Fractionating Pretreatment of Lignocellulosic Biomass as an Entry into Biomass Refining

Lignocellulose, mostly existing in the form of plant materials, is one of the most abundant organic materials in natural world. It has been estimated that there is an annual worldwide production of 10–50 billion tons of dry lignocellulose, accounting for about half of the global biomass yield . In recent years, due to the escalating energy crisis and environmental pollutions, more extensive attention has been paid to the production of biofuels and biochemicals from biomass via a “biorefinery” platform. According to National Renewable Energy Laboratory of the USA, biorefinery is defined as “a facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass”, which is analogous to today's petroleum refineries . It has been considered that lignocelluloe biorefinery will most probably be pushed through with highest success among the potential industrial biorefineries, because that the raw material situation is optimal and the conversion products have a good position in the traditional petrochemical as well as in the future bio-based product market . Pretreatment is a prerequisite step for enzymatic hydrolysis of cellulose for a subsequent bioconversion of the obtained fermentable sugar to fuels and chemicals. Various pretreatment techniques have been developed during last decades, which increase cellulose accessibility by modifying chemical compositions or cell wall structures . Among these pretreatment techniques, organosolv pretreatment, which uses organic solvents or their aqueous solution systems with or without added catalysts to pretreat biomass in temperature range of 100–250°C, seems to be a promising approach for an integrated utilization of biomass compositions . Generally, organosolv pretreatment yields three separate fractions: high-purity lignin, hemicellulosic syrup and a relatively pure cellulose fraction , all of which show promises for producing high value-added products. Therefore, organosolv pretreatment can be termed as a “fractionating” process to increase cellulose digestibility and obtain multiple products. In the present paper, we have reported the recent progress in our group on the fractionating pretreatment of herbaceous biomass (sugarcane bagasse and wheat straw) to obtain cellulosic solid, hemicellulosic sugars and lignin products. Further utilization of these products for productions of biofuels (ethanol), chemicals (furfural) and materials (solid acid catalysts) also have been presented.