Production of middle distillate in a dual-bed reactor from synthesis gas through wax cracking: Effect of acid property of Pd-loaded solid acid catalysts on the wax conversion and middle distillate selectivity

Abstract

Selective production of middle distillate (C10–C20) from synthesis gas (CO+H2) was carried out in a dual-bed reactor. Co-based catalysts were used in the first-bed reactor to produce wax (C21+) from synthesis gas, and Pd-loaded solid acid catalysts were used in the second-bed reactor to produce middle distillate from wax through hydrocracking. Co/TiO2 catalyst in the first-bed reactor produced more than 35wt% middle distillate and more than 20wt% wax. These products served as a suitable feed for the production of middle distillate through hydrocracking in the second-bed reactor. Pd-loaded solid acid catalysts used in the second-bed reactor retained three types of acid sites (weak-, medium-, and strong-acid sites). Correlations between medium acidity and catalytic activity of Pd-loaded solid acid catalyst revealed that wax conversion and increment of middle distillate selectivity in the second-bed reactor were increased with increasing medium acidity of the catalyst. Total acidity of Pd-loaded solid acid catalyst was increased with increasing medium acidity of the catalyst. Thus, the medium acidity (total acidity) of Pd-loaded solid acid catalyst served as a crucial factor in hydrocracking of wax. Among the second-bed catalysts, the Pd/mesoporous alumina (Pd/MA) catalyst with the highest medium acidity (total acidity) showed the best catalytic performance (ca. 83% wax conversion and ca. 15wt% increment of middle distillate selectivity).