Vapor–solid interaction among cellulose, hemicellulose and lignin

Abstract

Secondary reactions, including those caused by interactions between vapor and solid phases, are unavoidable during biomass pyrolysis. In this study, the vapor–solid interaction between biomass components (cellulose, hemicellulose, and lignin) was investigated in a two-stage fixed-bed reactor. The results indicated that volatiles from hemicellulose promoted the breakdown of cellulose glycoside bonds and pyran rings as well as the removal of branched aliphatic chains and O-containing functional groups of lignin at 280 °C. Moreover, volatiles from cellulose produced abundant anhydrosugar, which was more prone to re-polymerization and to form aromatic rings on the lignin structure at 315 °C. As a result of the vapor–char interactions at 650 °C, the secondary decomposition of cellulose volatiles to gas products (decreasing by ~8 wt%) was inhibited, but carbonized products (increasing by ~3 wt%) tended to form, whereas hemicellulose vapor was more prone to decompose into low-molecular-weight liquid compounds, resulting in a high liquid yield (increasing by ~6 wt%). In addition, vapor–solid interactions accelerated the removal of O-containing functional groups of lignin volatiles, such as carbonyl and carboxyl, but inhibited the decomposition of H-containing functional groups, such as methyl and methylene. The finding is conducive to the understanding of the interactive mechanisms of biomass pyrolysis.