Fischer-Tropsch Synthesis via Co-MOF-74-derived Catalysts and Catalytic Membranes

Abstract

Natural gas and biomass offer alternative carbon feedstocks for the production of liquid fuels. The low-temperature Fischer-Tropsch (FTS) synthesis process is a well-known method of converting these resources into liquid fuels, but currently the process suffers from high operating costs. Developing more active and selective reactors through novel catalyst design and reactor configurations will contribute to lowering operating costs. Pyrolysis of metal-organic frameworks is a recent technique used to prepare highly loaded and dispersed catalysts, for more active and selective performance. Catalysts derived from Co-MOF-74 were prepared and tested in a fixed-bed reactor, whilst chemical vapour deposition of acetylene was applied to improve performance. Loading the catalyst exclusively into the reactor resulted in very significant heat effects due to the highly exothermic nature of FTS, which was extremely detrimental to performance. Diluting the catalyst with inert particles showed significant improvement, whilst chemical vapour deposition of acetylene suggested further improvement. Comparing these catalysts to a conventionally prepared cobalt-based gamma-alumina supported catalyst, higher C7+ yields were obtained when the activity and local heat effect were considered. Two novel catalytic membrane reactors were prepared. A phase-inversion and sintering technique was used to prepare two uniquely micro-structured ceramic flat-disc membranes, with micro-channel diameters of around 50 to 200 μm, for the purpose of reducing transport limitations which may negatively impact selectivity and activity. The membranes were impregnated with cobalt and tested alongside a pellet-based and ground gamma-alumina supported cobalt catalysts. The membranes did not exhibit superior performance compared to the ground and pellet-based catalysts, likely due to intense heat effects in the micro-channel and poor dispersion of the Co active phase. The Co-MOF-74-derived catalyst was loaded into the membrane, however extremely high methane selectivity was observed.