Chapter 6 - Diffusion Accompanied by Chemical Reaction Through a Plane Sheet

Abstract

The main task of this chapter is to show the most important mass transfer processes accompanied by chemical reactions within the catalytic membrane layer under steady-state conditions. Mass transport can take place in the catalytic membrane layer by diffusive flow only. Two operation modes are distinguished and consequently discussed in every reaction kinetics presented, namely transport with diffusive outlet flow (transport with a sweeping phase on the permeate side of the catalytic membrane layer) and transport without outlet diffusive flow (transport without a sweeping phase on the permeate side). In this latter case, transport in the catalytic membrane can only be induced by chemical reaction, which can produce a concentration gradient of reactant as a function of the local coordinate, due to transport inside the membrane matrix. Regarding reaction kinetics, the effect of first-, zero-, and second-order reactions on diffusive mass transport is discussed, defining the inlet and outlet mass transfer rates, showing the concentration distribution within the catalytic membrane layer practically for every case discussed. The differential mass balance equations given do not have analytical solutions in the case of one-component or two-component second-order chemical reactions. Analytical approach solutions are presented for these cases, which give accurate values of transport properties. Additionally, mass transport with variable diffusion and/or reaction rate constants are also briefly discussed, using an analytical approach solution combined with the trial and error method to predict their effect on mass transfer rates. Investigation of the effect of the polarization layer is also an important portion of this study; this layer is generally located on the feed side of the catalytic membrane, and its effect is shown in some cases when boundary layers exist at both sides of the catalytic membrane layer.