Semibatch reactors second-order reactions

Example 4-11 Isothermal Semibatch Reactor with Second-Order Reaction... 

Fxanqde 4—11 Isothermal Semibatch Reactor with a Second-order Reaction Professional Reference Shelf... 

Consider the reaction A + B — C that is performed in a semibatch reactor as shown in Figure 5-19, where the reaction is first order and carried out by the controlled addition of reactant B. Assuming that the reaction is first order with respect to both A and B (i.e., second order overall), the rate of disappearance of components A and B is (—rA) = (—rB) - kiCACB. 

Solution The process described is neither flow nor batch, but semibatch in nature. However, with assumptions which are reasonably valid, the problem can be reduced to that for a constant-density batch reactor. If the density of the solution remains constant and the hydrogen chloride vaporizes and leaves the solution, the volume of the liquid-phase reaction will be constant. Then the relationship between the composition of the substances in the liquid phase is governed by rate expressions of the type used in this chapter. Assume that the reactions are second order. Then the rate of disappearance of benzene, determined entirely by the first reaction, is... 

Consider the process illustrated in Figure 4.17, where the second-order irreversible reaction A + B C is carried out in a semibatch reactor. Since there is a large excess of A present within the reactor, we may take the kinetics of the reaction to be pseudo-first-order in B, and since this is not a constant-volume operation let us write a molal balance on B. 

Finally a fourth boundary condition shall be valid to support the worst case character of the procedure. The reaction order necessary for the formal kinetic description of a process has a severe influence on the pressure/time and respectively the tempera-ture/time-profiles to be expected. Industrial experience has shown that approximately 90% of all processes conducted in either batch or semibatch reactors can be described with a second order formal kinetic rate law. But it remains uncertain whether this statement, which is related to isothermal or isoperibolic operation with a rather limited overheating, remains valid if the reaction proceeds adiabatically and if side reactions contribute to the gross reaction rate at a much higher degree. In consequence, it shall be assumed for a credible worst case evaluation that the disturbed process follows a first order kinetics. Any reactions occurring in reality will almost certainly proceed at a much lower rate. 

Parallel reactions (nonreacting products) The general case Effect of reaction order One of the reactants undergoes a second reaction Parallel-consecutive reactions Plug-flow reactor with recycle The basic design equation Optimal design of RPR Use of RPR to resolve a selectivity dilemma Semibatch reactors... 

The reaction should be carried out adiabatically in a semibatch reactor, feeding hexanol into the liquid maleic acid. The reactor volume is 500 dm, and no solvent is used. Maleic acid melts at 53°C. A maximum temperature of 100°C may not be exceeded due to the formation of by-products. The reaction is of second order, and the rate constant is expressed as... 

Within the function file, we define if as such in the first line. The set of ordinary equations Reactor is written as a function of the independent variable, t, and a vector of dependent variables x. In order to use variable names closer to the real ones, we can define fhem as columns of fhe dependent variables vector (i.e., I = x(l)). Next, in the second line, we write the global statement so that these variables can be used within the script. MATLAB needs that all the parameters, constants, or equations are explicit of the variables and defined before fhe system of differential equations. Thus, we write the rate constants and other parameters defined earlier. This reactor is a semibatch in the sense that we add the initiator during the first minute of the reaction at a constant rate. Thus, we define a rafe that is constant if the time is lower or equal to 60 s and 0 otherwise using the if-then-end syntax. Finally, we write the differential equations. The right-hand side of the differential equations must be the same word as the one we use in the title of the function Reactor. Each equation will be Reactor (n, 1). We present the results in Figure 4.17. 

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