A synergistic approach for lignin biofuel production: Integrating non-catalytic solvolysis with catalytic product upgrading

Enzymatic hydrolysis lignin (EHL) is a large-scale industrial waste generated from the bio-ethanol production process. Its complex and heterogeneous nature as well as its low solubility in common solvents, has posed a persistent barrier to its effective utilization. Here, EHL was converted into biofuel through a two-step process, involving non-catalytic solvolysis followed by catalytic product upgrading. The non-catalytic solvolysis step achieved complete EHL liquefaction in a mixture of isopropanol and H2O without char formation. In this step, H2O disrupts the hydrogen bonds in EHL and isopropanol break π-π stacking interactions between the aromatic rings in EHL·H2O also enhances EHL depolymerization, while isopropanol, as a hydrogen donor solvent, provides hydrogen that stabilizes active intermediates. In the catalytic product upgrading step, the liquid product of the first step was transformed into biofuels rich in cycloalkanes, arenes and alkylphenols, with a total carbon yield of 45.6 %. Isopropanol-H2O reforming reactions provided hydrogen for the upgrading process, avoiding the introduction of H2. This work demonstrates an effective approach for converting EHL into biofuels.