JPS5817493B2 - Improved ion exchange membrane and method for manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel cation exchange membrane in which the cation exchange membrane contains an inorganic substance, that is, a sparingly soluble hydroxide or hydrous oxide of a specific metal, and a method for producing the same.

Ion exchange membranes have a high density of ion exchange groups inside and are characterized by their selectivity towards cations or anions, and are used to separate various substances.

In this case, the physical properties required are good ion selectivity and ion permeability, as well as durability under the environment in which it is used.

In particular, membranes used in electrolysis are required to have durability under severe conditions, high current efficiency, and low resistance (sliding voltage), and it is not easy to obtain membranes that fully meet these requirements.

Further, current efficiency and resistance generally have an inverse correlation, and it is not easy to satisfy both.

The membrane used in the production of alkali hydroxide is a cation exchange membrane, but as the concentration of alkali hydroxide generated on the cathode side increases, the selective permeability of ions decreases, resulting in a significant decrease in current efficiency. cation exchange membranes, which are normally used for desalination and concentration of common salt, were not sufficient.

In order to obtain high current efficiency, a high net fixed anion concentration in the concentration of alkali hydroxide used is required.

The reduction in the fixed anion concentration is determined by the amount of exchange groups and the water content, and large swelling by water is not preferable because the fixed anion concentration decreases.

Therefore, in order to increase the concentration of fixed anions, it is common practice to increase crosslinking to suppress swelling of the resin due to water.

The present inventors conducted research on increasing the fixed ion concentration within the membrane, and found that, unlike the general method of increasing crosslinking, we introduced an ion exchanger inside the ion exchange membrane and effectively reduced the water content. By reducing the current efficiency, it was possible to obtain a film with high current efficiency, and the present invention was achieved.

Furthermore, it has been found that an inorganic ion exchanger is preferable as the ion exchanger to be introduced in terms of ease of introduction, heat resistance, and chemical resistance.

It has long been known that silicic acid, alumina gel, iron hydroxide, etc. adsorb salts well, but recently it has been discovered that sparingly soluble hydroxides and hydrous oxides of metals are ion exchangers. There is.

It has been found that the current efficiency can be improved by introducing these inorganic ion exchangers into the cation exchange membrane.

The hydrous oxides of the present invention are preferred because they are easy to introduce, are particularly stable against alkalis, and do not substantially swell with water.

The present invention provides a membrane that has excellent current efficiency when used for electrolysis by incorporating a hydrous oxide on the surface or inside of a conventionally used cation exchange membrane.

This membrane exhibits high current efficiency at high concentrations of alkali, and is used not only as an ion exchange membrane for electrolysis, but also exhibits extremely high selectivity even at low concentrations, for example in desalination, concentration, waste liquid treatment, etc. It can also be used for

The ion exchange membrane used in the present invention may be any known membrane, but is preferably a so-called homogeneous membrane.

Heterogeneous membranes such as mixtures of ion-exchange resins and non-ion-exchange resins inevitably have low current efficiency, leading to the presence of pores, but these relatively large pores are blocked by hydrous oxides. It is difficult to subdue.

In the case of a homogeneous membrane, the reaction occurs inside the membrane, and the place where the reaction occurs is the water layer where OH- diffuses, and the gel enters the fine parts, increasing the actual exchange group density. .

The material of the cation exchange membrane used in the present invention is acrylic acid or methacrylic acid polymer compound crosslinked with divinylbenzene etc., divinylbenzene styrene copolymer,
Polyethylene, polytetrafluoroethylene resin (including copolymers), polytetrafluoroethylene, polytrifluorochloride ethylene resin, polytrifluoroethylene resin, vinylidene fluoride resin, polyvinyl fluorocarbon ether copolymer Examples include polymers such as fluororesin.

Those into which a sulfone group or carbonyl group is introduced by copolymerization or chemical reaction are used.

These ion exchange membranes generally have acid and alkali resistance, but for example, ion exchange membranes for sodium chloride electrolysis may require even better acid and alkali resistance. As an ion exchange membrane with excellent properties, a perfluorosulfonic acid membrane manufactured and sold by EI DuPont under the trade name NAFION is particularly preferred.

The membrane is composed of a fluorinated copolymer having a cyclic structural unit of the following formula and having pendant sulfonic acid groups. , R5, R6 and R7 are fluorine or a perfluoroalkyl group having 1 to 10 carbon atoms, Y is a perfluoroalkylene group having 1 to 10 carbon atoms, m=o, 1, 2 or 3. n=0 or 1, p20 or 1, X is fluorine, chlorine, hydrogen or ]
・Rifluorometinope X or Xl is CF3 (CF2
)2, where 2 is O or an integer from 1 to 5.

Cation exchange membranes derived from 1,1,3-1-lifluorostyrene are also known to have good chemical resistance, and such membranes are also preferred.

In the present invention, a metal selected from zirconium, titanium, and cerium is used.

These metals give poorly soluble hydroxides or hydrated oxides, and since they are tetravalent or higher valent metals, the volume of the hydrated oxides produced is large, and the hydroxides or hydrated oxides have cation exchange properties. , giving lower resistance.

It also has excellent alkali resistance.

These hydroxides or hydrated oxides may be used alone or in combination.

Since it is impossible to introduce a hydrous oxide or hydroxide into the surface or inside of a membrane if it is a solid, a reaction is caused within the membrane to generate a gel, followed by drying.

For this purpose, metal ions or compounds are first adsorbed or absorbed on the membrane surface or inside, and then OH- ions are introduced and reacted, or 0H- is introduced into the membrane in advance, and then the metal ions or compounds are introduced into the membrane in advance. There is a method of infiltrating a compound into a membrane and causing a reaction.

Many metals that exist as water-soluble ions can be used as an aqueous solution.For example, in the case of Zr, first, a cation exchange membrane is made of ZrO(NO3)2.
After immersing the membrane in an acidic solution of hydrochloric acid to sufficiently adsorb or impregnate zirconium ions, the membrane is then poured into a NaOH solution, whereupon OH- diffuses and a gel is formed inside the membrane.

On the other hand, if the membrane is sufficiently swollen with NaOH, Na
When OH penetrates and then it is placed in a zirconium salt aqueous solution, Zr ions (ZrO) penetrate and a gel is formed.

Even if it is not an aqueous solution, it can be diffused into the membrane using a suitable solvent, or it can be introduced into the membrane in the form of an organometallic compound.

By appropriately selecting the concentration, time, method, etc. during introduction, it is possible to introduce a large number of gels or to contain gel only on one or both surfaces.

Examples of compounds to be applied or impregnated in the form of compounds include liquid metal compounds such as titanium tetrachloride, and those dissolved in solvents.

Although it is not necessary to dry the introduced gel, dry heat treatment is generally desirable because it improves the alkali resistance of the gel.

The amount of poorly soluble metal hydroxide or hydrated oxide introduced onto the surface or into the cation exchange membrane is determined by the amount of cation exchange membrane 1.
000 parts by weight, 0.1 to 20 parts by weight is used.

If it is less than 0.01 parts by weight, an ion exchange membrane with the desired high current efficiency cannot be obtained.G).

Moreover, if the amount is 20 parts by weight or more, depending on the type of ion exchange membrane used, the membrane may have weak mechanical strength, and the electrical resistance during electrolysis may increase, making it unsuitable for practical use.

As described above, the ion exchange membrane of the present invention in which a hydrous oxide of a metal is attached or introduced not only has excellent chemical resistance, but also has no particularly large increase in electrical resistance. This is an extremely useful membrane that increases the actual ion exchange capacity and prevents a decrease in current efficiency due to an increase in hydroxyl ion concentration in the cathode chamber during alkaline salt electrolysis.

The present invention will be explained below with reference to Examples.

Example 1 A NAFION 110 membrane (film thickness: 10 mils) manufactured by E.I. DuPont was cut out to a size of about 9 cm x 9 cm and heated at 110°C for 1 hour.
It was dried for 8 hours.

This was taken as the dry weight. Add this to 1 liter of IN hydrochloric acid at 80°C.
It was immersed for 1 hour in an aqueous solution in which 50 g of zirconyl nitrate was dissolved in oocc.

After that, take it out, quickly wipe the surface with filter paper, and then heat it to 80℃.
The sample was placed in a 30% NaOH solution and maintained for 1 hour.

Wash this membrane thoroughly with ion-exchanged water and heat it at 110℃ for 18 hours.
Dry for an hour.

The amount of hydrous oxide introduced into this treated membrane is 10
The amount was about 5.7 parts by weight compared to 0 parts by weight.

The cation exchange capacity of this product was measured and found to be 1.00 meq per dry weight (g).

0 for NAFION 110 membrane without such treatment.
．． Since the amount was 97 meq, an increase in exchange capacity of about 3% was observed.

When NaCl electrolysis was carried out using an untreated NAFIONl 10 membrane and the above-mentioned treated membrane in a two-chamber electrolytic cell, the following results were obtained.

The electrolytic conditions were as follows: a RhO2-coated titanium electrode was used as the anode, an iron electrode was used as the cathode, the distance between the electrodes was toin, and the decomposition rate was 1% or less.

Example 2 EI DuPont's NAFION 110 membrane (10 mil thickness) was mixed with 15% ceric ammonium nitrate.
It was immersed in an aqueous solution at room temperature for 2 hours.

The membrane was taken out, the surface thoroughly wiped, and then immersed in a 30% caustic soda aqueous solution at 100°C.

After 1 hour, this membrane was taken out of the caustic soda aqueous solution, thoroughly washed with water, immersed in a 1N hydrogen chloride aqueous solution for 1 hour, and after thoroughly washed with water, it was immersed again in the 15% aqueous solution of ceric ammonium nitrate at room temperature.

After soaking for 2 hours, take it out, wipe the surface thoroughly, and then add another 1
It was immersed in a 30% caustic soda aqueous solution at 00°C for 1 hour.

After thoroughly washing this membrane with ion-exchanged water, it was heated to 110℃ for 1 hour.
Let dry for an hour.

The amount of poorly soluble hydroxide introduced into this treated membrane was 2.3 parts by weight per 100 parts by weight of the cation exchange membrane.

The membrane was immersed in boiling water at 100°C for 1 hour, the surface was thoroughly wiped, and the water content was measured and found to be approximately 0.18 ji.
The H20 membrane was gdry resin.

In Example 2, the dry weight was the weight after drying at 110° C. for exactly 1 hour.

The fixed ion concentration in this membrane (me q/f!H20'
) 4 compared to untreated NAFION110 membrane, approx.
% increase.

Example 3 A NAFION 110 membrane (film thickness 10 mils) manufactured by EI DuPont was placed in a 24% titanium sulfate aqueous solution at 50°C.
Soaked for an hour.

After taking it out, wipe the membrane surface thoroughly with filter paper and heat it to 100℃.
The sample was immersed in a 30% caustic soda solution for 1 hour, thoroughly washed with water, and then placed in a 1N aqueous hydrogen chloride solution to form H-type.

After washing this membrane thoroughly with ion-exchanged water,
Immerse again in a 124% titanium sulfate aqueous solution for 1 hour at °C.
After thoroughly wiping the surface, it was immersed in a 30% caustic soda aqueous solution at 100°C for 1 hour.

After thoroughly washing this membrane with ion-exchanged water, it was heated to 110℃ for 1 hour.
Let dry for an hour.

The weight increase due to titanium hydroxide was 0.32 parts by weight per 100 parts by weight of the ion exchange membrane using the same method as in Example 2.

After soaking this membrane in boiling water for 1 hour and wiping the surface thoroughly, the water content was measured to be approximately 0.2Q, 9H20/&
It was dryresin.

The intramembrane fixed ion concentration (meq/'&H20) of this membrane was increased by about 9.5% compared to the untreated NAFION membrane by the same method as in Example 2.

The electrical resistance of this treated film at 25°C is 0.5M NaC
A! The result of measurement using a Kourausch bridge in an aqueous solution with 1000 cycles of alternating current was 3.45 Ω.

Example 4 A mixed solution of 75 parts of methyl methacrylate, 25 parts of triallyl isocyanurate, and 0.5 parts of benzoyl peroxide as a polymerization initiator was thoroughly soaked into a porous membrane (Polyflon PA-5L manufactured by Daikin Corporation) as a reinforcing agent. After this, the mixture was sandwiched between two Teflon sheets, which were then sandwiched between two smooth glass plates, and placed in a stainless steel polymerization container.

After purging with nitrogen, the container was kept at 60° C. for 16 hours to carry out polymerization.

After the temperature was further increased to 80° C. for 3 hours, a reinforced methyl methacrylate-trialyl isocyanurate resin film was obtained.

This membrane was immersed in 1,2 dichloroethane at room temperature for 1 hour, and then immersed in 85% concentrated sulfuric acid at room temperature for 200 hours to hydrolyze methyl methacrylate.

The membrane resistance was measured according to Example 3 and was 34Ω.

The exchange capacity of this membrane is 0.32 meq/F dry r
It was esin.

This membrane was immersed in a 224% titanium sulfate aqueous solution at 50°C for 1 hour, the surface was thoroughly wiped, and then immersed in a 30% caustic soda aqueous solution at 50°C for 1 hour.

This membrane was dried at 110°C for 2 hours.

After thorough washing of this membrane with ion-exchanged water, the dry weight increased by 261 parts by weight per 100 parts by weight of the ion-exchange membrane, and the exchange capacity of this membrane was 0.36 meq/gdry.
It was increasing with resin.

Moreover, the membrane resistance is 42 noodles.

Claims (1)

[Claims] 1. A cation exchange membrane 1 on the surface or inside of the cation exchange membrane.
00 parts by weight, zirconium, titanium. An exchange membrane characterized in that 0.1 to 20 parts by weight of a poorly soluble hydroxide or hydrated oxide of a metal selected from cerium is present. 2. When containing a hydrous oxide of a specific metal as described in claim 1, first, a solution containing hydroxide ions is applied or impregnated onto the surface or inside of a cation exchange membrane, and then the metal salt is added. Or, a method for producing an ion exchange membrane, which comprises bringing it into contact with a liquid containing a compound. 3. In order to contain the hydrated oxide of the specific metal described in claim 1, the cation exchange membrane is coated or impregnated in the form of the metal salt or compound, and then brought into contact with a solution containing hydroxide ions. A method for producing an ion exchange membrane, characterized by: