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

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.

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).

During organosolv treatment, the maximum delignification was found to be 71.03 ± 1.90% (w/w) in ethanol + FeCl₃ reflux, while the 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 was subjected to FTIR analysis which revealed the characteristic peaks comparable with the standard (pure) alkali/kraft lignin profile and the functional groups contained in extracted lignin were correlated in the NMR profile.

The chosen treatments result in notable delignification while maintaining the native structure of the lignin, hence reinforcing the viability of lignin extraction sustainably and economically.

This study underscores the transformative potential of coconut coir, a significant byproduct of coconut processing, as a robust biomass source for lignin extraction. Employing environmentally friendly solvent pretreatment methods such as Organosolv and Deep Eutectic Solvents, the research showcases the efficacy of these approaches in unlocking lignin’s commercial viability. Lignin, inherently hydrophobic, presents itself with both aliphatic and aromatic fractions, bearing considerable commercial promise. Our novelty is the extraction of lignin in its native form (hydrophobic state) rather than changing its nature through non-target specific acid or alkali treatments. The extracted lignin would further be opted for various industrial applications. By establishing sustainable and value-added technologies utilizing this waste resource, the study advocates for the adoption of eco-friendly practices within industries. The proposed methods mitigate waste and introduce novel avenues for product development, which are untapped according to the author’s knowledge. This advancement aligns with the broader ethos of sustainability, paving the way for an eco-friendly industrial environment.