Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process. (Part 7). Influence of Reaction Conditions at the First Stage on Deactivation Mechanism.

Abstract

Aging tests of hydrodesulfurization (HDS) catalysts were performed in the operation mode of constant sulfurremoval using product oils derived from hydrodemetallization (HDM) of Kuwait atmospheric residue under vanous reaction conditions. The used catalysts obtained were characterized to clarify the effects of HDM reaction conditions, focusing on reaction temperature, at the first-stage on the deactivation mechanism of the HDS catalysts at the second-stage. A good correlation occurred between the fouling rate of HDS catalysts and the content of hard-coke (insolubles in light gas oil) on the used HDS catalysts when the HDM and HDS temperatures were below 400°C, indicating that coke formation causes the HDS catalyst deactivation. When the HDM temperature at the first-stage was increased from 400 to 430°C, the HDS catalysts showed an increase in the fouling rate, despite a decrease in hard coke and metal deposits. This unusual phenomenon could be explained by introducing the concept of soft coke (solubles in light gas oil), which was removed during the preparation of used catalysts. Furthermore, details about the effect of HDM temperature on the deactivation mechanism of HDS catalysts were discussed.