In situ and conventional transesterification of rapeseeds for biodiesel production: The effect of direct sonication

• In situ and conventional transesterification of rapeseed oil was studied.
• Type of mixing affected reactive extraction yield but not FAME content.
• Type of mixing did not influence reaction rate constant.
• Transesterification reaction followed second order kinetics.
• Physicochemical properties of rapeseed biodiesel were determined.

Rapeseeds were used for the production of biodiesel via alkaline transesterification. The effect of direct sonication (24 kHz) during in situ and conventional transesterification was studied without the use of external heating and was compared to that of mechanical stirring (600 rpm, 60 °C). In the in situ transesterification the use of ultrasonication and mechanical stirring led to a similar high % FAME content (97.2 ± 0.4 and 95.7% ± 0.8 respectively) after 120 min. However the % yield of the extracted methyl esters using mechanical stirring was considerably lower compared to ultrasonication (37.0 and 80.6% respectively) when same conditions were applied (7.5% NaOH w/w of oil, 400:1 methanol to oil molar ratio). The kinetics study of the rapeseed oil methanolysis process via direct sonication and mechanical stirring showed that the reaction rate constant is not affected by the method of stirring under specific conditions. Properties of rapeseed biodiesel determined agree with the specifications of the European Standard EN 14214.