Structural Modifications of Cellulose and Lignin in Loblolly Pine arising from the Ethanol Organosolv Pretreatment, 2010 TAPPI PEERS Conference

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Due to the inherent recalcitrance of lignocellulosic biomass towards enzymatic deconstruction, pretreatments are necessary for their efficient conversion to bioethanol. In the ethanol organosolv pretreatment, biomass is treated with an aqueous organic solvent mixture, which effectively fractionates it into a cellulose-rich solid, hemicellulose-rich liquid stream and a relatively pure lignin fraction. Solid-state 13C NMR spectroscopy coupled with line-shape analysis was used to determine the structure and crystallinity of cellulose before and after organosolv pretreatment and enzymatic hydrolysis. Reduced crystallinity of the cellulose was observed following pretreatment, which renders the pretreated biomass easily hydrolysable by cellulase. After enzymatic hydrolysis, crystallinity increases indicating preferential hydrolysis of the less-ordered regions of cellulose. Milled wood lignin from untreated Loblolly pine, post organosolv pretreatment and ethanol organosolv lignin were characterized with quantitative 13C and 31P NMR and gel permeation chromatography. During organosolv pretreatment, acid catalyzed cleavage of β-O-4 linkages and ester bonds were the major mechanisms of lignin modification. This degradative pathway results in the formation of ethanol organosolv lignin which is more condensed and has lower molecular weight than the starting lignin. The residual and dissolved lignin fractions after pretreatment have a higher abundance of phenols and carboxylic acids and may be suitable as antioxidants or other value-added lignin products.