JPS6238205A - Semi-permeable membrane for separation - Google Patents

Abstract

PURPOSE:To produce a semi-permeable membrane for separation, hydrophilic for a long time, by making only the fine layer of membrane face asymmetric structure consisting of mixture of hydrophobic high polymer substance and hydrophilic high polymer substance treated to be insoluble. CONSTITUTION:The dope solution, in which such hydrophilic high polymers such as aromatic polysulfone, polyvinyl pyrrolidone and the like are solved with 2-pyrrolidone and the like, is flow-stretched over a nonwoven fabric, dipped in water to produce an asymmetric structure membrane and then dipped in hot water to produce a precursor membrane as desolvation agent. Said mem brane is then dipped in the solution of ammonium persulfate and the like and polyvinyl pyrrolidone is treated to be insoluble. THrough said process, a semi- permeable membrane for separation, the surface of which is a mixture of hydro phobic high polymer and insoluble hydrophilic high polymer and the backside made of porous bed of hydrophobic high polymer, is produced.

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 techniques using semipermeable membranes, have been put into practical use in various fields. has been done. Particularly, well-known materials for semipermeable membranes used in the ultraviolet filtration method include polyacrylonitrile, cellulose, and polysulfone.

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 drawbacks) However, aromatic polysulfone resin has low hydrophilicity and is a material that is difficult to wet with water. The water permeation rate is significantly lower than that of , and the f-perturbation rate is poor.

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

For example, JP-A-58-104940 discloses a polysulfone separation membrane containing polyvinylpyrrolidone having a molecular weight of 100,000 or more and a method for producing the same. However, in this method of adding a hydrophilic polymer having a molecular weight of 100,000 or more to a film-forming solution (called a dope), the polymer density of the dope increases, and the polysulfone film formed from such a dope increases. In system separation membranes, the added hydrophilic polymer remains in the entire membrane and is not removed even during subsequent use, resulting in an extremely dense structure that actually reduces the 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 glycol does not remain in the film and completely dissolves into the water.
The hydrophilicity of the polysulfone membrane is not substantially increased, and no significant improvement in water permeation rate can be expected.

Keita Journal Op Applied Polymer Science 20
Volume (1976) 2377-2394 contains molecules! 10,000~
There has been a report that attempts to improve the spinnability of hollow fiber membranes by incorporating a large amount of polyvinylpyrrolidone as a hydrophilic polymer into a membrane-forming dope, but in this case, a dense layer was formed on the membrane surface. t
No.

(Structure of the present invention) The present inventors solved the above-mentioned problems and developed a biomembrane for separation having an asymmetric structure mainly composed of a hydrophobic polymer substance with good r-permeability and high water permeation rate. As a result of intensive studies, we found that hydrophilic polymers exist within 5 μm from the membrane surface on the dense layer side in the membrane thickness direction of the semipermeable membrane for separation, and
We have invented an asymmetric separation membrane with a novel structure in which this does not exist on the back surface 1 from μm.

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 comprising a mixture with an insolubilized hydrophilic polymer substance.

In the present invention, the hydrophobic polymer has the following formula (1-(r)
An aromatic polysulfone polymer having the structure l) is representative.

+0+5O7-...(1) CR2 (x)0-@=S o, -@)-0-...-([1) As the water-soluble polymer to be insolubilized used in the present invention, polyvinylpyrrolidone is used. It is a typical water-soluble polymer obtained by polymerizing vinylpyrrolidone, and the optimal one is one 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 mentioned above, and the water permeation rate is rather reduced.

In addition, even if the average molecular weight is 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 membrane forming process, making the membrane hydrophilic and water permeable. Performance is not improved.

Next, as one embodiment of the present invention, a case in which the hydrophobic polymer is aromatic polysulfone and the hydrophilic polymer is insolubilized polyvinylpyrrolidone will be described in detail.

The dope composition for producing the precursor membrane for the semipermeable separation membrane of the present invention preferably contains 3 or less times of polyvinylpyrrolidone that has not been insolubilized based on the total weight of the dope. If it exceeds 7% by weight, the membrane structure will be destroyed, which is disadvantageous.

``Dissolve in a polar organic solvent such that the total polymer weight of the uninsolubilized hydrophilic polymer and hydrophobic polymer in the dope used during ``ffcff'' is 10 to 30 times the total weight of the dope. That's one thing.

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 and hexamethylphosphoramide, but are not particularly limited to these. It is also possible to add a non-solvent of either a hydrophobic polymer or a hydrophilic polymer that has not been insolubilized to such a polar organic solvent, or to add an electrolyte or the like.

In forming the precursor membrane of the semipermeable membrane for asymmetric separation of the present invention from the dope described above, a conventional method for producing a semipermeable membrane for asymmetric separation can be employed.

To form a separation membrane in the form of a sheet or tube, the dope is poured onto a suitable support (for example, a glass plate or tube, nonwoven fabric, cloth, etc.) in the form of a sheet or tube. The dope is cast in a range of 100 microns by an appropriate method, and then immersed in a coagulant bath to produce an asymmetric membrane by sol-gel phase conversion.Also, by spinning the dope through a hollow fiber forming nozzle in a known manner. , it is possible to produce asymmetric hollow fiber membranes.

The coagulant used in film formation is a non-solvent for aromatic polysulfone that easily mixes with polar organic solvents, such as water, a water bath solution of electrolytes such as salt or surfactants, dilute aqueous solutions of polar organic solvents, or aromatic polysulfone. Examples include non-bath additives or water bath solutions thereof, but water is particularly commonly used.

The asymmetric membrane obtained by the membrane forming method described above is -! The basic structure of the semipermeable separation membrane of the present invention is an asymmetric membrane in which only the surface dense layer is composed of a mixture of hydrophobic and hydrophilic polymers. It has a structure. However, in this membrane, the hydrophilic polymer is essentially not insolubilized, so if it is exposed to high-temperature hot water or solvent cleaning, or used for long-term water treatment, the hydrophilic polymer in the membrane will gradually disappear. This results in a disadvantage that hydrophilicity decreases due to elution and C-permeability also decreases.

Therefore, in order to obtain an inventive semipermeable membrane for separation, it is necessary to insolubilize the above precursor membrane under conditions that insolubilize the hydrophilic polymer in the membrane.

When polyvinylpyrrolidone is used, the insolubilization treatment is performed under known insolubilization treatment conditions for polyvinylpyrrolidone, such as immersing the precursor film in an aqueous solution of a strong base or persulfate and heating it at 90 to 100°C. Although a method of treating body membranes is mentioned, other methods such as crosslinking agents and radiation irradiation may also be used.

(Effects of the present invention) The semipermeable membrane for separation of the present invention manufactured in this way has an extremely hydrophilic membrane surface side, and this hydrophilicity can be maintained even by hot water washing or long-term water treatment. It has the characteristic that there is almost no deterioration, and therefore the initial high water permeability is not impaired. Moreover, the excellent heat resistance and chemical resistance characteristic of aromatic polysulfo/ are maintained, so conventional semipermeable membranes for separation based on hydrophilic polymers, such as semipermeable membranes for separation made of cellulose acetate, are resistant. It can be effectively used for membrane separation operations under harsh conditions that would otherwise be impossible.

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

Example 1 Aromatic polysulfone of formula (1) (trade name: Vlctrex
300p manufactured by ICI) and 18 parts by weight of polyvinylpyrrolidone (hereinafter abbreviated as PvP) with an average molecular IL of 40,000.
(manufactured by Company H) was dissolved in 80 parts by weight of a mixed solvent mainly containing 2-pyrrolidone. The viscosity of this dope is 1 at 25°C.
It was 4000 centiboise. This was cast onto a polyester nonwoven fabric to a thickness of 150 μm, and
After being left for 0 seconds, it was immersed in water at 10°C to obtain an asymmetric membrane. The asymmetric membrane reinforced with the obtained nonwoven fabric was further heated at 90°C.
It was immersed in hot water for 15 minutes to completely remove the solvent. The Lo of this film
Is it 4.5? ! 7ml/day/+ was 9/i, and the rate of decrease β was 4.2ch.

In addition, the rate for crows was 100%. In addition, the film 0)PVP content determined from elemental analysis was 7.2% (N content was 0.91%).
)Met.

This precursor film was immersed in an aqueous solution containing 5 parts by weight of ammonium persulfate and heated to 90° C. for 30 minutes.

L of the obtained asymmetric membrane for separation (1, is 5.5 days)
The rate of decrease β in kg was 3.1%. Also, the horse is 94
%Met. The N content of the film determined from elemental analysis is 0.9
It was 0chi.

Example 2 The asymmetric separation membrane of Example 1 was immersed in an aqueous solution containing 60 parts by weight of acetone at room temperature for 5 days. N of the membrane taken out
The content was found to be 0.85% by elemental analysis, indicating that the insolubilization of PvP in the film was almost complete.

Furthermore, there was almost no change in membrane performance.

Comparative Example 1 When the precursor film of Example 1 was treated in the same manner as in Example 2, the N content in the film was reduced to 0.07%, and the film performance was also significantly deteriorated.

Comparative Example 2 A film was formed in the same manner as in Example 1 except that PVP was not added and the mixed solvent was changed to 82 parts by weight, and then treated in the same manner as in Example 1 with an aqueous ammonium persulfate solution. Lll of the obtained film is 4. s 7? ! ”/ze・day・kg/li
,% was 100%, but the decrease rate β was 27%,
Water permeation rate decreases significantly over time. The N content of this film is 0.
It was 0.6%.

Example 3 Example 1 except that a glass plate with a smooth surface is used as the support.
A precursor film was formed in the same manner as described above. This asymmetric membrane without reinforcing material was subjected to insolubilization treatment in the same manner as in Example 1. This film was sufficiently dried and the total reflection infrared absorption (abbreviated as ATR-IR) spectrum of the film surface was measured, and the result shown in FIG. 1 was obtained.

The absorption of carbonyl groups derived from insolubilized PvP is 17
00 cm-1. However, A on the back side of the same membrane
When the TR-IR spectrum was measured, as shown in FIG. 2, no absorption of carbonyl groups was observed.

[Brief explanation of the drawing]

FIG. 1 is an ATR-IR spectrum of the surface of the asymmetric semipermeable membrane for separation of the present invention prepared in Example 3. FIG. 2 is an ATR-IR spectrum of the back surface of the mesentery.

Claims (4)

[Claims] (1) A semipermeable membrane for separation mainly made of a hydrophobic polymer substance with an asymmetric structure in which the front side is a dense layer and the back side is a porous layer, and only the dense layer side is insolubilized with the hydrophobic polymer substance. A semipermeable membrane for separation, characterized in that it is made of a mixture with a hydrophilic polymeric substance. (2) The hydrophobic polymer has the structural formula (I), (II) or (II)
The semipermeable membrane for separation according to claim 1, which 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) The semipermeable membrane for separation according to claim 1, wherein the hydrophilic polymer is insolubilized polyvinylpyrrolidone having an average molecular weight of 70,000 or less. (4) After wet film forming using a polymer solution containing a hydrophilic polymer that has not been insolubilized in an amount of 0.5% to 3% by weight based on the total weight of the solution as a film forming solution, The semipermeable membrane for separation according to claim 1, wherein the membrane (referred to as a precursor membrane) is treated under conditions to insolubilize the hydrophilic polymer.