KENTUCKY CAER REVIEWS FISCHER-TROPSCH WORK

B. Davis of the University of Kentucky Center for Applied Energy Research (CAER) discussed CAER's Fischer-Tropsch (F-T) research program in Energeia, Volume 8, Number 3, 1997.

Beginning in 1984 the initial work at the CAER on Fischer-Tropsch Synthesis (FTS) was to utilize isotopic tracers in an attempt to define the role of catalyst promoters. This work involved a 3-year United States Department of Energy (DOE) contract to conduct work directed toward understanding the reaction mechanism.

A few years later the CAER was successful in obtaining a DOE contract with the goal of developing an iron F-T catalyst suitable for utilization in the slurry bubble column reactor located at La Porte, Texas, and operated by Air Products for the DOE. When the contract was awarded, and even today, no commercial iron F-T catalyst was (is) available from catalyst manufacturers. During the course of the 3-year contract, and the 3-year extension, United Catalysts Inc. (UCI) prepared catalysts in a quantity sufficient to operate the pilot plant at La Porte, Texas.

During the course of the research, the CAER has established one of the best equipped F-T research facilities in the United States. This equipment includes eight 1-liter Continuous Stirred Tank Reactors (CSTRs), which are ideal for conducting long-term aging studies because all of the catalyst is exposed to a synthesis gas of the same composition. In addition to the CSTRs, the CAER has operated a variety of fixed-bed reactors to investigate the activation and activity of FTS catalysts. The CAER modified the direct-coal liquefaction pilot plant so that it could be operated as a 2-inch diameter by 6-foot long slurry bubble-column reactor.

During catalyst preparation, the CAER has developed a procedure that permits catalysts to be synthesized continuously. One ton of a slurry of the optimum catalyst formulation was prepared at the CAER and taken to UCI where it was formed into spherical particles using UCI's equipment.

Synthesis can be conducted using low or high temperature conditions. In addition, the catalyst can be formulated so that it will produce primarily low-boiling, intermediate-boiling or high-boiling products. Included in the initial goals of the CAER work was the objective to attain a 50 percent increase in the catalyst activity over that of the original catalysts developed in the 1950s and a much improved catalyst aging rate so that the decline in activity was less than 1 percent CO conversion per week. During the first 3-year contract, these two goals were met, and exceeded. For example, compared to the catalyst used in the United States Bureau of Mines studies in the early 1950s, the CAER catalyst formulation leading to low-boiling products (low alpha catalyst) is about 40 times more active. Thus, there has been a significant improvement in the catalytic activity so that the productivity of the catalyst/reactor volume is now adequate for commercial operation.

Based on catalyst considerations, CAER researchers suggested that it would be much more efficient to utilize two or more reactors in series, each of these operating at less than the 90 percent plus CO conversion, the goal at the outset of the CAER work.

A significant feature of the CAER operation is the ability to utilize both radioactive and stable isotopes. The CSTRs are equipped so that an isotopically labeled compound can be fed to the reactor during synthesis under the typical medium-pressure run conditions employed with iron catalysts.

In general, these results show that different mechanisms are involved for the iron and cobalt catalysts. For cobalt catalysts, CO dissociates on the catalyst surface to produce a surface carbide which is subsequently hydrogenated to a surface carbene species (CH2). Chain growth occurs by a polymerization of these CH2 groups on the catalyst surface. Eventually chain growth is terminated either by beta-H elimination to produce an alkene or by H addition to produce an alkane.

The CAER tracer data indicate the carbene mechanism is not valid for an iron catalyst, at least when operated under the medium-pressure synthesis conditions. With the iron catalyst, the data indicate that oxygen is retained in the growing chain. In addition, the mechanism with an iron catalyst involves different species for chain initiation and growth. The CAER data are consistent with the chain initiating species being, or at least resembling, a formate species that operates both for the water gas shift and FTS reactions. Chain growth involves a species derived from CO that differs from that of the chain initiating species.

As part of the technology transfer, CAER has conducted studies for Rema Corporation, Energy International and Syncrude. The CAER work has been incorporated in the preliminary planning for a pioneer plant for Kentucky that would feature integrated gasification combined cycle and a chemicals plant that would utilize FTS technology. Thus, CAER indirect coal liquefaction research has been utilized by many industrial organizations and has provided laboratory researchers much understanding of the research requirements that can lead to technology transfer.


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