TABLE OF CONTENTS At the end of the utilization cycle, spent hydroprocessing catalysts are removed from the reactor and replaced by either fresh or regenerated catalysts. Depending on the type of reactor, the replacement is performed either periodically on stream or during the shutdown of the operation. In order to ensure safety, a specially designed equipment has been used for catalyst withdrawal. Moreover, after the withdrawal from reactor, spent catalysts must be handled according to the procedures prescribed by the environmental and regulatory authorities who have been classifying spent hydroprocessing catalysts as the hazardous toxic wastes (41). De-oiling may be the only treatment performed on the refinery site. However, loading the catalyst for transportation and shipment to the off-site companies deserve attention as well. In most cases, additional treatments of spent catalysts are carried out off site. This may involve regeneration and/or rejuvenation for reuse, metal reclamation and other applications. The storage facilities approved by environmental and regulatory authorities must be used for the final disposal of spent catalysts to prevent release of the toxic species to ground water and the atmosphere.
Because of the extensive information available in the literature (68, 546, 588), only a brief account of regeneration is given with emphasis on the spent catalysts used for hydroprocessing of heavy feeds. For the purpose of this review, regeneration is considered to be a process for only removal of the coke deposited on catalyst surface with the aim to restore as much as possible of the original catalyst activity.
