CA1159391A - Thermoplastic polymer electrolysis diaphragm impregnated with siliceous composition - Google Patents
Thermoplastic polymer electrolysis diaphragm impregnated with siliceous compositionInfo
- Publication number
- CA1159391A CA1159391A CA000333779A CA333779A CA1159391A CA 1159391 A CA1159391 A CA 1159391A CA 000333779 A CA000333779 A CA 000333779A CA 333779 A CA333779 A CA 333779A CA 1159391 A CA1159391 A CA 1159391A
- Authority
- CA
- Canada
- Prior art keywords
- porous diaphragm
- fabric
- layer
- diaphragm
- support fabric
- 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
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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
- C25B13/04—Diaphragms; Spacing elements characterised by the material
- C25B13/05—Diaphragms; Spacing elements characterised by the material based on inorganic materials
- C25B13/07—Diaphragms; Spacing elements characterised by the material based on inorganic materials based on ceramics
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Chemical Or Physical Treatment Of Fibers (AREA)
Abstract
C-7476 DIAPHRAGMS FOR USE IN THE ELECTROLYSIS OF ALKALI METAL CHLORIDES ABSTRACT OF THE DISCLOSURE A diaphragm for use in the electrolysis of aqueous solutions of ionizable compounds in electrolytic diaphragm cells is comprised of a support fabric impregnated with particles of a siliceous composition having the formula: (X)m(Si)p(O)q(H)r ? nH2O wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al, Zn and mixtures thereof; p is a number from 1 to about 16; m is zero to about p; q is a number from 2 to about 5p + r; r is zero to about 4p; and n is zero to about 30. The siliceous compositions are capable of undergoing hydration when in contact with at least one of the ionizable compounds in the electrolytic cell. The diaphragms are physically and chemically stable, provide reduced cell voltages during operation of the cell and have increased operational life.
Description
~ 1 5939 ~
DIAPHRAG~S FOR USE IN THE
EI.ECTROLysIs OF ALKALI METAL CHLORIDES
This invention relates to diaphragm-type electrolytic cells for the electrolysis of aqueous solutions of ionizable compounds. More particularly, this invention rela~es to novel diaphragms for elec-trolytic diaphragm cells.
In an electrolytic diaphragm cell, the diaphragm represents the cell component which permits the cell to operate by producing, where the electrolyte is an aqueous solution of anionizable compound,products such as chlorine, alkali metal hydroxide, hydrogen and oxygen at current efficiencies which are high enough to be economically viable. The separation properties, as indicated by the current efficiencies, can be increased by, for example, increasin~ the thickness or density of the diaphragm. These changes, however, usually result in an increase in the electrical res:is-tance of the diaphragm, as indicated~ for example, by an increase in the voltage coefficient~ Fa~orable ; cell economic~ d~pend on increasin~ or main~aining at a high le~el the current ef~iciency while restraining o~ minimi~in~ -the increase in voltage coefficient.
.
1 ~93g ~ , For years commercial diaphragm cells have been used for the production of chlorine and alkali metal hydroxides, hydrogen and oxygen which employed a porous diaphragm of asbestos fibers. In employing asbestos diaphragms, it is thought that the effective diaphragm is a gel layer formed within the asbestos mat. This gel layer is formed by the decomposition of the asbestos fibers in contact with the electrolytes in the cell. When electrolyzing aqueous salt solutions, in addition to undergoing chemical decomposition during ; operation of the cell, the asbestos fibers also suffer from dimensional instability as they are distorted by dissolution swelling. Porous asbestos diaphragms while satisfactorily producing, for example, chlorin~, and alkali metal hydroxide solutions, have limited cell life and once removed from the cell, cannot be re-used. Further,asbestos has now been identified by the Environmental Protection Agency of the U.S.
Government as a health hazard.
:l l5~3~ ~
.Therefore there is a need for diaphragms having increased operating life while employing materials which are durable as well as inexpensive.
I~ is an object of the present invention to p~ovide a diaphragm having increased stability and a longer operational life when employed in the electrolysis of aqueous solutions of ionizable compounds.
Another object of the present invention is the use of ecologically acceptable non-polluting materials in diaphragm compositions.
Yet another object of the present invention i5 a diaphragm having reduced resistance to electric current.
An additional object of the present invention is a diaphragm having support materials which are chemically and physically stable during electrolysis.
A still further object of the present inven-tion is a diaphragm which can be handled easily during installation in and removal from the electrolytic cell.
These and other objects of the invention will be apparent Erom the following description of the invention~
~ ~59391 These and other objects of the invention are accomplished in a porous diaphragm for an electrolytic cell for the electrolysis of aqueous solutions of ionizable compounds which comprises a support fabric ~mpregnated with particles of a siliceous composition having the formula:
(X~m(Si~p(o~q(.H)r nH2 wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, ~1, Zn, and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
q is a number from 2 to about 5p + r;
r is zero to about 4p; and n is zero to about 30, the siliceous compositions being capable of undergoing hydration when in contact with at least one of the ionizable compounds in the electrolytic cell.
~ ~5~39~
Accompanying FIGURES 1-9 illustrate the novel diaphrac3m of the present invention.
FIGURE 1 illustrates a perspective view of one embodiment of the cliaphragm of the present invention.
FIGURE 2 shows a perspective view of one em~odiment of the diaphragm of the present in~ention suitable for use with a plurality of electrodes.
FIGURE 3 depicts a perspect:ive view o~ an additional embodiment vf the diaphrac3m of the present invention for use with a plurality of electrodes.
FIGURE 4 i5 a photomicrograph of a cross section of one embodiment of the support fabric employed in the diaphragms of the present invention (magnified 30 times).
FIGURE 5 is a photomicrograph of a planar cross section of an embodiment of the support fabric having fiber bundles (magnified 30 times).
FIGURE 6 is a cross section of FIGURE 5 taken along line 6-6.
FIGURES 7-9 illustrate a cross section of several embodiments of the support fabric.
FIGURE 1 illustrates a diaphragm of the present invention suitable ~or covering a cathode~
Diaphragm 1, comprised o~ fabric, has end portions 10 attached, for example, by sewing, to diaphragm body 12. Diaphragm body 12 is a hollow rectangle which is mounted on a cathode (not shown~ so that it surrounds the cathode on all sides. End portions 10 have openings 1~ which permit end portions 10 to be attached to the cell walls ~not shown)~
1 1 ~939 ~
FIGURE 2 depicts a diaphragm suitable for use with a plurality of electrodes. ~abric panel 20 has fabric casings 22 attached substantially perpendicular to the plane of panel 20~ Fabric casings 22 are suitably spaced apart from each other and are attached to fabric panel 20, for example, by sewing. Fabric panel 20 has openings (not shownl corresponding to the area where fabric casings 22 are attached to permit the electrodes to be inserted in fabric casings 22.
FIGURE 3 illustrates another embodiment o the diaphragm of the present invention. U-shaped fabric panel 30 has end portions 32 for attachment to the cell walls ~not shown~. Fabric casing 34 is attached to U-shaped fabric panel 30, for example, by sewing. An opening (not shown) at the bottom of fabric casing 34 permits the diaphragm to be instalied on a vertically positioned electrode.
FIGURE 4 shows a cross section of a poly-tetrafluoroethylene felt support fabric 40 having fibers 42 randomly oriented.
The embodiment of the support fabric 40 illustrated in FIGURE 5 has, at regular intervals, f~ber-bundles 44 which are-substantially perpendicular-to t~e plane of the outer surface of fabric 40. Fiber bundles 44 penetrate the entire width of support Eabric 40. The support fabr.ic is a polytetrafluoroethylene elt ~abric where the magnification shown in the photo-micrograph is 3~ times the original.
3 9 Jl FIGURE 6 illustrates fiber bundles 44 found in a cross section of FIGURE 5 alon~ line 6-6 where the magnification is 120 times~
Portra~ed in FIGURE 7 is an embodiment of support fabric 40 in which fiber bundles 44 only partially penetrate the support fabric leaving section 46 having fibers gPnerally oriented in a vertical direction.
Laye~ed support fabric 50, shown in FIGURE 8, has as a ~irst layer 52, a highly porous fabric. Con-tiguous to first layer 52 is second layex 54 having fiber bunclles 44 on a diagonal to the generally vertically oriented fibers 42.
The embodiment of layered support fabrics 50 illustrated in FIGURE 9 has first layer 52 of a highly porous fabric non-adjacent to second layer 54.
Second layer 54 has fiber bundles 44 partially pene-trating second layer 54. Section 46, having fibers generally oriented in a vertical direction is adjacent to first layer 52.
More in detail, the novel diaphragms of the present invention comprise a support fabric wh.ich is impregnated with the siliceous composition.
A fabric is employed which is produced from materials which are che~ically resistant to and dimen-sionally stable in the gases and electrolytes present in the electrolytic cell. The ~abric support is substantially non-swelling, non-conducting and non-dissolving during operat:ion of the electxolytic 3a cell. The fab.r.ic support is also non-rigid and is su~iciently ~lexible to be shaped to the contour o~` an electrode i~ desired.
~ ~5g39 1 Suitable fabric supports are those which can be handled easily without suffering ph~sic~l damage, This includes handling before and after they have been impregnated witn the active component~ Suitable support fabrics can be removed ~rom the cell following elec-trolysis, treated or repaired, if necessary,and replaced in the cell for further use without suffering substan-tial degradation or damage.
Support fabrics having uniform permeability throughout the fabric are quite suitable in diaphrayms of the present invention. FIGURE 4 illustrates support fabrics of this t~pe~ Prior to impregnation with the siliceous composition of Formula I, these support fabrics may have a permeability to gases such as air of, for example, from about 5 to about 500, preferably from about 20 to about 2ao and more preferably from about 30 to about 100 cubic feet per minute per square foot of fabric. Uniform permeability throughout thP support fabric is not, however, re~uired and it may be advan-tageous to have a greater permeability in one portion of the support fabric. When impregnated, this portion may be positioned closest to, for example, the anode in the electrolytic cell. Layered structures thus may be employed as support fabrics having, a first layer which ~hen the diaphragm is installed in the cell, will be in contact ~ith the anolyte, and a second layer which will be in contact with the catholyte. The first la~er may have, ~or example, an aix permeahility of, ~o~ example, ~rom about 100 to about 500 cubic eet per 3a minute. The ~lrst layer may be, for ex~mple, a net having openings which are sli~htly larger than the par-ticle si~e o~ the acti~e ingredient with which it is i~pregnated~
~ 15~39 ~
The second layer, in contact with the catholyte when installed in the cell may, for example, have an air permeability o~ fxom a~out 5 to abQut 100 cubic feet per minute~ For the purpose of using a s selected size of active component containing silica~
the layered support fabric can be produced by attaching, for example, a net to a felt fabric~ The net permits the particles to pass through and these are retained on the felt~
Permeability values for the support fabric may be determined, for example, using American Society for Testing Materials Method D737-75, Standard Test Method for Air Permeability of Textile Fabrics.
The support fabrics may be produced in any suitable manner. Suitable forms are those which promote absorption of the active component including sponge-like fabric forms. Preferred forms of support fabric are felt fabrics, i.e., fabrics having a high degree of -interfiber entanglement or interconnec-tion which are usually non-woven. When employing felt as a support fabric, fluids passing through the fabric take a tortuous route through the randomly distributed, highly entangled fibers. The permeability of these abrics ,; i~ OL a general nature, i.e., non-linear and non-controlled.
Permeability of these support fabrics may be increased by means which alter the structure of the support fabric~ As illustrated in FIGURES 5-9, the support fabrics ha~e been modified by providing means for linear permeability, for example,fiber bundles distribuked throughout the support Eabric~ Spaced apart at regular or irregular in-tervals, tha Eiber bundles improve permeabilit~ by providing regions through which ~he flow of fluids such as alkali metal chloride brines is suhstantially laminar. Laminar flow reduces tur-hulence or mixing of fluids in the xegion and results in a homogeneous fluid throughout the region.
""
~ 15~3~
To provide fiber bundles in the support fabric, the fabric is, for example, needled or punched at intervals along the surface of the fabric.
The depth of the needling may be controlled to provide fiber bundles which penetrate through the fabric, as shown in FIGURES 5-6 and 8, or fiber bundles which only partially penetrate the fabric, as illustrated in FIGURES 7 and ~.
Fiber bundles may ~2 positioned at any suitable angle to the plane of the outer surface of the support fabric. For example, the angle of the fiber bundles may be from about 90 to about 45 degrees from the vertical and preferably from about 90 to about 6 a degrees.
Fiber bundles contain a plurality of fibers, for example, up to several hundred fibers may comprise a bundle. The bundles are distributed throughout the support fabric, which may contain several hundred bundles per square inch of fabric.
The fi~er bundles provide linear permeability which substantially increases the permeability of the support fabric. Any suitable amount of total per-meability of the support fabric may be provided by the inclusion of fiber bundles. For example~ fiber bundles may provide from about 15 to about 70 percent of the permeahility of the support fabric~ Preferably, fiber bundles provide from about 20 to about 50 and more preferably ~rom about 30 to about 40 percent of the permeability o~ the support fabric.
~n addltion to improving the permeabilityr the ~iber bundles facili-tate the impregnation of the support ~abric with the siliceous compo~ition and aid in pro-viding a more uni~orm distribution of the siliceous composition within the support Eabric.
A ~urther advantage of the presence of fiber bundles in the support fabric is that electrical resistance is reduced.
3 ~ ~
Materials which are suitable for use as support fabrics include thermoplastic materials such as polyolefins which are polymers of olefins having from about 2 to about 6 carbon atoms in the primary chain as well a~ their chloro- and fluoro- derivatives.
Examples include polyethylen~, polypropylene, polybutylene, polypentylene, polyhexylene, polyvinyl chloride, pol~Jinylidene chloride, polytetrafluoro--ethylene, ~luorinated ethylene-propylene (FEP), polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride and copolymers of ethylene~
chlorotri~luoroethyiene.
Preferred olefins include the chloro- and fluoro- derivatives such as pol~tetrafluoroet~ylene, lS fluorinatea ethylene-propylene (FEP), polychlorotri-fluoroethylene, polyvi~yl fluoride, and polyvi~ylidene fluoride.
- Also suitable as support materials are fabrics of polyaromatic compounds such as polyarylene compounds.
DIAPHRAG~S FOR USE IN THE
EI.ECTROLysIs OF ALKALI METAL CHLORIDES
This invention relates to diaphragm-type electrolytic cells for the electrolysis of aqueous solutions of ionizable compounds. More particularly, this invention rela~es to novel diaphragms for elec-trolytic diaphragm cells.
In an electrolytic diaphragm cell, the diaphragm represents the cell component which permits the cell to operate by producing, where the electrolyte is an aqueous solution of anionizable compound,products such as chlorine, alkali metal hydroxide, hydrogen and oxygen at current efficiencies which are high enough to be economically viable. The separation properties, as indicated by the current efficiencies, can be increased by, for example, increasin~ the thickness or density of the diaphragm. These changes, however, usually result in an increase in the electrical res:is-tance of the diaphragm, as indicated~ for example, by an increase in the voltage coefficient~ Fa~orable ; cell economic~ d~pend on increasin~ or main~aining at a high le~el the current ef~iciency while restraining o~ minimi~in~ -the increase in voltage coefficient.
.
1 ~93g ~ , For years commercial diaphragm cells have been used for the production of chlorine and alkali metal hydroxides, hydrogen and oxygen which employed a porous diaphragm of asbestos fibers. In employing asbestos diaphragms, it is thought that the effective diaphragm is a gel layer formed within the asbestos mat. This gel layer is formed by the decomposition of the asbestos fibers in contact with the electrolytes in the cell. When electrolyzing aqueous salt solutions, in addition to undergoing chemical decomposition during ; operation of the cell, the asbestos fibers also suffer from dimensional instability as they are distorted by dissolution swelling. Porous asbestos diaphragms while satisfactorily producing, for example, chlorin~, and alkali metal hydroxide solutions, have limited cell life and once removed from the cell, cannot be re-used. Further,asbestos has now been identified by the Environmental Protection Agency of the U.S.
Government as a health hazard.
:l l5~3~ ~
.Therefore there is a need for diaphragms having increased operating life while employing materials which are durable as well as inexpensive.
I~ is an object of the present invention to p~ovide a diaphragm having increased stability and a longer operational life when employed in the electrolysis of aqueous solutions of ionizable compounds.
Another object of the present invention is the use of ecologically acceptable non-polluting materials in diaphragm compositions.
Yet another object of the present invention i5 a diaphragm having reduced resistance to electric current.
An additional object of the present invention is a diaphragm having support materials which are chemically and physically stable during electrolysis.
A still further object of the present inven-tion is a diaphragm which can be handled easily during installation in and removal from the electrolytic cell.
These and other objects of the invention will be apparent Erom the following description of the invention~
~ ~59391 These and other objects of the invention are accomplished in a porous diaphragm for an electrolytic cell for the electrolysis of aqueous solutions of ionizable compounds which comprises a support fabric ~mpregnated with particles of a siliceous composition having the formula:
(X~m(Si~p(o~q(.H)r nH2 wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, ~1, Zn, and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
q is a number from 2 to about 5p + r;
r is zero to about 4p; and n is zero to about 30, the siliceous compositions being capable of undergoing hydration when in contact with at least one of the ionizable compounds in the electrolytic cell.
~ ~5~39~
Accompanying FIGURES 1-9 illustrate the novel diaphrac3m of the present invention.
FIGURE 1 illustrates a perspective view of one embodiment of the cliaphragm of the present invention.
FIGURE 2 shows a perspective view of one em~odiment of the diaphragm of the present in~ention suitable for use with a plurality of electrodes.
FIGURE 3 depicts a perspect:ive view o~ an additional embodiment vf the diaphrac3m of the present invention for use with a plurality of electrodes.
FIGURE 4 i5 a photomicrograph of a cross section of one embodiment of the support fabric employed in the diaphragms of the present invention (magnified 30 times).
FIGURE 5 is a photomicrograph of a planar cross section of an embodiment of the support fabric having fiber bundles (magnified 30 times).
FIGURE 6 is a cross section of FIGURE 5 taken along line 6-6.
FIGURES 7-9 illustrate a cross section of several embodiments of the support fabric.
FIGURE 1 illustrates a diaphragm of the present invention suitable ~or covering a cathode~
Diaphragm 1, comprised o~ fabric, has end portions 10 attached, for example, by sewing, to diaphragm body 12. Diaphragm body 12 is a hollow rectangle which is mounted on a cathode (not shown~ so that it surrounds the cathode on all sides. End portions 10 have openings 1~ which permit end portions 10 to be attached to the cell walls ~not shown)~
1 1 ~939 ~
FIGURE 2 depicts a diaphragm suitable for use with a plurality of electrodes. ~abric panel 20 has fabric casings 22 attached substantially perpendicular to the plane of panel 20~ Fabric casings 22 are suitably spaced apart from each other and are attached to fabric panel 20, for example, by sewing. Fabric panel 20 has openings (not shownl corresponding to the area where fabric casings 22 are attached to permit the electrodes to be inserted in fabric casings 22.
FIGURE 3 illustrates another embodiment o the diaphragm of the present invention. U-shaped fabric panel 30 has end portions 32 for attachment to the cell walls ~not shown~. Fabric casing 34 is attached to U-shaped fabric panel 30, for example, by sewing. An opening (not shown) at the bottom of fabric casing 34 permits the diaphragm to be instalied on a vertically positioned electrode.
FIGURE 4 shows a cross section of a poly-tetrafluoroethylene felt support fabric 40 having fibers 42 randomly oriented.
The embodiment of the support fabric 40 illustrated in FIGURE 5 has, at regular intervals, f~ber-bundles 44 which are-substantially perpendicular-to t~e plane of the outer surface of fabric 40. Fiber bundles 44 penetrate the entire width of support Eabric 40. The support fabr.ic is a polytetrafluoroethylene elt ~abric where the magnification shown in the photo-micrograph is 3~ times the original.
3 9 Jl FIGURE 6 illustrates fiber bundles 44 found in a cross section of FIGURE 5 alon~ line 6-6 where the magnification is 120 times~
Portra~ed in FIGURE 7 is an embodiment of support fabric 40 in which fiber bundles 44 only partially penetrate the support fabric leaving section 46 having fibers gPnerally oriented in a vertical direction.
Laye~ed support fabric 50, shown in FIGURE 8, has as a ~irst layer 52, a highly porous fabric. Con-tiguous to first layer 52 is second layex 54 having fiber bunclles 44 on a diagonal to the generally vertically oriented fibers 42.
The embodiment of layered support fabrics 50 illustrated in FIGURE 9 has first layer 52 of a highly porous fabric non-adjacent to second layer 54.
Second layer 54 has fiber bundles 44 partially pene-trating second layer 54. Section 46, having fibers generally oriented in a vertical direction is adjacent to first layer 52.
More in detail, the novel diaphragms of the present invention comprise a support fabric wh.ich is impregnated with the siliceous composition.
A fabric is employed which is produced from materials which are che~ically resistant to and dimen-sionally stable in the gases and electrolytes present in the electrolytic cell. The ~abric support is substantially non-swelling, non-conducting and non-dissolving during operat:ion of the electxolytic 3a cell. The fab.r.ic support is also non-rigid and is su~iciently ~lexible to be shaped to the contour o~` an electrode i~ desired.
~ ~5g39 1 Suitable fabric supports are those which can be handled easily without suffering ph~sic~l damage, This includes handling before and after they have been impregnated witn the active component~ Suitable support fabrics can be removed ~rom the cell following elec-trolysis, treated or repaired, if necessary,and replaced in the cell for further use without suffering substan-tial degradation or damage.
Support fabrics having uniform permeability throughout the fabric are quite suitable in diaphrayms of the present invention. FIGURE 4 illustrates support fabrics of this t~pe~ Prior to impregnation with the siliceous composition of Formula I, these support fabrics may have a permeability to gases such as air of, for example, from about 5 to about 500, preferably from about 20 to about 2ao and more preferably from about 30 to about 100 cubic feet per minute per square foot of fabric. Uniform permeability throughout thP support fabric is not, however, re~uired and it may be advan-tageous to have a greater permeability in one portion of the support fabric. When impregnated, this portion may be positioned closest to, for example, the anode in the electrolytic cell. Layered structures thus may be employed as support fabrics having, a first layer which ~hen the diaphragm is installed in the cell, will be in contact ~ith the anolyte, and a second layer which will be in contact with the catholyte. The first la~er may have, ~or example, an aix permeahility of, ~o~ example, ~rom about 100 to about 500 cubic eet per 3a minute. The ~lrst layer may be, for ex~mple, a net having openings which are sli~htly larger than the par-ticle si~e o~ the acti~e ingredient with which it is i~pregnated~
~ 15~39 ~
The second layer, in contact with the catholyte when installed in the cell may, for example, have an air permeability o~ fxom a~out 5 to abQut 100 cubic feet per minute~ For the purpose of using a s selected size of active component containing silica~
the layered support fabric can be produced by attaching, for example, a net to a felt fabric~ The net permits the particles to pass through and these are retained on the felt~
Permeability values for the support fabric may be determined, for example, using American Society for Testing Materials Method D737-75, Standard Test Method for Air Permeability of Textile Fabrics.
The support fabrics may be produced in any suitable manner. Suitable forms are those which promote absorption of the active component including sponge-like fabric forms. Preferred forms of support fabric are felt fabrics, i.e., fabrics having a high degree of -interfiber entanglement or interconnec-tion which are usually non-woven. When employing felt as a support fabric, fluids passing through the fabric take a tortuous route through the randomly distributed, highly entangled fibers. The permeability of these abrics ,; i~ OL a general nature, i.e., non-linear and non-controlled.
Permeability of these support fabrics may be increased by means which alter the structure of the support fabric~ As illustrated in FIGURES 5-9, the support fabrics ha~e been modified by providing means for linear permeability, for example,fiber bundles distribuked throughout the support Eabric~ Spaced apart at regular or irregular in-tervals, tha Eiber bundles improve permeabilit~ by providing regions through which ~he flow of fluids such as alkali metal chloride brines is suhstantially laminar. Laminar flow reduces tur-hulence or mixing of fluids in the xegion and results in a homogeneous fluid throughout the region.
""
~ 15~3~
To provide fiber bundles in the support fabric, the fabric is, for example, needled or punched at intervals along the surface of the fabric.
The depth of the needling may be controlled to provide fiber bundles which penetrate through the fabric, as shown in FIGURES 5-6 and 8, or fiber bundles which only partially penetrate the fabric, as illustrated in FIGURES 7 and ~.
Fiber bundles may ~2 positioned at any suitable angle to the plane of the outer surface of the support fabric. For example, the angle of the fiber bundles may be from about 90 to about 45 degrees from the vertical and preferably from about 90 to about 6 a degrees.
Fiber bundles contain a plurality of fibers, for example, up to several hundred fibers may comprise a bundle. The bundles are distributed throughout the support fabric, which may contain several hundred bundles per square inch of fabric.
The fi~er bundles provide linear permeability which substantially increases the permeability of the support fabric. Any suitable amount of total per-meability of the support fabric may be provided by the inclusion of fiber bundles. For example~ fiber bundles may provide from about 15 to about 70 percent of the permeahility of the support fabric~ Preferably, fiber bundles provide from about 20 to about 50 and more preferably ~rom about 30 to about 40 percent of the permeability o~ the support fabric.
~n addltion to improving the permeabilityr the ~iber bundles facili-tate the impregnation of the support ~abric with the siliceous compo~ition and aid in pro-viding a more uni~orm distribution of the siliceous composition within the support Eabric.
A ~urther advantage of the presence of fiber bundles in the support fabric is that electrical resistance is reduced.
3 ~ ~
Materials which are suitable for use as support fabrics include thermoplastic materials such as polyolefins which are polymers of olefins having from about 2 to about 6 carbon atoms in the primary chain as well a~ their chloro- and fluoro- derivatives.
Examples include polyethylen~, polypropylene, polybutylene, polypentylene, polyhexylene, polyvinyl chloride, pol~Jinylidene chloride, polytetrafluoro--ethylene, ~luorinated ethylene-propylene (FEP), polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride and copolymers of ethylene~
chlorotri~luoroethyiene.
Preferred olefins include the chloro- and fluoro- derivatives such as pol~tetrafluoroet~ylene, lS fluorinatea ethylene-propylene (FEP), polychlorotri-fluoroethylene, polyvi~yl fluoride, and polyvi~ylidene fluoride.
- Also suitable as support materials are fabrics of polyaromatic compounds such as polyarylene compounds.
2 a Polyarylene compounds include polyphenylene, poly-naphthylene and polyanthracene derivatives. For example, polyarylene sulfides such as polyphenylene sulfide or polynaphthylene sulfide. Polyarylene sul~ides are well known compounds whose preparation and properties are described in the Encyclopedia of Polymer Science and_Technolo~y (In~erscience Publishers) Vol. 10, pages 653-659. In addition to the parent compounds, derivati~es having chloro-, fluoro- or alkyl suhsti~uents may be used suc~ as poly(per~luoro phenylene) sul~ide and poly(me~hylphenylene~ sul~ide.
Elabrics which are mixtures of fibers o~
polyole~ins and Ei~ers o~ polyarylene sul~ides can be ~uitably u~ed as well as layered support ~abrics in which the ~irs~ layer i5 a polyole~in such as polytetra-~luoroethylene and the second layex is a polyarylene sul~ide such as polyphenylene sulfide.
1 5~39 ~
The support fabric is impregnated with a siliceous composition having the formula:
(X)m(si~p~O)q(Hlr nH2O
wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al~ Zn, and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
~ is a number ~rom 2 to about 5p ~ r;
r is zero to about 4 p; and n is zero to about 30.
Siliceous compositions of Formula I include those in which m is a po~tive number and X is at least lS one metal from Group IIA of the periodic table. Suit-ahle examples are silicates of beryllium, magnesium, calcium, strontium or barium where the ratio of the metal to silicon is no greater than about 1:1. The compositions include magnesium-containing minerals such as sepiolites, meerschaums, augites, talcs and vermiculites; calcium-containing minerals such as wollastonite, as well as minerals such as tremoli-te having the ~ormula CaMg3lSiO3~4. Also suitable are synthetic silicates such as commercial magnesium silicatas having the approximate composition 2MgO 3SiO2 2H2O, as well as calcium silicate hydrate having the approximate composition CaO 3.5SiO2 1~8H2O.
Elabrics which are mixtures of fibers o~
polyole~ins and Ei~ers o~ polyarylene sul~ides can be ~uitably u~ed as well as layered support ~abrics in which the ~irs~ layer i5 a polyole~in such as polytetra-~luoroethylene and the second layex is a polyarylene sul~ide such as polyphenylene sulfide.
1 5~39 ~
The support fabric is impregnated with a siliceous composition having the formula:
(X)m(si~p~O)q(Hlr nH2O
wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al~ Zn, and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
~ is a number ~rom 2 to about 5p ~ r;
r is zero to about 4 p; and n is zero to about 30.
Siliceous compositions of Formula I include those in which m is a po~tive number and X is at least lS one metal from Group IIA of the periodic table. Suit-ahle examples are silicates of beryllium, magnesium, calcium, strontium or barium where the ratio of the metal to silicon is no greater than about 1:1. The compositions include magnesium-containing minerals such as sepiolites, meerschaums, augites, talcs and vermiculites; calcium-containing minerals such as wollastonite, as well as minerals such as tremoli-te having the ~ormula CaMg3lSiO3~4. Also suitable are synthetic silicates such as commercial magnesium silicatas having the approximate composition 2MgO 3SiO2 2H2O, as well as calcium silicate hydrate having the approximate composition CaO 3.5SiO2 1~8H2O.
3 '~ :~
~lso suitable are synthetic clay materials which are described, for example, in U.S. Patent Nos.
3,586,478 and 3,671,190 issued to B. S~ ~eumann;
U.S. Patent Nos. 4,040,974 and 4,054,537 issued to A. C. Wright et al; U.S. Patent No. 3,666,40~ issued to J. K~ Orlemann; U.S. Patent No. 3,844,979, issued to D. A. Hickson~ or U.S. Patent No. 3,855,147 issued to W. T~ Granquist.
Suitable representatives of siliceous composi-tions of Formula I where the metal is Ti or Zr incLude zirconium silicates and benîtoite (BaTiSi309)~
Where X is aluminum, suitable siliceous compositions of Formula I include alumi~um silicates, ; minerals such as albites, feldspars, labradorites, microclines, nephelines, orthoclases, pyrophyllites, and sodalites; as well as natural and synthetic zeolites.
Synthetic silicate minerals such as those descri~ed in U.S. Patent No. 3,~52,757 issued to W. T. Granquist or U.S. Patent No. 3,252,889 issued to R. G. Capell et al are suitable aluminum-containing compositions.
Also suitable are inorganic compositions in which X is zinc, such as zinc silicates.
Preferred embodiments of siliceous composi-tions of Formula I are those in which m is a positive number and X is at least one metal selected from the group consisting of Mg, Ca or ~1 or mixtures thereof, with siliceous compositions oE Formula I where X is 3a Mg, Al or mixtures thereo~ being more preferred.
Suitable examples o~ preferred embodLments :include -the minerals sepioli-tes or meerschaums.
` ~L 15~3~
.
Siliceous compositions of Formula I
may also include supplementary elements, such as vanadium, niobium, rare earth elements of the lanthanide series, germanium, tin and tungsten. Further, alkali metals such as sodium, potassium and lithium and their oxides are frequentl~
present in siliceous materials suitable as composi-tions of Formula I. When present in siliceous composi-;: tions of Formula I, the above supplementary elements do not represent X and are therefore not included in the determination of m.
In Formula I, where m and r arP zero, the siliceous compositions are silica-containing materials ~7hich are suitably represented by sand, quartz, silica sand, colloidal silica as well as cristobalite, tri-polite and chalcedony. The term "sand" includes com-positions having a silicon dioxide content of at least about 95 percent by weight.
As indicated by Formula I, the siliceous compositions may be in t~e form of a hydrate and various amounts of water of hydration can be present.
Siliceous compositions of Formula I may be formed in situ hy the interaction of salts of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al and Zn with, for example, silica or an alkali metal silicate. Where X is magnesium, magnesium compounds such as magnesium acetate, magnesium aluminate, magnesium carbonate, magnesium chloride and magnesium peroxide can be employedO For example, a mixture of the appropriate 3n amounts o~ magnesia (MgO) with silica in the presence o~ a cell electrolyte such as an alkali metal hydroxide will produce a siliceous composition o~ Formula I
suitable ~or use in the porous diaphragm o~ -the present invention.
~ :~5~39~
The presence of metals other than those included in Formula I or discussed above as supplemen-tary elements can ~e tolerated at low concentrations.
~or example, the concentration of metals such as Fe, Ni, Pb, Ag as well as other heavy metals which may be present in alkali metal chloride brines suitable for electrolysis are preferably below one part per million. Where these metals are present in minerals suitable as sil;ceous compositions of Formula I, it is preferred that their concentration be less than about 5 percent of the concentration of silicon present in the material.
Similarly, non-metallic materials such as ammonia as well as organic compounas, if present~
should be limited to moderate and preferably low levels of concentration. ' The degree to which the siliceous composition of ~ormula I is hydrated serves as a basis for selecting suitable particle sizes~ For those compositions which are readily hydrated in the electrolyte solutions used or produced in the cell, a particle size as large as about 100 microns is satisfactory. Where the component is less easil~ hydrated, the particle size may be substantially reduced. For these compositions, paxticles having a size in the range of from about 75 microns to about 0.1 micron are more suitable.
Aqueous solutions of ioniza~le compounds which ; are suitable as electrolytes include, for example, ~ alkali metal chlorides and alkali metal hydroxides.
~" `'' .
, ~ 15939 3.
, . .
The support fabrics may be impregnated with the siliceous composition of Formula I in any o~
several ways~ For example, a slurry of the composi-tion in a solution such as an alkali metal hydroxide or an alkali metal chloride is prepared and the support fabric is impregnated ~y soaking in the slurry. Another method is to attach the supporting fabric to the cathode and immerse the cathode in the slurry, using the fabric as a filter cloth. Suction means are employed to draw the slurry through the support fabric where the solid particles impregnate the fabric and the filtrate is withdrawn.
In a further embodiment, the support fabric may be impregnated with the siliceous composition by employing means such as rollers to contact the support fabric with the slurry.
It is not necessary to employ a solution or slurry for impregnation purposes. For example, the inorganic siliceous composition of Formula I may be used to form a fluidized bed. A vacuum is employed to ; suck the particles into the support fabric until the desired degree of impregnation is obtained.
When impregnated, the novel diaphragm of the present invention contains from about 10 to about 100, preferably from about 25 to about 75, and more preferably from about 30 to about 50 milligrams of the siliceous composition per square centimeter of support fahric.
Following impregnation ~ith the siliceous 3~ composition of Formula I, the diaphragms have a permeahil.~-ty to alkali metal chloride brines of Erom about 100 to about 1000, and preferably from about 200 to about sao millili-ters per minute per square meter o~
diaphragm at a head level difference between the anolyte and the catholyte of from about 0.1 to about 20 inches o~ brine .
'i 15~3g~
In order to provide similar brine permeability rates, deposited asbestos ~i~er diaphragms require a yreater density which results in higher electrical resistance as indicated by larger voltage coefficients at comparable operating conditions. The novel diaphragms of the present invention are thus more energy efficient than deposited asbestos diaphragms ancl provide reduced power costs.
The novel diaphragms of the present invention have handling properties which far exceed those of, for example, asbestos. The supported diaphragms can be removed from the cell, washed or treated to restore ~lowability and replaced in the cell without physical damage. During operation of the cell r the novel diaphragms remain dimensionally stable with the support material neither swelling nor being dissolved or deteriorated by the electrolyte, the siliceous composi-tion or the cell products produced.
Electrolytic cells in which the diaphragms of the present invention may be used include those which are employed commercially in the production of chlorine and alkali metal hydroxides by the electrolysis of alkali metal chloride brines. Alkali metal chlorida brines electrolyzed are aqueou~ solutions having high concentrations of the alkali metal chlorides. For example, where sodium chloride is the alkali metal chloride, suitable concentrations include brines having from about 200 to about 350, and preferably from about 250 to about 320 ~rams per liter of NaCl. The cells 3Q have an anode as~em~ly containing a plurality o~ ~oramij-nous me-~al or ~raph:ite anodes, a cathode assembly having a plurality o~ ~orclminous metal cathodes with the novel diaphragm separating the anodes from -the cathodes.
Suitable electrolyti.c cells which utilize the novel diaphragms of the present invention include, for example, those types illustrated by U.S. Patent Nos.
1,862,244; 2,370,087; 2,987,~63; 3,2~7,090; 3,477,938;
3,493,487; 3,617,461 and 3,642r604.
~ ~ 5~3~ ~
~iaphragms of the present invention may also be suitably used, for example, in cells whlch electrolyze alkali metal hydroxides to produce hydrogen and oxygen.
When employed in electrolytic cells, the diaphragms of the present invention are sufficiently flexible so that they may be mounted on or supported by an electrode such as a cathode.
During electrolysis of alkali metal chloride solutions, the siliceous compositions of Formula I
produce a gel like formation which is permeable to alkali metal ions. While the gel-like formations may be produced throughout the diaphragm they are normally produced within the support fabric in the portion which is adjacent to the anolyte side. Th~
extent of gel formation within the support fabric ~aries, for example, with the thickness of the support fabric and the concentration of alkali metal hydroxide in the catholyte liquor. Preferred diaphragms are those which have a gel-free portion in contact with the catholyte. Gel formation is believed to occur during hydration of the siliceous composition. The gel is believed to be soluhle in the catholyte liquor and it is desirable that the rate of dissolution be controlled to maintain a suitable equilibrium between gel formation and dissolution for efficient operation of the cell.
The presence of metals and compounds represented by X
in Formula I in the gel is believed to be one way of increasing the s tability of the gel and thus reduce iks rate o~ dissolution. Anokher way appears to be the salection of suikable partîcle sizes for tha lnorcJanic co~position. Gel-free por-tions of the 3 '3 ~
: .
diaphragm are attained, for example, by controlling the areas of the support fabric which are impregnated with the siliceous composition or by controlling the concentration of the electrolyte~ in the anode and cathode compartments. Efficient cell operation is ~ttained by controlling the equilibrium sufficiently to produce a caustic liquor containing silica in amounts of from about 10 to about 15Q parts per million. This may be obtained by periodically adding the inorganic siliceous composition of Formula I to the brine in suitable amounts. Alkali metal chloride brines used in the electrolytic process normally contain concen-trations of silica of from about 10 to about 30 parts per million and thus the brine may supply sufficient silica to maintain the equilibrium and supplemental addition of inorganic composition may not be necessary.
The porous diaphragms o the present invention are illustrated by the following examples without any intention of being limited thereby.
~, ;
.
3 '~ ~
~2Q-EXAMPL~ 1 Sepiolite, having particle sizes in the range between 44 microns and less than 1 micron, was added to sodium chloride brine having a concentration of 295~305 grams per liter of NaCl. The sepiolite was dispersed in th~ brine using a blender until the brine contained about 5 percent by volume of sepiolite.
Analysis of the sepiolite indicated oxides of the following elements were present as percent by weight:
Si 72.1; Mg 9.3; K 4~8; Ca 4.8; Al 1.4 and Fe 1.4.
A section o polytetrafluoroethylene felt 0.048 inch thick, in the form shown in FIGURE l,was washed in a caustic soda solution containing 15-20 percent NaOH and at a temperature of 30C for about 24 hours to remove residues and improve wettability. The ~elt was then fitted on a steel mesh cathode. The felt had an air permeability in the range o~ from about 20 to about 70 cubic feet per minute per square foot. The felt-covered cathode was immersed in the brine containing sepiolite and a vacuum applied to impregnate the felt with the dispersion until a vacuum of 23 to 27 inches was reached. The vacuum was shut off and the procedure repe~ted three times.
The impregnated, felt-covered cathode was installed in an electrolytic cell employing a ruthenium oxide coated titanium mesh anode and sodium chloride brine at a pH of 12, a concentration of 300+5 gramc;
o~ NaCl per liter and a temperature of 90C. Curr~nt was passed through the brine at a density of 2.0 kilo-amps per sqaure meter o~ anode surface~ The initial ~ ~ ~93~ ~
brine head level was a . 5 to 1 inch greater in the anode compartment than in the cathode compartment~ The permeability of the impregnated diaphragm was found to be in the range of from a~out 20a to about 250 milliliters per square meter of diaphragm by measuring the rate of catholyte liquor produced. After about six days of cell operation, the premixed dispersion of sepiolite in brine was added to the anolyte~ The amount added corresponded to about 3 percent of the volume of the anolyte compartment of the cell, the addition being made without interruption of the elec-trolysis process. After a period of six weeks, the cell voltage began to increase rapidly and current efficiency was reduced. While maintaining the cell in operation, a 5 percent HCl solution was fed to the anolyte compartment and the catholyte liquor was diluted with cold water. Cell performance after treat-ment of the anolyte and the catholyte was restored to that found earlier, as shown by the results in Table I
below.
The catholyte liquor produced had a sodium chloride concentration in the range of 130 to 170 grams per liter.
~ ~ ~939 ~
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r.~ r,~J r.~ r,~ r,~ ~ r,~ r,~ r,~ r,~l r,~l r.
o ~C
_ _ aJ r,~ r,~ ` r~ r~ ~O ro U~ In r~ r,~
: ~r1 ~ r r rx r~ r~ rx~ rx~ r~ r~ 0 c~ r r q~
~3 --HIJ/ U~ 9 0 r,~ r~ r.~ r~
_1 a ~ ~ O O O O o ~ ~ o r,~ r,~ rl~ r~ rq ' ~.~ r~ r~ r~ r~l ~ r~
$
Z r~o r,~l r3 ~ O O ~r r~ r~ ~O
r r~ ~D ~ O r,~ ~ r rl~ O r r.
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O
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u~r~ ~O r~ O ~r r rr~ r 1` r o o ~ u~
~ ~ ~ r~n u~ Ln a a o 1 ~ 5~3~ ~
:: -23-.
~_ O ~ o a~ 7 co co O
a~ x ~4--~: ~ o 11') r~ ~ ~ o o ~o 1` cn 0 C) ~ a~ 0 o~co 0 lU
_ ~ o ~ L~ n ~ ~ o O ~ O O O O ~ ~1 1 ~ ~ . . . . . . . . .
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Z -- ~r ~o o o o o ~ o o o o Lr) GO ~i 0 0 ~ 1 11-1 0 r~
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The procedure of Example 1 ~as duplicated using a polypropylene felt having a thickness of 0.18 of an inch. After one week of cell operation a mixture o~ colloidal silica and magnesium chLoride in a 10 percent aqueous solution was prepared. The mixture, containing a weight ratio of silica of MgC12 of 85:15, was added to the anolyte in an amount corresponding to about 3 percent of the vol~me of the anolyte compart-ment~ The cell was operated Eor a period of about 3 weeks at a cell voltage of 3.00-3.lQ volts, and produced ; catholyte liquor containing 122-142 grams per liter of NaOH at a cathode current efficiency of 86-92 percent.
A mixture of colloidal silica and magnesia in sodium chloride brine, having a concentration of 295-305 grams per liter was prepared. The mixture contained a weight ratio of SiO2 to MgO of 85:15.
A section of polytetrafluoroethylene ~elt 0.068 of an inch thick was impregnated with this mixtllre using the procedure of Example 1.
T~e impregnated diaphra~m was installed in a cell similar to that of Example 1 and operated using a brine and conditions identlfied to those used in Example 1. During 10 days of cell operation~ at a current den~ity oE 2 kiloamps, the cell volta~e was in the range of 2.90-3.08 volts while pro~ucing a ca-tholyte liquor having a concentra-tion of 108 to 128 grams per liter o~ NaOH at a cathode current eEflciency of 88-92 percent~
~ ~93~ ~
A porous diaphragm of the type of FIGURE 5 was produced from a ~elt fa~ric of polyphenylene sulfide (Phillips Petroleum Co. Ryton-PPS~, The felt fabric had a density of 0.28 grams per cubic centimeter, a thickness of 0.125 inch and an air permeability o~
52 cubic ~eet per meter. The surface of the fabric was needled to provide several hundred bundles of fibers containing about 100 fibers per ~undle pex square inch of ~abric. The fiber bundles penetrated the entire thickness of the felt fabric and were su~stantially perpendicular to the plane of the felt surface. This provided the felt fabric with a linear permeability which represented from about 30 to about 35 percent of the total permea~ility of the fabric~ The felt fahric was mounted on a cathode and the cathode immersed in a slurry of sepiolite ~30 percent by volume) in saturated sodium chloride brine~ A roller was used to apply the slurry and impregnate the fabric with sepiolite. The impregnated ~elt-covered cathode was installed in the electrolytic cell employed in Example 1 containing sodium chloride brlne at a concentration oE 300~5 grams of NaCl per liter at a pH of 12~ Current was applied at a density of 2.0 kiloamps per square meter of anode sur~ace. Elec-trolysis was conducted ~or 8 days during which a cell llquor having a concentration of 120-131 grams per :liter o~ NaOH was produced at a cell vol-tage of 3.1-3.2 volts. The cathode current e~ficiency was in the rang~ o~ 8h-98 percent.
~ :~5~3~
A section of a polyphenylene sulfide web was needled lightly ~o in-troduce fiber bundles per-pendicular to the plane of the surface of the web, Similarly, a section of polytetrafluoroethylene web was needled to introduce fiber bundles perpendicular to the plane of the surface. The polytetrafluoro-ethylene web was then placed on top of the poly-phenylene web and the polytetraf~uoroethylene needled to provide a felt fabric in which bundles of fibers of polytetrafluoroethylene penetrated the entire fabric, the bundles being perpendicular to the outer surface of the felt fabric. The felt produced had a weight ratio of 60 percent polyphenylene sulfide and 40 percent polytetrafluoroethylene. A fabric having a thickness of 0.143 of an inch was produced with an air permeability of 51.5 cubic feet per meter.
3 ~ ~L
EXAMPL~ 6 A section of polytetrafluoroethylene felt of the type of ~IGURE 5 was fitted on a steel mesh cathode and impregnated with a sepiolite slurry (40 percent by volume of sepiolite~ in sodium chloride brine. The felt had a thickness of 0.95 of an inch and an ai~ permeability in the range of 42-51 cubic feet per square meter of fabric. Of this permeability, 3Q to 35 percent was linear permeability provided by fiber ~undles distri~uted throughout the felt, the bundles being perpendicular to the plane of the outer surface of the felt and penetrating the entire felt th~ckness. It was estimated that the felt contained 300 to 500 fiber ~undles per square inch with each bundle containing from a~out 100 to about 120 fibers.
The felt-covered cathode was installed in an electrolytic cell employing a ruthenium oxide coated titanium mesh anode~ The anolyte was a brine containing 300-310 grams per liter of NaCl at a pH of 11 and a temperature of 85-gaoC, The cell was operated for 80 days to produce a caustic liquor containing 116-142 grams per liter of NaOH at cathode current efEiciencies in the range of 85-98 percent and a cell voltage of 3~1-3.2 volts.
3 ~ ~
EXA~PLE 7 Sodium silicate (50 5~, 20 g of ~ilica gel and 300 mls. of water admixed in a vessel and the mixture heated to 90-lQ0aC, Magnes~um oxide ~5 g~ was added and the slurry stirred for one hour. Aluminum chloride ~3 g~ was dissolved in 50 mls. of water and the solution added to the slurry. The slurry was neutralized with hydrochloric acid to a pH in the range of 5-7. Silica flour ~10 g~ was added and the slurry 1~ stirred for 24 hours. A section of polytetrafluoro-ethylene ~elt was fitted on a steel mesh cathode and immersed in the slurry. The felt was impregnated with the sluxry ~y mechanical rolling. The impregnated diaphragm was in an electrolytic cell of the type o Example 1. Saturated sodium chloride brine (300-310 gpl NaCl~ ~as electrolyzed to produce a catholyte li~uor containing 105-130 gpl of NaOH. The cell voltage was in the ran~e of 3.05-3~18 volts at a current density o~ 2.2 kiloamps per sqllare meter. Cathode current efficiency: 78-85 percent.
A synthetic siliceous clay mineral product (N~La Industries Barasym ~ IBH~ havinga Mg to Si ratio of 2:8 was added to sodium chloride brine to form a slurry containing 20-30 percent by volume of the mineral product~ A polytetrafluoroethylene felt of the type of FIGURE 5 wa~ impregnated with the slurry using the procedure o~ Example 4. Electrolysis in a cell o~
the t~pe o~ Example 1 ~or a period o~ 10 day~ produced 3~ a catholyte liquor having a concentration o~ 105-120 gpl o~ NaOH and a cathode C~IXrent e~ici.ency o~ 88-91 percent, Cell voltage, at a current density o~ 2.33 kiloamp~ per square meter, was 3 . lS-3 . ~5 volts.
~lso suitable are synthetic clay materials which are described, for example, in U.S. Patent Nos.
3,586,478 and 3,671,190 issued to B. S~ ~eumann;
U.S. Patent Nos. 4,040,974 and 4,054,537 issued to A. C. Wright et al; U.S. Patent No. 3,666,40~ issued to J. K~ Orlemann; U.S. Patent No. 3,844,979, issued to D. A. Hickson~ or U.S. Patent No. 3,855,147 issued to W. T~ Granquist.
Suitable representatives of siliceous composi-tions of Formula I where the metal is Ti or Zr incLude zirconium silicates and benîtoite (BaTiSi309)~
Where X is aluminum, suitable siliceous compositions of Formula I include alumi~um silicates, ; minerals such as albites, feldspars, labradorites, microclines, nephelines, orthoclases, pyrophyllites, and sodalites; as well as natural and synthetic zeolites.
Synthetic silicate minerals such as those descri~ed in U.S. Patent No. 3,~52,757 issued to W. T. Granquist or U.S. Patent No. 3,252,889 issued to R. G. Capell et al are suitable aluminum-containing compositions.
Also suitable are inorganic compositions in which X is zinc, such as zinc silicates.
Preferred embodiments of siliceous composi-tions of Formula I are those in which m is a positive number and X is at least one metal selected from the group consisting of Mg, Ca or ~1 or mixtures thereof, with siliceous compositions oE Formula I where X is 3a Mg, Al or mixtures thereo~ being more preferred.
Suitable examples o~ preferred embodLments :include -the minerals sepioli-tes or meerschaums.
` ~L 15~3~
.
Siliceous compositions of Formula I
may also include supplementary elements, such as vanadium, niobium, rare earth elements of the lanthanide series, germanium, tin and tungsten. Further, alkali metals such as sodium, potassium and lithium and their oxides are frequentl~
present in siliceous materials suitable as composi-tions of Formula I. When present in siliceous composi-;: tions of Formula I, the above supplementary elements do not represent X and are therefore not included in the determination of m.
In Formula I, where m and r arP zero, the siliceous compositions are silica-containing materials ~7hich are suitably represented by sand, quartz, silica sand, colloidal silica as well as cristobalite, tri-polite and chalcedony. The term "sand" includes com-positions having a silicon dioxide content of at least about 95 percent by weight.
As indicated by Formula I, the siliceous compositions may be in t~e form of a hydrate and various amounts of water of hydration can be present.
Siliceous compositions of Formula I may be formed in situ hy the interaction of salts of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al and Zn with, for example, silica or an alkali metal silicate. Where X is magnesium, magnesium compounds such as magnesium acetate, magnesium aluminate, magnesium carbonate, magnesium chloride and magnesium peroxide can be employedO For example, a mixture of the appropriate 3n amounts o~ magnesia (MgO) with silica in the presence o~ a cell electrolyte such as an alkali metal hydroxide will produce a siliceous composition o~ Formula I
suitable ~or use in the porous diaphragm o~ -the present invention.
~ :~5~39~
The presence of metals other than those included in Formula I or discussed above as supplemen-tary elements can ~e tolerated at low concentrations.
~or example, the concentration of metals such as Fe, Ni, Pb, Ag as well as other heavy metals which may be present in alkali metal chloride brines suitable for electrolysis are preferably below one part per million. Where these metals are present in minerals suitable as sil;ceous compositions of Formula I, it is preferred that their concentration be less than about 5 percent of the concentration of silicon present in the material.
Similarly, non-metallic materials such as ammonia as well as organic compounas, if present~
should be limited to moderate and preferably low levels of concentration. ' The degree to which the siliceous composition of ~ormula I is hydrated serves as a basis for selecting suitable particle sizes~ For those compositions which are readily hydrated in the electrolyte solutions used or produced in the cell, a particle size as large as about 100 microns is satisfactory. Where the component is less easil~ hydrated, the particle size may be substantially reduced. For these compositions, paxticles having a size in the range of from about 75 microns to about 0.1 micron are more suitable.
Aqueous solutions of ioniza~le compounds which ; are suitable as electrolytes include, for example, ~ alkali metal chlorides and alkali metal hydroxides.
~" `'' .
, ~ 15939 3.
, . .
The support fabrics may be impregnated with the siliceous composition of Formula I in any o~
several ways~ For example, a slurry of the composi-tion in a solution such as an alkali metal hydroxide or an alkali metal chloride is prepared and the support fabric is impregnated ~y soaking in the slurry. Another method is to attach the supporting fabric to the cathode and immerse the cathode in the slurry, using the fabric as a filter cloth. Suction means are employed to draw the slurry through the support fabric where the solid particles impregnate the fabric and the filtrate is withdrawn.
In a further embodiment, the support fabric may be impregnated with the siliceous composition by employing means such as rollers to contact the support fabric with the slurry.
It is not necessary to employ a solution or slurry for impregnation purposes. For example, the inorganic siliceous composition of Formula I may be used to form a fluidized bed. A vacuum is employed to ; suck the particles into the support fabric until the desired degree of impregnation is obtained.
When impregnated, the novel diaphragm of the present invention contains from about 10 to about 100, preferably from about 25 to about 75, and more preferably from about 30 to about 50 milligrams of the siliceous composition per square centimeter of support fahric.
Following impregnation ~ith the siliceous 3~ composition of Formula I, the diaphragms have a permeahil.~-ty to alkali metal chloride brines of Erom about 100 to about 1000, and preferably from about 200 to about sao millili-ters per minute per square meter o~
diaphragm at a head level difference between the anolyte and the catholyte of from about 0.1 to about 20 inches o~ brine .
'i 15~3g~
In order to provide similar brine permeability rates, deposited asbestos ~i~er diaphragms require a yreater density which results in higher electrical resistance as indicated by larger voltage coefficients at comparable operating conditions. The novel diaphragms of the present invention are thus more energy efficient than deposited asbestos diaphragms ancl provide reduced power costs.
The novel diaphragms of the present invention have handling properties which far exceed those of, for example, asbestos. The supported diaphragms can be removed from the cell, washed or treated to restore ~lowability and replaced in the cell without physical damage. During operation of the cell r the novel diaphragms remain dimensionally stable with the support material neither swelling nor being dissolved or deteriorated by the electrolyte, the siliceous composi-tion or the cell products produced.
Electrolytic cells in which the diaphragms of the present invention may be used include those which are employed commercially in the production of chlorine and alkali metal hydroxides by the electrolysis of alkali metal chloride brines. Alkali metal chlorida brines electrolyzed are aqueou~ solutions having high concentrations of the alkali metal chlorides. For example, where sodium chloride is the alkali metal chloride, suitable concentrations include brines having from about 200 to about 350, and preferably from about 250 to about 320 ~rams per liter of NaCl. The cells 3Q have an anode as~em~ly containing a plurality o~ ~oramij-nous me-~al or ~raph:ite anodes, a cathode assembly having a plurality o~ ~orclminous metal cathodes with the novel diaphragm separating the anodes from -the cathodes.
Suitable electrolyti.c cells which utilize the novel diaphragms of the present invention include, for example, those types illustrated by U.S. Patent Nos.
1,862,244; 2,370,087; 2,987,~63; 3,2~7,090; 3,477,938;
3,493,487; 3,617,461 and 3,642r604.
~ ~ 5~3~ ~
~iaphragms of the present invention may also be suitably used, for example, in cells whlch electrolyze alkali metal hydroxides to produce hydrogen and oxygen.
When employed in electrolytic cells, the diaphragms of the present invention are sufficiently flexible so that they may be mounted on or supported by an electrode such as a cathode.
During electrolysis of alkali metal chloride solutions, the siliceous compositions of Formula I
produce a gel like formation which is permeable to alkali metal ions. While the gel-like formations may be produced throughout the diaphragm they are normally produced within the support fabric in the portion which is adjacent to the anolyte side. Th~
extent of gel formation within the support fabric ~aries, for example, with the thickness of the support fabric and the concentration of alkali metal hydroxide in the catholyte liquor. Preferred diaphragms are those which have a gel-free portion in contact with the catholyte. Gel formation is believed to occur during hydration of the siliceous composition. The gel is believed to be soluhle in the catholyte liquor and it is desirable that the rate of dissolution be controlled to maintain a suitable equilibrium between gel formation and dissolution for efficient operation of the cell.
The presence of metals and compounds represented by X
in Formula I in the gel is believed to be one way of increasing the s tability of the gel and thus reduce iks rate o~ dissolution. Anokher way appears to be the salection of suikable partîcle sizes for tha lnorcJanic co~position. Gel-free por-tions of the 3 '3 ~
: .
diaphragm are attained, for example, by controlling the areas of the support fabric which are impregnated with the siliceous composition or by controlling the concentration of the electrolyte~ in the anode and cathode compartments. Efficient cell operation is ~ttained by controlling the equilibrium sufficiently to produce a caustic liquor containing silica in amounts of from about 10 to about 15Q parts per million. This may be obtained by periodically adding the inorganic siliceous composition of Formula I to the brine in suitable amounts. Alkali metal chloride brines used in the electrolytic process normally contain concen-trations of silica of from about 10 to about 30 parts per million and thus the brine may supply sufficient silica to maintain the equilibrium and supplemental addition of inorganic composition may not be necessary.
The porous diaphragms o the present invention are illustrated by the following examples without any intention of being limited thereby.
~, ;
.
3 '~ ~
~2Q-EXAMPL~ 1 Sepiolite, having particle sizes in the range between 44 microns and less than 1 micron, was added to sodium chloride brine having a concentration of 295~305 grams per liter of NaCl. The sepiolite was dispersed in th~ brine using a blender until the brine contained about 5 percent by volume of sepiolite.
Analysis of the sepiolite indicated oxides of the following elements were present as percent by weight:
Si 72.1; Mg 9.3; K 4~8; Ca 4.8; Al 1.4 and Fe 1.4.
A section o polytetrafluoroethylene felt 0.048 inch thick, in the form shown in FIGURE l,was washed in a caustic soda solution containing 15-20 percent NaOH and at a temperature of 30C for about 24 hours to remove residues and improve wettability. The ~elt was then fitted on a steel mesh cathode. The felt had an air permeability in the range o~ from about 20 to about 70 cubic feet per minute per square foot. The felt-covered cathode was immersed in the brine containing sepiolite and a vacuum applied to impregnate the felt with the dispersion until a vacuum of 23 to 27 inches was reached. The vacuum was shut off and the procedure repe~ted three times.
The impregnated, felt-covered cathode was installed in an electrolytic cell employing a ruthenium oxide coated titanium mesh anode and sodium chloride brine at a pH of 12, a concentration of 300+5 gramc;
o~ NaCl per liter and a temperature of 90C. Curr~nt was passed through the brine at a density of 2.0 kilo-amps per sqaure meter o~ anode surface~ The initial ~ ~ ~93~ ~
brine head level was a . 5 to 1 inch greater in the anode compartment than in the cathode compartment~ The permeability of the impregnated diaphragm was found to be in the range of from a~out 20a to about 250 milliliters per square meter of diaphragm by measuring the rate of catholyte liquor produced. After about six days of cell operation, the premixed dispersion of sepiolite in brine was added to the anolyte~ The amount added corresponded to about 3 percent of the volume of the anolyte compartment of the cell, the addition being made without interruption of the elec-trolysis process. After a period of six weeks, the cell voltage began to increase rapidly and current efficiency was reduced. While maintaining the cell in operation, a 5 percent HCl solution was fed to the anolyte compartment and the catholyte liquor was diluted with cold water. Cell performance after treat-ment of the anolyte and the catholyte was restored to that found earlier, as shown by the results in Table I
below.
The catholyte liquor produced had a sodium chloride concentration in the range of 130 to 170 grams per liter.
~ ~ ~939 ~
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~ o o o u~ O ~ ~ ~ r,~l ~ ~ ~ r O ~ ~ r,~ Ln r~ ~ r,~ r O It7 ~1 ~ r r~
I` r~ r~ rr) r~ r,~ r,~ ~ r~- r.~ r.
r.~ r,~J r.~ r,~ r,~ ~ r,~ r,~ r,~ r,~l r,~l r.
o ~C
_ _ aJ r,~ r,~ ` r~ r~ ~O ro U~ In r~ r,~
: ~r1 ~ r r rx r~ r~ rx~ rx~ r~ r~ 0 c~ r r q~
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$
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:: -23-.
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a~ x ~4--~: ~ o 11') r~ ~ ~ o o ~o 1` cn 0 C) ~ a~ 0 o~co 0 lU
_ ~ o ~ L~ n ~ ~ o O ~ O O O O ~ ~1 1 ~ ~ . . . . . . . . .
-- ~ ~ ~ ~ ~ ~7 H ~
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Z -- ~r ~o o o o o ~ o o o o Lr) GO ~i 0 0 ~ 1 11-1 0 r~
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The procedure of Example 1 ~as duplicated using a polypropylene felt having a thickness of 0.18 of an inch. After one week of cell operation a mixture o~ colloidal silica and magnesium chLoride in a 10 percent aqueous solution was prepared. The mixture, containing a weight ratio of silica of MgC12 of 85:15, was added to the anolyte in an amount corresponding to about 3 percent of the vol~me of the anolyte compart-ment~ The cell was operated Eor a period of about 3 weeks at a cell voltage of 3.00-3.lQ volts, and produced ; catholyte liquor containing 122-142 grams per liter of NaOH at a cathode current efficiency of 86-92 percent.
A mixture of colloidal silica and magnesia in sodium chloride brine, having a concentration of 295-305 grams per liter was prepared. The mixture contained a weight ratio of SiO2 to MgO of 85:15.
A section of polytetrafluoroethylene ~elt 0.068 of an inch thick was impregnated with this mixtllre using the procedure of Example 1.
T~e impregnated diaphra~m was installed in a cell similar to that of Example 1 and operated using a brine and conditions identlfied to those used in Example 1. During 10 days of cell operation~ at a current den~ity oE 2 kiloamps, the cell volta~e was in the range of 2.90-3.08 volts while pro~ucing a ca-tholyte liquor having a concentra-tion of 108 to 128 grams per liter o~ NaOH at a cathode current eEflciency of 88-92 percent~
~ ~93~ ~
A porous diaphragm of the type of FIGURE 5 was produced from a ~elt fa~ric of polyphenylene sulfide (Phillips Petroleum Co. Ryton-PPS~, The felt fabric had a density of 0.28 grams per cubic centimeter, a thickness of 0.125 inch and an air permeability o~
52 cubic ~eet per meter. The surface of the fabric was needled to provide several hundred bundles of fibers containing about 100 fibers per ~undle pex square inch of ~abric. The fiber bundles penetrated the entire thickness of the felt fabric and were su~stantially perpendicular to the plane of the felt surface. This provided the felt fabric with a linear permeability which represented from about 30 to about 35 percent of the total permea~ility of the fabric~ The felt fahric was mounted on a cathode and the cathode immersed in a slurry of sepiolite ~30 percent by volume) in saturated sodium chloride brine~ A roller was used to apply the slurry and impregnate the fabric with sepiolite. The impregnated ~elt-covered cathode was installed in the electrolytic cell employed in Example 1 containing sodium chloride brlne at a concentration oE 300~5 grams of NaCl per liter at a pH of 12~ Current was applied at a density of 2.0 kiloamps per square meter of anode sur~ace. Elec-trolysis was conducted ~or 8 days during which a cell llquor having a concentration of 120-131 grams per :liter o~ NaOH was produced at a cell vol-tage of 3.1-3.2 volts. The cathode current e~ficiency was in the rang~ o~ 8h-98 percent.
~ :~5~3~
A section of a polyphenylene sulfide web was needled lightly ~o in-troduce fiber bundles per-pendicular to the plane of the surface of the web, Similarly, a section of polytetrafluoroethylene web was needled to introduce fiber bundles perpendicular to the plane of the surface. The polytetrafluoro-ethylene web was then placed on top of the poly-phenylene web and the polytetraf~uoroethylene needled to provide a felt fabric in which bundles of fibers of polytetrafluoroethylene penetrated the entire fabric, the bundles being perpendicular to the outer surface of the felt fabric. The felt produced had a weight ratio of 60 percent polyphenylene sulfide and 40 percent polytetrafluoroethylene. A fabric having a thickness of 0.143 of an inch was produced with an air permeability of 51.5 cubic feet per meter.
3 ~ ~L
EXAMPL~ 6 A section of polytetrafluoroethylene felt of the type of ~IGURE 5 was fitted on a steel mesh cathode and impregnated with a sepiolite slurry (40 percent by volume of sepiolite~ in sodium chloride brine. The felt had a thickness of 0.95 of an inch and an ai~ permeability in the range of 42-51 cubic feet per square meter of fabric. Of this permeability, 3Q to 35 percent was linear permeability provided by fiber ~undles distri~uted throughout the felt, the bundles being perpendicular to the plane of the outer surface of the felt and penetrating the entire felt th~ckness. It was estimated that the felt contained 300 to 500 fiber ~undles per square inch with each bundle containing from a~out 100 to about 120 fibers.
The felt-covered cathode was installed in an electrolytic cell employing a ruthenium oxide coated titanium mesh anode~ The anolyte was a brine containing 300-310 grams per liter of NaCl at a pH of 11 and a temperature of 85-gaoC, The cell was operated for 80 days to produce a caustic liquor containing 116-142 grams per liter of NaOH at cathode current efEiciencies in the range of 85-98 percent and a cell voltage of 3~1-3.2 volts.
3 ~ ~
EXA~PLE 7 Sodium silicate (50 5~, 20 g of ~ilica gel and 300 mls. of water admixed in a vessel and the mixture heated to 90-lQ0aC, Magnes~um oxide ~5 g~ was added and the slurry stirred for one hour. Aluminum chloride ~3 g~ was dissolved in 50 mls. of water and the solution added to the slurry. The slurry was neutralized with hydrochloric acid to a pH in the range of 5-7. Silica flour ~10 g~ was added and the slurry 1~ stirred for 24 hours. A section of polytetrafluoro-ethylene ~elt was fitted on a steel mesh cathode and immersed in the slurry. The felt was impregnated with the sluxry ~y mechanical rolling. The impregnated diaphragm was in an electrolytic cell of the type o Example 1. Saturated sodium chloride brine (300-310 gpl NaCl~ ~as electrolyzed to produce a catholyte li~uor containing 105-130 gpl of NaOH. The cell voltage was in the ran~e of 3.05-3~18 volts at a current density o~ 2.2 kiloamps per sqllare meter. Cathode current efficiency: 78-85 percent.
A synthetic siliceous clay mineral product (N~La Industries Barasym ~ IBH~ havinga Mg to Si ratio of 2:8 was added to sodium chloride brine to form a slurry containing 20-30 percent by volume of the mineral product~ A polytetrafluoroethylene felt of the type of FIGURE 5 wa~ impregnated with the slurry using the procedure o~ Example 4. Electrolysis in a cell o~
the t~pe o~ Example 1 ~or a period o~ 10 day~ produced 3~ a catholyte liquor having a concentration o~ 105-120 gpl o~ NaOH and a cathode C~IXrent e~ici.ency o~ 88-91 percent, Cell voltage, at a current density o~ 2.33 kiloamp~ per square meter, was 3 . lS-3 . ~5 volts.
Claims (36)
1. A porous diaphragm for use in the electrolysis of aqueous solutions of ionizable compounds in electrolytic dia-phragm cells comprised of a thermoplastic organic polymer support fabric impregnated with particles of a siliceous composition having the formula:
(X)m(Si)p(O)q(H)r ? nH2O
wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al, Zn and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
q is a number from 2 to about 5p + r;
r is zero to about 4p; and n is zero to about 30;
said siliceous composition being capable of undergoing hydra-tion when in contact with at least one of said ionizable com-pounds in an electrolytic cell; said support fabric having regions through which the flow of said aqueous solutions is substantially laminar.
(X)m(Si)p(O)q(H)r ? nH2O
wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al, Zn and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
q is a number from 2 to about 5p + r;
r is zero to about 4p; and n is zero to about 30;
said siliceous composition being capable of undergoing hydra-tion when in contact with at least one of said ionizable com-pounds in an electrolytic cell; said support fabric having regions through which the flow of said aqueous solutions is substantially laminar.
2. The porous diaphragm of claim 1 in which X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, aluminum and mixtures thereof and m is a positive number.
3. The porous diaphragm of claim 2 in which said siliceous composition is present at a concentration of from about 10 to about 100 milligrams per square centimeter of said support fabric.
4. The porous diaphragm of claim 3 in which said support fabric is a polyolefin selected from the group consist-ing of olefins having from 2 to about 6 carbon atoms and their chloro- and fluoro- derivatives.
5. The porous diaphragm of claim 4 in which said support fabric is a polyolefin selected from the group consist-ing of polypropylene, polytetrafluoroethylene, fluorinated ethy-lene-propylene co-polymer, polychlorotrifluoroethylene, poly-vinyl fluoride and polyvinylidene fluoride.
6. The porous diaphragm of claim 5 in which said support fabric is selected from the group consisting of poly-tetrafluoroethylene and polyvinylidene fluoride.
7. The porous diaphragm of claim 6 in which X is a metal selected from the group consisting of Mg, Ca, Al and mixtures thereof.
8. The porous diaphragm of claim 1 in which from about 15 to about 70 percent of the total permeability of the support fabric is provided by said regions in which the flow is sub-stantially laminar.
9. The porous diaphragm of claim 6 in which said support fabric is polytetrafluoroethylene.
10. The porous diaphragm of claim 8 in which said support fabric is a felt fabric.
11. The porous diaphragm of claim 1.0 in which said siliceous composition is selected from the group consisting of sepiolites and meerschaums.
12. The porous diaphragm of claim 11 in which the permeability to alkali metal chloride brines is from about 100 to about 1000 milliliters per minute at a head level difference in said cell of from about 0.1 to about 20 inches of said alkali metal chloride brine.
13. The porous diaphragm of claim 3 in which said support fabric is a polyarylene sulfide selected from the group consisting of polyphenylene sulfide, polynaphthylene sulfide, poly(perfluorophenylene) sulfide, and poly(methylphenylene) sulfide.
14. The porous diaphragm of claim 13 in which said support fabric is polyphenylene sulfide.
15. The porous diaphragm of claim 1 or claim 8 in which said regions of laminar flow comprise a plurality of fiber bundles.
16. The porous diaphragm of claim 7 in which said support fabric comprises a first layer and a second layer.
17. The porous diaphragm of claim 16 in which said first layer of said support fabric is selected from the group consisting of polytetrafluoroethylene and polyvinylidene fluoride.
18. The porous diaphragm of claim 16 in which said first layer is a net and said second layer is a felt fabric.
19. The porous diaphragm of claim 17 in which said first layer is a felt fabric.
20. The porous diaphragm of claim 19 in which said second layer is polyphenylene sulfide.
21. The porous diaphragm of claim 20 in which said second layer is a felt fabric.
22. The porous diaphragm of claim 21 in which said siliceous composition is selected from the group consisting of sepiolites and meerschaums.
23. In an electrolytic diaphragm cell for the electro-lysis of aqueous solutions of ionizable compounds, said cell having an anode assembly containing a plurality of anodes, a cathode assembly having a plurality of cathodes, a diaphragm separating said anode assembly from said cathode assembly, and a cell body housing said anode assembly and said cathode assembly, the improvement which comprises a porous diaphragm comprising a thermoplastic organic polymer support fabric impregnated with particles of a siliceous composition having the formula:
(X)m(Si)p(O)q(H)r nH2O
wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al, Zn and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
q is a number from 2 to about 5p + r;
r is zero to about 4p; and n is zero to about 30;
said siliceous composition being capable of undergoing hydra-tion when in contact with at least one of said ionizable com-pounds in an electrolytic cell; said support fabric having regions through which the flow of said aqueous solutions is substantially laminar.
(X)m(Si)p(O)q(H)r nH2O
wherein X is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Al, Zn and mixtures thereof;
p is a number from 1 to about 16;
m is zero to about p;
q is a number from 2 to about 5p + r;
r is zero to about 4p; and n is zero to about 30;
said siliceous composition being capable of undergoing hydra-tion when in contact with at least one of said ionizable com-pounds in an electrolytic cell; said support fabric having regions through which the flow of said aqueous solutions is substantially laminar.
24. The porous diaphragm of claim 14 in which X is a metal selected from the group consisting of Mg, Ca, Al and mixtures thereof.
25. The porous diaphragm of claim 24 in which from about 15 to about 70 percent of the total permeability of the support fabric is linear permeability.
26. The porous diaphragm of claim 25 in which said support fabric is a felt fabric.
27. The porous diaphragm of claim 26 in which said siliceous composition is selected from the group consisting of sepiolites and meerschaums.
28. The porous diaphragm of claim 27 in which the permeability to alkali metal chloride brines is from about 100 to about 1000 milliliters per minute at a head level difference in said cell of from about 0.1 to about 20 inches of said alkali metal chloride brine.
29. The porous diaphragm of claim 23 or 24 in which said regions of laminar flow comprise a plurality of fiber bundles.
30. The porous diaphragm of claim 24 in which said support fabric comprises a first layer and a second layer.
31. The porous diaphragm of claim 30 in which said first layer of said support fabric is selected from the group consisting of polytetrafluoroethylene and polyvinylidene fluoride.
32. The porous diaphragm of claim 30 in which said first layer is a net and said second layer is a felt fabric.
33. The porous diaphragm of claim 31 in which said first layer is a felt fabric.
34. The porous diaphragm of claim 33 in which said second layer is polyphenylene sulfide.
35. The porous diaphragm of claim 34 in which said second layer is a felt fabric.
36. The porous diaphragm of claim 35 in which said siliceous composition is selected from the group consisting of sepiolites and meerschaums.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/947,235 US4207163A (en) | 1977-09-26 | 1978-09-29 | Diaphragms for use in the electrolysis of alkali metal chlorides |
| US947,235 | 1992-09-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1159391A true CA1159391A (en) | 1983-12-27 |
Family
ID=25485794
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000333779A Expired CA1159391A (en) | 1978-09-29 | 1979-08-15 | Thermoplastic polymer electrolysis diaphragm impregnated with siliceous composition |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5547388A (en) |
| AU (1) | AU5124479A (en) |
| BE (1) | BE879081A (en) |
| BR (1) | BR7906156A (en) |
| CA (1) | CA1159391A (en) |
| DE (1) | DE2939222A1 (en) |
| FR (1) | FR2437450A2 (en) |
| IT (1) | IT1120595B (en) |
| NL (1) | NL7907042A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3420388A1 (en) * | 1984-05-04 | 1985-11-07 | BBC Aktiengesellschaft Brown, Boveri & Cie., Baden, Aargau | Diaphragm for an electrochemical cell |
-
1979
- 1979-08-15 CA CA000333779A patent/CA1159391A/en not_active Expired
- 1979-09-21 NL NL7907042A patent/NL7907042A/en not_active Application Discontinuation
- 1979-09-26 BR BR7906156A patent/BR7906156A/en unknown
- 1979-09-26 AU AU51244/79A patent/AU5124479A/en not_active Abandoned
- 1979-09-27 DE DE19792939222 patent/DE2939222A1/en not_active Withdrawn
- 1979-09-28 JP JP12524479A patent/JPS5547388A/en active Pending
- 1979-09-28 FR FR7924272A patent/FR2437450A2/en active Pending
- 1979-09-28 IT IT50403/79A patent/IT1120595B/en active
- 1979-09-28 BE BE0/197386A patent/BE879081A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BR7906156A (en) | 1980-06-24 |
| IT7950403A0 (en) | 1979-09-28 |
| FR2437450A2 (en) | 1980-04-25 |
| NL7907042A (en) | 1980-04-01 |
| IT1120595B (en) | 1986-03-26 |
| BE879081A (en) | 1980-03-28 |
| JPS5547388A (en) | 1980-04-03 |
| DE2939222A1 (en) | 1980-04-17 |
| AU5124479A (en) | 1980-04-03 |
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