Multiple homogeneous reactions

The third reason for using fluid-fluid systems is to obtain a vastly improved product distribution for homogeneous multiple reactions than is possible by using the single phase alone. Let us turn to the first two reasons, both of which concern the reaction of materials originally present in different phases. 

The nature of electrode processes can, of course, be more complex and also involve phase fonnation, homogeneous chemical reactions, adsorption or multiple electron transfer [1, 2, 3 and 4],... 

The accessible peripheral catalytic groups enable reaction rates that are comparable to those of homogeneous systems, but the periphery-functionalized dendrimers contain multiple reaction sites and may have extremely high local catalyst concentrations, which can lead to cooperative effects in reactions that proceed via a... 

When multiple reactions take place on mixing two reactant fluids and when these reactions proceed to an appreciable extent before homogeneity is attained, segregation is important and can affect product distribution. 

This behavior of multiple reaction could provide a powerful tool in the study of partial segregation in homogeneous systems. It has been used by Paul and Treybal (1971) who simply poured reactant B into a beaker of A and measured the amount of R formed for a very fast reaction of Eq. 14. 

The classical problem of multiple solutions and undamped oscillations occurring in a continuous stirred-tank reactor, dealt with in the papers by Aris and Amundson (39), involved a single homogeneous exothermic reaction. Their theoretical analysis was extended in a number of subsequent theoretical papers (40, 41, 42). The present paragraph does not intend to report the theoretical work on multiplicity and oscillatory activity developed from analysis of governing equations, for a detailed review the reader is referred to the excellent text by Schmitz (3). To understand the problem of oscillations and multiplicity in a continuous stirred-tank reactor the necessary and sufficient conditions for existence of these phenomena will be presented. For a detailed development of these conditions the papers by Aris and Amundson (39) and others (40) should be consulted. 

The CSTR is particularly useful for reaction schemes that require low concentration, such as selectivity between multiple reactions or substrate inhibition in a chemostat (see Section IV). The reactor also has applications for heterogeneous systems where high mixing gives high contact time between phases. Liquid-liquid CSTRs are used for the saponification of fats and for suspension and emulsion polymerizations. Gas-liquid mixers are used for the oxidation of cyclohexane. Gas homogeneous CSTRs are extremely rare. 

In recent years there has been much interest in homogeneous hydrogenations catalyzed by transition metal complexes (7). One facet of research in this area is the search for chiral catalysts (catalysts that are dissymmetric, i.e., optically active) that can be used to produce chiral compounds via asymmetric reactions. In this review, we survey asymmetric homogeneous hydrogenation reactions, that is reactions that create asymmetric carbon atoms by the addition of hydrogen across multiple bonds under the influence of soluble chiral catalysts. 

Homogeneous reactions occur within one phase, here taken to be fluid. Included are reactions in which a reactant is supplied from another phase by mass transfer. Multistep reactions consist of a combination of elementary steps. No distinction is made between complex reactions (with trace-level intermediates) and multiple reactions (with intermediates at higher than trace concentrations). 

The rate equations considered under this heading were originally formulated on the concept of "nucleus branching" (Table 3.1), analogous to homogeneous chain reactions [5,8]. Occurrence of "branching", without restriction on multiplicative development or allowance for termination, would lead to an exponential dependence of flron t ... 

Perhaps the clearest way of explaining these methods of interpreting laboratory data is to carry out specific examples in some detail, pointing out the features of the method which are general and applicable to any reaction. In Example 4-4 the integration and differential methods are applied to a single-reaction system. Example 4-5, which is concerned with the homogeneous reaction of sulfur vapor and methane to produce carbon disulfide, involves multiple reactions. 

In many catalytic systems multiple reactions occur, so that selectivity becomes important. In Sec. 2-10 point and overall selectivities were evaluated for homogeneous well-mixed systems of parallel and consecutive reactions. In Sec. 10-5 we saw that external diffusion and heat-transfer resistances affect the selectivity. Here we shall examiineHEieHnfiuence of intrapellet res ahces on selectivity. Systems with first-order kinetics at isothermal conditions are analyzed analytically in Sec. 11-12 for parallel and consecutive reactions. Results for other kinetics, or for nonisothermal conditions, can be developed in a similar way but require numerical solution. ... 

Equation (3.1) exhibits the symmetry of the homogeneous BZ reaction, namely equivariance under the Euclidean group SE(2) of all translations S and rotations R in the plane. The group multiplication of (Rj, Si) G SE 2) is given by... 

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