Optimum process and kinetic study of Jatropha curcas oil pre-esterification in ultrasonical field

H2SO4 catalyzed pre-esterification of Jatropha curcas oil was investigated in this study. Ultrasound was used to enhance the mixing extent of methanol and oil. The experimental results showed that 18% methanol (wt% of oil), 1.2% H2SO4 catalyst (wt% of oil) and 900 W/L ultrasonic power density were the optimum conditions for the pre-esterification of J. curcas oil with a 20 mg KOH/g initial acid value (AV). The kinetics of the pre-esterification shows that the apparent forward reaction rate constant k+A increased with the rise of the amounts of methanol, catalyst and ultrasonic power density to some extent, while the reverse reaction rate constant was almost independent on these factors. Compared with mechanical stirring, ultrasonic radiation could greatly enhance the pre-esterification. Finally, a function of ultrasonic power density U   was embedded into the kinetic equation, and under the optimum conditions, k+A could be expressed as: k+A=0.034023(−10−6U2+0.002U+0.0531). The relative deviations between the experimental data and the results calculated by the equation are less than 5%.

► The pre-esterification of various initial acid values of Jatropha curcas oil was catalyzed by H2SO4.
► Oil reacted with different amounts of methanol and catalyst enhanced by ultrasonic irradiation or mechanical stirring.
► The optimum reaction condition was determined.
► The kinetic equation of the pre-esterification was found.
► We creatively embedded a function of ultrasonic power density U into the kinetic equation.