Abstract
Recently, deep eutectic solvent (DESs); being an innovative and green solvent has attracted increasing interest due to growing environmental concern arising from the uses of conventional organic solvents. In view of this, four choline chloride based deep eutectic solvents namely DES1 [Choline chloride /Urea (ChCl: U)], DES2 [Choline chloride /Oxalic acid (ChCl: OA)], DES3 [Choline chloride /Glycerol (ChCl: G)] and DES4 [Choline chloride /Ethylene Glycol (ChCl: EG)] were synthesized, characterized and used for pretreatment of sugarcane baggasse and corn cob respectively. The physicochemical and thermal properties of the synthesized DESs, such as viscosity pH, density, refractive index, surface tension, and thermal conductivity were found to be influenced by the constituents and composition of the DESs. The characterization results revealed that as temperature rises, the viscosity of the DESs decreases significantly. DES3 has the highest viscosity of 499.4 cPs followed by DES2, DES1 and DES4 having 305.72 cPs, 188.50 cPs and 131 cPs respectively. The untreated (raw) corn cob and sugarcane baggasse which contains 20.65 % and 19.06 % lignin were subjected to pretreatment using the synthesized DES1-DES4 under the same conditions in order to remove lignin. Lignin content reduced by 72 % for corncob and 83.26% for sugarcane baggasse compared to conventional solvents having a range of (41-63 %) lignin removal. In terms of lignin removal and holocellulose content, the DESs tested in this study demonstrated their potential as solvents for biomass pretreatment, with DES1 and DES2 performing better in terms of percentage lignin removal for both sugarcane bagasse and corncob, respectively.

Key words: Deep eutectic solvents, Pretreatment, Lignin, Choline chloride, Environmentally-friendly, Biomass