Catalytic Enzymatic Hydrolysis Lignin Hydroconversion Targeting Sustainable Aviation Fuels: Solvent Effect

In this study, we investigated the effect of the solvent on the hydroconversion of enzymatic hydrolysis lignin (EHL) using a NiMoS catalyst supported on an alumina-zeolite extrudate. The lignin was characterized via standard complementary techniques (size exclusion chromatography (SEC), NMR, and elemental analyses), with its low solubility to be taken into account. A comparison of the solvents for the conversion of EHL indicated that a H-donor solvent such as tetralin was indeed more effective in recovering a liquid fraction than hydrocarbon- and alcohol-based solvents. Alcohol solvents such as ethanol, in mixture with heptane, and isobutanol resulted only in a slight improvement in liquefaction under these operating conditions. The main drawbacks of alcohol and tetralin solvents are their tendency to react during hydroconversion, which complicates the analysis of the liquid fractions, making it difficult to assess the catalytic impact. Notably, the use of heptane enabled the production of a fully deoxygenated liquid fraction from EHL, consisting of a mixture of cycloalkanes, alkanes, and aromatics. Even if it is obtained with quite low yield from raw EHL, this mixture is fully consistent with the composition of jet fuel in terms of chemical groups and could easily be used, probably after finishing treatments, in the formulation of sustainable aviation fuels (SAFs).