JPH0260370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a composite membrane for gas separation that is easy to handle and has improved durability without damaging the thin selectively permeable membrane layer. be.

(Prior art) 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%. There is.

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.

Therefore, as methods for producing thin films for gas separation, there is a method in which a thin film of polysiloxane-polycarbonate copolymerization is made by spreading a polymer solution on the water surface (see JP-A-51-89564), and a method in which a thin film of polyolefin is made. (Refer to Japanese Unexamined Patent Publication No. 71605/1983) is known, and in order to use this as a separation membrane, this thin film is used by laminating it on a porous membrane.

In addition, after forming a polymer solution into a flat membrane or hollow fiber, part of the solvent is evaporated, and then immersed in a coagulating liquid.
A method for producing an asymmetric membrane in which a thin membrane separation active layer obtained by removing residual solvent and a porous membrane layer are integrated (see Japanese Patent Publication No. 52-21021 and Japanese Patent Application Laid-Open No. 57-7206); A so-called in situ film made by reacting polyamide polyisocyanate on a porous membrane through an interfacial reaction.
Film production method of composite membrane by polymerization method (Japanese Patent Application Laid-open No. 57-74476
(Refer to Publication No. 2004) are also known.

To use these membranes for actual separation, they are stacked or bundled together and assembled into a separation module.

However, in this case, as the thickness of the membrane becomes thinner, the strength of the membrane decreases, and the membrane can be damaged simply by touching the membrane surface with a hand or an object. Therefore, the membrane must be handled carefully, making it difficult to assemble the module. This is a very tedious task. Furthermore, since damaged membranes cannot be used, the percentage of them being used as products is low.

Furthermore, during separation operation, there is a risk of membrane damage due to solids contained in the supplied gas, and if a thin film is provided on the outside of the hollow fibers, the hollow fibers may come into contact with each other and damage the membrane. .

(Problem to be solved by the invention) Therefore, the present inventors discovered that there is no damage to the thin film surface.
As a result of intensive research to produce a durable gas separation membrane, it has been found that in order to obtain such a separation membrane, it is necessary to
A composite membrane with an integrated structure consisting of a porous support membrane layer with a thickness of m, a non-porous permselective membrane layer with a thickness of 0.5μm, and a porous protective membrane layer with a thickness of 300μm or less. It has been found that such a composite membrane can be manufactured industrially by the following method.

(Means for solving the problem) That is, in the present invention, the composite membrane as described above is
Porous support membrane layer with a thickness of 5-1000 μm and 0.5 μm
On top of a laminate of non-porous membrane layers consisting of a non-porous membrane having a gas selective permeability and having a thickness of not more than A more main solution is applied, and then the solvent or the solvent and the additive are removed to form a porous protective film layer having a thickness of 300 μm or less and having pores with an average pore diameter of 100 Å or more on the non-porous membrane. It is manufactured by a method for manufacturing a composite membrane for gas separation characterized by the following.

Since the porous support membrane layer used in the method of the present invention supports a thin non-porous permselective membrane with a thickness of 0.5 μm or less, it is preferable that the size of the pores on the surface be as uniform and small as possible. , generally between about 0.003 and 1 μm, preferably between 0.005 and 0.5 μm,
More preferably, it is 0.01 to 0.3 μm.

The base material for the porous support membrane includes glass porous materials, sintered metals, inorganic base materials such as ceramics,
Ordinary porous membrane substrates may be used, such as organic substrates such as cellulose ester, polystyrene, polysulfone, polypropylene, polyethylene, vinyl chloride polymer, and polyacrylonitrile, or inorganic-organic substrates such as silica-containing polyethylene.

The structure may be a symmetrical structure or an asymmetrical structure, but an asymmetrical structure with small pores on the surface and large pores on the inside is preferable because the gas permeation resistance is low and the amount of permeation is large.

Furthermore, it is appropriate to use a porous support membrane having an air permeability of 10 to 10,000 seconds, preferably 20 to 3,000 seconds, and more preferably 50 to 1,000 seconds, as measured by a JIS P8117 device. Those with an air permeability of 10 seconds or less often have large pores, which can easily cause defects if a thin permselective membrane is placed there. On the other hand, if the time is 10,000 seconds or more, if a separation membrane is used, it is likely that only a small amount of permeation will be produced.

The thickness of the porous support membrane layer used in the present invention is 5
~1000μm thick, preferably 10-500μm
m, more preferably 20 to 300 μm.
If it is thinner than 5 μm, it will be difficult to maintain its shape and it will be difficult to handle, while if it is 1000 μm or more, it will become a thick separation membrane and the size of the module will increase.

Note that the porous support membrane used in the present invention includes a sponge layer of an asymmetric membrane as long as it has the above characteristics. An asymmetric membrane has a structure in which its cross section is made of the same material and changes continuously from a non-porous layer with a selective permeation function to a porous sponge layer. layer)
It means that you are supporting.

On the other hand, the permselective membrane layer provided on the porous support membrane is essentially a dense, homogeneous membrane that is non-porous. In order to increase the amount of gas permeation, this layer is preferably as thin as possible, and its thickness is 0.5 μm or less, preferably 0.3 μm or less, particularly preferably 0.1 μm or less.

Methods for manufacturing this thin selectively permeable membrane layer include the above-mentioned water surface development method, asymmetric membrane method, and in-situ polymerization method, but there are also various other methods such as polymer solution coating method and plasma polymerization membrane method, but there are no particular limitations. It's not something you can do.

The material for the selectively permeable membrane is preferably one that has selective permeability to a specific gas.
In general, materials with the most efficient permeability and selectivity for separation are selected, depending on the gas to be separated. For example, in the case of oxygen and nitrogen separation, polysiloxane, siloxane-polycarbonate copolymer, polyphenylene oxide, polymethylpentene, polyvinyltrimethylsilane, polyallyltrimethylsilane copolymer, siloxane-containing polyurea, cellulose triacetate etc. can be given.

In the method of the present invention, a porous protective film is formed on the selectively permeable membrane, and the mixed gas to be separated is supplied to the outside of the protective layer, and the mixed gas passes through the pores of the porous protective film to the surface of the selectively permeable membrane. reached and separated. On the surface of a selectively permeable membrane, the concentration of gases that are difficult to permeate gradually increases and the separation efficiency decreases, so it is important for separation membranes to constantly send supply gas to the selectively permeable surface to renew the surface. Therefore, in the present invention, it is necessary that the porous protective film provided to cover the surface of the selectively permeable membrane does not hinder the surface renewal of the selectively permeable membrane.

From this point of view, it is preferable that the thickness of the porous protective film is as thin as possible, and the thickness is 300 μm or less,
Preferably 150μm or less, more preferably 100μm
m or less. However, if it is too thin, the strength of the protective layer will be lost, so the appropriate thickness is 0.5 μm or more, preferably 1 μm or more.

The porosity is important as a porous physical property to increase the amount of permeation without hindering surface renewal, and the porosity of the porous protective film is 30% or more, preferably 50% or more, and more preferably 60% or more. be. Also, regarding the size of the pores, it is preferable that the average pore diameter is larger as the permeation is not hindered, but the selectively permeable membrane is exposed. Therefore, the average pore diameter of the porous membrane protective layer is set to a minimum pore diameter of 100 Å or more.

In the present invention, the material of the porous membrane protective layer is selected from the same materials as the porous support membrane described above, but it is not necessary to use the same kind of material as the support membrane.

The composite membrane for gas separation obtained by the present invention has a structure in which three layers, a porous support membrane layer, a selectively permeable membrane layer, and a porous protective membrane layer, are integrated between each layer. Integral means that there is no misalignment between each of the three layers, and this ensures that when a module is assembled from this composite membrane or when separation is performed by applying pressure. , the supporting membrane layer and the protective layer each play a role to prevent damage to the selectively permeable membrane, and also to prevent destruction of the selectively permeable membrane by the protective membrane and the supporting membrane themselves.

As a method for producing the above-mentioned composite membrane for gas separation, a method is employed in which a composite membrane consisting of a porous support membrane and a selectively permeable membrane is first prepared, and then a porous protective membrane is provided on the selectively permeable membrane. Specifically, a solution of a polymer (high molecular compound) is applied to the surface of a selectively permeable membrane in a laminated composite membrane consisting of a porous support membrane and a separation membrane as described above, and a solvent or a solvent and an additive are extracted from the solution. A method is adopted in which a porous protective film with an average pore diameter of 100 Å or more and a thickness of 300 μm or less is formed on the surface of the selectively permeable membrane by removing the .

It is also possible to directly stack the porous protective film on top of the selectively permeable membrane, but this method often damages the thin and weakly strong selectively permeable membrane when layered, and the layered surface of the porous protective film It is not practical because it requires great care in determining the presence or absence of irregularities in the porous protective film and how to apply tension when overlapping the porous protective film.

On the other hand, the above method is a method in which a polymer solution or a polymer solution containing an additive is applied onto a selectively permeable membrane, and then the solvent or the solvent and the additive are removed to form a porous membrane. In this case, what is important is the selection of the solvent, which must not immerse the selectively permeable membrane and which dissolves the polymer that will become the porous membrane material.

Additives include non-solvents for polymers used as porous membrane materials, salts such as lithium chloride and calcium carbonate, and inorganic substances such as titanium oxide and silica, which act to actively open pores in the porous membrane. . This additive must also not damage the selectively permeable membrane.

The polymer solution may be applied onto the selectively permeable membrane by any method such as dipping, coating, spray coating, etc. that does not damage the selectively permeable membrane. After coating, it is immersed in a non-solvent that mixes with the solvent of the polymer solution, and the solvent is removed to form a porous membrane.

This method is applicable not only to flat membranes but also to hollow fiber membranes.

The composite membrane of the present invention can have any shape such as a flat membrane or a hollow fiber.

(Effects of the Invention) According to the method of the present invention, it is possible to easily produce a composite membrane, and the resulting composite membrane takes advantage of its ease of handling and good durability, and allows the gas of the selectively permeable membrane to be Depending on the characteristics of permeability and selectivity, it can be used for separating various gas mixtures.

For example, if a selectively permeable membrane is suitable for separating oxygen and nitrogen, it can be incorporated into equipment that produces oxygen-enriched air from air to improve the combustion efficiency of engines, heating equipment, etc., or it can be used to produce clean oxygen-enriched air. It can be used as a treatment machine for people with respiratory problems, or as an artificial lung. In addition, if it is suitable for separating hydrogen and carbon monoxide or hydrogen and nitrogen, it can be used for hydrogen recovery in water gas generation processes and ammonia synthesis processes, and if it is suitable for separating helium and air, liquefied helium can be used. It can be used to purify recovered helium gas in cryogenic equipment.

(Examples) 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.

Example 1 A dope consisting of 4 parts of poly-4-methylpentene, 6 parts of cyclohexenyl peroxide, and 90 parts of purified distilled cyclohexene was continuously supplied onto the water surface from a needle-shaped supply port while the supply port was in contact with water. Then, a non-porous ultra-thin film of poly-4-methylpentene is formed on the water surface. A polypropylene porous membrane (thickness 25 μm, pore size range) is placed on top of this ultra-thin membrane.
0.02 to 0.2 μm, average pore diameter 0.14 μm (1400 Å), porosity 38%, air permeability 800 seconds) and simultaneously apply vacuum suction from the porous membrane side to place the ultra-thin membrane on the polypropylene porous membrane. and pull it up.

Separately, on a membrane (thickness of the thin film of poly4-methylpentene 0.09 μm) consisting of the ultra-thin film of poly-4-methylpentene produced as described above and a porous polypropylene support film (average pore diameter of the support film 0.14 μm). 10 parts of prepared polysulfone, 5 parts of methylcellosolve
A porous polysulfone membrane (protective membrane) was provided on the selectively permeable membrane by casting a solution of 80 parts of dimethylformamide and 80 parts of dimethylformamide to a thickness of about 20 μm, and immediately placing it in a water bath to gel it. After air drying, the membrane was placed on a perforated plate and stabilized by vacuum suction.

The thickness of the polysulfone porous material was determined to be approximately 2 μm by measuring the total thickness.

In addition, when the pore diameter was determined by electron microscopy of the surface of the polysulfone porous membrane formed on the surface, it was found to be 100
There are many micropores of ~500Å, and the average pore diameter is
It was 0.023 μm (230 Å).

In order to determine the porosity, the same polysulfone solution was coated on a glass plate and the same procedure was performed to make only a polysulfone porous membrane, which was isolated and the porosity was determined to be 65%. The oxygen permeation rate of this composite membrane is 1.1×10 ^-4 cc
(STP)/ ^cm2・sec・cmHg, selectivity (oxygen/nitrogen)
was 3.8.

Furthermore, even if 10 layers of this film were stacked and left for one month, there was no change in performance.

Example 2 Polysulfone porous membrane (thickness 40 μm, surface pore diameter 50-600 Å,
Average pore diameter 0.025 μm (250 Å), air permeability 82 seconds, porosity
70%).

Dissolve 1 part of bis(3-aminopropyl)tetramethyldisiloxane in 49.5 parts of ethanol,
Furthermore, 49.5 parts of water was added and stirred. After immersing the polysulfone porous membrane in this solution for 5 minutes, the membrane was pulled out of the aqueous solution and held vertically for draining at room temperature for 10 minutes. Next, it was immersed in a 1% by weight n-hexane solution of 4,4'-diphenylmethane diisocyanate for 3 minutes and then dried at room temperature for 60 minutes to coat the surface of the polysulfone porous membrane with bis(3-aminopropyl)tetramethylsiloxane. A selectively permeable membrane of polyurea was formed by interfacial polymerization of polyurea and 4,4'-diphenylmethane diisocyanate.

The oxygen permeation rate of this composite membrane is 1.1×10 ^-5 cc
(STP)/ ^cm2・sec・cmHg, selectivity (oxygen/nitrogen)
was 5.3, and the thickness of the selectively permeable membrane was calculated from the permeation rate to be approximately 0.1 μm.

Apart from this, 5 parts of nylon, calcium chloride
Prepare a nylon solution consisting of 15 parts of methanol and 80 parts of methanol. This nylon solution is coated on the permselective membrane side surface of the composite membrane to a thickness of approximately 50 μm, and immediately immersed in water to desalt and remove the solvent, and then solidified to form a composite membrane with a protective membrane. was manufactured.

The thickness of the protective film determined from the overall thickness is approximately 2μm
It was hot. In addition, when the pore size is determined by observing the surface with an electron microscope, it is 0.1 to 0.5 μm, and the average pore size is
It was 0.35 μm (350 Å).

The porosity was determined by creating a model porous material in the same manner as in Example 1, and was found to be 72%.

The oxygen permeation rate of this composite membrane is 0.7×10 ^-5 cc
The selectivity was 4.6 (STP)/cm ² sec cmHg.

Example 3 3 parts of cellulose trilaurate were dissolved in 10 parts of tetrahydrofuran at 25°C. There 2-(2
-ethoxyethoxy) 7 parts of ethanol was added to obtain a homogeneous polymer solution. Pour this solution onto a glass plate.
Cast to a thickness of 300 μm and 90 μm at room temperature.
Leave for a second to volatilize some of the tetrahydrofuran,
The membrane on the glass plate was then immersed in methanol at 0° C. for 2 hours to complete gelation.

The membrane was then fixed under tension on a frame and dried under vacuum at room temperature for 20 hours. The thickness of this film is 40μm
It is. This membrane is an asymmetric membrane having a so-called surface dense layer in which a support membrane and a separation membrane are continuously connected. The oxygen permeation rate of the obtained membrane was 11.5×10 ^-6
cc(STP)/ ^cm2・sec・cmHg, and the thickness of the dense layer (this becomes the separation membrane) calculated from this is:
It was 0.44 μm. Also, the selectivity between oxygen and nitrogen is 2.4
It was hot.

Next, the surface of this membrane was coated with the nylon solution used in Example 2 to a thickness of about 50 μm and air-dried to form a protective film with an average pore diameter of 0.35 μm (350 Å) to obtain a composite membrane. The oxygen permeation rate of this composite membrane is
The value was 5.1×10 ⁻⁶ cc (STP)/cm ² ·sec·cmHg, and the selectivity was 2.1.

Example 4 20 parts of polysulfone, 70 parts of dimethylformamide
A solution of 10 parts of methyl cellosolve was used as a core liquid, and the solution was discharged from an annular slit and immersed in water at 25°C to solidify.
A polysulfone hollow fiber membrane with an inner diameter of 290 μm was obtained. The average pore size of this membrane was 0.025 μm.

In addition to tore, diamine of the following formula 1 part was added to a mixed solvent of ethanol/water (ethanol/
A solution was prepared by dissolving 99 parts of water (8/2 weight ratio), and the polysulfone hollow fiber membrane prepared earlier was immersed in this solution for 10 minutes, dried at room temperature for 10 minutes, and then The hollow fibers are immersed in a 1% by weight solution of enylmethane diisocyanate in n-hexane for 5 minutes so that no liquid enters the hollow fibers, thereby forming a selectively permeable membrane of polyurea by interfacial polymerization on the outside of the hollow fibers.

This single hollow fiber membrane was attached to a polycarbonate pipe and both ends were fixed with adhesive to create a 20 cm long hollow fiber module.The gas permeation performance was measured using a gas chromatograph, and the oxygen permeation rate was 2.1 × It was 10 ^-5 cc (STP)/cm ² ·sec · cmHg, and the selectivity (oxygen/nitrogen) was 4.9.

Separately, prepare a diacetate solution consisting of 10 parts of diacetyl cellulose, 5 parts of glycerin, and 85 parts of acetone. The hollow fiber membrane is immersed in this solution, taking care not to allow the diacetate solution to enter the hollow fiber, and immediately placed in water to form a porous protective membrane with an average pore diameter of 0.020 μm (200 Å) on the outside of the hollow fiber.

Additionally, 16 of these hollow fiber composite membranes were bundled together, packed into a polycarbonate pipe, and both ends were glued together to create a module. Oxygen permeation rate is 1.1×
10 ^-5 cc (STP)/ ^cm2・sec・cmHg, selectivity is 4.2
It was hot.

Performance was also measured after a large amount of air was flowed outside the hollow fibers so that the hollow fiber membranes moved inside the pipe and rubbed against each other, but there was no change in performance.

Claims (1)

[Claims] 1. A porous support membrane layer with a thickness of 5 to 1000 μm and
On a laminate of non-porous membrane layers consisting of a non-porous membrane having a gas selective permeability and having a thickness of 0.5 μm or less, a layer consisting mainly of a polymer compound and a solvent, or a polymer compound, additives and A solution consisting mainly of a solvent is applied, and then the solvent or the solvent and the additive are removed to form a porous protective film layer having a thickness of 300 μm or less and having pores with an average pore diameter of 100 Å or more on the non-porous membrane. A method for producing a composite membrane for gas separation, characterized by: