Flow Isothermal Perfectly Stirred Tank Reactor

CONTINUOUS FLOW ISOTHERMAL PERFECTLY STIRRED TANK REACTOR 

Industrial reactors operate in the steady state with the volume, concentration, and temperature of the reaction mixture being constant 

Fig ure 4-5. A battery of oontinuous flow stirred tank reaotors. 

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The theorems by Feinberg, Horn, Jackson and Vol pert provide sufficient conditions to exclude multistationarity. These theorems can be applied in the case of homogeneous systems, and in the case of inhomogeneous systems, if the system can be modelled by formal elementary reactions as shown several times above. An especially important case of an inhomogeneous systems is the isothermal continuous (flow) stirred tank reactor (CSTR). By a CSTR we mean one in which there is perfect mixing and in which, at each instant, every component within the reaction vessel is also contained in the effiuent stream. 

Reactors are mostly not isothermal, as heat is consumed or released, and perfect mixing or a perfect heat exchange with the surrounding is impossible. However, some reactors are almost isothermal, such as, for example, a well-mixed continuous stirred tank reactor (CSTR). In a batchwise operated stirred tank or in a plug-flow reactor (PFR), isothermal conditions with regard to reaction or residence time (axial position), respectively, are hard to realize. However, the assumption of an isothermal system is helpful for a first examination of reactor types as it simplifies the equations and we can focus on concentration and mixing effects only. Thus, here, we inspect isothermal reactors. Thermal effects are considered in Section 4.10.3. 

Example 9.11 Which type of isothermal reactor would produce the narrowest possible distribution of chain lengths in a free-radical addition polymerization continuous stirred tank reactor (CSTR, or backmix), batch (assume perfect stirring in each of the previous), plug-flow tubular, or laminar-flow tubular ... 

Reactor design usually begins in the laboratory with a kinetic study. Data are taken in small-scale, specially designed equipment that hopefully (but not inevitably) approximates an ideal, isothermal reactor batch, perfectly mixed stirred tank, or piston flow. The laboratory data are fit to a kinetic model using the methods of Chapter 7. The kinetic model is then combined with a transport model to give the overall design. 

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