Catalytic Cracking of Paraffins on Zeolite Catalysts for the Production of Light Olefins

摘要

Cracking of heptane and octane, typical components of naphtha, was carried out on various proton-type zeolite catalysts. The selectivity to light olefins increased with decreasing the pore diameter of zeolites. Among them, H-ferrierite showed the highest olefin selectivity. Ca~(2+)-exchange into H-ferrierite further increased the selectivity especially at higher conversions and also improved the catalyst stability. The amount of coke formed during the reaction decreased by the Ca~(2+)-exchange. It is suggested that the Ca cations located inside the pores hinder the diffusion of reactant, product and intermediate molecules to retard hydride transfer between carbenium intermediate and olefin product, a bi-molecular reaction to form paraffins and coke precursors. As a result, the formation of paraffins and coke would be effectively suppressed, which may result in the high selectivity and stability of Ca~(2+)-exchanged ferrierite.