Multicomponent space-charge transport model for ion-exchange membranes

✍ Scribed by Yahan Yang; Peter N. Pintauro

• Publisher: American Institute of Chemical Engineers
• Year: 2000
• Tongue: English
• Weight: 228 KB
• Volume: 46
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690460610

✦ Synopsis

A multicomponent space-charge transport model for ion-exchange membranes was de®eloped, where the membrane structure was modeled as an array of cylindrical pores with a uniform distribution of fixed-charge sites on the pore walls. Ionrfixed-charge site electrostatic interactions, electric-field-induced water dipole orientation, ion-hydration free-energy changes during ion partitioning, and concentration-dependent transport parameters were considered in the analysis. The model predicted experimental concentration ®s. time data accurately for Donnan dialysis separations with a DuPont Nafion 117 cation-exchange membrane, where the membrane separated a dilute H SO solution 2 4

from an aqueous mixture of either Cs SO q Li SO or Cs SO q Na SO . Both

computer predictions and experimental measurements showed that the alkali metal ( ) cation with the larger hard-sphere radius lower surface charge density was selecti®ely absorbed in and transported across the membrane during a multicomponent separation. The cationrcation transport permselecti®ity was less than the selecti®ity for equilibrium uptake due to slow ion transport near the pore wall, where discrimination between like-charge cations was greatest.