Sulfamic acid modified UiO-66 metal-organic framework for biodiesel production: Process optimization using response surface methodology, kinetics, and thermodynamic study

Abstract

A novel sulfamic acid-modified UiO-66 metal–organic framework (UiO-66/SA) catalyst was synthesized in this work for the esterification of oleic acid to biodiesel. Oleic acid was used as a test substrate as it constitutes a major proportion of several biodiesel feedstocks like Jatropha curcas oil, karanja oil, and waste cooking oil. The catalyst was extensively characterized by XRD, TGA, FT-IR, BET, SEM, CHNS and XPS. The catalyst demonstrated a high acidity of 1.4 mmol g−1 evaluated by ammonia-temperature programmed desorption (NH3-TPD) analysis. Central composite design (CCD) approach of response surface methodology (RSM) was used to process the optimization of various parameters (RSM) where, a maximum biodiesel yield of 94.4 ± 0.3 % was obtained under the optimized reaction conditions of methanol to oil molar ratio of 21.9:1, catalyst loading of 7.6 wt%, reaction temperature of 85 °C, and reaction time of 1.8 h. The activation energy for the esterification reaction was found to be 41.56 kJ mol−1 and further, the thermodynamic study confirmed the endothermic nature of the reaction. Multiple regressions and analysis of variance (ANOVA)were used to fit the experimental data to a quadratic equation.