reaction takes place. The Fischer-Tropsch product
contains a wide distribution of hydrocarbon products from C.sub.5
to greater than C.sub.100. The Fischer-Tropsch process is typically
run in a continuous mode. In this mode, the gas hourly space
velocity through the reaction zone typically may range from about
50 to about 10;000 hr.sup.-1, preferably from about 300 hr.sup.-1
to about 2,000 hr.sup.-1. The gas hourly space velocity is defined
as the volume of reactants per time per reaction zone volume. The
volume of reactant gases is at standard pressure of 1 atm or 101
kPa and standard temperature of 0.degree. C. The reaction zone
volume is defined by the portion of the reaction vessel volume
where reaction takes place and which is occupied by a gaseous phase
comprising reactants, products and/or inerts; a liquid phase
comprising liquid/wax products and/or other liquids; and a solid
phase comprising catalyst. The reaction zone temperature is
typically in the range from about 160.degree. C. to about
300.degree. C. Preferably, the reaction zone is operated at
conversion promoting conditions at temperatures from about
190.degree. C. to about 260.degree. C. The reaction zone pressure
is typically in the range of about 80 psia (552 kPa) to about 1000
psia (6895 kPa), more preferably from 80 psia (552 kPa) to about
600 psia (4137 kPa), and still more preferably, from about 140 psia
(965 kPa) to about 500 psia (3447 kPa).
[0078] For purposes of the present disclosure, certain terms are
intended to have the following meanings.
[0079] "Active metal" refers to any metal that is present on a
catalyst that is active for catalyzing a particular reaction.
Active metals may also be referred to as catalytic metals.
[0080] A "promoter" is one or more substances, such as a metal or a
metal oxide or metal ion that enhances an active metal's catalytic
activity in a particular process, such as a CPOX process or the
Fischer-Tropsch process (e.g., increase conversion of the reactant
and/or selectivity for the desired product). In some instances a
particular promoter may additionally provide another function, such
as aiding in dispersion of active metal or aiding in stabilizing a
support structure or aiding in reduction of the active metal.
[0081] A "modifying agent" is one or more substances, such as a
metal or a metal oxide or metal ion that modify at least one
physical property of the support material that it is deposited
onto, such as for example structure of crystal lattice, mechanical
strength, morphology.
[0082] With respect to the catalytic reaction such as partial
oxidation of light hydrocarbons such as methane or natural gas to
produce synthesis gas or conversion of synthesis gas to
hydrocarbons, references to "catalyst stability" refer to
maintenance of at least one of the following criteria: level of
conversion of the reactants, productivity, selectivity for the
desired products, physical and chemical stability of the catalyst,
lifetime of the catalyst on stream, and resistance of the catalyst
to deactivation.
[0083] A precursor or a compound of a metal is a chemical entity,
such as, for example, a water-soluble metal salt, that contains the
atoms of the metal (e.g., a catalytic metal, a catalytic promoter,
or a modifying agent) in an oxidation state that is not zero.
EXAMPLES
[0084] Preparation of Modified Alumina Supports
[0085] The unmodified alumina support was obtained as
.gamma.-Al.sub.2O.sub.3 spheres with the following characteristics:
a size in the range of 1.2 to 1.4 mm (average diameter of 1.3 mm.),
a bulk density of 0.44 g/ml, a surface area and pore volume measure
with N.sub.2 adsorption of 143 m.sup.2/g and 0.75 ml/g
respectively.
Example A
La.sub.2O.sub.3 Modified Al.sub.2O.sub.3
[0086] The .gamma.-Al.sub.2O.sub.3 spheres described above were
impregnated with a aqueous solution containing desired amount of
La(NO.sub.3).sub.3 so that the La.sub.2O.sub.3 amount in the final
material after drying and calcinations is approximately 3% by
weight. The Al.sub.2O.sub.3 spheres impregnated with
La(NO.sub.3).sub.3 solution were dried in oven at 120.degree. C.
overnight and then calcined at 1100.degree. C. for 3 hr. The
La.sub.2O.sub.3--Al.sub.2O.sub.3 spheres (Catalyst Support, CS-1)
were either subject to further modifications or used directly as
catalyst support.
Example B
La.sub.2O.sub.3 Modified Al.sub.2O.sub.3
[0087] The Al.sub.2O.sub.3 spheres described above were impregnated
with a solution containing desired amounts of both
La(NO.sub.3).sub.3 and Al(NO.sub.3).sub.3, and then the obtained
material was dried overnight in an oven at 120.degree. C. for 3 hrs
and calcined at 1100.degree. C. for 3 hrs.
Example C
BaO Modified Al.sub.2O.sub.3
[0088] The Al.sub.2O.sub.3 spheres described above were impregnated
with a solution containing desired amount of Ba(NO.sub.3).sub.2 and
then the obtained material was dried at 120.degree. C. for 3 hrs
and calcined at 1100.degree. C. for 3 hrs.
[0089] Table 1 lists the BET surface areas, pore volume, average
pore diameter, both measured by the BJH desorption method using
N.sub.2 as the adsorptive of commercially available unmodified
.gamma.-Al.sub.2O.sub.3 and modified Al.sub.2O.sub.3 catalyst
supports. Surface area and pore size distribution are obtained on a
Micromeritics TriStar 3000 analyzer after degassing the sample at
190.degree. C. in flowing nitrogen for five hours. Surface area is
determined from ten points in the nitrogen adsorption isotherm
between 0.05 and 0.3 relative pressure and calculating the surface
area by the standard BET procedure. Pore size distribution is
determined from a minimum of 30 points in the nitrogen desorption
isotherm and calculated using the BJH model for cylindrical pores.
The instrument control and calculations are performed using the
TriStar software and are consistent with ASTM D3663-99 "Surface
Area of Catalysts and Catalyst Carriers", ASTM D4222-98
"Determination of Nitrogen Adsorption and Desorption Isotherms of
Catalysts by Static Volumetric Measurements", and ASTM D4641-94
"Calculation of Pore Size Distributions of Catalysts from Nitrogen
Desorption Isotherms". The initial surface area of the catalyst is
the surface area of the catalyst structure prior to contact of
reactant gas. The pore volume of the catalyst (N.sub.2 as
adsorptive) is measured and calculated using the method described
above. Average pore size (diameter) based on N.sub.2 adsorptive is
calculated as 4 V/A.
1TABLE 1 Surface area, pore volume and average pore diameter of
support and catalyst examples after different calcination
temperatures of the support. Calcination Temp. of support, BET SA,
Pore volume, Avg. pore Examples Composition .degree. C. m.sup.2/g
ml/g diameter, nm control unmodified Al.sub.2O.sub.3 1100 80 0.54
21 1200 16 0.19 45 A La.sub.2O.sub.3--Al.sub.2O.sub.3 1100 89 0.63
21 1200 56 0.42 23 B La.sub.2O.sub.3--Al.sub.2O.sub.3* 1100 87 0.57
20 C BaO--Al.sub.2O.sub.3 1100 66 0.44 21 2
Rh/Sm.sub.2O.sub.3/La.sub.2O.sub.3-- 1100 71 0.54 24
Al.sub.2O.sub.3 *Prepared by impregnating Al.sub.2O.sub.3 with a
solution containing La(NO.sub.3).sub.3 and Al(NO.sub.3).sub.3;
[0090] As shown in Table 1, modification of the Al.sub.2O.sub.3
with La.sub.2O.sub.3 (Examples A and B) increases the surface area
of the material after calcinations at 1100.degree. C. (89 and 87
m.sup.2/g vs. 80 m.sup.2/g), while BaO modified Al.sub.2O.sub.3
(Example C) shows lower surface area than unmodified
Al.sub.2O.sub.3 (66 m.sup.2/g vs. 80 m.sup.2/g). The two
La.sub.2O.sub.3 modified Al.sub.2O.sub.3 samples prepared with
different methods (with or without an aluminum oxide solution) show
no significant difference in surface area (89 m.sup.2/g vs. 87
m.sup.2/g), but the Example A prepared with impregnating
La(NO.sub.3).sub.3-only solution possesses greater pore volume than
the Example B and its pore volume is also greater than that of
unmodified Al.sub.2O.sub.3 as well (0.63 ml/g vs. 0.54 ml/g).
Doping Al.sub.2O.sub.3 with BaO (Example C) reduces the total pore
volume, which decreases from 0.54 ml/g to 0.44 ml/g.
[0091] As the data in Table 1 shows, the higher calcination
temperature of 1200.degree. C. resulted in a significant reduction
in BET surface area and pore volume, with a simultaneous increase
of the average pore diameter for the unmodified alumina compared to
the modified alumina. The BET surface area, pore volume, and
average pore diameter for unmodified alumina and Example A after
calcination at 1200.degree. C. are 16 and 56 m.sup.2/g, 0.19 and
0.42 ml/g, 45 and 23 nm respectively. Without the presence of the
modifying agent, the phase transfer to .alpha.-alumina is more
prevalent in unmodified alumina at this higher calcination
temperature, and the high calcination temperature causes some
micropores to collapse and therefore increase the pore sizes and
decrease the surface area.
[0092] Modification of the Al.sub.2O.sub.3 with La.sub.2O.sub.3
does not change the pore diameter distribution significantly, as
shown in FIG. 1. The pore diameter is .about.21 nm for the four
catalyst supports listed in Table 2. The most probable average pore
diameter is about 17 nm for unmodified Al.sub.2O.sub.3 and the two
La.sub.2O.sub.3 modified Al.sub.2O.sub.3, while the most probable
pore diameter of BaO modified La.sub.2O.sub.3 decreased to
.about.13 nm (FIG. 1). The pore distribution curve of BaO modified
Al.sub.2O.sub.3 (Example C) was shifted down to the direction of
smaller sizes (FIG. 1). Consequently, both the BET surface area and
total pore volume of BaO-Al.sub.2O.sub.3 are lower than unmodified
Al.sub.2O.sub.3.
[0093] The X-Ray Diffraction traces of unmodified Al.sub.2O.sub.3
and Examples A-C are shown in FIG. 2. After calcinations at
1100.degree. C., the commercially available Al.sub.2O.sub.3
consists of gamma, theta, alpha phases (.gamma., .theta., and
.alpha. respectively), with a significant presence of .alpha.
phase. Compared with unmodified Al.sub.2O.sub.3, Examples A and B
(La.sub.2O.sub.3 doped Al.sub.2O.sub.3) possesses less .theta. and
almost no .alpha. phases, based on the relative intensity of XRD
signals shown in FIG. 2. As the phase transformations of
Al.sub.2O.sub.3 follow .gamma..fwdarw..theta..fwdarw..- alpha. with
progressive heating, it can be concluded that modifying the
Al.sub.2O.sub.3 with La.sub.2O.sub.3 inhibits the phase
transformations from .gamma. to .theta. to a, i.e., modification of
the Al.sub.2O.sub.3 stabilizes the structure of .gamma. phase.
Therefore, La.sub.2O.sub.3-Al.sub.2O.sub.3 (EXAMPLES A and B)
maintains higher surface area than unmodified Al.sub.2O.sub.3 and
it also preserves the original pore structure better after high
temperature calcination (see Table 1 and FIG. 1). On the other
hand, doping the Al.sub.2O.sub.3 with BaO (EXAMPLE C) facilitate
Al.sub.2O.sub.3 phase transformation to .alpha. phase. The signals
of XRD peaks due to a phase Al.sub.2O.sub.3 are stronger and
narrower in EXAMPLE C. (BaO modified Al.sub.2O.sub.3) as shown in
FIG. 2, reflecting the presence of significant
.alpha.-Al.sub.2O.sub.3 phase in larger crystalline size compared
to those present in unmodified Al.sub.2O.sub.3 and
La.sub.2O.sub.3-Al.sub.2O- .sub.3 materials (Example A and B). The
predominant .alpha.-Al.sub.2O.sub.3 phase in BaO-Al.sub.2O.sub.3
explains that BaO-Al.sub.2O.sub.3 possesses a lower surface area
than unmodified Al.sub.2O.sub.3 as BaO seems to de-stabilize the
surface structure of .gamma.-Al.sub.2O.sub.3 (Table 1).
[0094] Preparation of Catalysts
Example 1
4% Rh/La.sub.2O.sub.3-Al.sub.2O.sub.3
[0095] The La.sub.2O.sub.3-modified Al.sub.2O.sub.3 support
material described as EXAMPLE A was impregnated with a RhCl.sub.3
solution and the catalyst was dried in an oven overnight at
120.degree. C., calcined in air at 900.degree. C. for 3 hrs and
then reduced in H.sub.2 at 600.degree. C. for 3 hrs. The Rh metal
content in the catalyst was 4% by weight as calculated by mass
balance. after drying and calcination
Example 2
4% Rh-4% Sm/La.sub.2O.sub.3-Al.sub.2O.sub.3
[0096] The La.sub.2O.sub.3-modified Al.sub.2O.sub.3 support
material obtained as EXAMPLE A was impregnated with a
Sm(NO.sub.3).sub.3 solution. The material was dried in oven for
overnight at 120.degree. C. and then calcined at 1100.degree. C.
for 3 hrs. The Sm content in the catalyst was 4 wt %
Sm.sub.2O.sub.3 in the final material after drying and
calcinations. The so-obtained
Sm.sub.2O.sub.3/La.sub.2O.sub.3-Al.sub.2O.s- ub.3 catalyst
precursor was impregnated with a RhCl.sub.3 solution and the
catalyst was dried in oven for overnight at 120.degree. C.,
calcined at 900.degree. C. for 3 hr, and then reduced in H.sub.2 at
600.degree. C. for 3 hrs to metallic Rh form before being charged
into the reactor. The Rh metal content in the catalyst was 4% by
weight again determined by mass balance.
Example 3
4% Rh-4% Sm/La.sub.2O.sub.3--Al.sub.2O.sub.3
[0097] The catalyst sample was prepared similarly to Example 2,
except the calcination temperature used for
Sm.sub.2O.sub.3/La.sub.2O.sub.3--Al.sub.- 2O.sub.3 spheres was
1200.degree. C. (instead of 1100.degree. C.). The Rh metal content
in the catalyst was 4% by weight in the final material after drying
and calcinations.
Example 4
2% Rh-4% Sm/La.sub.2O.sub.3--Al.sub.2O.sub.3
[0098] The catalyst sample was prepared similarly to Example 3
(calcination of Sm.sub.2O.sub.3/La.sub.2O.sub.3--Al.sub.2O.sub.3
spheres at 1200.degree. C.), except that the Rh metal content in
the catalyst was 2% by weight in the final material after drying
and calcinations.
Example 5
1% Rh-4% Sm/La.sub.2O.sub.3--Al.sub.2O.sub.3
[0099] The catalyst sample was prepared similarly to Example 3
(calcination of Sm.sub.2O.sub.3/La.sub.2O.sub.3--Al.sub.2O.sub.3
spheres at 1200.degree. C.), except that the Rh metal content in
the catalyst was 1% by weight in the fmal material after drying and
calcinations.
Example 6
4% Rh-4% Ru/La.sub.2O.sub.3--Al.sub.2O.sub.3
[0100] A rhodium alloy catalyst was prepared with the method
described in EXAMPLE 1. The La.sub.2O.sub.3 modified
Al.sub.2O.sub.3 spheres (from EXAMPLE A) were impregnated with a
solution containing both RhCl.sub.3 and RuCl.sub.3 such that to
achieve 4 wt % for both Rh and Ru. The conditions for drying,
calcination, reduction, are the same as those described in Example
1. The Rh and Ru content of the catalyst was 4 wt % for each metal
in the final material after drying and calcinations.
Example 7
3.3% Rh/3.7% Sm on Co-Modified Alumina
[0101] A catalyst containing 3.3% Rh/3.7% Sm on a 2.19% Co modified
alumina support was prepared as follows. Tri-lobe gamma alumina
(Sud Chemie, Inc. Louisville, Ky.) was crushed into 20-30 mesh size
(0.595-0.841 mm range). An aqueous solution of a cobalt nitrate was
applied to the gamma alumina material and dried using a rotary
evaporator under vacuum and at a temperature of around 60.degree.
C. The drying was continued in an oven overnight at 90.degree. C.
The dried modified support was then heated up to 1100.degree. C. in
air and held at 1100.degree. C. for four hours. Aqueous solutions
of samarium nitrate and rhodium chloride were respectively applied
to the support by impregnation, then the impregnated modified
support was calcined by heating up to 700.degree. C. in air and
held at 700.degree. C. for two hours after each impregnation. The
Rh/Sm catalyst was then reduced at 500.degree. C. for three hours
in a combined 300 ml/min nitrogen and 300 ml/min hydrogen stream.
The resulting catalyst had the following composition of 3.3%
Rh/3.7% Sm on a 2.19% Co modified alumina support of 30-50 mesh
size (0.297-0595 mm). Physical and morphological characteristics of
the support and the resulting catalyst are given in Table 2. X-ray
diffraction analysis of this sample revealed corundum alumina
(alpha) and CoAl.sub.2O.sub.4/Co.sub.3O.sub.4 spinel in a very
distinct pattern. CoAl.sub.2O.sub.4 spinel was the major component.
Apparently due to the small crystalline size, both Sm and Rh were
undetectable.
Example 8
3.3% h/1.9% Sm on Mg Modified Alumina
[0102] A catalyst containing 3.3% Rh/1.9% Sm on a 5.1% Mg modified
alumina was prepared by similarly like EXAMPLE 7 except that the
cobalt nitrate solution was replaced by a magnesium nitrate
solution. The particle size of resulting catalyst was again 30-50
mesh (0.297-0595 mm). Physical and morphological characteristics of
the support and the resulting catalyst are given in Table 2. Upon
X-ray diffraction analysis, this sample revealed corundum alumina
(alpha) and MgAl.sub.2O.sub.4 spinel components in a very distinct
pattern. Again, the Sm and Rh components were not found due to the
small crystalline size.
Example 9
Rh/Sm on Si Modified Alumina
[0103] A catalyst comprising 3.7% Rh/3.7% Sm on Si modified alumina
was prepared by similarly like EXAMPLE 7 except that the Co nitrate
solution was replaced by a sodium silicate solution (from Aldrich).
The particle size of resulting catalyst was again 30-50 mesh.
Physical and morphological characteristics of the support and the
resulting catalyst are given in Table 2. X-ray diffraction analysis
indicates that the Si impregnated sample was still mainly in the
gamma alumina form, the Si component being very difficult to
identify. As in EXAMPLES 7 and 8, Sm and Rh were not apparent due
to the small crystalline size.
[0104] Catalyst compositions, metal surface area, and metal
dispersion for catalyst EXAMPLES 1-9 are summarized in the Table 2
below.
[0105] The metal surface area of the catalyst is determined by
measuring the dissociative chemical adsorption of H.sub.2 on the
surface of the metal. A Micromeritics ASAP 2010 automatic analyzer
system is used, employing H.sub.2 as a probe molecule. The ASAP
2010 system uses a flowing gas technique for sample preparation to
ensure complete reduction of reducible oxides on the surface of the
sample. A gas such as hydrogen flows through the heated sample bed,
reducing the oxides on the sample (such as platinum oxide) to the
active metal (pure platinum). Since only the active metal phase
responds to the chemisorbate (hydrogen in the present case), it is
possible to measure the active surface area and metal dispersion
independently of the substrate or inactive components. The analyzer
uses the static volumetric technique to attain precise dosing of
the chemisorbate and rigorously equilibrates the sample. The first
analysis measures both strong and weak sorption data in
combination. A repeat analysis measures only the weak (reversible)
uptake of the probe molecule by the sample supports and the active
metal. As many as 1000 data points can be collected with each point
being fully equilibrated. Prior to the measurement of the metal
surface area the sample is pre-treated. The first step is to
pretreat the sample in He for 1 hr at 100.degree. C. The sample is
then heated to 350.degree. C. in He for 1 hr. These steps clean the
surface prior to measurement. Next the sample is evacuated to
sub-atmospheric pressure to remove all previously adsorbed or
chemisorbed species. The sample is then oxidized in a 10%
oxygen/helium gas at 350.degree. C. for 30 minutes to remove any
possible organics that are on the surface. The sample is then
reduced at 400.degree. C. for 3 hours in pure hydrogen gas. This
reduces any reducible metal oxide to the active metal phase. The
sample is then evacuated using a vacuum pump at 400.degree. C. for
2 hours. The sample is then cooled to 35.degree. C. prior to the
measurement. The sample is then ready for measurement of the metal
surface. From the measurement of the volume of H.sub.2 uptake
during the measurement step, it is possible to determine the metal
surface area per gram of catalyst structure by the following
equation.
MSA=(V)(A)(S)(a)/22400/m
[0106] where MSA is the metal surface are in m.sup.2/gram of
catalyst structure;
[0107] V is the volume of adsorbed gas at Standard Temperature and
Pressure in ml.;
[0108] A is the Avogadro constant;
[0109] S is the stoichiometric factor (2 for H.sub.2 chemisorption
on rhodium);
[0110] m is the sample weight in grams; and
[0111] a is the metal cross sectional area.
[0112] As shown in Table 2, in which the metal in the equation is
rhodium, the presence of samarium oxide (Sm.sub.2O.sub.3) helps to
increase metal dispersion and metal surface area on the support
Example A.
[0113] For the Rh-only catalysts with a rhodium metal dispersion
measurement, i.e., Example 1 (4%
Rh/La.sub.2O.sub.3--Al.sub.2O.sub.3) and Example 2 (4% Rh-4%
Sm/La.sub.2O.sub.3--Al.sub.2O.sub.3), the presence of
Sm.sub.2O.sub.3 almost doubles the Rh metal dispersion from 4.5% to
8.5%. The Applicants believe that additional deposit of
Sm.sub.2O.sub.3 on the La.sub.2O.sub.3-modifed Al.sub.2O.sub.3 may
further strengthen the interaction of rhodium with the support and
thus help Rh dispersion.
2TABLE 2 Catalyst Compositions for Examples 1-9 (on modified
Al.sub.2O.sub.3), metal surface area, and rhodium dispersion. Metal
Surface Promoter Area, -m.sup.2/g Metal CATALYST Modifying Active
metal Loading, catalyst dispersion - EXAMPLES agent loading, wt %
wt % structure rhodium, % 1 La 4% Rh 0% Sm 0.8 4.5 2 La 4% Rh 4% Sm
1.5 8.5 3 La 4% Rh 4% Sm 0.53 3.0 4 La 2% Rh 4% Sm 0.35 5.5 5 La 1%
Rh 4% Sm 0.35 8.0 6 La 4% Rh + 4% Ru 0% Sm 1.3 3.7 7 Co 3.33% Rh
3.7% Sm 3.3 -- 8 Mg 3.3% Rh 1.9% Sm 7.7 -- 9 Si 3.7% Rh 3.7% Sm
0.63 --
[0114] Referring back to FIG. 1 which shows the pore size
distribution of the catalyst Example 2, introducing Sm.sub.2O.sub.3
and/or Rh on La.sub.2O.sub.3--Al.sub.2O.sub.3 caused almost no
change to the probabilities of pores with diameter greater than 20
nm, as one compares the pore distribution curves of support
Examples A or B (La.sub.2O.sub.3--Al.sub.2O.sub.3) and catalyst
Example 2 (4% Rh-4% Sm/La.sub.2O.sub.3--Al.sub.2O.sub.3); however,
the probabilities of pores with diameter less than 20 nm decreased
significantly. It is likely that Rh and Sm.sub.2O.sub.3 coated
preferentially on walls of <20 nm pores and reduced the pore
diameter of those pores on support surface.
[0115] The BET surface area, pore volume and average pore diameter
were determined for catalyst Example 2 (see Table 1) and can be
compared to those of the support Example A that was used to make
it. Both pore volume and BET surface area decrease compared to
those of the support (89 versus 89 m.sup.2/g and 0.63 versus 0.54
ml/g respectively) whereas the average pore diameter increases (24
versus 21 nm), which is expected after deposition of both metals
(Rh and Sm). The BET surface area is still quite high despite metal
deposition and additional calcination steps at temperatures greater
than 800.degree. C.
[0116] A temperature-programmed reduction was also performed for
catalyst Examples 1, 2 and 6. The TPR traces of 3 catalyst examples
supported on La.sub.2O.sub.3--Al.sub.2O.sub.3, one with rhodium
(Example 1), one with rhodium and Sm.sub.2O.sub.3 (Example 2), and
one with a rhodium-ruthenium alloy (Example 6). The reduction of
Examples 1, 2 and 6 started at temperatures of 150, 157, and
153.degree. C. respectively. The reduction peak temperature was
177, 183, and 183.degree. C., respectively, again for Example 1, 2
and 6.
[0117] For the alloy-containing Example 6, the reduction peak shape
is quite symmetrical. The single symmetrical reduction peak in the
TPR trace suggests that the Rh and Ru oxide species in this sample
are in intimate contact or may even form a bulk compound in
calcinations step; thus, H.sub.2 may spillover from one site to
sites of different nature once the reduction begins. As a result,
only one single reduction peak was observed for the reduction of
different oxide species (Rh and Ru).
[0118] For the Rh-only Examples 1 and 2, the presence of Sm species
caused the reduction of Rh species to become more difficult--the
reduction starts at higher temperature (150.degree. C. vs.
157.degree. C.) and the reduction peak position was also shifted
from 177.degree. C. to 183.degree. C. for Example 2 with
Sm.sub.2O.sub.3 addition. The difficulty of reduction for Example 2
compared to the reduction of Example 1, indicates that the
interaction between Rh species and support surface is stronger in
the Example 2 [4% Rh-4% Sm/La.sub.2O.sub.3--Al.sub- .2O.sub.3] than
that in Example 1 [4% Rh/La.sub.2O.sub.3--Al.sub.2O.sub.3]- .
Again, the stronger Rh metal and support interaction in Example 2
may contribute to its higher Rh dispersion on surface and metal
surface area than that of Example 1 (see Table 2).
Fixed Bed Reactivity Testing
[0119] These catalyst Examples 1-9 were tested with molecular
oxygen and natural gas as the hydrocarbon feed with a typical
composition of about 93.1% methane, 3.7% ethane, 1.34% propane,
0.25% butane, 0.007% pentane, 0.01% C.sub.5+, 0.31% carbon dioxide,
1.26% nitrogen (with % meaning volume percent). The hydrocarbon
feed was pre-heated at 300.degree. C. and then mixed with O.sub.2.
The reactants were fed into a fixed bed reactor at a carbon to
O.sub.2 molar ratio of 1.87 or a O.sub.2:natural gas mass ratio of
1.05 at gas weight hourly space velocities (GHSV) from about
161,000 to about 635,000 hr.sup.1. The gas hourly space velocity is
defined by the volume of reactant feed per volume of catalyst per
hour. The partial oxidation reaction was carried out in a
conventional flow apparatus using a 12.7 mm I.D. quartz insert
embedded inside a refractory-lined steel vessel. The quartz insert
contained a catalyst bed (comprising of 2.0 g of catalyst
particles, except for Example 7 where 1.65 g was used) held between
two inert 80-ppi alumina foams. The reaction took place for several
days at a pressure of about 90 psig (722 kPa) for Examples 1-6 and
for several hours at a pressure of about 4 psig for Examples 7-9,
and at temperatures at the exit of reactor between about
750.degree. C. and about 1200.degree. C. All the flows were
controlled by mass flow controllers. The reactor effluent as well
as feedstock was analyzed using a gas chromatograph equipped with a
thermal conductivity detector. Pressures at the inlet and outlet on
the reactor were measured by a differential pressure transmitter
which gives the overall pressure drop across the catalytic bed by
subtracting the pressure at the outlet from the pressure at the
inlet.
[0120] The data analyzed include catalyst performance as determined
by conversion and selectivity, and deactivation rate measured for
some over a period of over 100 hours. The catalyst performances
(CH.sub.4 conversion, H.sub.2 and CO selectivity) within a few
hours after reaction ignition are listed in the following Table 3
for Examples 1-8 and the observed deactivation rates are listed in
Table 4 for Examples 1, 2 and 6. Example 9 did not perform very
well, and it should be noted that the metal surface area (ca. 0.63
m.sup.2/g catalyst structure) of this catalyst Example 9 may have
been too low to be an effective catalyst in the partial oxidation
of methane with oxygen.
3TABLE 3 Test data with CH.sub.4 conversion, CO and H.sub.2
selectivity after 6 hours of reaction. Catalyst GHSV, CH.sub.4 CO
H.sub.2 Examples hr.sup.-1 conversion, % selectivity, %
selectivity, % 1 440,000 95 96 96 2 440,000 91 94 95 2* 440,000 94
97 97 3 675,000 91 96 95 4 635,000 91 95 94 5 635,000 93 94 96 6
438,000 91 96 95 7 161,000 95 96 89 8 175,000 96 97 90 *duplicate
run
[0121]
4TABLE 4 Deactivation measured over a time period from 24 to 104
hours at a GHSV of about 440,000 hr.sup.-1. Change in CH.sub.4
Catalyst Pressure Drop, conversion CO selectivity H.sub.2
Selectivity Examples psi loss, % loss, % loss, % 1 0.68 3 1 1 2
0.02 2 1 0 2* 0.03 1 1 1 6 0.20 3 1 1 *duplicate run
[0122] As shown in Table 3, all Examples have very good overall
catalytic performance. towards syngas production. Examples 1 and 2
have the best methane conversion, whereas Examples 1, 2, 3, and 6
have very good selectivity for H.sub.2 and CO. The oxygen
conversion (not shown) was also measured for all tests, and was
above 99% for all Examples. The best overall catalytic performance
is best with Examples 1 and 2 among the catalysts studied (listed
in Table 2). From Table 3, Example 2 runs clearly show the best
reactor performance. For direct comparison run-to-run, the data
were obtained at the same time on stream, for most runs from 6 to
104 hours after reaction initiation. The duplicate runs for Example
2 are nearly equivalent (see Table 3), demonstrating catalyst and
reactor reproducibility.
[0123] Catalyst Examples 7 and 8 performance test results are also
shown in Table. 3. A catalyst containing 3.9% Rh/4.2% Sm on a Co
modified alumina support was prepared the same way as Example 7 and
performed similarly to Example 7 in the laboratory scale fixed
reactor testing. A catalyst containing 3.7% Rh/3.8% Sm on a Mg
modified alumina support was prepared the same way as Example 8 and
performed similarly to Example 8 in the laboratory scale fixed
reactor testing.
[0124] The change of the pressure drop over the course of the tests
reported in Table 4 can be indicative of some catalyst
deactivation. Increasing differential pressure may result from
carbon deposition and/or poly-nuclear aromatic (PNA) formation on
the catalyst surface or reactor system. Loss of methane conversion
also can be indicative of formation of PNAs or PNA-precursors. As
seen in Table 4, Example 2 appears to deactivate at a slower rate
than Examples 1 and 6. Both runs for Example 2 show remarkable
stability in pressure drop over time compared to the other catalyst
examples 1 and 6. It is likely that Example 2 catalyst is less
susceptibility to carbonaceous deposit. Example 1 catalyst exhibits
higher loss of methane conversion than Example 2. Example 6
catalyst exhibits equivalent loss of methane conversion than
Example 1.
[0125] FIG. 3 shows the plots of the methane conversion and product
selectivity for a typical test run of catalyst Example 2,
demonstrating the great stability in partial oxidation of natural
gas, with only 1% loss in methane conversion and product
selectivity for the duration of the run (about 100 hours).
[0126] The examples and testing data show that the catalyst
compositions of the present invention represent an improvement over
prior art catalysts in their ability to resist deactivation over
sustained time periods while maintaining high methane conversion
and hydrogen and carbon monoxide selectivity values. While the
preferred embodiments of the invention have been shown and
described, modifications thereof can be made by one skilled in the
art without departing from the spirit and teachings of the
invention. The embodiments described herein are exemplary only, and
are not intended to be limiting. Many variations and modifications
of the invention disclosed herein are possible and are within the
scope of the invention. Accordingly, the scope of protection is not
limited by the description set out above, but is only limited by
the claims which follow, that scope including all equivalents of
the subject matter of the claims. The disclosures of all issued
patents, patent applications and publications cited herein are
incorporated by reference. The discussion of certain references in
the Description of Related Art, above, is not an admission that
they are prior art to the present invention, especially any
references that may have a publication date after the priority date
of this application.
* * * * *