Catalytic pyrolysis of n-paraffin coexisting with olefin over ZSM-5 based catalysts: Experiments, kinetics, and DFT calculations

This study investigates the co-cracking of n-hexane and 1-hexene, utilizing 1-hexene as an olefinic initiator to improve light olefin yields. Experimental investigations, kinetic analyses, and density functional theory calculations (DFT) were used to systematically explore cracking performance, interactions, and mechanisms for co-feeding. Comparied with single feeding of n-hexane, leading to higher light olefin yields (increased from 35.77 wt% to 58.61 wt%) when the olefin content is 20 wt%. Kinetic analysis revealed a shift from protolytic to hydrogen transfer cracking pathway when 1-hexene content exceeded 13.6 wt%, with the maximum cracking rate (13.12 h⁻¹) constant at 20 wt% olefin content. DFT calculations showed a lower energy barrier for hydrogen transfer cracking between n-hexane and 1-hexene, compared to n-hexane cracking alone. Therefore, a co-cracking mechanism was proposed, involving paraffin activation through carbocation intermediates generated by olefin, followed by β-cracking to generated light olefins and carbenium ion regeneration, establishing a framework for paraffin-olefin co-conversion.