System competitive consecutive

As briefly discussed in Section 1.2, chemical-reaction engineers recognized early on the need to predict the influence of reactant segregation on the yield of complex reactions. Indeed, the competitive-consecutive and parallel reaction systems analyzed in the previous section have been studied experimentally by numerous research groups (Baldyga and Bourne 1999). However, unlike the mechanical-engineering community, who mainly focused on the fluid-dynamics approach to combustion problems, chemical-reaction... 

Looking back over the steps required to derive (5.290), it is immediately apparent that the same method can be applied to treat any reaction scheme for which only one reaction rate function is finite. The method has thus been extended by Baldyga (1994) to treat competitive-consecutive (see (5.181)) and parallel (see (5.211)) reactions in the limiting case where k -> oo.118 For both reaction systems, the conditional moments are formulated in terms of 72(X> and can be written as... 

The two routes (one is Eqs. 2-37b and 2-37c the other is Eqs. 2-37a and 2-37d) together constitute a complex reaction system that consists simultaneously of competitive, consecutive and competitive, parallel reactions. 

The reaction system converts from one (Eq. 2-37), that is, from the kinetic viewpoint, simultaneously competitive, consecutive (series) and competitive, simultaneous (parallel) to one (Eq. 2-38) that is only competitive, simultaneous. The polymerization consists of the B and B functional groups reacting independently with A groups. The rates of disappearance of A, B, and B functional groups are given hy... 

The following competitive-consecutive reaction system was studied ... 

Example 44 Dimensioning of a tubular reactor, equipped with a mixing nozzle, designed for carrying out competitive-consecutive reactions 193 Example 45 Mass transfer limitation of the reaction rate of fast chemical reactions in the heterogeneous material system gas/liquid 197... 

C.T.Chen, The Kinetic System Consisting of Two Pairs of Competitive Consecutive Second-Order Reactions, The Journal of Physical Chemistry,... 

Fig. 1 illustrates the mixing problem for the competitive-consecutive case. R is the desired product and S is the undesired overreaction product. During the time from when the reactants are first contacted to when they are completely mixed on the molecular scale, reaction of A with B to form the desired product R occurs along with the undesired reaction of R with B to form S. When A and B are well mixed at the molecular scale, mainly R is formed, but when there is a boundary between A and B, a significant amount of undesired S appears. Competitive-parallel reactions can be subject to similar mixing effects where the first reaction is the desired one and the second is a simultaneous decomposition of A to form the undesired U. While these two reaction systems have received the most attention, the course of any reaction that is... 

Change the reaction system to reduce k2, thereby increasing the yield of R and decreasing S. Reacting systems were found that achieved reduced 2 at a favorable rate constant ratio. However, the primary reaction rate was also reduced, as is common for competitive-consecutive reaction systems, and was too slow for manufacturing purposes. 

The role of mixing has been studied in systems with more complex reaction schemes or considering more complex fluid-dynamical properties, and in the context of chemical engineering or microfluidic applications (for reviews on microfluidics see e.g. Squires (2005) or Ottino and Wiggins (2004)). Muzzio and Liu (1996) studied bi-molecular and so-called competitive-consecutive reactions with multiple timescales in chaotic flows. Reduced models that predict the global behavior of the competitive-consecutive reaction scheme were introduced by Cox (2004) and by Vikhansky and Cox (2006), and a method for statistical description of reactive flows based on a con-... 

The use of a single reaction requires the online measurement of the local species concentration along the flow. With such systems, one experiences the main drawback of physical methods with the local measurement and the influence of the probe size on the mixing quality estimation. For that reason, the so-called test reactions are very attractive. Two main systems, based on competitive chemical reactions, have been proposed for the investigation of mixing effects, that is, the competitive consecutive reaction system (Scheme 6.1) and the competitive parallel reaction system (Scheme 6.2). Let us consider the following simplest reactions schemes which do not exactly match the published real systems, but which facilitate the comparison ... 

This reaction system is consecutive with respect to the intermediate product, monochloro-p-cresol, whereas it is parallel with respect to chlorine. These kinds of reaction systems are called consecutive-competitive reactions. 

Goal development of a solid-liquid competitive-consecutive reaction system... 

Note This protocol is focused on mixing effects for the classic competitive-consecutive reaction system. Reaction systems may also include parallel reactions in which A, B, or R are reacting to form unwanted products that are not represented by the consecutive-competitive system as used to derive eq. (13-5). To keep these reactions from making more unwanted products on scale-up, the overall reaction (addition) time may have to be held constant. In this case, the mesomixing issue for the primary reactions, A - - B R and R - - B S, would predict that more S would be formed. These issues may require selection of an alternative reactor, such as an in-line mixer, for successful scale-up. 

Mixing-Kinetic Problem. The reaction scheme that has received the most attention in both theoretical and experimental investigations of the effects of mixing on selectivity is the competitive-consecutive reaction. In addition, the parallel reaction system is receiving attention for its importance in reactions and pH adjustments. These systems are discussed in Chapter 13 and highlighted here because of their fundamental importance in the fine chemicals and pharmaceutical industries. The reaction scheme is as follows ... 

The method of Markov chains provides a useful tool for the study of very complex kinetic systems that do not have studied analytical solutions. As an example, consider the competitive-consecutive mechanism [5]... 

In Chap. 8, we have learned that a flow microreactor system incorporating a micromixer is useful in controlling competitive consecutive reactions. The ultimate reaction system in which reactions occur in chains, or consecutively, is polymerization. This chapter describes how we can exploit the advantages of the flow microreactor system in controlling the molecular weight or molecular weight distribution in polymerization reactions, including cationic polymerizalion and anionic polymerization. 

In contrast to consecutive reactions, with parallel competitive reactions it is possible to measure not only the initial rate of isolated reactions, but also the initial rate of reactions in a coupled system. This makes it possible to obtain not only the form of the rate equations and the values of the adsorption coefficients, but also the values of the rate constants in two independent ways. For this reason, the study of mutual influencing of the reactions of this type is centered on the analysis of initial rate data of the single and coupled reactions, rather than on the confrontation of data on single reactions with intergal curves, as is usual with consecutive reactions. 

Zollinger and coworkers (Nakazumi et al., 1983) therefore supposed that the diazonium ion and the crown ether are in a rapid equilibrium with two complexes as in Scheme 11-2. One of these is the charge-transfer complex (CT), whose stability is based on the interaction between the acceptor (ArNj) and donor components (Crown). The acceptor center of the diazonium ion is either the (3-nitrogen atom or the combined 7r-electron system of the aryl part and the diazonio group, while the donor centers are one or more of the ether oxygen atoms. The other partner in the equilibrium is the insertion complex (IC), as shown in structure 11.5. Scheme 11-2 is intended to leave the question open as to whether the CT and IC complexes are formed competitively or consecutively from the components. ... 

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