Residence time semi-batch reactors

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

We base our design of batch and semi-batch reactors on the residence time required to produce specified product. We establish that residence time requirement in laboratory-sized reactors. We generally over-design commercial-sized batch and semi-batch reactors to allow for unexpected problems and unforeseen opportunities. 

For purely batch reactors, the reference time is naturally the residence time, as a function of which the conversion in the reactor is usually described. This batch time can also be used for analysis of semi-batch reactors. Nevertheless, as the reactant introduction in semi-batch reactors can have a drastic influence on the reactor performance, the feed time is more preferably used as the reference time 4]. 

For given concentrations, the scale-up rule would be cp = constant. It was shown in section 422.4, that for a CSTR (p is inversely proportional to the mean residence time X. For semi-batch reactors, x in eq. (4.13) has to be replaced by the feeding time t that is the time used for feeding reactant A into the reactor. 

When compared to a CSTR, the semi-batch reactor has some particular advantages the feeding rate of the reactant(s) can be controlled independently of the residence time, so that a more complete conversion may be obtained. By choosing various feeding programs a flexibility is obtained that is difficult to reali in a continuous reactor. Also the temperature can be changed during the process. And finally, this type of reactor is often preferred when more than one product has to be made in the same reactor. 

The main reaction leading to the desired product P is so rapid, that in the bulk of the reaction phase the conversion of B is complete. The reaction may be carried out in a semi-batch reactor or in a continuous stirred reactor. The feeing time in the semi-batch reactor and the mean residence time in the continuous reactor do not influence the conversion of 5, that is practically complete anyway. However, the feed rate of B and the meso-mixing rate will determine the formation of the undesired byproduct X. Esentially, the critical phenomena in a semi-batch reactor and in a CSTR are the same for this process. 

OS 88] [R 27] [P 68] A maximum yield of 80-85% was obtained at 4 s residence time and a temperature of 50 °C by micro reaction system processing [61, 62,127, 142,143]. Using ordinary laboratory-processing with standard laboratory glassware yielded only 25%. The continuous industrial process had a yield of 80-85% the previously employed semi-batch industrial process gave a 70% yield. The temperature and the residence time of industrial and micro reactor continuous processing were identical. 

The stirred tank with a jacket for heating or cooling (also called autoclave or digester) is the workhorse of the pharmaceutical, fine-chemicals, mineral and paper industries. It is used as a reactor, mixer, decanter, heater and cooler. The bubble and slurry-bubble columns too are akin to the STR. It is used as a batch reactor or semi- or fed-batch reactor for those reactions requiring a large residence time, as the tubular reactor would be too long and unwieldy. The STR is bulky, and the yield and selectivity could be low. 

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