4. Multiple Reactor Networks
4.1 Series and Parallel Combinations of Ideal Reactors
Multiple reactors (two or more reactors) are usually employed in the chemical process industries by connecting them either in series or in parallel configuration, e.g., three MFRs are used in series, four packed bed reactors (PBRs) in series, a PFR and a CSTR in series, a CSTR and a PFR in series, PFRs in parallel, MFRs in parallel, etc.
Following are some representative examples of situations where in the series configuration of reactors and parallel configuration of reactors are used:
(I) Series Arrangement of Reactors
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To enhance the overall conversion of the limiting reactant
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Modelling PFR as a combination of infinite number of MFRs in series
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Modelling tubular reactors (e.g.: tanks-in-series model)
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To overcome thermodynamic limitations (e.g.: oxidation of \(\ce{SO2}\) to \(\ce{SO3}\))
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To achieve the best multiple reactor scheme to carry out autocatalytic reactions
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Modelling catalyst decay in packed bed reactors (PBRs)
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Modelling transient temperature effects in plug flow reactors (PFRs)
(II) Parallel Arrangement of Reactors
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To increase the production rate
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To maximize the yield of the desired product in certain multiple reactions
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Optimizing the process conditions for an autocatalytic reaction (e.g., operating at the maximum possible rate)
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To illustrate the behavior of real reactors using compartment models
Note: Many living systems are modelled using the series / parallel / series-parallel combinations of ideal reactors: e.g., Compartmental models are able to describe
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the distribution and elimination of a drug administered to an animal / human being
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alcohol metabolism in a person, etc. Ref: Fogler, 4\(^{\text{th}}\) edition, pp. 441
In such a modelling practice, an organ or two organs (lumped together) is considered a compartment (an ideal reactor); for example stomach is considered an MFR and liver a PFR.
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