Controlling Transport Number of Anions through Anion Exchange Membranes with Temperature

6 Controlling Transport Number of Anions through Anion Exchange Membranes with Temperature 

It is desirable to perform electrodialysis at as high a temperature as possible to save energy, if the membranes and electrodialyzer permit.151 However, when conventional ion exchange membranes are used in high temperature electrodialysis, osmotic water and electro-osmotic water through the membranes increase with increasing temperature. Thus, the amount of water produced decreases in the desalination of saline water and the concentration of the concentrated solution decreases in a concentration processes. On the other hand, a serious problem in electrodialysis is the precipitation of calcium sulfate in the concentrated compartment and the anion exchange membrane. 

For anion exchange membranes containing a thermally responsive vinyl-monomer, the decreased water transfer through the membranes decreased permeation of sulfate ions, while that of nitrate ions increases with increasing temperature, which is a useful property, especially for the removal of nitrate ions from groundwater by electrodialysis. Such anion exchange membranes are also expected to find new fields of application. 

In recent years, molecular imprinting techniques have been actively studied to prepare resins and membranes with high selectivity for specific molecules and inorganic ions.152 Even the resolution of racemic mixtures of amino acids has been tried by electrodialysis.153 These concepts might provide a new aspect, in combination with other methods, to this research. 

3 Drinking Water Atlas of China, Institute of Environmental Health Monitoring, Chinese Academy of Preventing Medicine, China Cartographic Publishing House, Beijing, 1994, p. 147-148. 

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