A novel aqueous gallic acid-based natural deep eutectic solvent for delignification of hybrid poplar and enhanced enzymatic hydrolysis of treated pulp

Natural deep eutectic solvent (NADES) emerged as a promising solvent used for lignocellulosic biomass dissolution and lignin separation. In this work, we prepared an aqueous NADES from choline chloride and a type of aromatic hydrogen bond donor, gallic acid-monohydrate, according to the possible solute-solvent interactions where phenyl-based NADES possessed favorite interactions with lignin aromatic compounds. Aqueous gallic acid-based NADES induced a high lignin removal (50.0%) of poplar and enhancement of enzymatic hydrolysis yield of treated pulp (69.1%). Presence of water aided in decreasing NADES viscosity and improving mass transfer. Various characterization approaches of extracted lignin were employed to investigate changes of molecular weights, types and amounts of hydroxyl groups and crucial linkages. The aqueous gallic acid-based NADES exploited in this work exhibited desirable delignification performance. Formation of considerable hydrogen bonds and hydrophobic interactions between the aromatic gallic acid-based NADES and lignin contributed to the reduced re-aggregation and condensation of separated lignin fragments.