Unleashing the potential of lignin with innovative trifunctional binary deep eutectic solvent strategy: Isolation of uncondensed lignin
Haichao Li, Deqiang Li, Yuan He, Chaobing Luo, Wu Lan, Arthur J. Ragauskas, Tingting You, Feng Xu
Abstract
Highly efficient conversion of lignin into value-added chemicals and materials is trapped in the inevitable cleavage of β-O-4 linkages and formation of highly condensed structures with deep colors during lignin isolation. Here, we develop a trifunctional choline chloride/glyoxylic acid (ChCl/GA) binary deep eutectic solvent with a π-π conjugate structure and moderate acidity for the fast isolation of light-colored lignin with near proto-structures (exceeding 88% of delignification ratio for 1 hour). The synergetic interaction of GA and ChCl substantially reduced Gibbs free energy of acetal reaction and thoroughly captured reactive intermediates, precisely activating the following key functions: stabilizing β-O-4 linkages, inhibiting condensation reaction, and shielding -OH groups. These enabled efficient isolation of uncondensed, abundant β-O-4 linkage (45.80/100 C9; 79% retention) and light-colored lignin. A near-theoretical yield of aromatic monomers upon depolymerization and high performances as adhesives for lignocellulosic bioplastics were achieved. This work unleashes the valorization potential of lignin by a relatively green and fast strategy for sustainable biorefineries.