Biodiesel process intensification: the role of the liquid-liquid interface area in the achievement of a complete conversion in few seconds

Transesterification of vegetable oil with methanol, promoted by alkaline catalysts has been tested in many different reactors and surprisingly the reaction time, in some of these reactors, resulted very short, in the range of few seconds. In particular, by using static mixers, micro-reactors, oscillatory flow reactors, cavitational reactors, microwave reactors or centrifugal contactors, it is possible to obtain high biodiesel yields in a much shorter time than in stirred tank reactors. As the reaction occurs between two immiscible phases, a general conclusion could be that the higher the interface area the shorter the reaction time. In this paper, we will confirm this assumption because, by using a very efficient micro-mixer, followed by a void tube, very high conversions have been obtained in a few seconds of residence time. Another important observation is that passing from 1% to 2% b.w. of KOH catalyst concentration, a very high increase in the conversion is obtained. This means that the final conversion is not due to the chemical equilibrium but to the catalyst deactivation. For describing all the observed phenomena a new biphasic kinetic model based on a reliable mechanism has recently been developed and used here for quantitatively describing the performed runs.