Reaction system series 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. 

A reaction network, as a model of a reacting system, mas7 consist of steps involving same ar all of opposing reactions, which may or may not be considered to be at equilibrium, parallel reactions, and series reactions. Some examples ate dted in Section 5.1. 

In the present work, the theory for single-electrode reactions (E), series reactions (E.E) and parallel reactions (E + E) only will be considered. This represents a minimum theory set that is necessary for model calculation and graphical display and for integration into the data analysis system. In the experimental section, all the data over the entire potential range has been tested against this theory to find the most appropriate theory with which to interpret the experiments. 

An example of a series reaction system is the production of formaldehyde from methanol ... 

Mixed parallel and series reactions producing byproducts. In more complex reaction systems, both parallel and series reactions can occur together. Mixed parallel and series reactions are of the type... 

Multiple reactions in series producing byproducts. Consider the system of series reactions from Eq. (2.7) ... 

Again, it is difficult to select the initial setting of the reactor conversion with systems of reactions in series. A conversion of 50 percent for irreversible reactions or 50 percent of the equilibrium conversion for reversible reactions is as reasonable as can be guessed at this stage. 

Multiple reactions in series producing byproducts. For the series reaction system in Eq. (2.18), the series reaction is inhibited by low concentrations of PRODUCT. It has been noted already that this can be achieved by operating with a low conversion. 

If the reaction involves more than one feed, it is not necessary to operate with the same low conversion on all the feeds. Using an excess of one of the feeds enables operation with a relatively high conversion of other feed material, and still inhibits series reactions. Consider again the series reaction system from Example 2.3 ... 

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. 

The exponential fiinction of the matrix can be evaluated tln-ough the power series expansion of exp(). c is the coliinm vector whose elements are the concentrations c.. The matrix elements of the rate coefficient matrix K are the first-order rate constants W.. The system is called closed if all reactions and back reactions are included. Then K is of rank N- 1 with positive eigenvalues, of which exactly one is zero. It corresponds to the equilibrium state, witii concentrations r detennined by the principle of microscopic reversibility ... 

For the reaction system under consideration, experiments are made at a series of bulk-liqiiid and bulk-gas compositions representing the compositions to be expected at different levels in the commercial absorber (on the basis of a material balance). 

Exploitation of analytical selectivity. We have seen, in our discussion of the A —> B C series reaction (Scheme IX), that access to the concentration of A as a function of time is valuable because it permits to be easily evaluated. Modern analytical methods, particularly chromatography, constitute a powerful adjunct to kinetic investigations, and they render nearly obsolete some very difficult kinetic problems. For example, the freedom to make use of the pseudoorder technique is largely dependent upon the high sensitivity of analytical methods, which allows us to set one reactant concentration much lower than another. An interesting example of analytical control in the study of the Scheme IX system is the spectrophotometric observation of the reaction solution at an isosbestic point of species B and C, thus permitting the A to B step to be observed. 

From the intercept at AG° = 0 we find AGo = 31.9 kcal mol , and the slope is 0.77. As we have seen, if Eq. (5-69) is applicable, the slope should be 0.5 when AG = 0. In this example either the data cover too small a range to allow a valid estimate of the slope to be made or the equation does not apply to this system. Such a simple equation is not expected to be universally applicable. Recall that it was derived for an elementary reaction, so multistep reactions, even if showing simple rate-equilibrium behavior, introduce complications in the interpretation. The simple interpretation of Eq. (5-69) also requires that AGo be constant within the reaction series, but this condition may not be met. Later pages describe another possible reason for the failure of Eq. (5-69). 

Dr. Moeller I think to answer this question now is a bit difficult. It s just a mechanical problem of the maximum temperature the recycle compressor can handle. So, in the end, we will go to the inlet temperature to the compressor in the range of the inlet temperature to the reactor. So what we are endeavoring to attain is a simple reaction system consisting of an adiabatic reactor in series with waste heat boilers and nothing more than one recycle compressor. These compressors are used in the chemical industry with no problem in operation. So, in the end, you can go to hot recycle with an inlet compressor temperature the same as the inlet reactor temperature. All the heat from... 

With the development of HPLC, a new dimension was added to the tools available for the study of natural products. HPLC is ideally suited to the analysis of non-volatile, sensitive compounds frequently found in biological systems. Unlike other available separation techniques such as TLC and electrophoresis, HPLC methods provide both qualitative and quantitative data and can be easily automated. The basis for the HPLC method for the PSP toxins was established in the late 1970 s when Buckley et al. (2) reported the post-column derivatization of the PSP toxins based on an alkaline oxidation reaction described by Bates and Rapoport (3). Based on this foundation, a series of investigations were conducted to develop a rapid, efficient HPLC method to detect the multiple toxins involved in PSP. Originally, a variety of silica-based, bonded stationary phases were utilized with a low-pressure post-column reaction system (PCRS) (4,5), Later, with improvements in toxin separation mechanisms and the utilization of a high efficiency PCRS, a... 

The crude liquid chlorobenzenes stream leaving the second reactor is washed with water and caustic soda solution to remove all dissolved hydrogen chloride. The product recovery system consists of two distillation columns in series. In the first column (the benzene column ) unreacted benzene is recovered as top product and recycled. In the second column (the chlorobenzene column ) the mono- and dichlorobenzenes are separated. The recovered benzene from the first column is mixed with the raw benzene feed and this combined stream is fed to a distillation column (the drying column ) where water is removed as overhead. The benzene stream from the bottom of the drying column is fed to the reaction system. 

Mixed parallel and series reactions producing byproducts. Consider the mixed parallel and series reaction system from Equation 5.10 with the corresponding kinetic equations ... 

Multiple reactions in series producing byproduct. Consider the system of series reactions from Equation 5.68. Selectivity for series reactions of the types given in Equation 5.7 to 5.9 is increased by low concentrations of reactants involved in the secondary reactions. In the preceding example, this means reactor operation with a low concentration of PRODUCT, in other words, with low conversion. For series reactions, a significant reduction in selectivity is likely as the conversion increases. 

The results presented in this report correspond to systems where reactions 2 and 3 account for the decay of carbonyl triplets A series of copolymers of phenyl vinyl ketone and o-tolyl vinyl... 

Are Side Reactions Important What is the Stoichiometry of the Reaction When a mixture of various species is present in a reaction vessel, one often has to worry about the possibility that several reactions, and not just a single reaction, may occur. If one is trying to study one particular reaction, side reactions complicate chemical analysis of the reaction mixture and mathematical analysis of the raw data. The stoichiometry of the reaction involved and the relative importance of the side reactions must be determined by qualitative and quantitative anal-lysis of the products of the reaction at various times. If one is to observe the growth and decay of intermediate products in series reactions, measurements must be made on the reaction system before the reaction goes to completion. 

The reason for stressing the importance of working with relatively pure reagents and solvents is that the rates of many reactions are extremely sensitive to the presence of trace impurities in the reaction system. If there is reason to suspect the presence of these effects, a series of systematic experinlents may be carried out to explore the question by seeing how the reaction rate is affected by the intentional addition of impurities. In many cases, lack of reproducibility between experiments may be an indication that trace impurity effects are present. 

This section discusses the kinetic implications of series reactions. We will be concerned only with those cases where the progress of the various stages of the overall transformation is not influenced by either parallel or reverse reactions. The discussion will again be limited to constant volume systems. 

The first point that must be established in an experimental study is that one is indeed dealing with a series combination of reactions instead of with some other complex reaction scheme. One technique that is particularly useful in efforts of this type is the introduction of a species that is thought to be a stable intermediate in the reaction sequence. Subsequent changes in the dynamic behavior of the reaction system (or lack thereof) can provide useful information about the character of the reactions involved. 

This reaction set may be regarded as parallel reactions with respect to consumption of species B and as a series reaction with respect to species A, V, and W. Common examples include the nitration and halogenation of benzene and other organic compounds to form polysubstituted compounds. To characterize the qualitative behavior of such systems, it is useful to consider reactions 9.3.3 and 9.3.4 as mechanistic equations and to analyze the effects of different contacting patterns on the yield of species V. We shall follow the treatment of Levenspiel (7). 

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