Reactivity of Olefins and Thiophenes in Hydrodesulfurization of FCC Gasoline

Abstract

The reactivity of olefins and S-compounds and their distributions in different catalyst-bed lengths were experimentally evaluated with a FCC gasoline in a high-pressure fixed-bed continuous flow pilot unit over the CoMoS/γ-Al2O3 catalyst. The evaluation results demonstrated that the increased steric hindrances around the double bond (C=C) and that to the thiophene molecules could suppress the hydrogenation of olefins and hydrodesulfurization (HDS) of S-compounds, respectively. Meanwhile, the reaction temperatures could influence the acidic property of the CoMoS active phase confirmed by FT-IR analysis, and thus induced the different reactions. It was found that the isomerization of terminal olefins to internal olefins was promoted by the Brønsted acid sites (-SH) at low temperatures, as well as the skeletal isomerization by the strong Lewis acid sites occurred to a minor extent at high temperatures. Besides, the distributions of olefins and S-compounds in different catalyst-bed lengths showed that the removal of S-compounds reached 80% of its maximum conversion at the first 40% of the reactor length, however, the saturation of olefins increased linearly as the reactor length increased. Therefore, a new catalyst-loading method was developed, i.e., the upper 40% of the reactor length filling with catalyst of high HDS activity and the bottom 60% with catalyst of low olefin saturation activity, respectively. The evaluation results showed that the graded catalyst loading process showed higher selectivity in HDS of FCC gasoline.