JPS6051503A - Permselective membrane - Google Patents

Abstract

PURPOSE:To provide a permselective membrane having film forming property, chemical resistance and org. solvent resistance and excellent in filtering efficiency, obtained by using aromatic polyetherimide comprising a specific repeating unit as a membrane material. CONSTITUTION:Aromatic polyetherimide being a polymer having a repeating unit represented by general formula (1) (wherein Ar1 and Ar2 are bivalent aromatic group) is mixed with a good solvent such as N-methyl-2-pyrrolidone, a metal salt such as lithium chloride and a swelling agent such as ethylene glycol to form a resin solution. This solution is cast in a membrane form while the cast membrane is immersed in a coagulation liquid, which is the non-solvent of the resin and compatible with the solvent of the resin solution, to obtain a permselective membrane having easy film forming property, high water permeability and characteristics such as excellent heat resistance and chemical resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a selectively permeable membrane whose membrane material is made of aromatic polyetherimide.
Another object of the present invention is to provide a selectively permeable membrane having high filtration efficiency and excellent chemical resistance and organic solvent resistance.

Conventionally, cellulose acetate has been typically used as the material for selectively permeable membranes for membrane separation of liquid mixtures.While this membrane exhibits high fractionation and water permeability, it has poor heat resistance and pH resistance. , organic solvent resistance, bacterial resistance, and mechanical strength are not sufficient. Various polymers have been studied to solve these problems, but all of them have insufficient permeability or are difficult to form into films. New problems such as these have arisen, and further investigation is desired.For example, polyamide has been proposed, but its heat resistance, acid resistance, and alkali resistance are still insufficient.

Polysulfone, i.e. Polymers consisting of repeating units have been proposed.

This material is soluble in specific solvents, so it is easy to form a film, and the film has excellent heat resistance, acid resistance, and alkali resistance, but it has insufficient resistance to organic solvents, and due to its own hydrophobicity. When a membrane with a small pore size is used, a problem arises in that water permeation becomes small.

polyether sulfone, i.e. The use of polymers consisting of repeating units has also been proposed.

This product has the characteristics of polysulfone processing, organic solvent resistance,
Although the hydrophilicity has been slightly improved, it is still not sufficient. Polyimide polymers have also been proposed. Although this material generally has extremely excellent heat resistance and organic solvent resistance, on the other hand, this causes the problem of complicating the film forming process. For example, a method is used in which an organic solvent-soluble polyamic acid is synthesized from an aromatic dicarboxylic acid anhydride and an aromatic diamine, a film is formed using the solution, and then a ring-closing reaction is performed to form an aromatic polyimide film. However, this method has problems such as ensuring that the ring-closing reaction is completely carried out and voids due to the generation of condensed water, and inevitably requires strict process control.

As a result of research aimed at solving the above-mentioned problems with conventional selectively permeable membranes, the present invention found that using polyetherimide as a membrane material provides a balance in membrane formability and organic solvent resistance. This was completed after conducting various studies based on knowledge.

The present invention is a liquid selective permeable membrane characterized by comprising a polymer whose repeating units have the general formula (wherein Ar3 and Ar2 represent divalent aromatic groups).

Hereinafter, a polymer consisting of repeating units of structure (III) will be referred to as polyetherimide.

The polyetherimide used in the present invention has a heat distortion temperature of 18.6 k as a polymer in terms of film formability and heat resistance.
There is no particular limitation on the degree of polymerization as long as the degree of polymerization is sufficient to exceed 150° C. at a load of g/crA. Preferably, a polymer having an average degree of polymerization of 3QOOO or more is used. Some aromatic rings or alkyl groups in the main chain are alkyl groups, norogen, hydroxyl groups, thioalcohols, aldehyde groups, carboxyl groups, vinyl groups, allyl groups, aryl groups, amine groups, amide groups, sulfone groups, and nitro groups. , acid amide, ketoxime, epoxy or silanol groups, or compounds containing these functional groups can also be used. It is still possible to use these functional groups in crosslinking reactions to improve membrane properties. Mixtures with other polymers such as other polyimide polymers can also be used. In addition to mixing with polymers with good compatibility, special membranes can be created by forming a film using a mixture with a polymer with poor compatibility, for example, where the mixing ratio is limited at temperatures between room temperature and 80°C. It is also possible to create an organization. Examples of polymers with insufficient compatibility include polysulfone and polyethersulfone. It can also be mixed with other compounds for crosslinking and forming a coating layer.

Furthermore, the polyetherimide used in the present invention can also be used as a graft, block or random copolymer with components other than those having the above structure.

It is also possible to use as copolymerization components those capable of crosslinking or elimination reactions.

The selectively permeable membrane of the present invention may have any shape, such as a flat membrane, a hollow fiber membrane, or a composite membrane using other sheet substrates or porous materials as a support, and there are no limitations on the molecular weight cutoff or water permeability. , as described below, is available for a wide range of fractionation membranes. Regarding membrane structure, membranes whose surface layer is covered with a so-called skin layer so dense that no pores can be seen even under an electron microscope, membranes which are not covered with a skin layer, and membranes whose interior is porous are also finger-shaped. It is also possible to use different types depending on the purpose. It is also possible to form a composite membrane by bonding functional groups or compounds to the membrane surface, or by forming a layer made of other compounds or resin. In order to improve the properties, it is also possible to use a material that is subjected to a crosslinking reaction on the surface layer of the film.

Although any method can be used for manufacturing the selectively permeable membrane of the present invention, wet membrane formation is particularly preferably used.

That is, a resin solution consisting of polyetherimide, a good solvent for polyetherimide, a swelling agent, etc. is cast into a film, and this is turned into a coagulable liquid that is a non-solvent of the resin and is compatible with the solvent of the resin solution. This is a method of producing a selectively permeable membrane by immersion, and various membrane forming conditions such as resin solution, coagulation liquid composition, temperature, etc. are known depending on the membrane to be designed. If necessary, a good solvent or swelling agent for the resin may be included in the coagulation solution, or a method of sequentially immersing the resin in multiple coagulation solutions may be used. In order to create a porous permselective membrane, a method is known in which a substance to be dissolved and extracted in a subsequent process is mixed into a resin solution, and this method can also be used. Good solvents for polyetherimide include N-methyl-2-pyrrolidone, and swelling agents include metal salts such as lithium chloride, as well as alcohols such as ethylene carbonate and ethylene glycol.

The selective permeable membrane of the present invention has high water permeability and excellent heat resistance, and can achieve a wide range of fractionation, and is more resistant than conventional permeable membranes made of polysulfone and polyethersulfone. It has excellent organic solvent properties and can be easily formed without the need for a step of ring-closing reaction unlike conventional polyimide films. It also has excellent chemical properties comparable to polysulfone and polyethersulfone. Previously, selectively permeable membranes made of polyimide tended to be slightly sensitive to basicity.

This is thought to be because the ring-closing reaction after film formation is actually not complete, and the remaining unreacted amic acid portion deteriorates.

However, the reason why the polyetherimide used in the present invention is also excellent in base resistance is thought to be because the ring-closing reaction has already been substantially completed before film formation. As described above, the polyetherimide liquid-selective permeable membrane according to the present invention has many excellent features and is easy to form, so it can be used for applications such as precision filtration, ultra filtration, and reverse osmosis filtration. It is expected that it will work effectively in the fields of concentration and purification.

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

Example 1 N-
The mixture was added to a mixed solution of 114.8 parts of methyl-2-pyrrolidone and 49.2 parts of ethylene carbonate and dissolved at 95°C over 4 hours. 12 parts of ethylene glycol was added to this, and the mixture was further uniformly dissolved at 80° C. for 4 hours, followed by defoaming to prepare a dope solution. This liquid becomes cloudy when the temperature drops below 45°C. Next, 15 parts of water, 42 parts of N-methyl-2-pyrrolidone,
A coagulation solution consisting of 42.5 parts of ethylene carbonate is prepared.

The dope solution was cast onto a stainless steel belt which was also maintained at 60°C, and immediately immersed in a coagulating solution at 20°C to obtain a selectively permeable membrane with a thickness of 67μ. When the cross-sectional structure of the membrane was observed using an optical microscope, it was found that the finger-like structure was not developed and it was porous. The water permeability of the membrane is 5070 (t/
rr?・hr-atm) was passed through blue dextran. The surface of this membrane is not substantially covered with a skin layer and can be used as a selectively permeable membrane for precision filtration and plasma separation.

Example 2 12 parts of the same polyetherimide used in Example 1,
A mixed solution consisting of 85 parts of N-methyl-2-pyrrolidone and 3 parts of lithium chloride was uniformly dissolved at 95° C. over 4 hours, and then defoamed to prepare a dope solution. 25 dope liquid
The sample was cast onto a stainless steel belt kept at 25° C. and immediately immersed in water at 18° C. to obtain a selectively permeable membrane with a thickness of 85 μm. When the cross-sectional structure of the film was observed using an optical microscope, development of finger-like structures was observed. The water permeability of the membrane is 2
200 (t/m"·hr-atm) and ζ/ζ. There is a skin layer on the surface of this membrane, and it can be used as an ultrafiltration membrane.

Example 3 20 parts of the same polyetherimide used in Example 1,
A dope solution was prepared by uniformly dissolving 3 parts of ethylene glycol and 77 parts of N-methyl-2-pyrrolidone at 95 DEG C. over 4 hours for 5W and defoaming. The dope solution was maintained at 20°C, cast into a 60°C stainless steel bell), and immediately passed through a tunnel furnace at 120°C for 60 seconds. Further, it was immediately immersed in tertiary butyl alcohol at 20°C, and after 30 seconds, immersed in water at 18°C and left as it was for 100 minutes to obtain a selectively permeable membrane. Using 5% by weight sucrose aqueous solution, 25℃, 60k
When the filtration performance was measured under the conditions of y/cJ, the water permeability was 4
At 4t/d·hr, the inhibition rate of sucrose was 100t.

This membrane can be used as a reverse osmosis filtration membrane.

Note that the rejection rate was measured based on the refractive index.

Example 4 The same polyetherimide used in Example 1 was
The mixture was uniformly dissolved in methyl 2-pyrrolidone at 100° C. for 3 hours and then defoamed to obtain a dope solution with a resin concentration of 20% by weight. While keeping the dope solution at 20°C, it was cast onto a glass plate also at 20°C, and immediately immersed in water at 18°C to give a temperature of 90-1.
A 20μ selectively permeable membrane was obtained. 25℃, 10ky/C4
Table 1 shows the water permeability of the membrane and the Flux s rejection rate in a 05% by weight aqueous solution of Dextran T-70 under the following conditions.

Comparative Example 1 Polysulfone (UCCff, P-1700), polyethersulfone (manufactured by ICI, 600p and 200p)
were each dissolved in N-methyl-2-pyrrolidone and defoamed to prepare a dope solution with a resin concentration of 20% by weight. A film was formed under the same conditions as in Example 4, at 25°C and 40 kf/ca! Similar measurements were carried out under the following conditions. The results are summarized in Table 1. In this way, the selectively permeable membrane made of polyetherimide
It can be seen that higher water permeability can be obtained compared to polysulfone and polyethersulfone.

Table 1 Comparison of water permeability a) Unit 1/n? "hr-atm b) Unit C) Polyetherimide was measured under the conditions of 25°C 10kg/CrA. Others were measured under the condition of 25°C 40kg/CrA.

Example 5 A polyetherimide/N-methyl-2-pyrrolidone solution having the same resin concentration of 20 weight as used in Example 4 was defoamed to obtain a dope solution. A dope solution at 20°C was cast onto a stainless steel belt at 25°C, and immediately immersed in water at 22°C to obtain a selectively permeable membrane. Next, the obtained permeable membrane was heated to 18°C.
The film was immersed in methanol for 10 minutes, then cyclohexane at 18°C for 10 minutes, and then dried in a dryer at 80°C for 30 minutes to obtain a dry film. The dried film was cut into 4×4 crrL squares, immersed in various organic solvents at room temperature for 48 hours, and changes in appearance were observed.

The results are shown in Table 2.

Comparative Example 2 Polysulfone (manufactured by UCC, P17
00), polyether sulfone (manufactured by ICI, 600P)
A dry film was prepared and a similar appearance test for organic solvent resistance was conducted.

The results are summarized in Table 2.

Table 2 Organic solvent resistance Appearance test results A: No change in appearance, B: Dimensional change and shape change due to shrinkage observed, C:
was almost dissolved.

It can thus be seen that polyetherimide membranes have greater resistance to many organic solvents than polysulfone and polyethersulfone membranes.

Example 6 Furthermore, the influence of organic solvent resistance on alcohol permeability was observed. A dried polyneedleimide selectively permeable membrane was prepared under the same conditions as in Example 5, and soaked in various solvents at room temperature for 100 hours. Next, each membrane was immersed in methyl alcohol for 5 to 10 minutes, and the amount of methyl alcohol permeation was measured at 25° C. and latm.

The results are shown in Table 3.

Comparative Example 3 A dry film of polysulfone or polyethersulfone prepared in the same manner as in Comparative Example 2 was immersed in an organic solvent under the same conditions as in Example 6, and then immersed in methyl alcohol for 10 minutes, and then immersed at 25°C and 1 atm. The permeation amount of methyl alcohol was measured under these conditions.

The results are summarized in Table 3.

In this way, it can be seen that polyetherimide has superior organic solvent resistance compared to polysulfone and polyethersulfone in terms of alcohol permeability. Table 3: Change in methanol permeability after organic solvent treatment A; The amount of methanol permeable is up to 1.1 times that of the treated membrane. Below, a; t, i
~2.0 times, C, 2.0-10.0 times, D; 10-15
Double, E: Indicates that measurement is not possible due to membrane deterioration.

Example 7 The same dry polyetherimide selectively permeable membrane used in Example 5 was soaked in various acids and alkalis for 100 hours at room temperature. Next, after immersion in methyl alcohol for 10 minutes, permeation J1 of methyl alcohol was performed at 25° C. and 1 atm.

The results are shown in Table M4.

Comparative Example 4 A dried membrane of the same polysulfone and polynywool sulfone as in Comparative Example 2 was treated under the same conditions as in Example 7, and the permeation amount of methyl alcohol was measured.

The results are summarized in Table 4.

Thus, it can be seen that the polyetherimide film has chemical resistance comparable to polysulfone and polyethersulfone, which have excellent acid resistance and one-sided alkalinity.

Table 4: Change in clear alcohol content after chemical treatment (Note) A-E
is the same as the criteria in Table 3.

Example 8 12 parts of the same polyetherimide used in Example 1 was uniformly dissolved in 88 parts of N-methyl-2-pyrrolidone at 95° C. over 3 hours, and defoamed to obtain a dope solution. This dope solution was dried under the same conditions as in Example 5 to produce a polyetherimide selective permeable membrane. This was immersed in the same various organic solvents as in Example 6 at room temperature for 24 hours. Next, it was immersed in methyl alcohol for 5 to 10 minutes, and the amount of water permeation was measured at 25° C. and latm.

The results are shown in Table 5.

Comparative Example 5 The same polysulfone and polyether sulfone used in Comparative Example 2 were mixed with N having a resin concentration of 12% by weight in the same manner as in Example 8.
-Methyl-2-pyrrolidone solution was prepared, and a dried film was prepared under the same conditions as in Example 5 using this as a dope solution. Next, it was immersed in the same various organic solvents as in Example 8 under the same conditions, and after being subjected to the same treatment, the amount of water permeation was measured under the same conditions.

The results are summarized in Table 5.

In this way, even in terms of water permeability, polyetherimide membranes have superior organic solvent resistance compared to polysulfone and polyethersulfone membranes.

Table 5 Changes in water permeability due to organic solvent treatment (Note) A-E
is the same as the criteria in Table 3.

Example 9 Using the same polyetherimide dry membrane as in Example 8, immersion and treatment in the same various chemicals as in Example 7 under the same conditions,
The amount of water permeation was measured under the conditions of ℃ and 1 atm.

The results are shown in Table 6.

Comparative Example 6 The same polysulfone and polyether sulfone dry membranes as in Comparative Example 5 were subjected to the same treatment as in Comparative Example 4, and then heated at 25°C, lat.
The amount of water permeation was measured under the conditions of m.

The results are summarized in Table 6.

Looking at the changes in water permeability like this, polyetherimide membranes are comparable to polysulfone and polyneedle sulfone membranes in terms of acid and alkali resistance! I can see that.

Table 6: Change in water permeability after chemical treatment (Note) A-E is 0, which is the same as the standard in Table 3. 15-

Claims (1)

[Scope of Claims] A liquid selective permeable membrane comprising a polymer whose repeating unit has the general formula (wherein Ar1 and Ar2 represent divalent aromatic groups).