Sustainable Pathway for Bagasse Conversion Using Continuous Lactic Acid Catalysis: Production of Xylo-Oligosaccharides, Lignin Nanoparticles, and Dissolving Pulp

Organic acid pretreatment has the potential for cleaner production and efficient energy use. This work demonstrated the selective separation of hemicellulose and lignin from bagasse using lactic acid (LA), and improved the processability of cellulose. Initially, 0.1% LA hydrolysis of bagasse converted the xylan to xylo-oligosaccharides with a yield of 65.0%. Subsequently, lignin was isolated from the residue of bagasse by an 80% LA pretreatment, achieving an efficiency of 91.2%. Importantly, the solid residue retained a high glucan content of 88.2%. Following sodium hydroxide incubation, cellulase hydrolysis of solid residue achieved a saccharification efficiency of 92.5%, which was primarily due to the solubilization of pseudolignin and the de-esterification of cellulose. Additionally, the cellulose residue proved to be suitable for preparation of high-quality dissolving pulp with high purity and high Fock reactivity. The lignin recovered from the 80% LA pretreatment solution exhibited high purity (95.7%) and contained high carboxyl and hydroxyl contents, enabling it to self-assemble into uniformly sized lignin nanoparticles. Furthermore, even after five cycles of LA solution reuse, it maintained an excellent lignin dissolution capacity. Economic assessments also indicated that this process could generate substantial commercial benefits. The proposed LA gradient pretreatment provided a sustainable strategy for comprehensive value addition of biomass.