Consecutive reactions tank reactor

To illustrate the complexity of process optimization, suppose that we are to scale-up a semibatch stirred-tank reactor for carrying out the following consecutive reactions ... 

The design methods de.scribed above rely on correlations of the overall reactor average quantities obtained from experimental tanks of different scales. The most important deficiency of these methods is that local effects are not taken into consideration, while these might be responsible for the overall reactor performance. Accordingly, if none of the above scale-up criteria is found satisfactory (see e.g. data of Middleton et ai, 1986) a more fundamental approach must be applied, although not necessarily as complex as the one presented in Section 5.4.S.2. Such an approach was presented by Paul et al. (1971) who found that the yield of the desired intermediate in a system of consecutive reactions (iodination of L-tjrosine) correlates reasonably with fluctuations of the velocity, So, these fluctuations could be chosen as a criterion for scale-up of the reactor. The average value for u in the upper part of the tank was evaluated from ... 

The same consecutive reactions considered in Prob. 6.18 are now carried out in two perfectly mixed continuous reactors. Flow rates and densities are constant. The volumes of the two tanks (P) are the same and constant. The reactors operate at the same constant temperature. 

Fig. 1.27. Reactions in series—single continuous stirred-tank reactor. Concentration CF of intermediate product P for consecutive first-order reactions, A -> P -> Q...

Fig. 1.28. Reactions in series—comparison between batch or tubular plug-flow reactor and a single continuous stirred-tank reactor. Consecutive first-order reactions,...

To clarify the above points we consider a simple homogeneous continuous stirred tank reactor (CSTR), in which consecutive exothermic reactions... 

Exercise 7.1.8, A solution of substance A of concentration is fed at a rate q to an isothermal, constant-volume stirred tank reactor of volume y. Substance A undergoes consecutive first order reactions A —B —... 

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. 

A pipe reactor (tubular reactor) is much more suitable, when correctly designed (suppression of any back-mixing), for carrying out competitive-consecutive reactions than a stirred tank reactor. 

Example 4-8 An ideal continuous stirred-tank reactor is used for the homogeneous polymerization of monomer M. The volumetric flow rate is O, the volume of the reactor is V, and the density of the reaction solution is invariant with composition. The concentration of monomer in the feed is [M]o. The polymer product is produced by an initiation step and a consecutive series of propagation reactions. The reaction mechanism and rate equations may be described as follows, where is the activated monomer and P2, . . , P are polymer molecules containing n monomer units ... 

In some cases it may be desirable to use a series of stirred-.tank reactors, with the exit stream from the first serving as the feed to the second, and so on. For constant density the exit concentration or conversion can be solved by consecutive application of Eq. (4-6) to each reactor. MacDonald and Piret have derived solutions for a number of rate expressions and for systems of reversible, consecutive, and simultaneous reactions. Graphical procedures have also been developed. The kinds of calculations involved are illustrated for the simple case of a first-order reaction in Example 4-9. 

Fig. 4-16 Selectivity for consecutive reactions m stirred-tank and tubular-flow reactors...

Despite the experience with batch reactors it may be worthwhile to operate continuous reactors also for fine chemicals. Continuously operated reactors only demand for one start-up and one shut-down during the production series for one product. This increases the operating time efficiency and prevents the deactivation of dry catalysts this implies that the reactor volume can be much smaller than for batch reactors. As to the reactor type for three phase systems an agitated slurry tank reactor [5,6] is not advisable, because of the good mixing characteristics. Specially for consecutive reaction systems the yields to desired products and selectivities will be considerably lower than in plug flow type reactor. The cocurrent down flow trickle flow reactor... 

Cohen, D.S. J.P. Keener. 1976. Multiplicity and stability of oscillatory states in a continuous stirred tank reactor with exothermic consecutive reactions A B C. Chem. Eng. Sci. 31 115-22. 

Pfeil and coworkers presented a model for the synthetic pathway of formose, shown in Scheme 5. A similar, but more detailed, model was given by Mizuno and coworkers, who investigated the intermediates in the reaction by chromatographic fractionation of alditol acetate derivatives by g.l.c. (see Table IV). Weiss and coworkers conceptualized the formose reaction as a consecutive-parallel scheme (see Scheme 6) proceeding to the C level, and reported a series of experiments in the continuously stirred tank-reactor previously mentioned to determine the effect of various concentrations of formaldehyde and calcium hydroxide on the reaction rate. The advantage of the tank reactor is that conversions in the autocatalytic system can be controlled, and reaction rates can be measured directly. When the formaldehyde feed-rate was kept constant, and the feed rate for calcium hydroxide varied, products were obtained... 

As(III) may be oxidized to As(V) by S20 in aqueous alkaline solutions/ At pH > 12.0, the observed rate constant is 1.6 0.3 x 10 M s at an ionic strength of 0.1 M. Sustained oscillations in redox potential, pH, and the concentration of dissolved O2 are reported in the Cu(H)-catalyzed reaction betwen K2S2O8 and Na2S203 in a stirred tank reactor. A free radical mechanism involving Cu(I), Cu(II), and the radicals SO4 and S2O3 may be used to account for the dynamic behavior of this sytem. The kinetics and mechanism of the oxidation of thiosulfate coordinated to cobalt(IH) by peroxymonosulfate have been reported.The reaction proceeds via two consecutive nucleophilic additions of the terminal peroxy oxygen atom to the coordinated S20 . 

ILLUSTRATION 9.3 Quantitative Development of Consecutive Reaction Relationships for a Single Continuous Flow Stirred-Tank Reactor... 

For the set of first-order consecutive reactions considered in Illustration 9.2, determine the optimum space time in a single stirred-tank reactor from the standpoint of maximizing production of the intermediate. What will be the effluent concentration of V for this optimum operating condition It may be assumed that species V and W are not present in the feed stream. 

Figure 9.6 Dimensionless representation of product distributions for consecutive first-order irreversible reactions A -> V -> W (stirred-tank reactor).

Figure 19.5 Speciation plots for the competitive-consecutive second-order reactions of ammonia and ethylene oxide. Panel PFR plug flow reactor panel CSTR individual continuous flow stirred-tank reactor.

In the paper presented here, we will focus our interest on irreversible bimolecular consecutive reactions, where the substrate and interaediate product are in competition for the same reactant. As an example the selective hydrogenation of o-alkylphenol on a palladium catalyst in a stirred tank slurry reactor was investigated. To properly design such a system, the chemical reaction steps and prior physical steps, such as diffusion and sorption, must be considered. The rigorous description of a multiphase... 

Derive the steady-state mass balance equations for an isothermal contin-uous-stirred tank reactor in which a consecutive homogeneous reaction... 

It follows from calculations in the proceeding section that the necessa reactor volume of a continuous stirred tank reactor (CSTR) needed to obtain a high degree of conversion is relatively large. A so-called "cascade of CSTR s (a number of CSTR s in series) can be a practical alternative. Let us assume that we replace one CSTR with volume V by a series of n equal CSTR s that have the same total volume. The mean residence time in each reactor is then x/n. We can calculate the relative degree of conversion in each consecutive reactor, for any reaction order, with eq. (3.49), where X is replaced by x/n. We find then for... 

From the kinetic point of view, a BR is often presented as an attractive alternative. For the majority of various kinds of reaction kinetics— simple reactions with approximately elementary reaction kinetics, consecutive reactions, and mixed reactions—the BR gives a higher yield as well as a higher amount of desired intermediate products than a continuous stirred tank reactor (CSTR), and this is why the BR competes with a tube reactor in efficiency. 

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