Document wDJdXbkkrz6DaVDGepDQM4EDJ

FILE NAME: Olin (OLIN) DATE: 1984 Feb 14 DOC#: OLIN002 DOCUMENT DESCRIPTION: US Patent 4431502 - Sealing Means for Filter Press [It is desirable to take advantage of existing technology, particularly in diaphragm cells, but it is also necessary to provide cell designs which meet the requirements of these newer separator materials.] United States Patent m Ford [54] SEALING MEANS FOR FILTER PRESS CELLS [75] Inventor: James M. Ford, Cleveland, Tenn. [73] Assignee: Olin Corporation, NewHaven, Conn. [21] Appl. No.: 329,092 [22] Filed: Dec. 9,1981 Related U.S. Application Data [63] Continuation-in-part o f Ser. No. 204,127, Nov. 5, 1980. [51] Int. CL> ...................... C25B 9/00; C25B 11/10; C25B 13/08 [52] U.S. a ...................................... 204/ 252; 204/279; 204/290 F; 204/296 [58] Field of Search.............. 204/252, 279, 295, 296, 204/290 F, 253-258 [56] References Cited U.S. PATENT DOCUMENTS 3,980,544 4,026,782 4,175,025 4,207,165 4,210,516 4,253,932 4,342,460 4,378,286 9/1976 Adams et al........................ 204/253 X 5/1977 Bouy et al............................... 204/254 11/1979 Cream er et al......................... 204/253 6/1980 M ose et al............................... 204/258 7/1980 M ose et al............................... 204/284 3/1981 Mose et al........................... 204/279 X 8/1982 E ng ..................................... 204/279 X 3/1983 E ng et al............................ 204/279 X [11] 4,431,502 [45] Feb. 14, 1984 Primary Examiner--Donald R. Valentine Attorney, Agent, or Firm--James B. Haglind; Donald F. Clements ' [57] ABSTRACT The invention relates to an electrolytic cell which is comprised of a first frame member housing an electrode and a second frame member housing an electrode. A separator is positioned between the first frame member and the second frame member. A first sealing means contacts a side of the first frame member and one side of the separator. Contacting the second frame member and the opposite side of the separator is a second sealing means. The first sealing means and the second sealing means are elastomeric solids having a substantially rect angular cross-sectional area where the first sealing means is from about 1.1 to about 3 times the width of the second sealing means. Pressing means are provided which press the frames together against the sealing means and the separator to form a substantially fluidtight seal. The novel electrolytic cells provide the ad vantages of simultaneously: a. controlling gasket compression pressures, b. controlling gasket frame surface structural forces, c. efficiently forming a seal, and d. preventing gasket slippage. 9 a aims, 7 Drawing Figures 43,4? 46 U.S. Patent Feb. 14, 1984 Sheet 1 of 2 ,4 431,502 U.S. Paient Feb. 14, 1984 Sheet 2 of 2 4,431,502 J 4,431,502 1 2 for example, a 10/ l , 000ths of an inch spacing gap be SEALING MEANS FOR FILTER PRESS CELLS tween a gasket and an adjacent frame that is causing fluid leakage, it has been found necessary to tighten all This application is a continuation-in-part of applica of the gaskets 10/ l , 000ths of an inch to stop the leak. tion Ser. No. 204,127, filed Nov. 5, 1980. 5 Sealing means, including gaskets and other appropri The present invention relates to spacer means suitable ate apparatus, for cells employing ion exchange mem for use in a filter press-type electrolytic cell. More par branes as separators included those described in U.S. ticularly, the invention relates to spacer means utilized Pat. No. 4,026,782, issued May 31, 1977, to P. Bouy et to maintain a fixed and predetermined gap between the al, U.S. Pat. No. 4,175,025, issued Nov. 20, 1979, to E. adjacent electrode frames in an electrolytic cell. 10 D. Creamer et al, and U.S. Pat. No. 4,207,165, issued Commercial cells for the production of chlorine and June 10, 1980, to Mose et al. U.S. Pat. No. 4,026,782 alkali metal hydroxides have been continually devel teaches bipolar cells having frames with recesses into oped and improved over a period of time dating back to which the sealing members fit. In one of the recesses, a at least 1892. In general, chlor-alkali cells are of the diaphragm is sealed into the frame with a putty or deposited asbestos diaphragm type or the flowing mer 15 caulked gasket. This sealing arrangement requires a cury cathode type. During the past few years, develop complex frame structure which utilizes spacer appara ments have been made in cells employing separators tus that is part of one of the electrode frames. This having ion exchange properties which promise advan arrangement suffers from the disadvantage of not being tages over either diaphragm or mercury cells. It is desir able to vary the gap between the electrode frames with able to take advantage of existing technology, particu 20 simply the replacement of the sealing means should it be larly in diaphragm cells, but it is also necessary to pro necessary to have a different gap between the electrode vide cell designs which meet the requirements of these frames. newer separator materials. Since suitable separator ma U.S. Pat. No. 4,175,025 describes filter press frames terials, such as those marketed by E. I. duPont de Ne having at least one formed recess into which a gasket is mours and Company under the trademark Nafion 25 fit. The membrane is sized to extend beyond the edges and by Asahi Glass Company Ltd. under the trademark of the frame so that shrinkage of the membrane during Flemion , are available primarily in sheet form, the regeneration will not prevent its re-use. Adjacent most generally used cell employing such separators are frames may contain recesses which are opposite each of the "filter press" type. Filter press cells may employ other, but of different sizes. Gaskets having different electrode structures which are monopolar or bipolar. 30 hardnesses are used to seal the membrane between In the filter press cell, separators in sheet form are them. The gap between the electrode frames in this type clamped between the sides of frame members. The seal of sealing arrangement is entirely dependent upon the ing means employed, normally elastomeric gaskets, gasket height and the amount of compression applied to must effectively provide a fluid-tight seal between the the frames. Thus, the gap can vary between each pair of frame members and the separator without damaging the 35 adjacent frames as the thickness of the gaskets em separator. Part of the difficulty in obtaining a fluid-tight ployed varies or the recesses machined into the frames seal has been found to reside in the fact that the gaskets vary. utilized to separate the electrode frame members are To provide recesses in the frame members of the type available with thicknesses that widely vary because of disclosed in U.S. Pat. Nos. 4,026,782 and 4,175,025, large manufacturing tolerances. 40 operations such as machining must be employed. These It has been found in the assembly of filter press mem operations add undesired increases to the cost of pro brane cells that this difference in thickness between the ducing the frames. gaskets employed on adjacent electrode frame members The arrangement disclosed in U.S. Pat. No. 4,207,165 can present problems when attempting to compress the employs a fixed spacer member between the adjacent frames into a fluid-tight cell. Frequently, hydraulic 45 electrodes to establish a desired gap. However, the rams or other types of pressure-applying apparatus are method of securing the membrane between the gasket employed to compress the electrode frames and the members can promote tearing of the membrane or sepa separating gaskets together. Where there are differences rator. in the thickness of the gaskets, it has been found that It is an object of the present invention to provide each gasket is not subjected to an equal level of com 50 sealing means in filter press cells using frames which are pression. The thicker gaskets are naturally subjected to simple and in which direct contact between the separa greater compression than thinner gaskets. Where the tor and the frame member is avoided. difference in thickness is too great, a predetermined Another object of the present invention is to provide compression force applied to a cell and its component sealing means which prevent undesired slippage be electrode frames can leave spaces between the thinner 55 tween the sealing means and the slippery surfaces of the gaskets and adjacent frames so that fluid leakage will separator which is wet with electrolytes such as caustic occur. To correct this, additional pressure must be ap solutions. plied to the electrode frames to achieve a level of com A further object of the present invention is to provide pression in the separating gaskets that will form a fluid- sealing means which contribute to the control of the tight seal. Frequently, during this additional compres 60 compression pressures employed. sion-applying step, excessive force can be applied These and other objects of the invention are accom which causes the frames to deform or bend. Addition plished in an electrolytic cell comprising: ally, if the gaskets employed are not properly aligned, a. a first frame member housing an electrode, slippage can occur resulting in unequal stress on por b. a second frame member housing an electrode, tions of the separator and the gaskets resulting in unde 65 c. a separator positioned between the first frame sired wear and the promotion of tearing of the mem member and the second frame member, brane and unequal distribution of the compression loads d. a first sealing means contacting a side of the first on the sealing means resulting in fluid leaks. To correct, frame member and one side of the separator; the 4,431,502 3 4 first sealing means being an elastomeric solid hav during compression, between raised portion 64 of gas ing a substantially rectangular cross-sectional area, ket 62 and inset portion 68 of gasket 66. e. a second sealing means contacting a side of the FIG. 5 shows separator 24 sealed between inserts 75 second frame member and contacting the other which prevent undesired friction between separator 24 side of the separator, the second sealing means 5 and narrow gasket 72 and wider gasket 74. Gaskets 72 being an elastomeric solid having a substantially and 74 are positioned between sides 77 and 79 of bar rectangular cross-sectional area, the width of the shaped frames 76. first sealing means being from about 1.1 to about 3 FIG. 6 illustrates separator 24 sealed directly be times the width of the second sealing means, and tween compressed narrow gasket 72 positioned along f. pressing means for pressing the frames together 10 side 82 of metal anode frame 80 and compressed wide against the sealing means and the separator so as to gasket 74 positioned along side 86 of cathode frame 84. form a substantially fluid-tight seal. Lip 85 on side 86 retains wide gasket 74 within frame 84. Other advantages of the invention will become appar FIG. 7 represents a partial sectional view of an un ent from reading the description below and the inven compressed sealing means of the present invention hav tion will be better understood by references to the at 15 ing a rectangular cross-section where w is the initial tached drawings in which: width and t is the initial thickness of the sealing means. FIG. 1 illustrates a front elevation in perspective of a Suitable as sealing means are gaskets comprised of pair of adjacent electrodes employing the novel sealing elastomeric solids having a substantially rectangular means of the present invention. cross-sectional area. Examples of the elastomeric solids 20 include chlorobutadiene rubber (Neoprene), chlorosul- FIG. 2 is an enlarged partial sectional view of the electrodes of FIG. 1 taken along line 2--2 showing one fonated polyethylene (Hypalon), ethylene-propylene embodiment of the sealing means of the present inven dimonomer (EPDM), or gum rubber. The hardness of the sealing means is not critical and any suitable hard tion. ness may be selected independently for either gasket. FIG. 3 depicts a partial sectional view of another 25 Preferably, the gaskets have a low degree of hardness embodiment of the sealing means of the present inven which allows the gaskets to fill in irregularities on the tion. frame members and thus permit reduced tolerances FIG. 4 illustrates a partial sectional view of an addi which minimizes, for example, machining of metal tional embodiment of the sealing means of the present frames and thus reduces production costs. For example, invention. 30 elastomeric sealing means having a hardness of from FIG. 5 shows a partial sectional view of a further about 20 to about 60 and preferably from about 30 to embodiment of the sealing means of the present inven about 50 durometers are quite suitable; with the sealing tion used with bar shaped frames. means along the cathode frame being preferably in the FIG. 6 illustrates a partial sectional view of a still range of from about 30 to about 40 durometers, while further embodiment of the sealing means of the present 35 the sealing means along the anode frame is preferably invention in which a first sealing means has a width from about 40 to about 50 durometers. greater than a second sealing means. Gasket thicknesses are similarly not critical and any FIG. 7 represents a partial sectional view of a sealing suitable thicknesses may be independently selected for means of the present invention. each of the gaskets used. Electrodes 10 of FIG. 1 are comprised of frames 12 40 In the embodiments shown in FIGS. 5 and 6 where having tops 14, bottoms 16, and sides 18 and 20. Frames both sealing means are substantially flat, solid gaskets 12 house foraminous electrode surfaces 22. Separator 24 having a rectangular cross-sectional area the initial is positioned between adjacent electrodes 10. Electric width of the second gasket is selected to provide less current is supplied to and removed from electrodes 10 area of contact with the separator than the initial width through electrode connectors 24 connected to conduc 45 of the first gasket. Further, the width of the second tor rods 26 which are attached to electrode surfaces 22. gasket is selected to provide the desired control of the Outlets 28 in tops 14 of frames 12 permit removal of gasket compression pressures and the gasket frame sur electrolysis products. Inlets 30 permit a liquid to be fed face structural forces. Control of these pressures mini to electrode 10. Guides 32 are included on frames 12 to mizes compression set for gasket materials and bending allow for the proper alignment of electrodes 10. 50 or twisting of frame members. The initial width and FIG. 2 shows separator 24 positioned between gas initial thickness of an uncompressed sealing means hav kets 40 and 46 which are placed between sides 20 of ing a rectangular cross-sectional area is shown in FIG. frames 12. Gasket 40 is comprised of a base portion 7. which contacts edge 43 of side 20 and raised portion 44 The width of the second gasket is kept narrow which contacts one side of separator 24. Gasket 46 55 enough not to exceed the structural strength of the contacts edge 45 of adjacent side 20 and the other side frame member. The force on the frame member per of separator 24. The area of contact for gasket 46 with lineal inch of frame member is F ,--PX W where P is the separator 24 is greater than that of raised portion 44 of gasket pressure of the second gasket and W is the ex gasket 40. panded width of the second gasket in compression. In the embodiment of FIG. 3, separator 24 is sealed 60 The expanded width W = wh-(1--c) where w is the between gaskets 52 and 56 which extend beyond edges initial width of the second gasket and c is the fractional 43 and 45 of sides 20 of frames 12. Under compression, compression expressed as a decimal. The compression separator 24 is effectively sealed between raised portion factor c is selected high enough to assure sealing, de 54 of gasket 52 and gasket 56. pending upon the gasket material and may be from FIG. 4 illustrates an additional embodiment of the 65 about 0.05 to about 0.55 and preferably from about 0.2 sealing means of the present invention in which the bases of gaskets 62 and 66 rest against shoulders 65 of edges 61 and 63 of frames 60. Separator 24 is sealed, to about 0.4. To prevent the second sealing means from curling during compression and to control the amount of over 4,431,502 5 6 hang of the first sealing means, the first sealing means membrane cells in which the electrodes are oriented has an initial width of from about 1.1 to about 3, and generally vertically. Suitable filter press monopolar preferably from about 1.3 to about 2 times that of the membrane cells include those described in U.S. Pat. No. second sealing means. Thus, for example, at initial 4,056,458, issued Nov. 1,1977, to G. R. Pohto et al; U.S. widths normally employed in the cell, the first sealing 5 Pat. No. 4,210,516, issued July 1, 1980, to L. Mose et al means is from about i to about 2, and preferably from and U.S. Pat. No. 4,217,199, issued Aug. 12,1980, to H. about to about 4 of an inch wider than the second Cunningham. sealing means. Curling of the sealing means along, for Hydraulically permeable or impermeable separators example, a metal anode frame, in addition to causing an may be employed in the electrolytic cell of the present uneven distribution of compression forces, can expose 10 invention. Preferably, inert flexible separators having the metal anode frame to the attack of acidic brine, for ion exchange properties and which are substantially example, an alkali metal chloride such as sodium chlo impervious to the hydrodynamic flow of the electrolyte ride, which can promote crevice corrosion in the metal and the passage of gas products produced in the cell are anode frame. employed. Suitably used are cation exchange mem To prevent the sealing means from rolling up during 15 branes such as those composed of fluorocarbon poly assembly of the cell, a glue or adhesive may be applied mers having a plurality of pendant sulfonic acid groups to the side of the sealing means which contacts the or carboxylic acid groups or mixtures of sulfonic acid frame members. groups and carboxylic acid groups. The terms "sulfonic During assembly of a filter press electrolytic cell, acid groups" and "carboxylic acid groups" are meant to pressing means such as tie bolts are tightened around 20 include salts of sulfonic acid or salts of carboxylic acid the perimeter of the cell. This tightening of the tie bolts which are suitably converted to or from the acid groups bonds the individual electrodes, anodes, and cathodes by processes such as hydrolysis. One example of a suit alternately arranged, together. An adjacent electrode able membrane material having cation exchange prop pair, a cathode and an anode, are pressed together so erties is a perfluorosulfonic acid resin membrane com that the sealing means is compressed. Since each cath 25 posed of a copolymer of a polyfluoroolefin with a sulfo- ode and anode have individual sealing means which nated perfluorovinyl ether. The equivalent weight of extend about the entire periphery, the electrodes are the perfluorosulfonic acid resin is from about 900 to separated by the individual sealing means and the sepa about 1600 and preferably from about 1100 to about rator which is inserted therebetween. As the electrodes 1500. The perfluorosulfonic acid resin may be sup are compressed together by the application of a suitable 30 ported by a polyfluoroolefin fabric. A composite mem closure force, the gaskets deform in a manner which brane sold commercially by E. I. duPont de Nemours effects a fluid-tight seal between adjacent electrode frames, as well as securing the separator along both and Company under the trademark "Nafion" is a suit able example of this membrane. surfaces to avoid any undesired slippage. A second example of a suitable membrane is a cation As shown in FIG. 2, the electrodes have frames 12 35 exchange membrane using a carboxylic acid group as having generally planar opposing surfaces between which the first sealing means, the separator and the the ion exchange group. These membranes have, for example, an ion exchange capacity of 0.5-4.0 mEg/g of second sealing means are compressed. The frames are generally of a thick solid construction capable of with dry resin. Such a membrane can be produced by copo standing the considerable compression force exerted 40 lymerizing a fluorinated olefin with a fluorovinyl car upon them when the filter press cell is assembled. To boxylic acid compound as described, for example, in prevent the sealing means from "popping out" under U.S. Pat. No. 4,138,373, issued Feb. 6, 1979, to H. compression, the frames should be substantially flat. To Ukihashi et al. A second method of producing the avoid the considerable expense of machining and finish above-described cation exchange membrane having a ing, the opposing planar surfaces are free of recesses or 45 carboxyl group as its ion exchange group is that de grooves. scribed in Japanese Patent Publication No. 1976-126398 Electrode frame components may be in the shape of by Asahi Glass Kubushiki Gaisha issued Nov. 4, 1976. rectangular bars, C or U channels, cylindrical tubes, This method includes direct copolymerization of fluori elliptical tubes as well as being I-shaped or H-shaped. nated olefin monomers and monomers containing a Preferably, the frame components are in the shape of a 50 carboxyl group or other polymerizable group which C channel as shown in FIGS. 2-3. can be converted to carboxyl groups. Carboxylic acid The materials of construction for frame components type cation exchange membranes are available commer may be any which are resistant to corrosion by the cially from the Asahi Glass Company under the trade electrolytes and the products of electrolysis. For exam mark "Flemion". ple, metal anode frames used in the electrolysis of alkali 55 Electrolytic cells of the present invention provide the metal chlorides are constructed of valve metals such as advantages of simultaneously: titanium, tantalum, or tungsten and their alloys, with (a) controlling gasket compression pressures; titanium being preferred. Cathode frames may be con (b) controlling gasket frame surface structural forces; structed of metals such as iron, steel, stainless steel, (c) efficiently forming a seal; and nickel, or alloys of these metals may be used as well as 60 (d) preventing gasket slippage. plastic materials such as polypropylene, polybutylene, In addition, cell assembly tolerances are improved and polytetrafluoroethylene, FEP, and chlorendic acid construction costs reduced. Lower compression pres based polyesters. sures can be employed permitting the use of smaller The sealing means of the present invention may be compression means to further reduce cell costs. used in any suitable filter press cell, the structure and 65 What is claimed is: function of its central components being well known to 1. An electrolytic cell which comprises: one of skill in the art. Preferred filter press electrolytic a. a first frame member housing an electrode, cells for employing the present invention are monopolar b. a second frame member housing an electrode, 4,431,502 7 8 c. a separator positioned between said first frame hardness in the range of from about 20 to about 60 member and said second frame member, durometers. d. a first sealing means contacting a generally planar 3. The electrolytic cell of claim 2 in which said first side of said first frame member and one side of said separator, said first sealing means being an elasto meric solid having a substantially rectangular cross-sectional area, e. a second sealing means contacting a generally pla nar side of said second frame member and contact ing the other side of said separator, the second sealing means being an elastomeric solid having a substantially rectangular cross-sectional area, the initial width of said first sealing means being from about 1.1 to about 3 times the initial width of said second sealing means, and where the expanded width (W) of said second sealing means is defined by the formula: sealing means and said second sealing means are gas 5 kets. 4. The electrolytic cell of claim 3 in which said sepa rator is hydraulically permeable. 5. The electrolytic cell of claim 3 in which said sepa rator is a hydraulically impermeable cation exchange 10 membrane comprised of fluorocarbon polymers having cation exchange means selected from the group consist ing of sulfonic acid groups, carboxylic acid groups, and mixtures thereof. 6. The electrolytic cell of claim 3 in which said first 15 sealing means and said second sealing means is com prised of an elastomer selected from the group consist . ing of chlorobutadiene, chlorosulfonated polyethylene, ethylene-propylene dimonomer, and gum rubber. 7. The electrolytic cell of claim 6 in which said first 20 frame member houses a cathode. 8. The electrolytic cell of claim 7 in which said sec where w is the initial width, and c is from about 0.05 to about 0.55, and f. pressing means for pressing the frames together 25 against the sealing means and the separator so as to form a substantially fluid-tight seal. 2. The electrolytic cell of claim 1 in which said first sealing means and said second sealing means have a ond frame member houses an anode and is comprised of a valve metal selected from the group consisting of titanium, tantalum, and tungsten and their alloys. 9. The electrolytic cell of claim 8 in which said initial width of said first sealing means is from about 1.3 to about 2 times said initial width of said second sealing means. ***** 30 35 40 45 50 55 60 65 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PA TEN T NO. DATED : 4,431,502 : February 14, 1984 IN V E N T O R Y : Jam es M F o r d It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below: Column 5, line 7, delete "3/4" and insert -- 3/8-- . Column 6, line 38, delete "mEg/g" and insert -- mEq/g-- . Signed and Sealed this |SEAL| Attest: Twenty-fourth jD ay o f April 1984 Attesting Officer GERALD I. MOSSINGHOFF Commissioner o f Patents and Trademarks