JPS63264101A - Permselective membrane - Google Patents

Abstract

PURPOSE:To obtain the title permselective membrane having high oxygen permeation coefficient, oxygen separation coefficient, gaseous carbon dioxide permeation coefficient, and gaseous carbon dioxide separation coefficient, capable of being easily formed, and having high heat resistance by using a fluorine-contg. polymer having a cyclic structure in the principal chain. CONSTITUTION:For example, a polymerization initiator is added to perfluoroallyl vinyl ether, and the mixture is frozen, deaerated, and then polymerized to obtain the fluorine-contg. polymer. The polymer is dissolved in a solvent to obtain a coating soln., and the soln. is coated on the supporting membrane, etc., coated with the intermediate layer of polydimethylsiloxane to obtain a composite membrane. The membrane thus obtained is useful as an oxygen enriching membrane and a gaseous carbon dioxide-methane separation membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a selectively permeable membrane, and more specifically, to a selectively permeable membrane made of a specific fluorine-containing polymer having a ring structure in one chain.

[Prior Art and Problems] There is no known method for concentrating a specific component in a mixture through a selectively permeable membrane made of a polymeric material by utilizing the difference in the permeation rate of molecules through a polymeric material in a separation operation. It is used for recovering oxygen-enriched air from air or concentrating methane from carbon dioxide/methane mixtures.

Molecular permeability is specific to the material of the selectively permeable membrane;
In order to perform an efficient separation operation, it is necessary to select a material that has a large difference in permeability between the component of interest and the coexisting component, and has a large permeability of the component of interest. However, in general, there is a tendency that when the difference in permeability is large, the permeability of the component of interest is small, and conversely, when the permeability of the component of interest is large, the difference in permeability is small. The material was rare.

Moreover, what is required as a material for selective permeation is that it can be made into a thin film.

The permeation rate of a membrane is inversely proportional to its thickness, and materials that can be made into thin and virtually defect-free membranes are rare.

For example, when recovering oxygen-enriched air from air, the oxygen permeability coefficient (hereinafter sometimes abbreviated as PO□) is high, and the ratio (r 'o*/r+Ns: Hereinafter, a
(sometimes abbreviated as ox, N2)) is desired. Furthermore, it is desirable that the membrane be thin and have a high oxygen permeation rate (hereinafter sometimes abbreviated as qO2).

Conventional films include, for example, styrene polymers and a, ω-
Crosslinked copolymer obtained from difunctional polysiloxane (
Japanese Patent Publication No. 56-26506).

Hydrocarbon polymer having a ring structure (JP-A-6O-24
1903), poly-4-methyl-pentene-1, and polyphenylene oxide, but some of these materials have insufficient a (a, Ntl), and some are soluble in solvents. It has various drawbacks, such as being difficult to form, having poor film-forming properties, requiring only special film-forming methods, and having poor heat resistance.

Furthermore, the membrane-based method can also be applied to a process for concentrating methane from a carbon dioxide/methane mixture obtained from a gas field, for example. In this case as well, as in the case of recovering oxygen-enriched air, there is a high carbon dioxide permeation rate (hereinafter sometimes abbreviated as 0CO2) and a high carbon dioxide separation coefficient (hereinafter a (CO2)).
x, sometimes abbreviated as CIL-) is calculated. Furthermore, since gas obtained from gas fields contains components other than the above-mentioned components, chemical resistance is required.

For example, polysulfone and cellulose acetate are known as conventional membranes, but the Q (COx, C114) of selectively permeable membranes made from these materials is not always sufficient and is difficult to handle when exposed to high pressure carbon dioxide, methane gas, or mixed gases. For a (CO,.

C11,) further decreases. Furthermore, it is difficult to form a two-composite membrane using these materials because the solvent used during membrane formation dissolves the porous support. In addition, the above-mentioned Japanese Patent Application Laid-Open No. 60-2
A membrane made of a hydrocarbon-based polymer having a ring structure such as No. 41903 has a similar difficulty because it has a high affinity for methane gas and the like because it is a hydrocarbon-based material.

[Means for Solving the Problems] The present inventors have been aware of the above problems, and as a result of intensive research, the inventor has found that fluorine-containing polymers having a ring structure in the main chain have a high G (ox, Ni1 only). high Q (CL, C
It has been found that it also has I+41, high P2 and PCO□, and further has good solubility and film forming properties, and is extremely useful as a selectively permeable membrane.

Thus, the present invention has been completed based on the above findings, and provides a novel permselective membrane made of a fluorine-containing polymer having a ring structure in its main chain.

In the present invention, examples of fluorine-containing polymers having a ring structure in the main chain include those having ring structures such as o, p, and q. Typical examples include polymers having a ring structure such as the following.However, the content of the present invention is not limited to these.

CFa (:)'3 LVI, 1
There are two methods for producing these intermediates: However, it is not limited to these manufacturing methods.

1. By cyclization polymerization +11 CF, -C-F-rhoCFt-CF! -0-
CF-CF! +US+' 34111303. GO1
106344 etc.) +2) CF, ・C) -CFa-C
FCI-CF2-CF龜cFsFCI (USP 3202643 etc.) (3) CFi”CF-0-Ch-CF”CFiO-CF
.

2. Using cyclic monomers +7) (USP 39)
78030) Furthermore, there is no problem in using copolymerized components to the extent that the essence of these components is not impaired.

Other JII fi substances to be copolymerized are not particularly limited as long as they have radical polymerizability, and include a wide range of fluorine-containing compounds, hydrocarbon compounds, and others. Of course, these other monomers may be used alone by radical copolymerization with a monomer capable of introducing a specific ring structure as described in ii'i1 into one chain, or two or more of these monomers may be used as appropriate. They may be used together to carry out the above copolymerization reaction.In the present invention, it is usually desirable to select a fluorine-containing polymer such as a fluoroolefin or fluorovinyl ether as the other monomer.For example, Tetrafluoroethylene, perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, or perfluorovinyl ether containing functional groups such as carboxylic acid groups or sulfonic acid groups are preferred examples, and vinylidene fluoride, vinyl fluoride, chloro Trifluoroethylene and the like may also be exemplified.

As for the copolymer composition, in order to take advantage of solubility, film-forming properties, permselective properties, etc., the composition of the cyclic structure is preferably 20% or more, more preferably 40% or more.

Although there are no particular limitations on how to form a film from these polymers, a press film forming method or a film forming method using a solvent can be used. The latter is advantageous for forming a gJ film on the support crotch. The solvent to be used is not limited as long as it dissolves the above polymer, but examples include perfluorobenzene, "Afluid" (trade name: fluorinated solvent manufactured by Asahi Glass Co., Ltd.), "Fluorinert #" (trade name: manufactured by 3M Company). Liquids containing perfluoro(2-butyltetrahydrofuran)) and trichlorotrifluoroethane are suitable. As a matter of course, two or more appropriate types can be used in combination as a solvent.

Particularly in the case of a mixed solvent, hydrocarbons, chlorinated hydrocarbons, fluorochlorinated hydrocarbons, alcohols, and other organic solvents can also be used in combination. The solution concentration is O, (l1wt% to 50wt%, preferably 0.1wt% to 20wL%. Film forming methods using a solvent include a roll coater method, a casting method, a dipping method, using the above solution, There is no particular limitation as long as it is a method of forming a film from a solution such as a spin code method, a water casting method, a Langmuir-Prodgett method, or the like.

In order to manufacture a selectively permeable membrane using the specific fluorine-containing polymer of the present invention, it is preferable to form the membrane on a support membrane by the above-mentioned membrane forming method because the permeation rate can be increased. As the support membrane, a porous support membrane having a thickness of 5 to 500μ or the porous support membrane has an asymmetric structure in which one surface has an average pore diameter of 5 to 500 pores and the other surface has an average pore diameter larger than the above pore diameter. "Secondly, a film thickness of 0.0 made of a material having a larger permeability coefficient for selectively permeable molecules than the specific fluorine-containing polymer of the present invention.
A support membrane with a 5-5μ membrane as an intermediate layer is preferred.

There are no particular limitations to producing a porous support membrane, but there are
It is manufactured according to the method described in O3 Research and Development Progress Report J No. 359T1968).

Examples of the material include homopolymers or blends of polysulfone, polyethersulfone, ethyl cellulose, cellulose acetate, polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene fluoride, and the like.

Materials with high permeability coefficients for molecules that selectively permeate include:
Examples include, but are not limited to, silicone, fluorosilicone, phosphacene, polytrialkylsilylpropyne, and the like.

Examples of membrane shapes include flat membranes and tubular-1 hollow fibers.

The polymer can be formed into a film on the support crotch using the above film forming method. The film thickness is preferably 0.01 to 5 μm.

If it is thinner than 0 or old μ, large defects may occur in the membrane, and if it is thicker than 5 μ, the permeation rate will decrease.

[Function] In the present invention, the reason why the fluorine-containing polymer having a ring structure in the main chain is excellent as a selectively permeable membrane is not clear at all, but the following may be considered.

1. Since the polymer has a ring structure in its main chain, it is amorphous and has no crystalline portions that prevent the passage of molecules.

2. The polymer has a ring structure in its main chain and contains fluorine, which makes the main chain rigid and provides a large separation coefficient between permeate substances with different molecular diameters.

3. Since the polymer contains fluorine in its main chain, it has a low affinity for hydrocarbons such as methane and ethane, and has a large separation coefficient for helium/methane, hydrogen/methane, and carbon dioxide/methane.

It should be noted that this explanation is provided to assist in understanding the present invention, and is not intended to limit the present invention in any way.

[Example] Next, an example of the present invention will be specifically explained, but it goes without saying that the present invention is not limited to this explanation in any way.

Example 1 30 g of perfluoroallyl vinyl needle and 0.0 g of the polymerization initiator diisopropyl peroxydicarbonate.
3 g was placed in a glass Kolben of 1 Occ. After repeating freezing and degassing twice, the mixture was incubated at 25° C. for 16 hours. As a result of 6 polymerizations in which the pressure during polymerization was lower than atmospheric pressure, 4.5 g of polymer was obtained.

When the infrared absorption spectrum of this small 1 coalescence was measured, it was found that 1790cm-
'There was no nearby absorption. Further, when this polymer was dissolved in perfluorobenzene and an IF NMR spectrum was measured, a spectrum showing the following repeating structure was obtained.

0-CF.

The intrinsic viscosity [η] of this polymer is
C-75 (Product name: Liquid whose main component is perfluoro(2-butyltetrahydrofuran) manufactured by 3M Company, hereinafter referred to as F
It was found that the polymerization degree was 0.50 at 30C (abbreviated as C-75), indicating a high degree of polymerization.

The permeability coefficients of various gases of this polymer were measured. The measurement results and transmission coefficient ratios are shown below.

The measurement results show that this polymer contains helium/methane, helium/nitrogen, carbon dioxide/methane, hydrogen/nitrogen, and oxygen/
It was found to be useful as a material for nitrogen separation membranes.

Next, 2 g of this polymer was dissolved in 350 g of FC-75 to prepare a coating solution. This solution was dip-footed twice at a speed of 0.5 m/min onto the support membrane coated with the polydimethylsiloxane intermediate layer of Reference Example I. The gas permeation rate of the resulting composite membrane was measured. The measurement results and separation coefficients are shown below.

From the measurement results, it was found that this membrane is extremely useful as an oxygen enrichment membrane and a carbon dioxide/methane separation membrane.

After the above composite membrane was incubated under vacuum at 50° C. for 34 days, the gas permeation rate was measured again. As a result, there was no substantial decrease in permeation rate or separation coefficient. Therefore, it was found to have excellent durability and heat resistance.

Example 2 'A The coating solution of Example 1 was applied onto the polysulfone porous support membrane used in Reference Example 1 at a speed of 3 m/min.
Dip coated twice. The gas permeation rate of the resulting composite membrane was measured. The measurement results and separation coefficients are shown below.

Example 3 A 0.7 wt% solution of polyperfluoro(2,2-dimethyl-1,3-dioxole) was placed on the polydimethylsiloxane-coated support film of Reference Example 1 at 0.6 m/+++i.
Dip coating was performed at a speed of n. 0CO3 of the obtained film
is 0.18 m'/m"hr-aLm, and a (C
O.

C11,) was 32.

Example 4 0,8w of FCI poly-4-chloroperfluorohebutadiene
L% perfluoroben7ine solution was applied to the support crotch coated with polydimethylsiloxane of Reference Example 1 at a rate of 0.5 m/mi.
Dip coated three times at a speed of n. Mouth C of the obtained membrane
O, is 0.14m"7m"hr・aLm, and a (
COi, C114) was 34.

Reference Example 1 (Manufacture of support membrane) Surface pore size of approximately 50 pores lined with polyester nonwoven fabric,
An asymmetric porous support membrane (total membrane thickness 240 μm) made of polysulfone (oxygen gas permeation rate in a dry state of 9 f1 m"7 m"・h "・a Lm) with a back pore diameter of 1 μm was used.

A 0.5% solution of polydimethylsiloxane (degree of polymerization: !000) in trichlorotrifluoroethane was cast onto this and dried to obtain a composite membrane. The resulting composite membrane has a polysiloxane layer with a thickness of 0.3μ, and an oxygen permeation rate of 0x1.4m''
/m"h"・aLm(S'rP), acid/nitrogen permeation rate ratio a=2.0.

[9. Effect of light] The present invention has the advantage that a selectively permeable membrane having high permeability, high separation property, high durability, high heat resistance, and interlayer performance can be obtained using a fluorine-containing polymer having a ring structure. It has a certain effect.

Using this selectively permeable membrane, oxygen/nitrogen, carbon dioxide/
An effective method for conveniently separating gases such as methane, helium/methane, helium/air, helium/nitrogen, hydrogen/nitrogen, hydrogen/methane, and hydrogen/carbon oxide.
are doing.

Furthermore, since the polymer of the present invention contains fluorine, it is resistant to carbon-containing gases or liquids such as carbon dioxide gas, methane, ethane, and ethylene at normal or high pressures, which has been difficult until now. It has the effect of adapting to separated targets. In addition, the polymer of the present invention not only has good solubility and good film-forming properties, but also the solvent in which it is dissolved is a solvent that does not dissolve commonly used porous support membranes, so it can be used for composite membranes such as flat membranes and hollow fibers. The effect of easy production is also recognized.

Claims (1)

[Claims] 1. A selectively permeable membrane made of a fluorine-containing polymer having a ring structure in its main chain. 2. Claim 1 in which the ring structure is a fluorine-containing ring structure
The selectively permeable membrane described in Section 1. 3. The selectively permeable membrane according to claim 1 or 2, wherein the ring structure is a fluorine-containing ring structure containing an ether bond. 4. The selectively permeable membrane according to any one of claims 1 to 3, wherein the fluorine-containing polymer is a perfluoropolymer. 5. A porous membrane with a thickness of 5 to 500 μ, which has an asymmetric structure in which the average pore diameter on one surface is 5 to 500 Å and the average pore diameter on the other surface is larger than the pore diameter, is used as the support layer, and the main chain has a ring structure. The thin film layer of the fluorine-containing polymer has a thickness of 0.01
The permselective membrane according to any one of claims 1 to 4, which is formed on the support layer with a thickness of 5 μm. 6. A porous membrane with a thickness of 5 to 500 μm, which has an asymmetric structure with an average pore diameter of 5 to 500 Å on one surface and a larger average pore diameter on the other surface, is used as a support layer, and selective permeation is performed on the support layer. Form an intermediate layer with a thickness of 0.05 to 5μ made of a material with a molecular permeability coefficient larger than that of the fluoropolymer described below, and on the intermediate layer, a thin film layer of a fluoropolymer having a ring structure in the main chain with a thickness of 0.05 to 5 μm. The permselective membrane according to any one of claims 1 to 5, which is formed with a thickness of 0.01 to 5μ.