United States Patent
`
`[19]
`
`[11]
`
`3,984,303
`
`Peters et al.
`[451 Oct. 5, 1976
`
`
`
`154]
`
`[75]
`
`173]
`
`[221
`
`[211
`
`[52]
`
`1511
`
`[581
`
`[56]
`
`MEMBRANE ELECTROLYTIC CELL WITH
`CONCENTRIC ELECTRODES
`
`Inventors: Edward J. Peters, Chardon; J.
`Edward Loeffler, Jr., Willoughby,
`both of Ohio
`
`Assignee: Diamond Shamrock Corporation,
`Cleveland, Ohio
`
`'
`
`Filed:
`
`July 2, 1975
`
`Appl.~ No.: 592,385
`
`US. Cl. ................................ 204/260; 204/252;
`'
`204/259; 204/272
`Int. Cl.2 ....................... C258 1/24; C25B 1/26;
`C258 9/00; C258 11/00
`Field of Search ........... 204/260, 272, 265, 259,
`204/252
`
`References Cited
`
`1,982,224
`2,193,323
`
`UNITED STATES PATENTS
`11/1934 Michel ................................ 204/260
`3/1940 Nitzchke et al................. 204/260X
`
`2,228,264
`2,583,101
`3,282,823
`3,390,065
`3,404,083
`
`3,827,964
`
`Freedley ......................... 204/260 X
`l/l94l
`1/1952 Oliver .............. 204/260 X
`”/1966
`Richards ........... 204/272
`
`6/1968
`Cooper ............... 204/95
`
`10/1968 Kircher ................. 204/272
`8/1974 Okubo et al. ....................... 204/257
`OTHER PUBLICATIONS
`
`8388,701, Jan. 1975, Johnson, 204/258.
`
`Primary Examiner—John H. Mack
`Assistant Examiner—A. C, Prescott
`
`Attorney, Agent, or Firm—William A. Skinner
`
`ABSTRACT
`[5 7]
`Electrolytic cell in which hollow cylindrical electrodes
`are arranged concentrically, anode within the cathode,
`and having a tubular ion permeable membrane sup-
`ported on the outside of the anode separating the ano—
`1yte and the catholyte. The anolyte is contained within
`the membrane-anode structure, affording reduced
`construction cost and greater efficiency per unit of
`cell volume.
`
`15 Claims, 7 Drawing Figures
`
`
`
`Tennant Company
`Exhibit 1109
`
`Tennant Company
`Exhibit 1109
`
`

`

`US. Patent
`
`Oct 5, 1976
`
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`US. Patent
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`Oct. 5, 1976
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`US. Patent
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`Oct. 5, 1976
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`Sheet 3 of 4
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`US. Patent
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`Oct. 5, 1976
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`Sheet 4 of4
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`3,984,303
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`3,984,303
`
`1
`
`MEMBRANE ELECTROLYTIC CELL WITH
`CONCENTRIC ELECTRODES
`
`FIELD OF THE INVENTION.
`
`The present invention relates generally to an electro-
`lytic cell assembly for the production of alkali metal
`hydroxides and halogens. More particularly, the inven-
`tion concerns an electrolytic cell
`in which the elec-
`trodes are arranged concentrically one within the other
`and the anode is covered with a tubular ion permselec-
`tive membrane.
`
`BACKGROUND OF THE INVENTION
`
`Halogens and alkali metal hydroxides have been con-
`ventionally produced by the electrolysis of aqueous
`alkali metal halide solutions in diaphragm—type cells.
`Such cells generally have an opposed anode and cath-
`ode separated by a fluid permeable diaphragm, usually
`of asbestos, forming separate anode and cathode com—
`partments. In operation, brine is fed to the anode com-
`partment wherein halogen gas is generated at the an-
`ode, and the brine then percolates through the dia—
`phragm into the cathode compartment wherein alkali
`metal hydroxide is produced. The alkali metal hydrox-
`ide thus produced contains large amounts of alkali
`metal halide, which must be removed by further pro-
`cessing to obtain the desired product.
`Recently, electrolytic cells have been developed
`which utilize a permselective cation-exchange mem-
`brane in place of the conventional diaphragm. Such
`membranes, while electrolytically conductive under
`cell conditions, are substantially impervious to the hy-
`drodynamic flow of liquids and gases. In the operation
`of membrane cells, brine is introduced into the anode
`compartment wherein halogen gas is formed at the
`anode. Alkali metal
`ions are then selectively trans-
`ported through the membrane into the cathode com-
`partment. The alkali metal ions combine with hydrox-
`ide ions generated at the cathode by the electrolysis of
`water to form the alkali metal hydroxide.
`Membrane-type electrolytic cells have numerous
`advantages over conventional diaphragm cells, includ-
`ing the production of relatively pure alkali metal hy-
`droxide in high concentrations, the production of more
`halogen per unit of cell volume, and the ability to oper-
`ate at higher, more efficient, current densities. How-
`ever, ion permeable membranes used in such cells are
`not readily adaptable to the angular and planar config-
`uration of conventional cell apparatus. Additionally,
`due to their relatively soft and flexible nature, it is often
`difficult to position the membrane relative to the elec-
`trodes and to obtain a reliable sea] at the membrane-
`cell wall joints.
`Accordingly, it would be highly desirable to provide
`a cell design which retains the advantages inherent in
`use of the membranes, while avoiding the disadvan-
`tages.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the invention there is provided an
`electrolytic cell for the production of halogen gas and
`alkali metal hydroxide, having a hollow tubular cath-
`ode member with a hollow tubular anode member dis—
`
`posed concentrically within the cathode. Each elec-
`trode member has liquid permeable walls to allow the
`circulation of electrolyte. The anode, preferably of
`dimensionally stable construction,
`is covered on its
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`ion
`outer surface with an electrically conductive,
`permselective membrane. This membrane is tubular in
`shape, and is fitted over the outer surface of the anode,
`thereby separating the anode and cathode surfaces.
`An outer shell is placed around the cathode member,
`thereby forming a cathode compartment enclosed by
`the membrane surface and the outer shell. An anode
`compartment is also formed, enclosed by the inner
`surface of the membrane and suitable caps at the ends
`of the tubular anode member.
`
`'Means are provided for introducing alkali metal ha-
`lide brine into the tubular membrane-covered anode
`structure and for withdrawing halogen gas and spent
`brine from the anode compartment. Means are also
`provided for circulating fluid through the cathode com-
`partment, and for removing alkali metal hydroxide and
`hydrogen from the cathode enclosure. Suitable con-
`ductor means are attached to the anode and cathode
`members for supplying electric current along substan—
`tially their entire length.
`Such cells,
`in addition to being used as individual
`units, may also be connected in series fashion to form a
`larger multi—cell electrolyzer. Such an electrolyzer may
`utilize common catholyte inlet means and common
`alkali metal hydroxide and hydrogen outlet means,
`fitted to the outer shells of the individual cell units.
`
`Alternatively, the’cell units may be placed in a common
`housing which serves as a cathode compartment enclo—
`sure for the entire electrolyzer, thereby eliminating the
`individual outer shells.
`
`The membrane cell apparatus of the invention has
`numerous advantages,
`including an anode compart-
`ment in which the anolyte is contained within the mem-
`brane and anode. Such design substantially eliminates
`the need for a chemically resistant material for contain-
`ing the corrosive anolyte, with its associated high costs.
`Additionally, the tubular concentric electrode con-
`figuration allows the use of conductor means which can
`be placed in contact with the electrodes along substan—
`tially their entire length, providing more even current
`distribution and improved current density.
`Further, due to its tubular design, the problems of
`sealing the membrane at its junction with the cell walls
`is greatly reduced. The membrane sealing area per unit
`area of electrode is much smaller than in the conven-
`
`tional design, and the nature of the membrane material
`allows for either a forced fit or a shrink seal around the
`ends of the anode. Construction tolerances are also
`more easily achieved, since the cylindrical shape is
`inherently more stable than flat sheets of equivalent
`area.
`,
`
`The apparatus of the invention also provides for a
`greater efficiency per unit of cell volume and reduced
`cell construction costs, due to the elimination of nu-
`merous joints by use of the tubular design.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Other advantages of the invention will become ap-
`parent upon reading the following detailed description
`and upon reference to the drawings, in which:
`FIG. 1 is a simplified side elevational View, partly
`broken away and in section, of the electrolytic cell of
`this invention.
`FIG. 2 is a sectional view of the electrolytic cell of
`FIG. 1 along plane 2—2.
`FIG. 3 is a simplified side elevational view, partly
`broken away and in section, of a further embodiment of
`the cell of the invention.
`
`

`

`3,984,303
`
`3
`FIG. 4 is a longitudinal sectional view of another
`embodiment of the electrolytic cell of this invention.
`FIG. 5 is an end elevational View of the cell of FIG. 1.
`FIG. 6 is a top plan view of one embodiment of a
`multi-cell electrolyzer in accordance with this inven-
`tion.
`
`FIG. 7 is a side plan view of a further embodiment of
`a multi-cell electrolyzer in accordance with this inven-
`tion.
`While the invention will be described in connection
`with a preferred embodiment,
`i.e. the electrolysis of
`sodium chloride brine to produce chlorine and caustic
`soda, it is to be understood that this is only for purposes
`of illustration and is not intended to limit the invention
`to that embodiment. On the contrary, it is intended to
`cover all alternatives, modifications and equivalents as
`may be included within the spirit and scope of the
`invention as defined by the appended claims.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`Turning to the drawings, with particular reference to
`FIGS. 1—5, there is shown an electrolytic cell unit indi-
`cated generally as 8, comprising outer shell 10 which
`surrounds the hollow tubular cathode member 14 and
`encloses the cathode compartment 50 and liquid catho-
`lyte. Disposed concentrically within the cathode mem-
`ber 14 is a hollow tubular anode member 18. The
`anode member 18 is covered by an ion permeable tubu-
`lar membrane 16 which separates the cell into anode
`compartment 48 and cathode compartment 50 and
`which forms substantially the entire retainer for the
`anolyte. An anode conductor bar 22 is located within
`the anode member 18, along a common axis, and is
`electrically connected to the anode by radial anode
`conductors 20. Cathode conductor bars 12 lie along
`the outer surface of cathode member 14 in electrical
`contact therewith.
`
`In the particular cell illustrated, the outer shell 10
`may be constructed of any appropriate catholyte resis-
`tant material, most generally a metal such as mild steel
`or nickel, a rubber-lined metal, molded hard rubber, or
`a polymeric material such as polypropylene or chlori-
`nated polyvinylchloride. The outer shell 10 may have a
`diameter of from about 2 inches to about 26 inches, but
`usually ranges from 5 to 14 inches in diameter.
`The hollow tubular cathode member 14 is fabricated
`from a catholyte resistant, electroconductive material,
`generally a metal such as iron, mild steel, nickel or
`alloys thereof. The cathode member 14 is liquid perme-
`able, having an open area of from about 30 percent to
`about 70 percent, most commonly provided by ex—
`panded metal mesh rolled into tubular shape. Alterna-
`tively, the cathode member 14 may be rendered perme-
`able to the electrolyte by the use of perforations in the
`tubular cathode. The cathode member may have a
`diameter of from about one inch to about 24 inches,
`and usually is in the range of 4 to 12 inches.
`The hollow tubular anode member 18 is generally
`fabricated of a valve metal such as titanium, tantalum,
`zirconium, tungsten or the like which is resistant to the
`corrosive conditions of an electrolysis cell. The valve
`metals used in the anode are provided with an electri-
`cally conducting electrocatalytic coating of a platinum
`group metal, or mixed oxides of valve metals and plati-
`num group metal oxides, or other electrically conduct-
`ing electrocatalytic coatings. A composition which is
`dimensionally stable under the conditions existing in
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`the anolyte during the electrolysis of alkali metal halide
`solutions is preferred.
`Alternatively,
`the anode member 18 may be con-
`structed using an electroconductive core such as cop-
`per or aluminum, with a coating of anolyte resistant
`material such as titanium or tantalum. This coating has
`a layer of suitable electroconductive material such as a
`platinum group metal, an oxide or mixture of oxides of
`platinum group metal, or an oxygen-containing com-
`pound of a platinum group metal on its surface.
`The anode member 18 is also liquid permeable, hav-
`ing an open area of from about 30 percent to about 70
`percent. The anode is usually constructed from ex-
`panded metal mesh rolled into tubular shape, or it may
`be provided by perforated metal tubing, woven metal
`mesh, slitted metal plate, or the like formed in tubular
`configuration. Anode member 18 may range in diame-
`ter from about I to about 24 inches, but usually is 4 to
`12 inches in diameter.
`
`The ion permeable tubular membrane 16 is disposed
`upon and covers the outer surface of the anode mem-
`ber 18, thereby separating the anode l8 and cathode
`14. In this manner, separate anode compartment 48
`and cathode compartment 50 are formed, with the
`anolyte contained within the membrane-anode struc—
`ture. In one embodiment (FIG. 1) the tubular anode
`member 18 is connected to anolyte housing 40 at the
`point where the membrane-anode structure ends,
`thereby providing a continuation of the anode com-
`partment 48. This extension of the anode compartment
`may be rubber-lined metal, plastic, or other anolyte
`resistant material. In a further embodiment (FIG. 4)
`the membrane-anode structure is sealed directly in the
`apertures at the ends of outer shell 10 at membrane-
`anode seals 32, thereby providing a fluid-tight anode
`chamber substantially within the membrane-anode
`structure itself. This seal may be accomplished in a
`number of ways, including the use of collars, gaskets,
`compression rings and the like, as well as by the fit of
`anode endpiece 19.
`The membrane 16 preferably is of a material selec-
`tively permeable to the passage of ions and impervious
`to hydrodynamic flow of the electrolyte. A particularly
`suitable material for this membrane is a cation permea-
`ble perfluorocarbon polymer having pendant sulfonic
`groups (i.e. sulfonic acid and/or sulfonate groups). The
`membrane usually has a thickness of 0.001 to 0.010
`inches. This material is comparatively flexible in na-
`ture, and may be formed into tubular shapes of the
`desired diameter and length by extrusion or heat seal-
`ing of flat sheets, facilitating its use in the apparatus of
`the invention. The diameter of the tubular membrane
`may range from about I
`to about 24 inches, and the
`length'may be up to about 30 feet, although an overall
`cell length of 3 to 12 feet is preferred.
`Depending upon the length of the cell unit, the diam—
`eter of the electrodes, and other structural factors it
`may be desirable to place non-conducting spacers be-
`tween the membrane 16 and the cathode member 14 to
`maintain constant membrane-cathode spacing under
`actual operating conditions. Such non—conducting
`spacers may be in the form of O-rings, solid rods placed
`longitudinally, or the like.
`‘
`Electrolysis current is supplied to the anode member
`18 and the cathode member 14 by means of anode
`conductor bar 22 and cathode conductor bar 12 re-
`spectively. Anode conductor bar 22 may be located
`along the common longitudinal axis of the cell within
`
`

`

`3,984,303
`
`5
`the'anode member 18 and extends through a weld or
`other seal at housing 40. Conductor bar 22 is electri-
`cally connected to anode member 18 by means of ra-
`dial anode conductors 20. Both conductor bar 22 and
`radial conductors 20 are fabricated from an anolyte
`resistant, electroconductive valve metal such as tita-
`nium or tantalum. Alternatively, an electroconductive
`core metal such as copper or aluminum coated with
`anolyte resistant material such as titanium or tantalum
`may be used.
`The anode conductor bars 22 may also be positioned
`to lie along substantially the entire length of anode
`member 18, in direct electrical contact along substan-
`tially the entire length of the anode member, as in FIG.
`3. Alternatively, the conductor bars may be formed as
`an integral part of the anode member itself.
`The cathode conductor bars 12 are positioned in the
`annular space between the outer shell 10 and the cath-
`ode member 14, and lie along substantially the entire
`length of cathode member 14 so as to be in direct elec-
`trical contact
`therewith. The conductor bars pass
`through a Weld or other seal at outer shell 10. In an
`alternative embodiment, such as shown in FIG. 4, the
`cathode conductors may take the form of radial cath-
`ode conductors 13. Outer shell 10 and housing 40 are
`connected at their juncture by housing seal 42. The
`insulating housing seal 42 serves to provide a fluid—tight
`seal between the anode and cathode portions of the
`cell, as well as insulating them electrically. The seal
`may be constructed of a suitable electrolyte resistant
`rubber or polymeric material.
`Placement of anode conductor 22 along the length of
`the cell and within the anode member 18 insures an
`even distribution of current over the entire anode sur-
`face either through the radial anode conductors 20 or
`by direct contact with the anode member, and allows
`improved operation in terms of current density. These
`effects are further enhanced by the location of cathode
`conductor bars 12 along substantially the entire length
`of cathode member 14.
`As best shown in FIG. 5, an end view of one embodi<
`ment of the invention, electrolysis current is supplied to
`anode conductor bar 22 and cathode conductor bar 12
`through anode bus bar 36 and cathode bus bar 38 re—
`spectively. These bus bars- may connect individual cells
`in series fashion through intercell bus bars 37 to form
`an electrolyzer, as depicted in the top view of FIG. 6
`and in FIG. 7.
`
`In accordance with a further aspect of the invention,
`shown in FIG. 6, multiple cell units can be combined to
`form an electrolyzer and enclosed in a common hous-
`ing 34. This embodiment dispenses with the outer shell
`10 for individual units, and common housing 34 serves
`to define the cathode chamber for the entire electro-
`lyzer.
`Also in accordance with the invention, a multi-cell
`electrolyzer may utilize individual outer shells 10 fitted
`with common catholyte distributors 46 for introduction
`of fluid into the cathode compartment 50 and removal
`of alkali metal hydroxide and hydrogen gas products, as
`shown in ’FIG. 7.
`
`OPERATION
`
`During typical operation of the cell for the electroly-
`sis of for example, aqueous sodium chloride solution,
`brine having a sodium chloride concentration of
`120-310 grams per liter is introduced into the anode
`compartment 48 of the cell through inlet means 30,
`
`6
`while water or recirculating sodium hydroxide solution
`(25—43 percent) is introduced into the cathode com-
`partment 50 through inlet means 28. As the electrolyz—
`ing direct current is impressed'on the cell from a suit-
`able power source, chlorine gas is evolved at the anode
`18. The evolved chlorine is completely retained within
`the membrane-anode structure, and is removed from
`the cell along with the depleted brine solution through
`outlet means 24. The sodium ions formed in the anode
`compartment 48 selectively migrate through the mem—
`brane 16 into the cathode compartment 50, where they
`combine with hydroxyl ions formed at the cathode 14.
`The sodium hydroxide and hydrogen gas thus formed
`are removed from the cell through outlet means 26.
`Non-critical process parameters include operating tem-
`peratures within the range of 25—100° C., feed brine pH
`of l—6, and anode current densities on the order of
`1.0—5.0 amperes per square inch.
`In operation, the cell units may be disposed either
`horizontally or vertically. However a more or less verti—
`cal orientation is preferred since introduction of the
`brine at the cell bottom and removal of gaseous prod-
`ucts from the top are thereby facilitated.
`The concentric design of the cell also lends itself to
`operation under either reduced or higher than atmo-
`spheric pressure conditions. The tubular configuration
`has considerably more structural strength than planar-
`type cells of similar dimensions. Operation of the cell
`under pressures several times greater than atmospheric
`may result in the formation of smaller gas bubbles in
`the anolyte and correspondingly lower electrolysis volt-
`age requirements, as well as lessening the required
`compressor capacity for eventual liquefaction of the
`chlorine produced.
`Thus it is apparent that there has been provided, in
`accordance with the invention, as electrolytic cell that
`fully realizes the advantages set forth above. While the
`invention has been described in conjunction with spe-
`cific embodiments thereof, it is evident that many alter-
`natives, modifications, and variations will be apparent
`to those skilled in the art in light of the foregoing de-
`scription. Accordingly, it is intended to embrace all
`such alternatives, modifications, and variations as fall
`within the spirit and broad scope of the appended
`claims.
`What is claimed is:
`1. A cell for the electrolysis of alkali metal halide
`solutions, comprising in combination:
`,
`a hollow tubular cathode member having liquid per-
`meable walls;
`a hollow tubular anode member having liquid perme-
`able walls and disposed concentrically within the
`cathode member along a common axis;
`an ion permeable tubular membrane disposed upon
`and covering the outer surface of the anode mem-
`ber,
`thereby separating the anode and cathode
`surfaces and forming anode and cathode compart-
`ments;
`means for introducing alkali metal halide solution
`into the anode compartment and for withdrawing
`halogen gas and depleted solution from the anode
`compartment;
`means for introducing liquid into the cathode com-
`partment and for withdrawing gaseous and liquid
`products from the cathode compartment;
`an outer shell surrounding the cathode member to
`enclose the cathode compartment, and having ap-
`ertures at each end in which the cathode member,
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`

`3,984,303
`
`8
`13. A cell in accordance with claim 1 wherein the
`conductor means for applying current to the cathode
`member comprises at least one bar disposed within the
`annular space between the tubular cathode and the
`outer shell and maintained in electrical contact with
`the cathode along substantially its entire length.
`14. A cell in accordance with claim 1 wherein the
`anode and cathode members are more or less vertically
`disposed, the alkali metal halide solution is introduced
`into the bottom of the anode compartment, and halo—
`gen gas and depleted solution are withdrawn from the
`top of the anode compartment.
`15. An electrolyzer for the electrolysis of alkali metal
`halide solutions, comprising a housing with top, bot—
`tom, and sides which encloses an array of cell units,
`each unit characterized by:
`a hollow tubular cathode member having liquid per-
`meable walls;
`a hollow tubular anode member disposed concentri-
`cally within the cathode member along a common
`axis and having liquid permeable walls;
`an ion permeable tubular membrane disposed upon
`and covering the outer surface of the anode mem-
`ber,
`thereby separating the anode and cathode
`surfaces and forming a self-contained anode com-
`partment;
`means for introducing alkali metal halide solution
`into the anode compartment and for withdrawing
`halogen gas and depleted solution from the anode
`compartment;
`_
`means for introducing liquid into the housing to im-
`merse the exposed cathode members and for with—
`drawing gaseous and liquid products from the
`housing;
`_
`conductor means for applying an electrolysis current
`along substantially the entire length of the anode
`and cathode members;
`the housing having apertures on opposed sides
`through which the anode and cathode members
`extend and having means for sealing each cell unit
`in the apertures.*
`*
`*
`*
`*
`
`7
`membrane, and anode member are disposed and
`sealed.
`in accordance with claim 1 wherein the
`2. A cell
`tubular membrane is permeable to the passage of cat-
`ions and substantially impervious to hydrodynamic
`flow of electrolyte.
`3. A cell
`in accordance with claim 2 wherein the
`tubular membrane comprises a cation permeable per-
`fluorocarbon polymer having pendant sulfonic groups.
`4. A cell in accordance with claim 1 wherein the ion
`
`permeable membrane is in the form of an extruded
`tube.
`in accordance with claim 1 wherein the
`5. A cell
`anode member is a dimensionally stable composition.
`6. A cell
`in accordance with claim 1 wherein the
`anode member comprises a valve metal base coated
`with an electrocatalytically active material.
`7. A cell
`in accordance with claim 1 wherein the
`cathode member comprises a metal selected from mild
`steel, nickel or alloys thereof.
`8. A cell
`in accordance with claim 1 wherein the
`anode and cathode members are formed from an ex-
`panded metal mesh.
`9. A cell
`in accordance with claim 1 wherein the
`anode and cathode members are formed from a woven
`wire mesh.
`10. A cell in accordance with claim 1 wherein the
`anode and cathode members are formed from perfo-
`rated metal.
`11. A cell in accordance with claim 1 wherein the
`conductor means for applying current to the anode
`member comprises a bar disposed within the tubular
`anode along its entire longitudinal axis and maintained
`in electrical contact with the anode along substantially
`its entire length by a plurality of radial contact mem-
`bers.
`12. A cell in accordance with claim 1 wherein the
`conductor means for applying current to the anode
`member comprises at least one bar disposed within the
`tubular anode and in direct electrical contact therewith
`along substantially its entire length.
`
`5
`
`10
`
`IS
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`