JPH0696106B2 - Gas separation membrane - Google Patents

Description

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

Oxygen exists in the air at a concentration of about 21%, but if air with an increased oxygen concentration is supplied, combustion efficiency up in a boiler or automobile engine, combustion utilization of low-grade fuel, or respirator It is useful as breathing air for people with systemic diseases.

A membrane separation method is a simple method for separating oxygen in the air. However, in the membrane separation method, it is difficult to completely separate oxygen and nitrogen in the air by one-step separation, and what is actually being carried out is the production of so-called oxygen-enriched air with an increased concentration of oxygen. The high oxygen concentration that can be obtained by passing the membrane once is about 40% among those currently put into practical use. About 40% of the oxygen-enriched air is used for breathing air.

In order to obtain an enriched air with a relatively high oxygen concentration by the membrane separation method, it is necessary to select a membrane having good separability between oxygen and nitrogen, but generally a good separability is due to oxygen permeability. Tends to be small, and therefore it is actually necessary to select a membrane material having a good balance between oxygen and nitrogen separation and oxygen permeability. On the other hand, since the permeation rate of oxygen that permeates the membrane is inversely proportional to the film thickness, it is also important that the film can be formed to an extremely thin thickness in order to increase the permeation rate.

From this viewpoint, polymethylpentene or poly-2,6-dimethylphenylene ether, for example, is selected as a membrane material having good separability and relatively large oxygen permeability.
Various ultra-thin film forming methods have been proposed (see, for example, Japanese Patent Laid-Open No.
57-71605 and JP-A-51-89564).

However, each of these has a flat membrane shape, and is not suitable for a hollow fiber membrane capable of increasing the membrane area per module volume.

The present inventor has proposed a film material and a film forming method capable of easily forming an ultrathin film in the form of a flat film or a hollow fiber film (JP-A-58-193701 and JP-A-58-193703). See the bulletin).

Such a separation membrane can be varied from a high oxygen / nitrogen selectivity to a low oxygen / nitrogen selectivity depending on the content of dimethylsiloxane in the membrane structure. To change.

Thus, although it is known that the characteristics of the membrane can be varied, it is possible to obtain a relatively high concentration of oxygen-enriched air at an effective rate, that is, to keep the oxygen / nitrogen separation characteristics high. In addition, there are few membrane materials suitable for it from the viewpoint of a higher degree of balance that oxygen permeability is high.

Therefore, the present invention has been achieved as a result of intensive studies to obtain a separation membrane in which an ultra-thin film can be formed by interfacial polymerization and the oxygen / nitrogen separation characteristics and the oxygen permeability are well balanced.

That is, the present invention provides a compound represented by the following formula (I) and a compound represented by the following formula (II) A gas separation membrane mainly composed of an amine component and a polyisocyanate component in which the compound represented by the formula (II) is 45 mol% or less of the whole mixture.

In the membrane separation method of about 40%, when oxygen-enriched air, which has a relatively high concentration of oxygen, is obtained from air in a single-stage separation, the membrane separation characteristics required, that is, the permeation of oxygen and nitrogen. The selectivity expressed by the ratio of the coefficients should be 2.5 or more, but this is the case when the separation proceeds in the ideal state, and in reality, the difference between the pressure driving the separation driving force and the pressure applied to both sides of the membrane. Or the concentration polarization generated on the surface of the membrane deteriorates the separation.

Therefore, a membrane having higher selectivity than the ideal state is required.
At present, in the separation of air by a membrane, in order to reduce the energy required for the separation (actually, the driving power cost of the pump for generating the pressure), the permeate side of the membrane is often depressurized. , Pump capacity, etc. 150
Often set to ~ 200 Torr. In order to obtain about 40% oxygen-enriched air under such operating conditions, the selectivity of the membrane should be at least 3.5, preferably 3.7 or more. And
A material having such selectivity and high oxygen permeability is required. Practically, the oxygen permeability coefficient is at least 5 × 10 ^-10 cc (STP) · cm / cm ² · sec · cmHg. , Preferably 7 × 10 ⁻¹⁰ cc (STP) · cm / cm ² · sec · cmHg or more.

And it is important that such a membrane material can be formed into a thin film, and the thickness of the separation membrane in the case of a thin film is 0.2μ.
m or less, preferably 0.1 μm or less is suitably used.

The amine component used for forming such a separation membrane is a mixture of at least two kinds of compounds, and one of the components, an amine compound (referred to as amine component (I)), has the following formula (I): Is represented by. Here, n represents 1, 2 or 3.

As the amine compound having a larger n is used, the permeability is increased, but the selectivity is decreased.

A separation membrane can be formed only from such a diamine and polyisocyanate, and the performance of the formed membrane can be changed by changing the type of polyisocyanate used, but generally, these have high oxygen / nitrogen selectivity. However, only those with low oxygen permeability can be obtained.

Therefore, in order to increase oxygen permeability, a diamine represented by the following formula (II) (amine component (II)) is used as a copolymerization component.
Called. ).

Is the gist of the present invention.

By adding this, the permeation rate can be increased. That is, the oxygen permeation rate increases as the amine component (II) increases. On the other hand, although the selectivity decreases,
The film characteristics can be easily controlled by the amount added,
It is easy to find the optimum balance between oxygen / nitrogen selectivity and oxygen permeability.

The amount of the amine component (II) depends on the type of the amine component (I) and the type of polyisocyanate to be used, and the required characteristics of the film, but is usually 45 mol% or less of the total amine component, preferably Is 40 mol% or less, and 5 mol% or more, preferably 10 mol% or more of the total amine components.

The polyisocyanate component used in the present invention has at least two isocyanate groups in the molecule. For example, as the aromatic polyisocyanate, the following formula (III) A compound represented by the following formula (IV) And a compound represented by the following formula (V) [However, in the formula, m is a positive integer. ] The compound represented by
-Diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 3,4'-diphenyl ether diisocyanate, toluylene diisocyanate and phenylene diisocyanate. Also,
Examples of the alicyclic polyisocyanate include isophorone diisocyanate and cyclohexyl diisocyanate, and examples of the aliphatic polyisocyanate include hexamethylene diisocyanate and tetramethylene diisocyanate.

Among these, aromatic polyisocyanates having high reactivity with a diamine component are preferred, and aromatic diisocyanates are preferred, and further compounds represented by formula (III), particularly 4,4'-diphenylmethane diisocyanate, 4,
4'-diphenyl ether diisocyanate and 3,
4'-diphenyl ether diisocyanate is preferred because it has a good balance of transmission characteristics.

Therefore, particularly preferable configurations of the present invention include the following formulas (VI) and (VII) It is composed of repeating units represented by (VII) / {(V
An example is a separation membrane mainly composed of a polymer in which (I) + (VII)} is 0.45 or less.

The membrane of the present invention is a polymer solution obtained by polymerizing the diamine component and the polyisocyanate component in a solvent, and then casting and desolvating on a flat plate such as a glass plate, or on a porous support. Although it can be obtained by coating and removing the solvent, a characteristic of the composition of the membrane of the present invention is that polymerization and thin-film formation can be simultaneously performed on the porous support.

That is, (1) First, a solution of a diamine component is applied onto a porous support, and then a polyisocyanate component is contained,
In addition, a solution capable of forming an interface with the solution is applied and brought into contact with the solution to form a separation membrane on the porous support, or (2) the application order of the two solutions is reversed, and the support is applied. It is to form a separation film on the top.

At that time, the diamine component solution may be prepared by dissolving the diamine component in a solvent such as ethanol, isopropyl alcohol, methyl cellosolve, dioxane, ethylene glycol, diethylene glycol, glycerin or triethylene glycol, or a mixed solvent of two or more thereof. It is easily adjustable. Diamine component concentration is 10pp
It is m-10 wt%, preferably 100 ppm-5 wt%.

On the other hand, the polyisocyanate component solution is the compound n-
Dissolve in a solvent such as hexane, n-heptane, n-octane, cyclohexane, n-decane, n-tetradecane, hexadecene, benzene, toluene, xylene, carbon tetrachloride or trifluorotrichloroethylene or a mixed solvent of two or more thereof. To adjust. Its concentration is 10pp
It is from m to 10 wt%, preferably from 50 ppm to 5 wt%.

The choice of solvent for each compound should be made in a combination that is suitable for the reaction, because both compounds must undergo an interfacial reaction. However, even if there is mutual solubility to some extent, such a combination may be used as long as the interface is actually formed and the interface reaction is achieved.

The porous support is not particularly limited as long as it can support the permselective membrane and reinforce it in strength. Examples of the base material of such a support include inorganic materials such as glassy porous materials, sintered metals and ceramics, and organic polymers such as cellulose ester, polystyrene, vinyl butyral, polysulfone, polyvinyl chloride, polyester and polyacrylonitrile polyamide.

Among them, the polysulfone film has particularly excellent performance as the base material of the present invention, and polyacrylonitrile and aromatic polyamide are also effective. A method for manufacturing a polysulfone porous substrate is described in a report by the US Salt Water Agency (OSW R.epor
t) 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 these, the size of the pores on the surface may vary between 50 Å ~ 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 more, the air permeability of the composite film obtained by using the same is low.

Also, the substrate has a maximum pore size of 1 μm.
Hereafter, it is preferably 0.5 μm or less.

The shape of the support may be various depending on the shape of the target separation membrane, and specific examples thereof include a flat plate shape, a tube shape, and a hollow fiber shape. The thickness of the support is not limited, but is usually 10 μm to 10 mm, preferably 50 μm to 1000
μm.

The method of applying each solution to the support can be variously changed depending on the shape of the porous support and the type of solvent used, but typical methods include dipping, roll coating, wick coating and spray coating. Law etc. are mentioned. As a method for forming a membrane, for example, when the porous support is in the form of a flat membrane, the support may be immersed in one of the solutions, removed from the solution and drained, and then an interface with the solution may be formed. One method is to immerse it in the other solution to form an interface between the two solutions on the support and form a film by an interfacial reaction. The immersion can be performed by the patch method or the continuous method.

When the support is a hollow fiber, as in the case of a flat membrane, dip the reaction solution in the reaction solution one by one so that it does not enter the inside of the hollow fiber to form a film on the outside of the hollow fiber support. Alternatively, the reaction solution may be sequentially flown inside the hollow fiber support to form a membrane. This method of forming a membrane on the inner surface of the hollow fiber is very advantageous in handling the membrane since the ultrathin film having low mechanical strength can be handled without touching it after the membrane is formed.

After the film formation, the unreacted compound or solvent can be washed with an organic solvent or water having a low boiling point and / or a low viscosity. Further, a heat treatment can be carried out to complete the reaction. 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 1
20 minutes is good.

The performance of the membrane thus obtained is at least 3.5, preferably 3.7 or more as the oxygen / nitrogen selectivity and at least 5 × 1 as the oxygen permeability coefficient as described above as the original performance of the membrane.
0 ^-10 cc (STP) ・ cm / cm ²・ sec ・ cmHg, preferably 7 × 10
^-10 cc (STP) · cm / cm ² · sec · cmHg or more.

The practical thickness of the separation membrane is 0.2 μm or less, preferably 0.1 μm or less.

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

In particular, in the separation of air, a relatively high concentration of oxygen-enriched air can be obtained, and it can be used as a treatment device for respiratory illnesses and as a device for improving combustion efficiency such as combustion and engine, In addition, for other industrial uses, separation of hydrogen and carbon monoxide can be performed efficiently, and helium can be concentrated from natural gas and sulfur dioxide or carbon dioxide can be efficiently separated from exhaust gas.

Further, the membrane of the present invention can also be used as a membrane for pervaporation which performs separation of an ethanol water system.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

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

Example 1 Polyethylene terephthalate non-woven fabric (weight per unit area 180 g /
on the m ^2), polysulfone (Udel 3500) 15 parts%, N-
A solution consisting of 85% by weight of methylpyrrolidone was cast at a thickness of 300 μm, and the polysulfone layer was immediately gelled in a water bath at room temperature to obtain a nonwoven fabric-reinforced porous polysulfone membrane.

Separately, 70 mol% of bis (3-aminopropyl) hexamethyltrisiloxane (n = 2 in the compound of formula (I)) and 3
An amine component consisting of 30 mol% of-(2-aminoethylaminopropyl) tolu (trimethylsiloxane) silane.
A solution prepared by dissolving 1 part in 99.9 parts of ethylene glycol was prepared and the non-woven reinforced porsulfone support membrane was immersed in the solution for 10 minutes.
After pulling up, drain with a rubber roller, 4, 4'-
Diphenyl methane diisocyanate was immersed in a 0.05 wt% hexadecene solution for 3 minutes for reaction.

Then, it was immersed in water, washed with water, and then air-dried to obtain a composite film.

The performance of this membrane was measured by an isobaric method while sending pure oxygen and pure nitrogen to the thin film side and sweeping the permeate side with helium using a gas permeability measuring device by gas chromatography.

The results are shown in Table-1.

In Examples 2 to 3 and Comparative Examples 1 to 3, as the amine component, a 0.1 wt% ethylene glycol solution having the composition shown in Table 1 was used, and the isocyanate component was used as Table 2.
A 0.05 wt% hexademan solution of the compound 1 was used to form a film in the same manner as in Example 1, and the performance was determined.

The results are shown in Table-1.

Example 4 A solution consisting of 20 parts of polysulfone (udel 3500), 57 parts of N-methylpyrrolidone, 3 parts of lithium chloride and 20 parts of 2-methoxyethanol was discharged from a cyclic slit using water as a core liquid and immersed in water to coagulate. Outer diameter obtained by
A polysulfone hollow fiber support having a diameter of 900 μm and an inner diameter of 600 μm was packed in a polycarbonate pipe and both ends were solidified with an adhesive to obtain a hollow fiber membrane module.

Separately, 75 mol% of bis (3-aminopropyl) hexamethyltrisiloxane and 25 mol% of 3- (2-aminoethylaminopropyl) tris (trimethylsiloxane) silane.
The amine component consisting of 0.1 wt% was dissolved in an ethylene glycol solution and introduced into the inside of the hollow fiber support to drain the liquid, and then a 4,4'-diphenyl ether diisocyanate solution of 250 ppm in octadecene was also added inside. It was sent to. After feeding the solution for 3 minutes, a hexane solution was flown inside to wash, and then washed once in running water and air-dried sufficiently to obtain a hollow fiber composite membrane.

When the permeation performance of this membrane was measured under the same pressure as the flat membrane, the oxygen permeation rate (KO ₂ ) was 24 × 10 ^-4 cc / cm ² · sec · cmH.
g, selectivity (KO ₂ / KN ₂ ) 3.8.

Claims (2)

[Claims] 1. A compound represented by the following formula (I) and a compound represented by the following formula (II) A gas separation membrane mainly composed of an amine component and a polyisocyanate component in which the compound represented by the formula (II) is 45 mol% or less based on the whole mixture. 2. The polyisocyanate component is selected from 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate and 3,4'-diphenyl ether diisocyanate. The gas separation membrane according to claim 1.