CA1179635A - Technique of prestressing semi-permeable membranes - Google Patents
Technique of prestressing semi-permeable membranesInfo
- Publication number
- CA1179635A CA1179635A CA000213657A CA213657A CA1179635A CA 1179635 A CA1179635 A CA 1179635A CA 000213657 A CA000213657 A CA 000213657A CA 213657 A CA213657 A CA 213657A CA 1179635 A CA1179635 A CA 1179635A
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- Canada
- Prior art keywords
- anode
- cell
- compartment
- cathode
- barrier
- 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
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
- C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/20—Manufacture of shaped structures of ion-exchange resins
- C08J5/22—Films, membranes or diaphragms
- C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
- C08J5/2218—Synthetic macromolecular compounds
- C08J5/2231—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds
- C08J5/2237—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds containing fluorine
-
- 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
- C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
- C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
- C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
- C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Metallurgy (AREA)
- Electrochemistry (AREA)
- Inorganic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
- Electrolytic Production Of Metals (AREA)
- Water Treatment By Electricity Or Magnetism (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An electrolytic cell suitable for use in electrolyzing ionizable chemical compounds, particularly alkali metal halide brines and hydrohalic acids, which comprises a cell body having an anode compartment containing a porous anode and a cathode compartment containing a cathode said compartments being sepa-rated from each other by a barrier which is substantially impervious to gases and liquids and which is selected from a hydrolyzed copolymer of a perfluorinated hydrocarbon and a sulfonated perfluorinated hydrocarbon and a sulfonated perfluoro-vinyl ether, and a sulfostyrenated perfluorinated ethylene propylene polymer, said barrier being clamped or stretched to the front face of said porous anode.
Such cells can be operated at constant low voltage, and are not subject to erratic operating voltages which are due, in part at least, to the accumulation of gases between the anode and diaphragm.
An electrolytic cell suitable for use in electrolyzing ionizable chemical compounds, particularly alkali metal halide brines and hydrohalic acids, which comprises a cell body having an anode compartment containing a porous anode and a cathode compartment containing a cathode said compartments being sepa-rated from each other by a barrier which is substantially impervious to gases and liquids and which is selected from a hydrolyzed copolymer of a perfluorinated hydrocarbon and a sulfonated perfluorinated hydrocarbon and a sulfonated perfluoro-vinyl ether, and a sulfostyrenated perfluorinated ethylene propylene polymer, said barrier being clamped or stretched to the front face of said porous anode.
Such cells can be operated at constant low voltage, and are not subject to erratic operating voltages which are due, in part at least, to the accumulation of gases between the anode and diaphragm.
Description
;35 Field o This invention relates to improYements in e1ectrolytic cel 1 s . More parti cul arly i t rel ates ~o i mprovements i n el ectrolyti c cells wherein the anode and cathode are separated by a cation-active S perms~lecti~e membrane.
The electrolysis of aqueous solutions of ionizable chemical compounds, particularly of brine solutions, 1n a cell equipped with an anode and a cathode separa~ed by a porous diaphragm, l barrier, or septum, k well known in this art. In mcst instances, such cells, be they two compartment or multicompartment cells, are operated under conditions such that ionic and molecular migrati~n through the porous diaphragm occurs to ~ substankial degree result-ing ~n contaminat~on o~ the cathode liquor with undecomposed elec-trolyte and of th~ anode liquor with reac~lon products o~ the cathodic material and the anodlc materials.
It hds b~en proposed to replac~ the porous diaphragm in such cells wlth ~ barrler ~mpervious, or sub~tantially so, to both liqulds and gases thereby ~o control bo~h ionic and molecular migrat~on during electrolysis. Many pa~ents~ such as USP 2,967~07, USP 3~390~O55D ~nd French Patent 1D510~2650 disclose electrolytic cells incorporat~ng as the b~rrier, membranes fabricated from synthetic organlc ion-exchange resins. However such res~ns have not been entirely satis~actory due ~o their sens~tlv~ty to the stron~ caustic ar acid~c media with which they wer~ ~n cantact 7~3~;~3~
during use, or the voltage drop through the membrane became excess;ve as the ca~stic concentration increased, or such resins and/or their fabric-ation were too costly.
More recently, as disclosed in Canadian Patent 9~8,051, E.H. Cook Jr et al., issued April 27~ 1976, high purity products in high yield without undue loss of electrical current and loss of product yield due to ionic and/or molecular migration could be obtained when the electrolytic cells comprised a barrier formed from a permselective membrane composed essentially of a hydrolyzed copolymer of tetrafluoroethylene and a sulfonated perfluorovinyl ether. This barrier material was found to possess the desirable attributes of retaining its effectiveness, that is chemical inertness, over extended periods oF use in electrolytic cells.
~owever the barrier material was found to expand duriny use under the cell operating conditions. This resulted in the development of folds and/or creases on the anode side of the barrier and the entrapment of chlorine gas (when brine was used as the anolyte~ in the folds and/or creases. Such entrapment of gaseous products resulted in half cell voltage read1ngs in both anode and cathode compartments which were about n.4 to 0.6 volts higher than normally expected.
Moreover, in such cells9 the membrane is positioned apart ~rom the electrodes so that a gap of about 1/8 inch or more between the membrane and the surface of the anode was maintained. This gap was found to result in cell voltages under normal operating conditions which were in excess of those which, were to be expected from the conductivity of the brine solution. ~areful volta geanalysis of the o~erating cells has shcwn that khe erratic voltages were, in part, associated wikh a~asing problem at khe anode. It has been observed that at times gas would accumulate at the upper portion of the anode structure causing an uneven distribution of the electrical cllrrent on the anode.
This invenkion seeks to provide an effective methcd for khe production of barriers for use in electrolytic cells which do not ~ ~ergo subskantial e~pansion durlng operation of the cell.
75~3S
The ir~ention also seeks to provide imprcved bar~iers for use m electrolytic cells which do not cause substantial increases in the half cell voltages of the anode and catho~e ccmpartments of the cell during operation thereof.
Still further the invention seeks to assemble such a cell con-taining a cation-active permselective membrane barrier in such a manner as to consistently maintain the lowest possible operating cell voltage.
In accordance with the invention there is provided a cathode and a barrier me~ber which is substantially impervious to gases an~
1 0 fluids which carrier member is positioned firmly against the front face of the anode i.e., the surface of the anode which faces the cathode member of the cell. In this configuration, all of the gas generated at the anode is forced to the backside of the anode and consequently cannot accumulate between the ancde and the membrane thus causing erratic or uneven distribution of the current at the anode. In particular the barrier member may be ccmposed of at least one cation-active perm-selective material.
The barrier may ccmprise a support, a porous anode rnounted on the support and at leask one permselective memhrane afflxed to the support wherein the me~rane covers onc face of the porous anode.
In placing the membrane barrier member on the anode, the ~brane is suitably boiled in water ~ox at least one hour prior to mount-ing, stretched, clar~ped in place and then glued in place by means of a suitable adhesive or the like methcds flrther described hereir~fter.
Thus in accordance with one aspect of the invention there is provided an electrolytic cell which comprises a cell bcdy having an anode ccmpHrtment containing a porous anode, connected to an electrical input source, a ca~hode canpartment containing a cath~de said compartments being separated frorn each other by a ~arrier which i5 substantially impervious to gases ar~ fluids, said barrier being mounted across the front face of said porous anode.
63~;
In accordance with another aspect of the invention there is prcvided a process for the electrochenical decomposition of an aquecus solution of an ionizable che~ical compcund which comprises introducing an aqueous so~ution of alkali metal halide or hydrochloric acid into the anode compartment of an electrolytic cell, comprlsing a cell kcdy having an anode ccmparbment containing a F~rous ancde, a cathode comparbment con-taining a ca~hode said comparbments keing separated fran each other by a barrier which is substantially impervious to gases and fluids, said barrier being affixed to the front face of said porcus anode, and effect-ing the electrolytic deco~position of said aqueous solution by passing an electric current between the anode and cathode of said cell.
In still another aspect of the invention there is provided an electrolytic cell which comprises a cell bcdy having an ancde compartment containing a porous anode, a cathode compartment coNtaining a cathode said ccmpartments being separated fr~n each other by a barrier which is substantially impervicus to gases and fluids, said karrier having been pretreatsd by boiling in water for at least one hour, tautly stretched, dried at ambient temperatures and cemented acros~ the front fa~e of said porous anode.
In each c~ase the barrier is select~d fran ta) a hydroly~ed copolymer of a perfluRrinated hydrocarbon sulfonated perEluorovinyl ether a~d (b) a sulfostyrenated perfluRrinated ethylene propylene polymer.
In yet another aspect of the invention there is provided a barrier section for use in electrolytic cells comprising:
1) a karrier support,
The electrolysis of aqueous solutions of ionizable chemical compounds, particularly of brine solutions, 1n a cell equipped with an anode and a cathode separa~ed by a porous diaphragm, l barrier, or septum, k well known in this art. In mcst instances, such cells, be they two compartment or multicompartment cells, are operated under conditions such that ionic and molecular migrati~n through the porous diaphragm occurs to ~ substankial degree result-ing ~n contaminat~on o~ the cathode liquor with undecomposed elec-trolyte and of th~ anode liquor with reac~lon products o~ the cathodic material and the anodlc materials.
It hds b~en proposed to replac~ the porous diaphragm in such cells wlth ~ barrler ~mpervious, or sub~tantially so, to both liqulds and gases thereby ~o control bo~h ionic and molecular migrat~on during electrolysis. Many pa~ents~ such as USP 2,967~07, USP 3~390~O55D ~nd French Patent 1D510~2650 disclose electrolytic cells incorporat~ng as the b~rrier, membranes fabricated from synthetic organlc ion-exchange resins. However such res~ns have not been entirely satis~actory due ~o their sens~tlv~ty to the stron~ caustic ar acid~c media with which they wer~ ~n cantact 7~3~;~3~
during use, or the voltage drop through the membrane became excess;ve as the ca~stic concentration increased, or such resins and/or their fabric-ation were too costly.
More recently, as disclosed in Canadian Patent 9~8,051, E.H. Cook Jr et al., issued April 27~ 1976, high purity products in high yield without undue loss of electrical current and loss of product yield due to ionic and/or molecular migration could be obtained when the electrolytic cells comprised a barrier formed from a permselective membrane composed essentially of a hydrolyzed copolymer of tetrafluoroethylene and a sulfonated perfluorovinyl ether. This barrier material was found to possess the desirable attributes of retaining its effectiveness, that is chemical inertness, over extended periods oF use in electrolytic cells.
~owever the barrier material was found to expand duriny use under the cell operating conditions. This resulted in the development of folds and/or creases on the anode side of the barrier and the entrapment of chlorine gas (when brine was used as the anolyte~ in the folds and/or creases. Such entrapment of gaseous products resulted in half cell voltage read1ngs in both anode and cathode compartments which were about n.4 to 0.6 volts higher than normally expected.
Moreover, in such cells9 the membrane is positioned apart ~rom the electrodes so that a gap of about 1/8 inch or more between the membrane and the surface of the anode was maintained. This gap was found to result in cell voltages under normal operating conditions which were in excess of those which, were to be expected from the conductivity of the brine solution. ~areful volta geanalysis of the o~erating cells has shcwn that khe erratic voltages were, in part, associated wikh a~asing problem at khe anode. It has been observed that at times gas would accumulate at the upper portion of the anode structure causing an uneven distribution of the electrical cllrrent on the anode.
This invenkion seeks to provide an effective methcd for khe production of barriers for use in electrolytic cells which do not ~ ~ergo subskantial e~pansion durlng operation of the cell.
75~3S
The ir~ention also seeks to provide imprcved bar~iers for use m electrolytic cells which do not cause substantial increases in the half cell voltages of the anode and catho~e ccmpartments of the cell during operation thereof.
Still further the invention seeks to assemble such a cell con-taining a cation-active permselective membrane barrier in such a manner as to consistently maintain the lowest possible operating cell voltage.
In accordance with the invention there is provided a cathode and a barrier me~ber which is substantially impervious to gases an~
1 0 fluids which carrier member is positioned firmly against the front face of the anode i.e., the surface of the anode which faces the cathode member of the cell. In this configuration, all of the gas generated at the anode is forced to the backside of the anode and consequently cannot accumulate between the ancde and the membrane thus causing erratic or uneven distribution of the current at the anode. In particular the barrier member may be ccmposed of at least one cation-active perm-selective material.
The barrier may ccmprise a support, a porous anode rnounted on the support and at leask one permselective memhrane afflxed to the support wherein the me~rane covers onc face of the porous anode.
In placing the membrane barrier member on the anode, the ~brane is suitably boiled in water ~ox at least one hour prior to mount-ing, stretched, clar~ped in place and then glued in place by means of a suitable adhesive or the like methcds flrther described hereir~fter.
Thus in accordance with one aspect of the invention there is provided an electrolytic cell which comprises a cell bcdy having an anode ccmpHrtment containing a porous anode, connected to an electrical input source, a ca~hode canpartment containing a cath~de said compartments being separated frorn each other by a ~arrier which i5 substantially impervious to gases ar~ fluids, said barrier being mounted across the front face of said porous anode.
63~;
In accordance with another aspect of the invention there is prcvided a process for the electrochenical decomposition of an aquecus solution of an ionizable che~ical compcund which comprises introducing an aqueous so~ution of alkali metal halide or hydrochloric acid into the anode compartment of an electrolytic cell, comprlsing a cell kcdy having an anode ccmparbment containing a F~rous ancde, a cathode comparbment con-taining a ca~hode said comparbments keing separated fran each other by a barrier which is substantially impervious to gases and fluids, said barrier being affixed to the front face of said porcus anode, and effect-ing the electrolytic deco~position of said aqueous solution by passing an electric current between the anode and cathode of said cell.
In still another aspect of the invention there is provided an electrolytic cell which comprises a cell bcdy having an ancde compartment containing a porous anode, a cathode compartment coNtaining a cathode said ccmpartments being separated fr~n each other by a barrier which is substantially impervicus to gases and fluids, said karrier having been pretreatsd by boiling in water for at least one hour, tautly stretched, dried at ambient temperatures and cemented acros~ the front fa~e of said porous anode.
In each c~ase the barrier is select~d fran ta) a hydroly~ed copolymer of a perfluRrinated hydrocarbon sulfonated perEluorovinyl ether a~d (b) a sulfostyrenated perfluRrinated ethylene propylene polymer.
In yet another aspect of the invention there is provided a barrier section for use in electrolytic cells comprising:
1) a karrier support,
2) a porous anode m~unted on said karrier suppo~t, an~
3) at least one permselective membrane consisting essentially of a hydrolyzed copolymer of tetrafluor oe thylene and a sulfonated polyfluorc~inyl ether of the fornula:
FSO2CF2CF20CF(CF2)CF2CCF 2 said memhrane having been imnersed in boiling aquec~s medium for at least one ho~r, stretchel, dried in the stretched condition at ambient 6~S
temperature and then sec~rely affixed while ~aut to said b~rrier sup~ort, s~;~ membrane c w ering one face of said porous anode.
"Membrane Material" as used in the following description refers to such material consisting essentially of at least one cation-active permselective material selected fram the group consisting of a hydrolyzed cop~lymer of a perfluorinated hydrocarbon an~d a fluorosulonated per-fluor w inyl ether, and a sulfostyrenated perfluorinated ethylene propylene polymer.
In order that the invention may be more readily understood, it ]O will be described with specific reference to varicus apparatus and methods suitable for the electrolysis of an aqueous solution of sodium chloride whereby chlorin~, caustic soda, and hydrogen are efficiently and economically produ~ed. It is not, however, -to be construed as limited thereto except as defined in the appended claims.
In the following description of the preferred e~kodiments of the present invention references will be made to the draw mgs attached hereto of which -Fig. 1 is a schematic representation of a conventional two compartment electrolysis embodying the novel anode configuration.
Fig. 2 is a partial sectional view of a Eorc~mmous screen anode haviny ernplaced on one surface thereof a cation-active pe~m-selective membrane.
Fig. 3 is a partial sectional view of a double porous anode having a m~mbrane member securely affixed to the front face of each of the porcus anodes.
Fig. 4 is a sectional view of a rnulticomQartment cell, camprisin~ a single kuff~r comparbment incorporating the present invention.
Fig. 5 is a schematic view of the three frames making up a buffer section in accordance with a preferred m~dification of the present invention.
- 5a -1~l7~t~3~
Fig. 6 is a sectional view of a three ~ ~partment electrolysis cell incorporating a preferred modification o~ the present invention.
Thus, in accordance with a preferred mcde of carrying out this invention, an elertrolyt}c cell for decomposing aqueous sodium chloride solutions is shcwn in Fig. 1 wherein the electroly~ic cell, 1, comprises a porcus anode, 2, and a cathode 3, which are separated by a cation-active permselective me~brane position on one sur-face of the anode and held in place thexeon by m~ans o suitable support m~ans, such as clamps, not shown, or cemented in place thereon by suitable adhesive means. There is thus formed an anolyte compartment 13, and a catholyte compartment 14. The cell 1, has an inlet 5, in the anolyte compartment, for the electrolyte, i.e., the brine solution, an outlet 10, for the spent electrolyte and an outlet 6, for the chlorine gas formed on~the back face of the porous anode.
1~7~3~3S
There is also provided an inlet, 7, for charging liquids, such as dilute aqueou~ caustic soda, ~o the catholyte compartment, 14~ an outlet9 8~ for discharging N~OH liquor from the catholyte compartment and an outlet, 9~ for d~scharging gas, such as hydrogen gas, ~srmed a~ the surface of the cathode.
In opera~ion of this electrolytic cell, 1, sa~urated br~ne preferably, brine which has been acidified by the additjon thereto of an acid, such as hydrochloric acid~ to a pH of about 3 to abou~ 5~ is continuously circulated in the anolyte compartment, 13, by introductng the brine through ~nlet, S, and ~lithdra~ing it through outlet for overflow, 70~ to ~he replenishing zone~ 117 where the spent brine is resa~urated with sodium chloride and acidified with acld, e.g ~Cl,~if desired. The replenished brine flows, v~a line 12, to reonter the oel1, 1, at lnlet 5~
Conourrently, d11u~e aqueous liquor, such as ~ilute aqu~ous caustic soda is charged to the catholyte compartment, 14, throutJh liquid inlet, 7, and discharged ~rom said comPartm~nt, 14, through overflow outlet, ~. Thereby the aqu~ous liquor ls ooncentrated with respect to the product ~ormed at the cathode, e.g.~ caustic soda, and the dlsoharged liquor contaln~ng little or substant~ally no sodium chloride~ is directed tn a suitable recovery means for concentrat1On and sep~rat~on of the desired produc~. Additional dilute aqueous liquor is charged to ~he catho7.yte compartmen~ which together with the water wh~oh passes through the permselective diaphragm by osmcsis serves as makeup for the catholy~e. Gaseous products, e.g., hydrogerl, form2d at the ~hode, are diseharged ~rom the cell through gaseous outlet, 9.
~ 3 S
By positioning the cation-active permselective membrane firmly in place on ~he ~ront face of ~he porous anodet i.e., the surface of the anode which is spaced from bu~ facing the cathode member, the membrane remains fixed thereon wi~hout sags or gaps~ and the evolution of gas is restric~ed to the back ~ace o~ the anode. Thereby, the diff~culties of erratio voltages occasioned by the aceumu1ation of gas be~een the anode and the membrane are avoided and more consistent voltages can be obtain~d.
As indicated above the anode member i5 a porous anode, preferably a mesh or screen anodeO Such a porous anode is required to provide a path ~5~ ~he passage of ions, e~g.~ sodium ions ~hrough the cation-active pern~elective membrane from the anolyte compartment into ~he catholy~e compartnlent. A schemati - vlew of a preferred screen anode having the membrane affixsd thereto is shown in Fig. 2, As illustrated in this schematic view of a portion of the anode, which is a partial sectional view, the anode member, 22, is a foraminous mesh screen having ernplaced therein, a membranous barri~r menlber, 21.
The n~mbrane may b~ adhesively f1xe~ ln place on the foram~nous mesh screen surface or maintalned ~n place by means of clamps, bars and the like (not shown). The membrane ~s securely ma~n~ained in place on the surface o~ the ~oraminous soreen so as to prevent the formation of gaps or sags in the diaphr~gm, By this arrangemen~ evclut-on of gas occurs solely on the back side of the porous anode and such gas is readily discharged from the anode and thence from the cell.
Another anode des~gn incorporating the present invention is ~llustrated in Flg, 3 which ls a par~al sectional view of a double L7~6~3S
Porous anode having a membrane ~ixedly secured over the front face of each of the foraminous screen anodes. This anode arrangemen~ is ; suitable for use in ~he so-called fil~er-press type of electrolysis cell. As shown in th1s ~igure a ~rame me~ber 31 is provided with a br~ne outlet, 35O a br~ne 1nlet~ 34, and a gas outlet, 36 The frame serves as a support ~ember for two foram~nous screen anodes 32~ on the front sur~ace of wh~ch is placed a cat~on-active permselect~ve membrane, 33. The membrane is held in place over the surface of the porous anode by the nut and bolt arrangemænt9 37 38 placed at the outer periphery of the membrane and extends through the flange merrber, 39~
of frame~ 31. Curre. ~ ~s supplied to ~he porous anode members 32 by means of risers, solid bars of conductive metal9 40. By this arrange-ment~ brine admitted to the cell is decomposed on the back face o~ the anode and the liberated chlorine gas travels unimpeded to the gas outlet. Inasmuch as no sags or ~aps appear in the men~rane, no electrolysis occurs on the covered sur~ace of the anode ~nd henoe no chlorine iis liberated or trapped at th~s interface. Sodlum i ons travel through the porous ano~e and m~grate through the cation~active membrane into th~ cathode compartment. Substantially no sod1llm chloride passes through the impervlous barrier into the cathode com-partment As shown in the drawing the covered surface of the porous anode is offset from t:he flange ~mber of the frameO Such an arrangement is to be preferred, since the membrane in passing over the shoulder formed by the offset portion of the anode to the flan~e is stretched and thus ~s more rigidly held in place on the surface of the _ g ~7~ 5 anode. As will be obvious, the anode face may be in a flush arrangement wtth the flange member, also. In this alterna~e arrangement, the membrane is held firmly in place on the surface o~ the anode by the bol~n~ or clamping mean~, alone.
The ~orous~anode having a ca~ion-active permselective membrane ~ held firmly in place on one surface thereof may be used nok only in a ; two compar~mænt electrolytic cell as described above but also ;n electrolytic sells con~ainlng three or more compartmen~s. In such cells~ wh kh are su~table also for the electroly~ic deco~position of hydro~alic acid solut~on e~g~, hydrochloric acid solution, alkali metal hallde br~nes and the l~ke~ there is provlded a cell body having an anode compartment contain~ng a porous anode, a cathode eompartment contain~ny a cathode, and at least one buf~er compartment between sa~d anode and cathode compartments, sa~d compar~ments being separated ~rom each oth~r hy a barrier compr1s1ng a cation~active pernselectiYe ~emb~ane which 1s imper~10us to ~luids and gases. Such ~ m~lt1com-partment cell is shown ~n F~gure 4, whlch ls a schematic represen~ation of a three comp~r~men~ cell ~ncorpora~lng the presen~ invention.
In this representation, the cell hou~1ng or body~ 50, is formed Z 1nto an anode compartment, 51, a cathode compartment~ 58, and a bu~fercompart~nt, 55 whlch separates the anode and ca~hode compartments.
A porous anode, 62~ shown herein as a foraminous gcreen or mesh anode, and a cathode, 52,~are disposed with-n the anode and cathode compartm2nts ` respectively. Forming ~he buffer compartment, 55, and separating it 25 from the anode compartment~ 51, and the cathode compartment~ 5~ are barriers or membranes. The membrane, 63, separa~ing the buffer oom-partment from the anode colnpartment is f~xedly positioned on the inside face of the anode, 62" wh~le the membrane, 64, separating the buffer compartment from the cathsde compar~ment is positioned apart from the cathode~ 52, in the usual manner. Both membranes, 63 and 64, are fonmed of cation-actiYe permselective fluorocarbon material as has been above defined.
The anode compartment~ 51, is provided wi~h an inlet~ 59, - throush which the electrolyte~ such as an alkali metal chloride brine solution is introduced. An outlet, 60, is also provided in the anode compartment through which the depleted electrolyte is re~oved from the ; anode compartmentO Addit~onally, the anode compartment is provlded with a gas outlet~ 619 through ~Ihich the gaseous decomposition products of the electrolysis, such as chlorine, which are formed substantially entirely on the back face of the anode, are discharged from the anode compartment. Although the br~ne inlet and etllorlne outlet are shown as being located in the upper portiGn of the anode compartment with the brine outlet in ~he lcwer port10n, o~her ~rr~ngements of ~hese appurten-ances m~y be utilized i~ desired.
The buffer compartmentl 55, ls provided ~lith an 1nlet, 56, and an outlet~ 57. When the electrolytic cell i5 used for the electrolysis o~ sodium chlorine to produce chlorine and caustic soda~ water may be introduced through inlet~ 56, as a feed to the buffer compartment and d~lute aqueous caustic soda may be w1thdrawn through outlet, 57.
The cathode compar~ment, 58, is provided wi~h a liquid inlet>
53, a liqu1d outlet~ 65, through wh1ch, respectively, in the electrolysis of a sod~um chloride brine, wa~er or dilute aqueous caustic soda are introduced and concentrated aqueous caustic soda, of high purity, is recovered as a produc~ of the electrolysis. The cathode compartment is provided~ also with an outlet, 54~ for the gaseous by-product, i.e., ~17~;35 hydrogen~ As in the instance of the anode com~artment, the positioning of the inlets and ou~lets of the buf~er and cathode compartments can be varied from that shown in Figure 4.
Further, the electrolysis cell shown in Figure 4 contains a single buffer compartment. Other cells containlng more than one buffer compartment between the anode and cath~de compartmen~s can be provided by insertion of one or more additional barrler or membrane members in the space provided between ~he said anode compartments9 as will be bbvious to those skilled in this art.
In accordance with another preferred mode of carrying out the invention~ a-membrane of predetermined dimenslons, sufficient to completely cover the anode member to which the mæ~brane is to be placed ln barrier relat~onship, is immersed in boiling water for a period of time~ generally about 1 to 4 h w rs, to render the membrane soft and pllable~ Thereafter the softened membrane is placed on a su1table fra~e, having the approximate d1rnenslons sf the said anode member. T~h~ mer~ane ~s stretched diagonally and clamped at khe corners o~ the frame. The sides of th~ mer~rane are then stretched and clamped to the sides of the frame~ The corner clamps are removed to leave a flat unobs~ructed surfaee.
The stretched ~embrane ~s left to dry at ambient conditions on the frame. After appl~cation of adhes~ve, for example an epoxy cement, to the flange portion of the anode member~ the frame is positioned on the anode member, so that the stretched membrane surface ls in contact with ~he adhesive containing side of the anode member. The frame ls pressed against the adhesive flange and clamped thereon.
~ ~ ~7~ ~3 ~
When the cement has set, about 1 to 3 hoursJ the elamps are removed and the frame is l;fted off the membrane, which is secured to the flange of the anode member. Preferably~ the slack~ i.e.~ the excess portion of the membrane overhanglng the anode member is trimmed and the edges cemented to flange with a s~itable adhesive materi al .
This alternate preferred meth~d and apparatus as used in forming the buffer section of a three compartment electrolysis cell will be described with reference to Fig. 5 of the attached drawings wh~ch sh~w schem~tic views of three frames making up a buffer section~
the first ~rame~ 71~ having pegs~ 74, along the sides o~ sa~d frame, a second frame, 72, having holes along the sides of said frame through wh~ch the pegs, 74, of sald first frame, 71~ fit, said second frame, 72, conta~ning a 11quid outle~, 76, and a l~qu~d ~nlet, 77, a third frame~ 73~ having hole~, ~8, along ~he sides thereof adapted to receive the pegs~ 74, of said ~irst fram~. Two membraneg sized to fit sver said second sect~on~ are 1ml~rsed ln boilin~ water until the membranes have become soft and pliable~ Therea~ter the softened membranes are plaoed on a stretching frarne, stretched diagonally and clamped a~ the corners of the said frame. The membrane slack is pulled over the side edges of the fra~e ~nd clamped at the sides~ The corn~r clamps ~re remvved and the stretohed membrane after be1ng perm1tted ~o dry is pos~tionad on one s~de of the above deser~bed second frame, 72, on wh1ch a layer of adhesive has been applied. The procedure ~s repeated with the second softened membrane and it is pos~t~oned on the oppos~te face of said second ~rame~ 72. Thereafter the membrane sandwich is ctamped 11'7~63E;
on the second frame~ 72, and the adhesive is p~nnitted ~o set or "dry". Then, a~ter clamps and stretching ~rames are removed, leaving the membrane seeurely attached to the faces of the said ~econd frame~ 72. Holes are punched ln the membranes corresponding to the holes, 75~ 1n the second frame, 72. The buffer sec~on assembly is completed by placing the first frame, 71~ on one side of the second frame, 72, w~th the pegsC 74, fitting through the holes, 75, of the seeond frame~ and the third frame, 73, on the opposite side of the second frame~ 725 with the holes, /8, meshing with the pegs, 74, extending through said second fra~e, 72, There is thus formed a bu~fer compartment through which a dilute bu ffer solution may be circulated, whlch compartment is separated from the anode compartment by a cat~on-active permselective barrier~ and from the cathode compartment by a second cation-active permselective barrier as ls sh~n in Fig. 6. When a suitable voltage is lmpressed between th~ anode and cathode of this three compartment cell the current ~s carrled substantially entirely by the flow of ~ons ~rom the anode compartment through the ~irst cat~on~act1ve permselective barrter into and through the bu~er compartment, through t~e second cation~actlve permselective barrier into the oathode compartment~
Leakage of the anolyte and anodic products into the cathode compartment is substantially prevented, as is the back m~gra~ion o~ catholyte and cathod1c products by the cation~active permselective barrlers and the buffer compartm~n~
The present inventlon has the desirable advantage over the prlor methods of ~nserting barriers in electrolytic cells~ in that by this proc~dure the half cell v~ltages ~n the anode and 3~a~3~3~
cathode sections of the cells do not increase substantial1y oYer those expected in such cells dur~ng normal operation. The me~branes remain fixed in pl~ce and do not ~orm the folds and/or creases which often occurred in prior membranes~
Thus ~he new procedure and apparatus results in the more efficient utilkation of electric power in the production of highly pure~ i.e. essentially salt free caustic soda and hydrogen free chlorine, operation o~ the cell at low cell voltage and high current effic~ency.
The ~embrane ra~erial used in th~s invention consists essentially of at least one cation~active permselective material selected from the group consisting of a hydrolyzed copolymer o~ a perfluortnated hydroca~bon and a fluorosulfonated per~luorovinyl ether and a sulfostyrenated perfluorina~ed ethylene propylene polym2r.
In a pre~erred embodiment of th~s invent~on the cation-active permselectlve membrailes are composed esserlt1ally o~
co~pclymers of te~ra~luoroethylene and a sulfonated p~rfluorovinyl-ether havin~ the formula FS02CF2CF20CF(~F3)CF20CF-CF2 sa~d copolymer having an equivalent ~eight o~ from about 900 to abvut 1600. Preferably the equivalent weight of the copolymer ts in the range of from about 1100 to about 1400.
Co-polymers of the character referred to above are pre-pared as disclosed ~n USP 3,2821875, by reacting, at a temperature bel~w about 110 de~rees centigrade a perfluorovinylether of the formula ~L7~3~
FS02CF2CF20CF(CF3)CF20CF-CFZ
with tetrafluoroethylene in an aqueous liquid phase, preferably at a pH of 8 or below, and in the presence of a free radical initiator such as ammonium persulfate. Subsequently this co-polymer is hydrolyzed : S to the free ac~d or salt formed by conventlonal means.
Thus~ the presently preferred cation selective ~embrane material is o~ a hydrolyzed copoly~er o~ a per~luorinated hydrocarbon and a fluorosulfonated per~luorovinyl ether. The perfluorinated hydrocarbon is preferably tetrafluoroethyiene al~hough other per-fluor~nated saturated and unsaturated hydrocarbons of from 2 to 5 carbon atoms can also be utilized, of which the monoolefinic hydro-: carbons are preferred9 especially those of 2 to 4 carbon atoms and most espec~ally those of 2 to 3 carbon atoms, e.g., tetrafluoroethylene, ànd hexafluoropropylene. The sulfonated perfluorovinyl ~ther which is most useful is that o~ the formula , ~02CF2CF20CF(CF3)cF20cF=cF2 Th~s material, named as perfluoro C2-~2-~luorosulfonylethoxy)-propyl~
v~nyl ether, may b~ modifted to e~ulvalent monomers, ~s by modifylng th~ ~nternal perfluorosul~onyle~hoxy moiety to the correspond~ng pro-poxy motety, and by altering the propyl group to ethyl or butyl group, and by rearrangin~ the posit~ons of subst~tutes of the sulfonyl group . thereon and by utilizat~on o~ the perfluoro lower alkyl groups respectively.
: The method of manufacture of the fluorosul~onyl copslymer is described ~n Example XY~I of the above referred to USP 3~282,875 and an alternate method ~s d~sclosed ~n Canadian patent 849,670, which also discloses the use of these and analogous membranes in fu~l cells, 7~63~
characterized therein as electrochemical ce'lls. In short, the copolymer can be made by reacting fluorosulfonated per~luorovinyl ether or the equ;valent w;th tetrafluoroethylene or equ;valent ;n the des;red prop-ortions in water at elevated temperatures and pressures for over an hour after which time the reaction mass is cooled. The mixture separates into a lower perfluoroether layer and an upper layer of an aqueous dispersior of the desired polymer. The molecular weight of the latter is indeterminate but the equivalent weight is from about 900 to about 1600, preferably from about 1100 to about 1400, and the percentage of the fluorosulfon-ated perfluorovinyl ether or corresponding compound is about 10 to 30 percent by weight, preferably about 15 to 20 percent by weight and most preferably about 17 percent by ~eight. The unhydrolyzed copolymer may be compression molded at high temperatures and pressures to produce sheets or membranes which may vary in thickness from about 0.002 to 0.5 mm. These then may be further treated to hydrolyze the pendant -502F
to ~ S03H groups as by boiling in water or in lO percent aqueous sulfuric acid or by the methods of the patents previously mentioned,. The presence of the -S03H groups may he verified by titration with standard base as described in the Canadian patent prevlously mentioned. Additional details of varlous processing steps are described in Canadian patent 752,427 and U.S. patent 3,041,317.
As discussed above, because it has been found that some expansion or swelling accompanies the hydrolysis of the copolymer, 3~i ;t is advantageous to posltion the copolymer membrane into a frame or other support means to hold it in place on the surFace of the electrode in the electrochemical cell. Thereafter it may bé clamped or cemented in place on the electrode and will be true without sags or gaps. The membrane material is preferably joined to the backing material, e.g., tetrafluoroethylene or other suitable filamentary - material prior to hydrolysis when the copolymer is still thermoplastic so ~hat the film of co-polymer covers each filament penetrating into the spaces or interstices of the backing material between them and even around behind them, the films becoming slightly thinner in the process where it covers the filaments.
The cation-active permselective membrane material described above is far superior when utilized in the electrochemical cell as described herein compared to previously suggested materials. The new material is more stable at elevated temperatures, e.g., above 75 C. It lasts for much longer periods in the medium of the electrolyte and does not beconle brittle when exposed to chlorine at high cell temperatures. Moreover when the rnembrane has been assembled on the face of the electrode elements of the cell as described herein, the permissable gap between the electrodes can be substantially reduced and maintained constant resulting in increased - power efficiency. Considering the savings in time, maintenance, and fabrication costs, these membranes are more economical. The voltage drop through the membranes is acceptable, does not vary due to the formation of gaps and sagging and does not become inordinately high as it does with many other membrane materials, when the caustic concentration in the cathode compartment increases to above about .
. ", , ..
1 ~ ~7~ 3 ~
2009/1. The selectivity of the me~brane and its compatability with the electrolyte does not decrease as the hydroxyl concentration of the catholyte l~quor ;ncreases, as has been noted with other membrane materials, nor does the caustic efficiency o~ the electrolysis diminish as significantly as it does with other membranes as the electrolysis proceeeds. Thus these improvements in the present membranes and the manner of emplacement thereof in the cell make it more practicable whereas previously disclosed ion-exchange me~brane mater~als haYe not attained commercial acceptance. While the more preferred copolymers are those having equivalent weights of from about 9ûO to about 160û, with about 1100 to about 1400 being especially preferred, some useful resinous membranes of this same genre have equivalent wei~hts within the range of about 500 to 4000. The intermediate equivalent weight copolymers are preferred because they are of satisfactory strengtil, stability, permselect1vity~ enahle better selective ion exchange to take place and are of lower ~nternal reslstance, all o~ which are 1mportant in the electrochem~cal art.
Improved vers10ns o~ th0 above-descr~bed copolymers may be made by chemi~al kreat~ent o~ the surfaces thereo~ as by treatments to modify the -S03H groups thereon. For example, the sulfonic acid groups may be altered or replaced in whole or in part w~th other moieties.
Such change~ may be made ~n th~ copolymer manufacturing proeess or after production of the membrane. When effected as a subsequen~ treatment of the membrane, the depth of the treatment will usually be from O.Q01 to 0.01 mm. Caustic efficienc1es of the improved processes using such rod~fied versions of the pres~n~ ~mproved membranes can increase about 3 to about 20% or more~ usually about 5 to 15%.
~L~l7~3~
Exemplary of such treatments is th~t described in french Pa~ent 2,152,194 of March 26, 1973 in which one stde of ~he ~luorocarbon membrane is treated with ammonia to convert the pendant sulfonyl groups to sulfonamide groups.
In addition to the copolymers d;scussed aboYe, including ~odif~cations thereof, 1t has been found that another membrane matertal is also sup~rior to prior art film for applica~ions in electrochemical cells. Although it aprlears that tetrafluDroethylene polynlers which are sequentially styrenated and sulfonated are not useful for making satisfactory cation-acti~e pern~elective ~mbranes acceptable for use in electrochemical processes, i~ has been found that per~luorinated ethylene propylene polymer whlch h~s been styrenated and sulfonated does make a useful cation-ac~iYe permselective membrane material.
Whereas useful ltves of as much as thr~e years or more (that o~ the preferred eopoly~r mater~al) may not be ob~alned w~th th~s alternate material, it is surprisingly resistant to hardening und~r normal use conditions.
To ~anu~cture the sul~ostyrenated perfluorinated ethylene propyl~ne polymers~ a commercially ava~lable perfluoroethylene propylene poly~er ~s styren~ted and then the styrenated product is sulfona~edg A solut~on o~ styrene ~n methylene chlor~de, benzene, or analogous solvent at a sui~able concentration in the range of about 10 to about 20 percent by welght ~s prepared and a sheet of the polymer having a ~hickness of about 0.02 ~o 0.5 mm9 preferably 0.05 to 0.15 mm, is in~nersed 1n the soluti~n. A~t~r removal" the sheet is subiected to a rad~ation treatment~, ustng a cobal~ 60 radiat1On source. The rate of application may be in the range of about 8000 rads~hr. and a totaï
- ~0 -~ 3 S
radiation application shou1d be about 0.9 me~erads. After rinsing the irradiated sheet with water~ the phenyl nuclei of the styrene port;on of the polyn~r are monosulfonated, preferably in the para position, by treatment with chlorosulfonic acid, fuming sulfuric acid (oleum) or sulfur trioxide, Prefer~bly chlorosulfonic acid in chloroform is used and the sulfonation may be completed in about l/2 hour at ambient temperature.
Examples of such useful membranes made by the abo~e described process are products of RAI Research Corporation, Hauppauge, New York, ln and are identified as 18STl2S and 16STl3S~ the former being 1~% styrenated and having about 2/3 ~f the phenyl nuclei monosul~onated and the latter being 16% styrenated and having 13/16 of the phenyl nucle1 monosulfonated.
To obtain 18% styrenation, a solution of 17 l/2% styrene in methylene chloride is utilized and to obtain a 16% styrenation, a 1&% styrene solution in methylene chlorld~ is employed.
Th~ products r~sultln~ from this process compare favorably with the pre~erred copolymers previously described gtving voltage drops o~ about 0.2 volt each fn a typ~cal electrochemical cell at a current density of 2 amperes/sq. in about the same as is obtained w~th the preferred copolymer.
The membran0s useful in the practlce of the present inven tion can be advantag~ously prepared and util ke~ in the form.of a th~n film, either as such or deposited on a inert support such as . a cloth woven of Teflon~ or glass f~bers. The thickness of such supported me~branes can be varied over a considerable range, for example, from about 5 to about 15 mils in thickness, ~L~796~
; The membrane can be fabrica~ed in any desired shape. As generally prepared the preferred co-polymer membrane material is obtained in the form o~ the sulfonyl fluorlde. In this non-acid form the polynmer ls somewh~t soft and pliable and can be seam- or bu~t-welded forming welds which are as strong as the membrane material itself. It is preferred that the polymeric material be shaped and formed in this non-acid sta~e. Foll~wing shaping and forming into the desired næmbrane configura~ion~ the material is conditioned for use as a barr~er by hydrolyzing the sulfonyl fluoride groups to free acid or sodium sul~onate groups by boiling in water or aqueous caustic soda solut~on. On bo11iny in water for about 16 hours, the conditioned n~mbrane undergoes swelling, about 28 percent, which is lsotropic, about 9 percent 1n each dlreotion, and the material becomes soft and pliable.
If desired the cQndltioning process, that is the hydrolysis of the sulfonyl fluoride groups~ can be combin~d w~th the 1nitial s~ep of this lnvention by carry~n~ out ~h~ immerslon ~n bo111ng aqueous medla for an exkended period over the 1 tv 4 hours required, merely to soften the co-polyner.
The electrodes for the present electrolytic c211 m~y be formed of any electrically conductive material which will resist the corrosive attack of the various cell reactan~s and products with which they may come in oontact, su~h as alkali metal hydroxides, hydrochloric acid~ and chlorine, Typically, the ca~hodes may be constructed of graphite, 1ron, steel~ or the like, with steel being g~n~rally preferred.
Similarly, the anodes may be forn~d of graphite or may be nætallic anodes. Typically~ the porous metalllc anodes may be fonmed of a so-called "valve" metal~ such as ~itan~um, ~an~al~m or niob1um as well as allsys of these in which the valve metal constitutes at least about ~ 3 ~
90% of the alloy. The surface o~ the va1ve metal may be made active by means of a coating comprising one or more noble metals, noble metal oxides, or mixtures o~ such oxides, either alone or with oxides of other metals. The noble metals which may be used include ruthenium, rhodium, palladium, iridium, and platinum. Particularly preferred metal anodes are those formed of titanium and having a mixed titanium - oxide and ruthenium oxide coating on the surface, as is described in U.S. Patent 3,632,498. Additionally, the valve metal substrate may be clad on a more electrically conductive metal core, such as aluminum, steel~ copper, or the like.
The cell body or container is formed into at least one set or unit of compartments made up of an anode compartment, containing the anode, a cathode compartment, containing the cathode, and may contain one or more buffer compartments between the anode and cathode compartments. Typically, the electrolytTc cell may conta~n a plural~y of these sets, e.g., 20 to 30 or more, depending upon the size o~
the cell.
The following example wlll illustrate the present invention.
Parts and percentages are by weight and temperatures are ~iven in degrees centigrade, unless otherwise specified.
LXAMPLE l A 37 inch tall, three compartment electrochemical cell was utilized in this example. In this cell the anode compartment containing a ruthenium oxide coated titanium clad steel anode was fed with a circulatin~ concentrated brine solution. The cathode compartment was filled initially with dilute aqueous caustic soda which during the electrolysis was continuously circulated. The cathode and anode com-partments were separated by a buffer compartmen~ which was ~o~led by placing t~Jo membranes one on the anode and one on the cathode. The membranes were composed of the hydroly2ed copolymer of perf1uoro-ethylene and a sulfonated perfluorovinylether as described herein-above. A dilute aqueous solution of sodium hydroxide ~Jas continuously circulated through this buffer compartment.
- In operating this three compartment cell an opera~lng current density of 2 amperes per square inch of anode surface was ap~lied and maintained. Anolyte to buffer to catholyte head differentials of from 0 to 12 inches were established and the voltage drop was measured periodically at several of the head differentials. By this means, the membrane separating the anode compartment was pushed from the anode surface and the effect of positioning the membrane apart from the anode surface on the cell volta~e was measured. The data obtained is set out ~n the tahle below, and in~licates that the cell voltage increased with increased differential head ~Ih~ch shows that the cell voltage increased as the gap between the anode surface and the membrane increased.
ABLE
Anolyte ~ead Diff~rential ~oltage Corrected to 2ASl in inches _ _ Current ~ensity o 4.ns
FSO2CF2CF20CF(CF2)CF2CCF 2 said memhrane having been imnersed in boiling aquec~s medium for at least one ho~r, stretchel, dried in the stretched condition at ambient 6~S
temperature and then sec~rely affixed while ~aut to said b~rrier sup~ort, s~;~ membrane c w ering one face of said porous anode.
"Membrane Material" as used in the following description refers to such material consisting essentially of at least one cation-active permselective material selected fram the group consisting of a hydrolyzed cop~lymer of a perfluorinated hydrocarbon an~d a fluorosulonated per-fluor w inyl ether, and a sulfostyrenated perfluorinated ethylene propylene polymer.
In order that the invention may be more readily understood, it ]O will be described with specific reference to varicus apparatus and methods suitable for the electrolysis of an aqueous solution of sodium chloride whereby chlorin~, caustic soda, and hydrogen are efficiently and economically produ~ed. It is not, however, -to be construed as limited thereto except as defined in the appended claims.
In the following description of the preferred e~kodiments of the present invention references will be made to the draw mgs attached hereto of which -Fig. 1 is a schematic representation of a conventional two compartment electrolysis embodying the novel anode configuration.
Fig. 2 is a partial sectional view of a Eorc~mmous screen anode haviny ernplaced on one surface thereof a cation-active pe~m-selective membrane.
Fig. 3 is a partial sectional view of a double porous anode having a m~mbrane member securely affixed to the front face of each of the porcus anodes.
Fig. 4 is a sectional view of a rnulticomQartment cell, camprisin~ a single kuff~r comparbment incorporating the present invention.
Fig. 5 is a schematic view of the three frames making up a buffer section in accordance with a preferred m~dification of the present invention.
- 5a -1~l7~t~3~
Fig. 6 is a sectional view of a three ~ ~partment electrolysis cell incorporating a preferred modification o~ the present invention.
Thus, in accordance with a preferred mcde of carrying out this invention, an elertrolyt}c cell for decomposing aqueous sodium chloride solutions is shcwn in Fig. 1 wherein the electroly~ic cell, 1, comprises a porcus anode, 2, and a cathode 3, which are separated by a cation-active permselective me~brane position on one sur-face of the anode and held in place thexeon by m~ans o suitable support m~ans, such as clamps, not shown, or cemented in place thereon by suitable adhesive means. There is thus formed an anolyte compartment 13, and a catholyte compartment 14. The cell 1, has an inlet 5, in the anolyte compartment, for the electrolyte, i.e., the brine solution, an outlet 10, for the spent electrolyte and an outlet 6, for the chlorine gas formed on~the back face of the porous anode.
1~7~3~3S
There is also provided an inlet, 7, for charging liquids, such as dilute aqueou~ caustic soda, ~o the catholyte compartment, 14~ an outlet9 8~ for discharging N~OH liquor from the catholyte compartment and an outlet, 9~ for d~scharging gas, such as hydrogen gas, ~srmed a~ the surface of the cathode.
In opera~ion of this electrolytic cell, 1, sa~urated br~ne preferably, brine which has been acidified by the additjon thereto of an acid, such as hydrochloric acid~ to a pH of about 3 to abou~ 5~ is continuously circulated in the anolyte compartment, 13, by introductng the brine through ~nlet, S, and ~lithdra~ing it through outlet for overflow, 70~ to ~he replenishing zone~ 117 where the spent brine is resa~urated with sodium chloride and acidified with acld, e.g ~Cl,~if desired. The replenished brine flows, v~a line 12, to reonter the oel1, 1, at lnlet 5~
Conourrently, d11u~e aqueous liquor, such as ~ilute aqu~ous caustic soda is charged to the catholyte compartment, 14, throutJh liquid inlet, 7, and discharged ~rom said comPartm~nt, 14, through overflow outlet, ~. Thereby the aqu~ous liquor ls ooncentrated with respect to the product ~ormed at the cathode, e.g.~ caustic soda, and the dlsoharged liquor contaln~ng little or substant~ally no sodium chloride~ is directed tn a suitable recovery means for concentrat1On and sep~rat~on of the desired produc~. Additional dilute aqueous liquor is charged to ~he catho7.yte compartmen~ which together with the water wh~oh passes through the permselective diaphragm by osmcsis serves as makeup for the catholy~e. Gaseous products, e.g., hydrogerl, form2d at the ~hode, are diseharged ~rom the cell through gaseous outlet, 9.
~ 3 S
By positioning the cation-active permselective membrane firmly in place on ~he ~ront face of ~he porous anodet i.e., the surface of the anode which is spaced from bu~ facing the cathode member, the membrane remains fixed thereon wi~hout sags or gaps~ and the evolution of gas is restric~ed to the back ~ace o~ the anode. Thereby, the diff~culties of erratio voltages occasioned by the aceumu1ation of gas be~een the anode and the membrane are avoided and more consistent voltages can be obtain~d.
As indicated above the anode member i5 a porous anode, preferably a mesh or screen anodeO Such a porous anode is required to provide a path ~5~ ~he passage of ions, e~g.~ sodium ions ~hrough the cation-active pern~elective membrane from the anolyte compartment into ~he catholy~e compartnlent. A schemati - vlew of a preferred screen anode having the membrane affixsd thereto is shown in Fig. 2, As illustrated in this schematic view of a portion of the anode, which is a partial sectional view, the anode member, 22, is a foraminous mesh screen having ernplaced therein, a membranous barri~r menlber, 21.
The n~mbrane may b~ adhesively f1xe~ ln place on the foram~nous mesh screen surface or maintalned ~n place by means of clamps, bars and the like (not shown). The membrane ~s securely ma~n~ained in place on the surface o~ the ~oraminous soreen so as to prevent the formation of gaps or sags in the diaphr~gm, By this arrangemen~ evclut-on of gas occurs solely on the back side of the porous anode and such gas is readily discharged from the anode and thence from the cell.
Another anode des~gn incorporating the present invention is ~llustrated in Flg, 3 which ls a par~al sectional view of a double L7~6~3S
Porous anode having a membrane ~ixedly secured over the front face of each of the foraminous screen anodes. This anode arrangemen~ is ; suitable for use in ~he so-called fil~er-press type of electrolysis cell. As shown in th1s ~igure a ~rame me~ber 31 is provided with a br~ne outlet, 35O a br~ne 1nlet~ 34, and a gas outlet, 36 The frame serves as a support ~ember for two foram~nous screen anodes 32~ on the front sur~ace of wh~ch is placed a cat~on-active permselect~ve membrane, 33. The membrane is held in place over the surface of the porous anode by the nut and bolt arrangemænt9 37 38 placed at the outer periphery of the membrane and extends through the flange merrber, 39~
of frame~ 31. Curre. ~ ~s supplied to ~he porous anode members 32 by means of risers, solid bars of conductive metal9 40. By this arrange-ment~ brine admitted to the cell is decomposed on the back face o~ the anode and the liberated chlorine gas travels unimpeded to the gas outlet. Inasmuch as no sags or ~aps appear in the men~rane, no electrolysis occurs on the covered sur~ace of the anode ~nd henoe no chlorine iis liberated or trapped at th~s interface. Sodlum i ons travel through the porous ano~e and m~grate through the cation~active membrane into th~ cathode compartment. Substantially no sod1llm chloride passes through the impervlous barrier into the cathode com-partment As shown in the drawing the covered surface of the porous anode is offset from t:he flange ~mber of the frameO Such an arrangement is to be preferred, since the membrane in passing over the shoulder formed by the offset portion of the anode to the flan~e is stretched and thus ~s more rigidly held in place on the surface of the _ g ~7~ 5 anode. As will be obvious, the anode face may be in a flush arrangement wtth the flange member, also. In this alterna~e arrangement, the membrane is held firmly in place on the surface o~ the anode by the bol~n~ or clamping mean~, alone.
The ~orous~anode having a ca~ion-active permselective membrane ~ held firmly in place on one surface thereof may be used nok only in a ; two compar~mænt electrolytic cell as described above but also ;n electrolytic sells con~ainlng three or more compartmen~s. In such cells~ wh kh are su~table also for the electroly~ic deco~position of hydro~alic acid solut~on e~g~, hydrochloric acid solution, alkali metal hallde br~nes and the l~ke~ there is provlded a cell body having an anode compartment contain~ng a porous anode, a cathode eompartment contain~ny a cathode, and at least one buf~er compartment between sa~d anode and cathode compartments, sa~d compar~ments being separated ~rom each oth~r hy a barrier compr1s1ng a cation~active pernselectiYe ~emb~ane which 1s imper~10us to ~luids and gases. Such ~ m~lt1com-partment cell is shown ~n F~gure 4, whlch ls a schematic represen~ation of a three comp~r~men~ cell ~ncorpora~lng the presen~ invention.
In this representation, the cell hou~1ng or body~ 50, is formed Z 1nto an anode compartment, 51, a cathode compartment~ 58, and a bu~fercompart~nt, 55 whlch separates the anode and ca~hode compartments.
A porous anode, 62~ shown herein as a foraminous gcreen or mesh anode, and a cathode, 52,~are disposed with-n the anode and cathode compartm2nts ` respectively. Forming ~he buffer compartment, 55, and separating it 25 from the anode compartment~ 51, and the cathode compartment~ 5~ are barriers or membranes. The membrane, 63, separa~ing the buffer oom-partment from the anode colnpartment is f~xedly positioned on the inside face of the anode, 62" wh~le the membrane, 64, separating the buffer compartment from the cathsde compar~ment is positioned apart from the cathode~ 52, in the usual manner. Both membranes, 63 and 64, are fonmed of cation-actiYe permselective fluorocarbon material as has been above defined.
The anode compartment~ 51, is provided wi~h an inlet~ 59, - throush which the electrolyte~ such as an alkali metal chloride brine solution is introduced. An outlet, 60, is also provided in the anode compartment through which the depleted electrolyte is re~oved from the ; anode compartmentO Addit~onally, the anode compartment is provlded with a gas outlet~ 619 through ~Ihich the gaseous decomposition products of the electrolysis, such as chlorine, which are formed substantially entirely on the back face of the anode, are discharged from the anode compartment. Although the br~ne inlet and etllorlne outlet are shown as being located in the upper portiGn of the anode compartment with the brine outlet in ~he lcwer port10n, o~her ~rr~ngements of ~hese appurten-ances m~y be utilized i~ desired.
The buffer compartmentl 55, ls provided ~lith an 1nlet, 56, and an outlet~ 57. When the electrolytic cell i5 used for the electrolysis o~ sodium chlorine to produce chlorine and caustic soda~ water may be introduced through inlet~ 56, as a feed to the buffer compartment and d~lute aqueous caustic soda may be w1thdrawn through outlet, 57.
The cathode compar~ment, 58, is provided wi~h a liquid inlet>
53, a liqu1d outlet~ 65, through wh1ch, respectively, in the electrolysis of a sod~um chloride brine, wa~er or dilute aqueous caustic soda are introduced and concentrated aqueous caustic soda, of high purity, is recovered as a produc~ of the electrolysis. The cathode compartment is provided~ also with an outlet, 54~ for the gaseous by-product, i.e., ~17~;35 hydrogen~ As in the instance of the anode com~artment, the positioning of the inlets and ou~lets of the buf~er and cathode compartments can be varied from that shown in Figure 4.
Further, the electrolysis cell shown in Figure 4 contains a single buffer compartment. Other cells containlng more than one buffer compartment between the anode and cath~de compartmen~s can be provided by insertion of one or more additional barrler or membrane members in the space provided between ~he said anode compartments9 as will be bbvious to those skilled in this art.
In accordance with another preferred mode of carrying out the invention~ a-membrane of predetermined dimenslons, sufficient to completely cover the anode member to which the mæ~brane is to be placed ln barrier relat~onship, is immersed in boiling water for a period of time~ generally about 1 to 4 h w rs, to render the membrane soft and pllable~ Thereafter the softened membrane is placed on a su1table fra~e, having the approximate d1rnenslons sf the said anode member. T~h~ mer~ane ~s stretched diagonally and clamped at khe corners o~ the frame. The sides of th~ mer~rane are then stretched and clamped to the sides of the frame~ The corner clamps are removed to leave a flat unobs~ructed surfaee.
The stretched ~embrane ~s left to dry at ambient conditions on the frame. After appl~cation of adhes~ve, for example an epoxy cement, to the flange portion of the anode member~ the frame is positioned on the anode member, so that the stretched membrane surface ls in contact with ~he adhesive containing side of the anode member. The frame ls pressed against the adhesive flange and clamped thereon.
~ ~ ~7~ ~3 ~
When the cement has set, about 1 to 3 hoursJ the elamps are removed and the frame is l;fted off the membrane, which is secured to the flange of the anode member. Preferably~ the slack~ i.e.~ the excess portion of the membrane overhanglng the anode member is trimmed and the edges cemented to flange with a s~itable adhesive materi al .
This alternate preferred meth~d and apparatus as used in forming the buffer section of a three compartment electrolysis cell will be described with reference to Fig. 5 of the attached drawings wh~ch sh~w schem~tic views of three frames making up a buffer section~
the first ~rame~ 71~ having pegs~ 74, along the sides o~ sa~d frame, a second frame, 72, having holes along the sides of said frame through wh~ch the pegs, 74, of sald first frame, 71~ fit, said second frame, 72, conta~ning a 11quid outle~, 76, and a l~qu~d ~nlet, 77, a third frame~ 73~ having hole~, ~8, along ~he sides thereof adapted to receive the pegs~ 74, of said ~irst fram~. Two membraneg sized to fit sver said second sect~on~ are 1ml~rsed ln boilin~ water until the membranes have become soft and pliable~ Therea~ter the softened membranes are plaoed on a stretching frarne, stretched diagonally and clamped a~ the corners of the said frame. The membrane slack is pulled over the side edges of the fra~e ~nd clamped at the sides~ The corn~r clamps ~re remvved and the stretohed membrane after be1ng perm1tted ~o dry is pos~tionad on one s~de of the above deser~bed second frame, 72, on wh1ch a layer of adhesive has been applied. The procedure ~s repeated with the second softened membrane and it is pos~t~oned on the oppos~te face of said second ~rame~ 72. Thereafter the membrane sandwich is ctamped 11'7~63E;
on the second frame~ 72, and the adhesive is p~nnitted ~o set or "dry". Then, a~ter clamps and stretching ~rames are removed, leaving the membrane seeurely attached to the faces of the said ~econd frame~ 72. Holes are punched ln the membranes corresponding to the holes, 75~ 1n the second frame, 72. The buffer sec~on assembly is completed by placing the first frame, 71~ on one side of the second frame, 72, w~th the pegsC 74, fitting through the holes, 75, of the seeond frame~ and the third frame, 73, on the opposite side of the second frame~ 725 with the holes, /8, meshing with the pegs, 74, extending through said second fra~e, 72, There is thus formed a bu~fer compartment through which a dilute bu ffer solution may be circulated, whlch compartment is separated from the anode compartment by a cat~on-active permselective barrier~ and from the cathode compartment by a second cation-active permselective barrier as ls sh~n in Fig. 6. When a suitable voltage is lmpressed between th~ anode and cathode of this three compartment cell the current ~s carrled substantially entirely by the flow of ~ons ~rom the anode compartment through the ~irst cat~on~act1ve permselective barrter into and through the bu~er compartment, through t~e second cation~actlve permselective barrier into the oathode compartment~
Leakage of the anolyte and anodic products into the cathode compartment is substantially prevented, as is the back m~gra~ion o~ catholyte and cathod1c products by the cation~active permselective barrlers and the buffer compartm~n~
The present inventlon has the desirable advantage over the prlor methods of ~nserting barriers in electrolytic cells~ in that by this proc~dure the half cell v~ltages ~n the anode and 3~a~3~3~
cathode sections of the cells do not increase substantial1y oYer those expected in such cells dur~ng normal operation. The me~branes remain fixed in pl~ce and do not ~orm the folds and/or creases which often occurred in prior membranes~
Thus ~he new procedure and apparatus results in the more efficient utilkation of electric power in the production of highly pure~ i.e. essentially salt free caustic soda and hydrogen free chlorine, operation o~ the cell at low cell voltage and high current effic~ency.
The ~embrane ra~erial used in th~s invention consists essentially of at least one cation~active permselective material selected from the group consisting of a hydrolyzed copolymer o~ a perfluortnated hydroca~bon and a fluorosulfonated per~luorovinyl ether and a sulfostyrenated perfluorina~ed ethylene propylene polym2r.
In a pre~erred embodiment of th~s invent~on the cation-active permselectlve membrailes are composed esserlt1ally o~
co~pclymers of te~ra~luoroethylene and a sulfonated p~rfluorovinyl-ether havin~ the formula FS02CF2CF20CF(~F3)CF20CF-CF2 sa~d copolymer having an equivalent ~eight o~ from about 900 to abvut 1600. Preferably the equivalent weight of the copolymer ts in the range of from about 1100 to about 1400.
Co-polymers of the character referred to above are pre-pared as disclosed ~n USP 3,2821875, by reacting, at a temperature bel~w about 110 de~rees centigrade a perfluorovinylether of the formula ~L7~3~
FS02CF2CF20CF(CF3)CF20CF-CFZ
with tetrafluoroethylene in an aqueous liquid phase, preferably at a pH of 8 or below, and in the presence of a free radical initiator such as ammonium persulfate. Subsequently this co-polymer is hydrolyzed : S to the free ac~d or salt formed by conventlonal means.
Thus~ the presently preferred cation selective ~embrane material is o~ a hydrolyzed copoly~er o~ a per~luorinated hydrocarbon and a fluorosulfonated per~luorovinyl ether. The perfluorinated hydrocarbon is preferably tetrafluoroethyiene al~hough other per-fluor~nated saturated and unsaturated hydrocarbons of from 2 to 5 carbon atoms can also be utilized, of which the monoolefinic hydro-: carbons are preferred9 especially those of 2 to 4 carbon atoms and most espec~ally those of 2 to 3 carbon atoms, e.g., tetrafluoroethylene, ànd hexafluoropropylene. The sulfonated perfluorovinyl ~ther which is most useful is that o~ the formula , ~02CF2CF20CF(CF3)cF20cF=cF2 Th~s material, named as perfluoro C2-~2-~luorosulfonylethoxy)-propyl~
v~nyl ether, may b~ modifted to e~ulvalent monomers, ~s by modifylng th~ ~nternal perfluorosul~onyle~hoxy moiety to the correspond~ng pro-poxy motety, and by altering the propyl group to ethyl or butyl group, and by rearrangin~ the posit~ons of subst~tutes of the sulfonyl group . thereon and by utilizat~on o~ the perfluoro lower alkyl groups respectively.
: The method of manufacture of the fluorosul~onyl copslymer is described ~n Example XY~I of the above referred to USP 3~282,875 and an alternate method ~s d~sclosed ~n Canadian patent 849,670, which also discloses the use of these and analogous membranes in fu~l cells, 7~63~
characterized therein as electrochemical ce'lls. In short, the copolymer can be made by reacting fluorosulfonated per~luorovinyl ether or the equ;valent w;th tetrafluoroethylene or equ;valent ;n the des;red prop-ortions in water at elevated temperatures and pressures for over an hour after which time the reaction mass is cooled. The mixture separates into a lower perfluoroether layer and an upper layer of an aqueous dispersior of the desired polymer. The molecular weight of the latter is indeterminate but the equivalent weight is from about 900 to about 1600, preferably from about 1100 to about 1400, and the percentage of the fluorosulfon-ated perfluorovinyl ether or corresponding compound is about 10 to 30 percent by weight, preferably about 15 to 20 percent by weight and most preferably about 17 percent by ~eight. The unhydrolyzed copolymer may be compression molded at high temperatures and pressures to produce sheets or membranes which may vary in thickness from about 0.002 to 0.5 mm. These then may be further treated to hydrolyze the pendant -502F
to ~ S03H groups as by boiling in water or in lO percent aqueous sulfuric acid or by the methods of the patents previously mentioned,. The presence of the -S03H groups may he verified by titration with standard base as described in the Canadian patent prevlously mentioned. Additional details of varlous processing steps are described in Canadian patent 752,427 and U.S. patent 3,041,317.
As discussed above, because it has been found that some expansion or swelling accompanies the hydrolysis of the copolymer, 3~i ;t is advantageous to posltion the copolymer membrane into a frame or other support means to hold it in place on the surFace of the electrode in the electrochemical cell. Thereafter it may bé clamped or cemented in place on the electrode and will be true without sags or gaps. The membrane material is preferably joined to the backing material, e.g., tetrafluoroethylene or other suitable filamentary - material prior to hydrolysis when the copolymer is still thermoplastic so ~hat the film of co-polymer covers each filament penetrating into the spaces or interstices of the backing material between them and even around behind them, the films becoming slightly thinner in the process where it covers the filaments.
The cation-active permselective membrane material described above is far superior when utilized in the electrochemical cell as described herein compared to previously suggested materials. The new material is more stable at elevated temperatures, e.g., above 75 C. It lasts for much longer periods in the medium of the electrolyte and does not beconle brittle when exposed to chlorine at high cell temperatures. Moreover when the rnembrane has been assembled on the face of the electrode elements of the cell as described herein, the permissable gap between the electrodes can be substantially reduced and maintained constant resulting in increased - power efficiency. Considering the savings in time, maintenance, and fabrication costs, these membranes are more economical. The voltage drop through the membranes is acceptable, does not vary due to the formation of gaps and sagging and does not become inordinately high as it does with many other membrane materials, when the caustic concentration in the cathode compartment increases to above about .
. ", , ..
1 ~ ~7~ 3 ~
2009/1. The selectivity of the me~brane and its compatability with the electrolyte does not decrease as the hydroxyl concentration of the catholyte l~quor ;ncreases, as has been noted with other membrane materials, nor does the caustic efficiency o~ the electrolysis diminish as significantly as it does with other membranes as the electrolysis proceeeds. Thus these improvements in the present membranes and the manner of emplacement thereof in the cell make it more practicable whereas previously disclosed ion-exchange me~brane mater~als haYe not attained commercial acceptance. While the more preferred copolymers are those having equivalent weights of from about 9ûO to about 160û, with about 1100 to about 1400 being especially preferred, some useful resinous membranes of this same genre have equivalent wei~hts within the range of about 500 to 4000. The intermediate equivalent weight copolymers are preferred because they are of satisfactory strengtil, stability, permselect1vity~ enahle better selective ion exchange to take place and are of lower ~nternal reslstance, all o~ which are 1mportant in the electrochem~cal art.
Improved vers10ns o~ th0 above-descr~bed copolymers may be made by chemi~al kreat~ent o~ the surfaces thereo~ as by treatments to modify the -S03H groups thereon. For example, the sulfonic acid groups may be altered or replaced in whole or in part w~th other moieties.
Such change~ may be made ~n th~ copolymer manufacturing proeess or after production of the membrane. When effected as a subsequen~ treatment of the membrane, the depth of the treatment will usually be from O.Q01 to 0.01 mm. Caustic efficienc1es of the improved processes using such rod~fied versions of the pres~n~ ~mproved membranes can increase about 3 to about 20% or more~ usually about 5 to 15%.
~L~l7~3~
Exemplary of such treatments is th~t described in french Pa~ent 2,152,194 of March 26, 1973 in which one stde of ~he ~luorocarbon membrane is treated with ammonia to convert the pendant sulfonyl groups to sulfonamide groups.
In addition to the copolymers d;scussed aboYe, including ~odif~cations thereof, 1t has been found that another membrane matertal is also sup~rior to prior art film for applica~ions in electrochemical cells. Although it aprlears that tetrafluDroethylene polynlers which are sequentially styrenated and sulfonated are not useful for making satisfactory cation-acti~e pern~elective ~mbranes acceptable for use in electrochemical processes, i~ has been found that per~luorinated ethylene propylene polymer whlch h~s been styrenated and sulfonated does make a useful cation-ac~iYe permselective membrane material.
Whereas useful ltves of as much as thr~e years or more (that o~ the preferred eopoly~r mater~al) may not be ob~alned w~th th~s alternate material, it is surprisingly resistant to hardening und~r normal use conditions.
To ~anu~cture the sul~ostyrenated perfluorinated ethylene propyl~ne polymers~ a commercially ava~lable perfluoroethylene propylene poly~er ~s styren~ted and then the styrenated product is sulfona~edg A solut~on o~ styrene ~n methylene chlor~de, benzene, or analogous solvent at a sui~able concentration in the range of about 10 to about 20 percent by welght ~s prepared and a sheet of the polymer having a ~hickness of about 0.02 ~o 0.5 mm9 preferably 0.05 to 0.15 mm, is in~nersed 1n the soluti~n. A~t~r removal" the sheet is subiected to a rad~ation treatment~, ustng a cobal~ 60 radiat1On source. The rate of application may be in the range of about 8000 rads~hr. and a totaï
- ~0 -~ 3 S
radiation application shou1d be about 0.9 me~erads. After rinsing the irradiated sheet with water~ the phenyl nuclei of the styrene port;on of the polyn~r are monosulfonated, preferably in the para position, by treatment with chlorosulfonic acid, fuming sulfuric acid (oleum) or sulfur trioxide, Prefer~bly chlorosulfonic acid in chloroform is used and the sulfonation may be completed in about l/2 hour at ambient temperature.
Examples of such useful membranes made by the abo~e described process are products of RAI Research Corporation, Hauppauge, New York, ln and are identified as 18STl2S and 16STl3S~ the former being 1~% styrenated and having about 2/3 ~f the phenyl nuclei monosul~onated and the latter being 16% styrenated and having 13/16 of the phenyl nucle1 monosulfonated.
To obtain 18% styrenation, a solution of 17 l/2% styrene in methylene chloride is utilized and to obtain a 16% styrenation, a 1&% styrene solution in methylene chlorld~ is employed.
Th~ products r~sultln~ from this process compare favorably with the pre~erred copolymers previously described gtving voltage drops o~ about 0.2 volt each fn a typ~cal electrochemical cell at a current density of 2 amperes/sq. in about the same as is obtained w~th the preferred copolymer.
The membran0s useful in the practlce of the present inven tion can be advantag~ously prepared and util ke~ in the form.of a th~n film, either as such or deposited on a inert support such as . a cloth woven of Teflon~ or glass f~bers. The thickness of such supported me~branes can be varied over a considerable range, for example, from about 5 to about 15 mils in thickness, ~L~796~
; The membrane can be fabrica~ed in any desired shape. As generally prepared the preferred co-polymer membrane material is obtained in the form o~ the sulfonyl fluorlde. In this non-acid form the polynmer ls somewh~t soft and pliable and can be seam- or bu~t-welded forming welds which are as strong as the membrane material itself. It is preferred that the polymeric material be shaped and formed in this non-acid sta~e. Foll~wing shaping and forming into the desired næmbrane configura~ion~ the material is conditioned for use as a barr~er by hydrolyzing the sulfonyl fluoride groups to free acid or sodium sul~onate groups by boiling in water or aqueous caustic soda solut~on. On bo11iny in water for about 16 hours, the conditioned n~mbrane undergoes swelling, about 28 percent, which is lsotropic, about 9 percent 1n each dlreotion, and the material becomes soft and pliable.
If desired the cQndltioning process, that is the hydrolysis of the sulfonyl fluoride groups~ can be combin~d w~th the 1nitial s~ep of this lnvention by carry~n~ out ~h~ immerslon ~n bo111ng aqueous medla for an exkended period over the 1 tv 4 hours required, merely to soften the co-polyner.
The electrodes for the present electrolytic c211 m~y be formed of any electrically conductive material which will resist the corrosive attack of the various cell reactan~s and products with which they may come in oontact, su~h as alkali metal hydroxides, hydrochloric acid~ and chlorine, Typically, the ca~hodes may be constructed of graphite, 1ron, steel~ or the like, with steel being g~n~rally preferred.
Similarly, the anodes may be forn~d of graphite or may be nætallic anodes. Typically~ the porous metalllc anodes may be fonmed of a so-called "valve" metal~ such as ~itan~um, ~an~al~m or niob1um as well as allsys of these in which the valve metal constitutes at least about ~ 3 ~
90% of the alloy. The surface o~ the va1ve metal may be made active by means of a coating comprising one or more noble metals, noble metal oxides, or mixtures o~ such oxides, either alone or with oxides of other metals. The noble metals which may be used include ruthenium, rhodium, palladium, iridium, and platinum. Particularly preferred metal anodes are those formed of titanium and having a mixed titanium - oxide and ruthenium oxide coating on the surface, as is described in U.S. Patent 3,632,498. Additionally, the valve metal substrate may be clad on a more electrically conductive metal core, such as aluminum, steel~ copper, or the like.
The cell body or container is formed into at least one set or unit of compartments made up of an anode compartment, containing the anode, a cathode compartment, containing the cathode, and may contain one or more buffer compartments between the anode and cathode compartments. Typically, the electrolytTc cell may conta~n a plural~y of these sets, e.g., 20 to 30 or more, depending upon the size o~
the cell.
The following example wlll illustrate the present invention.
Parts and percentages are by weight and temperatures are ~iven in degrees centigrade, unless otherwise specified.
LXAMPLE l A 37 inch tall, three compartment electrochemical cell was utilized in this example. In this cell the anode compartment containing a ruthenium oxide coated titanium clad steel anode was fed with a circulatin~ concentrated brine solution. The cathode compartment was filled initially with dilute aqueous caustic soda which during the electrolysis was continuously circulated. The cathode and anode com-partments were separated by a buffer compartmen~ which was ~o~led by placing t~Jo membranes one on the anode and one on the cathode. The membranes were composed of the hydroly2ed copolymer of perf1uoro-ethylene and a sulfonated perfluorovinylether as described herein-above. A dilute aqueous solution of sodium hydroxide ~Jas continuously circulated through this buffer compartment.
- In operating this three compartment cell an opera~lng current density of 2 amperes per square inch of anode surface was ap~lied and maintained. Anolyte to buffer to catholyte head differentials of from 0 to 12 inches were established and the voltage drop was measured periodically at several of the head differentials. By this means, the membrane separating the anode compartment was pushed from the anode surface and the effect of positioning the membrane apart from the anode surface on the cell volta~e was measured. The data obtained is set out ~n the tahle below, and in~licates that the cell voltage increased with increased differential head ~Ih~ch shows that the cell voltage increased as the gap between the anode surface and the membrane increased.
ABLE
Anolyte ~ead Diff~rential ~oltage Corrected to 2ASl in inches _ _ Current ~ensity o 4.ns
4.68 12 to 12.5 4.75 to 4.80 (Anode to cathode gap held constant at l/8 in.) These data indicate that an increase oF 0.7 volt in current density occurred as the anolyte membrane was "pushed back" from - ~4 -6~3~
the surface of the anode by the force of about a one foot increase in the anolyte to buffer-cathode head differential. This voltage diff-erence is greater than that which can be accounted for by ~he conduct-ivity of the anolyte brine solution. The data show that by securely positioning the permselective membrane on the surface of anode sub-stantial savings in current consumption can be obtained.
EXAMPLE II
- A conventional two compartment cell was utilized in this example. In this cell the anode compartment containing a ruthenîum oxide coated titanium clad steel mesh anode was fed with an acidifi~d concentrated brine solution which was circulated continuously during the electrolysis. The cathode compartment was filled initially with dilute aqueous caustic soda which during the electrolysis was fed continuously to the cathode compartment as make up. The anode and cathode compartments were separated by a membrane composed of a hydrolyzed copolymer of per~
fluoroethylene and a sulfonate perPluorovinyl ether supported on a Teflon* cloth as descrihed hereinabove. The membrane was about 7 mlls in thlckness and ~as positioned on the front face of the anode and held the eon during the run.
The cell ~as operated over a period of 30 hours by applying a decomposition voltage of 2 amperes per square inch of anode surface.
During this run a constant voltage of 3.88 volts was observed. The other operating conditions during this run were:
Caustic concentration 155 gpl Catholyte temperature 90 to 94 Anolyte temperature 88 to 91 Anolyte salt concentration 292 to 309 gpl Anolyte pH 3.8 to 4.6 * Trade Mark - 25 ~'79~
The caustic soda li~uor produced in the cathode compartnent con-ta~ned less than 1.0 percent sodium chloride. The chlorine evolved from the anode co~partment was free from hydrogen, and the hydrogen evolved from the cathode compartment was ~ree from chlorine.
the surface of the anode by the force of about a one foot increase in the anolyte to buffer-cathode head differential. This voltage diff-erence is greater than that which can be accounted for by ~he conduct-ivity of the anolyte brine solution. The data show that by securely positioning the permselective membrane on the surface of anode sub-stantial savings in current consumption can be obtained.
EXAMPLE II
- A conventional two compartment cell was utilized in this example. In this cell the anode compartment containing a ruthenîum oxide coated titanium clad steel mesh anode was fed with an acidifi~d concentrated brine solution which was circulated continuously during the electrolysis. The cathode compartment was filled initially with dilute aqueous caustic soda which during the electrolysis was fed continuously to the cathode compartment as make up. The anode and cathode compartments were separated by a membrane composed of a hydrolyzed copolymer of per~
fluoroethylene and a sulfonate perPluorovinyl ether supported on a Teflon* cloth as descrihed hereinabove. The membrane was about 7 mlls in thlckness and ~as positioned on the front face of the anode and held the eon during the run.
The cell ~as operated over a period of 30 hours by applying a decomposition voltage of 2 amperes per square inch of anode surface.
During this run a constant voltage of 3.88 volts was observed. The other operating conditions during this run were:
Caustic concentration 155 gpl Catholyte temperature 90 to 94 Anolyte temperature 88 to 91 Anolyte salt concentration 292 to 309 gpl Anolyte pH 3.8 to 4.6 * Trade Mark - 25 ~'79~
The caustic soda li~uor produced in the cathode compartnent con-ta~ned less than 1.0 percent sodium chloride. The chlorine evolved from the anode co~partment was free from hydrogen, and the hydrogen evolved from the cathode compartment was ~ree from chlorine.
Claims (22)
1. An electrolytic cell which comprises a cell body having an anode compartment containing a porous anode, a cathode compartment containing a cathode said compartments being separated from each other by a barrier which is sub-stantially impervious to gases and fluids selected from (a) a hydrolyzed copolymer of a perfluorinated hydrocarbon sulfonated perfluorovinyl ether and (b) a sulfostyrenated perfluorinated ethylene propylene polymer, said barrier having been pre-treated by boiling in water for at least one hour, tautly stretched, dried at ambient temperatures and cemented across the front face of said porous anode.
2. The electrolytic cell as claimed in claim 1, wherein the barrier is a hydrolyzed copolymer of tetrafluoroethylene and a sulfonated perfluorovinyl ether having the formula FSO2CF2CF2OCF(CF3)CF2OCF=CF2 which copolymer has an equivalent weight of from about 900 to 1600.
3. The electrolytic cell as claimed in claim 2, wherein the copolymer has an equivalent weight of from about 1100 to about 1400 and contains from about 10 to 30% of the ether compound.
4. The electrolytic cell as claimed in claim 3, wherein the anode is a metallic anode.
5. The electrolytic cell as claimed in claim 3, wherein the cell is formed with at least one buffer compartment between the anode compartment and the cathode compartment.
The electrolytic cell as claimed in Claim 1 wherein the barrier is a sulfostyrenated perfluorinated ethylene propylene polymer.
The electrolytic cell as claimed in Claim 4 wherein the copolymer is styrenated to from about 16 to 18 percent by weight and from about 2/3 to 13/16 of the phenol groups are monosulfonated.
The electrolytic cell as claimed in Claim 7 wherein the anode is a metallic anode.
The electrolytic cell as claimed in Claim 6 wherein the cell is formed with at least one buffer compartment between the anode com-partment and the cathode compartment.
The electrolyic cell as claimed in Claim 1 wherein the anode is a metallic anode.
The electrolytic cell as claimed in Claim 10 wherein the cell is formed with at least one buffer compartment between the anode compartment and the cathode compartment.
The electrolytic cell as claimed in Claim 1 wherein the cell is formed with at least one buffer compartment between the anode com-partment and the cathode compartment.
The electrolytic cell as claimed in Claim 1, wherein said porous anode is formed of a valve metal the surface of which has been made active by means of a coating comprising a noble metal, noble metal oxide or a mixture thereof.
14. The electrolytic cell as claimed in claim 13, wherein said valve metal is titanium and said coating comprises ruthenium oxide.
15. The electrolytic cell as claimed in claim 1, wherein the porous anode is mounted on a frame, the front face of said anode being offset from said frame and projecting toward the cathode.
16. A barrier section for use in electrolytic cells com-prising:
1) a barrier support, 2) a porous anode mounted on said barrier support, and 3) at least one permselective membrane consisting essentially of a hydrolyzed copolymer of tetra-fluoroethylene and a sulfonated polyfluorovinyl ether of the formula FSO2CF2CF2OCF(CF2)CF2OCF=CF2 said membrane having been immersed in boilding aqueous medium for at least one hour, stretched, dried in the stretched condition at ambient temperature and then securely affixed while taut to said barrier support, said membrane covering one face of said porous anode.
1) a barrier support, 2) a porous anode mounted on said barrier support, and 3) at least one permselective membrane consisting essentially of a hydrolyzed copolymer of tetra-fluoroethylene and a sulfonated polyfluorovinyl ether of the formula FSO2CF2CF2OCF(CF2)CF2OCF=CF2 said membrane having been immersed in boilding aqueous medium for at least one hour, stretched, dried in the stretched condition at ambient temperature and then securely affixed while taut to said barrier support, said membrane covering one face of said porous anode.
17. A barrier section as described in claim 18, wherein said porous anode is positioned on said support with a front face of said anode offset from a frame of said support, said front face being covered by said membrane.
18. An electrolytic cell which comprises a cell body having an anode compartment containing a porous anode, connected to an electrical input source, a cathode compart-ment containing a cathode said compartments being separated from each other by a barrier which is substantially impervious to gases and fluids selected from (a) a hydrolyzed copolymer of a perfluorinated hydrocarbon and a sulfonated perfluorovinyl ether and (b) a sulfostyrenated per-fluorinated ethylene propylene polymer, said barrier being mounted across the front face o-f said porous anode.
19. A process for the electrochemical decomposition of an aqueous solution of an ionizable chemical compound which comprises introducing an aqueous solution of alkali metal halide or hydrochloric acid into the anode compartment of an electrolytic cell, comprising a cell body having an anode compartment containing a porous anode, a cathode compartment containing a cathode said compartments being separated from each other by a barrier which is substantially impervious to gases and fluids selected from (a) a hydrolyzed copolymer of a perfluorinated hydrocarbon and a sulfonated perfluorovinyl ether and (b) a sulfostyrenated perfluorinated ethylene propylene polymer said barrier being affixed to the front face of said porous anode, and effecting the electrolytic decomposition of said aqueous solution by passing an electric current between the anode and cathode of said cell.
20. A process according to claim 19, wherein said aqueous solution is an aqueous solution of alkali metal halide.
21. A process according to claim 20, wherein an aqueous solution of an alkali metal hydroxide is introduced into the cathode compartment.
22. A process according to claim 19, wherein said aqueous solution is an aqueous solution of hydrochloric acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41691673A | 1973-11-19 | 1973-11-19 | |
| US416,916 | 1973-11-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1179635A true CA1179635A (en) | 1984-12-18 |
Family
ID=23651824
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000213657A Expired CA1179635A (en) | 1973-11-19 | 1974-11-12 | Technique of prestressing semi-permeable membranes |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS534073B2 (en) |
| AR (1) | AR219042A1 (en) |
| CA (1) | CA1179635A (en) |
| DE (2) | DE2454827C3 (en) |
| FI (1) | FI333574A (en) |
| FR (1) | FR2251637B1 (en) |
| GB (1) | GB1435477A (en) |
| IT (1) | IT1025822B (en) |
| NL (1) | NL7415078A (en) |
| NO (1) | NO138665C (en) |
| SE (2) | SE402132B (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3984303A (en) * | 1975-07-02 | 1976-10-05 | Diamond Shamrock Corporation | Membrane electrolytic cell with concentric electrodes |
| JPS526374A (en) * | 1975-07-07 | 1977-01-18 | Tokuyama Soda Co Ltd | Anode structure for electrolysis |
| US4274928A (en) * | 1978-07-27 | 1981-06-23 | Ppg Industries, Inc. | Process for electrolyzing brine in a permionic membrane electrolytic cell |
| GB2051870B (en) * | 1979-06-07 | 1983-04-20 | Asahi Chemical Ind | Method for electrolysis of aqueous alkali metal chloride solution |
| JPS5623290A (en) * | 1979-08-02 | 1981-03-05 | Shiro Yoshizawa | Method of electrolytic synthesis of organic compound |
| US4417959A (en) * | 1980-10-29 | 1983-11-29 | Olin Corporation | Electrolytic cell having a composite electrode-membrane structure |
| ZA824471B (en) * | 1981-06-26 | 1983-04-27 | Ici Australia Ltd | Polymers |
| WO1983000487A1 (en) * | 1981-08-07 | 1983-02-17 | Markus, Michael, Vojtech | Cation exchange resin by graft polymerization process |
| US4992126A (en) * | 1986-08-08 | 1991-02-12 | The Dow Chemical Company | Method for making a current collector bonded to a solid polymer membrane |
| GB9002247D0 (en) * | 1990-02-01 | 1990-03-28 | Atomic Energy Authority Uk | Electrodes |
-
1974
- 1974-10-31 GB GB4725274A patent/GB1435477A/en not_active Expired
- 1974-11-08 AR AR256470A patent/AR219042A1/en active
- 1974-11-12 CA CA000213657A patent/CA1179635A/en not_active Expired
- 1974-11-15 NO NO744121A patent/NO138665C/en unknown
- 1974-11-18 SE SE7414467A patent/SE402132B/en unknown
- 1974-11-18 JP JP13309374A patent/JPS534073B2/ja not_active Expired
- 1974-11-18 FI FI3335/74A patent/FI333574A/fi unknown
- 1974-11-19 DE DE2454827A patent/DE2454827C3/en not_active Expired
- 1974-11-19 IT IT29591/74A patent/IT1025822B/en active
- 1974-11-19 DE DE19742462490 patent/DE2462490A1/en active Pending
- 1974-11-19 NL NL7415078A patent/NL7415078A/en unknown
- 1974-12-20 FR FR7442262A patent/FR2251637B1/fr not_active Expired
-
1977
- 1977-09-22 SE SE7710641A patent/SE7710641L/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| SE7414467L (en) | 1975-05-20 |
| DE2454827B2 (en) | 1977-06-30 |
| NO138665C (en) | 1978-10-18 |
| NO744121L (en) | 1975-06-16 |
| AR219042A1 (en) | 1980-07-31 |
| FR2251637A1 (en) | 1975-06-13 |
| NL7415078A (en) | 1975-05-21 |
| SE402132B (en) | 1978-06-19 |
| DE2462490A1 (en) | 1977-04-21 |
| DE2454827C3 (en) | 1978-06-01 |
| NO138665B (en) | 1978-07-10 |
| GB1435477A (en) | 1976-05-12 |
| IT1025822B (en) | 1978-08-30 |
| JPS5080974A (en) | 1975-07-01 |
| JPS534073B2 (en) | 1978-02-14 |
| SE7710641L (en) | 1977-09-22 |
| FI333574A (en) | 1975-05-20 |
| FR2251637B1 (en) | 1976-12-31 |
| DE2454827A1 (en) | 1975-05-28 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |