The selectivity of Fischer-Tropsch synthesis (FTS) is highly sensitive to variations in process parameters. The undesired product of FTS is methane and its selectivity is higher than expected from the Anderson-Schulz-Flory (ASF) distribution model. In our work we analyzed the dependence of methane formation from temperature, pressure, H2/CO ratio and conversion level over 25%Co/0.48%Re/Al2O3 catalyst in a stirred tank slurry reactor. An increase in CH4 and a decrease in C5+ selectivity were observed with increasing temperature and inlet H2/CO ratio, while the increase in pressure and conversion level had an opposite effect. We also analyzed the effect of process parameters on the values of chain growth probabilities for different chain lengths (αn). We found that both changes in CH4 and C5+ selectivity can be correlated with values of αn and that the growth probability of C1 intermediate (α1) has the most dominant effect on selectivity. While α1 shows significant changes with variations in process parameters, the values of C2+ growth probabilities remain relatively constant [1]. This result suggests that one of the main reasons for variation of overall FTS selectivity is the formation of methane and that secondary olefin reactions only play a minor role. Understanding the pathways for methane formation in FTS is the key to improvement of cobalt-based catalyst performance. Acknowledgments - This publication was made possible by NPRP grant 08-173-2-050 from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors. References: [1] B. Todic, W. Ma, G. Jacobs, B.H. Davis and D.B. Bukur, J. Catal., 311 (2014) 325.

Importance of methane formation in determining overall selectivity of Fischer-Tropsch synthesis over cobalt-based catalyst

249th National Meeting (2015)

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