JPH07114937B2 - Separation membrane - Google Patents

Description

The present invention relates to a separation membrane, in particular a separation membrane having a selective permeability to a gas mixture, and more particularly to a separation membrane suitable for obtaining oxygen-enriched air from air.

Currently, devices that utilize combustion energy, such as household heating appliances, automobile engines, and boilers, are designed on the basis that oxygen is present in the air at a concentration of about 20%,
It's being used. However, if the air having an increased oxygen concentration is supplied, not only the problems such as environmental pollution due to incomplete combustion can be solved but also the combustion efficiency can be improved.

Further, the air having an increased oxygen concentration is also useful as a breathing air for a person having a respiratory disease or when immature.

For this purpose, various separation membranes having selective gas permeability have been developed for obtaining air having an increased oxygen concentration from ordinary air. This separation membrane is required to have a property of separating oxygen and nitrogen in the air and allowing the oxygen to permeate the membrane at a sufficiently large rate. Silicone rubber, which was first used as a membrane material to separate oxygen and nitrogen in the air, has a separation coefficient (α) of 2.0 and an oxygen permeability coefficient of 6 × 10 ^-8 c.
It has the performance of c (STP) · cm / cm ² · sec · cmHg. This material has a high transmission coefficient but a low separation coefficient,
Therefore, the development of materials with high permeability and separation coefficient has been developed.

By the way, the amount of gas that permeates the homogeneous membrane is expressed by the following formula Y = ( P × Δρ × A) / l It is represented by. Therefore, if a material having a high separation coefficient (α) can be found, even if the transmission coefficient ( P ) is small, the permeation rate can be increased by making the film thickness (1) as thin as possible. As one of such directions, a method has been developed in which a monomolecular film of an organic polymer is developed on a water surface to form an ultrathin film, and the ultrathin film is supported by a porous support to form a gas separation membrane. (JP-A-57-71)
605 and JP-A-51-89564).

However, in this method, the membrane to be formed is limited to a flat membrane, the mechanical strength is limited because it is an ultrathin film, and the material is limited in order to make it a practical separation membrane. Has the drawback of.

On the other hand, a thin film of a reactive compound solution is formed on a support, and a solution containing a compound that reacts with the compound and forming an interface with the solution is brought into contact with the solution thin film to cause an interfacial reaction on the support. There is a method of forming an ultrathin film on a support. This method is advantageous as a film forming method in that it hardly has the above-mentioned drawbacks of the water surface development method.

Examples of gas separation membranes formed by such a method include the inventions described in JP-A-58-193703 and JP-A-59-49805.

Each of these uses a polymer based on the formation of a urea bond by the reaction of an amino group and an isocyanate group.

As described above, as the separation membrane, the thinner the membrane, the more the amount of permeation increases, which is preferable. However, as the film becomes thinner, the strength of the film becomes smaller, which is conversely a problem in terms of mechanical properties such as damage to the film and deterioration of durability.

In particular, this thin film forming method has a tendency that the degree of polymerization does not easily rise because it is interfacial polymerization without stirring even though it is called interfacial polymerization.

Therefore, it is necessary to increase the strength of the membrane, and as a measure for that, it is conceivable to increase the degree of polymerization of the polymer or to introduce a crosslinked structure.

Among them, when using a polyfunctional compound having three or more functional groups as a method for introducing a crosslinked structure, the probability of forming a bond is higher than that of the reaction between the bifunctional compounds, the molecular weight of the polymer increases, and It also improves the degree.

Both polysiloxane compounds and polyisocyanate compounds are conceivable as the three or more polyfunctional compounds, but there have been many examples of conventional polysiloxane compounds. However, in order to increase the oxygen and nitrogen selectivity of the film, a polysiloxane compound having a low siloxane content is suitable, and in that case, most of the bifunctional siloxane compounds are preferable.
Therefore, a polyfunctional compound is required as an isocyanate component.

On the other hand, the reactivity of isocyanate groups to amino groups is
Usually, the order is aromatic>alicyclic> aliphatic, with aromatic being most preferred. Therefore, the present invention has been achieved as a result of intensive studies on aromatic and polyfunctional isocyanate compounds.

That is, the present invention provides a porous support (A), a polysiloxane compound having two or more amino groups, and an isocyanate compound represented by the following formula (I). And a polyurea-based selective permeation membrane (B) mainly formed from a reaction product of

The isocyanate compound used in the present invention, that is, tris (4-isocyanatophenyl) methane, is a white solid having a melting point of 89 to 90 ° C. obtained by reacting tris (4-aminophenyl) methane, which is a corresponding amine compound, with phosgene.

The isocyanate compound of the present invention can be easily dissolved in an aliphatic, alicyclic, aromatic or halogenated hydrocarbon solvent in the same manner as the diisocyanate compound, and the combination of the interfacial polymerization solvent can be applied without any difference from the conventional diisocyanate compound. .

In the present invention, aromatic compounds such as 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, toluylene diisocyanate and m-phenyl diisocyanate having two isocyanate groups within the range not impairing the object of the present invention. Aliphatic-aromatic diisocyanates such as diisocyanate, m-xylylene diisocyanate, alicyclic diisocyanates such as 4,4′-cyclohexylmethane diisocyanate and isophorone diisocyanate, diisocyanate compounds such as hexamethylene diisocyanate and tetramethylene diisocyanate Can be added.

Of course, an aromatic diisocyanate compound is preferable from the viewpoint of reactivity. The amount of such diisocyanate is preferably 50 mol% or less of all isocyanate components.

As the compound having an amino group which reacts with such an isocyanate compound, a polyamine compound having a siloxane structure having a structure having excellent permeability is used. That is, a polysiloxane compound having two or more amino groups is used in the present invention. Examples of such a compound include the following formula (II) Having at least two structural units represented by
Moreover, the polysiloxane which has at least one -Si-O-Si- bond in a molecule can be mentioned.

More specific examples of such compounds are represented by the following formula (II
Examples include I) and (IV).

If these are shown more concretely, the following can be mentioned as preferable ones.

These compounds can be used alone or as a mixture of two or more kinds.

Since the polysiloxane compound having an amino group used in the present invention forms a polymer by the polyaddition reaction with the isocyanate compound of the formula (I), the number of amino groups in the polysiloxane compound is at least two. A compound having three or more primary and / or secondary amino groups is used in order to make the crosslinked structure dense, but as described above, introduction of the crosslinked structure is achieved even with a compound having two amino groups. it can.

Aliphatic polyamines such as ethylenediamine, hexamethylenediamine, triethylenetetramine, polyethyleneimine and polyvinylamine having at least two primary and / or secondary amino groups having no siloxane bond within the range not impairing the object of the present invention. Alicyclic polyamines such as cyclohexanediamine and piperazine, aromatic polyamines such as metaphenylenediamine, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl ether and polyaminostyrene can be added. The amount of such polyamine is preferably 50 mol% or less based on all amine components.

The porous support (A) in the present invention is not particularly limited as long as it can support the selective permeable membrane (B) and reinforce it in strength. As a base material of such a support (A), a glassy porous material, a sintered metal, an inorganic material such as ceramics,
Cellulose ester, polystyrene, polyvinyl butyral, polysulfone, polyvinyl chloride, polyester,
Examples thereof include organic polymers such as polyacrylonitrile and polyamide.

The polysulfone membrane has particularly excellent performance as the base material of the present invention, and polyacrylonitrile and aromatic polyamide are also effective. The method for producing the polysulfone porous substrate is described in US Salt Water Report (OSW Report) No. 359.

Such substrates generally have a surface pore size of about 50 to 10,000.
Å, preferably between 100 and 1000 Å, but not limited to this, the size of the surface term may vary between 50 and 10000 Å depending on the final membrane application etc. . These substrates can be used in a symmetrical structure or an asymmetric structure, but preferably have an asymmetric structure.

As these base materials, those having an air permeability measured by a device of JIS P8117 of 20 to 3000 seconds, more preferably 50 to 1000 seconds are used. When the air permeability is 20 seconds or less, defects are likely to occur in the composite film obtained by using it, and the selectivity is likely to be lowered. Further, when the time is 3000 seconds or less, the air permeability of the composite film obtained by using the same is low.

Further, it is preferable that the base material has a maximum pore size of 1 μm or less, preferably 0.5 μm or less.

The shape of the support (A) may be various according to the shape of the target separation membrane, and specific examples include a flat plate shape, a tube shape, and a hollow shape. The thickness of the support is not limited, but is usually 10 μm to 10 mm, preferably 50 μm to
It is 1000 μm.

The selective permeable membrane (B) of the present invention usually has a thickness of 30Å to 10 μm.
m, preferably 50Å to 2000Å, more preferably 100Å
It is ~ 1000Å. Such a selectively permeable membrane (B) is obtained by (1) applying a polyaminopolysiloxane solution onto the porous support (A), and then forming a solution containing an isocyanate compound and capable of forming an interface with the above polyaminopolysiloxane solution. The selective permeation membrane (B) is formed on the support (A) by coating and contacting, or (2) The selective permeation on the support (A) is performed by reversing the coating order of the solution in (1). A film (B) can be formed.

At that time, the polyaminopolysiloxane solution is prepared by adding the compound to water, methanol, ethanol, isopropanol, methyl cellosolve, dioxane, ethylene glycol, diethylene glycol, triethylene glycol, glycerin, n-hexane, n-decane, hexadecene, benzene,
It can be easily prepared by dissolving it in a solvent such as toluene or xylene or a mixed solvent of two or more kinds of these, and the concentration of the polyaminopolysiloxane is 10%.
ppm to 10 wt%, preferably 100 ppm to 5 wt%.

On the other hand, the solvent for the isocyanate compound is preferably an aliphatic, alicyclic or aromatic hydrocarbon having 6 to 20 carbon atoms, or a halogenated hydrocarbon, and specific examples include:
n-hexane, n-heptane, n-octane, n-decane, n-
Examples thereof include tetradecane, hexadecene-1, octadecene-1, cyclohexane, cyclohexene, benzene, toluene, xylene, carbon tetrachloride, trifluorotrichloroethylene and the like.

It is also used in the form of a mixed solvent of two or more of these. The concentration is 10 ppm to 10 wt%, preferably 500 ppm to 5 wt%.

The selection of the solvent for each compound should be made in such a combination as to have an interface-forming property suitable for the reaction because both compounds need to cause an interfacial reaction. However, even if they have a little mutual solubility, if such an interface is actually formed and an interfacial reaction is achieved, such a combination is acceptable.

The method for applying each solution to the support (A) may be variously changed depending on the shape of the porous support (A) and the type of solvent used, but typical methods include dipping, roll coating and wick coating. Method and spray coating method.

As a method for forming a membrane, for example, when the porous support (A) is in the form of a flat membrane, the support (A) is immersed in a solution of polyaminopolysiloxane, taken out of the solution and drained, and then an interface with the solution is formed. One of the methods is to immerse in the solution containing the obtained isocyanate compound to form an interface between the two kinds of solutions on the support (A) and form a film by an interfacial reaction.

The order can also be reversed if both are solutions. Immersion can be carried out by a batch method or a continuous method. When the support (A) is in the form of hollow fiber, the polyaminopolysiloxane solution is impregnated into the outside or inside of the hollow fiber in the same manner as in the case of the flat membrane, and if it is outside, it is immersed in an isocyanate solution or In some cases, a membrane can be formed by flowing an isocyanate solution inside the hollow fiber. Of course, the order can be reversed. This method of forming a membrane on the inner surface of the hollow fiber is very advantageous in handling the membrane since the formed ultrathin film having low mechanical strength can be handled without touching it with hands.

After film formation, the unreacted compound or solution can be washed with a low boiling point and / or low viscosity organic solvent or water. In addition, a heat treatment for completing the reaction can also be performed. The temperature is a temperature that does not cause deformation of the support or the membrane, and is usually in the range of 50 to 200 ° C, and the time is 1 to 120.
Minutes are good.

Further, in the present invention, a protective layer may be provided on the film of the present invention. The protective layer is effective for further improving the mechanical strength of the film and repairing fine defects in the film. As the material for the protective layer, it is desirable to avoid lowering the permeability of the membrane, and therefore, a material having excellent permeability, such as polysiloxane or poly (substituted acetylene), is suitable.

Among them, the curable polysiloxane is particularly preferable because the precursor is dissolved in a solvent and applied, so that it can be applied thinly because of its low viscosity, and the coating film after curing has elongation and the surface curing degree can be easily adjusted. .

The membrane of the present invention can be used for separation of various gases by utilizing its excellent permeability and excellent selectivity.

For example, a combustion furnace installed in a device that concentrates oxygen from air,
Improve combustion efficiency of engine, etc., as a treatment device for patients with respiratory diseases, and industrially for separation of carbon monoxide, concentration of helium from natural gas, separation of sulfur dioxide or carbon dioxide from exhaust gas Can do well.

Further, the membrane of the present invention can be used as a membrane for bar vaporization for separating ethanol-water system.

The present invention is described below with reference to examples, but the present invention is not limited thereto.

In the examples, "part" represents part by weight.

Example 1 0.3 part of an amine compound represented by the following formula And a solution consisting of 99.7 parts of ethylene glycol, a flat membrane polysulfone porous membrane lined with a polyester non-woven fabric [using polysulfone (Udel p3500), air permeability 2.1 x 1
0 ^-2 cc / cm ² · sec · cmHg] was soaked for 10 minutes and then pulled up and drained sufficiently.

Then tris (4-isocyanatophenyl) methane 0.
It was immersed in a solution consisting of 3 parts and hexadecene-199.7 parts for 5 minutes. After pulling up, it was left at room temperature for 30 minutes, washed with an n-hexane solution, then with water and dried to obtain a film. When the gas permeation performance was measured at a temperature of 20 ° C using a Seikaken gas permeability meter manufactured by Rika Seiki Co., Ltd. at 20 ° C, the oxygen permeation rate was 2.8 × 10 ^-4 cc / cm ² · sec.・ CmHg, oxygen and nitrogen selectivity (oxygen permeation rate / nitrogen permeation rate) was 3.4.

Example 2 Amine compound represented by the following formula A composite membrane was obtained by the same operation as in Example 1 except that was used.

The oxygen permeation rate of the composite membrane was 4.5 × 10 ^-4 cc / cm ² · sec · cmHg Oxygen and nitrogen selectivity was 3.0.

Example 3 20 parts of polysulfone (Udel p3500), N-methylpyrrolidone
57 parts, lithium chloride 3 parts and 2-methoxyethanol 20
Part of the solution was prepared, and the solution was discharged from the annular slit at 30 ° C. using water as the core liquid and immersed in water at 25 ° C. to solidify. Thus, a polysulfone hollow porous support having an outer diameter of 800 μm and an inner diameter of 500 μm was obtained. This hollow porous support was packed in a polycarbonate pipe and both ends were solidified with an adhesive to obtain a hollow fiber module.

The air permeation rate of this hollow porous support at 20 ° C. when dried was 1.1 × 10 ⁻² cc / cm ² · sec · cmHg.

A 0.4 part% ethylene glycol solution of the amine compound used in Example 1 was poured inside the hollow fiber module, and the inside of the hollow fiber module was kept at 1 Kg / cm ² -G pressure for 10 minutes to make the amine solution porous. It was filled in the support.

Then, nitrogen gas was flown to remove the liquid, and then a 0.4 part% tris (4-isocyanatophenyl) methane solution in hexadecene was flowed for 5 minutes inside the support.

Then, flush with nitrogen gas, drain and wash with hexane to wash, then immerse the hollow fiber module in water and wash with water,
Then, it was dried to obtain a composite film. Pure oxygen and pure nitrogen were passed inside the membrane at 20 ° C, respectively, and oxygen and nitrogen that had permeated through the membrane were extracted with a large amount of helium gas and analyzed by gas chromatography to determine the permeation rate of oxygen and nitrogen. It was measured.

As a result, the oxygen transmission rate is 2.0 × 10 ^-4 cc / cm ² · sec · cmH.
g, selectivity was 3.4.

Example 4 The film forming operation was performed in the same manner as in Example 3. Of the amine compound of the formula A 0.1 part% ethylene glycol solution is first loaded into the porous support, and then a 0.1 part hexadecene solution of tris (4-isocyanatophenyl) methane is run inside the support for 5 minutes. Then, drain, wash with water and dry.

After that, a solution of 3 parts of curable silicone consisting of terminal silanol polydimethylsiloxane (average molecular weight of 30,000), methyltrimethoxysilane as a cross-linking agent and alkyl titanate as a catalyst, and 97 parts of hexane was poured inside the hollow fiber support, After cutting, it was left for 24 hours to cure.

The membrane thus obtained has an oxygen transmission rate of 4.1 × 10 ^-4 cc / cm ² s
The ec · cmHg, selectivity was 2.9.

Example 5 A film was obtained in the same manner as in Example 3 except that the amine compound represented by the following formula was used.

The oxygen permeation rate of this membrane is 4.4 × 10 ^-4 cc / cm ²・ sec ・ cmHg,
The selectivity of oxygen and nitrogen was 3.0.

Claims (1)

[Claims] 1. A porous support (A), a polysiloxane compound containing two or more amino groups, and an isocyanate compound represented by the following formula (I): A separation membrane comprising a polyurea-based selective permeation membrane (B) mainly formed from a reaction product of