Abstract
Ion-exchange membranes have found many uses for their special separation capabilities and are used currently in electrolysis and fuel cells, batteries, and chemical separations. Bilayer membranes have been particularly useful in improving the performance of chlor-alkali electrolysis cells. In order to understand better and to develop these membranes, an ability to analyze their behavior is required. The objective of this work was to develop multicomponent, two-dimensional models which can be used to study the concentration, potential, and velocity distributions within the pores of a bilayer membrane. These models are used to analyze the internal behavior of the membrane and to determine the chemical species fluxes through the membrane. Electrokinetic transport theory is used with a straight cylindrical capillary physical model of the ion exchange membrane. The model involves solving simultaneously Poisson's equation (for the potential), the momentum balance, and the component material balances. A simplified form of the model which uses an assumed parabolic axial velocity profile is developed also. The models are used to produce two-dimensional profiles for the potential, radial velocity, axial velocity, and concentrations of Na+, OH-, Cl-, and H2O, and to derive transport numbers and the ratio of water flux to sodium ion flux as functions of current density. The membrane models show that delamination of bilayer membranes may be caused in part by a sharp membrane polymer contraction caused by a drop in hydration of the layers near the interlayer junction. Also, the results of the study show that the potential field within the membrane has a significant effect on the velocity profiles which develop in the pore. These include significant radial velocities and axial variations in wall potential which have been ignored in previous models. Finally, the models confirm that the construction of a bilayer membrane with a thin barrier layer of higher equivalent weight toward the cathode side of a chlor-alkali electrolysis cell achieves the best suppression of hydroxide transport from the catholyte to the anolyte, where the hydroxide produces undesirable side reactions and a decrease in the electrical efficiency of the cell.
Walton, Clifford Wayne (1987). Multicomponent transport in a bilayer ion-exchange membrane. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -747650.