4. Response of Biomass Species to Hydrothermal Pretreatment

Considerable effort has been devoted to the development of biofuels from renewable lignocellulosic biomass. To resolve the challenges associated with the structural barrier of lignocellulosic biomass, hydrothermal pretreatment is applied to alter the structure and improve the accessibility of carbohydrate sugars to microorganisms or chemicals in the subsequent conversion processes. Hydrothermal pretreatment takes advantage of high moisture content of biomass and efficiently converts polysaccharides into monomeric sugars and their corresponding degradation products. To achieve this goal, multiple technologies have been explored using liquid water as the media, with or without addition of chemicals (acids or alkalis). However, there are difficulties in developing an optimized and universal treatment approach due to the heterogeneity of biomass. In this chapter, four major biomass types, wood, bamboo, agricultural residues, and agave, are discussed and compared with respect to feedstock composition and response to the various hydrothermal pretreatments. Moreover, the reaction pathways of individual biomass components (hemicellulose, cellulose, lignin, extractive, and ash) under different treatment conditions (acidic and alkaline) are also comparatively reviewed. Finally, the effects of pH, biomass solid loading, and reactor selection on pretreatment are presented.