RATES OF ISOBUTANE CRACKING CATALYZED BY HZSM-5 - THE CARBONIUM-ION ROUTE

Low conversions (< 1%) of isobutane catalyzed by the zeolite HZSM-5 were measured with a steady-state flow reactor at 450-500-degrees-C and an isobutane partial pressure of 7.98 kPa. The major products were methane and propylene, formed in equimolar amounts and indicative of cracking proceeding through a carbonium ion intermediate formed by protonation of isobutane. The rate of the reaction at 475-degrees-C is 1.4 X 10(-6) mol per g catalyst per s; the apparent activation energy is 57 kcal mol-1. Isobutylene was also formed as a primary product, at rates several-fold less than the cracking rate. Propane appeared to be a primary product, possibly formed in a hydrogen transfer reaction. Nonprimary products included ethylene, but-1-ene and but-2-enes.