Biodiesel Process Intensification by Using Static Mixers Tubular Reactors

Biodiesel is usually produced by reacting triglycerides, contained in vegetable oils, with methanol in the presence of KOH, NaOH, or related alkoxides as catalysts. In industry, the reaction is performed in stirred tank reactors and requires 1-2 h of reaction time being the reaction rate strongly affected by mass transfer limitation. We have recently shown, by using a Corrugated Plates Heat Exchanger Reactor, that a very high productivity (about 2 tons/day L) can be obtained by working at 60-100 degrees C thanks to the presence of an intense local micromixing. Moreover, we have recently tested the performances obtained in a tubular reactor filled with stainless steel spheres of different diameters. By opportunely changing the spheres diameters it is possible to obtain microchannels in a range of 300-1000 mu m with an intense local micromixing. Again, thanks to micromixing we obtained very high productivities. However, in these last reactors the void portion of the reactor is low and the productivity per overall reactor volume is relatively low. It is possible to obtain better results, in terms of productivity, by filling the tubular reactor with stainless steel wool, being in this case the void fraction about 0.9. In the present work, some of the mentioned systems will be compared for their performances by using different amounts of KOH as catalyst (1 or 2% b.w. of oil). A dramatic change in biodiesel yield has been observed in all cases passing from 1 to 2% of catalyst independently of the reactants flow rate. These behaviors cannot be interpreted with the pseudomonophasic kinetic models, normally reported in the literature. At this purpose, for interpreting all the observed kinetic behaviors a new biphasic kinetic model, based on a reliable catalytic mechanism, has been developed. This model has been applied, first of all, to data reported in the literature related to runs performed in batch conditions with the scope of estimating the kinetic parameters, and then it has been applied to all the runs performed in continuous reactors with a satisfactory agreement.