Alkali-catalysed sunflower oil transesterification: a comparison between the energetic efficiencies of mechanical agitation and static mixing

This study focused on the investigation of innovative mixing techniques for the alkali-catalysed transesterification of vegetable oil with methanol. In particular, we tested the employment of static mixers and of mechanical agitation configurations characterized by the combination of different types of impellers and by the variation of agitation speed with time. The different mixing techniques were compared in terms of reaction time required to attain a given conversion of the transesterification reaction (t75, t90) and corresponding specific energy requirement, expressed as J/kg biodiesel produced (e75, e90). The best reaction performances were obtained with the utilization of 1 SMV static mixer operated at a 1.3 m/s superficial velocity, and with a mechanical agitation configuration characterized by the combination of a radial (Rushton) and an axial hydrofoil (A310) impeller and by the complete halt of agitation after 1 minute. These configurations resulted in a 7-130 fold reduction of specific energy consumption in comparison with the traditional, non-optimized mixing configurations.