Mechanisms of Thermochemical Biomass Conversion Processes. Part 1: Reactions of Pyrolysis

Abstract

The present work is a study on the pyrolysis mechanisms of biomass structural constituents. Biomass resources include wood and wood wastes, agricultural crops and their waste byproducts, municipal solid waste, animal wastes, waste from food processing, and aquatic plants and algae. The major organic components of biomass can be classified as cellulose, hemicelluloses, and lignin. The pyrolysis is thermal degradation of biomass by heat in the absence of oxygen, which results in the production of charcoal (solid), bio-oil (liquid), and fuel gas products. Thermal degradation of cellulose proceeds through two types of reaction: a gradual degradation, decomposition, and charring on heating at lower temperatures; and a rapid volatilization accompanied by the formation of levoglucosan on pyrolysis at higher temperatures. The hemicelluloses reacted more readily than cellulose during heating. Of the hemicelluloses, xylan is the least thermally stable, because pentosans are most susceptible to hydrolysis and dehydration reactions. Dehydration reactions around 473 K are primarily responsible for thermal degradation of lignin. Between 423 K and 573 K, cleavage of α- and β-aryl-alkyl-ether linkages occurs. Around 573 K, aliphatic side chains start splitting off from the aromatic ring.