Oriented valorization of cellulose and xylan into anhydrosugars by using low-temperature pyrolysis

Abstract

Fast pyrolysis is a promising method to convert cellulose and hemicellulose into anhydrosugars, but the current method is energy intensive and provides poor yield and selectivity for anhydrosugars. The possibility of using mineral acid pretreatment to achieve oriented pyrolysis of cellulose and xylan at low temperature was explored in this study. The pyrolysis behaviors and mechanism of cellulose and xylan were investigated by pyrolysis–gas chromatography/mass spectrometry and in-situ diffuse reflectance infrared Fourier transform spectroscopy combined with two-dimensional perturbation correlation infrared spectroscopy. The results showed that H2SO4-impregnation and HCl-demineralization achieved the oriented pyrolysis of cellulose and xylan into anhydrosugars at 300 °C. The highest yields of levoglucosan and levoglucosenone (33.3 and 9.7%) were obtained from pyrolysis of 0.1%H2SO4-impregnated cellulose at 300 °C, while those of xylosan and 1,5-anhydro-4-deoxypent-1-en-3-ulose (19.4 and 8.4%) were produced from pyrolysis of HCl-demineralized xylan at 300 °C. It is inferred that H2SO4 could promote the condensation of hydroxyls at C6 and C1 positions and the cleavage of glycosidic bonds to form levoglucosan. And AAEMs could inhibit the intra-molecular dehydration of C3 hydroxyl and C2 hydrogen atom of levoglucosan to form levoglucosenone. The demineralization of xylan could promote the cleavage of glycosidic bonds and dehydration reactions to form xylosan and 1,5-anhydro-4-deoxypent-1-en-3-ulose. These findings provide a simple method to achieve oriented pyrolysis of cellulose and xylan at low temperature.