Sulfur Dioxide Pretreatment
Sulfur dioxide pretreatment involves exposure of the biomass to sulfur dioxide gas under pressure at about 200°C for 2-10 min. The impregnation of biomass with gaseous sulfur dioxide can be more effective than with H2SO4 in terms of rapid, uniform distribution and offers better recyclability, although recovery and recycling costs can be high. The effects of sulfur dioxide during pretreatment include removal of a major portion of hemicellulose sugars, disruption of the lignin-carbohydrate complex, and substantial depolymerization and sulfonation of lignin [179]. Sulfur dioxide pretreatment has been applied to pretreat a wide range of lignocel — lulosic biomass forms and has shown good adaptability to various feedstocks, including agricultural residues such as corn stover and sugarcane bagasse, hardwood and softwood; some representative results are summarized in Table 5.8.