CA1193999A - Ion enchange membrane having porous non-oxide ceramic particles on the surface - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:

An ion exchange membrane electrolytic cell comprises an anode, a cathode, an anode compartment and a cathode compartment partitioned by an ion exchange membrane. A gas and liquid permeable porous non-electrode layer composed of non-oxide ceramics particles is bonded to at least one side of the ion exchange membrane. With use of such a mem-brane, the cell voltage can considerably reduced in the electrolysis of water, an alkali metal halide, an alkali metal carbonate, etc.

Description

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The present invention relat:es to an ion exchange membrane electrolytic cell. More particularly, it relates to an ion exchange membrane electrolytic cell sui-table for the electrolysis of water or an aqueous solution of an acid, a base, an alkali metal sulfa-te, an alkali metal carbonate, of an al}cali metal halide and to an ion exchange membrane for the electrolytic cell.

As a process for producing an alkali metal hydrox-ide 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 prevent pollution.

It has been proposed to use an ion exchange mem-brane in place of asbestos as the diaphragm to produce an alkali metal hydroxide by ~lectrolyzing an aqueous solution of an alkali metal chloride so as to obtain an alkali metal hydroxide having high purity and high concentration.

However, it is desirable to save energy and it is desirable to minimize the cell voltage in such technology.

It has been proposed to reduce a cell voltage by improvements in the materials, compositions and configura-tions of the anode and cathode and the compositions of the ion exchange membrane and the type of ion exchange group.

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q~3 It has been proposed to attain electrolysis by -the so-called solid polymer electrolyte type electrolysis of an alkali metal chloride wherein a cation exchange membrane made of a fluorinated polymer is bonded to a gas-liqu.id permeable catalytic anode on one surface and a gas-liquid permeable catalytic ca-thode on the other surface oE the membrane (British Patent No. 2,009,795, U.~. Paten-t No. 4,210,501 and No. 4,214,958 and No. 4,217,401).

This electrolytic method is very advantageous for the electrolysis at a lower cell voltage because the electric resistance caused by the electrolyte and the electric resis-tance caused by bubbles of hydrogen gas and chlorine gas generated in the electrolysis, can be greatly decreased, these parameters having been considered difficult to reduce in conventional electrolysis.

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The anode and the cat:hode in this electrolyti.c cell are bonded on the surface~of the ion exchange membrane so as to be partially embedded. The gas and -the electroly-te solution are .readily permeated so as to easily remove, from the electrode, the gas :Eormed during the electrolysis at -the electrode layer con-tacting ~t-h the membrane. Such porous electrode is usually a thin porous layer which is formed by uniformly mixing par-ticles which act as an anode or a cathode with a binder, such as graphite or other electric conductive material. However, it has been found that when an electrolytic cell having the electrode bonded directly to an ion exchange membrane is used, the anode in the electrolytic cell is brought into contact with hydroxyl ion which is reversely diffused from the cathode compartment, and accordingly, both(i~)chlor-ine resistance and an ~ ~e~resistance for anode material are required and an expensive material must be used. When the electrode layer is bonded to the ion exchange membrane, a gas is formed by the electrode reaction between the electrode and membrane and a deformation phenomenon of the ion exchange . ~ .

membrane is caused which deteriorate the characteristics of the membrane. I-t is difficult to work Eor a long -time under s-table conditions. In such an electrolytic cell, the curren-t collector for -the electric supply to the electrode layer bonded -to the ion exchange membrane should closely contact the electrode layer. When a firm contact is not ob-tained, the cell voltage may be increased. The cell structure for securely contacting the current collec-tor to -the electrode layer is disadvantageously complicated.
The inventors have investigated the operation of the electrolysis of an aqueous solution at a minimized load voltage and have found that this can be satisfactorily attained by using a cation exchange membrane having a gas and liquid permeable porous non-electrode layer on at least one of surfaces of the cation exchange membrane facing the anode or cathode which is disclosed in European Patent Publication No. 0029751 or applicant's Canadian Patent application No. 365,540 filed November 26, 1980.
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The effect of reduction of the cell voltage by the use of the cation exchange membrane having such a porous layer on the surface depends upon the type of the material, the porosity and the thickness of the porous layer. Thus, it is surprising that -the effect: of reducing the cell volt-age is attained by the use of the porous layer made of a non-conductive material. The effect of reducing the cell voltage is also attained even though electrodes are placed with a gap Erom the membrane without contacting the electrode wlth the membrane, although the extent of the effect is not high.

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The present invention thus provides an electro-lytic cell in which the reduction of the cell voltage is as high as possible.

The present invention al~:o provides an elec-troly-tic cell having a low and stable cell voltage for a long period of time.

The present invention further reduces the content of particles used Eor a gas and liquid permeable porous non-electrode layer bonded on at leas-t one surface of a cation exchange membrane.

It has now been unexpectedly found that the above can satisfactorily be accomplished by using a cation exchange membrane having a gas and liquid permeable porous non-electrode layer composed of non-oxide ceramic particles having little or no electroconductivity, on at least one side thereof facing either the anode or the cathode.
Thus, the present invention provides an ion ex-change membrane electrolytic cell comprising an anode, a cathode, an anode compartment and a cathode ccmpartment partitioned by an ion exchange membrane, wherein a gas and liquid permeable porous non-electrode layer composed of non-oxide ceramic particles is bonded to at least one of the surfaces of the ion exchange membrane.

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The present invention will be further illustrated by way of the accompanying drawings, in which:--F`igure 1 is an enlarged cross sectional view of a S part of an embodiment of the cation exchange membrane of the present invention;

Figure 2 is an enlarged cross sec-tional view of a part of another embodiment of the cation exchange membrane of the present invention; and Figures 3(i) and 3(ii) are enlarged cross sectional views of parts of the membranes illustrating the porous layers formed by sparsely depositing particles onto the surfaces of the respective membranes.

The extent of cell voltage-red~3ction obtainable by the use of the cation exchange membrane having such a porous layer on its surface, varies depending upon the type of the ceramic particles constituting the porous layer and the porosity and thickness of the poxous layer. However, it is quite unexpected that such voltage-reduction is obtainable when the porous layer on the surface of the membrane is formed by ceramic particles which have no or extremely small con-ductivity, as will be described hereinafter, and which are therefore incapable of functioning as an electrode. Further, when the ion exchange membrane having such a porous layer is used, it is preferred that the electrodes are disposed in contact with the membrane. When the electrodes are, however, disposed with a space from the membrane, it is still possible to reduce the cell voltage.

Figure 1 is a cross sectional view of a part of an - embodiment of the cation exchange membrane according to the present invention, and Figure 2 is a cross sectional view of a part of another embodiment of the present inven-tion.
Figure 1 illustrates a case where a dense porous layer is formed on the surface of the membrane with -the non-oxide ceramic par-ticles, in which the surface of the ion exchange membrane 1 is densely covered with a great number of par-ticles

2. Figure 2 illustrates a case where a low densi-ty porous layer is formed with the ceramic particles. In this case, particles 12 or groups of particles 13 are bonded to the surface of the membrane partially or wholly discontinuously.
The amount of the ceramic particles to be bonded on the surface of the membrane to form the porous layer, may vary depending on the shape and size of the particles. How-ever it has been found that the amount is preferably within a range of 0.001 to 50 mg/cm2, more preferably 0.005 to 10 mg/cm2. If the amount is excessively small, the desired voltage-saving will not be obtained. If the amount is excessively large, it is likely that the cell voltage will thereby be increased.
As described above, the particles constituting the gas and liquid permeable porous layer on the surface of the cation exchange membrane of the present invention, are com-posed of non-oxide ceramic particles. Such ceramic particles usually have little electroconductivity and they are extremely hard and have high corrosion resistance and heat resistance.
If such particles are used to fo:rm a porous layer on the surface of the ion exchange membrane, each particle always maintains its original shape and a porous layer thereby formed, always has constant physical properties. Accordingly, an ion exchange membrane having superior properties is there-by obtainable.

The non-oxide ceramics particles to be used in the present invention are preferably a carbide, a nitride, a silicide, a boride or a sulfide. Any compound selected from carbides, nitriàes, silicides, borides and sulfides may be used in the present invention, so long as it is ceramic . For instance, as the carbide, there may be mentioned HfC, TaC, ZrC, SiC, B 4C, WC, TiC, CrC, UC or E~eC . The nitride may be, for instance, BN, Si3N4, TiN or AlN. The silicide may be, for instance, a silicide of Cr, Mo, W, Ti, Nb or La. The boride may be, for instance, a boride of Ti, Zr, Hf, Ce, Mo, W, Ta, Nb or La. As the sulfide, there may be mentioned, for instance, Fe3S~ or MoS2. Among them, c~-SiC, B-SiC:, B4C, BN, Si3N4, TiN, AIN, MoSi2 and LaB6 are particularly preferred.
These non-oxide ceramic particles are used in the form of preferably having a particle size of 0.01 to 300,u, particularly 0.1 to 100,u. The formation of a porous layer by bonding such particles to the surface of the membrane iSpreferab1y c~rried out in the following manner.
Namely, the ceramic particles to form the porous layer are formed into a dispersion thereof or a syrup or paste containing them with use of a suitable assisting agent or medium as the case requires. In such a form, they are applied to the surface of the membrane. In the prepara-tion of the dispersion or the syrup or paste containing such particles, a fluorinated polymer such as polytetrafluoroethylene may be incorporated as a binder, if necessary.
If desirable, it is possible to use a viscosity controlling agent.
Suitable viscosity controlling agents include water soluble materials, such as cellulose derivatives e g . carboxymethyl cellulose, methylcellulose and hydroxyethyl cellulose; and polyethyleneglycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium polyacrylate, polyvinyl ether, casein or ~3~?"3~

polyacrylamide. Such a binder or viscosity controlling agent is used preferably in an amount of 0 to 50% by weight, particularly 0.5 to 30% by weight, based on the powder of the ceramic particles.

Further, if necessary, a sui-table surface active agent, such as a long chain hydrocarbon or a fluorinated hydrocarbon may be incorporated to facilitate the formation of the dispersion, syrup or paste.

The porous layer composed of the non-oxide cera-mic particles can be formed on the ion exchange membrane, for instance, by a method which comprises adequately mixing the ceramic particles, if necessary, together with the binder, and the viscosity controlling agent in a suitable medium, such as an alcohol, ketone or hydrocarbon to form a paste and transferring or printing the paste on the membrane.
According to the present invention, it is also possible that instead of the paste, a syrup or slurry of polymer particles is directly sprayed on the membrane to deposit the particles to the surface of the ion exchange membrane.

The porous layer of particles on groups of parti-cles formed on the ion exchange membrane is preferably heat pressed on the membrane by a press or a roll at a temperature from 80 to 220C under a pressure of ~rom 1 to 150 kg/cm (or kg/cm), to bond the layer to the membrane, preEerably until the particles or groups of particles are partially embedded into the surface of the membrane. The resulting porous non-electrode layer bonded to the membrane preferably has a porosity of 30 to 99%, especially 40 to 95% and a thickness of 0.01 to 200~, especially 0.1 to 100~, which is less than that of the membrane.

Further, in a case where the porous layer is for-med by depositing the ceramic particles sparsely on the membrane as shown in Figure 2, -the thickness of the porous layer is calculated as follows. Namely, if each particle or group of particles has -the same heigh-t (a) to form a thickness from the surface of the membrane as shown in Figure 3(i), the value (a) is -taken as the thickness of the layer. Whereas, in a case where each particle or group of particles has a differen-t height to form a non-uniform thick-ness Erom the surface of the membrane as shown in Figure 3(ii), an average value (b) is taken as the thickness of the layer.
Accordingly, the porosity oE the porous layer is a porosity calculated on the basis of such a thickness of the porous layer.

In the present invention, the porous layer composed of the non-oxide ceramic particles, is preferably provided on the cathode side of the ion exchange membrane. In this - case, a ~h voltage ~and stable voltage can be attained over a long period of time since the non-oxide ceramic par-ticle is extremely hard and exhibits high corrosion resistance to the catholyte and hydrogen gas. In the case where the layer composed of the non-oxide ceramic particles is provided on the cathode side of the membrane, a gas and liquid per-meable porous non-electrode layer composed of metal or metal oxide particles is preferably bonded on the anode side of the ion exchange membrane. In this case, the metal is preferably a metal belonging to Group IV-A (preferably germanium, tin or lead), Group IV-B (preferably titanium, zirconium or hafnium), Group V-B (preferably niobium or tantalum) of the Periodic Table, or an iron group metal (preferably iron, cobalt or nickel).

The method for forming the gas and liquid permeable porous layer of metal or metal oxide particles on the mem-brane may be the same as the above-mentioned method used for the formation of the porous layer of the non-oxide ceramic particles. Further, the porous layer is likewise . ~ ~

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required to have the same physical properties as required for the porous layer of the non~oxide ceramic particles.

In the present invention, the ion exchange mem-brane on which the porous layer is formed, is preferably a membrane made of a fluorine-containing - lOa -.

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polymer havin~ cation exchange groups. Such a membrane is preferably made OI a copolymer of a vinyl moncane:r, such as tetrafluoroethylene or chlorotri1uoroethylene with a fluvrovinyl monomer contairling ion exchange ~IC:
,3roup5,such as sulfonic acid groups, carboxylic acid groups and phospho~c acid groups.

The ion exchange membrane is preferably made of a :fluorinated polymer having the following units (M) ~ CF2-CXX'~

~N) ~ CF2- ICX ) Y -A

10 wherein X represents fluorine, chlorine or hydrogen atom or -CF3;

X' represents X or CF3(CH2)m; m represents an integer of 1 to 5.

The typical examples of Y have the structures bonding A to a fluorocarbon group ~CF2~ , -OtCF2~ , t O-cF2-lcF~

--CF ( O-CF -CF~ , ~ O-CF2-- ICF )x ( O-CF2- IC~ and Z ~ Rf --O-CF2~ CF-O-CF2 )~ (- CF2 )y ~-~CF2-0-CF~
Rf x, y and z respectively represent an integer of 1 to 10i Z and Rf represent -F or a Cl - C10 perfluoIQalkyl group; and A represents -COOM
or -SO3M, or a functional group which is convertible into -COOM or -SO3M
20 by hydrolysis or neutralization~ such as -CN, -COF, -COOR ~, -S02F
and -CONR2R3 or -SO2NR2R3 and M represents hydrogen or an alkali metal atom; Rl represents a C1 - C10 alkyl group; and R2 and R3 represent H or a C 1 ~ C 10 alkyl group -It is preferable to use a fluorinated ion exchange membrnne having an ion exchange group content of 0.5 to 4.0 mi1iequiva1ents/gram ~ ~ 3 ~3~
dry polymer, especia11y 0.3 to 2.0 milliequivalen-ts/gram of dry polymer as above.

In the ion exchange membrane made of a copolymer having the units (M) and ~N), the amount oF the units (N) is preferably in a range of 1 to ~0 mol ~ more preferably 3 to 25 mol %.

The ion exchange membrane used in this invention is not limited -to that made oF only one type of polymer or a polymer having only one type of the ion exchange group. It is possible to use a laminated membrane made of two types oF the polymers having lower ion exchange capacity on the cathode side, or an exchange membrane having a weak acidic ion exchange group, such as carboxylic acid group on the cathode side and a strong acidic ion exchange group, such as sulFonic acid group on the anode side.

The ion exchange membranes used in the present invention can be fabricated by various conventional methods and they can preferably be reinforced by a fabric such as a woven fabric or a net, a non-woven fabric or a porous film made of a fluorinated polymer, such as polytetrafluoroethylene or a net or perforated plate made of a metal.
The thickness of the membrane is preferab1y 50 to 1000 microns, especially 50 to 400 microns, more especially 100 to 500~.

The porous non-electrode layer is formed on the anode side, the cathode side or both sides of the ion exchange mem-brane by bonding to the ion exchange membrane in a suitable manner which does not decompose ion exchange groups, preferably, in a form of an acid or ester in the case of carboxylic acid groups or in a form of -S02F in the case of sulfonic acid group.

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In the electroly-tic cell of the present invention, various electrodes can be used, for example, foraminous electrodes having openings, such as a porous p]ate, a screen a punched me-tal or an expanded me-tal are preEerably used.
The electrode having openings is preferable a punched metal with holes having an opening area of 30 -to 90~ or an expanded metal with openings of a major length oE 1.0 to 10 mm and a minor length of 0.5 to 10 mm, a width of a mesh of 0.1 to 1.3 mm and an opening area of 30 -to 90%.
A plurality of plate electrodes can be used in layers. In the case of a plurality of electrodes having different opening areas being used in la~ers, the electrode having the smaller opening area is placed close to the membrane.
The anode is usually made of a platinum group metal, a conductive platinum group metal oxide or a conductive re-duced oxide thereof.

The cathode is usually made of a platinum group metal, a conductive platinum group metal oxide or an iron group metal.

The platinum group metal can be Pt, Rh, Ru, Pd or Ir. The iron group metal is iron, cobalt, nickel, Raney nickel, stabilized Raney nickel, stainless steel, a stainless steel treated by etching with a base (U.S. Patent No. 4 255 247) Raney nickel plated cathode (U.S. Patent No. 4,170,536 and No.

4,116,804), or nickel rhodanate plated cathode (V~S. Patent No. 4,190,514 and No. 4,190,5:L6).

When an electrode having openings is used, the electrode can be made completely of the materials for the anode or the cathode. When the platinum metal or the con-ductive platinum metal oxide is used, it is preferable to coat such material on an expanded metal made of a valve metal, ~3~3~
such as titanium or tantalum.

When the electrodes are placed in the electrolytic cell of the present invention, i-t preferable to con-tac-t -the electrode with -the porous non-electrode layer so as to reduce the cell voltage. The elec-trode, however, can be placed leaving a proper space from the porous non-electrode layer. When the electrodes are placed in contact wi-th the porous non-electrode layer, it is preEerable to contact them under low pressure e.g. 0 to 2.0 kg/cm2, rather than high pressure.

When the porous non-electrode layer is formed on only one surface of the membrane, the electrode at the other side of the ion exchange membrane having no porous layer can be placed in contact with the membrane or with a space from the membrane.

The electrolytic cell used in the present invention can be of the monopolar or bipolar type. The elec-trolytic cell used for the electrolysis of an aqueous solution of an alkali metal chloride, is made of a material resistant to the aqueous solution of the alkali metal chloride and chlorine, such as valve metal e.g. titanium in the anode compartment and is made of a material resistant to an alkali metal hydroxide and hydrogen, such as iron, stainless steel or nickel in the cathode compartment.

In the present invention, the process conditions for the electrolysis of an aqueous solution of an alkali metal chloride may be the conventional conditions as dis-closed in the above-mentioned Japanese Laid-Open Patent Application No. 112398/79 filed by General Electric Co. and published September 3, 1979.

For example, an aqueous solution of an alkali metal chloride (2.5 to 5.0 NGrmal) is fed into the anode compartment, -- 1~ --and water or a dilute solution of an alkali metal hydroxide is fed into the cathode compartment and -the elec-trolysis is preferably carried out at a -temperature from 80 to 120C and at a current density of 10 to 100 A/dcm2.
s In this case, heavy metal ions, such as calcium or magnesium ions, in the aqueous alkali metal chloride solution tend to lead to degradation of the ion exchange membrane, and it is desirable -to minimize such ions as far as possible. Further, i.n order to prevent the generation o-E
oxyc~en at the anode, an acid such as hydrochloric acid may be added to the aqueous alkali metal solution.

Although the electrolytic cell for the elec-trolysis of an alkali metal chloride has been illustrated, the electro-lytic cell of the present invention can likewise be used for the electrolysis of wa-ter, a halogen acid (HCl, HBr) an alkali metal carbonate, e-tc.

The present invention will be further illustrated by certain examples which are provided for purposes of illustration only and are not intended to limit the present invention.

EXAMPLE 1:

A mixture comprising 10 parts o~ ~-silicon carbide powder having an average particle size of 2~, one part of modified PTFE particles having a particle size of at most 0.5~ and com-posed of polytetrafluoroethylene particles coa-ted with a copolymer of tetrafluoroethylene with CF2=CFO(CF2)3COOCH3, 0.3 part of methyl cellulose (a 2~ aqueous solution having a viscosity of 1500 cps), 14 parts of water, 0.2 part of cyclohexanol and 0.1 part of cyclohexanone, was kneaded to obtain a paste.

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3~3 The paste was screen-printed on -the cathode side surEace of an ion exchange membrane composed of a copolymer of polytetrafluoroethylene with CF2=CFO(C~2)3COocH3 and having an ion e~change capacity of 1-4~ me~/g dry`resin a thickness of 280~, with use of a printing device compris-ing a Tetoron (a trademark of Toray Industries, Inc., for polyethylene terephthala-te fiber) screen having 200 mesh and a thickness of 75~ and a screen mask provided thereunder and having a thickness of 30~, and a polyurethane squeegee.
The printed layer formed on -the - 15 a -3~q'3~
cathode side surface of the ion exchange membrane was dried in the air.
Then, rutile-type TiO~ powder having an average part;cle size of 5,u was screen~printed on the anode side surface of the ion ex-change membrane in the same manner as above, and then dried in the air.
Thereafter, the titanium oxide powder and the silicon carbicle powder were pressed onto the ion exchange membrane at a temperature of 140C
under pressure of 30 kg/cm2. The amounts oP the titanium oxide powder and the silicon carbide thereby attached to the surface of the membrane were 1.1 mglcm and 0.8 mg/cm, respectively. Each thickness of the porous layer made o~ titanium oxide and silicon carbide was 7~ and 8,u, respectively. Then, the ion exchange membrane was dipped in an aqueous solution containing 25g6 by weight of sodium hydroxide at 90C fcr 16 hours for the hydrolysis of the membrane.

EXAMPLES 2 to 8:

Cation exchange membranes having a porous layer on their surface were prepared in the same manner as in Example 1 except that the modified PTFE was used to prepare the paste of Example 1 and the composition was modified by using the materials, particle sizes and amounts of deposition as shown in Table 1.
The particles were prepared from commercial products by pulverizin~ and classifying them, as the case required, to have the particle sizes as shown in Table 1. In Example 8, it was observed by the microscopic observation that particles or groups of particles in the porous layer were deposited Oll the surface of the membrane with a space from one another.

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T able -Materials, (Par-ticle sizes), Amounts of deposition Example _ _ __ No. Anode side Thick- Cathode side Thick-_ _ _ ness ~11 ) ~ __ ness ( 11 ) 2 Fe203 ~3~) 0.3 mglcm 7 B4C (2~u) 0.9 mg/cm2 10 3 SnO2 (2~ 0 " 4 Si3N~1 ~211) 1.1 " 9 4 Zr2 ~5,u) 1. n ~ 6 ~-SiC (5~1) 1.1 " 10 Nb~05 t51~ 0 " 6 BN ~3u) 0.8 " 9 6 TiO2 (5~) 1.0 " ~ MoSi~ (7~1) 0.8 " 10 7 MnO2 t7~) 1-2 " 10 AlN (5~) 0.9 " 8 8 TiO2 (2-lO,u)O.O1 '' B-SiC(5-20~) 0.01 " 15 . _ EXAMPLE 9:
.

A suspension containing 10 g. of B-silicon carbide having an average particle size of 5~1 in 100 ml. of water, was sprayed on both sides of the same ion exchange membrane as used in Example 1 which was placed on a hot plate a-t 140C, with use of a spray gun. The spray-ing rate was controlled so that the water in the sprayed suspension was dried up within 15 seconds after the spraying. Then, the porous layer formed by the spraying was pressed onto the ion exchange membrane at a temperature of 190C under pressure of 30 kg/cm . On both sides ~ of the ion exchange membrane, B-silicon carbide was deposited in an amolmt of 0.8 mg/cm . The thickness of the porous layers made of ~-silicon carbide was 9,u. Thereafter, the ion exchange membrane was dipped in an aqueous solution containing 25% by weight of sodium hydroxide at a temperature of 90C for the hydrolysis of the membrane.

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EXAMPLE 10_ An ion exchange membrane having 1.1 mg/cm2 of titanium oxide powder and 0.8 mg/cm2 of silicon carbide powder deposited on the anode side and the cat~lode side, respectively, of the membrane, was prepared in t]le same manner as in Example 1 except that as the ion exchange membrane, a cation exchange membrane (the ion exchange capacity: 0.87 meq/g dry resin, the thickness: 30011 ) composed of a copolymer of CF2=CF2 with CF2=CFOCF2CF(CF3)0CF2CF2S02F was used.
Each thickness of the porous layer made of titanium oxide and silicon 10 carbide was 711 and 8,u, respectively.
Now, the electrolytic characteristics of the ion exchange membranes according to the present invention, as actually used, will be described with reference to VVorking Examples.

Test No. 1:

An anode composed of an expanded metal (the minor length:
2. 5 mm, the major length: 5 mm) OI titanium coated with a so~id solution of ruthenium oxide, indium oxide and titanium oxide and having a low chlorine overvoltage, was pressed against the anode side of an ion ex-change membrane to contact therewith, and a cathode prepared by subject-20 ing an expanded metal (the minor length: 2.5 mm, the major length: 5 mm) of SUS 304 to etching treatment in an aqueous solution containing 52?6 by weight of sodium hydroxide at 150C for 52 hours, to have a low hydrogen-over voltage, was pressed against the cathode side of the ion exchangemembrane to contact therewith. Electrolysis was conducted at 90C under 25 40 Aldm2 while supplying a 5N sodium chloride aqueous solution to the anode compartment and water to the cathode compnrtment and maintaining the sodium chloride concentration in the anode compnrtment to be 4N and the sodium hydroxide concentration in the cathode compartMent to be 35~6 by weight. The results thereby obtained are shown in Table ~.

In Tests, the ion exchange membranes having a porouslayer are identified by the numbers of Examples.

T able 2 No ~Membranes Cell voltages Current s. _ (Nos of Exam~les) (V) efficiencies (%) 1 1 3.25 92 2 2 3.23 92.5 3 3 3.22 91 4 ~ 3.24 92.5 3.20 92 6 6 3.19 92 7 7 3.25 92.5 g 8 3.31 93 9 9 3.23 92 _ 10 3.26 85 Test No. 2:

Electrolysis was conducted in the same manner as in Test No. 1 except that the anode and the cathode were respectively spaced S.~
from the ion exchange membrane for 1.0 mm, instead of contacting the membrane. The results thereby obtained are shown in Table 3.

Table 3 Membranes Cell voltages Current Nos. (Nos. OI Examples) (V) efficiencies (%) 11 1 3.30 93 12 3 3.26 92.5 13 S 3.25 93.5 l14 7 3.29 94 ~l~;i~

,3 Test No. 3:

Prior to the use, the ion exchange membrane was hydrolyzed in an aqueous solution containing 20% by weight of potassium hydroxide instead of the aqueous solution containing 25~ by weight of sodium

5 hydroxide. '~he electrodes as used in Test No. 1 were pressed against the ion exchange membrane having a porous layer, to contact therewith. Electrolysis ~vas conducted at a temperature of 90C under 40 A/dm2 while supplying a 3.5N potassium chloride aqueous solution to the anode compartment and water to the cathode compartment and maintain-10 ing the potassium chloride concentration in the anode compartment to be2.5N and the potassium hyroxide concentration in the cathode compartment to be 3S~ by weight. The results thereby obtained are shown in Table 4.

Table 4 Membranes Cell voltages Cui~rent os. (Nos. of Eacamples) _(V) ef~ci_ncles (O

2 3.19 95.0 4 3 . 20 96. 0 Test No. g:

An expanded metal (the minor length: 2.5 mm, the major length: 5 mm) of nickel was pressed against $he anode side OI the ion 20 exchange membrane to contact therewith, and the cathode as used in Test No. 1 was pressed against the cathode sicle Or the membrane to contact therewith. Electrolysis of water was conducted at a temperature of 90C
under 50 A/dm2 while supplying an aqueous solution containing 30~ by weight of potassium hydroxide to the anode compartment and water to the 25 cathode compartment and maintaining the potassium hydroxide concentrations 3~

in the anode and cathode compartm~nts to be 20%. T:he results thereby obtained are shown in Table 5.

T able 5 _ . . _ __ _ o~ Membrane (No.of Example) Cell voltage ~V) 17 .L __ 10 _ 2. 30 ~I .

OMPARATIVE li XAMPLE:

Electrolysis was conducted in the same manner and conditions as in Test No. 1 except that the ion exchange memb~ane as in Examl~le 1 having no porous layer was used. The results therehy ob~ained are shown below.

Cell voltage (V) Current efficiency (~2 3.61 93.5

Claims (26)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLU-SIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an ion exchange membrane electrolytic cell which comprises an anode, a cathode, an anode compartment and a cathode compartment partitioned by an ion exchange membrane; the improvement in which a gas and liquid per-meable porous non-electrode layer composed of non-oxide ceramic particles is bonded to at least one of surfaces of said ion exchange membrane in an amount of 0.001 to 50 mg/cm2.

2. The electrolytic cell according to Claim 1 wherein the gas and liquid permeable porous non-electrode layer composed of non-oxide ceramic particles is bonded to the cathode side surface of the ion exchange membrane.

3. The electrolytic cell according to Claim 2 wherein the non-oxide ceramic is silicon carbide, boron car-bide, silicon nitride, boron nitride or molybdenum silicide.

4. The electrolytic cell according to Claim 1, 2 or 3 wherein the gas and liquid permeable porous non-electrode layer has a porosity of 10 to 99% and a thickness of 0.10 to 300µ.

5. The electrolytic cell according to Claim 1, 2 or 3 wherein the non-oxide ceramic particles are bonded to the surface of the membrane in an amount of 0.005 to 10 mg/cm.

6. The electrolytic cell according to Claim 1, 2 or 3 wherein the non-oxide ceramic particles are bonded to the surface of the membrane with a binder composed of a fluorinated polymer.

7. The electrolytic cell according to Claim 1, 2 or 3 wherein the ion exchange membrane is a fluorine-containing ion exchange membrane having sulfonic acid groups, carboxylic acid groups or phorphoric acid groups.

8. The electrolytic cell according to claim 1, 2 or 3 wherein at least one of the anode and cathode is disposed in contact with the ion exchange membrane.

9. The electrolytic cell according to claim 1, 2 or 3 wherein the cathode is disposed in contact with the ion exchange membrane.

10. The electrolytic cell according to claim 1, 2 or 3 wherein the anode and the cathode are an expanded metal with openings having a major length of 1.0 to 10 mm, a minor length of 0.5 to 10 mm and an opening area of 30 to 90%.

11. The electrolytic cell according to claim 1, 2 or 3 wherein the anode and the cathode are a punched metal with holes having an opening area of 30 to 90%.

12. The electrolytic cell according to claim 1, 2 or 3 wherein a plurality of foraminous electrodes having different opening areas are used, and electrodes having smaller opening areas are disposed closer to the membrane.

13. An ion exchange membrane which comprises a gas and liquid permeable porous non-electrode layer composed of non-oxide ceramic particles, which is bonded to at least one surface of said membrane in an amount of 0.001 to 50 mg/cm2.

14. The ion exchange membrane according to claim 13 wherein a gas and liquid permeable porous non-electrode layer composed of a metal or metal oxide is bonded to the opposed surface of the membrane.

15. The ion exchange membrane according to Claim 13 or 14 wherein the non-oxide ceramic is a carbide, a nitride, a boride or a sulfide.

16. The ion exchange membrane according to Claim 13 or 14 wherein the non-oxide ceramic is silicon carbide, boron carbide, silicon nitride, boron nitride or molybdenum silicide.

17. The ion exchange membrane according to Claim 14 wherein said metal is a single substance or alloy of a metal belonging to Group IV-A, IV-B or V-B of the Periodic Table, an iron group metal, chromium, manganese or boron.

18. The ion exchange membrane according to Claim 13 or 14 wherein the gas and liquid permeable layer has a porosity of 10 to 99% and a thickness of 0.01 to 200µ.

19. The ion exchange membrane according to Claim 13 or 14 wherein the non-oxide ceramic particles are bonded to the surface of the membrane in an amount of 0.01 to 50 mg/cm.

20. The ion exchange membrane according to Claim 13 wherein the non-oxide ceramic particles are bonded to the surface of the membrane with a binder composed of a fluorinated polymer.

21. The ion exchange membrane according to Claim 20 wherein the fluorinated polymer is a tetrafluoroethylene polymer.

22. The ion exchange membrane according to Claim 13 or 14 which contains ion exchange groups selected from sulfonic acid groups, carboxylic acid groups and phosphoric acid groups.

23. The ion exchange membrane according to Claim 13 or 14 which has an ion exchange capacity of 0.5 to 4.0 meq/g dry resin.

24. The ion exchange membrane according to claim 13, wherein the membrane is made of a perfluorocarbon polymer.

25. The ion exchange membrane according to claim 24, wherein said perfluorocarbon polymer has the following units (M) and (N):
(M) (N) wherein X represents fluorine, chlorine or hydrogen atom or -CF3; X' represents X or CF3(CH2)m; m represents an integer of 1 to 5; and Y is selected from wherein x, y and z respectively represent an integer of 1 to 10; Z and Rf represent -F or a C1-C10 perfluroalkyl group;
and A represents -COOM or -SO3M, or a functional group which is convertible into -COOM or -SO3M by hydrolysis or neutral-ization, and M represents hydrogen or an alkali metal atom.

26. The ion exchange membrane according to claim 24, in which A represents a group selected from -CN, -COF, -COOR1, -SO2F, and -CONR2R3 or -SO2NR2R3 where R1 represents a C1-C10 alkyl group; R2 and R3 represent H or a C1-C10 alkyl group.