Fischer-Tropsch Synthesis Using H sub(2)/CO/CO sub(2) Syngas Mixtures over an Iron Catalyst

• Published in: Industrial & engineering chemistry research Vol. 50; no. 19; pp. 11002 - 11012-11002-11012
• Main Authors: Yao, Yali, Liu, Xinying, Hildebrandt, Diane, Glasser, David
• Format: Journal Article
• Language: English
• Published: 05.10.2011
• Subjects: Carbon dioxide; Carbon monoxide; Catalysts; Hydrocarbons; Hydrogenation; Partial pressure; Synthesis; Thermodynamic equilibrium
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie200690y

A series of low-temperature Fischer-Tropsch synthesis (FTS) experiments using a wide range of H sub(2)/CO/CO sub(2) syngas mixtures have been performed to provide further insight into the effect of the CO sub(2) on an iron-based catalyst during FTS. In comparison with CO hydrogenation, the reactivity for CO sub(2) hydrogenation was lower and produced more CH sub(4)-rich short chain paraffins. Based on the correlation between the experimental results and the thermodynamic equilibrium calculations for the water gas shift (WGS) reaction, although the WGS reaction is far from the thermodynamic equilibrium under low-temperature FTS conditions, its equilibrium constraints determine the pathways and in particular whether CO is converted to CO sub(2) or CO sub(2) to CO. It is possible for CO sub(2) to convert to hydrocarbons only when the composition of co-fed CO sub(2) has a value higher than that set by the equilibrium constraints. A remarkable feature of our experimental results was that when the FTS system was not consuming but forming CO sub(2), the reaction rates of both the FT and the WGS reactions were independent of the partial pressures of CO and CO sub(2). Furthermore, with a decrease in the ratio of CO sub(2)/(CO+CO sub(2)) in the feed gas, it was observed that the hydrocarbon product formation rate reached a maximum and then maintained this value, even at a very high concentration of CO sub(2) in the H sub(2)/CO/CO sub(2) feed mixture. These results could justify the inclusion of CO sub(2) in the syngas feed to the iron-based catalyst FTS processes.