US20110168567A1

US20110168567A1 - Control of hard water scaling in electrochemical cells

Info

Publication number: US20110168567A1
Application number: US12/986,312
Authority: US
Inventors: Kim R. Smith; Jenna M. Johnson; Erik C. Olson; Patrick H. Kilawee
Original assignee: Ecolab USA Inc
Current assignee: Ecolab USA Inc
Priority date: 2010-01-11
Filing date: 2011-01-07
Publication date: 2011-07-14
Also published as: WO2011083443A2; WO2011083443A3

Abstract

A threshold agent composition and methods of using the same to produce hypochlorite and other effluent streams from an electrochemical cell without the detrimental effects of hard water scaling are disclosed. The invention further discloses use of chemistries to prevent hard water scale formation in various electrochemical cells to enhance cell longevity without decreasing chlorine, hypochlorite or other effluent production.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional application of U.S. Provisional Application No. 61/293,968, filed Jan. 11, 2010, which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention pertains to the field of water electrolysis and more particularly, threshold agent compositions and methods of use for preventing hard water scale formation in electrochemical cells to enhance cell longevity. In particular, hard water scale formation is prevented through the use of a threshold agent without having to soften the water source for the electrochemical cell or cause any decrease in the production rate of sodium hypochlorite or other effluent from an electrochemical cell.

BACKGROUND OF THE INVENTION

Electrolysis as a water treatment process produces two forms of altered water: a reduced or alkaline water; and an oxidized or acidic water. Electrolysis uses an electric current to split water into its two constituent elements: hydrogen and oxygen. Electricity enters the water at a cathode, a negatively charged terminal, passes through the water and exits through an anode, a positively charged terminal. Hydrogen is collected at the cathode (negatively charged electrical current) and oxygen is collected at the anode (positively charged electrical current). The reaction of water in an electrolytic cell is a redox process, as an oxidation reaction occurs at the anode while a reduction reaction occurs at the cathode.
Conventional electrolysis cells are equipped with at least an anode and a cathode in the interior and often have a dual structure in which the anode and cathode are separated by a membrane to divide the cells into an anode chamber and a cathode chamber. The barrier membrane provides the advantage of preventing the products at the anode chamber from mixing with the products from the cathode chamber. Various electrolysis cells and methods for electrolyzing water for various purposes are disclosed, for example in U.S. Pat. No. 3,616,355, U.S. Pat. No. 4,062,754, U.S. Pat. No. 4,100,052, U.S. Pat. No. 4,761,208, U.S. Pat. No. 5,313,589, and U.S. Pat. No. 5,954,939 and are compatible with the threshold agents and methods for using the threshold agents according to the invention disclosed herein.
Electrolysis cells are used for a variety of purposes. For example, electrochemical cells may be used to produce hypochlorite solutions or chlorine for use as bleach, surface sanitizers and other disinfectant purposes. The electrolysis of salt to generate chlorine is well established. In one application, sodium hypochlorite may be used as a 3-6 wt-% solution for a household bleaching agent. More concentrated solutions are used for chlorination of water and disinfecting applications. Still further concentrated solutions are used for chlorination of swimming pools. Chloride molecules in an electrolyzed cell (residual or added, such as by adding sodium chloride salt) can be converted to sodium hypochlorite, chlorine gas and other chlorine-containing oxidants, providing a source of a chlorine-based disinfectant with numerous sanitizing capabilities. These chlorine-containing oxidants are biocidal agents that are effective in killing bacteria, viruses, parasites, protozoa, molds, spores and other pathogens. The electrolysis of aqueous sodium chloride (brine) produces chlorine gas at the anode and hydrogen gas at the cathode. This is a result of the reduction of water at the cathode to form hydroxyl ions and hydrogen gas and the oxidation of chloride ions from sodium chloride solution at the anode to produce chlorine gas. A basic solution of sodium hydroxide (or “caustic” or “alkali”) as well as an acidic solution of hypochlorous acid (formed from the reaction of chlorine with water) are formed. Depending upon the structure of an electrochemical cell, various effluents may be produced. For example, a cell divided by a membrane produces both hypochlorous acid and sodium hydroxide (caustic). Alternatively, if the electrochemical cell is not divided by a membrane, the chlorine gas or hypochlorous acid and caustic react to form hypochlorite (sodium hypochlorite, commonly referred to as bleach).
Large and small scale electrochemical cells are utilized to produce industrial chlorine-based disinfectants, for example in municipal water-treatment plants, as well as for swimming pools. On-site production of chlorine-containing oxidant products such as sodium hypochlorite, hypochlorous acid, chlorine and/or Cl₂from aqueous sodium chloride solutions is desirable, as production from an electrolyzed water process prevents the need to transport diluted aqueous solutions of the corrosive products such as hypochlorite or difficult to transport corrosive and flammable gases such as chlorine gas. Alternatively, electrolysis cells may be used to generate alkaline sources, such as potassium hydroxide and potassium sulfate through electrolyzing sodium sulfate. See e.g., U.S. Pat. No. 6,375,824. Electrolytic cells are also described as a way to produce other difficult to handle or unstable materials such as hydrogen peroxide and chlorine dioxide.
The effectiveness and convenience of utilizing electrolysis systems are frequently limited due to the failure of the electrodes and membranes of the cells caused by both corrosion and hard water scaling. The longevity of the electrodes and membranes of the cells are significantly diminished when scaling and/or corrosion are observed in the cell. See e.g., U.S. Pat. No. 4,248,690. Most often, calcium and magnesium ions are contained in either the water source or salt solutions added to electrochemical cells, resulting in the previously considered unavoidable scaling in cells, resulting in detrimental effects to the cells by forming hydroxide precipitates and scale. The precipitate and scale eventually coat the surface of the electrodes and membranes causing an increased voltage demand by the cell and may potentially lead to short-circuiting of the cell. Therefore, a significant disadvantage to the use of electrochemical cells, such as for the production of hypochlorite, is the required use of softened water to prevent hard water scaling. Electrolysis systems use softened and conditioned water from a variety of sources to optimize cell performance and avoid scaling; including for example, water filtration, temperature and pressure control to maximize scale solubility, calcium and magnesium removal via ion exchange (e.g., exchanging calcium and magnesium ions in the water with sodium associated with a resin bed in a water softening unit), reversing polarity of the electrodes to partially dislodge scale from the electrodes, and incorporating a builder/chelant/sequestrant. See e.g., U.S. Pat. No. 5,954,939 and U.S. Pat. No. 4,434,629 for further discussion.
In addition to requiring treated water for use in electrochemical cells, chemical methods such as acid-washing are still required to remove the build-up of scale from the electrodes and membranes of the cells. See e.g., U.S. Pat. No. 5,932,171. This is undesirable as acids are very corrosive and may erode the electrodes, specifically the electrode coatings. Additional means of increasing the efficiency and lifespan of electrochemical systems are known, such as the use of: corrosion-resistant electrodes, using titanium-palladium or other corrosion-resistant alloys (see e.g., U.S. Ser. No. 12/381,962); sodium ion conductive ceramic membranes (U.S. Ser. No. 11/613,857); and membrane electrolyzers preventing the clogging of membranes with calcium and magnesium carbonate precipitates (WO 2008/155755). However, these and other means of maintaining and repairing electrochemical cells are undesirable and costly for consumers. Despite the various means for preventing scaling and corrosion, eventually the electrochemical cells become permanently fouled or ineffective, requiring consumers to pay for expensive maintenance and repairs and/or replacement. Therefore, there remains a significant need to inhibit water scaling in order to prolong the lifetime of an electrochemical system. There is also great demand for high-economic-efficiency operation conditions for improved electrolysis systems.
Accordingly, it is an objective of the claimed invention to formulate improved chemistries to increase the lifespan of electrochemical cells.
A further object of the invention is to develop methods and compositions to stop the formation of hard water scale on the electrodes and membranes of electrolytic cells with chemistries that do not interfere with effluent production.
A further object of the invention is to develop a compatible blend of threshold agents to prevent the formation of hard water scale in an electrochemical cell.
A still further object of the invention is to develop a threshold agent capable of inhibiting hard water scale without softening the water utilized in an electrochemical cell.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to electrochemical processes for the production of sodium hypochlorite and other effluent sources with the use of threshold agents to prevent hard water scale formation in electrochemical cells to enhance cell longevity. According to an aspect of the invention, a method for producing hypochlorite and reducing hard water scaling in an electrochemical cell without decreasing hypochlorite production includes obtaining an electrochemical cell configured with at least one anode and cathode to produce a hypochlorite source, providing a water and a sodium chloride source to the cell, adding a threshold agent to the cell, and applying an electric current the cell to produce hypochlorite and reduce hard water scaling without decreasing hypochlorite production. In a further aspect of the invention, the threshold agent is added in the amount of up to about 10,000 ppm and is a water soluble polycarboxylate capable of preventing hard water scale formation on electrodes and membranes.
According to an aspect of the invention a method for reducing hard water scaling in a water source and electrochemical cell producing hypochlorite for a water source without decreasing hypochlorite production includes obtaining a hypochlorite source in a pool, spa or other water source treated with an electrochemical cell, contacting the hypochlorite source with a threshold agent in the amount of up to about 10,000 ppm, wherein the threshold agent is a water soluble polycarboxylate with a molecular weight less than 5,000, and reducing hard water scale formation on electrodes and membranes of the electrochemical cell without decreasing hypochlorite production.
According to an aspect of the invention a method for increasing longevity of an electrochemical cell by reducing hard water scaling includes obtaining an electrochemical cell configured with at least one anode and cathode to produce a hypochlorite source, wherein a water and a sodium chloride source are circulated through said electrochemical cell to produce said hypochlorite, adding a threshold agent to the electrochemical cell in the amount of up to about 10,000 ppm, wherein said threshold agent is a water soluble polycarboxylate with a molecular weight less than 5,000, and applying an electric current to the electrochemical cell to produce at least one effluent without causing the precipitation of water hardness ions from the water source and forming hard water scaling.
According to further aspects of the various embodiments of the invention, the threshold agent may be a water-insoluble resin. The threshold agent may be a polycarboxylate is selected from the group consisting of homopolymers and copolymers of polyacrylates, polyolefinic systems, polymaleic systems, derivatives and salts of the same, and combinations of the same. According to particular aspects of the invention the polycarboxylate is Acumer 1000.
According to still further aspects of the invention the threshold agent may be added in the amount of up to about 1,000 ppm or in the amount of from about 50 ppm to about 500 ppm. The threshold agent may have a molecular weight less than 5,000, preferably less than 2,000. Preferably, the hypochlorite produced according to embodiments of the invention effectively cleans and/or sanitizes surfaces without depositing streaks or spotting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the effect of Acumer 1000 on hypochlorite formation in an electrochemical cell.

FIG. 2 shows the comparative effects of Acumer 1000 and Acusol 445N on hypochlorite formation in an electrochemical cell.

FIG. 3 shows the increased voltage demands in a cell over time due to the effects of scaling showing NaOCl generated at constant Amps in 1000 ppm NaCl and soft water with 300 ppm sodium acetate.

FIG. 4 shows the increased voltage demands in a cell over time due to the effects of scaling showing NaOCl generated at constant Amps in 1000 ppm NaCl and soft water with 300 ppm sodium bisulfate.

FIG. 5 shows the increased voltage demands in a cell over time due to the effects of scaling showing NaOCl generated at constant Amps in 1000 ppm NaCl and soft water.

FIG. 6 shows the increased voltage demands in a cell over time due to the effects of scaling showing NaOCl generated at constant Amps in 1000 ppm NaCl and 5 grain water.

FIG. 7 shows the increased voltage demands in a cell over time due to the effects of scaling showing NaOCl generated at constant Amps in 1000 ppm NaCl and 10 grain water.

FIG. 8 shows the increased voltage demands in a cell over time due to the effects of scaling showing NaOCl generated at constant Amps in 1000 ppm NaCl and 17 grain water.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiments of this invention are not limited to particular treatment methods for electrochemical cells and threshold agent compositions for such treatment methods for electrochemical cells, which can vary and are understood by skilled artisans. It is further to be understood that all terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting in any manner or scope. For example, as used in this specification and the appended claims, the singular forms “a,” “an” and “the” can include plural referents unless the content clearly indicates otherwise. Further, all units, prefixes, and symbols may be denoted in their SI accepted form. Numeric ranges recited within the specification are inclusive of the numbers defining the range and include each integer within the defined range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the invention pertain. Many methods and materials similar, modified, or equivalent to those described herein can be used in the practice of the embodiments of the present invention without undue experimentation, the preferred materials and methods are described herein. In describing and claiming the embodiments of the present invention, the following terminology will be used in accordance with the definitions set out below.
The term “about,” as used herein, refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients used to make the compositions or carry out the methods; and the like. The term “about” also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term “about”, the claims include equivalents to the quantities referred and variations in the numerical quantities that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients used to make the compositions or carry out the methods; and the like.
The term “bleaching agent,” as used herein can refer to agents used for example to sanitize, lighten or whiten a substrate, and may include bleaching compounds capable of liberating an active halogen species, such as Cl₂, Br₂, I₂, ClO₂, BrO₂, IO₂, OCl⁻, —OBr⁻and/or, —OI⁻, under conditions typically encountered during the cleansing process. Bleaching agents for use in the present invention include, for example, chlorine-containing compounds such as a chlorite or a hypochlorite.
The terms “chelating agent” and “sequestrant” as used herein, refer to a compound that forms a complex (soluble or not) with water hardness ions in a specific molar ratio. Chelating agents that can form a water soluble complex include for example, sodium tripolyphosphate, EDTA, DTPA, NTA, citrate, and the like. Sequestrants that can form an insoluble complex include for example, sodium triphosphate, zeolite A, and the like.
The term “chlorine-containing oxidant,” as used herein, refers to oxidants produced according to electrolysis methods of sodium hydroxide solutions and may include for example, inorganic hypochlorite salts (such as sodium hypochlorite), hypochlorous acid, chlorine and Cl₂(gas).
The term “hard water,” as used herein, refers to water having a level of calcium and magnesium ions in excess of about 100 ppm. Often, the molar ratio of calcium to magnesium in hard water is about 2:1 or about 3:1. Although most locations have hard water, water hardness tends to vary from one location to another. Further, as used herein, the term “solubilized water hardness” refers to hardness minerals dissolved in ionic form in an aqueous system or source, i.e., Ca⁺⁺and Mg⁺⁺. Solubilized water hardness does not refer to hardness ions when they are in a precipitated state, i.e., when the solubility limit of the various compounds of calcium and magnesium in water is exceeded and those compounds precipitate as various salts such as, for example, calcium carbonate and magnesium carbonate. Salts formed from water hardness ions have low solubility in water as they are formed by metal cations interacting with inorganic anions. As concentration in a solution increases and/or temperature or pH of a water source increases, the salts will precipitate from solution, crystallize and form hard deposits or scales on surfaces, causing the undesirable effects on equipment such as electrochemical cells. A threshold inhibitor or threshold agent (as used synonymously) inhibits the crystallization of water hardness ions from solution, without necessarily forming a specific complex with the water hardness ion, thereby inhibiting the scaling, film and/or residue traditionally observed in cells. Not wishing to be limited by theory, it is believed that the threshold inhibitors work by interfering with the growth of the scale crystals.
The terms “scale,” “scaling,” “film,” and “filming” as used herein, may exemplarily refer to either bicarbonate, carbonate, sulfate, phosphate or hydroxide scaling, caused by salts of bicarbonate, carbonate, sulfate, phosphonate and/or hydroxide with calcium, magnesium, or other metal ions as observed in an electrochemical cell and described herein. Scaling as discussed herein and alleviated according to the threshold agent compositions and methods of the present invention are distinct from cell corrosion. Corrosion of an electrochemical cell generally refers to the gradual weight loss of metallic components through a chemical process or series of chemical reactions. Most often metals that come into prolonged contact with aqueous systems containing oxidants (such as chlorine, acid, bleach, caustic, etc.) are prone to corrosion. In an electrochemical cell, distinct from scaling, corrosion most frequently occurs at the anode due to the more acidic conditions.
The term “hypochlorite,” as used herein, refers to a salt of hypochlorous acid. A hypochlorite ion is ClO⁻and therefore a hypochlorite compound is a chemical compound containing this group having a chlorine in the oxidation state (+1). The oxidative state results in very low stability, causing hypochlorites to be very strong oxidizing agents. One skilled in the art may recognize that other chlorine-containing bleaches such chlorate ions or even chlorine dioxide can be formed by modifying the pH or starting materials for an electrochemical cell. A common example of a hypochlorite is the bleaching agent sodium hypochlorite. As used herein, sodium hypochlorite (NaOCl) may be used interchangeably with hypochlorite. Hypochlorous acid is a more effective sanitizer than hypochlorite and is chemically preferred when the pH of a bleach solution is decreased. For purposes of describing the present invention, the description of the use of threshold agents for electrochemical cells producing hypochlorite shall also be understood to incorporate cells producing hypochlorous acid. For further purposes of the present invention, hypochlorite and hypochlorous acid shall also refer to a chlorine-containing oxidant as described herein.
The terms “threshold agent” and “threshold inhibiting agent,” as used herein, refer to a compound that inhibits crystallization of water hardness ions from solution, but that need not form a specific complex with the water hardness ion. Threshold agents are capable of maintaining hardness ions in solution beyond its normal precipitation concentration. See e.g., U.S. Pat. No. 5,547,612. This distinguishes a threshold agent from a chelating agent or sequestrant; however, according to the invention the threshold agent may be either a chelating agent and/or sequestrant. Threshold agents may include, for example and without limitation, polycarboxylates, such as polyacrylates, polymethacrylates, olefin/maleic copolymers, and the like. The threshold agent according to the invention must survive the electrochemical cell's conditions to ensure it is not deactivated and prevented from inhibiting scaling, and further must not cause any decrease in chlorine generation. As used herein, the terms “chelating agent” and “sequestrant” refer to a compound that forms a complex (soluble or not) with water hardness ions (from the wash water, soil and substrates being washed) in a specific molar ratio. According to the invention, the threshold agent is preferably characterized as substoichiometric, such that the threshold agent is effective at concentration levels that are lower than would be expected based on a stoichiometric equivalence of the threshold agent and the scale-causing component present in the electrochemical cell or treated water source.
The terms “water” and “feed water,” as used herein, refer to any source of water that can be used with the methods and compositions according to the present invention. Exemplary water sources suitable for use as a feed water in the present invention include, but are not limited to, water from a municipal water source, or private water system, e.g., a public water supply or a well. The water can be city water, well water, water supplied by a municipal water system, water supplied by a private water system, and/or water directly from the system or well. The feed water can also include water from a used water reservoir, such as a recycle reservoir used for storage of recycled water, a storage tank, or any combination thereof. In some embodiments, the water source is not industrial process water. In other embodiments, the water source is not a waste water stream.
The term “water soluble,” as used herein, refers to a compound that can be dissolved in water at a concentration of more than 1 wt-%. The term “water insoluble,” as used herein, refers to a compound that can be dissolved in water only to a concentration of less than 0.1 wt-%. For example, magnesium oxide is considered to be insoluble as it has a water solubility (wt %) of about 0.00062 in cold water, and about 0.00860 in hot water. Other insoluble compounds include, for example: magnesium hydroxide with a water solubility of 0.00090 in cold water and 0.00400 in hot water; aragonite with a water solubility of 0.00153 in cold water and 0.00190 in hot water; and calcite with a water solubility of 0.00140 in cold water and 0.00180 in hot water. The terms “slightly soluble” or “slightly water soluble,” as used herein, refer to a compound that can be dissolved in water only to a concentration of 0.1 to 1.0 wt-%.
The term “weight percent,” “wt-%,” “percent by weight,” “% by weight,” and variations thereof, as used herein, refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100. It is understood that, as used here, “percent,” “%,” and the like are intended to be synonymous with “weight percent,” “wt-%,” etc.
The hard water scale inhibiting agent composition and methods of using the compositions according to the embodiments of the invention present a significant improvement in the prior art and represent a significant change in industries using electrochemical cells for on-site production of hypochlorite, caustic or other effluent sources. According to one embodiment, the threshold inhibiting agent composition described obviates the need for softening water prior to use in electrochemical cells, such as those producing hypochlorite. As a result, the methods of electrolysis according to the invention are compatible with numerous water sources, including hard water, without experiencing the detrimental effects of hard water scaling in the cells. The inclusion of a threshold agent in an electrochemical cell further obviates the need for harsh acid-washing to maintain cell viability due to the prevention of hard water scaling in the cells.
Additionally, the threshold agent composition is an improvement over the use of chelating agents and/or sequestrants to partially prevent scale formation, such as the use of phosphate feeds. The prior use of phosphate feeds produced erratic feed streams and production of chlorine and required large quantities to control hard water scale due to stoichiometric-based calcium chelation. Other builders such as aminocarboxylates and hydroxyacids also require stoichiometric-based chelation and have been shown to further chelate ruthenium on a hypochlorite electrode's surface. Therefore, use of the threshold agent composition according to the invention overcomes these disadvantages to provide an effective means of preventing hard water scaling in electrochemical cells without causing any reduction in the production of chlorine. Further, according to a preferred embodiment the threshold agent does not use any phosphate for methods and/or compositions according to the invention.
Threshold agents are well-known to modify the crystal size and precipitation of hard water precipitants and hardness ions. See e.g., U.S. Pat. No. 6,365,101 and U.S. Pat. No. 7,537,705. They are commonly used in combination with detergent solutions to control hard water scaling caused by detersive agents. See e.g., U.S. application Ser. No. 12/052,880. However, the use of threshold agents to prevent scaling during the electrochemical generation of hypochlorite has not been tested in the prior art, nor is it apparent to one skilled in the art that the precipitation mechanism for calcium and other metal ions occurring in a detergent solution would have any connection to that in an electrochemical cell. This is illustrated by the fact that scaling in an electrochemical cell occurs primarily on the cathode and membranes, leaving the anode substantially free of the scaling. The present invention first recognizes that the hard water scale formation on the cathode and membranes proceeds by a different pathway than that for a detergent solution (requiring an alkaline pH for hard water scaling, for example, a pH in excess of 8 causes the formation of carbonate forms which lead to scaling of calcium carbonate or magnesium carbonate).
Although not intending to be limited by a particular theory, the present invention recognizes that an initial film of calcium or magnesium carbonate and/or hydroxide forms on the cathode's inner surface due to the interaction of calcium or magnesium metal ions with impurities, such as hydroxide, carbonate and bicarbonate, at the cathode as represented by the following formula:
2H₂O+2e ⁻→H₂+2OH⁻
Na⁺ +e ⁻→Na
2Na⁺+2H₂O→2Na⁺+2OH⁻+H₂
As shown in the formula above, hydrogen ions and hydrogen gas are produced at the cathode and metallic ions (such as sodium ions) are reduced to become metals as a very transitory intermediate species which then reacts with water to form the corresponding metal hydroxide near the cathode of the electrochemical cell. If the water source in the electrochemical cell contains impurities or hardness ions such as calcium or magnesium, during electrolysis these ions by further reaction with the sodium hydroxide may undergo anion exchange and form the corresponding calcium or magnesium hydroxide, which can also undergo further anion exchange with carbonate in the water to produce hydroxides and carbonates causing scaling, as observed as deposits on the surface of the cathode in the cell. The production of the alkalinity in the case of the cathodic electrode is quite localized near the cathode with scale being formed even when the pH of the bulk salt solution is neutral to slightly acidic and explains why the anode, which is not the point of hydroxide formation, does not collect hard water scale in the electrochemical cell.
The threshold agent utilized according to the invention prevents the scaling of the electrodes and membranes in electrochemical cells, namely the cathode of a cell. According to a preferred embodiment, the threshold agents according to the invention are water soluble polymeric systems capable of preventing hard water scale formation on both electrodes and resin or ceramic membranes. According to the invention, the threshold agents are compatible for inhibiting scaling caused by hard water deposits, particularly in systems supplied with water having high levels of carbonate, hydroxide and/or phosphate ions along with water hardness ions traditionally leading to buildup in cells causing the unsightly residue, film and scaling that is detrimental to cells. According to an embodiment of the invention, water impurities such as calcium and magnesium are not deleterious to the electrolytic water once threshold agents are utilized to prevent crystallization and scaling with bicarbonate, carbonate, hydroxide, sulfate and/or phosphate ions. Accordingly, use of the threshold agent of the present invention obviates the need to “soften” the water source used in an electrochemical cell.
More preferably, the threshold agents according to the invention are substantially stable in the presence of chlorine or are substantially chemically-resistant to chlorine and the corrosive conditions of the electrochemical cell. Further, the threshold agents according to the invention do not increase the viscosity of the aqueous electrolytic solution. According to a further embodiment of the invention, the threshold agents do not result in any decrease of hypochlorite production of an electrochemical cell. According to a still further embodiment of the invention, the threshold agent does not result in a decreased concentration of hypochlorite or other chlorine-containing oxidant and does not deactivate the oxidizing effects of hypochlorite or other chlorine-containing oxidant if the threshold agent is added directly to a source (such as a swimming pool) containing such hypochlorite or other chlorine-containing oxidant.
According to a further aspect of the invention the threshold agents are further utilized in non-hypochlorite electrochemical cells. For example, any cell where hydroxide is formed on the water side of a cell is suitable for use according to the embodiments of the invention, including for example cells producing hydrogen peroxide, peracid or caustic, wherein water is split to form hydroxide. According to such embodiments, the threshold agents do not result in any decrease in production of the hydrogen peroxide, peracid or caustic.
According to a preferred embodiment, the threshold inhibiting agents may be a polycarboxylate or related copolymer. Polycarboxylates refer to compounds having a plurality of carboxylate groups. A variety of such polycarboxylate polymers and copolymers are known and described in patent and other literature, and are available commercially. Exemplary polycarboxylates that may be utilized as threshold inhibiting agents according to the invention include for example: homopolymers and copolymers of polyacrylates; polyacrylates; polymethacrylates; noncarboxylated materials such as polyolefinic and polymaleic copolymers, such as olefinic and maleic hydride copolymers; and derivatives and salts of all of the same.
Suitable polycarboxylates and related copolymers according to the invention may include water soluble polycarboxylate polymers, including for example homopolymeric and copolymeric agents. Additional suitable polycarboxylates may include homopolymeric and copolymeric agents, such as polymeric compositions with pendant (—CO₂H) carboxylic acid groups, including polyacrylic acid, polymethacrylic acid, polymaleic acid, acrylic acid-methacrylic acid copolymers, acrylic-maleic copolymers, hydrolyzed polyacrylamide, hydrolyzed methacrylamide, hydrolyzed acrylamide-methacrylamide copolymers, hydrolyzed polyacrylonitrile, hydrolyzed polymethacrylonitrile, hydrolyzed acrylonitrile methacrylonitrile copolymers, or mixtures thereof. According to a further embodiment, the water soluble salts or partial salts of these polymers and copolymers may further be suitable threshold agents according to the invention. Additional description of exemplary polycarboxylates is provided in U.S. Pat. No. 7,537,705.
Examples of oligomeric or polymeric polycarboxylates suitable as threshold agents include for example: oligomaleic acids as described, for example, in EP-A-451 508 and EP-A-396 303; co- and terpolymers of unsaturated C4-C8-dicarboxylic acids, possible co-monomers which may be present being monoethylenically unsaturated monomers from group (i) in amounts of up to 95% by weight, from group (ii) in amounts of up to 60% by weight, from group (iii) in amounts of up to 20% by weight. Examples of suitable unsaturated C4-C8-dicarboxylic acids include maleic acid, fumaric acid, itaconic acid and citraconic acid. Suitable co- and terpolymers are disclosed, for example, in U.S. Pat. No. 3,887,806.
The group (i) includes monoethylenically unsaturated C3-C8-monocarboxylic acids, such as acrylic acid, methacrylic acid, crotonic acid and vinylacetic acid, for example acrylic acid and methacrylic acid. Group (ii) includes monoethylenically unsaturated C2-C22-olefins, vinyl alkyl ethers with C1-C8-alkyl groups, styrene, vinyl esters of C1-C8-carboxylic acids, (meth)acrylamide and vinylpyrrolidone, for example C2-C6-olefins, vinyl alkyl ethers with C1-C4-alkyl groups, vinyl acetate and vinyl propionate. Group (iii) includes (meth)acrylic esters of C1-C8-alcohols, (meth)acrylnitrile, (meth)acrylamides of C1-C8-amines, N-vinylformamide and vinylimidazole.
Suitable polyacrylates, homopolymers and copolymers of polyacrylates, polyolefinic and polymaleic systems for threshold agents according to the invention may include organic compounds, including both polymeric and small molecule agents, including for example polyanionic compositions, such as polyacrylic acid compounds. Polymeric agents commonly comprise polyanionic compositions such as polyacrylic acid compounds. Polymers such as Acusol 448 (Rohm & Haas) and others are commercially available and may be useful according to the present invention. For example, exemplary commercially available acrylic-type polymers include acrylic acid polymers, methacrylic acid polymers, acrylic acid-methacrylic acid copolymers, and water-soluble salts of the said polymers. These include polyelectrolytes such as water soluble acrylic polymers such as polyacrylic acid, maleic/olefin copolymer, acrylic/maleic copolymer, polymethacrylic acid, acrylic acid-methacrylic acid copolymers, hydrolyzed polyacrylamide, hydrolyzed polymethacrylamide, hydrolyzed polyamide-methacrylamide copolymers, hydrolyzed polyacrylonitrile, hydrolyzed polymethacrylonitrile, hydrolyzed acrylonitrile-methacrylonitrile copolymers, hydrolyzed methacrylamide, hydrolyzed acrylamide-methacrylamide copolymers, and combinations thereof. Such polymers, or mixtures thereof, include water soluble salts or partial salts of these polymers such as their respective alkali metal (for example, sodium or potassium) or ammonium salts can also be used. The weight average molecular weight of the polymers is from about 2,000 to about 20,000. According to a preferred embodiment, the threshold agent for use in the compositions and methods of the present invention is the commercially-available Acumer 1000.
According to an additional embodiment of the invention, sulfonated polymers may be used as the threshold agent for inhibiting scaling in an electrochemical cell. These may include a variety of sulfonated polymers and copolymers, such as for example, carboxylic sulfonated polymers and copolymers, carboxylic sulfonated nonionic terpolymers, sulfonated styrene/maleic acid copolymers and various other sulfonated polymers and copolymers as may be ascertained by those of ordinary skill in the art to which the invention pertains.
Examples of suitable commercially available threshold agents include, for example: Acusol 588 and Acusol 420 (all available from Rohm & Haas).
One skilled in the art will understand the methods of synthesis of such polymers and co-polymers if commercially available threshold agents are not utilized. It is to be understood according to the threshold agents described herein, that such polymers refer to compositions produced by polymerization of one or more monomers with no restriction on the number of types of monomers incorporated in the polymer. Further it is to be understood that co-polymers refer to compositions produced according to a variety of known methods of polymerization with no restriction on the number of types of monomers incorporated in the polymer.
Although not intending to be limited according to a particular theory, the threshold agents suitable for use according to the present invention are preferably short chain polymers with low molecular weights that do not cause decreased chlorine production or increased voltage demand as a result of a large molecular weight and long chain interfering with electrical flow in an electrochemical cell. According to an embodiment of the invention, suitable threshold agents have a molecular weight less than at least 5,000, more preferably less than 4,000, more preferably less than 3,000 and according to a most preferred embodiment less than 2,000.
According to an additional embodiment of the invention, the threshold agent may be a water-insoluble resin. For example, a threshold agent may be obtained as the result of running water over a water-insoluble resin to release a water soluble polymeric threshold agent, such as a resin bead. A commercially-available resin bead is available from Dow® under the tradename Amberlyte IRC-76®, which represents a preferred embodiment of the invention. Additional suitable water-insoluble resins for generating threshold agents in a water source treated by an electrochemical cell are disclosed in U.S. patent application Ser. No. 12/764,621 filed on Apr. 21, 2010 entitled “Methods and Apparatus for Controlling Water Hardness” (Attorney Docket No. 2699USU1), the entire content of which is hereby incorporated by reference.
It is expected that other types of scale inhibitors meeting the requirements described herein according to the invention can be included with the threshold agent according to the invention, if desired. Particularly, additional scale inhibitors may be added to handle a particular type of scaling in a given application or environment, such as a unique water supply. One skilled in the art will ascertain the need for such additional scale inhibitors according to the invention.
It is desirable to provide the threshold agent in a concentration that is sufficient to provide a desired level of scale inhibition. According to the invention, the ratio of threshold agent to be added to a hypochlorite or chlorine-containing oxidant source or the ratio of threshold agent added to an electrochemical cell producing hypochlorite may vary. According to an embodiment, the threshold agent can be provided at a concentration up to about 10,000 ppm to achieve a desired level of scale inhibition. According to a preferred embodiment, the threshold agent can be provided at a concentration up to about 5,000 ppm or up to about 1,000 ppm. According to a still further preferred embodiment, the threshold agent can be provided in concentrations from about 50 to about 500 ppm. According to particular embodiments a most preferred concentration to provide a desired level of scale inhibition may be about 100 ppm threshold agent. According to the invention, the effective amounts of threshold agents utilized refers to an amount sufficient to provide an inhibitory effect on the water scaling in an electrochemical cell as compared with an identical composition and electrochemical cell that does not contain a sufficient amount of the threshold agent to inhibit such water scaling.
The threshold agent composition according to the invention may be formulated into a variety of composition formulations, such as for example a solid or a flowable liquid. According to one embodiment, the composition is incorporated into the salt feed for the electrochemical cell, forming a solution with the water source upon entry into the cell. The formulation of the threshold agent with the salt may be in either a flowable liquid incorporated into the salt feed for the electrochemical cell or solid form. According to an alternative embodiment, the solid composition may be a block, powder, or other pelleted material. According to an additional embodiment, the solid threshold agent may be provided in a block formulation to be added to an electrochemical cell for a slow or extended time-release of the threshold agent in a cell. Alternatively, the threshold agent may be introduced into the water feed for the electrochemical cell in either a solid or flowable liquid. According to further embodiments of the invention, the threshold agent may be added directly into the electrochemical cell as a separate feed from the water or salt.
Various threshold agent compositions are disclosed as embodiments of the invention. According to one aspect of the invention, a water scaling-inhibiting composition may comprise, consist of or consist essentially of about 50 ppm to about 10,000 ppm of a threshold agent and an aqueous sodium chloride source. The threshold agent according to the invention is a water soluble polymeric system capable of preventing hard water scale formation on electrodes and membranes, preferably a polycarboxylate selected from the group consisting of homopolymers and copolymers of polyacrylates, polyolefinic systems, polymaleic systems, derivatives and salts of the same, and combinations of the same. According to a preferred embodiment, the polycarboxylate is Acumer 1000. The threshold agent may further be a product of rinsing a water insoluble resin with water.
According to a further aspect of the invention, a water scaling-inhibiting composition may comprise, consist of or consist essentially of about 50 ppm to about 10,000 ppm of threshold agent and a solid sodium chloride source, wherein the threshold agent is a water soluble polymeric system capable of preventing hard water scale formation on electrodes and membranes. Preferably, the threshold agent is a polycarboxylate selected from the group consisting of homopolymers and copolymers of polyacrylates, polyolefinic systems, polymaleic systems, derivatives and salts of the same, and combinations of the same. More preferably, the threshold agent is the polycarboxylate is Acumer 1000.
According to a further embodiment, the threshold agent may be used in water sources supplied hypochlorite or other oxidant-containing products, such as a swimming pool or spa. According to one embodiment, the threshold agent according to the invention may be added separately from the hypochlorite source into such a water source. For example, a pool may have a small device locally-producing small amounts of chlorine or bleach to treat the pool water, such as a one compartment electrochemical cell, and the threshold agent may be added directly to the pool to prevent hard water scaling in the electrochemical cell within the water system. According to an alternative embodiment the threshold agent may be added directly to a water source such as a pool in solution with hypochlorite, providing not only a scale inhibition benefit to the body of recreational water but also giving protection to the electrochemical cell as the water in systems such as pools, spas, hot tubs is often used as the water feed going into the electrochemical cell set-up to provide hypochlorite for those bodies of water. As described herein, the threshold agents of the invention and the methods of using the same may be utilized in a variety of methods comprising providing a water source and either creating or providing a brine source to be electrolyzed by a direct current applied to the solution to produce hypochlorite and/or caustic.
According to the invention, which may be utilized in a variety of electrochemical cells having differing structures (such as number of chambers and types of membranes), the threshold agent may be added according to the various descriptions set forth above to any of the cell chambers or a variety of the chambers. A skilled artisan will recognize these and other various embodiments to the formulations of the threshold inhibiting agents used directly with an electrochemical cell according to the invention. These and others are encompassed within the scope of the present invention.
The methods and compositions according to the invention maybe utilized with various types of electrolysis cells. Exemplary electrochemical cells include, but are not limited to those described in U.S. Pat. No. 6,773,575, U.S. Pat. No. 6,767,447, U.S. Pat. No. 6,761,815 and U.S. Pat. No. 6,712,949. For example, electrolysis cells utilized according to the invention may include Mercury cells, Diaphragm cells, and Membrane cells. The methods and compositions according to the invention may be adapted for use according to the type and structure of the electrochemical cell, such that the threshold agent according to the invention may be preferably added to any type of electrochemical cell. For purposes of convenience, the disclosure is primarily directed to chlor-alkali electrolytic cells and cells using no ion exchange membranes, cation exchange membranes, and anion exchange membranes; but as one skilled in the art can appreciate, the methods and compositions according to the invention are also applicable to other electrolytic cells used for conducting an electrochemical process.
As set forth, in a non-limiting embodiment of the invention, the electrochemical process is used for the electrolysis of inorganic materials, such as the aqueous inorganic metal salt solution of sodium chloride brine. According to this embodiment, the threshold agent is added directly to the brine source of an electrochemical cell. However, according to the invention the structure of the cell may vary, for example the cell may produce a single hypochlorite product stream from a one compartment cell. Alternatively, cells may be utilized to produce more than one effluent product, such as for example, hypochlorite, sodium hydroxide, hydrogen peroxide, etc. According to these embodiments there are more than one compartments, separated by a membrane which results in the production of distinct effluent streams from a cell. However, according to the invention, regardless of the cell structure the threshold agent beneficially inhibits water scaling to improve the longevity of the cell, as all such systems will produce caustic making the cell susceptible to scaling.
According to one embodiment, the threshold agent is added to the feed water going into the electrochemical cell. According to another embodiment, the threshold agent is added to the cathodic chamber of an electrochemical cell having two or more chambers. In a further embodiment, the threshold agent is added to the central chamber of a three compartment cell. In a still further embodiment, the threshold agent is added to the anodic chamber and crosses over a membrane into the cathodic chamber. According to a further embodiment, the threshold agent can be added to a chlorine generator for use in the swimming pool industry, such as in-line systems. Alternatively, the threshold agent may be added directly into pool water, where low voltage DC electricity is applied to the cells to produce chlorine gas, hydrogen gas, sodium ions and hydroxide ions forming hypochlorous acid and hypochlorite ion in the water that is then recirculated back into the pool. Still further, the threshold agent may be added directly to a water source, such as a pool, where a hypochlorite source is also added.
According to an embodiment of the invention, a method of making a hypochlorite source includes obtaining an electrochemical cell configured with at least one anode and cathode to produce hypochlorite, providing a water and a sodium chloride source to the electrochemical cell and applying an electric current to the electrochemical cell to produce hypochlorite. According to an embodiment, the threshold agent described according to the invention may be added directly to the electrochemical cell.
The threshold agent according to the invention does not require buffers for achieving sufficient threshold inhibition of scale formation as described herein. However, according to an embodiment of the invention, the pH of the electrolysis cell for hypochlorite product may be controlled by a buffer. According to an alternative embodiment the pH of the electrolytic solutions may further be buffered as required according to the preferred use of the acidic and/or basic electrolytes generated. For example, the acidic electrolytic water generated generally has a pH in the range of about 2.0 to about 3.5; whereas the pH of the alkaline electrolytic water has a pH in the range of about 10.5 to about 12.0. Additionally, the temperature of the electrochemical cell and the electrolytic water does not effect the threshold inhibition of scale formation as described herein.
The methods and compositions according to the invention may be further utilized with various types of feed water and aqueous sodium chloride feed. According to an embodiment, any feed water may be utilized without the requirement for softening the source. According to a further embodiment, aqueous sodium chloride feed may be pure or impure, for example salt water or brine. Preferably, the concentration of sodium chloride in the aqueous solution is at or below the saturation limit in water. Additionally, the methods and compositions according to the invention may be further utilized with various types of electrodes known by those of ordinary skill in the art to electrolyze water. For example, any variety of electrodes, including corrosion-resistant electrodes, may be utilized according to the methods and compositions of the invention. The electrode materials useful according to the invention are electrical conductors that are stable in the media to which they are exposed. These may include for example, titanium alloy, aluminum, niobium, chromium, manganese, molybdenum, ruthenium, tin, tantalum, vanadium, zirconium, nickel, cobalt, iron, copper, iridium and combinations of the same known to one of ordinary skill in the art. Additionally, one skilled in the art may ascertain the voltage required by the electrolytic cell according to the invention, based upon factors such as anolyte and catholyte solutions, membrane thickness and conductivity and other factors such as hypochlorite production. Determination of these and other optimum parameters for a particular electrochemical system can be readily ascertained by those skilled in the art through routine experimentation based upon the beneficial description provided herein.
According to the invention, the threshold agent compositions and methods of using the threshold agent to inhibit water scaling provide beneficial improvements in cell longevity. Additionally, the threshold agents and methods of using the same according to the invention do not interfere with or disrupt the production of chlorine or hypochlorite in an electrochemical cell. According to an embodiment of the invention, use of the threshold agent may increase the rate of hypochlorite formation from an electrochemical cell. Unlike the sequestrants and chelating agents of the prior art, the threshold agents according to the invention do not cause any detrimental effects on the rate of chlorine production or the concentration of chlorine produced in the cell. According to a further embodiment, the use of the threshold agent does not decrease the efficacy of the sanitizing hypochlorite effluent from the electrochemical cell, based upon EPA standards for sanitization. According to a preferred embodiment, the use of the threshold agent improves the efficacy of the hypochlorite as an antimicrobial agent that produced by an electrochemical cell.
According to the invention, the threshold agent unexpectedly results in a hypochlorite product having improved cleaning capabilities. Although not intending to be limited according to a particular theory, according to certain embodiments of adding the threshold agent to a brine source for hypochlorite production, an enhanced cleaning result is obtained. The presence of the threshold agent results in a cleaning, sanitizing and bleaching product that provides a cleaner result, without visible streaking or spotting. For example, use of the threshold agent-treated hypochlorite on clear surfaces such as glass or mirrors provides the unexpected result of a dried surface without streaking or spotting since the threshold agent inhibited the crystallization of salts in the hypochlorite. This is extremely beneficial for one compartment electrochemical cells producing hypochlorite or other cleaning materials where the caustic is not separated from the hypochlorite and unconverted chloride salt. According to this embodiment, the hypochlorite or other cleaning material has a high total dissolved solids remaining in the water interfering with a cleaned surface. In another embodiment, the hypochlorite product has a low total solids and the threshold agent provides reduced streaking and spotting on a treated surface due to the water hardness ions used to generate the hypochlorite.
All publications and patent applications in this specification are indicative of the level of ordinary skill in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated by reference.
It should be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes a composition having two or more compounds. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

EXAMPLES

Embodiments of the present invention are further defined in the following non-limiting Examples. It should be understood that these Examples, while indicating certain embodiments of the invention, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the embodiments of the invention to adapt it to various usages and conditions. Thus, various modifications of the embodiments of the invention, in addition to those shown and described herein, will be apparent to those skilled in the art from the foregoing description. For example, the threshold agent according to the invention and methods of using the same may be further utilized with electrochemical cell producing various effluents in addition to hypochlorite, such as hydrogen peroxide, sodium hydroxide (caustic), etc. Such modifications are also intended to fall within the scope of the appended claims.

Example 1

Electrode Scaling in Hard Water. A clean 1″×6″ pair of ruthenium (Ru) coated DSA electrodes for hypochlorite production was analyzed for hard water scaling. The pair of electrodes were placed in a stirred 4 L solution of 1000 ppm of sodium chloride. The sodium chloride solution was made using 17 grain (gpg) hard water. The electrodes in the sodium chloride solution were energized with about 8-12 volts/0.5 amps from a DC power source. After 4 hours in the electrochemical cell of the sodium chloride solution, the electrodes were removed and air dried. The electrodes were visually examined, revealing a heavy white scale covering the inside of the cathode.

Example 2

Prevention of Electrode Scaling in Hard Water With Threshold Agent. The same methods from Example 1 were repeated using a variety of polyacrylate threshold agents and a known reverse EO-PO copolymer threshold agent. The threshold agents were added to the 17 grain hard water sodium chloride solution.
First, using a clean 1″×6″ pair of Ru-coated DSA electrodes for hypochlorite production. The electrodes were placed in a stirred 4 L solution of 1000 ppm of sodium chloride and 100 ppm Acumer 1000 (an acrylic homopolymer of about 2000 molecular weight, available from Rohm & Haas as a 48% solids product). The electrodes in the sodium chloride solution were energized with about 8-12 volts/0.5 amps from a DC power source. After 4 hours, the electrodes were removed and air dried. No build-up of hard water scale was observed on the cathode submerged in the electrochemical cell containing the threshold agent.
The methods were repeated using solutions containing alternative threshold agents. Electrodes placed in a solution of 1000 ppm of sodium chloride and 100 ppm Acusol 448 (a acrylic acid/maleic acid copolymer of about 3200 molecular weight, available from Rohm & Haas) and treated using the same volts/amps from a DC power source resulted in a very slight build-up of hard water scale on the cathode. Electrodes placed in a solution of 1000 ppm of sodium chloride and 100 ppm Acusol 587 (an acrylic/sulfonic acid copolymer with a molecular weight of about 10,800, available from Rohm & Haas as a 37% solid product) and treated in an electrolyzed cell using the same volts/amps from a DC power source resulted in a very slight build-up of hard water scale on the cathode. Still further, electrodes placed in a solution of 1000 ppm of sodium chloride and 100 ppm Acusol 588 (an acrylic/sulfonic acid copolymer with a molecular weight of about 12,000, available from Rohm & Haas as a 37% solid product) according to the same methods and materials, resulted in a noticeable build-up of hard water scale on the cathode.
Electrodes placed in a solution of 1000 ppm of sodium chloride and 100 ppm Versa TL-4 (a sulfonated styrene/maleic acid copolymer with a molecular weight of about 20,000, commercially available from Alco as a 25% solids product) and treated in an electrolyzed cell using the same volts/amps from a DC power source resulted in a heavy build-up of hard water scale on the cathode. Electrodes tested in an electrolyzed cell containing a solution of 1000 ppm of sodium chloride and 100 ppm Acusol 460N (an olefin/maleic acid copolymer with a molecular weight of about 15,000, commercially available from Rohm & Haas as a 25% solid product) resulted in a noticeable build-up of water scale on the cathode. Additionally, electrodes tested in an electrolyzed cell containing a solution of 1000 ppm of sodium chloride and 100 ppm Pluronic N3 (a nonionic surfactant which is a reverse copolymer of ethylene oxide-propylene oxide available from BASF) also resulted in a noticeable build-up of water scale on the cathode.

Example 3

Effect of Threshold Inhibiter on Hypochlorite Formation Rate. A stirred 4 L solution of 1000 ppm of sodium chloride and 100 ppm Acumer 1000 (a polyacrylate of about 2000 molecular weight available from Akzo) was made using 17 grain hard water. A clean 1″×6″ pair of Ru-coated DSA electrodes for hypochlorite production were placed in the solution. The electrodes were energized with about 8-12 volts/0.5 amps from a DC power source in the electrochemical cell. Samples were periodically removed from the solution and titrated for available chlorine. FIG. 1 shows a plot of the titration data versus time, demonstrating that the threshold agent Acumer 1000 did not result in any decrease in the rate of hypochlorite formation in the electrochemical cell. Therefore, the polyacrylate threshold agent is capable of preventing hard water scale formation on the cathodes of the electrolyzed cell without decreasing the product of hypochlorite.
The methods were repeated using the same threshold agent (Acumer 1000) and compared to Acusol 445N. FIG. 2 shows a plot of the titration data versus time, comparing the effect on hypochlorite formation in the electrochemical cell of the threshold agent Acumer 1000 versus Acusol 445N. Although Acusol 445N caused reduction in scaling in the cell, the polymer significantly decreased the production of hypochlorite.
Although not intending to be limited to a particular theory, according to the invention, the Acusol 445 polymer interferes with hypochlorite production as a result of the polymer being water soluble and situating itself between the site of formation of the hydroxide (primarily at the cathode surface between electrode plates). The Acusol 445 polymer binds too tightly to the Ru-electrode surface and interferes with the electrochemical cell and production of the hydroxide. The Acumer 1000 polymer threshold agent is also a water soluble agent that may bind to the electrode surface, however, the polymer does not bind as tightly to interfere with the cell. One skilled in art would be able to select other threshold agents according to the invention based upon the material and construction of electrodes and the binding mechanism identified by Applicants.

Example 4

Effect of Threshold Inhibiter on Pool/Spa Applications Effecting Cell Longevity. FIGS. 3-7 show the pattern of increased voltage necessary in cells over time due to the detrimental effects of scaling. As described in the detailed description of the invention, as scale builds up on the cathode, the cell becomes less efficient and requires an increased amount of voltage to maintain hypochlorite production.
Kim, why do the volts not remain constant in FIGS. 3 and 4 (but remain constant with the hard water systems in FIG. 5-7)?
As one skilled in the art shall appreciate, the power supply of an electrochemical cell can run at either constant Amps or voltage (i.e. current (amps)=voltage/resistance). As a result, the equation (and figures shown herein) demonstrate that as scale builds up on electrodes of an electrochemical cell, the electrical resistances increases in order to maintain the constant Amps, resulting in an increase in voltage. Often commercial systems utilizing electrochemical cells, such as pools or spas, first receive an indication that damage is occurring in a cell as a result of increased Amps or voltage required to operate a system. This is often a result of the fact that the electrodes of a cell are not clearly visible for a person of ordinary skill in the art to detect the presence of scaling. However, the gradual and significant increase in Amps or voltage required to operate a system are an indicator that the system is not operating properly and require use of a threshold agent according to the invention.
FIGS. 3-7 show voltage requirements without the addition of the threshold agent according to the invention. FIGS. 3-4 show the use of the pH buffer sodium bisulfate in a cell. FIGS. 5-8 show hypochlorite production based on varying levels of water hardness, demonstrating the increased voltage demands with increasing water hardness as a result of scale forming on the cathodes. In all of FIGS. 3-8 the voltage is shown at a constant Amp to the cell.

Example 5

The threshold agent Acumer 1000 was added into an effluent stream of a one compartment cell for treating pools/spas. The effluent stream containing the threshold agent Acumer 1000 was added directly into the pool/spa to obtain a 100 ppm dilution of the Acumer 1000 threshold agent in the pool/spa water. The water diluted with the threshold agent according to the invention was run through the electrochemical cell with brine to be converted to hypochlorite and be continually circulated through the system. The effect of water scaling on the electrochemical cell was observed to determine effect on cell longevity.
The threshold agent can be added one-time to the pool system and recirculated for use through the electrochemical cell. Alternatively, the threshold agent may be added on an ongoing basis to replenish the threshold agent as needed, such as upon removal or purging of a large portion or the entirety of the water source of the pool. In addition, according to the invention, the threshold agent may be introduced as a low level constant stream to the system.
After nearly one year of testing, no noticeable scale has formed or built-up in the cell. In addition, no change in hypochlorite generation from the electrochemical cell producing hypochlorite for the pool/spa has been observed after over nearly one year of testing, demonstrating that according to the invention a threshold agent can be added directly to a water source treated with an electrochemical cell for the threshold agent to run through the cell with sodium chloride.

Example 6

The same methods from Examples 1-3 were repeated using a combination of threshold agents. The threshold agents Acusol 460 and Acusol 445 were combined in amounts and added to the 17 grain hard water sodium chloride solution. The combination of polymers demonstrated synergistic effects in the prevention of scale formation. After 3-4 hours of the harsh test conditions for the electrochemical cell, the electrodes were dried and observed for scale formation on the cathode. No formation was present.

Claims

1. A method for producing hypochlorite and reducing hard water scaling in an electrochemical cell without decreasing hypochlorite production comprising:

(a) obtaining an electrochemical cell configured with at least one anode and cathode to produce a hypochlorite source;

(b) providing a water and a sodium chloride source to said electrochemical cell;

(c) adding a threshold agent to said electrochemical cell in the amount of up to about 10,000 ppm, wherein said threshold agent is a water soluble polycarboxylate capable of preventing hard water scale formation on electrodes and membranes; and

(d) applying an electric current to the electrochemical cell to produce hypochlorite and reduce hard water scaling in said electrochemical cell, wherein said threshold agent does not decrease said hypochlorite production.

2. The method of claim 1 wherein said threshold agent is a water-insoluble resin.

3. The method of claim 1 wherein said polycarboxylate is selected from the group consisting of homopolymers and copolymers of polyacrylates, polyolefinic systems, polymaleic systems, derivatives and salts of the same, and combinations of the same.

4. The method of claim 3 wherein said polycarboxylate is Acumer 1000.

5. The method of claim 1 wherein said threshold agent is added in the amount of up to about 1,000 ppm and has a molecular weight less than 5,000.

6. The method of claim 1 wherein said threshold agent is added in the amount of from about 50 ppm to about 500 ppm and has a molecular weight less than 2000.

7. The method of claim 1 wherein said hypochlorite effectively cleans and/or sanitizes surfaces without depositing streaks or spotting.

8. A method for reducing hard water scaling in a water source and electrochemical cell producing hypochlorite for a water source without decreasing hypochlorite production comprising:

(a) obtaining a hypochlorite source in a pool, spa or other water source treated with an electrochemical cell;

(b) contacting said hypochlorite source with a threshold agent in the amount of up to about 10,000 ppm, wherein said threshold agent is a water soluble polycarboxylate with a molecular weight less than 5,000; and

(c) reducing hard water scale formation on electrodes and membranes of said electrochemical cell without decreasing hypochlorite production of said electrochemical cell.

9. The method of claim 8 wherein said threshold agent does not deactivate the oxidizing effects of said hypochlorite source in said pool, spa or other water source.

10. The method of claim 8 wherein said threshold agent is a polycarboxylate selected from the group consisting of homopolymers of polyacrylates, copolymers of polyacrylates, derivatives and salts of the same, polyolefinic systems, polymaleic systems and combinations of the same.

11. The method of claim 10 wherein said polycarboxylate is Acumer 1000.

12. The method of claim 8 wherein said threshold agent is added in the amount of up to about 1,000 ppm and has a molecular weight less than 2,000.

13. A method for increasing longevity of an electrochemical cell by reducing hard water scaling comprising:

(a) obtaining an electrochemical cell configured with at least one anode and cathode to produce a hypochlorite source, wherein a water and a sodium chloride source are circulated through said electrochemical cell to produce said hypochlorite;

(b) adding a threshold agent to said electrochemical cell in the amount of up to about 10,000 ppm, wherein said threshold agent is a water soluble polycarboxylate with a molecular weight less than 5,000; and

(c) applying an electric current to the electrochemical cell to produce at least one effluent without causing the precipitation of water hardness ions from the water source and forming hard water scaling.

14. The method of claim 13 wherein said threshold agent is added in the amount of from about 50 ppm to about 5,000 ppm.

15. The method of claim 13 wherein said sodium chloride source is brine.

16. The method of claim 13 wherein said polycarboxylate is selected from the group consisting of homopolymers of polyacrylates, copolymers of polyacrylates, derivatives and salts of the same, polyolefinic systems, polymaleic systems and combinations of the same.

17. The method of claim 16 wherein said polycarboxylate is Acumer 1000.

18. The method of claim 13 wherein said threshold agent is added in the amount of up to about 1,000 ppm and has a molecular weight less than 2,000.

19. The method of claim 18 wherein said threshold agent is added in the amount of from about 50 ppm to about 500 ppm.