Kinetic Modeling of Secondary Methane Formation and 1-Olefin Hydrogenation in Fischer-Tropsch Synthesis over a Cobalt Catalyst

Abstract

A detailed kinetic model of Fischer-Tropsch synthesis (FTS) product formation, including secondary methane formation and 1-olefin hydrogenation, has been developed. Methane formation in FTS over the cobalt-based catalyst is well known to be higher-than-expected compared to other n-paraffin products under typical reaction conditions. A novel model proposes secondary methane formation on a different type of active site, which is not active in forming C2+ products, to explain this anomalous methane behavior. In addition, a model of secondary 1-olefin hydrogenation has also been developed. Secondary 1-olefin hydrogenation is related to secondary methane formation with both reactions happening on the same type of active sites. The model parameters were estimated from experimental data obtained with Co/Re/-Al2O3 catalyst in a slurry-phase stirred tank reactor over a range of conditions (T = 478, 493, and 503 K, P = 1.5 and 2.5 MPa, H-2/CO feed ratio = 1.4 and 2.1, and X-CO = 16-62%). The proposed model including secondary methane formation and 1-olefin hydrogenation is shown to provide an improved quantitative and qualitative prediction of experimentally observed behavior compared to the detailed model with only primary reactions.