Consecutive reactions, batch reactor first-order

EP.ll The consecutive reaction is A—KR S performed in a batch reactor. The reaction rates are first order and irreversible. The ratio at 50°C is known as ... 

The first-order consecutive exothermic reaction sequence, A —> B —> C, is carried out in a thick-walled, jacketed batch reactor, provided with both jacketed heating and cooling, as shown below. 

Two consecutive, first-order reactions take place in a perfectly mixed, isothermal batch reactor. 

Jl An isothermal perfectly mixed batch reactor has consecutive first-order reactions... 

With consecutive—parallel systems in which the reaction steps are not first order, analytical expressions for species concentrations as functions of time (which would apply to batch reactors) are sometimes unobtainable. Numerical procedures can be used. However, analytical procedures can still be used to obtain some indication of relative yields of reaction... 

Fig. 1.25. Reaction in series—batch or tubular plug-flow reactor. Concentration Cr 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,...

Equation (19-22) indicates that, for a nominal 90 percent conversion, an ideal CSTR will need nearly 4 times the residence time (or volume) of a PFR. This result is also worth bearing in mind when batch reactor experiments are converted to a battery of ideal CSTRs in series in the field. The performance of a completely mixed batch reactor and a steady-state PFR having the same residence time is the same [Eqs. (19-5) and (19-19)]. At a given residence time, if a batch reactor provides a nominal 90 percent conversion for a first-order reaction, a single ideal CSTR will only provide a conversion of 70 percent. The above discussion addresses conversion. Product selectivity in complex reaction networks may be profoundly affected by dispersion. This aspect has been addressed from the standpoint of parallel and consecutive reaction networks in Sec. 7. 

TABLE 7-2 Consecutive and Parallel First-Order Reactions in an Isothermal Constant-Volume Ideal Batch or Plug Flow Reactor. 

Suppose the consecutive first-order reactions described on page 77 occur at constant density in a batch reactor, with an initial mixture containing only AdXz. concentration [ ]o- Show on a triangular diagram the reaction paths for three cases k jk — 0.5, 1.0, and 2.0. 

Viewed from the perspective of ethylene oxide, these reactions are competitive by contrast, from the perspective of the amines, they are consecutive. Consider a research scale batch reactor operating at 60°C and 20 bar to maintain all species in the liquid phase. Actual production of these commodity products on a large scale would be conducted in flow reactors, as described in Illustration 9.5. The rate laws are of the mixed second-order form (first-order in each reactant), with hypothetical rate constants ki, k2, and equal to 1,0.4, and 0.1 L-moCV min, respectively. MEA and DEA are both high-volume chemicals, while TEA is less in demand. The distribution of alkanolamine products obtained under the specified conditions can be influenced by controlling the initial mole ratio of EO to A and the time of reaction. 

For the situation in which each of the series reactions is irreversible and obeys a first-order rate law, eqnations (5.3.4), (5.3.6), (5.3.9), and (5.3.10) describe the variations of the species concentrations with time in an isothermal well-mixed batch reactor. For consecutive reactions in which all of the reactions do not obey simple first-order or pseudo first-order kinetics, the rate expressions can seldom be solved in closed form, and it is necessary to resort to numerical methods to determine the time dependence of various species concentrations. Irrespective of the particular reaction rate expressions involved, there will be a specific time at which the concentration of a particular intermediate passes through a maximum. If interested in designing a continuous-flow process for producing this species, the chemical engineer must make appropriate allowance for the flow conditions that will prevail within the reactor. That disparities in reactor configurations can bring about wide variations in desired product yields for series reactions is evident from the examples considered in Illustrations 9.2 and 9.3. 

R. L. Luus and O. N. Okongwu [Chem. Eng. J., IS, 1-9 (1999)] studied several issues relevant to the practical optimal control of batch reactors. In particnlar, they considered the sequence of consecutive first-order reactions... 

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