EP0156795A1

EP0156795A1 - Compartmentalized cathode cell

Info

Publication number: EP0156795A1
Application number: EP83903024A
Authority: EP
Inventors: Robert C. Sutter
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-08-31
Filing date: 1983-08-31
Publication date: 1985-10-09
Also published as: WO1985001072A1

Abstract

Electrode à gaz compartimentée, utilisée de préférence dans une cellule de chlore-alcali (10) contenant au moins une cathode à oxygène (air) compartimentée (17) dans laquelle l'oxygène ou l'air est mis en contact dans des milieux liquides avec une couche active d'électrodes de manière à produire une réaction électrochimique. Une telle cellule comprend un compartiment de catholyte commun (18), plusieurs éléments cathodiques horizontaux, compartimentés et disposés verticalement (17), autant d'entrées (21) et de sorties (22) pour chaque cathode compartimentée pour l'introduction et la sortie de gaz contenant de l'oxygène et provenant d'une source commune d'oxygène ou d'air, et plusieurs points d'alimentation (41) et d'extraction (43) de gaz pouvant être commandés individuellement pour chaque compartiment (25) de sorte que la pression du gaz du côté gaz de chaque compartiment (25) de chaque cellule soit sensiblement proportionnelle à la pression hydraulique du catholyte liquide sur le côte catholyte (18) de chaque compartiment. Dans les cas faisant appel à une cathode d'oxygène, l'oxygène ou l'air est approvisionné à partir d'un distributeur commun (40) séparément au travers d'orifices (41) des compartiments individuels de cathodes d'oxygène (25). Les admissions (41) et les sorties (42) d'oxygène ou d'air et de chaque compartiment peuvent être un orifice calibré (43) ou une soupape réglable (45) de sorte que l'air ou l'oxygène entrant et sortant de chaque compartiment passent par un distributeur commun (40) sur chaque cadre cathodique (23). Le passage de courant se fait à partir de la périphérie de la cellule compartimentée qui est conductrice et fonctionne comme une barre omnibus (20).Compartmentalized gas electrode, preferably used in a chlor-alkali cell (10) containing at least one compartmentalized oxygen (air) cathode (17) in which oxygen or air is contacted in liquid media with an active layer of electrodes so as to produce an electrochemical reaction. Such a cell comprises a common catholyte compartment (18), several horizontal cathode elements, compartmentalized and arranged vertically (17), as many inputs (21) and outputs (22) for each cathode compartmentalized for the introduction and the exit. of gas containing oxygen and coming from a common source of oxygen or air, and several gas supply (41) and extraction (43) points which can be controlled individually for each compartment (25) so that the gas pressure on the gas side of each compartment (25) of each cell is substantially proportional to the hydraulic pressure of the liquid catholyte on the catholyte side (18) of each compartment. In cases using an oxygen cathode, oxygen or air is supplied from a common distributor (40) separately through orifices (41) of the individual compartments of oxygen cathodes (25 ). The oxygen or air inlets (41) and outlets (42) and each compartment can be a calibrated orifice (43) or an adjustable valve (45) so that the air or oxygen entering and leaving of each compartment pass through a common distributor (40) on each cathode frame (23). The current flow takes place from the periphery of the compartmentalized cell which is conductive and functions as a bus bar (20).

Description

COMPARTMENTALIZED CATHODE CELL

Technical. Field

This invention relates to chlor-al ali manufacturing electrochemical cells, and more specifically to oxygen cathode type chlor-alkali electrochemical cells.

Background of the Invention

Within the field of electrochemistry, there exists a category of electrolytic cells known as gas electrodes. In such electrodes, there is a reaction between a gas, e.g., oxygen or CO--free air as in the case of oxygen va.ir) cathode-containing cells, and a catalytic material positioned within what is termed "active layer" present in the cathode structure. A catholyte liquor, e.g., sodium hydroxide, potassium hydroxide, etc., of a corrosive nature is usually present within the catholyte chamber on the cathode face obverse, to the gaseous reactant.

When seeking to build commercial-size cells of substantial dimensions containing gas cathode, e.g. in the range of approximately 1 by 1 meters or larger, a substantial differential can exist in the hydraulic pressure between the bottom of such cells and the top thereof in the catholyte liquor. Catholyte pressure at the bottom of the cell can be significantly greater than, at the top of the cell, resulting in flow of catholyte

OMP into the gas compartment near the cell bottom. Catholyte flow into the gas compartment wets or floods a portion of the gaseous side of the cathode thereb . restricting or inhibiting reaction of the gas with the catalyst or active material contained in the cathode active layer. Experience has shown that such a restriction significantly reduces the effective life of gas cathodes.

Generally*, the larger the cell, the greater the height of the hydrostatic head and the hydrostatic pressure which ^" builds up on the. catholyte side of an oxygen cathode within the cell; making it difficult to utilize an electrolytic cell containing an oxygen cathode in commercial-size cells of substantial dimensions. Generally where the cell measures more than about 12" in height hydrostatic head and pressure can complicate cell operation. This problem is particularly difficult when utilizing oxygen cathodes in chlor-alkali cells.

In the field of electrochemistry, chlor-alkali cells, are well known. In such cells, an electric current is passed through a saturated^'-brine (generally of sodium chloride salt) to produce chlorine ^'gas and caustic soda (sodium hydroxide) . A large portion of the chlorine and caustic .soda used in the chemical and plastics industries are produced in chlor-alkali cells.

Generally such cells are divided by a separator into anode and cathode compartments. The separator characteristically can be a substantially hydraulically impermeable membrane, e.g., a hydraulically impermeable cation exchange membrane, such as commercially available NAFION , manufactured by the E. I. duPont de Nemours and Company. Alternatively, the separator can be a porous diaphragm, e.g. of asbestos, which can be in the form of vacuum-deposited fibers or asbestos paper sheet well known in the art. The anode can be a valve metal, e.g., titanium, provided with a noble metal or noble metal oxide coating to yield what is known in the art as a

OM dimensionally stable anode marketed as DSAR by Diamond

Shamrock Corporation.

One by-product evolved in conventional chlor-alkali cells is hydrogen which forms at the cell cathode. Hydrogen formation increases the electrical power requirement for the overall electrochemical process in the cell, and eliminating hydrogen formation is one desired result in optimizing chlor-alkali cell operation.

It has been estimated that 25 percent of the electrical energy required to operate a chlor-alkali cell is utilized in the formation^' of hydrogen at the cell cathode. Hence, the prevention of hydrogen formation, e.g., by reacting water with oxygen at the cathode resulting in the formation of hydroxide, can lead to substantial savings resulting from the reduced electrical power required to operate such cells.

Recently, attention has been directed to various forms of what are known as oxygen (air) cathodes. These cathodes prevent the formation of molecular .hydrogen at the cathode and instead reduce oxygen to form hydroxyl ions. Savings in electrical power costs are thereby achieved.

Hence, it is a desired objective in the chlor-alkali cell field to utilize oxygen cathodes in ^• commercial-size electrolytic cells of substantial dimensions while avoiding or overcoming the flooding of the oxygen cathode due to hydrostatic head on the catholyte side in order to maintain the ability of the oxygen cathode to suppress hydrogen formation.

British Patent 432,698 describes a system for installing an electrolyzer for hydrogen and oxygen generation in a pressure vessel filled with a fluid (oil) so that all parts of the cell are at the same pressure.

It is stated that this simplifies cell construction inasmuch as there are no pressure differences across the various parts of the cell and the cell piping from inside to outside. Clearly this patent does not deal with situations created by having different pressures in different parts of an electrolytic cell nor does it make any attempt to balance different hydraulic pressures in different parts of a cell.

U.S. Patent 1,983,296 discloses pressure balancing from cell to cell controlled by area and slope. There is no provision for controlling different pressures in different parts of the same electrolytic cell.

U.S. Patent 2,681,884 describes a diaphragm cell utilizing an unsubmerged cathode. Since the cathode is not submerged, there is little danger of catholyte solution seeping into the^* air compartment of the oxygen cathode. Note column 5, lines 65-70 in this respect. In a diaphragm cell, liquor flows from the anolyte to the catholyte at a rate controlled by the characteristics of the diaphragm. In U.S. Patent 2,681,884 partially depleted brine from the anolyte into the catholyte compartment is allowed to flow freely from the bottom of the catholyte compartment avoiding hydraulic head in the catholyte compartment. -

U.S. Patent 3,098,768 shows a pressure and flow control scheme for individual single cells. No provisions are made for different pressure control in different parts of a single cell.

U.S. Patent 3,106,494 is directed to a fuel cell wherein provision is made for differential pressure control in a single cell and not a single cell with multiple compartments for differential pressure control at various portions of the cell.

U.S. Patent 3,269,932 is directed to an electrochemical reactor, not an electrochemical cell. There is described a plurality of cells, but nothing is disclosed concerning pressure balance or flow control therein.

U.S. Patent 3,359,135 is directed to an immiscible liquid separator wherein flow is directed into the separator in such a fashion as to provide for gravity

O separation of two immiscible liquids or fluids of different gravities.

U.S. Patent 3,525,641 is directed to a method of controlling pressures in various parts of the cell wherein the method of control concerns two gases. The present invention on the other hand is directed to controlling the flow and pressure of one gas which is in the environment of a common liquid,- viz., alkali, catholyte. The present invention is directed to balancing a hydrostatic head in a common catholyte chamber by utilizing compartmentalized vertically stacked oxygen cathodes in which the oxygen or air pressure is controlled in each cell so as to create a uniform condition on the gas side of the electrode to avoid hydraulic pressure causing catholyte seepage into the gas side of the cell.

U.S. Patent 3,708,341 describes a fuel cell distinguished by the fact that absorbent layers are provided between the anode and cathode to prevent static buildup of the electrolyte. In other words, in this cell the air side is at atmospheric pressure throughout the cell, and the electrolyte in the cathode compartment is broken up by absorbent materials and the multiplicity of collectors to direct the electrolyte away from the gas surface.

U.S. Patent 3,856,651 is directed to a bipolar electrolyzer and a method for maintaining uniform liquid levels in each of the plurality of cells. There are no provisions for controlling different parts of a single cell.

U.S. Patent 3,881,956 is directed to fuel cells wherein the objective is a simple structure having many parallel flows in a series stacked cell configuration. The principal objective is to avoid current leakage and voltage losses in the stacks. There is no flow or pressure balancing involved.

U.S. Patent 3,902,918 is directed to a battery, the distinguishing features of which are pumps placed between -cells to compensate for a pressure drop through each cell in a series flow configuration such that electrolyte pressures are kept at a constant average pressure for each cell in the multiple cell series. This is different from the problem^*confronting applicant, viz., controlling different pressures within a single cell.

U.S. Patent 3,930,151 describes a system for diverting gas away from the electrodes in a diaphragm cell. As in all diaphragm cells, pressure balancing is not a problem. - -

U.S. Patent 3,963,595 describes an electrode (anode) . The electrode described utilizes a conductor bar bent so that the conductor may be attached to the side wall of a cell rather than to the bottom thereof.

U.S. Patent 3,963,596 is very similar to U.S. Patent 3,963,595' except that the conductors are angled to provide for a side wall attachment.

U.S. Patent 3,976,550 is directed to a horizontal diaphragm cell. Pressure balancing is not a requirement nor a feature of such cells. As in all diaphragm cells, a pressure differential between the anode and the cathode is essential to insure a flow through the diaphragm.

U.S. Patent 3,994,748 describes fuel cell with a scheme for distributing gas flow through a plurality of cells, the objective being to insure gas flow over every electrode. No suggestion is made of hydraulic pressure balancing.

U.S. Patent 4,008,143 is very similar to U.S. Patent 3,963,595 and U.S. Patent 3,963,596 discussed above. In U.S. Patent 4,008,143 an electrode is shown permitting side wall attachment rather than the bottom attachment employed in the more conventional electrodes.

U.S. Patent 4,014,776 is directed to a vertically stacked electrolytic monopolar cell. The objective of this device is to save floor space. No suggestion is made of hydraulic pressure balancing. U.S. Patent 4,038,458 discloses a zinc air battery. The basic objective of this patent is to provide electrolyte flow to balance the electrical potential. Since this patent utilizes an electrolyte with solids in suspension (zinc) _> the hydraulic flow considerations are different from those involved with solutions, and provisions are made for such contingency. Moreover, no mention is made of balancing hydraulic pressures, and particularly no mention is made of attempting to balance hydraulic pressures against gaseous, (air) pressures on opposing sides of a separator.

U.S. Patent 4,053,684 is concerned with a liquid-liquid fuel cell. Each cell contains two compartments, one for the anolyte and one for the catholyte with means to control different pressures in each compartment. No mention is made of breaking up an individual cell into multiple parts for pressure control. This design may be effective for liquid-liquid cells but appears unable to overcome problems to which the present invention is directed involving liquid-gaseous cells with significant gravity differences between the liquid and the air.

U.S. Patent 4,073,715 is directed to what has been known as the deNora Glynor cell, which is a diaphragm cell with provisions for liquid-gas separation within the anolyte and the catholyte compartments. There is no attempt to control pressure within the cell. This patent illustrates a diaphragm cell where such pressure balancing is not necessary.

U.S. Patent 4,176,213 is directed to a fuel cell battery with parallel flow into and out of a multiple cell stack. There are no provisions made for hydraulic pressure balancing within each cell.

DISCLOSURE OF THE INVENTION The electrolytic cell according to this invention has an arrangement of features not present in

_ OMPI the -references. These features include hydrostatic head (pressure) control achieved by compartmentalization of the gas cathode and by distribution of reactant gas, e.g., oxygen or air, in accordance with a system wherein either the gas inlet orifices to each compartmentalized cathode element and/or the gaseous outlet orifices can be either of fixed opening or variable (diameter) opening, each individual air (oxygen) compartment thereby having air flow and pressure within the compartment controlled independently of the other compartments.

According to a preferred embodiment of this invention, the current distribution within each compartmentalized cathode is such as to avoid large voltage drops across the cell. This can be achieved by distributing the current in a direction generally perpendicular to the major current feed to the current distributor of the oxygen cathode rather than by flows generally parallel to.the direction of major current feed. Characteristically, distribution of electrical current is generally perpendicular to a -longitudinal (long) axis of. the plurality of compartmentalized cathodes comprising a cell, each cathode compartment being many times longer in a longitudinal direction than in a vertical direction when assembled within the cell.

The above and other features and advantages of the instant invention may be better understood when considered with a detailed description of the invention and the accompanying drawings, forming a part of the specification.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an electrolytic cell of the monopolar, membrane-type utilizing a gaseous cathode system, e.g., oxygen (air) cathode, as contemplated herein for use in chlor-alkali cells.

Figure 2 is an isometric perspective view of the common cathode-catholyte-anode unit as shown in Figure 1, each common catholyte chamber serving all of the compartmentalized, vertically stacked cathode units.

Figure 3 is an isometric view in perspective of one preferred embodiment of this invention showing a cathode assembly.

Figure 4 is a sectional view taken along A-A of Fig. 3 illustrating an oxygen (air) inlet and spent oxygen (air) outlet to each compartmentalized cathode chamber.

. Figure 5 is a sectional view taken along B-B of Fig. 3 illustrating the compartmentalized cathode chamber.

Figure 6 is a section of a preferred alternate spent oxygen (air) outlet.

Figure 7 is partial sectional view of Fig. 1.

BEST EMBODIMENT OF THE INVENTION

Referring, to the drawings. Figure 1 shows a typical chlor-alkali electrolyzer cell 10 embodying the invention. Externally, the chlor-alkali electrolyzer cell is comprised of end bulkheads 11, held together by tie rods 12 and fasteners such as nuts 13. The electrolyzer bulkhead 11 rests on bulkhead end support risers 16 which are separated from footers 14 by insulator supports 15.

Between the bulkheads in each electrolyzer 10, a. plurality of monopolar cells are arranged, each comprising a compartmentalized oxygen cathode 17, a catholyte feed frame 18, and an anode 19 seen best in Fig. 2. Each respective cathode assembly includes an individual cathode bus bar 20. Each anode has a respective anode bus bar (not shown). The bus bars as contemplated herein for both the anode and cathode are in accordance with known technology. Referring to Fig. 3, oxygen (air) inlets 21 and spent oxygen (air) outlets 22 are provided to carry oxygen or air to each cathode within the plurality making up the oxygen cathode cell and remove air therefrom.

OM - Referring to Figure 2,- each compartmentalized oxygen (air) cathode 17 is comprised of a cathode frame 23, a cathode grid 24 or plate and individualized cathode compartments 25: in electrical communication with the cell by connection to the cathode bus bar 20. By grid or plate what is meant is sheet like structure, generally electrically conductive, arranged to receive a plurality of oxygen cathode elements and retainers therefore. Bulkhead gaskets 26 are used at both ends of the electrolyzer to insulate the cell components from the exterior bulkheads. These bulkhead gaskets 20 can be made of rubber, elastomers or other materials used conventionally in the art for this purpose and customarily encompass the entire cross-sectional area of tho cell as it meets the end bulk- heads.

Between each respective cathode assembly (comprised of cathode frame 23, cathode bus bar 20, cathode grid or plate 24, the individual oxygen (air) cathode compartments 25) and each catholyte feed frame 18, a peripheral or edge gasket 27 is positioned, which can be made of rubber, elastomer or other conventional gasketing _ material such as that employed in fabricating the bulk¬ head gasket 26. Peripheral gaskets 28 and 29 of a similar nature are employed to separate respectively the catholyte feed frame 18 from a membrane or other separator 30 and to separate and insulate the anode 19 from the membrane 30.

One feature of the present invention is the utilization in combination of a common catholyte (caustic) chamber and a compartmentalized oxygen cathode. Pressure in each compartment of the oxygen cathode is adjusted to balance the hydrostatic head existing in the catholyte chamber at the point adjacent or opposite each compartment. Catholyte (caustic) inlets 31 and corresponding outlets 32 are utilized to introduce and control the flow of catholyte within the electrolyzer.

While Figures 1-3 illustrate the introduction of the air or oxygen via the bottom of each respective oxygen (air) cathode and its removal at the sides of the oxygen cathode, it should be recognized that the present invention contemplates introduction of the oxygen (air) and removal thereof at any position along the bottom, top or sides of each respective oxygen cathode compartment. A similar variation in the location of catholyte inlets and outlets is possible. While the catholyte feed as shown in

Figures 1 and 2 is introduced adjacent the bottom of the cell and removed near the top_. portion, the present invention contemplates introducing .the catholyte feed

^"intermediately on either side or at the top and withdrawal of catholyte from the bottom or from either side.

.Similarly, the caustic can be introduced at the bottom portion of the cell on one side and removed at an outlet located at the top on the other side of the cell.

As will be apparent from Figures 1 and 2, the brine solution is introduced in the bottom of the anode chamber 19 at a brine feed inlet 33 and the spent brine and chlorine being generated are removed at a brine and chlorine discharge outlet 34-as shown in Figure 2.

The anodes 19 are comprised essentially of an anode frame 35 and a suitable or conventional wire mesh 36.

Referring to the drawings. Figure 3 shows individual oxygen (air) cathode compartments 25 formed in the cathode plate 24, each capped with oxygen cathode element 37. A plurality of such oxygen cathode elements 37 corresponding to the number of individual oxygen cathode compartments 25 are utilized in each cathode contained in the chlor-alkali cell.

The geometry of each individual oxygen cathode element 37 is such that the longitudinal or horizontal dimension thereof is many times that of the vertical dimension. This geometric configuration is employed to enable control of the individual oxygen or air supply entering each compartment 25 so that the hydraulic head present in each respective vertical section of the common

OM catholyte chamber is balanced by the respective oxygen (air) pressure in a corresponding cathode compartment 25, to avoid catholyte leakthrough.

While a variety of specific air delivery and removal systems can be employed in accordance with this invention, referring to Figs. 3-5, in one preferred embodiment a tubular air delivery header is connected to inlets 21 which are provided with orifices in accordance with the invention. The header is located internally within the peripheral cathode frame -23. According to one ^"preferred embodiment of this^' invention, an individual inlet orifice 41 is provided of a fixed diameter controlling the quantity of oxygen containing gas admitted to the cell. An outlet orifice 43 is provided, variable in one preferred embodiment, and enabling control of the oxygen containing gas pressure in an individual cathode compartment 25. According to another preferred embodiment of this invention, each compartment has a fixed orifice each orifice being of a particular size established by the vertical position of each compartment upon the cathode, thereby providing the variability necessary for individual compartment pressure control.

In accordance with preferred embodiments of this invention, the oxygen cathode elements 37 can be of a laminated construction including an active layer comprising active carbon particles present within an unsintered network (matrix) of fibrillated carbon black/ polytetrafluoroethylene. The active layer is laminated on its working surface to a current distributor (not shown) and on its opposite surface to a porous, coherent, hydrophobic polytetrafluoroethylene-containing wetproofing layer. The active carbon particles can contain a precious metal catalyst, such as silver, platinum, and the like. LaminatedOxygen cathode elements are shown and described in U.S. Patent Application Serial No. 202,585 filed on October 31, 1980.

f O P In accordance with an alternate preferred embodiment of this invention, the oxygen cathode elements 37 may be three-layer laminates including an active layer or sheet containing from about 60 to about 85 weight percent active carbon, the remainder being unsintered, fibrillated polytetrafluoroethylene in intimate admixture with the active carbon. The active layer in this embodiment is laminated on its working surface to a current ^"distributor and on its .opposite surface to a porous, coherent, hydrophobic polytetrafluoroethylene- containing wetproofing layer. The active layer of such a laminated oxygen cathode likewise can contain precious metal catalysts. Such laminated oxygen cathode elements are shown and described in U.S. Patent Application Serial No. 202,577 filed on October 31, 1980.

In accordance with a still further preferred embodiment of this invention, oxygen cathode elements 37 may be a non-bleeding gas electrodes comprising a hydrophobic, polytetrafluoroethylene-containing, porous backing layer, an active layer containing high surface area carbon particles and a current distributor; the active layer having pores sufficiently large to relieve internal liquid pressures in the active layer. These oxygen cathode elements can likewise contain carbon particles having deposited precious metal catalysts upon and/or within the carbon particles. Such non-bleeding gas electrodes are shown and described in U.S. Patent Application Serial No. 202,564 filed on October 31, 1980.

While several satisfactory specific oxygen cathode elements 37 have been described herein, it should be understood that the present electrolyzer may utilize a wide variety of suitable or conventional oxygen cathode elements.

Referring to Figure 2, each individual monopolar cell present in the electrolyzer 10 is divided by a separator 30 into anode and cathode compartments. The separator characteristically can be a substantially

' OM hydraulically impermeable membrane, e.g., a hydraulically impermeable cation exchange membrane such as the commercially available NAFION manufactured by the E. I. duPont De Nemours and Company. Alternatively, the separator can be a porous diaphragm, e.g., asbestos, which can be in the form of vacuum deposited fibers, asbestos sheet or other suitable or conventional separators well known in the art.

Figure 4 is a sectional view showing a detail of the oxygen inlet and outlet _.control system for each individual oxygen cathode compartment 25 and illustrating a preferred manner of introducing and removing the oxygen or air to each oxygen cathode compartment present in the oxygen cathodes*, of the electrolyzer 10. As is noted from Figures 4 and 5, each oxygen cathode compartment has an oxygen inlet orifice 41, in the preferred embodiment of fixed diameter, and an oxygen outlet 22, in one preferred embodiment of variable flow capacity.

An inlet orifice 41^" can be of either fixed or variable dimension. Generally it is preferred that the inlet orifice to a particular compartment 25 be of fixed dimension. However, it is often desirable that the dimension of orifices feeding compartments arranged vertically upon the cathode frame 23 be of larger or smaller dimension - depending upon relative vertical position.

In Figure 4, the oxygen outlet 22 includes an orifice 43 of fixed dimension calculated to provide a given oxygen containing gas pressure within a compartment 25 figured from the pressure of the oxygen containing gas supply pressure, and the size of the inlet orifice 41 (Fig. 5) . The size of this orifice 43 is partially dependent upon the relative vertical position of the cathode compartment utilizing that orifice upon the cathode frame. Vertically more elevated compartments generally utilize a larger dimensional orifice.

O Referring to the drawings. Fig. 6 shows an alternate preferred outlet having a variable orifice for gaseous release. Each oxygen outlet .22 contains a variable orifice control mechanism comprised of oxygen outlet control stem valve 45 having hollowed stem portion 48 received in a valve body 46. A seat 47 is provided for threadably receiving the stem 48. By rotating the stem valve portion 48, the valve can be adjusted for controlling oxygen or air exhaust through the valve stems. A pressure gauge 44 is mounted on each oxygen outlet valve 45. By mounting the valve on the hollow stem, viz., on the interior surface thereof as shown in Figure 6, the operator can see readily an indication of the pressure within the chamber, facilitating pressv.re control in each oxygen cathode chamber of each oxygen cathode compartment 25. An oxygen inlet control device 41 is present on each oxygen inlet tube for controlling the quantity of air or oxygen introduced into each oxygen cathode compartment 25. Drains, not shown, can be provided between oxygen compartments 25 adjacent the bottom for draining any water or catholyte (caustic) which might penetrate into these air compartments.

Referring to Figure 7, the plurality of tubular oxygen cathode frame members 23 contain a plurality of tubular oxygen feed inlets 21 which feed air or oxygen to the cathode. The brine solution is introduced into the anode chamber 19 through a plurality of similar tubular brine feed inlets 33 which pass through a central portion of the anode frame 35. Catholyte (caustic) is fed through a plurality of catholyte inlets 31 of generally tubular configuration as indicated in Figure 7. The catholyte inlets 31 are positioned for feeding catholyte to the respective caustic chambers which in turn are positioned between the anodes and cathodes.

Re erring to Figure 7, it may _be seen that hydraulically impermeable membranes 30 are located between cathode chambers 17 and respective anode assemblies 19. A gasket 28 is positioned between each such membrane 30 and the catholyte and a gasket 29 is positioned between each membrane 30 and the brine solution contained in the anode assembly 19. The tie rods 12 function to compress the various elements of the electrolyzer 10 in assembled form. One preferred embodiment of a cathode grid or plate and frame arrangement is shown in Figure 3. A pair of formed unitary cathode grids or plates 24 are positioned on opposite sides of a centrally located cathode frame ^'23. The cathode .frame 23 in turn is comprised of a pair of lateral or side channel cathode frame members 56 and 57 and upper and lower channel cathode frame members 58 and 59, respectively, and is positioned between the cathode^*grids 24. The lateral side channel cathode frame member 57 provides an air supply channel for the oxygen or air being utilized in the oxygen (air) cathode compartments 25. Cathode elements 37 are fitted into respective compartments 25 on the cathode grids 24 and secured utilizing a pair of hold down bars 60 having openings 61 corresponding to openings 62 in the unitary cathode grids. Suitable or conventional fasteners such as screws, or bolts 63 and nuts 64 are utilized to secure the cathode elements 37 with hold down bars 60 as shown in Fig. 7. A sandwich arrangement of cathode grids and cathode frame results. A bus connector 42 facilitates connection of the cathode frame to the cathode bus 20, the cathode plate 24 being generally welded to the frame 23 but attachably by any suitable means providing for electrical conductivity.

PREFERRED MATERIALS OR FABRICATION

A wide variety of materials can be employed to fabricate the respective parts and means set forth hereinabove in the detailed discussion Figures 1 through 7 of the drawings; in accordance with various embodiments of this invention, the following tabulated fabrication or

OMP construction materials are preferred for utilization in accordance with this invention:

ITEM, MEMBER OR ELEMENT: PREFERRED MATERIALS OF

FABRICATION"

11. Bulkheads steel

12. Tie Rods 13. Nuts steel

14. Footers concrete

15. Insulator Supports ceramic or fiberglass

16. Bulkhead and Support steel Risers

18. Catholyte Feed Frame nickel

19. Anode titanium

20. Cathode Bus Bars copper

21. Oxygen (Air) Inlets stainless steel

22. Oxygen (Air) Outlets stainless steel

23. Cathode Frame steel

24. Cathode Plate ^•nickel plated copper

26. Bulkhead Gaskets neoprene

27. Peripheral Edge Gaske . neoprene

28. Peripheral Gasket neoprene

29. Peripheral Gasket neoprene

30. Membrane or other Separator Nafion^R (duPont)

31. Catholyte (caustic) Inlet nickel

32. Catholyte (caustic) Outlet nickel

33. Brine Feed Inlet titanium

34. Brine and Chlorine Discharge titanium Outlet

35. Anode Frame titanium

36. Anode Mesh titanium

40. Valve stainless steel

41. Individual air inlets stainless steel

42. Cathode bus connector copper

43. Valve Seat of 40 stainless steel

45. Valve stainless steel 46. Outlet valve body stainless steel

47. Outlet seat stainless steel

48. Outlet valve stem stainless steel

57. Lateral Side Channel Cathode stainless steel Frame Members

58. Upper Channel Cathode Frame steel Member

60. Hold down Bars nickel

63. Screws or other Fastening Devices nickel plated s.s.

64. Nut stainless steel

PREFERRED PROCESS AND OTHER VARIATIONS

The electrolyzer of the present invention has a compartmentalized oxygen cathode approximately four feet square fabricated according to one preferred embodiment of this invention of nickel plated copper plates made in two halves and bolted back to back and supported by a steel tubing frame. The four foot square structures are divided horizontally into approximately one dozen compartments, each individual oxygen cathode compartment being approximately 4 inches wide and 4 feet long. Catholyte (caustic) flows between the membrane and the oxygen cathodes which are secured or attached to co-functioning oxygen cathode plates or grids, the grids preferably being made of copper. The catholyte flow is introduced at the bottom and is removed out of the top such that there is a hydraulic head of approximately four feet of caustic in the catholyte compartment. As mentioned previously, one advantage of compartmentalization as disclosed herein is to balance the pressure on the air side of the oxygen cathode to be substantially equal to the hydraulic pressure on the catholyte side in each respective oxygen cathode compartment thereof along the four foot vertical hydraulic head.

M - As will be noted from the foregoing description, each individual oxygen, cathode compartment is provided with an oxygen (air) flow controlled independently of each other oxygen cathode compartment both in and out. Also, each compartment may be provided with a drain connection for draining each compartment independently when it is necessary or desirable to do so.

The air flow control means both on the the inlet and outlet side and the drain valves are preferably built into the steel tubing structure _.so. that the air supply is in a common header and is controlled through orifices into each of the compartments. The outlet of each such compartment for the oxygen (air) can be either a fixed opening or an adjustable orifice or valve which may discharge the air from the individual cathode. Preferably the cathode plates or grids are made of copper and serve as current-carrying members to the current distributor present in each compartment of the oxygen cathodes. These individual current distributors can be silver-plated nickel screen wire current distributors embedded in the cathode element. It may be seen that these copper plates or grids serve both to define each compartment and also to carry electrical current from the current supply into the individual compartmentalized oxygen cathode element screens so that the electrical power does not have to travel any further than approximately one-half of the height of each fine nickel screen current distributor anywhere within each individual oxygen cathode compartment. While the four inch by four foot dimensions are preferable in electrolytic cells such as those shown for use in chlor-alkali cells; it should be realized that it is within the purview of this invention to vary the dimensions thereof both vertically and horizontally for each compartmentalized portion of the cell on the oxygen cathode side.

In operation, brine and catholyte are circulated through the cell, and oxygen containing gas such as air or

OMP

NOT TO BE TAKEN

INTO CONSIDERATION FOR

THE PURPOSES OF INTERNATIONAL

PROCESSING (See Section 309(c) (iii) of the Administrative Instructions)

It will be apparent to those skilled in the art that the present compartmentalized electrolytic cell possesses a combination of features as follows: provision is made to distribute electrical current to avoid large voltage drops across the compartmentalized cell within the individual oxygen cathodes; control is established to compensate for differences in hydrostatic head (pressure) vertically from compartment to compartment within the compartmentalized cell; the . various compartments containing the^* oxygen (air) cathode elements being provided with means in the form of a combination of fixed and/or variable oxygen gas containing inlets and outlets to balance the hydrostatic head present at various vertical locations in the common catholyte chambers; means having been disclosed for fastening the active material (oxygen cathode elements 37) to the oxygen frame-plate assembly.

OMPI

Claims

WHAT IS -CLAIMED IS:

1. In an oxygen cathode electrochemical cell having a cathode including a frame, a busbar; means for circulating catholyte through the cathode, and a cathode plate, the improvement comprising the cathode plate being divided into a plurality of individual horizontal cathode compartments arranged vertically upon the cathode plate; an oxygen cathode element arranged covering each individual cathode compartment; means for introducing an oxygen containing gas separately into each individual cathode compartment; and means for controlling the flow of the gas into the each individual cathode compartment and for controlling pressure within each cathode compartment.

2. The improved apparatus of claim 1, the means for controlling flow of oxygen containing gas into each individual cathode compartment comprising a flow restricter positioned -in a gas- stream being introduced into the individual cathode compartment, and an adjustable valve and pressure gauge positioned in a flow of the oxygen containing gas exiting the individual cathode compartment.

3. The apparatus of either of claims 1 and 2, the oxygen cathode elements including a current distributor for distributing electrical current from the cathode frame throughout the oxygen cathode element.

4. A method of operating an oxygen cathode type electrochemical cell having anode and cathode compartments fed respectively with anolyte and catholyte and an oxygen cathode supplied with a gaseous stream containing oxygen comprising the steps of: (1) segregating the cathode into a plurality of individual horizontal . cathode compartments arranged vertically on the cathode;

(2) arranging an oxygen cathode element over each individual oxygen cathode compartment within the cell;

(3) introducing catholyte in contact with one surface of each oxygen cathode element;

(4) controllably introducing an oxygen containing gas into contact with, the- opposite surface of each oxygen cathode element;

(5) controlling the flow and pressure of the oxygen containing gas to each oxygen cathode compartment whereby as the hydrostatic head of catholyte contained within the cathode decreases from bottom to top of the cathode, the pressure of oxygen containing gas in the individual cathode compartments correspondingly decreases.