Clean production of ethyl levulinate from kitchen waste

A clean and highly efficient catalytic system for the synthesis of ethyl levulinate (EL) from kitchen waste was developed. A heterogeneous catalyst (Sn/ZrP–SO3H) was prepared and the Brønsted and Lewis acid sites on the surface of the catalyst were evaluated by pyridine FT-IR. Other physicochemical properties were also characterized using XRD, SEM, FT-IR, XPS, BET, NH3-TPD. The yield of EL obtained was 49.27%, when glucose was used as the starting material and subjected to 170 °C for 10 h in the presence of the solid acid catalyst, Sn/ZrP–SO3H. The prepared catalyst was also combined with several metal triflates; (Al(OTf)3, Fe(OTf)3, Sm(OTf)3) to form a catalytic system for the efficient preparation of EL from kitchen waste. Sn/ZrP–SO3H/Al(OTf)3 had superior activity compare to other catalyst combinations. In single factor experiments, the yield of EL reached 52.52% after heating at 170 °C for 4 h. In addition, four-factor and three-level experiments were performed using response surface methodology (RSM) to analyze the interaction between each factor. The optimal reaction conditions predicted by the model (163 °C, 7.63 h, 20 mg Al(OTf)3, 40 mg Sn/ZrP–SO3H and 79.98 mg of kitchen waste) estimated a maximal yield for EL of 51.24%. The experimental yield of EL however was 52.03% which confirms the reliability of the model. This work provides a cleaner production technology for the synthesis of the high value-added chemical EL, and a sustainable route for the utilization of kitchen waste.