Mg-Al Hydrotalcite as Heterogeneous Catalyst for Transesterification of Jatropha Curcas Oil: Theoretical and Experimental Analysis

Background: Jatropha curcas oil is a potential feedstock in biodiesel (fatty acid alkyl esters) production due to low acidity, good oxidation stability and excellent cold flow properties. Mg-Al hydrotalcites are potentially interesting for the transesterification, given its characteristics as anion exchangers, solid base catalyst and adsorbents. In this paper, a theoretical and experimental study of the mechanism and the kinetics of the transesterification of Jatropha curcas oil using Mg-Al hydrotalcite is presented. Methods: Design experimental was used to evaluate the influence of operational parameters on conversion of reaction, being concentration of catalyst, followed by alcohol/oil molar ratio and temperature the significant factors. Equations were formulated for predicting the conversion of reaction. Optimum geometries and chemical and physic steps of the reaction mechanism were evaluated using DFT calculation. Results: The experimental study includes catalysts characterization, ANOVA evaluation of transesterification of Jatropha curcas oil and definition of regressions models for reactions using calcined catalysts at different temperature. The stability and chemical reactivity were evaluated by the correlation of energies of the frontier orbitals in theoretical study. The results suggest the possibility of transesterification of jathopha curcas oil occurs on the surface of catalyst of hydrotalcite, specifically on the acid sites of the species of Mg2+. Conclusion: Experimental and theoretical results demonstrated that transesterification of Jatropha curcas oil using hydrotalcite Mg-Al as catalyst occur by LHHW mechanism and the chemical reaction is the rate-determining step. These results were also corroborated by frontier molecular orbital theory.