Reactions in parallel

Examples of reacting systems with networks made up of parallel steps are  

The simplest case of reactions in parallel can be written as, decomposition of component A by two competing paths (both elementary reaction) given by 

Let us consider the case of one reactant only but different orders of reaction for the two reaction paths. 

A - Q unwanted product with the corresponding rate equations  

In these equations it is understood that CA may be (a) the concentration of A at a particular time in a batch reactor, (b) the local concentration in a tubular reactor operating in a steady state, or (c) the concentration in a stirred-tank reactor, possibly one of a series, also in a steady state. Let St be an interval of time which is sufficiently short for the concentration of A not to change appreciably in the case of the batch reactor the length of the time interval is not important for the flow reactors because they are each in a steady state. Per unit volume of reaction mixture, the moles of A transformed into P is thus 9LAP6t, and the total amount reacted (9lAP + 3tAQ)St. The relative yield under the circumstances may be called the instantaneous or point yield pA, because CA will change (a) with time in the batch reactor, or (b) with position in the tubular reactor. 

In order to And the overall relative yield PA, i.e. the yield obtained at the end of a batch reaction or at the outlet of a tubular reactor, consider an element of unit volume of the reaction mixture. If the concentration of A decreases by SCA either (a) with time in a batch reactor or (b) as the element progresses downstream in a tubular reactor, the amount of A transformed into P is - pASCA. The total amount 

For a stirred-tank reactor consisting of a single tank in a steady state, the overall yield is the same as the instantaneous yield given by equation 1.62 because 

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Multiple reactions in parallel producing byproducts. Rather than a single reaction, a system may involve secondary reactions producing (additional) byproducts in parallel with the primary reaction. Multiple reactions in parallel are of the tj ie... 

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... 

Figure 2.2 summarizes these arguments to choose a reactor for systems of multiple reactions in parallel. 

Multiple reactions in parallel producing byproducts. Once the reactor type is chosen to maximize selectivity, we are in a position to alter selectivity further in parallel reaction systems. Consider the parallel reaction system from Eq. (2.20). To maximize selectivity for this system, we minimize the ratio given by Eq. (2.21) ... 

Das Chemidabor im Mikrochip, Blick durch die Wirtschafi, December 1997 Chemtel glass chip of Orchid Biocomputer, Princeton 144 cells for parallel processing matchbox-sized system with many devices micro pumps with no movable parts 10 nl internal volume carrying out of different reactions in parallel fashion complete chemistry laboratory en miniature 10 000 cells as future-development task [223],... 

Multiple reactions in parallel producing byproducts. Consider the system of parallel reactions from Equation 5.4 with the corresponding rate equations1-3 ... 

This technique is readily adaptable for use with the generalized additive physical approach discussed in Section 3.3.3.2. It is applicable to systems that give apparent first-order rate constants. These include not only simple first-order irreversible reactions but also irreversible first-order reactions in parallel and reversible reactions that are first-order in both the forward and reverse directions. The technique provides an example of the advantages that can be obtained by careful planning of kinetics experiments instead of allowing the experimental design to be dictated entirely by laboratory convention and experimental convenience. 

For reactions in parallel, it is the fast step that governs. Thus, if A B and A C are two competing reactions, and if kAB kAC, the rate of formation of B is much higher than that of C, and very little C is produced. Chemical rates can vary by very large factors, particularly when different catalysts are involved. For example, a metal catalyst favors dehydrogenation of an alcohol to an aldehyde, but an oxide catalyst often favors dehydration. 

Apply the tanks-in-series model to the following kinetics scheme involving reactions in parallel ... 

At sufficiently high anodic potentials, only the anodic reaction (1) wiU proceed at the experimental electrode. Then on the counter electrode the reactions (2) or (3) causing CMT measurements will proceed at the same electrical rate. These CMT measurements should coincide with the value of current measured electrically. The only restriction in this case (other than those discussed in Section II.2) is that dissolved metal ions must not be plated onto the counter electrode in a cathodic reaction in parallel with (2) or (3). 

Imposing oscillations in the feed concentrations for a continuous back-mixed reactor can also result in beneficial changes of reaction selectivity [58]. Such changes are likely to be more significant with intermediates in consecutive reactions than with products from simultaneous reactions in parallel [59]. 

For multiple reactions a change in the observed activation energy with temperature indicates a shift in the controlling mechanism of reaction. Thus, for an increase in temperature Eq s rises for reactions or steps in parallel, Eobs falls for reactions or steps in series. Conversely, for a decrease in temperature E s falls for reactions in parallel, E s rises for reactions in series. These findings are illustrated in Fig. 2.3. 

Irreversible Reactions in Parallel. Consider the simplest case, A decomposing by two competing paths, both elementary reactions ... 

For reactions in parallel, the concentration level of reactants is the key to proper control of product distribution, A high reactant concentration favors the reaction of higher order, a low concentration favors the reaction of lower order, while the concentration level has no effect on the product distribution for reactions of the same order. 

Chapter 7 considered reactions in parallel. These are reactions where the product does not react further. This chapter considers all sorts of reactions where the... 

For these reactions the concentration-time curves are of little generality for they are dependent on the concentration of reactant in the feed. As with reactions in parallel, a rise in reactant concentration favors the higher-order reaction a lower concentration favors the lower-order reaction. This causes a shift in and this property can be used to improve the product distribution. 

For reactions in series we calculate the maximum production rate of R directly, as shown in Chapter 8. However, for reactions in parallel we find it useful to first evaluate the instantaneous fractional yield of R, or... 

The Trambouze Reactions—Reactions in parallel. Given the set of elementary reactions with a feed of AO = 1 mol/liter and v = 100 liters/min we wish to maximize the fractional yield, not the production of S, in a reactor arrangement of your choice. 

For reactions in parallel of the same reaction order the product distribution is the same in fixed and BFBs. 

Figure 4-11 Plot of differential selectivity for the example of three reactions in parallel. If C is desired, the CSTR gives a larger Sc, and this occurs when the reactor is operated at O = 1 mole/liter.

In this section, some analytical solutions of fluidized-bed models are presented. Specifically, model solutions will be given for the case of a gas-phase reactant and a single solid-catalyzed reaction of the form A —> products and bubbling fluidized bed (Type B fluidization). The same analysis holds for a reaction of the form A + B —> products, if the reaction depends only on the concentration of A. Some solutions for the cases of a single reversible reaction, for two reactions in parallel, and two reactions in series will be given as well. 

SynPhase crowns may be used to perform large numbers of optimization reactions in parallel. This library of reaction conditions may be analyzed by assaying product purities after cleavage from the solid phase using high-throughput techniques such as HPLC and ESMS. Overall, this approach can greatly reduce the time required for this critical step of compound library development. 

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