Case B. Semi-Batch Reactor

A semi-batch reactor is used to convert reactant, A, to product, B, by the reaction A — 2B. The reaction is carried out adiabatically. The reaction kinetics are as before 

The balances, for the two components. A, and B, with flow of A, into the reactor, 

With initial conditions for the initial molar quantities of A and B (V CA, V CB), the initial temperature, T, and the initial volume of the contents, V, specified, the resulting system of equations can be solved to obtain the time varying quantities, V(t), VCA(t), VCB(t), T(t) and hence also concentrations, CA, and CB, as functions of time. Examples of semi-batch operations are given in the simulation examples HMT, SEMIPAR, SEMISEQ, RUN and SEMIEX. 

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Styrene-acrylonitrile copolymerization in a semi-batch reactor Two cases (a) maximization of monomer conversion and minimization of polydispersity index at the end of reaction, and (b) maximization of monomer conversion at the end of reaction while minimizing polydispersity index at the end of reaction and molar ratio of unreacted monomer in the reactor at any time. NSGA-11 The decision variables for optimization were trajectories of addition rate of a monomer-solvent-initiator mixture and reactor temperature. Nayak and Gupta (2004)... 

In this case, we maximize Sp by maintaining a low [A]. Maintaining a high [B] ensures a high P formation rate. Thus, we would choose a semi-batch reactor for this process we would charge the reactor with B and feed A at a rate appropriate to obtain a high p. If a < 7 and P<6, then... 

Two Reactions, Different Orders—In the case of a desired second-order reaction and an undesired first-order reaction, such as A + B - C and A — D, where C is the desired product, the batch, semi-batch, or plug-flow reactor is preferred. 

Study the system for the kinetic case nAi = nA2 and nB1semi-continuously with slow feeding of B and (ii) as a batch reactor with B charged initially to the reactor and zero feed of B. Compare the results obtained for the two differing modes of reactor operation. 

The advantages of a semi-batch reaction, that is, a better selectivity in the case of multiple reactions or a better control of the reaction course in the case of exothermal reactions, are obtained if the reaction rate is controlled by the progressive addition of one or more reactants. Indeed, this objective can only be achieved if the added reactant is immediately converted and does not accumulate in the reactor [3]. Often a reaction is said to be feed controlled only because a reactant is fed. This is not always the case, since the feed rate must be adapted to the reaction rate, and the concentration of the added compound (B) is maintained at a low level during the reaction. 

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