A modified coating method for preparing a mono-valent perm-selective cation exchange membrane: I. The evolution of membrane property corresponding to different preparing stages

Abstract

In this work, enlightened by the preparation of the Tokuyama BP-1 bipolar membrane, a modified coating method is attempted to prepare the mono-valent perm-selective cation exchange membrane (CEM). That is, a surface-roughening step is introduced into conventional coating technology to increase the contacting area and strengthen the interaction between modification layer and base membrane. Furthermore, a post-quaternization is carried out after the formation of the cross-linked chitosan layer to weaken the effect of the electrostatic repulsion among the cationic charged macromolecules on the compactness of the modification layer. The SEM images and the diffusion experiments of solute confirm the formation of a dense and smooth cationic modification layer. The electrodialysis experiments of the CEMs corresponding to different preparing stages with respect to H⁺/Zn²⁺ system and Na⁺/Mg²⁺ system show that the mono-valent perm-selectivity can be endowed successfully to the ordinary CEM. For example, the separation ability of the CEM modified by the cross-linked quaternized chitosan to protons and Zn²⁺ in solution of 2.5 g/L ZnSO₄ in 0.25 M H₂SO₄ increases almost 10 times. However, a remarkable increase of the electrical resistance and decrease of limiting current density is also observed after CEM modification.

Keywords:

• Mono-valent perm-selectivity
• Cation exchange membrane
• Electrodialysis
• Surface modification
• Chitosan

Acknowledgments

This research is supported in part by the National Science foundation of China (No. 21276245) and Natural Science Foundation of Shandong Province (ZR2011EMQ004).