Enhancement of Fischer-Tropsch Synthesis by Periodical Draining of the Wax-Filled Pores of a Cobalt Catalyst by Hydrogenolysis

Abstract

Fischer-Tropsch reactors operated in a steady state suffer from a low pore effectiveness factor and a high methane selectivity caused by internal mass transfer limitations due to the accumulation of long-chain hydrocarbons inside the catalyst pores. Therefore, an alternating process switching between Fischer-Tropsch synthesis (FTS) and drainage of the pores by hydrogenolysis is proposed. The periodical cracking of the accumulated waxes within the (partially) filled pores, realized by a switch from syngas (H2, CO) to pure hydrogen, results in a higher overall catalyst productivity and a more favorable product distribution. The influence of temperature and time of FTS on drainage time and product distribution was experimentally investigated at typical temperatures of FT fixed bed processes in a range of 210 to 240°C. Alternating drainage of the pores by hydrogenolysis at a hydrogen partial pressure of just 1 bar leads to an improvement of the rate of CO conversion by up to 90% (240°C, 2 h FTS) and an improvement of even 120% concerning the rate of production of non-methane hydrocarbons (240°C, 2 h FTS).