Battery of CSTR

A reaction battery of CSTRs in series, although both mechanically and operationally more complex and expensive man a tubular reactor, provides flexibility. Relatively slow reactions are best conducted in a stirred tank reactor battery. A tubular reactor is used when heat transfer is needed, where high pressures and/or high (or low) temperatures occur, and when relatively short reaction times suffice. 

The CSTR can either be used by itself or, in the manner shown in Figure 1-11, as part of a series or battery of CSTRs. It is relatively easy to maintain good temperature control with a CSTR, There is, however, the disadvantage that the conversion of reactant per volume of reactor is the smallest of the flow reactors. Cons iueiit y, very large reactors are necessary to obtain high conversions. 

As we noted earlier, there may be temperature con-trol/heat transfer considerations or other factors that dictate the use of a CSTR even when the yield considerations are unfavorable. In such cases the yield of the desired product may be significantly increased by using a battery of CSTRs in series. If desired, one has the additional flexibility granted by using tanks with different volumes or tanks... 

As is the case for conventional homogeneous reactions taking place in batteries of CSTRs, one quickly reaches a point of diminishing retnms with respect to the benefits of addition of another identical CSTR to a cascade. Because issues of genetic stability and prevention of contamination by alien microorganisms exacerbate the problem of diminishing returns, very rarely does a cascade of CSTBRs exceed three or four in number. 

A third-order irreversible reaction A B with rate equation (r ) = kC is carried out in a battery of six numbers ideal CSTRs of equal volumes connected in series. The rate constant is fc = 0.1 (mVkmol) /min. The feed concentration of A is 2 kmol/m. The space time of each one of the CSTRs is 2 min. (i) What is the net conversion of A achieved in the battery of CSTRs (ii) What is the conversion in one single CSTR having space time equal to the sum of space times of all the six CSTRs ... 

CSTRs (as well as tubular flow reactors to be addressed in the next chapter) are often connected in series in such a manner that the exit stream of one reactor is the feed stream for another reactor. This series or cascade of reactors is pictured in Figure 9.2 and discussed later in this chapter. Under these conditions it is convenient to define the conversion at any point downstream in the battery of CSTR reactors in terms of inlet conditions, rather than with respect to any one of the reactors in the series. The... 

The CSTR is identical to one of the battery of CSTRs shown in Professional Reference Shelf RI.3 Figure 1.2. except the feed and exit. streams are at the top. 

---