Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using disinfecting or sterilizing substance
Patent
1998-06-17
2000-07-04
Anthony, Joseph D.
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using disinfecting or sterilizing substance
422 37, 134 2, 81081, 25218721, 25218723, 25218724, 25218725, 25218727, 25218734, A61L 218, A61L 222, C01B 1102, C01B 1104, C01B 1110
Patent
active
060834579
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the preparation of chlorine dioxide, to a solution capable of releasing chlorine dioxide and to a method of introducing chlorine dioxide to a system requiring bleaching and/or disinfection and/or other benefits derived from the oxidising effect of chlorine dioxide such as, for example, odour control.
The use of chlorine dioxide as a bleaching Agent and disinfectant is well known. In particular, the use of chlorine dioxide as a disinfectant in both industrial and potable water systems has become increasingly important in recent years because in contrast to chlorine, the most widely used oxidising biocide, its use does not give rise to the significant production of trihalomethanes. However the adoption of chlorine dioxide has been restricted because of the hazardous nature of the chemical.
Chlorine dioxide is an unstable gas which is explosive at pressures greater than 40 kPa (3000 mmHg). It has been found impossible to compress and store chlorine dioxide gas either alone or in combination with other gases. Chlorine dioxide is therefore manufactured at its point of use. The equipment used to produce chlorine dioxide is costly and has to take account of the hazardous nature of the chemical. Large consumers of the chemical, e.g. those involved in the bleaching of wood pulp, have used somewhat complicated processes based on the reduction of sodium chlorate. For use in smaller applications oxidation of chlorite is favoured. However, all these processes require considerable capital expenditure, an understanding of the chemistry involved and skilled personnel to operate the units efficiently and safely.
There is therefore a need to be able to produce chlorine dioxide safely and cost effectively in relatively small quantities that will allow a greater number of industrial and potable water systems to take advantage of the superior disinfection and stability properties of the chemical without the need for large capital investments and specially trained personnel.
To an extent this need has been satisfied by the introduction in recent years of "stabilised" solutions of chlorine dioxide sold under a variety of trade names. These products claim to be solutions of chlorine dioxide stabilized in solution through the formation of a variety of complexes.
Thus for example, the producers of Purogene claim to have produced a stable aqueous solution whose active ingredient is chlorine dioxide. They state that during water treatment 50-70% of the chlorine dioxide reacted will immediately appear as chlorite and the remainder as chloride. The chlorite, it is stated, will continue to react with remaining oxidisable material reducing entirely to chloride. The reactions occurring being as follows:
(1) ClO.sub.2 +e.sup.- .fwdarw.ClO.sub.2 .sup.- (chlorite)
(2) ClO.sub.2.sup.- +4H.sup.+ +4e-.fwdarw.Cl.sup.- +2H.sub.2 O (chloride)
Viscona limited claim have a 5% (50,000 ppm) aqueous stabilised chlorine dioxide Solution chemically buffered at a pH of 9 which releases chlorine dioxide in around 20 minutes when activated. Release of chlorine dioxide is achieved by lowering the pH of the solution to approximately 2 using a suitable acid (with a chlorine donor for rapid results). Activation with citric acid converts only approximately 10% of the available chlorine dioxide to free chlorine dioxide, in aqueous solution, after about 15 minutes. It is stated subsequent activation would continue at a very slow rate. Much a method is not sufficiently rapid for use in disinfection where a need for an activation rate of 50% or more is required.
The rate of activation can be increased using a stronger acid. For example adding 30 to 35% hydrochloric acid to bring the pH down to 1.5 activates 15% of the potential chlorine dioxide in 1 hour, 25% in 2 hours and 50% in 24 hours.
By adding a chlorine donor, e.g. hypochlorite, around a 70 to 80% release in about 15 minutes can be achieved.
Another product, OCS Dioxide produced by Odour Control Systems Limited, is stated to be a combination of oxygen and chlorin
REFERENCES:
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patent: 4247531 (1981-01-01), Hicks
patent: 4296103 (1981-10-01), Laso
patent: 4499077 (1985-02-01), Stockel et al.
patent: 4889654 (1989-12-01), Mason et al.
patent: 5165910 (1992-11-01), Oikawa et al.
patent: 5451398 (1995-09-01), Vigh
patent: 5696046 (1997-12-01), Green
Harris Arthur
Parkinson Timothy John
Anthony Joseph D.
BTG Inter-Corporate Licensing Limited
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