Kinetically Limited Adiabatic Reactors Batch and Plug Flow

5 Kinetically Limited Adiabatic Reactors (Batch and Plug Flow) 

An infinite reactor volume, or an infinite weight of catalyst, is required to bring the effluent from a reactor exactly into chemical equilibrium. The composition and temperature of the effluent from any real reactor will be determined by the kinetics of the reaction. Nevertheless, the type of equilibrium analysis illustrated in the preceding section can be valuable as a means of understanding an important limiting case of reactor behavior. 

In order to size or analyze a nonisothermal reactor, the material balance(s) and the energy balance must be solved simultaneously. This solution is relatively straightforward if the reactor is adiabatic, so that s where our discussion will begin. For an adiabatic reactor, with a single reaction taking place, the temperature is directly related to the fractional conversion, as shown in Section 8.4.3. Let s consider a situation where the energy balance reduces to a linear relationship between temperature and fractional conversion, i.e., where Eqn. (8-20) is valid. 

The analyses of an ideal batch reactor and an ideal PFR are essentially identical, so let s illustrate with the PFR. The design equation for an ideal PFR in differential form is 

The dependence of —rA on xa and Tis shown explicitly in this equation to remind us that, in general, the reaction rate depends on both temperature and the various species concentrations. The reaction rate depends on temperature because the constants that appear in the rate equation, e.g., the rate constant, the equilibrium constant, and the adsorption/binding constants, generally depend on temperature. 

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