Consecutive-Competitive Reactions

This can be illustrated by results of Bourne and Hilber (1990) and Bourne and Thoma (1991) who studied the competitive, consecutive reactions ... 

More complicated reactions schemes, including first-order reversible consecutive processes and competitive consecutive reactions, are considered in a textbook by Irwin [89]. Professor Irwin s textbook also includes computer programs written in the BASIC language. These programs can be used to fit data to the models described. 

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. 

V average molecular velocity for competitive consecutive reactions... 

In chemical-engineering applications, the competitive-consecutive reactions are often studied in the limit where k oo. In this limit, the first reaction-progress variable Y can be written in terms of Y2 and f. From the reaction rate expression for Y, it can be seen that the limiting value is given by... 

Hence, competitive-consecutive reactions will be sensitive to mixing for values of the mean mixture fraction in the range 0 < (f) < fmax for which 0 < F2 ((f ) < F y((f)). 

In most experimental investigations involving competitive-consecutive reactions, species A is in stoichiometric excess, so that 0 < (f) < fst. In this range, only F x is non-zero, and thus its value serves as a measure of the rate of micromixing. Ideally, in order to maximize the value of Cs = BofstF2co (and thus facilitate its measurement), the... 

Paul, E. L. and R. E. Treybal (1971). Mixing and product distribution for a liquid-phase, second-order, competitive-consecutive reaction. AIChE Journal 17, 718-724. 

Starting with separate feeds of reactant A and B of given concentration (no dilution with inerts permitted), for the competitive-consecutive reactions with stoichiometry and rate as shown... 

Horn and Huber47 have comprehensively studied the acetolysis of tetraethyllead by acetic acid in solvent anhydrous toluene. In contrast to Robinson2 who observed only reaction (32) when acetic acid was used as solvent, Horn and Huber showed that the two competitive consecutive reactions (32) and (33)... 

Chemical processes often involve multiple, competing reactions. A common situation is that of a competitive-consecutive reaction, such as that described in Section 1.1, where reactant A and the desired product R are competing for reactant B. The selectively for waste product S can be defined as... 

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... 

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... 

Competitive- Consecutive Reaction in a CSTR Micromixing Effects on Selectivity... 

Next we consider the competitive-consecutive reaction between species A and B of the type... 

In this example, we examine the effects of mixing and mass transfer limitations on the yields of competitive-consecutive reactions of the type... 

Fio. 19. Influence of micromixing and mass transfer limitations on the yield of competitive-consecutive reactions (of which one reaction is homogeneous and the other is wall-catalyzed) in a tubular reactor. 

The accuracy of low-dimensional models derived using the L S method has been tested for isothermal tubular reactors for specific kinetics by comparing the solution of the full CDR equation [Eq. (117)] with that of the averaged models (Chakraborty and Balakotaiah, 2002a). For example, for the case of a single second order reaction, the two-mode model predicts the exit conversion to three decimal accuracy when for (j>2(— pDa) 1, and the maximum error is below 6% for 4>2 20, where 2(= pDd) is the local Damkohler number of the reaction. Such accuracy tests have also been performed for competitive-consecutive reaction schemes and the truncated two-mode models have been found to be very accurate within their region of convergence (discussed below). 

Paul, E. L., and Treybal, R.E. "Mixing and Product Distribution for a Liquid-Phase, Second-Order, Competitive-Consecutive Reaction", presented at 62nd Annual Meeting A.I.Ch.E., Washington, D. C. (November 1969). 

Fig. 1 Diffusion and chemical reaction at an A-B mixing surface. In this competitive-consecutive reaction the first reaction, which forms the desired product...

The term expected (ideal) yield, Fexp, is used to denote the yield that would be obtained for a competitive-consecutive reaction under conditions of perfect mixing and complete conversion of the limiting reactant, as presented in Eq. (2) ... 

Once the reaction is established, three key factors must be addressed for successful development and scale-up of homogenous reactions 1) the effect of concentration on yield for competitive-consecutive reactions 2) the effect of feed rate or addition time on yield and 3) feed pipe backmixing. 

Competitive-Consecutive Reaction Example Solid-Liquid Compared with Homogenous ° ... 

Fig. 4 Simultaneous mass transfer and reaction in the films around solid particles, gas bubbles, and liquid drops. For a heterogeneous competitive-consecutive reaction, mass transfer rates, reaction rates, and mixing rates can play a role. (View this art in color at www.dekker.com.)...

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. 

If the reaction rate is comparable with the rate of the local micro-mixing, similar information can be obtained from competitive parallel reactions as from competitive consecutive reactions. However, parallel reactions offer the experimenter greater degrees of freedom with respect to different feed sequences or different stoichiometric ratios. 

This back-flow eddy is advantageous for a rapid intermixing in the pipe. It is, however, absolutely to be avoided if competitive-consecutive reactions are to be carried out in a pipe reactor, see Section 8.5.2. 

Chemical reactions, which proceed extremely fast and without considerable heat of reaction, should not be carried out in stirred tanks, but in pipe reactors. This particularly applies for complex reactions of the type competitive-consecutive reactions, in which care must be taken, so that the desired product formed does not come into contact with the educt. Otherwise an undesired secondary reaction would take place, whereby the selectivity would be reduced. 

---