This paper investigates the production of biodiesel from palm oil using a combined mechanical stirred
and ultrasonic reactor (MS–US). The incorporation of mechanical stirring into the ultrasonic reactor
explored the further improvement the transesterification of palm oil. Initial reaction rate values were
54.1, 142.9 and 164.2 mmol/L min for the mechanical-stirred (MS), ultrasonic (US) and MS–US reactors,
respectively. Suitable methanol to oil molar ratio and the catalyst loading values were found to be 6 and 1
of oil, respectively. The effect of ultrasonic operating parameters; i.e. frequency, location, and number of
transducer, has been investigated. Based on the conversion yield at the reactor outlet after 1 h, the number
of transducers showed a relevant role in the reaction rate. Frequency and transducer location would
appear to have no significant effect. The properties of the obtained biodiesel (density, viscosity, pour
point, and flash point) satisfy the ASTM standard. The combined MS–US reactors improved the reaction
rate affording the methyl esters in higher yield.