Production of Short-Chain Oligomers from Cellulose Via Selective Hydrolysis in Molten Salt Hydrates and Separation

Cellulose is the most abundant homopolysaccharide in nature which consists of D-glucose units connected through β(1→4) glycosidic bonds. Selective production of glucose from hydrolysis of cellulose is the key step for efficient conversion of lignocellulosic biomass. Cellulose can be dissolved and hydrolyzed into glucose with a high selectivity in specific solvents, including ionic liquids, deep eutectic solvents and molten salts hydrates (MSHs). However, the separation of the formed glucose is challenging due to its high solubility in these solvents.

To address this issue, a stepwise method is introduced, where cellulose is hydrolyzed into short-chain glucan oligomers in the MSH of LiBr.¹ It was found that cellulose can be efficiently hydrolyzed into short-chain oligomers with a degree of polymerization of 4-11 under mild conditions in the MSH of LiBr. We demonstrated that compared to glucose, the formed glucan oligomers can be efficiently separated from the MSH hydrolysate by an anti-solvent precipitation method.² Under optimized conditions, 90.3% of glucan oligomers can be produced from crystalline cellulose and separated from the MSH with the addition of methanol, and the precipitated glucan oligomer can be hydrolyzed into glucose with a yield of 99.7% using dilute sulfuric acid. The precipitation efficiency is influenced by the glucan oligomer chain-length, glycoside bond type and concentration. The obtained oligomer can be selectively converted into monosaccharide or might be used in other emerging applications such as healthcare and agriculture.

1. Liu, Q.; Ma, Q.; Sabnis, S.; Zheng, W.; Vlachos, D. G.; Fan, W.; Li, W.; Ma, L., Production of high-yield short-chain oligomers from cellulose via selective hydrolysis in molten salt hydrates and separation. Green Chemistry 2019, 21 (18), 5030-5038.

2. Liu, Q.; Luo S.; Fan, W.; Ouyang X.; Qiu X., Separation of short-chain glucan oligomers from molten salt hydrate and hydrolysis to glucose, submitted.