Slurry-phase hydrocracking of vacuum residue with a disposable red mud catalyst

Abstract

In this study, red mud (RM) was used as a catalyst in slurry-phase hydrocracking of vacuum residue (VR) in batch system. Without RM, thermal cracking occurred and a lighter fraction and higher conversion was achieved than in the presence of catalyst. However, the catalytic cracking obviously inhibited both the coke formation and residue cracking reaction. We investigated the influence of reaction temperature, reaction time and RM concentration on VR conversion. Reaction temperature and time significantly improved the yield of naphtha, diesel and vacuum gas oil; unfortunately, they also increased the gas fraction, which is an undesirable product. Catalyst concentration negligibly affected the VR conversion while vacuum gas oil fraction in product distribution increased with catalyst concentration, indicating that the cracking reaction was suppressed in the presence of catalyst. Through the characterization of fresh and spent catalysts by diverse techniques, it has been determined that the crystalline iron oxide of RM transforms into pyrrhotite (Fe(x−1)Sx), an active phase for the hydrocracking reaction, due to presence of sulfur in VR. Our results show that RM is possibly self-activated during the reaction and the pretreatment step can be eliminated.