Compositions – Oxidative bleachant – oxidant containing – or generative – Free halogen or oxy-halogen acid type
Patent
1998-05-11
1999-10-26
Anthony, Joseph D.
Compositions
Oxidative bleachant, oxidant containing, or generative
Free halogen or oxy-halogen acid type
25218723, 25218724, 25218725, 25218732, 422 29, 422 37, C01B 1102, C01B 1104, C01B 1108
Patent
active
059722380
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a process for the production of aqueous chlorine dioxide solutions through oxidation of chlorite with oxo acids and/or oxo acid anions having a suitable redox potential in a buffered aqueous medium.
b) Description of the Related Art
Numerous attempts have been made up to the present, without satisfactory results, to kill Legionella in hot water systems in order to reduce potential health risks. Further, conditions exist in industrial cold water systems which favor bacterial growth and which lead to a biofilm on the surfaces of transporting lines which has been countered up to the present by biostatic means. For example, isothiazolone, thiocyanates, quaternary ammonium compounds and chlorine-containing compounds are used for this purpose. A great disadvantage of these biostatic means consists in that the cold water often has CSB/BSB values above the limiting values due to the large amounts used. In fact, only an increase in temperature to about 73.degree. C. and an increase in the flow volume have proven suitable for killing Legionella in water systems. However, there is a risk that after a certain period of time the Legionella which have not been killed will propagate again from the biofilm and encrusted deposits in the water line system, especially from so-called dead strains, and will once again cause lasting contamination of the system. Therefore, nonionic phosphonic acids with hydrogen peroxide (EP 0 540 772 A1) or grapefruit seed extract (EO 0 602 891 A1) were recently proposed for combatting Legionella. However, none of these methods has been successful.
Aqueous chlorine dioxide solutions are promising candidates for the areas of application mentioned above. However, the known processes for industrial production of aqueous chlorine dioxide solutions have grave disadvantages which pose obstacles to the use of chlorine dioxide solutions produced by these methods in drinking water and in related areas.
According to the process in DE-PS 27 28 170, 7 to 21 parts by weight of chlorite, 7.5 to 22.5 parts by weight of hypochlorite and 0.5 to 1.5 parts by weight carbonate are dissolved, in that order, in 35 to 105 parts by weight water. In order to adjust a slightly alkaline pH, 7.5 to 22.5 parts by weight of diluted inorganic or organic acid are added. A stabilizer, especially in the form of a peroxide, is advantageously mixed in beforehand.
According to DE-AS 27 30 883, an aqueous chlorine dioxide solution is produced by acidifying a chorite solution to a pH of about 4 and subsequently raising the pH value to about 7.0 to 7.2 by adding a water-soluble metal hydroxide. This is followed by the addition of carbonate. The teaching disclosed in DE-AS 27 30 883 offers the advantage that the aqueous chlorine dioxide solution remains stable exclusively through the sodium carbonate, so that additional stabilizers in the form of peroxides, for example, can be dispensed with. The stabilized chlorine dioxide solution is said to be storable for long periods of time, that is, months and years, and is suitable particularly for treatment of drinking water.
According to the teaching of the two processes mentioned above, the carbonate serves to ensure buffering in the basic pH range. However, the incorporation of the carbonate stabilizing in the alkaline range leads to a high pH value which is undesirable for various reasons: a high pH promotes the reformation of chlorite ions so that the known chlorine dioxide solutions always contain an unwanted proportion of chlorite ions. Moreover, in the alkaline range, highly toxic and therefore undesirable chlorate can form through various types of reactions. For example, when alkaline hypochlorite solution is mixed with chlorite solution, the oxidation of the chlorite beyond the oxidation stage of the chlorine dioxide leads to chlorate. Further, chlorine dioxide tends in the alkaline range toward disproportionation in chlorate and the by-product chlorite.
The process according to DE-PS 34 03 631 is al
REFERENCES:
patent: 4574084 (1986-03-01), Berger
patent: 5110580 (1992-05-01), Rosenblatt et al.
patent: 5165910 (1992-11-01), Oikawa et al.
patent: 5405549 (1995-04-01), Pitochelli
Kueke Fritz
Rimpler Manfred
Rimpler Marcus
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