A Two-Step Approach for the Conversion of Technical Lignins to Biofuels

Abstract

Lignocellulose is a widely available carbon source and a promising feedstock for the production of advanced second-generation biofuels. Nonetheless, lignin, one of its major components, is largely underutilized and only considered an undesired byproduct. Through catalytic hydrotreatment, the highly condensed lignin can be partially depolymerized into a range of monomers. However, its recalcitrance and the presence of aromatic fragments linked by C-C bonds require extensive cracking, which is challenging to achieve. Here, a two-step strategy is reported in which an initial pretreatment step with ozone is used prior to catalytic hydrotreatment to boost lignin depolymerization. Three types of lignin (Kraft, pyrolytic, and Fabiola organosolv) are used as feedstocks and the ozonation step is performed under ambient conditions with either methanol or ethanol as the solvent. The pretreatment is shown to have a positive effect on the subsequent hydrotreatment reaction (Pd/C, 350 °C, 100 bar H2) and gives product oils with significantly lower Mw (up to 43% lower), higher volatility, and improved calorific values (up to 45.3 MJ kg−1) compared to a direct hydrotreatment.