JPS6182823A - Gas-permeable composite membrane - Google Patents

Abstract

PURPOSE:To obtain the titled gas-permeable compositle membrane capable of maintaining a high gas permeation characteristic for a long period by providing a coating layer having >=90 deg. contact angle with water on the surface in contact with a gaseous mixture and having low critical surface tension. CONSTITUTION:A gas selective membrane layer 2, used for separating a specified gas from a gaseous mixture and concentrating the gas and consisting of at least one layer, and a coating layer 1 formed on the layer 2 are provided. The critical surface tension of the coating layer 1 is low, and the contact angle with water on the surface in contact with the gaseous mixture is at >=90 deg.. The thickness of the coating layer 1 is controlled to about 50-200Angstrom . The critical surface tension is preferably regulated to <=30dyn/cm. Said material can be selected from polyolefin, diene polymers, polyorganosiloxane, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a gas-permeable composite membrane that is used to separate and concentrate a specific gas from a gas mixture and that can maintain stable characteristics for a long period of time.

Conventional configurations and their problems Many proposals have been made in recent years regarding methods of separating and concentrating specific gases from mixed gases using polymer membranes1.
For example, technologies for separating hydrogen, nitrogen, oxygen, and other useful gases from factory exhaust, natural gas, or the atmosphere have already been put into practical use.

However, since these proposals involve bringing the gas mixture into direct contact with the membrane, the environmental conditions during operation are harsh, and maintaining the gas permeability of the membrane over a long period of time has become an important issue.

For example, JP-A-51-121485 describes a gas permeable composite membrane of polyphenylene oxide/polydimethylsiloxane/polycarbonate having a surface of polydimethylsiloxane/polycarbonate; however, according to experiments conducted by the present inventors, The above composite membrane was formed on a porous polypropylene sheet, this composite membrane was made into a module, placed near the exhaust port of a factory, and continued to be operated under suction at a pressure of -63'O Hf. Approximately 1000 hours elapsed. At this point, the gas permeation flow rate of the composite membrane was reduced by 20 to 30% in some cases. In addition, when similar experiments were conducted using the polyhydroxystyrene-polysulfone-polydimethylsiloxane copolymer described in JP-A-58-14928, the gas permeation rate of the composite membrane was also found to be In some cases, the amount decreased by 20 to 30%.

In this way, even if a composite membrane exhibits excellent gas permeability in its initial state, under actual operating conditions, its properties deteriorate over time to the point that it is no longer worth using. Ta.

Purpose of the Invention The present invention has been made in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a gas permeable composite membrane that is truly suitable for practical use and can maintain high gas permeability properties during long-term operation under severe conditions. With the goal.

Structure of the Invention In order to achieve this object, the present invention includes a gas-selective membrane layer consisting of at least one layer for separating/condensing a specific gas from a mixed gas, and a gas-selective membrane layer formed on the gas-selective membrane layer.
C coating layer, the critical surface tension of the # M coating layer is small, and the contact angle of the surface in contact with the mixed gas with water is θ or 9.
The object of the present invention is to provide a gas permeable composite membrane characterized by an angle of 0° or more.

Separation methods using gas permeable membranes require a process in which a mixed gas is brought into direct contact with the membrane surface and permeated therethrough, and is therefore subject to various external influences. According to experiments conducted by the present inventors, the main cause of aging deterioration of gas-permeable composite membranes is the unremovable fine particles (diameter ζ 1 μm) in the mixed gas that contacts the membrane surface.
This was thought to be because oil droplets, microsols, etc. of ~0.1μ) adhered to the membrane surface. Generally speaking, one way to make solid surfaces less susceptible to contamination is to coat them with substances that exhibit surface energy to create water- and oil-repellent surfaces, but these substances generally have low gas permeability; It was extremely difficult to apply it to composite membranes. Therefore, as a result of intensive study, the present inventors provided a coating layer made of a substance with low surface energy on the gas-selective membrane layer, and controlled the overall thickness of this coating layer to about 60 to 200 layers. At the same time, by adjusting the contact angle θ of water on the surface of the coating layer in contact with the gas mixture to be 90° or more, we were able to create a gas-permeable composite membrane that does not change the gas permeation flow rate and is less likely to be contaminated. . Surfaces with θ less than 90° are hydrophilic and susceptible to contamination and other effects. Even if a coating material with low surface tension is used, if the thickness of the coating layer is 50 Å or less, the surface will be greatly influenced by the surface properties of the underlying gas-selective membrane layer. may become small. On the other hand, if it is 200 Å or more, the gas permeability is low as mentioned above, so the permeation flow rate of the gas permeable composite membrane decreases.
If the film thickness is adjusted to 0, the coating film is not dense and minute holes are generated, so it is thought that a surface to which fine particles in the gas are difficult to adhere and also has good gas permeability can be obtained. What is important here is not the properties of the coating material as a whole (e.g. surface tension, flexibility, etc.), but rather whether the surface exhibits water and oil repellency when formed on the gas-selective membrane layer. and the critical surface tension is 30 dyn, m'
This means that the following polymers should not be used in their entirety, but that the θ of the finished surface should be 90° or more by baking or catalytic treatment.

Therefore, as the surface film material, the chemical structural formula of the surface is -CF + -CF -, -OF, -〇F2-C
FH-.

0F2-41CI-, -CF2-CH2-, -CFH
-C;H2-.

CM.

OF, RF (However, RF is -OF3.- CH2-OF5.-CH
2-CH2-CF3. ) or other fluorine-based polymers such as polybutene, polyimbutene, polypentene, polymethylpentene, polyhexene, polymethylhexene, polyheptene, polycyclohexylpentene, polystyrene, polyα-methylstyrene, polybutadiene, polyisoprene, polycyclohexyl
A material capable of forming a surface with θ of 90' or more may be selected from polyolefins such as Kutashie 7, diene polymers, polyorganosiloxanes, and the like.

For example, fluorinated alkyl methacrylate, poly-4
-Methylpentene-1 and polymethylalkyl fluoride/loxane can be prepared into dilute solutions, spread on the water surface, and after desolvation, a flat film with low surface energy can be obtained.
These protective effects are extremely high. Further, when the coating material is a liquid, the coating layer can be formed by spraying directly onto the gas-selective membrane. The surface can also be made water- and oil-repellent by heat treatment using a catalyst such as hydrogen silane.

The gas-selective membrane layer only needs to consist of at least one layer, and good results can be obtained if the layer that adheres to the coating layer contains at least a polyhydroxystyrene-polysulfone-polydimethylsiloxane copolymer. ing.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a gas permeable composite membrane in each embodiment of the present invention. 1 is a coating layer, 2 is a gas-selective membrane layer, and 3 is a porous support. FIG. 2 is a graph showing changes in gas permeation flow rate in each example and the conventional example.

<Example 1> Methylhydrodiene polysiloxane with an ro of 11 ayn, m-'' is used as the material for the coating layer 1, and 3 wt% of tetrabutyltin is added as a catalyst to the coating material. Gas-selective membrane layer Using bol + hydroxystyrene-bo-11 sulfone-polydimethylsiloxane copolymer as the polymer constituting 2, a 2 to 4 wt% benzene solution was prepared and spread on the water surface.The thin film obtained after solvent removal The support is 3D.

It was adhered onto Lagard 24oo (manufactured by Polyplastics Co., Ltd.), and the above-mentioned coating material was further sprayed onto it to form a coating layer. After air drying, bake at 70'Q for 8 to 9 minutes to obtain a surface water contact angle θ of 100 to 1100.
The gas permeable composite membrane shown in the figure was constructed.

Next, we made a module of 30 CIrL x 30 CIrL using the above composite membrane, installed it near the exhaust port of the factory, and continuously operated it with a vacuum pump to reduce the pressure to -536 tnmHg. In this example, as shown in Figure 2A, the decrease was only about 7% even after 500 hours, whereas in the conventional membrane module without a coating layer, as shown in Figure 2A, the decrease was only about 7%. After 100 hours had passed, it had already decreased by 30%.Also, as a comparative example of the coating layer, γ was 20.8 dyn, c!IL
A benzene solution of 2 to 4 wt% is prepared using dimethylpolysiloxane of
A similar life test was conducted using a gas permeable composite membrane as shown in Fig. 1 having an angle of 3°. As shown in Figure 2 (c), the lifespan was three times longer than the one without the coating layer, but the flow rate decreased by 30% after 3000 hours, and compared to this example, the permeation rate was 3 times longer. The effect of stabilizing the characteristics was extremely small. As described above, in this example, the surface of the gas selective membrane layer 2 is covered with the coating layer 1 having a large finished surface θ. It is clear that it is effective for

In this example, a catalyst was used for methylhydrodiene polysiloxane, but by increasing the amount of this catalyst, it is possible to shorten the baking time 9 and lower the baking temperature, which can be used to reduce the heat resistance of gas-selective membranes and supports. It can also be used as a covering material when a body is used.

<Example 2> In Example 1, fluorinated alkyl methacrylate was used as the material constituting the coating layer 1, and a 2 to 4 wt% trifluorotrichloroethane solution was prepared and spread on the water surface. The thin film obtained after solvent removal was stacked on a gas-selective membrane placed on a support to construct the gas-permeable composite membrane shown in FIG. The configuration of this example has a finished surface θ of 99 to 10.
At 6°, as shown in FIG. 2, the change in gas permeation flow rate was small, and was about 6% after 6000 hours.

<Example 3> In Example 1, a polyphenylene oxide/polydimethylronoxane-bo-11 carbonate copolymer was used as the material constituting the gas-selective membrane layer to construct a composite membrane. In the configuration of this example, the finished surface θ is 100 to 11.
At o0, the gas permeation flow rate of the uncoated membrane module shown in Figure 2 E decreases by nearly 40% in 1000 hours, while it decreases by only about 7% in 6000 hours as shown in Figure 2 A. There wasn't.

<Example 4> In implementation flJ 1, γ was used as the material constituting the coating layer 1. A composite membrane was constructed by using polymethylfluorosiloxane having a particle diameter of 21 dyn, cm-1, which was spread in a large container, and a gas-selective membrane on a support was brought into contact with the liquid surface. In the configuration of this example, the θ of the finished surface is 96 to 98 degrees, and as shown in FIG.
Even after 000 hours, the decrease was about 8%.

<Example 5> In Example 2, polyester was used as the material constituting the coating layer 1.
Using 1-methylpentene-1, a composite membrane with a finish of 9 surfaces and θ of 110 to 113° was constructed. As shown in FIG. 2, even after continuous operation for 6,000 hours, the gas permeation flow rate of the configuration of this example decreased by only about 5%.

In these examples, only four sides are shown as the coating layer 1 and only two sides are shown as the gas-selective membrane layer, but similarly for the other polymers mentioned above, even after 6000 hours, the gas permeation flow rate change was 5 to 5. A good result of about 10% has been obtained. Further, the gas-selective membrane layer may be of one type as in Example 1, or may be a laminate of polymers of two types or more.

Effects of the Invention As described above, the present invention includes a gas-selective membrane layer consisting of at least one layer for separating and concentrating a specific gas from a mixed gas, and a coating layer formed on the gas-selective membrane layer. , the gas permeable composite membrane is characterized in that the critical surface tension (γ) of the coating layer is small, and the contact angle θ of the surface in contact with the mixed gas with respect to water is 900 or more, so it is different from conventional gas permeable membranes. Compared to , it is highly practical as it can maintain stable gas permeation characteristics for a long period of time even in poor operating environments. As mentioned in the examples, the operating life of conventional gas permeable membranes is short, and after 1000 to 150Q hours, the permeation flow rate decreases by 2Q% at the smallest and 6Q% at the largest. As shown in Figure 2 A, 2, F, and G, there is almost no change in the elapsed flow rate even after 5,000 to 8,000 hours have passed.

Therefore, in actual operation, maintenance related to the membrane module can be greatly reduced, and it can be used even under conditions where operation cannot be stopped for a long time.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a gas permeable composite membrane according to an example of the present invention, and Figure 2 is a diagram showing the relationship between the rate of decrease in gas permeation flow rate and elapsed time for each example of the present invention and a comparative example. be. 1... Coating layer, 2... Gas selective membrane layer, 3... Porous support.

Claims (8)

[Claims] (1) A gas-selective membrane layer consisting of at least one layer for separating and concentrating a specific gas from a mixed gas, and a coating layer formed on the gas-selective membrane layer, the critical surface tension of the coating layer being A gas permeable composite membrane characterized in that (γ_c) is small and the contact angle θ of the surface in contact with mixed gas with water is 90° or more. (2) The gas permeable composite membrane according to claim 1, wherein γ_c of the coating layer is 30 dyn·cm^-^1 or less. (3) The gas permeable composite membrane according to claim 1, wherein the coating layer is methylhydrogenpolysiloxane. (4) The gas permeable composite membrane according to claim 1, wherein the coating layer is a fluorinated alkyl methacrylate. (5) The gas permeable composite membrane according to claim 1, wherein the coating layer is poly-4-methylpentene-1. (6) The gas permeable composite membrane according to claim 1, wherein the coating layer is polymethylfluoroalkylsiloxane. (7) The gas-permeable composite according to claim 1, wherein the layer that adheres to the coating layer of the gas-selective membrane layer consisting of at least one layer contains at least a polyhydroxystyrene-polysulfone-polydimethylsiloxane copolymer. film. (8) The gas permeable composite membrane according to claim 1, wherein the coating layer is a membrane formed by applying a dilute solution of the coating material to a water surface.