Efficiency of bronsted acidic ionic liquids in the dissolution and depolymerization of lignin from rice husk into high value-added products.

• 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]