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CloSure Method of Chlorous Acid Generation Disclosure Number: IPCOM000130537D
Publication Date: 2005-Oct-26
Document File: 2 page(s) / 19K

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CloSure Method of Chlorous Acid Generation

Chlorous acid is a relatively weak antimicrobial and must therefore be used at concentrations that are more typical of a preservative. The recommended amount of chlorous acid will depend upon the process, the types of microorganisms and their concentrations in the systems being treated. A typical working range of chlorous acid is 500-2000 ppm. Prior to the Closure method of chlorous acid generation, chlorous acid was made by the acidification of its salt, such as sodium chlorite (NaClO2), with either a mineral (e.g. phosphoric) or organic (e.g. citric) acid. The choice of particular chlorite salt and acid is largely based on the availability and economics of these precursors. The rapid blending and accurate proportioning of the precursors are critical to render the solution biocidal. Chlorous acid is itself unstable and therefore rapid blending and distribution of the activated solution is necessary to achieve a controlled activity. The concentration of chlorous acid can be determined by titration with sodium thiosulfate in the presence of iodine as per the method 4500-ClO2 E in Standard Methods for the Examination of Water and Wastewater, 20th e., 1998, or equivalent alternative method. Furthermore, the correct amount of acid in solution can be ascertained by monitoring the pH of the batched solution. If insufficient acid is present, the chlorite will remain in the salt form and no antimicrobial activity will be established. If the pH of the solution is too low, chlorate ions will form resulting in diminished antimicrobial activity. In addition to controlling the pH, the amount of sodium chlorite added to the blend is equally critical. If the amount of chlorite salt is too low, a diminished antimicrobial activity will result. If excessive chlorite salt is used, it could neutralize the acid resulting in a sub-optimal chlorous acid concentration and potentially render the mixture highly corrosive to stainless steel.

The novelty and utility of the CloSure method of chlorous acid generation obviates all the aforementioned undesirable consequences of improper blending and proportioning by using ion exchange to generate chlorous acid. Specifically, sodium chlorite is passed through a cation exchange resin that is in the hydrogen state (acid). As the sodium chlorite passes through the cation exchange resin, the sodium is exchanged for the proton resulting in an effluent of chlorous acid. It is impossible to over or under acidify the sodium chlorite because the acid released from the ion exchange is done in a 1:1 molar ratio of the chlorite salt. The concentration of chlorous acid is therefore a function of the amount of chlorite salt added to the water stream ahead of the vessel containing the ion exchange resin. A water meter and proportioning pump is all that is necessary to achieve the desired concentration of chlorous acid. The pH of the chlorous acid solution will depend upon the concentra...