US3923630A

US3923630A - Electrolytic cell including diaphragm and diaphragm-support structure

Info

Publication number: US3923630A
Application number: US497864A
Authority: US
Inventors: Shyam D Argade; Stephen M Collins; James B Armitage
Original assignee: BASF Wyandotte Corp
Current assignee: BASF Corp
Priority date: 1974-08-16
Filing date: 1974-08-16
Publication date: 1975-12-02
Anticipated expiration: 1992-12-02
Also published as: FR2281999A1; CA1058559A; GB1516196A; IT1041242B; NL7509777A; JPS5145697A

Abstract

In a conventional diaphragm electrolytic cell for the production of chlorine and caustic from aqueous alkali metal chloride solutions, the asbestos diaphragm is replaced by a continuous sheet or an endless band of porous polymeric diaphragm material attached to its own support members. Typically, the new diaphragm assembly of this invention is made up of three components, an upper diaphragm support frame, the continuous sheet of porous polymeric diaphragm material and the lower diaphragm support frame. The diaphragm can be made from polymeric material with a fluorocarbon polymer being illustrative of a suitable material.

Description

United States Patent Argade et al. Dec. 2, 1975 [541 ELECTROLYTIC CELL INCLUDING 3,398,080 8/1968 Steffanson et al. 204/283 X DIAPHRAGM AND DIAPHRAGMSUPPORT 3,408,281 10/1968 Barnard et al. 204/283 X STRUCTURE P [75] lnventors: Shyam D. Argade, Woodhaven;

Stephen. Conms Trenton; l Attorney, Agent, or FirmBernhard R. Swick; Joseph B. Armltage, Dearborn, all of Mich. D Michaels, Robert E Dunn [73] Assignee: BASE Wyandotte Corporation,

Wyandotte, Mich. [57] ABSTRACT [22] Filed: 1974 In a conventional diaphragm electrolytic cell for the [21] A l, N 497,864 production of chlorine and caustic from aqueous alkali metal chloride solutions, the asbestos diaphragm is replaced by a continuous sheet or an endless band [52] US. Cl. 204/266, 204/252,.204/258, of porous polymeric diaphragm material attached to 2 204/283 204/295 204/296 its own support members. Typically, the new dia- [51] Int. Cl. C25B 13/02 phragm assembly of this invention is made up of three [58] Field of Search 204/252, 258, 266, 283, components, an upper diaphragm Support frame, the

204/295 296 continuous sheet of porous polymeric diaphragm material and the lower diaphragm support frame. The di- [56] References C'ted aphragm can be made from polymeric material with 21 UNITED STATES PATENTS fluorocarbon polymer being illustrative of a suitable 1,963,959 6/1934 Enzor 204/258 m ri l- 3,312,614 4/1967 Schick 204/266 3,344,053 9/1967 Neipert 204/266 8 Clam, 4 Drawmg Flgures I I I I- a I r I I I I I I I I I r S I i r I I I I I z I I I.

US. Patent Dec. 2, 1975. Sheetlof2 3,923,630

/4 20ZJT//////// ///u My U.S. Patent Dec. 2, 1975 Sheet 2 of2 ELECTROLYTIC CELL INCLUDING DIAPHRAGM AND DIAPHRAGM-SUPPORT STRUCTURE BACKGROUND 1. Field of the Invention This invention relates to the use of an endless band or continuous sheet of porous polymeric diaphragm material attached to its own support members as a replacement for asbestos diaphragms now found in the conventional diaphragm electrolytic cell.

2. Description of the Prior Art The production of chlorine from an aqueous alkali metal chloride solution by the use of a diaphragm electrolytic cell is well known. This type of cell is described in some detail in the well-known textbook Chlorine, Its Manufacture Properties and Uses, J. S. Sconce, Editor, American Chemical Society Monograph No. 154, Reinhold Publishing Corporation, New York, New York (1962) beginning at page 90. Among the cells described therein is the Hooker cell which has a fingertype of cathode construction. This cell and other similarly described diaphragm cells employ as the dia phragm an asbestos diaphragm made in situ from a water-based slurry. The asbestos slurry-type diaphragm has an important advantage in the cells inasmuch as the diaphragm conforms to the convoluted contours of the cathode and presents no attachment problems. The cathode fingers are particularly fabricated from wire screen mesh so that the asbestos diaphragms can be deposited on the cathode from the asbestos slurry. The use of other types of asbestos such as asbestos paper wrapped over the finger-type cathode and sealed at the top and bottom with cement and putty provide a poor seal and loss of current efficiency.

There are economic advantages in replacing the asbestos diaphragms by new types of preformed continuous sheet diaphragms, in particular, power and steam savings. Also with the commercialization of metal anodes which last a long time, e.g., 3 to years, a durable diaphragm which lasts as long as the anode would effect savings in cell maintenance and reconstruction. Furthermore, health problems which may be involved with the handling of asbestos would be minimized by the replacing of asbestos diaphragms with preformed continuous sheet diaphragms.

The use of other materials as the diaphragm in electrolytic apparatus appears to be limited to situations where the anode/cathode configuration is such that the diaphragm material can be maintained as a flat sheet simply by stretching between the opposing anode and cathode. An early patent, US. Pat. No. 1,464,689, discloses simply stretching a diaphragm material between a pair of cooperating jaws when the anode is flat. A later patent, US. Pat. No. 3,335,079, discloses that in an electrodialysis apparatus having a flat vertical anode and a flat vertical cathode at opposite ends of the unit the diaphragm or membrane between the two electrodes can be installed with one free end, if desired.

SUMMARY OF THE INVENTION In accordance with the invention there is provided in a diaphragm-type cell for the production of chlorine and caustic from aqueous alkali metal chloride solutions having a plurality of anodes mounted at the bottom of said cell, a cathode between adjacent anodes and spaced between each cathode and anode a diaphragm which divides the cell into anolyte and catholyte compartments the improvement which comprises:

a diaphragm assembly composed of an upper diaphragm support, a lower diaphragm support and a continuous diaphragm extending from said upper support to said lower support, both said diaphragm,

supports being made of an electrically nonconductive polymeric composition, said lower support resting on or adjacent to the bottom of said cell and having openings therein which allow said anodes to extend through said lower support, said diaphragm being in mechanical connection with said upper and lower supports so that all of the flow of electrolyte from the anode to the cathode is through said diaphragm, said diaphragm being maintainable in place without the use of keepers, retainers or the like, said cathode being at all times separated from said anode by said diaphragm and- /or upper and lower diaphragm supports.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view of a conventional diaphragm electrolytic cell showing the present invention installed therein.

FIG. 2 is a top cross-sectional view of the electrolytic cell taken along line 2-2 of FIG. 1.

FIG. 3 is an expanded schematic drawing showing the elements of the invention and their relationship to the conventional diaphragm electrolytic cell.

FIG. 4 is a side cross-sectional view of the conventional diaphragm electrolytic cell wherein an optional modification of the invention has been installed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention, as shown in FIG. 1, is installed in a typical electrolytic diaphragm cell having cell bottom and bus bar means 10 which is coated a nonconductive sealant layer 12 and through which sealant layer 12 protrudes a series of spaced anode metal stems 40 for connecting anodes 24 with bus bar means 10. The stem 40 is secured to the bus bar means 10 by use of nut 42. The cell is completed with the installation of cell sides 16 and cell top 14 along with weak cell liquor outlet 18, hydrogen outlet 20 and chlorine outlet 22, the exact positioning of the foregoing outlets being a matter of choice. The porous cathode 26 is typically made of a ferrous metal with a woven wire construction although other means of fabricating can be employed. The cathode 26 is so formed that it will be one continuous piece but containing a series of openings or passageways through which the anodes 24 can pass and most of the surface of cathode 26 will be parallel to the anodes 24. As a matter of convenience, the cathode 26/diaphragm 36 assembly can be prepared prior to insertion of diaphragm 36 into the cell. This can be conveniently accomplished by attaching each of the continuous sheet or endless belt diaphragm 36 to the lower diaphragm support 30, then lowering the cathode 26 down onto the lower diaphragm support 30 so that the diaphragm 36 extends upwardly through the passageways previously provided for the anode 24 and, thereafter, applying the upper diaphragm support 32 to the other edge of the endless band diaphragm 36. This assembly is then set into the cell so that the anode 24 extends through the passageways made by the diaphragm 36 which parallels the passageways of the cathode 26. The cathode 26 and lower diaphragm support 30 are then placed in mechanical and electrical attachment with the cell so that proper position of the cathode 26 and diaphragm 36 will be maintained. Gas seals (not shown) between sidewall 16 and lower diaphragm support 30 and between sidewall 16 and upper diaphragm support 32 complete the separation between the cathode and anode chambers.

The spacial relationships between the anode 24, diaphragm 36 and cathode 26 are more clearly shown in the top cross-sectional view of FIG. 2. In this view it will be noted that the anode 24 is surrounded by diaphragm 36 and the diaphragm 36 is in turn surrounded by the cathode 26. Both the diaphragm 36 and the cathode 26 having a fixed spaced relationship with the anode 24 whereby at any given point on the surface of anode 24 the cathode 26 and diaphragm 36 are in substantially the same spaced position as at any other point on anode 24. In no case is anode 24 in contact with cathode 26 each being at all times distinctly separated from each other by diaphragm 36. The diaphragm 36 thereby forms an anolyte and catholyte chamber for each anode 24 or cathode 26 pair.

The invention is illustrated schematically in FIG. 3'

wherein the expanded drawing shows an anode 24 embedded in cell bottom and extending through the nonconductive sealant layer 12. The lower diaphragm support 30 contains slots or openings which accommodate the insertion of anode 24. The cathode 26 is of woven wire-mesh construction and is so woven that it has openings shaped corresponding to the openings or slots in the lower diaphragm support 30 but of a slightly larger nature thereby accommodating the endless belt diaphragm 36 which is attached to the lower diaphragm support 30 and the upper diaphragm support 32 which has the same configuration as the lower diaphragm support 30.

The lower diaphragm support 30 and the upper diaphragm support 32 are constructed of a chemically inert, electrically non-conducting thermoplastic material such as polyolefin derived form an olefin containing 2 to 4 carbon atoms including polyethylene, polypropylene, polybutene-l and mixtures thereof; polytetrafluoroethylene, copolymers of tetrafluoroethylene and polyperfluoroalkoxy compounds, chlorofluoropolyethylene, polyvinylidene fluoride polymers and acrylonitrile butadiene styrene terpolymers. The properties of these polymers are improved by adding inert, non-conducting yet reinforcing fillers such as asbestos, glass fibers, mica, kaolin or carbon black. An exemplary composition for use in this invention is an asbestos filled polypropylene composition, e.g., as disclosed in British Patent 1,246,034, which for the sake of brevity is incorporated herein by reference. Another equally suitable material is a polytetrafluoroethylene polymer or copolymer. The upper diaphragm support 32 and the lower diaphragm support 30 are made from the foregoing polymeric materials in such a manner that the

support members

30, 32 are both electrically non-conducting and are incapable of permitting the flow of electrolyte from one chamber to the other chamber. It is also within the scope of this invention to make the support frames 30, 32 out of a suitable metal or wire which is completely covered and encased with an insulating polymeric material disclosed above.

The endless belt diaphragm 36 can be made out of the same polymeric material as the

diaphragm support members

30, 32 are made out of or it can be one of the other suitable polymeric materials, e.g., those enumerated above. The endless belt diaphragm 36, however, is so fabricated with appropriate physical, chemical and electrochemical properties that it is porous and will permit the flow of electrolyte from one chamber to the other chamber. The endless belt diaphragm 36 is attached to the diaphragm supports 30, 32 in any one of several conventional techniques used in fabricating polymeric objects such as heat-sealing, cementing or friction fit snap-in techniques. It is also within the scope of this invention to use a combination of the attachment techniques mentioned above to attach the diaphragm 36 to the

supports

30, 32. For instance, the diaphragm 36 can be heat-sealed to the lower or bottom support 30 and mechanically, i.e., friction fitted, to the upper diaphragm support 32. The fabricated diaphragm 36 may properly be classified as a porous membrane, or a felted fabric such as are presently employed in the various phases of electrolytic cell technology. It is also known in the cell technology to insert between diaphragm 36 and the electrodes, either or both anode 24 and cathode 26, an inert screen (not shown) to facilitate and improve the functioning of the cell. This modification can be used in conjunction with the present invention, if desired.

While the invention has been set forth in terms of the conventional woven wire screen cathodes 26 of the Hooker and Diamond type cells, it is equally applicable to and useful with cathodes 26 made of perforated metal plate formed to a similar spacing arrangement.

The anode 24 can be either a solid metal sheet, a woven wire arrangement or an expanded metal mesh as desired, the exact configuration of the anode 24 being beyond the scope of the present invention. Typically, the anode 24 is made of a valve metal and, thereafter, coated. By a valve metal it is meant metal of tungsten, titanium, zirconium, tantalum and niobium. Preferably, titanium or tantalum is employed and it is normally a commercially pure grade such as electrolytic grade. Alloys of valve metals can be employed as long as the alloy meets the criterion of passivity, metal alloys which become passivated when polarized anodically and can remain passive well beyond anodic potential needed to convert a chloride ion to chlorine. The phenomenon of passivity in this connection is discussed in an article by Greene appearing in the April 1962 issue of Corrosion, pages l36-t to l42-t, wherein reference may be made to FIG. 1 of the article which describes typical active-passive transition of a metal towards a corrosive medium. Titanium alloys of aluminum, vanadium, palladium, chromium or tin can be employed in which the latter metals are present as less than 10 percent of the alloy.

It is also well known to coat the anode 24 with at least one platinum group metal or metal compound, e.g., oxide, to enhance its utility. The platinum group metals include platinum, ruthenium, osmium, rhodium, iridium and palladium and alloys of two or more of the foregoing metals. Many means for applying and the formulations of platinum group metals and compounds for these coatings are known, for instance, see US. Pat. Nos. 3,632,498; 3,630,768; 3,616,446; 3,242,059; and 3,177,131 which for the sake of simplicity and brevity are herein incorporated by reference.

FIG. 4 shows an optical modification of the present invention which is designed to secure the benefits of the present invention to the diaphragm cell equipped with the conventional Hooker woven wire cathode employed therein. The Hooker woven wire type cathode is well known in the art and generally disclosed in the Sconce textbook discussed above in the background section. In this modification the cell bottom and bus bar 10, the nonconductive sealant layer 12 and anodes 24 with metal stem 40 and retaining nut 42 remain positioned without change as shown in FIG. 1. However, in contrast to the cathode 26/diaphragm 36 arrangement of FIG. 1, the continuous sheet or endless belt diaphragm 36, the lower diaphragm support 30 and upper diaphragm support 32 are rearranged so that they form a series of equal distance-spaced closed openings on both sides. This is accomplished by attaching the endless belt diaphragm 36 to the anode 24 openings of the lower diaphragm support 30 as previously disclosed. However, the upper diaphragm support 32 is now realigned so that the prior axial alignment of the openings in the lower diaphragm support 30 and the openings in the upper diaphragm support 32 are completely out of register. From a top view the openings in the upper support 32 are now spaced equidistant from each two adjacent openings in the lower support 30. The free end of the endless belt diaphragm 36 for attaching to the upper diaphragm support 32 is now in register with and contacting the solid portion of the upper diaphragm support 32 which is equidistant spaced between two adjacent openings shown in FIG. 3. When the diaphragm 36, upper support 32 and lower support 30 are assembled, the diaphragm 36 is positioned around the anode 24 as before. However, in this case, the Hooker woven wire cathode 26 is inserted from above into the openings of the upper diaphragm support 32. In this case the cathode 26 is separated as before from the anode 24 by the diaphragm 36 and the diaphragm supports 30, 32. But, unlike the case as shown in FIGS. 1, 2 and 3 the cathode 26 is not encased by the diaphragm 36 and diaphragm supports 30, 32 and can be disengaged from the diaphragm 36 without disassembly of the diaphragm 36 diaphragm supports 32, 30 arrangement. Under this arrangement the conventional diaphragm electrolytic cell can be used as is without modification of the location of the chlorine outlet 22. Gas seal (not shown) between sidewall 16 and lower diaphragm support 30 completes the separation between the cathode and anode chambers.

Many other modifications and ramifications will naturally suggest themselves to those skilled in the art based on this disclosure. These ramifications and modifications are intended to be comprehended as within the scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a diaphragm cell for the production of chlorine and caustic from aqueous alkali metal chloride solutions having a plurality of anodes mounted at the bottom of said cell, cathodes between adjacent anodes and spaced between each cathode and anode a diaphragm which divides the cell into anolyte and catholyte compartments the improvement which comprises:

a diaphragm assembly composed of an upper diaphragm support, a lower diaphragm support and an endless band diaphragm extending from said upper support to said lower support, both said diaphragm supports being made of an electrically nonconductive polymeric composition, said lower support resting on or adjacent to the bottom of said cell and having openings therein which allow said anodes to extend through said lower support, said diaphragm being in connection with said upper and lower supports thereby defining a continuous barrier separating said anodes from said cathodes so that all of the flow of electrolyte from the anode to the cathode is through said diaphragm.

2. The electrolytic cell of claim 1 wherein the openings of the upper diaphragm support and the lower diaphragm support are in axial alignment with each other and the cathode is encased within the upper diaphragm support, the diaphragm and the lower diaphragm support.

3. The electrolytic cell of claim 1 wherein the upper diaphragm support and the lower diaphragm support openings are non-axially aligned so that the system of diaphragm supports and diaphragm form a complete barrier between said anodes and said cathodes without encasing said cathodes.

4. The electrolytic cell of claim 1 wherein the diaphragm support and the diaphragm are made from polytetrafluoroethylene polymers or copolymers.

5. The electrolytic cell of claim 1 wherein the diaphragm is a porous sheet material.

6. The electrolytic cell of claim 1 wherein the diaphragm is heat-sealed to the upper and lower diaphragm support members.

7. The electrolytic cell of claim 1 wherein the diaphragm is heat-sealed to the lower diaphragm support member and is mechanically sealed to the upper diaphragm support member.

8. The electrolytic cell of claim 1 wherein separating screens are interposed between the diaphragm and'th'e anode and the cathode.

Claims

1. AIN A DIAPHRAGM CELL FOR THE PRODUCTION OF CHLORINE AND CAUSTIC FROM AQUEOUS ALAKLIE METAL CHLORIDE SOLUTIONS HAVING A PLURALITY OF ANODES MOUNTED AT THE BOTTOM OF SAID CELL, CATHODES BETWEEN ADJACENT ANODES AND SPACED BETWEEN EACH CATHODE AND ANODE A DIAPHRAGM WHICH DIVIDES THE CELL INTO ANOLYTE AND CATHOLYTE COMPARTMENTS THE IMPROVEMENT WHICH COMPRISES: A DIAPHRAM ASSEMBLY COMPOSED OF AN UPPER DIAPHRAGM SUPPORT, A LOWER DIAPHRAGM SUPPORT AND AN ENDLESS BAND DIAPHRAGM EXTENDING FROM SAID UPPER SUPPORT TO SAID LOWER SUPPORT, BOTH SAID DIAPHRAGM SUPPORTS BEING MADE OF AN ELECTRIALLY NON-CONDUCTIVE POLYMERIC COMPOSITION, SAID LOWER SUPPORT RESTING ON OR ADJACENT TO THE BOTTOM OF SAID CELL AND HAVING OPENINGS THEREIN WHICH ALLOW SAID ANODES TO EXTEND THROUGH SAID LOWER SUPPORT, SAID DIAPHRAGM BEING IN CONNECTION WITH SAID UPPER AND LOWER SUPPORTS THEREBY DEFINING A CONTINUOUS BARRIER SEPARATING SAID ANODES FROM SAID CATHODES SO THAT ALL OF THE FLOW OF ELECTROLYTE FROM THE ANODE TO THE CATHODE IS THROUGH IS DIAPHRAGM.

8. The electrolytic cell of claim 1 wherein separating screens are interposed between the diaphragm and the anode and the cathode.