Electrolyzer for electrochlorination process and self-cleaning electrochlorination system

Abstract

The present invention relates to a chlorination electrolyzer comprising a housing with an inlet and an outlet suitable for the circulation of brine and at least one pair of bipolar electrodes positioned opposite each other in said housing. The electrolyzer is characterized in that each of said at least one pair of bipolar electrodes comprises a valve metal substrate, an active coating comprising at least one layer of a catalytic composition comprising ruthenium and titanium deposited on said substrate, and a top coating comprising at least one layer of a composition comprising an oxide of tantalum, niobium, tin or a combination thereof deposited on said active coating. The present invention also relates to a self-cleaning electrochlorination system comprising such a substrate, a method for its manufacture, its use in normal salinity and low salinity pools for the disinfection of water via hypochlorite, and a method for the disinfection of water via hypochlorite.

Description

[Technical Field]

[0001] The present invention relates to a chlorination electrolyzer operating under polarity reversal conditions, a method for producing the same, and a self-cleaning electrochlorination system. [Background technology]

[0002] The electrochlorination process consists of producing hypochlorite in saltwater by electrolysis. The resulting sodium hypochlorite can be used for a variety of water disinfection and oxidation applications, such as drinking water, swimming pool water treatment, or microbial control in cooling towers.

[0003] Sodium hypochlorite is effective against bacteria, viruses and fungi, and has the advantage that microorganisms cannot develop resistance to its effects.

[0004] In contrast to chlorine gas or tablets that can be added to water to achieve similar results, electrochlorination generates the active chemical in situ, avoiding transportation, environmental, and / or storage issues. The method is carried out by applying a suitable current to an electrolytic cell containing at least two electrodes and an electrolyte, which includes brine, a mixture of salt and water in various concentrations depending on the application. The electrochemical reaction results in the production of sodium hypochlorite and hydrogen gas.

[0005] Titanium electrodes with active coating compositions containing a mixture of valve metals and precious metals, particularly rare transition metals from the platinum group, have been used successfully in the past as anodes in these types of cells. However, over time, scale develops on the active surface of the electrode, adversely affecting the hypochlorite production efficiency of the cell.

[0006] To prevent / mitigate scale formation, periodic polarity reversals can be applied to the electrodes to promote self-cleaning. Polarity reversals also reduce ionic bridges between the electrodes, potentially preventing uneven electrode wear.

[0007] Under polarity reversal conditions, where each electrode alternately functions as a cathode and an anode, some elements sometimes used in the active coating composition become unstable and dissolve in the electrolyte after several reversal cycles, resulting in poor electrode life.

[0008] Generally, polarity reversal is a detrimental operation for the active coating of the electrode, rapidly causing deactivation of the electrode by delamination.

[0009] To mitigate these problems, bipolar electrodes used under polarity reversal conditions must have a much higher coating loading than when each electrode functions solely as an anode or cathode. In general, electrode durability depends on the frequency of polarity reversal and the coating loading.

[0010] Increasing coating loadings negatively impacts electrode cost, both in terms of the amount of material and the length of the manufacturing process. Furthermore, because many active coating compositions rely on rare transition metals that are difficult to obtain, increasing loadings also exacerbates some of the associated procurement issues.

[0011] It would be desirable to have a self-cleaning electrode for an electrochlorination system that exhibits improved life and efficiency over a wide range of possible applications and operating conditions, potentially maintaining reduced manufacturing costs. It would be even more desirable to use such an electrochlorination system in normal-salinity and low-salinity pools, i.e., pools operating at salinity levels of 6 g / L or less (typically 0.5-2.5 g / L NaCl for low-salinity applications and 2.5-4 g / L NaCl for normal-salinity applications).

[0012] International patent application WO 2019 / 215944 A1 describes an ozone generating electrolyzer with electrodes having a thick dielectric surface layer to increase the oxygen overpotential for oxygen evolution at local noble metal sites in the interlayer. These electrodes are not suitable for chlorine production or for operation under polarity reversal conditions. Summary of the Invention

[0013] The present invention relates to a chlorination electrolytic cell comprising a housing with an inlet and an outlet suitable for the circulation of brine, and at least one pair of bipolar electrodes positioned opposite each other within the housing, each bipolar electrode comprising: (i) a valve metal substrate; (ii) an active coating comprising at least one layer of a catalytic composition comprising ruthenium and titanium deposited on the substrate; and (iii) a top coating comprising at least one layer of a composition comprising an oxide of tantalum, niobium, tin, or a combination thereof disposed on the active coating.

[0014] In another aspect, the present invention relates to a self-cleaning electrochlorination system comprising: (i) the above-described chlorination electrolytic cell; (ii) an electrolyte comprising a 1-30 g / L NaCl brine solution circulating within the electrolytic cell; and (iii) an electronic system electrically connected to the bipolar electrodes and positioned outside the housing of the electrolytic cell for periodically reversing the polarity of a pair of bipolar electrodes.

[0015] In another aspect, the present invention relates to a method for producing a chlorination cell according to the present invention.

[0016] In another aspect, the present invention relates to the use of the above-mentioned chlorination electrolyzer in normal salinity and low salinity swimming pools for disinfection of water via hypochlorite.

[0017] In yet another aspect, the present invention relates to a method for water disinfection via hypochlorite using the above-described chlorination electrolyzer under polarity reversal conditions. DETAILED DESCRIPTION OF THE INVENTION

[0018] In one aspect, the present invention relates to a chlorination electrolytic cell comprising a housing having an inlet and an outlet suitable for circulation of brine, and at least one pair of bipolar electrodes positioned opposite each other within the housing, wherein each bipolar electrode of the pair comprises: (i) a valve metal substrate; (ii) an active coating comprising at least one layer of a catalytic composition comprising ruthenium and titanium deposited on the substrate; and (iii) a top coating comprising at least one layer of a composition comprising an oxide of tantalum, niobium, tin, or a combination thereof deposited on the active coating.

[0019] At least one layer of the catalyst composition comprising ruthenium and titanium is essentially uniform in terms of its electrical properties, and at least one layer of the catalyst composition is also uniform in terms of its morphological properties, constituting essentially a solid solution comprising ruthenium and titanium, preferably a homogeneous solid solution in which the metals are primarily oxides, i.e., ruthenium oxide and titanium oxide.

[0020] The chlorination electrolyzer according to the invention can be used for water disinfection via hypochlorite in various applications such as swimming pools, wastewater disinfection (municipal water treatment, grey water treatment, seawater chlorination, etc...).

[0021] It can advantageously operate under polarity reversal conditions, thereby ensuring self-cleaning of the electrodes and avoiding scale formation.

[0022] Each electrode of a pair can be coated on one or both sides. Conventionally, the two opposing electrodes should be positioned with their coated sides facing each other.

[0023] The chlorination electrolyzer may comprise a plurality of bipolar electrode pairs, resulting in a stack of coated electrodes arranged substantially parallel to one another.

[0024] The housing shall be designed to allow the bipolar electrode pair to be electrically connected to an external generator, which may advantageously be equipped with a system for reversing the polarity of the electrodes at a pre-set frequency, typically ranging from 30 minutes to 10 hours, depending on the application and operating conditions, such as water contaminants and water hardness, as is well known in the art.

[0025] The valve metal substrate may be in any shape commonly used in this field, including but not limited to, a slab, a perforated sheet, a mesh, a louver, etc. Preferably, the substrate is made of titanium because of its durability, cost, and ease of surface treatment.

[0026] Prior to applying the active coating, the substrate is preferably cleaned, sandblasted and etched to ensure proper adhesion.

[0027] The active coating can be applied directly onto the valve metal substrate using roller coater, brushing, and spraying techniques. Alternatively, the claimed invention allows for an intermediate coating to be inserted between the substrate and the active coating, for example, to improve adhesion of the active coating. In this case, the latter shall still be considered to be applied, even if indirectly, onto the substrate.

[0028] In one embodiment, the catalytic composition of the chlorination electrolyser according to the invention comprises, expressed as weight percentages of the elements, 25% to 45% ruthenium and 55% to 75% titanium.

[0029] In another embodiment, the catalyst composition may optionally contain 2% to 5% of a doping element selected from the group consisting of scandium, strontium, hafnium, bismuth, zirconium, aluminum, copper, rhodium, iridium, platinum, palladium, and combinations thereof. These dopants can advantageously contribute to improving the life of the chlorination electrolyzer and the efficiency of free available chlorine.

[0030] By applying an insulating top coating of tantalum, niobium, or tin oxide (in combination or individually) over the active coating according to any of the above embodiments, the Ru loading can be reduced by up to 38% without affecting efficiency for a given life target of the electrode.

[0031] The reduced loading of Ru provides significant advantages, especially because of its rarity and resulting procurement and cost issues, compared to the metal oxides used in the top coating compositions of the present invention.

[0032] The inventors have found that Sn contributes more to Cl transport in the active layer than Ta or Nb. - We have discovered that tin oxide top coatings work particularly well in the practice of the present invention because they appear to form oxides that facilitate good ion diffusion. Additionally, Sn top coatings are less prone to forming dislocations that cause the typical cracks observed in, for example, tantalum oxide surfaces, resulting in a less cracked surface. The less cracked the surface, the more likely the electrolyte will dissolve unstable portions of the active layer.

[0033] In further embodiments, the top coating is preferably sufficiently thin, between 0.5 and 7 microns, as this may contribute to maintaining the free available chlorine (FAC) efficiency of the active layer.

[0034] In any of the above embodiments, the active coating may be in the range of 1 to 30 g / m 2 which can work for both applications with salinities above 6 g / L (but preferably below 30 g / L), such as, for example, seawater chlorinator applications, and applications with salinities below 6 g / L, such as 0.5 to 4 g / L found in swimming pools.

[0035] For pool applications, the top coating should be 2-6g / m 2 It is preferred to have a total loading of

[0036] Without limiting the invention to any particular theory, the top coating according to the invention forms a net rather than a barrier, reducing mechanical wear of the active coating surface due to friction of the gas bubbles, and keeping the material in a partially dissolved state when polarity reversal occurs, thereby preventing delamination of the coating and dissolution of ruthenium and other optional dopants in the electrolyte. At the same time, the porosity and thinness of the top coating allow the electrolyte to reach the catalytic center of the active coating.

[0037] In another aspect, the present invention relates to a self-cleaning electrochlorination system comprising: (i) the chlorinator electrolytic cell described above; (ii) an electrolyte comprising a 1-30 g / L NaCl brine solution circulating within the electrolytic cell; and (iii) an electronic system for periodically reversing the polarity of the bipolar electrodes of the electrolytic cell, the electronic system preferably being located outside the housing of the electrolytic cell and electrically connected to the bipolar electrodes.

[0038] The electronic system for periodically reversing the polarity of the bipolar electrodes is equipped with an internal clock that allows the polarity of the bipolar electrodes to be reversed at preset time intervals ranging from 30 minutes to 10 hours.

[0039] In pool applications, the inventors have observed that self-cleaning electrochlorination systems according to the present invention perform particularly well when the electronic system reverses the polarity of the bipolar electrode pair at preset intervals of 1 to 4 hours.

[0040] Stacks containing 5 to 15 bipolar electrode pairs connected in parallel have been found to be useful in the practice of the present invention.

[0041] The electronic system of the present invention has a current of approximately 200 to 600 A / m 2 , preferably 200 to 400 A / m 2 It can be advantageously operated at a current density of

[0042] In another aspect, the present invention provides a method for producing a pharmaceutical composition comprising: a) applying an active coating solution containing ruthenium and titanium precursors to a valve metal substrate, thereby obtaining a coated substrate; b) baking the coated substrate at a temperature of 450 to 550°C for 2 to 10 minutes; c) repeating steps a) and b) until the desired ruthenium loading is reached; d) applying a top coating solution containing precursors of tantalum, niobium, tin, or combinations thereof to the coated substrate; e) baking the coated substrate at a temperature of 450 to 550°C for 2 to 10 minutes; f) repeating steps d) and e) until a desired loading of tantalum, niobium, tin, or a combination thereof is achieved; g) Final heat treatment is carried out at a temperature in the range of 450 to 550°C. The present invention relates to a method for producing the aforementioned chlorination electrolytic cell, comprising the steps of producing each electrode of at least one pair of bipolar electrodes according to the following successive steps:

[0043] The precursors of ruthenium and titanium, as well as the precursors of tantalum, niobium or tin, are compounds selected from the group consisting of methoxides, ethoxides, propoxides, butoxides, chlorides, nitrates, iodides, bromides, sulfates or acetates of the metals, and mixtures thereof.

[0044] Optionally, after step a) and / or after step d), the coated substrate may be air dried at a temperature of 20-80° C. for 2-10 minutes.

[0045] In general, the chlorination electrolyzer according to the invention can be successfully used in any hypochlorite production application that undergoes polarity reversal, in particular with regard to bipolar electrode configurations, in order to reduce the precious metal loading of the active coating or to demonstrate an increased lifetime without compromising the FAC efficiency when the same loading is applied.

[0046] The inventors have found that chlorination electrolyzers work particularly well in pool applications operating at salinity levels of 0.5 to 4 g / L.

[0047] In a further aspect, the present invention is directed to the use of a chlorination electrolyzer according to the invention in normal salinity and low salinity pools for disinfection of water via hypochlorite, i.e. in pools operating at salinity levels of 6 g / L or less (typically 0.5-2.5 g / L NaCl for low salinity applications, 2.5-4 g / L NaCl for normal salinity applications).

[0048] The following examples are included to demonstrate specific ways of reducing the invention to practice, the utility of which is largely attested in value by the claims.

[0049] The present invention provides a method for hypochlorite mediated water disinfection comprising: a) circulating an electrolyte comprising a 1-30 g / L NaCl brine solution in at least one chlorination electrolyzer as defined above, said chlorination electrolyzer comprising one or more bipolar electrode pairs; b) applying a current to the bipolar electrode pair to generate hypochlorite in the NaCl brine solution; and c) periodically reversing the polarity of at least one pair of bipolar electrodes during the application of said current.

[0050] According to one embodiment of the present invention, the polarity of the at least one pair of bipolar electrodes is reversed at a time interval selected from the range of 1 minute to 20 hours, preferably from the range of 30 minutes to 10 hours, and particularly preferably from the range of 1 hour to 4 hours.

[0051] In a preferred embodiment of the present invention, the current is 200 to 600 A / m 2 range, preferably 200 to 400 A / m 2 A current density selected from the range of

[0052] Those of skill in the art should appreciate that the devices, compositions, and techniques disclosed below represent devices, compositions, and techniques discovered by the inventors to function well in the practice of the invention, but that those skilled in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the scope of the invention. [Example]

[0053] Experimental preparation In all electrode samples used in the following examples and counterexamples, a pair of bipolar electrodes was fabricated by starting with a grade 1 titanium plate measuring 100 mm x 100 mm x 1 mm, degreasing it with acetone in an ultrasonic bath, followed by blasting and etching with 22% HCl at full boiling.

[0054] The catalyst solutions used to prepare electrode samples E1, E2a, E2b, and samples C1–C3 were obtained by dissolving ruthenium and titanium chloride salts in 10% aqueous HCl solution, such that the final concentration of ruthenium in each catalyst solution was 45 g / L, with a Ru:Ti ratio equal to 28:72 in weight percent on an elemental basis.

[0055] The solution thus prepared was stirred for 30 minutes.

[0056] In all electrode samples E1, E2a, E2b, and C1 to C3, the titanium substrate was 0.8 g / m 2 The plates were coated with the catalyst solution described above using brush application at increasing rates of ruthenium.

[0057] After each coating was applied, the samples were fired at a temperature of 500-550°C for 10 minutes.

[0058] The above coating procedure was repeated for each of Samples E1, E2a, E2b, C1-C3 until a total loading of ruthenium according to Table 1 below was achieved. TIFF0007792416000001.tif36170

[0059] Example 1 Sample E1 obtained from "Experimental Preparation" was further coated with a top coating solution obtained from a Sn acetate solution diluted with acetic acid to reach a final concentration of 40 g / L. The top coating solution was applied with a brush in four layers, resulting in a total Sn loading of 4.5 g / m. 2 After each layer, the sample was subsequently fired at a temperature of 500-550°C for 10 minutes.

[0060] After the last layer, the samples were post-calcined at a temperature of 500-550°C for 3 hours.

[0061] Sample electrode E1 was tested according to the following accelerated test procedure: A pair of identical electrode samples was placed in a housing with an inlet and an outlet, an inter-electrode gap of 3 mm, and containing 1 L of an aqueous solution of 4 g / L NaCl and 70 g / L NaSO at 25°C.

[0062] The electrode pair is set at 1000A / m 2 The electrode pair was operated at a current density of 1000 kJ / min and subjected to polarity reversals every minute for the duration of the test. 2 The test conditions were maintained until the "accelerated life" (measured in hours) was exceeded.

[0063] The results are recorded in Table 2.

[0064] As listed in Table 2, E1 lifetime performance in hours, equivalent to 145 hours online (HOL), was selected as the target performance for the bipolar electrode.

[0065] The FAC of the sample was measured in a 3g / L NaCl aqueous solution at 300A / m 2 The measurements were carried out at a temperature of 25°C.

[0066] Example 2 Samples E2, both E2a and E2b from "Experimental Preparation," were further coated with a top coating solution prepared by dissolving 80 g of TaCl5 in 1 L of 20% HCl and stirring the solution at room temperature for 30 min. For each E2 sample, the top coating solution was applied with a brush in one layer, resulting in a total Ta loading of 1 g / m. 2 The sample was first fired at a temperature of 300 to 350°C for 10 minutes, and then fired at a temperature of 500 to 550°C for 10 minutes.

[0067] Sample E2 was tested according to the same test procedure as described in Example 1.

[0068] The results of sample E2 were analyzed and E2b was the only sample that met the performance targets of E1, and its performance is shown in Table 2.

[0069] Counterexample 1 Samples C, ie, C1-C3 obtained from "Experimental Preparation", were post-calcined at temperatures between 500 and 550°C for 3 hours and tested according to the test procedure described in Example 1.

[0070] The results of sample C were analyzed and C3 was the only sample that met the target performance of E1. Its performance is shown in Table 2. TIFF0007792416000002.tif54170

[0071] The foregoing description is not intended to limit the invention, which can be used in accordance with different embodiments without departing from the scope of the invention, which scope is defined only by the appended claims.

[0072] Throughout the specification and claims of this application, the term "comprise" and variations thereof, such as "comprising" and "comprises," are not intended to exclude the presence of other elements, components or further processing steps.

[0073] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the invention. No suggestion or implication is intended that any or all of such matters formed part of the prior art or were common general knowledge in the art relevant to the invention prior to the priority date of each claim in this application.

Claims

1. a housing provided with an inlet and an outlet suitable for the circulation of brine; at least one pair of bipolar electrodes positioned opposite each other within said housing, Each of the at least one pair of bipolar electrodes a valve metal substrate; an active coating comprising at least one layer of a catalytic composition in solid solution comprising ruthenium and titanium deposited on said substrate; a top coating comprising at least one layer of a composition comprising an oxide of tantalum, niobium, tin or a combination thereof deposited on said active coating; A chlorination electrolytic cell comprising:

2. a housing provided with an inlet and an outlet suitable for the circulation of brine; at least one pair of bipolar electrodes positioned opposite each other within said housing; A chlorination electrolytic cell comprising: Each of the at least one pair of bipolar electrodes a valve metal substrate; an active coating comprising at least one layer of a catalytic composition comprising ruthenium and titanium deposited on said substrate; a top coating comprising at least one layer of a composition comprising an oxide of tin deposited on said active coating, said top coating not comprising an oxide of tantalum or niobium; A chlorination electrolytic cell comprising:

3. 3. A chlorination electrolytic cell according to claim 1 or 2, wherein the catalytic composition comprises, expressed as weight percentages of the elements, 25% to 45% of ruthenium and 55% to 75% of titanium.

4. 4. The chlorination electrolytic cell of claim 3, wherein the catalytic composition further comprises 2% to 5% of a doping element selected from the group consisting of scandium, strontium, hafnium, bismuth, zirconium, aluminum, copper, rhodium, iridium, platinum, palladium, and combinations thereof with one another.

5. The active coating is 1 to 30 g / m ２ 5. A chlorination cell according to claim 1, having a ruthenium loading of

6. 6. A chlorination cell according to any one of claims 1 to 5, wherein the top coating comprises tin oxide.

7. 7. A chlorination cell according to any one of claims 1 to 6, wherein the top coating has a thickness of 0.5 to 7 microns.

8. The top coating has a total loading of 2 to 6 g / m ２ 8. The chlorination electrolytic cell according to claim 1, wherein

9. 9. A chlorination electrolytic cell according to any one of claims 1 to 8, wherein the valve metal substrate is titanium.

10. a chlorination electrolytic cell according to any one of claims 1 to 9; an electrolyte comprising a 1-30 g / L NaCl brine solution circulating in the chlorination cell; an electronic system for periodically reversing the polarity of at least one pair of bipolar electrodes and electrically connected to the bipolar electrodes; A self-cleaning electrochlorination system comprising:

11. 10. A process for the production of a chlorination electrolytic cell according to any one of claims 1 to 9, comprising the steps of: a) applying an active coating solution containing ruthenium and titanium precursors to a valve metal substrate, thereby obtaining a coated substrate; b) firing the coated substrate at a temperature of 450-550°C for 2-10 minutes to form a solid solution containing ruthenium and titanium; c) repeating steps a) and b) until the desired ruthenium loading is reached; d) applying a top coating solution containing precursors of tantalum, niobium, tin, or combinations thereof to the coated substrate; e) baking the coated substrate at a temperature of 450-550°C for 2-10 minutes; f) repeating steps d) and e) until the desired loading of tantalum, niobium, tin, or a combination thereof is achieved; g) performing a final heat treatment at a temperature in the range of 450 to 550°C; manufacturing each electrode of at least one pair of bipolar electrodes according to the sequential path the precursors of ruthenium and titanium, and the precursors of tantalum, niobium or tin are compounds selected from the group consisting of methoxides, ethoxides, propoxides, butoxides, chlorides, nitrates, iodides, bromides, sulfates or acetates of the metals, and mixtures thereof; Method for manufacturing chlorination electrolytic cells.

12. 10. A process for the production of a chlorination electrolytic cell according to any one of claims 1 to 9, comprising the steps of: a) applying an active coating solution containing ruthenium and titanium precursors to a valve metal substrate, thereby obtaining a coated substrate; b) baking the coated substrate at a temperature of 450-550°C for 2-10 minutes; c) repeating steps a) and b) until the desired ruthenium loading is reached; d) applying a top coating solution to the coated substrate comprising a precursor of tin, said top coating solution being free of oxides of tantalum or niobium; e) baking the coated substrate at a temperature of 450-550°C for 2-10 minutes; f) repeating steps d) and e) until the desired loading of tin is achieved; g) performing a final heat treatment at a temperature in the range of 450 to 550°C; manufacturing each electrode of at least one pair of bipolar electrodes according to the sequential path 1. A method for producing a chlorination electrolytic cell, wherein the ruthenium and titanium precursors, and the tin precursor, are compounds selected from the group consisting of metal methoxides, ethoxides, propoxides, butoxides, chlorides, nitrates, iodides, bromides, sulfates or acetates, and mixtures thereof.

13. 10. Use of a chlorination electrolyzer according to any one of claims 1 to 9 in normal salinity and low salinity swimming pools for disinfection of water via hypochlorite.

14. 1. A method for hypochlorite mediated water disinfection comprising: a) circulating an electrolyte comprising a 1 to 30 g / L NaCl brine solution through at least one chlorination electrolyzer according to any one of claims 1 to 9, said chlorination electrolyzer comprising one or more bipolar electrode pairs; b) applying a current to the bipolar electrode pair to generate hypochlorite in the brine solution; c) periodically reversing the polarity of at least one pair of bipolar electrodes during application of said current; 1. A method for hypochlorite mediated water disinfection, comprising:

15. 15. The method of claim 14, wherein the polarity of the at least one pair of bipolar electrodes is reversed at a time interval selected from the range of 1 minute to 20 hours.

16. Current: 200 to 600 A / m ２ 16. The method of claim 14 or 15, wherein a current density selected from the range of

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