JPH04190837A - Porous membrane of crosslinked sulfonated poly(vinylidene fluoride) resin and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a porous membrane having sulfonic acid groups enough to effect cation exchange by processing a poly(vinylidene fluoride)resin porous membrane with a mixture of sulfuric acid anhydride, and dry air or inert gas. CONSTITUTION:By processing a poly(vinylidene fluoride) resin porous membrane with a mixture of sulfuric acid anhydride, and dry air or inert gas, a crosslinked sulfonated poly(vinylidene fluoride) resin porous membrane is produced. A melt membrane formation method of this membrane is such that molten polymer is delivered in the form of a flat membrane or a hollow fiber membrane and stretched to form a porous structure. Crosslinked sulfonating reaction depends on temperature of sulfuric acid anhydride, reaction temperature and reaction time and by controlling these factors, a crosslinked sulfonated porous membrane can be produced. As methods for producing such membranes, there are batch method, continuous method, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a crosslinked sulfonated polyvinylidene fluoride resin porous membrane and a method for producing the same. More specifically, the present invention relates to a crosslinked sulfonated polyvinylidene fluoride resin porous membrane that removes ionic substances, colloids, fine particles, etc. at once in the water treatment field and a method for producing the same.

[Prior Art] Conventionally, ion exchangers have been widely used as adsorbents for various ionic substances, catalysts for chemical reactions, and the like. In particular, membrane-like ion exchangers can be applied to diaphragms for electrolysis reactions, electrolytic treatment of wastewater, oxidation treatment and reduction treatment of metal ions, diaphragms for fuel cells, as well as regular dialysis, electrodialysis, etc. It's spreading. Among these, strong acid type cation exchange membranes having sulfonic acid groups are particularly important.

A strong acid type polyvinylidene fluoride resin cation exchange membrane having such a sulfonic acid group is disclosed in Japanese Patent Application Laid-Open No. 56-5783.
6 and JP-A No. 57-141.432, these use fuming sulfuric acid as a sulfonating agent, so the resulting porous membranes contain cations that support crosslinking groups such as -302-. If enough sulfonic acid groups are introduced for exchange, the polymer becomes water-soluble and becomes difficult to put into practical use. In addition, 1. In addition to severe deterioration due to side reactions during sulfonation, the manufacturing process is complicated because it is necessary to dilute the sulfuric acid attached to the obtained porous membrane and the waste sulfuric acid after use in stages. Cost increases.

[Problem to be solved by the invention] The purpose of the present invention is to provide a porous membrane having sufficient sulfonic acid groups for cation exchange, and to provide a simple method for producing a crosslinked sulfonated porous membrane. It is something to do.

[Means for Solving the Problem] As a result of intensive studies to solve this problem, the present inventors have developed a polyvinylidene fluoride resin porous membrane using a mixed gas of sulfuric anhydride and dry air or inert gas. It was discovered that both a crosslinking group and a sulfonic acid group can be introduced by treatment, and the present invention was completed.

The present invention has the following configuration.

(1) A porous membrane made of polyvinylidene fluoride resin, in which the resin has -502- as a sulfonic acid group and a crosslinking group.
A cross-linked sulfonated polyvinylidene fluoride resin porous membrane comprising:

(2) A method for producing a crosslinked sulfonated polyvinylidene fluoride resin porous membrane, which comprises treating the polyvinylidene fluoride resin porous membrane with a gas mixture of anhydrous sulfuric acid and dry air or an inert gas.

The present invention will be explained in detail below.

The polyvinylidene fluoride resin referred to in the present invention refers to a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and vinyl fluoride, and a mixture thereof.

The shape of the polyvinylidene fluoride resin porous membrane of the present invention may be a flat membrane or a hollow fiber membrane, and the flat membrane usually has a thickness of 1-20,000 μm, preferably 5 μm to 10,000 μm.
m, and hollow fiber membranes usually have an inner diameter of 5 μm to 10,000 μm.
m1 Film thickness is 1 μm to 10,000 μm1 Preferably, inner diameter is 1
The film thickness is 0 μm to 10,000 μm and 5 μm to 5,000 μm.

The porous membrane has a large number of continuous micropores penetrating the wall membrane from the inside to the outside, and the average diameter of the micropores is usually 1 nm to 5,000 nm, preferably 20,000 to 1,000 nm. nm
selected within the range.

The polyvinylidene fluoride resin porous membrane of the present invention is characterized by containing a sulfonic acid group and a crosslinking group.

If a crosslinking group is not present, introducing a sufficient amount of sulfonic acid groups for ion exchange will result in excessive swelling in water or elution of the polymer. The sulfonic acid group of the present invention is -8O
3I", -3O-, M (M is Li.

Refers to substances that form salts such as Na5K, Mg, Ca, NH, ions, etc.

The sulfonic acid group replaces the hydrogen bonded to carbon in the main chain of polyvinylidene fluoride and is directly covalently bonded to the carbon. The amount of sulfonic acid groups is usually 0.1 to 5 milliequivalents, preferably 0.5 to 4 milliequivalents, per gram of dry resin. The crosslinking group of the present invention can be represented by -8O2-, or
Each is covalently bonded directly to a carbon in the main chain.

The polyhynylidene fluoride porous membrane of the present invention can be obtained by a known method. For example, melt film forming methods include a method in which a porous structure is formed by discharging a molten polymer in the form of a flat film or a hollow fiber film and stretching it; Examples include a method in which the material is mixed, discharged into a flat membrane or hollow fiber membrane, and then the bore forming agent is eluted. In the solution casting method, a polymer solution as it is or with a bore forming agent added thereto is discharged into the air or into a coagulable liquid in the form of a flat membrane or hollow fiber membrane, and the solvent and bore forming agent are eluted. I can list methods etc.

The sulfuric anhydride of the present invention may be of the α type, β type, or γ type, but the γ type, which is liquid at room temperature, is preferable.

In the present invention, sulfuric anhydride is used after being diluted with dry air or an inert gas. The crosslinking sulfonation reaction is influenced by the concentration of sulfuric anhydride, reaction temperature, and reaction time, but by controlling these, the desired crosslinked sulfonation porous membrane can be produced. If the concentration of sulfuric anhydride is too high, the membrane will be severely degraded, and if it is too low, the rate of crosslinking and sulfonation will be slow, so it is usually 0. It is selected in the range of 1 to 50%, preferably O15 to 20%. The reaction temperature depends on the concentration of sulfuric anhydride, but if it is too high, the membrane will deteriorate rapidly, and if it is too low, the rate of sulfonation will be slow (not only will the crosslinking reaction not occur, so the temperature is usually 20 to 120°).
C1 preferably 40 to 100°C, more preferably 5
The temperature range is selected from 0 to 90°C. The reaction time largely depends on the concentration of sulfuric anhydride and temperature, but is usually 10
The time period is selected in the range of seconds to 2 hours, preferably 30 seconds to 1 hour.

Dry air or an inert gas is used as the gas to dilute sulfuric anhydride, but if moisture is present, sulfuric acid will immediately form and become a mist, which will adhere to the membrane and cause side reactions. Quantity is an important condition. The water concentration is usually 0. 5% or less, preferably 0. It is 2% or less, more preferably 0.1% or less. Examples of the inert gas include nitrogen gas, helium gas, and argon gas, but nitrogen gas is preferably selected from the viewpoint of ease of handling and cost.

Examples of the method for producing the crosslinked sulfonated porous membrane of the present invention include a batch method and a continuous method. Batch methods include a reduced pressure method in which a porous membrane is placed in a reactor, the pressure is reduced and diluted sulfuric acid anhydride gas is sealed in, and a distribution method in which diluted sulfuric acid anhydride gas is continuously supplied to a reactor containing a porous membrane. An example is the law. As a continuous method, a porous membrane is fed into a device containing diluted anhydrous sulfuric acid gas,
Examples include a method of moving the material within the device and continuously taking it out. However, in order to uniformly introduce a sufficient amount of sulfonic acid groups, a reduced pressure method or a continuous method is preferably used.

Since the production method of the present invention performs the reaction in the gas phase, excess sulfuric anhydride after the reaction can be removed under reduced pressure or by flowing dry air or nitrogen gas. In addition, since the only thing produced by the reaction is a trace amount of water that is generated during the formation of sulfonic acid groups and crosslinking groups, it is necessary to remove the sulfuric acid attached to the reaction product in a stepwise manner, as in the case of reacting with fuming sulfuric acid. No need to dilute. Furthermore, since no waste sulfuric acid is generated, the manufacturing process can be greatly simplified.

Examples will be described below, particularly regarding hollow fiber membranes, but the present invention is not limited thereto.

Example As an indicator of the pore size of the active surface of the porous membrane, a latex of polystyrene fine particles with a uniform particle size (Dow Uniform Latex Pa manufactured by Dow Chemical Company) was used.
Using a 200 ppm dispersion of polystyrene fine particles, the rejection rate was calculated from the amount of light transmitted before and after filtration.

The tensile strength at break (kg/M2) and tensile elongation at break (%) of the porous membrane were measured using a Tensilon type tensile tester.

The amount of permeated water was measured by supplying pure water by external pressure total filtration at 25°C. The unit was expressed in ml/hr-mmHg-po.

Exchange capacity (milliequivalents/g) was used as an indicator of the amount of sulfonic acid groups. A membrane equivalent to 0.5 g was immersed in 50 ml of a 0.1N aqueous sodium hydroxide solution, shaken for 2 hours, and then exactly 5 ml was taken and determined by titration.

Total organic carbon content (TOC) was used as an index of elution of organic matter from the porous membrane. A membrane equivalent to 0.5 g was immersed in 5° Oml of pure water (1ooppb) with a known TOC, and
After being left for 12 hours at ℃, the TOC of the immersion water was measured using an automatic analyzer model TOC710 manufactured by Enciniaring Co., Ltd.

(Example 1) Polyvinylidene fluoride (“Kyn” manufactured by Pennwalt)
ar 460”) 2 parts by weight of dimethyl sulfoxide
A spinning stock solution was prepared by dissolving in parts by weight. This was spun using a hollow fiber production spinneret using a dimethyl sulfoxide SO% aqueous solution as an internal injection liquid to obtain a polyvinylidene fluoride porous hollow fiber membrane.

The polyvinylidene fluoride porous hollow fiber membrane obtained had an inner diameter/membrane thickness of -335/SO .mu.m1.The rejection rate of polystyrene fine particles was 99% at a particle size of 0.085 .mu.m and 65% at a particle size of 0.038 .mu.m. The strength was 0°85 kg/mm2, the elongation was 60%, and the water permeability was 350 ml/hr-body Hg·d.

Approximately 10g of dried polyvinylidene fluoride porous hollow fiber membrane
(50 cm x 500 tubes) was packed in a glass column, and dry nitrogen gas with a water concentration of 0.08% was passed through the hollow fiber membrane to remove moisture from the hollow fiber membrane. 12ONl 1 minute, temperature 70'C, up'70- for 30 minutes. The amount of sulfuric anhydride fed reached 320 g. After the reaction, excess sulfuric anhydride was removed with nitrogen gas and further washed with water to obtain a crosslinked sulfonated polyvinylidene fluoride porous hollow fiber membrane of the present invention.

The obtained crosslinked sulfonated hollow fiber membrane had an inner diameter/membrane thickness of −35
0795 μm, the rejection rate of polystyrene fine particles is
．． 085μrn 99%, 0.038μm 70%
The strength is 0.90kg/nun2 and the elongation is 45%.
The water permeability was 3SOm1/hr-IIImHg·i, and the exchange capacity was 2.5 milliequivalents/g. Furthermore, when an eluate test was conducted, the TOC was 150 ppb, and the elution was almost negligible.

As described above, the crosslinked sulfonated polyvinylidene fluoride resin porous membrane of the present invention has sufficient cation exchange groups and has no eluate, making it highly practical.

Furthermore, the membrane obtained by the production method of the present invention shows no major changes in surface pore size, strength/elongation, or water permeability, indicating that it is an excellent production method.

(Comparative Example 1) Approximately 10 g (50 cm x 500 pieces) of the polyvinylidene fluoride porous hollow fiber membrane obtained in Example 1 was reacted at SO° C. for 2 hours in fuming sulfuric acid containing 25% free sulfuric anhydride. The obtained sulfonated hollow fiber membrane had an inner diameter/membrane thickness of 350/1.
The rejection rate of 00μm1 polystyrene fine particles is
99% at 85μm, SO% at 0.038μm, strength 0.40kg/mm2, elongation 30%, water permeability 3
00m1/h "・mmHg-rr?, exchange capacity is 2.5
milliequivalent/g, and was extremely brittle. Furthermore, when an eluate test was conducted, the TOC significantly increased to 1 ppm, indicating that the sulfonated polymer was eluted.

[Effects of the Invention] Even though the crosslinked sulfonated polyvinylidene fluoride resin porous membrane of the present invention has sufficient sulfonic acid groups for cation exchange, it has a crosslinked structure, so it has excellent mechanical strength and no eluates. High permeation rate of water or chemical solution. Therefore, cation exchangers have been used in fields such as the electronics industry, etc.
Ionic substances and fine particles can be separated at the same time in water treatment at nuclear power plants, collection of useful or unnecessary metals from wastewater, purification of chemicals, etc.

In the production method of the present invention, the amount of sulfonic acid groups can be easily controlled and the production process can be greatly simplified, so that a cation exchange porous membrane suitable for the purpose can be efficiently obtained.

Claims (2)

[Claims] (1) A porous membrane made of polyvinylidene fluoride resin, in which the resin has -SO_2 as a sulfonic acid group and a crosslinking group.
- A cross-linked sulfonated polyvinylidene fluoride resin porous membrane comprising: (2) A method for producing a crosslinked sulfonated polyvinylidene fluoride resin porous membrane, which comprises treating the polyvinylidene fluoride resin porous membrane with a gas mixture of anhydrous sulfuric acid and dry air or an inert gas.