WO2010019491A1

WO2010019491A1 - Methods and composition for making chlorine dioxide on demand

Info

Publication number: WO2010019491A1
Application number: PCT/US2009/053258
Authority: WO
Inventors: William D. Sanderson
Original assignee: Sanderson William D
Priority date: 2008-08-12
Filing date: 2009-08-10
Publication date: 2010-02-18

Abstract

Provided are compositions and methods for making chlorine dioxide on demand using ozone, a metal chlorite and a metal salt.

Description

METHODS AND COMPOSITION FOR MAKING CHLORINE DIOXIDE ON DEMAND

This application claims priority to U.S. Provisional Patent Application Serial No. 61/088,093, filed 12 August 2008, the complete disclosure of which is incorporated herein by reference.

Field of Inventions

The inventions relate to stable solid compositions that produces chlorine dioxide in a continuous stream upon reaction with ozone. The inventions also relate to methods for producing chlorine dioxide on demand using ozone.

Background

Chlorine dioxide is a highly reactive yellowish-green gas that produces useful aqueous solutions in a number of applications such as disinfection, sterilization, and odor control. It is a potent antimicrobial agent, bleaching agent, and as a germicide has found increasing receptivity of its use in municipal and drinking water treatment, cooling towers, and food processing.

Recent regulatory approvals have led to growing acceptance of its use in reducing pathogens in food processing applications such as poultry chill water tanks, beef and pork carcasses washes, and raw agricultural commodities.

Chlorine dioxide has many advantages over traditional chlorine-based biocides due to its higher oxidation potential and greater selectivity towards bacterial cell membranes. However, several drawbacks have limited the implementation of chlorine dioxide where its superior safety and environmental profile would benefit a wide variety of industries.

The biggest disadvantage of using chlorine dioxide is that it must be produced at the-point-of use, i.e. on demand. Chlorine dioxide gas is prohibited from transportation. See 49 CFR 172.101 . It is explosive in air at concentrations of about 10% and has a low threshold limit value (TLV) classification by OSHA of 0.1 ppm to workers.

Chlorine dioxide cannot be compressed and stored, as can chlorine, and aqueous solutions of chlorine dioxide rapidly degrade through evaporation and sun light. Aqueous chlorine dioxide chemistry is highly complex and often unwanted side reactions occur which yield lower and higher valent oxy-chloro species such chloride, chlorite, and chlorate. As a result of these limitations, it must be produced at the-point-of use.

The manufacture and transportation of chlorine dioxide formulations presents serious safety and stability challenges. The precursors for dry formulations are hydroscopic and deliquescent - thus requiring expensive desiccant systems to maintain a low humidity environment (<20%RH) in material handling operations. The active ingredient sodium chlorite is combustible in the presence of organic materials at elevated temperatures. There are maximum allowable limits to the amount of material that can be packaged together in a single package. Furthermore US DOT regulations do not permit the aircraft transport of solid mixtures of activated sodium chlorite (UN 3121 Packing Group I) within the United States.

Chlorine dioxide solid compositions are classified as oxidizers and are thus a fire hazard. They must be specially labeled according to UN and DOT regulations and are subject to shipping and storage restrictions. Example hazard ratings of ingredients in various chlorine dioxide release formulations: Sodium chlorite (UN hazard class 5.1 -oxidizer); sodium dichloroisocyanurate (UN hazard class 5.1 - oxidizer); sodium bisulfate (UN hazard class 8.0 - corrosive solid. This disadvantage is discussed in U.S. patent No. 6,602,442 in column 7, lines 4 - 58.

U.S. patent No. 6,699,404 describes solid chlorine dioxide releasing "massive bodies," which comprise a mixture of granular particulate ingredients where the size of the particles is substantially smaller than the size of the massive body.

The massive body is formed from the mixture of particulate ingredients by compression and is essentially a large tablet. The tablets releases chlorine dioxide when added to water.

U.S. patent No. 6,602,442 describes a "dry composition" comprising lithium hypochlorite, sodium chlorite, and sodium hydrogen sulfate. Although this mixture was found to very soluble and rapidly yield chlorine dioxide upon addition to water, a substantial amount of chlorine gas is undesirably released since chlorine is produced above its solubility in water. See column 2, line 55-56 of this patent. Furthermore, the stability of the dry mixture is limited, especially in high humidity environments. These drawbacks limit the addition of large amounts to water since the excess chlorine production could cause the mixture to "flash".

Currently practiced methods employing liquid-based chlorine dioxide formulations (ie. sodium chlorite solutions or stabilized chlorine dioxide) typically require that the solutions be activated at high concentration, such as 1000 - 3000 ppm, in a smaller container and then diluted to a larger volume of water to yield a desired working concentration 50 - 300 ppm. The high concentration of chlorine dioxide generated in these methods is hazardous and inconvenient to handle. This problem is discussed in U.S. patent No. 6,602,442 at column 7, line 63 to column 8 line 12. Furthermore, if the precursors are added directly to a large volume of water, it was found that the final concentration was unpredictable and significantly below what would be expected if complete conversion of chlorite to chlorine dioxide took place.

Solid-based chlorine dioxide compositions have been reviewed in US 6,699,404, and WO07078838A3 which are incorporated herein by reference. Awareness of the convenience and safety of chlorine dioxide tablets is increasing. However despite the benefits of solid-based chlorine dioxide compositions the biggest drawback is that their use is almost exclusively confined to batch operations of chlorine dioxide production. In applications that require a continuous stream of chlorine dioxide, solid-based chlorine dioxide precursors are usually impractical. While attempts have been made to produce chlorine dioxide using sodium chlorite and ozone, unacceptably low yields and side products have only been produced. Thus, there is a need in the industry for a high yield solid-based composition that is practical for continuous production of chlorine dioxide in either gas or aqueous phase upon reaction with ozone.

Summary

An objective of the inventions is to provide a stable, solid composition that produces chlorine dioxide in a continuous stream in aqueous or gas phase upon reaction with ozone.

Other objects of the inventions include:

Provide a concentrated and stable composition for chlorine dioxide production that is safe for storage and transportation.

Provide a stable dry formulation of chlorine dioxide that does not require individual packaging or wrapping.

Provide continuous production of chlorine dioxide without using acids, chlorine donors, or chemical oxidizers in the formulation.

Provide a highly transportable method of continuously producing chlorine dioxide safely and conveniently at any site.

Provide a simplified method of producing chlorine dioxide using only a single precursor feed stream.

Provide a method of producing a pH neutral solution of chlorine dioxide. Provide a method of producing solutions of chlorine dioxide at a wide range of concentrations, such as for example 0.5 - 1000 ppm, in a single step.

Provide a method of converting existing ozone generators to chlorine dioxide generators

These objectives and other objectives are met by a system comprising a source of ozone and a composition comprising at least one metal chlorite and at least one metal halide, which is free of an oxidizer.

The objectives are also obtained by a method comprising adding a solid composition comprising a metal chlorite and a metal halide to water and adding ozone to the water in the absence of electrolysis, wherein the ozone reacts with the composition to form chlorine dioxide.

Brief Description of the Drawings

Fig. 1 illustrates an apparatus and method for making chlorine dioxide on demand using ozone; and

Fig. 2. illustrates an apparatus and method for making chlorine dioxide on demand using ozone.

Detailed Description

Composition of Dry Chlorite Mixture

The above objectives, and other objectives, are met by a system for producing chlorine dioxide on demand comprising a source of ozone and a composition comprising at least one metal chlorite and at least one metal halide.

The composition for producing chlorine dioxide comprises at least one metal chlorite and at least one metal halide. The metal chlorite is preferably sodium chlorite. The metal chlorite is preferably present in an amount of about 1 % to about 90% by weight. The chlorite is preferably present from about 20% to about 60%. All weight percentages are based on the total weight of the composition unless otherwise stated.

Suitable examples of metal halides include sodium chloride, potassium chloride, lithium chloride, calcium chloride, zinc chloride, and magnesium chloride, sodium bromide, potassium bromide, lithium bromide, calcium bromide, zinc bromide, magnesium bromide. Preferably the metal halide is metal bromide. The metal halide is preferably present in an amount of from about 1 % to about 90% by weight. The metal halide is preferably sodium bromide or sodium chloride and is preferably present from about 10% to about 80%. The metal halide is more preferably present from about 20% to about 60%. The metal halide is preferably present in an amount which increases the yield of chlorine dioxide.

In another embodiment, the composition comprises at least one metal chlorite and an ammonium chloride or ammonium bromide. The ammonium chloride or ammonium bromide is preferably present in an amount from about 5 to about 90% by weight, more preferably about 10 to about 40% by weight.

A pH buffering material can optionally be added to the composition to provide stability and longevity to the produced chlorine dioxide solution. The buffer can be any conventional buffer as desired, but the preferred buffer for the present invention is potassium hydrogen phosphate. The buffer can optionally provide a pH from about 6 to about 9, or more preferably from a pH of about 6.5 to about 8.

The solid composition can be produced in any desired shape or form. Preferably, the solid composition is formed into a tablet. The composition can include inert ingredients, such as fillers, binders, and flow agents. Preferably the binder is a non-organic compound. Most preferably the binder material is a metal salt of sulfate, carbonate, phosphate, or borate. The dry composition is stable and can be readily transported to the site where chlorine dioxide production is desired. For the sake of convenience the composition of the current invention is hereafter referred to as a chlorite-halide mixture (CHM).

Method of Producing Chlorine Dioxide from Chlorite-Halide Mixture

The chlorite-halide mixture of the present invention is formulated free of oxidizing agent. Therefore to release chlorine dioxide, the CHM must be subjected to an oxidizing agent or process. Various oxidizing process can be successfully employed such as electrolysis, ultraviolet light, ozone, hydrogen peroxide (or peroxide radical precursors), potassium monopersulfate, or sulfate free radicals (disclosed by Martin in US application 2006/0293177). The preferred oxidizing process is ozone. Ozone can also be produced by many methods such as corona discharge, ultraviolet light, electrolysis, plasma, or other high energy discharges. The current invention is practiced by corona discharge method although another method would be acceptable. Ozone generators are commercially available and economical for the purpose of producing chlorine dioxide. Ozone generators using a hybrid corona discharge ozone system as discussed in patent numbers 6,426,053; 6,342,154, and 6,192,91 1 are acceptable devices to practice the invention.

Chlorine dioxide is released by subjecting the chlorite-halide mixture to a steady stream of ozone. Ozone is a highly reactive gas so it must be produced on-site. The ozone can be injected into a circulating loop of a solution of dissolved CHM or be diffused directly into a container of CHM solution.

A surprising result is that chlorine dioxide can be rapidly produced using ozone according to the present invention. This investigator could not find any reference in the academic literature or published patent prior art to a method of producing chlorine dioxide from chlorite using a combination of ozone and a halide salt. While there is a prior art reference that teaches producing chlorine dioxide through a combination of electrolysis and ozonation. See US Patent #6,814,877, which is incorporated herein for reference. This patent discusses producing sodium chlorite through the electrolysis of the hypochlorite ion and ozone. The sodium chlorite is then further oxidized by ozonation in combination with required electrolysis to produce chlorine dioxide. Injection or addition of sodium chlorite into the system and the addition of a metal salt are not disclosed.

Literature references to chlorite ion reactions with ozone show the stoichiometric formation of chlorate. See WJ. Masschelein (1979), "Chlorine Dioxide" (page 36):

NaCIO2 + 03 = NaCIO3 + 02

In other words, the literature teaches away from the concept of using ozone to produce chlorine dioxide.

The reactions in the present inventions are very fast and the conversion ratio of chlorite to chlorine dioxide surprisingly approaches 100%. The present inventions are able to achieve a rapid and high yield of chlorine dioxide by reacting ozone with the chlorite-halide mixture, i.e the addition of the metal halide to the chlorite provides unexpectedly high yields of chlorine dioxide. This surprising outcome identifies a novel method for continuous generation of chlorine dioxide.

The exact chemical mechanism is not fully understood but, without being limited to any theory, is thought to be a two stage reaction. The halide salt is first oxidized to hypohalous acid by the high energy ozone molecule, which reaction in other mechanisms such as described in U.S. Patent No. 5,603,840 is known.

Subsequently, the produced hypohalous acid then converts the chlorite ion to yield chlorine dioxide: 2NaCIO2 + HOX = 2CIO2 + NaX + NaOH.

Figure 1 shows a method of injecting ozone into a solution of the chlorite mixture and was also used in the Experimental Section. Oxygen (1 ) from a compressed cylinder (Praxair) was flowed into an (2) Ozone Generator (Ozone Solutions Model OZV-8) at 1 .5 liters per minute. The produced ozone was diffused into the solution (4) by a diffuser stone (3). The small ozone bubbles (5) dissolved in the solution and initiated the production of chlorine dioxide. Chlorine dioxide was measured by a Hach Model DR-2500 spectrometer at 443 nm.

Figure 2 shows a closed loop of circulating chlorite-halide mixture solution (8). Concentrated chlorite-halide mixture solution (12) is injected into the closed loop (6) by a metering pump (9). Ozone is produced by an ozone generator (1 1 ) and injected through a Mazzei venturi injector (10). The circulation pump (7) then pumps the chlorine dioxide rich solution to the top of the container where it mixes with the bulk of the chlorite-halide mixture solution (8).

Experimental Section

Example 1

In a 2L beaker the following was added to 2L water:

Sodium chlorite 4 gram

Sodium bromide 2 gram

Potassium hydrogen phosphate 5 gram pH = 6.94

Ozone generator Model OZV-8: ozone output 8 grams per hour (with bottle oxygen).

O₂ flow = 1.5 liters/min Ozone delivered at roughly 1 .2 grams per hour

Chlorine dioxide produced = 0.812 grams Sodium chlorite conversion ratio = 68.25% Time (min) Concentration (ppm) of chlorine dioxide

1 105

2 177

3 223

4 276

5 310

6 344

6.5 361

7 362

8 385

9 397

10 407

1 1 406

^**Example 3 - Comparative

NaCIO₂ 4 gram

NaCI 4 gram

KHP 5 gram

pH = 6.87

Time Concentration

5 min 358

7 min 428

8 min 441

Experimental Results

^**Example 1 and 3 clearly demonstrates that chlorine dioxide is immediately produced when ozone is bubbled through the mixed chlorite halide solution. The experimental rate of chlorine dioxide production is greater in the beginning of the run, ie. 1 to 3 minutes. This is due to chlorine dioxide lost by diffusion. As the concentration of CIO₂ rises, the amount lost by diffusion to atmosphere increases geometrically. Therefore, the theoretical rate of chlorine dioxide production should be constant and the conversion ratio of sodium chlorite to chlorine dioxide would be higher and approach 100%.

While the claimed invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made to the claimed invention without departing from the spirit and scope thereof.

Claims

I claim:

1 . Method for generating chlorine dioxide on demand comprising: adding a solid composition comprising at least one metal chlorite and at least one metal halide to water; and adding ozone to the water in the absence of electrolysis, wherein the ozone reacts with the composition to form chlorine dioxide.

2. Method according to claim 1 , wherein the solid composition is free of an oxidizer.

3. Method according to claim 1 , wherein the metal chlorite comprises sodium chlorite.

4. Method according to claim 1 , wherein the metal chlorite is present in an amount of from 20% to 60%, based on the total weight of the composition.

5. Method according to claim 1 , wherein the metal halide comprises at least one of sodium chloride, potassium chloride, lithium chloride, calcium chloride, zinc chloride, magnesium chloride, sodium bromide, potassium bromide, lithium bromide, calcium bromide, zinc bromide, or magnesium bromide.

6. Method according to claim 1 , wherein the metal halide comprises metal bromide.

7. Method according to claim 1 , wherein the metal halide is present in an amount of from 10% to 80%.

8. Method according to claim 1 , wherein the metal halide is present in an amount which increases the yield of chlorine dioxide.

9. A system for generating chlorine dioxide on demand comprising: a source of ozone; and a solid composition comprising at least one metal chlorite and at least one metal halide, wherein the composition is free of an oxidizer.

10. A system for generating chlorine dioxide comprising: a source of ozone; and a solid composition comprising at least one metal chlorite and at least one of ammonium chloride or ammonium bromide, wherein the composition is free of an oxidizer