CA1171026A - Method of bonding electrode to cation exchange membrane - Google Patents
Method of bonding electrode to cation exchange membraneInfo
- Publication number
- CA1171026A CA1171026A CA000357242A CA357242A CA1171026A CA 1171026 A CA1171026 A CA 1171026A CA 000357242 A CA000357242 A CA 000357242A CA 357242 A CA357242 A CA 357242A CA 1171026 A CA1171026 A CA 1171026A
- Authority
- CA
- Canada
- Prior art keywords
- cation exchange
- exchange membrane
- electrode
- membrane
- ion exchange
- 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
- 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
- C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A cation exchange membrane made of a fluorinated polymer is used in a form of ion exchange groups having the formula , wherein X represents an alkali metal atom, an alkaline earth metal atom or -NRR' and R and R' respectively represent hydrogen atom or a lower alkyl group; and m is a valence for the group X. The membrane in the form of ion :
exchange groups having the formula -COOL, wherein L represents hydrogen atom or a C1-C20 alkyl group, is melt-bonded to said electrode and then, converting the ion exchange groups in the form of -COOL into the ion exchange groups in the form of
A cation exchange membrane made of a fluorinated polymer is used in a form of ion exchange groups having the formula , wherein X represents an alkali metal atom, an alkaline earth metal atom or -NRR' and R and R' respectively represent hydrogen atom or a lower alkyl group; and m is a valence for the group X. The membrane in the form of ion :
exchange groups having the formula -COOL, wherein L represents hydrogen atom or a C1-C20 alkyl group, is melt-bonded to said electrode and then, converting the ion exchange groups in the form of -COOL into the ion exchange groups in the form of
Description
1 171~26 The present invention relates to a method of bonding an electrode to a cation exchange membrane. More particularly, the present invention relates to a method of bonding a porous, gas permeable, catalytic electrode to a cation exchange membrane made of a fluorinated polymer having carboxylic acid groups as cation exchange groups which is used in an electrolytic cell in the production of an alkali metal hydroxide by electrolysis of an aqueous solution of an alkali metal chloride at low voltage and high current efficiency.
For the production of an alkali metal hydroxide by the electrolysis of an aqueous solution of an alkali metal chloride, the diaphragm method has been mainly employed instead of the mercury method to avoid pollution of public facili-ties.
It has been proposed to use an ion exchange membrane in place of asbestos as the diaphragm to produce the alkali metàl hydroxide by electrolyzingan aqueous sol-ution of an alkali metal chloride so as to obtain an alkali metal hydxoxide having high purity and high concentration. It is of course always desirable to conserve energy and thus it is desirable to minimize the cell voltage in ~such technology. Varlous methods have been proposed to decrease the cell voltage. It has been proposed to improve materials, components, shapes, and configurations of an anode and~a cathode or to select a formulation and a type of ion exchange membrane.
These improvements have had a certain success. Most of them, however, have disadvantages that the maximum concentration of an alkali metal hydroxide obtained is not high and a substantial increase in cell voltage or decrease in current efficiency occurs in the case of an excess of concentration of the alkali metal hydroxide over the maximum range and the durability of a low cell voltage are not satisfactory. Thus, they have not been always satisfactory for an industrial process.
It has heen also proposed to effect the electrolysis 0 2 ~
using a cation exchange membrane made o~ a fluorinated polymer bonded to gas-liquid permeable catalytic anode on one surface and a gas~liquid permeable catalytic cathode on the other surface of the membrane (British Patent ~,009,795). This method is very advantageous for the electrolysis a-t a lower cell voltage because the electrical resistance caused by the electro-lyte and the electric resistance caused b~ bubbles of hydrogen gas and chlorine gas generated in the electrolysis, can be substantially decreased which it has been considered to be difficult to reduce in the electrolysis.
When a cation exchange membrane made of a fluorinated polymer having carboxylic acid groups or sulfonic acid groups, especially carboxylic acid groups, is used for said electrolysis as an ion exchange membrane, an alkali metal hydroxide having.
a high concentration can be produced at a low cell voltage and a high current efficiency. One of the important factors for such an advantageous effect is to uniformly and firmly bond the catalytic electrodes to the cation exchange membrane made of a fluorinated polymer having carboxylic acid groups. When they are not satisfactorily bonded or the bonding strength is low, the cell voltage is increased or the electrodes arepeeled off frorn the membrane by a gas generation at the interface of elec trode and membrane. ~n adhesive is considered for bonding them.
~ost adhesives are poorly conductive and increase the elec-trically resistance. No adhesive effective for bonding an electrode to the cation exchange membrane made of a fluorinated polymer has been suggested. The me~.t-bonding method has been considered in which the surface of the membrane is partially melted to bond to the electrode.
When a cation exchange membrane made of a fluorinated polymer having carboxylic ac.id groups is used, it has been found that the electrode is not satisfactorily bonded to the membrane ! ~ 71026 or the required satisfactory electrolytic characteris-tlcs are not attained even though the membranes can be bonded, if the form of carboxyllc aci.d yroups of the membrane is not appropxiate.
Such disadvantage has been found in the case that the membrane having carboxylic acid groups having the formula ~~~C~ m X
is melt-bonded to the electrode wherein X represents an alkali metal or alkaline earth metal atom or -NRR'; R and R' respectively represent hydrogen atom or a lower alkyl group; and m is a valence for X.
The present invention provides a method of bonding an electrode to a cation exchange membrane without substantially reducing the electrolytic characteristics and uniformly and firmly contacting them without increasing the electric resistance.
According to the present invention there is provided ~n a method of bonding an electrode to a cation exchange membrane made of a fluorinated polymer whlch is used in a form of ion exchange groups having the formula ( COO ~ X, wherein X
represents an alkali metal atom, an alkaline earth metal atom or -NRR' and~R and R' respectively represent hydrogen atom or a lower alkyl group; and m i5 a ~alence for the group X, improvement in which said memhrane in the form of ion exchange groups having the formula COOL, wherein L represents hydrogen atom or a Cl-C20 alkyl group, is melt-bonded to said electrode and then, the ion exchange groups in the form of -COOL are converted into the ion exchange groups in the form of~ COO ~ X.
Thus, in accordance wi.th the present invention the cation exchange membrane having the ion exchange groups in a form of -COOL.wherein L represents hydrogen atom or a Cl - C
alkyl group .is bonded to the electrode.
The cation exchange membrane made of a fluorinated polymer having carboxylic acid groups as ion exchange groups bonded to the porous gas-liquid permeable electrode has the ion
For the production of an alkali metal hydroxide by the electrolysis of an aqueous solution of an alkali metal chloride, the diaphragm method has been mainly employed instead of the mercury method to avoid pollution of public facili-ties.
It has been proposed to use an ion exchange membrane in place of asbestos as the diaphragm to produce the alkali metàl hydroxide by electrolyzingan aqueous sol-ution of an alkali metal chloride so as to obtain an alkali metal hydxoxide having high purity and high concentration. It is of course always desirable to conserve energy and thus it is desirable to minimize the cell voltage in ~such technology. Varlous methods have been proposed to decrease the cell voltage. It has been proposed to improve materials, components, shapes, and configurations of an anode and~a cathode or to select a formulation and a type of ion exchange membrane.
These improvements have had a certain success. Most of them, however, have disadvantages that the maximum concentration of an alkali metal hydroxide obtained is not high and a substantial increase in cell voltage or decrease in current efficiency occurs in the case of an excess of concentration of the alkali metal hydroxide over the maximum range and the durability of a low cell voltage are not satisfactory. Thus, they have not been always satisfactory for an industrial process.
It has heen also proposed to effect the electrolysis 0 2 ~
using a cation exchange membrane made o~ a fluorinated polymer bonded to gas-liquid permeable catalytic anode on one surface and a gas~liquid permeable catalytic cathode on the other surface of the membrane (British Patent ~,009,795). This method is very advantageous for the electrolysis a-t a lower cell voltage because the electrical resistance caused by the electro-lyte and the electric resistance caused b~ bubbles of hydrogen gas and chlorine gas generated in the electrolysis, can be substantially decreased which it has been considered to be difficult to reduce in the electrolysis.
When a cation exchange membrane made of a fluorinated polymer having carboxylic acid groups or sulfonic acid groups, especially carboxylic acid groups, is used for said electrolysis as an ion exchange membrane, an alkali metal hydroxide having.
a high concentration can be produced at a low cell voltage and a high current efficiency. One of the important factors for such an advantageous effect is to uniformly and firmly bond the catalytic electrodes to the cation exchange membrane made of a fluorinated polymer having carboxylic acid groups. When they are not satisfactorily bonded or the bonding strength is low, the cell voltage is increased or the electrodes arepeeled off frorn the membrane by a gas generation at the interface of elec trode and membrane. ~n adhesive is considered for bonding them.
~ost adhesives are poorly conductive and increase the elec-trically resistance. No adhesive effective for bonding an electrode to the cation exchange membrane made of a fluorinated polymer has been suggested. The me~.t-bonding method has been considered in which the surface of the membrane is partially melted to bond to the electrode.
When a cation exchange membrane made of a fluorinated polymer having carboxylic ac.id groups is used, it has been found that the electrode is not satisfactorily bonded to the membrane ! ~ 71026 or the required satisfactory electrolytic characteris-tlcs are not attained even though the membranes can be bonded, if the form of carboxyllc aci.d yroups of the membrane is not appropxiate.
Such disadvantage has been found in the case that the membrane having carboxylic acid groups having the formula ~~~C~ m X
is melt-bonded to the electrode wherein X represents an alkali metal or alkaline earth metal atom or -NRR'; R and R' respectively represent hydrogen atom or a lower alkyl group; and m is a valence for X.
The present invention provides a method of bonding an electrode to a cation exchange membrane without substantially reducing the electrolytic characteristics and uniformly and firmly contacting them without increasing the electric resistance.
According to the present invention there is provided ~n a method of bonding an electrode to a cation exchange membrane made of a fluorinated polymer whlch is used in a form of ion exchange groups having the formula ( COO ~ X, wherein X
represents an alkali metal atom, an alkaline earth metal atom or -NRR' and~R and R' respectively represent hydrogen atom or a lower alkyl group; and m i5 a ~alence for the group X, improvement in which said memhrane in the form of ion exchange groups having the formula COOL, wherein L represents hydrogen atom or a Cl-C20 alkyl group, is melt-bonded to said electrode and then, the ion exchange groups in the form of -COOL are converted into the ion exchange groups in the form of~ COO ~ X.
Thus, in accordance wi.th the present invention the cation exchange membrane having the ion exchange groups in a form of -COOL.wherein L represents hydrogen atom or a Cl - C
alkyl group .is bonded to the electrode.
The cation exchange membrane made of a fluorinated polymer having carboxylic acid groups as ion exchange groups bonded to the porous gas-liquid permeable electrode has the ion
2 6 exchange groups havin~ the ~ormula ( COO ~ X, where.in m and X
are defined above, for.use ~n the electrolysis of an aqueous solution of an alkali metal chloriae. In the electrolysis, X
is preferably the same alkali metal atom as that of the alkali metal chloride forming the electrolyte, The ion exchange capacity of carboxylic acid groups is important since it relates to the characteristics of the membrane in the electrolysis, and depends upon the types of the fluorinated polymer forming the membrane, and is preferably in a range of 0.5 to 2.5 meq/g. dry polymer especially 1.0 to 2.0 meq/g. dry polymer in view of electrochemical characteristics and mechanical characteristics. The cation exchange membrane is preferably made of a fluorinated polymer having the following units:
~- CF2-CXX ' wherein X represents fluorine, chlorine or hydrogen atom or -CF3; X' represents X or CF3(CF2 )m ; m represents an integer of 1 to 5.
Typical examples of Y have the structures bonding A to a fluorocarbon group such as CF2 ~ A, -O-~-CF2 ~ A, --t--O--CF2-1F ~ A, -CF----~O-CF2-CF ~ A, ~--O-CF2-ICF -tx--~O-CF2-ICF--ty--Aand Z Z Rf -O-CF2~ IF-o-cF2~cF2~ CF2-0-CF~A
x, y and z respectively represent an integer of 1 to 10; Z and Rf represent -F or a Cl - C10 perfluoroalkyl group; and A
represents a functional group which is convertible to--~COO ~ X
during the electrolysis.
The N mole % of the units of- ( CF2 - CX~- is preferably ~ :~ 7~026 in a range of 1 to 40 mole % especially 3 to 25 mole % in view of the above-mentioned ion exchange capacity of -the membrane.
The molecular welght of the fluorinated polymer for the cation exchange membrane used in the present invention is important since it relates to the electrochemical characteristics of the resulting rnembrane. The molecular weight of the fluorin-ated polymer is preferably in the range of 1 x 105 to 2 x 106, especially 1.5 x 105 to 1 x 106.
In the production of the perfluoro polyer, various processes can be employed.
In the preparation of such perfluoro polymer, one or more monomers for forming -the-units (~) and (N) can be used, if necessary, with a third monomer so as to improve the characteristics of the membrane. For example, the flexibility of the membrane can be improved by incorporating CF2 = CFORf (Rf is a Cl - C10 perfluoroalkyl group), or the mechanical strength of the membrane can be improved by crosslinking the copolymer with a divinyl monomex such as CF2=CF-CF=CF2 or CF2=CFO(CF2)1 3 CF=CF2.
The copolymerization of the ~luorinated olefin monomer and a monomer having carboxylic acid group or a functional group which is convertible into carboxylic acid group and, if necessary, ,.~i; '~f~ d fS~ er~ c~ f~e.
.~ the ~ r monomer/can be carried out by a conventional process.
The polymerization can be carried out if necessary, using a solvent such as halohydrocarbons by catalytic polymerization, thermal polymerization or radiation-induced polymerization.
The particular me-thod of fabrication of the ion exchange membrane from the resulting copolymer is not critical, for example it can be a conventional method such as the press-moulding 3U method, the roll-molding method, the extrusiQn-moulding method, the solution spreading method, the dispersion molding method or the powder moldiny method. The thickness of the membrane is preferably 20 to 600 microns especially 50 to 400 microns. The cation exchange membrane used in the present invention can be fabricated by blending a polyolefin such as polyethylene, poly-propylene, preferably a fluorinated polymer such as polytetra-fluoroethylene and a copolymer of ethylene and tetrafluoroe-thylene.
The ~embrane can be reinforced by supporting said copolymer on a fabric, such as a woven fabric or a net, a non-woven fabric or a porous film made of said polymer to be blended.
The weight of the polymers for the blend or the suppoxt is not considered in the measurement of the ion exchange capacity.
When the functional groups of the ca-tion exchange membrane for bonding to the electrode are in the form of -COOL
(L is defined above), the-membrane can be bonded to the electrode without any modification. When the functional groups of the membrane are in the form of ( COO ~ X, (X and m are defined above), the groups are converted into the groups in the form of -COOL (L is defined above).
The conversion of the ion exchange groups into the form of -COOL need not be effected in the whole of the membrane and only t~le surface layer bonding to the electrode need to be converted, preferably in a thickness oE less than 30~ , especially less than 50~. The method of conversion of the ion exchange ~'C'LIpS~
groups may be selected depending upon the type of the ~u~ X
and L. For example, ln order to convert the ion exchange groups into -COO~I groups, the membrane is brought into contact with an aqueous solution of an inorganic acid or an organic acid, preferably in the presence of a polar organic compound. The inorganic acid may be hydrochloric acid, sulfonic acid, nitric acid and phosphoric acid. The organic acid may be acetic acid, propionic acid, perfluoroacetic acid, and p-toluenesulEonic acid. The acid is usually used as an aqueous solution having a concentration of 0.5 to 90 wt.%.
--6~
The polar organic compound which is ~t-i-eé~ added, may be methanol, ethanol, propanol, ethyleneglyco], dimethyl-sulfo~ide, acetic acid and phenol. The polar organic acid is preferably added to the aqueous solution of the acid at a concentra~ion of 5 to 90 wt.%. The contacting trea-tment of the membrane with the aqueous solu-tion of the acid is preferably carried out at 10 to 120~C for 30 minutes to 20 hours.
When the ion exchange groups are converted into -COOL
groups wherein L is a Cl - C20 alkyl group, the groups are converted into the acid form and then, further converted into khe ester form by reaction with the corresponding alcohol. The acid form can be also converted into the acid halide form by ~ l osf~J~o r .~5 reaction with ~s~h3r~s trichloride or phosphorus oxychloride, and then converted into the ester form by reaction with an alcohol. The groups in the acid form can be also converted into the aeid anhydride form by reaction with acetic anhydride or perfluoroacetic anhydride and then converted into the groups in the ester form by reaction with an alcohol. If necessary, the mem~rane (-~-COO ~ ~ type ) is treated with a chloride, sueh as ~0 thionyl chloride, phosphorus trichloride, phosphorus oxychloride, at 0 to 120C for 1 to 25 hours so as to convert the groups --~ COO ~ X into the groups in the form of acid anhydride and then, is treated with an alcohol to convert the groups in the ester form. The membrane (-~-COO ~ X type ) can be treated in:an alcohol in the presence of the organic acid or -the inorganie acid to convert the groups of -~COO ~ X into the groups of -COOL. The aleohol used for the esterifieation of the acid, the acid halide or the acid anhydride is preferably a Cl - C20 aleohol, sueh as methanol, ethanol, propanol, butanol, dodeeyl alcohol and sebaeyl aleohol. In the esterification, the membrane can be dippea into an aqueous solution of an inorganic acid or organie acid which is the sarne or different from the acid used for the conversion of the groups of ~ COO -~m--X. The di.pping treatment is preferably carried out at 30 to 120C for 30 minutes to 40 hours.
When the cation exchanye membrane made of a fluorinated polymer havi.ng the groups of -COOL is bonded to th~ electrode, it is pre*erable to have a desired melt-viscosity in the molten state. It has been found that the desired melt-viscostiy is usu-ally in a range of 102 to 101 poise, preferably 103 to 109 poise.
The membrane is melted under the appxopriate conditions of a temperature and a pressure so as to give the desired melt-viscosity.
When the pressure is high, the temperature can be lower. How-ever, ~hen the pressure is low, the temperature should be high.
. When the ion exchange groups of the membrane are in the form of -COOL, the decomposition temperature of the fluorinated polymer (the temperature at which 5~ of a weight loss of the poly-mer occurs in raising the temperature at a rate of 10C/min. in an N2 atmosphere) is in a range of 350 to 370C. Therefore, the de-composition of the fluorinated polymer of the membrane is not caused by bonding the pOI OUS electrode to the membrane. Although parts of the membrane intrude into the pores on the surface o~ the electrode in the bonding, the porous electrode is not damaged and maintains the stable bonding for a long time, and maintains the low cell voltage stable for a long time.
In bonding the electrode to the surface of the cation exchange membrane made of a fluorinated polymer the surface of the membrane is heated to about lO0 to 330C preferahly about 120 to 300C. It is sufficient to apply a pressure of from 0.01 to 1000 kg/cm2, preferably l to 300 kg/cm2 to the bonding area. The means for heating in the bonding step may be a press-heating device, an ultrasonic wave heating device, an impulse heating device and a ~ ~71~26 ~riction heating device. When the membrane is in the form of -COOH, it is possible to use a high frequency heating device.
In order to improve the bonding strength, it is possihle to pretreat the surface of the membrane, for example b~
a sand-blast treatment of the bonding surface or applying a coating of a swelling agen-t or a solvent for the fluorinated polymer (-COOL type) on the bonding surface. The bonding conditions depends upon the bonding method, the type of the fluorinated polymer forming the membrane and the thickness of the membrane.
For example/ with the impulse heating device, the bonding operation is carried out at a temperature from 130 to 350C under a pressure of 0.1 to 300 kg/cm2 for 30 seconds to 1 hour.
In the present invention, at least one of the anode and the cathode is bonded to the cation exchange membrane. It is sufficient to convert the groups on the bonding surface into the groups in the form of -COOL in the case of bonding the electrode on only one surface of the membrane. The electrode bonded to the membrane should have a permeability for the gas generated by the electrolysis and the electrolyte. In order to have such a property, the electrode should be a porous substrate, preferably a layer having a thickness of 0.1 to 100~, especially 1 to 50 ~. In such a porous electrode, the pore diametèr, the porosity and the air permeability should be in the desired ranges. The electrodes used as the anode and the cathode preferably have an average porosity of 0.01 to 100~ and a porosity o~ 30 to 99%. When the average pore diameter and the porosity are less than said ranges, the gas, such as hydrogen and chlorine, generated by the electrolysis are not easily removed from the electrode causing high electric resistance~ When they are above said ranges, the electric resistance is disadvantageously large. When the average pore diameter is in the range of 0.1 to 501J, and the porosity is in the range o 35 to 95 %, the gas 2¢
is easily removed ~rom the electrode and the electric resistance may be small. Stable operation can be continued for a long time.
The substances for forming the porous electrodes may be as follows:-The substances suitable for the anode include platinumgroup metals such as Pt, Ir, Pd and Ru, alloys thereof and oxides of the platinum group metal or alloy, a heat-stabilized reducible oxide of the platinum group metal or alloy and graphite. When the platinum group metal, the alloy or the oxide of the metal or alloy is used for the anode, the cell ~oltage may be advantageously decreased in the electrolysis of the alkali metal chloride.
The substances suitable for the cathode include platinum group metals, alloys thereof, graphite, nickel, Raney nickel, developed Raney nickel and stainless steel and iron group metals.
When the platinum group metal or the alloy or the Raney nickel is used for the cathode, the overvoltage for forming hydro-gen may be advantageously decreased in the electrolysis of water or an aqueous solution of the alkali metal chloride.
The porous electrodes can be prepared from the above sub-stances for the anode and cathode by the following processes.
The powdery substances having an average particle dia-me~er of from 0.01 to lOOy, preferably 0.1 to 50~, is bound, if necessary with a suitable binder. The binder is preferably a fluorinated polymer especially polytetrafluoroethylene. An aqueous dispersion of polytetrafluoroethylene having an average diameter of less than 1~ is preferably used. The wei~ht ra~io of the binder to the powdery substrate for the electrode is prefer-ably in a range~of 0.05 to 5 wt. parts, especially 0.1 to 3 wt.
parts per 10 wt. parts of the powdery substance for the electrode.
When the weight ratio of binder is too high, the potential of the electrode is disadvantageously high whereas when ~ 3 71 0~
it is too low, the powdery substance of the electrode is dis-advantageously separated~ In the preparation of the electrodes, it is possible to incorporate a desired solvent or surfactant so as to uniformly blend the powdery substance for the electrode and the binder. It is also possible to incorporate an electri.c conductive filler, such as graphite, or a water soluble additive, such as carboxymethyl cellulose and polyvinyl alcohol. The components are thoroughly mixed and deposited as a cake on a filter by a filtering method. The cake is contacted with the cation exchange membrane under pressure~ The mixture of the components for the electrode can be prepared in a form of a paste and the paste is coated on the cation exchange membrane. The paste can be also coated on an aluminum foil and the paste layer is contacted with the cation exchange membrane to form the electrode layer on the membrane. The method of forming the elec-.
trode layer on the cation exchange membrane disclosed in U.S.Patent 3,134,~97 can be employed.
The porous electrode layer on the cation exchange membrane can be bonded on the membrane by the press-bonding machine and the like according to this invention. A part of the porou~ electrode layer is preferably embedded into the surface layer of the membrane. The cation exchange membrane bonded to the electrode is in the form of -COOL. The ion exchange groups in the form of -COOL are converted into the groups in the form of ---t COO ~ X by suitable treatment such as a hydrolysis or a neutralization.
The electrolytic cell having the electrode layers and the cation exchange membrane may be a unipolar or bipolar type electrolytic cell. As material for the electrolytic cell, a material which is resistant to the aqueous solution of alkali metal chloride and chlorine, such as titanium, is used for the anode compartment and a material which is resistant to the alkali ~ 171~2~
metal hydroxide of high concentration and hydrogen, such as iron, stainless steel or nickel, is used for the cathode compartment in the electrolysis of an alkali metal chloride.
When the porous electrodes are used in the present invention, each current collector for feeding the current i5 placed outside each electrode. The current collectors usually have the same or higher overvoltage for chlorine or hydrogen compared ~ith that of the electrodes. For example, the current collector at the anode side is made of a precious metai or a valve metal coated with a precious metal or oxide thereof and -the current collector at the cathode side is made of nickel, stainless steel or expanded metal in a form of a mesh or a net.
The current collectors are contacted with the porous electrodes under a pressure.
In the present invention, the process condition for the electrolysis of an aqueous solution of an alkali metal chloride may be those conditions disclosed in the prior art, such as in Brltish Patent 1,009,795.
~ For example, an aqueous solution of an alkali metal chloride (2.5 to S.O Normal~ is fed into the anode compartment and water or a dilute solution of an alkali metal hydroxide is fed into the cathode compartment and the electrolysis is preferably carried;out at ~0 to 120C and a current density of 10 to 100 A/dm .
In the electrolysis, calcium ions or magnesium ions or the other heavy metal ions in the aqueous solu-tion of the alkali metal chloride cause the deterioration of the cation exchange membrane and accordingly, they should be reduced as far as possible. In order to prevent the generation of oxygen in the anode compartment, it is advantageous to incorporate an acid, such as hydrochloric acid, in the aqueous solution of the alkali metal chloride.
~. .
2 ~
The process for producing the alkali metal hydroxide and chlorine by the electrolysis of the aqueous solution of the alkali metal chloride has been illustrated. The present invention is not limited to the embodiment and can be also applied for the preparation of the cells for an electrolysis of water, an elec-trolysis of a desired alkali metal salt, such as sodium sulfate and a fuel cell.
The present invention will be further illustrated by the following Examples and References.
EXAMPLE 1:
Platinum black powder was suspended in water and a dispersion of polytetra1uoroèthylene (Teflon 30 J a trademark of the ~u Pont Company) was~added at a weight ratio of poly-tetrafluoroethylene to platïnum black of 1/10. A non-ionic surfactant (Triton X-100 a~trademark of Rohm & E~aas Co.) was added dropwise and the mixture was blended with an ultrasonifi-cation whilst cooling with ice. The mixture was sucked on a porous polytetrafluroèthylene membrane to provide a thin layer made of platinum black (5 mg/cm2) for the anode. A thin layer made of a stabilized Raney nickel (7 mg/cm2) for a cathode was obtained by the same ~rocess.
A cation exchange membrane made of a copolymer of 2 2 CF2 CFO(CF2)3COOCH3 having an ion exchange capacity of 1.45 meg/g. polymer and a thickness of 250~ was used.
Both the electrode layers were contacted with each of the surfaces of the cation exchange membrane so as to each have a porous polytetrafluoroethylene membrane on the outer surface. They were heated and pressed at 150C under a pressure of 25 kg/cm2 to bond the electrode layers to the cation exchange membrane and then,-the porous polytetrafluoroethylene membranes were peeled off to obtain the cation exchange membrane bonding the electrodes.
.. o ~ ~
The cation exchange memhrane bonding the electrodes was dipped in 2S wt.~ of an aqueous solution of sodium hydroxide at 90C for 16 hours to hydrolyze the cation exchange membrane. A
nickel mesh (40 mesh) and a platinum mesh (40 mesh) as the current collectors were respectively contacted with the anode and the cathode under pressure.
The electrolysis was carried out whilst maintaining a 4 Normal concentration of sodium chloride in the anode compart-ment and maintaining a 35 wt.% concentration of sodium hydroxide as the catholyte by feeding water into the cathode compartment~
The results are as follows.
Current density Cell voltage (V) (A/dm ) 2.7~
2.84
are defined above, for.use ~n the electrolysis of an aqueous solution of an alkali metal chloriae. In the electrolysis, X
is preferably the same alkali metal atom as that of the alkali metal chloride forming the electrolyte, The ion exchange capacity of carboxylic acid groups is important since it relates to the characteristics of the membrane in the electrolysis, and depends upon the types of the fluorinated polymer forming the membrane, and is preferably in a range of 0.5 to 2.5 meq/g. dry polymer especially 1.0 to 2.0 meq/g. dry polymer in view of electrochemical characteristics and mechanical characteristics. The cation exchange membrane is preferably made of a fluorinated polymer having the following units:
~- CF2-CXX ' wherein X represents fluorine, chlorine or hydrogen atom or -CF3; X' represents X or CF3(CF2 )m ; m represents an integer of 1 to 5.
Typical examples of Y have the structures bonding A to a fluorocarbon group such as CF2 ~ A, -O-~-CF2 ~ A, --t--O--CF2-1F ~ A, -CF----~O-CF2-CF ~ A, ~--O-CF2-ICF -tx--~O-CF2-ICF--ty--Aand Z Z Rf -O-CF2~ IF-o-cF2~cF2~ CF2-0-CF~A
x, y and z respectively represent an integer of 1 to 10; Z and Rf represent -F or a Cl - C10 perfluoroalkyl group; and A
represents a functional group which is convertible to--~COO ~ X
during the electrolysis.
The N mole % of the units of- ( CF2 - CX~- is preferably ~ :~ 7~026 in a range of 1 to 40 mole % especially 3 to 25 mole % in view of the above-mentioned ion exchange capacity of -the membrane.
The molecular welght of the fluorinated polymer for the cation exchange membrane used in the present invention is important since it relates to the electrochemical characteristics of the resulting rnembrane. The molecular weight of the fluorin-ated polymer is preferably in the range of 1 x 105 to 2 x 106, especially 1.5 x 105 to 1 x 106.
In the production of the perfluoro polyer, various processes can be employed.
In the preparation of such perfluoro polymer, one or more monomers for forming -the-units (~) and (N) can be used, if necessary, with a third monomer so as to improve the characteristics of the membrane. For example, the flexibility of the membrane can be improved by incorporating CF2 = CFORf (Rf is a Cl - C10 perfluoroalkyl group), or the mechanical strength of the membrane can be improved by crosslinking the copolymer with a divinyl monomex such as CF2=CF-CF=CF2 or CF2=CFO(CF2)1 3 CF=CF2.
The copolymerization of the ~luorinated olefin monomer and a monomer having carboxylic acid group or a functional group which is convertible into carboxylic acid group and, if necessary, ,.~i; '~f~ d fS~ er~ c~ f~e.
.~ the ~ r monomer/can be carried out by a conventional process.
The polymerization can be carried out if necessary, using a solvent such as halohydrocarbons by catalytic polymerization, thermal polymerization or radiation-induced polymerization.
The particular me-thod of fabrication of the ion exchange membrane from the resulting copolymer is not critical, for example it can be a conventional method such as the press-moulding 3U method, the roll-molding method, the extrusiQn-moulding method, the solution spreading method, the dispersion molding method or the powder moldiny method. The thickness of the membrane is preferably 20 to 600 microns especially 50 to 400 microns. The cation exchange membrane used in the present invention can be fabricated by blending a polyolefin such as polyethylene, poly-propylene, preferably a fluorinated polymer such as polytetra-fluoroethylene and a copolymer of ethylene and tetrafluoroe-thylene.
The ~embrane can be reinforced by supporting said copolymer on a fabric, such as a woven fabric or a net, a non-woven fabric or a porous film made of said polymer to be blended.
The weight of the polymers for the blend or the suppoxt is not considered in the measurement of the ion exchange capacity.
When the functional groups of the ca-tion exchange membrane for bonding to the electrode are in the form of -COOL
(L is defined above), the-membrane can be bonded to the electrode without any modification. When the functional groups of the membrane are in the form of ( COO ~ X, (X and m are defined above), the groups are converted into the groups in the form of -COOL (L is defined above).
The conversion of the ion exchange groups into the form of -COOL need not be effected in the whole of the membrane and only t~le surface layer bonding to the electrode need to be converted, preferably in a thickness oE less than 30~ , especially less than 50~. The method of conversion of the ion exchange ~'C'LIpS~
groups may be selected depending upon the type of the ~u~ X
and L. For example, ln order to convert the ion exchange groups into -COO~I groups, the membrane is brought into contact with an aqueous solution of an inorganic acid or an organic acid, preferably in the presence of a polar organic compound. The inorganic acid may be hydrochloric acid, sulfonic acid, nitric acid and phosphoric acid. The organic acid may be acetic acid, propionic acid, perfluoroacetic acid, and p-toluenesulEonic acid. The acid is usually used as an aqueous solution having a concentration of 0.5 to 90 wt.%.
--6~
The polar organic compound which is ~t-i-eé~ added, may be methanol, ethanol, propanol, ethyleneglyco], dimethyl-sulfo~ide, acetic acid and phenol. The polar organic acid is preferably added to the aqueous solution of the acid at a concentra~ion of 5 to 90 wt.%. The contacting trea-tment of the membrane with the aqueous solu-tion of the acid is preferably carried out at 10 to 120~C for 30 minutes to 20 hours.
When the ion exchange groups are converted into -COOL
groups wherein L is a Cl - C20 alkyl group, the groups are converted into the acid form and then, further converted into khe ester form by reaction with the corresponding alcohol. The acid form can be also converted into the acid halide form by ~ l osf~J~o r .~5 reaction with ~s~h3r~s trichloride or phosphorus oxychloride, and then converted into the ester form by reaction with an alcohol. The groups in the acid form can be also converted into the aeid anhydride form by reaction with acetic anhydride or perfluoroacetic anhydride and then converted into the groups in the ester form by reaction with an alcohol. If necessary, the mem~rane (-~-COO ~ ~ type ) is treated with a chloride, sueh as ~0 thionyl chloride, phosphorus trichloride, phosphorus oxychloride, at 0 to 120C for 1 to 25 hours so as to convert the groups --~ COO ~ X into the groups in the form of acid anhydride and then, is treated with an alcohol to convert the groups in the ester form. The membrane (-~-COO ~ X type ) can be treated in:an alcohol in the presence of the organic acid or -the inorganie acid to convert the groups of -~COO ~ X into the groups of -COOL. The aleohol used for the esterifieation of the acid, the acid halide or the acid anhydride is preferably a Cl - C20 aleohol, sueh as methanol, ethanol, propanol, butanol, dodeeyl alcohol and sebaeyl aleohol. In the esterification, the membrane can be dippea into an aqueous solution of an inorganic acid or organie acid which is the sarne or different from the acid used for the conversion of the groups of ~ COO -~m--X. The di.pping treatment is preferably carried out at 30 to 120C for 30 minutes to 40 hours.
When the cation exchanye membrane made of a fluorinated polymer havi.ng the groups of -COOL is bonded to th~ electrode, it is pre*erable to have a desired melt-viscosity in the molten state. It has been found that the desired melt-viscostiy is usu-ally in a range of 102 to 101 poise, preferably 103 to 109 poise.
The membrane is melted under the appxopriate conditions of a temperature and a pressure so as to give the desired melt-viscosity.
When the pressure is high, the temperature can be lower. How-ever, ~hen the pressure is low, the temperature should be high.
. When the ion exchange groups of the membrane are in the form of -COOL, the decomposition temperature of the fluorinated polymer (the temperature at which 5~ of a weight loss of the poly-mer occurs in raising the temperature at a rate of 10C/min. in an N2 atmosphere) is in a range of 350 to 370C. Therefore, the de-composition of the fluorinated polymer of the membrane is not caused by bonding the pOI OUS electrode to the membrane. Although parts of the membrane intrude into the pores on the surface o~ the electrode in the bonding, the porous electrode is not damaged and maintains the stable bonding for a long time, and maintains the low cell voltage stable for a long time.
In bonding the electrode to the surface of the cation exchange membrane made of a fluorinated polymer the surface of the membrane is heated to about lO0 to 330C preferahly about 120 to 300C. It is sufficient to apply a pressure of from 0.01 to 1000 kg/cm2, preferably l to 300 kg/cm2 to the bonding area. The means for heating in the bonding step may be a press-heating device, an ultrasonic wave heating device, an impulse heating device and a ~ ~71~26 ~riction heating device. When the membrane is in the form of -COOH, it is possible to use a high frequency heating device.
In order to improve the bonding strength, it is possihle to pretreat the surface of the membrane, for example b~
a sand-blast treatment of the bonding surface or applying a coating of a swelling agen-t or a solvent for the fluorinated polymer (-COOL type) on the bonding surface. The bonding conditions depends upon the bonding method, the type of the fluorinated polymer forming the membrane and the thickness of the membrane.
For example/ with the impulse heating device, the bonding operation is carried out at a temperature from 130 to 350C under a pressure of 0.1 to 300 kg/cm2 for 30 seconds to 1 hour.
In the present invention, at least one of the anode and the cathode is bonded to the cation exchange membrane. It is sufficient to convert the groups on the bonding surface into the groups in the form of -COOL in the case of bonding the electrode on only one surface of the membrane. The electrode bonded to the membrane should have a permeability for the gas generated by the electrolysis and the electrolyte. In order to have such a property, the electrode should be a porous substrate, preferably a layer having a thickness of 0.1 to 100~, especially 1 to 50 ~. In such a porous electrode, the pore diametèr, the porosity and the air permeability should be in the desired ranges. The electrodes used as the anode and the cathode preferably have an average porosity of 0.01 to 100~ and a porosity o~ 30 to 99%. When the average pore diameter and the porosity are less than said ranges, the gas, such as hydrogen and chlorine, generated by the electrolysis are not easily removed from the electrode causing high electric resistance~ When they are above said ranges, the electric resistance is disadvantageously large. When the average pore diameter is in the range of 0.1 to 501J, and the porosity is in the range o 35 to 95 %, the gas 2¢
is easily removed ~rom the electrode and the electric resistance may be small. Stable operation can be continued for a long time.
The substances for forming the porous electrodes may be as follows:-The substances suitable for the anode include platinumgroup metals such as Pt, Ir, Pd and Ru, alloys thereof and oxides of the platinum group metal or alloy, a heat-stabilized reducible oxide of the platinum group metal or alloy and graphite. When the platinum group metal, the alloy or the oxide of the metal or alloy is used for the anode, the cell ~oltage may be advantageously decreased in the electrolysis of the alkali metal chloride.
The substances suitable for the cathode include platinum group metals, alloys thereof, graphite, nickel, Raney nickel, developed Raney nickel and stainless steel and iron group metals.
When the platinum group metal or the alloy or the Raney nickel is used for the cathode, the overvoltage for forming hydro-gen may be advantageously decreased in the electrolysis of water or an aqueous solution of the alkali metal chloride.
The porous electrodes can be prepared from the above sub-stances for the anode and cathode by the following processes.
The powdery substances having an average particle dia-me~er of from 0.01 to lOOy, preferably 0.1 to 50~, is bound, if necessary with a suitable binder. The binder is preferably a fluorinated polymer especially polytetrafluoroethylene. An aqueous dispersion of polytetrafluoroethylene having an average diameter of less than 1~ is preferably used. The wei~ht ra~io of the binder to the powdery substrate for the electrode is prefer-ably in a range~of 0.05 to 5 wt. parts, especially 0.1 to 3 wt.
parts per 10 wt. parts of the powdery substance for the electrode.
When the weight ratio of binder is too high, the potential of the electrode is disadvantageously high whereas when ~ 3 71 0~
it is too low, the powdery substance of the electrode is dis-advantageously separated~ In the preparation of the electrodes, it is possible to incorporate a desired solvent or surfactant so as to uniformly blend the powdery substance for the electrode and the binder. It is also possible to incorporate an electri.c conductive filler, such as graphite, or a water soluble additive, such as carboxymethyl cellulose and polyvinyl alcohol. The components are thoroughly mixed and deposited as a cake on a filter by a filtering method. The cake is contacted with the cation exchange membrane under pressure~ The mixture of the components for the electrode can be prepared in a form of a paste and the paste is coated on the cation exchange membrane. The paste can be also coated on an aluminum foil and the paste layer is contacted with the cation exchange membrane to form the electrode layer on the membrane. The method of forming the elec-.
trode layer on the cation exchange membrane disclosed in U.S.Patent 3,134,~97 can be employed.
The porous electrode layer on the cation exchange membrane can be bonded on the membrane by the press-bonding machine and the like according to this invention. A part of the porou~ electrode layer is preferably embedded into the surface layer of the membrane. The cation exchange membrane bonded to the electrode is in the form of -COOL. The ion exchange groups in the form of -COOL are converted into the groups in the form of ---t COO ~ X by suitable treatment such as a hydrolysis or a neutralization.
The electrolytic cell having the electrode layers and the cation exchange membrane may be a unipolar or bipolar type electrolytic cell. As material for the electrolytic cell, a material which is resistant to the aqueous solution of alkali metal chloride and chlorine, such as titanium, is used for the anode compartment and a material which is resistant to the alkali ~ 171~2~
metal hydroxide of high concentration and hydrogen, such as iron, stainless steel or nickel, is used for the cathode compartment in the electrolysis of an alkali metal chloride.
When the porous electrodes are used in the present invention, each current collector for feeding the current i5 placed outside each electrode. The current collectors usually have the same or higher overvoltage for chlorine or hydrogen compared ~ith that of the electrodes. For example, the current collector at the anode side is made of a precious metai or a valve metal coated with a precious metal or oxide thereof and -the current collector at the cathode side is made of nickel, stainless steel or expanded metal in a form of a mesh or a net.
The current collectors are contacted with the porous electrodes under a pressure.
In the present invention, the process condition for the electrolysis of an aqueous solution of an alkali metal chloride may be those conditions disclosed in the prior art, such as in Brltish Patent 1,009,795.
~ For example, an aqueous solution of an alkali metal chloride (2.5 to S.O Normal~ is fed into the anode compartment and water or a dilute solution of an alkali metal hydroxide is fed into the cathode compartment and the electrolysis is preferably carried;out at ~0 to 120C and a current density of 10 to 100 A/dm .
In the electrolysis, calcium ions or magnesium ions or the other heavy metal ions in the aqueous solu-tion of the alkali metal chloride cause the deterioration of the cation exchange membrane and accordingly, they should be reduced as far as possible. In order to prevent the generation of oxygen in the anode compartment, it is advantageous to incorporate an acid, such as hydrochloric acid, in the aqueous solution of the alkali metal chloride.
~. .
2 ~
The process for producing the alkali metal hydroxide and chlorine by the electrolysis of the aqueous solution of the alkali metal chloride has been illustrated. The present invention is not limited to the embodiment and can be also applied for the preparation of the cells for an electrolysis of water, an elec-trolysis of a desired alkali metal salt, such as sodium sulfate and a fuel cell.
The present invention will be further illustrated by the following Examples and References.
EXAMPLE 1:
Platinum black powder was suspended in water and a dispersion of polytetra1uoroèthylene (Teflon 30 J a trademark of the ~u Pont Company) was~added at a weight ratio of poly-tetrafluoroethylene to platïnum black of 1/10. A non-ionic surfactant (Triton X-100 a~trademark of Rohm & E~aas Co.) was added dropwise and the mixture was blended with an ultrasonifi-cation whilst cooling with ice. The mixture was sucked on a porous polytetrafluroèthylene membrane to provide a thin layer made of platinum black (5 mg/cm2) for the anode. A thin layer made of a stabilized Raney nickel (7 mg/cm2) for a cathode was obtained by the same ~rocess.
A cation exchange membrane made of a copolymer of 2 2 CF2 CFO(CF2)3COOCH3 having an ion exchange capacity of 1.45 meg/g. polymer and a thickness of 250~ was used.
Both the electrode layers were contacted with each of the surfaces of the cation exchange membrane so as to each have a porous polytetrafluoroethylene membrane on the outer surface. They were heated and pressed at 150C under a pressure of 25 kg/cm2 to bond the electrode layers to the cation exchange membrane and then,-the porous polytetrafluoroethylene membranes were peeled off to obtain the cation exchange membrane bonding the electrodes.
.. o ~ ~
The cation exchange memhrane bonding the electrodes was dipped in 2S wt.~ of an aqueous solution of sodium hydroxide at 90C for 16 hours to hydrolyze the cation exchange membrane. A
nickel mesh (40 mesh) and a platinum mesh (40 mesh) as the current collectors were respectively contacted with the anode and the cathode under pressure.
The electrolysis was carried out whilst maintaining a 4 Normal concentration of sodium chloride in the anode compart-ment and maintaining a 35 wt.% concentration of sodium hydroxide as the catholyte by feeding water into the cathode compartment~
The results are as follows.
Current density Cell voltage (V) (A/dm ) 2.7~
2.84
3.27 The current efficiency for producing sodium hydroxide at a current density of 20 A/dm was 94%. When the electrolysis at 20 A/dm2 was continued for 100 days, the cell voltage remained at the initial 2.85 V.
REFERENCE 1:
Thin layers as the cathode and the anode were prepared by the process of Example 1. A cation exchange membrane made of a copolymer of CF2 = CF2 and CF2 ~ CFO(CF2)3COOH3 having an ion exchange capacity of 1.45 meq/g. polymer and a thickness of 250~
was used. Both of the electrode layers were heat-bonded on each of the surfaces of the cation exchange membrane at 200C under a pressure of 100 kg/cm to obtain the cation exchange membrane having the electrodes on both surfaces.
In accordance with the process of Example 1, the electroly-sis was carried ` ~ ~7~02~
out. The results are as follows.
Current density Cell voltage (V) (A/dm2 ) 2.85 3'05 3.31 3.60 The current ef~iciency for producing sodium hydroxide at a current density of 20 A/dm2 was 91%. ~7hen the electrolysis at 20 A/dm2 was continued for 10 days, the electrodes were partially peeled off from the cation exchange membrane ~eeeby being impossible to continue the electrolysis.
EXAMPLE 2:
A cation exchange membrane made of a copolymer of CF2 = CF2 and CF2 = CFO(CF2)3COOCH3 having an ion exchange capacity of 1.43 meg/g. polymer and a thickness of Z40~ ~Jas dipped into a 25 wt.% aqueous solution of sodium hydroxide at 90C for 16 hours and then, it was aipped into lN-HCl. at the ambient temperature for 24 hours and dried in air.
A paste A was prepared by blending 5 wt. parts of platinum black powder having a particle diameter of less than 44~, 0.8 wt. part of 60 wt. % of aqueous dispersion of poly- ~-tetrafluoroethylene (PTFE) having a particle diameter of less than 1~ and 10 wt. parts of 1.5 wt.~ of aqueous solution of carboxymethyl cellulose. The paste A was screen-printed on one surface of the treated cation exchange membrane and the printed ~-layer was dried in air to solifify the paste thereby forming an anode layer containing platinum black in an amount of 2 mg/cm2.
A paste B was prepared by blending 5 wt. parts of stabilized Raney nickel obtained by dissolving aluminum component from Raney nickel alloy with a base and partially oxidizing it, 10 wt. parts of an aqueous solution of 1.5 wt.~ carboxymethyl ~ ~ 7:l~2~
cellulose and 0.8 wto parts of a 60 wt.% aqueous dispersion of polytetrafluoroethylene. The paste B was screen-prin-ted on the other surface of the treated cation exchange membrane thereby forming a cathode layer containing stabilized Raney nickel in an amount of 5 mg/cm2. The printed layers were bonded to the cation exchange membrane at 165C under a pressure of 60 kg/cm and then, dipped into a 25 wt.% aqueous solution of sodium hydroxide at 90C for 16 hours.
A platinum gauze (40 mesh) was contacted with the platinum black layer and a nickel gauze (20 mesh) was contacted with the stabilized Raney nickel layer under pressure.
The electrolysis was carried out whilst maintaining a 4 Normal concentration of sodium chloride in the anode compart-ment and maintaining a 35 wt.% concentration of sodium hydroxide as the catholyte by feeding water into the cathode compartment.
The result 5 are as follows.
Current density Cell voltage (V) tA/dm2 ) 2.65 20 20 2.87 3.05 3.20 The current efficiency for producing sodium hydroxide at a current density of 20 A/dm2 was 93%.
EXAMPLE 3:
Tlle cathode and anode thin layers were prepared by the same process as in Example 1 except that polytetrafluoroethylene was not added :in the electrode layer. Both of the electrode layers which do not contain polytetrafluoroethylene as a binder were heat-bonded on each surface of the cation exchange membrane at 160~C under a pressure of 60 kg/cm . The cation exchange membrane with electrode layers on both surface was obtained. In -16~
~ :~ 7 10~, accordance with the process and condition of Example 1, the electrolysis was carried out. The results are as follows.
Current density (A/dm ) Cell voltage (V) 2.82 3.23 The current efficiency for producing sodium hydroxide at a current density of 20 A/cm was 92%.
';
~17-
REFERENCE 1:
Thin layers as the cathode and the anode were prepared by the process of Example 1. A cation exchange membrane made of a copolymer of CF2 = CF2 and CF2 ~ CFO(CF2)3COOH3 having an ion exchange capacity of 1.45 meq/g. polymer and a thickness of 250~
was used. Both of the electrode layers were heat-bonded on each of the surfaces of the cation exchange membrane at 200C under a pressure of 100 kg/cm to obtain the cation exchange membrane having the electrodes on both surfaces.
In accordance with the process of Example 1, the electroly-sis was carried ` ~ ~7~02~
out. The results are as follows.
Current density Cell voltage (V) (A/dm2 ) 2.85 3'05 3.31 3.60 The current ef~iciency for producing sodium hydroxide at a current density of 20 A/dm2 was 91%. ~7hen the electrolysis at 20 A/dm2 was continued for 10 days, the electrodes were partially peeled off from the cation exchange membrane ~eeeby being impossible to continue the electrolysis.
EXAMPLE 2:
A cation exchange membrane made of a copolymer of CF2 = CF2 and CF2 = CFO(CF2)3COOCH3 having an ion exchange capacity of 1.43 meg/g. polymer and a thickness of Z40~ ~Jas dipped into a 25 wt.% aqueous solution of sodium hydroxide at 90C for 16 hours and then, it was aipped into lN-HCl. at the ambient temperature for 24 hours and dried in air.
A paste A was prepared by blending 5 wt. parts of platinum black powder having a particle diameter of less than 44~, 0.8 wt. part of 60 wt. % of aqueous dispersion of poly- ~-tetrafluoroethylene (PTFE) having a particle diameter of less than 1~ and 10 wt. parts of 1.5 wt.~ of aqueous solution of carboxymethyl cellulose. The paste A was screen-printed on one surface of the treated cation exchange membrane and the printed ~-layer was dried in air to solifify the paste thereby forming an anode layer containing platinum black in an amount of 2 mg/cm2.
A paste B was prepared by blending 5 wt. parts of stabilized Raney nickel obtained by dissolving aluminum component from Raney nickel alloy with a base and partially oxidizing it, 10 wt. parts of an aqueous solution of 1.5 wt.~ carboxymethyl ~ ~ 7:l~2~
cellulose and 0.8 wto parts of a 60 wt.% aqueous dispersion of polytetrafluoroethylene. The paste B was screen-prin-ted on the other surface of the treated cation exchange membrane thereby forming a cathode layer containing stabilized Raney nickel in an amount of 5 mg/cm2. The printed layers were bonded to the cation exchange membrane at 165C under a pressure of 60 kg/cm and then, dipped into a 25 wt.% aqueous solution of sodium hydroxide at 90C for 16 hours.
A platinum gauze (40 mesh) was contacted with the platinum black layer and a nickel gauze (20 mesh) was contacted with the stabilized Raney nickel layer under pressure.
The electrolysis was carried out whilst maintaining a 4 Normal concentration of sodium chloride in the anode compart-ment and maintaining a 35 wt.% concentration of sodium hydroxide as the catholyte by feeding water into the cathode compartment.
The result 5 are as follows.
Current density Cell voltage (V) tA/dm2 ) 2.65 20 20 2.87 3.05 3.20 The current efficiency for producing sodium hydroxide at a current density of 20 A/dm2 was 93%.
EXAMPLE 3:
Tlle cathode and anode thin layers were prepared by the same process as in Example 1 except that polytetrafluoroethylene was not added :in the electrode layer. Both of the electrode layers which do not contain polytetrafluoroethylene as a binder were heat-bonded on each surface of the cation exchange membrane at 160~C under a pressure of 60 kg/cm . The cation exchange membrane with electrode layers on both surface was obtained. In -16~
~ :~ 7 10~, accordance with the process and condition of Example 1, the electrolysis was carried out. The results are as follows.
Current density (A/dm ) Cell voltage (V) 2.82 3.23 The current efficiency for producing sodium hydroxide at a current density of 20 A/cm was 92%.
';
~17-
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method of bonding an electrode having a porosity of 30 to 99% to a cation exchange membrane made of a fluorinated polymer which is in a form having ion exchange groups having the formula wherein X represents an alkali metal atom, an alkaline earth metal atom or NRR' and R and R' respectively re-present hydrogen atom or a lower alkyl group, the ion exchange capacity of carboxylic acid groups of said cation exchange membrane being in a range of 0.5 to 2.5 meq/g. dry polymer; and m is a valence for the group X, the improvement in which said membrane in the form having ion exchange groups having the formula -COOL, wherein L represents hydrogen atom of a C1-C20 alkyl group, is melt-bonded to said electrode and then, the ion exchange groups in the form of -COOL are converted into the ion exchange groups in the form of .
2. The method according to claim 1, wherein said elec-trode is porous having a gas and liquid permeability, an average pore diameter of from 0.01 to 100µ, and a thickness of 0.1 to 100µ.
3. The method according to claim 2, wherein said elec-trode is a porous anode obtained by binding a powder of a platinum group metal, or an electrically conductive oxide thereof or a heat stabilized reduced oxide with a binder.
4. The method according to claim 2, wherein said elec-trode is a porous cathode obtained by bonding a powder of a plati-num group metal, an electrically conductive oxide thereof, an iron group metal or Raney nickel with a binder.
5. The method according to claim 3 or 4, wherein said binder is a fluorinated polymer.
6. The method according to claim 1, wherein said cation exchange membrane is made of a fluorinated polymer having the units wherein X represents fluorine, chlorine or hydrogen atom or -CF3; X' represents X or CF3(CF2)m; m represents an integer of 1 to 5; Y represents the following unit; , , , , and x, y and z respectively represent an integer of 1 to 10; Z and Rf represent -F or C1-C10 perfluoroalkyl group; and A repre-sents a functional group which is convertible into the group having the formula in the electrolysis.
7. The method according to claim 1 or 6, wherein said cation exchange membrane is made of a perfluoropolymer.
8. The method according to claim 1, wherein said cation exchange membrane is melt-bonded to said electrode with the surface layer having ion exchange groups in the form of -COOL in a thickness of at most 50µ.
9. The method according to claim 1, wherein the bonding part of said cation exchange membrane bonded to said electrode is melted at a melt-viscosity of from 102 to 109 poise.
10. The method according to claim 1, 8 or 9, wherein the bonding part of said cation exchange membrane bonded to said electrode is heated at 100 to 330°C and is bonded under a pressure of 0.01 to 1000 kg/cm2.
11. The method according to claim 1, 8 or 9, wherein said bonding is carried out by a heating means of a press-heating device, an ultrasonic heating device, an impulse heating device, a friction heating device or a high frequency heating device.
12. The method according to claim 1, 2 or 3, in which the molecular weight of the fluorinated polymer is in the range of from 1 x 105 to 2 x 106.
13. The method according to claim 1, 2 or 3, in which the molecular weight of the fluorinated polymer is in the range of from 1.5 x 105 to 1 x 106.
14. The method according to claim 1, wherein said electrode is formed with an electric conductive powder and a binder and said hinder is bonded to said cation exchange membrane in the form of ion exchange groups having the formula -COOL.
15. The method according to claim 14, wherein said binder is a fluorinated polymer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP96097/1979 | 1979-07-30 | ||
| JP9609779A JPS5620178A (en) | 1979-07-30 | 1979-07-30 | Closely sticking method for ion exchange membrane and electrode |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1171026A true CA1171026A (en) | 1984-07-17 |
Family
ID=14155883
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000357242A Expired CA1171026A (en) | 1979-07-30 | 1980-07-29 | Method of bonding electrode to cation exchange membrane |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0026969A3 (en) |
| JP (1) | JPS5620178A (en) |
| CA (1) | CA1171026A (en) |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5827352B2 (en) * | 1979-08-31 | 1983-06-08 | 旭硝子株式会社 | Manufacturing method of ion exchange membrane with electrode layer attached |
| NL8100168A (en) * | 1980-02-11 | 1981-09-01 | Ppg Industries Inc | SOLID POLYMERIC ELECTROLITE AND METHOD FOR MANUFACTURING THAT. |
| US4421579A (en) * | 1981-06-26 | 1983-12-20 | Diamond Shamrock Corporation | Method of making solid polymer electrolytes and electrode bonded with hydrophyllic fluorocopolymers |
| JPS5816082A (en) * | 1981-07-21 | 1983-01-29 | Permelec Electrode Ltd | Electrolytic device using ion exchange membrane and production thereof |
| GB2117797B (en) * | 1981-12-28 | 1985-08-07 | Gen Electric | Fabricating membrane-electrode assembly |
| EP0120212B1 (en) * | 1983-02-25 | 1986-10-01 | BBC Aktiengesellschaft Brown, Boveri & Cie. | Process for producing an electrically conductive layer on a solid electrolyte surface, and electrically conductive layer |
| GB2161107B (en) * | 1984-07-06 | 1988-03-02 | Advanced Semiconductor Mat | Method and apparatus for cold runner transfer molding |
| JPH043769Y2 (en) * | 1986-12-26 | 1992-02-05 | ||
| US5415888A (en) * | 1993-04-26 | 1995-05-16 | E. I. Du Pont De Nemours And Company | Method of imprinting catalytically active particles on membrane |
| US5330860A (en) * | 1993-04-26 | 1994-07-19 | E. I. Du Pont De Nemours And Company | Membrane and electrode structure |
| US5547911A (en) * | 1994-10-11 | 1996-08-20 | E. I. Du Pont De Nemours And Company | Process of imprinting catalytically active particles on membrane |
| DE19509749C2 (en) * | 1995-03-17 | 1997-01-23 | Deutsche Forsch Luft Raumfahrt | Process for producing a composite of electrode material, catalyst material and a solid electrolyte membrane |
| DE19509748C2 (en) * | 1995-03-17 | 1997-01-23 | Deutsche Forsch Luft Raumfahrt | Process for producing a composite of electrode material, catalyst material and a solid electrolyte membrane |
| DE19705468C2 (en) * | 1997-02-13 | 2000-01-05 | Forschungszentrum Juelich Gmbh | Production of a membrane with an applied electrode by means of ultrasound |
| JP4093439B2 (en) * | 1999-08-27 | 2008-06-04 | 松下電器産業株式会社 | Method for producing electrode for polymer electrolyte fuel cell |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3134697A (en) * | 1959-11-03 | 1964-05-26 | Gen Electric | Fuel cell |
| JPS597795B2 (en) * | 1975-04-17 | 1984-02-21 | 株式会社トクヤマ | Cathode iron for electrolysis |
| JPS526374A (en) * | 1975-07-07 | 1977-01-18 | Tokuyama Soda Co Ltd | Anode structure for electrolysis |
| US4148979A (en) * | 1976-04-27 | 1979-04-10 | Toyo Soda Manufacturing Co., Ltd. | Method of improving characteristics of cation-exchange membrane by swelling in water miscible organic solvent |
| JPS53144481A (en) * | 1977-05-24 | 1978-12-15 | Asahi Glass Co Ltd | Method of joining fluorine contained cation exchange resin membrane |
| DE2844496C2 (en) * | 1977-12-09 | 1982-12-30 | General Electric Co., Schenectady, N.Y. | Process for producing halogen and alkali metal hydroxides |
-
1979
- 1979-07-30 JP JP9609779A patent/JPS5620178A/en active Pending
-
1980
- 1980-07-29 CA CA000357242A patent/CA1171026A/en not_active Expired
- 1980-07-30 EP EP80302611A patent/EP0026969A3/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP0026969A3 (en) | 1981-08-26 |
| EP0026969A2 (en) | 1981-04-15 |
| JPS5620178A (en) | 1981-02-25 |
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| MKEX | Expiry |