Molecular insights into dissolution of lignin bunch in ionic liquid-water mixture for enhanced biomass conversion

Abstract

Globally, the shift towards lignocellulosic biorefinery has opened avenues for valorizing lignin, a majorly accumulated recalcitrant by-product. A targeted lignin processing by ionic liquid-cosolvent mixtures can be an effective biomass conversion strategy. An understanding of lignin-ionic liquid dissolution can enable in designing a significant lignin processing technique to synthesis lignin-based renewable products. Here, we explored the molecular interaction during the dissolution of lignin containing five guaiacyl decamer chains in various (1-Ethyl-3-Methylimidazolium Acetate) EmimOAc-water mixtures using molecular dynamics simulation. The analysis showed that in only water, lignin formed a compact aggregate. Nevertheless, in 50%, 80%, and 100% EmimOAc-water, lignin underwent a segregated chain disentanglement with widespread dynamic motion. A detailed multifaceted analysis of Emim+, OAc− and water distribution on the polar and non-polar sites of lignin units was illustrated. An effective lignin dissolution was observed for 50% and 80% EmimOAc-water systems. The OAc− distribution was stronger around lignin's alkyl chains and alcoholic hydroxy groups. The Emim+ tails significantly impacted the benzene ring, whereas Emim+ heads were distributed around methoxy and hydroxy groups. Altogether, this study explores the lignin dissolution at atomistic level in EmimOAc-water mixtures; these understanding could serve as a cornerstone for engineering new ionic liquid-mediated lignin biorefinery.