Preparation of bi-polar membranes and their application to sodium hypochlorite generation
K. Y. Kim1, H. S. Shin2, C. S. Kim2, J. W. Rhim1*
1Department of Chemical Engineering, Hannam University, Daejeon, Korea
2Techwin Co. Ltd., Cheongju City, Choongcheongbuk-do, Korea
Traditionally, ion exchange membranes are classified into anion exchange membranes and cation exchange membranes relying on the type of ionic groups attached to the membrane surface. They are used in a number of industrial application areas owing to their ecological safeness and comparative low energy consumption.
The principle of hypochlorite generation is as follows. When both electrodes are applied with voltage, protons and hydroxyl ions are yielded from the CEM and AEM, respectively. In the anode chamber, dissociation of water produces hydronium ions and oxygen while oxidation of chlorine ion produces chlorine gas; however, overall neutrality is maintained due to the dissociation of water yielding an equal number of hydroxyl ions at the AEM and the initial pH does not change. The generated chlorine gas dissolves in the caustic soda solution, producing sodium hypochlorite. Meanwhile, in the cathode chamber, dissociation of water produces hydrogen gas and hydroxyl ions. In theory, this yields the same number of protons at the CEM.
This study will focus on the production of hypochlorites using bi-polar membranes equipped in the electrodialysis process. Polysulfone(PSf) and polyetherimide(PEI) were aminated respectively and polyether ether ketone was sulfonate. Bi-polar membranes were characterized via the measurement of FT-IR, swelling degree, ion exchange capacity(IEC), and ion conductivity.
Then the surfaces of these membranes were modified by the surface fluorination using 2000 ppm F2gas against N2gas for 2h at room temperature. The surface fluorinated APSf and APEI membranes were characterized again to determine any differences between the pristine and fluorinated membranes.
Bi-polar membranes were prepared by varying the IEC of the APSf and APEI at the fixed IEC value of SPEEK. The hypochlorite concentration generated by using the surface fluorinated bi-polar membranes was dependent on the IEC of the APSf and ranged from 48.5 to 53.2 ppm. Also, for APEI the produced hypochlorite concentration was ranged from 29.8 to 58.3 ppm.
1. Xu, T. (2005), "Ion exchange membranes: State of their development and perspective", J.
of Membrane Sci., 263, 1–29.
2. Beezina, N. P., Kononenko, N. A., Dyomina, O. A., and Gnusin, N. P. (2008),
Charcaterization of ion-exchange membrane materials: Properties vs. structure, Adv. in
Colloid and Interface Sci., 139, 3-28.
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