Systems Involving Multiple Reactions

Single reactions. Most reaction systems involve multiple reactions. In practice, the secondary reactions can sometimes be neglected, leaving a single primary reaction to consider. Single reactions are of the type... 

The selection of reactor pressure for vapor-phase reversible reactions depends on whether there is a decrease or an increase in the number of moles. The value of AN in Equation 6.25 dictates whether the equilibrium conversion will increase or decrease with increasing pressure. If AN is negative, the equilibrium conversion will increase with increasing pressure. If AN is positive, it will decrease. The choice of pressure must also take account of whether the system involves multiple reactions. 

For reaction systems involving multiple reactions producing by products, selectivity and reactor yield can also be enhanced by appropriate changes to the reactor temperature, pressure and concentration. The appropriate choice of catalyst can also influence selectivity and reactor yield. The arguments are summarized in Figure 6.912. 

Most interesting chemical reaction systems involve multiple reactions, which we wiU consider in the next chapter. In this section we examine several reaction systems that involve nearly a single reaction and are both industrially important and involve some interesting reaction engineering issues. 

Chapter 5 Chemical Systems Involving Multiple Reactions... 

Although multiple reactors can be used for single reaction systems, they are potentially not required. For systems involving multiple reactions, reactor stiuctures may be essential— unlocking certain states that would not... 

Note that the kinetics supplied in this example resulted in having to employ a numerical nonlinear solver in order to solve the CSTR equation. To produce a locus of CSTR solutions, the aforementioned procedure would need to be repeated for a range of different t values. This may result in a large amount of computation. The PFR by comparison is easy to solve for, even when nonlinear kinetics is used. Unfortunately, many real-world systems involve multiple reactions with nonlinear kinetics. Furthermore, due to the nature of the CSTR equation, multiple solutions may exist for the same feed point and residence time. 

We believe that if designers begin to think about reactor problems in terms of reactor networks—as opposed to single reactors—then more effective designs may be achieved overall. Furthermore, reactive systems involving multiple reactors, termed reactor structures, are necessary when systems involving multiple reactions are involved, and so familiarity with this approach is valuable in achieving the best performance from complex reactive systems. 

This discussion can be naturally extended to multicomponent systems involving multiple reactions. Importantly, as long as the number of molecules of reactants and products is large, reactions are regarded as deterministic rate processes and reaction rate equations are written for... 

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