JPH01123618A - Composite gas separation membrane - Google Patents

Abstract

PURPOSE:To obtain the above composite membrane having excellent gas permeability and gas separability by applying a soln. of the nonionic surfactant having a fluorocarbon chain-contg. long-chain alkyl group and an amine oxide hydrophilic group on a porous supporting membrane, and drying the soln. CONSTITUTION:The nonionic surfactant having an amine oxide hydrophilic group and a fluorocarbon chain-contg. long-chain alkyl group expressed by the formula [Rf is CF3(CF2)n-1, (n) is 2-16, R1 is (CH2)m, (m) is 0-6, X is COO, SO3, CONR4, SO2NR4, (l) is 2-6, and R2-R4 are alkyls] is applied on the porous supporting membrane, etc., and dried. The obtained composite membrane has excellent gas permeability and gas separability. According to example 1, for instance, alphaO2/N2=2.96, QO2=0.7m<3>(STP)/m<3>.H.atm, and alphaCO2/CH4=6.3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas selective permeation composite membrane for selectively separating at least one gas from a mixed gas.

[Prior Art] Differences in the permeation rates of gas molecules through a polymeric substance are used in gas separation operations to concentrate specific components in a gas mixture through a gas selective element having a selectively permeable layer made of a polymeric substance. This method is well known and has been used to recover oxygen-enriched air from the air.

The permeability of gas molecules is unique to the material of the selectively permeable layer, and in order to perform efficient separation operations, it is necessary to have a large difference in permeability between the target component and coexisting components, and a large permeability of the target component. It is necessary to select the material. Considering the membrane material, there is a general tendency that increasing the gas separation selectivity (a) causes the gas permeability coefficient P to decrease, and increasing the gas permeability coefficient P tends to decrease the gas separation selectivity α.

Additionally, the amount of gas permeating through a uniform membrane is generally expressed by the following equation.

Here, Q is the gas permeation rate mβ (STP) / 5ec
P is the gas permeability coefficient mA (STP) cm/cm!・
cmHg-sec P, P is the partial pressure of gas on the supply side and permeation side of the membrane (cmHg) l is the membrane thickness (cm) A is the membrane area (cm'').

Therefore, in order to satisfy both gas selectivity and gas permeability, it is necessary to use a material with a relatively high gas permeability coefficient P among those having the desired gas separation property a, and at the same time reduce the film thickness 1. be.

For this purpose, a composite membrane is generally used in which a layer of a polymer having gas separation properties is coated on a porous support that does not have gas separation properties.

For example, JP-A-56-40415 discloses a membrane in which a polymer mainly consisting of poly(4-methylpentene-1) is composited onto a porous membrane by a water surface spreading method. Although the αOs/Nn of the poly(4-methylpentene) material itself is as high as 3 or more, it is inferior at POa = 3x10-@ and there is a limit to the thinning of the film, so the QO! of the composite film was not sufficient.

Further, JP-A-50-41958 discloses a membrane made of an organopolysiloxane-polycarbonate copolymer. The POl of this is 2X 10-” (cc: c
m (STP) 7 cm"sec-cmllg), which is large, but aL/N2 is small, 2 to 2.2, and there is a limit to the oxygen concentration of the oxygen-enriched air that can be obtained.

On the other hand, JP-A No. 60-114323 discloses an oxygen separation and concentration film characterized by being composed of a bilayer film made of an amphiphilic compound having a long-chain alkyl group containing a fluorocarbon group. .

However, the PO of this bilayer membrane alone is 1.74XI
O-'', which is high, but C0,/N = 2.27, which is not sufficient, and by mixing a polar polymer for the purpose of improving the formability of the membrane, QOs/Na = 2.29 to 3.
Although it is high at 13, the pot is 6.7X 10-10 to 0.
There was a tendency to increase the size to 097XIQ-10.

[Problems to be solved by the invention] As described above, a material that has a good balance between gas selectivity and gas permeability and has sufficient thin film forming ability to form a composite membrane, and a composite membrane using the same, are Previously, it was rarely seen.

[Means for Solving the Problems] In recognition of the above problems, the present inventors have conducted extensive research and have developed a nonionic product having a long-chain alkyl group containing a fluorocarbon group and having an amine oxide as a hydrophilic group. A composite membrane with high oxygen permeability and oxygen and nitrogen separation properties can be obtained by bringing a surfactant solution into contact with a porous membrane that does not have gas separation properties and then drying it to form a composite. The present invention was achieved based on the discovery that

In the present invention, the nonionic surfactant having a long chain alkyl group containing a fluorocarbon group and having an amine oxide as a hydrophilic group is represented by the following formula (1): R30-R8 [Rf is CF3 (CFII)] n-1 (however, n is 2~
represents an integer of 16) and R1 is (C1h) −
(where m represents an integer of O to 6) or -3-NR4-, where R4 represents 11 or an alkyl group having 2 to 6 carbon atoms) 1 represents an integer of 2 to 6 , Ra represents an alkyl group having 1 to 6 carbon atoms.

] The porous support in the present invention has a gas permeation rate of 0.1m"7m".h+"atm or more, an average pore diameter of 10 to 10,000 on the side covered with the gas selective permeation membrane layer, and the other side It is preferable to have an asymmetric structure in which the average pore size of the pores is larger than the above pore size.Among these, an asymmetric structure with a gas permeation rate of 0.5m"7m"・hr"atm or more and an asymmetric structure with an average pore size of 50 to 5[100" on the surface Particularly preferred is one having such a structure because it has low gas resistance and can maintain the gas selectively permeable membrane layer under high pressure without being damaged.

Further, it is preferable that the surface shape is smooth and has small irregularities because it is difficult to form defects in the gas selectively permeable membrane layer.

As the material for the porous body, any material that can form the above-mentioned porous shape can be used, such as polysulfone, polyethersulfone, polypropylene, polytetrafluoroethylene, polyamide, polyimide, polyacrylonitrile, polycarbonate, and cellulose. There are polymers such as esters, and inorganic materials such as porous glass and porous ceramics.

The shape of these porous supports may be sheet-like, hollow fiber-like, or tube-like depending on the purpose.

Composite membranes made of these porous supports and nonionic surfactants having fluorocarbon group-containing long-chain alkyl groups having amine oxide as hydrophilic groups have a fluorocarbon group-containing long-chain alkyl group having amine oxide as hydrophilic groups. This can be carried out by bringing a porous support into contact with an aqueous or organic solution of a nonionic surfactant, coating the porous support thinly and uniformly, and then drying with hot air. Solvents for nonionic surfactants having long-chain alkyl groups containing fluorocarbon groups include water, methanol, alcohols such as ethanol and isopropyl alcohol, dioxane, tetrahydrofuran, Freon solvents, and mixtures thereof. A known method can be used for coating the porous support with an organic solution of a highly permeable polymer selected depending on the combination with the porous support. In this way, a thin film having a thickness of preferably 0.03 to 5 μm, particularly 0.05 to 2 μm can be obtained by, for example, a dip coating method or a reverse roll method.

Although the above explanation uses oxygen and nitrogen as examples, the present invention is not limited to this system, but can also be applied to, for example, recovery of methane and helium from natural gas, separation of carbon oxide and hydrogen, etc. I can do that. The present invention will be specifically explained below based on Examples, but it goes without saying that the present invention is not limited by such explanations.

[Example] Example 1 Polyester nonwoven fabric lined surface with a pore diameter of about 50,
Back side hole diameter: 50μ thick made of polysulfone with a diameter of 16m
m sheet-like asymmetric porous support membrane (air permeation rate 20
m'/ m"old atm) to CFa (CF+1) nC
0NII (CIla) +IN (CHs) * (
After immersing in a 2% Ichikawa aqueous solution of a fluorosurfactant with a number structure where n is 8 on average, it was stored at room temperature and air-dried to reduce the thickness of the selected layer to μm.
A composite membrane was obtained.

When we measured the separation performance of this composite membrane for oxygen, nitrogen, carbon dioxide, and methane, we found that Qz = o, 7m' (STP) 7m''・ll・a
tm, 0 mouth 2/Na□2.96, Q Qa= 2.0
m” (STP) / m”11・atm, a CO
2//CIL・6.3.

Example 2 CF3 (CF2) n(C1la) as surfactant
, SNll-(CIlx) 3N (CH31m (
A composite membrane was obtained in the same manner as in Example 1, except that a selective layer (thickness: 0.16 μm) of a fluorine-based ↓ surfactant having a structure in which n is 8 on average was used.

The performance of this membrane is QO3=0.58m'(STP)/m
”ilatm %aOa/NgT=2.78, Q CO
*g1.6m' (STP)/ m"H・atm %a
The cOIl/CHn' was 5.3.

Comparative Example 1 CHs (C1la) r IN (
CH3) A composite film was formed in the same manner as in Example 1 except that a non-fluorine surfactant having the structure ↓ was used. The performance of this film is Q L = 18.2m” (STP) /m”・
Atm%a L/Nx = 0.99, which was almost the same as the performance of the porous support membrane.

Example 3 Surface pore diameter approximately 50, outer diameter 350 μm, inner diameter 150 μm
polysulfone (air permeation rate 5 m'/m"・t
CFa (CFi) after air drying m) at 70°C. C0N
H(CHi) aN-(C1la) z (n is 8 on average
) in a 2% by weight aqueous solution↓, and then dried at 80°C for 1 minute to obtain a composite membrane. When the performance of this film was measured, Q Qa = 0.4m” (STP)/m2・h+”a
tm %a 02/N2 =2.58.

Claims (2)

[Claims] (1) A composite gas separation membrane in which a membrane made of a nonionic surfactant having a long-chain alkyl group containing a fluorocarbon chain and having an amine oxide as a hydrophilic group is laminated on a porous support membrane as a gas-selective layer. (2) The composite gas separation membrane according to claim 1, wherein the nonionic surfactant having a long-chain alkyl group containing a fluorocarbon chain and having an amine oxide as a hydrophilic group is represented by the following formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [Rf represents CF_3 (CF_2)_n_-_1 (where n represents an integer from 2 to 16), and R_1 represents (CH_2
)_m (where m represents an integer from 0 to 6); , l represents an integer from 2 to 6, R_2,
R_3 represents an alkyl group having 1 to 6 carbon atoms. ]