Principles and Development of Lignocellulosic Biomass Pretreatment for Biofuels

Lignocellulosic biomass has been considered as the second generation feedstock for biorefinery to produce biofuels and bio-based products. Bioconversion is one of the major pathways involved in the development of biorefinery. However, it is significantly hindered by the structural and chemical complexity of biomass, which makes cellulosic biofuel economically unfit. Fermentable sugars of biomass carbohydrates such as cellulose and hemicellulose necessary for fermentation are trapped inside the cross-linking structure of the lignocellulose. Therefore, pretreatment of biomass is always required to convert lignocellulosic biomass from its native form, in which it is recalcitrant to biodegradation by enzymatic and microbial attacks, into a form amenable to biodegradation. The pretreatment itself is one of key cost contributors to the economics of biofuels while it also affects the cost efficiency of the downstream bioconversion processes. As a result, extensive research has been done on pretreatment. This chapter reviews currently existing pretreatment methods including physical, chemical and biological pretreatment with the focus on the principles, advantages/disadvantages, characteristics and recent development. In addition, we also cover the impact of biomass structural and compositional features on the pretreatment, the current status and challenges of pretreatment research and the future research targets.