JPH07155568A - Production of inner surface nonporous layer type hollow yarn inhomogeneous membrane - Google Patents

Abstract

PURPOSE:To produce a hollow yarn inhomogeneous membrane excellent in separation performance and having a non-porous layer formed on the inner surface by making the oxygen concn. of a gas used as a core agent higher than the oxygen concn. of a gas in contact with the outside of a hollow yarn precursor in fused state and below the oxygen concn. of air. CONSTITUTION:A hollow yarn like molding non-porous as the whole is obtained by melt-spinning a crystalline thermoplastic polymer into hollow yarn. That is, the hollow yarn is obtained by using a hollow yarn spinning nozzle, melt- extruding the polymer with the gas as the core and cooling to solidify while ventilating. At this case, the oxygen concn. of the gas used as the core agent is made higher than the oxygen concn. of the gas in contact with the outside of the hollow yarn precursor in fused state and below the oxygen concn. of air. As a result, the non-porous layer is easily formed on the inner surface of the hollow yarn inhonaogenious membrane and is used for an application for allowing the inside of the hollow yarn inhomogeneous membrane to contact with a liquid, such as a membrane type artificial lung and a pervaporation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a membrane oxygenator, a degasser from a liquid, a gas dissolution into a liquid, a pervaporation, a gas separation, a dehumidification, etc. The present invention relates to a method for producing a hollow fiber heterogeneous membrane having a porous layer.

[0002]

2. Description of the Related Art A crystalline thermoplastic polymer is melt-spun into a hollow fiber and then stretched to keep at least one surface of the hollow fiber non-porous while the other hollow fiber walls are made porous. A method for producing a hollow fiber heterogeneous membrane (hereinafter referred to as a melting method) is known (for example, JP-A-59-19670).
6). In the melt spinning process of the melting method, the molten resin extruded from the nozzle is cooled by gas and solidified,
Air has usually been used as the cooling gas. Further, in order to melt-spin into a hollow fiber shape, a gas is used as a core agent and melt-spun and extruded, but air and nitrogen have been used as the core agent gas.

[0003]

For applications in which a liquid is brought into contact with the inside of a hollow fiber heterogeneous membrane, such as membrane oxygenator, deaeration of liquid, dissolution of gas in liquid, pervaporation, etc. When used or when used to permeate gas or vapor from the inside to the outside of the hollow fiber heterogeneous membrane, for example, when producing nitrogen-enriched air or dehumidifying gas, the hollow fiber heterogeneous membrane It is preferable that a non-porous layer is formed on the inner surface because it is difficult for the liquid to fill the inside of the pores and the clogging of the pores due to contaminants.

However, in the production of a hollow fiber heterogeneous membrane by the melting method, a non-porous layer is easily formed on the outer surface of the hollow fiber, and when a non-porous layer is formed on the inner surface, the thickness of the non-porous layer is large. And the non-porous layer is likely to be formed on the outer surface at the same time, and the total thickness of the non-porous layer is large, resulting in poor performance as a separation membrane. Therefore, the problem to be solved by the present invention is to produce a hollow fiber heterogeneous membrane in which a non-porous layer having excellent separation performance is formed on the inner surface.

[0005]

Means for Solving the Problems As a result of intensive studies by the present inventors on the formation mechanism of a hollow fiber heterogeneous membrane by the melting method, the formation of a non-porous layer was found to be a hollow state in a molten state extruded from a nozzle. The inventors have found that there is an influence of the oxygen concentration of the gas that comes into contact with the yarn precursor, and arrived at the present invention.

That is, the gist of the present invention is to use an inner surface non-porous layer type hollow fiber in which a crystalline thermoplastic polymer is extruded into the gas from a hollow fiber nozzle using a gas as a core agent, melt-spun into a hollow fiber, and then stretched. A method for producing a heterogeneous membrane, wherein the oxygen concentration of the gas used as the core agent is higher than the oxygen concentration of the gas contacting the outside of the hollow fiber precursor in the molten state, and not more than the oxygen concentration of the air. A method for producing a hollow fiber heterogeneous membrane having a characteristic inner surface non-porous layer.

The present invention will be described in more detail below. The heterogeneous membrane is a membrane having a structure in which a non-porous layer made of the same material as the porous layer is integrally formed on the surface of the porous layer which functions as a support for maintaining strength. The hollow fiber heterogeneous membrane obtained by the production method of the present invention has a non-porous layer (a layer having no pores) on the inner surface of the hollow fiber, and the inner and outer sides are porous layers. It is an inner surface non-porous layer type hollow fiber heterogeneous membrane.

The polymer used in the present invention is a crystalline thermoplastic polymer. The polymer having an ultimate crystallinity of 30% or more is preferable for producing a heterogeneous film having excellent performance. Further, in order to fully exert the effects of the present invention, it is preferable that the crystalline thermoplastic polymer used in the present invention is a substance exhibiting oxidative decomposition by oxygen.

Examples of crystalline thermoplastic polymers include polyolefins such as polyethylene, polypropylene, poly-4-methylpentene-1 and poly-3-methylbutene-1, polyacetal, polyoxyethylene, polyphenylene oxide and the like. Polythioethers such as polyether, polymethylene sulfide, polyethylene sulfide, chlorine-containing polymers such as polyvinylidene chloride, fluorine-containing polymers such as polyvinylidene fluoride,
Examples thereof include polyamides such as nylon 6 and nylon 66, polyesters such as polyethylene terephthalate, polystyrene, and the like. Of course, these copolymers may be used.

Among these, poly-4-methylpentene-
A copolymer containing 1, and 4-methylpentene-1 as a main component (containing 50% by weight or more) has a high gas permeation rate and a high oxygen / nitrogen separation coefficient, and also has a high crystallinity excess. It is preferable because it exhibits oxidative decomposability. Four
-Examples of preferred copolymerization components of the copolymer having methylpentene-1 as a main component include olefins such as ethylene, propylene, butene-1, isobutylene, pentenes, hexenes, and other α-olefins. To be

In the production method of the present invention, a hollow fiber is first melt-spun by using a crystalline thermoplastic polymer (which may be simply referred to as a polymer hereinafter) to form a hollow fiber-like molded article which is entirely non-porous. Obtained (hereinafter referred to as hollow fiber). That is, a hollow fiber spinning nozzle is used to melt and extrude a polymer with a gas as a core, and the polymer is cooled and solidified while being drafted (stretched in a molten state) to obtain a hollow fiber. The present invention is
The oxygen concentration of the gas used as the core may be higher than the oxygen concentration of the gas contacting the outside of the molten hollow fiber precursor, and the core may be equal to or lower than the oxygen concentration of air (about 21 mol%). It is a feature. The hollow fiber precursor in a molten state as used herein refers to a molten polymer which has been extruded from a nozzle to form a hollow fiber, but has not yet solidified. The oxygen concentration itself of the gas used as the core agent can be relatively arbitrarily selected as long as it is equal to or lower than the oxygen concentration of air. However, if the oxygen concentration is too low, the formation of the inner non-porous layer becomes insufficient, so that 10 mol%
Above, that is, 10 to 21 mol% is preferable. The components other than oxygen of the core agent gas are arbitrary. For example, nitrogen, carbon dioxide,
Argon and the like can be mentioned, but nitrogen is preferable. Industrially, the core gas is preferably air. Even if the oxygen concentration of the core agent is equal to or lower than that of air, if the oxygen concentration of the gas contacting the outside of the molten hollow fiber precursor is equal to or higher than the oxygen concentration of the core agent, the hollow fiber heterogeneous membrane It is unsuitable because a non-porous layer is likely to be formed on the outer side or both sides of.

The gas contacting the outside of the hollow fiber precursor in a molten state is the gas contacting the portion of the resin extruded from the nozzle until the resin is solidified, and is usually a cooling gas. In the present invention, the oxygen concentration needs to be lower than the oxygen concentration of the core gas. As a component other than oxygen, any component which is also non-reactive with the molten polymer may be used. For example, nitrogen, carbon dioxide gas, argon, etc. may be mentioned. Nitrogen or nitrogen-enriched air is preferable as the gas that comes into contact with the outside of the molten hollow fiber precursor. Nitrogen-enriched air can be produced by a separation membrane system or PSA (adsorption system).

The type and composition of the gas that further cools the hollow fiber, which is still hot after solidification, can be different from the composition of the gas that contacts the portion of the resin extruded from the nozzle until it solidifies. That is, the gas for further cooling the hollow fiber which is still hot after solidification is optional. For example,
From the economical aspect of manufacturing, it is also possible to contact nitrogen or nitrogen-enriched air to the part where the resin extruded from the nozzle is solidified, and to use air as a gas to further cool the still hot hollow fiber after solidification. preferable.

In the present invention, in melt spinning, the oxygen concentration of the gas used as the core agent is made higher than the oxygen concentration of the gas in contact with the outside of the hollow fiber precursor in the molten state, and below the oxygen concentration of the air. It is possible to produce a hollow fiber heterogeneous membrane whose inner surface is a non-porous layer, by which the oxygen concentration of the gas used as the core agent is sufficient to achieve the effect. It is preferable to sufficiently increase the oxygen concentration ratio of the gas contacting the outside of the molten hollow fiber precursor. That is, it is preferable that the oxygen concentration of the gas used as the core agent is at least twice as high as the oxygen concentration of the gas contacting the outside of the molten hollow fiber precursor,
More preferably, it is 3 times or more higher. By increasing this ratio, the allowable range of manufacturing conditions becomes wider, and
There is no non-porous layer on the outer surface of the hollow fiber, and it becomes easy to form a defect-free non-porous layer on the inner surface.

The melt spinning conditions are such that the oxygen concentration of the gas used as the core agent is higher than the oxygen concentration of the gas contacting the outside of the hollow fiber precursor in the molten state, and the core agent is below the oxygen concentration of the air. Other than that, the method is the same as the known method for producing a heterogeneous film by the melting method, and the optimum conditions for the film to be formed may be selected depending on the kind of the polymer used. That is, the melt extrusion temperature is a temperature above the crystalline melting point (Tm) of the polymer,
The temperature is preferably (Tm + 20) ° C. to (Tm + 200) ° C., and the draft is 50 to 10,000, preferably 200 to
It is 1500. The cooling is cooling in a gas, and the temperature and the wind speed of the cooling gas are adjusted so that the solidification point of the extruded hollow fiber is preferably 5 to 200 mm, more preferably 10 to 50 mm from the nozzle.

The step of forming the melt-spun hollow fiber into a heterogeneous film is the same as in the known method for producing a heterogeneous film by the melting method. The process will be described below. The melt-spun hollow fiber is heat-treated if necessary. The heat treatment temperature is not lower than Tg (glass transition point) and not higher than Tm (crystal melting point) of the polymer. By performing the heat treatment, the crystallinity of the polymer can be increased and the crystal defects can be reduced, and the inside of the hollow fiber wall can be easily made porous.

The melt-spun or heat-treated hollow fiber is stretched to make the inside of the hollow fiber wall porous. The mechanism by which the inside of the hollow fiber wall is made porous is the melt-extruded crystalline polymer under appropriate tension by drafting,
It is said that when cooled under an appropriate temperature gradient, a laminated lamella crystal develops in a plane perpendicular to the fiber axis, and when the lamella crystal is stretched and the crystals are cleaved to form a porous body.

The stretching temperature, the stretching ratio, the stretching speed, etc. are not particularly limited, and an appropriate value can be selected according to the polymer. For example, the stretching temperature is preferably (Tm-10) ° C or lower, and preferably (Tg + 50) ° C or lower. It is not necessary to set the lower limit of the stretching temperature, and the liquid nitrogen temperature (minus 196 ° C.) is also possible. The stretch ratio is preferably 1.3 to 6, and more preferably 2 to 4. The higher the stretching temperature, the higher the stretching ratio is preferably.

The stretching may be multi-stage stretching, preferably multi-stage stretching in which the temperature is successively increased. In the case of multi-stage stretching, it is preferable that the stretching temperature includes (Tg + 50) ° C. or less. In the case of multi-stage drawing, the draw ratio of each stage is preferably 1.1 or more, and the total draw ratio is preferably 1.3 to 6, and 2 to 4
Is more preferable. The higher the drawing temperature, the higher the draw ratio of that step.

The stretched hollow fiber heterogeneous membrane is preferably heat-fixed to impart dimensional stability and heat resistance. The heat treatment temperature is not lower than Tg and not higher than Tm of the polymer and higher than the stretching temperature.

In the present invention, by making the oxygen concentration of the gas used as the core agent during spinning higher than the oxygen concentration of the gas contacting the outside of the molten hollow fiber precursor, the inner surface of the hollow fiber is It has a structure that is less likely to become porous than the part. Therefore, by selecting conditions such as spinning, heat treatment, and stretching, the inner surface does not become porous,
It is possible to find a critical condition that the other part, that is, the inside and the outside of the hollow fiber wall, becomes porous. For example,
As the spinning temperature is increased, it becomes difficult to make both the inside and outside surface layers of the hollow fiber wall porous. Therefore, by conducting an experiment in which the spinning temperature is sequentially increased, it is possible to find a spinning temperature at which the inner surface is not made porous yet, but the other portions, that is, the inside of the hollow fiber wall and the outer surface are made porous. The same applies to conditions such as spinning draft, spinning cooling conditions, heat treatment, drawing, and heat setting.

The formed hollow fiber heterogeneous membrane having a non-porous layer on its inner surface (hereinafter simply referred to as hollow fiber membrane) may have any dimensions, but the outer diameter is 0.1 to 3 mm and the thickness of the porous layer is 0. .0
The thickness is preferably 1 to 1 mm, the thickness of the non-porous layer is 0.05 to 5 μm, and the average pore size of the pores in the porous layer is 0.01 to 10 μm.

[0023]

EXAMPLES The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the present invention. [Example 1] <Production of hollow fiber membrane> Poly- as a crystalline thermoplastic polymer
4-methylpentene-1 (manufactured by Mitsui Petrochemical Industry Co., Ltd.,
TPX-RT-18), 6-hole outer diameter 6 mm
Melt spinning was performed at a spinning temperature of 285 ° C. using a circular spinning nozzle. At this time, the polymer was extruded from the annular spinning nozzle, air was introduced from the core agent introducing hole provided inside the annular ring, and the air was taken in by the draft 700 while the oxygen concentration was 5%.
The sample was cooled by a 0.1 m / sec air flow of nitrogen-enriched air, and wound up. The resulting hollow fiber was entirely non-porous.

This hollow fiber was heat treated in an air bath at 195 ° C. for 1 minute, and then stretched at 25 ° C. with a draw ratio of 1.4 and then 1
Draw at a draw ratio of 1.4 at 30 ° C, then 195 ° C
Heat setting was performed by allowing the sample to stay in the air bath for 1 minute.

The obtained hollow fiber membrane has an outer diameter of 254 μ.
m, inner diameter 198 μm, scanning electron microscope (SE
As a result of observation with M), no pores were observed on the inner surface, and a large number of pores having a pore size of about 0.05 μm were present on the outer surface. There were pores with a pore size of about 0.03 μm.

The gas permeability of this hollow fiber membrane is determined by ASTM,
The oxygen permeation rate was 1.6 × 10 ⁻⁵ [cm ³ (STP) / cm ² (inner surface area), s, cmHg), and the nitrogen permeation rate was 3.8 ×, as measured by the D-1434 pressure method. 1
0 ^-6 [cm ³ (STP) / cm ² (inner surface area), s, cm
Hg), and the oxygen / nitrogen separation coefficient was 4.2.

Regarding the polymer (TPX-RT-18), a melt press film produced at 300 ° C.
The crystallinity of the sample heat-treated at 30 ° C. for 30 minutes was about 55% as measured by X-ray diffractometry.

<Deaeration Test> 10,000 hollow fiber membranes were bundled and loaded into a cylindrical housing, and both ends of the hollow fiber membrane were sealed with a resin to obtain a membrane area (hollow fiber inner surface area) of 3.0 m ^2. The membrane module of While depressurizing the outside of the hollow fiber membrane of this module to about 30 torr with a water flow aspirator,
When tap water having a dissolved oxygen concentration of 8 ppm by weight was flowed inside the hollow fiber membrane at 100 l / hr, the dissolved oxygen concentration of water flowing out from the module was 0.49 ppm by weight. Furthermore, instead of tap water, the dissolved oxygen concentration is 8.1 wtpp
m was subjected to a degassing test of tap water containing 0.5% by weight of sodium alkylbenzenesulfonate-based surfactant, the dissolved oxygen concentration of the outflow solution was 0.48 ppm by weight.
The value was almost the same as that of tap water.

[Example 2] <Production of hollow fiber membrane> The spinning temperature was 295 ° C, nitrogen-enriched air with an oxygen concentration of 10% was used as the core material, and nitrogen was added to a portion up to 10 cm below the nozzle. Concentration 99.99
% Nitrogen was flown at a wind speed of 0.1 m / sec, and a hollow fiber membrane was prepared in the same manner as in Example 1 except that air was blown below it at a wind speed of 0.1 m / sec.

The size of the obtained hollow fiber membrane has an outer diameter of about 245.
The inner diameter was about 186 μm. As a result of SEM observation, no pores were observed on the inner surface, and pores with a pore size of about 0.04 μm were recognized on the entire outer surface. The cross section of the hollow fiber cut obliquely had a pore size of about 0. A 03 μm pore was observed.

The oxygen permeation rate of this hollow fiber membrane was 8.8 × 1.
0 ^-6 (cm ³ (STP) / cm ² (inner surface area), s, cm
Hg), nitrogen permeation rate is 2.1 × 10 ^-6 [cm ³ (ST
P) / cm ² (inner surface area), s, cmHg), and the oxygen / nitrogen separation coefficient was 4.3.

<Deaeration test> Using this hollow fiber membrane, a membrane module similar to that of Example 1 was prepared and a deaeration test similar to that of Example 1 was conducted. The residual dissolved oxygen concentration of the surfactant aqueous solution was 0.50 ppm by weight and 0.49 ppm by weight.

Comparative Example 1 <Production of Hollow Fiber Membrane> Hollow fiber membrane was produced in the same manner as in Example 1 except that nitrogen having a concentration of 99.99% was used as the core agent and air was used as the cooling gas. A thread film was prepared.

The size of the obtained hollow fiber membrane has an outer diameter of about 257.
The inner diameter was about 201 μm. As a result of SEM observation, pores having a pore size of about 0.03 μm were found on the entire inner surface, and no pores were found on the outer surface, and the cross section obtained by obliquely cutting the hollow fiber had a pore size of about 0. A 03 μm pore was observed.

The oxygen permeation rate of this hollow fiber membrane is 1.5 × 1.
0 ^-5 [cm ³ (STP) / cm ² (external surface area), s, cm
Hg), nitrogen permeation rate is 3.6 × 10 ^-6 [cm ³ (ST
P) / cm ² (external surface area), s, cmHg) and the oxygen / nitrogen separation coefficient were 4.2.

<Deaeration test> Using this hollow fiber membrane, a membrane module similar to that of Example 1 was prepared and a deaeration test similar to that of Example 1 was conducted. 0.49 weight ppm and the same value as in Example 1, but
The residual dissolved oxygen concentration of the aqueous surfactant solution is 1.1 weight pp.
It was m. It can be seen that, as compared with Example 1, the deaeration performance of the surfactant-containing water is poor.

[0037]

EFFECT OF THE INVENTION It is easy to form a non-porous layer on the inner surface of a hollow fiber heterogeneous membrane, and a hollow fiber heterogeneous membrane having a non-porous layer formed on the inner surface can be obtained. Therefore, the application of contacting the liquid inside the hollow fiber heterogeneous membrane, for example, membrane oxygenator,
In applications such as degassing of liquid, dissolution of gas in liquid, pervaporation, etc., it can be used stably for a long period of time because the liquid does not fill the inside of the pores. High performance can be exhibited even when contacting with an organic solvent (and its aqueous solution).

When the hollow fiber heterogeneous membrane is used for permeating gas or vapor from the inside to the outside, for example, for producing nitrogen-enriched air or dehumidifying gas, the pores are clogged with contaminants. Is less likely to occur.

Claims (5)

[Claims] 1. A method for producing an inner surface non-porous layer type hollow fiber heterogeneous membrane in which a crystalline thermoplastic polymer is extruded from a hollow fiber nozzle into a gas by using gas as a core agent, melt-spun into a hollow fiber, and then stretched. The oxygen concentration of the gas used as the core agent is higher than the oxygen concentration of the gas contacting the outside of the hollow fiber precursor in the molten state, and is less than or equal to the oxygen concentration of the air. A method for producing a porous layer type hollow fiber heterogeneous membrane. 2. The method according to claim 1, wherein the oxygen concentration of the gas used as the core agent is at least twice as high as the oxygen concentration of the gas contacting the outside of the molten hollow fiber precursor. 3. The oxygen concentration of the gas used as the core agent is 1
The production method according to claim 1, which is 0 to 21 mol%. 4. The method according to claim 1, wherein the gas used as the core agent is air. 5. The production method according to claim 1, wherein the polymer is a 4-methylpentene-1 type polymer.