10-07: Characterization of lignin after water-only pretreatment

The conversion of lignocellulosic biomass to ethanol requires the recovery of the sugars contained in the hemicellulose and cellulose with high yields. High temperature water-only pretreatment can be used to hydrolyze and solubilize hemicellulose prior to the enzymatic hydrolysis of the cellulose left in the solids to glucose. As lignin is a well-known inhibitor of enzymatic hydrolysis and fermentation, its alteration and removal are frequently cited as important pretreatment goals. However, there is a limited knowledge about lignin's behavior during pretreatment. Two possibilities are that lignin depolymerizes (Li et aI. , 2007) or melts (Donohoe et aI. , 2008) during pretreatment. It has been difficult to study lignin removal in batch pretreatment reactors because the final cooling may cause lignin precipitation from the liquid phase. In comparison, biomass pretreatment in a fixed bed flowthrough reactor removes lignin from the reactor prior to final cooling. Both types of reactor will be applied to study the effects of pretreatment on lignin isolated from poplar at two temperatures over a range of times. The pretreatment liquor will be analyzed for phenols, such as 4-hydroxybenzoic acid and coniferyl alcohol. The morphology and composition of the solids before and after pretreatment will be characterized using an array of techniques, such as SEM and NMR. Differences between the raw and pretreated lignin will provide insight into lignin's behavior during pretreatment, while differences in the batch and flowthrough pretreated lignin should identify artifacts created when the reaction is quenched.