JPS61101206A - Preparation of membrane - Google Patents

Abstract

PURPOSE:To prepare a membrane having gas permeable characteristics such that oxygen transmission coefficient is high and the separation factor of oxygen and nitrogen is also high, by forming a thermoplastic crystalline polymer into a film by melt extrusion and, after stretching and heating treatments, further applying stretching to the treated film before thermal fixation. CONSTITUTION:A membrane material comprises a thermoplastic crystalline polymer of which the ultimate crystallinity is 20% or more and polyolefin, a vinyl polymer, a fluorocarbon polymer or polyamide are used. Melt spinning temp. is higher than the m.p. Tm of the polymer but does not exceed Tm+200 deg.C and the draft ratio at the time of spinning is 5-10,000. A film thickness is pref. set to 0.5-1,000mum and an emitted yarn is quenched. Thereafter, the film is stretched by 10-250% at Tg-20-Tg+50 deg.C and heat-treated at Tg+20-Tm-50 deg.C without releasing stretching force while the treated film is further stretched by 1.1-4 times at Tg-50-Tm-10 deg.C and thermally fixed at temp. of Tg-Tm.

Description

[Detailed Description of the Invention] <Industrial Application Field> In recent years, separation of mixed gases using membranes, that is, gas diaphragm separation technology, has attracted attention for many reasons such as energy saving, separation equipment, and simplification of operation. production of oxygen-enriched air, recovery of CO2H2 from combustion gas, NO2 and SO from waste gas
Applications are being considered in many fields, such as removal of 2, purification and adjustment of synthesis gas H2/Co in C1 chemistry, and separation and recovery of inert gases such as He from natural gas. In these fields, high gas separation ability and high permeation rate are key points for commercialization and widespread use in terms of economic efficiency, and there is a strong desire to develop membranes that are excellent in these respects.

The present invention responds to such demands, and the present invention
The present invention provides a membrane with high performance, high permeation rate, and excellent mechanical properties, and a method for efficiently manufacturing the same, and relates to a novel membrane formed by melt molding and a method for manufacturing the same. .

<Prior Art> In the technical field of gas diaphragm separation, it is required not only to have a high gas separation capacity as described above, but also to have a high permeation rate from the viewpoint of economical efficiency. In order to achieve this goal, as described in JP-A No. 50-41958, a method using a polymer material with a high gas permeability coefficient such as polyorganosiloxane, and a method of using a polymer material with a high gas permeability coefficient such as polyorganosiloxane, a method of using a polymer material with a high gas permeability coefficient, and a method of using polymer materials with a high gas permeability coefficient, as described in JP-A-50-41958, ) As described on page 167, a method of using a polymer material with a large separation coefficient such as polyimide in a thin film has been studied. However, in the former method, there is a limit to the separation ability of polymeric materials such as polyorganosiloxane, which have a large gas permeability coefficient, because the separation coefficient is small.

On the other hand, in the latter method, materials with large separation coefficients generally have small permeation coefficients, and as a result, in order to obtain a permeation rate at a level that is practical for oxygen enrichment membranes, it is necessary to use extremely thin membranes, making it difficult to manufacture In addition to requiring additional techniques, problems arose in that the membrane strength decreased and the separation ability decreased due to the formation of pinholes. In addition, as described in Japanese Patent Application Laid-Open No. 5S-TESSOJ, ultra-a!
A method of forming the film on a porous support was also considered, but in this case, the thin film is formed from a polymer solution by the water spreading method, so the thin film produced is amorphous, with high orientation and high crystallinity. The gas separation coefficient is lower than that of
W.

La5oski et al, J, Polym S
ci, + 36.21 (1959)), and at present no manufacturing method has been found that satisfies both the transmission coefficient and the separation coefficient at the same time.

<Problems to be solved by the invention> As mentioned above, in the field of gas separation membranes, it is necessary to satisfy both high separation performance and high permeation rate. It is difficult to satisfy this requirement, and no molding method has been found that particularly increases both the permeability coefficient and separation coefficient of the material.

<Means for solving the problem> In order to obtain a membrane with improved permeation rate and separation coefficient, the present inventors added a non-containing material to the surface of a porous structure or a microporous layer (support) to serve as a separation active layer. With the aim of forming a so-called heterogeneous membrane structure with a porous layer and making the non-porous layer a higher-order structure that exhibits high separation performance, we investigated the relationship between the higher-order polymer structure and gas permeation properties. As a result of intensive research on the processing conditions to be realized, it was discovered that both the transmission coefficient and the separation coefficient, which were considered to be in a contradictory relationship with conventional techniques, could be improved at the same time, and the present invention was completed.

The present invention is a closed-cell or single-pore membrane manufactured by melt-extruding a thermoplastic crystalline polymer and then stretching the membrane, and the apparent oxygen permeability coefficient of ttJIll at 25°C is higher than that of melt-extrusion. It is more than twice the oxygen permeability coefficient of an amorphous homogeneous membrane of the same material manufactured by film forming, and the oxygen and nitrogen separation coefficient α (O2/N2
) is larger than the separation coefficient of an amorphous homogeneous membrane made of the same material produced by melt extrusion film forming.

The gas permeability coefficient PO and separation coefficient α of gas separation membranes due to the dissolution-diffusion mechanism are basically values specific to the material, but it is known that they change depending on differences in higher-order structure such as degree of orientation and crystallinity. . That is, compared to a polymer in a low-oriented amorphous state, the degree of orientation increases due to stretching, the degree of crystallinity increases due to heat treatment,
The gas permeability coefficient decreases due to fragmentation and rearrangement of crystals caused by stretching the crystallized sample. Further, it seems that the oxygen/nitrogen gas separation coefficient generally exhibits a higher value as the structure has a lower permeability coefficient. That is, the transmission coefficient and the separation coefficient have an inverse relationship, and no structure or processing method has been known that improves both simultaneously.

During research on the relationship between the higher-order structure of polymers and gas permeation properties, the present inventors found that polymer membranes processed under special conditions had a higher oxygen permeation rate than low-orientation, amorphous membranes. We discovered the surprising fact that the separation coefficient is high and also exhibits a larger value, and conducted further research to arrive at the present invention.

The present invention will be explained in more detail below.

In the present invention, a thermoplastic crystalline polymer (1) has a melting temperature of Tm to (Tm+200)°C (where Tm is the crystal melting point);
A hollow fiber or film obtained by melt extrusion film forming under the condition that the draft ratio Df is 20≦l)f≦10000 is (2+
After stretching 5 to 200% of the original length at (Tg-20) to (7g+50)°C (where ? is the glass transition temperature), heat treatment is performed at a salinity of +31 Tg-Tm, and then,
Stretched at a temperature of +41 (Tg -50) to (Tm-10) °C to a stretching ratio of 1.1 to 5.0, then (51tg
” 25, characterized by heat-setting at a temperature of Ta+.
The apparent oxygen permeability coefficient at ℃ is more than twice the oxygen permeability coefficient of an amorphous homogeneous membrane of the same material manufactured by melt-extrusion membrane formation, and the oxygen and nitrogen separation coefficient α (O2 /N2) is larger than the separation coefficient of an amorphous homogeneous membrane of the same material produced by melt extrusion film formation, and a method for producing a closed-cell or single-pore membrane. It is something.

The membrane material that can be used in the present invention is a thermoplastic crystalline polymer having an ultimate crystallinity of 20% or more, such as polyethylene, polypropylene, poly-3-methyl-butene-1, poly-4-methyl-pentene. -1, etc. polyolefins,
Vinyl polymers such as polystyrene and polymethyl methacrylate, fluorine-based polymers such as polyvinylidene fluoride and polyvinyl ethylene fluoride/tetrafluoroethylene copolymer, polyamides such as nylon 6, nylon 66, and nylon 12, and polyethylene teretsu. Polyesters such as crate, polybutylene terephthalate, polyethylene-2,6-naphthalate, poly-4,4'-dioxydiphenyl-2
, polycarbonate such as 2-propane carbonate,
Blends or copolymers of polyethers such as polyoxymethylene and polymethylene sulfide, polythioethers, polyphenylene oxide, polyphenylene sulfide, etc., having an attained crystallinity of 20% or more may be used. Furthermore, compositions containing 70% or more of the above polymers, such as blends with other amorphous polymers or blends with inorganic substances, can also be used in the present invention, and antioxidants, antistatic agents, and antifungal agents can also be used in the present invention. , a lubricant, a surfactant, etc., may be contained in appropriate amounts as required.

As a membrane manufacturing method similar to the manufacturing method of the present invention, a method for manufacturing a continuous porous JR membrane by a melting method has already been disclosed in Japanese Patent Publication No. 46-40119, Japanese Patent Application Laid-Open No. 52-15627, etc. There is. The common feature of these continuous pore porous membrane manufacturing methods is that they all use thermoplastic crystals to develop laminated lamellar crystals with fewer defects for the purpose of generating communicating pores that penetrate the membrane. Melt-molding (spinning,
After extrusion, inflation), if necessary, heat treatment is performed to develop the laminated lamellar crystals more completely, and then cold stretching is performed to cleave the crystals to create communicating holes, followed by heat setting. be.

Although the melting method does not improve the separation coefficient, it is also possible to produce a heterogeneous membrane with gas separation ability (
Japanese Patent Application No. 58-69900, Japanese Patent Application No. 58-90400).

The production method of the present invention seems to be based on a principle similar to the above production method in that voids are generated inside the membrane, but the conditions for each step such as melt spinning (or melt film extrusion etc.) and stretching etc. By optimizing the balance between the two, it is possible to produce a membrane with improved oxygen permeation rate and oxygen/nitrogen separation coefficient.

Melt-spinning temperature of hollow fiber (or melt-extrusion temperature of film) (Hereinafter, to simplify the explanation, we will discuss the case of hollow fiber membranes. The story is similar in the case of film extrusion and inflation.) is higher than the melting point TIm of the polymer, and preferably does not exceed the melting point by more than 200°C. The suitable spinning temperature depends on the crystallization rate of the polymer, the molecular weight of the polymer, cooling conditions, spinning speed, draft ratio, and subsequent steps. Generally speaking, when a polymer with a slow crystallization rate or a low molecular weight polymer is used, or when the spinning speed or draft ratio is relatively small, (Tm + 10) ~
(1 layer + 50)"C lower temperature is preferable, 2 below the melting point
At temperatures higher than 00°C, it is difficult to obtain a membrane with a high gas permeation rate.

Draft ratio (-take-up speed/discharge speed) is 5 to 10,000
is preferably 5 to 20 in the case of a high molecular weight polymer having a melt viscosity of 7000 voids or more at the spinning temperature.
A relatively low draft ratio of 0 is suitable, but 50 or higher is generally preferred. In particular, when slow cooling is performed using a low molecular weight polymer with a melt viscosity of too poise or less,
A high draft of 0 or more is required. Additionally, in general, when the discharge yarn is rapidly cooled, the draft ratio can be lowered compared to when it is slowly cooled. Even if the draft ratio is outside this range, it is possible to manufacture the membrane of the present invention, but in addition to not being able to expect high gas permeation performance, there are also disadvantages such as difficulty in manufacturing.

The extrusion speed can be chosen relatively arbitrarily. If the speed is too slow or too fast, thread breakage is likely to occur, but this can be determined according to equipment requirements.

As the hollow fiber spinning nozzle, a conventional hollow fiber spinning nozzle such as an annular type, a horseshoe type, a bridge type, etc. can be used. The die for film extrusion is T die or circle 1 for inflation silane.
A film or sheet gooey used in 1IT1, such as an R2-shaped die, can be used.

The outer diameter of the hollow fiber varies from 5 to 5 depending on the nozzle dimensions, draft, etc.
It is preferable to set it to 5000 μm. If the diameter is greater than 5 μm or greater than 5000 μm, it becomes difficult to obtain a pattern with a high transmission rate. It is preferable that the thickness of the hollow fiber or film is similarly set to 0.5 to 1000 μm.

Outside this range, a good porous membrane will not be formed ((), and the gas permeation rate will be low.

When using the membrane produced according to the present invention as the gas component M19, hollow fibers are more advantageous than film (flat membrane) shapes because they have a larger surface area, and their outer diameter is 20 to 300 μm.
The thickness of one layer is more preferably 2 to 20 μm.

It is preferable to cool the discharge thread rapidly.In order to produce a membrane with communicating holes by the melting method, it is essential to rapidly cool the discharge thread and crystallize it in the presence of stress and temperature gradient. In the manufacturing method of the invention, there are no very strict restrictions on the cooling conditions for the discharged yarn.

However, by rapidly cooling the discharge thread, a pattern with better gas permeation rate and separation coefficient can be stably obtained.

In addition to blowing air, cooling methods include chill rolls and water (or hot water).
Ordinary cooling methods such as cooling can be used. The cooling temperature is generally preferably (Tg-50) to (Tm-50)°C, although it depends on the crystallization rate of the polymer.

Hollow fibers obtained by melt spinning have Tg-20 to (Tg-20) to (
The greatest feature of the present invention is that the film is stretched by 10 to 250% at Tg+50)°C (this treatment will be referred to as amorphous stretching), and that the amorphous stretching and heat treatment described below are performed. It is thought that by adding this treatment, the width of the laminated lamellar crystal becomes smaller, and closed cells are generated instead of continuous pores. The stretching ratio needs to be 20% or more for samples spun under quenching conditions. For samples that have been cooled slightly or slowly, it is preferably 5% or more. In the case of the sample that was slowly cooled, whitening of the yarn was observed during this step, and it seems that some voids were generated inside, but this is not a problem.

However, the present invention is superior in the following points. Firstly, a membrane with better gas permeation rate and separation coefficient can be produced. This includes melt spinning or melt film extrusion! li! This is because by separating the I-film process and the amorphous stretching process, the processing conditions for each process can be set to the conditions most suitable for the purpose.

Secondly, the uniformity and reproducibility of the product increases, which is industrially advantageous. this is,! li! This is because conditions can be set that are less susceptible to subtle differences in cooling conditions and fluctuations in melting temperature in the film process. It is also possible to correct errors in film forming conditions in the subsequent amorphous stretching step.

The amorphous stretched hollow fiber or film is subsequently heat treated without releasing the tension, and the heat treatment temperature is (1g+20) ~
(Tm-5)°C is preferred. In addition, heat treatment is performed by D R1,O
It may be performed while stretching at a speed of 3.0 to 3.0. Heat treatment with a DR of less than 1, that is, under relaxing conditions, is not preferred because it generates communicating pores and causes a decrease in the separation coefficient. Heat treatment under a high stretching ratio of DR 3.0 or higher is undesirable because both the apparent i3 excess coefficient and separation coefficient become low values.

The shape of the membrane of the present invention can be arbitrarily selected depending on the intended use. For example, it can be in the form of a hollow fiber or a tubular 1 flat membrane. In addition, various forms can be made as necessary, such as by introducing a structure to improve the film strength or by changing the film thickness. The appropriate outer diameter of the hollow fiber (including tubular fibers) is 3 to 5000 μm, and 1
More preferably 0 to 200 μm. It is possible to manufacture a hollow fiber membrane with an outer diameter of 3 μm or less or 5000 μm or more, but the manufacturing cost and membrane performance are inferior, and there is no merit. The appropriate membrane thickness is 0.2 to 1000 μm. It is. If it is 0.2 μm or less, it is difficult to obtain mechanical strength, and if it is 1000 μm or more, the apparent transmission coefficient will decrease. Regarding the film thickness, the same applies to the case of a flat film.

When attempting to separate a selected gas (including reduction and removal) from a mixture of two or more gases by a diaphragm separation method, the performance of the separation device should be the preferred gas selectivity,
A good concentration ratio, a high permeation rate, etc. are required, but these performances are largely determined by the performance of the membrane. It is something you have. The choice of gas separation is the separation coefficient α
(The same applies when selectively separating -[171 or more gases] from a mixture of three or more gases).

Therefore, the membrane of the present invention can be used in the system for which it is used (mixed gas!!
It can be manufactured by selecting a material (polymer) that passes through JWi, mixing ratio, type of gas to be separated, etc.).

<Function> Gas separation systems in which the membrane of the present invention can be used include, for example, production of oxygen-enriched air from air, recovery of CO5H2 from combustion waste gas, removal of NO2 and SO2 from waste gas, Separation of Go102, separation of H2/Co, H2102
separation, separation and recovery of inert gases such as He, separation of methane/ethane, etc., but are not limited to these.

The membranes of the invention also provide selective removal of gases dissolved in a liquid.
Selective melting of a selected gas in a mixed gas into a liquid, separation of a selected liquid from a mixed liquid (so-called liquid-liquid separation or pervaporation), etc. are achieved by i3 filtration of a non-porous Wg membrane. Can be used for separation and concentration.

The membranes of the present invention are particularly useful for the production of oxygen-enriched air from air, especially by O2/N2 separation. Oxygen-enriched air has a high utility value of 4N for medical purposes and combustion air, but in order to use it for these purposes, it is necessary to have a high oxygen concentration and a high generation rate of oxygen-enriched air. is very important. That is, a membrane with a high oxygen permeation rate is required.

The membrane and manufacturing method of the present invention meet these requirements and have the following excellent features. That is, it is possible to use a material with excellent oxygen permeability coefficient Po (O2) and separation coefficient α (O2/N2), so that a high concentration of oxygen can be obtained (for example, poly-4-methylpentene 1 : P (O2)).
2) -1,3×IF? , α(O2/N2) =3.
6) , ■ The thickness of the non-porous thin membrane, which is the active layer for gas separation, can be reduced to 1/10 or less of the apparent membrane thickness, and the permeation rate per membrane surface area can be increased. , it is possible to form a thin hollow fiber membrane (for example, when the outer diameter of the hollow fiber is 30 μm, the surface area per d is
10”n (packing density is about 100 times that of a flat membrane), ■ Mechanical strength is high even in thin hollow fibers, that is, the pressure applied to the membrane (-subpressure) can be increased, ■ Manufacturing process It is simple, has high productivity, and is therefore inexpensive.

In particular, the above characteristics (■ to ■) are features that are not found in heterogeneous membranes manufactured by wet or semi-dry wet methods, and are not known to date in terms of overall membrane performance such as permeation rate and oxygen enrichment concentration. ,
This shows that the separation membrane has performance superior to heterogeneous membranes and other composite membranes manufactured by wet methods, semi-dry wet methods, and other composite membranes. It goes without saying that the above characteristics are exhibited not only when used as an oxygen-enriching membrane, but also when separating gases.

The membrane of the present invention is subjected to treatments such as vapor deposition of a metal such as Nt, 8g, or Pd on its surface, coating with a polymer such as polyvinylpyridine or polyethylene glycol, or impregnation with a liquid such as liquid polyethylene glycol. It can also be used as a gas separation membrane with a higher separation coefficient.

<Example> This will be explained below by giving examples.

Example 1 Poly-4-methylpentene-1 with a melt index (according to ASTM D-1238) of 26 was directly processed! Using a 5-tsuru one-slit type hollow fiber spinning nozzle, the spinning temperature was 295°C, the take-up speed was 420 m/min, and the draft ratio was 20.
Melt spinning was carried out at 00, outer diameter 65μm, membrane r￥9.0μ
m hollow fibers were obtained.

At this time, the area 5 to 55 cm below the nozzle was rapidly cooled with a cross wind at a temperature of 20 DEG C. and a wind speed of 1 m/sec. The obtained hollow fibers were continuously subjected to amorphous stretching using a roller system at a temperature of 35° C. so that the stretching ratio D R = 1.3, and then the fibers were stretched without releasing the tension (190° C.). Heat treatment was performed by introducing the fiber into a hot air circulation constant temperature bath at ℃ and holding it at a constant length for 1 second.The heat-treated hollow fiber was then cold-stretched by DRl, 2 at a temperature of 35℃ and a distance of 10 cm between rollers. Heat stretching was performed at 130°C for DRl, 3 without releasing the tension, and heat setting was performed at 190°C for 3 seconds while maintaining the length.The obtained hollow fibers had an outer diameter of 56 μm and a membrane shape. Pi
(The diameter was 7.9 μm. This hollow fiber had a white color, and the generation of pores was expected, but it was
Since no pores were observed in the inspection of the inner and outer surfaces of the hollow fibers by M), it is presumed that the fibers were closed cells.

The i21 excess coefficient and separation coefficient of oxygen and nitrogen of the produced hollow fibers were measured. The measurement conditions were to pressurize the inside of the hollow fiber at a pressure of 1 kg/aJ and measure the flow rate of gas permeating to the outside. The membrane thickness and membrane area were determined by microscopic observation of the cross section of the hollow fiber. The measurement result is P (O2)-6,8X10″″
(-(STP) ・cIll/d・sec -cmf
lg), α-4,6 0 The value of the amorphous hollow fiber obtained using the same spinning device as in this example Po(O2) −
When compared with 1,3×l O-9 (same units) and α-3,6, the i3 excess coefficient is improved by 5.2 times, and the separation factor is also improved by 1.28 times.

Example 2 The gas permeation properties of a membrane produced in the same manner as in Example 1 except that the heat treatment was performed while adding DR1,3 stretching were as follows: P (O2) = 6. IX10-, α-5,
It was 2.

Comparative Example 1 The gas permeation property of a membrane manufactured by the same method as Example 1 except that the heat treatment temperature was 200°C was P (O2)
= 1.5 x IO'', α = 2.0, and no improvement in the separation coefficient was observed.

Example 3 The gas permeation properties of a membrane produced under the same conditions as in Example 1 except that the heat treatment conditions were 200°C and the stretching magnification during dry treatment was 3 were P (O2) = 7.7 x 10-' ,α
=3.9. Comparative example! Even in comparison with Hq
Improvements in the properties of steel 1i can be achieved by delicately combining the machining strengths of each machining process.

Comparative Example 2 Spinning was carried out at a room temperature of 30°C without blowing cooling air.
An attempt was made to manufacture a gas separation membrane using the same process as in Example 1, except that the membrane was stretched and the draft ratio was 500, but the yarn broke during the cold stretching process, making it impossible to manufacture.

Comparative Example 3 The gas permeation properties of a membrane produced in exactly the same manner as in Example 1 except for not performing amorphous stretching were P, (O2) = 8.
4 X l O', α=0.95, and had no gas separation ability. It is thought that communicating pores are formed, and an amorphous stretching process is necessary.

Comparative Example 4 The gas permeation property of a membrane manufactured in the same manner as in Example I except that D R0.8 was set in the heat treatment step was P (O2
) −1,OX 10−”, α=0.94.

It can be seen that the effect of amorphous stretching is offset by relaxation during heat treatment.

Comparative Example 5 A film produced in exactly the same manner as in Example i except that no amorphous stretching was carried out and instead a 1.5 stretch was carried out during heat treatment was P(
O2) = 4.0X10→, α-1,8. Although the permeation rate increases, no change in separation coefficient is observed.

Example 4 An annular nozzle with a diameter of 10 wa was used, the melting temperature was 285°C, the take-up speed was 820 m/min, and the draft ratio was 100.
The membrane was manufactured in the same manner as in Example 1, except that it was spun at 0.0 (The membrane produced by the same method had an outer diameter of 155 μm and a membrane thickness of 14 μm, and the gas permeation properties of this membrane were P (O2) = 6.I X l O-
, α-4,6.

<Effects of the Invention> As shown in the examples above, the separation membrane produced by the method of the present invention not only has excellent gas separation ability such as oxygen/M element, but also
It has a high gas permeation rate and is used in a wide range of fields that require the separation of mixed gases, such as the production of oxygen-enriched air from air, the recovery of CO1H2 from combustion gas, and the recovery of inert gases such as He from natural gas. This facilitates the design of a highly efficient and economical gas separation device. Furthermore, the present separation membrane and manufacturing method are also effective in fields other than gas separation, such as in the separation of organic liquids by barheparation, as can be easily analogized from the membrane structure.

Claims (1)

[Claims] 1. The thermoplastic crystalline polymer (1) has a melting temperature of Tm ~
(Tm + 200) °C (where Tm is the crystal melting point) and the draft ratio Df is 20≦Df≦10000.
0) to (Tg+50)°C (Tg is the glass transition temperature)
After stretching 5 to 200% of the original length, (3) Tg
Heat treatment is performed at a temperature of ~Tm, and then (4) (Tg-
Stretching ratio 1.1 to 5 at a temperature of 50) to (Tm-10)°C
．． 0, and then heat-set at a temperature of (5) Tg to Tm. is more than twice the oxygen permeability coefficient of
Separation coefficient α of oxygen and nitrogen at 5℃ (O_2/N_2
) is greater than the separation coefficient of an amorphous homogeneous membrane of the same material produced by melt extrusion membrane formation, and a method for producing a closed-cell or semi-open pore membrane.