Molten Salt Hydrate System as a Platform for Saccharification and Conversion of Lignocellulosic Biomass to Sugars, Chemicals, and Fuels

A molten salt hydrate (MSH) is a highly concentrated solution of a hygroscopic inorganic salt, typically having a water to salt molar ratio close to the coordination number of the cation of the salt. MSHs have some unique properties, such as very high salt solubility, extremely high boiling point elevation and freezing point depression, very depressed water vapor pressure, and high enthalpy of mixing. Some MSHs have been found to be able to swell and solubilize cellulose. Compared to ionic liquids, MSHs are inexpensive and easier to prepare and recover. Recently, we found that lignocellulosic biomass (such as corn stover, switchgrass, hardwood and softwood) could be directly and quickly saccharified without any pretreatment under moderate conditions (120-140 °C for 10-60 min) in molten salt hydrate systems. Both cellulose and hemicellulose in lignocellulosic biomass were completely hydrolyzed into fermentable sugars with high yield and selectivity (>90%). Lignin in the biomass was remained as insoluble residue and could be easily separated for co-products development. In addition, we found that MSHs could be used for direct conversion of cellulose and hemicellulose to furfural and hydroxymethylfurfural, isomerization of glucose to fructose, and even conversion of the carbohydrates into the precursors for drop-in fuels. In this presentation, we report our latest progress in this area, including evaluation of different molten salt systems for biomass saccharification and conversion, optimization of process conditions, establishment of mass balance, proposal of reaction mechanisms, and the separation and recovery of the MSHs.