Key Role of Pore Volume of Zeolite for Selective Production of Propylene from Olefins

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A plausible reaction mechanism for propylene (C_3H_6) production from ethylene (C_2H_4) was investigated, based on the amounts of effluent hydrocarbons and hydrocarbons produced in the pores of various zeolites. Propylene was produced via an oligomerization-cracking mechanism. On the basis of this mechanism, the conversions of C_2H_4, 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 C_3H_6 . The selectivity for C_3 H_6 was crucially dependent upon the pore volume of the zeolite. Highly selective production of C_3H_6 from olefins (C_2H_4 , 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 C_3 H_6 and C_2 H_4 involving primary cations can be controlled by the pore volume of a zeolite.