Biodiesel synthesis from waste cooking oil using heterogeneous acid catalyst: Statistical optimization using linear regression model

In this study, a heterogeneous acid catalyst composed of 12-molybdophosphoric acid (H3PMo12O40.xH(2)O) anchored in titanium oxide (TiO2) was synthesized using the incipient-wetness method. The catalyst was characterized by acid-base titration method in order to determine surface acidity, thermogravimetric analysis, and x-ray diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy, and energy dispersion x-ray spectroscopy. The catalyst was applied in transesterification reactions for biodiesel production from the waste cooking oil following a central composite design of centered face 2(3) and a statistical model was developed in order to describe the behavior of the ester content as a function of the independent variables temperature, alcohol:oil molar ratio, and catalyst dosage. The statistical model (R-2=0.8943) was validated and showed a relative error below 3% between the experimental and predicted values. By means of linear regression methods and response surface methodology, the conditions of biodiesel synthesis reaction were optimized and 94.5% conversion into esters was obtained at 190 degrees C, alcohol:oil molar ratio of 90:1, and catalyst dosage of 5wt. %. The univariate study of the reaction time showed that the reaction processed in 4 h presented the highest conversion in terms of ester content in the biodiesel produced. The proposed catalyst showed good catalytic activity up to the fourth reaction cycle, indicating its good development and application prospectus.