Porosity roles of micro-mesostructured ZSM-5 in catalytic fast pyrolysis of cellulolytic enzyme lignin for aromatics

Abstract

Cellulolytic enzyme lignin could be utilized to produce aromatic-rich bio-oil in the catalytic fast pyrolysis (CFP) process, in which strong-acidic ZSM-5 is often used as the catalyst. The introduction of mesopores into conventional ZSM-5 catalysts can improve the diffusion of heavy components and thus enable the modulation of pyrolysis products. To investigate the effect of mesoporous structure parameters on the diffusion of heavy phenols and the regulation of pyrolysis products by different types of pore structures, three different mesoporous ZSM-5 were prepared (core-shell, hierarchical, composites), with textural properties being compared in detail. The structural parameters were adopted to analyze the relationship between mesopores distribution and catalytic performance, revealing the significant effect of equivalent mesopore size. Among the prepared catalysts, a micro-mesostructured composite zeolite (ZMA) with internal hierarchical pores and ununiform mesolayer shell had a suitable mesostructure, of which the interconnected meso-channels improved the accessibility of inner acidic sites. Also, it was optimum to balance aromatic yield (above 7.5 wt%) and the product distribution (MAHs/PAHs approaching 6), revealing that its moderate equivalent pore size maintained a certain shape-selectivity to suppress PAHs formation. It was further shown that the applicable catalyst to lignin ratio (C/L) ranges differed with various mesostructures, as ZMA and hierarchical samples were suitable for higher and lower ratios, respectively.