JPH04110025A - Production of permeating and vaporizing membrane - Google Patents

Abstract

PURPOSE:To obtain the permeating and vaporizing membrane having stabilized separating performance even when industrially used for a long period by treating a semipermeable asymmetric membrane consisting of an aromatic condensed polymer in a humid hot atmosphere. CONSTITUTION:An asymmetric semipermeable membrane consisting of an aromatic condensed polymer such as polysulfone and polyimide and having a dense layer on at least one surface is treated in a humid hot atmosphere at 90-200 deg.C. The high-temp. vapor molecule as the heating medium is allowed to intrude into the gap between the membranes in the treatment, the separative performance is controlled in a desired range, and the elongation of the membrane for an org. solvent is suppressed. Accordingly, a permeating and vaporizing membrane exhibiting stabilized separative performance even when industrially used for a long time is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a separation membrane (hereinafter also simply referred to as a pervaporation membrane) used in an improved pervaporation method. More specifically, the present invention relates to a method for improving the permselective performance and dimensional stability of a pervaporation membrane made of an aromatic condensation polymer and having a dense layer on at least one surface.

[Conventional technology and its problems]

The pervaporation method, which is generally effective as a separation technology for organic liquid mixtures or solutions of organic compounds, especially for compounds with close boiling points and azeotropic mixtures, requires separation membranes that have good separation performance and are industrially durable. Desired. In other words, in this type of pervaporation method, an organic liquid mixture is supplied to one side through a separation membrane, and the other side is reduced in pressure or vacuum to vaporize and take out specific liquid components. A separation membrane that has durability in terms of chemical resistance, heat resistance, mechanical strength, and dimensional stability is required.

Conventionally, semipermeable polymeric membranes made of cellulose, polyvinyl alcohol, polyamide, polyester, polysulfone, polycarbonate, polyimide, or copolymers similar to these have been known as separation membranes used in this pervaporation method. ing. Among these, polymers generally known as engineering plastics have good heat resistance and chemical resistance, but they are not yet sufficient as materials for separation membranes that exhibit good separation performance in the pervaporation method described above. Therefore, membranes whose surfaces are further treated with electron beams, etc., and membranes whose ion exchange groups such as sulfonic acid groups, carboxylic acid groups, and quaternary ammonium bases are introduced into condensed polymer chains having aromatic rings (especially Kaihei 2-3s92o
) has been proposed.

However, when membranes made of aromatic condensation polymers are subjected to the pervaporation method described above, the organic solvent to be separated permeates into the membrane and causes the membrane to swell. It is difficult to obtain stable separation performance over a period of time. Moreover, such swelling of the membrane not only changes the structure of the membrane and deteriorates the separation performance, but also causes cracking and leakage. In addition, in a composite membrane using different types of polymers, one of which is a support layer and the other an active layer, cracks are more likely to occur because the swelling degree of each polymer is different. Therefore, in order to maintain stable separation performance, particularly in the separation of organic solvents by pervaporation, it is necessary to suppress the swelling of the separation membrane as much as possible. Therefore, a sufficient swelling suppressing effect cannot be obtained unless a method is adopted in which the membrane is heat-treated in advance.

Additionally, JP-A-2-139022 proposes a method of subjecting porous membranes made of aromatic polysulfone to moist heat treatment in order to improve only the water permeation rate without substantially changing other membrane properties. There is. However, this JP-A-2-1
Publication No. 39022 does not suggest anything about the semipermeable membrane having a dense structure (substantially not a porous membrane) used in the pervaporation method, and the effect of suppressing the swelling thereof.

[Means for solving problems]

The present inventors conducted extensive research in order to solve the above problems. As a result, by treating the pervaporation film made of aromatic condensation polymer in a moist heat atmosphere,
The present invention was achieved by discovering that separation performance and dimensional stability in organic solvents can be suppressed within desired ranges. That is, the present invention provides a semipermeable membrane (hereinafter also simply referred to as a semipermeable asymmetric membrane) made of an asymmetric aromatic condensation polymer having a dense layer on at least one surface at 90°C.
This is a method for producing a pervaporation membrane characterized by processing in a moist heat atmosphere at a temperature of 200°C to 200°C.

The aromatic condensation polymer that is the material for the pervaporation membrane in the present invention is generally known as an engineering plastic, such as polysulfone, polyethersulfone, polyimide, polyetherimide, polyamide, polyphenylene oxide, poly-2, All conventional condensation polymers having an aromatic ring, such as 6-dimethylphenylene oxide and polyphenylene sulfide, are effective.

The shape of such a semipermeable asymmetric membrane having a dense layer on at least one surface made of an aromatic condensation polymer is not particularly limited, and may be, for example, a flat membrane, a spiral membrane, a hollow fiber membrane, or a tubular membrane. The membrane is selected as appropriate depending on the manner of use as a separation membrane in the pervaporation method, the type of processing liquid to be separated, etc. For example, as the hollow fiber separation membrane, a semipermeable asymmetric membrane having a thickness of generally 30 to 500 μm and an inner diameter of 0.03 to 2 mm is preferably used.

The semipermeable asymmetric membrane in the present invention is manufactured using a solution (dope solution) prepared by dissolving an aromatic condensation polymer in an organic solvent. As the organic solvent for dissolving the aromatic condensation polymer, those having compatibility with the coagulating liquid described below are preferably used, such as dimethylacetamide, N-methyl-2-pyrrolidone, dimethylformamide, 2-pyrrolidone, and tetrachloroethane. Examples include. Also,
In order to facilitate molding into a film-like material as described below, it is preferable that the concentration of the aromatic condensation polymer in the dope solution is generally adjusted to 10 to 30% by weight, particularly 15 to 25% by weight.

Furthermore, if necessary, to adjust the dense layer of the semipermeable asymmetric membrane, e.g. polyvinylpyrrolidone, lithium chloride,
A dope solution can also be prepared by adding potassium nitrate or the like.

In order to obtain a flat film as a film-like product, a method is employed in which the above-mentioned dope solution is cast onto a flat plate and then immersed in a coagulation liquid to solidify it. In the case of a membrane-like material or a hollow fiber membrane, a publicly known method of extruding a dope solution into a coagulating solution using an annular nozzle for producing hollow fibers is generally employed. for example,
Using a tube-in-orifice type nozzle with a tube or protruding tube at the center of an orifice opening in the center of the nozzle bed, the tope liquid is poured from the annular gap between the inner peripheral surface of the opening of the orifice and the outer peripheral surface of the tube. This method forms hollow fibers by extruding and simultaneously supplying core liquid from the inner hole of the tube. The core liquid should be a liquid that does not coagulate the dope liquid from inside the hollow fiber and does not dissolve the aromatic condensation polymer of the tope liquid.
Generally water is used. Next, the unsolidified hollow fiber membrane thus formed is immediately immersed in a predetermined coagulating liquid.
A solidified hollow fiber membrane can be obtained by coagulating from the outside of the hollow fiber. It is also possible to form a hollow fiber membrane by immersing a tube-in-orifice nozzle under the water surface of a coagulation bath and simultaneously coagulating the inside and outside of the extruded hollow fiber membrane. In addition, it is recommended to maintain the temperature of the coagulating liquid at 20° C. or lower, preferably 1 to 10° C., in order to obtain a semipermeable asymmetric membrane having a dense layer that is good as a pervaporation membrane.

The greatest feature of the present invention is that the semipermeable asymmetric membrane formed by the method described above is treated in a moist heat atmosphere of 90° to 200°C, and as a pervaporation membrane, it has excellent separation performance and dimensions for organic solvents. Stability can be controlled within a desired range.

The treatment in a moist heat atmosphere in the present invention may be performed by heating the semipermeable asymmetric membrane to a temperature of 90 to 200°C in the presence of moisture, for example, in a heat-resistant container such as a glass container. This can be achieved by exposing the semipermeable asymmetric membrane to hot water at a temperature of 100°C to 100°C, or by exposing the semipermeable asymmetric membrane to high-temperature, high-pressure steam at 100°C or higher in a pressure-resistant container such as an autoclave. The treatment temperature is generally 90°C to 200°C, particularly preferably 100°C to 150°C. Further, the treatment time generally requires 1 minute or more, and in order to obtain particularly stable membrane performance, 5 minutes to 100 minutes is preferable. As a more specific treatment mode, for example, the semipermeable asymmetric membrane may be immersed in an autoclave filled with water, and then heated to an internal temperature of 90°C to 200°C. By varying the maximum temperature reached at this time, the separation performance of the semipermeable asymmetric membrane as a pervaporation membrane and the dimensional stability against organic solvents can be controlled within a desired range. However, because
In the method of simply heating the semipermeable asymmetric membrane in the atmosphere, the desired effect cannot be obtained, probably because the heat is not sufficiently conducted to the inside of the membrane. Furthermore, if the treatment temperature is lower than 90°C, sufficient effects will not be achieved, and if the treatment temperature is higher than 200°C, the properties of the film will be impaired, which is undesirable.

[Action and effect of the invention]

The present invention provides a semipermeable asymmetric membrane having a dense layer on at least one surface made of an aromatic condensation polymer.
This is a simple method in which the semipermeable asymmetric membrane is treated in a heated atmosphere of The elongation of the film can be suppressed to within 2%. The reason for this is not clear, but high-temperature steam molecules (water molecules) are the heat medium in thermal treatment.
Alternatively, it is presumed that the desired effect of heat treatment can be significantly achieved by penetrating into the polymer interstices of the film.

Therefore, the pervaporation membrane obtained by the present invention exhibits stable separation performance during long-term industrial use, and is extremely useful in industry.

〔Example〕

EXAMPLES Hereinafter, the content of the present invention will be specifically explained using Examples, but the present invention is not limited to these Examples.

Example 1 Repeating unit represented by the following formula (where Ar, Arl represent a divalent aromatic group)
After mixing and dissolving 100 parts by weight of polyetherimide (manufactured by General Electric Company, trade name: Ultem 1000) in 400 parts by weight of N-methyl-2-pyrrolidone, which is a good solvent, it was filtered and defoamed to obtain a spinning dope (dope). liquid)
I got it. This stock solution is discharged from the outer tube of the double-tube nozzle, water is supplied to the core of the inner tube, and then passed through a coagulation water bath at 5°C to undergo a phase change to form hollow fibers. After immersing it in the same 5° C. cleaning tank for 24 hours to completely remove the internal solvent, it was dried at room temperature. Observation of the resulting polyetherimide hollow fiber membrane using a scanning electron microscope revealed that the outer diameter was 1000 μm, the inner diameter was 600 μm, and the membrane thickness was 200 μm, with a uniform 5 μm thickness on the inner and outer peripheries of the membrane.
A compact tank was confirmed. This polyetherimide hollow fiber membrane was treated in an autoclave for 60 minutes in a moist heat atmosphere in the presence of water vapor at various temperatures shown in Table 1, and then dried at room temperature.

Next, each of the above-mentioned hollow fiber membranes was cut into 15 ann pieces, 10 of them were bundled and inserted into a glass tube, and both ends were treated with resin to form a module. Using a pervaporation device equipped with this module, the feed liquid was passed through the hollow fiber membrane at a linear velocity of Loan/sec, the outside of the hollow fiber membrane was set at 2 Torr, and water/isopropyl alcohol = 10/sec. Pervaporation separation was carried out at 60° C. using a mixed solution of 90 (wt% ratio) as a feed liquid, and the permeation flux (g/hr-rrV), separation coefficient, and elongation rate of the membrane were measured.

Note that the permeation flux is obtained by collecting gas on the permeate side using a tri-ice-methanol trap, and is expressed as the weight of permeate per unit membrane area and unit time.

Further, the separation coefficient (α) is defined for a water-alcohol mixture. In the formula, F (H2O) and F(
R, OH) are the weight fractions of water and alcohol in the feed, respectively, and P (H2O) and P (ROH
) indicate the weight fraction of water and alcohol in the permeate, respectively, and were determined using a gas chromatograph. The elongation rate (%) of the membrane is defined as, where X is the length of the membrane before pervaporative separation and Y is the length of the membrane in the longitudinal direction after pervaporative separation. .

The results are shown in Table 1.

Table 1 The elongation rate was measured and the results are shown in Table 2.

Table 2 Example 2 The polyetherimide hollow fiber membrane obtained in Example 1 was treated in an autoclave in a moist heat atmosphere at 140° C. for different treatment times. Using the membranes before and after such treatment, the separation coefficient (α), permeation flux (Q) and the like were measured in the same manner as in Example 1. Membrane Example 3 Polyetherimide hollow fiber membrane obtained in Example 1 was treated in a heated atmosphere at 140° C. for 160 minutes in an autoclave. Using this hollow fiber membrane, it was made into a module in the same manner as in Example 1, and installed in a pervaporation device.

Using this pervaporation device, the feed liquid is passed inside the hollow fiber membrane at a linear velocity of 10 cm/sec, and the outside of the hollow fiber membrane is
Torr, water/ethanol (wt% ratio) or 10/
90. Pervaporative separation was carried out at 55°C using the 5/95 mixed liquid as the feed liquid, and the permeation flux (
Q), separation coefficient (α) and membrane elongation rate were measured. The results are shown in Table 3.

Table 3 Note) Floor 3 in the table corresponds to a comparative example, and Example 1
This is a polyetherimide hollow fiber membrane that has not been treated in a moist heat atmosphere.

Example 4 The tope liquid obtained in Example 1 was cast onto a glass plate to a thickness of about 300 μm, and then immersed in water at 5° C. to solidify, thereby forming a flat film of polyetherimide with a thickness of about 100 μm. I got it. Next, this polyetherimide film was heated to 140°C.
After being treated in a moist heat atmosphere for 60 minutes and dried at room temperature, it was made into a module by the same method as in Example 1 and installed in a pervaporation device.

Using this pervaporation device, supply a mixed solution of water/isopropyl alcohol = 10/90 (wt, % ratio),
When pervaporation was performed at 60℃, the separation coefficient (α) was 6.
30. The permeation flux (Q) was 750 g/hr-rd, and no wrinkles or wrinkles due to swelling of the membrane were observed.

There was no change in separation performance after one week of continuous implementation.

On the other hand, when conducting the test using a flat polyetherimide membrane that has not been treated in a moist heat atmosphere, the separation coefficient (α)
The permeation flux (Q) was 390 g/hr-m, the permeation flux (Q) was 1480 g/hr-m, wrinkles were observed due to swelling of the membrane, and the separation coefficient (α) decreased to 200 after one week of continuous operation.

Example 5 Polysulfone containing a repeating unit represented by the following formula (trade name: Lldel Po1) obtained from Amoco Chemical Japan
ysul-fone, flL average molecular weight 35.000
) was mixed and dissolved in 400 parts by weight of N-methyl-2-pyrrolidone, which is a good solvent, and then filtered.
Defoaming was performed to obtain a spinning stock solution (dope solution). A hollow fiber membrane was produced in the same manner as in Example 1 using this dope solution.

The obtained polysulfone hollow fiber membrane was treated in a moist heat atmosphere at 140° C. for 60 minutes and dried at room temperature, and then modularized in the same manner as in Example 1 and installed in a pervaporation device.

As a result of carrying out pervaporation separation similar to Example 1 using this pervaporation device, the separation coefficient (α) was 410, the permeation flux (Q) was 830 g/hr-nf, and the elongation rate of the membrane was 1. It was 9%.

On the other hand, when using a polysulfone hollow fiber membrane that has not been treated in a moist heat atmosphere, the separation coefficient (α) is 220, the permeation flux (Q) is 1940 g/hr-ffl, and the elongation rate of the membrane is 5.7%. there were.

Example 6 The polyetherimide hollow fiber membrane obtained in Example 1 was
It was treated in boiling water at ℃ for 60 minutes. This hollow fiber membrane was made into a module using the same method as in Example 1 and installed in a pervaporation device.

Using a pervaporation device, the supply liquid was passed through the inside of the hollow fiber using a wire bundle of 10 on/see, the outside of the hollow fiber was set at 2 Torr, and water/isopropyl alcohol (
The permeation flux (Q), separation coefficient (α), and elongation rate of the membrane were measured at 60° C. using mixed solutions of 5/90 and 5/95 (wt% ratio) as feed liquids, respectively. The results are shown in Table 4.

Table 4 Table 4 Comparative Example 1 The polyetherimide hollow fiber membrane obtained in Example 1 was treated in a dryer at 140° C. in the atmosphere for 60 minutes.

This hollow fiber membrane was made into a module in the same manner as in Example 1 and installed in a pervaporation device.

Using this pervaporation device, the feed liquid is pumped into the inside of the hollow fiber.
The liquid was passed with a line flux of 0 cm/sec, and the outside of the hollow fiber was 2 To
rr, water/isopropyl alcohol (wt% ratio)
Using a mixed solution of 10/90.5/95 as a feed liquid, pervaporative separation was performed at 60° C., and the permeation flux (Q), separation coefficient (α), and elongation rate of the membrane were measured.

The results are shown in Table 5.

In addition, when the above-mentioned pervaporation separation was carried out continuously for another month, the hollow fiber membrane gradually stretched, and breakage occurred at the end treatment part of the module.

Claims (1)

[Claims] 1. A semipermeable membrane made of an aromatic condensation polymer with an asymmetric structure having a dense layer on at least one surface,
A method for producing a pervaporation membrane, characterized by processing in a moist heat atmosphere at 0°C.