Effects of oxidative torrefaction on the physicochemical properties and pyrolysis products of hemicellulose in bamboo processing residues

Abstract

Torrefaction pretreatment is applied to improve the fuel quality of biomass. However, in industrial production, oxygen can be unintentionally involved in the torrefaction process due to insufficient airtightness of the torrefaction reaction equipment or the presence of voids in the biomass particles. In this study, hemicellulose was extracted from the bamboo processing residue and was used as raw material for torrefaction experiment. We mainly studied the effects of oxidative torrefaction on physical and chemical properties of torrefied hemicellulose and the distribution of pyrolysis products under different oxygen concentrations and torrefaction temperatures. Results showed that a lower torrefaction temperature (200 °C) yielded solid products with higher HHV even when the oxygen concentration was increased to 15%. With a 5% oxygen concentration, a higher torrefaction temperature can apparently reduce the oxygen and hydrogen contents, and decrease atomic O/C and H/C ratios in torrefied hemicellulose. In terms of the pyrolysis products, at torrefaction temperature of 230 °C and 5% oxygen concentration, pyrolysis products had the lowest acid (7.85%) and the highest ester (6.32%) contents, indicating the highest quality of chemical compounds. A higher oxygen concentration of 5% was beneficial for the formation of alcohols in pyrolysis products. The highest content of furans (34.75%) in the pyrolysis products was achieved after torrefaction pretreatment at 260 °C and 5% oxygen concentration. The production of phenolics compounds favored lower temperature of 200 °C and 0% oxygen concentration in torrefaction pretreatment. This work provides a new avenue to improve the quality of pyrolysis products of biomass through oxidative torrefaction. Effects of oxidative torrefaction on the physicochemical properties and pyrolysis products distributions of hemicellulose derived from bamboo processing residues. • Effects of oxidative torrefaction on hemicellulose properties were investigated. • Hemicellulose underwent dehydrogenation, and deoxygenation, and less extent decarbonization during torrefaction. • Torrefaction pretreatment of hemicellulose at 230 °C and 5% oxygen concentration favored high-value pyrolysis products.