From models to real waste biomass: a novel and sustainable strategy for ethyl levulinate production

Levulinic acid (LA) is one of the top 12 most promising bio-derived compounds for generating value-added products. However, due to the essential upgrading processes required for its production, purification and transformation, the cost of LA remains high in the global market. Consequently, research efforts are increasingly focused on developing simpler processes for producing LA derivatives. Ethyl levulinate (EL) meets these criteria, as it can be produced directly from biomass via an acid-catalysed alcoholysis reaction and offers easier purification. Therefore, the present work aimed to produce EL from real waste biomass, by adopting ethanol as a green reagent/reaction medium and sulfuric acid as cheap homogeneous catalyst. Initially, the study focused on using sucrose as a model substrate, optimizing EL formation through a multivariate approach to assess the synergistic effects of temperature, reaction time, and sulfuric acid loading. In this way, the highest EL yield of 54.6 mol% was achieved with an H2SO4 loading of 0.5 wt% at 158 °C for 4.6 h, minimising the formation of side products such as diethyl ether (DEE). Subsequently, the optimal conditions identified were applied to the valorization of thick juice (TJ), an intermediate sugar refinery product with high sucrose content, resulting in a favourable EL yield (37.6 mol%). Based on these results, the work subsequently shifted to the valorisation of real waste biomass, specifically bread waste (BW). As one of the largest contributors to global food waste, BW appears as an attractive low-cost raw material for EL production due to its high starch content. Thus, the ethanolysis of BW was investigated using a One-Factor-at-a-Time (OFAT) approach, adopting H2SO4 as the catalyst, resulting in good EL yields of about 40 mol%. In conclusion, this study utilized sucrose as a model substrate in ethanolysis reactions for EL production and the obtained results enabled to study the transition to the valorization of real substrates, such as an industrial by-product (TJ) and a food waste (BW) contributing to a more sustainable approach to EL production.