Method of operating electrolytic diaphragm cells having horizontal electrodes

Abstract

Disclosed is a method of operating an electrolytic cell divided into an anolyte chamber and a catholyte chamber by a substantially horizontal, permeable barrier. The anolyte chamber is above the permeable barrier while the catholyte chamber is below the permeable barrier. Electrolyte passes from the anolyte chamber through the permeable barrier to the catholyte chamber. An electrical current passes through the cell, thereby evolving chlorine gas on the anode and hydrogen gas on the cathode. The electrical current is in excess of the unaided flow of electrolyte through the permeable barrier resulting in diminished cathode current efficiency and necessitating augmentation of the flow of electrolyte to restore the current efficiency to acceptable values. According to the disclosed method, chlorine gas is collected at super-atmospheric pressure in the anolyte chamber, and withdrawn from the anolyte chamber while maintaining the chlorine gas at such elevated pressure. The elevated pressure of chlorine augments the flow of electrolyte through the permeable barrier to the catholyte chamber.

Description

BACKGROUND

Multiple electrolyte processes, i.e., diaphragm cell and permionic membrane cell processes, for the electrolysis of alkali metal chloride brine to yield chlorine, hydrogen, and either caustic soda or potassium hydroxide require a head of brine to force electrolyte through the diaphragm or the permionic membrane. This is especially true of electrolytic processes using either modified diaphragms, e.g., diaphragms treated with various agents to increase their life, or permionic membranes.

Stacked bipolar electrolyzers, i.e., bipolar electrolyzers having a plurality of bipolar electrolytic cells, each divided into an anolyte chamber and a catholyte chamber by a horizontal diaphragm or permionic membrane, with the anolyte chamber of a cell above the diaphragm or permionic membrane of the cell and the catholyte chamber of the cell below the diaphragm or permionic membrane, where a plurality of such cells are stacked one atop the other, provide a high amount of electrode area per unit of floor space. However, in such stacked, bipolar, horizontal cells, economies of construction and operation are realized with a low individual cell height. For this reason, the provision of a tall individual cell to provide a brine head may counter-balance the economies resulting from the stacked, bipolar, horizontal cell configuration.

Additionally, the horizontal cell configuration finds use in mercury cell conversions. Such conversions, necessitated by environmental considerations, result in an electrolytic cell having the original mercury cell horizontal anode above a horizontal cathode, with a horizontal diaphragm of permionic membrane interposed therebetween. The existing cell structure and bus bars of the mercury cell circuit militates against providing electrolyte head means within the electrolytic cell.

One way of augmenting the flow of electrolyte through the permeable barrier is to draw a vacuum on the catholyte side. However, the provision of a vacuum on the catholyte side may also draw chlorine gas through the permeable barrier, thereby resulting in chlorine gas being present in the catholyte chamber with the hydrogen gas. This is objectionable for safety reasons.

SUMMARY

It has now been found that the beneficial effects of a high hydrostatic head may be provided in a horizontal cell by providing a chlorine gas pad, at an elevated pressure, within the anolyte chamber. According to this invention, such an elevated pressure chlorine gas pad is provided within the anolyte chamber while removing chlorine from the chamber.

DETAILED DESCRIPTION OF THE INVENTION

The invention may be understood by reference to the figures.

FIG. 1 is a perspective, partial cutaway view of one apparatus for obtaining a high chlorine partial pressure within the anolyte chamber of an electronic cell.

FIG. 2 is a schematic diagram of the apparatus of FIG. 1 with an associated horizontal cell.

FIG. 3 is a partial cutaway view of a horizontal bipolar diaphragm cell in combination with the apparatus of FIG. 1.

FIG. 4 is a partial cutaway view of a converted mercury cell in combination with the apparatus of FIG. 1.

In an electrolytic cell 1 with a horizontal, permeable barrier 11, the electrolyte chamber is divided by a permeable barrier 11 into an anolyte chamber 21 above the permeable barrier 11 and a catholyte chamber 31 below the permeable Within 11. Wiithin such a cell 1, the electrodes are substantially parallel to each other and to the permeable barrier 11 with the anode 23 being in the anolyte chamber 21, above the permeable barrier 11, and the cathode 33 being in the catholyte chamber 31, below the permeable barrier 11. Such cells 1 are referred to herein as horizontal cells.

Modern horizontal cells are also characterized by a low vertical clearance between the anode 23 and the top 25 of the anolyte chamber 21. For this reason, the space above the anode 23 for the anolyte liquor to provide a hydrostatic head is limited. The amount of vertical space may be less than 2 feet, frequently less than 18 inches, and even less than 1 foot. Such a height is insufficient to provide a head of brine sufficient to drive the electrolyte through the permeable barrier.

In the operation of a horizontal electrolytic cell 1, a brine feed containing from about 275 to about 325 or more grams per liter of sodium chloride is fed to the anolyte chamber. This brine feed may be saturated or even super-saturated. An electrical current is passed through the cell 1 from the anode 23 through the electrolyte to and through the permeable barrier 11 to the cathode 33. Chlorine gas is generated on the anodes 23 and anolyte liquor passes through the permeable barrier 11 to the catholyte chamber 31. Within the catholyte chamber 31 hydrogen gas is generated on the cathode 33 and a catholyte liquor of sodium hydroxide and sodium chloride is obtained.

Catholyte liquor containing from about 120 to about 150 grams per liter of sodium hydroxide and from about 175 to about 225 grams per liter of sodium chloride in a diaphragm cell and from about 80 to about 440 grams per liter of sodium hydroxide and about 0.10 to about 10 grams per liter of sodium chloride in a permionic membrane equipped cell, is recovered from the catholyte chamber. Additionally, some of the anolyte liquor may be removed from the anolyte chamber, refortified or resaturated with brine, and recirculated to the anolyte chamber.

While the operation of the electrolytic cell system is illustrated with reference to sodium chlorine brines, it is also useful in the electrolysis of other alkali metal halide brines, such as potassium chlorine brines.

The permeable barrier 11 may be in the form of an electrolyte permeable, cation permeable barrier. Such a barrier is called a diaphragm. Most commonly, asbestos is used to provide the diaphragm. The diaphragm may be deposited onto the upper surface of the cathode from a slurry of asbestos in water, in aqueous sodium chloride, or in cell liquor. Most commonly, diaphragms are deposited from a cell liquor slurry containing about 1 to 2 weight percent chrysotile asbestos, 120 to 150 grams per liter of sodium hydroxide, and 175 to about 225 grams per liter of sodium chloride. Alternatively, the asbestos may be provided by asbestos paper or asbestos cloth. The asbestos diaphragm may be treated to increase the effective life thereof. For example, the asbestos diaphragm may be treated with an organic resin having fluorocarbon and fluorocarbon acid moieties, such as DuPont NAFION resin or an inorganic material such as a silicate or the asbestos diaphragm may be subjected to thermal treatment.

The permeable barrier may also be a cation permeable barrier of limited electrolyte permeability, such as an ion exchange resin. For example, the permeable barrier may be provided by a fluorocarbon-fluorocarbon acid resin ion exchange membrane, i.e., such as DuPont NAFION or the like.

According to the preferred method of this invention, the operation of the electrolytic cell is facilitated by providing a chlorine gas pad 41 at the top 25 of the anolyte chamber 21. The chlorine gas pad 41 is at an elevated pressure so as to provide a hydrostatic head within the anolyte chamber 21. Typically the chlorine gas pad is at a pressure of from about 0.5 to about 5.0 pounds per square gauge. The hydrostatic head augments the flow of electrolyte through the permeable barrier 11. According to this invention, the chlorine gas pad 41 is maintained at an elevated pressure while withdrawing chlorine from the anolyte chamber 21. This may be accomplished by providing a high pressure manifold or by discharging the chlorine into a head of liquid.

Most commonly, the chlorine gas pad 41 will be maintained within the anolyte chamber by discharging chlorine into a head of liquid. For example, as shown in FIGS. 2, 3, and 4, the chlorine gas may be withdrawn from the anolyte chamber 21 of a cell 1 to a liquid-containing tank 51 and discharged into the liquid 53 in the liquid-containing tank 51. A level 55 of liquid 53 sufficient to provide a hydraulic head within the anolyte compartment 21 is maintained within the liquid-containing tank 51. This head should be sufficient to drive the electrolyte from the anolyte chamber 21 to and through the permeable barrier 11 into the catholyte chamber 31, thereby augmenting the flow of electrolyte through the barrier 11. In this way, the hydrostatic head is sufficient to force electrolyte through the barrier 11 against the pressure of the evolved chlorine, thereby maintaining a high cathode current efficiency.

The upper level 55 of liquid 53 in the liquid-containing tank 51 is sufficiently above the level of the gas discharge 59 into the tank 51 to discharge the chlorine gas into a positive head of liquid, thereby to provide a hydrostatic head within the anolyte chamber 21. For example, the upper level 55 of the liquid 53 liquid-containing tank 51 may be from about 1 foot to about 4 or more or even 5 or 6 feet above the level of the gas discharge 59 into the liquid tank 51. The level 55 of the liquid 53 may be regulated, e.g., by movable pipe 60 whereby to regulate the pressure of the chlorine gas pad. In this way, a higher head can be provided, for example when the diaphragm has "tightened" or the current density is high. The chlorine gas is recovered from chlorine recovery means 54 in the upper portion of tank 51, and the overflow liquid, e.g., brine, is recovered from movable pipe 60.

In FIG. 3 is shown one exemplification of an electrolytic cell 7 utilizing the method and apparatus of this invention. In FIG. 3, a horizontal cell 3 of a stacked, bipolar diaphragm cell electrolyzer is shown. While only two cells 3 and 3 are shown in the figure, there may be five or more, for example, 11 or 15 or 20 cells in the electrolyzer. These cells 3 are in bipolar configuration with the cathode 33 of one cell electrically in series with the anode 23 of the cell directly below. This is accomplished by a common repeating structural member, i.e., a bipolar unit 61. A bipolar unit 61 includes the cathode 33 of one cell 3, an impermeable housing with a metal horizontal floor or surface 63, and the anode 23 of the next adjacent cell.

The upper surface 65 of the horizontal floor 63 is fabricated of a catholyte-resistant material and provides the floor or bottom of the catholyte chamber of the upper or prior cell in the electrolyzer. The cathodic portion is fabricated of a catholyte-resistant material, such as iron, cobalt, nickel, steel, stainless steel, or the like. The cathodic half cell portion of the bipolar unit 61 includes means 71 for removing cell liquor from the catholyte chamber 31 of an individual cell 3. The means 71 for removing cell liquor are generally near the bottom of the cathodic half cell. The cathodic half cell also includes means for removing hydrogen 73 generally near the top of the cathodic half cell. Alternatively, the same line may be used for recovering the cell liquor and the hydrogen.

The cathodic half cell includes a cathode 33. The cathode 33 may be in the form of mesh, rods, perforated plate, or expanded mesh. The cathode is generally fabricated of iron, cobalt, nickel, steel, stainless steel, or the like. Additionally, the cathode 33 may include means thereon for lowering the hydrogen overvoltage of the cathode.

The cathode 33 is connected to the bipolar unit 61 by electrical conducting means 68. The electrical conducting means 68 may be in the form of studs, copper conductors, conductive spring clips, or the like. The conducting means 68 permit the cathode 33 to be maintained at a pre-determined spacing from the anode 23 of the cell 3 and to be maintained in an electroconductive relationship with the anode 23 of the next adjacent cell in the electrolyzer.

A permeable barrier 11 is provided above the cathode. The permeable barrier may be in the form of a diaphragm or permionic membrane as described hereinbefore. Typically, the cathode half cell has a height measured from the catholyte-resistant floor to the top of the cathode of from about 1 inch to about 5 inches.

The lower half of the bipolar unit 61 includes the anodic half cell of the next adjacent individual cell in the electrolyzer. The anodic half cell is fabricated of an anolyte-resistant material on the ceiling 67 and walls of the anodic half cell. The anolyte-resistant material may be the structural material on the half cell. Alternatively, the anolyte-resistant material may be a coating, film, lamination, or layer upon the structural material used to fabricate the cathodic half cell.

Typically, the anolyte-resistant material is a valve metal. The valve metal are those metals which form a corrosion-resistant, electrically insulating oxide upon exposure to acidic aqueous media.

The valve metals include titanium, zirconium, hafnium, columbium, tantalum, and tungsten. Most commonly, titanium or tantalum is the valve metal utilized for the anolyte-resistant, anolyte-retaining structure of chlor-alkali electrolytic cells. Titanium is preferred for this service because of its cost and ready availability. However, the anolyte-resistant material may also be a rubber or plastic coating or sheathing upon the catholyte-resistant material used in fabricating the upper half of the cell.

The anodic half cell includes brine feed means 77. The brine feed means 77 may be in the form of sparger 78 for spraying the brine feed out of apertures 79 therein at either a horizontal angle or upwardly inclined from the horizontal. Alternatively, the brine feed may be in the form of a simple pipe leading into the anolyte chamber.

The anodic half cell includes the anode 23. The anode 23 may be in the form of a valve metal having a suitable electroconductive coating thereon, where the valve metals are as described hereinabove. Most commonly, the anode will be fabricated of titanium or tantalum, with titanium being preferred for chlor-alkali service. The electroconductive coating on the anode is provided by a corrosion-resistant material having a low chlorine overvoltage, e.g., below about 0.250 volt at 200 Amperes per square foot. The electroconductive coating is most frequently provided by a metal of the platinum group, i.e., ruthenium, rhodium, palladium osmium, iridium, platinum, and alloys thereof; oxides of the platinum group metal as ruthenium oxide, rhodium oxide, palladium oxide, osmium oxide, iridium oxide, platinum oxide, and oxides thereof; oxygen-containing compounds of the platinum group metals such as alkaline earth ruthenates, alkaline earth rhodates, alkaline earth ruthenites, alkaline earth rhodites, cobalt palladite, cobalt platinate, ruthenium titanate, ruthenium titanite, and the like. Alternatively, the electroconductive coating may be provided by mixed crystals of the oxides of the platinum group metal and the oxides of the valve metals, i.e., the electroconductive surface may be provided by a mixture of ruthenium oxide and titanium dioxide or ruthenium dioxide and zirconium dioxide or rhodium oxide and titanium dioxide or rhodium oxide and zirconium dioxide or the like. Additionally, other oxide materials may be present in the electroconductive surface, such as, for example, tin oxide, lead oxide, bismuth, antimony, arsenic, or the like.

Generally, the anodic half cell has a height of from about 3 inches to about 24 inches or more and most frequently from about 4 inches to about 7 inches when measured from the bottom of the anode 23 to the ceiling 65 of the anolyte chamber 21.

An individual electrolytic cell 3 of the bipolar electrolyzer is formed by the anodic half cell of one bipolar unit and the cathode half cell of the next adjacent bipolar unit with the anode above the permeable barrier, the cathode below the permeable barrier, and the anode-cathode permeable barrier being parallel to each other and in horizontal relationship.

In the operation of such a cell, a head of brine is maintained within the anolyte chamber 21 by a chlorine gas pad 41 in the upper portion of the anolyte chamber 21. A chlorine line 43 leads from the anolyte chamber 23 to liquid-containing tank 51. The level of the outlet to pipe 43 from the anolyte chamber 21 is referred to as the overflow level of the cell.

Within the liquid-containing tank 51 the chlorine is discharged in such a way as to cause the chlorine to be discharged as many small bubbles rather than as a few large bubbles. For example, the chlorine may be discharged downward into the liquid through a downward facing pipe through a screen or mesh. Alternatively, the chlorine gas discharged into an upward facing pipe 58 within a bubble cap 59 or the like thereabove. As shown in the figures, the bubble cap 59 may be provided having serrated edges in order to break up the flow of chlorine into small bubbles. In this way, a uniform pressure of from about 0.5 to about 5.0 pounds per square inch gauge is provided within the anolyte chamber 21.

The method of this invention may also be used in mercury cells 5 that have been converted to diaphragm cell operation. Such a mercury cell conversion 5 is shown in FIG. 4. Mercury cells 5 typically have an inclined metal plane or surface 35 for conveying the mercury. Cathode bus bars 81 feed the current to the inclined surface 35. The inclined surface 35 is most commonly fabricated of iron, cobalt, nickel, steel, stainless steel, or any material that is not readily attacked by nascent hydrogen, caustic soda, or mercury. Generally, the bottom 35 has a slope of from about 1/2 percent to about 2 percent in the direction of the mercury flow. In a mercury cell converted to diaphragm cell service, sufficient slope should be maintained to allow the cell liquor to be collected at one end of the cell, but the slope should not be so great as to permit the opposite end of the cell to run dry. For example, a slope of from about 1/4 of 1 percent to about 1/2 of 1 percent may be maintained.

The anodes 23 are typically suspended from the cell top 83 and spaced from the cell bottom 35 a distance sufficient to provide a spacing of from about 0.085 inch to about 0.125 inch above the mercury, i.e., a spacing of from about 0.15 inch to about 0.30 inch above the cell bottom. A typical mercury cell 5 also includes brine feed means and mercury feed means at the higher end of the cell, brine recovery and mercury recovery at the lower end of the cell, and chlorine recovery along the length of the cell.

When, however, it is necessary to convert a mercury cell to diaphragm cell operation, an electrolyte permeable cathode 33 spaced from the cell bottom 35 is provided. The electrolyte permeable cathode 33 is generally spaced from about 2 inches to about 5 inches from the cell bottom 35 and is spaced therefrom by channel frames 37. The channel frames 37 may have perforations therein to allow cell liquor to flow along the length of the cell 35 to the cell liquor recovery means 71. The channel frames 37 may be joined to the cell bottom 35, for example, by welding or bolting. Alternatively, the channel frames 37 may simply be laid upon the cell bottom 35. The cathode 33 may be joined to the channel frames 37 by welding or bolting of the like. Alternatively, the cathode 33 may just be laid on top of the channel frames 37.

The channel frames 37 may conduct current from the cathodes 33 to the cathode bus bars 81. Alternatively, electrical conductors 85 may conduct the electrical current from the cathodes 33 to the cathode bus bars 81. The electrical contact may be provided by clips 86 on the cell bottom 35 engaging the cathode 33 or by clips on the cathode engaging conductors on the cell bottom 35.

Permeable barrier means 11 are provided on the cathode 33. The permeable barrier means 11 define the upper limit of the catholyte chamber 31 and the lower limit of the anolyte chamber 21.

In a mercury cell conversion 5, the anodes 23 are raised above the normal mercury cell anode position to allow for the cathode 33 and permeable barrier 11 to be inserted in the cell 5. In this way, the cathodes 33 originally intended for use with the cell 5 may be salvaged and used for diaphragm cell or permionic membrane cell operation, therefore effecting an economy of capital investment. Generally, the anodes 23 are spaced from about one-sixteenth inch to about three-fourths inch above the cathode 33, and generally less than three-eighths inch above the cathode 33 when the permeable barrier is a deposited asbestos diaphragm. However, when the barrier is an asbestos paper diaphragm, as a 50 ml asbestos paper diaphragm, the anode may be spaced as close as from about 0.05 inch to about 0.125 inch above the cathode.

In a mercury cell conversion, the cell top conventionally used for mercury cell operation may be replaced by a metal or heavy plastic cell top 83 to allow for the containment of the pressurized chlorine gas pad 41.

In the operation of the cell shown in FIG. 4, brine feed is through the brine feed means 77. An electrical current passes from the anode 23 through the permeable barrier 11 to the cathode 33 thereby causing chlorine to be generated on the anodes 23 and hydrogen to be generated on the cathode 33. Chlorine gas evolved at the anode 33 is removed through conduit 43 under elevated pressure, e.g., from about 0.50 pounds per square inch to about 5.0 pounds per square inch gauge to a liquid-containing tank 51.

Discharge of the chlorine into the liquid-containing tank 51 is from a conduit 43 which delivers the chlorine into the liquid 53. The downward direction of the discharge into the liquid may be brought about either by a bubble cap arrangement 59 or by a downward-facing conduit within the liquid-containing tank. By either method, the pressure of the chlorine gas pad 41 is maintained at between 0.50 pounds per square inch gauge and 5.0 pounds per square inch gauge, thereby to augment the flow of anolyte liquor to the permeable barrier.

The liquid within the liquid-containing tank 51 may be brine or water. Most frequently the liquid will be brine, which may be either saturated brine of depleted brine. Brine is preferred because of the overflow into the tank 51 from the cell 1, 3, or 5 through conduit 43 and the backflow into the cell 1, 3, or 5 from the tank 51 through the conduit 43. Frequently, especially at high current density operations, e.g., above about 400 Amperes per square foot, and especially above about 600 or even 800 or more Amperes per square foot, a considerable excess of brine is fed to the cell, e.g., a 400 percent or 600 percent, or even an 800 percent excess of brine is fed to the cell. The excess brine may be recovered through conduit 43 and movable pipe 60 and recycled to the cell with the feed brine.

It is to be understood that although the invention has been described with specific reference to specific details and particular embodiments thereof, it is not to be so limited in that changes and alterations therein may be made which are in the full intended scope of this invention as defined by the appended claims.

Claims

We claim:

1. A method of operating an electolytic cell which cell has an electrolyte chamber divided horizontally by a permeable barrier into an anolyte chamber containing a substantially horizontal anode above said permeable barrier, and a catholyte chamber containing a substantially horizontal cathode below said horizontal barrier; which method comprises feeding alkali metal chloride brine to said anolyte chamber; passing electrical current through said cell at a current density high enough to generate sufficient hydrogen gas on said cathode to oppose the unaided flow of electrolyte through said permeable barrier from said anolyte chamber to said catholyte chamber; generating chlorine gas on said anode; collecting the chlorine gas in said anolyte chamber above the anolyte therein to maintain a chlorine gas pad in said anolyte chamber; withdrawing the chlorine gas from said anolyte chamber to a liquid-containing tank; discharging the chlorine gas from said cell into the liquid in said liquid-containing tank and maintaining a level of liquid in said liquid-containing tank above the level of anolyte liquor in said cell sufficient to augment the flow of anolyte liquor through said permeable barrier against the pressure of the hydrogen to said catholyte chamber.

2. The method of claim 1 wherein the bottom of said catholyte chamber is inclined from the horizontal.

3. The method of claim 1 wherein the chlorine gas is discharged into said liquid-containing tank upwardly into a bubble cap.

4. The method of claim 1 wherein an excess of brine is fed to the cell, and the excess brine is recovered with the evolved chlorine gas, and recirculated to the cell.

5. A method of operating an electrolytic cell which cell has an electrolyte chamber divided into an anolyte chamber and a catholyte chamber by a substantially horizonta, permeable barrier, said anolyte chamber being above said permeable barrier and containing an anode, said catholyte chamber being above said permeable barrier and containing a cathode, whereby electrolyte in said anolyte chamber passes through the permeable barrier to the catholyte chamber; which method comprises feeding an alkali metal chloride brine to said cell; maintaining a head of brine above said permeable barrier; passing electrical current through said cell; evolving chlorine gas on the anode; collecting and maintaining the chlorine gas as a gas pad at super-atmospheric pressure in said anolyte chamber above the brine; and withdrawing said chlorine while maintaining the gas pad at an elevated pressure whereby to augment the head of brine above the permeable barrier and the flow of brine through the permeable barrier to the catholyte chamber.

6. The method of claim 5 comprising withdrawing the chlorine from the anolyte chamber to a liquid-containing tank, and discharging the chlorine gas into said liquid.

7. The method of claim 6 where an excess of brine is fed to the cell, and the excess brine is recovered from the cell and recirculated to the cell.

8. The method of claim 7 comprising maintaining a level of liquid in the liquid-containing tank to provide a pressure of chlorine in said anolyte chamber sufficient to aid the flow of electrolyte through the permeable barrier.

9. The method of claim 6 wherein the chlorine is upwardly discharged into a bubble cap in said liquid-containing tank.

10. The method of claim 6 comprising varying the level of liquid in said liquid-containing tank whereby to vary the pressure of chlorine in said liquid-containing tank.

11. The method of claim 5 wherein the pressure of chlorine in said anolyte chamber is greater than 0.5 pounds per square inch gauge.

12. An electrolytic cell which cell has an electrolyte chamber divided horizontally by a permeable barrier into an anolyte chamber containing a substantially horizontal anode above said permeable barrier, and a catholyte chamber containing a substantially horizontal cathode below said horizontal barrier; means for feeding alkali metal chloride brine to said anolyte chamber; means for passing electrical current through said cell whereby to generate chlorine on said anode; means to collect and maintain chlorine gas at a super-atmospheric pressure in said anolyte chamber whereby to maintain a super-atmospheric chlorine gas pad in said anolyte chamber; means to withdraw chlorine gas from said anolyte chamber to a liquid-containing tank while maintaining gas within said anolyte chamber at a super-atmospheric pressure; means to discharge chlorine gas from said cell into the liquid in said liquid-containing tank while maintaining a level of liquid in said liquid-containing tank above the level of anolyte liquor in said cell and maintaining gas within said anolyte chamber at a super-atmospheric pressure.

13. The electrolytic cell of claim 12 wherein the bottom of said catholyte chamber is inclined from the horizontal.

14. The electrolytic cell of claim 12 wherein the means to discharge chlorine gas from said anolyte chamber into said liquid-containing tank comprises a conduit from said anolyte chamber to said liquid-containing tank; an upward extension of said conduit into said tank, and a bubble cap above said upward extension above said conduit.

15. The electrolytic cell of claim 12 including means to vary the level of liquid in said liquid-containing tank.