Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Integration of alkaline pulping with alkaline pre-extraction of hemicelluloses and lignins from woody biomass for conversion to fuels chemicals is one route for potentially adding value to current pulp mills. The goal of this work is to better characterize the impacts of extraction conditions on the properties of the solubilized biopolymers and the potential for solubility-based separations to recover hemicellulose and lignin fractions. Biomass feedstocks include four hardwoods: sugar maple (Acer saccharum), hybrid poplars (Populus tremuloides x tremula, P. nigra x maximowiczii), and silver birch (Betula pendula). Alkali extraction at mild temperature was capable of extracting approximately 30% of the xylan from both sugar maple and the hybrid aspen, while the 3 times more lignin was extracted from the hybrid aspen. The polymers recovered from the extraction liquor were characterized by size-exclusion chromatography (SEC) and a novel adaptation of the 2-2’-bincinchoninate acid (BCA) reducing sugar assay to determine the number average degree of polymerization (DP) of xylans. Using SEC, sugar maple lignins were identified in the range of 1200-12000 Da, while hemicellulose aggregates showed an apparent DP range of 100-1000 units with a number average DPs greater than 300 while the reducing end method showed an increase in the number average DP with increasing NaOH concentration up to a value of approximately 70 units with the discrepancy attributed to xylan aggregation. The contribution of glucuronic acid substitution on the solubility and aggregation potential of xylans is also investigated in this work.