Hydrothermal and microwave-assisted synthesis of levulinic acid from watermelon residue

Levulinic acid (LA) is considered a versatile chemical building block and has emerged as one of the leading platforms for products derived from biomass. It is regarded as important from an economic perspective. The main route of synthesis to obtain LA is from the degradation of cellulose by acid catalysis, with lignocellulosic biomass being a promising and sustainable way to obtain it. In this study, for the first time, the use of watermelon residues was proposed for the synthesis of levulinic acid, adding value to a residual biomass that has still been little explored for this purpose. Watermelon residues were subjected to acid hydrolysis using H2SO4 or HCl. Two reactors were analyzed for this purpose -autoclave and microwave assisted. The experiments were optimized through a central composite design, where temperature, biomass load, and acid concentration in the microwave were evaluated as variables. In the autoclave, the variables investigated were catalyst concentration and biomass loading. The highest yields, 14.8% and 17% by weight, were obtained with solid fraction (SF) in micro wave (MW). In the best condition obtained in the central composite design, the liquid fraction (LF) and SF were analyzed. It was observed that a clean product, containing only levulinic acid and formic acid, was in the liquid fraction. The MW was more efficient and is a promising alternative for reactions requiring energy. This study contributes to an energy-saving strategy, using waste and low-cost catalysts, sustainably contributing to a circular carbon economy based on agricultural waste. (c) 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd.