Boron promoted catalysts and fischer-tropsch processes

Details Boron promoted catalysts and fischer-tropsch processes Boron promoted catalysts and fischer-tropsch processes

2002-01-14

2004-04-27

Parsa, J. (Department: 1621)

Chemistry: fischer-tropsch processes; or purification or recover

Group viii metal containing catalyst utilized for the...

C518S721000

Reexamination Certificate

active

06727289

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
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. Particularly, this invention relates to the use of supported catalysts containing boron and a Fischer-Tropsch catalytic metal (such as cobalt, cobalt/ruthenium, and the like) for the Fischer-Tropsch process.
BACKGROUND OF THE INVENTION
Large quantities of methane, the main component of natural gas, are available in many areas of the world. Methane can be used as a starting material for the production of hydrocarbons. The conversion of methane to hydrocarbons is typically carried out in two steps. In the first step methane is reformed with water or partially oxidized with oxygen to produce carbon monoxide and hydrogen (i.e., synthesis gas or syngas). In a second step, the syngas is converted to 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).
The Fischer-Tropsch reaction involves the catalytic hydrogenation of carbon monoxide to produce a variety of products ranging from methane to higher aliphatic alcohols. The process has been considered for the conversion of carbonaceous feedstock, e.g., coal or natural gas, to higher value liquid fuel or petrochemicals. The methanation reaction was first described in the early 1900's, and the later work by Fischer and Tropsch dealing with higher hydrocarbon synthesis was described in the 1920's. The first major commercial use of the Fischer-Tropsch process was in Germany during the 1930's. More than 10,000 B/D (barrels per day) of products were manufactured with a cobalt based catalyst in a fixed-bed reactor. This work has been described by Fischer and Pichler in Ger. Pat. No. 731,295 issued Aug. 2, 1936, hereby incorporated herein by reference. Commercial practice of the Fischer-Tropsch process has continued from 1954 to the present day in South Africa in the SASOL plants. These plants use iron-based catalysts, and produce gasoline in relatively high-temperature fluid-bed reactors and wax in relatively low-temperature fixed-bed reactors.
The Fischer-Tropsch synthesis reactions are highly exothermic and reaction vessels must be designed for adequate heat exchange capacity. Because the feed streams to Fischer-Tropsch reaction vessels are gases while the product streams include liquids, the reaction vessels must have the ability to continuously produce and remove the desired range of liquid hydrocarbon products. Motivated by production of high-grade gasoline from natural gas, research on the possible use of the fluidized bed for Fischer-Tropsch synthesis was conducted in the United States in the mid-1940s. Based on laboratory results, Hydrocarbon Research, Inc. constructed a dense-phase fluidized bed reactor, the Hydrocol unit, at Carthage, Tex., using powdered iron as the catalyst. Due to disappointing levels of conversion, scale-up problems, and rising natural gas prices, operations at this plant were suspended in 1957. Research has continued, however, on developing Fischer-Tropsch reactors such as slurry-bubble columns, as disclosed in U.S. Pat. No. 5,348,982 issued Sep. 20, 1994, hereby incorporated herein by reference.
Catalysts for use in the Fischer-Tropsch synthesis usually contain a catalytically active metal of Groups 8, 9, 10 (in the New notation of the periodic table of the elements, which is followed throughout). In particular, iron, cobalt, nickel, and ruthenium, and combinations thereof, have been abundantly used as the catalytically active metals. Cobalt and ruthenium have been found to be particularly suitable for catalyzing a process in which synthesis gas is converted to primarily hydrocarbons having five or more carbon atoms (i.e., where the C
5
+
selectivity of the catalyst is high). However, due to its expense and rarity, ruthenium is typically used in combination with another of the catalytically active metals, such as cobalt. For example, U.S. Pat. No. 4,088,671, hereby incorporated herein by reference, discloses a process for the synthesis of higher hydrocarbons from the reaction of CO and hydrogen at low pressure in the contact presence of a catalyst comprising as the active ingredients a major amount of cobalt and a minor amount of ruthenium.
Additionally, the catalysts often contain a support or carrier material. Supports for catalysts used in Fischer-Tropsch synthesis of hydrocarbons have typically been refractory oxides (e.g., silica, alumina, titania, zirconia or mixtures thereof, such as silica-alumina). A support may be used to provide a high surface area for contact of the catalytically active metal with the syngas, to reduce the amount of catalytically active metal used, or to otherwise improve the performance or economics of catalysts and catalytic processes.
Additionally, Fischer-Tropsch catalysts often contain one or more promoters. For example, promoters that have been used for cobalt-ruthenium catalysts include thorium, lanthanum, magnesium, manganese, and rhenium. A promoter may have any of various desirable functions, such as improving activity, productivity, selectivity, lifetime, regenerability, or other properties of catalysts and catalytic processes.
There are significant differences in the molecular weight distributions of the hydrocarbon products from Fischer-Tropsch reaction systems. Product distribution or product selectivity depends heavily on the type and structure of the catalysts and on the reactor type and operating conditions. Accordingly, it is highly desirable to maximize the selectivity of the Fischer-Tropsch synthesis to the production of high-value liquid hydrocarbons, such as hydrocarbons with five or more carbon atoms per hydrocarbon chain.
Research is continuing 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. High value hydrocarbons include those useful for further processing to yield gasoline, for example C
5+
hydrocarbons, particularly C
5
-C
10
hydrocarbons, and those useful for further processing to yield diesel fuel, for example C
11+
hydrocarbons are, particularly C
11
-C
20
hydrocarbons. A number of studies describe the behavior of iron, cobalt or ruthenium based catalysts in various reactor types, together with the development of catalyst compositions and preparations. For example, see the articles “Short history and present trends of Fischer-Tropsch synthesis,” by H. Schlutz, Applied Catalysis A 186, 3-12, 1999, and “Status and future opportunities for conversion of synthesis gas to liquid fuels, by G. Alex Mills, Fuel 73, 1243-1279, 1994, each hereby incorporated herein by reference in their entirety.
Notwithstanding the above teachings, it continues to be desirable to improve the activity and reduce the cost of Fischer-Tropsch catalysts and processes. In particular, there is still a great need to identify new promoted catalysts useful for Fischer-Tropsch synthesis, particularly catalysts that provide high C
11
+
hydrocarbon selectivities to maximize the value of the hydrocarbons produced and thus the process economics.
SUMMARY OF THE INVENTION
This invention provides a process and catalyst for producing hydrocarbons, and a method for preparing the catalyst. The process comprises contacting a feed stream comprising hydrogen and carbon monoxide with a catalyst in a reaction zone maintained at conversion-promoting conditions effective to produce an effluent stream comprising hydrocarbons.
In accordance with this invention, the catalyst used in the process comprises boron and a Fischer-Tropsch metal. The Fischer-Tropsch metal may include cobalt. Further, the Fischer-Tropsch metal additionally includes ruthenium or platinum.
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