Elucidation of reaction network and effective control of carbon number distribution in the three phase Fischer–Tropsch synthesis

Reactions over olefins introduced during FT synthesis have been studied in a trickle bed reactor. Incorporation of 1-olefins into a growing alkyl chain could remarkably enhance the selectivity up to around 90% in heavy wax or middle distillate from syngas and could decrease the yields of lighter hydrocarbons with a higher CO conversion compared to the conventional FT synthesis. Results showed two significant processes the degradation of 1-olefins with successive demethylation, and its chain growth with incorporation by methylene species formed from demethylation, which is defined as the disproportionate reaction. The disproportionate reaction is competitive with introduced 1-olefins incorporating CH2 species formed from syngas into heavier hydrocarbons and is effectively controllable; Such control strongly depends on the process conditions. In general, the elimination of diffusion limitations for introduced 1-olefins and operating conditions that give a high intrinsic chain growth probability (α value) are favorable for suppressing the disproportionate reaction and for promoting the chain growth by the incorporation of syngas-formed CH2 species to increase the yields of heavier FT products.

This article is to deal with the secondary reactions of 1-olefins during Fischer–Tropsch and to selectively synthesize the “FT” products in the desired range (middle distillates and wax) by controlling the pathway reaction shown in the Figure below. In this study, around 90% selectivity in middle distillates and heavy wax has been achieved in olefin-added FT synthesis. We have also experimentally evidenced the disproportionate reaction of 1-olefins in the presence of hydrogen only. Figure optionsDownload as PowerPoint slide