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Coconut shell, a natural biopolymer, is available in high amounts as waste in many countries. It could potentially be a crucial renewable source of raw materials for the carbon fiber industry. In this study, a series of aprotic ionic liquids, [Bmim][Ace], [Bmim]Cl, [Emim][Ace], and [Emim]Cl, were used in the dissolution and regeneration process of coconut shell. The results indicate that the dissolution of coconut shell (up to 70 mg of coconut shell per g of solvent) can occur in aprotic ionic liquids under a nitrogen atmosphere at 110 °C (6 h) and 150 °C (2 h). The extraction efficiency was greatly influenced by temperature, time, particle size, and types of cations and anions in the ionic liquids. At 150 °C, 10% regenerated lignin was obtained in [Emim][Ace], which was higher compared with [Emim]Cl, [Bmim][Ace], and [Bmim]Cl. The recyclability of the ionic liquids during the dissolution process (up to four times) was also scrutinized. The structure and properties of the untreated coconut shell and regenerated lignin were characterized by Fourier transform infra-red (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, and proton nuclear magnetic resonance (1H NMR). [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]