Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process (Part 3). Influence of Asphaltene Content of Feedstock and Hydrodesulfurization Temperature at Second-stage.

Abstract

Aging tests of a hydrodesulfurization (HDS) catalyst in a two-stage resid desulfurization process, which consisted of hydrodemetallization (HDM) and HDS, were carried out on a small-scale pilot plant. The purpose was to determine the influence of asphaltene content of feedstock and that of HDM temperature in the first stage on HDS catalyst deactivation in the second stage under various reaction temperatures (HDS temperature). As feedstocks, resids of various asphaltene content were prepared by adding propane deasphalted (PDA) asphalt to atmospheric residue of Arabian light crude. Results show that at HDS temperatures below 400°C, an increase either in asphaltene content or in HDM temperature gradually increased the fouling rate, and at HDS temperatures above 400°C, this increase rapidly increased the fouling rate. These results suggest that, at lower HDS temperatures, coke precursor formed in the HDM reaction plays a key role in the HDS catalyst deactivation, and at higher HDS temperatures, coke precursor formed in the HDS reaction also significantly affects the HDS catalyst deactivation. The results also suggest that in the deactivation mechanism of HDS catalyst in the second stage, coke had a stronger effect on the HDS catalyst deactivation than did metal deposits.