Evaluation on the properties of deep eutectic solvent-extracted lignin for potential aromatic bio-products conversion

Lignin represents a major aromatic resource in future bio-economy due to its natural abundancy. However, it is mostly produced as paper pulping by-product with heavily modified structure. The application of deep eutectic solvent (DES) has introduced an alternative lignin-first extraction method. In this work, the structural and thermal properties of DES-extracted lignin (DEEL) from oil palm empty fruit bunch using choline chloride:lactic acid (CC-LA) and choline chloride:formic acid (CC-FA) were evaluated to examine the potential of DEEL for further valorisation. CC-FA was more destructive towards the lignin’s structure, leading to a highly condensed DEEL. In contrast, CC-LA managed to preserve more β-O-4′ linkages, the usual chemical modification site. Thus, it might be more suitable for smaller chemicals production through depolymerisation process. The pyrolysis products were mainly phenolic compounds (>50 %), indicating the prospect of DEEL for phenolic-based chemicals production. The collective results demonstrate that DEEL can potentially be employed as a precursor for fuel and aromatic chemicals production.