Collaborative Research: Low-Energy Tandem Process for Fractionation and Reversible Preservation of Lignocellulose Using Multifunctional Aldehyde Sulfonic Acids

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Lignocellulose is a promising alternative to fossil resources for the production of fuels, chemicals, and materials. However, most current biomass fractionation processes face issues such as unwanted loss of carbohydrate fractions (cellulose fibers and hemicellulose sugars) and significant structure changes of lignin (aromatic compounds) during the process, both of which devalue the fractionated components. The proposed project will develop an energy-efficient, inexpensive, and value-preserving biomass fractionation system using aldehyde sulfonic acids. The success of the proposed research will directly impact the U.S. lignocellulose-based biorefinery, pulp and paper industries, and other related sectors. It will also contribute to a low-carbon bioeconomy by replacing petroleum feedstocks and reducing energy consumption in the fractionation process. The project will promote STEM education in biorefineries, bioenergy, and bioproducts (3B) through graduate and undergraduate student training (particularly female and minority students) and curriculum development. This project will also include outreach activities with K-12 students by providing lab tours, summer practicums, and research projects for the students interested in the 3B fields. The proposed research uses novel aldehyde sulfonic acids (aldehyde-containing aromatic sulfonic acids) to accomplish a rapid and near-complete fractionation of lignocellulosic biomass without the need for significant biomass size-reduction pretreatment. This process not only maximizes the production of cellulose, hemicellulose, and lignin but it also reduces process energy consumption relative to existing methods. Using a model-based molecular design approach, aldehyde sulfonic acids with tunable structure, physical properties, and reactivity will be synthesized from inexpensive aldehyde-containing aromatics by sulfonation. Mechanistically, aldehyde sulfonic acids fractionate lignocellulose through the sulfonic acid group and then protect carbohydrates and lignin from degradation and condensation by interaction with the aldehyde group. Because of their multifunction nature as a catalyst, solvent, and preserver, aldehyde sulfonic acids are expected to fractionate centimeter-sized lignocellulose feedstocks rapidly and nearly completely under mild conditions into cleavable and upgradable lignin, cellulose, and hemicellulose. This research will test the central hypothesis that aldehyde sulfonic acid would be more effective and selective than current combinations of mineral/organic acids and aldehydes in fractionating lignocellulose. Mathematical models will be developed using quantitative structure-performance analysis to predict structural properties and performance of a range of aldehyde sulfonic acids. The tandem depolymerization and reversible preservation of lignin and hemicellulose will be mechanistically elucidated through these modeling studies to understand the cleavage reaction kinetics of the acid-labile linkages and the formation of protective chemical groups.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.