Adiabatic Reactor With and Without Catalyst

The numerical example used in Chapter 5 has two reactions. The feed is 0.025 kmol/s of a mixture of propylene (90 mol%) and chlorine (10 mol%) at 400 K. The adiabatic reactor is 1 m in diameter and 10 m in length, giving a total volume for reaction of ml )2 (10)/4 = 7.854 m3 if the reactor is empty (containing no catalyst). The temperature of the reactor effluent leaving the reactor is 583 K. 

Two cases are considered an adiabatic reactor with no catalyst and an adiabatic reactor with catalyst. The void volume of the catalyst is 0.5, so the total volume of the reactor with catalyst must be twice as large as the volume of the reactor without catalyst. The reactor length is increased to 20 m in this case. The density of the solid catalyst is 2000 kg/m3, so the total amount of catalyst in the reactor is 

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Effect Of Number Of Lumps If the number of plotting points in Aspen Plus is set at 10 (the default), the resulting exit temperature from the reactors under steady-state conditions in Aspen Dynamics is 578 K. Remember that it should be 583 K from the rigorous integration of the ordinary differential equations describing the steady-state tubular reactor that are used in Aspen Plus. Changing the number of points to 20 produces an exit temperature of 580 K. Changing the number of points to 50 produces an exit temperature of 582 K, which is very close to the correct value. Therefore a 50-lump model should be used. 

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Dynamics of Adiabatic Reactors with and without Catalyst We want to show the difference in the dynamic responses between an adiabatic reactor without catalyst and one with catalyst. A plot is set up in the usual way using Tools on the top toolbar and selecting New Forms and Plot. The variables to be plotted are dragged and dropped from the feedstream and from the reactor block. The feed temperature and the reactor exit temperatures are plotted. In addition, the temperatures at several locations down the length of the reactor with catalyst are plotted the temperatures at 5, 10, and 15 m in the 20 m reactor containing the catalyst. The models of the two adiabatic reactors use 20 lumps. 

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