US3222270A

US3222270A - Multi-electrolytic cells

Info

Publication number: US3222270A
Application number: US796856A
Authority: US
Inventors: Edwards George Ernest
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1958-03-18
Filing date: 1959-03-03
Publication date: 1965-12-07
Anticipated expiration: 1982-12-07
Also published as: USB230799I5; FI41014B; DE1421051A1; GB845043A; NL125501C; ES247601A1; CH389578A; DE1421051B2; NL237121A; DK105980C; SE334866B

Description

'Dec. 7, 1965 G. E. EDWARDS MULTI-ELEGTROLYTIC CELLS 3 Sheets-Sheet 1 Filed March 5, 1959 IN VENTOR George Ernesf- Ezwards, y M f A T TORNEYS.

Dec. 7, 1965 G. E; EDWARDS MULTI-ELECTROLYTIC CELLS Filed March 5, 1959 3 Sheets-Sheet 2 IO ll If?! [VIP l I l: illll- 1/1I/1/I111/1111111 1 II 91111 11/11/12 FlG.3

FIG. 2

INVENTOR George Ernesf Edwards, WW M 1' MW ATTORNEYS".

Dec. 7, 19 65 V EDWARDS 3,222,270

MULT I ELECTROLYTI C CELLS Filed March 5, 1959 3 Sheets-Sheet 5 01 IOHIOII II/II 1/1,

Fl6.4 FIG-.5

INVENTOR Z G eorge E rn esl' Edwards,

BYMW, M W

A TTORNEYSI United States Patent M 3,222,27 0 MULTI-ELECTROLYTIC CELLS George Ernest Edwards, Widnes, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Mar. 3, 1959, Ser. No. 796,856 Claims priority, application Great Britain, Mar. 18, 1958, 8,7 15/ 58 15 Claims. (Cl. 204-469) The present invention relates to improvements in or relating to multi-electrolytic cells and particularly to multi-electrolytic cells of the kind adaptable for the production, of for example, chlorine, a hypochlorite or a chlorate from aqueous solutions of a chloride of an alkali metal for example sodium chloride and comprising a plurality of unit electrolytic cells.

Multi-electrolytic cells arev known, for instance, wherein the anode of one unit cell is separated from the cathode of an adjacent unit cell by a partition of non-conducting inert material, for example concrete, and wherein said anode and said cathode are connected electrically by electro-conducting connections passing through said partition. If desired these cells may be so constructed, for instance, that each unit cell has a conventional type of asbestos diaphragm placed between its anode and cathode to prevent the products formed at the anode and cathode from mixing and so to permit these products to be collected.

The object of the present invention is to employ an electro-conducting chemically inert partition in the form of titanium metal sheet as a chemically inert partition which separates the anode of one unit electrolytic cell from the cathode of an adjacent unit electrolytic cell.

According to the present invention a multi-electrolytic cell of the kind adaptable for the production of for example chlorine, a hypochlorite or a chlorate from aqueous solutions of a chloride of an alkali metal, for example sodium chloride and comprising a plurality of unit electrolytic cells and wherein an inert partition sep arates the anode of one unit electrolytic cell from the cathode of an adjacent unit electrolytic cell is characterised in that the inert partition is a chemically inert partition of titanium metal sheet.

The term titanium metal sheet includes a metal sheet of a titanium alloy consisting essentially of titanium.

In accordance with one embodiment of the invention a multielectrolytic cell is so constructed that each unit cell has a diaphragm, for instance a conventional type of asbestos diaphragm, between its anode and cathode to permit for instance caustic sodaand chlorine to be collected. However, the diaphragm between the anode and the cathode of each unit cell may comprise a cationic exchange resin.

In accordance with a second embodiment of the invention the anode in each unit cell is of graphite and at least a portion of that face of the titanium metal sheet which faces the anode has a layer of a noble metal of the platinum group.

By the term a noble metal of the platinum group is meant ruthenium, rhodium, palladium, osmium, iridium or platinum, or an alloy of two or more of such metals (hereinafter called generically a platinum metal).

In accordance with a third embodiment of the inven tion the anode in each unit cell is of graphite treated to be impermeable to chlorine and at least a portion of that face of the titanium metal sheet which faces the anode has a layer of a metal of high electrical conductivity,

3,222,270 Patented Dec. 7, 1965 In accordance with a fourth and preferred embodiment of the invention in each unit cell the anode is a layer of a platinum metal which is on one side of the titanium metal sheet and the cathode is that opposed side of the next titanium metal sheet which is free from a layer of a platinum metal.

In said fourth and preferred embodiment of the invention the layer of a platinum metal can be a film or surface coating of a platinum metal secured or deposited on one side of the titanium metal sheet in any convenient manner. The coating of a platinum metal may be constituted, if desired, by a thin sheet or foil which is welded to the titanium metal sheet. However, it is preferred for the layer of the platinum metal to be electrolytically deposited on the titanium surface since in this way a given weight of the platinum metal can be spread over a greater surface of titanium metal sheet. If desired, other methods may likewise be utilised for applying the coating of the platinum metal to the titanium metal sheet, for example, roll-bonding, cathode sputtering, vacuum deposition, metal spraying, rolling a platinum metal powder into the surface of the titanium metal sheet and coating of a titanium metal sheet with a platinum-bearing preparation and subsequently heating as for example in the manner practised in the ceramic industry.

In said second to fourth mentioned embodiments of the invention each unit cell may, if desired, be provided with a diaphragm and means for recycling anolyte and/ or catholyte through the respective compartments of each unit cell may also be provided.

Furthermore, if desired, a multi-electrolytic cell of the invention can consist of mercury unit cells so as to permit sodium amalgam to be collected from its cathodes and chlorine from its anodes.

Multi-electrolytic cells of the invention have the followinlg advantages.

The replacement of non-conducting inert material, for example concrete, by thin titanium sheets makes the multi cell more compact.

Titanium is extremely resistant to chlorinated brine.

Titanium sheet permits quick assembly operations.

The overall weight of a battery of multi-electrolytic cells of the invention is much less than a battery of multi-electrolytic cells wherein in each multi-electrolytic cell the partition between the anode of one unit cell and the cathode of an adjacent unit cell is of non-conducting inert material, for example concrete.

In a multi-electrolytic cell of the invention there are no pervious joints between the anode of one unit cell and the cathode of an adjacent unit cell.

In so far as the first three aforementioned embodiments are concerned it can be pointed outthat the titanium sheet can be compressed firmly, against for instance a graphite plate and so give good electrical contact between the anode of one unit cell and the cathode of an adtrical contact in the multi-electrolytic cell of the inven-' tion without this cell being under a high degree of com: pression.

The fourth-mentioned embodiment of the invention has the advantage that it is even more compact than the first three mentioned embodiments, that the distance between the anode and cathode of any one unit electrolytic cell is constant while the multi-electrolytic cell of the invention is in operation and that chlorine discharged at the anode is free from carbon dioxide.

When a multi-eleetrolytic cell according to this fourth and preferred embodiment of the invention is supplied with saturated sodium chloride solutions and is connected to a suitable source of direct electric current, chlorine and caustic soda are produced at current efficiencies comparable to those of conventional diaphragm cells having graphite anodes and asbestos diaphragms supported on steel gauze cathode screens. When operated at a current density of 1.5v ka. per m. of cathode area at 85 C. for a period of 8 weeks the chlorine product contains less than 0.4% of impurities, of which 0.2% is oxygen. The depleted sodium chloride solution which leaves the cell contains 120 grams of sodium hydroxide per litre of solution.

A comparison at given current densities of the mean unit cell voltages for a diaphragm multi-electrolytic cell incorporating means for recycling anolyte and catholyte according to said fourth and preferred embodiment of the invention and for a commercial diaphragm cell of the kind aforementioned is given in the following table.

Four embodiments of a diaphragm multi-electrolytic cell according to the invention are illustrated by way of example in the diagrammatic drawings accompanyinging the provisional specification. FIGURE 1 represents a cross-section of said four aforementioned embodiments of the invention. FIGURES 2 and 3 represent different views of one embodiment in which each unit electrolytic cell comprises a graphite anode, a cathode and a conventional asbestos diaphragm which separates the anode from the cathode and in which a titanium plate separates the graphite anode of one unit electrolytic cell from the cathode of an adjacent unit electrolytic cell. FIGURE 4 represents, with respect toFIGURE 1, one view of an embodiment in which electrical connection between a graphite anode of a unit electrolytic cell and a titanium metal sheet which separates said graphite anode from the cathode of an adjacent unit electrolytic cell is provided by a thin layer ofa metal of high electrical conductivity deposited on the whole or part of those faces of the titanium plate which would otherwise be in directcontact with the graphite anode. Said graphite anode, in'accordance with another embodiment of the invention, hasbeen treated to make it impervious to chlorine andchlorinated brine. FIGURE 5 represents, with respect to'FIGURE 1, one view of an embodiment of a diaphragm multi-electrolytic cell according to the invention in which each unit electrolytic cell comprises as anode a thin coating of a platinum metal which is on one side of a titanium metal plate, a cathodic surface on the opposed side of the corresponding titanium metal plate of an adjacent unit electrolytic cell and an intervening conventional asbestos diaphragm supported on a metal gauze screen in good electrical contact with said cathodic surface of the titanium metal plate and in which except at the ends a titanium plate having on one side thereof a layer of a platinum metal separates the platinum metal layer anode of the unit electrolytic cell on one side thereof from the cathode of the adjacent unit electrolytic cell on the other side thereof.

Referring more specifically to FIGURES 1 to 3, FIG-

URES

2 and 3 represent vertical part sections of the first-mentioned embodiment of a multi-electrolytic cell according to the invention through AA and BB respectively in FIGURE 1, which in turn represents the vertical cross-section of a unit electrolytic cell through C-C in FIGURE 2.

Graphite anodes 1 are held in position against titanium plates 2 by clamping plates 3 of mechanically strong and corrosion resistant material, for example rubber covered steel. There are intervening sheets 4 of flexible material such as natural or synthetic rubber between the titanium plates 2 and the clamping plates 3. 5 are highly compressed portions of the flexible sheets 4 positioned between the adjacent edges of the graphite anodes 1 and the clamping plates 3. The thickness of the flexible sheets 4 is such that when the multi-electrolytic cell is held together under a suitable degree of of compression the graphite anodes 1 are held firmly against the titanium plates 2. 6 are conventional asbestos diaphragms and these are supported on metal gauze screens 7 which are set in metal plates 8. Thin layers 9 of suitable corrosion resistant material are bonded by conventional means to these faces of the metal plates 8 which face towards the graphite anodes 1. The graphite anodes 1 are maintained at a suitably small distance from the asbestos diaphragm 6 by frames 10 of corrosion resistant materials. Additional frames 11 of corrosion resistant material separate the metal plates 8 from the adjacent titanium plates 2 of adjacent unit electrolytic cells. Frames 11 differ from frames 10 in their thickness and in that they are reversed laterally with respect to frames 10, The titanium plates 2 are provided with a series of embossed nipples 12 which are disposed regularly over those portions of the titanium plates 2 which face the metal gauze screens 7. These embossed nipples 12 protrude towards the metal gauze screens 7 for such a distance that when the multi-electrolytic cell is held together under a suitable degree of compression the nipples 12 are in sufiiciently close contact with the metal gauze screens 7 that there is negligible resistance to the flow of electrical current between the metal gauze screens 7 and the adjacent faces of the titanium plates 2. Should it be necessary this resistance can be reduced by welding together the metal gauze screens 7 and the titanium plates 2. The metal gauze screens 7 and the adjacent faces of the titanium plates 2 form together the cathodes of the multi-electrolytic cell.

The titanium plates 2, the clamping plates 3, the flexible sheets 4, the frames 10, the metal plates 8 and the frames 11 are each provided with four

corresponding apertures

13, 14, 15 and 16 to form

ducts

17, 18, 19 and 20 respectively. The

apertures

13, 14, 15 and 16 in the titanium plates 2 and the metal plates 8 are enlarged to allow the insertion of bushes 21 of corrosio resistant and electrically insulating material. These bushes 21 are sealed to the titanium plates 2 and the metal plates 8' by a suitable adhesive composition (not shown).

The frames 10 are provided with rectangular apertures 22 of such dimensions as will conform closely to the dimensions of the graphite anodes 1 and the asbestos diaphragms 6. These aperture are connected to the diagonally opposite apertures 13 and 14 by

channels

24 and 25 respectively. Frames 11 have rectangular apertures 23 of similar dimensions to apertures 22 in frames 10. Apertu-res 23 are connected to the diagonally

opposite apertures

15 and 16 respectively by channels 26 and 27.

In this embodiment of a multi-electrolytic cell of the invention the components for a suitable number of unit electrolytic cells are positioned as aforementioned and are held together under a suitable degree of compression by conventional means. The seals between adjacent components are effected by conventional methods as for example by intervening films of suitable adhesive materials or by thin layers of flexible jointing compounds (not shown). Alternatively the frames and 11 may be of suitable flexible material when no further means of sealing are required other than compression. 28 and 29 are current leads to the anode and cathode titanium end plates 2. The rectangular apertures 22 in the frames 10 form anode compartments which are connected to the

ducts

17 and 18 by

channels

24 and 25 respectively. Similarly the rectangular apertures 23 in the frames 11 form cathode compartments which are connected to the ducts 19 and by the channels 26 and 27 respectively. The duct 18 serves for the introduction of sodium chloride solution into the anode compartments 22 through the channels by means of suitable external connections (not shown). If this solution is controlled at a level 30 there will be at least a partial flooding of the duct 17. If, however, the solution is controlled at level 31 there is no flooding of the duct 17. The sodium chloride solution percolates through the asbestos diaphragm 6 into the cathode compartment 23 attaining a controlled level. If the sodium chloride solution is controlled at a level 32 there will be partial flooding of the duct 19. The solution then leaves the multi-electrolytic cell by the channels 27 and the duct 20 through suitable external connections (not shown). Should the solutionbe controlled at a level 33 there is no flooding of the duct 19.

If desired means can be provided for the return of the anolyte from duct 17 to duct 18 and/or of the catholyte from duct 19 to duct 20 and for the circulation of the anolyte and catholyte respectively through the apertures 22 and the apertures 23.

During electrolysis the chlorine which is liberated at the graphite anodes 1 passes through the channels 24 and the duct 17 and leaves the multi-electrolyti-c cell by suitable external connections (not shown). The hydrogen which is liberated at the composite cathode formed by the metal gauz'e screen 7 and the titanium plate 2 leaves the multielectrolytic cell by the channels 26 and the duct 19 through suitable external connections (not shown) while the sodium hydroxide which is formed in the cathode compartment 23 leaves the multi-electrolytic cell together with the depleted sodium chloride solution by the channels 27 and the duct 20 as aforementioned.

FIGURE 4 represents those two embodiments of the invention wherein good electrical connection between the graphite anodes 1 and the titanium plates 2 is obtained by a thin layer 34 of a metal of high electrical conductivity which is deposited, either chemically or electrically, on the whole or parts of those faces of the titanium plates 2 which would otherwise be in direct contact with the graphite anodes 1. The layers 34 may either be a platinum metal or a less noble metal, for example copper. If the layers 34 are of a less noble metal this metal may be protected from corrosion by impregnating those parts of the graphite anode 1 adjacent to the metal layer 34 with an inert material so as to render said parts of the graphite anode 1 completely impervious to the gases or liquids contained in the multi-electrolytic cell. If the layers 34 are a noble metal such as platinum no such protection is necessary.

FIGURE 5 represents a v'ertical part section through a multi-electrolytic cell corresponding to a section through A--A in FIGURE 1. In the embodiment of the invention illustrated in FIGURE 5 there are no graphite anodes 1, no clamping plates 3, and no flexible layers 4. Those faces, however, of the titanium plates 2 which are adjacent to the asbestos diaphragm 6 are provided with a thin coating of a platinum metal. This thin coating 35 is deposited on the titanium plates 2 either chemically or electrolytically to form the anodic part of this embodiment of a multi-electrolytic cell according to the invention.

What I claim is:

1. A multi-electrolytic cell comprising a plurality of unit electrolytic cells, each unit electrolytic cell having an anode and a cathode, said unit electrolytic cells being arranged with the anode of one unit electrolytic cell juxtaposed to the cathode of the next unit electrolytic cell with an inert partition separating the anode of one unit electrolytic cell from the cathode of the adjacent unit electrolytic cell, each inert partition being a chemically inert electroconducting partition of titanium metal sheet, each of said titanium metal sheets having on one surface an electrically conducting layer which is in electrical contact with said titanium sheet over essentially all of said titanium surface, said layer constituting the anode in each unit electrolytic cell, the other surface of each said sheet comprising titanium and constituting the cathode of the next adjacent unit electrolytic cell, said anode and cathode constituting the sole essential working electrodes in each said unit cell.

2. A multi-electrolytic cell as claimed in claim 1 wherein each unit cell has a diaphragm between its anode and cathode.

3. A multi-electrolytic cell as claimed in claim 2 wherein the diaphragm is an asbestos diaphragm.

4. A multi-electrolytic cell as claimed in claim 2 wherein the diaphragm comprises a cationic exchange resin.

5. A multi-electrolytic cell as claimed in claim 1 wherein the anode in each unit cell is graphite, and essentially all of the surface of the titanium metal sheet which carries the anode has a layer of a noble metal of the platinum group providing electrical contact between said sheet and said anode, the opposite face of said titanium sheet comprising the cathode of the adjoining cell with the titanium as the cathodically operative surface.

6. A multi-electrolytic cell as claimed is claim 1 wherein the anode in each cell is graphite rendered impermeable to chlorine and essentially all of the surface of the titanium metal sheet which carries the anode has a layer of a metal of high electrical conductivity which forms good electrical contact both with the titanium metal sheet and the graphite, the opposite face of said titanium sheet comprising the cathode of the adjoining cell.

7. A multi-electrolytic cell as claimed in claim 1 wherein the anode is graphite applied directly to said one surface of said titanium metal sheet.

8. A multi-electrolytic cell as claimed. in claim 6 wherein the metal of high electrical conductivity which forms good electrical contact both with the titanium metal sheet and the graphite is selected from the group consisting of copper, silver, and platinum.

9. A multi-electrolytic cell as claimed in claim 1 wherein the plurality of unit electrolytic cells are mercury unit cells.

10. A multi-electrolytic cell of the bipolar electrode filter-press type for the electrolysis of alkali metal chlorides and comprising a plurality of unit electrolytic cells, each unit electrolytic cell having an anode and a cathode, said unit electrolytic cells being arranged with the anode of one unit electrolytic cell juxtaposed to the cathode of the next unit electrolytic cell with an inert partition separating the anode of one unit electrolytic cell from the cathode of the adjacent unit electrolytic cell, each inert partition being a chemically inert electroconducting partition of titanium metal sheet, each of said titanium metal sheets having on one surface a layer of a platinum metal, said layer constituting the anode in each unit electrolytic cell, the other surface of each said sheet comprising titanium as the operative surface and constituting the cathode of the next adjacent unit electrolytic cell, said anode and cathode constituting the sole essential working electrodes in each said unit cell.

11. A multi-electrolytic cell as claimed in claim 10 wherein the layer of platinum metal is a film of a platinum metal secured on one side of the titanium metal sheet.

12. A multi-electrolytic cell as claimed in claim 11 wherein the film of a platinum metal is a thin sheet or foil which is welded to the titanium metal sheet.

13. A multi-electrolytic cell as claimed in claim 10 wherein the layer of platinum metal is a surface coating of a platinum metal deposited on one side of the titanium metal sheet.

14. A multi-electrolytie cell as claimed in claim 13 wherein the surface coating of a platinum metal is an electrolytic deposit on the titanium surface.

15. A multi-electrolytic cell as claimed in claim 13 wherein the surface coating of a platinum metal on the titanium surface is a subsequently heated coating of a platinum bearing preparation,

References Cited by the Examiner UNITED STATES PATENTS Baum 2049-290 Niederreither 204256 Gunn et al. 204256 Suggs et al. 204290 Rosenblatt 204290 Zdansky 204256 Tirrell 204290 JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner.

Claims

1. A MULTI-ELECTOLYTIC CELL COMPRISING A PLURALITY OF UNIT ELECTROLYTIC CELLS, EACH UNIT ELECTROLYTIC CELL HAVING AN ANODE AND A CATHODE, SAID UNIT ELECTROLYTIC CELLS BEING ARRANGED WITH THE ANODE OF ONE UNIT ELECTROLYTIC CELL JUXTAPOSED TO THE CATHODE OF THE NEXT UNIT ELECTROLYTIC CELL WITH AN INERT PARTITION SEPARATING THE ANODE OF ONE UNIT ELECTROLYTIC CELL FROM THE CATHODE OF THE ADJACENT UNIT ELECTROLTYE CELL, EACH INERT PARTITION BEING A CHEMICALLY INERT ELECTROCONDUCTING PARTITION OF TITANIUM METAL SHEET, EACH OF SAID TITANIUM METAL SHEETS HAVING ON ONE SUFACE AN ELECTRICALLY CONDUCTING LAYER WHICH IS IN ELECTRICAL CONTACT WITH SAID TITANIUM SHEET OVER ESSENTIALLY ALL OF SAID TITANIUM SURFACE, SAID AYER CONSTITUTING THE ANODE IN EACH UNIT ELECTROLYTIC CELL, THE OTHER SURFACE OF EACH SAID SHEET COMPRISING TITANIUM AND CONSTITUTING THE CATHODE OF THE NEXT ADJACENT UNIT ELECTROLYTIC CELL, SAID ANODE AND CATHODE CONSTITUTING THE SOLE ESSENTIAL WORKING ELECTRODES IN EACH SAID UNIT CELL.