Low temperature deconstruction of lignocellulose biomass using metal salt hydrate deep eutectic solvent (MSH-DES)

Abstract

Multiple deep eutectic solvents (DES) are already been studied for the fractionation of lignocellulose. But most of them requires a high temperature of fractionation which necessitates for higher cost of operation and makes it a challenge for commercialization. Recently, a metal salt hydrate DES (MSH-DES) has been studied that can dissolve cellulose at room temperature. In this study, the said MSH-DES composed of ZnCl2, water and H3PO4 in molar ratio of 1:3:0.6 was used for deconstruction and fractionation of lignocellulose biomass specifically of soft wood (Finnish pine). It was determined that the MSH-DES can fractionate the biomass at ideal condition of 45 oC, for 4 hours at DES to biomass ratio of 20. This then results to a solid recovery of 76% generating 3 solids. The first solid was a water-insoluble lignin-rich solid with a lignin composition of as high as 93%. The said MSH-DES lignin was also determined to be more dispersible in water than the commercial kraft lignin which could be better for industrial usage. Additionally, two solids were generated that is of amorphous (ethanol-insoluble solid) and crystalline (partially water-insoluble solid) in nature that has both cellulose and hemicellulose. It was shown that the recovery of these hemicellulose and cellulose is affected by the fractionation time where longer fractionation decreases their recovery. This study showcased the ability of the ZnCl2-3H2O/H3PO4 MSH-DES to be able to fractionate and deconstruct lignocellulose at low temperature of 45 oC which can be further explored and optimized for future studies.