(330d) Fractionation and Recovery of Lignin and Xylan From Alkali Liquors – Characterization for Biorefinery Processes
Understanding the behavior of plant cell wall biopolymers during alkaline biorefining processes and how their properties are affected by the processing conditions is important for maximizing value from woody lignocellulosic feedstocks. In this work, the fractionation of alkali pulping liquors was investigated to characterize the extractability, recoverability, and properties of the solubilized hemicelluloses and lignin during the alkali impregnation and heat-up stages of alkali organosolv pulping or soda pulping for three hardwood species: sugar maple (Acer saccharum), silver birch (Betula pendula), and a hybrid poplar (Populus nigra x maximowiczii cv. NM6). Recoverability of the solubilized biopolymers were determined using a variety of methods including aggregation and precipitation by acidification as well as ultrafiltration. The xylan showed a decreasing degree of polymerization (DP) with increasing temperature during reactor heat-up, which stabilized at a DP between 10-30. Lignin aliphatic and aromatic hydroxyl content was characterized by 1H NMR and the lignin molecular weight distributions were determined by gel permeation chromatography (GPC). These properties showed a clear dependence on the extraction conditions and were clearly linked to recoverability of lignin by either acidification or ultrafiltration.