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978-3-8439-3326-1, Reihe Apparatedesign
Design and Characterisation of a Small-Scale Modular Multistage Agitated Reactor
159 Seiten, Dissertation Technische Universität Dortmund (2016), Softcover, A5
This work investigates a modular multistage agitated reactor as potentially interesting technology for the implementation of continuous processes with a throughput in the range of a few kg/h. The technology is of particular interest for slow reactions because a narrow residence time distribution can be achieved even at long residence times and because the input of mixing energy is independent of the net flow velocity.
Based on initial experiments with a previously existing prototype a modular reactor design is developed which is subsequently characterised in more detail.
The residence time distribution in the reactor is characterised experimentally and a correlation for its prediction is derived. For validation, the correlation is coupled with the reaction kinetics of the saponification of ethyl acetate and the experimentally determined conversions are in good agreement with the predicted ones from the process model.
The heat transfer coefficients are determined experimentally and through CFD simulations with the overall specific heat transfer coefficients lying in the range from 110 to 230 kW/(m³ K). The well-established Nusselt correlation for stirred vessels can be adapted to generalise the CFD results and hence reduce the simulation effort in future projects. Considering the heat transfer coefficient in the heat transfer jacket, it is shown that the correlation by Stein and Schmidt from 1986 is more suitable the investigated reactor than the existing alternatives.
The robustness in the presence of solid-forming reactions is investigated through a test reaction. It is found that the shear forces in the reactor are not sufficient to prevent encrustation induced through heterogeneous nucleation at the wall. Already formed particles, however, pass through the reactor without building a fouling layer.
As an application example, the technology is used to implement a continuous Buchwald-Hartwig amination with a throughput of 0.9 kg/h. Quantitative conversion of the substrate is achieved and the product can be selectively extracted in the subsequent extraction. The employed process sequence including reaction, quenching with water and extraction under mildly acidic conditions should be generally applicable to this type of reaction.