Rice Husk Lignin to Vanillin: IonoSolv as a Way Forward for Value-Added Biomass Depolymerization

Abstract

The depolymerization of natural biomass-based lignin is a definitive challenge, as it involves the integral breakdown of complex and well-constructed natural structures. A sustainable method called ‘ionoSolv pretreatment’ employs ionic liquids in biomass processing. In this study, Bronsted acidic IL (BAIL); 1-methyl-3-(3-sulfopropyl)-imidazolium chloride, [C₃SO₃HMIM]Cl was synthesized and commendably used to both assist the depolymerization of lignin under mild reaction conditions as well as to benefit from the commercially valuable vanillin. About 68% degree of depolymerization (DD) of lignin was achieved under optimized conditions (120 °C, 60 min), yielding ca. 43% of tetrahydrofuran (THF) soluble products. The influence of BAIL on the depolymerization was investigated using chromatographic (gas chromatography-mass spectrometry, gel permeation chromatography, and high performance liquid chromatography (HPLC) and spectroscopic techniques (Fourier transform infrared). The HPLC analysis of the depolymerized lignin detected the clear presence of 12% of vanillin was obtained from 2 wt.% of rice husk’s lignin.