Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the...
Reexamination Certificate
2001-06-13
2003-09-02
Parsa, Jafar (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
C518S713000, C518S714000, C518S700000, C518S719000, C518S720000, C518S721000
Reexamination Certificate
active
06613808
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a process for the preparation of hydrocarbons from synthesis gas, i.e., a mixture of carbon monoxide and hydrogen, typically labeled the Fischer-Tropsch process. More particularly, this invention relates to the use of acrylate polymer matrix structures for catalysts for the Fischer-Tropsch process. Still more particularly, the present invention relates to Fischer-Tropsch catalysts formed by polymerizing an acrylate with a catalytically active metal.
BACKGROUND
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 the use of methane as a starting material for the production of higher hydrocarbons and hydrocarbon liquids, which are more easily transported and thus more economical. The conversion of methane to hydrocarbons is typically carried out in two steps. In the first step, methane is converted into a mixture of carbon monoxide and hydrogen (i.e., synthesis gas or syngas). In a second step, the syngas is converted into hydrocarbons.
This second step, the preparation of hydrocarbons from synthesis gas, is well known in the art and is usually referred to as Fischer-Tropsch synthesis, the Fischer-Tropsch process, or Fischer-Tropsch reaction(s). Fischer-Tropsch synthesis generally entails contacting a stream of synthesis gas with a catalyst under temperature and pressure conditions that allow the synthesis gas to react and form hydrocarbons.
More specifically, the Fischer-Tropsch reaction is the catalytic hydrogenation of carbon monoxide to produce any of a variety of products ranging from methane to higher alkanes and aliphatic alcohols. Research continues on the development of more efficient Fischer-Tropsch catalyst systems and reaction systems that increase the selectivity for high-value hydrocarbons in the Fischer-Tropsch product stream.
There are continuing efforts to find catalysts that are more effective at producing these desired products. Product distribution, product selectivity, and reactor productivity depend heavily on the type and structure of the catalyst and on the reactor type and operating conditions. It is particularly desirable to maximize the production of high-value liquid hydrocarbons, such as hydrocarbons with five or more carbon atoms per hydrocarbon chain (C
5+
).
Catalyst supports for catalysts used in Fischer-Tropsch synthesis of hydrocarbons have typically been oxides (e.g., silica, alumina, titania, zirconia or mixtures thereof, such as silica-alumina). The products prepared by using these catalysts usually have a very wide range of molecular weights. It has been asserted that the Fischer-Tropsch synthesis reaction is only weakly dependent on the chemical identity of the metal oxide support (see E. Iglesia et al. 1993, In: “Computer-Aided Design of Catalysts,” ed. E. R. Becker et al., p. 215, New York, Marcel Dekker, Inc.). Nevertheless, because it continues to be desirable to improve the activity of Fischer-Tropsch catalysts, other types of catalyst supports have been investigated.
The use of divinylbenzene cross-linked polystyrene as a support for Fischer-Tropsch catalysts is disclosed in U.S. Pat. No. 4,292,415 and U.S. Pat. No. 4,725,568. Similarly, U.S. Pat. No. 4,230,633 discloses polymer supported metal complexes wherein the ligand is a cycloalkadienyl radical with metals from Group VIII of the Periodic Table. This patent relates to the conversion of carbon monoxide and hydrogen to hydrocarbons in a liquid reaction medium. Nevertheless, despite the research in this field, there is still a desire to identify new, more effective catalysts. In particular, catalysts that provide high C
5+
and C
11+
productivities are desired.
SUMMARY OF THE INVENTION
The present invention provides a catalyst system that is effective for producing C
5+
and C
11+
hydrocarbons. In accordance with a preferred embodiment, the present catalyst comprises (1) cobalt and at least one other metal selected from the group consisting of silver, iron, zinc and zirconium and (2) a matrix structure comprising a polymer selected from the group consisting of polyacrylates and polymethacrylates. The catalyst so formed is preferably treated with hydrogen at a temperature of at least 400° C. prior to use. Catalyst systems constructed in accordance with the invention compare favorably to previously known catalysts in activity and durability.
The present invention further comprises a process for using the present catalyst system to produce hydrocarbons. The process comprises contacting a feed stream comprising hydrogen and carbon monoxide with the present catalyst system in a reaction zone maintained at conditions that are effective to produce an effluent stream comprising hydrocarbons.
DETAILED DESCRIPTION
The present catalyst system comprises a catalytic composition integrated into a polymeric matrix structure. The catalytic composition preferably comprises at least one Group VIII metal, namely iron, nickel, cobalt, rhenium, ruthenium, chromium, and iridium or mixtures thereof, and at least one other metal selected from the group consisting of silver, iron, zinc and zirconium. Of these, cobalt/silver is most preferred. The catalytic composition may further include one or more promoters selected from the group consisting of alkali and alkaline earth metal in free or combined form, boron, and mixtures thereof.
The polyacrylate and polymethacrylate matrix structures used in the process of this invention can be prepared by the polymerization of metal acrylates and/or metal methacrylates. Several alternative techniques are suitable for achieving the desired polymerization.
Formation of Cobalt acrylate
In one preferred technique, the present catalysts are formed by mixing the desired monomer with a salt of the desired metal catalyst and an initiator in a solvent. Polymerization occurs with mixing, producing a polymerized mass. The metal salt is preferably suspended in water and reacted with the acrylic acid or methacrylic acid at a temperature between about 40 and about 60° C. By way of example only, suitable metal salts include but are not limited to: basic cobalt carbonate, silver carbonate or silver oxide, iron carbonate or iron oxide, zinc carbonate or zinc oxide and zirconium carbonate or zirconium hydroxide. The reactions are carried out for about 5 hours with gradual addition of the acrylic acid or methacrylic and constant stirring. The solid product is extracted with ethanol and the extract is filtered and evaporated to dryness.
Technique I
The present catalysts can be prepared by dissolving a metal acrylate or metal methacrylate, such as cobalt acrylate, cobalt carbonate, or cobalt methacrylate (described above) and at least one other metal acrylate or methacrylate in methanol, ethanol or another suitable alcohol. The alcohol can contain as much as 25 wt % water. The polymerization is preferably carried out at reflux temperature using 2,2′-azobisisobutyronitrile as an initiator. The polymerization reaction mixture is refluxed for at least 3 hours with constant stirring. The reaction product is filtered off, washed several times with ethanol and then dried under vacuum at 40 to 60° C.
Technique II
Alternatively, the present catalysts can be prepared by dissolving polyacrylic acid or polymethacrylic acid in water, followed by addition of the cobalt and at least one metal acrylate or metal methacrylate to the polymer solution under stirring. The solution gels and is evaporated to dryness.
Catalyst
The metal-containing polyacrylate or polymethacrylate catalysts produced by any of the preceding tec
Maslov Sergej A.
Schwarz Stephan
Conley Rose & Tayon
Conoco Inc.
Parsa Jafar
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