JP3360580B2 - Polyetherimide-based dehumidifying film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyetherimide-based dehumidifying film. More specifically, the present invention relates to a polyetherimide-based dehumidifying film which is considered to be caused by a capillary condensation effect.

[0002]

2. Description of the Related Art Compressed air is used in various industrial fields, and its applications are diverse. On the other hand, pneumatic equipment is becoming more and more precise in order to meet the needs of many uses, and under such a background, specific components in the compressed air, particularly moisture, are not used for the equipment. It is also a major cause of failure. In the field of semiconductors and the like, it is also true that the clarification of the air used greatly contributes to the product yield.

At present, a refrigeration type is mainly used for dehumidification in compressed air, but a dryer using a membrane has recently been put on the market from the viewpoint of decarbonization. . Dehumidifying membranes that are actually commercially available include fluorine-based,
There are imide-based and urethane-based hollow fiber membranes, but the fluorine-based and urethane-based hollow fiber membranes have no resistance to oil contained in a considerable amount in compressed air and can be used for a long time. There is a problem that the film performance deteriorates.

In view of the dehumidifying performance of the hollow fiber membrane, the fluorine-based membrane employs an ion hydration method, and the imide-based and urethane-based membranes employ a dissolution / diffusion method. Although the method has a large separation coefficient between water vapor and air, it has a drawback that a large water vapor transmission coefficient is required, so that a large membrane area is required, and an increase in the size of the module is inevitable.

[0005] In order to solve these problems, in order to further study a hollow fiber membrane material made of imide from the viewpoint of oil resistance, polyimide resin is originally insoluble in solvents and the like. It is difficult to form a film, so polyamic acid which is a precursor of polyimide is synthesized in a solvent, the solvent is removed as a cast to form a film, and then imidized by heating to about 200 to 300 ° C. The method is generally taken. However, it is not easy to manufacture a hollow fiber membrane capable of controlling the separation performance by using such a membrane forming method.

[0006]

An object of the present invention is to provide a hollow fiber membrane formed from an organic solvent-soluble imide material by a dry-wet method, which can be effectively used as a dehumidifying membrane. It is in.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
90-60% by weight of polyetherimide and polyamideimide 10
Achieved by a dehumidifying membrane consisting of a hollow fiber membrane formed from a blend with 〜40 % by weight . Such a hollow fiber membrane is coated on its inner surface side with polyvinylpyrrolidone,
Alternatively, it is preferable to impregnate and use a humectant.

[0008]

DETAILED DESCRIPTION OF THE INVENTION As a polyetherimide, a repeating unit represented by the following general formula is used. Is used, and is actually a commercially available product, for example, a repeating unit represented by the following general formula General Electric Co., Ltd. product ULTEM1000 having the above can be used as it is.

As the polyamide imide used by blending with the polyether imide, a commercially available product such as Toron 4000T manufactured by Amoco Japan having a repeating unit represented by the following general formula can be used as it is.

Although polyetherimide and polyamideimide are imide-based materials, they themselves have the property of dissolving in a solvent, so that it is easy to form a hollow fiber membrane by a dry-wet method, and moreover, it has a high durability. Excellent in chemical properties.

When a hollow fiber membrane made of polyetherimide or polyamideimide alone is modularized and used as a dehumidifying membrane, steam-saturated air (humidity 18% RH, pressure 0.4MPa) sent from the inlet side of the module is used. Humidity at the primary air outlet (module outlet) is 1% to 3% RH for polyether imide, and several% RH for polyamide imide, and has sufficient performance as a dehumidifying film. Is not good.

It is effective to use a hollow fiber membrane formed from a blend of a polyetherimide and a polyamideimide blended in a small amount, specifically, about 10 to 40% by weight, preferably about 15 to 25% by weight in the mixture. In this case, the formation of voids inside the hollow fiber membrane of polyetherimide alone is effectively suppressed (confirmed by SEM photograph). The generation of voids causes a decrease in mechanical strength and the generation of pinholes. Therefore, by suppressing the generation thereof, improvement in durability is achieved.

Therefore, a hollow fiber membrane formed from a blend of polyetherimide and polyamideimide is used as a dehumidifying membrane. These hollow fiber membranes are modularized, and steam-containing air sent from the inlet of the module is converted into a module. When dehumidified by the hollow fiber membrane and obtained as dry air at the primary air outlet (module outlet), the dehumidified water vapor passes through the hollow fiber membrane and is discharged from the secondary side of the module body.
In fact, when steam accumulates on the secondary side, the difference in partial pressure of steam with the primary side (driving force for dehumidification) disappears,
A part of the obtained dry air is flowed to the secondary side to achieve constant dehumidification.

In practice, such an operation is performed. However, without performing such a partial reduction of the dry air, if only the air permeation amount to the module secondary side is measured purely by a flow meter. In the case of a hollow fiber membrane formed from a blend of polyetherimide and polyamideimide, the value becomes considerably large, which means that the amount of dry air obtained on the primary side decreases accordingly, The yield will be bad.

Therefore, if the dehumidifying performance is the same, it is desirable that the air permeation amount to the secondary side of the module is small. Therefore, the method of coating the inner surface side of the hollow fiber membrane with polyvinylpyrrolidone or the hollow fiber membrane is preferred. A method of impregnating a humectant is used, and by adopting these methods, the amount of air permeated to the module secondary side can be greatly reduced.

[0016] The blend of polyetherimide and polyamideimide is a good solvent thereof such as dimethylformamide, dimethylacetamide, diethylformamide,
In an organic solvent such as diethylacetamide, N-methyl-2-pyrrolidone, morpholine, dioxane, and dichloromethane, preferably an aprotic polar solvent, the solution concentration is about
It is used by dissolving it in a proportion so as to account for 18 to 30% by weight, preferably about 20 to 25% by weight. This film-forming stock solution (dope solution)
If the concentration of air is increased further, the air permeability at the primary outlet will increase while the air permeability of the module secondary air approaches zero, while at lower concentrations the air humidity at the primary outlet will increase Not only that, the amount of air permeated through the module secondary side is significantly increased.

The hollow fiber membrane formed from a blend of polyetherimide and polyamideimide is preferably used as a dehumidifying membrane after the following treatment. (1) Coating of the inner surface side with polyvinylpyrrolidone: This coating is carried out by using an aqueous solution of polyvinylpyrrolidone as a core liquid during spin-dry spinning. Polyvinyl pyrrolidone has a molecular weight of about 10,000 to 1,200,00
0, preferably about 10,000-50,000, about 1-15 weight
%, Preferably about 3 to 10% by weight aqueous solution.

[0018] Polyvinylpyrrolidone is a hydrophilic polymer, has a high affinity for water, and has a high hygroscopicity, so that it is most suitable as a coating agent for the surface of a film. It is easy to uniformly coat the inner surface of the film.

By coating the inner surface side of the hollow fiber membrane with such polyvinylpyrrolidone, water adsorbability to the inner surface of the membrane is improved, and capillary condensation easily occurs in the internal pores of the membrane. It is considered that the barrier properties of the film are improved in the pores by the action of a mask. The coating with polyvinylpyrrolidone can also be performed after the formation of the hollow fiber membrane or after the modularization.

(2) Impregnation of a humectant: As the humectant, polyhydric alcohols such as glycerin, ethylene glycol and propylene glycol are used.
Wt%, preferably about 10-30 wt% in aqueous humectant solution,
This is performed by immersing the hollow fiber membrane during or after film formation. By the impregnation of the humectant, the barrier property of the film in the water vapor transmission is improved,
In other words, improvement of the repetitive pressure resistance, prevention of sticking during drying in the production of the hollow fiber membrane bundle, and the like are achieved.

In a separation membrane utilizing a capillary condensation action, uniformity of pores is required, but such a membrane is not always obtained. Therefore, by impregnating the membrane with a humectant that has high affinity for water and easily adsorbs water vapor,
Masking of a hole having a larger hole diameter can be performed without impairing the ability to take in water vapor into the membrane. In addition, it is considered that the part also exhibits a liquid film function and contributes to water vapor permeation.

The hollow fiber membranes treated by these methods are bundled and modularized, and wet compressed air or the like is passed through the hollow fiber membrane to the primary inlet (inside the hollow fiber membrane) of the membrane. During this time, water vapor that has passed through the hollow fiber membrane is discharged from the body of the module, and dry compressed air or the like can always be obtained from the primary outlet of the membrane.

[0023]

As described above, in a separation membrane capable of continuously and constantly dehumidifying, the separation membrane is formed from a blend of polyetherimide and polyamideimide having good affinity for water. By coating the inner surface with polyvinylpyrrolidone or impregnating with a humectant, the dehumidifying ability can be further enhanced.

[0024]

Next, the present invention will be described with reference to examples.

Example 1 A dimethylacetamide solution in which 16% by weight of polyetherimide (ULTEM1000) and 4% by weight of polyamideimide (TORON 4000T) were respectively dissolved was used as a dope solution, and a 5% by weight aqueous solution of polyvinylpyrrolidone (molecular weight 10,000) was used. Dry-wet spinning was performed from a double annular nozzle using the core liquid. The obtained hollow fiber membrane (outside diameter: 570 μm, inside diameter: 350 μm) was washed with water, and then dried in an oven at 50 ° C. to obtain a blend hollow fiber membrane whose inner surface was coated with polyvinylpyrrolidone.

500 hollow fiber membranes of this blend were bundled to form a module (diameter 30 mm, length 250 mm), and 25
Steam-saturated air (humidity: 18% RH) that has passed through water at ℃ is sent under the conditions of piping pressure of 4 kg / cm ² and supply air flow rate of 10 L / min, and air permeation to the module secondary side (body side) The volume was measured and a value of 200 ml / min was obtained. The humidity at the primary air outlet was reduced to 5% RH.

Example 2 In Example 1, the module of the blend hollow fiber membrane obtained by using water as the core liquid was the same as the module 2
A value of 5000 ml / min of air permeation to the secondary side and a humidity of 5% RH at the primary side air outlet were obtained.

Example 3 The blended hollow fiber membrane of Example 2 was immersed in a 20% by weight aqueous glycerin solution and impregnated to obtain a module.
5 ml / min of air permeation to the secondary side, humidity of primary side air outlet
A value of 3% RH was obtained.

It should be noted that the number of times of folding endurance is 100 times or more compared to 2 times for the non-impregnated material, and the flexibility of the film can be improved even when a repetitive pressure is applied depending on the use conditions such as compressed air. Secured.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 67/00-71/82 510 B01D 53/22

Claims (5)

(57) [Claims] 1. A polyetherimide-based dehumidifying membrane comprising a hollow fiber membrane formed from a blend of 90-60% by weight of polyetherimide and 10-40% by weight of polyamideimide. 2. The polyetherimide-based dehumidifying film according to claim 1, which is dry-wet spinning from a spinning solution in which polyetherimide and polyamideimide are dissolved at a ratio of 18 to 30% by weight. 3. The polyetherimide-based dehumidifying membrane according to claim 1, wherein the inner surface of the hollow fiber membrane is coated with polyvinylpyrrolidone. 4. The polyetherimide-based dehumidifying film according to claim 3, wherein the coating with polyvinylpyrrolidone is performed by dry-wet spinning using a core solution composed of an aqueous solution of polyvinylpyrrolidone. 5. The polyetherimide-based dehumidifying membrane according to claim 1, comprising a hollow fiber membrane impregnated with a humectant.