US2467892A - Regenerator chamber for mercury cathode electrolytic cell - Google Patents

Description

APrll 19, 1949- R. A. HORST REGENERATOR CHAMBER FOR MERCURY CATHODE ELECTROLYTIC CELL Filed sept. 18, 1942 b9-- .Y mw

W -,---lmJ m Patented Apr. 19, 1949 REGENERATOR CHAMBER FOR MERCURY CATHODE ELECTROLYTIC CELL Roy A. Horst, Syracuse, N. Y., assignor to Allied Chemical & Dye Corporation, a corporation of New York Application September 18, 1942, Serial No. 458,844

2 Claims.

This invention relates to the electrolysis of brine and is particularly concerned with a new and improved mercury cathode apparatus for the conduct of such electrolyses.

In the past Various types and designs of mercury cathode electrolytic apparatuses have been proposed.

An early apparatus is the type commonly known as the Castner cell. The Castner cell (U. S. Patent 518,135 of 1894) involves a pair of brine chambers in which brine is electrolyzed to form an amalgam and an intermediate washing chamber in which amalgam is washed with water to remove the active metal and regenerate or reclaim the mercury. The apparatus is so balanced and actuated that by tipping the apparatus first in one direction and then in the other, the mercury is caused to flow from one brine chamber, through the washing chamber, to the second brine chamber and then back in the reverse direction.

Later apparatus substituted stationary brine and washing chambers at different levels and provided various types of elevators for conveying the mercury from the lower to the higher chamber. Such apparatus is illustrated by the Whiting cell of U. S. P. 951,228 of 1910. The Whiting cell involved a brine chamber and a washing chamber situated side by side. The brine chamber was arranged at a slightly higher elevation than the washing chamber so that mercury would flow by gravity from the former to the latter. A bucketwheel elevator was provided for raising the mercury from the low elevation of the Washing chamber to the higher elevation of the brine chamber.

The present invention is concerned with modifications in apparatus of the latter general type, i. e., with electrolytic apparatus having a relatively high brine chamber and low washing chamber and an elevator for raising the mercury.

The apparatus of the invention is applicable to the electrolysis of salts of amalgam-forming metals in general but is especially applicable to the electrolysis of salts of the metals which react with water, for example, the electrolysis of the chlorides and bromides of the alkali-metals. That chamber in which the metal salt is electrolyzed to form an amalgam of the free metal will be referred to herein as the brine chamber and that chamber in which the free metal is washed from the amalgam, thus restoring the mercury to its initial condition, as the regenerator or,\since when water is employed as the washing liquid, as is customarily the case, free hydrogen and metal hydroxide are formed, as the hydrogen or hydroxide chamber.

The apparatus of the invention is characterized by a novel arrangement of brine chamber and regenerator each having an approximately hori- Zontal mercury supporting bed or tray, the regenerator tray being directly beneath the brine` slightly farther chamber tray. The two trays are apart at one end than at the other and at the end of greater separation an elevator is provided.v while at the opposite end there is a free flow-` mercury seal. This arrangement causes the mercury in passing through the cell to follow a path resembling an endless belt about a large drive pulley and a smaller driven pulley.

By the above placement of parts numerous ad-.l

accessible. Since any necessary access to the balance of the cell may be from one side, the cells of the battery may be arranged in juxtaposed pairs and thus placement space may be still further conserved. The brine chamber may be placed directly upon the regenerator, thus serving as a cover to complete the enclosure of the latter and secure the advantages of a closed unit. Moreover, an extremely rigid unitary construction may be employed comprising parallel channel irons or I-beams as side members for the regenerator, so disposed as to serve as a supporting frame for the brine chamber. The inherent rigidity of this assembly permits a lighter weight construction than otherwise necessary, thus permitting not only lower apparatus costs but also lower costs for foundations and supporting structures. As an additional important advantage, the heat generated in the cell is retained in the cell to a substantially greater degree than in previous cells. This feature assistsk operation of the cell at higher than atmospheric temperatures; in the electrolysis of sodium chlo-V ride and potassium chloride brines to produce chlorine and caustic soda or caustic potash,vit enables one to secure unusually high concentrations of caustic solutions without application or external heat to the cell, caustic concentrations between 50% and 60% being readily obtainable.

The cell of the invention is preferably at least five times as long as it is wide; i. e. the -brine chamber mercury bed has a width not more than one-fifth its length. The brine chamber is pro'- vided with a plurality of cross-members or baies positioned on top of the anodes at more or less regular intervals to confine the flow of brine .primarily to the narrowspace between the mercury cathode and the anodes disposed thereabove. The regenerator chamber is also provided with cross members or bailles which cooperate with a mercury supporting tray having longitudinal fins to dam the flow of water or other washing liquid above the fins and thus provide a series of pools from which the washing liquid flows in a large number of small parallel streams dened by the mercury on the bottom, the iins on the sides, and the baffles on the top. By this arrangement an orderly and progressive flow of vwashing liquid from one end of the unit to the other is insured.

The baiile members in the regenerator are preferably pivoted and provided with means outside the cell for moving these baffles to an inoperative position. This construction facilitates flushing of the regenerator. reduces the flushing period, and increases the average efficiency of regeneration and thus, indirectly, the attainable caustic concentration.

The abnormally long brine chamber and the baiiies so placed as to concentrate the flow of brine in the zone between the anode and cathode co-operate to provide a high velocity of flow of brine in this zone. This high velocity of the brine scours from the anodes the small bubbles of chlorine which normally tend to adhere to their surface. The prompt removal of these bubbles not only substantially improves the voltage efficiency of the cell but also tends to inhibit irregular erosion of the anodes and thus not only to further increase the voltage efficiency but at the same time to prolong the useful life of the anodes.

In order to secure the greatest advantage from the scouring effect of the brine, it is desirable to provide chlorine escape channels transverse to the flow of brine. This may be accomplished by provision of many spaced anodes, each fairly narrow, so that chlorine is provided with frequent passages for escape upwards between anodes, or it may be accomplished by slotting the anodes vertically to provide even more frequent channels. A preferred form lof anode is deeply grooved on its underface to provide gas channels. Chlorine collecting in the channels finds its way out at the ends of the anodes whence it can escape to the gas space above. This escape may be still further facilitated by provision of one or more holes from each channel to the upper face of the anode. The grooved anodes have substantially greater rigidity and substantially less electrical resistance than anodes of comparable size in which slots are cut all the way through.

Another important feature of the apparatus of the invention is the provision of co-current brine and mercury ow, which in combination with the directing eect of the brine chamber baffles sweeps any foreign matter rapidly forward toward the outlet whence it may be removed whenever the accumulation of such material is sufcient to warrant it. Since the efficiency of a mercury cathode electrolytic cell is substantially impaired by the accumulation of foreign material on the surface of the mercury in the Zone of electrolysis, the rapid and efficient removal of such material from the zone of electrolysis contributes considerably to the electrical efficiency of the cell.

The practical application of my invention is illustrated by the specic embodiment described in' detail below in connection with the accompanying drawing, wherein Fig. 1 is a side elevation showing a specific embodiment of the invention. The-apparatus is shown partly in sectional View and partly phantom view to show more clearly the construction of the apparatus.

Fig. 2 is an enlarged cross-section on line A--A 0f Fig. 1.

In the apparatus illustrated the cell comprises a, brine chamber I and a regenerator chamber 2. By reference to Fig. 2 it will be seen that the brine chamber is constructed as a long chamber comprising a steel shell 3 provided with a lining of concrete or other suitable material d.

For a cell having a capacity of -about a half metric ton of chlorine per day and a rated load of 16,000 amperes, chamber i may be in the neighborhood of 21/2 feet wide by 40 feet long. As will be apparent from Fig. l, the floor of this chamber is a succession of steps and the depth of the chamber is accordingly somewhat greater at one end than at the other. The floor of the brine chamber I may be constructed of concrete or other alkali-resistant materials of construction. A particularly suitable type of construction involves the use of a poured concrete lining supporting precast concrete working surfaces as more fully described in U. S. applic-ation Serial No. 458,847 of even date, now abandoned.

A pair of channel-shaped steel structural members 5 form the sides of the regenerator chamber. One side-face of each channel provides a supporting surface for shell 3. The channel irons are separated from shell 3 by Sealing gaskets 6 to prevent leakage of hydrogen from or air into chamber 2. The shell may be secured to the members 5 by a series of bolts l. The floor of regenerator chamber 2 has a gentle slope with its high end beneath the low end of chamber I and its low end beneath the high end of chamber I. This slope, which is at the rate of about le inch per linear foot, may be provided by a concrete fill 8. The door of the regenerator chamber is preferably composed of compressed graphite sections $3 having vertical ns Il running longitudinally of the chamber and providing channels for 'flow of mercury from the high end of the regenerator chamber to the low end thereof as more clearly shown in Fig. 2. The ends of sections 9 may be beveled or notched, if desired, to provide transverse channels Illa.

At the left end of the cell an elevator I I, which may be of the bucket-wheel type, is provided for elevating mercury from the low end of the regenerator to the high end of the brine chamber. At the opposite end of the cell a mercury seal construction I2 is provided for permitting mercury to flow from the brine chamber down to the upper end of the regenerator chamber.

Flow of brine in the cell illustrated is from left to right and the brine chamber is provided with a brine inlet conduit I3 and brine overflow and chlorine outlet conduit iii. In the regenerator, ow of regenerating liquid, which is normally water or dilute alkali-metal hydroxide when alkali-metal hydroxide is being produced, is also from left to right from inlet I5 to hydroxide overflow and hydrogen outlet I6.

The brine chamber I is provided with a removable top or cover I'l supported on spacing elements or shims I8. Spacing elements I8 preferably are composed of a material having very little plasticity since the thickness of these elements determines the position of the anodes with respect to the mercury cathode. Leakage of chlorine from the chamber between the cover I1 and the lining Il may be avoided by applying. a suitable caulking material Ia, such as putty, between thelining 4 and the cover I1.

The cover I1 is provided with a plurality of apertures I9, one for each anode. Projecting through apertures I9 are a series of carbon anode supporting rods 2D to which the carbon anodes 2l `are aixed in any suitable manner; they are shown threaded to the supporting rods. A shoulder of supporting rods 20` may rest against the cover I1 or may be separated therefrom by spacing Washers 22 to initially adjust each anode so that its underface is the desired distance from the mercury level in the cell. This distance may be 'in the neighborhood of 1/4 inch. The anode supporting rods 2|] may be secured firmly to the cover I1in any suitable manner, for instance by means of clamps or cement. The anodes 2| are graphite blocks which have a length substantially equal tothe Width of the brine chamber and normally have a Width about half of this. Their thickness may be around 3 inches initially and during the operative life of the anode gradually diminishes to about 1 inch.

I prefer to provide the anodes 2I with channels or grooves 23 disposed along the underface of the anodes in a direction substantially perpendicular to the ow of brine and mercury thereunder. These channels, while they may extend tothe upper surface of the anodes, preferably extend initially about one-third of the way through and are connected with the space above tl'ie anodes by means of apertures 24.

Y Electrical connection t'o the anodes is secured by means of electrically conductive supporting rods 2|] and metallic connectors 25 and bus bar 26. Connectors 25 may be exible or rigid and maybe aixed to rod 20 by a stud bolt or a poured lead connection, or a clamp.

Electrical `contact between the current source and the mercury cathode is obtained through the shell 3 of the brine chamber; electrically conductive bus bar 21 is riveted or otherwise aflixed to the shell preferably along its entire length in order to avoid voltage losses through the shell. Conductive rods 28 are welded to the shell 3| and project up to near the upper surface of the floor lining 4. Mercury owing through the chamber fills the cups formed by the tops of these conductive rods and the lining and thus makes electrical connection with shell 3 and'bus bar 21.

Each anode 2l is provided with a baffle 29 extending from the upper edge of the anode to a point above the-level of brine in the brine chamber. These ballles may be afxed to the anodes in any suitable manner, for instance by means of dowels. vSince the end of each anode and the -accompanying baiiie present a wall opposing the longitudinal iiow of liquid through the cell, liquid is forced beneath the anodes and the primary llow takes place in the space between the lower anode surface and the mercury.

The regenerator chamber 2 is supplied with transverse bales 30 supported on pivots 3I in side Walls 5 and provided with operating handles 32 located outside the cell so that bailles 30 may be manually raised to a horizontal position near the top of the regenerator. Suitable provision, such as valve-stem gaskets or washers, are provided to avoid leakage where handles 32 extend through the side wall 5 of the regenerator. The normal operative position of baffles 30 is as shown in the drawing with their lower edges resting upon fins IU. In this position the baflles. which extend above the normal liquid level in the regenerator, force the liquid in flowing from inlet I5 to outlet I6,to pass under each baille. This provides a progressive vliow of the regenerating liquid essential for securing at the same time high alkali-metal hydroxide concentration and Aeffective removal of alkali-metal from mercury.

It is not necessary that the bailles be pivotally mounted for iixed baliies would perform the functionof preventing lengthwise diffusion of the regenerative liquid as well. 'Ihe pivoted baffles, however, facilitate cleaning as explained below.

A pair of outlets 33 and 34 have been shown at op-posite ends of the cell. The outlet 33 preferably is disposedat approximately the mercury level in the cell when the cell is not operating; that is, when mercury in the upper chamber has all collected at the 10W end of the regenerator. This outlet has been shown as a simple capped pipe. Outlet 34, which is preferably disposed at about the normal mercury level when the cell is operating, is -illustrated as a swivel type outlet Which may be opened by swinging the high end to a point below the liquid level in the brine chamber.

For the production ofv highly concentrated alkali-metal hydroxide, it is desirable to limit heat loss by provision of suitable insulation. Since chamber I is so constructed that heat loss from this chamber is normally small, it is not necessary to provide additional insulation for this chamber. at the seal end of the cell, particularly Where mercury contacts the exterior metal walls of the unit. Thus, if the Walls of mercury seal I2 are composed of metal considerable loss of'heat at this point may occur unless adequate insulation is provided.v It is also desirable to insulate side walls 5 of chamber 2 to conserve heat, particularly when causticvsoda of about 50% concentration is being produced. Since the shell 3 loses some heat and is an active electrical conductor, it may be advantageously protected by a suitable material serving as both a heat and electrical insulator.

In assembling the above apparatus for operaition, the unit is completely assembled and the required amount of mercury introduced with cover I1 removed. Anodes 2| are fixed to the cover with suitable adjustment of distances so that when the cover is placed upon spacers I8, which may be up to 3A inch thick or, in some cases, up to about 11/8 inches thick, the underfaces of the anodes are within about T26 of an inch of the mercury surface. Since it is desirable to avoid as much as possible working around the cell, there is an advantage in securing bus bar 25 rigidly to the anodes and treating this bus bar as a part of the cover assembly. Baiiles 29 are aiixed to the anodes 2l and the cover is then placed on spacing elements I8 of the aforementioned thickness. The cover I1 is then sealed in place by means of putty I8a.

To start operating the cell, elevator I I is set in operation to provide a sufficient flow of mercury through the cell so that the floor of the brine chamber is covered with a thin layer of mercury. Brine is introduced through inlet I3 until it begins to flow out through overow outlet I4 and water is introduced at I5 until it begins to ow out through overflow outlet I6.

The following description illustrates the operation of the cell for the production of chlorine and aqueous 50% sodium hydroxide solution from sodium chloride brine.

Aqueous 25% sodium chloride solution is introduced at I3 at an hourly rate of labout 355 liters and at a temperature of about 30 C. A suicient voltage is applied between bus bars 26 and 21 to The primary loss of heat occurs` provide a cathode current density of about 211/2 amperes per square decimeter. The ilow of water into the regenerator chamber may be controlled 'to provide the concentration of sodium hydroxide desired, for example 50-52% NaOI-I. Under normal operating conditions with a cell of the type described, with elevator ll and mercury seal I2 insulated to avoid heat loss, an adequate removal of sodium from the amalgam is secured in travel of amalgam from the mercury seal I2 to elevator Il. Under these conditions of operation the unit is capable of producing in the neighborhood of .500 kilograms of chlorine gas and a corresponding amount of 52% sodium hydroxide solution per day.

As the operation of the cell continues, the underfaces of anodes 2| are gradually worn or oxidized away and consequently the spacing between the mercury and the active anode surfaces increases. When this spacing has increased to about 1/2 inch, which may be after 2 to 6 months operation more or less, operation of the cell is discontinued and the spacing of the anodes is readjusted by removal of the required number of shims i8 to lower cover il and thus bring the active anode surfaces approximately to their original position. This adjustment may be coincided with the customary cleaning of the cell to remove any accumulation of foreign material from the anodes, the walls of the cell and from the mercury For removing foreign material from the mercury, the arm on outlet 34 may be swung into a lower position to permit brine and foreign material to flow out through this outlet. For

cleaning the regenerator chamber, bailles 30, if

of the movable type, are turned to inoperative position to permit washing liquid to ow freely conjunction with a mercury cathode electrolytic cell, having vertical side and end walls and an inclined iioor provided with a series of substantially vertical fins arranged to provide a plurality ofparallel longitudinal channels, an entrance for liquid at the higher end of said floor and an outlet for liquid at the lower end, whereby flow of amalgam may be maintained longitudinally of 'the chamber, a second liquid inlet and a second liquid outletu positioned above said first mentioned inlet and outlet and in opposite relation thereto,

whereby aqueous regenerating liquid may be caused to ow longitudinally of the chamber and counter-current to the flow of amalgam, and a plurality of transverse baiiles within said regenerator, the upper edges of which are above the levels of the second liquid inlet and outlet and the lower edges of which extend downwardly substantially to the level of the top of the ns, said bailies being disposed so as to provide a plurality of pools of aqueous regenerating liquid and to conne ow of said liquid from one pool to another to the longitudinal channels on the floor'of the chamber. 2. A regenerator chamber, adapted for use in conjunction with a mercury cathode electrolytic cell, having vertical side and end walls and an inclined oor provided with a series of substantially vertical iins arranged to provide a `plurality of parallel longitudinal channels, an entrance lfor liquid at the higher end of said floor and an outlet for liquid at the lower end, whereby ow of amalgam may be maintained longitudinally of the chamber, a second liquid inlet and a second liquid outlet positioned above said first mentioned inlet and outlet and in opposite relation thereto, whereby aqueous regenerating liquid may be caused to flow longitudinally of the chamber and counterwurrent to the flow of amalgam, a plurality oi transverse baiiles within said regenerator, the upper edges of which are above the levels ci the second liquid inlet and outlet and the lower edges of which extend downwardly substantially to the level of the top of the fins, said baiiles being disposed so as to provide a plurality of pools of aqueous regenerating liquid and to conine flow of said liquid from one pool to another to the longitudinal channels on the floor of the chamber, and means for pivoting said transverse baiies so as to swing the bailes to an inoperative position while flushing the regenerator. ROY A. HORST.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 501,783 Hermite July 18, 1893 627,193 Kelly June 20, 1899 908,545 Carrier Jan. 5, 1909 1,063,707 Lummus June 3, 1913 1,081,949 Du Pont Dec. 23, 1913 1,121,532 Newberry Dec. 15, 1914 1,178,551 Heinemann Mar. 21, 1916 1,374,291 Dunkley Apr. 12, 1921 1,420,211 Paulus June 20, 1922 2,232,128 Muller Feb. 18, 1941 2,311,744 Gardiner Feb. 23, 1943

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