Reactions parallel reactions

The chemical composition of many systems can be expressed in terms of a single reaction progress variable. However, a chemical engineer must often consider systems that cannot be adequately described in terms of a single extent of reaction. This chapter is concerned with the development of the mathematical relationships that govern the behavior of such systems. It treats reversible reactions, parallel reactions, and series reactions, first in terms of the mathematical relations that govern the behavior of such systems and then in terms of the techniques that may be used to relate the kinetic parameters of the system to the phenomena observed in the laboratory. 

In this chapter, we examine in depth the kinetics of reversible reactions, chain reactions, parallel reactions, and other reactions. 

Similar to conjugated (interfering) reactions, parallel reactions must be synchronous, which is their obvious fundamental property. 

EIS has the ability to distinguish between influences from different processes, especially when the system involves multiple-step reactions, parallel reactions, or additional processes such as adsorption. Generally speaking, the measurements and analysis of the EIS for a PEMFC are complicated compared with those of the polarization curve. However, the results from both methods are not insular, and some relationships exist between the complicated impedance spectrum and the simple polarization curve [22],... 

Westerterp K.R. and Ptasinsky K.J. "Safe design of cooled tubular reactors for exothermic, multiple reactions. Parallel reactions. Development of criteria". Chem. Eng. Sci. in print. 

During ECM, electrochemical dissolution of anode and cathodic evolution of hydrogen proceeds on the electrodes (the WP and TE, respectively). Along with these basic reactions, parallel reactions proceed concurrently, for example, oxygen anodic evolution, cathodic reduction of nitrate ions, if NaNC>3 electrolyte is used. It is important to note that electrochemical reactions in a narrow IEG result in gas evolution. The temperature of the electrolyte in the IEG and the void fraction increase as the electrolyte flows along the gap. This leads to a variation in the electrolyte conductivity that has an effect on the distributions of current and metal dissolution rate over the WP surface. The electrode processes and the processes in... 

The stoichiometric chemical equation. Reactions may be divided in this manner into five major types simple reactions, parallel reactions, series reactions, complex series reactions, and reversible reactions. 

ParaUel Reactions. Parallel reactions are those in which more than one product is formed by separate reactions and where the products, once formed, do not react again. Some typical parallel reactions are... 

These types of equations can be applied to more complex reaction schemes such as sequential reactions,parallel reactions and solid state reactions.Table 1 shows some of the reaction schemes where such equations can be written. 

Kinetic measurements show that the simple rate laws known from the last chapter are often not sufficient for a correct description of the temporal course of a reaction or the composition of a reaction mixture. Many reactions take place by mechanisms that involve several elementary steps. Three fundamental types of composite reactions are discussed in this chapter opposing or equilibrium reactions, parallel reactions, and consecutive reactions. Composite reactions not only play a large role in industrial applications (e.g., heterogeneous catalysis) but are also very important in nature (e.g., enzyme reactions). 

A chemical reaction is a process that results in the interconversion of chemical species Table 4.3 summarizes the base reaction types. Chemical reactions might be elementary reactions or stepwise reactions. A stepwise reaction consists of at least one reaction intermediate and involves at least two consecutive elementary reactions. Parallel reactions are several simultaneous reactions that form different respective products from a single set of reactants (Svehla 1993, Muller 1994). 

In order to understand the complexity in oscillatory reactions, it would be worthwhile to examine their relationship with different types of chemical reactions [10], which have been summarized in Fig. 9.8 in increasing order of complexity viz., irreversible reactions -> reversible reactions parallel reaction consecutive reaction -> autocatalytic reactions damped oscillations aperiodic oscillations spatio-temporal oscillations chaotic oscillations. Further, Fig. 9.8 shows the concentration... 

In this chapter, the dynamics of ideally stirred tank reactors will be analyzed. First, the assumptions, required to limit model complexity, will be discussed. Next, various types of reaction will be considered such as simple first-order reactions, equilibrium reactions, parallel reactions, etc. Subsequently, the analysis will be expanded to include non-isothermal reactors. Numerical examples of chemical reactors are given and the non-linear model descriptions are compared with the linearized model descriptions. 

Complex reaction mechanisms can conveniently be grouped within the following classification consecutive reactions, parallel reactions and reversible reactions. Parallel reactions are those in which the same species participates in two or more competitive steps. Consecutive reactions are characterised by the product of the first reaction being a reactant in a subsequent process, leading to formation of the final product. Reversible reactions are those in which the products of the initial reaction can recombine to regenerate the reactant. 

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... 

An example of a parallel reaction system occurs in the production of ethylene oxide ... 

Here the ethylene oxide undergoes parallel reactions, whereas the monoethanolamine undergoes a series reaction to diethanolamine and triethanolamine. 

Consider the system of parallel reactions from Eq. (2.4) with the corresponding rate equations. " ... 

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 2.3 Choice of reactor type for mixed parallel and series reactions when the parallel reaction has a higher order than the primary reaction.

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) ... 

An example of such recychng in a parallel reaction system is in the Oxo process for the production of C4 alcohols. Propylene and synthesis gas (a mixture of carbon monoxide and hydrogen) are first reacted to ra- and isobutyraldehydes using a cobalt-based catalyst. Two parallel reactions occur ... 

In fact, it is often possible with stirred-tank reactors to come close to the idealized well-stirred model in practice, providing the fluid phase is not too viscous. Such reactors should be avoided for some types of parallel reaction systems (see Fig. 2.2) and for all systems in which byproduct formation is via series reactions. 

Figure 3-2. Two reaction equations showing two completely different uses for the (+) symbol a) giving a fully balanced single reaction, b) combining two parallel reactions into a single equation that is not stoichiometrically balanced.

Ilvespaa (98) has demonstrated that, using some amines, the 2-chloro-5-nitrothiazole undergoes an opening reaction in a competitive reaction parallel to the normal substitution process. This confirms the sensitivity of position 4 to nucleophilic attack when a nitro group is present in position 5 (Scheme 16). 

Although it is not universally true that the activation energies of reactions parallel their heats of reaction, this is approximately true for the kind of addition reaction we are discussing. Accordingly, we can estimate E = k AH, with k an appropriate proportionality constant. If we consider the difference between two activation energies by combining this idea with Eq. (7.21), the contribution of the nonstabilized reference reaction drops out of Eq. (7.21) and we obtain... 

Acetaldehyde oxidation generates peroxyacetic acid which then reacts with more acetaldehyde to yield acetaldehyde monoperoxyacetate [7416-48-0], the Loesch ester (26). Subsequently, parallel reactions lead to formation of acetic acid and anhydride plus water. 

Step 4 of the thermal treatment process (see Fig. 2) involves desorption, pyrolysis, and char formation. Much Hterature exists on the pyrolysis of coal (qv) and on different pyrolysis models for coal. These models are useful starting points for describing pyrolysis in kilns. For example, the devolatilization of coal is frequently modeled as competing chemical reactions (24). Another approach for modeling devolatilization uses a set of independent, first-order parallel reactions represented by a Gaussian distribution of activation energies (25). 

The abihty of a four-parameter, two-parallel reaction model to correlate pilot-scale rotary kiln, toluene-desorption results (26) is shown in Figure 6. The model assumes that the adsorbed toluene consists of two fractions, T and F, which are tightly and loosely bound, respectively. 

Sulfites. The Hterature concerning dialkyl sulfites is extensive, although less than for sulfates. Reactions involving alkylation are similar to those of sulfates. Sulfites also undergo elimination, transesterification, and isomerization. The last two parallel reactions of phosphites. 

With Alcohols. These reactions parallel those of ethylene oxide with water. The primary products are monoethers of ethylene glycol secondary products are monoethers of poly(ethylene glycol) (42). Most are appreciably water-soluble. 

Having a 5-methyl group, thymine is not nitrated or halogenated normally, but with aqueous bromine it does give the dihydropyrimidine (948) (25JBC(64)233) its other reactions parallel those of uracil although its behavior on irradiation is somewhat different (Section 2.13.2.1.4). 

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