U.S. patent application number 13/358832 was filed with the patent office on 2012-05-17 for ultra high temperature shift catalyst with low methanation.
This patent application is currently assigned to L'AIR LIQUIDE SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE. Invention is credited to Michael W. Balakos, Chandra Ratnasamy, Jon P. Wagner.
Application Number | 20120121500 13/358832 |
Document ID | / |
Family ID | 41063255 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120121500 |
Kind Code |
A1 |
Wagner; Jon P. ; et
al. |
May 17, 2012 |
ULTRA HIGH TEMPERATURE SHIFT CATALYST WITH LOW METHANATION
Abstract
A water gas shift catalyst for use at temperatures above about
450.degree. C. up to about 900.degree. C. or so comprising rhenium
deposited on a support, preferably without a precious metal,
wherein the support is prepared from a high surface area material,
such as a mixed metal oxide, particularly a mixture of zirconia and
ceria, to which may be added one or more of a high surface area
transitional alumina, an alkali or alkaline earth metal dopant
and/or an additional dopant selected from Ga, Nd, Pr, W, Ge, Fe,
oxides thereof and mixtures thereof.
Inventors: |
Wagner; Jon P.; (Louisville,
KY) ; Balakos; Michael W.; (Buckner, KY) ;
Ratnasamy; Chandra; (Louisville, KY) |
Assignee: |
L'AIR LIQUIDE SOCIETE ANONYME POUR
L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE
Paris
KY
SUD-CHEMIE INC.
Louisville
|
Family ID: |
41063255 |
Appl. No.: |
13/358832 |
Filed: |
January 26, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12048673 |
Mar 14, 2008 |
8119558 |
|
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13358832 |
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Current U.S.
Class: |
423/655 ;
423/656; 502/300; 502/302; 502/304; 502/305; 502/338; 502/340;
502/344; 502/349; 502/355 |
Current CPC
Class: |
B01J 35/1014 20130101;
B01J 23/36 20130101; C01B 3/16 20130101; Y02P 20/52 20151101; B01J
23/10 20130101; B01J 21/066 20130101; B01J 21/06 20130101; Y10S
502/524 20130101; B01J 35/1019 20130101 |
Class at
Publication: |
423/655 ;
502/300; 502/304; 502/344; 502/355; 502/302; 502/305; 502/349;
502/338; 502/340; 423/656 |
International
Class: |
C01B 3/16 20060101
C01B003/16; B01J 21/06 20060101 B01J021/06; B01J 23/889 20060101
B01J023/889; B01J 23/36 20060101 B01J023/36 |
Claims
1. A water gas shift catalyst for use at temperatures above about
450.degree. C. up to about 900.degree. C. comprising rhenium
deposited on a support, wherein the support comprises a high
surface area material with a surface area from about 30 m.sup.2/g
to about 200 m.sup.2/g, and wherein the catalyst does not include a
precious metal selected from the group consisting of platinum,
palladium, rhodium, ruthenium, iridium, osmium, silver, gold and
mixtures thereof.
2. The water gas shift catalyst of claim 1, wherein the high
surface area material comprises two or more metal oxides selected
from the group consisting of oxides of cerium, zirconium,
lanthanum, yttrium, praseodymium, neodymium, samarium, tungsten,
barium, strontium and molybdenum and mixtures thereof.
3. The water gas shift catalyst of claim 1, wherein the high
surface area material comprises a mixed metal oxide comprising two
or more metal oxides selected from the group consisting of
zirconia, ceria, praseodymia and neodymia.
4. The water gas shift catalyst of claim 1, wherein the high
surface area material comprises a transitional phase, high surface
area promoted alumina, wherein the alumina is promoted with an
oxide selected from oxides of cerium, zirconium, lanthanum,
yttrium, praseodymium, neodymium, samarium, tungsten, barium,
strontium and molybdenum and mixtures thereof.
5. The water gas shift catalyst of claim 1, wherein the catalyst
does not include platinum, palladium, rhodium or ruthenium.
6. The water gas shift catalyst of claim 1, wherein rhenium
comprises from about 0.05 to about 10% of the catalyst, by
weight.
7. The water gas shift catalyst of claim 1, wherein the high
surface area material comprises ceria and zirconia.
8. The water gas shift catalyst of claim 7, wherein the support
further comprises praseodymium oxide or neodymium oxide.
9. The water gas shift catalyst of claim 1 further comprising an
alkali or alkaline earth metal dopant.
10. The water gas shift catalyst of claim 9, wherein the dopant is
selected from the group of consisting of sodium, potassium, cesium,
and rubidium oxides and mixtures thereof.
11. The water gas shift catalyst of claim 9, wherein the alkali or
alkaline earth dopant comprises from about 0.1 to about 10% of the
catalyst, by weight.
12. The water gas shift catalyst of claim 1, wherein a dopant is
added to the catalyst selected from the group consisting of Ga, Nd,
Pr, W, Ge and Fe, their oxides and mixtures thereof.
13. A water gas shift catalyst for use at temperatures above about
450.degree. C. up to about 900.degree. C. comprising rhenium
deposited on a support, wherein the support comprises a mixture of
metal oxides comprising zirconia and ceria, and wherein the
catalyst does not include any precious metal from the group
consisting of platinum, palladium, rhodium, ruthenium, iridium,
osmium, silver, gold and mixtures thereof.
14. The catalyst of claim 13, wherein the mixed metal oxides
further comprise praseodymium oxide or neodymium oxide.
15. The water gas shift catalyst of claim 13 further comprising an
alkali or alkaline earth metal dopant.
16. A water gas shift catalyst for use at temperatures above about
450.degree. C. up to about 900.degree. C. comprising rhenium on a
support, wherein the support comprises two or more metal oxides
selected from ceria, zirconia, praseodymia and neodymia, and an
alkali or alkaline earth metal dopant, wherein the catalyst does
not include any precious metal from the group consisting of
platinum, palladium, rhodium, ruthenium, iridium, osmium, silver,
gold and mixtures thereof.
17. A water gas shift process for use at temperatures above about
450.degree. C. up to about 900.degree. C. comprising preparing a
feed stream containing carbon monoxide and steam and passing that
feed stream over a water gas shift catalyst comprising rhenium
deposited on a support, wherein the support comprises a high
surface area material with surface area from about 30 m.sup.2/g to
about 200 m.sup.2/g at a pressure above about 50 psi, (3.4 bar),
wherein the support comprises ceria and zirconia, and wherein the
catalyst does not include any precious metal from the group
consisting of platinum, palladium, rhodium, ruthenium, iridium,
osmium, silver, gold and mixtures thereof.
18. The process of claim 17 wherein the quantity of carbon monoxide
in the feed stream is between about 1 and 15% and a molar steam to
dry gas ratio in the feed stream is from about 0.1 to about 5.
19. The process of claim 17, wherein the support further comprises
praseodymium oxide or neodymium oxide.
20. The process of claim 17, wherein the catalyst further comprises
an alkali or alkaline earth metal dopant.
Description
RELATED APPLICATION
[0001] This Application is a divisional application of application
Ser. No. 12/048,673, filed Mar. 14, 2008.
[0002] The invention relates to water gas shift catalysts,
particularly for use at ultra high temperatures. More particularly,
one embodiment of the invention relates to a water gas shift
catalyst comprising rhenium deposited upon a support, wherein the
support is a high surface area material, such as a mixed metal
oxide. In a further preferred embodiment, no precious metals,
particularly platinum, palladium, ruthenium or rhodium are added to
the catalyst. A further embodiment adds various dopants and/or
additives to the catalyst and/or the support for the catalyst to
enhance its performance.
BACKGROUND OF INVENTION
[0003] Conventional iron-chrome high temperature water gas shift
catalyst typically operate at temperatures from 350.degree. C. to
450.degree. C. and have been proven to be active and stable.
However, there are unique H.sub.2 production designs being
developed where active, stable and selective water gas shift
catalysts are required to operate at much higher temperatures.
These temperatures can occur, for example, in reforming systems
that have been developed for on-site hydrogen production for
industrial and high temperature fuel cell applications. In these
situations the temperature for the first water gas shift stage can
be as high as 900.degree. C., thereby matching the reforming
catalyst exit temperature and/or matching the temperature of the
fuel cell stack. At these temperatures conventional iron-chrome
catalysts degrade due to physical loss of strength. When operated
at these temperatures, these catalysts also are prone to make heavy
hydrocarbons via a Fischer-Tropsch reaction.
[0004] On-site hydrogen production units and high temperature fuel
cell power plants that utilize a fuel cell stack for producing
electricity from a hydrocarbon fuel are known. One example of these
power plants is a molten carbonate or a solid oxide fuel cell where
the operating temperatures are from 600-1000 C. With these systems,
matching the water gas shift catalyst operating temperature to the
reforming catalyst or fuel cell operating temperatures is
beneficial as the system is simplified by elimination of heat
exchangers and other associated equipment and controls.
[0005] The hydrocarbon fuel for such fuel cell stacks can be
derived from a number of conventional fuel sources, with preferred
fuel sources including, but not limited to, natural gas, propane
and LPG.
[0006] In order for the hydrocarbon fuel to be useful in the fuel
cell stack, it must first be converted to a hydrogen rich fuel
stream. After desulfurization, the hydrocarbon fuel stream
typically flows through a reformer, wherein the fuel stream is
converted into a hydrogen rich fuel stream at temperatures up to
900.degree. C. This converted fuel stream contains primarily
hydrogen, carbon dioxide, water and carbon monoxide. The quantity
of carbon monoxide can be fairly high, up to 15% or so.
[0007] Anode electrodes, which form part of the fuel cell stack,
are adversely affected by high levels of carbon monoxide.
Accordingly, it is necessary to reduce the quantity of carbon
monoxide in the fuel stream prior to passing it to the fuel cell
stack. Reduction of the quantity of carbon monoxide is typically
performed by passing the fuel stream through a water gas shift
converter. In addition to reducing the quantity of carbon monoxide
in the fuel stream, such water gas shift converters also increase
the quantity of hydrogen in the fuel stream.
[0008] Water gas shift reactors are well known and typically
contain an inlet for introducing the fuel stream containing carbon
monoxide into a reaction chamber, a down stream outlet, and a
catalytic reaction chamber, which is located between the inlet and
outlet. The catalytic reaction chamber typically contains catalytic
material for converting at least a portion of the carbon monoxide
and water in the fuel stream into carbon dioxide and hydrogen. The
water gas shift reaction is an exothermic reaction represented by
the following formula:
CO+H.sub.2O.revreaction.CO.sub.2+H.sub.2.
[0009] Water gas shift reactions are usually carried out in two
stages: a high temperature stage, at temperatures typically from
about 350.degree. C. to 450.degree. C. and a low temperature stage
at temperatures typically from 180.degree. C. to 240.degree. C.
While the lower temperature reactions favor more complete CO
conversion, the higher temperature reactions allow recovery of the
heat of reaction at a sufficient temperature level to generate high
pressure steam.
[0010] Because of various unique operating conditions, as discussed
above, water gas shift reactions sometimes occur at temperatures
above 550.degree. C. and even as high as 900.degree. C. or so.
However, at these temperatures, the excess production of methane
and the formation of higher hydrocarbons, generally by a Fischer
Tropsch reaction, by the water gas shift catalyst are significant
issues.
[0011] In addition, conventional water gas shift catalysts are not
able to physically withstand these higher operating temperatures.
These high temperatures are experienced in reformer designs where
the high temperature reforming steps are thermally integrated in
so-called heat exchanger reactors. Such high temperatures also
occur when the water gas shift catalysts are thermally integrated
with high temperature fuel cells.
[0012] There are a number of water gas shift catalysts that are
known in the art. For instance, known water gas shift catalysts may
contain chromium, copper or precious metals, preferably platinum,
palladium, rhodium or ruthenium, as the active component, deposited
on a support. In one preferred embodiment Pt and/or Ru and/or Pd
and/or Rh are deposited on a conventional support. Such precious
metal based water gas shift catalyst generally operate at
300.degree. C. to 400.degree. C. Conventional iron-chrome water gas
shift catalysts are generally operated at temperatures from
350.degree. C. to 450.degree. C.
[0013] Notwithstanding the existence of various compositions for
catalysts for use in water gas shift converters, there is still a
need for improvements in the performance of these water gas shift
catalysts, particularly in activity, stability and limitation on
methanation and higher hydrocarbon production at high temperatures
above 550.degree. C. up to 900.degree. C. or so. Further, at these
high temperatures, conventional water gas shift catalysts
physically degrade.
[0014] In addition, when conventional water gas catalysts are
modified to prevent the formation of higher molecular weight
hydrocarbons and by-products, activity of the catalysts is
frequently reduced.
[0015] Many precious metal water gas shift catalysts, particularly
platinum, rhodium, palladium and/or ruthenium-based water gas shift
catalysts, cause methanation of CO and/or CO.sub.2 as a side
reaction when operated at temperatures above about 325.degree. C. A
large quantity of the hydrogen present in the feed stream can be
consumed by these methanation reactions and thereby, reduce the
overall yield of hydrogen. Further, methanation of carbon oxides is
accompanied by a strong exothermic reaction which causes a rapid
temperature increase, thereby making control of the reaction
difficult and reducing the stability of the catalyst.
[0016] For purposes of this disclosure "high or higher temperature"
water gas shift reactions are those that occur at a temperature
greater than about 450.degree. C., generally greater than
550.degree. C. and up to as high as about 900.degree. C., or
so.
[0017] Accordingly, it is one object of one embodiment of the
invention to provide an improved water gas shift catalyst that
retains activity to achieve equilibrium, particularly at high
temperatures.
[0018] It is a further object of one embodiment of the invention to
provide an improved water gas shift catalyst for use at high
temperatures that does not result in any substantial methanation
reactions or the production of substantial quantities of higher
hydrocarbons.
[0019] It is the further object of one embodiment of the invention
to provide an improved water gas shift catalyst with increased
stability over the lifetime of the catalyst.
[0020] It is further object of one embodiment of the invention to
provide a process for the preparation of these improved water gas
shift catalysts.
[0021] It is understood that the forgoing detailed description is
explanatory only and not restrictive of the invention.
SUMMARY OF THE INVENTION
[0022] In accordance with one embodiment of the invention, there is
provided an improved water gas shift catalyst for high temperature
reactions comprising rhenium deposited upon a support, wherein the
support comprises a high surface area material, preferably a metal
oxide support.
[0023] A further embodiment of the invention comprises an improved
water gas shift catalyst, especially for use at high temperatures
with low methanation and reduced production of higher hydrocarbons,
comprising rhenium deposited upon a support, wherein the support
comprises a high surface area material, preferably a metal oxide
support, and wherein no precious metals are added to the catalyst,
particularly platinum, rhodium, palladium or ruthenium.
[0024] A further embodiment of the invention comprises an improved
water gas shift catalyst for use at high temperatures comprising
rhenium deposited upon a support without a precious metal dopant,
wherein the support comprises a high surface area material,
preferably a metal oxide and an alumina, preferably a transitional
phase, high surface area alumina, more preferably gamma
alumina.
[0025] A further embodiment of the invention comprises an improved
water gas shift catalyst for use at high temperatures comprising
rhenium deposited upon a support without a precious metal dopant,
wherein the support comprises a high surface area material,
preferably a metal oxide, wherein an alkali or alkaline earth metal
dopant is added to the catalyst and/or the support.
[0026] A further embodiment of the invention comprises a water gas
shift reaction for use at high temperatures whereby at least a
portion of the carbon monoxide and water in a fuel stream is
converted to hydrogen and carbon dioxide by utilization of a
catalyst comprising rhenium deposited on a support, preferably
without a precious metal dopant, wherein the support comprises a
high surface area material, particularly a metal oxide and wherein
there is low production of methane and higher hydrocarbons.
[0027] A further embodiment of the invention comprises a process
for the preparation of an improved water gas shift catalyst for use
in high temperatures with low methanation and low production of
higher hydrocarbons comprising preparing or selecting a support,
wherein the support comprises a high surface area material,
preferably a metal oxide support, wherein the metal oxides are
selected from cerium oxide, zirconium oxide, titanium oxide,
silicon oxide, neodymium oxide, praseodymium oxide, yttrium oxide,
samarium oxide, lanthanum oxide, tungsten oxide, molybdenum oxide,
calcium oxide, chromium oxide, magnesium oxide, barium oxide,
strontium oxide, and mixtures thereof. In one preferred embodiment,
at least two of these metal oxides are mixed to form the high
surface area support. In a more preferred embodiment, the mixed
metal oxides comprise zirconia and ceria. Following preparation or
selection of the support, rhenium, preferably with no precious
metal dopants, and optionally with an alkali or alkaline earth
metal oxide dopant, are deposited or impregnated on the support of
the catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 compares the methane production of three catalysts on
a ceria/zirconia support, wherein the active metal component on the
catalysts comprise respectively, platinum and rhenium, platinum
alone or rhenium alone operated at various temperatures up to
450.degree. C. and at a pressure of 225 psig (15.8 bar).
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
[0029] The water gas shift catalyst for use at high temperature of
one embodiment comprises rhenium deposited upon a support, wherein
the support comprises a high surface area material. For purposes of
this disclosure "high surface area" means from about 30 to about
200 m.sup.2/g prior to usage in a reactor.
[0030] One preferred high surface area material is a metal oxide,
which may be selected from the following: zirconia, ceria, titania,
silica, lanthana, praseodymium oxide, neodymium oxide, yttria,
samarium oxide, tungsten oxide, molybdenum oxide, calcium oxide,
chromium oxide, manganese oxide, barium oxide, strontium oxide and
magnesium oxide. One particularly preferred support comprises a
mixed metal oxide with the metal oxides selected from the foregoing
list, preferably comprising zirconia and ceria with the preferred
ratio of zirconia to ceria being about 1 to about 10 to about 10 to
about 1. In another particularly preferred embodiment, praseodymia
and/or neodymia are added to the ceria/zirconia support. Each of
the praseodymia and/or neodymia preferably comprises from about 1%
to about 30% of the support, by weight. When both are present in
the support, the ratio of the praseodymia to the neodymia is
preferably from 1 to 1 to about 3 to 1.
[0031] The mixed metal oxide support can be produced by blending
together the metal oxides using conventional procedures or the
mixed metal oxides can be purchased from conventional sources
separately or after combination of the separate metal oxides.
[0032] Alternatively, the high surface area material may comprise a
promoted alumina, preferably gamma alumina, promoted with dopants
including oxides selected from cerium, zirconium, lanthanum,
yttrium, praseodymium, neodymium, samarium, tungsten, barium,
strontium and molybdenum and the like and mixtures thereof. One
particularly preferred high surface area material comprises gamma
alumina promoted with ceria, zirconia and barium oxide.
[0033] In a further alternative embodiment, the high surface area
material comprises a high surface ceria, titania, zirconia, or
silica and mixtures thereof.
[0034] To form the support, the high surface area materials, if
multiple materials are used, are physically mixed by conventional
procedures. Conventional liquids, such as water and/or acetic acid
are preferably added to the high surface area materials to permit
them to be processed, for example, by extrusion, to form
extrudates, or to form tablets, or to form a slurry to be
washcoated on a conventional monolith or other substrate.
[0035] In a particularly preferred embodiment, no precious metal is
added to the catalyst of the invention. Many prior art water gas
shift catalysts have contained as the active metal component one or
more precious metals, preferably platinum, rhodium, palladium
and/or ruthenium. For purposes of this disclosure, "precious
metals" include gold, silver, platinum, palladium, iridium,
rhodium, osmium, and ruthenium.
[0036] The inventors have surprisingly discovered that when water
gas shift catalysts containing these precious metals are utilized
in water gas shift reactions conducted at temperatures of the
feedstream greater than about 325.degree. C., and certainly at
temperatures greater than 450.degree. C., methane is often produced
by the catalysis of CO or CO.sub.2 with hydrogen. The production of
methane during the water gas shift reaction is a side reaction that
reduces the quantity of hydrogen that is present in the feed stream
and also increases the temperature of the feedstream, because the
methanation reaction is highly exothermic. Because hydrogen
production is diminished by this methanation reaction, the
methanation reaction is a major disadvantage from the use of
precious metal water gas shift catalyst at high temperatures.
[0037] The inventors have surprising discovered that when the
precious metal(s) are removed from these catalysts and replaced
with rhenium, the production of methane is substantially reduced
and the CO conversion is maintained at adequate levels when the
temperature of the WGS reaction is greater than about 450.degree.
C., particularly when it is greater than 550.degree. C., up to
about 900.degree. C. or so. This was a surprising result and
unanticipated as it was assumed that a rhenium based catalyst would
react in a similar manner to prior art precious metal based water
gas shift catalysts. Thus, in a preferred embodiment the catalyst
of the invention does not include any precious metals, even though
precious metals, particularly platinum, palladium, rhodium and/or
ruthenium, have been utilized on high temperature water gas shift
catalysts of the prior art.
[0038] The inventors have also surprisingly discovered that when
precious metals are removed from WGS catalysts and replaced with
rhenium, the levels of higher hydrocarbons are also reduced when
the water gas reaction occurs at high temperatures greater than
about 325.degree. C., especially at temperatures above about
450.degree. C.
[0039] The quantity of the rhenium that is deposited on the support
is from about 0.05 to about 10% by weight, preferably from about
0.1 to about 5% by weight.
[0040] In an alternative embodiment, there is added to the high
surface area material, up to about 40%, by weight, of an alumina.
The preferred alumina is a transitional phase, high surface area
alumina, more preferably a gamma alumina, with a surface area
greater then about 200 m.sup.2/g. The alumina is blended with the
high surface area material to assist in binding the support
materials together. By use of the transitional phase, high surface
area alumina, a support with improved mechanical stability,
especially at higher temperatures, is produced. (The referenced
"support" is the support for the rhenium and other dopants, if any,
and does not refer to the use of a monolith or other such
mechanical support used with a catalytic coating.)
[0041] In an alternative embodiment, an alkali or alkaline earth
metal oxide is added to the support as a dopant, preferably
comprising from about 0.1 to about 10% by weight, and more
preferably 1.0 to 1.5%, by weight of the support. In a preferred
embodiment the dopant is an alkali metal oxide selected from
sodium, potassium, cesium and rubidium oxides and mixtures thereof
with sodium and/or potassium oxides particularly preferred. When an
alkali or alkaline earth metal dopant is added, it can be added to
the support with the rhenium or it can be combined with the other
components of the support at any stage in the processing of the
support. The dopant can be added by conventional procedures, such
as impregnation. In a preferred embodiment, the alkali or alkaline
earth metal dopant is impregnated into the support after
formulation of the support.
[0042] In a further preferred embodiment, additional dopants may be
added to the catalyst which dopants are selected from Ga, Nd, Pr,
W, Ge, and Fe, and their oxides and mixtures thereof, with Ga and
Nd and their oxides preferred.
[0043] Once the support has been prepared, the rhenium, alkali or
alkaline earth metal oxide dopant, and additional dopant, if
desired, are deposited upon the support using conventional
procedures, such as impregnation. In one preferred procedure the
rhenium and dopants, if desired, are impregnated onto the support
material in the form of a salt or other type of solution. For
example, for the deposition of rhenium, the support material is
immersed in a rhenium solution, such as perrhenic acid, and then
dried and calcined at a temperature from about 350.degree. to about
650.degree. C. for about 1 to about 5 hours to transform the
rhenium salt to rhenium oxide. Depending upon the target loading,
multiple impregnation steps may be needed.
[0044] After formation of the water gas shift catalyst, its surface
area is preferably at least about 30 m.sup.2/g, more preferably
from about 40 to about 100 m.sup.2/g.
[0045] The water gas shift catalyst of the preferred embodiment
preferably is produced in the form of moldings, especially in the
form of spheres, pellets, rings, tablets or extruded products, in
which the later are formed mostly as solid or hollow objects in
order to achieve higher geometric surfaces with a simultaneously
low resistance to flow. Alternatively, monoliths, or other
substrates, are coated with the catalytic materials as preferred
embodiments.
[0046] The catalyst is preferably employed in a process in which
carbon monoxide and steam are converted to hydrogen and carbon
dioxide at a temperature above 450.degree. C., preferably above
550.degree. C., and up to about 900.degree. C. or so and under
pressures above ambient, preferably above about 50 psi (3.4 bar),
more preferably above about 100 psi (6.9 bar), and most preferably
above about 150 psi (10.3 bar) up to about 400 psi, (28 bar) or
so.
[0047] In a preferred embodiment the carbon monoxide comprises from
about 1 to about 15% of the feed stream and the molar ratio of the
steam to the dry gas is from about 0.1 to about 5.
[0048] It has surprisingly been discovered that there is adequate
CO conversion in comparison to the performance of conventional
water gas shift catalysts when the catalysts of the disclosed
embodiments are used at high temperatures with a significant
reduction in methanation and other hydrocarbon by-products.
[0049] It has also been surprisingly discovered that adequate water
gas shift activity is retained even without the presence of
precious metals on the catalyst, particularly platinum, rhodium,
palladium and/or ruthenium.
[0050] Further, it was surprisingly discovered that catalysts of
the invention retain adequate water gas shift conversions even at
temperatures greater than 450.degree. C. with reduced methanation,
even when the temperature of the feedstream approaches 900.degree.
C. or so.
EXAMPLES
[0051] Catalysts in the form of tablets are produced for use in a
reactor. Each catalysts is prepared on a ceria/zirconia support.
The ceria/zirconia support is purchased from a conventional
supplier and comprises 80% ceria and 20% zirconia. Impregnated on
the support is one of the following: a) 0.5% platinum in the form
of platinum oxide b) 0.38% rhenium in the form of rhenium oxide or
c) 0.5% of a combination of 0.25% rhenium and 0.25% platinum in the
form of rhenium oxide and platinum oxide combined. A water gas
shift reaction for each catalyst is run at varying temperatures and
at a pressure of 225 psig (15.5 bar). At temperatures of
400.degree. C. and especially at temperatures of 450.degree. C.,
the catalyst comprising rhenium oxide on the ceria/zirconia support
produce the least quantity of methane in the exit gas. The
production of methane for each of the three catalysts at different
temperatures is shown on FIG. 1.
[0052] The conditions of the reactor are a dry gas inlet comprising
10% CO, 15% CO.sub.2, 10% N.sub.2, with the remaining amount
comprising hydrogen. The temperature within the reactor is set at
different temperatures from 200.degree. C. to 450.degree. C. The
pressure is 225 psig (15.5 bar) with a DGSV of 27,200 l/hr, a wet
gas space velocity of 40,000 l/hr and a S/G ratio of 0.47. The gas
stream is passed over a catalyst bed under these conditions for
various hours on stream.
[0053] From this information it is clear that catalysts comprising
rhenium deposited on a support comprising high surface area
materials produce a water gas shift catalyst with lower production
of methane at temperatures of 400.degree. C. and 450.degree. C.
[0054] Accordingly, the inventors have discovered that catalysts
utilizing rhenium deposited on a support prepared from one or more
high surface area materials when operated high temperatures
retained adequate water gas shift activity with low methanation and
reduced production of higher hydrocarbons in comparison to precious
metal based WGS catalysts.
[0055] The inventors have also discovered that the performance of
these catalysts may be improved by the addition of a high surface
area transitional alumina, preferably gamma alumina, as an
additional component of the support.
[0056] The inventors have also discovered that the performance of
these catalysts may be further improved by impregnating the
catalysts with dopants selected from Ga, Nd, Pr, W, Ge, and Fe and
their oxides and mixtures thereof.
[0057] Although one or more embodiments of the invention have been
described in detail, it is clearly understood that the descriptions
are in no way to be taken as limitations. The scope of the
invention can only be limited by the appended claims.
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