Enhancing the Synergistic Effect of Cellulose and Polypropylene for Petrochemical Production during Catalytic Fast Pyrolysis by Mesoporous Gallium-MFI Zeolites

Abstract

Co-feeding plastic waste has been considered to be an attractive method to enhance aromatic production and mitigate coke formation during catalytic fast pyrolysis (CFP) of lignocellulosic biomass with zeolite catalysts. However, insignificant synergistic effects for aromatic production have been observed for the cofeed CFP of cellulose and polypropylene (PP) during CFP with the conventional ZSM-5 zeolites. In this study, a series of mesoporous ZSM-5 and gallium (Ga)-containing MFI zeolites were prepared by desilication of conventional ZSM-5 zeolite with alkaline treatment (DS-ZSM-5) and hydrothermal synthesis of galloaluminosilicate with or without post-alkaline treatment (GaMFI and DS-GaMFI). These zeolites were then tested for the cofeed CFP of cellulose and PP mixture. The results indicate that the generation of mesopores in microporous MFI zeolite by alkaline treatment can alleviate the steric hindrance effect of PP-derived branched olefins on their catalytic conversion, while the incorporation of Ga can considerably increase the dehydrogenation activity of the zeolites, thus enhancing the transformation of alkanes and olefins to aromatics. Therefore, these zeolites considerably enhanced the synergistic effect of cellulose and PP for aromatic production during the cofeed CFP, compared to the conventional ZSM-5 zeolite. The aromatic yield increased markedly from 32.9 C% for ZSM-5 to 40.9 C%, 47.9 C%, and 52.7 C% for the DS-ZSM-5, GaMFI, and DS-GaMFI zeolites, respectively. Meanwhile, the formation of undesired coke was moderately mitigated during cofeed CFP with the DS-ZSM-5 and DS-GaMFI zeolites. The results of this study demonstrate that the DS-GaMFI zeolite can provide an effective catalyst to enhance aromatic production in the cofeed CFP of lignocellulosic biomass and plastics.