Title: Nickel-rhodium based catalysts for synthesis gas production
Abstract: A nickel-rhodium alloy based catalyst for catalyzing the production of synthesis gas from a light hydrocarbon and O.sub.2 by a net catalytic partial oxidation process is disclosed. Preferred nickel-rhodium alloy based catalysts comprise about 1-50 weight percent nickel and about 0.01-10 weight percent rhodium on a porous refractory support structure. In certain embodiments, the catalyst also contains a lanthanide element, zirconium, cobalt, manganese or magnesium.
Patent Number: 6,878,667 Issued on 04/12/2005 to Gaffney, et al.
| Inventors:
|
Gaffney; Anne M. (West Chester, PA);
Corbin; David R. (West Chester, PA)
|
| Assignee:
|
ConocoPhillips Company (Houston, TX)
|
| Appl. No.:
|
125717 |
| Filed:
|
April 18, 2002 |
| Current U.S. Class: |
502/241; 502/242; 502/251; 502/252; 502/259; 502/302; 502/303; 502/324; 502/326; 502/327; 502/328 |
| Intern'l Class: |
B01J 021//08 |
| Field of Search: |
502/241,242,251,252,259,302,303,324,326,327,328,335
|
References Cited [Referenced By]
U.S. Patent Documents
| 3334055 | Aug., 1967 | Dowden et al. | 252/273.
|
| 3953363 | Apr., 1976 | Yamauchi et al. | 252/443.
|
| 4209424 | Jun., 1980 | Le Goff et al. | 252/454.
|
| 4325842 | Apr., 1982 | Slaugh et al. | 252/443.
|
| 4444898 | Apr., 1984 | Schwartz et al.
| |
| 4690777 | Sep., 1987 | Valenyi et al. | 252/373.
|
| 4877550 | Oct., 1989 | Goetsch et al. | 252/373.
|
| 5039510 | Aug., 1991 | Pinto.
| |
| 5149464 | Sep., 1992 | Green et al. | 252/373.
|
| 5447705 | Sep., 1995 | Petit et al. | 423/418.
|
| 5500149 | Mar., 1996 | Green et al. | 252/373.
|
| 5510056 | Apr., 1996 | Jacobs et al. | 252/373.
|
| 5648582 | Jul., 1997 | Schmidt et al. | 585/652.
|
| 5653774 | Aug., 1997 | Bhattacharyya et al. | 48/198.
|
| 5744419 | Apr., 1998 | Choudhary et al. | 502/326.
|
| 6060420 | May., 2000 | Munakaa et al. | 502/302.
|
| 6254807 | Jul., 2001 | Schmidt et al.
| |
| 6447745 | Sep., 2002 | Feeley et al.
| |
| 2002/0002794 | Jan., 2002 | Figueroa et al.
| |
| 2002/0004450 | Jan., 2002 | Gaffney et al.
| |
| 2002/0012624 | Jan., 2002 | Figueroa et al.
| |
| 2002/0035036 | Mar., 2002 | Figueroa et al.
| |
| 2002/0172642 | Nov., 2002 | Dindi et al.
| |
| 2003/0045423 | Mar., 2003 | Dindi et al.
| |
| 2003/0083198 | May., 2003 | Xu et al. | 502/527.
|
| Foreign Patent Documents |
| 0333037 | Mar., 1989 | EP | .
|
| 1040066 | Aug., 1966 | GB.
| |
| 2008147 | May., 1979 | GB.
| |
Other References
Chemical Abstracts CA 130:5518 Basile et Al Studies in Surface Science and
Catalyst 1998, vol. 119 pp. 693-698.*
Catalyst Behaviour of Ni and Rh containing Catalyst in Partial Oxidation of
Methane at Short Residence Times. F. Basini et Al CA 130:5518 from Natural
Gas Conversion V 1998 PP693-698.*
Xu, Xiaoding, and Jacob A. Moulijn (Chapter 21), Transformation of a
Structural Carrier into a Structured Catalyst in Structured Catalysts and
Reactors, (Andrzej Cybulski and Jacob A. Moulijn, eds.), Marcel Dekker,
Inc. 599-615 (1998).
Claridge, John B., York, Andrew P.E., Brungs, Attila J., Alvarez, Carlos
Marquez-, Sloan, Jeremy, Tsang, Shik Chi, and Malcolm Green, L.H., New
Catalysts for the Conversion of Methane to Synthesis Gas: Molybdenum and
Tungsten Carbide, Journal of Catalysis 180, 85-100 (1998).
Vernon, Patrick D. F., Green, Malcolm L.H., Cheetham, Anthony K. and
Ashcroft, Alexander T., Partial Oxidation of Methane to Synthesis Gas,
Catalysis Letters 6, 181-186, (1990).
Choudhary, V.R., Uphade, B.S., and Mamman A.S., Oxidative Conversion of
Methane to Syngas over Nickel Supported on Commercial Low Surface Area
Porous Catalyst Carriers Precoated with Alkaline and Rare Earth Oxides,
Journal of Catalysis 172, 281-293 (1997).
Choudhary, V.R., Rajput, A.M., and Mamman, A.S., NiO-Alkaline Earth Oxide
Catalysts for Oxidative Methane-to-Syngas Conversion: Influence of
Alkaline Earth Oxide on the Surface Properties and Temperature-Programmed
Reduction/Reaction by H.sub.2 and Methane, Journal of Catalysis 178,
576-585 (1998).
Choudhary, V.R., Uphade, B.S. and Mamman, A.S., Large enhancement in
methane-to-syngas conversion activity of supported Ni catalysts due to
precoating of catalyst supports with MgO, CaO or rare-earth oxide,
Catalysis Letters 32, 387-390 (1995).
PCT Search Report for PCT/US00/28648.
V.R. Choudhary, S.D. Sansare and A.S. Mamman, Low-temperature selective
oxidation of methane to carbon monoxide and hydrogen over cobalt-MgO
catalysts, Applied Catalysis A: General, 90 (1992) Li-L5.
V.R. Coudhary, A.S. Mamman, S.D. Sansare, Selective Oxidation of Methane to
CO and H.sub.2 over Ni/MgO at Low Temperatures, COMMUNICATIONS, Angew.
Chem. Int. Ed. Engl. (1992) 31, No. 9, 1189-1190.
Y.H. Hu and E. Ruckenstein, Binary MgO-Based Solid Solution Catalysts for
Methane Conversion to Syngas, Catalysts Reviews, 44(3) (2002) 423-453.
|
Primary Examiner: Bos; Steven
Assistant Examiner: Wright, Sr.; William G.
Attorney, Agent or Firm: Conley Rose P.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. patent application Ser. No.
09/687,684 filed Oct. 13, 2000 now U.S. Pat. No. 6,409,940 which claims
the benefit under 35 U.S.C. 111(b) of U.S. Provisional Patent Application
No. 60/160,100 filed Oct. 18, 1999, the disclosure of both said
applications is incorporated herein by reference.
Claims
What is claimed is:
1. A supported catalyst comprising a catalytic nickel-rhodium alloy, a
support structure and at least one other metal selected from the group
consisting of lanthanide elements, zirconium, manganese and magnesium,
said catalyst having activity for catalyzing the partial oxidation of
methane to synthesis gas under partial oxidation promoting conditions in a
short contact time reactor.
2. The catalyst of claim 1 comprising about 1-50 weight percent nickel and
about 0.01-10 weight percent rhodium.
3. The catalyst of claim 1 wherein said support structure comprises a
substance chosen from the group consisting of spinels, perovskites,
magnesium oxide, pyrochlores, brownmillerites, zirconium phosphate,
magnesium stabilized zirconia, zirconia stabilized alumina, silicon
carbide, yttrium stabilized zirconia, calcium stabilized zirconia, yttrium
aluminum garnet, alumina, cordierite, ZrO.sub.2, MgAl.sub.2 O.sub.4,
SiO.sub.2 and TiO.sub.2, said rhodium and nickel being disposed on said
support structure.
4. The catalyst of claim 3 wherein said support structure comprises a
substance chosen from group consisting of spinels, perovskites,
pyrochlores and brownmillerites.
5. The catalyst of claim 3 wherein said substance is a refractory oxide.
6. The catalyst of claim 1 wherein said support structure comprises a foam
structure.
7. The catalyst of claim 6 wherein said foam structure comprises about
12-60 pores per centimeter of structure.
8. The catalyst of claim 5 wherein said support structure comprises a
honeycomb monolith structure.
9. The catalyst of claim 1 comprising 1 wt % rhodium, 3 wt % manganese and
13 wt % nickel on a MgAl.sub.2 O.sub.4 support structure.
10. The catalyst of claim 1 comprising 1 wt % rhodium and LaZr.sub.0.5
Ni.sub.0.5 O.sub.3.
11. The catalyst of claim 1 comprising Rh.sub.0.02 Ni.sub.0.03 Mg.sub.0.9
O.
12. The catalyst of claim 1 comprising rhodium, nickel and cobalt on a
support structure comprising ZrO.sub.2.
13. The catalyst of claim 1 comprising rhodium and nickel on a support
structure comprising Al.sub.2 O.sub.3.
14. The catalyst of claim 13 comprising 1% rhodium, 10.9% nickel and 8.6%
magnesium on a support structure comprising 99% Al.sub.2 O.sub.3.
15. The supported catalyst of claim 1 wherein said at least one other metal
comprises a lanthanide element.
16. The supported catalyst of claim 15 wherein said lanthanide element
comprises lanthanum.
17. The supported catalyst of claim 1 wherein said a least one other metal
comprises zirconium.
18. The supported catalyst of claim 1 wherein said at least one other metal
comprises manganese.
19. The supported catalyst of claim 1 wherein said at least one other metal
comprises magnesium.
20. The supported catalyst of claim 1 wherein said support structure
comprises a monolith.
21. The supported catalyst of claim 1 wherein said support structure
comprises a refractory metal oxide.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes for producing synthesis gas from
light hydrocarbons (e.g., natural gas) and oxygen. More particularly, the
invention relates to supported nickel-rhodium based catalysts, their
methods of making, and to processes employing such catalysts for net
partial oxidation of light hydrocarbons (e.g., natural gas) to products
comprising CO and H.sub.2.
2. Description of Related Art
Large quantities of methane, the main component of natural gas, are
available in many areas of the world, and natural gas is predicted to
outlast oil reserves by a significant margin. However, most natural gas is
situated in areas that are geographically remote from population and
industrial centers. The costs of compression, transportation, and storage
make its use economically unattractive.
To improve the economics of natural gas use, much research has focused on
methane as a starting material for the production of higher hydrocarbons
and hydrocarbon liquids. The conversion of methane to hydrocarbons is
typically carried out in two steps. In the first step, methane is reformed
with water to produce carbon monoxide and hydrogen (i.e., synthesis gas or
syngas). In a second step, the syngas is converted to hydrocarbons, for
example, using the Fischer-Tropsch process to provide fuels that boil in
the middle distillate range, such as kerosene and diesel fuel, and
hydrocarbon waxes.
Current industrial use of methane as a chemical feedstock proceeds by the
initial conversion of methane to carbon monoxide and hydrogen by either
steam reforming, which is the most widespread process, or by dry
reforming. Steam reforming currently is the major process used
commercially for the conversion of methane to synthesis gas, proceeding
according to Equation 1.
CH.sub.4 +H.sub.2 O{character pullout}CO+3H.sub.2 (1)
Although steam reforming has been practiced for over five decades, efforts
to improve the energy efficiency and reduce the capital investment
required for this technology continue.
The catalytic partial oxidation of hydrocarbons, e.g., natural gas or
methane to syngas is also a process known in the art. While currently
limited as an industrial process, partial oxidation has recently attracted
much attention due to significant inherent advantages, such as the fact
that significant heat is released during the process, in contrast to steam
reforming processes.
In catalytic partial oxidation, natural gas is mixed with air,
oxygen-enriched air, or oxygen, and introduced to a catalyst at elevated
temperature and pressure. The partial oxidation of methane yields a syngas
mixture with a H.sub.2 :CO ratio of 2:1, as shown in Equation 2.
CH.sub.4 +1/2O.sub.2 {character pullout}CO+2H.sub.2 (2)
This ratio is more useful than the H.sub.2 :CO ratio from steam reforming
for the downstream conversion of the syngas to chemicals such as methanol
and to fuels. The partial oxidation is also exothermic, while the steam
reforming reaction is strongly endothermic. Furthermore, oxidation
reactions are typically much faster than reforming reactions. This allows
the use of much smaller reactors for catalytic partial oxidation
processes. The syngas in turn may be converted to hydrocarbon products,
for example, fuels boiling in the middle distillate range, such as
kerosene and diesel fuel, and hydrocarbon waxes by processes such as the
Fischer-Tropsch Synthesis.
The selectivities of catalytic partial oxidation to the desired products,
carbon monoxide and hydrogen, are controlled by several factors, but one
of the most important of these factors is the choice of catalyst
composition. Difficulties have arisen in the prior art in making such a
choice economical. Typically, catalyst compositions have included precious
metals and/or rare earths. The large volumes of expensive catalysts needed
by prior art catalytic partial oxidation processes have placed these
processes generally outside the limits of economic justification.
For successful operation at commercial scale, the catalytic partial
oxidation process must be able to achieve a high conversion of the methane
feedstock at high gas hourly space velocities, and the selectivity of the
process to the desired products of carbon monoxide and hydrogen must be
high. Such high conversion and selectivity must be achieved without
detrimental effects to the catalyst, such as the formation of carbon
deposits ("coke") on the catalyst, which severely reduces catalyst
performance. Accordingly, substantial effort has been devoted in the art
to the development of catalysts allowing commercial performance without
coke formation.
A number of process regimes have been proposed in the art for the
production of syngas via catalyzed partial oxidation reactions. For
example, the process described in U.S. Pat. No. 4,877,550 employs a syngas
generation process using a fluidized reaction zone. Such a process
however, requires downstream separation equipment to recover entrained
supported-nickel catalyst particles.
To overcome the relatively high pressure drop associated with gas flow
through a fixed bed of catalyst particles, which can prevent operation at
the high gas space velocities required, various structures for supporting
the active catalyst in the reaction zone have been proposed. U.S. Pat. No.
5,510,056 discloses a monolithic support such as a ceramic foam or fixed
catalyst bed having a specified tortuosity and number of interstitial
pores that is said to allow operation at high gas space velocity.
Catalysts used in that process include ruthenium, rhodium, palladium,
osmium, iridium, and platinum. Data are presented for a ceramic foam
supported rhodium catalyst at a rhodium loading of from 0.5-5.0 wt %.
U.S. Pat. No. 5,648,582 discloses a process for the catalytic partial
oxidation of methane at space velocities of 800,000 hr.sup.-1 to
12,000,000 hr.sup.-1 on certain supported Rh, Ni or Pt catalysts. The
exemplified catalysts are rhodium and platinum, at a loading of about 10
wt %, on alumina foams. The small catalyst bed used in this process is
said to eliminate hot spots which are typical of relatively thick catalyst
beds.
Catalysts containing Group VIII metals such as nickel or rhodium on a
variety of supports are known in the art. For example, V. R. Choudhary et
al. ("Oxidative Conversion of Methane to Syngas over Nickel Supported on
Low Surface Area Catalyst Porous Carriers Precoated with Alkaline and Rare
Earth Oxides," J. Catalysis 172:281-293 (1997)) disclose the partial
oxidation of methane to syngas at contact times of 4.8 ms (at STP) over
supported nickel catalysts at 700 and 800.degree. C. The catalysts were
prepared by depositing NiO--MgO on different commercial low surface area
porous catalyst carriers consisting of refractory compounds such as
SiO.sub.2, Al.sub.2 O.sub.3, SiC, ZrO.sub.2 and HfO.sub.2. The catalysts
were also prepared by depositing NiO on the catalyst carriers with
different alkaline and rare earth oxides such as MgO, CaO, SrO, BaO,
Sm.sub.2 O.sub.3 and Yb.sub.2 O.sub.3.
U.S. Pat. No. 4,690,777 also discloses catalysts comprising Group VIII
metals, such as Ni, on porous supports, for use in reforming hydrocarbons
to produce CO and H.sub.2.
U.S. Pat. No. 5,149,464 discloses a method for selectively converting
methane to syngas at 650.degree. C. to 950.degree. C. by contacting the
methane/oxygen mixture with a solid catalyst comprising a supported
d-Block transition metal, transition metal oxide, or a compound of the
formula M.sub.x M'.sub.y O.sub.z wherein M' is a d-Block transition metal
and M is Mg, B, Al, GA, Si, Ti, Xr, Hf or a lanthanide.
U.S. Pat. No. 5,500,149 discloses various transition metals that can act as
catalysts in the reaction CO.sub.2 +CH.sub.4.fwdarw.2CO+2H.sub.2, and
demonstrates how reaction conditions can affect the product yield. The
partial oxidation of methane to synthesis gas using various transition
metal catalysts under a range of conditions has been described by Vernon,
D. F. et al. (Catalysis Letters 6:181-186 (1990)). European Pat. App. Pub.
No. 640561 discloses a catalyst for the catalytic partial oxidation of
hydrocarbons comprising a Group VIII metal on a refractory oxide having at
least two cations.
U.S. Pat. No. 5,447,705 discloses a catalyst having a perovskite
crystalline structure and the general composition: Ln.sub.x A.sub.1-y
B.sub.y O.sub.3, wherein Ln is a lanthanide and A and B are different
metals chosen from Group IVb, Vb, VIb, VIIb or VIII of the Periodic Table
of the Elements.
U.S. Pat. No. 5,653,774 discloses a nickel-containing catalyst for
preparing synthesis gas which are prepared by heating hydrotalcite-like
compositions having the general formula:
[M.sup.2+.sub.(1-X) M.sub.x.sup.3+ (OH.sub.2)].sup.x+
(A.sub.x/n.sup.n-1).multidot.mH.sub.2 O.
A previous attempt at synthesis gas production by catalytic partial
oxidation to overcome some of the disadvantages and costs typical of steam
reforming is described in European Patent No. EPO 0 303 438, entitled
"Production of Methanol from Hydrocarbonaceous Feedstock."
One disadvantage of many of the existing catalytic hydrocarbon conversion
methods is the need to include steam in the feed mixture to suppress coke
formation on the catalyst. Another drawback of some of the existing
processes is that the catalysts that are employed often result in the
production of significant quantities of carbon dioxide, steam, and C.sub.2
+ hydrocarbons. Also, large volumes of expensive catalyst are typically
required in order to achieve satisfactory conversion of the feed gas, and
to achieve the necessary level of selectivity for CO and H.sub.2 products.
None of the existing processes or catalysts are capable of providing high
conversion of reactant gas and high selectivity of CO and H.sub.2 reaction
products. Accordingly, there is a continuing need for a process and
catalyst for the catalytic partial oxidation of hydrocarbons, particularly
methane, or methane containing feeds, in which the catalyst retains a
higher level of activity and selectivity to carbon monoxide and hydrogen
under conditions of high gas space velocity, elevated pressure and high
temperature.
SUMMARY OF THE INVENTION
The present invention provides catalysts and processes for preparing
synthesis gas from any gaseous hydrocarbon having a low boiling point
(e.g. C.sub.1 -C.sub.5 hydrocarbons, particularly methane, or methane
containing feeds) and a source of molecular oxygen. One advantage of the
new catalysts is that they retain a high level of activity and selectivity
to carbon monoxide and hydrogen under conditions of high gas space
velocity, elevated pressure and high temperature.
The new processes of the invention are particularly useful for converting
gas from naturally occurring reserves of methane which contain carbon
dioxide. Another advantage of the new catalysts and processes is that they
are economically feasible for use in commercial-scale conditions. In a
short contact time reactor, the new Ni--Rh based catalysts are highly
active for catalyzing the oxidation of methane to syngas by an overall or
net partial oxidation process. "Net partial oxidation" means that the
partial oxidation reaction predominates over reforming reactions, and the
ratio of the H.sub.2 :CO products is about 2. The short contact time
reactor permits the reactant gas mixture to contact or reside on the
catalyst for no longer than about 10 milliseconds, operating at high space
velocities.
In accordance with certain embodiments of the present invention a supported
catalyst is provided for catalyzing the net partial oxidation of a
hydrocarbon. The supported catalyst contains about 1-50 weight percent
nickel and about 0.01-10 weight percent rhodium, and a support structure.
Preferably, the support structure comprises a spinet, a perovskite,
magnesium oxide, a pyrochlore, a brownmillerite, zirconium phosphate,
magnesium stabilized zirconia, zirconia stabilized alumina, silicon
carbide, yttrium stabilized zirconia, calcium stabilized zirconia, yttrium
aluminum garnet, alumina, cordierite, ZrO.sub.2, MgAl.sub.2 O.sub.4,
SiO.sub.2 or TiO.sub.2. The rhodium and nickel are disposed on or within
the support structure. In some of the more preferred embodiments, the
catalyst support structure is a spinet, a perovskite, a pyrochlore or a
brownmillerite, and the nickel-rhodium alloy is incorporated into the
support structure. In some embodiments the catalyst comprises a solid
solution of rhodium-nickel-magnesium-oxide.
In certain embodiments of the catalysts the support structure comprises a
refractory oxide, which may be in the form of a foam structure. Preferably
such a foam structure comprises about 12-60 pores per centimeter of
structure. Alternatively, the support structure may be in the form of a
honeycomb monolith structure.
In some embodiments, the catalyst comprises a mixture of rhodium and nickel
on a support structure comprising Al.sub.2 O.sub.3. Some embodiments
comprise an alloy of 1% rhodium, 3% manganese and 13% nickel on a
MgAl.sub.2 O.sub.4 support structure. In some embodiments the catalyst
comprises 1% rhodium and LaZr.sub.0.5 Ni.sub.0.5 O.sub.3 (expressed as
stoichiometric amounts). Another catalyst embodiment comprises Rh.sub.0.02
Ni.sub.0.03 Mg.sub.0.95 O, and yet another comprises rhodium, nickel and
cobalt on a support structure comprising ZrO.sub.2. Certain catalysts of
the invention comprise 1% rhodium, 10.9% nickel and 8.6% magnesium on a
support structure comprising 99% Al.sub.2 O.sub.3.
Also provided by the present invention are processes for the net partial
oxidization of a 1-5 carbon containing hydrocarbon to form a product gas
mixture comprising CO and H.sub.2. In some embodiments the process
comprises contacting a reactant gas mixture comprising the hydrocarbon and
a source of oxygen with a catalytically effective amount of a Ni--Rh
alloy-containing catalyst having a composition as described above. The
process also includes maintaining the catalyst and the reactant gas
mixture at conversion promoting conditions of temperature, gas flow rate
and feed composition during contact with the reactant gas mixture.
Preferably the process includes maintaining the reactant gas mixture and
the catalyst at a temperature of about 600-1,200.degree. C. during
contact. In some embodiments the temperature is maintained at about
700-1,100.degree. C.
In some embodiments of the process the reactant gas mixture and the
catalyst are maintained at a pressure of about 100-12,500 kPa during the
contacting, and in some of the more preferred embodiments the pressure is
maintained at about 130-10,000 kPa.
Certain embodiments of the processes for converting hydrocarbons to CO and
H.sub.2 comprise mixing a methane-containing feedstock and an
oxygen-containing feedstock to provide a reactant gas mixture feedstock
having a carbon:oxygen ratio of about 1.25:1 to about 3.3:1. In some of
these embodiments, the mixing step is such that it yields a reactant gas
mixture feed having a carbon:oxygen ratio of about 1.3:1 to about 2.2:1,
or about 1.5:1 to about 2.2:1. In some of the most preferred embodiments
the mixing step provides a reactant gas mixture feed having a
carbon:oxygen ratio of about 2:1.
In some embodiments of the processes the said oxygen-containing gas that is
mixed with the hydrocarbon comprises steam or CO.sub.2, or a mixture of
both. In some embodiments of the processes the C.sub.1 -C.sub.5
hydrocarbon comprises at least about 50% methane by volume, and in some of
the preferred embodiments the C.sub.1 -C.sub.5 hydrocarbon comprises at
least about 80% methane by volume.
Certain embodiments of the processes for preparing synthesis gas comprise
preheating the reactant gas mixture. Some embodiments of the processes
comprise passing the reactant gas mixture over the catalyst at a space
velocity of about 20,000 to about 100,000,000 normal liters of gas per
kilogram of catalyst per hour (NL/kg/h). In certain of these embodiments,
the gas mixture is passed over the catalyst at a space velocity of about
50,000 to about 50,000,000 NL/kg/h. Preferably the residence time of the
reactant gas mixture on the catalyst is no more than about 10 milliseconds
duration.
In some embodiments of the processes of the present invention the catalyst
is retained in a fixed bed reaction zone. These and other embodiments,
features and advantages of the present invention will become apparent with
reference to the following description.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred Ni--Rh based catalysts for catalytically converting C.sub.1
-C.sub.5 hydrocarbons to CO and H.sub.2 comprise an alloy of about 1 wt %
to about 50 wt % nickel and 0.01 to 10 wt % rhodium on supports of
spinels, perovskites, magnesium oxide, pyrochlores, brownmillerites,
zirconium phosphate, magnesium stabilized zirconia, zirconia stabilized
alumina, silicon carbide, yttrium stabilized zirconia, calcium stabilized
zirconia, yttrium aluminum garnet, alumina, cordierite, ZrO.sub.2,
MgAl.sub.2 O.sub.4, SiO.sub.2 or TiO.sub.2. The Rh and/or Ni may be
incorporated into the structure of the spinel, perovskite, pyrochlore or
brownmillerite. Alternatively, a solid solution of Rh--Ni--Mg-oxide may be
used. Preferably the catalyst is a Ni--Rh alloy. A Rh--Ni based catalyst
is prepared as described in the following examples and utilizing
techniques known to those skilled in the art, such as impregnation, wash
coating, adsorption, ion exchange, precipitation, co-precipitation,
deposition precipitation, sol-gel method, slurry dip-coating, microwave
heating, and the like, or any of the other methods known in the art.
Preferred techniques are impregnation, sol-gel methods and
co-precipitation. For example, a Rh--Ni based catalyst is prepared by
impregnation of a ceramic foam of a refractory oxide with rhodium and
nickel.
Alternatively, the catalyst components, with or without a ceramic support
composition, may be extruded to prepare a three-dimensional form or
structure such as a honeycomb, foam, or other suitable tortuous-path
structure. Additionally the catalyst components may be added to the
powdered ceramic composition and then extruded to prepare the foam or
honeycomb. Suitable foams for use in the preparation of the catalyst
include those having from 30 to 150 pores per inch (12 to 60 pores per
centimeter). Alternative forms for the catalyst include refractory oxide
honeycomb monolith structures, or other configurations having longitudinal
channels or passageways permitting high space velocities with a minimal
pressure drop. Such configurations are known in the art and described, for
example, in Structured Catalysts and Reactors, A. Cybulski and J. A.
Moulijn (Eds.), Marcel Dekker, Inc., 1998, p. 599-615 (Ch. 21, X. Xu and
J. A. Moulijn, "Transformation of a Structured Carrier into Structured
Catalyst")
Any suitable reaction regime may be applied in order to contact the
reactants with the catalyst. One suitable regime is a fixed bed reaction
regime, in which the catalyst is retained within a reaction zone in a
fixed arrangement. Particles of catalyst may be employed in the fixed bed
regime, retained using fixed bed reaction techniques well known in the
art. Alternatively, the catalyst may be in the form of a foam, or porous
monolith.
Process of Producing Syngas
A feed stream comprising a hydrocarbon feedstock and an oxygen-containing
gas is contacted with one of the above-described Rh--Ni alloy catalysts in
a reaction zone maintained at conversion-promoting conditions effective to
produce an effluent stream comprising carbon monoxide and hydrogen.
Preferably a millisecond contact time reactor is employed. The hydrocarbon
feedstock may be any gaseous hydrocarbon having a low boiling point, such
as methane, natural gas, associated gas, or other sources of light
hydrocarbons having from 1 to 5 carbon atoms. The hydrocarbon feedstock
may be a gas arising from naturally occurring reserves of methane which
contain carbon dioxide. Preferably, the feed comprises at least 50% by
volume methane, more preferably at least 75% by volume, and most
preferably at least 80% by volume methane.
The hydrocarbon feedstock is in the gaseous phase when contacting the
catalyst. The hydrocarbon feedstock is contacted with the catalyst as a
mixture with an oxygen-containing gas, preferably pure oxygen. The
oxygen-containing gas may also comprise steam and/or CO.sub.2 in addition
to oxygen. Alternatively, the hydrocarbon feedstock is contacted with the
catalyst as a mixture with a gas comprising steam and/or CO.sub.2.
Preferably, the methane-containing feed and the oxygen-containing gas are
mixed in such amounts to give a carbon (i.e., carbon in methane) to oxygen
(i.e., oxygen) ratio from about 1.25:1 to about 3.3:1, more preferably,
from about 1.3:1 to about 2.2:1, and most preferably from about 1.5:1 to
about 2.2:1, especially the stoichiometric ratio of 2:1.
The process is operated at atmospheric or superatmospheric pressures, the
latter being preferred. The pressures may be from about 100 kPa to about
12,500 kPa, preferably from about 130 kPa to about 10,000 kPa.
The process is preferably operated at temperatures of from about 60.degree.
C. to about 1200.degree. C., preferably from about 700.degree. C. to about
1100.degree. C. The hydrocarbon feedstock and the oxygen-containing gas
are preferably pre-heated before contact with the catalyst.
The hydrocarbon feedstock and the oxygen-containing gas are passed over the
catalyst at any of a variety of space velocities. Space velocities for the
process, stated as normal liters of gas per kilogram of catalyst per hour,
are from about 20,000 to about 100,000,000 NL/kg/h, preferably from about
50,000 to about 50,000,000 NL/kg/h. Preferably the catalyst is employed in
a millisecond contact time reactor for syngas production. The product gas
mixture emerging from the reactor is collected and analyzed for CH.sub.4,
O.sub.2, CO, H.sub.2, CO.sub.2, etc.
EXAMPLES
Catalyst Preparation
Exemplary and comparative catalysts were prepared with and without the
inclusion of rhodium, as described Examples 1-12, below. In these
examples, calcining was conducted according to the following program: heat
at a rate of 10.degree. C./min. up to within about 50.degree. of the
target temperature, hold about 30 min., then heat at a rate of 1.degree.
C./min up to the desired final temperature. Catalyst activities were
tested in partial oxidation reactions at defined high gas hourly space
velocities, temperature and feed composition. The level of CH.sub.4
conversion and selectivities to CO and H.sub.2 products are reported
below.
Example 1
3% Mn, 13% Ni/MgAl.sub.2 O.sub.4
The 3% Mn, 13% Ni/MgAl.sub.2 O.sub.4 catalyst was prepared by dissolving Ni
(NO.sub.3).sub.2.6H.sub.2 O(19.325 g) and Mn(NO.sub.3).sub.2.6H.sub.2 O
(4.702 g) in distilled water (50 ml) and wet impregnating calcined
(600.degree. C. for 3 hours) MgAl.sub.2 O.sub.4 (25.2 g). The slurry was
mixed with a spatula, dried at 110.degree. C. and calcined at 800.degree.
C. for 2 hours. A portion of the calcined material (15 g) was reduced in
flowing hydrogen (about 100 cc/minute) for 4 hours at 800.degree. C.
Example 2
1% Rh added to 3% Mn, 13% Ni/MgAl.sub.2 O.sub.4
Rh (E) chloride (0.264 g) was dissolved in 250 ml of acetone and 5 ml of
water. The catalyst of 3% Mn, 13% Ni on MgAl.sub.2 O.sub.4 (10 g) was
added to the solution and acetone was evaporated off. The solid was
calcined at 600.degree. C. for 1 hr and then reduced at 600.degree. C. for
4 hours with 10% H.sub.2 in N.sub.2 at a flow of 100 ml/min. High
Resolution Transmission Electron Microscopy (HRTEM) and X-ray Adsorption
Spectroscopy (XAS) analyses indicated that the catalyst was comprised of a
Ni--Rh alloy.
Example 3
LaZr.sub.0.5 Ni.sub.0.5 O.sub.3
To a round bottom flask was added 61.61 g of ZrO.sub.2, 100 ml of 1M
La(NO.sub.3).sub.3 and 50 ml of 1M Ni(NO.sub.3).sub.2. The water was
removed from the mixture on a rotoevaporator and dried in a vacuum oven.
Calcination was carried out at 900.degree. C. for 100 hours with daily
grinding and mixing.
Example 4
1% Rh on LaZr.sub.0.5 Ni.sub.0.5 O.sub.3
Rh (III) chloride (0.0176 g) was dissolved in 50 ml of acetone and 1 ml of
water. The catalyst of LaZr.sub.0.5 Ni.sub.0.5 O.sub.3 (0.6811 g) was
added to the solution and acetone was evaporated off. The solid was
calcined at 600.degree. C. for 1 hr and then reduced at 600.degree. C. for
4 hours with 10% H.sub.2 in N.sub.2 at a flow of 100 ml/min. HRTEM and XAS
analyses indicated that the catalyst was comprised of a Ni--Rh alloy.
Example 5
Ni.sub.0.03 Mg.sub.0.97 O
The nickel magnesia solid solution was prepared by the co-precipitation
method. From a mixed aqueous solution (1 L) of 4.50 g of nickel acetate
tetrahydrate and 150.38 g of magnesium nitrate hexahydrate, their mixed
carbonate was deposited by adding (1 L) 3 M potassium carbonate aqueous
solution at 60.degree. C. After being filtered and washed with hot water,
the precipitate was dried overnight at 120.degree. C. for 12 hours, and
then calcined in air at 950.degree. C. for 10 h to yield 25 g of catalyst.
The catalyst was reduced by hydrogen at 850.degree. C. for 0.5 h.
Example 6
Rh.sub.0.02 Ni.sub.0.03 Mg.sub.0.95 O
An acetone solution of 1.93 g of rhodium acetylacetonate complex was
impregnated onto 10 g of the calcined Ni.sub.0.03 Mg.sub.0.97 O. The
solvent was evaporated off at room temperature and the solid material was
calcined in air at 950.degree. C. for 10 hours and then reduced by
hydrogen at 850.degree. C. for 0.5 h. HRTEM and XAS analyses indicated
that the catalyst was comprised of a Ni--Rh alloy.
Example 7
Co, Ni/ZrO.sub.2
A mixture containing 2.24 g of Co(NO.sub.3).sub.2.6H.sub.2 O and 2.22 g of
Ni(NO.sub.3).sub.2.6H.sub.2 O was prepared. To this mixture was added
sufficient water to give a final volume of 15 ml. The resulting solution
was added to 30 g of ZrO.sub.2 (1/8" pellets, dried at 110.degree. C.).
The "wet" pellets were air dried with stirring every 4 hours to ensure
uniform drying. The air-dried pellets were calcined in air at 600.degree.
C. for 3 hours.
Example 8
Co, Ni, Rh/ZrO.sub.2
A mixture containing 2.22 g of Co(NO.sub.3).sub.2.6H.sub.2 O, 2.23 g of
Ni(NO.sub.3).sub.2.6 H.sub.2 O and 12.63 g of a 10% solution of
Rh(NO.sub.3).sub.3 was prepared. To this mixture was added sufficient
water to give a final volume of 15 ml. The resulting solution was added to
30 g of ZrO.sub.2 (1/8" pellets, dried at 110.degree. C.). The "wet"
pellets were air dried with stirring every 4 hours to ensure uniform
drying. The air-dried pellets were calcined in air at 600.degree. C. for 3
hours. HRTEM and XAS analyses indicated that the catalyst was comprised of
a Ni--Rh alloy.
Example 9
NiAl.sub.2 O.sub.4
Al(NO.sub.3).sub.3 .9H.sub.2 O (3.75 g) and Ni(NO .sub.3).sub.2 .6H.sub.2 O
(1.45 g) were dissolved in 10 ml distilled H.sub.2 O with 0.1 g of
polyvinyl alcohol added for improved viscosity. To 1 g of alpha alumina
spheres (diameter 2 mm) was added 2 mL of this solution. The solvent was
removed with a rotoevaporator at high temperature and the resulting
material was calcined at 800.degree. C. for 2 hrs. HRTEM analysis
confirmed formation of NiAl.sub.2 O.sub.4.
Example 10
1% Rh/NiAl.sub.2 O.sub.4
NiAl.sub.2 O.sub.4 (0.8025 g) was impregnated with a solution of 0.0208 g
of RhCl.sub.3 3H.sub.2 O dissolved in 0.15 g of H.sub.2 O and 2.0 g of
acetone. The solvent was evaporated off at room temperature and the
resulting material was dried in a vacuum oven over night at 110.degree. C.
and then calcined at 600.degree. C. for 1 hour. Subsequent reduction was
carried out at 600.degree. C. for 4 hours with 90 mL/min N.sub.2 and 10
mL/min H.sub.2. HRTEM and XAS analyses indicated that the catalyst was
comprised of a Ni--Rh alloy.
Test Procedure for Examples 1-10
The catalysts were evaluated in a laboratory scale short contact time
reactor, i.e., a 25 cm long.times.4 mm i.d. quartz tube reactor equipped
with a co-axial quartz thermocouple well. The void space within the
reactor was packed with quartz chips. The catalyst bed was positioned with
quartz wool at about the mid-length of the reactor. The catalyst bed was
heated with a 4 inch (10.2 cm) 600 watt band furnace at 90% electrical
output. All runs were done at a CH.sub.4 :O.sub.2 molar ratio of 2:1 and
at a pressure of 5 psig (136 kPa). The reactor effluent was analyzed using
a gas chromatograph equipped with a thermal conductivity detector. The C,
H and O mass balance were all between 98% and 102%. The runs were
conducted over two operating days with 6 hours of run time each day. The
comparative results of these runs are shown in Table 1, wherein gas hourly
space velocity is indicated by "GHSV." As shown in Table 1, no evidence of
catalyst deactivation occurred after 12 hours. The comparative sets of
examples, with and without Rh, show that the inclusion of Rh into the
respective catalyst compositions resulted in higher CH.sub.4 conversion
and selectivities to CO and H.sub.2 and lower catalyst bed temperatures.
TABLE 1
Temp GHSV .times. % CH.sub.4 /% O.sub.2 % CO/% H.sub.2
Ex. .degree. C. 10.sup.5 Conv. Sel. H.sub.2 :CO
1 850 3.045 92/100 99/97 1.96
1 850 6.09 86/100 94/90 1.91
2 700 3.045 99/100 100/100 2.0
2 700 6.09 91/100 99/100 2.02
3 875 1.523 57/99 87/77 1.77
4 720 3.48 88/100 98/99 2.02
4 720 5.916 83/100 96/94 1.96
5 830 3.045 67/95 95/78 1.64
6 810 3.045 91/100 98/97 1.98
7 820 1.826 81/100 93/91 1.96
8 795 1.826 90/100 97/97 2.00
9 725 2.436 76/96 94/83 1.77
10 650 2.436 82/100 100/92 1.84
Example 11
12.7% Ni, 8.2% Mg on 99% Al.sub.2 O.sub.3 (12 mm OD.times.10 mm ceramic
foam of 80 ppi)
The Al.sub.2 O.sub.3 monolith (1.1688 g) was first impregnated with a
solution of 1.3839 g of Mg(NO.sub.3).sub.2 6H.sub.2 O in 1 mL of H.sub.2 O
followed by evaporating off the solvent at room temperature, drying in a
vacuum oven at 110.degree. C. for overnight, then calcining at 900.degree.
C. for 4 hrs. The monolith was subsequently impregnated with one half the
volume of a solution of 0.9990 g of Ni(NO3).sub.2 6H.sub.2 O dissolved in
2 mL of water. The solvent was evaporated off at room temperature, dried
in a vacuum oven at 110.degree. C. overnight, and calcined at 600.degree.
C. for 1 hr. The impregnation procedure was repeated with the remaining Ni
nitrate solution and again the impregnated monolith was dried in a vacuum
oven at 110.degree. C. overnight and calcined at 600.degree. C. for 1 hr.
Example 12
1% Rh, 10.9% Ni, 8.6% Mg on 99% Al.sub.2 O.sub.3 (12 mm OD.times.10 mm
ceramic foam of 80 ppi)
The Al.sub.2 O.sub.3 monolith (1.1356 g) was first impregnated with a
solution of 1.3997 g of Mg(NO.sub.3).sub.2 6H.sub.2 O in 1 mL of H.sub.2 O
followed by evaporating off the solvent at room temperature, drying in a
vacuum oven at 110.degree. C. overnight, then calcining at 900.degree. C.
for 4 hrs. The monolith was subsequently impregnated with one half the
volume of a solution of 0.8308 g of Ni(NO.sub.3).sub.2 6H.sub.2 O
dissolved in 2 mL of water. The solvent was evaporated off at room
temperature, dried in a vacuum oven at 110.degree. C. overnight, and
calcined at 600.degree. C. for 1 hr. The impregnation procedure was
repeated with the remaining Ni nitrate solution and again the impregnated
monolith was dried in a vacuum oven at 110.degree. C. overnight and
calcined at 600.degree. C. for 1 hr. RhCl.sub.3 3H.sub.2 O (0.0394 g) was
dissolved in 2 drops of H.sub.2 O and 1 mL of acetone and the solution was
dripped onto the monolith. The solvents were evaporated at room
temperature, dried in a vacuum oven at 110.degree. C. overnight, and
calcined at 600.degree. C. for one hr. HRTEM and XAS analyses indicated
that the catalyst was comprised of a Ni--Rh alloy.
Test Procedure for Examples 11 and 12
The partial oxidation reactions were done with a conventional flow
apparatus using a 19 mm O.D..times.13 mm I.D. and 12" long quartz reactor.
A ceramic foam of 99% Al.sub.2 O.sub.3 (12 mm OD.times.5 mm of 45 ppi)
were placed before and after the catalyst as radiation shields. The inlet
radiation shield also aided in uniform distribution of the feed gases. An
Inconel sheathed, single point K-type (Chromel/Alumel) thermocouple (TC)
was placed axially inside the reactor touching the top (inlet) face of the
radiation shield. A high temperature S-Type (Pt/Pt 10% Rh) bare-wire TC
was positioned axially touching the bottom face of the catalyst and was
used to indicate the reaction temperature. The catalyst and the two
radiation shields were sealed tight against the walls of the quartz
reactor by wrapping them radially with a high purity (99.5%) alumina
paper. A 600 watt band heater set at 90% electrical output was placed
around the quartz tube, providing heat to light off the reaction and to
preheat the feed gases. The bottom of the band heater corresponded to the
top of the upper radiation shield. In addition to the TCs placed above and
below the catalyst, the reactor also contained two axially positioned,
triple-point TCs, one before and another after the catalyst. These
triple-point thermocouples were used to determine the temperature profiles
of reactants and products subjected to preheating and quenching,
respectively.
All runs were carried out at a CH.sub.4 :O.sub.2 molar ratio of 2:1 with a
combined flow rate of 7.7 standard liters per minute (SLPM) (431,720 GHSV)
and at a pressure of 5 psig (136 kPa). The reactor effluent was analyzed
using a gas chromatograph equipped with a thermal conductivity detector.
The C, H and O mass balance were all between 98% and 102%. Table 2 shows
the results for the comparative set, with and without Rh. The inclusion of
Rh in the catalyst composition resulted in higher CH.sub.4 conversion and
higher selectivities to CO and H.sub.2 products.
TABLE 2
Preheat
Temp. Catal. Temp. % CH.sub.4 /% O.sub.2 % CO/% H.sub.2
Ex. .degree. C. .degree. C. Conv. Sel. H.sub.2 :CO
11 360 890 86/97 97/93 1.92
12 300 890 92/100 98/96 1.96
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 patents and publications cited herein are incorporated
by reference in their entirety.
*
