Device for producing an aqueous chlorine dioxide solution

Details Device for producing an aqueous chlorine dioxide solution Device for producing an aqueous chlorine dioxide solution

2000-06-27

2004-07-20

Warden, Sr., Robert J. (Department: 1744)

Chemical apparatus and process disinfecting, deodorizing, preser

Physical type apparatus

Including gas generating means

C422S120000, C222S003000, C252S187210, C423S477000

Reexamination Certificate

active

06764661

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to apparatus and methods for producing aqueous chlorine dioxide solutions, and particularly to such apparatus and methods that utilize dry chemicals that react to form chlorine dioxide when exposed to water.
Chlorine dioxide is an excellent disinfectant and oxidizer with bleaching, deodorizing, bactericidal, viricidal, algicidal and fungicidal properties. It is frequently used to control microorganisms on or around foods because it destroys the microorganisms without forming byproducts that pose a significant adverse risk to human health, e.g., chloramines and chlorinated organic compounds. Chlorine dioxide is an effective antimicrobial agent at a concentration as low as 0.1 ppm and over a wide pH range. It is thought to penetrate cell walls and cell membranes and react with vital amino acids in the cytoplasm of the cell to kill the organism.
Unfortunately, chlorine dioxide is not stable during storage and can be explosive at high concentrations. As a result, chlorine dioxide gas is not produced and shipped under pressure. It must generally be generated on site using conventional chlorine dioxide generators or other means of generation. Conventional chlorine dioxide generation can be carried out in an efficient manner in connection with large-scale operations such as those in pulp and paper or water treatment facilities. In other applications, however, generating chlorine dioxide on site is not a good option. Conventional on-site chlorine dioxide generation can be costly, cumbersome and difficult because of the need for a generator and the need to handle the generator and the chemicals associated with the generation process.
Chlorine dioxide can also be generated by combining chlorite anions and acid in an aqueous solution. Typically, an acid is added to a solution containing in the range of from about 0.01 to about 32 percent by weight sodium chlorite and having a pH in the range of from about 8 to about 13. The acid can be any acid capable of lowering the pH of the solution to a level below about 7. For example, when approximately 10 grams of citric acid powder are added to an aqueous solution containing approximately 3.35% by weight sodium chlorite, the pH of the solution is lowered to about 2.9 and a solution containing approximately 7% by weight chlorine dioxide is formed.
A solution of a metal chlorite and water wherein the pH of the solution is maintained at 8 or above is sometimes referred to as a stabilized chlorine dioxide solution. Unfortunately, stabilize chlorine dioxide solutions are of limited use if they are needed at remote locations because of the difficulty and expense associated with handling and shipping the solutions. Also, in order to activate a “stabilized” chlorine dioxide solution, the pH of the solution must be lowered to below 5, typically to a range of from about 2 to about 3. Although lowering the pH of the solution to such a level can be done on site, it is not typically a good alternative because of the danger associated with handling acids manually (e.g., the danger associated with inadvertent skin contact and inhalation of acid vapors).
In order to avoid the difficulty of using conventional chlorine dioxide generators, the expense associated with handling and shipping stabilized chlorine dioxide solutions and related precursor solutions and the dangers associated with activating chlorine dioxide solutions, dry compositions containing chemicals (e.g., sodium chlorite and acid) that react to form chlorine dioxide when placed in water have been developed. The compositions can be easily shipped to remote locations in dry form. The necessary water can be merely added on site. For example, in an application wherein a disinfectant solution is needed to clean surfaces, a dry composition containing a metal chlorite and an acid can be mixed with water on site which causes the components to react and produce an aqueous chlorine dioxide solution. The solution is then used to disinfect the surfaces. The aqueous chlorine dioxide solution is produced (chlorite anion is converted to chlorine dioxide) according to the following equation:
5ClO
2
−
+5H
+
→4ClO
2
+HCl+2H
2
O
Dry compositions for generating chlorine dioxide solutions are known in the art. For example, U.S. Pat. No. 2,022,262, issued to White on Nov. 26, 1935, discloses stable stain-removing compositions made from a dry mixture of water-soluble alkaline chlorite salt, an oxalate and an acid. U.S. Pat. No. 2,071,091, issued to Taylor on Feb. 16, 1937, discloses the use of chlorous acid and chlorites to kill fungi and bacterial organisms by exposing the organisms to the compounds at a pH of less than about 7. The patent also discloses using dry mixtures of chlorites and acids to produce stable aqueous solutions useful as bleaching agents. U.S. Pat. No. 2,482,891, issued to Aston on Sep. 27, 1949, discloses stable, solid, substantially anhydrous compositions comprising alkaline chlorite salts and organic acid anhydrides which release chlorine dioxide when contacted with water.
Canadian Patent No. 959,238, issued to Callerame on Dec. 17, 1974, discloses using two water-soluble envelopes, one containing sodium chlorite and one containing an acid, to generate chlorine dioxide. The envelopes are placed in water and the sodium chlorite and acid dissolve in the water and react to produce a chlorine dioxide solution. U.S. Pat. No. 2,071,094, issued to Vincent on Feb. 16, 1937, discloses deodorizing compositions in the form of dry briquettes formed of a mixture of soluble chlorite, an acidifying agent, and a filler of relatively low solubility. Chlorine dioxide is generated when the briquettes contact water.
U.S. Pat. No. 4,585,482, issued to Tice et al. on Apr. 29, 1986, discloses a long-acting biocidal composition comprising a microencapsulated mixture of chlorite and acid that when added to water releases chlorine dioxide. The primary purpose of the microencapsulation is to provide for hard particles that will be free flowing when handled. The microencapsulated composition also protects against water loss from the interior of the microcapsule. The microcapsules produce chlorine dioxide when immersed in water. Unfortunately, the microcapsules release chlorine dioxide relatively slowly and are therefore not suitable for applications that require the preparation of chlorine dioxide on a relatively fast basis.
PCT Application PCT/US98/22564 (WO 99/24356), published on May 20, 1999, discloses a method and device for producing chlorine dioxide solutions wherein sodium chlorite and an acid are mixed and enclosed in a semi-permeable membrane device. When the device is placed in water, water penetrates the membrane. The acid and sodium chlorite dissolve in the water and react to produce chlorine dioxide. The chlorine dioxide exits the device through the membrane into the water in which the device is immersed producing a chlorine dioxide solution that can be used as an anti-microbial solution or for other purposes. The primary disadvantage of the disclosed device and method is that ambient moisture can penetrate the semi-permeable membrane and initiate the reaction prematurely.
In general, the prior art devices and methods using membranes are susceptible to premature activation by water or water vapor and therefore have a reduced shelf life unless sufficient steps are taken to protect the devices from exposure to ambient moisture or water. Such devices and methods are typically slow to interact with water and produce the desired chlorine dioxide. Also, in order to comply with U.S. Department of Transportation and other regulations, many prior art devices require that special and sometimes burdensome handling and shipping procedures be utilized in connection with the devices. For example, if sodium chlorite and acid are packaged together, certain restrictions may apply.
As a result, there is a need for a device for producing an aqueous chlorine dioxide solution that has an extended shelf life compared to prior art devices, th

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