Pretreatment of lignocellulosic feedstocks

Abstract

With the aim of reducing greenhouse gas (GHG) emissions and with our dependence on non-renewable fossil fuels, lignocellulose has been proposed to be an alternative sugar-rich raw material for renewable biofuel production, especially for the transportation sector. Biorefineries can efficiently convert lignocellulosic biomass into fuels, value-added chemicals, and other forms of energy. When lignocellulose is transformed using biochemical routes, via sugar conversion platform the highly recalcitrant structure of lignocellulosic materials hampers the conversion process by limiting the accessibility of the chemical building blocks. It is therefore imperative to include a pretreatment step to reach high overall yields and productivity in subsequent hydrolysis and fermentation steps. The main purpose of pretreatment is to break down the structure of lignin and/or to solubilize hemicellulose in order to improve the accessibility of cellulose towards hydrolytic enzymes. The effects of pretreatment on the different lignocellulosic polymers depends on the type of pretreatment itself and the conditions used. This chapter outlines the most common physical, chemical, physicochemical, and biological pretreatment technologies that have been developed and optimized over last four decades for disruption and/or fractionation of lignocellulosic feedstocks. The mechanisms of action and the potential benefits and drawbacks of each pretreatment are listed and discussed. Furthermore, the pretreatment technologies are also analyzed from an economic and environmental point of view to evaluate their sustainability.