Sustainable Extraction Strategy for Lignin from Coconut Coir using Organosolv and Deep Eutectic Solvents (DES)

Abstract Purpose Lignocellulosic biomass serves as a potential source for the production of biomaterials and chemicals. Hence, this study focuses on utilizing a mild chemical route for lignin extraction to retain its native state thereby enhancing sustainability and cost-effectiveness. Methods Coconut coir, the selected biomass for lignin extraction is subjected to organosolv and Deep Eutectic Solvent (DES) treatments. Under the organosolv treatment strategy, two solvent-catalyst combinations were employed viz., ethanol and diethylene glycol (50%, v/v) along with FeCl₃ and NaOH (3%, w/v) as a catalyst. Whereas, the DES treatments involve Choline Chloride (ChCl) and lactic acid (1:2), ChCl and urea (1:2) and ChCl and oxalic acid (1:1). Results During organosolv treatment, the maximum delignification was found to be 71.03 ± 1.90% (w/w) in ethanol + FeCl₃ reflux, while DES treatment resulted in a maximum delignification of 60.93 ± 5.30% (w/w) with ChCl and urea at 120°C ± 2. The recovered lignin FTIR analysis revealed characteristic peaks comparable with the standard pure alkali/kraft lignin profile and the functional groups contained in lignin are correlated and indicated in the NMR profile as well. Conclusion The chosen treatments, show notable delignification while maintaining the native structure of the lignin, hence reinforcing the viability of lignin extraction sustainably and economically.