JPS61402A - Semipermeable membrane for separation - Google Patents

Abstract

PURPOSE:To obtain a semipermeable membrane having good filtering efficiency and a high water permeation speed, in a semipermeable membrane for separation based on a hydrophobic high-molecular substance having an asymmetric structure consisting of a dense layer and a porous layer, by constituting only the dense layer of said semipermeable membrane from a mixture consisting of a hydrophobic high-molecular substance and a hydrophilic high-molecular substance. CONSTITUTION:As a hydrophobic polymer, an aromatic polysulfone represented by formulae I -III is used and, as a hydrophilic polymer, polyvinyl pyrrolidone is used and both of them are dissolved in a polar org. solvent to prepare a dope which is, in turn, cast onto a sheet like or tubular support while the coated support is subsequently immersed in a coagulant bath to prepare an asymmetric separation semipermeable membrane by sol-gel phase conversion. By this method, an asymmetric structure, such that the hydrophilic polymer is present in the dense layer side of the membrane but no hydrophilic polymer is present in the porous layer side of the membrane back surface, is obtained and the water permeability of the formed membrane is improved while the heat resistance and chemical resistance of the aromatic polysulfone are kept.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Background) The present invention relates to a semipermeable membrane for asymmetric separation having a novel structure. In recent years, reverse osmosis and ultrafiltration methods, which are separation technologies using semipermeable membranes, have been put into practical use in various fields, and semipermeable membranes made from materials suitable for each of these various uses are applied. ing. In particular, polyacrylonitrile-based, cellulose-based, and polysulfone-based materials are well-known as materials for semipermeable membranes used in ultraf-filtration methods.

Among these membrane materials, aromatic polysulfone-based membranes are attracting attention as they have high mechanical strength and excellent heat resistance and chemical resistance.

(Prior art and its disadvantages) However, aromatic polysulfone-based arborescent material has low hydrophilicity and is a material that is difficult to wet with water. The water permeation rate is significantly lower than that of membranes, and the f-permeability rate is poor.

Therefore, various attempts have been made to improve the water permeability of aromatic polysulfone separation membranes.

For example, JP-A-58-104940 discloses a polysulfone separation membrane containing polyvinylpyrrolidone with a molecular weight of 100,000 or more and a method for producing the same. However, in this method, a hydrophilic polymer having a molecular weight of 100,000 or more is added to a molten solution (called a dope), which increases the polymer density of the dope. The hydrophilic polymer added to the polysulfone separation membrane remains intact throughout the membrane, and is not removed even during subsequent use, resulting in an extremely dense structure and a decrease in water permeation rate. .

On the other hand, JP-A-54-26283 discloses a method in which polyethylene glycol having a molecular weight comparable to that of an oligomer is added to a polysulfone solution and used as a dope.

However, this method uses water as a coagulation bath for film formation, and oligomer-level polyethylene glyfur is completely eluted into the water without remaining in the film.
The hydrophilicity of the polysulfone membrane is not substantially increased, and no significant improvement in water permeation rate can be expected.

Also, in the Journal of Polymer Science Vol. 20 (1976) 2377-2394, polyvinylpyrrolidone, a hydrophilic polymer with a molecular weight of 10,000 to 40,000, is incorporated in a large amount into a membrane-forming dope to form hollow fiber membranes. Although there have been reports aimed at improving spinnability, in this case no dense layer is formed on the membrane surface, and the asymmetric structure as in the present invention is not achieved.

(Structure of the present invention) The present inventors have solved the above-mentioned problems and have developed a separated phase semi-membrane having an asymmetric structure mainly composed of a hydrophobic polymer substance with high f′ permeability and high water permeation rate. As a result of intensive studies, we have developed a new structure in which hydrophilic polymers exist within 5 μm from the membrane surface on the R-dense layer side in the membrane thickness direction of the semipermeable membrane for separation, and do not exist from 5 μm to the back surface. We have invented an asymmetric membrane with an asymmetrical content.

In other words, the present invention is a semipermeable separation membrane mainly composed of a hydrophobic polymer substance having an asymmetric structure with a dense layer on the surface and a porous layer on the back side, in which only the dense layer side is composed of the hydrophobic polymer substance. A semipermeable membrane for separation characterized by being made of a mixture with a hydrophilic polymeric substance.

The hydrophobic polymer referred to in the present invention has the following formula (I) ~ @)
Typical examples are aromatic boria and sulfone polymers having the structure H3. Polyvinylpyrrolidone is a typical example of the water-soluble polymer used in the present invention. Optimal is a polymer with an average molecular weight of 70,000 or less and 10,000 or more. If the average molecular weight exceeds 70,000, the polymer density of the membrane becomes too large, as described above, and the water permeation rate actually decreases. Furthermore, even with an average molecular weight of 70,000 or less, molecular weights on the order of oligomers, that is, molecular weights on the order of several thousand, are too water-soluble and are almost completely extracted when immersed in water during the film forming process.
A case in which the hydrophilicity and water permeability of the membrane is improved by aromatic polysulfone and the hydrophilic polymer is polyvinylpyrrolidone will be described in detail.

The dope composition for producing a semipermeable membrane for separation preferably contains 3% by weight or less of the above-mentioned polyvinylpyrrolidone based on the total weight of the dope. If the concentration exceeds 3% by weight, the first
As shown in the figure, destruction of the membrane structure is observed, which is inconvenient.

Further, it is desirable to dissolve the hydrophilic polymer and the hydrophobic polymer in the polar organic solvent in an amount of 10 to 30% by weight based on the total weight of the dope, which is the total weight of the hydrophilic polymer and hydrophobic polymer in the dope used in the present invention.

Examples of the polar organic solvent include N,N-dimethylacetamide, N,N-dimethylformamide, and N-methyl-
2-pyrrolidone, dimethyl sulfoxide, sulfolane,
Examples include 2-pyrrolidone, hexamethylphosphor SF', etc., but the present invention is not limited thereto. Also, for such polar organic solvents,
It is also possible to add a non-solvent of either a hydrophobic polymer or a hydrophilic polymer, or to add an electrolyte.

In forming the semipermeable membrane for asymmetric separation of the present invention from the dope described below, it is possible to employ a method for producing a semipermeable membrane for asymmetric separation, which is conventionally used for −n=6.

To form a separation membrane in the form of a sheet or tube, a dope is applied to a thickness of several tens of microns to several hundred microns on a suitable support (for example, a glass plate or tube, nonwoven fabric, cloth, etc.) in the form of a sheet or tube. Casting by an appropriate method,
Thereafter, the coagulant bath Ki is crushed to produce a semipermeable membrane for asymmetric separation by sol-gel phase conversion. Furthermore, by spinning the fibers through a doped hollow fiber forming nozzle using a known method, it is possible to produce an asymmetrical hollow system membrane for division.

The coagulant used in film formation is a non-solvent for aromatic polysulfone, which is easily miscible with polar organic solvents, such as water, aqueous solutions of electrolytes such as salt and surfactants, dilute aqueous solutions of polar organic solvents, or aromatic polysulfone. Examples include non-solvents and water-soluble versions thereof, but water is particularly commonly used.

The characteristics of the semipermeable membrane for asymmetric separation of the present invention are manifested by the membrane formation process 1 described above. That is, its characteristic feature is an asymmetric structure in which the presence of a hydrophilic polymer is observed on the membrane surface by Fourier transform infrared absorption A and TR spectrum analysis, but its presence is not observed on the back surface of the membrane.

Figure 2 shows the Fourier transform infrared absorption ATR spectrum (hereinafter referred to as FT-IRATR spectrum) of the membrane surface of the asymmetric membrane of the present invention. The vertical axis is the transmittance (%), and the horizontal axis is the wave number (crn- '). In this figure, the amide I absorption band 1660 crn-' (arrow in Figure 2) shows the absorption of the carbonyl group of the amide of the hydrophilic polymer polyvinylpyrrolidone.
is clearly recognized. - Figure 3 shows the spectrum of the back side of the same film, but similar absorption was not observed at all.

(Effects of the present invention) It is clear that by making the membrane surface side extremely hydrophilic, the aromatic polysulfone-based semipermeable membrane for separation, which is originally hydrophobic, has become extremely hydrophilic. Performance is improved. Moreover, the excellent heat resistance and chemical resistance that are characteristic of aromatic polysulfone are maintained, so that conventional semipermeable membranes for separation based on hydrophilic polymers, such as semipermeable membranes for separation made of cellulose acetate, can withstand them. It can be effectively used for membrane separation operations under harsh conditions.

Next, the present invention will be specifically explained with reference to Examples. It is defined in a patent characterized by the Lp value after 7 hours of hearing loss.

Example 1 Aromatic polysulfone of formula (1) (trade name Victrcx
30.0pICE Co., Ltd. sea bream) 18 parts by weight and polyvinylpyrrolidone (hereinafter abbreviated as PVP) with an average molecular weight of 40,000.
C, manufactured by lt Co., Ltd.) was dissolved in 80 parts by weight of a mixed solvent mainly containing 2-pyrrolidone. The viscosity of this dope is 2
It was 14,000 centivoids at 5°C. This was cast onto a polyester non-woven fabric to a thickness of 150 μm, left in a room temperature atmosphere for 20 seconds, and then immersed in water at 10°C to obtain a semipermeable membrane for asymmetric separation. The obtained nonwoven fabric-reinforced asymmetric semipermeable membrane was further immersed in hot water at 90° C. for 15 minutes to completely remove the solvent. The Lp of this film is 4.5 nl
/ m”・day-Kg/crux (25°C), the reduction rate β was 42%. Also, RO was 100%. Also, the PVP content of the film determined from elemental analysis was 45%.
Met.

("Example 4') When the asymmetric separation membrane of Example 1 was immersed in hot water at 90°C for 50 hours, Lz was 4.F3Bdl??I'-day・Kg
/cm, β was 37%, RO was 100%, and no deterioration of membrane performance was observed. The pvr' content is also 48%.
Substantially no elution of PVP was observed.

Comparative Example 1 A film was formed in the same manner as in Example 1 except that PVP (manufactured by Wako Pure Chemical Industries, Ltd.) having an average molecular weight of 700,000 was used. R of the obtained film
O was 100%, but L was 101 quiet/? ? 72・
It decreased to 7 days/cm.

Comparative Example 2 PVP (manufactured by Aldrich) with an average molecular weight of 40,000 was
A film was formed in the same manner as in Example 1 except that 2 parts by weight and 778 parts by weight of the mixed solvent were used. The RO of the obtained membrane was 96%
The Lp also decreased to 2.72 nl/+r?・Japanese・K
It decreased to 910d.

Comparative Example 3 A film was formed in the same manner as in Example 1, except that PVP was not added and the mixed solvent was 82 parts by weight. The resulting membrane arch is 4.
77 nl/n?・Japanese/Ky/cr1. Although the Ro rejection rate was 100%, the decrease rate β was 266%, and the water permeation rate decreased significantly over time.

Example 3 Example 1 except that a glass plate with a smooth surface is used as the support.
The film was formed in the same manner as above. When this unreinforced asymmetric separation membrane was thoroughly dried and the ATR-IR spectrum of the membrane surface was measured, the result shown in Figure 2 was obtained. The absorption band of PVP is clear. However, when the A, TR-IR spectrum of the back surface of the same film was measured, no PVP absorption band was observed as shown in FIG.

Furthermore, FIG. 4 is an electron micrograph showing the cross-sectional structure of the semipermeable membrane obtained here, and no destruction of the membrane structure as shown in FIG. 1 is observed.

Example 4 Poly(2-vinylpyridine) (Al
A film was formed in the same manner as in Example 1, except that the film was manufactured by Dric++ Co., Ltd.). The resulting membrane arch is 7.56 m'/n?
・It showed a large value of K4/crl, and the RO was 100%. The polyvinylpyridine content of the film determined from elemental analysis was 29%.

Example 5 The membrane of Example 4 was produced using a glass plate with a smooth surface as a support. ATR on the membrane surface after thorough water washing and drying
- When the IR spectrum was measured, an absorption band of the pyridine ring was observed at 1440 cm-' (arrow in FIG. 5) as shown in FIG. However, ATR-I on the back side of the same membrane
When the R spectrum was measured, as shown in Figure 6, 14
No absorption band of pyridine ring was observed at 40α-1.

that's all

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph of a cross section of a membrane prepared in Comparative Example 2 using a glass plate with a smooth surface as a support. Figure 2 shows Ii'T-IR of the surface of the film prepared in Example 3.
This is an ATR spectrum. FIG. 3 is an FT-RATR spectrum of the back side of the same film. FIG. 4 is a scanning electron micrograph of a cross section of the membrane obtained in Example 3. FIG. 5 is an FT-IRATR spectrum of the front surface of the membrane obtained in Example 5, and FIG. 6 is an FT-IRATR spectrum of the back surface of the membrane obtained in Example 5. Patent Applicant: Daicel Chemical Industry Co., Ltd. Figure 1 Figure 4 Procedural Amendment (Voluntary)

Claims (5)

[Claims] (1) A separation semipermeable membrane mainly composed of a hydrophobic polymer substance with an asymmetric structure in which the surface is a dense layer and the back side is a porous layer, and only the dense layer side is hydrophilic with the hydrophobic polymer substance. A semipermeable membrane for separation characterized by being made of a mixture with a polymeric substance. (2) The hydrophobic polymer has the structural formula (I), (II) or (II)
A semipermeable membrane for separation according to claim 1, characterized in that it is an aromatic polysulfone having any one repeating unit of I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼
...(I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(II) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(III) (3) Claim 1, characterized in that the hydrophilic polymer is polyvinylpyrrolidone with an average molecular weight of 70,000 or less.
Semipermeable membrane for separation as described in section. (4) The semipermeable membrane for separation according to claim 1, wherein the hydrophilic polymer is polyvinylpyridine or a vinylpyridine copolymer. (5) The separating half according to claim 1, in which a polymer solution containing a hydrophilic polymer of 0.5% by weight or more and 3% by weight or less based on the total weight of the solution is used as the membrane forming solution. Permeable membrane.