Deactivation by coking of zeolite catalysts. Prevention of deactivation. Optimal conditions for regeneration

摘要

The deactivation of acid zeolite catalysts used in hydrocarbon transofrmations is mainly due to the deposit inside the pores of heavy secondary products generally known as coke. It is sown how the rate of coking and the deactivating effect of the coke molecules are affected by the pore structure and the acidity of the zeolites as well as by the operating conditions. Directives for minimizing the deactivation by coking are proposed: (1) cholice of tridimensional zeolites without trap cavities (large cavities with small apertures); (2) adjustment of the density and strength of the acid sites to the lowest values necessary for the selective formation of the desired products; and (3) chloice of operating conditions in order to avid the formation of coke-maker molecules (alkenes, polyaromatics).