Key role of the pore volume of zeolite for selective production of propylene from olefins

A plausible reaction mechanism for propylene (C3H6) production from ethylene (C2H4) was investigated, based on the amounts of effluent hydrocarbons and hydrocarbons produced in the pores of SAPO-34. Propylene was produced via an oligomerization-cracking mechanism. On the basis of this mechanism, the conversions of C2H4, pentenes, and hexenes were examined. The catalytic performance was compared, in order to investigate the role of the pore volume of zeolites with 8-, 10-, and 12-membered rings in the selective production of C3H6. The selectivity for C3H6 was crucially dependent upon the pore volume of the zeolite. Highly selective production of C3H6 from olefins (C2H4, pentenes, and hexenes) can be accomplished by employing a new concept: adjusting the pore volume of a zeolite to accommodate the volume of an olefin and/or its carbenium cations, as opposed to a conventional molecular sieve approach. For example, an unimolecular cracking of pentenes into C3H6 and C2H4 involving primary cations can be controlled by the pore volume of a zeolite.