Research on Reactive Adsorption Desulfurization over Ni/ZnO−SiO2−Al2O3 Adsorbent in a Fixed-Fluidized Bed Reactor

Abstract

Reactive adsorption desulfurization of FCC gasoline over a Ni/ZnO−SiO2−Al2O3 adsorbent was carried out in a fixed-fluidized bed reactor at low pressures in the presence of hydrogen. The results show that high temperature, high pressure, high molar ratios of hydrogen-to-oil, and low weight hourly space velocity are favorable to improve the desulfurization ability of adsorbent but not conducive to maintaining the octane number of FCC gasoline throughout the condition range examined. Under optimal operating conditions, ultralow sulfur gasoline can be produced, and the RON loss is only 1 unit. Furthermore, the effect of prereduction and adsorbent characterization data (SEM/EDX, N2 adsorption) reveal that reduction increases the interaction between Ni and S compounds and improves the pore structure of adsorbent, leading to a significant improvement in the desulfurization capability of adsorbent. Take 3-methylthiophene for example, after adsorbing on an active Ni atom via the S−Ni bond, the sulfur of 3-methylthiophene is removed by direct hydrogenolysis of the C−S bond, resulting in the formation of NiSx and 2-methyl-1,3-butadiene in hydrogen atmosphere. The latter is mainly hydrogenated to 2-methyl-2-butene and 2-methylbutane. ZnO acts as a sulfur-acceptor, which can regenerate the active Ni in situ in hydrogen atmosphere. The complete sulfidation of adsorbent particles takes place by ion diffusion.