PNNL

Abstract

The complex and heterogeneous nature of the lignin macromolecule has presented a lasting barrier to its utilization. There is no method capable of separating lignin from plant biomass with controlled structural properties. We have discovered that a N-heterocycle based deep eutectic solvent formed between lactic acid and pyrazole (La-Py DES) has a binary hydrogen bonding functionality leading to a higher affinity to lignin. Up to 93.7% of lignin were extracted from wheat straw biomass at varying conditions from 90°C to 145°C. Through selection of treatment conditions as well as lactic acid to pyrazole ratios, lignin with controlled levels of ether linkage contents, hydroxyl group contents, and average molecular weight can be generated. Under mild extraction conditions (90°C-120°C), native-like lignin can be produced, whereas, ether linkage free lignin with low polydispersity can be obtained at 145°C treatment. This study offers a new strategy for native lignin extraction, and a breakthrough toward lignin valorization.