Batch multiple reactions

Multiple reactions in parallel producing byproducts. Consider again the system of parallel reactions from Eqs. (2.16) and (2.17). A batch or plug-flow reactor maintains higher average concentrations of feed (Cfeed) than a continuous well-mixed reactor, in which the incoming feed is instantly diluted by the PRODUCT and... 

The component balance for a batch reactor. Equation (1.21), still holds when there are multiple reactions. However, the net rate of formation of the component may be due to several different reactions. Thus,... 

The extension to multiple reactions is done by writing Equation (3.1) (or the more complicated versions of Equation (3.1) that will soon be developed) for each of the N components. The component reaction rates are found from Equation (2.7) in exactly the same ways as in a batch reactor. The result is an initial value problem consisting of N simultaneous, first-order ODEs that can be solved using your favorite ODE solver. The same kind of problem was solved in Chapter 2, but the independent variable is now z rather than t. 

The fed-batch scheme of Example 14.3 is one of many possible ways to start a CSTR. It is generally desired to begin continuous operation only when the vessel is full and when the concentration within the vessel has reached its steady-state value. This gives a bumpkss startup. The results of Example 14.3 show that a bumpless startup is possible for an isothermal, first-order reaction. Some reasoning will convince you that it is possible for any single, isothermal reaction. It is not generally possible for multiple reactions. 

A batch or plug-flow reactor should be used for multiple reactions in series. 

Multiple Reactions—Choosing a reactor type to obtain the best selectivity can often be made by inspection of generalized cases in reaction engineering books. A quantitative treatment of selectivity as a function of kinetics and reactor type (batch and CSTR) for various multiple reaction systems (consecutive and parallel) is presented in [168]. 

The need for preconditioning is not only somewhat bothersome, but it also has the potential of introducing minor artifacts since the reference spectra are not exact for each reaction condition. Thus, the direct application of Eq. (2) without preconditioning was undertaken. In addition, instead of performing multiple reaction runs, a semi-batch approach was adopted, whereby a reaction is started and then perturbations are performed throughout the duration. The semi-batch approach is potentially much more frugal with experimental resources. 

In this chapter we consider the performance of isothermal batch and continuous reactors with multiple reactions. Recall that for a single reaction the single differential equation describing the mass balance for batch or PETR was always separable and the algebraic equation for the CSTR was a simple polynomial. In contrast to single-reaction systems, the mathematics of solving for performance rapidly becomes so complex that analytical solutions are not possible. We will first consider simple multiple-reaction systems where analytical solutions are possible. Then we will discuss more complex systems where we can only obtain numerical solutions. 

For a batch reactor with multiple reactions the mass-balance equation on species j is... 

At the same time, as a chemist I was disappointed at the lack of serious chemistry and kinetics in reaction engineering texts. AU beat A B o death without much mention that irreversible isomerization reactions are very uncommon and never very interesting. Levenspiel and its progeny do not handle the series reactions A B C or parallel reactions A B, A —y C sufficiently to show students that these are really the prototypes of aU multiple reaction systems. It is typical to introduce rates and kinetics in a reaction engineering course with a section on analysis of data in which log-log and Anlienius plots are emphasized with the only purpose being the determination of rate expressions for single reactions from batch reactor data. It is typically assumed that ary chemistry and most kinetics come from previous physical chemistry courses. 

COMPARISON OF BATCH, TUBULAR AND STIRRED-TANK REACTORS FOR MULTIPLE REACTIONS. REACTOR YIELD... 

The advantages of a semi-batch reaction, that is, a better selectivity in the case of multiple reactions or a better control of the reaction course in the case of exothermal reactions, are obtained if the reaction rate is controlled by the progressive addition of one or more reactants. Indeed, this objective can only be achieved if the added reactant is immediately converted and does not accumulate in the reactor [3]. Often a reaction is said to be feed controlled only because a reactant is fed. This is not always the case, since the feed rate must be adapted to the reaction rate, and the concentration of the added compound (B) is maintained at a low level during the reaction. 

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