Selective production of aromatics from catalytic pyrolysis of biomass wastes: Effects of feedstock properties and key oxygenated intermediates on aromatics formation

The catalytic pyrolysis is a promising method for obtaining value-added aromatics, especially benzene, toluene and xylene (BTX). For different biomass-based materials, the dual catalyst system composed of CaO-based and ZSM-5-based catalysts showed an obvious selectivity for the BTX production. This study chose CaO derived from organic calcium precursors (Org-CaO) and nano-sized ZSM-5 (NZSM-5), and comprehensively investigated the effects mechanism of biomass components on the formation pathways of BTX via Py-GC/MS. Under the catalysis of NZSM-5, the BTX yields were only 7.8-30%. The BTX yields on Org-CaO/NZSM-5 were as follows: lipid (63.1%) > hemicellulose (55.4%) > cellulose (40.2%) > lignin (21.7%). Typical pyrolysis intermediates were employed to quantitatively reveal the intermediate reactions. Pyrolysis intermediates exhibited low BTX-forming reactivity over NZSM-5. The pre-catalysis of Org-CaO selectively converted part undesired intermediates (fatty acids and furans) into BTX precursors (short-chain olefins and ketones), facilitating the remarkable increase of BTX yield in the subsequent NZSM-5 catalysis process. However, the pre-catalysis of Org-CaO can hardly make the ring opening reaction of lignin-derived phenolic compounds that have very low reactivity on NZSM-5, and thence high-lignin biomass obtained low BTX production during catalytic pyrolysis by Org-CaO/NZSM-5. These findings afforded a new route for increasing the BTX yields by directionally forming BTX precursors or controlling biomass components.