Modification of FCC catalysts by addition of ZSM-5

ZSM-5 is now used frequently in FCC operations to modify the selectivity of the active zeolite Y base. A small addition, generally no more than 2.5% crystal in a separate catalyst substrate, has a pronounced effect on both LPG and gasoline yields and in addition produces an enhancement of gasoline octane rating. This paper studies the role of ZSM-5 in more detail by examining hydrocarbon type distributions in the C{sub 1}-C{sub 10} region of cracked product. A first series of experiments examines the effect of ZSM-5 deactivation on activity and selectivity of a steam deactivated commercial FCC catalyst in order to simulate the effect of fresh ZSM-5 addition to an equilibrium catalyst. At zero, or minimal deactivation, ZSM-5 has a positive influence on overall activity but there is a preponderance of C{sub 2}-C{sub 4} alkanes. Further deactivation lessens activity and produces relatively more LPG olefinicity and reaction mechanisms are proposed to account for the product distribution.