Separation of high-yield and high-purity lignin from <i>Elm wood</i> using ternary deep eutectic solvents

Abstract This study indicates that superior performance of novel ternary deep eutectic solvents (DES) system, formulated from choline chloride (ChCl) mixture of formic acid (Fa), pyruvic acid (Pa), and tartaric acid (Ta), exhibits remarkable efficacy in selective separation and purification of lignin from biomass. The woody biomass of Elm was pretreated with ternary of carboxylic-acid-based DES of ChCl as hydrogen bond acceptor (HBA), Lac, Fa, Pa, and Ta served as hydrogen bond donors (HBD) under the predetermined conditions. Benefitting from the efficient process, using optimized DES system (ChCl/Lac/Fa, 1:6:1, 6 h and 120 °C), it showed that the yield and purity of lignin obtained from material was 86.53 % and 90.45 %, which was more efficient than the results of binary DES system of the pretreatment process. In addition, the recovered lignin was subjected to comprehensive structural characterization employing Fourier transform infrared spectroscopy and two-dimensional nuclear magnetic resonance techniques. DES lignin was found to have a complete aromatic structure, that consisted mainly of β-β, β-O-4 bonds in different contents. These findings confirm the significant advantages of the new novel ternary DES system, which facile separated lignin from the lignocellulosic matrix under mild conditions, that providing a new reference value for efficient separation of biomass resources.