Advancements and applications of microwave-assisted deep eutectic solvent (MW-DES) lignin extraction: a comprehensive review

Abstract

Lignocellulosic biomass biorefineries present an environmentally friendly avenue for generating biofuels and bioproducts, curbing emissions, and advancing environmental stewardship. Yet, the intricate structure of biomass poses obstacles to its efficient conversion into bio-derived products while conserving the native bonding motifs, especially for lignin. The limitations of conventional methodologies stimulated the exploration of innovative solvents and processes. Deep eutectic solvents (DESs), a class of solvents composed of mixtures of hydrogen-donor and hydrogen-acceptor compounds, boasting low toxicity, remarkable solubility, adaptability in synthesis, and selectivity, have garnered increasing attention as sustainable solvents for lignin extraction. The incorporation of microwave-assisted heating can further enhance DES-based lignin extraction efficiency and potential for value creation. This comprehensive review underscores the potential of the MW-DES technique in harnessing lignin—a prized renewable resource—for the sustainable production of energy and materials. From dissecting DES's elemental composition to elucidating DES–microwave–biomass interactions, scrutinizing the MW-DES lignin extraction process factors, and delving into extracted lignin characterization, this review aims to thoroughly evaluate the MW-DES approach's promise in leveraging lignin's potential across diverse industrial sectors.