Preparation of the F ⁻ -SO ₄ ^2- /MWCNTs catalyst and kinetic studies of the biodiesel production via esterification reaction of oleic acid and methanol

A novel solid Lewis acid catalyst F ⁻ -SO ₄ ^2- /MWCNTs was prepared by impregnating multi-walled carbon nanotubes with sulfuric acid and NaF solution. It was characterized by several techniques. Catalytic activity of F ⁻ -SO ₄ ^2- /MWCNTs was evaluated in the esterification reaction of oleic acid and methanol. It exhibited high catalytic activity, giving an oleic acid conversion of 90% when the reaction was conducted with 0.9 wt% catalyst and a methanol/oil molar ratio of 12:1 at 65 °C over 6 h. A kinetic study of F ⁻ -SO ₄ ^2- /MWCNTs catalyzed esterification reaction of oleic acid and methanol was implemented after reaction conditions have been optimized, and it was described by the reversible pseudo second-order reaction rate law. Kinetic constant was correlated with the molar ratio of methanol to oleic acid, catalyst concentrations and reaction temperature. Pre-exponential factor (A) and activation energy (Ea) of the positive and reverse reactions of the F ⁻ -SO ₄ ^2- /MWCNTs-catalyzed esterification were obtained. The values of A and Ea of the forward reaction were 1.88 L mol ⁻¹ h ⁻¹ and 32.73 kJ mol ⁻¹ , and the values of the reverse reaction were 1.90 L mol ⁻¹ h ⁻¹ and 32.61 kJ mol ⁻¹ , respectively. The biodiesel product obtained in this study meet the requirements of the ASTM D6751 standard.