JPS6260130B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a separation membrane having permselectivity for mixed gases. In particular, the present invention relates to a separation membrane that allows a large amount of air to permeate and has excellent oxygen permselectivity when producing oxygen-enriched air from air by a membrane separation method. In recent years, there has been remarkable progress in separation technology using membranes, and some of them have already been put into practical use on an industrial scale. For example, liquid-liquid separation or liquid-solid separation has been put into practical use in seawater desalination, factory waste treatment, food concentration, etc.
There are almost no practical examples of gas separation, that is, separation of two or more types of mixed gases. The reasons why membrane separation of mixed gases has not been put into practical use are that the selectivity of the membrane is low, making it difficult to selectively obtain high-purity gas in one-step separation, and the permeation rate is small, making it impossible to produce large amounts of gas. Depends on things etc. However, from the point of view of selective permeability, there are many fields where high purity gas is not necessarily required for the end use of the gas. For example, in the case of oxygen, high purity oxygen is not required for blast furnace ventilation, fuel supplementation, medical breathing, etc. In fact, if the purity is high, the combustion temperature will rise too much, causing damage to the furnace and the risk of fire.
In many cases, it is even more inconvenient, such as blindness in premature babies. Conventionally, the method for producing moderately oxygen-enriched air with an oxygen concentration of about 25 to 60% has been to mix high-purity oxygen produced by cryogenic separation with air using a mixer, etc. This is not only complicated to operate, but also requires a pressure vessel such as a cylinder, and is therefore dangerous in handling. For example, when applying a membrane separation method to air, it is difficult to obtain air with a high purity oxygen concentration through one stage of membrane separation, but it is relatively easy to obtain air enriched with moderate oxygen concentration. can get. In other words, in the membrane separation method, the oxygen concentration is approximately 25
~60% oxygen-enriched air can be produced directly from air, and there is no need to handle mixers or cylinders, making it a simple and economically advantageous method. Many polymers have been proposed as membranes for separating oxygen from a mixture of oxygen and nitrogen such as air, and among these, the most suitable materials for this purpose are polysiloxane and organopolysiloxane-polycarbonate. Polymers, methylpentene polymers, etc. are known. However, although polysiloxane and organopolysiloxane-polycarbonate copolymers have a large oxygen permeability coefficient, the oxygen to nitrogen separation coefficient is small and there is a limit to the oxygen concentration that can be obtained.On the other hand, methylpentene polymers have a large oxygen separation coefficient but The oxygen permeability coefficient is about 1/10 that of siloxane-based polymers. Therefore, several methods for improving the permeability of methylpentene polymers have been proposed, such as the
-37639 proposes that adding a large amount of silicone oil and/or putene oil to methylpentene polymer increases the amount of oxygen permeation, but this improvement method does not improve the selectivity of oxygen to nitrogen. It was lower than that. Recently, it has been proposed in JP-A-54-40868 to mix and add organopolysiloxane-polycarbonate copolymer to methylpentene polymer, but this film is intended to improve the strength of ultra-thin methylpentene polymer films. There is no mention of improvement in membrane permeability or selectivity, and in particular, selectivity remains unchanged from before addition. The present inventors conducted intensive research to obtain a separation membrane with high oxygen permeability and selectivity for oxygen to nitrogen, and found that vinyl polymers having a structure similar to methylpentene polymers, especially α-
It has been found that a polymer made from olefin has good compatibility with a methylpentene polymer, and that the oxygen permeability of a membrane obtained by mixing this polymer is improved. However, the selectivity between oxygen and nitrogen was slightly lower than that of the original methylpentene polymer. Therefore, we conducted further studies and found that a polymer obtained by alternately copolymerizing maleic anhydride, which is easily copolymerized with α-olefin, with α-olefin was added to methylpentene polymer to form a film, and its properties were investigated. The present invention was achieved by discovering that both permeability and selectivity between oxygen and nitrogen are improved, particularly oxygen permeability is greatly improved. That is, the present invention comprises 100 parts by weight of a methylpentene polymer, an alternating copolymer of α-olefin having 2 to 30 carbon atoms, maleic anhydride and/or its water, and a lower alcohol ring-opened product (hereinafter sometimes referred to as maleic acids). This invention relates to a selective membrane for gas separation mainly composed of ~100 parts by weight of a mixed polymer. According to the present invention, by adding an alternating copolymer of α-olefin and maleic anhydride to the methylpentene polymer alone,
Not only the oxygen permeability and selectivity are improved, but also the film formability is improved. Methods for forming a film from the alternating copolymer of α-olefin and maleic anhydride and the methylpentene polymer mixed polymer of the present invention include a melt extrusion method, a casting method from a solution, and a casting method on a liquid surface. Methods such as the following can be used. However, when used as a gas separation membrane, the amount of gas permeated is inversely proportional to the thickness of the membrane, so in order to create a compact separation device with a large amount of permeation, it is necessary to make the membrane thickness as thin as possible. Film uniformity is required. That is, if the membrane has poor uniformity and is prone to pinholes, or if the membrane is extremely thin or weak, gas leakage or membrane damage during use will easily occur, resulting in a decrease in separation performance.
Pinholes and the like are more likely to occur as the film thickness becomes thinner. Generally, methylpentene polymers are highly crystalline polymers, and there are only a few types of solvents that can dissolve these polymers, and their solubility in solvents is also low. Therefore, when a film is formed using methylpentene polymer alone, it easily crystallizes and becomes non-uniform, especially when forming a thin film, or when a film is formed using a solvent, the methylpentene polymer easily precipitates. This results in a cloudy, uneven film, which is prone to pinholes and extremely weak areas. However, when an alternating copolymer of α-olefin and maleic anhydride is added to the methylpentene polymer, the copolymer acts as a plasticizer, increasing the flexibility of the membrane and improving its spreadability. Holes and extremely weak parts are eliminated, making it easy to obtain a separation membrane with a large area. Moreover, the durability as a separation membrane is also improved. Furthermore, the mixed polymer of the present invention has also brought about a significant improvement effect on the method of manufacturing ultra-thin films formed on water surfaces. In other words, there is a method for making a film with a thickness of 0.5μ or more by dropping a polymer solution onto the liquid surface, especially on the water surface, and allowing the polymer solution to spread spontaneously on the water surface to obtain an extremely thin film.However, in general, non-polar polymers are The polymer solution does not diffuse onto the surface, or even if it spreads, only a small membrane area can be obtained. In the case of methylpentene polymer, the spread is also small. The ability to manufacture large membranes as separation membranes is preferable from the viewpoints of membrane productivity and device assembly. In the present invention, when an alternating copolymer of α-olefin and maleic anhydride is added to the methylpentene polymer, it is possible to form a film having an area more than twice as large as that of the methylpentene polymer alone; As mentioned above, the uniformity is excellent and there are no pinholes or extremely thin areas. The present inventors believe that the reason why the mixed polymer solution of the present invention spreads well on the water surface and forms a uniform film is that the copolymer has an acid anhydride group in its structure, which has an affinity for water. At that time, the α-olefin part of the copolymer has an affinity for the methylpentene polymer, so as the copolymer spreads, the methyl This is thought to be due to the pentene polymer also spreading. In particular, it is thought that the α-olefin portion in the copolymer also acts as a plasticizer for the methylpentene polymer. As mentioned above, the alternating copolymer of α-olefin and maleic anhydride not only improves the selective permeability of oxygen but also improves the uniformity of the membrane. It was found that this had a significant effect on membrane spreading. The methylpentene polymers used in the present invention include poly4-methylpentene-1, poly-3-methylpentene-1, poly2-methylpentene-1
and copolymers mainly composed of these monomers and one or more other monomers copolymerizable therewith, and have a degree of polymerization that allows film formation. Among these, poly 4-methylpentene-1
Or a copolymer thereof is preferred. The α-olefin referred to in the present invention is an α-olefin having 2 to 30 carbon atoms, and may be linear or branched. Preferably, it is an α-olefin having 10 to 20 carbon atoms, which has a large plasticizing effect on the methylpentene polymer, and more preferably an α-olefin having 14 to 18 carbon atoms. Specifically, ethylene, propylene, 1-pentene, 1-hexene, 4-methyl-1-hexene, 6-methyl-1-heptene, 1-decene, 1
-dodecene, 1-tetradecene, 1-heptadecene, 1-hexadecene, 1-octadecene, etc. A copolymer of α-olefin and maleic anhydride is generally an alternating copolymer obtained by polymerizing using a radical initiator. The degree of polymerization of the copolymer may be such that it has film-forming properties by itself, or even if it has a low degree of polymerization that does not have film-forming properties by itself, it can have film-forming properties when mixed with a methylpentene polymer. You can use anything. The copolymer of the present invention may also have a structure in which an acid anhydride group is ring-opened with water or a lower alcohol. The methylpentene polymer in the present invention and α
- The proportion of the alternating copolymer of olefin and maleic anhydride is 1 to 100 parts by weight, preferably 2 to 50 parts by weight, per 100 parts by weight of methylpentene. When the proportion of the copolymer of α-olefin and maleic anhydride is less than 1 part by weight, the effect of improving the permeability and selectivity of the methylpentene polymer is small, while when the proportion is 100 parts by weight, the strength of the formed membrane is decreases and becomes unsuitable for practical use. Generally, gas permeability is inversely proportional to membrane thickness, so in order to increase the gas permeability of a membrane, it is preferable to make the membrane thickness as thin as possible as long as practical strength is maintained. Thus, the thickness of the gas separation membrane formed from the mixed polymer of the present invention is suitably in the range of 0.01 to 100μ, particularly 0.05 to 50μ. The membrane in the present invention may be in any form such as a flat membrane, a tubular membrane, or a hollow fiber, and the membrane may be in the form of a uniform membrane or an asymmetric membrane. Furthermore, it is also possible to combine it with a porous support. The membrane of the present invention can be used as a separation membrane for producing oxygen-enriched air by separating oxygen and nitrogen from air using a diaphragm, but is not necessarily limited thereto. The membrane of the present invention has high gas permeability in general as well as oxygen permeability, so it can be used for the separation of other mixed gases, such as He gas separation from natural gas or Hz gas purification from hydrodesulfurization plants. Can be done. The present invention will be explained in detail with reference to Examples below. The examples are intended to be illustrative and not limiting. In addition, parts in Examples indicate parts by weight. Examples 1 to 4 100 parts of poly-4-methylpentene-1 (manufactured by Mitsui Petrochemical Industries, Ltd., grade DX810) and a copolymer of 1-octadecene and maleic anhydride (manufactured by GULF Corporation,
Polyanhydride RoSin PA―18, Inherent
Viscosity (25℃ in methyl ethyl ketone) 0.144)
5.3 parts, 11.1 parts, 33.3 parts, and 66.7 parts of each were mixed to prepare 5% by weight cyclohexene solutions. This solution was applied onto a glass plate, air-dried for 1 hour, and then dried at 90°C for 1 hour to obtain a film. Table 1 shows the gas permeation characteristics of this membrane. In addition, Comparative Examples 1 and 2 are cases without a copolymer of 1-octadecene and maleic anhydride and cases in which poly 4-
120 parts of copolymer to 100 parts of methylpentene-1
In addition, a film was formed in the same manner as in the example.

[Table] Examples 5 to 8 A copolymer of maleic anhydride and various α-olefins was synthesized, and a predetermined amount was added to a cyclohexene solution of poly-4-methylpentene-1 to prepare a mixture solution. A membrane was prepared from this solution in the same manner as in Example 1. Table 2 shows the gas permeability of the obtained membrane. Example 9 The copolymer of 1-octadecene and maleic anhydride used in Example 1 was placed in ethanol and slowly reacted at 40°C. Since no characteristic absorption of the acid anhydride group is observed in the infrared absorption spectrum of the obtained reaction product, the acid anhydride group is ring-opened with ethanol and becomes a half ester. 33.3 parts of this reaction product and poly 4-methylpentene-1
A membrane consisting of 100 parts was prepared from a cyclohexene solution in the same manner as in Example 1, and its gas permeability was examined; the membrane thickness was 18μ, and the oxygen permeability coefficient was 3.61×10 ^-9
CC (STP) cm/cm ²・sec・cmHg, selectivity (PO ₂
/PN ₂ ) It was 3.6.

【table】

Claims (1)

[Scope of Claims] 1 100 parts by weight of a methylpentene polymer and 1 to 100 parts by weight of an alternating copolymer of α-olefin having 2 to 30 carbon atoms, maleic anhydride and/or its water, and a lower alcohol ring-opened product. A selectively permeable membrane for gas separation mainly composed of mixed polymers. 2. The selectively permeable membrane according to item 1, wherein the methylpentene polymer is a 4-methylpentene-1 polymer. 3. The selectively permeable membrane according to item 1 or 2, wherein the α-olefin is an α-olefin having 10 to 20 carbon atoms.