(12) Patent Application Publication (10) Pub. No.: US 2007/0116636A1 Hemker Et Al

Home , Ammonium persulfate, Potassium persulfate

US 20070116636A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2007/0116636A1 Hemker et al. (43) Pub. Date: May 24, 2007

(54) GENERATION OF CHLORINE DIOXIDE Publication Classification (51) Int. Cl. (76) Inventors: Wilfred J. Hemker, Berea, OH (US); COB II/02 (2006.01) Melissa A. Thompson, Cuyahoga Falls, (52) U.S. Cl...... 423/477 OH (US) (57) ABSTRACT Correspondence Address: A method for point-of-use generation of chlorine dioxide RENNER, KENNER, GREIVE, BOBAK, wherein the chlorine dioxide is generated quickly and at TAYLOR & WEBER acceptable concentrations to avoid the need for Subsequent FIRST NATIONAL TOWER FOURTH FLOOR dilutions and keeping the product non corrosive to the 106 S. MAN STREET surface to be treated. A persulfate solution and a chlorite AKRON, OH 44308 (US) solution are mixed at a molar ratio of persulfate to chlorite (21) Appl. No.: 11/285,124 of greater than 2. The chlorite solution is buffered to a pH of from 9 to 12. The persulfate solution is buffered to a pH of (22) Filed: Nov. 21, 2005 from 3 to 9. US 2007/01 16636A1 May 24, 2007

GENERATION OF CHLORINE DOXDE oxidizers, proton donors, or combinations of these reaction initiators, these reactions produce relatively high concentra TECHNICAL FIELD tions of chlorine dioxide, greater than 1000 parts per million (ppm). This highly concentrated product is then immediately 0001. The present invention generally relates to a method diluted for potable water purification, using acid buffers to for the generation of chlorine dioxide, and, more particu control the reaction rate, or semi-permeable devices to larly, relates to a method for point-of-use generation of control the rate of release and purity of chlorine dioxide chlorine dioxide. In accordance with this method, chlorine delevered. dioxide may be generated over a broad pH range, and may be made Suitable for various uses, including hard Surface 0006 The present invention goes beyond the teaching of disinfecting and topical skin or biological product surface the prior art to provide a method for point-of-use generation disinfecting. of chlorine dioxide, wherein the chlorine dioxide is gener ated quickly and at acceptable concentrations to avoid BACKGROUND OF THE INVENTION subsequent dilutions. Additionally, the chlorine dioxide product is not corrosive or degrading to the Surface to be 0002 There are many known methods for generating treated. chlorine dioxide, including both chemical and electrolytic processes. In the chemical processes, chlorine dioxide is typically generated from oxidizing chlorite or reducing SUMMARY OF THE INVENTION chlorate. These chemistries often result in very corrosive and 0007. In light of the foregoing, it is an object of this Sometimes unsafe disinfecting by-products. Electrolytic pro invention to generate chlorine dioxide at safe and effective cesses typically generate chlorine gas to oxidize chlorite or concentrations (typically 2-300 parts per million (ppm)) at generate a proton to reduce chlorates to chlorine dioxide. the point of use. Although they achieve the desired end result of producing chlorine dioxide, these electrolytic cells can be very large in 0008. It is another object of the invention to provide a size and expensive. They may also contain fragile ion method for point-of-use generation of chlorine dioxide, separation membranes, and may be too cumbersome for wherein the chlorine dioxide may be selectively generated to generating chlorine dioxide at the point of use. These prior have a pH of from about 3 to about 10. art technologies are corrosive, contaminated with impurities, 0009. It is an additional aspect of this invention to costly, or too slow in reaction rates for producing point-of provide a method for point-of-use generation of chlorine care products incorporated chlorine dioxide. dioxide wherein desired concentrations of chlorine dioxide 0003 U.S. Pat. No. 2,323,593 discloses a process for the are generated rapidly. production of chlorine dioxide wherein chlorite ions are 0010. It is yet another aspect of this invention to provide oxidized with persulfate ions in an aqueous reaction mix a method for point-of-use generation of chlorine dioxide ture. The reaction is taught as proceeding acceptably at wherein strong, corrosive acids are not employed. ambient temperatures and at a reaction mixture pH of from 3 to 11. The patent teaches reacting the persulfate and 0011. It is another object of this invention to provide a chlorite in a molar ratio of persulfate to chlorite of from method for point-of-use generation of chlorine dioxide about 0.6:1 to about 0.75:1, and teaches that ratios of 1:2 or wherein persulfate is the sole oxidant/reactant with chlorite. smaller should be avoided because they decrease the reac tion rate. The chlorine gas is collected in an absorption tower 0012. At least one or more of the foregoing objects is by passing an inert gas through the reaction mixture. This is accomplished by the method herein described. a costly and hazardous practice. 0013 In accordance with one embodiment of this inven 0004 U.S. Pat. No. 6,171,485 discloses a process for the tion, a method is provided for point-of-use generation of production of chlorine dioxide wherein chlorite ions are chlorine dioxide. In accordance with this method, an aque oxidized with an oxidizing agent, with the oxidizing agent ous persulfate Solution is mixed with an aqueous chlorite being present in an amount between once and twice the solution at a molar ratio of persulfate to chlbrite of greater Stoichiometric amount necessary for oxidation of the chlo than 2. This creates a chlorine dioxide product solution. rite to chlorine dioxide, and with the reaction solution at a 0014. In accordance with preferred embodiments, the pH of from 5.5 to 9.5, achieved through the presence of buffering and concentration of the reactant solutions and proton donors. Two solutions are employed, an aqueous ratio at which they are mixed are chosen to produce a chlorite Solution and an aqueous oxidizing agent solution, chlorine dioxide product solution having a pH maintained mixed to form the reaction mixture that produces chlorine between 3 and 12, with between 2 and 300 parts per million dioxide. A buffer substance is also preferably employed to by weight of chlorine dioxide being generated in the chlo form a buffering system active between pH 5.5 and 9.5 in the reaction mixture. This process was found to produce chlo rine dioxide product solution within 5 minutes. rine dioxide fairly rapidly, with a 95% conversion of chlorite 0015. In accordance with preferred embodiments, persul to chlorite ions to chlorine dioxide occurring in about 12 fate ion is present in the aqueous persulfate Solution at a days. With the inclusion of catalytic amounts of ions of concentration of from 0.01 to 1.0 moles persulfate per liter, transition metals present in the reaction mixture, even faster and the persulfate solution is preferably buffered to a pH of conversions are realized—on the order of about 98% con from 3 to 9. Similarly, the chlorite ion is present in the version at 7 days. This patent focuses on producing chlorine aqueous chlorite solution at a concentration of from 0.01 to dioxide for the treatment of water, and does not address the 1.0 moles chlorite per liter, and the chlorite solution is production of chlorine dioxide for surface treatment such as preferably buffered to a pH of from 9 to 12. Solutions within hard Surfaces and biological Surfaces. these pH and concentration ranges are mixed in appropriate 0005 Although the prior art teaches that chlorine dioxide ratios to produce a chlorine dioxide product solution at a pH may be generated from metallic chlorites reacted with of from 3 to 12, with a concentration of between 2 and 300 US 2007/01 16636A1 May 24, 2007

ppm chlorine dioxide being generated in the chlorine diox within five minutes. It should be appreciated that, at too high ide product solution within 5 minutes. a chlorine dioxide concentration there is the problem that chlorine gas will come out of water (i.e., no longer be fully PREFERRED EMBODIMENT FOR CARRYING dissolved), and, additionally, the concentrated chlorine diox OUT THE INVENTION ide might be corrosive to Surfaces or irritating or harmful to the skin. Thus, in particularly preferred embodiments, at 0016. In accordance with the present method, two aque least 2 ppm chlorine dioxide is generated in 15 seconds ous buffered solutions are mixed to react and generate while no more than 300 ppm is generated in 5 minutes. The chlorine dioxide. A buffered persulfate solution is combined reactant Solutions should be tailored (pH, concentration) and with a buffered chlorite solution, yielding chlorine dioxide. mixed (at a persulfate:chlorite ratio greater than 2) Such that The reaction of sodium persulfate with sodium chlorite is the concentration of chlorine dioxide in the product solution provided below as a representative example of the genera is above 2 and less than 300 ppm five minutes after mixing. tion of chlorine dioxide from persulfate and chlorite ions: Additionally, the reactant solutions should be tailored and mixed and the buffer system chosen such that the resultant 0017. The persulfate is preferably provided by Group I pH of the product solution is from 3 to 12. metal persulfates or ammonium persulfate. More particu 0022. In accordance with one embodiment, the concen larly, the persulfate is preferably provided by sodium per tration of persulfate in the persulfate Solution, the concen Sulfate, potassium persulfate, ammonium persulfate, and tration of chlorite in the chlorite solution, the pH of the mixtures thereof. The persulfate is present at a concentration persulfate solution, the pH of the chlorite solution, and the of from 0.01 to 1.0 moles per liter (M). In other embodi molar mix ratio of persulfate to chlorite are chosen to ments, the concentration of persulfate is from 0.055 to 1.0 generate a product chlorine dioxide solution at a pH of from M. The chlorite is preferably provided by Group I metal 5 to 8 so as to be suitable for application to biological chlorites, more preferably sodium chlorite. The chlorite is Surfaces. present at a concentration of from 0.01 to 1.0 M. In other embodiments, the concentration of chlorite is from 0.01 to 0023. In accordance with another embodiment, the con 0.2 M, and in another embodiment, from 0.01 to 0.03M. centration of persulfate, the concentration of chlorite, the pH of the persulfate solution, the pH of the chlorite solution, and 0018. Both the persulfate and the chlorite solution are the molar mix ratio of persulfate to chlorite are chosen to buffered in accordance with this invention. The persulfate generate a product chlorine dioxide solution at a pH of from solution is preferably buffered by salts selected from citrate 3 to 12 so as to be suitable for application to hard surfaces. salts, phosphate salts, borate salts, and mixtures thereof. The Such surfaces may include porcelain, glass, metal, wood, sodium chlorite solution is preferably buffered by metallic plastic, fabric and the like. hydroxide salts. 0024. The concentration of the chlorite in the chlorite 0019. The persulfate solution is preferably buffered to a solution is preferably kept below 0.2 M, and more preferably pH of from 3 to 9, while the chlorite solution is preferably less that 0.05 M. In particular embodiments the concentra buffered to a pH of from 9 to 12. The pH of each solution tion is from 0.01 to 0.03 M. At higher concentrations of should be tailored in accordance with the molar ratio at chlorite Solution and a molar excess of persulfate Solution which the persulfate and the chlorite are to be mixed, the yields more chlorine dioxide at a faster rate. Chlorine molar concentration of the persulfate and chlorite in their dioxide might be generated too quickly if a highly concen respective solutions, as well as the desired end use of the trate chlorite solution is employed. chlorine dioxide that will be generated. For example, when disinfecting hard surfaces, the pH of a chlorine dioxide 0025 The persulfate oxidizes chlorite without the assis disinfecting Solution employed may be more acidic (for tance of chlorine gas or proton donor Sources (such as strong example on porcelain or ceramic) or alkaline than, for and corrosive acids), metallic catalysts, or costly and com instance, when the chlorine dioxide solution is to be plex electrolytic cells. Preferably, persulfate is the sole employed to treat biological Surfaces, and, thus, the pH of oxidant for chlorite, i.e., in particular embodiments, the each reactant Solution, the concentration of chlorite and reaction mixture is devoid of oxidants other than persulfate. persulfate therein, and the mix ratio of persulfate to chlorite Advantageously, this reaction can take place in the absence may be chosen differently when the resultant chlorine diox of catalysts. ide product is to be used to treat such differing surfaces. 0026. This invention also contemplates the use of certain 0020. The persulfate solution and chlorite solution are excipients chosen according to the desired use of the chlo mixed to achieve a molar ratio of persulfate to chlorite of rine dioxide. These excipients may including functional greater than 2. Thus there is an excess of persulfate. This mix agents, cleaning Surfactants, wetting Surfactants, foaming ratio minimizes the presence of excess chlorite ions which Surfactants, gelling agents, thickening agents, film forming may be corrosive or toxic. The reaction is driven toward agents, Surface conditioning agents, skin conditioning chlorine dioxide formation, minimizing chlorite residuals agents, anticorrosion agent, colorants, fragrances, stabiliz and other chlorine species. In other embodiments, the mix ers, preservatives, abrasives and the like. ratio is preferably greater than 3, in yet others, greater than 0027. The excipients will be employed in amounts com 4, and yet others, greater than 5. mensurate with their use in the prior art. It is preferred that 0021. The reactant solutions are preferably tailored to the excipients be included in the chlorite solution to avoid produce a chlorine dioxide product solution having from 2 their oxidation by persulfate, but stabilizers may be to 300, preferably 10 to 70, and more preferably 20 to 50 employed in the persulfate solution to prevent degradation parts per million chlorine dioxide, by weight, generated of the persulfate compound. US 2007/01 16636A1 May 24, 2007

0028. In accordance with the method disclosed herein, Chlorite Solution chlorine dioxide is generated rapidly upon the mixing of the chlorite solution with the persulfate solution. Generally, 0033) acceptable levels of chlorine dioxide are generated in under seconds. Typically it will be generated in 15 seconds or less. It has been found that, at the mix ratio of persulfate to Ingredient Description Weight % chlorite disclosed, chlorine dioxide is generated very Sodium chlorite chlorite source, 1.35 (0.15M) quickly at low molar concentrations of chlorite, on the order technical grade of less that 0.2M. In accordance with this invention, the decyl glucoside chloride wetting agent 2.O chlorite solution and persulfate solution can be retained (50% solution) separately, transported to the site for chlorine dioxide use, Mystramine Oxide Surfactant 1.5 and mixed at the site to create and use the chlorine dioxide. (30% solution) anticorrosion agent It is contemplated that various types of dispensers could be borate buffer buffer, 10 mM, pH 10 q.S. to 50% employed for this purpose.

EXPERIMENTAL Persulfate Solution Skin Sanitizing Foam 0034) 0029. A chlorine dioxide foam product for use on the skin was produced in accordance with this invention, as follows. An aqueous chlorite and an aqueous persulfate solution were Ingredient Description Weight % produced according to the following: Sodium persulfate persulfate source, 10.75 (0.45M) technical grade Chlorite Solution disodium EDTA stabilizer, prevent O.OS (30% solution) Sodium degradation sodium phosphate buffer, 50 mM, pH 5.5 q.S. to 50% 0030) buffer

Ingredient Description Weight % These solutions were placed in a dual chamber liquid dispenser, and, upon activating the dispenser, the Solutions Sodium chlorite chlorite source, 0.9 (0.05 M) technical grade were mixed in a 1:1 Volume ratio and a foam was produced. Lauryldimonium HP foaming agent, 2O.O At 30 seconds the chlorine dioxide concentration was 55 decylglucoside chloride (30% solution) ppm, and the foam has a pH of 8.5. Polyguaternium-10 skin conditioning agent O.2 borate buffer buffer, 10 mM, pH 10 q.S. to 50% Other Examples 0035). With reference to Table 1 and 2 below, various samples of chlorine dioxide were generated in accordance Persulfate Solution with this invention. Table 1 shows the generation of chlorine dioxide in a system buffered by borate salt to a pH 9.0. Table 0031) 2 shows the generation of chlorine dioxide in a system buffered by phosphate salt to a pH of 7.0. The first row lists the molar concentration of chlorite in a sodium chlorite Ingredient Description Weight % Solution and the molar concentration of persulfate in a sodium persulfate persulfate source, 7.15 (0.3M) persulfate solution. The second row lists the molar ratio of technical grade chlorite to persulfate in a reaction mixture of the sodium cetrimonium chloride Surfactantskin 4.0 chlorite and sodium persulfate solutions. The third, fourth, (30% solution) conditioning agent fifth, and sixth rows list the concentration of chlorine disodium EDTA stabilizer, prevent O.OS sodium degradation dioxide generated from the mixture of sodium chlorite and sodium phosphate buffer, 50 mM, pH 5.5 q.S. to 50% Sodium persulfate (in accordance with columns 1 and 2), at buffer 1 minute, 5 minutes, 15 minutes and 1 hour, respectively.

TABLE 1. These solutions were placed in a dual chamber foaming liquid dispenser, and, upon activating the dispenser, the Seneration of Chlorine Dioxide in Borate Buffer pH 9.0 Solutions were mixed in a 1:1 Volume ratio and a foam was Sodium Sodium Sodium Sodium produced. At 30 seconds the chlorine dioxide concentration Chlorite Chlorite Chlorite Chlorite (0.05M) + (0.02M) + (0.02M) + (0.01M) + was 22 ppm, and the foam has a pH of 5.7. Sodium Sodium Sodium Sodium PerSulfate Persulfate Persulfate Persulfate Hard Surface Disinfecting Spray Composition (0.25M) (0.1M) (0.2M) (0.1M) 0032. A chlorine dioxide spray product for use on hard Molar Ratio 1:5 1:5 1:10 1:10 Surfaces was produced in accordance with this invention, as Chlorite:Per follows. An aqueous chlorite and an aqueous persulfate sulfate Solution were produced according to the following: US 2007/01 16636A1 May 24, 2007

What is claimed is: TABLE 1-continued 1. A method for point-of-use generation of chlorine diox ide comprising the steps of Generation of Chlorine Dioxide in Borate Buffer pH 9.0 providing an aqueous persulfate solution; Sodium Sodium Sodium Sodium providing an aqueous chlorite Solution; Chlorite Chlorite Chlorite Chlorite mixing the persulfate solution and the chlorite Solution at (0.05M) + (0.02M) + (0.02M) + (0.01M) + a molar ratio of persulfate to chlorite of greater than 2. Sodium Sodium Sodium Sodium 2. The method of claim 1, wherein the persulfate solution PerSulfate Persulfate Persulfate Persulfate is buffered to a pH of from 3 to 9. Composition (0.25M) (0.1M) (0.2M) (0.1M) 3. The method in accordance with claim 2, wherein the persulfate solution is buffered by salts selected from citrate Chlorine 46.4 7.5 15.6 5.3 salts, phosphate salts, borate salts, and mixtures thereof. Dioxide (ppm) 4. The method in accordance with claim 1, wherein the (a) 1 min. chlorite solution is buffered to a pH of from 9 to 12. Chlorine 1942 25.9 52.8 11.8 5. The method in accordance with claim 4, wherein the Dioxide (ppm) chlorite solution is buffered by metallic hydroxide salts. (a) 5 min. 6. A method in accordance with claim 1, wherein the Chlorine 690.6 65.8 226.6 32.9 concentration of persulfate in the persulfate Solution, the Dioxide (ppm) concentration of chlorite in the chlorite solution, the pH of (a) 15 min. the persulfate solution, the pH of the chlorite solution, and Chlorine 1350 2O3.9 531.5 113.3 the molar mix ratio of persulfate to chlorite are chosen to generate a product chlorine dioxide solution at a pH of from Dioxide (ppm) 3 to 12 so as to be suitable for application to hard surfaces. (a) 1 hr. 7. A method in accordance with claim 1, wherein the concentration of persulfate in the persulfate solution, the concentration of chlorite in the chlorite solution, the pH of 0036) the persulfate solution, the pH of the chlorite solution, and the molar mix ratio of persulfate to chlorite are chosen to TABLE 2 generate a product chlorine dioxide solution at a pH of from Generation of Chlorine Dioxide in Phosphate Buffer pH 7.0 5 to 8 so as to be suitable for application to biological Surfaces. Sodium Sodium Sodium Sodium Chlorite Chlorite Chlorite Chlorite 8. The method of claim 1, wherein the chlorite solution in (0.05M) + (0.02M) + (0.02M) + (0.01M) + said step of providing a chlorite Solution includes excipients Sodium Sodium Sodium Sodium selected from the group consisting of functional agents, PerSulfate Persulfate Persulfate Persulfate cleaning Surfactant, wetting Surfactant, foaming Surfactant, Composition (0.25M) (0.1M) (0.2M) (0.1M) gelling agents, thickening agents, film forming agents, Sur Molar Ratio 1:5 1:5 1:10 1:10 face conditioning agents, colorants, fragrances, stabilizers, Chlorite:Per sulfate preservatives, abrasives, and mixtures thereof. Chlorine 36.2 5.9 11.3 2.7 9. The method of claim 1, wherein said step of mixing Dioxide (ppm) takes place and the chlorine dioxide is generated in the (a) 1 min. Chlorine 148.9 18.8 48.5 8.0 absence of a catalyst. Dioxide (ppm) 10. The method of claim 1, wherein the persulfate is the (a) 5 min. sole oxidant for the chlorite. Chlorine 439.7 52.8 124.1 2O.S Dioxide (ppm) 11. A method for point-of-use generation of chlorine (a) 15 min. dioxide comprising the steps of Chlorine 2158.4 167.3 437.O 70.1 Dioxide (ppm) providing an aqueous persulfate solution that is buffered (a) 1 hr. to a pH of from 3 to 9 by the presence of buffers Selected from citrate salts, phosphate salts, borate salts, and mixtures thereof; 0037 Thus it can be seen that one or more of the objects of this invention is satisfied by the methods presented herein. providing an aqueous chlorite solution that is buffered to While in accordance with the patent statutes only the best a pH of from to 12 by the presence of buffers selected mode and preferred embodiment of the invention has been from metallic hydroxide salts: presented and described in detail, the invention is not limited mixing the aqueous persulfate solution and the aqueous thereto or thereby. Accordingly, for an appreciation of the chlorite solution to produce chlorine dioxide. scope and breadth of the invention reference should be made to the following claims.