Process optimisation and kinetic study for esterification of levulinic acid and n-butanol using sulfonated titania-zirconia heterogeneous catalyst

Background: Butyl levulinate (BL) was produced by the esterification of levulinic acid (LA) and n-butanol (BOH) using a sulfonated nanocomposite of titania-zirconia as catalyst. A full factorial design was employed for studying the effects of reaction time, mole ratio and catalyst loading on LA conversion.Results: The synthesised catalyst was subjected to various characterisation techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller measurements, thermogravimetric analysis, temperature-programmed desorption and scanning electron microscopy-energy dispersive X-ray analysis indicating the presence of a nanocrystalline structure with good surface area and good stability at the operating temperature. The experimental data were analysed using the response surface method, and a complete quadratic regression model was built. The LA conversion was 85.37% for the optimised reaction conditions of 1:7 mole ratio, a catalyst loading of 1 wt% and a reaction time of 5 h at 110 degrees C. Based on the Langmuir-Hinshelwood-Hougen-Watson model, a kinetic model was developed. The activation energy was found to be 20.4 +/- 0.8 kJ mol(-1) from an Arrhenius plot. Reusability and leaching results are also reported.Conclusion: The catalyst exhibited good reusability and stability. Sulfonated TiO2-ZrO2 used to catalyse the reaction between LA and BOH to produce BL has proved to be a good candidate as a green catalyst. The results presented play an important part in directing subsequent research and commercialisation activities aimed at valorising LA to fuel additive. (c) 2023 Society of Chemical Industry (SCI).