Decoking and Regeneration of a Hydrotreating Catalyst by Supercritical Extraction

Abstract

An industrially spent hydrotreating catalyst from naphtha service was extracted with tetrahydrofuran, carbon dioxide, pyridine and sulfur dioxide under subcritical and supercritical conditions. After extraction, the catalyst activity, coke content, and pore characteristics were measured. Tetra hydrofuran was not effective in the removal of coke from catalyst, but the other three solvents could remove from 18% to 54% of the coke from catalyst. The coke was removed predominantly from pores in the range of 4-12 nm, resulting in a bimodal pore size distribution and an increase in the pore volume and surface area. The amount of coke removed depended on the extraction temperature, pressure and duration. In the most severe extraction conditions, the silica foulant of the catalyst could also be removed as fine particles. Pyridine poisoned the catalyst during extraction, however its removal by acetone wash could restore the catalyst activity.Hydrotreating catalysts are extensively used in petroleum processing, coal liquefaction, and generally in upgrading of liquid fossil fuels. These catalysts deactivate by coverage of their active sites with poisoning compounds and by blockage of their pores by deposition of carbonaceous solids and metallic foulants. Depending on the type of feedstock, the catalyst life may vary from a few months for heavy oils to a few years for naphthas. At the end of their active lives, the spent catalysts are removed from the reactor and replaced by fresh catalysts. Most of the spent catalysts are disposed of as solid wastes in landfills or used for metals reclamation. Only a small fraction of these catalysts is regenerated by controlled oxidation and reused as low activity catalyst in guard chambers. At present, no in-situ regeneration technique is available for these catalysts. This work discusses the merits of in-situ catalyst regeneration and investigates the