Study on catalytic pyrolysis mechanism of natural rubber (NR) over Zn-modified ZSM5 catalysts

Abstract

In this work, NR and D-limonene were pyrolyzed using ZSM5, Zn/ZSM5, ZnO/ZSM5 and ZnS/ZSM5 catalysts on a Py-GCMS system. The effects of Zn loading (1, 3, 5 wt%) and catalyst preparation methods (impregnation method, ion-exchange method) on catalytic pyrolysis experiments were studied. The results indicated the introduction of Zn species into zeolites can form new Lewis acid (L acid) sites at the expense of Brønsted acid (B acid) sites. For Zn/ZSM5 catalysts prepared by impregnation method, Zn species mainly existed in the form of the divalent zinc cation at the exchange sites and ZnO, and the proportion of ZnO increased with the Zn loading increasing. For Zn/ZSM5 catalyst prepared by ion-exchange method, most Zn2+ were tightly interacted with zeolite framework. For ZnO/ZSM5 and ZnS/ZSM5 catalysts, the Zn species primarily existed in the form of ZnO and ZnS, respectively. Py-GC/MS experimental results showed that proper Zn loading helped to improve the selectivity of aromatic hydrocarbons in NR pyrolysis products, especially BTEX (Benzene, Toluene, Ethylbenzene, Xylene), but excessive Zn loading had a negative effect. Compared with impregnation method, Zn/ZSM5 catalyst prepared by ion-exchange method showed higher selectivity towards BTEX due to more Zn species existed in the form of divalent zinc ions.