The nature of lignin from steam explosion/enzymatic hydrolysis of softwoods: Structural features and possible uses

Effective utilization of the lignin by-product is a pre-requisite to the commercial viability of ethanol production from softwood wastes using a steam explosion (SE)/enzymatic hydrolysis (EH)/fermentation process. Changes in the chemical composition of Douglas fu wood upon SO2-catalyzed SE followed by EH were assessed using conventional analytical methods and new halogen probe techniques. A significant solubilization of hemicelluloses was observed in the SE stage, the severity of which affected subsequent fermentation of cellulose and sorption of enzymes. Steam explosion of softwood resulted in dramatic changes in the chemical structure of lignin in the residual material involving chemical reactions via the benzyl cation. This leads to a more condensed lignin with partly blocked alpha-reaction centres. Possible uses for this lignin are discussed.