ABSTRACT
This chapter reviews state-of-the-art lignocellulosic biomass pretreatment in preparation for enzymatic digestion, with emphasis on lignocellulose-to-ethanol production. Pretreatment techniques are classified by chemical application and type, and by product stream. The chapter provides various pretreatment reactor designs, reaction kinetics, and engineering constraints and challenges. It discusses the structural and Compositional Factors that affect the susceptibility of lignocellulosic biomass to enzyme attack, including cellulose crystallinity, lignin and hemicellulose protection of cellulose, accessible surface area of cellulose, and degree of acetylation of hemicelluloses. Pretreatment techniques can generally be grouped into three categories—physical, chemical, and biological—according to chemical and microorganism application. Physical pretreatment techniques do not involve chemical application. Typical examples are comminution, irradiation, steaming/steam explosion, and hydrothermolysis. The chapter summarizes the various product streams derived from the three major lignocellulosic material components—cellulose, hemicellulose, and lignin—as a result of pretreatment. The goal of pretreatment is to prepare biomass to facilitate bioconversion or paper-making.
