Texture Evolution of Hard-Templated Hierarchically Porous Alumina Catalyst in Heavy Oil Hydroprocessing

Abstract

The study is devoted to the deactivation behavior of alumina “guard-type” mesoporous and hierarchical catalysts in long-term 800 h hydroprocessing of heavy oil under conditions close to industrial ones. The purely mesoporous sample had only 10–15 nm mesopores by Hg porosimetry whereas the hierarchical catalyst possessed a bimodal pore size distribution with maximum at 15 nm (55 vol%) and 40 nm (45 vol%, related to the mouths of 200 nm spherical macropores). Both catalysts had similar activities for the first 200 h of hydroprocessing. The mesoporous catalyst underwent the rapid deactivation in hydrodesulfurization (HDS) and hydrodemetallization (HDM) of V after 200 h on stream, and the remarkable decrease in hydrodeaspaltenization (HDAs) and Ni removal after 300–400 h on stream due to the intensive mesopore plugging by 55% of the total volume. The hierarchical catalyst did not show any decline in HDS and HDAs during the 800 h experiment, though its HDM activity also reduced due to the surface poisoning and coke deposition, albeit to a lesser extent. The intrinsic mesopores of the hierarchical alumina were shown to narrow down to 10 nm but did not experience substantial blocking observed for the mesoporous catalyst. Hierarchical texture seems not only to provide wide macro- and mesopores less prone to plugging by coke species, but to ensure effective transport of reaction products out of the small pores which prevents them from blockage.