Upgrading the quality of biomass by advanced oxidative torrefaction pretreatment: Rebuilding the oxidative torrefaction mechanism based on hemicellulose, cellulose, and lignin

Abstract

The oxidative torrefaction pretreatment (OTP) is a promising approach to upgrade the quality of biomass. This work investigated the oxidative torrefaction mechanism based on the OTP experiment of biomass pseudo component (cellulose, hemicellulose, and lignin) at varying OTP temperatures and oxygen concentrations. Results showed that more mass of biomass was transferred into the torrefied gaseous and liquid products with OTP temperature and oxygen concentration increasing, remaining less mass in torrefied solid product. The element distribution in biomass pseudo component was optimized after OTP, presenting as the removal of oxygen element and the enrichment of carbon element. The variation of these two elements in hemicellulose after OTP was much higher than that of cellulose and lignin due to the more intensive thermal decomposition reaction in hemicellulose. The chemical compounds in torrefied liquid products from biomass pseudo component were highly differentiated with each other, the anhydrosugars (e.g., levoglucosenone (LGO) and levoglucosan (LG)) and furans (e.g., furfural (FF)) from OTP of cellulose, the furans (e.g., furfural (FF)) and acids (e.g., acetic acid (AA)) from OTP of hemicellulose, the phenols from OTP of lignin. The concentrations of the released gas components during OTP of biomass pseudo component were ranked as CO2 > CO > H2 ≈ CH4. The thermal degradation mechanism of biomass OTP was revealed.