Two-phase semi-batch reactors

The most common example of a two-phase semi-batch reactor is the semi-batch gas/liquid reactor, with a reaction of the type  

Before the start, the reactor is filled with the liquid phase, containing at least one reactant, and possibly a catalyst. From a given moment onwards, a gas flow 

To arrive at a model describing this sort of process, we proceeed in three steps. First the mass transfer and the reaction of reactant A (present in the gas phase) is described in terms of a quasi steady state. From this we find an effective rate constant. In the second step a mass balance is made for the gas flow, describing the relation between the concentrations of reactant A in the in- en outgoing streams. In the third step a mass balance is made for reactant B in the liquid phase over a certain peri( of time. The conc tration of B changes with time,with a rate coefficient found in the first step. 

The calculation methods required for the first step have been described for several different situations in sections 53.4,1 and 5.4,2,I, In general, the relevant rate equation can be expressed either by eq. (5.20) or (5.44), depending on die value of the Hatta number. The effective reaction rate per unit volume r is expresses as 

This constant is a measure for the interfacial area, the solubility of A, the various kinetic constants that determine the rate of the process and the concentration o/ B in the liquid phase. In a mixed reactor, it may be assumed that this concentration and the effective rate constant are both constants throughout the reactor, though they do change with time. 

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