(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2003/0042134 A1
`
`Mar. 6, 2003
`(43) Pub. Date:
`Tremblay et al.
`
`US 20030042134A1
`
`HIGH EFFICIENCY ELECTROLYSIS CELL
`FOR GENERATING OXIDANTS IN
`SOLUTIONS
`
`(22)
`
`Filed:
`
`Dec. 21, 2001
`
`Related US. Application Data
`
`(54)
`
`(75)
`
`Inventors: Mario Elmen Tremblay, West Chester,
`OH (US); Craig Merillat Rasmussen,
`Loveland, OH (US); Charles Andrew
`Hong, Cincinnati, OH (US); Donald
`Stephen Bret], West Chester, OH (US)
`
`Correspondence Address:
`THE PROCTER & GAMBLE COMPANY
`INTELLECTUAL PROPERTY DIVISION
`WINTON HILL TECHNICAL CENTER - BOX
`161
`6110 CENTER HILL AVENUE
`CINCINNATI, OH 45224 (US)
`
`(73)
`
`Assignee: The Procter & Gamble Company
`
`(21)
`
`Appl. N0.:
`
`10/027,667
`
`(60)
`
`Provisional application No. 60/300,211, filed on Jun.
`22, 2001.
`
`Publication Classification
`
`(51)
`(52)
`
`Int. C1.7 .............................. C25B 15/00, C25B 9/00
`US. Cl.
`...................... 204/228.1; 204/232, 204/238;
`204/237, 204/275.1
`
`ABSTRACT
`
`(57)
`Amethod for killing microorganisms in water, by passing an
`aqueous feed solution comprising of water containing some
`form of halide salt into a non-membrane electrolysis cell
`comprising an anode and a cathode, adjacent to the anode,
`While flowing electrical current between the anode and the
`cathode t0 electrolyze the aqueous feed solution and convert
`the halide salt to anti-microbial mixed oxidants.
`
`
`
`Tennant Company
`Exhibit 1145
`
`1
`
`Tennant Company
`Exhibit 1145
`
`

`

`Patent Application Publication Mar. 6, 2003 Sheet 1 0f 9
`
`US 2003/0042134 A1
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`US 2003/0042134 A1
`
`Mar. 6, 2003
`
`HIGH EFFICIENCY ELECTROLYSIS CELL FOR
`GENERATING OXIDANTS IN SOLUTIONS
`
`FIELD OF THE INVENTION
`
`[0001] This invention relates to devices and methods for
`generating mixed oxidants, such as hypochlorite and chlo-
`rine, from aqueous solutions containing naturally present
`salts (e.g. naturally present NaCl) or added salts (e.g. added
`NaCl). Our approach employs a voltage potential across a
`pair of electrodes to induce current flow through the water,
`to electrolyze the water that passes between the electrodes,
`thereby sterilizing the water. As contaminated water passes
`between the electrodes, the microorganisms are killed and
`the water is sterilized. Additionally, the treated water also
`retains some residual biocidal benefit, due to the reactions
`involving residual chloride ions within the water that gen-
`erate biocidal agents such as free chlorine (C12), hypochlo-
`rous acid ions (OCL'), and other biocidal ions and free
`radicals. Two of the key parameters that have led to the
`improvements in efficiency of the electrolysis of the chloride
`ions, to enable effective kill of microorganisms in water, are
`the elimination of the membrane separating the anode and
`cathode and the close proximity of the two electrodes (e.g.
`<0.5 mm). As a result, we have developed several small,
`efficient, portable, battery-powered devices that can effec-
`tively kill microorganisms in contaminated solutions.
`
`BACKGROUND OF THE INVENTION
`
`[0002] Various oxidants, such as hypochlorite, chlorine,
`chlorine dioxide and other chlorine based oxidants, are some
`of the most effective antimicrobial agents for use in indus-
`trial and domestic process and services, and for commercial
`and consumer products. The strong oxidative potential of
`these oxidant molecules make it ideal for a wide variety of
`uses that include disinfecting and sterilizing. Concentrations
`of oxidant species in an aqueous solution as low as 1 part per
`million (ppm) or less, are known to kill a wide variety of
`microorganisms, including bacteria, viruses, molds, fungi,
`and spores. Higher concentrations of oxidants, up to several
`hundred ppms, provide even higher disinfection and oxida-
`tion of numerous compounds for a variety of applications,
`including the wastewater treatment, industrial water treat-
`ment (e.g. cooling water), fruit-vegetable disinfection, oil
`industry treatment of sulfites, textile industry, and medical
`waste treatment. Oxidants can react with and break down
`
`phenolic compounds, and thereby removing phenolic-based
`tastes and odors from water. Oxidants are also used in
`
`treating drinking water and wastewater to eliminate cya-
`nides, sulfides, aldehydes and mercaptans.
`
`[0003] While separate-compartment, membrane-contain-
`ing electrolysis cells have been used to make hypochlorite
`and other oxidants on a commercial scale, they have not
`been completely satisfactory at
`the consumer level (i.e.
`small and portable). Even though there have been some
`electrochemical units that we developed for consumer appli-
`cations using the electrochemical approach,
`these have
`proven to be more expensive to produce and have required
`larger amounts of power to achieve the desired efficacy. The
`electrolysis cells in commercial use, and disclosed in the
`prior art
`that utilize ion permeable membranes or dia-
`phragms, require that the anolyte solution be substantially
`free of divalent cations, such as magnesium and calcium, to
`avoid the formation of precipitated calcium or magnesium
`
`11
`
`salts that would quickly block and cover the membrane, and
`significantly reduce or stop the electrolysis reaction.
`
`[0004] Consequently, there remains a need for a simple,
`safe method and apparatus for manufacturing these antimi-
`crobial oxidants for domestic uses, under a wide variety of
`situations. The present invention describes a method and an
`apparatus for making antimicrobial oxidants inexpensively,
`easily and effectively.
`
`SUMMARY OF THE INVENTION
`
`invention relates to a method for
`[0005] The present
`making antimicrobial oxidants from an aqueous solution
`comprising of naturally present salts (e.g. water naturally
`containing NaCl), or added salts (e.g. water to which NaCl
`was added) using a non-membrane electrolysis cell. A non-
`membrane electrolysis cell is an electrolysis cell that com-
`prises an anode electrode and a cathode electrode, and
`having a cell chamber, and which does not have an ion
`permeable membrane that divides the cell passage into two
`(or more) distinct anode and cathode chambers. The various
`salts are converted to antimicrobial oxidants as electricity
`passes through the aqueous feed solution in a passage that
`forms a portion of the cell chamber adjacent to the surface
`of the anode.
`
`[0006] The present invention provides a method for mak-
`ing antimicrobial oxidants, comprising the steps of:
`(1)
`providing an aqueous feed solution comprising of natural
`water or water to which a chloride salt is already present or
`to which chloride salt has been added; (2) passing the
`aqueous feed solution into a cell chamber of a non-mem-
`brane electrolysis cell comprising an anode and a cathode,
`and along a passage adjacent to the anode; (3) flowing an
`electrical current between the anode and the cathode,
`thereby electrolyzing the aqueous feed solution in the pas-
`sage, whereby a portion of the salt
`in the passage is
`converted to antimicrobial oxidants; and (4) passing the
`electrolyzed aqueous solution out of the electrolysis cell,
`thereby forming an aqueous effluent comprising antimicro-
`bial oxidants not needed based on the approach we chose as
`listed in claims 1.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0007] The various advantages of the present invention
`will become apparent to skilled artisans after studying the
`following specification and by reference to the drawings in
`which:
`
`[0008] FIG. 1 shows an electrolysis cell used in the
`practice of the present invention;
`
`[0009] FIG. 2 shows a sectional view of the electrolysis
`cell of FIG. 1 though line 2-2;
`
`[0010] FIG. 3 shows a sectional view of an alternative
`electrolysis cell used in the practice of the present invention;
`
`[0011] FIG. 4 is a sectional view of another electrolysis
`cell having a porous anode;
`
`[0012] FIG. 5 is a sectional view of yet another electroly-
`sis cell having a porous anode;
`
`[0013] FIG. 6 is a sectional view of another electrolysis
`cell having a porous anode and a porous flow barrier;
`
`11
`
`

`

`US 2003/0042134 A1
`
`Mar. 6, 2003
`
`[0014] FIG. 7 is a sectional view of yet another electroly-
`sis cell having a porous anode and a porous flow barrier;
`
`[0015] FIG. 8 is a sectional view of still another elec-
`trolysis cell having a porous anode and a porous flow barrier;
`
`[0016]
`ration;
`
`FIG. 9 is a block diagram of a flow cell configu-
`
`[0017] FIG. 10 is a block diagram of a recirculation cell
`configuration;
`
`[0018] FIG. 11 is a block diagram of a flow cell having a
`filter mechanism;
`
`[0019] FIG. 12 is a block diagram of a recirculation cell
`having a filter mechanism;
`
`[0020] FIG. 13 is a block diagram of a flow cell having an
`off/on sensor;
`
`[0021] FIG. 14 is a block diagram of a recirculation cell
`having an off/on sensor;
`
`[0022] FIG. 15 is a block diagram of a flow cell having an
`ion exchange resin; and
`
`erably maximize the flow of the aqueous feed solution
`through this surface layer adjacent the anode, in order to
`maximize the conversion of antimicrobial oxidants. Addi-
`
`tionally, the removal of the membrane, that typically sepa-
`rates the anode and cathode compartment, also increases the
`reaction rate by preventing the slow migration of ions across
`this membrane.
`
`[0027] The present invention relates to the production of
`one or more mixed oxidant products and can include
`hypochlorite, chlorine, chlorine dioxide, ozone, hydrogen
`peroxide, and several other chlor-oxigenated species.
`
`[0028] The aqueous feed solution comprises of an elec-
`trolytic solution made of at least one halide salt, which for
`simplicity will be exemplified herein after by the most
`preferred halide salt, sodium chloride. Sodium chloride is a
`salt ordinarily found in tap water, well water, and other water
`sources. Consequently, there is usually sufficient chloride
`ion in the water to yield a desired concentration of mixed
`oxidants. It is also possible that an amount of the sodium
`chloride salt is added into the aqueous feed solution at a
`desired concentration generally of at least 0.1 ppm.
`
`[0023] FIG. 16 is a block diagram of a recirculation cell
`having an ion exchange resin.
`
`[0029] The level of chloride salt comprised in the aqueous
`feed solution can be selected based on the level of disinfec-
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`[0024] The present invention employs an electrical current
`passing through an aqueous feed solution between an anode
`and a cathode to convert
`low levels of salt precursors,
`whether they are naturally present in water (e.g. rivers or
`wells) or later dissolved within the solution (e.g. added salts
`such as NaCl). When an aqueous solution flows through the
`chamber of the electrolysis cell, and electrical current is
`passed between the anode and the cathode, several chemical
`reactions occur that involve the water, as well as one or more
`of the other salts or ions contained in the aqueous solution.
`
`[0025] At the anode, within a narrow layer of the aqueous
`solution in the passage adjacent to the anode surface, the
`following chlorine generating reaction occurs:
`2Cl’<——>Cl2 (g)+2e’.
`
`[0026] Chlorine gas (C12) generated by the chlorine reac-
`tion dissolves in the water to generate hypochlorite ions
`(OCL‘). Note that several other potential chlorine-oxygen
`reactions (e.g. chlorine dioxide) may also take place. With-
`out being bound by any particular theory, it is believed that
`the anode electrode withdraws electrons from the water and
`
`to the anode, which results in the
`other ions adjacent
`formation of antimicrobial oxidative species in the narrow
`surface layer of aqueous feed solution. This surface layer, at
`the anode interface, is believed to be about 100 nanometers
`in thickness. As a result, the smaller gap size has led to
`higher efficiency conversion than a larger gap size. Of
`course, a certain limitation will exist as which point it is no
`longer possible to flow the aqueous solution without sig-
`nificant back pressure or the gap is so small that a very large
`current is drawn due to the low resistance between the
`
`electrodes. Flow dynamics, which include the movement of
`molecules in a flowing solution by turbulence, predict that
`the conversion of salts will increase as the solution flow path
`nears the anode surface layer. Consequently, electrolysis
`cells and electrolysis systems of the present invention pref-
`
`tion required by the chlorine containing species (e.g.
`hypochlorite), in addition to the conversion efficiency of the
`electrolysis cell to convert the sodium chloride to the mixed
`oxidant products. The level of sodium chloride naturally
`present or added is generally from about 1 ppm to about 500
`ppm. For disinfection of a water source, a sodium chloride
`level is preferably from about 1 ppm to about 300 ppm, and
`more preferably about 10 ppm to about 200 ppm. The
`resulting mixed oxidant product level is from about 0.1 ppm
`to about 10 ppm, preferably from about 1 ppm to about 2
`PPm
`
`[0030] The range of mixed oxidant conversion from the
`chloride salt that is achievable in the electrolysis cells of the
`present invention generally ranges from less than about 1%
`to about 99%. The level of conversion is dependent most
`significantly on the design of the electrolysis cell, herein
`after described, as well as on the electrical current properties
`used in the electrolysis cell.
`
`[0031] The aqueous feed solution can optionally comprise
`one or more other salts in addition to the sodium chloride.
`
`These optional salts can be used to enhance the disinfection
`performance of the effluent
`that
`is discharged from the
`electrolysis cell, or to provide other mixed oxidants in
`response to the passing of electrical current through the
`electrolysis cell. Another preferred salt is sodium bromide.
`Apreferred apparatus and method for electrolyzing aqueous
`solutions comprising alkali halides is disclosed in co-pend-
`ing, commonly assigned US. provisional patent application
`60/280,913 (Docket 8492P), filed on Apr. 2, 2001. Other
`preferred salts consist of alkali halite, and most preferably
`sodium chlorite. A preferred apparatus and method for
`electrolyzing aqueous solutions comprising alkali halites is
`disclosed in as exampled in US. patent application Ser. No.
`09/947,846 which is hereby incorporated by reference.
`
`[0032] The present invention can optionally use a local
`source of chloride salt, and a means for delivering the
`chloride salt to the aqueous feed solution. This embodiment
`is advantageously used in those situations when the target
`
`12
`
`12
`
`

`

`US 2003/0042134 A1
`
`Mar. 6, 2003
`
`water to be treated with the electrolysis cell does not contain
`a sufficient amount, or any, of the chloride salt. The local
`source of chloride salt can be released into a stream of the
`
`aqueous solution, which then passes through the electrolysis
`cell. The local source of chloride salt can also be released
`
`into a portion of a reservoir of aqueous solution, which
`portion is then drawn into the electrolysis cell. Preferably, all
`the local source of chloride salt passes through the elec-
`trolysis cell, to maximize the conversion to mixed oxidants,
`and to limit the addition of salts to the reservoir generally.
`The local source of chloride salt can also supplement any
`residual
`levels of chloride salt already contained in the
`aqueous solution.
`
`[0033] The local source of chloride salt can be a concen-
`trated brine solution, a salt tablet in fluid contact with the
`reservoir of electrolytic solution, or both. Apreferred local
`source of chloride salt is a solid or powdered material. The
`means for delivering the local source of chloride salt can
`comprise a salt chamber comprising the chloride salt, pref-
`erably a pill or tablet, through which a portion of the aqueous
`solution passes, thereby dissolving a portion of the chloride
`salt to form the aqueous feed solution. The salt chamber can
`comprise a salt void formed in the body of the device that
`holds the electrolysis cell, which is positioned in fluid
`communication with the portion of aqueous solution that
`will pass through the electrolysis cell.
`
`[0034] Any water source can be used to form the aqueous
`feed solution,
`including well water,
`tap water, softened
`water, and industrial process water, and waste waters. How-
`ever, for many applications of the invention, untreated water,
`such as river water or well water is most preferred to form
`an effluent solution with essentially only naturally present
`chloride ions present. Since these types of natural water
`contain sufficient amounts of salts, including sodium chlo-
`ride, appreciable amounts of mixed oxidants will be formed.
`
`[0035] The addition of other salts or electrolytes into the
`selected water source will increase the conductivity of the
`water, which will increase the amount of mixed oxidants
`produced. However, the increase in conductivity may not
`result in higher productivity efficiency, since the increase in
`conductivity will increase the current draw. Therefore, while
`more mixed oxidants will be produced, more power will be
`drawn. A suitable mixed oxidant productivity equation is
`expressed by equation I,
`TI=(CM0”‘Q)/(1"‘V)
`
`(I)
`
`[0036] wherein:
`
`11 units are micrograms of mixed oxidant per
`[0037]
`minute, per watt of power used;
`
`[0038] CMO is the concentration of the generated
`mixed oxidants in milligrams per liter (mg/l);
`
`[0039]
`
`I is the electric current in amps;
`
`[0040] Q is the volumetric flow rate in milliliters per
`minute (ml/m); and
`
`[0041] V is electric potential across the cell in volts.
`
`[0042] The aqueous feed solution containing the sodium
`chloride can be fed to the electrolysis cell from a batch
`storage container. Alternatively,
`the feed solution can be
`prepared continuously by admixing a concentrated aqueous
`solution of sodium chloride with a second water source, and
`
`13
`
`passing continuously the admixture to the electrolysis cell.
`Optionally, a portion of the aqueous feed solution can
`comprise a recycled portion of the effluent from the elec-
`trolysis cell. And, the aqueous feed solution can comprise a
`combination of any of the forgoing sources. The aqueous
`feed solution can flow continuously or periodically through
`the electrolysis cell.
`
`Electrolysis Cell
`
`[0043] The electrolysis cell generates mixed oxidants
`from the chloride ions by flowing electrical current through
`the aqueous feed solution that passes through the cell
`chamber. The non-barrier electrolytic cell comprises at least
`a pair of electrodes, an anode and a cathode. The cell also
`comprises a cell chamber through which the aqueous feed
`solution passes, and includes a passage that is adjacent to the
`anode. The passage includes the narrow surface layer adja-
`cent to the anode surface where the conversion reaction
`
`occurs. It is preferred to pass as much of the mass of the
`aqueous effluent solution through the passage and its narrow
`anode surface region as possible.
`
`In one embodiment of the present invention, the
`[0044]
`cell comprises an anode and a confronting (and preferably,
`co-extensive) cathode that are separated by a cell chamber
`that has a shape defined by the confronting surfaces of the
`pair of electrodes. The cell chamber has a cell gap, which is
`the perpendicular distance between the two confronting
`electrodes. Typically,
`the cell gap will be substantially
`constant across the confronting surfaces of the electrodes.
`The cell gap is preferably 0.5 mm or less, more preferably
`0.2 mm or less.
`
`[0045] The electrolysis cell can also comprise two or more
`anodes, or two or more cathodes. The anode and cathode
`plates are alternated so that an anode is confronted by a
`cathode on each face, with a cell chamber there between.
`Examples of electrolysis cells that can comprise a plurality
`of anodes and cathodes are disclosed in US. Pat. No.
`5,534,120, issued to Ando et al. on Jul. 9, 1996, and US. Pat.
`No. 4,062,754, issued to Eibl on Dec. 13, 1977, which are
`incorporated herein by reference.
`
`the electrolysis cell will have one or
`[0046] Generally,
`more inlet openings in fluid communication with each cell
`chamber, and one or more outlet openings in fluid commu-
`nication with the chambers. The inlet opening is also in fluid
`communication with the source of aqueous feed solution,
`such that the aqueous feed solution can flow into the inlet,
`through the chamber, and from the outlet of the electrolysis
`cell. The effluent solution (the electrolyzed aqueous feed
`solution that exits from the electrolysis cell) comprises an
`amount f mixed oxidant that was converted within the cell
`
`passage in response to the flow of electrical current through
`the solution. The effluent solution can be used as a source of
`
`mixed oxidants, for example, for disinfecting articles, or for
`treating other volumes of water or aqueous solutions. The
`effluent can itself be a treated solution, where the feed
`solution contains microorganisms or some other oxidizable
`source material that can be oxidized in situ by the mixed
`oxidant solution that is formed.
`
`[0047] The present invention also provides a mixed oxi-
`dant generating system, comprising:
`[0048]
`a) a source of an aqueous feed solution com-
`prising a halide salt;
`
`13
`
`

`

`US 2003/0042134 A1
`
`Mar. 6, 2003
`
`b) a non-membrane electrolysis cell having a
`[0049]
`cell chamber, and comprising an anode and a cath-
`ode, the cell chamber having a passage adjacent to
`the anode, and an inlet and an outlet in fluid com-
`munication with the cell chamber;
`
`c) a means for passing the aqueous feed
`[0050]
`solution into the cell chamber, along the passage, and
`out of the outlet; and
`
`d) an electric current supply to flow a current
`[0051]
`through the aqueous solution in the chamber,
`to
`convert a portion of the halide salt in the passage to
`mixed oxidants, and thereby form an aqueous efflu-
`ent comprising of mixed oxidants.
`
`[0052] FIG. 1 and FIG. 2 show an embodiment of an
`electrolysis cell 10 of the present invention. The cell com-
`prises an anode 21 electrode, and a cathode 22 electrode.
`The electrodes are held a fixed distance away from one
`another by a pair of opposed non-conductive electrode
`holders 30 having electrode spacers 31 that space apart the
`confronting longitudinal edges of the anode and cathode to
`form a cell chamber 23 having a chamber gap. The chamber
`23 has a cell
`inlet 25 through which the aqueous feed
`solution can pass into of the cell, and an opposed cell outlet
`26 from which the effluent can pass out of the electrolysis
`cell. The assembly of the anode and cathode, and the
`opposed plate holders are held tightly together between a
`non-conductive anode cover 33 (shown partially cut away)
`and cathode cover 34, by a retaining means (not shown) that
`can comprise non-conductive, water-proof adhesive, bolts,
`or other means,
`thereby restricting exposure of the two
`electrodes only to the electrolysis solution that flows through
`the chamber 23. Anode lead 27 and cathode lead 28 extend
`
`laterally and sealably through channels made in the elec-
`trode holders 30.
`
`[0053] FIG. 2 shows cell chamber 23 and the passage 24
`along the anode 21 surface. The passage 24 is a portion of
`the cell chamber 23, though it is shown with a boundary 29
`only to illustrate its adjacent to the anode 21, and not to show
`the relative proportion or scale relative to the cell chamber.
`
`[0054] Another embodiment of the electrolysis cell of the
`present invention is shown in FIG. 3. This electrolysis cell
`has an anode outlet 35. The anode outlet removes a portion
`of the electrolyzed feed solution flowing in the passage 24
`adjacent the anode 21 as an anode effluent. The remainder of
`the cell effluent exits from the cell outlet 26, which hereafter
`will also be referred to as the cathode effluent and the
`
`cathode outlet, respectively. Similar electrolysis cells that
`remove a portion of the electrolyzed solution flowing adja-
`cent the anode through an anode outlet are described in US.
`Pat. No. 5,316,740, issued to Baker et al. on May 31, 1994,
`US. Pat. No. 5,534,120 issued to Ando et al. on Jul. 9, 1996,
`and US. Pat. No. 5,858,201, issued to Otsuka et al. on Jan.
`12, 1999. Particularly preferred is an electrolysis cell as
`shown in FIG. 3 of US. Pat. No. 4,761,208 that uses a
`physical barrier (element 16) positioned between the anode
`and the cathode adjacent the outlet, whereby mixing of the
`solution adjacent the anode with the solution adjacent the
`cathode can be minimized or eliminated prior to removal
`through the anode outlet. Preferably, the cathode effluent,
`which will comprise a low level or no mixed oxidant
`product, is passed back to and mixed into the aqueous feed
`solution.
`
`14
`
`[0055] An electrode can generally have any shape that can
`effectively conduct electricity through the aqueous feed
`solution between itself and another electrode, and can
`include, but is not limited to, a planar electrode, an annular
`electrode, a spring-type electrode, and a porous electrode.
`The anode and cathode electrodes can be shaped and posi-
`tioned to provide a substantially uniform gap between a
`cathode and an anode electrode pair, as shown in FIG. 2. On
`the other hand, the anode and the cathode can have different
`shapes, different dimensions, and can be positioned apart
`from one another non-uniformly. The important relationship
`between the anode and the cathode is for a sufficient flow of
`
`through the anode at an appropriate voltage to
`current
`promote the conversion of the halide salt to mixed oxidants
`within the cell passage adjacent the anode.
`
`[0056] Planar electrodes, such as shown in FIG. 2, have a
`length along the flow path of the solution, and a width
`oriented transverse to the flow path. The aspect ratio of
`planar electrodes, defined by the ratio of the length to the
`width,
`is generally between 0.2 and 10, more preferably
`between 0.1 and 6, and most preferably between 2 and 4.
`
`[0057] The electrodes, both the anode and the cathode, are
`commonly metallic, conductive materials, though non-me-
`tallic conducting materials, such as carbon, can also be used.
`The materials of the anode and the cathode can be the same,
`but can advantageously be different. To minimize corrosion,
`chemical resistant metals are preferably used. Examples of
`suitable electrodes are disclosed in US. Pat. No. 3,632,498
`and US. Pat. No. 3,771,385. Preferred anode metals are
`stainless steel, platinum, palladium, iridium, ruthenium, as
`well as iron, nickel and chromium, and alloys and metal
`oxides thereof. More preferred are electrodes made of a
`metals such as titanium, tantalum, aluminum, zirconium,
`tungsten or alloys thereof, which are coated or layered with
`a Group VIII metal that is preferably selected from platinum,
`iridium, and ruthenium, and oxides and alloys thereof. One
`preferred anode is made of titanium core and coated with, or
`layered with, ruthenium, ruthenium oxide, iridium, iridium
`oxide, and mixtures thereof, having a thickness of at least
`0.1 micron, preferably at least 0.3 micron.
`
`[0058] For many applications, a metal foil having a thick-
`ness of about 0.03 mm to about 0.3 mm can be used. Foil
`
`electrodes should be made stable in the cell so that they do
`not warp or flex in response to the flow of liquids through the
`passage that can interfere with proper electrolysis operation.
`The use of foil electrodes is particularly advantageous when
`the cost of the device must be minimized, or when the
`lifespan of the electrolysis device is expected or intended to
`be short, generally about one year or less. Foil electrodes can
`be made of any of the metals described above, and are
`preferably attached as a laminate to a less expensive elec-
`trically-conductive base metal, such as tantalum, stainless
`steel, and others.
`
`[0059] A particularly preferred anode electrode of the
`present inventions is a porous, or flow-through anode. The
`porous anode has a large surface area and large pore volume
`sufficient to pass there through a large volume of aqueous
`feed solution. The plurality of pores and flow channels in the
`porous anode provide a greatly increased surface area pro-
`viding a plurality of passages, through which the aqueous
`feed solution can pass. Porous media useful in the present
`invention are commercially available from Astro Met Inc. in
`
`14
`
`

`

`US 2003/0042134 A1
`
`Mar. 6, 2003
`
`Cincinnati, Ohio, Porvair Inc. in Henderson, NO, or Mott
`Metallurgical in Farmington, Conn. Alternately US. Pat.
`Nos. 5,447,774 and 5,937,641 give suitable examples of
`porous media processing. Preferably, the porous anode has
`a ratio of surface area (in square centimeters) to total volume
`(in cubic centimeters) of more than about 5 cm'l, more
`preferably of more than about 10 cm'l, even more prefer-
`ably more than about 50 cm'l, and most preferably of more
`than about 200 cm'l. Preferably the porous anode has a
`porosity of at least about 10%, more preferably of about
`30% to about 98%, and most preferably of about 40% to
`about 70%. Preferably, the porous anode has a combination
`of high surface area and electrical conductivity across the
`entire volume of the anode, to optimize the solution flow rate
`through the anode, and the conversion of chloride salt
`contained in the solution to the mixed oxidant product.
`
`[0060] The flow path of the aqueous feed solution through
`the porous anode should be sufficient,
`in terms of the
`exposure time of the solution to the surface of the anode, to
`convert the chloride salt to the mixed oxidant. The flow path
`can be selected to pass the feed solution in parallel with the
`flow of electricity through the anode (in either the same
`direction or in the opposite direction to the flow of electric-
`ity), or in a cross direction with the flow of electricity. The
`porous anode permits a larger portion of the aqueous feed
`solution to pass through the passages adjacent to the anode
`surface, thereby increasing the proportion of the halogen salt
`that can be converted to the halogen containing mixed
`oxidant product.
`
`[0061] FIG. 4 shows an electrolysis cell comprising a
`porous anode 21. The porous anode has a multiplicity of
`capillary-like flow passages 24 through which the aqueous
`feed solution can pass adjacent to the anode surfaces within
`the porous electrode. In the electrolysis cell of FIG. 4, the
`aqueous feed solution flows in a parallel direction to the flow
`of electricity between the anode and the cathode.
`
`[0062] Another embodiment of an electrolysis cell having
`a porous anode is shown in FIG. 5. In this embodiment, the
`flow of aqueous feed solution is in a cross direction to the
`flow of electricity between the anode and the cathode.
`Because the flow passages through the porous anode are
`generally small (less than 0.2 mm), the flow of a unit of
`solution through a porous anode will require substantially
`more pressure that the same quantity flowing through an
`open cell chamber. Consequently, if aqueous feed solution is
`introduced into an electrolysis cell having a porous anode
`and an open chamber, generally the amount of solution
`flowing through the porous anode and across its surfaces
`will be significantly diminished, since the solution will flow
`preferentially through the open cell chamb