US3140991A

US3140991A - Mercury cathode electrolytic cells

Info

Publication number: US3140991A
Application number: US156574A
Authority: US
Inventors: William C Gardiner
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1961-12-04
Filing date: 1961-12-04
Publication date: 1964-07-14
Anticipated expiration: 1981-07-14
Also published as: GB1001112A

Description

July 14, 1964 w. c. GARDINER MERCURY CATHODE ELECTROLYTIC CELLS Filed Dec. 4, 1961 @EEEEW INVENIOR.

WILLIAM C.GARD|NER By K" W AGENT United States Patent 3,140,991 MERCURY CATHODE ELECTROLYTIC CELLS William C. Gardiner, Darien, Conn, assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Dec. 4, 1961, Ser. No. 156,574 2 Claims. (Cl. 204-219) This invention relates to electrolytic cells for the electrolysis of aqueous solutions. The invention more particularly relates to a new method for supporting the aiibdes in horizontal mercury cells. Previously anodes have been supported on a rigid frame work resting on the cell walls or outside cell structure. Examples of other previous modes of supporting anodes are described in US. Patents 2,328,665 and 2,627,501. See also Industrial and Engineering Chemistry, 153 (vol. 45, No. 9), pages 1824-1835. The use of the anode support of the present invention on other cells of similar construction is also included within the scope of this invention. Horizontal mercury cells usually consist of an enclosed, elongated trough sloping slightly towards one end. The cathode is a flowing layer of mercury which is introduced at the higher end of the cell and flows along the bottom of the cell toward the lower end. The anodes are generally composed of rectangular blocks of graphite suspended from conductive lead-ins, for example, graphite or protected copper tubes or rods, in such a manner that the bottom of the graphite anode is spaced a short distance above the flowing mercury cathode. The bottom and sides of the trough are generally steel with a corrosion resistant hard rubber lining on the sides and under the cover. Concrete, stone or other non-conducting material may also be used for the sides. The lining may comprise concrete which is further coated with resin, or has natural stone set in the concrete lining.

In the operation of this type of cell the electrolyte, which may be brine or an aqueous solution of any electrolyte which upon electrolytic decomposition will give the products desired, is introduced at the upper end of the cell and flows toward the lower end of the cell. For example, a solution of sodium chloride may be electrolyzed in such a cell. Electric current passes through the solution between the anodes and the mercury cathode. When sodium chloride is the electrolyte, chlorine is formed at the anodes and passes to the top of the cell and out through an opening in the cell cover which is provided for this purpose. Sodium is formed at the cathode as an amalgam with the mercury cathode. The sodium amalgam is withdrawn at the lower end of the cell, cycled to a decomposer packed with graphite where it is contacted with water to form sodium hydroxide, hydrogen and mercury. The mercury is recycled to the cell for reuse as the cathode. It will be understood that other electrolytes, such as potassium chloride, barium chloride, lithium chloride, sodium sulfate and the like may also be electrolyzed in such a cell.

In cells of this type the distance between the graphite anodes and the mercury cathode is very important. This distance should be as small as possible to reduce consumption of energy but if this distance is too small, secondary reactions take place, particularly the direct attack of sodium amalgam by chlorine bubbles. The graphite anodes are generally suspended by attaching them to lead-ins in turn extending through the cover of the cell and suspended from a structure above the cell cover. Each graphite anode is thus supported at a proper distance from the cathode. The cell cover is usually a steel plate covered with rubber and sufliciently strong to support the anodes and the electrical connections thereto. Stoneware or hard rubber covers are sometimes used but cathode is determined by the way in which the cover fits on the cell and the adjustment of the anodes in the cell cover.

In operation the graphite anodes are consumed thereby increasing the distance between the anodes and cathode and resulting in reduced energy efiiciency. To maintain the proper distance or spacing between anodes and cathodes it is necessary in this type of prior art apparatus to adjust each anode individually. Another disadvantage is that lifting of the cover of the cell for inspection or repair moves all the anodes and disturbs their adjustment.

Explosions resulting from a combination of electrolytic product gases occasionally occur in cells of this type with improperly adjusted anodes as well as in electrolytic cells of other types with consequent damage to the cover for the cell and complete disarrangement of the anodes as well as possible danger to operating personnel in the cell room.

Attempts have been made to solve the problem of anode to cathode spacing by providing strips or shims between the cover and the sides of the cell. These strips or shims were removed after a certain amount of consumption of the anodes had taken place to lower the cell cover and thereby reduce the spacing between the anodes and the cathode. However, accurate adjustment by such a method was not possible. In the most commonly used prior art construction the anodes are individually attached to the cover of the cell which rests on the side walls of the cell trough and are individually adjustable thereon.

One of the objects of this invention is to provide a combination bus bar and anode support for supporting the anodes of a mercury cathode cell and permitting adjustment of the spacing between the anodes and the oathode, at the same time supplying current to the anodes.

Another object of this invention is to provide a simplified support for the anodes of an electrolytic cell which will permit easy adjustment of the distance between the anodes and the cathodes.

Another object of this invention is to provide a support for the anodes of an electrolytic cell which will allow simultaneous adjustment of several anodes.

Various other objects and advantages of the invention will appear in the course of the following description.

These objects are accomplished and the disadvantages of the prior art structures are overcome by the use of the present invention.

The invention thus comprises apparatus for electrolyzing conductive solutions which comprises an elongated inclined trough, a perforated, self-supporting cover over the trough, fixed upright members, transverse electrically conductive metallic channel-shaped members resting on said upright members, anode assemblies suspended from said transverse members, adjustable means to maintain the anode assemblies at a specified height above the bottom of said trough, a mercury cathode flowing over the bottom of said trough and means for imposing an electric current on said anodes and cathode.

The transverse channel-shaped members of this invention provide structural strength to support the anodes without significant deflection and they maintain their position in use. Anodes once adjusted remain in the same fixed position until readjusted. All the anodes suspended from one bus bar usually wear away at the bottom at 7 approximately the same rate, even though the rate may rially reduced. However, individual anodes can be adjusted when necessary.

The transverse channel-shaped members also serve as bus bars to carry the current to the anodes. Appropriately they are of electrically conductive metals including particularly copper, aluminum, silver, and alloys containing at least about 60 percent thereof. Most of the common brasses contain about 60 percent or more of copper.

The dimensions of the bus bar-support are not critical but depend on the width of the cell, the number and weight of the anode assemblies supported thereon and the structural strength and electrical conductivity of the metal. For supporting three to five anode assemblies in a four foot width cell, a copper channel is suitably about 5 to 8 inches in width, having 2 to 4 inch flanges and a thickness of about to /2 inch. The bus bar-supports are suitably dimensioned to carry both the mechanical and electrical load.

In the attached figure, 11 is the combination copper bus feed bar and anode support. It is a copper channel closed by a copper plate 12 silver brazed at one end of the channel. To end plate 12 is connected a flexible copper connector 13 which in turn is connected to a bus bar (not shown) carrying the current to the anodes. Flexible connector 13 is connected to the plate 12 by bolt 14 and nut 15. Channel 11 is drilled with holes at suitable spacings to receive anode lead-ins 16 and with holes near the ends of the channel to receive jacking screws 17. The channel is supported on jacking screws 17 by adjusting nuts 18 by which the distance of the channel above the cell cover can be adjusted. The jacking screws are attached to cell cover 19 by screwing them into nuts 20 welded to the cell cover.

Lead-in 16 is attached at its lower end to anode 21 by means of lead button 22. The lead-in is tinned at its lower end and held in position in a mold which is then filled by molten lead. The lead-in 16 advantageously has drilled holes near the lower end. The holes in the lower end of the lead-in 16 are filled and covered by the lead affording firm support. The lead button is machined, threaded and fitted into corresponding threads in a recess in the top of the graphite anode. A gasket 23 of rubber is placed around the lead-in in contact with the lead button and top of the anode and then protective sleeve 24 is lowered into place. It is protected by another rubber gasket 25 covering its upper end and nut 26 is tightened to hold the sleeve in place, surrounding the lead-in and separated therefrom by an annular space.

The anode assembly is suspended from the bus bar and supporting channel 11 by lower lead-in nut 27 and upper lead-in nut 28 both threaded on lead-in 16 and together locking the anode assembly in its proper elevation with respect to cell bottom 29. The aperture in cell cover 19 through which the anode lead-in and its surrounding sleeve 24 are suspended is closed by means of flexible rubber boot 30. The boot 30 is sealed against sleeve 24 by clamp 31 held by screw 32. Boot 30 at its lower edge is held tightly against cell cover lining 33 which is turned through the aperture and lies against the top of the cell cover. Clamp 34 maintains the seal in position. Boot 30 thus closes the aperture through the cell cover 19 and prevents the escape of cell gas while allowing vertical adjustment of the anode with respect to bottom 29 by adjusting

nuts

27 and 28.

Anodes 21 are suspended in theelectrolyzer chamber of the mercury cell consisting of cell bottom 29 and side channels 35. The side channels 35 are lined with hard rubber coating 36. A strip of soft rubber 37 lies between rubber lining 36 and cell bottom 29 While another strip of soft rubber 3S lies between rubber coating 36 and lining 33 of cell cover 19.

Side channels 35 are held in place by bolts 39 and nuts 4- 40 extending through the flanges of the channel and through the cell bottom. Side channels 35 are sealed to top 19 by means of C-clamps (not shown) spaced at suitable intervals along the side of the cell cover 19. The cell rests on transverse I-beams 41 and longitudinal I-beams 42.

Example A battery of mercury cathode cells was constructed for a chlorine-caustic plane. Each cell was about 4 /2 feet wide by about 40 feet long and contained anodes supported on 40 four foot bus feed channels of copper.

Each channel supported four anodes, 12 inches on centers and ran transversely of the cell. Longitudinally channels were spaced 12 inches on centers. The anodes were 11% x11% x4 inch blocks of graphite. Each channel was 7 x 3% x /8 inchthick drilled through the web to receive the anode lead-ins. These were locked into place with a nut above and one below the channel on threads on each lead-in. The channels were similarly locked in place on threaded jacking screws at each end of the channel. The jacking screws were attached to the cell cover by nuts welded to the cover. Current was supplied to the anodes by flexible copper connectors attached to an end plate of copper silver-brazed to close one end of each channel. The circuit was closed by supplying current to the cell bottom.

In use each cell was supplied with brine and mercury at its upper end and depleted brine, amalgam and chlorine was removed from its lower end. The amalgam was decomposed to form aqueous caustic and the mercury was returned to the cell. Depleted brine was dechlorinated, resaturated, purified and returned to the cell. In the course of several months operation, adjustment of the height of the anodes above the mercury cathode was greatly simplified. Usually each group of four anodes was satisfactorily adjusted by means of the nuts on the jacking screws without any change in the nuts on the individual lead-ins. Only occasionally was it necessary to adjust an individual anode.

What is claimed is:

1. In an apparatus for electrolyzing conductive solutions comprising an elongated inclined trough, a perforated, self-supporting cover over the trough, anodes adjustably suspended through the perforations in said cover at a specified height above the bottom of said trough, a mercury cathode flowing overthe bottom of said trough and means for imposing an electric current on said anodes and cathode, the improvement in the means of suspension of said anodes and in the means for conducting the electric current to said anodes consisting of transverse, electrically conductive, metallic channel-shaped members resting adjustably on upright members located above the sides of said trough, the webs of said channel-shaped members arranged horizontally with the flanges vertical, perforations in said webs for supporting said anodes di rectly from said channel-shaped members, perforations near the ends of said channel-shaped members for receiving said upright members and electrical current carrying means attached to said channel-shaped members.

2. The improvement of claim 1 in which said transverse, electrically conductive, metallic channel-shaped members are composed of a metal containing at least 60 percent of an element selected from the group consisting of copper, silver and aluminum.

References Cited in the file of this patent UNITED STATES PATENTS 2,599,363 Bennett et al. June 3, 1952 2,627,501 Gardiner Feb. 3, 1953 2,958,635 De Nora Nov. 1, 1960 FOREIGN PATENTS 985,185 France July 16, 1951

Claims

1. IN AN APPARATUS FOR ELECTROLYZING CONDUCTIVE SOLUTIONS COMPRISING AN ELONGATED INCLINED TROUGH, A PERFORATED, SELF-SUPPORTING COVER OVER THE TROUGH, ANODES ADJUSTABLY SUSPENDED THROUGH THE PERFORATIONS IN SAID COVER AT A SPECIFIED HEIGHT ABOVE THE BOTTOM OF SAID TROUGH, A MERCURY CATHODE FLOWING OVER THE BOTTOM OF SAID TROUGH AND MEANS FOR IMPOSING AN ELECTRIC CURRENT ON SAID ANODES AND CATHODE, THE IMPROVEMENT IN THE MEANS OF SUSPENSION OF SAID ANODES AND IN THE MEANS FOR CONDUCTING THE ELECTRIC CURRENT TO SAID ANODES CONSISTING OF TRANSVERSE, ELECTRICALLY CONDUCTIVE, METALLIC CHANNEL-SHAPED MEMBERS RESTING ADJUSTABLY ON UPRIGHT MEMBERS LOCATED ABOVE THE SIDES OF SAID TROUGH. THE WEBS OF SAID CHANNEL-SHAPED MEMBERS ARRANGED HORIZONTALLY WITH THE FLANGES VERTICAL, PERFORATIONS IN SAID WEBS FOR SUPPORTING SAID ANODES DIRECTLY FROM SAID CHANNEL-SHAPED MEMBERS, PERFORATIONS NEAR THE ENDS OF SAID CHANNEL-SHAPED MEMBERS FOR RECEIVING SAID UPRIGHT MEMBERS AND ELECTRICAL CURRENT CARRYING MEANS ATTACHED TO SAID CHANNEL-SHAPED MEMBERS.