CA1114777A - Sealed casing for diaphragm cell having closed end and closed sides - Google Patents
Sealed casing for diaphragm cell having closed end and closed sidesInfo
- Publication number
- CA1114777A CA1114777A CA291,017A CA291017A CA1114777A CA 1114777 A CA1114777 A CA 1114777A CA 291017 A CA291017 A CA 291017A CA 1114777 A CA1114777 A CA 1114777A
- Authority
- CA
- Canada
- Prior art keywords
- casing
- closed
- seal
- tab portion
- comprised
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B13/00—Diaphragms; Spacing elements
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/60—Constructional parts of cells
- C25B9/63—Holders for electrodes; Positioning of the electrodes
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Sealing Battery Cases Or Jackets (AREA)
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE A casing suitable for covering a substantially rectangular electrode for a diaphragm-type electrolytic cell comprises a closed end, an open end, and two closed sides, at least one of the closed sides having a tab adjacent to the open end. The casing is formed of a flexible material which is folded or sealed to provide a closed end and then sealed to form two closed sides. The seal along a major portion of the sides is substantially linear while the seal along the edge of the tab is angular to and contiguous with the linear seal. The tabs, which can be twisted or turned to provide a flat surface, permit the casing to be easily sealed along the top and bottom edges to provide separa-tors for diaphragm-type electrolytic cells which are leak-proof and expand or contract during cell operation without detrimental mechanical stress.
Description
1~14~'~ 7 C-6958 This invention relates to diaphragm-type elec-trolytic cells for the electrolysis of aqueous salt solutions. More particulary, this invention relates to a method of forming a casing for an electrode in a diaphragm-type electrolytic cell.
For years commercial diaphragm cells have been used for the production of chlorine and caustic soda which employed a deposited fiber diaphragm, usually asbestos. While quite satisfactory for producing chlorine, the caustic soda was of a relatively low concentration and contained considerable amounts of undesired sodium chloride.
Recently materials have been produced which may be employed as diaphragms to produce caustic soda of increased concentration with significantl~ reduced sodium chloride content. These materials, having ion exchange properties, are produced from one or a combination of polymeric materials. The materials may be fabricated in the form of continuous sheets to extend over a group of electrodes. They may also be produced in the form of a casing which is attached to individual electrodes. It is important that the attachment of the fabricated diaphragms be accomplished in a manner which will effectively seal the diaphragm to prevent undesired leakage into or out of the electrode compartment. Leakage resulting from poor ',,' ~' .
~ -2-. - ' '` ~
.
, .
- . . . : ,, : ~ , .
. . ~ . : .
: . ' : :
~L$3~
~-6958 seals along seams or joints can result in a substantial reduction in current efficiency.
It is known in the prior art to attach fabri-cated diaphragms, for example, by means of clamps or expandable retainers. U.S. Patent No. 1,797,377 employs clamps having offset claws which straddle two ends of the diaphragm covered electrode, pinching them together and pressing the edges between the clamp and a support plate. This method does not effectively seal the area ~10 across the top of the electrodes and requires the diaphragm be separately clamped to each electrode with no coopera-tion between adjoining clamps.
Flexible retainers are employed to secure a diaphragm in U.S. Patent No. 3,878,082 where a U-shaped compressible retainer is used in combination with a crescent-shaped expansible retainer. The crescent-shaped retainer is placed over the diaphragm in the area between adjacent cathodes so that one end extends over a portion of one cathode and the other end covers a portion of the adjacent cathode. The U-shaped retainer is placed on top of the cathode so that it clamps down over one end each of two adjacent crescent-shaped retainers.
~' ' . .
. . .
,, : ' U.S. Patent No. 3,980,544 discloses securing a fabricated diaphragm covering electrodes using clamps which seal an adjoining edge of each of two adjacent diaphragms.
The clamps are thus positioned between adjacent electrodes, with a pair of clamps being required for each electrode.
While the clamps satisfactorily seal the open ends of the diaphragm, it is desirable to improve the ease of sealing the diaphragm along the top and bottom edges.
Therefore, it is an object of the present invention to provide a casing for enclosing an electrode which provides a perimeter in the form of a flat plane.
Another object of the present invention is to provide a casing for enclosing an electrode which allows the use of simplified methods of clamping.
These and other objects of the present invention are accomplished in a casing for a substantially rectangular electrode for a diaphragm-type electrolytic cell, the casing comprising a closed end, an open end, and two closed sides, at least one of the closed sides having a major portion and a tab portion, said tab ~ -: portion being adjacent to the open end.
The novel casing of the present invention is formed by a method which comprises:
a) forming a closed end of the casing, and ;~ b) forming two closed sides of the casing, at least one of the closed sides having a `~
major portion and a tab portion, where the tab portion is adjacent to the open end, by ''~: ' .:
:' , ' .
'~ .
' . ,' : ~' . .
Lt~"'~
C-6958 applying a substantially linear seal to the major portion, sealing the tab portion, the seal being at an angle to that of the seal on the major portion, with the seal on the tab portion being contiguous with the seal on the major portion.
Accompanying Figures 1-9 illustrate the novel casing of the present invention. Corresponding parts have the same numbers in all Figures.
Figure 1 represents a side view in perspective of one embodiment of the casing of the present invention.
Figure 2 illustrates a rear view of the casing of Figure 1.
Figure 3 shows details of one tab on the casing of Figure 1.
; Figure 4 depicts a side view in perspective of another embodiment of the casing of the present inven~
tion.
Figure 5 represents a front view of a partial section of the casing of Figure 4.
Figure 6 illustrates a side view in perspec-tive of an additional embodiment of the casing of the present invention.
Figure 7 illustrates a front view of a pair of -electrodes covered by the casing of the present invention.
. . ' . .
'' ' -.
. . .
C-6958 Figure 8 represents a side view of one elec-trode of Figure 7.
Figure 9 illustrates a partial section of Figure 7 taken along line 9-9.
Figures 1-3 illustrate one embodiment of the present invention in which casing 10, made of a flexible material has a closed end 12 and an open end 14 and tabs 16 form the upper and lower extremities of open end 14.
Closed edges 18 are formed by providing substantially ~ ~ .
linear seals which terminate at tabs 16. Tabs 16 are sealed along edges 20 adjacent to closed edges 18 by providing a seal which is angular to the seals of closed ~ :
edges 18. For the embodiment of Figures 1-3, the external angle of the seal is about 90, as ~est illus- ~ .
~ trated in Figure 3.
: Figures 4 and 5 show another embodiment of the casing of the present invention in which casing 10 ~ :
is formed by bonding border sections 22 to central section 24 where different materials are employed for the border sections and the central section. Closed edges 18 and tabs 16 are formed on the border section. The external angle between the seal on edge 20 of tabs 16 and the ~ :
linear seals on closed edges 18 is greater than 90.
Figure 6 represents a further embodiment of the casing 10 in which the external angle between the seal along edges 20 of tabs 16 and the seal along closed :
edges 18 Ls less than 90 ,: .~ :
:~
C-6958 Figure 7 is a front view of a pair of electrodes covered by the casing of the present invention. As shown in the side view of Figure 8, electrode 26 is enclosed by casing 10 having closed end 12. Tabs 16 are twisted and are ~overed in part by clamp 28. Clamp 28 seals tabs 16 against flange 30, for example, using bolts 38.
Clamps 28, as illustrated in Figure 9, have an upper portion 34 and a lower portion 36 which are joined ~ -by bolt 38 and seal tabs 16 against flange 30 so that it lies coplanar to backplate 40 to which flange 30 is attached, for example, by welding.
The novel casing of the present invention is comprised of a material which can be used as a porous ~-diaphragm or an ion exchange membrane in an electrolytic cell of the diaphragm type. The material should be flexible and capable of being sealed, for example, by means such as heat sealing, sewing, or by the application of sealants. Suitable materials include plastics such as polytetrafluoroethylene, polypropylene or polyvinylidene chloride; sheets or fabrics of inorganic materials such as asbestos; and ion exchange resins.
Ion exchange resins which can be used as casing materials include fluorocarbons having the units:
., , ," , .~ , . , - .
- : . -: - . . .
~ F ~ ~4~
Cm ~ M and --\CF2 ~ CF N
~ X
where m is from 2 to 10, the ratio of M to N
is sufficient to provide an equivalent weight of from 600 to 2000, and X is selected from:
(i) A, or (ii) 4OCF2 - CF~ A
Z -. ,~ .
where p is from 1 to 3 and Z is F or a perfluoroa~yl group having from 1 to 10 carbon atoms provided that in either of these cases (i) and (ii), A is a group selected from~
SO3H~
CF2SO3H, CC12SO3H . .
X'SO3H, .
03H2~ :~
P2H2 ' COOH, and X'OH
where X' is an arylene group.
. .. . . ..
~b' ~ 7 C-6958Preferred ion exchange resins are those in which X is COOH, SO3H, OCF2-CF2-SO3H, or OCF2-CF2-COOH.
Suitable casing are fabricated from perfluoro-carboxylic acid resins having the formula~
CF2CF2cFcF2 (OCF2fF)n - OCF2CF2COOH
where n is an integer of 0 to about 3.
~ ' . --";~' ' - . :
.. .. . ~ . ,: .. ... .... :. .: ~
... . .. ... .. . . . .
C-6958 Preferred materials for the casings of the present invention are perfluorosulfonic acid resins comprised of copolymers of a perfluoroolefin and a fluorosulfonated perfluorovinyl ether. Suitable perfluoroolefins include tetrafluoroethylene, hexafluoro-propylene, octafluorobutylene and higher homologues.
Preferred perfluoroolefins include tetrafluoroethylene and hexafluoropropylene, with tetrafluoroethylene being particularly preferred. The fluorosulfonated perfluoro-vinyl ethers are compounds of the formula FSO2CFRCF2O[CFYCF2O]n CF=CF2(I), where R is a radical selected from the group consisting of fluorine and per-fluoroalkyl radical having from 1 to about 8 carbon atoms, Y is a radical selected from the gxoup consisting of fluorine and trifluoromethyl radicals; and n is an integer of 0 to about 3. Illustrative of such fluorosulfonated perfluorovinyl ethers are:
FSO2cF2cF20cF=cF2 ' Fso2cF2cF2ocF(cF3)cF2ocF(cF3)cF2ocF=cF
FSO2CF2CF2CF2CF2OCF(CF3)CF2OCF=CF2, and FS02CF2CF20CF(CF3)CF20CF=CF2.
Preferred sulfonated perfluorovinyl ethers are those of formula I above in which R is fluorine and Y is trifluoromethyl.
..:
-10- , , ' '' , ~, ' Y~ 7 C-6958 A particularly preferred sulfonated perfluoro-vinyl ether is that of the formula:
FSO2CF2CF2OCF(CF3)CF2OCF=CF2, perfluoro[2-(2-fluorosulfonylethoxy) propyl vinyl ether].
The sulfonated perfluorovinyl ethers are prepared by methods described in U.S. Patent No. 3,041,317 to Gibbs et al, 3,282,875 to Connolly et al, 3,560,568 to Resnick, and 3,718,627 to Grot.
The copolymers employed in the cationic perm-selective membrane of the present invention are prepared by methods described in U.S. Patent Nos. 3,041,317 to Gibbs et al, 3,282,875 to Connolly et al, and 3,692,569 to Grot.
The solid fluorocarbon polymers are prepared by copolymerizing the perfluoroolefin, for example, tetra-fluoroethylene with the sulfonated perfluorovinyl ether followed by converting the FSO2 group to SO3H or a sul-fona~e group (such as an alkali metal sulfonate) or a mixture thereof. The equivalent weight of the perfluoro-carbon copolymer ranges from about 900 to about 1600, and preferably from about 1100 to about 1500. The equivalent - weight is defined as the average molecular weight per ., .
sulfonyl group. ~ ;;
.... ..
. . . ..... ,: ~ . - ,,~ .. . : : :
. - ,: , .: -. . . . ~, ; 7 A particularly preferred cation permselective membrane is a perfluorosulfonic acid resin composite membrane produced by E. I. DuPont de Nemours and Co. and sold Commercially under the trademark "NAFION".
Also suitable as a casing is a commercially available material containing a stable perfluorinated compound which is sold by W. L. Gore and Associates, Inc., Elkton, Maryland, under the trademark~"GORE-TEX".
Casings of the present invention have a closed end, an open en~, and two closed sides. At least one closed side has a tab portion which is adjacent to the open end. The tab portion is flexible and can be turned or twisted to provide a substantially flat surface on which clamping means can be used to effectively seal the casings along the upper and lower edges.
The closed end of the casing may be formed by folding a section of the material or by appropriately sealing two sections of material. A major portion of the closed sides has a substantially linear seal. A
tab portion has a seal which is angular to the seal on the major portion. In addition, the seal on the tab portion is contiguous with the seal on the major portion sotthat the casing is leakproof along the sides. AS ~:
illustrated in Figures 1, 3-4, and 6, the angle on the seal on the tab may be any suitable one, for example, an external angle of from about 60 to about 120, preferably from about 80 to about 100. The internal angle is thus . . ~
. . .' C-6958 from about 300 to about 240, and preferably from about 280C to about 260. As illustrated in Figure 3, the external angle is measured from a line which passes through or is parallel to the substantially linear seal along the major portion of the closed sides. The length of the tab portion is any suitable one which will provide a tab which can be twisted or turned so as to provide a substantially flat surface for sealing purposes.
For example, tab portions which have a length of from about l to about 8, and preferably from about 2 to about 6 inches are satisfactory. Any suitable width may be used for the tab portions.
To provide a casing with suitable properties as a separator and also with suitable mechanical proper-ties, it may be desirable, as shown in the embodiment ;
illustrated in Figure 4, to employ two different materials in ~orming the casing. The central section, which serves primarily as the separator during electrolysis has attached along at least one edge a strip of material having desirable sealing properties and mechanical properties. The strip or border section forms the closed side including the tab and is attached to the central portion, for example by heat sealing, as illustrated in Figures 4-5. Each strip is then sealed to itself to form a closed edge, the seal being substantially linear along the major portion of the side and angular along the tab portion. The tab can be pre-cut or its portion can be formed ; . . . . , , ... : - : --. . - . ~ : , . : .
. ... ..
. . : - . , , . ;. .
' . . ~ .
; 7 C-6958 by cutting the material along the outside of the angular seal to separate the major portion from the tab portion.
While it is preferred to have a tab portion on each of the closed edges, a suitable seal can be obtained by providing a tab on one closed side and sealing the other closed side, for example, by the clamping method described in U.S. Patent No. 3,980,544, issued to J. O. Adams, K. E. Woodard, Jr., and S. J. Specht.
In the method of forming the casing of the present invention, it is preferred to seal the materials by heat sealing. For example, where the casing is formed of a perfluorosulfonic acid resin, heat sealing temperatures of from about 50 to about 360 C., preferably from about 100 to about 300 C. are quite suitable. Sealing pressures which may be employed include those of from about 1 to about lO Kg/cm2, and preferably from about 2 to about 6 Kg/cm2. Using these temperatures and pressures, suitable dwell times during sealing include those of from about 1 to about lO seconds, preferably from about 2 to about 6 seconds.
The present invention is further illustrated by the following examples.
Two sheets of a perfluorosulfonic acid membrane material (E. I. DuPont de Nemours' NAFION~ 427) were cut to provide a tab as illustrated in Figure 1. NAFION~
427 is a homogeneous film 7 mils thick of 1200 equivalent weight perfluorosulfonic acid resin laminated with a T-12 fabric of polytetrafluoroethylene. Two edges of the sheets were heat sealed at a temperature of 260 C., a pressure of 3.0 Kg/cm2 and a dwell time of 4.5 seconds on a thermal impulse heat sealing machine (Vertrod Inc., Brooklyn, New York) to form a closed end. The sheets were then sealed linearly along each side up to the edge of the tab using the same heat sealing conditions as above. A
heat seal was then applied to the tab portion at an angle of about 90 from the linear seal along each side.
' The seal was applied so that it interconnected with the linear seal along the major portion of the side edge.
The tab portion was approximately 3 inches long. The casing was installed on an electrode used in a cell for the electrolysis of sodium chloride in the production of chlorine and sodium hydroxide. To provide a flat surface for sealing a casing along the top and bottom edges, the tabs were twisted and a clamp applied, as shown in Figure 9. During electrolysis, the casing was found to be leak-proof and expanded or contracted with changes in cell operating conditions without placing a detrimental -mechanical stress on the separator material. -,'~, .
--1 5-- , .
' ' : . ,' . ' , ' .': ' .. . ...
-. : : ,, . : :
A casing o~ the type illustrated in Figures 1-3 was fabricated starting with a sheet of a perfluoro-sulfonic acid membrane material (E. I. DuPont de Nemours' NAFION~ 391). NAFION~ 391 is a composite film having a layer 1 mil thick of 1500 equivalent weight perfluoro-sulfonic acid resin bonded to a layer 4 mils thick of 1100 equivalent weight perfluorosulfonic acid resin with the film being laminated to a T-9OOG fabric of polytetra-fluoroethylene. Along the top edge and bottom edges -of this sheet two strips of a second perfluorosulfonic acid membrane material (NAFION~ 427) were heat sealed at a temperature of 260 C., a pressure of3.0 Kg/cm2 and a dwell time of 4.0 seconds, employing the heat sealing apparatus used in Example 1. The strips had been pre-cut to provide a tab adjacent to the end which would serve as the open end. The sheet was folded to form the closed end. The strips were then sealed together linearly along the top edge and along the bottom edge. The tab was then sealed to interconnect with the linear seals and at an angle of about 90 from the linear edge. These seals were made at the temperature and pressure employed above with a dwell time of 4.5 seconds. The casing fabricated with the border strips provided tabs of a material having superior mechanical stress properties to that used for the body of the casing.
.
For years commercial diaphragm cells have been used for the production of chlorine and caustic soda which employed a deposited fiber diaphragm, usually asbestos. While quite satisfactory for producing chlorine, the caustic soda was of a relatively low concentration and contained considerable amounts of undesired sodium chloride.
Recently materials have been produced which may be employed as diaphragms to produce caustic soda of increased concentration with significantl~ reduced sodium chloride content. These materials, having ion exchange properties, are produced from one or a combination of polymeric materials. The materials may be fabricated in the form of continuous sheets to extend over a group of electrodes. They may also be produced in the form of a casing which is attached to individual electrodes. It is important that the attachment of the fabricated diaphragms be accomplished in a manner which will effectively seal the diaphragm to prevent undesired leakage into or out of the electrode compartment. Leakage resulting from poor ',,' ~' .
~ -2-. - ' '` ~
.
, .
- . . . : ,, : ~ , .
. . ~ . : .
: . ' : :
~L$3~
~-6958 seals along seams or joints can result in a substantial reduction in current efficiency.
It is known in the prior art to attach fabri-cated diaphragms, for example, by means of clamps or expandable retainers. U.S. Patent No. 1,797,377 employs clamps having offset claws which straddle two ends of the diaphragm covered electrode, pinching them together and pressing the edges between the clamp and a support plate. This method does not effectively seal the area ~10 across the top of the electrodes and requires the diaphragm be separately clamped to each electrode with no coopera-tion between adjoining clamps.
Flexible retainers are employed to secure a diaphragm in U.S. Patent No. 3,878,082 where a U-shaped compressible retainer is used in combination with a crescent-shaped expansible retainer. The crescent-shaped retainer is placed over the diaphragm in the area between adjacent cathodes so that one end extends over a portion of one cathode and the other end covers a portion of the adjacent cathode. The U-shaped retainer is placed on top of the cathode so that it clamps down over one end each of two adjacent crescent-shaped retainers.
~' ' . .
. . .
,, : ' U.S. Patent No. 3,980,544 discloses securing a fabricated diaphragm covering electrodes using clamps which seal an adjoining edge of each of two adjacent diaphragms.
The clamps are thus positioned between adjacent electrodes, with a pair of clamps being required for each electrode.
While the clamps satisfactorily seal the open ends of the diaphragm, it is desirable to improve the ease of sealing the diaphragm along the top and bottom edges.
Therefore, it is an object of the present invention to provide a casing for enclosing an electrode which provides a perimeter in the form of a flat plane.
Another object of the present invention is to provide a casing for enclosing an electrode which allows the use of simplified methods of clamping.
These and other objects of the present invention are accomplished in a casing for a substantially rectangular electrode for a diaphragm-type electrolytic cell, the casing comprising a closed end, an open end, and two closed sides, at least one of the closed sides having a major portion and a tab portion, said tab ~ -: portion being adjacent to the open end.
The novel casing of the present invention is formed by a method which comprises:
a) forming a closed end of the casing, and ;~ b) forming two closed sides of the casing, at least one of the closed sides having a `~
major portion and a tab portion, where the tab portion is adjacent to the open end, by ''~: ' .:
:' , ' .
'~ .
' . ,' : ~' . .
Lt~"'~
C-6958 applying a substantially linear seal to the major portion, sealing the tab portion, the seal being at an angle to that of the seal on the major portion, with the seal on the tab portion being contiguous with the seal on the major portion.
Accompanying Figures 1-9 illustrate the novel casing of the present invention. Corresponding parts have the same numbers in all Figures.
Figure 1 represents a side view in perspective of one embodiment of the casing of the present invention.
Figure 2 illustrates a rear view of the casing of Figure 1.
Figure 3 shows details of one tab on the casing of Figure 1.
; Figure 4 depicts a side view in perspective of another embodiment of the casing of the present inven~
tion.
Figure 5 represents a front view of a partial section of the casing of Figure 4.
Figure 6 illustrates a side view in perspec-tive of an additional embodiment of the casing of the present invention.
Figure 7 illustrates a front view of a pair of -electrodes covered by the casing of the present invention.
. . ' . .
'' ' -.
. . .
C-6958 Figure 8 represents a side view of one elec-trode of Figure 7.
Figure 9 illustrates a partial section of Figure 7 taken along line 9-9.
Figures 1-3 illustrate one embodiment of the present invention in which casing 10, made of a flexible material has a closed end 12 and an open end 14 and tabs 16 form the upper and lower extremities of open end 14.
Closed edges 18 are formed by providing substantially ~ ~ .
linear seals which terminate at tabs 16. Tabs 16 are sealed along edges 20 adjacent to closed edges 18 by providing a seal which is angular to the seals of closed ~ :
edges 18. For the embodiment of Figures 1-3, the external angle of the seal is about 90, as ~est illus- ~ .
~ trated in Figure 3.
: Figures 4 and 5 show another embodiment of the casing of the present invention in which casing 10 ~ :
is formed by bonding border sections 22 to central section 24 where different materials are employed for the border sections and the central section. Closed edges 18 and tabs 16 are formed on the border section. The external angle between the seal on edge 20 of tabs 16 and the ~ :
linear seals on closed edges 18 is greater than 90.
Figure 6 represents a further embodiment of the casing 10 in which the external angle between the seal along edges 20 of tabs 16 and the seal along closed :
edges 18 Ls less than 90 ,: .~ :
:~
C-6958 Figure 7 is a front view of a pair of electrodes covered by the casing of the present invention. As shown in the side view of Figure 8, electrode 26 is enclosed by casing 10 having closed end 12. Tabs 16 are twisted and are ~overed in part by clamp 28. Clamp 28 seals tabs 16 against flange 30, for example, using bolts 38.
Clamps 28, as illustrated in Figure 9, have an upper portion 34 and a lower portion 36 which are joined ~ -by bolt 38 and seal tabs 16 against flange 30 so that it lies coplanar to backplate 40 to which flange 30 is attached, for example, by welding.
The novel casing of the present invention is comprised of a material which can be used as a porous ~-diaphragm or an ion exchange membrane in an electrolytic cell of the diaphragm type. The material should be flexible and capable of being sealed, for example, by means such as heat sealing, sewing, or by the application of sealants. Suitable materials include plastics such as polytetrafluoroethylene, polypropylene or polyvinylidene chloride; sheets or fabrics of inorganic materials such as asbestos; and ion exchange resins.
Ion exchange resins which can be used as casing materials include fluorocarbons having the units:
., , ," , .~ , . , - .
- : . -: - . . .
~ F ~ ~4~
Cm ~ M and --\CF2 ~ CF N
~ X
where m is from 2 to 10, the ratio of M to N
is sufficient to provide an equivalent weight of from 600 to 2000, and X is selected from:
(i) A, or (ii) 4OCF2 - CF~ A
Z -. ,~ .
where p is from 1 to 3 and Z is F or a perfluoroa~yl group having from 1 to 10 carbon atoms provided that in either of these cases (i) and (ii), A is a group selected from~
SO3H~
CF2SO3H, CC12SO3H . .
X'SO3H, .
03H2~ :~
P2H2 ' COOH, and X'OH
where X' is an arylene group.
. .. . . ..
~b' ~ 7 C-6958Preferred ion exchange resins are those in which X is COOH, SO3H, OCF2-CF2-SO3H, or OCF2-CF2-COOH.
Suitable casing are fabricated from perfluoro-carboxylic acid resins having the formula~
CF2CF2cFcF2 (OCF2fF)n - OCF2CF2COOH
where n is an integer of 0 to about 3.
~ ' . --";~' ' - . :
.. .. . ~ . ,: .. ... .... :. .: ~
... . .. ... .. . . . .
C-6958 Preferred materials for the casings of the present invention are perfluorosulfonic acid resins comprised of copolymers of a perfluoroolefin and a fluorosulfonated perfluorovinyl ether. Suitable perfluoroolefins include tetrafluoroethylene, hexafluoro-propylene, octafluorobutylene and higher homologues.
Preferred perfluoroolefins include tetrafluoroethylene and hexafluoropropylene, with tetrafluoroethylene being particularly preferred. The fluorosulfonated perfluoro-vinyl ethers are compounds of the formula FSO2CFRCF2O[CFYCF2O]n CF=CF2(I), where R is a radical selected from the group consisting of fluorine and per-fluoroalkyl radical having from 1 to about 8 carbon atoms, Y is a radical selected from the gxoup consisting of fluorine and trifluoromethyl radicals; and n is an integer of 0 to about 3. Illustrative of such fluorosulfonated perfluorovinyl ethers are:
FSO2cF2cF20cF=cF2 ' Fso2cF2cF2ocF(cF3)cF2ocF(cF3)cF2ocF=cF
FSO2CF2CF2CF2CF2OCF(CF3)CF2OCF=CF2, and FS02CF2CF20CF(CF3)CF20CF=CF2.
Preferred sulfonated perfluorovinyl ethers are those of formula I above in which R is fluorine and Y is trifluoromethyl.
..:
-10- , , ' '' , ~, ' Y~ 7 C-6958 A particularly preferred sulfonated perfluoro-vinyl ether is that of the formula:
FSO2CF2CF2OCF(CF3)CF2OCF=CF2, perfluoro[2-(2-fluorosulfonylethoxy) propyl vinyl ether].
The sulfonated perfluorovinyl ethers are prepared by methods described in U.S. Patent No. 3,041,317 to Gibbs et al, 3,282,875 to Connolly et al, 3,560,568 to Resnick, and 3,718,627 to Grot.
The copolymers employed in the cationic perm-selective membrane of the present invention are prepared by methods described in U.S. Patent Nos. 3,041,317 to Gibbs et al, 3,282,875 to Connolly et al, and 3,692,569 to Grot.
The solid fluorocarbon polymers are prepared by copolymerizing the perfluoroolefin, for example, tetra-fluoroethylene with the sulfonated perfluorovinyl ether followed by converting the FSO2 group to SO3H or a sul-fona~e group (such as an alkali metal sulfonate) or a mixture thereof. The equivalent weight of the perfluoro-carbon copolymer ranges from about 900 to about 1600, and preferably from about 1100 to about 1500. The equivalent - weight is defined as the average molecular weight per ., .
sulfonyl group. ~ ;;
.... ..
. . . ..... ,: ~ . - ,,~ .. . : : :
. - ,: , .: -. . . . ~, ; 7 A particularly preferred cation permselective membrane is a perfluorosulfonic acid resin composite membrane produced by E. I. DuPont de Nemours and Co. and sold Commercially under the trademark "NAFION".
Also suitable as a casing is a commercially available material containing a stable perfluorinated compound which is sold by W. L. Gore and Associates, Inc., Elkton, Maryland, under the trademark~"GORE-TEX".
Casings of the present invention have a closed end, an open en~, and two closed sides. At least one closed side has a tab portion which is adjacent to the open end. The tab portion is flexible and can be turned or twisted to provide a substantially flat surface on which clamping means can be used to effectively seal the casings along the upper and lower edges.
The closed end of the casing may be formed by folding a section of the material or by appropriately sealing two sections of material. A major portion of the closed sides has a substantially linear seal. A
tab portion has a seal which is angular to the seal on the major portion. In addition, the seal on the tab portion is contiguous with the seal on the major portion sotthat the casing is leakproof along the sides. AS ~:
illustrated in Figures 1, 3-4, and 6, the angle on the seal on the tab may be any suitable one, for example, an external angle of from about 60 to about 120, preferably from about 80 to about 100. The internal angle is thus . . ~
. . .' C-6958 from about 300 to about 240, and preferably from about 280C to about 260. As illustrated in Figure 3, the external angle is measured from a line which passes through or is parallel to the substantially linear seal along the major portion of the closed sides. The length of the tab portion is any suitable one which will provide a tab which can be twisted or turned so as to provide a substantially flat surface for sealing purposes.
For example, tab portions which have a length of from about l to about 8, and preferably from about 2 to about 6 inches are satisfactory. Any suitable width may be used for the tab portions.
To provide a casing with suitable properties as a separator and also with suitable mechanical proper-ties, it may be desirable, as shown in the embodiment ;
illustrated in Figure 4, to employ two different materials in ~orming the casing. The central section, which serves primarily as the separator during electrolysis has attached along at least one edge a strip of material having desirable sealing properties and mechanical properties. The strip or border section forms the closed side including the tab and is attached to the central portion, for example by heat sealing, as illustrated in Figures 4-5. Each strip is then sealed to itself to form a closed edge, the seal being substantially linear along the major portion of the side and angular along the tab portion. The tab can be pre-cut or its portion can be formed ; . . . . , , ... : - : --. . - . ~ : , . : .
. ... ..
. . : - . , , . ;. .
' . . ~ .
; 7 C-6958 by cutting the material along the outside of the angular seal to separate the major portion from the tab portion.
While it is preferred to have a tab portion on each of the closed edges, a suitable seal can be obtained by providing a tab on one closed side and sealing the other closed side, for example, by the clamping method described in U.S. Patent No. 3,980,544, issued to J. O. Adams, K. E. Woodard, Jr., and S. J. Specht.
In the method of forming the casing of the present invention, it is preferred to seal the materials by heat sealing. For example, where the casing is formed of a perfluorosulfonic acid resin, heat sealing temperatures of from about 50 to about 360 C., preferably from about 100 to about 300 C. are quite suitable. Sealing pressures which may be employed include those of from about 1 to about lO Kg/cm2, and preferably from about 2 to about 6 Kg/cm2. Using these temperatures and pressures, suitable dwell times during sealing include those of from about 1 to about lO seconds, preferably from about 2 to about 6 seconds.
The present invention is further illustrated by the following examples.
Two sheets of a perfluorosulfonic acid membrane material (E. I. DuPont de Nemours' NAFION~ 427) were cut to provide a tab as illustrated in Figure 1. NAFION~
427 is a homogeneous film 7 mils thick of 1200 equivalent weight perfluorosulfonic acid resin laminated with a T-12 fabric of polytetrafluoroethylene. Two edges of the sheets were heat sealed at a temperature of 260 C., a pressure of 3.0 Kg/cm2 and a dwell time of 4.5 seconds on a thermal impulse heat sealing machine (Vertrod Inc., Brooklyn, New York) to form a closed end. The sheets were then sealed linearly along each side up to the edge of the tab using the same heat sealing conditions as above. A
heat seal was then applied to the tab portion at an angle of about 90 from the linear seal along each side.
' The seal was applied so that it interconnected with the linear seal along the major portion of the side edge.
The tab portion was approximately 3 inches long. The casing was installed on an electrode used in a cell for the electrolysis of sodium chloride in the production of chlorine and sodium hydroxide. To provide a flat surface for sealing a casing along the top and bottom edges, the tabs were twisted and a clamp applied, as shown in Figure 9. During electrolysis, the casing was found to be leak-proof and expanded or contracted with changes in cell operating conditions without placing a detrimental -mechanical stress on the separator material. -,'~, .
--1 5-- , .
' ' : . ,' . ' , ' .': ' .. . ...
-. : : ,, . : :
A casing o~ the type illustrated in Figures 1-3 was fabricated starting with a sheet of a perfluoro-sulfonic acid membrane material (E. I. DuPont de Nemours' NAFION~ 391). NAFION~ 391 is a composite film having a layer 1 mil thick of 1500 equivalent weight perfluoro-sulfonic acid resin bonded to a layer 4 mils thick of 1100 equivalent weight perfluorosulfonic acid resin with the film being laminated to a T-9OOG fabric of polytetra-fluoroethylene. Along the top edge and bottom edges -of this sheet two strips of a second perfluorosulfonic acid membrane material (NAFION~ 427) were heat sealed at a temperature of 260 C., a pressure of3.0 Kg/cm2 and a dwell time of 4.0 seconds, employing the heat sealing apparatus used in Example 1. The strips had been pre-cut to provide a tab adjacent to the end which would serve as the open end. The sheet was folded to form the closed end. The strips were then sealed together linearly along the top edge and along the bottom edge. The tab was then sealed to interconnect with the linear seals and at an angle of about 90 from the linear edge. These seals were made at the temperature and pressure employed above with a dwell time of 4.5 seconds. The casing fabricated with the border strips provided tabs of a material having superior mechanical stress properties to that used for the body of the casing.
.
Claims (19)
1. A casing for a substantially rectangular electrode for a diaphragm-type electrolytic cell, comprised of a porous diaphragm or ion exchange membrane, said casing comprising a closed end, an open end, and two closed sides, at least one of said closed sides having a major portion and a tab portion, said tab portion being adjacent to said open end, and said tab being twistable to provide a substantially flat surface for sealing.
2. The casing of Claim 1 in which said tab portion has a length of from about 1 to about 8 inches.
3. The casing of Claim 2 in which said casing is comprised of a plastic selected from the group consisting of polytetrafluoroethylene, polypropylene or polyvinylidene chloride.
4. The casing of Claim 2 in which said casing is comprised of copolymers of a perfluoroolefin and a fluorosulfonated perfluoro-polyvinyl ether where said copolymers have an equivalent weight of from about 900 to about 1600.
5. The casing of Claim 4 in which said tab portion has a length of from about 2 to about 6 inches.
6. The casing of Claim 5 in which said copolymers have an equivalent weight of from about 1100 to about 1500.
7. The casing of claim 2 in which said casing is comprised of a central section comprised of a first material, at least one border section attached to said central section, said border section forming a closed side and being comprised of a second material.
8. The casing of claim 7 in which said first material is a copolymer of a perfluoroolefin and a fluorosulfonated perfluoro-polyvinyl ether where said copolymer has an equivalent weight of from about 900 to about 1600.
9. The casing of claim 7 in which said second material is a copolymer of a perfluoroolefin in and a fluorosulfonated perfluoro-polyvinyl ether where said copolymer has an equivalent weight of from about 900 to about 1600.
10. A method of forming a casing adapted to cover a substantially rectangular electrode, said casing being comprised of a flexible material suitable for use as a separator in a diaphragm-type electrolytic cell for the electrolysis of alkali metal chlorides, said casing having, a closed end, two closed sides and an open end, said method comprising:-a) forming a closed end of said casing, and b) forming two closed sides of said casing, at least one of said closed sides having a major portion and a tab portion, where said tab portion is adjacent to said open end, by applying a substantially linear seal to said major portion, sealing said tab portion to provide a further seal which is at an angle to said linear seal of said major portion; with said further seal on said tab portion being contiguous with said linear seal on said major portion.
11. The method of Claim 10 in which said closed sides are formed by heat sealing.
12. The method of Claim 11 in which the external angle between said seal on said tab portion and said seal on said major portion is from about 60 to about 120 degrees.
13. The method of Claim 10 in which the length of said tab portion is from about 1 to about 8 inches.
14. The method of Claim 10 in which said closed end is formed by folding a section of said material.
15. The method of claim 10 in which said casing is formed from two sheets of said material, said closed end being formed by sealing said sheets along one end.
16. The method of claim 12 in which said ex-ternal angle between said seal on said tab portion and said seal on said major portion is from about 80 to about 100 degrees.
17. The method of claim 11 in which said casing is comprised of a perfluorosulfonic acid resin and said sides are formed by heat sealing at a temperature of from about 50° to about 360° C., a pressure of from about l to about 10 Kg/cm2 and a dwell time of from about l to about 10 seconds.
18. The method of claim 17 in which said heat sealing is conducted 2. a temperature of from about 100° to about 300° C., a pressure of from about 2 to about 6 Kg/cm2, and a dwell time of from about 2 to about 6 seconds.
19. The casings of claim 2 in which said casing is comprised of perfluorocarboxylic acid resins having the formula:
n - OCF2CF2COOH
where n is an integer of 0 to about 3.
n - OCF2CF2COOH
where n is an integer of 0 to about 3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US77241277A | 1977-02-28 | 1977-02-28 | |
| US772,412 | 1977-02-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114777A true CA1114777A (en) | 1981-12-22 |
Family
ID=25094986
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA291,017A Expired CA1114777A (en) | 1977-02-28 | 1977-11-16 | Sealed casing for diaphragm cell having closed end and closed sides |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS53106679A (en) |
| AU (1) | AU3097377A (en) |
| BE (1) | BE864400A (en) |
| BR (1) | BR7708418A (en) |
| CA (1) | CA1114777A (en) |
| DE (1) | DE2808556A1 (en) |
| FR (1) | FR2381837A1 (en) |
| IT (1) | IT1090946B (en) |
| NL (1) | NL7713138A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2121352B (en) * | 1982-05-25 | 1986-03-19 | Chlorine Eng Corp Ltd | Bonding of cation exchange membrane |
-
1977
- 1977-11-16 CA CA291,017A patent/CA1114777A/en not_active Expired
- 1977-11-25 AU AU30973/77A patent/AU3097377A/en active Pending
- 1977-11-29 NL NL7713138A patent/NL7713138A/en not_active Application Discontinuation
- 1977-12-14 IT IT52210/77A patent/IT1090946B/en active
- 1977-12-16 FR FR7738147A patent/FR2381837A1/en not_active Withdrawn
- 1977-12-19 BR BR7708418A patent/BR7708418A/en unknown
-
1978
- 1978-01-18 JP JP417378A patent/JPS53106679A/en active Pending
- 1978-02-28 DE DE19782808556 patent/DE2808556A1/en active Pending
- 1978-02-28 BE BE185544A patent/BE864400A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FR2381837A1 (en) | 1978-09-22 |
| NL7713138A (en) | 1978-08-30 |
| JPS53106679A (en) | 1978-09-16 |
| BR7708418A (en) | 1978-09-12 |
| IT1090946B (en) | 1985-06-26 |
| DE2808556A1 (en) | 1978-08-31 |
| AU3097377A (en) | 1979-05-31 |
| BE864400A (en) | 1978-08-28 |
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| MKEX | Expiry | ||
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