Compositions – Oxidative bleachant – oxidant containing – or generative – Free halogen or oxy-halogen acid type
Reexamination Certificate
2000-02-02
2002-08-13
Anthony, Joseph D. (Department: 1714)
Compositions
Oxidative bleachant, oxidant containing, or generative
Free halogen or oxy-halogen acid type
C252S187210
Reexamination Certificate
active
06432322
ABSTRACT:
BACKGROUND OF THE INVENTION
Free molecular chlorine dioxide in solution is an effective agent for the control of microorganisms and biological film deposits. However, the most common way to produce such solutions of free chlorine dioxide is to use an expensive and complicated chemical generator (see for example U.S. Pat. No. 5,009,875).
British patent 608,068 teaches the use of organic acid anhydrides to convert chlorite anion to free chlorine dioxide at a generally neutral pH. The fire and explosion dangers that result from combining a strong oxidizing chemical, such as sodium chlorite, with an organic chemical are also well known. As a result of the low conversion ratio produced by the compositions of this British patent, and the dangers inherent in compositions combining sodium chlorite and organic chemicals, the compositions of this British patent have received little commercial interest.
Recently, a membrane type device containing powdered chlorine dioxide precursor chemicals that produces a solution of free molecular chlorine dioxide when the device is immersed in water was described, see WO 99/24356. While this membrane device is superior to the prior art methods of producing chlorine dioxide solutions, the device has some shortcomings. It is relatively expensive (due to the cost of the membrane and of assembly), and the rate of chlorine dioxide delivery can be too slow for certain applications. Also, the device may float on the surface of the water/solution (due to entrapped air or chlorine dioxide gas), and this can result in the loss of some chlorine dioxide to the gas phase. Finally, the preferred membranes are insoluble in water, and may need to be removed from the chlorine dioxide solution after the chlorine dioxide generating reactions are completed. Removal of the spent membrane from the chlorine dioxide solution may, at times, be considered inconvenient.
The prior art also describes attempts to produce chlorine dioxide solutions from solid mixtures, including solid compacts such as tablets and briquettes, which are comprised, of materials that will generate chlorine dioxide gas when contacted with liquid water.
U.S. Pat No. 2,071,094 discloses dry solid compositions, including briquettes, comprised of a soluble chlorite and an acidifying agent which when contacted with water produce a “deodorizing reaction” as the dry composition begins to dissolve (see col. 1, lines 34-38 and col. 2, lines 24-27). Upon reading this patent, it is not clear what is produced when the composition comes into contact with water. The substance, chlorine dioxide, is never mentioned and the only time the word “solution” is used it is with reference to an aqueous solution of sodium chlorite (see col. 1, line 58). Thus, it cannot be ascertained whether the inventor was attempting to, or indeed ever did obtain an aqueous solution of chlorine dioxide when his briquette was contacted with water.
U.S. Pat. No. 5,324,447 describes, inter alia, a tablet comprising a chlorine dioxide precursor (e.g., sodium chlorite) and an activator component (e.g., an organic acid anhydride) which are present in amounts effective to produce (contact) lens disinfecting amounts of chlorine dioxide in a liquid medium (see, col. 3, lines 10-16). The term disinfecting amount is defined as such amount as will reduce the microbial burden by one log order preferably in ten (10) minutes or less (see col. 4, lines 11-15). This amount represents very little free chlorine dioxide, as even as little as 2 ppm of free chlorine dioxide can result in a 6 log bacterial reduction in 15 minutes. The patent does not disclose the amount of chlorine dioxide that is generated when a tablet of the invention is dissolved in water. Thus, all of the examples utilize aqueous solutions of stabilized chlorine dioxide and not water to test the tablets.
U.S. Pat. No. 5,399,288 discloses a solid composition releasing chlorine dioxide immediately after dissolution in water (see col. 1, lines 5-7). The composition comprises a chlorite salt, an oxidizing chlorine releasing agent and a proton donor present in the ratio of 4:1:3 (see col. 1, lines 65-67). When the oxidizing chlorine-releasing agent is omitted from the composition, the final yield of chlorine dioxide obtained was 63% but after three days (see Example 5). Further, and importantly, this patent does not discuss the preparation of tablets (see col. 2, lines 19-21). Thus, it appears that only powdered mixtures of reactants are disclosed.
U.S. Pat. No. 5,719,100 discloses production of chlorine dioxide in an aqueous solution from a tablet comprising a composition of sodium chlorite and an acid activator wherein the composition requires a reaction-preventing barrier between the sodium chlorite, [i.e., a protective reactive coat is formed on the sodium chlorite before it is mixed with the acid activator (see col. 4, lines 61-63) and the acid activator such that the two active ingredients do not “explosively react” together prematurely (see col. 4, line 53), i.e., a stable composition is obtained (see col. 4, line 46 through col. 5, line 9).
The present invention provides an improved device in the form of a massive body for the production of chlorine dioxide solutions. This new device rapidly provides high yield solutions of chlorine dioxide and overcomes shortcomings of prior art solid compositions for producing such solutions.
DESCRIPTION OF THE INVENTION
This invention provides a massive body that rapidly produces a solution of chlorine dioxide when immersed in water. The invention also includes the solutions obtained when a massive body is immersed in water. As used herein the term “massive body” means a solid shape, preferably a porous solid shape, comprising a mixture of granular particulate ingredients wherein the size of the particles comprising the ingredients is substantially smaller than the size of the massive body. Such massive bodies may be formed by a variety of means known in the art, such as tabletting, briqueting, extrusion, sintering, granulating and the like. The preferred method of forming such massive bodies is by compression, also known as tabletting. For reasons of convenience, hereinafter references to tablets and tabletting shall be understood to be representative of massive bodies made by any method.
The tablet is comprised of a source of chlorite anions such as an alkali or alkaline earth metal chlorite, preferably sodium chlorite and one or more dry solid acid sources. Examples of such dry solid acid sources include inorganic acid salts, such as sodium acid sulfate, potassium acid sulfate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate; salts comprising the anions of strong acids and cations of weak bases, such as aluminum chloride, aluminum nitrate, cerium nitrate, and iron sulfate; solid acids that can liberate protons into solution when contacted with water, for example a mixture of the acid ion exchanged form of molecular sieve ETS-10 (see U.S. Pat. No. 4,853,202) and sodium chloride; organic acids, such as citric acid and tartaric acid; and mixtures thereof. Preferably the solid acid source is a solid inorganic acid source, and most preferably is sodium bisulfate. Surprisingly, a very high conversion rate of the chlorite anion to chlorine dioxide is obtained by use of the tablets of the invention. Thus, when the equivalent weights of tablet ingredients in powdered form are added to the same volume of water as the corresponding tablet, a much larger amount of chlorine dioxide is produced by the tablet than from the powder. Reasonable variations in stirring rate and/or water temperature have little to no effect on this surprising phenomenon. Thus, the tablets of the invention have been observed rapidly to produce a highly converted solution of free molecular chlorine dioxide, meaning that the conversion ratio (chlorite anion to chlorine dioxide) is >0.25. The term, conversion ratio, when utilized herein means the calculated ratio of the free chlorine dioxide concentration in the product solution to the sum of free chlorine dioxide pl
Koermer Gerald S.
Moini Ahmad
Speronello Barry K.
Thangaraj Appadurai
Anthony Joseph D.
Engelhard Corporation
Miller Stephen I.
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