JPH057750A - Composite membrane for separating substance - Google Patents

Abstract

PURPOSE:To obtain a composite membrane excellent in separation characteristics at the time of the separation of a substance by a dissolving- dispersing mechanism, improved in membrane forming properties and excellent in permeability by constituting said membrane of a porous support layer and a siloxane-containing polyimide polymer membrane layer. CONSTITUTION:A composite membrane is constituted of a porous support layer and a siloxane-containing polyimide polymer membrane layer. A siloxane- containing polyimide polymer consisting of an amine component and an acid anhydride component contains an amino modified compound represented by formula (wherein R1 is a l-5C divalent aliphatic group or a 6 or more C aromatic group and R2 and R3 may be same or different and are a monovalent aliphatic group or an aromatic group) as the amine component at least in an amount of 5% or more by wt. of the total components. Further, the siloxane containing polyimide polymer membrane is formed by a solution coating method, a water surface developing method and an interface film forming method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite membrane for substance separation, and more particularly to a composite membrane for substance separation comprising a porous support layer and a siloxane-containing polyimide polymer thin film layer.

[0002]

2. Description of the Related Art Membrane separation technology is expected to develop in the future as an energy-saving and highly efficient separation technology, and among them, gas separation membranes and separation of liquid mixtures by pervaporation method are particularly attracting attention. . The point in the development of these gas separation membranes and pervaporation membranes is that the permeation separation mechanism generally follows the dissolution-diffusion theory, so there is no defect in the membrane that can substantially separate substances,
And to make it as thin as possible. From such a point of view, in order to make a silicone resin having excellent permeability characteristics into a thin film, composite membranes laminated on various porous supports and methods for producing the same have been proposed.
(For example, JP-A-58-92430)

However, since they are basically laminated with a silicone resin having a very poor thin film-forming property on a porous support, in order to reproducibly and completely close the pores of the porous support, it is substantially several microns. Under the present circumstances, the above film thickness is required, and since the strength of the silicone resin itself is weak, the composite film itself has a short life.

[0004]

In view of such a situation, the present inventors have attempted to separate substances by laminating a siloxane-containing polyimide thin film, which is excellent in permeation characteristics and thin film-forming property, on a porous support. We came to obtain a composite membrane.

[0005]

SUMMARY OF THE INVENTION The present invention is a composite membrane for substance separation comprising a porous support layer and a siloxane-containing polyimide polymer thin film layer, and in particular, a siloxane-containing polyimide comprising an amine component and an acid anhydride component. It is a composite membrane for substance separation, wherein the polymer contains an amino-modified compound represented by the general formula (1) as an amine component in an amount of at least 5% by weight or more based on the constituent monomer ratio of all components. The siloxane-containing polyimide polymer thin film can be obtained by a solution coating method, a water surface spreading method, or an interfacial film forming method.

The present inventors have conducted extensive studies to obtain a polymer membrane for separating a gas and a liquid mixture, and as a result, the amino-modified compound represented by the above general formula (1) was used as a siloxane component to form a polyimide. 5 out of raw materials for polymer synthesis
Siloxane-containing polyimide polymer containing more than wt% has high gas selective permeability similar to silicone resin, and trace organic substances contained in water (for example, organic chlorine compounds such as trihalomethane, trichloroethane, tetrachloroethylene, trichloroethylene and other hydrophobic organic compounds). It was found that the siloxane-containing polyimide thin film has the property of being selectively removed by pervaporation and has a superior thin-film forming property compared to general silicone resins, and forms this siloxane-containing polyimide thin film on a porous support. By doing so, a composite membrane having a substantially high permeation flux was obtained without lowering the high selective permeability of the siloxane-containing polyimide.

Generally, in a separation membrane in which a substance is permeated through a dense layer on the surface such as a gas separation membrane or a pervaporation separation membrane in the membrane separation method to perform separation, the permeated substance is first dissolved in the dense layer and then dissolved. This substance diffuses and moves in the dense layer and reaches the other surface to achieve separation. That is, the selectivity of the permeate is determined by the difference in solubility in the dissolution process and the difference in diffusion rate in the diffusion process. From this, in the substance separation by the dissolution-diffusion mechanism, the separability is determined by the composition and structure of the separation membrane and does not depend on the thickness of the membrane.
On the other hand, since the amount of permeation of a substance is proportional to the reciprocal of the film thickness, in order to improve the permeation flux in a separation membrane device, it is desired to reduce the film thickness of the part that controls separation as much as possible. However, the problem with thinning is the defect and strength of the film, and the conventional composite film in which a silicone-based resin is laminated on the porous support has problems with this defect and strength. The composite membrane for substance separation in the present invention is obtained to solve the above-mentioned problems.

That is, in the present invention, the siloxane-containing polyimide that substantially controls the substance separation contains at least 5% by weight or more of the amino-modified compound represented by the formula (1) among the monomers constituting the polyimide polymer, Other acid anhydride components and amine components are not particularly limited, and examples thereof include 4,4′-oxydiphthalic acid dianhydride, pyromellitic dianhydride and 3,3 ′. , 4,4'-
Benzophenone tetracarboxylic acid dianhydride, 2,2 ', 3,3'-
Benzophenone tetracarboxylic acid dianhydride, 2,3,3 ', 4'-
Benzophenone tetracarboxylic acid dianhydride, 3,3 ', 4,4'-
Biphenyltetracarboxylic dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride, and the like, and as an amine component other than the amino-modified silicone compound represented by the formula (1), m -Phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-
Diaminodiphenylmethane, 3,3'-diaminodiphenyl ether, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 2,4-diaminotoluene, 1,3-bis (3- Aminophenoxybenzene), 1,4-bis (3-aminophenoxybenzene), 1,3-bis (4-aminophenoxybenzene), 2,2-bis (4- (4-aminophenoxy) phenyl) propane, 2 , 2-bis (4- (4-aminophenoxy) phenyl) hexafluoropropane, etc. The above-mentioned acid anhydride and amino compound may be used alone or in combination of two or more kinds.

When the amino-modified compound represented by the formula (1) is 5% by weight or less as a constituent monomer ratio of the siloxane-containing polyimide, the obtained polyimide has a low substance permeability and is not suitable for use as a separation membrane. In particular,
Since the permeation coefficient is extremely low, the permeation flux is practically small even if the membrane is thinned, and it cannot be an efficient separation membrane.

The porous support used in the present invention can be used without any limitation as long as it has a pore diameter of 5 μm or less. According to the experiments conducted by the present inventors, the best characteristics were given when a polypropylene or polyethylene porous membrane was used. However, even when a polysulfone, polyether sulfone or polyimide porous membrane was used, a sufficient separation membrane was obtained. Had the characteristics of. As described above, the composite membrane for substance separation according to the present invention has excellent properties as a separation membrane because the siloxane-containing polyimide polymer has both high substance separation properties and thin film forming properties.

Further, as a method for laminating the siloxane-containing polyimide polymer on the porous support, a method of dissolving the polymer in an appropriate solvent and directly coating the solution on the porous support (solution coating method), Spread the polymer solution on the water surface,
A method of transferring the polymer thin film formed at the gas-liquid interface to a porous support (water surface development method), or dissolving the polymer in a solvent immiscible with water (for example, a solvent such as chloroform or trichlene), A method (interfacial film forming method) in which a polymer thin film formed at the interface by contacting the solution with water is laminated on the porous support is mentioned. The siloxane-containing polyimide described in this patent can easily form a defect-free thin film layer on the porous support layer by these methods, and an excellent separation membrane can be obtained.

[0012]

EXAMPLES Examples of the present invention will be described in detail below.
The invention is in no way limited by these examples.

Example 1 In a four-neck separable flask equipped with a thermometer, a stirrer, a raw material inlet, and a dry nitrogen gas inlet tube, 4,4'-oxydiphthalic acid dianhydride 49.63 g (0.1
6 mol) was charged and dissolved in 450 g of N-methyl-2-pyrrolidone. There, formula (2)

[0014]

[Chemical 2]

Amino-modified silicone compound 9 represented by
Add 6.7 g (0.08 mol) and add 2,4-diaminotoluene
9.77 g (0.08 mol) was added and reacted for 5 hours. During the reaction, if necessary, the mixture was cooled with an ice bath or the like, and nitrogen gas was introduced while always maintaining the system at 20 ° C. Subsequently, toluene 13 was added to this system.
Add 0 g, remove the dry nitrogen gas introduction tube, attach the Dean-Stark trap instead, remove the ice bath and heat in an oil bath, and azeotrope the water generated by imidization with toluene to the outside of the system. Removed. The obtained polyimide resin solution was poured into water, and the obtained solid matter was collected and dried to obtain a siloxane-containing polyimide.

The siloxane-containing polyimide resin obtained above was dissolved in dioxane to form a 2% solution, filtered through a 0.3 μm membrane filter, and then cast on a polypropylene porous body (Tokuyama Soda NF-100). Then, it was dried to obtain a composite film 1. The thickness of the siloxane-containing polyimide layer calculated from the increase in weight was 0.2 μm. In order to evaluate the performance of this composite membrane, the gas permeation characteristics and the permeation characteristics of the liquid mixture by the pervaporation method were evaluated. The gas permeation characteristics showed a typical active diffusion type permeation behavior, and it was found that the pores of the porous body were completely closed. Table 1 for other permeation characteristics (gas separation characteristics and pervaporation separation characteristics)
Shown in.

(Example 2) The siloxane-containing polyimide polymer synthesized in Example 1 was dissolved in chloroform to obtain a 1% solution. When this solution was spread on the water surface, the solution instantly spread over the entire surface to form a thin film. This thin film was laminated on the porous body and sufficiently dried to obtain a composite film 2. Similar to the composite membrane 1, the composite membrane 2 was shown by gas permeation behavior that the pores of the porous support were completely closed, and when observed by an electron microscope, the thickness of the siloxane-containing polyimide thin film layer was 0.06 μm. Met. Other permeation characteristics (gas separation characteristics and pervaporation separation characteristics) are shown in Table 1.

(Example 3) The siloxane-containing polyimide polymer synthesized in Example 1 was dissolved in chloroform to obtain a 1% solution. A thin film of the siloxane-containing polyimide polymer was formed at the interface by gently pouring water over the solution. This thin film was laminated on the porous body and sufficiently dried to obtain a composite film 3. Similar to the composite membrane 1, the composite membrane 3 showed that the pores of the porous support were completely closed by gas permeation behavior, and when observed by an electron microscope, the thickness of the siloxane-containing polyimide thin film layer was 0.1.
was μm. Other permeation characteristics (gas separation characteristics and pervaporation separation characteristics) are shown in Table 1.

Comparative Example 1 Silicone rubber was used in place of the siloxane-containing polyimide in Example 1. That is, silicone rubber compound (Shin-Etsu Chemical KE-45
T) was dissolved in toluene to form a 2% solution, which was cast on a polypropylene porous body in the same manner as in Example 1 and allowed to stand for 1 day and night to obtain a composite film. The film thickness was 0.8 μm, which was thicker than that in the case of using the siloxane-containing polyimide in Example 1, but the gas permeation behavior was a typical Knudsen flow, and the pores of the porous support were not completely closed. . Therefore, the performance of the separation membrane could not be evaluated.

Comparative Examples 2 and 3 Silicone rubber compounds were used in the same manner as in Comparative Example 1 to obtain Examples 2 and 3, respectively.
Thin film formation was tried by the water surface development method and the interface film formation method shown in. However, the water surface expansion method does not spread evenly on the water surface,
In addition, the interfacial film forming method does not have sufficient strength when laminated on a porous support, so that a thin film layer cannot be formed on a porous body over a wide area. Therefore, as in Comparative Example 1, the performance of the separation membrane could not be evaluated.

(Comparative Example 4) In Example 1, 49.63 g (0.160 mol) of 4,4'-oxydiphthalic dianhydride was used as a raw material for siloxane-containing polyimide synthesis, and 2.418 g (3 mmol of amino-modified silicone compound of the formula (2)). ) And 2,4-diaminotoluene (19.30 g, 0.158 mol), a siloxane-containing polyimide was synthesized such that the proportion of the amino-modified silicone compound was 5% by weight or less of all the constituent monomers. Dissolve the obtained resin in dioxane to make a 2% solution, 0.3 μm
After being filtered with a membrane filter of No. 3, the mixture was cast on a polypropylene porous body and dried to obtain a composite membrane 4. The thickness of the siloxane-containing polyimide layer calculated from the increase in weight was about 0.3 μm.

In order to evaluate the performance of this composite membrane, the gas permeation characteristics and the permeation characteristics of the liquid mixture by the pervaporation method were evaluated. The gas permeation characteristics showed a typical active diffusion type permeation behavior, and it was found that the pores of the porous body were completely closed, but the permeation characteristics showed that the permeation flux was small and that of the chloroform / water system. Separation factor of chloroform is 80
Was extremely lower than that of the composite films 1 to 3. Details of the transmission characteristics are shown in Table 1 in comparison with other composite membranes.

[0023]

[Table 1]

[0024]

As described above, according to the present invention, dissolution-
In a separation membrane that separates substances by a diffusion mechanism, the siloxane-containing polyimide that substantially controls the separation of the substances has excellent separation characteristics, and the thin-film forming property is good. The resulting membrane is excellent in both separability and permeability.

Claims (3)

[Claims] 1. A composite membrane for substance separation comprising a porous support layer and a siloxane-containing polyimide polymer thin film layer. 2. A siloxane-containing polyimide polymer composed of an amine component and an acid anhydride component contains, as an amine component, an amino-modified compound represented by the general formula (1) in an amount of at least 5% by weight based on the constituent monomer ratio of all components. Item 7. A composite membrane for substance separation according to item 1. [Chemical 1] 3. The composite membrane for substance separation according to claim 1, wherein the siloxane-containing polyimide polymer thin film is formed by a solution coating method, a water surface spreading method, or an interface film forming method.