HYDROGEN TRANSFER IN CATALYTIC CRACKING

Hydrogen transfer is an important secondary reaction of catalytic cracking reactions, which affects product yield distribution and product quality. It is an exothermic reaction with low activation energy around 43.3 kJ/mol. Catalyst properties and operation parameters in catalytic cracking greatly influence the hydrogen transfer reaction. Satisfactory results are expected through careful selection of proper catalysts and operation conditions.Fluid catalytic cracking (FCC) is one of the major refining processes for converting vacuum distillates and residues into gas, high octane gasoline and diesel fuels over solid acidic catalysts. Cracking catalyst promotes cracking reactions, the reaction mechanism can be explained by carbonium ion theory [1] . Hydrogen transfer is a bimolecular reaction which requires two adjacent acid sites, where hydrogen usually transfers from a heavier hydrocarbon molecule to a lighter alkene molecule, the latter desorbs as an isoalkane molecule, and the former that donates hydrogen becomes more aromatic and finally coke [2] . Hydrogen transfer activity has long been recognized as relating to the acid site density of the catalyst. Thus the alkene content and composition of cracked naphtha and of product gas are expected to be adjusted by hydrogen transfer reaction occurred in FCC process. In this study, many factors affecting hydrogen transfer reaction, such as different kinds of zeolite catalysts used, reaction temperature, reaction time and coke deposit, were investigated. It will be helpful for the refiners to control proper extent of hydrogen transfer reaction in FCC process operation to adapt to different purposes and various options, such as maximizing gasoline yield, maximizing or minimizing olefins in gasoline, maximizing or minimizing gas olefins or iso olefins in product etc..