Abstract
To obtain higher chlorine purity hydrochloric acid can be added to the feed brine of membrane cells in alkali chloride electrolysis. During the electrolytic process hydroxide ions migrate from the cathode compartment into the anode compartment. Hydrochloric acid neutralizes these hydroxide ions and, hence, formation of the by-products (oxygen in the anode gas and sodium chlorate in the anolyte) is reduced. With laboratory membrane cells the effects of varied amounts of hydrochloric acid on concentrations and current efficiencies of these by-products have been studied. Under normal operating conditions (with pH of feed brine between 2 and 11) the formation of by-products is not influenced by the addition of acid. Effects can only be observed at brine pH values<1. Maximum effects occur if the brine pH is 0.1 and the anolyte pH is 2. The latter value is the limiting pH given by the membrane suppliers. At this point 6.3 dm3 hydrochloric acid (37% HCl) per 1 m3 of the feed brine have to be added in order to obtain an anode gas with 0.4% oxygen by volume. The formation of sodium chlorate is completely suppressed. Problems connected with this process and its application to industrial electrolysis are discussed.
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Bergner, D. Reduction of by-product formation in alkali chloride membrane electrolysis. J Appl Electrochem 20, 716–722 (1990). https://doi.org/10.1007/BF01094296
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DOI: https://doi.org/10.1007/BF01094296