Production of high-yield short-chain oligomers from cellulose via selective hydrolysis in molten salt hydrates and separation

Abstract

Molten salt hydrates (MSH) are unique in overcoming the characteristic recalcitrance of crystalline cellulose. We show that cellulose can be efficiently hydrolyzed into short-chain oligomers and glucose under mild conditions in concentrated LiBr solution without using any additional acid catalyst. Under optimized reaction conditions, short-chain oligomers with a yield of 90.4% can be obtained. Selective hydrolysis in the MSH is effective even at a high initial cellulose concentration (higher than 10 wt%). The obtained oligomers are solvated and soluble in the MSH. We show that amorphous carbon of a large surface area is effective for adsorption of the short-chain oligomers, cellobiose, and glucose from the MSH. The adsorption capacity and adsorption affinity of the carbon increases by ∼4 and ∼15 times in MSH with increasing the oligomer chain length compared to glucose and is negatively influenced by the ion concentration of the MSH. A stepwise hydrolysis process for converting crystalline cellulose into glucose is developed, whereby cellulose is firstly hydrolyzed into soluble short-chain oligomers in the MSH. The oligomers are then separated from the MSH using amorphous carbon and finally hydrolyzed into glucose under mild reaction conditions.