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

Abstract

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.