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The depolymerization of natural biomass-based lignin is a definitive challenge, as it involves the integral breakdown of complex and wellconstructed 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. [ABSTRACT FROM AUTHOR]

• BAILs were used as a medium solvent to dissolve rice husk and depolymerize the lignin. • 78 % of regenerated lignin was effectively extracted from rice husk by [C 3 SO 3 HMIM]Cl. • Acidic properties of BAILs improve the delignification process. • [C 3 SO 3 HMIM][HSO 4 ] was successfully depolymerized the lignin into low molecular weight aromatic products. Lignocellulosic agricultural waste, like rice husk, is generated abundantly from rice milling industries. It is no longer mere waste but has become a treasure trove of outstanding potentials for sustainable environment growth. In this study, a series of Bronsted acidic ionic liquids (BAILs) were synthesized, characterized and used as a medium solvent to dissolve rice husk. Fractionation of rice husk into lignin, cellulose and hemicellulose was successfully achieved after 6 h of stirring at 100 °C. About 78 % and 53 % of the regenerated lignin were effectively extracted from rice husk by 1-methyl-3-(3-sulfopropyl)-imidazolium chloride, [C 3 SO 3 HMIM]Cl and 1-methyl-3-(3-sulfopropyl)-imidazolium acetate, [C 3 SO 3 HMIM][Ace] respectively, while 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulfate, [C 3 SO 3 HMIM][HSO 4 ] only extracted 11 % (based on the original rice husk). The regenerated lignin and cellulose were characterized using FTIR and TGA. Among the BAILs, [C 3 SO 3 HMIM]Cl was found to be a good medium solvent to extract lignin from rice husk and could be recycled up to four times. The regenerated lignin was further depolymerized using the synthesized BAILs at 120 °C (1 h) to generate low molecular weight aromatic products, which were analysed using gas chromatography-mass spectrometry (GC–MS). During depolymerization process, [C 3 SO 3 HMIM][HSO 4 ] was identified as an excellent solvent to depolymerize the lignin into low molecular weight aromatic products. [ABSTRACT FROM AUTHOR]