Lignin-Derived Oil Palm Biomass Using Deep Eutectic Solvent

Abstract

Deep Eutectic Solvent (DES) are eutectic mixes of hydrogen bond acceptors (HBA) and donors (HBD) with melting points significantly lower than their constituents. Choline chloride (ChCl) and glycerol were chosen as HBA and HBD because they are simple to prepare, have low toxicity, are biodegradable, and are environmentally friendly. As a result, the study aims to determine the feasibility of extracting lignin from oil palm fronds (OPF) and empty fruit bunches (EFB) using DES. The molar ratios of DESs were investigated to determine their effect on OPF solubility and lignin yield. The reaction is carried out at a solid loading ratio of 1:10, 150°C, and 6 hours. Because the DES medium induces homogeneous swelling and breakdown of small fibre fragments but not dissolution, both OPF and EFB are insoluble in DES. Small fragment disintegration suggests rapid dissolution, which will be easily dissolved in the DESs. The lignin yield and solubility of EFB and OPF in DESs are significantly reduced when the molar concentration of glycerol is increased. The highest lignin yields, 27.6% (EFB) and 16.1% (OPF) were obtained with a ChCl/glycerol molar ratio of 1:3. The comparatively low lignin yield achieved for both OPF and EFB is ascribed to the poor hydrogen bonding between the chloride ion and the hydroxyl group of the DES due to the low acidity of the DES. Despite this, lignin is extracted successfully due to the presence of chloride ions in ChCl, which target β-O-4 bonds and successfully cleave the ether bonds present in the lignin-carbohydrate linkage.