Reactions of model compounds over steamed ZSM-5 at simulated FCC reaction conditions

Abstract

C 6 C 10 normal paraffins and olefins were cracked over steamed ZSM-5 in a fixed-bed reactor in order to determine the dominant reactions that occur when ZSM-5 is added to an FCC unit. Conditions were chosen to approximate the reaction severity in industrial FCC reactors. For all three paraffins, conversion was less than 1%. Conversions of the olefins to lower carbon number species ranged from 26% for hexene to 83% for decene. Olefin isomerization was faster than olefin cracking. Formation of aromatics and paraffins was very low (about 1 %). These results indicate that equilibrated ZSM-5 does little cracking of gasoline-range paraffins in the FCC unit. Most of the reduction in paraffins which is observed upon ZSM-5 addition is likely due to the cracking away of gasoline-range olefins (especially C 7+, leaving fewer of these olefins available for conversion to paraffins by hydrogen transfer reactions over the base catalyst. Experiments with hexene reaction over sequential beds of ZSM-5 and Y base catalysts demonstrated that cracking of olefins over ZSM-5 can reduce paraffin formation by REY and USY catalysts.