Structural Characterization of Isolated Poplar and Switchgrass Lignins During Dilute Acid Treatment
A key step in converting cellulosic biomass into sustainable fuels and chemicals is thermochemical pretreatment to reduce plant cell wall recalcitrance. An improved understanding of the chemistry of lignin as it undergoes this processing is critical to the development of renewable biofuel production. Researchers at the Department of Energy’s BioEnergy Science Center (BESC) have studied the behavior of lignin during dilute acid pretreatment (DAP). They isolated lignin from poplar and switchgrass using a cellulolytic enzyme system and then treated it under DAP conditions. Results highlighted that lignin is subjected to depolymerization reactions within the first 2 minutes of DAP, and these changes are accompanied by increased generation of aliphatic and phenolic hydroxyl groups of lignin. These developments are followed by a competing set of depolymerization and repolymerization reactions that lead to a decrease in the content of guaiacyl lignin units and an increase in condensed lignin units as the reaction residence time is extended beyond 5 minutes. A detailed comparison of changes in functional groups and molecular weights of cellulolytic enzyme lignins demonstrated that several structural parameters related to lignin’s recalcitrant properties are altered during DAP conditions. This deeper understanding of the chemical structure of lignin as it undergoes processing is an important step toward the goal of efficient conversion of lignocellulose into renewable biofuel products.
Sun, Q., Y. Pu, X. Meng, T. Wells, and A. J. Ragauskas. 2015. “Structural Transformation of Isolated Poplar and Switchgrass Lignins During Dilute Acid Treatment,” ACS Sustainable Chemistry and Engineering 3(9), 2203-10. DOI: 10.1021/acssuschemeng.5b00426.