And series reactions

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... 

An example of mixed parallel and series reactions is the production of ethanolamines by reaction between ethylene oxide and ammonia ... 

Mixed parallel and series reactions producing byproducts. Consider the mixed parallel and series reaction system from Eq. (2.10) with the corresponding kinetic equations ... 

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.

Mixed parallel and series reactions producing byproducts. As with parallel and series reactions, use of an excess of one of the feeds can be effective in improving selectivity with mixed reactions. As an... 

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. 

Competitive consecutive reactions are combinations of parallel and series reactions that include processes such as multiple halogenation and nitration reactions. For example, when a nitrating mixture of HN03 and H2S04 acts on an aromatic compound like benzene, N02 groups substitute for hydrogen atoms in the ring to form mono-, di-, and tri-substituted nitro compounds. 

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 this chapter, we develop some guidelines regarding choice of reactor and operating conditions for reaction networks of the types introduced in Chapter 5. These involve features of reversible, parallel, and series reactions. We first consider these features separately in turn, and then in some combinations. The necessary aspects of reaction kinetics for these systems are developed in Chapter 5, together with stoichiometric analysis and variables, such as yield and fractional yield or selectivity, describing product distribution. We continue to consider only ideal reactor models and homogeneous or pseudohomogeneous systems. 

Since multiple reactions are so varied in type and seem to have so little in common, we may despair of finding general guiding principles for design. Fortunately, this is not so because many multiple reactions can be considered to be combinations of two primary types parallel reactions and series reactions. 

Figure 8.9 shows that the concentration of intermediate in reversible series reactions need not pass through a maximum, while Fig. 8.10 shows that a product may pass through a maximum concentration typical of an intermediate in the irreversible series reaction however, the reactions may be of a different kind. A comparison of these figures shows that many of the curves are similar in shape, making it difficult to select a mechanism of reaction by experiment, especially if the kinetic data are somewhat scattered. Probably the best clue to distinguishing between parallel and series reactions is to examine initial rate data—data obtained for very small conversion of reactant. For series reactions the time-concentration curve for S has a zero initial slope, whereas for parallel reactions this is not so. 

Figure 4-3 Energy diagrams for a single reaction (left) and for parallel reactions (center) and series reactions (right). For parallel and series reactions there are severaal activation energies that must be...

Previously in this chapter we have implicitly assumed that the density of the fluid did not change as the reaction proceeded. In our parallel and series reactions, A B, A —> C,... 

For both parallel and series reactions we have not derived these equations in the PFTR. This involves writing equations such as dXi/dr =. . . and solving the differential equations for Xi and X2. This would be uninstructive because the answers are identical to those derived without using these variables (assuming no mistakes). 

Frequently, several reactions proceed simultaneously, and consequently selectivity and yield in networks of parallel and series reactions with respect to a certain desired target component D are essential quantities. 

Fig. 12.18. Comparison of the optimized reduced amounts that should be dosed and the corresponding internal compositions for a fixed-bed reactor (discrete dosing, top) and a membrane reactor (continuous dosing, bottom). A triangular network of parallel and series reactions was analyzed using an adapted plug-flow reactor model, Eq. 48. One stage (left) and 10 stages connected in series (right) were considered. All reaction orders were assumed to be 1, except for those with respect to the dosed component in the consecutive and parallel reactions (which were assumed to be 2) [66].

Table 5.6 Rate constants for phenol hydrogenation following the parallel (kh k3) and series reactions (kh k2) at 423 K over Pd catalyst (after Park et al. [15]).

In complex reaction systems consisting of combinations of parallel and series reactions the availability of software packages (ODE solvers) makes it much easier to solve problems using moles Nj or molar flow rates Fj rather than conversion. For liquid systems, concentration may be the preferred variable used in, the mole balance equations. The resulting coupled differential equations can be easily solved using an ODE solver. In fact, tltis section has been developed to take advantage of the vast number of computational techniques now available on mainframe (e.g., Simulsolv) and personal computers (POLYMATH). 

A brief discussion of a number of pertinent references on parallel and series reactions is given in... 

This class of reactions, carried out in fluidized beds, involves parallel and series reactions, with reaction intermediates being the desired products. Industrial examples include partial oxidation of n-butane to maleic anhydride and o-xylene to phthalic anhydride. The vigorous solid mixing of fluidized beds is valuable for these reactions because they are highly exothermic. However, gas backmixing must be minimized to avoid extended gas residence times that lead to the formation of products of total combustion (i.e., CO2 and H2O). For this reason, fluidized bed catalytic partial oxidation reactors are operated in the higher velocity regimes of turbulent and fast-fluidization. 

The reaction is first order in molecular oxygen and first order in methanol therefore, we say both the reaction and the rate law are elementary. This forn of the rate law can be derived from Collision Theory as shown in the Profes- sion Reference Shelf 3A on the CD-ROM. There are many reactions where the stoichiometric coefficients in the reaction are identical to the reaction orders but the reactions are not elementary owing to such things as pathways involving active intermediates and series reactions. For these reactions that are not elementary but whose stoichiometric coefficients are identical to the reaction orders in the rate law. we say the reaction follows on elememary rate /aw. For example, the oxidation reaction of nitric oxide discussed earlier. 

There are four basic types of multiple reactions series, parallel, complex, and independent. These types of multiple reactions can occur by themselves, in pairs, or all together. V en there is a combination of parallel and series reactions. they are often referred to as complex reactions. 

Load Division 5. Labs 3 and 4 of The Reactor Lab for batch reactor which parallel and series reactions, respectively, can be carried Investigate how dilution with solvent affects the selectivity for diffe reaction orders, and write a memo describing your findings. 

Figs. 2-2 to 2-4. Time-ccmcen-tration curves for simple, parallel, and series reactions. 

Table 3-3. Paballel and Series Reactions. Equations Relatino to Conversion and Holding Time... 

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