Vapor-solid interaction among cellulose, hemicellulose and lignin

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.