Promotion on light olefins production through modulating the reaction pathways for n-pentane catalytic cracking over ZSM-5 based catalysts

Abstract

Insights into reaction mechanism were vital to direct naphtha catalytic cracking process to produce light olefins. In order to reveal influences of reaction pathways modulation on light olefins production, Zr-ZSM-5, Ag-ZSM-5, and the regenerated HZSM-5 (ZSM-5(R2)) were prepared and employed in n-pentane catalytic cracking. It was found that light olefins yield obtained over Zr-ZSM-5, Ag-ZSM-5, and ZSM-5(R2) at 500°C was 58%, 81%, and 113% higher than that over the parent HZSM-5 (12.0%), respectively. Promotion on light olefins production caused by Zr-incorporation can be attributed to the enhancement of hydride transfer reactions increasing the utilization of Brønsted acid sites and the catalytic activity accompanied with the proximate stability compared to the parent HZSM-5. Different from Zr-ZSM-5, Ag-ZSM-5 and ZSM-5(R2) respectively introduced dehydrogenation cracking and redox cracking to n-pentane catalytic cracking, which selectively promoted the formation of light olefins and significantly enhanced n-pentane protolytic cracking. However, both Ag-ZSM-5 and ZSM-5(R2) went through a rapid deactivation at 550°C, which was probably due the selective enhancement of alkenes accelerating the side reactions to coke formation.