Electrolyzer chlor-alkali, membrane developments

The current state-of-the-art proton exchange membrane is Nafion, a DuPont product that was developed in the late 1960s primarily as a permselective separator in chlor-alkali electrolyzers. Nation s poly(perfluorosulfonic acid) structure imparts exceptional oxidative and chemical stability, which is also important in fuel cell applications. 

For a long time, conventional alkaline electrolyzers used Ni as an anode. This metal is relatively inexpensive and a satisfactory electrocatalyst for O2 evolution. With the advent of DSA (a Trade Name for dimensionally stable anodes) in the chlor-alkali industry [41, 42[, it became clear that thermal oxides deposited on Ni were much better electrocatalysts than Ni itself with reduction in overpotential and increased stability. This led to the development of activated anodes. In general, Ni is a support for alkaline solutions and Ti for acidic solutions. The latter, however, poses problems of passivation at the Ti/overlayer interface that can reduce the stability of these anodes [43[. On the other hand, in acid electrolysis, the catalyst is directly pressed against the membrane, which eliminates the problem of support passivation. In addition to improving stability and activity, the way in which dry oxides are prepared (particularly thermal decomposition) develops especially large surface areas that contribute to the optimization of their performance. 

Remarkable advances in ion exchange membranes have been made since their inception and application to chlor-alkali cells in the 1970fs, and since that time many patents have issued on their applications. Several companies besides duPont have developed proprietary membranes and electrolyzers for commercial application. 

Development of these new zero gap membrane cell electrolyzers represents a major new approach in the membrane cell technology and promises to provide even more rapid development in this quiet revolution of the membrane cell chlor alkali process. 

Since then, several membrane-cell technologies were developed in Japan, as a pollution-free chlor-alkali process. Japanese contributions include composite membranes and several electrolyzer designs. Japan was the first major chlorine producing country to convert entirely to membrane cell technology. As of January 2003, 35% of world production of chlorine is by membrane-cell technology, generating 52,000 metric tons caustic/day. 

A. Hironaga, M. Okura, S. Katayama, and Y. Take, Development of the Advanced Bipolar Membrane Electrolyzer (BiTAC ), In R.W. Curry (ed.). Modem Chlor-Alkali Technology, vol. 6, The Royal Society of Chemistry, Cambridge (1995), p. 205. 

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