Modification of Fischer-Tropsch process for selective production of aromatics via syn-gas conversion

Abstract

Products of Fisher-Tropsch synthesis (FTS) reaction are widely distributed from C1 to C40+ following the Anderson-Shulz-Flory model (ASF). Catalyst and process studies have been conducted to overcome ASF product distribution. Recently, the modifications of the FTS process to improve product selectivity have been suggested as addition cracking and oligomerization reactions using zeolite, and research on the Syn-gas to Aromatics (STA) through the bonding of the H-ZSM5 (HZ5) catalytic reaction has drawn attention. Complex studies on process variables, Fisher-Tropsy catalysts, and HZ5 characteristics are needed for modifying FTS reaction to optimize the yield of aromatic compounds from the syn-gas. In this study, the STA reaction behavior according to the control of porximity of Fe-based catalysts and HZ5, process condition variation, acidity modifying of HZ5, and influence of distribution of FTS products was investigated. The proximity of Fe-based catalysts and HZ5 was changed by controlling the catalyst mixing method in the two-stage reaction and the one-stage reaction system, and the optimal conditions were investigated by varying the temperature, pressure, and HZ5 acidity of the two-stage reaction. The BTEX selectivity was optimized to 36.7% in the two-stage reaction of linking FTS and 400 oC-1 bar aromatization reactions of 320 oC-20 bar. The two-stage reaction system was individually optimized FT reaction and aromatization conditions, thereby lower methane selectivity and higher aromatic selectivity compared to the one-stage reaction system were achieved. In the optimazation of two-stage STA reaction, high aromatics selectivity was increased with increasing acidity of HZ5. In order to enhance the acidity of HZ5, it was modified using NH4F and ethylene aromatization behavior was investigated. Fluorination of HZ5 using fluorine at an appropriate concentration improved the reaction characteristics of ethylene to aromatics (ETA), but BTEX selectivity was decreased in the two-stage STA reaction using fluorinated HZ5 due to the enhanced cracking rate by high acidity. In addition, in order to investigate the effect of FT-derived product distribution on the STA reaction and simplify the process, a Fe-based catalyst with various ratios of Mn promoters was manufactured to investigate the reaction behavior of first-stage STA. The Mn promoter increased the C6-C10 olefin distribution in FT-derived hydrocarbons, and high BTEX selectivity of 33.6% was achieved due to the relatively low C6-C10 olefin dehydrogenation energy compared to C2-C4 olefin in the first-stage STA reaction.