CO/CO2 hydrogenation for the production of lighter hydrocarbons over SAPO-34 modified hybrid FTS catalysts

Abstract

Fischer-Tropsch synthesis (FTS) is known as the catalytic reactions which convert syngas (CO + H2) to value-added hydrocarbon products. GTL (gas to liquid)-FPSO (floating, production, storage, and offloading) process is one of the solutions for the monetization of CO2 rich natural gas or stranded natural gas in offshore. In this work, for the compact design of the GTL-FPSO process, the hybrid FTS catalyst was designed by the physical mixing of the Co/γ-alumina with the hydrocracking catalyst (γ-alumina and SAPO-34), and also Co/SAPO-34 catalyst was prepared without any γ-alumina. SAPO-34 was synthesized by the hydrothermal procedure, and Co/γ-alumina and Co/SAPO-34 catalysts were prepared by the impregnation method. The relationship of catalytic activity, methane selectivity, and C5+ selectivity with the acid sites were studied for hybrid FTS catalyst. It was found that by adding SAPO-34 to Co/γ-alumina catalyst, a lighter fuel can be produced. Also, the effect of CO2/(CO + CO2) ratio over the Co/SAPO-34 catalyst on the carbon conversion and product distribution was investigated for the first time. It was found that there is an optimum value for CO2/(CO + CO2) ratio in the feed that is around 0.25. At this ratio, the C5+ selectivities and carbon conversion are the highest, and the methane selectivity is the lowest. It was considered that the high amount of CO2 in the feed promotes the hydrocracking and the methanation reaction over Co/SAPO-34 catalyst.