JPS6118402A - Hollow yarn membrane for gas separation and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain a hollow yarn membrane having high formability, high permeation velocity of oxygen, and high separation factor by coating a clogging material having high permeability coefft. for oxygen on porous hollow fiber comprising poly-2,6-disubstituted phenylene oxide. CONSTITUTION:A spinning soln. is prepd. by dissolving poly-2,6-dimethyl-phenylene oxide in a solvent and a hollow yarn membrane is formed by injecting air into the soln. The membrane is dipped in a coagulating bath, washed with water, and treated by heating. Then, the hollow yarn is dipped in a dil. soln. of a clogging material having higher permeability coefft. of oxygen than that of the raw material for the hollow yarn membrane, e.g. phenylene/siloxane block copolymer expressed by formula 1, then the material is dried with hot air, and wound. By clogging defects such as pinholes of the porous hollow yarn with a material having higher permeability coefft. for O2, a membrane having higher separation factor than that of the clogging material is obtd. while maintaining the permeability and increasing the separation factor of the membrane larger than that of the clogging material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hollow fiber membrane for gas separation and a method for producing the same. The present invention relates to a hollow fiber membrane with a high selectivity and a method for producing the same.

[Prior Art] The method of separating and concentrating a specific gas from a gas mixture using a membrane is already well known, but when obtaining oxygen-enriched air from air, no matter how small the I-package is, A major technical challenge is how to obtain a large amount of gas permeation. Permeation rate of oxygen (and nitrogen) through a normal homogeneous membrane QOZ
, Qiz and the separation coefficient (α) are expressed by the following equation.

QOL= P o＞/n% QNZ=PI
J2L/αα= Pa2/ PNZ = Qo, / Q
sz.

Q: gas permeation rate [a(/ad -sec -cmH
q ]P: Gas permeability coefficient [cy#-ava/cl-
sea -ci+)1o] α: Separation coefficient Q: WI thickness [cm] In other words, Po, Pu2, α are factors determined by the membrane material, and the development of materials with large Pot and α,
A technique for reducing the film thickness (n) of the material is important.

Furthermore, in actual use, the form of the membrane is also important, and hollow fiber membranes having a larger surface area per unit volume are generally considered to be more advantageous than flat membranes.

Now, various so-called composite hollow fiber membranes for gas separation, in which a functional polymer is coated on a porous hollow fiber support, are known. For example, JP-A-54-102292 discloses a composite hollow fiber in which a thin film of a polymer such as silicone, poly-2,6 dimethylphenylene oxide, or ethyl cellulose is formed on a hollow fiber such as polypropylene.

In this method, a support hollow fiber with a relatively high N2 gas permeation rate is used, but it is not possible to create a thin and defect-free coating film on such a rough surface, and it is necessary to maintain a high α. Therefore, the film thickness must be increased.

Therefore, there was a drawback that the permeation rate of the composite membrane was low. In addition, JP-A-53-86684 describes the separation performance and structure of the support membrane that affect the separation performance of the composite membrane, but since Po of the support membrane material is relatively small to begin with, the permeation of the composite membrane is The speed had to be reduced. In addition, Japanese Patent Publication No. 54-17052 discloses a cellulose acetate hollow fiber coated with silicone, and JP-A-54-103788 discloses a porous polyvinylidene chloride hollow fiber coated with a thin polymer film. However, the situation does not change much.

Heretofore, poly-2,6-disubstituted phenyleneoxyethylene has been used as a coating material because of its high oxygen permselectivity. Poly 2,6-disubstituted phenylene oxide hollow fiber membranes can also be produced as porous hollow fibers that have a uniform layer on the surface (that is, the separation coefficient is close to the value unique to poly 2,6-disubstituted phenylene oxide) by selecting manufacturing conditions. It is possible.

However, if this is attempted, the thickness of the dense layer will inevitably increase and the oxygen permeation rate will decrease.

Therefore, if manufacturing conditions are selected so that the dense layer becomes thinner, the separation coefficient of the hollow fiber membrane becomes lower than the original properties of poly2,6-disubstituted phenylene oxide. In other words, it is impossible to create a thin, defect-free dense layer.

[Problems to be Solved by the Invention] The object of the present invention is to provide a material that has sufficient formability as a hollow fiber porous membrane material, has a high oxygen permeation rate (Qo, ), and has an excellent separation coefficient (α). The object of the present invention is to obtain a hollow fiber membrane mainly composed of poly-2,6-disubstituted phenylene oxide.

[Means for solving problems] The present invention has the following configuration.

(1) Poly 2.6-di-substituted phenylene oxide based porous hollow fibers coated with a plugging material having a higher oxygen permeability coefficient than the polymer material. A hollow fiber membrane for gas separation.

(2) The oxygen permeability coefficient of the plugging material is i, oxio-a7
-am/al-sea-csHg (25°C) or higher, the hollow fiber membrane for gas separation according to claim 1.

The hollow fiber membrane for gas separation according to claim 1, which is a polymer comprising:

The polyphenylene oxide used in the present invention also includes blends mainly composed of this polymer.

A typical example of such a polymer is poly-2.6 dimethylphenylene oxide. Low molecular weight polymers of the above-mentioned poly-2,6-disubstituted phenylene oxide are not preferred because they have problems in spinnability, and those with a number average molecular weight (GPC method) of 10,000 or more, more preferably 30,000 or more are preferable.

There are no particular restrictions on the solvent for poly-2,6-disubstituted phenylene oxide, but specific examples include benzene, toluene, chloroform, N-methyl-2-pyrrolidone, dimethylformamide, which becomes a homogeneous solution upon heating, Dimethylacetamide and the like can be mentioned. Furthermore, if necessary, a non-solvent of poly2,6-disubstituted phenylene oxide can be added as an additive.

The spinning solution differs slightly depending on the selected solvent and additives, but the concentration of poly2,6-disubstituted phenylene oxide is 2.
0 to 40% overlap is preferred.

If the polymer concentration is too low, it is not preferable because the viscosity of the stock solution decreases, making it difficult to form a hollow fiber membrane by the gas injection method, and the spinnability (stringinability) of the discharged stock solution flow decreases. On the other hand, if the polymer concentration is too high, depending on the amount of additives, the degree of porosity of the resulting hollow fiber membrane will be small, and the spinning temperature will be set high due to the high viscosity of the raw solution, resulting in a wet-dry spinning method. It is thought that the formation of a dense layer on the surface of the hollow fiber membrane in the dry section is excessively promoted. Therefore, such a hollow fiber membrane has a low oxygen permeation rate and is not preferable.

Further, the spinning stock solution of the present invention varies somewhat depending on the combination of solvent and additives and its composition, but when the stock solution temperature decreases, the stock solution rapidly increases in temperature and gels. This property is very advantageous when forming hollow fiber membranes by the gas injection method. It also has the characteristic of co←phase separation with gelation to form an opaque gel. Therefore, setting the spinning temperature (orifice temperature) is also important. If the set temperature is too low, the spinnability will be lost and the spinning state will become unstable, and the coagulated yarn will become extremely weak, which is disadvantageous in terms of handling. Furthermore, if the set temperature is too high, the viscosity of the stock solution becomes too low, making it difficult to form a hollow fiber membrane by the gas injection method.

If the spinning temperature is set high and the hollow fibers in the sol state extruded from the spinneret are introduced into the coagulation bath before gelation and phase separation progress, a hollow fiber membrane with a relatively dense surface can be obtained; If the spinning temperature is set to a low value, a hollow fiber membrane with a relatively rough structure will be obtained. In other words, by setting the spinning temperature to a high value and evacuating the dry section (1!111 points from the spinneret to the surface of the coagulating liquid), a hollow fiber membrane that exhibits selectivity (α>1) can be obtained as it is.

Although it varies depending on the conditions, the spinning temperature is selected in the range of 50 to 160°C, and the dry section is selected in the range of 211 to 50 m1.

Next, a solution of the used solvent is used as a coagulation bath,
When the solvent is water-soluble, an aqueous solution is preferably used.

Usually, the bath composition preferably contains 5% or more of a solvent. If the proportion of the solvent is too small, the formation of a so-called skin layer during solidification tends to be transiently promoted, and i% II
[Same as when using the stock solution, the separation coefficient (α) is good, but the hollow fiber membrane tends to have a low oxygen permeation rate.

There is no particular restriction on the coagulation bath temperature, but a bath temperature of 10 to 60°C is preferably used. The higher the bath temperature, the rougher the membrane structure on average; conversely, the lower the temperature, the more the membrane structure becomes so-called uniform membrane with very small surface porosity, similar to the hollow fiber membrane obtained from the high-concentration stock solution mentioned above. This results in a hollow fiber membrane with a high separation coefficient but a low oxygen permeation rate.

Further, the hot water treatment temperature is preferably in the range of 50 to 100°C. This hot water treatment step is important in terms of fixing the membrane structure formed by coagulation.

In other words, solvents and additives remaining in the hollow fiber membrane are removed and heat treatment is performed to suppress dimensional changes during drying of the hollow fiber. This step is indispensable in order to enable dipping treatment of the plugging material directly connected to spinning.

In the poly 2,6-disubstituted phenylene oxide porous hollow fiber used in the present invention, separation is not performed by the difference in the mean free path of gas molecules, but by the dissolution rate and diffusion rate of the gas into the membrane. It is a porous hollow fiber that separates mixed gases based on the difference in the separation coefficient (Qo, /Quz) exceeding 1.0.

In other words, it is a hollow fiber membrane that exhibits oxygen enrichment performance to some extent even without treatment with a plugging material.

In order to achieve the effects of the present invention, the separation coefficient of the poly2,6-disubstituted phenylene oxide membrane before clogging is more than 1.0 and less than 2.5, more preferably more than 1.0 and less than 2.5. Less than 0 is better. If the separation coefficient is less than 1.0, the oxygen enrichment performance by the plugging material will not be fully realized, and if it is more than 2.5,
The amount of oxygen permeation becomes too small and a sufficient effect cannot be obtained.

The meaning of "hollow fiber membrane J for gas separation mainly composed of poly-2゜6-disubstituted phenylene oxide" described in claim 1 of the present invention is as described above, and is a membrane having no separation performance at all. This is different from a composite hollow fiber membrane in which a porous support is coated with a material with good oxygen enrichment performance.

As a plugging material, the oxygen permeability coefficient is equal to or higher than that of poly2.6-disubstituted phenylene oxide, that is, 1°6x10-9o.
(・CI/r:d-sec-co+HG (25℃)
Above, more preferably 1.0x10-8cyJ-cm
lli -sec -cml-I 0 or more is preferred. Specific examples thereof include polymers containing silicon in their side chains, such as polymers containing silicon in their side chains, such as vinyl silane polymers.

Examples of the latter include, for example, trimethylvinylsilane polymers, but the nails described above (a material with a large permeability coefficient is more desirable as a plugging material used in the present invention), It is preferably selected from among the polymers containing.

That is, among the polymers used as the plugging material used in the present invention, particularly preferred is a silphenylene-siloxane block copolymer represented by the following formula, and the length of each sea fence of the preferred copolymer is m, Each n is 10≦m
≦5000. Own≦500.0≦n/m≦20.

If n/m is too large, the strength of the block copolymer film decreases, which is undesirable.

Among these polymers, specifically n=380, n/m
The silphenylene-siloxane copolymer with =7 has excellent film forming properties, and Poz = 2.2x10-fad -all
It has a large oxygen permeability coefficient of 0(-sea-ciHa) and is particularly preferably used.

The solvent for these plugging materials may be any solvent that dissolves the above polymer, but specifically, halogenated hydrocarbons such as methylene chloride, trichloroethylene, chloroform, etc.
Desirable examples include ether compounds such as tetrahydrofuran and dioxane, hydrocarbon compounds such as cyclohexane, isopentane, n-hexane, and toluene, and ketone compounds such as acetone and cyclohexanone.

Among the above-mentioned solvents, cyclohexane, toluene, and chloroform are particularly preferably used, but they are used in combination with isopentane, n-hexane, etc. so that they can be applied thinly to the supported hollow fiber membrane and dried quickly.

The concentration of the dilute solution of the plugging material used in the plugging process is 0.
0.01 to 5.0% by weight, more preferably 0.1 to 2% by weight
It is desirable that it be within the range of . When it is lower than this range, the clogging effect is not sufficient, and when it is higher than this range, thickness unevenness tends to occur.

The process of dipping the plugging material in a dilute solution is to
Although 11H may be wound up once and then carried out, it is preferable to carry out continuous processing directly connected to spinning.

The immersion time depends on the concentration of the solution, but is usually 1 minute or less, preferably 10 seconds or less. If the treatment time is long, the amount of solution taken in will increase, resulting in increased clogging and/or coverage, which is not preferable. In other words, forming a thick and uniform coating results in a decrease in the amount of gas permeation.

The thickness of the coating film does not need to be uniform, and is preferably 3 μm or less even in the thickest portions. More preferably it is 1μ or less, and most preferably 0.1μ or less.

It is desirable that the hollow fiber membrane after the immersion treatment be at least surface-dried by non-contact drying. More hot air if necessary,
It is dried and rolled up using a heated roller or the like. The drying temperature is usually selected in the range of 30 to 100°C. .

[Function] By plugging defects such as pinholes in the porous hollow IIAH with a material having a high oxygen permeability coefficient, it is possible to increase the separation coefficient while maintaining the permeation amount and obtain a membrane with a higher separation coefficient than the plugging material. can. By using a material with a large oxygen permeability coefficient, the amount of permeation is not significantly impaired. That is, the latent oxygen enrichment performance of poly2,6-disubstituted phenylene oxide is brought to light by the plugging material.

[Example 2] Performance evaluation of the hollow fiber membranes obtained in the following examples was carried out using a small glass tube module.

Specific Niha, outer diameter 0D (C1ll), effective length ff (cm
l) A small module made by bundling n (n) hollow fiber membranes is supplied with oxygen whose pressure is adjusted to 1.0 to 9104-G from a cylinder, and the unit time for oxygen to pass through the hollow fiber membranes and come out of the module. The oxygen flow mq (mα/min) per unit was measured using a thin film flow cutter. The permeation direction was from the outer surface of the hollow fiber to the inner surface, and the oxygen permeation rate QOt (m'/Tn2·hr-atlR) was calculated using the following formula, using the outer surface area of the hollow fiber membrane as the effective membrane area.

Qoz=□01. oc,,LX 0,6 [vn'/
m2-hr-atm The nitrogen permeation rate QNz was also evaluated and measured using the same method, and from these values the separation coefficient (
α-QOz/QN? −) was calculated. Note that these gas permeation flow rates are calculated at 25° C. and 760 m1HG.

Also, the permeation rate of helium and carbon dioxide gas, Q He %
Qcoz was also measured in the same manner. In addition, the coating film thickness was determined by transmission electron microscopy observation of a 0604-stained ultrathin section (cross section) of the plugged membrane.The average coating film thickness is the coating film thickness observed at 5 points per sample. is the average of

Examples 1-7 Poly2.6 dimethyl-phenylene oxide (Mn=3
2,000, hereinafter abbreviated as PPO) to 420 parts of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) to 120 parts.
The mixture was stirred and dissolved at ℃. While stirring at the same temperature, 35 parts of ethylene glycol (hereinafter abbreviated as EG) was added dropwise and mixed to obtain a uniform solution. This solution started to phase (opaque) at 85°C and showed virtually no stringiness at 80°C. This solution was kept in a hopper at 120°C and filtered through a 400-mesh stainless steel filter.
φ) into the air through 2. It was discharged at H1/min. At the same time, nitrogen was injected into the hollow fiber at an injection pressure of 7 mmH2O. The spinning temperature (pack temperature) at this time was 86° C., and the distance between the spinneret and the coagulation liquid level (dry length) was maintained at 5 mi. Next, 80CI11 was immersed in a 30°C coagulation bath consisting of a 30% NMP aqueous solution, washed with water, and further heated at 80°C for about 50°C.
A second hot water treatment was performed. Then, after being continuously immersed in a 0.3% solution of plugging material for about 0.2 seconds, it was passed through a non-contact type hot air drying cylinder and dried by being brought into contact with 35°C hot air in a countercurrent flow.20111/1ain It was wound at a speed of In addition, a membrane that was not immersed in the plugging material solution was similarly dried and wound up as an untreated hollow fiber membrane. The obtained hollow fiber membrane has an outer diameter of 534μ, a membrane thickness of 71μ, and a perfect circular diameter (minor diameter/
The length was 96%.

Furthermore, Table 1 shows the performance of hollow fiber membranes obtained in the same manner by changing the stock solution composition, spinning temperature, hot water treatment conditions, etc., and the performance of an untreated membrane as a reference example.

The dilute solution of the plugging material used was prepared by dissolving silphenylene-siloxane copolymer, which is a polymer shown in the structural formula below, in cyclohexane to prepare a 10% solution, and diluting this homogeneous solution with isopentane. A plugging material with a concentration of 0.3% was used.

(n=380, n/m=7) α=2.0 Poz=2.2xlO-8 (a+t-cmlaK ・sec -cmf-I Q
) *Qo,: 1JIi elementary transmission element overspeed'/yn2・h
r -ate ] Concentration: 0.3% Immersion time: Approximately 0.2 seconds Examples 8 to 11 245 parts of the poly-2,6-disubstituted phenylene oxide used in Example 1 was added to 455 parts of dimethylformamide (hereinafter abbreviated as DMF). The mixture was stirred and dissolved at 120°C to obtain a homogeneous solution.

This solution was processed in the same manner as in Example 1 at a spinning temperature of 70°C.
Discharged from a hollow fiber nozzle of 1°411φ-1,1■φ with a dry length of 12111, and a 10% DMF aqueous solution at 10℃.
immersed in a coagulation bath. After washing, the hollow fiber membranes were treated in a hot water bath at 80°C for 50 seconds, followed by clogging treatment under various conditions, dried with hot air at 45°C, and wound up.

゛ The performance of the obtained hollow fiber membrane is shown in Table 2. The performance of hollow fiber membranes dried and wound without clogging treatment is Q.
Ch= 5, 17 (yn"/171'-hr-a
tllll), α=1.05.

Table 2 Example 12 Helium permeation rate (QSa) and carbon dioxide gas permeation rate (Qc) for the hollow fiber membranes obtained in Examples 2, 3.7 and 9.
o-) was measured. The results are Q 01 and Q SJ
It is shown in Table 3 as a gas permeation rate ratio together with the results of z. The Ql-1c/Qs ratio is high, indicating that these hollow fiber membranes are also effective as helium separation membranes.

The configuration of the present invention achieves both high oxygen permeation and separation performance. Such an effect cannot be easily obtained with a hollow fiber membrane made solely of poly-2,6-disubstituted phenylene oxide.

[Effects] The hollow fiber membrane of the present invention is superior in oxygen enrichment performance compared to the composite hollow fiber membranes described in the previously mentioned known examples, and can reduce the size of the device without changing the permeation amount of oxygen-enriched air. It becomes possible to

In addition, the manufacturing method of the present invention is a gas injection method, and it is possible to continuously immerse the filling material into the hollow *H after hot water treatment or after drying, and if it is dried as it is, it will freeze. A high-performance gas separation membrane can be produced by a method that is extremely advantageous in practice without using time-consuming methods such as drying or solvent replacement.

Claims (4)

[Claims] (1) Mainly made of poly-2,6-disubstituted phenylene oxide, which is characterized by coating poly-2,6-disubstituted phenylene oxide-based porous hollow fibers with a plugging material that has a higher oxygen permeability coefficient than the polymer material. A hollow fiber membrane for gas separation. (2) The oxygen permeability coefficient of the plugging material is 1.0×10^-^8c
m^3・cm/cm^2・sec・cmHg (25℃)
The hollow fiber membrane for gas separation according to claim 1, which is as described above. (3) The filling material is a polymer containing a silphenylene structural unit ▲A mathematical formula, a chemical formula, a table, etc. are available▼ and a siloxane structural unit ▲A mathematical formula, a chemical formula, a table, etc. are available▼ in the repeating unit. Hollow fiber membrane for gas separation according to item 1. (4) Plugging and/or coating a poly2,6-disubstituted phenylene oxide-based hollow fiber membrane by immersing it in a solution containing 0.01 to 5.0% by weight of a plugging material. A method for producing a hollow fiber membrane for gas separation, characterized by: