Membrane Reactor to Improve Selectivity in Multiple Reactions
Membrane reactors have a semipermeable membrane that can be used to selectively add reactants or remove products and thus shift the equilibrium. This Demonstration compares multiple reactions taking place in a membrane reactor and a plug flow reactor (PFR). The membrane reactor shows a significant improvement in selectivity over the PFR.
Consider the following chemical reactions that take place in the gas phase , , where is the desired product and the rates of reaction are and .
Here, and are reaction constants, while and are the reactant concentrations. The selectivity of with respect to is
In order to maximize , the concentration of must be high and the concentration of low; therefore we feed through the membrane. The molar rate of entering the reactor is equal to that of entering through the membrane, 4 mols/s; enters along with in the PFR. The reactor volume is 50 and the entering total concentration is 0.8 mols/.
The molar flow rates of the reactants and products (, , , ) are calculated along the length of the reactors for selected values of and . The parameters used are given in equations E6.9 to E6.18 of Chapter 6 in .
 H. S. Fogler, Elements of Chemical Reaction Engineering, 4th ed., Upper Saddle River, NJ : Prentice Hall PTR, 2006 pp. 348–351.