Green Process for Extraction of Lignin by the Microwave-Assisted Ionic Liquid Approach: Toward Biomass Biorefinery and Lignin Characterization

A facile and efficient strategy for the extraction of lignin and lignocellulosic biomass processing is crucial for sustainability of current biorefineries. In this work, lignin was extracted from eucalyptus by a ionic liquid-based microwave-assisted approach. The lignin samples were analyzed and compared to evaluate the extraction efficiency of the approach in terms of yields, associated sugars, and S/G ratios. It was found that 97.6% (w/w) of eucalyptus biomass was extracted by ILs-MAE process at 140 °C and 24.6% of lignin (based on Klason lignin) was released. Nearly half the amount of lignin (45.8%) was extracted by [C2C1 im][OAc] under low-intensity microwave irradiations. Changes in microwave power showed great changes in biomass deconstruction and lignin extraction by ILs. The 2D HSQC NMR results indicated that more number of C–C and C–O–C bonds could be degraded by this green extraction process. The depolymerization mechanism of the lignin extracted by IL-MAE process was proposed. This study provides panoramic perspectives of the green avenues for lignin extraction and depolymerization of biomass and helps us to develop more cost-effective strategies for biomass biorefineries.