Regeneration of dehydrocyclodimerization catalyst

Abstract

A process for catalytic dehydrocyclodimerization and regeneration of the catalyst. C.sub.2 to C.sub.5 aliphatic hydrocarbons are reacted to produce aromatics, using a water-sensitive catalyst of a composition especially adapted to minimize deposition of coke on the catalyst. The catalyst is comprised of alumina which contains phosphorus, gallium, and a crystalline aluminosilicate having a silica to alumina ratio of at least 12. The use of this catalyst has resulted in a five-fold reduction in the rate of coke deposition, compared to a conventional dehydrocyclodimerization catalyst. However, the activity of this catalyst is significantly reduced by exposure to water at the temperatures normally used in removing the coke, which is accomplished by burning the coke in a combustion zone in the presence of oxygen, producing carbon dioxide and water. At least a portion of the gas leaving the combustion zone catalyst bed is combined with air and recycled back to the combustion zone. This mode of operation causes the concentration of water in the recycled stream to increase to an unacceptable value. Therefore, to obtain the benefit of this superior catalyst, it is necessary to utilize water removal steps in the catalyst regeneration procedure.