Industrial catalytic processes intensification through the use of microreactors
Turco, Rosa (2011) Industrial catalytic processes intensification through the use of microreactors. [Tesi di dottorato] (Inedito)
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The aim of this work was the intensification of two interesting industrial processes: 1. Biodiesel Production 2. Epoxidized Oils Production In the first case the reaction in traditional industrial reactors is strongly limited by mass transfer, due the presence of two immiscible liquid reactants phases, thus it requires very long residence times in order to create a high interfacial area to promote the reaction. For the vegetable oils epoxidation reaction, a part from the mass transfer limitations, there are limitations related to the heat transfer, due to very exothermicity of the reaction. It was shown that the intensification of epoxidation process could be possible through the shift from the pulse fed batch reactors (current technology) to continuous ones able to mix the immiscible reagents and remove the heat released by the reaction. The use of the microreactors represents the best solution in this case, taking account the high dispersion capability of these devices, that could enhance the mass and heat transfer. Such shift could be obtained only by acquiring sufficient insight on the reaction kinetics and by developing a reliable physical model able to describe the evolution of all the components involved, considering in particular the secondary reactions that decrease the selectivity. For this purpose, it was developed a kinetic model, that contains the main physico-chemical peculiarities of the considered reacting system: components partition between the two liquid phases, mass transfer limitation across liquid-liquid interface, heat transfer between the reacting mixture and reactor jacket, different reactivity in epoxidation and oxirane ring opening (degradation) of the different types of double bonds (trienic, dienic, monoenic). The model was successfully applied, in a first step, to a set of experimental fed-batch runs, and then with the aim to further validate the model, to a set of conventional continuous tubular reactor runs. The very good agreement between the experimental data and the model prediction confirmed that the model was able to describe the behavior of reaction in different conditions. In perspective, the model will be useful to design a continuous epoxidation operation in safe conditions and could be the basis for the process intensification in microreactors. Moreover, in this work the feasibility of the intensification of the epoxidation process could be possible through the use of only hydrogen peroxide as oxidant reactant, in presence of a heterogeneous catalyst, was evaluated. Concerning to the biodiesel production process intensification several reactors able to improve the mass transfer between the immiscible liquid reagents, through the creation a very high interfacial area and a very intensive local micromixing, were studied. For this purpose a corrugated plates heat exchanger reactor (CP-HEX) was applied to promote the transesterification of soybean oil with methanol for the biodiesel production. A very high productivity (420 kg/day) was obtained with a very small device of 450 cm3 of overall volume and 200 cm3 of working volume. This was explained by assuming a very high intensity micromixing occurred in this type of the reactors through the formation of eddies between plates. Then, the effect of different types of static mixers on the intensification of the biodiesel synthesis were deeply investigated. It was shown that a tubular reactor filled with different elements of different sizes and shape can usefully be used to simulate the behavior of both a “static mixer” and a “microreactor”. As a matter of fact, with this type of device it is possible to change opportunely the size of the microchannels, so simulating microreactors, or the intensity of local micromixing by changing feeding flow rates, so simulating static mixers. At last, a new biphasic model based on a more reliable reaction mechanism was developed in this work and successfully applied to continuous runs in tubular reactor filled with different static mixer elements.
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