Application of hierarchical zeolites in FCC catalyst

摘要

With the depletion of crude oil reserves,more focus have been shifted towards the catalytic cracking of heavier hydrocarbons for the production of transportation fuels.Fluidized catalytic cracking(FCC)of vacuum gas oil(VGO)is considered as a promising process for enhancing the gasoline yield to fulfill the global energy demand.Recent literature on FCC catalyst indicates the room for increasing the efficiency of regular FCC zeolites based catalysts.This is due to the complex feed compositions,diffusion limitations,less yield of desired hydrocarbons and instability of the catalyst due to the coking and poisoning by the sulphur,nitrogen and oxygen bearing species in the feedstock.The inclusion of hierarchical zeolite catalyst systems have been considered as most suitable option.Although,it has been proved that FCC catalyst mesoporosity enhances the catalyst performance but it does not mean that ultra large pore size of zeolite are necessarily suitable active component of FCC catalysts.Both MCM-41 and US Y zeolites have been tested for the large molecules cracking but MCM-41 performs poorer due to its low thermal stability at the high temperature which prevents its use in severe FCC cracking process conditions.Apart from ZSM-5 and Y zeolite,Beta zeolite has also been tested for the FCC cracking but thermal stability and economics impedes its application to use it in large scale.A catalyst mixture of ZSM-5 and ITQ-33 had more yield of middle distillate and propylene as compared to US-Y Zeolite but stability and economics limits its widespread applications.These new trends of catalyst made possible to process heavier crude oil fractions to increasing amount of propylene and gasoline range fuels.