Unraveling the critical role of initial isomerization in n-hexane catalytic cracking over HZSM-5 with molecular kinetic model

Abstract

Although HZSM-5 zeolite is widely used in catalytic cracking reactions, most relevant studies have not thoroughly examined the initial reaction behavior of n-hexane catalytic cracking, leading to an insufficient understanding of molecular-scale reaction mechanisms. Herein, we conducted precise catalyst tests to establish a molecular-scale reaction kinetic model for n-hexane catalytic cracking. The results showed that isohexane is an important primary product of the reaction. Two reaction networks, with and without n-hexane isomerization to isohexane, were compared, revealing that isohexane directly influences ethylene and propylene formation pathways and indirectly affects substances like isobutane. Results from the kinetic model showed that consideration of the pathway of n-hexane isomerization to isohexane helps reduce model errors. The detailed investigation indicated that the pathway of n-hexane isomerization exerts opposite effects on the formation of ethylene and propylene, and the model conclusions were confirmed by co-feeding experiments, which demonstrated that adding isohexane boosts ethylene selectivity and suppresses propylene formation. The present study deepens the understanding of the n-hexane cracking mechanism and provides a basis for the directional regulation of reaction pathways and the optimization of industrial process conditions.

Graphical abstract

Keywords

n-hexane / catalytic cracking / kinetic model / isomerization / HZSM-5 catalyst

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