CA1084874A - Cation-exchanging membrane - Google Patents
Cation-exchanging membraneInfo
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- CA1084874A CA1084874A CA248,845A CA248845A CA1084874A CA 1084874 A CA1084874 A CA 1084874A CA 248845 A CA248845 A CA 248845A CA 1084874 A CA1084874 A CA 1084874A
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- membrane
- cation
- polymer membrane
- water
- exchange
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/20—Manufacture of shaped structures of ion-exchange resins
- C08J5/22—Films, membranes or diaphragms
- C08J5/2287—After-treatment
- C08J5/2293—After-treatment of fluorine-containing membranes
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
- C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
- C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
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- Engineering & Computer Science (AREA)
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- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
Abstract of the Disclosure A cation-exchange polymer membrane made of a fluorinated resin containing in the molecules thereof electronegative groups of sulfonic-, carboxyl- or phenolic-group, which is improved by dis-persing into the polymer membrane, by means of a chemical reaction, a water-insoluble inorganic ion-exchanger such as hydroxide, hydrated oxide, phosphate, molybdate and tangstate of a metallic element. This cation-exchange polymer membrane is particularly use-ful for electrolysis of brine.
Description
1~84~14 This invention relates to a cation-exchange polymer membrane, and more particularly to an improved cation-exchange polymer membrane mainly for use in electrolysis of brine, which contains an inorganic ion exchanger dispersed homogeneously therein.
An ion-exchange membrane is used for the electro-dialysis aiming at water production or ~acl production from sea-water, for electrolysis of various salts, or for other applications. Presently, such industrial use of the ion-exchange membrane is being advanced. For example, when an ion-exchange membrane having cation selectivit~ is used in the i electrolysis of an aqueous solution of alkali halide, a halogen gas, hydrogen gas and caustic alkali can be ob`tained ~; by an electrolysis processO Since these electrolysis products are industrially important chemicals which are significantly employed in large amounts in various industrial field, there is an increasing demand for exploitation of an ion-exchange polymer membrane having excellent characteristics such as durability to use under low power consumption and other severe conditions.
In order to reduce the power consumption of an electrolysis, a decrease in the cell voltage and an elevation in the current efficiency are required. For the purpose of raising current efficiency during the electrolysis of an aqueous solution of alkali halide, it is essentially important to allow a cation-exchange polymer membrane to have high selectivity of cations. Conventionally, the increase of the density of anions fixed in the polymer membrane is known as a cations selectivity-increasing means. Even if, however, such anion to be fixed in the membrane are simply introduced into the membrane, the - 1- ~ie .
8~;'4 nydrophilic nature of the membrane is also usually greatly strengthened. Accordingly, the membrane comes to contain a large amount of water. As a result~ difficulties are presented in substantially raising the density of the ions fixed to the membrane. In order to suppress the water swelling tendency of the membrane, the following, for example, are proposed:
(1) A large amount of cross-links are introduced into a polymer which forms the membrane.
An ion-exchange membrane is used for the electro-dialysis aiming at water production or ~acl production from sea-water, for electrolysis of various salts, or for other applications. Presently, such industrial use of the ion-exchange membrane is being advanced. For example, when an ion-exchange membrane having cation selectivit~ is used in the i electrolysis of an aqueous solution of alkali halide, a halogen gas, hydrogen gas and caustic alkali can be ob`tained ~; by an electrolysis processO Since these electrolysis products are industrially important chemicals which are significantly employed in large amounts in various industrial field, there is an increasing demand for exploitation of an ion-exchange polymer membrane having excellent characteristics such as durability to use under low power consumption and other severe conditions.
In order to reduce the power consumption of an electrolysis, a decrease in the cell voltage and an elevation in the current efficiency are required. For the purpose of raising current efficiency during the electrolysis of an aqueous solution of alkali halide, it is essentially important to allow a cation-exchange polymer membrane to have high selectivity of cations. Conventionally, the increase of the density of anions fixed in the polymer membrane is known as a cations selectivity-increasing means. Even if, however, such anion to be fixed in the membrane are simply introduced into the membrane, the - 1- ~ie .
8~;'4 nydrophilic nature of the membrane is also usually greatly strengthened. Accordingly, the membrane comes to contain a large amount of water. As a result~ difficulties are presented in substantially raising the density of the ions fixed to the membrane. In order to suppress the water swelling tendency of the membrane, the following, for example, are proposed:
(1) A large amount of cross-links are introduced into a polymer which forms the membrane.
(2) The water swelling tendency is locally suppressed by ~aminating two membranes.
However, the above countermeasures are accompanied with a decrease in the mechanical strength of the membrane or an increase in the electric resistance thereof, with the result that the membrane performance is not raised.
Generally, the ion-selectivity of an ion-exchange polymer membrane depends upon the density of fixed ions, that is, the relative amount of fixed ions based on the water content in the membrane. Therefore, by introduction of a third substance into the membrane, this water content can be decreased, and if said third substance is an ion-exchanger, the electric resistance of the membrane would become small.
This invention is characterized by dispersing a water-insoluble inorganic ion-exchanger into a cation-exchange polymer membrane in order to increase the density of anions fixed to the membrane, whereby the cation selectivity of the membrane is raised. We have discovered that, through causing a water-swollen portion of the cation-exchange polymer membrane to be filled with the inorganic ion exchanger, and further causing ion-exchange groups of the polymer membrane to be combined with the inorganic ion exchanger, the cation-selectivity of the membrane increases ~84~4 ~reatly. We have succeeded in reducing the water content in the membrane by dispersing homogeneously an inorganic ion-exchanger into the interior of a cation-exchange polymer membrane, and partially replacing a water-existent portion of the membrane with said ion-exchangerO Thus, we have obtained an improved polymer membrane bringing an increased current efficiency in electrolysis.
The inorganic ion-exchanger used in this invention is a water-insoluble hydroxide, hydrated oxide, or polybasic salt of a metallic element.
When the improved membrane of this invention is ; empl~yed in the electrolysis of an alkali halide, a highly con-` centrated alkali hydroxide solution can be obtained with a high current efficiencyO The membrane according to this invention is ~-not only employed in the electrolysis, but, since it exhibits an excellent cation-selectivity even in a dilute solution, it can also be applied to a use involving, for example, a water-- ~
refreshing process, a solution-concentrating process or a waste ~ -liquor treating process.
The base cation-exchange polymer membrane used in this invention should be a homogeneous membrane. A heterggeneous membrane such as a mixed membrane of an ion-exchange resin and a nonionic resin is not preferable since it unavoidably has low current efficiency and low ion selectivity, because the pores of relatively large diameter existing in the heterogeneous membrane can not be filled easily with the inorganic ion-exchanger.
The base cation-exchange polymer membrane used in this invention may be any membrane whose resin material has with high density electronegative groups such as a sulfonic group, 10~4874 arboxylic group, or phenolic group, which are bonded to the skeletal structure of a corrosion-resistant and sometimes highly cross-linked polymer. These xesin materials include cross-linked acrylic resin, cross-linked methacrylic resin (using, for example, vinyl benzene and trivinyl benzene as a cross-linking agent), sulfonated copolymer of styrene and divinyl benzene, fluorinated resin having sulfonic groups, hydroxystyrene polymer and a graft polymer of hydroxystyrene.
Especially suitable as a membrane having chlorine resistance and acid resistance is that made of a fluorinated resin. Used as this fluorinated resin is that prepared by introducing sulfonic groups, carboxylic groups or phenolic groups into a polymer or a copolymer consisting mainly of tetrafluoroe-thylene, hexafluoropropylene, trifluorochloroethylene, trifluoroe-thylene, fluorovinylidene, a,~,~- trifluorostyrene or perfluoro-vinylether. Particularly preferable as said base polymer membrane is a tetrafluorosulfonic acid membrane sold under the trade mark of "NAFION~ (E.I. Du Pont de Nemours & Co. Inc.). This membrane is made of a fluorinated resin having the following cyclic unit structure having pendant-type sulfonic groups:
~ IRl --_ (I)p and [ CXXl CFR3 (R)n SO3H (Na or K) where, R represents a unit structure of ~ O - CR4R5 - C~R7 tm ;
R1~ R2, R, R4J R5, R~ and R7 each represents a fluoroalky group having 1 to 10 carbon atoms; Y represents a perfluoroalkylene group having 1 to 10 carbon atoms; m = O, 1, 2 or 3;
n = O or l; p = 0 or 1; X represents fluorine, chlorine, hydrogen or trifluoromethyl radical; and X represents CF3(CF2) , ... .
1084~4 ~here q = 0 or an integer of 1 to 5.
Suitably used as said fluorinated resin is also that prepared by introducing, without using the above-mentioned polymer or copolymer~ sulfonic groups into a benzene ring, or by subjecting a styrene monomer or an acrylic acid monomer to graft polymerization, and then introducing ion-exchange groups into the resulting graft polymer through sulfonization or hydrolysis.
The cations forming the inorganic ion-exchanger used in this invention include zirconium, titanium, tin (IV), cerium, 10 thorium, lanthanum, manganese (II), silicon, niobium, tantalum, an~mony~(V), molybdenum (VI), antimony (III), bismuth, indium, manganese (III), iron (III), gallium, aluminium, cadmium, zinc, magnesium beryllium and hafnium. It is known that these cations provide water-insoluble hydroxides, hydrated oxides or polybasic salts. Among them, tetraor more multivalent metallic ions are preferable since they are capable of providing hydrated o~ides which have high ion-exchanging capacity. Further, those of said cations whose hydroxides, hydrated oxides or polybasic salts have cation-eXchangeability are also preferable since they have low electric resistance. Fùrthermore, the cations having high alkaline resiqtance are preferable. From these points of view, particularly preferable are zirconium, titanium, cerium, thorium, niobium, tantalum, antimony and hafnium. Further, the mixtures of these elements can also be used as the ion-exchanger according to this invention. As acid radicals capable of forming the water-insoluble polybasic salts, there are phosphoric acid groups, molybdic acid groups and tungstic acid grQ~ps~
As mentioned above, the cation-exchange polymer membrane containing as the inorganic ion-exchanger hydroxides, hydrated 1~4~74 ~xides or polybasic salts of the metallic element has an improved cation-selectivity. As a result of dispersing said hydroxides, hydrated oxides or polybasic salts into the membrane, the water content in the membrane decreases, the ion-exchange capacity of the membrane increases, and the density of ions fixed to the membrane rises. ~or the purpose of bringing about these effects, at least 0.1% by weight of the inorganic metallic ion-exchanger based on the weight of cation-exchange polymer membrane is usually required to be present therein. If the amount of inorganic metallic ion-exchanger is less than 0.1%
by weight, the effect of dispersing this inorganic ion-exchanger into the polymer membrane will not be realized sufficiently.
Conversely, the dispersion of the inorganic ion-exchanger in excess would cause the resultant membrane to have an increased slectric resistance. In this meaning, 30 or less % by weight of inorganic ion-exchanger is usually employed in order to permit the resultant membrane to perform as a cation-exchanging membrane. In the case of said polybasic salts, for example, their structures may be of the type wherein polybasic salts are connected to the periphery of the skeletal structure of the polymer.
The cation-exchange polymer membranes according to this invention containing therein hydroxides, hydrated oxides or polybasic salts of the aforementioned metals gives preferable results from both aspects of water-swelling characteristics and action as an ion-exchanger. That is, a water-swollen portion within the membrane is partially substituted by the water-insoluble inorganic ion-exchanger which is incapable of being swollen by water. For example, as stated in the later described Examples, when the membrane contains therein only 0.32%
1~4t~`74 ,y weight oE titaniu~ hydroxide, about 16% rise in the fixed ion density (meg/g ~l2) of the membrane rsults. If, in the electrolysis oE brine, a polybasic metal salt such as zirconium phosphate is dispersed into the membrane, such rise in the fixed ion density will provide as extremely high current' efficiency of 95% or more under the condition in which the concentration of caustic soda in the cathode chamber is 20%.
Since the improved cation-exchange polymer membrane is of high durability, the metallic ions contained in the hydroxides, hydrated oxides or polybasic acid salts which are dispersed in the membrane will not be dissociated easily therefrom even under severe conditions, For example, the zirconium component of a zirconium phosphate dispersed into a cation-exchange polymer membrane (NAFI0~ 110), when measured by fluorescence -X rays method, did not decrease prominently even when allowed to stand for 600 or more hou~s in a saturated aqueous solution of chlorine at 80C, an aqueous solution of hypochlorous acid (effective chlorine concentration of about 5% at 110C, or an aqueous solution of 40/O caustic soda at 8~ C).
The above-mentioned water-insoluble inorganic ion-exchanger can be dispersed into the polymer membrane in a manner that it is mixed with a raw resin material, or alternatively, said ion-exchanger is dispersed into the surface layer or a substantially whole layer of the cation-exchange polymer membrane after manufacturing the membrane. In the former method, however, the dispersion of this inorganic compound in the resin material is generally apt to be non-uniform. Therefore, only the latter method is adopted in this invention. Since, in this case, it is impossible to disperse the inorganic compound directly into the interior of the membrane in a solid state, this dispersion is 1084t~';'4 omogeneously effected by using a solution of solvent-soluble' inorganic ion exchanger, or a liquefied metal compound, causing the solution to be absorbed into the membrane surface layer or interior thereof in the form of a metallic ion or metal compound, and thereafter dispersing a solution of hydroxyl ions or acid groups into the membrane to cause them to react with each other.
Conversely, it is possible to disperse first a solution of hydroxyl ions or acid groups into the membrane, and then disperse the solution of metallic ions or metal compounds into said mem-brane to cause the former to react with the latter. For example, -a cation-exchange polymer membrane is immersed in an aqueous solution of a zirconium salt such as ZrO(N03) to cause zirconium ions to be absorbed into the surface layer of the membrane, and is again immersed in an aqueous caustic soda solution or water-soluble polybasic acid to produce a gel of hydroxide or polybasic acid salt of~zirconium in the surface layer of the membrane.
When, conversely, first absorbing caustic soda or polybasic acid in the surface layer of the membrane and then immersing the resultant membrane in the aqueous solution of zirconium salt, the gel is similarly obtained. In these case~, other solvents than water can be used. Further, if a liquid compound such as tetra-butyl titanium is used, the solvent will not always be required.
Further, it is also possible to once produce a pre-cursory form of water Insoluble salt in the membrane and then change it into an objective inorganic ion-exchanger. For example, it is possible to first form a hydroxide or hydrated oxide of metal in the membrane and then change it into a phosphate.
Furthermore, the amount of inorganic ion-exchanger in the membrane can be controlled by properly selecting the concentration of the solution used and the time period of immersion. For example, 10848~4 _nrough dispersing a water-insoluble hydroxide, hydrated oxide or polybasic salt of metallic element into one side of the surface layer of the membrane, a rise in the electric resistance of the membrane itself can be suppressed.
The above-mentioned method of dispersing the inorganic ion-exchanger into one side of the surface of the membrane consists usu~lly in coating a solution containing the metallic ions on ~*id one side of the surface of the membrane, or allowing filter paper, woven fabric or nonwoven fabric containing the metall~c ion solution to contact with said one side of the surface of the membrane, thereby dispersing the metallic ion into only said one side of the surface layer of the membrane, and thereafter allowing the metallic ions to contact hydroxyl or acid groups.
As another example of being dispersed into the membrane in the form of a compound, there is a liquid metal compound such as titanium tetrachloride or antimony pentochloride, or an aqueous solution of these compounds.
A gel of the substantially water-insoluble hydroxide, hydrated oxide, or polybasic salt of the metallic ions dis-persed into the polymer membrane in accordance with the above-mentioned method should be desiccated. Usually, the higher the ' temperature of desiccating, the higher resistance to eorrosion and mechanical shocks. However, many of said metal compounds tend to decrease their ion exchange capacities when desiccated at an extremely high temperature. Usually, the desiccating temperature suitably ranges from 30C to 200C. Further, depending upon the drying temperature of desiccating, the electric resistance and current efficiency of the electrolysis using the resultant membrane are liable to be varied. For example, the cell voltage was 3065 volts in a brine electrolysis _ g _ 10~ 4 ~sing a cation-exchange polymer membrane containing zirconium phosphate which was not desiccated after dispersing said phosphate thereinto, whereas when, in said case, the membrane was fully desiccated at 110C, the cell voltage was increased up to 4.0 volts under the same electrolyzing condition. Usually, the desiccated membrane provides an increased cell voltage as compared with the membrane subjected to no desiccation treat-ment, and provides a greatly increased ion selectivity, that is, current efficiency. In the above example, the membrane free from the desiccation treatment provided a current efficiency of 86% whereas the desiccated membrane provided an increased current efficiency of 96%. Therefore, it is preferred that, after dispersing the inorganic ion exchanger, the desiccating temperature of the membrane should be properly adjusted in accordance with the purpose of using the cation-exchange polymer membrane.
The improved cation-exchange polymer membrane according to this invention is not only limited to the above-mentioned single layer membrane, but a bonded two layer-membrane having different ion exchanging capacity from each other is also effective.
The improved cation-exchange polymer membrane according to this invention-is used by being installed in various electrolytic cellsO HoweverJ in the electrolysis of an alkali halide, contraction, or expansion by swelling of the membrane sometimes occurs and has an effect upon the cell voltage or causes damage to the membrane, For this reason, the membrane is preferred to be installed in the electrolytic cell in a state as swollen as possible. Usually, to this end, the cation-exchange polymer membrane is to be sufficiently water-swollen, or once -- 10 -- , lu848~4 mmersed in hot water or boiling water, prior to the installation thereof.
This invention will be more fully understood from the following Examples, although not limited thereto.
Example 1 :
A polymer membrane of NAFION No. 110 having a thickness of 10 mils was dried at 110C for 1 hour, and immersed in a 10%
aqueous solution of zirconyl chloride at room temperature for 2 hours, and thereafter immersed in a 85% aqueous solution of phosphoric acid at room temperature for 30 minutes to disperse the salt of zirconium phosphate into the membrane.
After being washed with sufficient amount of water, the polymer membrane was dried at 110C for 1 hour. The amount of zirconium phosphate introduced was 1.2% by weight based on the whole amount of the original polymer membrane as dried.
The water content, the cation-exchange capacity and the density of ions fixed to the membrane are presented in Table l. !
The water content represented is the percentage by weight of water weight after the polymer membrane is immersed in water of 15C for 1 hour. For comparison, the corresponding measured values of a membrane of NAFION ~o. 110 free from the dispersion of zirconium phosphate, are shown together in Table l.
Table l Characteristics of Cation-Exchange Pol ~mer Membranes \ Introduced amount Water Ion exchange Density of -~
\ of zirconium conteOnt capacity ions fixed \ phosphate(wt.%) at 15 C ~meg/g dry to membrane - _ ~ (wt.%) resin) ~meg/g H2O) . ___ Example 1.2 10.5 1.02 9.7 .
'~Control 0 12.6 0.98 7.8 10~4~4 As seen from Table 1, the zirconium phosphate-dispersed membrane had an increased density of ions fixed to the membrane. This membrane was immersed in water at room temperature for 2 hours after being dried at 110C. Then,:the electrolysis of brine was made using this membrane under the electrolyzing conditions indicated in Table 2, the results being shown in Table 3.
Table 2 Electrolyzing Condition ~node Titanium-ruthenium oxide Cathode Stainless wire net (8 Tyler mesh) ~node-to- 5 mm cathode .
d~stance Brine concentration of 26 Cell 80C
tem~erature Current 20 A/dm density Table 3 Results of Electrolysis Concentration of NaOH Cell voltage Current ~:
\ in the cathode chamber efficiency \ (O (V) ( Example 1 21.2 3~75 =
Control 18.0 3-65 70 As is apparent from Tables 1 and 3, the membrane containing zirconium phosphate as the polybasic salt of metallic :~
ions has not only an increased density of ions fixed to the membxane, but also an excellent cation exchangeability permitting a high current efficiencyO
. . . ;
- :. .. . .
10~4~ 4 _xample 2 ~ membrane of NAFIO~ No. 110 having a thickness of 10 mils was cut out into a size of about 9 cm x 9 cm, and was dried at 110C for 18 hours. The resultant membrane was immersed for 1 hour in an aqueous solution prepared by dissolving 50 grams of zirconyl nitrate in 100 cc of lN hydrochloric acid of 80C.
Thereafter, the membrane was drawn out of the solution, and its surface was rapidly wiped off by filter papers, and then the membrane was immersed in a 30~ NaOH solution of 80C to be held therein for 1 hour. The resultant membrane was sufficiently washed with water, and dried at 110C for 18 hours.
When measurement of the cation-exchange capacity of the above-treated membrane was carried out, it was found to be ;
1.00 meg per gram of the membrane as dried. The membrane of NAFION No. 110 free from the above-mentioned treatment had a cation-exchange capacity of 0.97 meg per gram thereof. Therefore, there was about a 3% increase in the cation-exchange capacity ~`
with respect to the above-treated membrane. When brine electrolysis were performed with the use-of the above-treated membrane and the non-treated membrane, respectively, results indicated in Table 4 were obtained. Note that the brine electrolysis was carried out under the conditions wherein graphite and iron were used as the anode and cathode material, respectively; the anode-to-cathode distance was 10 mm; the concentration of brine was 26%; the cell temperature was 50C:
and the current density was 20 A/dm .
~)84874 Table 4 Resu}ts of Electrolysis Temperature Concentration of ¦ Cell Current \ NaOH in the volt- efficiency ~ \ cathode chamber age : \(C) (N) (V) (~) \
Example 2 50 4.2 3.8 81 Control50 4.1 3. a 75 Exam~les 3 to 5 After drying three membranes of NAFION No. 110 having a thickness of 10 mils at 110C for 1 hour, the hydroxides and the polybasic salt of metallic ions shown in Table 5 were dispersed into the membranes, respectively.
As seen from Table 5, the above-treated membranes of this invention had an increased density of ions fixed to the membrane, respectively, as compared with a non-treated membrane of NAFION No. 110 shown as a control in said Table~
Table 5 \ - , l \ Metallic OH-group ntro- Water Within-a-\ ion or acid ducing content membrane \ radical amount (%) fixed ion \ (wt.%) density \ _ _ (meg/g H O) _ ~ .
Example Titanium OH 0.32 11, 4 9ol Example 4Cerium OH 2.3 9,6 11.7 Example 5Cerium Molybdic 1.8 10.7 9.8 (IV) radidCal Control 0 12 o6 7 ~ 8 ~ 14 ~
~xample 6 A membrane of ~AFI0~ No. 110 having a thickness of 10 mils was immersed in an aqueous solution prepared by dis-solving 50 grams of zirconyl nitrate in 100 ml of lN hydro-chloric acid at 80 to 90C for 10 minutes. After the surface of the resultant membrane was sufficiently wiped off, this membrane was immersed in a 20% aqueous solution of caustic soda at 100C for 20 minutes. However, the formation of a gel in said aqueous solution of caustic soda was little recognized.
When, after being sufficiently washed with water, this membrane was immediately immersed in a 80~ aqueous solution of phosphoric acid at 120C for 10 minutes, the membrane became whitish, whereas the formation of a gel of zirconium phosphate in said aqueous solution of phosphoric acid was not recognized at all.
Of course the phosphoric acid was able to be reused. The resultant membrane, after washed with water, was dried at 110C
for 1 hour, and thereafter allowed to stand at room temperature for one day, and then zirconium phosphate was dispersed into said membrane. The concentrations of zirconium and phosphorus measured by the fluorescence -X rays method are presented in Table 6 below.
Table 6 characteristics of membrane treated Zr-Welqnt X lUU P-Welqht X lUU Zr-Po4welght X 100 I Zr Total weight Total weight Total weight P04 of membrane _ of membrane of membrane (mol 2030 o.l6 2.79 4.69 Brine-electrolysis was carried out with the use of the membrane containing zirconium phosphate under the conditions wherein the anode and cathode were made of titanium-rutheniu~
oxide and iron, respectively; the anode-to-cathode distance was 10 mm; the concentration of brine was 26~; the cell temperature was 50 to 55C; the effective area of membrane was 25 cm ; the current density was 20 A/dm ; and the concentration of NaOH in the cathode chamber was 6N. At this case, the cell voltage and the current density were 4.0 volts and 75% respec-tively. When, for comparison, brine-electrolysis was carried out under the same electrolyzing conditions with the use of a membrane of NAFION No. 110 containing no inorganic ion ex-changer, the cell voltage was 3.8, but the current density wasdecreased to 67%.
ExamPle 7 A NAFION No. llO-membrane of sulfonic acid type having a thickness of 10 mils was dried at 100C for 1 hour, and then immersed in a 30~ aqueous solution of Zro (NO3 ) ~o 2H20 at room temperaturefor 15 hours. The resultant membrane was immersed in a 85% aqueous solution of phosphoric acid and washed with water, and thereafter was dried at 100C for 1 hour to obtain a cation-exchange polymer membrane containing zirconium phosphate. The amount of zirconium phosphate introduced into this membrane was 5.0~ by weight based on the weight of original membrane. When a NAFION No. llO-membrane of sodium sulfonate type was similarly treated, the amount of zirconium phosphate introduced into the resultant membrane was 7.4% by weight based on the weight of original membrane. When the above sulfonic acid type and sodium sulfonate type membranes were again subjected to the same treatment as mentioned above, the amounts of zirconium phosphate introduced into both said membranes were 11.2% and 13.8~ by weight based on the weight of original membranes respectively.
4~74 Further, when the above twice treated sulfonic acid type membrane was again subjected to the same treatment as the above-mentioned initial treatment, the amount of zirconium phosphate contained in the resultant membrane was to 17.3% by weight based on the weight of original membrane. With respect to the above-mentioned sodium sulfonate type membrane, after completion of the second treatment, it was subjected to boiling water treatment at 100C for 1 hour, and thereafter immersed in a 30~ aqueous solution of ZrO(NO3)2 2H@O for 15 hours, and further immersed in a 85% aqueous solution of phosphoric acid for 1 hour. After being sufficiently washed with waterJ the resultant membrane was dried at 100C for 1 hour. As a result, the amount of zirconium phosphate contained in the resulting membrane was 23.5% by wei~ht based on the weight of original membrane. From the above, it will be appreciated that the amount of zirconium phosphate introduced can be adjusted de-pending upon the frequency of dispersion.
ExamPles 8 and 9 A cation-exchanger polymer membrane of NAFION No. 390, which is a sodium 8ul. fonate type cation-0xchange polymer membrane prepared by subjecting EW-1100* and EW-1500* membranes to be plied up through a mesh formed of ethylene tetrafluoride resin and rayon interposed therebetween, was immersed in a 50~ aqueous solution of zirconyl chloride at room temperature for about ~
hours. After the surface of the membrane was sufficiently wiped off by filter papers, it was immersed in a 85% aqueous solution of phosphoric acid, thereby dispersing zirconium phosphate into the membrane~ The resultant membrane, 30 minutes later, was taken out from said solution and sufficiently washed with water, and thereafter dried at 110C (Example 9) and at 75C(Example 10) * trade mark - 1~7 -'74 for 1 hour respectively. In both Examples, the amount of each zirconium phosphate introduced into the resulting both membranes was a~out 3.2% by weight based on the weight of original membranes.
In both Examples, the membrane thus dried was kept in water at room temperature for two days, and was installed in an electrolytic cell so as to permit the EW-1100 membrane side thereof to;face the anode side. Electrolysis of brine was carried out separately under the same conditions as indicated 3 in Table 2 of Example 1, the results being presented in Table 7.
For comparison, with the use of a ~AFION ~o. 390-membrane con-taining no zirconium phosphate, simply dried at 110C for 1 hour and allowed to stand in water, brine electrolysis was carried out under the same electrolysis conditions, the result being presented together in Table 7.
Table 7 Results of Electrolysis Drying Concentration Cell Current \temperature NaOH in the volt- efficiency \(C) cathode chamber a(v)e (%) Example 9110 24.0 4.0 95-3 Example 10 75 22.3 3.9 93.2 ~ontrol110 21.7 3.6~ 87.8 As is obvious from Table 7, the membrane of NAFION
No. 390, that is, a bonded membrane of two ion-exchange mem-branes having different ion-exchange capacities, naturally provides a relatively high current efficiency. When the membrane is allowed to contain zirconium phosphate therein, it causes only a little increase in the cell voltage, and at the 1~)84874 same time, it permits the maintenance of such an extremely high current efficiency which is not attainable with the membrane not containing zirconium phosphate.
The detailed reason why the membrane of NAFION NoO 390 prepared by bonding two ion-exchange polymer membranes having different ion-exchange capacities provides a relatively good current efficiency has not yet been clarified. We, however, suppose that this reason may be as follows. The EW-1500 membrane has a small swelling tendency against water for its large ion-exchange capacity, and as a result has a high density of ions fixed to the membrane in an electrolyte solution. This plays the role of a barrier for inhibiting the diffusion of hydroxyl groups from the cathode. Further, in the neighbourhood of the boundary between the EW-1500 and EW-1100 membranes, the ion-exchange capacity of the EW-1100 membrane has its own-exchange capacity and yet the swelling tendency thereof against water is suppressed by the bondage of EW-1500 membrane, with the result that the density of ions fixed to the bonded membrane in said neighbourhood is increased.
When an inorganic ion exchanger is dispersed into such a bonded membrane, the exchanger is liable to be adhered to those portions of the membrane where it has a higher density of ions fixed to the membrane, and said density at said portions of the membrane is further increased, causing the characterizing features of the membrane to be further promoted to present an extremely high selectivity to cations.
ExamPle 10 A sheet of filter paper previously immersed in a 10%
aqueous solution of zirconyl chloride was stuck to the EW-1500 .. . , .
~,. , . , . ~ .
i()848'~4 side of a membrane of NAFION No. 390 (sodium sulfonate type), and the resultant membrane was allowed to stand at room tempera-ture for 15 minutes. Thereafter, said sheet of filter paper was exfoliated from the membrane, and another sheet of filter paper permeated thereinto sufficiently with a 85% aqueous solution of phosphoric acid was stuck to the exfoliated side of said membrane, thereby introducing zirconium phosphate only into the EW-1500 side of the NAFION No. 390-membraneO
After being sufficiently washed with water, said zirconium phosphate-introduced membrane was dried at 110C for 1 hour, and then allowed to stand in water at 15C for 1 hour.
The amount of zirconium phosphate dispersed was about 0.23% by weight based on the weight of original membrane.
The above-treated membrane was installed in an electrolytic cell so as to permit the EW-1500 side to face the cathode, and electrolysis of brine was carried out under the same electrolyzing conditions as shown in Table 2 of Example 1.
The results were that the cell voltage was 3.7 volts; the concentration of NaOH in the cathode chamber was 22.6%; and the current efficiency was 94~9%O Thus~ the membrane had a very good selective permeability of cations.
Example 11 A membrane of NAFIO~ ~o. 315, which is of sulfonic acid type, and is a bonded membrane of EW-1100 and EW-1500 membranes together with a mesh consisting of ethylene tetra-fluoride resin interposed therebetween, was immersed in a 85%
aqueous solution of phosphoric acid at 120C for 2 hours, and then, after the surface of the resultant membrane was sufficiently wiped off, this membrane was immersed in a 10~
aqueous solution of zirconyl chloride at 100C for 10 minutes.
- ; .. .. ,,~, .
.
1084~4 After being sufficiently washed with water, the resultant membrane was dried at 110C for 2 hours. The amount of zirconium phosphate introduced was about 3% by weight based on the weight of original membrane.
Using the above-treated membrane, electrolysis of brine was carried out, at which time the membrane was installed in the electrolytic cell so as to permit the EW-1500 side to face the cathode. The electrolyzing conditions were as indicated in Table 2 of Example 1, excepting that the cell temperature was 70C~ The results of this electrolysis are shown in Table 8, together with the results of brine electrolysis carried out, for comparison, under the same electrolyzing conditions using a NAFION No. 315-membrane not containing zirconium phosphate. ~-Table 8 Results of Electrolysis Concentration of Cell Current \ ~aOH in the voltage efficiency \ cathcde cha~oer ~ ~V~ L
,_ , Example 12 20.0 4.5 9.8 .
~ontrol 20.1 4.2 __ ::
., ,~ ,
However, the above countermeasures are accompanied with a decrease in the mechanical strength of the membrane or an increase in the electric resistance thereof, with the result that the membrane performance is not raised.
Generally, the ion-selectivity of an ion-exchange polymer membrane depends upon the density of fixed ions, that is, the relative amount of fixed ions based on the water content in the membrane. Therefore, by introduction of a third substance into the membrane, this water content can be decreased, and if said third substance is an ion-exchanger, the electric resistance of the membrane would become small.
This invention is characterized by dispersing a water-insoluble inorganic ion-exchanger into a cation-exchange polymer membrane in order to increase the density of anions fixed to the membrane, whereby the cation selectivity of the membrane is raised. We have discovered that, through causing a water-swollen portion of the cation-exchange polymer membrane to be filled with the inorganic ion exchanger, and further causing ion-exchange groups of the polymer membrane to be combined with the inorganic ion exchanger, the cation-selectivity of the membrane increases ~84~4 ~reatly. We have succeeded in reducing the water content in the membrane by dispersing homogeneously an inorganic ion-exchanger into the interior of a cation-exchange polymer membrane, and partially replacing a water-existent portion of the membrane with said ion-exchangerO Thus, we have obtained an improved polymer membrane bringing an increased current efficiency in electrolysis.
The inorganic ion-exchanger used in this invention is a water-insoluble hydroxide, hydrated oxide, or polybasic salt of a metallic element.
When the improved membrane of this invention is ; empl~yed in the electrolysis of an alkali halide, a highly con-` centrated alkali hydroxide solution can be obtained with a high current efficiencyO The membrane according to this invention is ~-not only employed in the electrolysis, but, since it exhibits an excellent cation-selectivity even in a dilute solution, it can also be applied to a use involving, for example, a water-- ~
refreshing process, a solution-concentrating process or a waste ~ -liquor treating process.
The base cation-exchange polymer membrane used in this invention should be a homogeneous membrane. A heterggeneous membrane such as a mixed membrane of an ion-exchange resin and a nonionic resin is not preferable since it unavoidably has low current efficiency and low ion selectivity, because the pores of relatively large diameter existing in the heterogeneous membrane can not be filled easily with the inorganic ion-exchanger.
The base cation-exchange polymer membrane used in this invention may be any membrane whose resin material has with high density electronegative groups such as a sulfonic group, 10~4874 arboxylic group, or phenolic group, which are bonded to the skeletal structure of a corrosion-resistant and sometimes highly cross-linked polymer. These xesin materials include cross-linked acrylic resin, cross-linked methacrylic resin (using, for example, vinyl benzene and trivinyl benzene as a cross-linking agent), sulfonated copolymer of styrene and divinyl benzene, fluorinated resin having sulfonic groups, hydroxystyrene polymer and a graft polymer of hydroxystyrene.
Especially suitable as a membrane having chlorine resistance and acid resistance is that made of a fluorinated resin. Used as this fluorinated resin is that prepared by introducing sulfonic groups, carboxylic groups or phenolic groups into a polymer or a copolymer consisting mainly of tetrafluoroe-thylene, hexafluoropropylene, trifluorochloroethylene, trifluoroe-thylene, fluorovinylidene, a,~,~- trifluorostyrene or perfluoro-vinylether. Particularly preferable as said base polymer membrane is a tetrafluorosulfonic acid membrane sold under the trade mark of "NAFION~ (E.I. Du Pont de Nemours & Co. Inc.). This membrane is made of a fluorinated resin having the following cyclic unit structure having pendant-type sulfonic groups:
~ IRl --_ (I)p and [ CXXl CFR3 (R)n SO3H (Na or K) where, R represents a unit structure of ~ O - CR4R5 - C~R7 tm ;
R1~ R2, R, R4J R5, R~ and R7 each represents a fluoroalky group having 1 to 10 carbon atoms; Y represents a perfluoroalkylene group having 1 to 10 carbon atoms; m = O, 1, 2 or 3;
n = O or l; p = 0 or 1; X represents fluorine, chlorine, hydrogen or trifluoromethyl radical; and X represents CF3(CF2) , ... .
1084~4 ~here q = 0 or an integer of 1 to 5.
Suitably used as said fluorinated resin is also that prepared by introducing, without using the above-mentioned polymer or copolymer~ sulfonic groups into a benzene ring, or by subjecting a styrene monomer or an acrylic acid monomer to graft polymerization, and then introducing ion-exchange groups into the resulting graft polymer through sulfonization or hydrolysis.
The cations forming the inorganic ion-exchanger used in this invention include zirconium, titanium, tin (IV), cerium, 10 thorium, lanthanum, manganese (II), silicon, niobium, tantalum, an~mony~(V), molybdenum (VI), antimony (III), bismuth, indium, manganese (III), iron (III), gallium, aluminium, cadmium, zinc, magnesium beryllium and hafnium. It is known that these cations provide water-insoluble hydroxides, hydrated oxides or polybasic salts. Among them, tetraor more multivalent metallic ions are preferable since they are capable of providing hydrated o~ides which have high ion-exchanging capacity. Further, those of said cations whose hydroxides, hydrated oxides or polybasic salts have cation-eXchangeability are also preferable since they have low electric resistance. Fùrthermore, the cations having high alkaline resiqtance are preferable. From these points of view, particularly preferable are zirconium, titanium, cerium, thorium, niobium, tantalum, antimony and hafnium. Further, the mixtures of these elements can also be used as the ion-exchanger according to this invention. As acid radicals capable of forming the water-insoluble polybasic salts, there are phosphoric acid groups, molybdic acid groups and tungstic acid grQ~ps~
As mentioned above, the cation-exchange polymer membrane containing as the inorganic ion-exchanger hydroxides, hydrated 1~4~74 ~xides or polybasic salts of the metallic element has an improved cation-selectivity. As a result of dispersing said hydroxides, hydrated oxides or polybasic salts into the membrane, the water content in the membrane decreases, the ion-exchange capacity of the membrane increases, and the density of ions fixed to the membrane rises. ~or the purpose of bringing about these effects, at least 0.1% by weight of the inorganic metallic ion-exchanger based on the weight of cation-exchange polymer membrane is usually required to be present therein. If the amount of inorganic metallic ion-exchanger is less than 0.1%
by weight, the effect of dispersing this inorganic ion-exchanger into the polymer membrane will not be realized sufficiently.
Conversely, the dispersion of the inorganic ion-exchanger in excess would cause the resultant membrane to have an increased slectric resistance. In this meaning, 30 or less % by weight of inorganic ion-exchanger is usually employed in order to permit the resultant membrane to perform as a cation-exchanging membrane. In the case of said polybasic salts, for example, their structures may be of the type wherein polybasic salts are connected to the periphery of the skeletal structure of the polymer.
The cation-exchange polymer membranes according to this invention containing therein hydroxides, hydrated oxides or polybasic salts of the aforementioned metals gives preferable results from both aspects of water-swelling characteristics and action as an ion-exchanger. That is, a water-swollen portion within the membrane is partially substituted by the water-insoluble inorganic ion-exchanger which is incapable of being swollen by water. For example, as stated in the later described Examples, when the membrane contains therein only 0.32%
1~4t~`74 ,y weight oE titaniu~ hydroxide, about 16% rise in the fixed ion density (meg/g ~l2) of the membrane rsults. If, in the electrolysis oE brine, a polybasic metal salt such as zirconium phosphate is dispersed into the membrane, such rise in the fixed ion density will provide as extremely high current' efficiency of 95% or more under the condition in which the concentration of caustic soda in the cathode chamber is 20%.
Since the improved cation-exchange polymer membrane is of high durability, the metallic ions contained in the hydroxides, hydrated oxides or polybasic acid salts which are dispersed in the membrane will not be dissociated easily therefrom even under severe conditions, For example, the zirconium component of a zirconium phosphate dispersed into a cation-exchange polymer membrane (NAFI0~ 110), when measured by fluorescence -X rays method, did not decrease prominently even when allowed to stand for 600 or more hou~s in a saturated aqueous solution of chlorine at 80C, an aqueous solution of hypochlorous acid (effective chlorine concentration of about 5% at 110C, or an aqueous solution of 40/O caustic soda at 8~ C).
The above-mentioned water-insoluble inorganic ion-exchanger can be dispersed into the polymer membrane in a manner that it is mixed with a raw resin material, or alternatively, said ion-exchanger is dispersed into the surface layer or a substantially whole layer of the cation-exchange polymer membrane after manufacturing the membrane. In the former method, however, the dispersion of this inorganic compound in the resin material is generally apt to be non-uniform. Therefore, only the latter method is adopted in this invention. Since, in this case, it is impossible to disperse the inorganic compound directly into the interior of the membrane in a solid state, this dispersion is 1084t~';'4 omogeneously effected by using a solution of solvent-soluble' inorganic ion exchanger, or a liquefied metal compound, causing the solution to be absorbed into the membrane surface layer or interior thereof in the form of a metallic ion or metal compound, and thereafter dispersing a solution of hydroxyl ions or acid groups into the membrane to cause them to react with each other.
Conversely, it is possible to disperse first a solution of hydroxyl ions or acid groups into the membrane, and then disperse the solution of metallic ions or metal compounds into said mem-brane to cause the former to react with the latter. For example, -a cation-exchange polymer membrane is immersed in an aqueous solution of a zirconium salt such as ZrO(N03) to cause zirconium ions to be absorbed into the surface layer of the membrane, and is again immersed in an aqueous caustic soda solution or water-soluble polybasic acid to produce a gel of hydroxide or polybasic acid salt of~zirconium in the surface layer of the membrane.
When, conversely, first absorbing caustic soda or polybasic acid in the surface layer of the membrane and then immersing the resultant membrane in the aqueous solution of zirconium salt, the gel is similarly obtained. In these case~, other solvents than water can be used. Further, if a liquid compound such as tetra-butyl titanium is used, the solvent will not always be required.
Further, it is also possible to once produce a pre-cursory form of water Insoluble salt in the membrane and then change it into an objective inorganic ion-exchanger. For example, it is possible to first form a hydroxide or hydrated oxide of metal in the membrane and then change it into a phosphate.
Furthermore, the amount of inorganic ion-exchanger in the membrane can be controlled by properly selecting the concentration of the solution used and the time period of immersion. For example, 10848~4 _nrough dispersing a water-insoluble hydroxide, hydrated oxide or polybasic salt of metallic element into one side of the surface layer of the membrane, a rise in the electric resistance of the membrane itself can be suppressed.
The above-mentioned method of dispersing the inorganic ion-exchanger into one side of the surface of the membrane consists usu~lly in coating a solution containing the metallic ions on ~*id one side of the surface of the membrane, or allowing filter paper, woven fabric or nonwoven fabric containing the metall~c ion solution to contact with said one side of the surface of the membrane, thereby dispersing the metallic ion into only said one side of the surface layer of the membrane, and thereafter allowing the metallic ions to contact hydroxyl or acid groups.
As another example of being dispersed into the membrane in the form of a compound, there is a liquid metal compound such as titanium tetrachloride or antimony pentochloride, or an aqueous solution of these compounds.
A gel of the substantially water-insoluble hydroxide, hydrated oxide, or polybasic salt of the metallic ions dis-persed into the polymer membrane in accordance with the above-mentioned method should be desiccated. Usually, the higher the ' temperature of desiccating, the higher resistance to eorrosion and mechanical shocks. However, many of said metal compounds tend to decrease their ion exchange capacities when desiccated at an extremely high temperature. Usually, the desiccating temperature suitably ranges from 30C to 200C. Further, depending upon the drying temperature of desiccating, the electric resistance and current efficiency of the electrolysis using the resultant membrane are liable to be varied. For example, the cell voltage was 3065 volts in a brine electrolysis _ g _ 10~ 4 ~sing a cation-exchange polymer membrane containing zirconium phosphate which was not desiccated after dispersing said phosphate thereinto, whereas when, in said case, the membrane was fully desiccated at 110C, the cell voltage was increased up to 4.0 volts under the same electrolyzing condition. Usually, the desiccated membrane provides an increased cell voltage as compared with the membrane subjected to no desiccation treat-ment, and provides a greatly increased ion selectivity, that is, current efficiency. In the above example, the membrane free from the desiccation treatment provided a current efficiency of 86% whereas the desiccated membrane provided an increased current efficiency of 96%. Therefore, it is preferred that, after dispersing the inorganic ion exchanger, the desiccating temperature of the membrane should be properly adjusted in accordance with the purpose of using the cation-exchange polymer membrane.
The improved cation-exchange polymer membrane according to this invention is not only limited to the above-mentioned single layer membrane, but a bonded two layer-membrane having different ion exchanging capacity from each other is also effective.
The improved cation-exchange polymer membrane according to this invention-is used by being installed in various electrolytic cellsO HoweverJ in the electrolysis of an alkali halide, contraction, or expansion by swelling of the membrane sometimes occurs and has an effect upon the cell voltage or causes damage to the membrane, For this reason, the membrane is preferred to be installed in the electrolytic cell in a state as swollen as possible. Usually, to this end, the cation-exchange polymer membrane is to be sufficiently water-swollen, or once -- 10 -- , lu848~4 mmersed in hot water or boiling water, prior to the installation thereof.
This invention will be more fully understood from the following Examples, although not limited thereto.
Example 1 :
A polymer membrane of NAFION No. 110 having a thickness of 10 mils was dried at 110C for 1 hour, and immersed in a 10%
aqueous solution of zirconyl chloride at room temperature for 2 hours, and thereafter immersed in a 85% aqueous solution of phosphoric acid at room temperature for 30 minutes to disperse the salt of zirconium phosphate into the membrane.
After being washed with sufficient amount of water, the polymer membrane was dried at 110C for 1 hour. The amount of zirconium phosphate introduced was 1.2% by weight based on the whole amount of the original polymer membrane as dried.
The water content, the cation-exchange capacity and the density of ions fixed to the membrane are presented in Table l. !
The water content represented is the percentage by weight of water weight after the polymer membrane is immersed in water of 15C for 1 hour. For comparison, the corresponding measured values of a membrane of NAFION ~o. 110 free from the dispersion of zirconium phosphate, are shown together in Table l.
Table l Characteristics of Cation-Exchange Pol ~mer Membranes \ Introduced amount Water Ion exchange Density of -~
\ of zirconium conteOnt capacity ions fixed \ phosphate(wt.%) at 15 C ~meg/g dry to membrane - _ ~ (wt.%) resin) ~meg/g H2O) . ___ Example 1.2 10.5 1.02 9.7 .
'~Control 0 12.6 0.98 7.8 10~4~4 As seen from Table 1, the zirconium phosphate-dispersed membrane had an increased density of ions fixed to the membrane. This membrane was immersed in water at room temperature for 2 hours after being dried at 110C. Then,:the electrolysis of brine was made using this membrane under the electrolyzing conditions indicated in Table 2, the results being shown in Table 3.
Table 2 Electrolyzing Condition ~node Titanium-ruthenium oxide Cathode Stainless wire net (8 Tyler mesh) ~node-to- 5 mm cathode .
d~stance Brine concentration of 26 Cell 80C
tem~erature Current 20 A/dm density Table 3 Results of Electrolysis Concentration of NaOH Cell voltage Current ~:
\ in the cathode chamber efficiency \ (O (V) ( Example 1 21.2 3~75 =
Control 18.0 3-65 70 As is apparent from Tables 1 and 3, the membrane containing zirconium phosphate as the polybasic salt of metallic :~
ions has not only an increased density of ions fixed to the membxane, but also an excellent cation exchangeability permitting a high current efficiencyO
. . . ;
- :. .. . .
10~4~ 4 _xample 2 ~ membrane of NAFIO~ No. 110 having a thickness of 10 mils was cut out into a size of about 9 cm x 9 cm, and was dried at 110C for 18 hours. The resultant membrane was immersed for 1 hour in an aqueous solution prepared by dissolving 50 grams of zirconyl nitrate in 100 cc of lN hydrochloric acid of 80C.
Thereafter, the membrane was drawn out of the solution, and its surface was rapidly wiped off by filter papers, and then the membrane was immersed in a 30~ NaOH solution of 80C to be held therein for 1 hour. The resultant membrane was sufficiently washed with water, and dried at 110C for 18 hours.
When measurement of the cation-exchange capacity of the above-treated membrane was carried out, it was found to be ;
1.00 meg per gram of the membrane as dried. The membrane of NAFION No. 110 free from the above-mentioned treatment had a cation-exchange capacity of 0.97 meg per gram thereof. Therefore, there was about a 3% increase in the cation-exchange capacity ~`
with respect to the above-treated membrane. When brine electrolysis were performed with the use-of the above-treated membrane and the non-treated membrane, respectively, results indicated in Table 4 were obtained. Note that the brine electrolysis was carried out under the conditions wherein graphite and iron were used as the anode and cathode material, respectively; the anode-to-cathode distance was 10 mm; the concentration of brine was 26%; the cell temperature was 50C:
and the current density was 20 A/dm .
~)84874 Table 4 Resu}ts of Electrolysis Temperature Concentration of ¦ Cell Current \ NaOH in the volt- efficiency ~ \ cathode chamber age : \(C) (N) (V) (~) \
Example 2 50 4.2 3.8 81 Control50 4.1 3. a 75 Exam~les 3 to 5 After drying three membranes of NAFION No. 110 having a thickness of 10 mils at 110C for 1 hour, the hydroxides and the polybasic salt of metallic ions shown in Table 5 were dispersed into the membranes, respectively.
As seen from Table 5, the above-treated membranes of this invention had an increased density of ions fixed to the membrane, respectively, as compared with a non-treated membrane of NAFION No. 110 shown as a control in said Table~
Table 5 \ - , l \ Metallic OH-group ntro- Water Within-a-\ ion or acid ducing content membrane \ radical amount (%) fixed ion \ (wt.%) density \ _ _ (meg/g H O) _ ~ .
Example Titanium OH 0.32 11, 4 9ol Example 4Cerium OH 2.3 9,6 11.7 Example 5Cerium Molybdic 1.8 10.7 9.8 (IV) radidCal Control 0 12 o6 7 ~ 8 ~ 14 ~
~xample 6 A membrane of ~AFI0~ No. 110 having a thickness of 10 mils was immersed in an aqueous solution prepared by dis-solving 50 grams of zirconyl nitrate in 100 ml of lN hydro-chloric acid at 80 to 90C for 10 minutes. After the surface of the resultant membrane was sufficiently wiped off, this membrane was immersed in a 20% aqueous solution of caustic soda at 100C for 20 minutes. However, the formation of a gel in said aqueous solution of caustic soda was little recognized.
When, after being sufficiently washed with water, this membrane was immediately immersed in a 80~ aqueous solution of phosphoric acid at 120C for 10 minutes, the membrane became whitish, whereas the formation of a gel of zirconium phosphate in said aqueous solution of phosphoric acid was not recognized at all.
Of course the phosphoric acid was able to be reused. The resultant membrane, after washed with water, was dried at 110C
for 1 hour, and thereafter allowed to stand at room temperature for one day, and then zirconium phosphate was dispersed into said membrane. The concentrations of zirconium and phosphorus measured by the fluorescence -X rays method are presented in Table 6 below.
Table 6 characteristics of membrane treated Zr-Welqnt X lUU P-Welqht X lUU Zr-Po4welght X 100 I Zr Total weight Total weight Total weight P04 of membrane _ of membrane of membrane (mol 2030 o.l6 2.79 4.69 Brine-electrolysis was carried out with the use of the membrane containing zirconium phosphate under the conditions wherein the anode and cathode were made of titanium-rutheniu~
oxide and iron, respectively; the anode-to-cathode distance was 10 mm; the concentration of brine was 26~; the cell temperature was 50 to 55C; the effective area of membrane was 25 cm ; the current density was 20 A/dm ; and the concentration of NaOH in the cathode chamber was 6N. At this case, the cell voltage and the current density were 4.0 volts and 75% respec-tively. When, for comparison, brine-electrolysis was carried out under the same electrolyzing conditions with the use of a membrane of NAFION No. 110 containing no inorganic ion ex-changer, the cell voltage was 3.8, but the current density wasdecreased to 67%.
ExamPle 7 A NAFION No. llO-membrane of sulfonic acid type having a thickness of 10 mils was dried at 100C for 1 hour, and then immersed in a 30~ aqueous solution of Zro (NO3 ) ~o 2H20 at room temperaturefor 15 hours. The resultant membrane was immersed in a 85% aqueous solution of phosphoric acid and washed with water, and thereafter was dried at 100C for 1 hour to obtain a cation-exchange polymer membrane containing zirconium phosphate. The amount of zirconium phosphate introduced into this membrane was 5.0~ by weight based on the weight of original membrane. When a NAFION No. llO-membrane of sodium sulfonate type was similarly treated, the amount of zirconium phosphate introduced into the resultant membrane was 7.4% by weight based on the weight of original membrane. When the above sulfonic acid type and sodium sulfonate type membranes were again subjected to the same treatment as mentioned above, the amounts of zirconium phosphate introduced into both said membranes were 11.2% and 13.8~ by weight based on the weight of original membranes respectively.
4~74 Further, when the above twice treated sulfonic acid type membrane was again subjected to the same treatment as the above-mentioned initial treatment, the amount of zirconium phosphate contained in the resultant membrane was to 17.3% by weight based on the weight of original membrane. With respect to the above-mentioned sodium sulfonate type membrane, after completion of the second treatment, it was subjected to boiling water treatment at 100C for 1 hour, and thereafter immersed in a 30~ aqueous solution of ZrO(NO3)2 2H@O for 15 hours, and further immersed in a 85% aqueous solution of phosphoric acid for 1 hour. After being sufficiently washed with waterJ the resultant membrane was dried at 100C for 1 hour. As a result, the amount of zirconium phosphate contained in the resulting membrane was 23.5% by wei~ht based on the weight of original membrane. From the above, it will be appreciated that the amount of zirconium phosphate introduced can be adjusted de-pending upon the frequency of dispersion.
ExamPles 8 and 9 A cation-exchanger polymer membrane of NAFION No. 390, which is a sodium 8ul. fonate type cation-0xchange polymer membrane prepared by subjecting EW-1100* and EW-1500* membranes to be plied up through a mesh formed of ethylene tetrafluoride resin and rayon interposed therebetween, was immersed in a 50~ aqueous solution of zirconyl chloride at room temperature for about ~
hours. After the surface of the membrane was sufficiently wiped off by filter papers, it was immersed in a 85% aqueous solution of phosphoric acid, thereby dispersing zirconium phosphate into the membrane~ The resultant membrane, 30 minutes later, was taken out from said solution and sufficiently washed with water, and thereafter dried at 110C (Example 9) and at 75C(Example 10) * trade mark - 1~7 -'74 for 1 hour respectively. In both Examples, the amount of each zirconium phosphate introduced into the resulting both membranes was a~out 3.2% by weight based on the weight of original membranes.
In both Examples, the membrane thus dried was kept in water at room temperature for two days, and was installed in an electrolytic cell so as to permit the EW-1100 membrane side thereof to;face the anode side. Electrolysis of brine was carried out separately under the same conditions as indicated 3 in Table 2 of Example 1, the results being presented in Table 7.
For comparison, with the use of a ~AFION ~o. 390-membrane con-taining no zirconium phosphate, simply dried at 110C for 1 hour and allowed to stand in water, brine electrolysis was carried out under the same electrolysis conditions, the result being presented together in Table 7.
Table 7 Results of Electrolysis Drying Concentration Cell Current \temperature NaOH in the volt- efficiency \(C) cathode chamber a(v)e (%) Example 9110 24.0 4.0 95-3 Example 10 75 22.3 3.9 93.2 ~ontrol110 21.7 3.6~ 87.8 As is obvious from Table 7, the membrane of NAFION
No. 390, that is, a bonded membrane of two ion-exchange mem-branes having different ion-exchange capacities, naturally provides a relatively high current efficiency. When the membrane is allowed to contain zirconium phosphate therein, it causes only a little increase in the cell voltage, and at the 1~)84874 same time, it permits the maintenance of such an extremely high current efficiency which is not attainable with the membrane not containing zirconium phosphate.
The detailed reason why the membrane of NAFION NoO 390 prepared by bonding two ion-exchange polymer membranes having different ion-exchange capacities provides a relatively good current efficiency has not yet been clarified. We, however, suppose that this reason may be as follows. The EW-1500 membrane has a small swelling tendency against water for its large ion-exchange capacity, and as a result has a high density of ions fixed to the membrane in an electrolyte solution. This plays the role of a barrier for inhibiting the diffusion of hydroxyl groups from the cathode. Further, in the neighbourhood of the boundary between the EW-1500 and EW-1100 membranes, the ion-exchange capacity of the EW-1100 membrane has its own-exchange capacity and yet the swelling tendency thereof against water is suppressed by the bondage of EW-1500 membrane, with the result that the density of ions fixed to the bonded membrane in said neighbourhood is increased.
When an inorganic ion exchanger is dispersed into such a bonded membrane, the exchanger is liable to be adhered to those portions of the membrane where it has a higher density of ions fixed to the membrane, and said density at said portions of the membrane is further increased, causing the characterizing features of the membrane to be further promoted to present an extremely high selectivity to cations.
ExamPle 10 A sheet of filter paper previously immersed in a 10%
aqueous solution of zirconyl chloride was stuck to the EW-1500 .. . , .
~,. , . , . ~ .
i()848'~4 side of a membrane of NAFION No. 390 (sodium sulfonate type), and the resultant membrane was allowed to stand at room tempera-ture for 15 minutes. Thereafter, said sheet of filter paper was exfoliated from the membrane, and another sheet of filter paper permeated thereinto sufficiently with a 85% aqueous solution of phosphoric acid was stuck to the exfoliated side of said membrane, thereby introducing zirconium phosphate only into the EW-1500 side of the NAFION No. 390-membraneO
After being sufficiently washed with water, said zirconium phosphate-introduced membrane was dried at 110C for 1 hour, and then allowed to stand in water at 15C for 1 hour.
The amount of zirconium phosphate dispersed was about 0.23% by weight based on the weight of original membrane.
The above-treated membrane was installed in an electrolytic cell so as to permit the EW-1500 side to face the cathode, and electrolysis of brine was carried out under the same electrolyzing conditions as shown in Table 2 of Example 1.
The results were that the cell voltage was 3.7 volts; the concentration of NaOH in the cathode chamber was 22.6%; and the current efficiency was 94~9%O Thus~ the membrane had a very good selective permeability of cations.
Example 11 A membrane of NAFIO~ ~o. 315, which is of sulfonic acid type, and is a bonded membrane of EW-1100 and EW-1500 membranes together with a mesh consisting of ethylene tetra-fluoride resin interposed therebetween, was immersed in a 85%
aqueous solution of phosphoric acid at 120C for 2 hours, and then, after the surface of the resultant membrane was sufficiently wiped off, this membrane was immersed in a 10~
aqueous solution of zirconyl chloride at 100C for 10 minutes.
- ; .. .. ,,~, .
.
1084~4 After being sufficiently washed with water, the resultant membrane was dried at 110C for 2 hours. The amount of zirconium phosphate introduced was about 3% by weight based on the weight of original membrane.
Using the above-treated membrane, electrolysis of brine was carried out, at which time the membrane was installed in the electrolytic cell so as to permit the EW-1500 side to face the cathode. The electrolyzing conditions were as indicated in Table 2 of Example 1, excepting that the cell temperature was 70C~ The results of this electrolysis are shown in Table 8, together with the results of brine electrolysis carried out, for comparison, under the same electrolyzing conditions using a NAFION No. 315-membrane not containing zirconium phosphate. ~-Table 8 Results of Electrolysis Concentration of Cell Current \ ~aOH in the voltage efficiency \ cathcde cha~oer ~ ~V~ L
,_ , Example 12 20.0 4.5 9.8 .
~ontrol 20.1 4.2 __ ::
., ,~ ,
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a cation-exchange polymer membrane made of a fluorinated resin containing in the molecules thereof elect-ronegative groups selected from the group consisting of sulfonic-, carboxyl- and phenolic-, an improvement characterized in that a precipitate or gel of a water-soluble inorganic ion-exchange material selected from the group consisting of hydroxide, hydrated oxide, phosphate, molybdate and tungstate of a metallic element is dispersed into the polymer membrane by means of a chemical reaction; the amount of said inorganic ion-exchanger contained in the modified polymer membrane ranging from 0.1 to 30 percent by weight based on the weight of original polymer membrane.
2. The cation-exchange polymer membrane of claim 1 wherein the metallic element is selected from the group con-sisting of zirconium, titanium, tin (IV), cerium, thorium, lanthanum, manganese (II), silicon, niobium, tantalum, antimony (V), molybdenum (VI), antimony (III), bismuth, indium, manganese (III), iron (III), gallium, aluminium, cadmium, zinc, magnesium, beryllium and hafnium.
3. The cation-exchange polymer membrane of claim 1, wherein the fluorinated resin is the one selected from the group consisting of polymer or copolymer of tetrafluoroethylene, hexafluoropropylene, trifluorochloroethylene, trifluoroethylene, fluorovinylidene, .alpha.,.beta.,.beta.- trifluorostyrene and perfluorovinylether.
4. The cation-exchange polymer membrane of claim 1, wherein the water-insoluble inorganic ion-exchanger is dist-ributed homogeneously in the base polymer membrane.
5. The cation-exchange polymer membrane of claim 1, wherein the water-insoluble inorganic ion-exchanger is distri-buted into one side of the surface of the base polymer membrane.
6. The cation-exchange polymer membrane of claim 1, wherein said membrane consists of two bonded membrane layers having different ion exchanging capacity from each other.
Applications Claiming Priority (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP37789/75 | 1975-03-31 | ||
| JP50037789A JPS51112783A (en) | 1975-03-31 | 1975-03-31 | Ion exchange membrane and process for producing the same |
| JP79857/75 | 1975-06-27 | ||
| JP50079857A JPS5817493B2 (en) | 1975-06-27 | 1975-06-27 | Improved ion exchange membrane and method for manufacturing the same |
| JP85243/75 | 1975-07-14 | ||
| JP50085243A JPS582971B2 (en) | 1975-07-14 | 1975-07-14 | Shinkiyo Ion Kokanmaku Oyobi Sonoseizouhouhou |
| JP91613/75 | 1975-07-29 | ||
| JP9161375A JPS5215487A (en) | 1975-07-29 | 1975-07-29 | Improved process for producing ion exchange membranes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084874A true CA1084874A (en) | 1980-09-02 |
Family
ID=27460468
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA248,845A Expired CA1084874A (en) | 1975-03-31 | 1976-03-25 | Cation-exchanging membrane |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1084874A (en) |
| DE (1) | DE2614058C2 (en) |
| FR (1) | FR2306010A1 (en) |
| GB (1) | GB1534359A (en) |
| IT (1) | IT1057469B (en) |
| SE (1) | SE7603539L (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE850594A (en) * | 1977-01-21 | 1977-05-16 | Studiecentrum Kernenergi | UNIT FOR AN ELECTROCHEMICAL CELL |
| NL7907632A (en) * | 1978-10-20 | 1980-04-22 | Ppg Industries Inc | Diaphragm with zirconium and magnesium compounds in a porous matrix. |
| AU535261B2 (en) * | 1979-11-27 | 1984-03-08 | Asahi Glass Company Limited | Ion exchange membrane cell |
| JPS57172927A (en) * | 1981-03-20 | 1982-10-25 | Asahi Glass Co Ltd | Cation exchange membrane for electrolysis |
| NZ203337A (en) * | 1982-02-26 | 1986-02-21 | M S M Lefebvre | Immobilised inorganic counter diffusion barriers and their applications |
| WO1996029752A1 (en) * | 1995-03-20 | 1996-09-26 | E.I. Du Pont De Nemours And Company | Membranes containing inorganic fillers and membrane and electrode assemblies and electrochemical cells employing same |
| US7572534B2 (en) * | 2004-09-20 | 2009-08-11 | 3M Innovative Properties Company | Fuel cell membrane electrode assembly |
| US8101317B2 (en) | 2004-09-20 | 2012-01-24 | 3M Innovative Properties Company | Durable fuel cell having polymer electrolyte membrane comprising manganese oxide |
| EP1912272A4 (en) * | 2005-07-12 | 2009-12-02 | Asahi Glass Co Ltd | Electrolyte membrane for use in solid polymer-type fuel cell, process for production of the membrane and membrane electrode assembly for use in solid polymer-type fuel cell |
| US8652705B2 (en) | 2005-09-26 | 2014-02-18 | W.L. Gore & Associates, Inc. | Solid polymer electrolyte and process for making same |
| US7622217B2 (en) | 2005-10-12 | 2009-11-24 | 3M Innovative Properties Company | Fuel cell nanocatalyst |
| US8628871B2 (en) | 2005-10-28 | 2014-01-14 | 3M Innovative Properties Company | High durability fuel cell components with cerium salt additives |
| US8367267B2 (en) | 2005-10-28 | 2013-02-05 | 3M Innovative Properties Company | High durability fuel cell components with cerium oxide additives |
| US7989115B2 (en) | 2007-12-14 | 2011-08-02 | Gore Enterprise Holdings, Inc. | Highly stable fuel cell membranes and methods of making them |
-
1976
- 1976-03-23 SE SE7603539A patent/SE7603539L/en not_active Application Discontinuation
- 1976-03-24 GB GB11883/76A patent/GB1534359A/en not_active Expired
- 1976-03-25 CA CA248,845A patent/CA1084874A/en not_active Expired
- 1976-03-30 DE DE19762614058 patent/DE2614058C2/en not_active Expired
- 1976-03-31 FR FR7609347A patent/FR2306010A1/en active Granted
- 1976-03-31 IT IT48797/76A patent/IT1057469B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| FR2306010A1 (en) | 1976-10-29 |
| DE2614058A1 (en) | 1976-10-07 |
| IT1057469B (en) | 1982-03-10 |
| GB1534359A (en) | 1978-12-06 |
| FR2306010B1 (en) | 1981-06-19 |
| DE2614058C2 (en) | 1981-12-17 |
| SE7603539L (en) | 1976-10-01 |
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