Effect of zeolite structure and addition of steam on naphtha catalytic cracking to improve olefin production

Abstract

In this study, steam catalytic cracking of dodecane (a model representative of naphtha) was investigated both with and without steam. The reaction utilized the different 3D sinusoidal microporous channels in submicron ZSM-5 and BEA zeolite crystals to convert dodecane to light olefins. Although both synthesized submicron catalysts (400–500 nm) have similar Brønsted/Lewis acid ratios, the BEA zeolite exhibited higher surface acidity than ZSM-5 zeolite. In addition, the steam addition has significantly affected the zeolites structure, even though their cracking activity was not affected. However, the zeolites structural modification has shown significant effect on the pore shape selectivity which result in different light olefins yields. During catalytic cracking in the absence of steam, hydrogen transfer reaction was less favored over BEA zeolite, which result in higher light olefins selectivity and dry gas formation than with ZSM-5 zeolite. In the presence of steam, ZSM-5 pore-shape modification favored the monomolecular cracking pathway leading to achieving higher light olefin yield than that observed over BEA zeolite. The study demonstrated that ethylene/propylene ratio (E/P) is impacted by zeolite structure which is affected by the steam addition during the reaction.