JPH022608B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for producing a permselective composite membrane with good gas permeability, and particularly to a method for producing a separation membrane effective for obtaining oxygen-enriched air from air. It is. Currently, devices that utilize combustion energy, such as home heating appliances, automobile engines, and boilers, are designed and operated on the basis that oxygen exists in the air at a concentration of approximately 20%. If air with increased oxygen concentration were now supplied, not only would problems such as environmental pollution caused by incomplete combustion be solved, but it would also be possible to increase combustion efficiency. The air with increased oxygen concentration is also useful for breathing by people with respiratory disorders and premature infants. As a method of obtaining air with such a high oxygen concentration, there is a method of selectively separating and concentrating oxygen in the atmosphere using a polymer membrane. Generally, the amount of gas permeating through a homogeneous membrane is expressed by the following equation. X=P×△p×A/l [Here, X is the gas permeation rate (cc (STP/sec),
P is the gas permeability coefficient (cc(STP)・cm/ ^cm2・sec・
cmHg), Δp is the partial pressure difference on both sides of the membrane (cmHg), and l is the membrane thickness (cm). ] Therefore, in order to increase the amount of gas permeation as much as possible with a compact device, it is necessary for the membrane separation method to select a material with a large gas permeability coefficient and to make the membrane thickness as thin as possible. On the other hand, thin film forming methods for gas separation include a method in which a thin film is formed by spreading a polymer solution on the water surface (for example, see Japanese Patent Application Laid-Open No. 1983-41958), or a method in which a film is formed from a polymer solution and a part of the solvent is evaporated. Various methods have been proposed, such as an asymmetrical film forming method in which the membrane is formed by soaking in a coagulating solution after drying (for example, see US Pat. No. 4,120,098), but as a thin film forming method different from these methods, composite membrane forming is There is a law. This method is a film forming method using in-situ polymerization on a porous support membrane. A polymer or monomer solution is coated on the porous membrane support, and then a solution of a polyfunctional reactant is brought into contact with the solution, resulting in solution-solution contact. This is a method for forming ultra-thin films. This membrane production method is often applied to the production of liquid phase separation membranes such as reverse osmosis membranes, rather than gas separation membranes.
This film forming method using solution-solution contact has the following drawbacks. Due to liquid-liquid contact, the thickness of the thin film formed is difficult to be uniform due to fluctuations in the liquid phase during contact.
It is also prone to defects. Generally, a highly volatile solvent that is immiscible with water is used as a solvent for dissolving a polyfunctional reactant, but it is uneconomical to use the solvent and there are dangers such as fire and toxicity of the solvent. Therefore, in the case of liquid phase separation membranes, the manufacturing method involves contacting a water-soluble polymer with functional groups coated on a porous support with steam containing a polyfunctional cross-linking agent capable of cross-linking with this water-soluble polymer. A method of forming a thin film was proposed (see Japanese Patent Application Laid-Open No. 147604/1983). However, when the membrane obtained by this method is used as a separation membrane for mixed gases, the amount of permeation is small and it is not suitable for practical use. The reason for this is that unreacted polymers in the porous membrane block the pores in the porous membrane, and in liquid phase separation, especially separations that involve water, the water-soluble unreacted polymers are washed away by water. In the case of gas separation, this is not the case, and it is thought that this is because the permeation of gas is obstructed and the amount of permeation is reduced. In order to avoid such drawbacks, it is conceivable to use a monomer as the compound coated on the porous membrane, but it is extremely difficult to form a membrane with no defects and a high degree of polymerization using monomers. If this is a liquid phase separation membrane, defects will only cause a slight reduction in rejection rate, but in gas separation, minute defects will cause a large drop in selectivity, making it almost impractical. . As a result of intensive research into composite membranes for gas separation that do not have such drawbacks, the present inventors selected an amine compound with a specific viscosity as a compound to be coated on a porous support membrane, and added it to a composite membrane with at least two isocyanate groups or We have discovered that a gas separation composite membrane with high permeability and high selectivity can be produced by contacting with the vapor of a compound having a thioisocyanate group, and have arrived at the present invention. That is, the present invention exhibits a liquid state at room temperature and at 25°C.
A polyamino compound having at least two primary and/or secondary amino groups having a viscosity of 1000 centistokes or less is dissolved in a soluble solvent, and the resulting solution is applied onto a porous support membrane. A composite for gas separation, characterized in that the membrane base thus obtained is brought into contact with a vapor containing a compound having at least two isocyanate groups and/or thioisocyanate groups to form an ultra-thin film on the support membrane. This is a method for manufacturing a permeable membrane. According to the present invention, it is the vapor of the compound having an isocyanate group or a thioisocyanate group that comes into contact with the solution of the amino compound on the support membrane, and the above-mentioned problems in solution-solution contact are also solved. A stable membrane can be produced. The polyamine compound used in the present invention is liquid at room temperature and has a viscosity of 1000 centistokes or less at 25°C. If the viscosity is larger than this value, it is difficult for the permeate gas to wash away the amino compound stuck in the pores of the porous membrane support, blocking the flow path of the permeate gas, resulting in a decrease in the amount of permeation. The viscosity is 1000 centistokes or less, preferably 500 centistokes or less, more preferably
200 centistokes or less. Furthermore, if the polyamino compound is solid at room temperature, it will remain in the pores of the porous membrane support and will obstruct the gas flow path, which is undesirable. such at least two primary and/or secondary
Specific examples of polyamino compounds having a class amino group include aliphatic or alicyclic polyamines such as ethylene diamine, propylene diamine, trimethylhexamethylene diamine, diaminocyclohexane, isophorone diamine, diethylene triamine, triethylene triamine, and dipropylene triamine. be able to. In particular, in the present invention, a separation membrane with even better permeability can be obtained by using a diamine having a siloxane structure represented by the following general formula (). [However, in the formula, l and m are the same or different, an integer of 2 to 10, preferably 3 to 8, n is an integer of 1 to 200, preferably 1 to 100, R ₁ is a hydrogen atom, a methyl group, an ethyl group, or a phenyl group, _R2 , _R3 , _R2 ' and _R3 ' are the same or different and represent an alkyl group, an alkenyl group or a phenyl group having 1 to 5 carbon atoms. ] All diamines having a siloxane structure of the above formula () have at least
It is desirable to use 50 mol%, preferably at least 70 mol%. Specific examples of such diamines of formula () include the following. Furthermore, polysiloxanes having the following repeating units can also be used as polyamines. for example [In these formulas, a, b, and c represent an integer of 1 or more. ] The polyamino compounds explained above can be used alone, but a mixture of two or more can also be used in the same way. Among these polyamino compounds, diamines and/or the polysiloxanes having the siloxane structure of the formula () are preferable because of their high gas permeability; Particularly preferred are diamines having In the present invention, the compound having at least two isocyanate groups and/or thioisocyanate groups to be reacted with the polyamino compound needs to have a certain vapor pressure under the film forming conditions described below. Cannot be used if it causes decomposition. Examples of usable isocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate, phenyl diisocyanate, and diphenylmethane diisocyanate, and aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, cyclohexane diisocyanate, metaxylylene diisocyanate, and the like. be able to. Furthermore, a diisocyanate having a siloxane structure as represented by the following formula can be used similarly. Specific examples of the thioisocyanate compound include compounds in which the isocyanate group in the isocyanate compound described above is replaced with a thioisocyanate group. The porous support membrane used in the method of the present invention is preferably one whose surface pore size is generally between about 100 and 1000 angstroms, but is not limited to this, depending on the final use of the membrane, etc. depending on,
The stated pore size can vary between 10 Å and 5000 Å. These substrates can be used in either symmetrical or asymmetrical structures, but asymmetrical structures are preferable. However, these base materials are JIS P 8117
The air permeability measured by the above device is 20 to 3000 seconds, more preferably 50 to 1000 seconds. If the permeability is 20 seconds or less, the composite membrane obtained is likely to have defects and its selectivity may be reduced. Also,
If the time is longer than 3000 seconds, only a composite membrane with low air permeability can be obtained. Examples of the base material for such a support film include porous glass materials, sintered metals, ceramics, and organic polymers such as cellulose esters, polystyrene, vinyl butyral, polysulfone, and vinyl chloride. Polysulfone membranes have particularly excellent performance as substrates in the present invention, and polyvinyl chloride is also effective. The manufacturing method for polysulfone porous substrates is published in the U.S. Office of Salt Water Report (OSW Report)
It is also listed in No.359. In the method of the present invention, first, a solution of the polyamino compound is applied onto the porous support. The coating method may be any method such as a dipping method, a roll coating method, a wick coating method, or a spray coating method. Further, as a solvent for dissolving the polyamino compound, any solvent may be used as long as it dissolves the polyamino compound, does not damage the base material of the porous membrane support membrane, and does not have an amino group that reacts with an isocyanate group or a thioisocyanate group. Although it is possible to use water, methanol, ethanol, isopropanol, methylcellobutdioxane, tetrahydrofuran, toluene, xylene methyl ethyl ketone, or a mixture of two or more of these solvents are usually used. The concentration of the polyamino compound in the solution is determined by its ability to be applied evenly onto the porous membrane support membrane, and is not particularly limited, but is usually 0.1.
~10% by weight, preferably 0.2-5% by weight is suitable. In extreme cases, it is also possible to apply the polyamino compound itself. The coating thickness of the polyamino compound solution is usually
It is recommended that the thickness be in the range of 0.1 to 50μ, preferably 0.5 to 10μ. Next, the membrane base obtained by coating the polyamino compound solution on the porous support membrane in this way is
A film is formed on the porous film by contacting it with vapor of a compound having at least two isocyanate groups and/or thioisocyanate groups (hereinafter referred to as a reaction compound). The vapor pressure of the reaction compound used in the vapor atmosphere varies depending on the reaction compound used and the temperature, but it is desirable to have a vapor pressure of 0.1 mmHg or more, preferably 0.2 mmHg or more during use. . In the case of a reaction compound with a low vapor pressure, it is necessary to raise the temperature to increase the vapor pressure. However, if the temperature is raised too much, the polyamino compound and solvent coated on the porous support membrane will evaporate.
The temperature is 150℃ or less, preferably 95℃ or less,
More preferably, the temperature is 70°C or lower. In addition, the contact time in the reaction compound vapor atmosphere varies depending on the combination of the reaction compound and polyamino compound used, the temperature, etc.
The contact time is preferably 1 second to 1,800 seconds, but if a film can be formed, the contact time is preferably as short as possible to reduce the film thickness. In the present invention, gases other than the vapor, such as air, nitrogen, argon, neon, organic chlorofluorocarbons, etc., which do not participate in the reaction between the reaction compound and the polyamino compound may also be used together with the reaction compound vapor in the reaction compound vapor atmosphere. can. This makes it possible to dilute the concentration of the reaction compound and prevent dangers such as explosions, and also to generate the reaction compound vapor elsewhere and to flow the gas such as air or nitrogen to react on the substrate surface of the porous support membrane. It is also possible to send a vapor containing a compound and bring it into contact. A thin composite membrane with permselectivity on a porous support membrane is thus obtained, which, by drying, can be used as a separation membrane. The thickness of the permselective membrane in the membrane is not strictly defined, but can have a total thickness of at least 100 angstroms, usually from 300 to 7000 angstroms. The porous support membrane of the present invention can be in any shape such as a flat membrane or a hollow fiber. Accordingly, the composite membrane of the present invention can be in any form such as a flat membrane or a hollow fiber. Especially when using hollow fiber supports,
A membrane can be formed either on the outside or inside of the hollow fiber by flowing vapor containing the reactive compound on the outside or inside of the hollow fiber. Taking advantage of its excellent gas permeability and selectivity, the membrane of the present invention can be incorporated into devices that produce oxygen-enriched air from air, for example, to improve the efficiency of roasting carrots, heating equipment, etc. It can be used as a substitute for air, as a nursery box for premature babies, as a treatment device for people with respiratory disorders, or as an artificial lung or artificial gills, but is not necessarily limited thereto. The present invention will be described below with reference to Examples, but the present invention is not limited thereto. In the examples, "parts" indicate parts by weight. Reference Example 1 (Production method of non-woven fabric-reinforced polysulfone porous membrane) A densely woven Dacron non-woven fabric (basis weight: 180 g/m ² ) was placed on a glass plate. Next, a solution containing 12.5 wt% polysulfone, 12.5 wt% methylcellosolve, and the remainder dimethylformamide was cast on the nonwoven fabric in a layer having a thickness of about 0.2 μm, and the polysulfone layer was immediately gelled in a water bath at room temperature. A nonwoven reinforced porous polysulfone membrane was obtained. Electron micrographs show that the porous polysulfone layer thus obtained has a thickness of approximately 40 to 70μ, has an asymmetric structure, and has many micropores of approximately 50 to 600Å on its surface. observed.
Further, these porous substrates had an air permeability of 150 to 300 seconds using a JIS P 8117 device. Reference example 2 (Production method of polysulfone hollow fiber membrane) 20 parts of polysulfone (Nissan Chemical, Udel P3500),
70 parts of dimethylformamide, 10 parts of methyl cellosolve
Using water as the core liquid, a solution (25°C) consisting of
A 290 μm polysulfone hollow fiber membrane was obtained. These 16 hollow fibers were packed into a polycarbonate pipe, and both ends were fixed with adhesive to obtain a hollow fiber membrane module with a length of 20 cm. The amount of air permeation through this hollow fiber membrane at 25℃ is 5×10 ^-3 (cc (STP)/cm ²・sec・cm
Hg). Example 1 (viscosity 24 centistokes at 25°C) 1% by weight
The polysulfone porous membrane obtained in Reference Example 1 was immersed in the solution (mixed solvent of ethanol/water = 8/2) for 5 minutes, and then the porous membrane was pulled out from the solution, held vertically, and drained for 10 minutes at room temperature. Leave this in a container. On the other hand, tolylene diisocyanate is placed in a three-necked flask and heated to 40°C, and nitrogen is flowed through it at a flow rate of about 1/min. A nitrogen stream containing this tolylene diisocyanate vapor was introduced into a container containing a porous membrane kept at room temperature for about 15 minutes to form a membrane. When the gas permeation rate was measured at 25°C using a Seikaken gas permeability meter manufactured by Rika Seiki Kogyo Co., Ltd., the oxygen permeation rate was 2.4 × 10 ^-5 cc (STP) / cm ² .
The selectivity for oxygen and nitrogen in sec cmHg was 5.3. Example 2 A composite membrane was obtained by the same procedure as in Example 1, except that ethylene diamine (viscosity at 25°C: 170 centistokes) was used instead of the siloxane-containing diamine. When the performance of this membrane was measured, the oxygen permeation rate was 7.8×10 ^-6 cc (STP)/cm ² ·sec·cmHg, and the selectivity (O ₂ /N ₂ ) was 4.9. Comparative Example 1 A composite membrane was obtained in the same manner as in Example 1, except that polyethyleneimine (viscosity at 25°C: 2000 centistokes) was used instead of the siloxane-containing diamine. When the performance of this membrane was measured, the oxygen permeation rate was 1.1×10 ^-6 cc (STP)/cm ² .
sec·cmHg, the selectivity (O ₂ /N ₂ ) was 2.8, and the oxygen permeation rate was low. Furthermore, the selectivity was low and the formation of a film was not sufficient. Example 3 (viscosity 55 centistokes (25℃)) 2% by weight
The ethanol solution is poured into the inside of the hollow fiber obtained in Reference Example 2 and applied. Then, using the same apparatus as in Example 1, a nitrogen stream containing vapor of dolly diisocyanate was passed inside the hollow fibers for 40 minutes to obtain a hollow fiber composite membrane. The performance of this composite membrane was measured at a temperature of 25°C using a gas permeability measuring device using a gas chromatograph. The oxygen permeation rate is 3.1×10 ^-5 cc (STP)/
cm ² ·sec·cmHg and selectivity (O ₂ /N ₂ ) were 4.6. Examples 4 to 6 Composite membranes were produced in the same manner as in Example 1 using various polyamine compounds and compounds having various isocyanate groups or thioisocyanate groups. The performance of the obtained composite membrane is shown in Table 1. 【table】

Claims (1)

[Claims] 1. It is liquid at room temperature and has a viscosity at 25°C.
A polyamino compound having at least two primary and/or secondary amino groups of 200 centistokes or less is dissolved in a soluble solvent, and a solution obtained is coated on a porous support membrane. A composite permeable membrane for gas separation, characterized in that the resulting membrane substrate is brought into contact with vapor containing a compound having at least two isocyanate groups and/or thioisocyanate groups to form an ultra-thin membrane on the support membrane. manufacturing method. 2. The polyamino compound contains at least 50% of the
is the following general formula () [However, in the formula, l and m are the same or different, and 2 to 10
, n is an integer of 1 to 200, R ₁ is a hydrogen atom, methyl group, ethyl group, or phenyl group, R ₂ , R ₃ ,
R ₂ ′ and R ₃ ′ are the same or different and have 1 to 5 carbon atoms.
represents an alkyl group, an alkenyl group, or a phenyl group. ] The manufacturing method according to item 1, which is a diamine represented by: