WO2003042112A1

WO2003042112A1 - Electrochemically activated carbonate and bicarbonate salt solutions

Info

Publication number: WO2003042112A1
Application number: PCT/ZA2002/000177
Authority: WO
Inventors: Suha Rawhani; Jacobus Johannes Viljoen
Original assignee: Radical Waters IP Pty Ltd
Current assignee: Radical Waters IP Pty Ltd
Priority date: 2001-11-13
Filing date: 2002-11-13
Publication date: 2003-05-22
Anticipated expiration: 2004-05-13
Also published as: ZA200403656B

Abstract

The invention relates to the production of electrochemically activated aqueous solutions and to solutions so produced which, while retaining the advantages of chlorine-based anolyte and catholyte, overcome the disadvantages of corrosion and residual chlorine associated with chlorine-based solutions. Particularly, the invention provides electrochemically activating an aqueous solution of a carbonate and/or a bicarbonate salt. The invention also extends to an electromechanically activated dilute aqueous solution of a carbonate and/or a bicarbonate salt, and to use of the same in different applications.

Description

ELECTROCHEMICALLY ACTIVATED CARBONATE AND BICARBONATE SALT SOLUTIONS

Introduction This invention relates to a composition for the production of electrochemically activated aqueous salt solutions, to a method for the production of electrochemically activated aqueous salt solutions and to the use of such electrochemically activated solutions.

Background to the invention Electrochemical activation or electro-activation of dilute salt solutions in water has been the subject matter of several prior patents and publications. The prior art commonly discloses the use of electrochemical activation to produce an anolyte solution and a catholyte solution. Those who are engaged in the art will appreciate that an anolyte solution has a positive oxidation-reduction potential (ORP) or redox potential, which is oxidising and which has microbicidal properties. The catholyte solution, on the other hand, has a negative ORP, which has dispersive and surface active properties and can be used as a reducing agent.

Salts used in the prior art almost exclusively refer to sodium chloride (NaCI) and in most prior art applications chloride-based salts are used in a diluted form. However, there are various applications in which anolyte or catholyte are used in an undiluted form, but in many of these applications a major disadvantage of chloride based or chloride-derived activated solutions is that they are corrosive to the materials with which they come into contact. This is particularly intolerable in applications such as medical applications, where the solutions could typically be used for cold sterilisation of medical instruments such as endoscopes.

Chloride based or chloride-derived activated solutions, or halogen based or halogen derived activated solutions also cause a substantial problem in the food-processing industry, where the solutions could otherwise conveniently be used for disinfection and sterilisation of equipment. In addition to the disadvantage associated with its corrosive properties, these solutions may further be problematic under certain conditions of high dosage in the food industry where there is a real risk that the chlorine-based or halogen based solutions could come into direct contact with foodstuffs, leaving chlorine or halogen residues in such foodstuffs. This not only affects taste of the foodstuffs, but also may have health implications.

Another disadvantage associated with the use of chlorine-based anolyte and catholyte concerns use of the same in water treatment applications. During the treatment of water with chlorine-based or halogen based, anolyte and catholyte solutions, organohalides such as trichloromethane form. Although the concentration levels of such organohalides are usually low, future trends are towards totally halogen-free water, which would render the use of chlorine-based or chloride-derived, or halogen based or halogen derived anolyte and catholyte unsuitable.

Object of the invention

It is accordingly an object of the present invention to provide a method of producing an activated aqueous salt solution and a salt solution so produced which, while retaining the advantages of chlorine-based anolyte and catholyte, will overcome or at least minimise the disadvantages of corrosion and residual chlorine associated with the latter, or at least to provide a useful alternative to chlorine-based anolyte and catholyte.

It is a further object of the invention to provide for the use of such an activated aqueous salt solution in the treatment of water and biofilm.

Summary of the invention

According to the invention there is provided a method of producing an activated aqueous salt solution, the method comprising the steps of preparing a dilute aqueous solution of a carbonate and/or a bicarbonate salt; and applying electrical energy to the aqueous salt solution to electrochemically activate the same.

The method may include the step of electrochemically activating the dilute aqueous solution of carbonate or bicarbonate salt such that the solution includes separable and both of an aqueous, mixed oxidant, predominantly anion-containing solution and an aqueous, mixed reductant, predominantly cation-containing solution.

The salt may be selected from a group comprising alkali, alkali earth, base metal, or other carbonates and bicarbonates (as the case may be) as major constituents; and chlorides, phosphates, sulphates, nitrates, bicarbonates and carbonates (respectively, as the case may be) as minor or trace constituentsfor example, industrial grade sodium bicarbonate, medical or chemically pure-grade sodium carbonate or bicarbonate, potassium carbonate or bicarbonate, calcium carbonate or bicarbonate, magnesium carbonate or bicarbonate, zinc carbonate or bicarbonate, copper carbonate or bicarbonate (respectively, as the case may be), or a mixture of two or more of such salts. The electrochemically activated, aqueous solution may be produced from a relatively low concentration of the aqueous salt solution. Depending on the particular process being performed and the method of producing the electrochemically activated solution (e.g. with or without pre-dilution of the feed solutions) the aqueous salt solution concentration may be between 0.0001 % and 10%. For some specific systems without pre-dilution of the feed, the concentration of the aqueous salt solution may be between about 0.05% and 0.5%.

The electrochemically activated aqueous solution may be selected from a group comprising an anion-containing solution; a cation-containing solution; a mixture of an anion-containing solution and a cation-containing solution; an anion-containing solution having been prepared from an anion-containing solution, a cation-containing solution or a mixture of an anion-containing solution and a cation-containing solution; and a cation- containing solution having been prepared from an anion-containing solution, a cation- containing solution, or a mixture of an anion-containing solution and a cation-containing solution.

The anion-containing solution is referred to hereinafter for brevity as the "anolyte solution" or "anolyte" and the cation-containing solution is referred to hereinafter for brevity as the "catholyte solution" or "catholyte.

The salt solution may be electrolysed to produce anolyte and catholyte with mixed oxidant and mixed reductant species. These species may be labile and after about 96 hours, the concentration and activity of the various activated species may reduce substantially with relatively little, alternatively, no active residues remaining. The anolyte solution may have a redox potential of about between +300mV and +1 200mV. The anolyte solution may have a pH of between 2 and 9.5, and more preferably 7. Depending on the source of the water, the minor and trace salt(s) in the feed stream and the activation process, the anolyte solution may include species such as H⁺; H.; OH^"; H₂O₂;

H₃O⁺; HO.; HO₂; HO₂.; HO₂ ^"; O₃; O₂; 0₂.; 3O₂; 1 O₂; O.; HCO₃ ^"; CO₃ ^2"; C₂O₆ ^2""; Cl.; Cl₂;

CIO.; CIO; CIO-; CI₂O; CIO₂ ^"; HCI; HCIO; CI₂O₆ ^2"; CI₂O₇; S₂O₈ ^2"; H₂SO₄ and HS0₃CI.

The catholyte solution generally may have a pH of between 7 and 13, and preferably about

11.5, and a redox potential of between -200mV and -1100mV, and preferably about - 800mV. Depending on the minor and trace salt(s) in the feed stream and used in the activation process, the catholyte solution may include species such as OH^"; HO, H₂, H₂ ^'; H₂ ^"

, H₃ ^"; O₂; O₂ ^"; HO^"; HO₂ ; HO₂ ^" ; H₂O₂; H₃O₂ ^"; NaOH, KOH, Zn(OH)₂; Cu(OH); Ca(OH)₂,

and Mg(OH)₂. Analysis of the inorganic components of these solutions has shown varying

quantities of aluminium, calcium, magnesium, manganese, potassium, sodium, molybdenum, ammonium, orthophosphate, silica and chloride.

The anolyte and the catholyte may be produced by an electrochemical reactor or so-called electrolysis device, having a through-flow electrochemical cell with two co-axial cylindrical electrodes, with a tubular ceramic diaphragm located co-axially between the two electrodes so as to separate an annular inter-electrode space into a co-axial, annular catholytic and an annular anolytic chamber arrangement. The electrochemical cell may have predetermined design and geometrical relationships, ensuring optimum fluid flow and re- circulation patterns. The cell may have a relatively small, annular, cross-sectional total open area for fluid flow, thus causing turbulent fluid flow there through so as to ensure maximum exposure of the solutions to the electric field. The anolyte and catholyte may be produced in the electrochemical cell under predetermined operational parameters, including a relatively low current, preferably of about 5A to 15 A, and a relatively high voltage, preferably of about 6V to 48V, and more preferably between 12V and 36V, thus providing a relatively high voltage gradient or electric field intensity at the interface between the electrode surface and electrolyte, estimated to be about 10⁶ V/cm.

Varying levels of saline concentration and mineral content of the feed water, as well as the operational variables of the electrochemical reactor, particularly flow rates, flow regimes, flow paths and -rates of recycle, currents and potential differences, may be adjustable so as to produce anolyte and catholyte with various physical and chemical characteristics, specific conductivity, redox potential and pH, concentration of "activated" species and other characteristics, suitable for different particular applications.

According to another aspect of the invention there is provided an electrochemically activated aqueous solution prepared by means of electrolysis of a dilute aqueous solution of a salt, characterised therein that the salt is a carbonate and/or a bicarbonate salt.

The solution may further be characterised therein that it includes separable and both of an aqueous, mixed oxidant, predominantly anion-containing solution and an aqueous, mixed reductant, predominantly cation-containing solution.

In particular, the electrochemically activated aqueous solution may be prepared by means of electrolysis of an aqueous solution of a carbonate or a bicarbonate salt according to the method hereinbefore defined.

According to yet a further aspect of the invention there is provided at least three activated carbonate and/or bicarbonate base products, namely a solution of anolyte, a solution of catholyte and a solution of a mixture of anolyte and catholyte.

The activated carbonate and/or bicarbonate base products may be produced by a method as hereinbefore defined.

According to another aspect of the invention there is provided the use of an electrochemically activated aqueous salt solution, wherein the salt is characterised therein that it is a carbonate and/or a bicarbonate salt, in the treatment of water.

According to another aspect of the invention there is provided the use of an electrochemically activated aqueous salt solution, wherein the salt is characterised therein that it is a carbonate and/or a bicarbonate salt, in the production of water treatment reagents for use in the treatment of water.

The aqueous solution may be a relatively dilute carbonate or a bicarbonate salt solution.

According to yet a further aspect of the invention there is provided the use of an electrochemically activated aqueous salt solution, wherein the salt is characterised therein that it is a carbonate and/or a bicarbonate salt, in the treatment of biofilm.

According to another aspect of the invention there is provided the use of an electrochemically activated aqueous salt solution, wherein the salt is characterised therein that it is a carbonate and/or a bicarbonate salt, in the production of biofilm treatment reagents for use in the treatment and/or removal of biofilm.

According to another aspect of the invention there is provided a composition of the electrochemically activated aqueous salt solution, wherein the salt is characterised therein that it is a carbonate and/or a bicarbonate salt, and wherein the electrochemically activated aqueous salt solution after activation may contain species selected from a group including H⁺; H.; OH^"; H₂O₂; H₃O⁺; HO.; HO₂; HO₂.; HO₂ ^"; O₃; O₂; 0₂.; 3O₂; 10₂; O.; HCO₃ ^"; CO₃ ^2";

C₂O₆ ^2""; Cl.; Cl₂; CIO.; CIO; CIO^"; CI₂O; CIO₂ ^"; HCI; HCIO; CI₂O₆ ^2"; CI₂O_?; S₂O₈ ^2"; H₂SO₄ ,

HSO₃CI , OH^"; HO, H₂, H₂ ; H₂ ^", H₃ ^"; O₂; O₂ ^"; HO^"; HO₂-; HO₂ ^" ; H₂O₂; H₃O₂ ^"; NaOH, KOH,

Zn(OH)₂; Cu(OH); Ca(OH)₂, and Mg(OH)₂.

Specific embodiment of the invention Without limiting the scope of the invention, the tables hereunder illustrate some of the test results that have been obtained by laboratory testing of the activated aqueous salt solution according to the invention on various species of bacteria under different test conditions as set out below.

o The operating conditions were adjusted so as to obtain an anolyte stream with a pH of 7 units.

o Bacterial species tested as indicators: 4 - Eschrichia coli, Escherichia faecalis,

Staphilococcus aureus, Bacilus subtilis. o Microbial "challenge": log 6 or approximately 10⁶ organisms / ml o Contact times: 2 - 5 and 30 minutes. o Solution strengths / Dilutions: 4, Undiluted, 10%, 1 % and 0.1 % o The tables show bacterial colony counts after the test. No kill is equivalent to "too numerous to count" - TNTC

5 TEST 1 - Sodium bicarbonate anolyte

TEST 2 - Sodium bicarbonate catholvte

10

TEST 3 - Sodium bicarbonate mixed anolyte + catholvte in the ratio of approximately 2:1

15

TEST 4 - Sodium carbonate anolyte

TEST 5 - Sodium carbonate catholvte

TEST 6 - Sodium carbonate mixed anolyte + catholvte in the ratio of approximately 1 :3

10

Summary of operating conditions and parameters

It will be appreciated from the tables above, that anolyte produced from both bicarbonate 15 and carbonate salts is fully microcidal against the indicator organisms tested up to a dilution of 1 :10, or to a minimum concentration of 10% at both contact times of 5 and 30 minutes.

For the bicarbonate salt, catholyte and the mixture of anolyte and catholyte, as tested in 20 the ratio of approximately 2: 1 , was also efficacious as a microcidal agent in concentrations above 10%. The test results also indicate that the carbonate based catholyte and mixture of anolyte and catholyte in the ratio 1 :3, however, were not as effective in eliminating the indicator microorganisms as the bicarbonate derived ones.

It will be appreciated that many variations of the invention are possible without departing from the spirit or scope of the invention as defined in the claims.

Claims

1. A method of producing an electrochemically activated aqueous solution, the method comprising the steps of preparing an aqueous solution of either one or both of a carbonate and/or a bicarbonate salt; and applying electrical energy to the aqueous salt solution to electrochemically activate the same.

2. The method as claimed in claim 1 including the step of electrochemically activating the aqueous solution of the carbonate and/or bicarbonate salt such that the solution includes separable and both of an aqueous, mixed oxidant, predominantly anion- containing solution and an aqueous, mixed reductant, predominantly cation- containing solution.

3. The method as claimed in claim 1 characterised therein that the salt is selected from a group comprising alkali, alkali earth, base metal, or other carbonates and bicarbonates (as the case be) as major constituents; and chlorides, phosphates, sulphates, nitrates, bicarbonates and carbonates (respectively, as the case be) as minor or trace constituents, for example, industrial grade sodium bicarbonate, medical or chemically pure-grade sodium carbonate or bicarbonate, potassium carbonate or bicarbonate, calcium carbonate or bicarbonate, magnesium carbonate or bicarbonate, zinc carbonate or bicarbonate, copper carbonate or bicarbonate

(respectively, as the case be), or a mixture of two or more of such salts.

4. The method as claimed in claim 1 characterised therein that the electrochemically activated, aqueous solution is produced from a relatively low concentration of the aqueous solution of the carbonate and/or a bicarbonate salt, particularly a concentration of between 0.0001 % and 10%, and for some specific systems without pre-dilution of the feed, a concentration of between about 0.05% and 0.5%.

5. The method as claimed in claim 1 characterised therein that the electrochemically activated aqueous solution is selected from a group comprising an anion-containing solution; a cation-containing solution; a mixture of an anion-containing solution and a cation-containing solution; an anion-containing solution having been prepared from an anion-containing solution, a cation-containing solution or a mixture of an anion-containing solution and a cation-containing solution; and a cation-containing solution having been prepared from an anion-containing solution, a cation- containing solution, or a mixture of an anion-containing solution and a cation- containing solution.

6. The method as claimed in claims 1 and 2 characterised therein that the salt solution is electrolysed to produce anolyte and catholyte with mixed oxidant and mixed reductant species that are labile and after about 96 hours disappear with relatively little, alternatively no active residues remaining.

7. The method as claimed in claims 1 and 2 characterised therein that the anolyte solution has a redox potential of between about +300mV and +1 200mV, and a pH of between 2 and 9.5, and preferably 7; and wherein the catholyte solution has a redox potential of between -200mV and -1100mV, and preferably about -800mV, and a pH of between 7 and 13, and preferably about 11.5.

8. The method as claimed in claims 1 and 2 characterised therein that the anolyte solution includes species such as H ; H.; OH^"; H₂O₂; H₃O ; HO.; HO₂; HO₂.; HO₂ ^";

O₃; O₂; O₂.; 3O₂; 1 O₂; O.; HCO₃ ^"; CO₃ ^2"; C₂O₆ ^2"; CL; Cl₂; CIO.; CIO; CIO^"; CI₂O;

CIO₂ ^"; HCI; HCIO; CI₂O₆ ^2"; CI₂O₇; S₂O₈ ^2"; H₂SO₄; and HSO₃CI.

9. The method as claimed in claims 1 and 2 characterised therein that the catholyte solution includes species such as OH^"; HO, H₂, H₂ ^'; H₂ ^", H₃ ^"; O₂; O₂ ^"; HO^"; HO₂-;

HO₂ ^" ; H₂O₂; H₃O₂ ^"; NaOH, KOH, Ca(OH)₂ and Mg(OH)₂.

10. The method as claimed in claims 1 and 2 characterised therein that the anolyte and the catholyte are produced by an electrochemical reactor or so-called electrolysis device, having a through-flow electrochemical cell with two co-axial cylindrical electrodes, with a tubular ceramic diaphragm located co-axially between the two electrodes so as to separate an annular inter-electrode space into a co-axial, annular catholytic and an annular anolytic chamber arrangement, and wherein the electrochemical cell has an annular cross-sectional total open area for fluid flow of between 100 and 1000 mm² for causing turbulent fluid flow there through.

11. The method as claimed in claim 10 characterised therein that the anolyte and catholyte are produced in the electrochemical cell under a current of about 5A to 15A, and a voltage of about 6V to 48V, and preferably a voltage of between 12V and 36V.

12. The method as claimed in claim 10 characterised therein that the physical and chemical characteristics, including specific conductivity, redox potential and pH, concentration of activated species and other characteristics of the anolyte and catholyte are adjusted for particular applications by varying such parameters as the levels of saline concentration and the mineral content of the feed water, as well as the operational variables of the electrochemical reactor, including flow rates, flow regimes, -paths and -rates of recycle, currents and potential differences.

13. An electrochemically activated aqueous solution prepared by means of electrolysis of a dilute aqueous solution of a salt, characterised therein that the salt is a carbonate and/or a bicarbonate salt.

14. The electrochemically activated aqueous solution as claimed in claim 13 characterised therein that the solution includes separable and both of an aqueous, mixed oxidant, predominantly anion-containing solution and an aqueous, mixed reductant, predominantly cation-containing solution.

15. The electrochemically activated aqueous solution as claimed in claim 13 characterised therein that the solution is prepared by means of electrolysis of an aqueous solution of a carbonate or a bicarbonate salt, produced by an electrochemical reactor or so-called electrolysis device, having a through-flow electrochemical cell with two co-axial cylindrical electrodes, with a tubular ceramic diaphragm located co-axially between the two electrodes so as to separate an annular inter-electrode space into a co-axial, annular catholytic and an annular anolytic chamber arrangement, and wherein the electrochemical cell has a relatively small annular cross-sectional total open area for fluid flow for causing turbulent fluid flow there through, and under a current of about 5A to 15A, and a voltage of about 6V to 48V, and preferably a voltage of between 12V and 36V.

16. The use of an electrochemically activated aqueous salt solution, characterised therein that the salt is a carbonate and/or a bicarbonate salt, in the treatment of water.

17. The use of an electrochemically activated aqueous salt solution, characterised therein that the salt is a carbonate and/or a bicarbonate salt, in the production of water treatment reagents for use in the treatment of water.

18. The use of an electrochemically activated aqueous salt solution, characterised therein that the salt is a carbonate and/or a bicarbonate salt, in the treatment of biofilm.

19. The use of an electrochemically activated aqueous salt solution, characterised therein that the salt is a carbonate and/or a bicarbonate salt, in the production of biofilm treatment reagents for use in the treatment and/or removal of biofilm.