Published December 2006
This Review deals with iron catalysts and their performance under varying process and catalytic conditions for production of Fischer-Tropsch (F-T) products, mainly the transportation fuels. Iron catalysts are known to be cheap, versatile to produce a variety of products (olefins, gasoline, oxygenates, waxes and diesel), capable of functioning with low syngas compositions (e.g. coal-derived syngas), and highly tolerant to water and CO 2 (a constituent of syngas as well as a byproduct of F-T reaction). The waxes can, subsequently, be hydroprocessed to produce diesel of a high cetane number. Due to low costs, iron catalysts can be comfortably discarded after their useful life, or when deactivated (though an undesirable step environmentally). Unlike cobalt catalysts, the iron catalysts generate more CO 2 in the system through the water-gas shift reaction, and F-T product has a high olefinic hydrocarbons concentration. Iron catalysts are used in two-types of F-T syntheses: a) High-Temperature F-T Synthesis b)
Low-Temperature F-T Synthesis. High-Temperature F-T process is operated at 572 – 662°F (300 – 350°C) in fixed fluidized bed (FFB) type of reactor. Low-Temperature F-T process is run at 410 – 500°F (210 – 260°C) in fixed-bed or slurry-bubble column reactor (SBCR). Depending, upon the composition of catalyst and methodology of its preparation and activation protocol, the product slate from the two processes is markedly different. Other process variables such as temperature, pressure, space velocity, type of reactor, syngas composition, etc. also affect the product composition significantly. Study of effects of such parameters in qualitative and quantitative terms upon catalysts activity and selectivity is the main theme of this Review. The discussion in the Review is based upon the research results of different companies and universities, published in technical articles and patents during the last ten years. Our conclusions in regard to the suitability of iron catalysts for F-T fuels production are presented in the end of Review.
