Acid catalyzed biodiesel synthesis from Jatropha oil: Mechanistic aspects of ultrasonic intensification

• Esterification/trans-esterification of Jatropha with H2SO4 under sonication.
• Statistical design of experiments coupled with simulations of cavitation bubble dynamics.
• Simultaneous esterification/transesterification of Jatropha oil suffers from water inhibition.
• Transesterification system found to controlled by intrinsic kinetics.
• No sono-chemical effect of cavitation observed.

In this study, we have investigated the ultrasound assisted acid catalyzed transesterification of Jatropha oil. A statistical experimental design (Box–Behnken) is coupled to simulations of cavitation bubble dynamics. Acid catalyzed esterification was rather insensitive to ultrasound irradiation, while the beneficial effect of sonication on transesterification reaction was only through the intense micro-mixing induced by ultrasound. Transient cavitation in methanol did not render any impressive effect. The transesterification system was revealed to be strongly controlled by intrinsic kinetics and mass transfer resistance. The optimum values of experimental variables have been determined as: alcohol to oil molar ratio ≈ 7, catalyst concentration ≈ 6% w/w oil and temperature ≈ 70 °C. The influence of these variables is highly involved and interlinked, and any deviation from its optimum value leads to sharp reduction in the FAME yield. Results of this study illustrate that sonication does not change the chemistry of acid-catalyzed transesterification and the beneficial effect is only of physical nature, which is further limited by the intrinsic kinetics and mass transfer.

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