Patent Application
20130168260
The present invention relates to a method for forming hypohalous acid and further relates to at least a single liquid chamber electrolytic device for generation of pH-controlled hypohalous acid aqueous solutions for disinfectant applications. This method and device has the advantage whereby the pH of the solution is regulated and optimized. Such a method and device is particularly useful for preparing hypochlorous acid. Specifically, the resultant effluent exiting the device, which may be HClO in aqueous solution, is suitable for use in hand sanitizers.
Others have attempted to produce hypohalous acids using a variety of methods. For example, one method of producing low-chloride aqueous solutions of hypochlorous acid (HClO) includes spraying fine droplets of aqueous alkali metal hydroxides or alkaline earth metal hydroxides in a reactor dryer with chlorine gas to make hypochlorous acid gas and solid metal chloride. Creating the spray of fine droplets requires high pressures, and thus, a high energy input. The hypochlorous acid gas is then condensed along with the water vapor, requiring refrigeration equipment to achieve condensing temperatures, to produce concentrated hypochlorous acid. Disadvantages of this process include difficulty in handling the solid salt, high chlorine ratios, and energy inefficiency.
Another process which shares the aforementioned disadvantages for making aqueous hypochlorous acid includes spraying a solution of alkali metal hydroxide into a chlorine atmosphere resulting in HClO vaporization and a dry solid salt. With this process, aqueous HClO solution is produced by absorption of the HClO in water as opposed to the condensation of the HClO and water vapor.
Still another process uses an organic solvent to extract HClO from a brine solution. This process suffers from a need to further remove the HClO from the organic solvent to produce an aqueous HClO solution, a need to remove residual solvent from the brine solution, and undesirable reactions of HClO with the organic solvent.
Despite the several known processes for producing hypochlorous acid, there remains a need for a quick, safe, and efficient process for producing hypochlorous acid solutions suitable for disinfectant applications. Therefore, methods which do not require handling of solid salt by-products or chlorine gas input have been sought, as have more energy efficient methods been desired which do not require large heating/cooling cycles or high pressure on the liquid feed.
One method for producing hypochlorous acid solutions suitable for use as a disinfectant in food processing describes controlling the hypochlorite/hypochlorous acid balance of a stream by mixing liquid acid with a pressurized carrier stream which has been chlorinated by the addition of a chlorination agent. By decreasing the pH of the liquid stream, the relative ratio of hypochlorous acid to hypochlorite of the liquid stream is increased. This process allowed for the manipulation of the pressurized streams in order to produce specific concentrations of hypochlorous acid providing greater control over the reaction process; however this process necessitates the introduction of a gaseous species other than air at preferred elevated temperatures.
Electrolytic cells have been utilized in prior inventions as related to production of acidic liquids. One such described invention provides an electrolytic cell and process for the production of hydrogen peroxide solution and hypohalide by electrolysis, whereby hypohalide and hydrogen peroxide are produced in an anode chamber and a cathode chamber, respectively. The invention specifically relates to a seawater treatment method where both the desired products hydrogen peroxide and hypochlorous acid are reintroduced into the seawater to efficiently treat the water. However, the invention necessitates the use of a dual chamber device, and hydrogen peroxide would not be suitable for a daily hand sanitizing formulation.
Electrochemical devices have also been used previously to produce strong acid sterilizing liquids. One such device for use in water treatment facilities utilizes an apparatus for generating and dispensing a strong acid sterilizing liquid which contains hypochlorous acid at low concentrations and whose pH is 3 or less. In that apparatus, salt water is passed through a channel formed between a positive electrode plate and a negative electrode plate disposed to face opposite surfaces of a barrier membrane in which DC voltage is applied between the electrodes to electrolyze the salt water. The barrier membrane prevents the mixing of the products at the positive electrode and the products at the negative electrode. Acid liquid containing hypochlorous acid can be obtained by taking the aqueous solution flowing through the space between the barrier membrane and the positive electrode out of the electrolytic cell.
In another method directed toward obtaining a low pH aqueous acid solution, also using a two-chamber-type electrolytic cell device, a strong acid water containing a reduced amount of chloride for use in sterilization is produced whereby chloride ions are oxidized at the anode. With this apparatus, as with the previously described invention, the end product is desired to have a pH less than 3 and therefore is not suitable for a daily hand sanitizing formulation.
Chlorination is long known as a method for killing undesirable microorganisms. Chlorine may be provided in multiple forms including chlorine gas (Cl2), a relatively cheap and highly effective antimicrobial agent; however, it is also a highly toxic and corrosive gas. Hypochlorites, such as NaOCl or Ca(OCl)2, are a much safer alternative, but are considerably more expensive than gaseous chlorine. Finally, hypochlorite solutions (i.e., bleach) may also be utilized; however, these are rarely used in large scale applications because they are bulky and hazardous. Regardless of the chlorine source, hypochlorous acid (HClO) and the hypochlorite ion (OCl−) are the final desirable antimicrobial products. In any application for a hand sanitizer, however, hypochlorous acid is preferred for safe use in contact with human skin.
Beyond safety, the bactericidal activity of an aqueous solution of hypochlorous acid needs to be considered, particularly for use in disinfectant applications. The composition of an aqueous solution of hypochlorous acid varies with the pH of the solution because the form of chlorine compounds dissolved in the aqueous solution varies with pH. At low pH, typically above pH 3, HClO is the predominant form, while at high pH, typically above pH 8, OCl− predominates. The HClO form is about 80 times more effective than OCl− for killing microorganisms because HClO crosses cell membranes easier than the hypochlorite ion.
When the pH of an aqueous solution of hypochlorous acid is 8 or more, or the aqueous solution of hypochlorous acid is alkaline, hypochlorous acid ions (ClO−) having fairly low bactericidal activity are mainly present in the aqueous solution. Thus, the bactericidal activity of an alkaline aqueous solution of hypochlorous acid is fairly low.
When the pH of aqueous solution of hypochlorous acid is 7 or less, or the aqueous solution of hypochlorous acid is acidic, the amount of hypochlorous acid (HClO) having a bactericidal activity 10 to 100 times larger than that of hypochlorite ions is larger than the amount of hypochlorite ions. Thus, the bactericidal activity of an acidic aqueous solution of hypochlorous acid is high.
When the pH of an aqueous solution of hypochlorous acid is between 3 and 5.5, substantially 100% of the chlorine compound dissolved in the aqueous solution is hypochlorous acid. Thus, the bactericidal activity of the aqueous solution of hypochlorous acid becomes even higher.
When the pH of an aqueous solution of hypochlorous acid is 3 or less, a part of the chlorine compound dissolved in the aqueous solution becomes chlorine gas (Cl2) having yet higher bactericidal activity than that of hypochlorous acid. Thus, the bactericidal activity of the aqueous solution of hypochlorous acid becomes even higher. However, human skin may be damaged by application of acid sterilizing liquid of such a low pH.
It would be desirable to control the pH of the chlorinated solution to increase the antimicrobial effectiveness of the chlorination process and also to ensure safety for uses such as hand sanitizer. Previous processes and systems for adjusting the pH of a water stream have been described. These processes include using carbon dioxide by injection into water by a direct gas feed, or bubbler; or in another method for injecting carbon dioxide into water by aspirating the carbon dioxide into a stream of water using a Venturi-type eductor. It is, however, difficult to control the efficiency of the carbon dioxide gas usage and these processes are inherently inefficient.
In the present device, an aqueous solution containing halide ions is introduced into an electrolytic device for generation of pH-controlled hypohalous acid aqueous solutions, whereby at least a single liquid chamber may be utilized in which reactions are taking place at the interface between the each of the electrodes and the electrolyte solution to produce an effluent of HClO in aqueous solution. As reactions are taking place in the presence of excess water, the reactions occurring in the single liquid chamber release an effluent which may be monitored for pH, a desired pH range between about 4 and about 9. This method and device has an advantage in that storage of gaseous species, such as chlorine gas, is not needed. Also, the source electrolyte is economical and safe for handling, while the end product may be directly used for disinfectant purposes at a controlled pH level suitable for use as a hand sanitizer without irritation or damage.
More specifically, the present invention provides an electrolytic device for the generation of hypohalous acid in aqueous solutions, the device comprising: a single liquid chamber having an inlet for receiving an aqueous solution containing halide ions, the single liquid chamber having an exterior wall and a solid anode contained within the single liquid chamber providing for the oxidation of the halide ions to provide an aqueous solution of hypohalous acid; and a gas permeable cathode forming at least a portion of the exterior wall of the single liquid chamber, the cathode providing for the reduction of oxygen to provide hydroxyl ions within the single liquid chamber to mix with the hypohalous acid produced at the anode, the cathode having a hydrophobic surface for receiving oxygen from outside the single liquid chamber and a hydrophilic surface in contact with the electrolyte solution allowing for reduction of dioxygen.
Further, the present invention provides an electrolytic device for the generation of hypohalous acid in aqueous solutions, the device comprising: an anolyte chamber having an inlet for receiving an aqueous solution containing halide ions, the anolyte chamber having an exterior wall and a solid anode contained within the anolyte chamber providing for the oxidation of the halide ions to provide an anolyte effluent of hypohalous acid in aqueous solution; a catholyte chamber having an inlet for receiving an aqueous electrolyte, wherein the catholyte chamber is defined by at least one exterior wall or portion thereof comprising a gas permeable cathode, the cathode having a hydrophobic surface for receiving oxygen from outside the catholyte chamber and a hydrophilic surface allowing for reduction of dioxygen; and an ionomeric membrane for partitioning the anolyte chamber from the catholyte chamber; wherein the anolyte chamber further includes an outlet including a pH control for determining and regulating the pH of the exiting anolyte effluent to between about 4 and 9.
The present invention further provides a method for the generation of hypohalous acid comprising: oxidizing halide ions in the presence of water within a single liquid chamber to form an aqueous solution of hypohalous acid; feeding oxygen through a gas permeable cathode to reduce the oxygen in the presence of water to form hydroxyl ions, wherein the gas permeable cathode forms at least a portion of the exterior wall of the single liquid chamber; mixing the solution containing the hydroxyl ions in an amount sufficient to complete the electrical circuit within the device and to produce hypohalous acid; determining the pH of the hypohalous acid to ensure that the pH is between about 4 and 9; and removing the hypohalous acid.
In addition, the present invention further provides a method for the generation of hypohalous acid comprising: oxidizing halide ions in the presence of water within an anolyte chamber to form an anolyte effluent containing hypohalous acid; feeding oxygen through a gas permeable cathode to reduce the oxygen in the presence of water to form a catholyte effluent containing hydroxyl ions, wherein the gas permeable cathode forms at least a portion of an exterior wall of a catholyte chamber; mixing the hydroxyl ions in an amount sufficient to complete the electrical circuit within the device to produce hypohalous acid; controlling the pH of the hypohalous acid to ensure that the pH is between about 4 and 9; and removing the hypohalous acid.
By way of example and to make the description more clear, reference is made to the accompanying drawings in which:
Examples of the process of the invention for the production of hypohalous acid in aqueous solution will be described hereinafter, but the invention should not be construed as being limited thereto. One embodiment of the invention provides an electrolytic device 1 for the production of pH-regulated hypohalous acid aqueous solutions in a single liquid chamber as shown in schematic diagram
One representative form of an electrolytic device for the generation of hypohalous acid is shown in the cross-sectional view of
The single liquid chamber 12 has a single liquid chamber exterior wall 32 and a solid anode 20 contained within the single liquid chamber 12 providing for the oxidation of the halide ions to produce hypohalous acid in aqueous solution. Alternatively, the solid anode 20 could be the wall, or a portion thereof, of the container, as it is not necessary that the anode be immersed fully in the electrolyte.
The solid anode 20 used in the invention may be, for example, a dimensionally stable anode (DSA), commercially available from a supplier such as De Nora Tech.
The gas permeable cathode 22 forms a portion of the single liquid chamber exterior wall 32 and provides for the reduction of oxygen to provide hydroxyl ions in solution within the single liquid chamber which will then mix with the products of the anode. The cathode, having a hydrophobic surface for receiving oxygen from outside the single liquid chamber 12 and a hydrophilic surface allowing for reduction of dioxygen, used for this invention may be, for example, a gas diffusion electrode (GDE), commercially available from various suppliers including BASF Fuel Cell, Inc., containing high area carbon and high area Pt (platinum) as the electrocatalyst. The use of an electrocatalyst is desired to reduce the overall power consumption of the electrolytic device by reducing the overvoltage required to reduce dioxygen to water. Other electrocatalysts, such as certain metals and oxides including species derived from the pyrolysis of certain organic materials, may be used as well, and are generally to be used in porous form. Alternatively, the catalyst may be supported on a plate, metal gauge, sintered powder or sintered metal fiber of a corrosion-resistant material such as stainless steel, zirconium, silver and carbon. By forming a hydrophobic sheet on the side of the cathode opposite the single liquid chamber, access of gas to the reactive surface can be enhanced.
In one alternative, the exterior of the single liquid chamber 12 as defined by the gas permeable cathode 22 may be exposed to atmospheric air. In another embodiment, as shown in
Within the single liquid chamber, the products of the reactions at the interfaces between the solid anode 20 and the gas permeable cathode 22 combine to yield an exiting effluent hereby also referred to as a mixed effluent.
In an example whereby the hypohalous acid produced is hypochlorous acid, and the halide ions are chloride ions, anodic oxidation takes place in the single liquid chamber 12 to produce HClO via the oxidation of chloride ion:
Cl−+H2O→HClO+2e−+H+
While in the presence of water, the chlorine gas Cl2 (which forms first) instantaneously transforms to HClO yielding results corresponding to the above reaction. The gas permeable cathode 22 is responsible for the reduction of dioxygen to water according to this equation:
O2+2H2O+4e−→4OH−
The electrochemical reactions occur at or near the interfaces between the electrodes and the electrolyte solution, not in the aqueous stream. The products are all water soluble.
The single liquid chamber 12 further includes an outlet 28, through which the exiting mixed effluent leaves the single liquid chamber 12 through single liquid chamber exterior wall 32, thereafter, the exiting effluent passes through a pH sensing electrode or pH meter, denoted in
In the embodiment as depicted in
Another representative form of an electrolytic device for the generation of hypohalous acid in the present invention is shown in the three-dimensional view of
As with the embodiment described in
It is also possible, as with the device in
As with the embodiment described in
As with the single liquid chamber electrolytic cell devices of
In this dual chamber configuration, the gas permeable cathode 322 can be positioned such that the catholyte chamber 314 has at least one wall that includes at least, in part, the gas permeable cathode 322. The cathode has a hydrophobic surface for receiving oxygen from outside the catholyte chamber 314 and a hydrophilic surface allowing for reduction of dioxygen and for maintaining the aqueous-based catholyte effluent within the catholyte chamber 314 of the electrolytic device 300.
Furthermore, the cell as shown in
Separate inlets for feeding into the anolyte chamber 312 and catholyte chamber 314 are maintained by inlet 318 and inlet 326 respectively. While there are many ways to accomplish feeding the cell, it may be viewed as depicted in
In the dual chamber embodiment of the invention as shown in
Cl−+H2O→HClO+2e−+H+
While in the presence of water, chlorine gas Cl2 (which forms first) instantaneously transforms to HClO yielding results corresponding to the above reaction. Sodium cations (Na+) may pass from the anolyte chamber 312 through the membrane 344 into the catholyte chamber 314. The hydrophilic side of the gas permeable cathode 322 in the catholyte chamber 314 is responsible for the reduction of dioxygen to water according to this equation:
O2+2H2O+4e−→4OH−
The electrochemical reactions occur at or near the interfaces between the electrodes and the electrolyte solution, not in the aqueous stream. The products are all water soluble. In this dual liquid chamber device, the sodium cations may migrate through the membrane 344 from the anolyte chamber 312 to the catholyte chamber 314 with minimal electrical resistance. In the catholyte chamber 314, the sodium cations and hydroxyl groups remain as such dissolved in water to yield the catholyte effluent.
In an alternative cylindrical embodiment not shown, drawn similarly to the single chamber device concept shown in
In the embodiment of the invention as depicted in
The catholyte chamber 314 may contain unreacted aqueous solution, e.g., water and/or reacted catholyte. The electrolytic device further includes an outlet 346 for releasing reacted catholyte effluent remaining in the catholyte chamber 314. It will be appreciated that any reacted catholyte effluent will be alkaline in nature. A valve 348 regulates flow of the catholyte effluent through outlet 346 exiting from the catholyte chamber; thereafter the exiting catholyte is mixed with the exiting anolyte effluent to form a mixed effluent of higher pH than of the anolyte effluent alone. The mixed effluent may be measured with pH sensing device or pH meter 334. The pH control, which may also include a computer controlled servo, makes it possible to regulate the flow of the exiting liquid which passes through valve 336 to be in the desired range of pH between about 4 and 9. In practice, the pH meter 334 placed at the exit stream measures the pH of the exiting effluent. If the exiting effluent is too acidic, valve 348 may be opened to allow catholyte to flow also, thereby, introducing the alkaline solution to the exit stream. Repeated adjustments to regulate the catholyte effluent flow to combine with the effluent of the anolyte released may be made as necessary until the exiting solution reaches the desired pH range between about 4 and 9.
Further, the pH may be controlled by recirculating the anolyte or the mixed anolyte and catholyte effluent through a recirculator 338 back into inlet 318 for reintroduction into the anolyte chamber 312. As depicted in
Whereas
In all embodiments, the electrolytic cell 10, 100, 200, 300 is preferably made of a glass lining material, carbon, or corrosion-resistant titanium, stainless steel or PTFE resin from the standpoint of durability and stability.
Examples of the process of the invention for the production of HClO solution will be described hereinafter, but the invention should not be construed as being limited thereto.
As shown experimentally in the laboratory of the assignee, one embodiment of a single liquid chamber device of the type described in
In the present device, a method for the generation of hypohalous acid comprising oxidizing halide ions in the presence of water within a single liquid chamber to form an anolyte effluent is achieved. On the cathode side, oxygen is being fed through, or in the case of utilizing a pump being forced through, a gas permeable cathode to reduce the oxygen in the presence of water to form hydroxyl groups. In this device the gas permeable cathode forms at least a portion of an exterior wall of the single liquid chamber. The step of mixing the hydroxyl groups in an amount sufficient to complete the electrolyte circuit within the device to produce hypohalous acid is achieved. The pH may be determined by a pH meter and the hypohalous acid may be removed from the electrolytic device. Control of pH may be attained by adjusting the current to the circuit as applied by the DC constant current power or by adding a buffering agent to the halide aqueous feed. Desired range for use as hand sanitizer is pH between about 4 and 9. The step of feeding oxygen to the gas permeable cathode may include delivering oxygen from a gas compartment, wherein the portion of the exterior wall of the single liquid chamber comprised of the gas permeable cathode is included in the gas compartment. Alternatively, the step of feeding oxygen to the gas permeable cathode may include exposing the hydrophobic exterior of the gas permeable cathode to atmospheric air.
A method of this invention utilizing a two liquid chamber electrolytic device for the generation of pH-controlled hypohalous acid aqueous solutions, such as HClO in aqueous solution, is achieved. The method includes, on the anode side, oxidizing halide ions in the presence of water within an anolyte chamber to form an anolyte effluent containing hypohalous acid. On the cathode side, oxygen is fed through a gas permeable cathode to reduce the oxygen in the presence of water to form a catholyte effluent containing hydroxyl groups, wherein the gas permeable cathode forms at least a portion of an exterior wall of a catholyte chamber. The hydroxyl groups are mixed in an amount sufficient to complete the electrolyte circuit within the device to produce hypohalous acid. This device allows for controlling pH of the hypohalous acid to ensure that the pH is between about 4 and 9. Determining the pH of the hypohalous acid may include use of a pH meter. The hypohalous acid may be removed from the electrolytic device.
The pH may be further controlled and regulated in the two liquid chamber electrolytic device, for example, by mixing the exiting anolyte and catholyte effluents in an amount sufficient to increase the pH of the hypohalous acid to ensure that the pH is between about 4 and 9. The method further comprises the step of determining the pH after mixing the exiting anolyte and catholyte effluents, wherein the step includes the use of a pH meter. This method is advantageous in that the pH of the hypohalous acid produced may be controlled to ensure that the pH is between about 4 and 9 before removing the hypohalous acid for use as end product.
Regulating the pH of the hypohalous acid produced by the two liquid chamber electrolytic device may further be accomplished by recirculating the flow of the hypohalous acid back into the anolyte chamber if the pH of the hypohalous acid is above pH 9; wherein the method further comprises the step of determining the pH of the hypohalous acid after recirculating the flow of the hypohalous acid back to the anolyte chamber, wherein the step includes the use of a pH meter.
In another embodiment, it will be appreciated that the user could also regulate the pH of the hypohalous acid produced by the dual liquid chamber of the electrolytic device if the pH is below 4 alternatively by (1) recirculating the flow of the hypohalous acid back to the anolyte chamber where the input from the feed may also be altered of buffered or (2) closing off the valve 354 shown in
The step of feeding oxygen to the gas permeable cathode may include delivering oxygen from a gas compartment, wherein the portion of the exterior wall of the catholyte chamber comprised of the gas permeable cathode is included in the gas compartment. Alternatively, the step of feeding oxygen to the gas permeable cathode may include exposing the hydrophobic exterior of the gas permeable cathode to atmospheric air.
The method and device of this invention further has the advantage in that storage of gaseous species, such as chlorine gas, is not needed. Also, the source electrolyte is economical and safe for handling, while the end product may be directly used for disinfectant purposes at a controlled pH level suitable for use as a hand sanitizer without irritation or damage to human skin.
In light of the foregoing, it should thus be evident that the process of the present invention, providing a device and method for producing hypohalous acid in aqueous solution with controlled pH, substantially improves the art. While, in accordance with the patent statutes, only the preferred embodiments of the present invention have been described in detail hereinabove, the present invention is not to be limited thereto or thereby. Rather, the scope of the invention shall include all modifications and variations that fall within the scope of the attached claims.
This application is a divisional application of U.S. patent application Ser. No. 12/243,457, filed Oct. 1, 2008, the disclosure of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12243457 | Oct 2008 | US |
| Child | 13778710 | US |
