Rapid microwave-assisted biomass delignification and lignin depolymerization in deep eutectic solvents

Biomass deconstruction and lignin depolymerization was performed using three different deep eutectic solvents. Various temperature (110 degrees, 130 degrees, and 150 degrees C) and time (1, 5, 10, 15 min) conditions were tested in a 2450 MHz microwave reactor. Oxalic acid (130 degrees C, 15 min) and formic acid DES (150 degrees C, 15 min) gave the highest lignin yield. Microwave heating reduced the processing time significantly. NMR characterization shows that microwave heating promotes selective bond cleavage during lignin depolymerization and has a narrow molecular weight distribution compared to conventional heating techniques. Molecular dynamic simulations showed that certain lignin bonds are stretched under the electric field imparted during microwave irradiation, increasing its probability of breaking.