Valorisation of waste biomass and plastics toward light aromatics: Co-catalytic fast pyrolysis of torrefied bamboo and polyethylene over alkali and acid treated hierarchical HZSM-5

Abstract

Light aromatics are extremely important building blocks which can be prepared from the co-catalytic fast pyrolysis (Co-CFP) of biomass and polyethylene. In this study, the bamboo was torrefied to remove part of oxygen element prior to pyrolysis, then being co-fed with polyethylene (HDPE, PE and LDPE) during CFP over alkali (NaOH and Na2CO3) and acid (H3PO4 and HCl) treated HZSM-5. 40.3% oxygen element in bamboo could be eliminated at torrefaction temperature of 300 °C. After the acid dealumination or alkali desilication treatments, the mesopore was creased in HZSM-5, transforming into hierarchical structure with larger pore size and lower acidity. The effect of torrefaction temperature, the species of alkali or acid solutions and their concentrations, the mass ratio of HDPE-to-torrefied bamboo, the CFP temperature on the yields of light aromatics was systematically discussed. The maximum yield of BTX was 4.39 × 108 a.u./mg which was obtained by Co-CFP of torrefied bamboo (250 °C) and HDPE at mass ratio of 1:2 with 800 °C over 0.2 M NaOH treated hierarchical HZSM-5. The aromatization reaction of olefins, the deoxygenation reaction of oxygenates, and the Diels-Alder reaction between furans and olefins were key reactions for the formation of BTX during Co-CFP of torrefied bamboo and polyethylene.