JPH0363413B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a gas separation membrane for selectively transporting a certain gas from a gas mixture. Specifically, a gas in which a liquid containing a substance in water that has a selective affinity for gas is held on the surface of an asymmetric membrane consisting of a water-repellent dense layer and a porous layer and/or on the surface with pores on the back side of the dense layer. In separation membranes, asymmetric membranes are 10 ^-5 cm ³
(STP)/ ^cm2・sec・cmHg or more of a substance that has a nitrogen permeation rate and has a selective affinity for gas to either surface of the asymmetric membrane and/or the surface with pores on the back side of the dense layer. A hydrogel layer formed containing an aqueous solution or a plasma polymerized layer whose surface is wetted with the aqueous solution is formed, and the pressure on the first side holding the liquid and the pressure on the second side when passing through this membrane. The difference is 0.5
The present invention relates to a gas separation membrane that prevents water from leaking out as droplets to the second side even at a pressure of Kg/cm ² or more, preferably 1 Kg/cm ² or more. Conventionally, examples of selectively promoting transport of a specific gas by retaining an affinity substance that interacts with a specific gas in a membrane include separation of oxygen by hemoglobin, separation of carbon dioxide by alkali metal bicarbonate, and separation of carbon dioxide by chloride. Separation of carbon monoxide using copper, separation of olefins using silver acetate, and many others are known. When a gas mixture is separated by simple dissolution and diffusion in a polymer membrane, gases with a relatively high permeation rate and gases with a relatively low permeation rate are separated selectively to some extent based on the difference in permeation rate. However, it is difficult to selectively separate only a specific gas, and the range of applicable applications is limited depending on the type and composition of the gas mixture, the composition of the separated product, etc. It was getting worse. Therefore, if a membrane that selectively permeates only a specific gas is developed, it can be applied to a wide range of applications because it can separate highly concentrated gases regardless of the composition of the gas mixture to be separated. The conventional methods for retaining an affinity substance that interacts with a specific gas in the form of a solution in a membrane include retaining the solution on a homogeneous film or between two homogeneous films, or using a gel membrane. or a method of impregnating a porous membrane with a solution. However, among these methods, the former method uses a material with the highest gas permeability coefficient, such as silicone rubber, as a homogeneous film, and the film thickness can be reduced to the limit that maintains the minimum strength. There is a limit to the film thickness, and the rate of gas permeation through this homogeneous film is low, causing a rate-limiting step and making it impossible to obtain sufficiently efficient performance. Although the latter method can achieve a high permeation rate, if there is a pressure difference on both sides of the membrane, the solution will leak out. A balance must be struck. The present invention was developed by considering how to compensate for the drawbacks of these conventional methods and take advantage of the advantage of using a solution of an affinity substance that interacts with a specific gas. In other words, if a membrane material that is water repellent and has a large permeability coefficient is used to form an asymmetric membrane with an extremely thin dense layer, and a solution of an affinity substance that interacts with a specific gas is held in this membrane, the rate of permeation will be determined. Even if the thickness of the liquid membrane is made sufficiently thin, the stage exists in the solution area of the affinity substance, and not only high selectivity and high permeation rate are obtained, but also the dense layer prevents leakage of the solution and prevents the membrane from leaking. It can be used even if there is a substantial pressure difference on both sides. Furthermore, in order to retain a solution of an affinity substance in a thin film thickness and obtain a high permeation rate in such an asymmetric membrane with a high gas permeation rate, it is necessary to use a hydrogel layer containing a solution of an affinity substance or an asymmetric membrane. A possible method is to form a thin film layer of a crosslinked polymer film on the surface of the dense layer of the film by plasma polymerization, and wet this with a solution of an affinity substance. The gist of the present invention lies in the above points. Next, the content of the present invention will be explained in more detail. The asymmetric membrane is formed of a dense layer with a thickness of 10μ or less, preferably 0.00μ to 1μ, and a porous layer with a thickness of 10μ or more, preferably 100μ or more, as measured from the permeability coefficient and permeation rate. It is preferable for the dense layer to be formed of a material with a high gas permeability coefficient in order to obtain a high permeation rate, and for the porous layer, the magnitude of the permeability coefficient of the material does not matter much. Such an asymmetric membrane is produced, for example, by the method described in Japanese Patent Publication No. 52-21021 and US Pat. No. 3,852,388. Examples of materials that have a large permeability coefficient and can form asymmetric membranes consisting of a dense layer and a porous layer include poly2,6-dimethylphenylene oxide, polytrimethylvinylsilane, polycarboate, and polyvinylidene fluoride. is exemplified. The shape of the asymmetric membrane is flat,
It can take any shape such as tubular, spiral, hollow fiber, etc. The affinity substance that can be used in the present invention is not particularly limited as long as it can interact reversibly with a specific gas, but examples include aliphatic substances such as ethylene, propylene, butene, butadiene, pentene, and hexene. Silver compounds such as AgNO ₃ , AgCl ₄ , AgBF ₄ that can form complexes with unsaturated hydrocarbons, copper compounds such as cuprous that can form complexes with ethylene,
Alkali metal bicarbonates such as sodium bicarbonate, potassium bicarbonate, and cesium bicarbonate that dissociate carbon dioxide; alkali sulfite compounds such as potassium sulfite and sodium sulfite that dissociate sulfur dioxide; and transport functions for oxygen or carbon monoxide. Hemoglobin with Cu, which can form complexes with carbon monoxide
Examples include (NH ₃ ) ₂ ⁺ and Cu(Cl ₃ ) ^2- . Additionally, substances that have the effect of substantially increasing the concentration of affinity substances that can interact with gases such as Na ₂ AsO ₂ and carbonic anhydrase in the facilitated transport of carbon dioxide by alkali metal bicarbonates are also used. Can be added. The concentration at which the affinity substance is dissolved in water as a solvent is not particularly limited, but for example,
Concentrations as low as 0.1 mmol up to as high as 10 molar can be implemented. The affinity substance can also be present in water as a solution, suspension or slurry. In order to hold an aqueous solution containing a substance having selective hydrophilicity to gas, it can be held on the surface of the asymmetric membrane having a dense layer or the surface having pores on the back side thereof. In order to retain the affinity substance as a thin liquid film, a hydrogel layer is formed on the surface of the asymmetric membrane that has a dense layer or on the surface that has pores on the back side.A hydrogel contains an affinity substance. A gel containing an aqueous solution. The hydrogel layer is created by dissolving the affinity substance and the substance forming the hydrogel in water.
In some cases, a gelling promoter may be added and applied onto either side of the asymmetrical film, and the film may be formed by gelling by means of heating, cooling light, radiation irradiation, etc., if necessary. The following substances are exemplified as materials constituting the framework of the hydrogel. Namely, starch, amylose, amylopectin, cellulose, dextran, inulin, agar, gum arabic, pectic acid, alginic acid, heparin, hyaluronic acid, other glucan, fructan, xylan, mannan, galactan, polyuronic acid, chitin, mucopolysaccharide, etc. Polysaccharides, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, carboxymethyl starch, dialdehyde starch, sodium alginate and other modified products of the above polysaccharides, polyvinyl alcohol, polyacrylic acid, polyhydroxyethyl methacrylate-ethylene glycol, Hydrophilic polymers such as methacrylate copolymer, polyethylene oxide, polyvinylpyrrolidone, polyacrylamide gel, polyvinyl ether, styrene-divinylbenzene copolymer, styrene-butadiene copolymer, acrylic acid-dinylbenzene copolymer, methacryl Examples include acid-divinylbenzene copolymers, ion-exchange polymers obtained by sulfonating, chloromethylating, or aminating these copolymers, various polymer electrolytes, and polymer ion complexes. Another method for retaining an aqueous solution containing a substance having a selective affinity with gas is to form a plasma polymerized membrane layer on the surface of the asymmetric membrane and wet it with the aqueous solution. Any compound can be used as the substance forming the plasma polymerized film layer as long as it is hydrophilic and can form a crosslinked polymerized thin film layer. for example,
Examples include compounds such as hydroxyethyl methacrylate, ethylene glycol dimethacrylate, allyl alcohol, acrylic acid, methacrylic acid, vinylpyridine, vinylpyrrolidone, and vinyl acetate. These compounds can be introduced as vapor into a plasma polymerization reactor and polymerized onto the surface of the asymmetric membrane on the substrate, or can be applied directly to the asymmetric membrane, or applied as a solution and then coated onto the asymmetric membrane by evaporating the solvent. This is then subjected to plasma discharge to form a polymerized layer. The above compounds can be used alone, or two or more of the above compounds can be mixed to form a plasma polymerized layer. The thickness of the hydrogel layer or plasma polymerized layer is not particularly limited, but is preferably 1000μ or less, preferably
It is formed to have a thickness of 0.01μ to 100μ, more preferably 0.1μ to 10μ. The gas separation membrane of the present invention thus obtained is useful for separating various gas mixtures and can be used for many purposes. For example, oxygen separated from air is useful for chemical reactions and activated sludge treatment.
By mixing this with air, oxygen-enriched air useful for energy-saving combustion systems and medical purposes can be obtained. Also, coke gas, blast furnace gas,
Carbon monoxide separated from steelmaking gas such as converter gas is useful as a raw material for chemical reactions. ethylene,
Propylene and the like are used as petrochemical raw materials in the production of many products, and the gas separation membrane of the present invention is useful for recovering and utilizing unreacted raw materials contained in waste gas. Separation of carbon gas from gas and combustion gas in other ammonia plants, etc.
It is useful for removing sulfur dioxide gas from waste gas. The content of the present invention will be illustrated below with examples; however, these examples are merely for illustrative purposes, and should not be construed as limiting the present invention to the specific materials, methods, etc. shown therein. No. Comparative Example 1 A commercially available porous membrane, Millipore Filter (trademark) VSWP (manufactured by Millipore Limited, average pore diameter 0.025 μm), was attached to a membrane cell. Membrane area is 12.6cm ²
It was hot. Next, 5 ml of a 2N silver nitrate aqueous solution (liquid film thickness: 4 mm) was added onto this membrane to coat the surface of the Millipore filter with the silver nitrate aqueous solution. On the other hand, a mixed gas containing 35% n-butane, 35% 1-butene, and 30% 1,3-butadiene was prepared in a pressure vessel.
This was flowed into the primary side of the membrane cell at about 1.2 atmospheres.
An attempt was made to measure the volume and composition of the permeating gas by making the secondary side of the membrane almost vacuum (approximately 500 mmHg), but droplets of the silver nitrate aqueous solution leaked out, making it impossible to conduct the permeation experiment under appropriate conditions. Comparative Examples 2 to 5 A polytrimethylvinylsilane asymmetric membrane formed according to the method described in Japanese Patent Publication No. 52-21021 was attached to a membrane cell. The membrane area was 12.6 cm ² . Next, apply a predetermined concentration (0.2M, 0.7M, 2.0M, 5.0M) on top of this membrane.
5 ml of a silver nitrate aqueous solution (liquid film thickness: 4 mm) was added to coat the surface of the polytrimethylvinylsilane asymmetric membrane with the silver nitrate aqueous solution. On the other hand, n-
Butane 35%, 1-butene 35%, 1,3-butadiene
A mixed gas containing 30% was flowed into the primary side of the membrane cell at approximately 1.2 atmospheres. The secondary side of the membrane was evacuated to a vacuum of 10 cmHg or less, and the composition of the gas that permeated and the amount of permeation per hour were measured. The results are shown in Table 1. 1-butene and 1,3-butadiene permeate selectively compared to n-butane, and an aqueous solution of silver nitrate permeates through the membrane even under a pressure difference of approximately 1.2 atmospheres. There was no leakage. However, the thickness of the liquid film is thick, and although 1-butene and 1,3-butadiene permeate selectively relative to n-butane, their permeation rates are lower than expected, so the film thickness must be made thinner. I needed to.

[Table] For reference, nitrogen, n-butane, 1-butene, 1,3 for only the polytrimethylvinylsilane asymmetric membrane used in this comparative example before adding silver nitrate aqueous solution to the polytrimethylvinylsilane asymmetric membrane
−The permeation rate of butadiene mixed gas is 10 ^-4 in both cases.
cm ³ /cm ²・sec・cmHg or more, n-butane, 1
-The composition of the mixed gas of butene and 1,3-butadiene after permeation through the membrane was almost unchanged from that before permeation through the membrane. Comparative Example 6 A polytrimethylvinylsilane asymmetric membrane from the same membrane production lot as in Comparative Examples 2 to 5 was attached to a membrane cell. The membrane area was 12.6 cm ² . Next, 0.2 ml of a 2N silver nitrate aqueous solution (liquid film thickness 0.16 mm) was added to this film to coat the surface of the polytrimethylvinylsilane asymmetric film. did not spread over the entire membrane surface. When reducing the amount of liquid in the liquid film to make the film thinner, it is necessary to take measures to spread the liquid film over the surface of the asymmetric membrane. Examples 1 to 8 The same lot of polytrimethylvinylsilane and asymmetric membrane as in Comparative Examples 2 to 5 was cut into 5 cm square pieces and placed on a substrate in a Bergier type plasma polymerization reactor. 9.9 g of hydroxyethyl methacrylate and 0.1 g of ethylene glycol dimethacrylate were placed in a dish, which was also inserted into the plasma polymerization reactor. The inside of the reactor was vacuumed and discharged, and the reaction was carried out for 30 minutes at RF power of 25 W and pressure of 0.3 to 0.4 mbar, forming a thin polymer layer mainly composed of hydroxyethyl methacrylate on the surface of the polytrimethylvinylsilane anisotropic film. did. After a predetermined time, the pressure in the reactor was restored with argon or helium, and the plasma polymerized film was taken out. This plasma polymerized membrane was attached to a membrane cell. (Membrane area: 12.6cm ² ) Next, on this membrane, a silver nitrate aqueous solution with a predetermined concentration (0.2M, 0.7M, 2.0M, 5.0M) was applied to 2ml in Examples 1 to 4 (the thickness of the liquid film was 1.6 mm), and in Examples 5 to 8, 0.2 ml (the thickness of the liquid film corresponds to 0.16 mm) was added to coat the surface of the plasma polymerized film. In Examples 5 to 8, excess liquid on the plasma polymerized film was wiped off with filter paper, and the thickness of the liquid film was made even smaller than 0.16 mm. The same procedure as in Comparative Examples 2 to 5 was carried out to obtain the results shown in Table 2.

[Table] 1-Butene and 1,3-butadiene selectively permeated. In addition, in Examples 5 to 8, the plasma polymerized membrane was wetted with a liquid film to make the liquid film easier to spread and to reduce the thickness of the liquid film.
It was possible to increase the permeation rate of -butene and 1,3-butadiene. Furthermore, since the asymmetric membrane in contact with the plasma-polymerized membrane is water-repellent, the silver nitrate aqueous solution did not permeate through the membrane and leak out even when there was a pressure difference of 1.2 atmospheres on both sides of the membrane. Furthermore, because the asymmetric membrane has high permeability, this part does not act as a barrier, and 1-butene and 1,
High permeation rates of 3-butadiene were obtained. Examples 9 and 10 Polytrimethylvinylsilane asymmetric membranes from the same membrane production lot as in Comparative Examples 2 to 5 were attached to membrane cells. (Membrane area: 12.6 cm ² ) Silver nitrate aqueous solutions containing gelatin were prepared by dissolving 5% gelatin in 1M silver nitrate aqueous solution or 10% gelatin in 2M silver nitrate aqueous solution. When 0.5 ml of each of the above two types of solutions (liquid film thickness: 0.4 mm) was separately added to two membrane cells equipped with polytrimethylvinylsilane asymmetric membranes, the solution appeared on the surface of the polytrimethylvinylsilane asymmetric membrane in both cases. It spread evenly. This was cooled and gelatinized, and a gelatin gel membrane containing an aqueous silver nitrate solution held on the polytrimethylvinylsilane asymmetric membrane obtained in this way was heated using a mixed gas containing 47% propylene and 53% propane at a pressure of 1.2 atm. 10cm from the secondary side of the membrane.
The volume and composition of gas permeated over a certain period of time were measured under reduced pressure below Hg. The measurement results are shown in Table 3.

[Table] By forming a gelatin hydrogel membrane containing a silver nitrate aqueous solution that has a selective affinity for propylene on a water-repellent and highly permeable asymmetric membrane, a pressure difference of 1.2 atmospheres is created on both sides of the membrane. In this case, the aqueous silver nitrate solution did not leak through the membrane, and propylene permeated with high selectivity and at a high rate. The aqueous solution retained in such a hydrogel membrane does not flow out even if the membrane cell is tilted.

Claims (1)

[Scope of Claims] 1. A hydrogel layer formed by containing an aqueous solution of a substance that has a selective affinity for gas or a plasma polymerized membrane layer whose surface is wetted with the aqueous solution, and a water-repellent dense layer and a porous layer. A gas separation membrane that is in contact with either the surface of the asymmetric membrane and/or the surface with pores on the back side of the dense layer, where the asymmetric membrane is 10 ^-5 cm ³
It has a nitrogen permeation rate of (STP)/ ^cm2・sec・cmHg or more, and the pressure on the inflow side (first side) to the membrane holding the liquid when passing through this membrane and the pressure on the outflow side (first side) from the membrane. Second
A gas separation membrane characterized in that the membrane does not allow water to leak out as droplets to the second side even if the pressure difference between the two sides is 0.5 kg/cm ² or more. 2 Asymmetric membrane is 10 ^-4 cm ³ (STP)/cm ²・sec・cmHg
The gas separation membrane according to claim 1, which has a nitrogen permeation rate of at least 10%.