JPS5924844B2 - Method for manufacturing gas selective permeability composite membrane - Google Patents

Description

Detailed Description of the Invention The present invention provides a gas-selective permeability film in which a porous polymer film is coated with a thin siloxane compound, and more preferably an ultra-thin film having a crosslinked structure obtained by plasma polymerization is laminated thereon. The present invention relates to a method for manufacturing a composite membrane.

In recent years, active consideration has been given to separating and purifying fluid mixtures using permselective membranes instead of energy-intensive processes that involve phase changes such as distillation and deep cooling.

The present invention has also been made to provide a gas selectively permeable composite membrane for efficiently accomplishing the above object. Among membrane separation and purification processes for liquid mixtures, the main ones that have been put into practical use on an industrial scale are liquid-liquid separation and liquid-solid separation, such as seawater desalination, factory wastewater treatment, and food concentration. There is little to no gas-gas separation.

The reason why membrane separation of gases is difficult to put into practical use is that the selective permselectivity is low, that is, there is no membrane that selectively passes a specific gas while almost blocking the passage of other gases. This method requires a multi-stage method in which membrane separation is repeated many times, resulting in a large-sized device, and the low gas permeability makes it difficult to process large amounts of gas. In particular, when the permselectivity is increased, the gas permeability deteriorates, and when the gas permeability is increased, the permselectivity tends to decrease, and this seems to be because this relationship could not be improved rapidly. Therefore, the present inventor sought to achieve the above objective by combining materials with different functions in order to simultaneously satisfy physical properties such as permselectivity, permeability, heat resistance, chemical resistance, and strength. As a result of various trials and studies, the present invention was completed.

That is, in terms of heat resistance and strength, a material that meets the purpose is selected from commercially available porous polymer materials.

Porous polysulfone, polyimide, etc. may be used, but cellulose ester, vinyl chloride, polypropylene, polycarbonate, polyvinyl alcohol, etc. are not so preferred. However, from the point of view of heat resistance and strength, a porous support made of tetrafluoroethylene resin is most preferable, and also has the advantage of satisfying chemical resistance at the same time. Regarding gas permeability, the challenge is to select a material with excellent properties and to develop a manufacturing method that makes the membrane as thin as possible.

Therefore, in the present invention, a siloxane compound was selected as a material having excellent gas permeability, and a method of forming a thin film thereof on a porous support was investigated. A method for thinning a siloxane compound is to prepare a mixed solution with an organic solvent, apply it to a porous support, evaporate the solvent, and vulcanize and harden the solution. However, when a thin solution of a siloxane compound is applied directly to a porous support, a solution layer is formed on the surface and at the same time it penetrates into the porous interior, resulting in the formation of deep roots within the porous space. Therefore, the film thickness does not become substantially thinner. Therefore, in order to reduce the film thickness of the siloxane compound, the present inventor developed a method in which a thin film is first formed on a smooth plane and then this thin film is transferred to a porous support.
That is, it was diluted with an organic solvent onto a smooth surface. The siloxane compound is applied and the solvent is evaporated to increase the viscosity of the siloxane compound, allowing vulcanization and curing to proceed partially, but the siloxane compound becomes a thin film that thickens the porous support while vulcanization is still incomplete. layer on top. Although the siloxane compound has increased viscosity, since the positive part has fluidity, it becomes shallowly rooted on the porous support side, and after vulcanization has completely progressed, the support is removed from the flat surface. When peeled off, a composite thin film layered on the support side is obtained. The feature of this method is that the thickness of the thickened siloxane compound can be made extremely thin. In principle, it should be possible to obtain a thinner film by diluting it with an organic solvent, but if it is applied directly onto a porous support, it will be sucked into the porous space due to capillary energy. The degree of this inhalation is closely related to the viscosity of the solution, and becomes more pronounced as the viscosity is lower and the vulcanization rate is slower. On the other hand, if the viscosity is increased, the flow into the porous space will be reduced, but it will be difficult to create a thin solution layer, and the coating thickness itself will become thicker. According to the present invention, a thin solution layer is first formed on a smooth surface using a diluted solution, the solvent is volatilized there to form a concentrated solution, and a part of the solution is further vulcanized to give the strength of the thin film, after which a porous support is formed. In particular, at a concentration of 50% by weight or less, preferably 30% by weight or less, a thin film of 20μ or less or 10μ or less can be formed. Next, after the siloxane compound is laminated on the porous support, a plasma polymerized thin film of 0.3 μm or less is laminated on the surface thereof.

For this purpose, the pressure in the system is reduced to 2 t0rr or less, a polymerizable gas is introduced, and the predetermined output is 500 W or less, for example, 1
When high frequency blow discharge is performed in the reaction vessel at 0 W, the polymerizable gas undergoes plasma polymerization to form a thin film, which is laminated on the surface layer of the composite structure of the crosslinked siloxane compound and porous polymer film. This laminated thickness changes almost linearly by increasing the glow discharge time, and for example, a thickness change of 0.3 μm can be selected depending on the discharge time. Also, depending on the flow rate of the polymerizable gas and the increase or decrease in the output during glow discharge, the laminated thickness may increase or decrease, or the layer may become powdered or oily, but these conditions are determined by those familiar with the technology in this field. It is relatively easy for anyone to optimize. As the polymerization gas, a compound containing tertiary carbon C-CH-C in the repeating unit of the polymer, and a compound containing tertiary organosilicon C-Sl-C instead of tertiary carbon are selected as the polymerization gas. It is preferable to use it because it has excellent transparency.

Compounds containing tertiary carbon include benzene derivatives such as 4-methyl-1 benzene, 4-methyl-2-benzene, 2,4,4, trimethyl-1-benzene, or 4,4-dimethyl-1 benzene, or 1-octene, 2-octene, Examples include octene derivatives such as 3-octene, 4-octene, and isooctene.

In addition, tertiary type organosilicon compounds can be represented by: X is Ct, NH2, NHCH
3,N(CH3)2,CH3,CH=CH2,C:CH
can be given.

As explained above, the composite membrane created under limited conditions has extremely excellent permselective properties for mixed gases, and has the potential to contribute industrially as an energy-saving gas separation method. It's large.

The present invention will be explained below by way of examples.

Example 1 KElO8RTV (siloxane compound, manufactured by Shin-Etsu Chemical Co., Ltd.) diluted to 50% by weight with xylene is applied to a glass plate whose surface has been cleaned with alcohol using a doctor knife with a thickness of 25 μm.

Next, for some time before the degree of vulcanization and curing is completed, Fluorobore FP-022 (average pore diameter 0.22μ, polytetrafluoroethylene resin porous membrane made by Sumitomo Electric Industries) is layered and the entire surface is uniformly rubbed by hand. Hold it down. Next, the siloxane compound is completely vulcanized,
When the Fluorobor was removed from the glass plate after curing, a thin film of the siloxane compound was completely transferred to the surface of the Fluorobor. Table 1 shows the relationship between the elapsed time from application of the siloxane compound to the overlaying of Fluorobor, the thickness of the thin film formed by transfer, the oxygen permeation rate PO2, and the selective permeability coefficient of oxygen to nitrogen PO2/PN2. Example 2 Produced by the method of Experiment Black 7 of Example 1.

13.56MH on the surface of the dimethylsiloxane laminated support.
When we measured the gas permeability coefficient of a composite membrane made by plasma polymerizing vinyltrimethylsilane for 30 minutes with a high frequency output of z・10Watt, the oxygen permeation rate was 1.2X10-5i/
Cd-SeC-(V7!Hr.Nitrogen is 3.3X10-6
cd/Cd・Sec-? Ht. Therefore, the selective permeation coefficient is 3
．． It was 6. Example 3 The polymerizable gas fed into the plasma reactor was changed from vinyltrimethylsilane to the type shown in the table below. A composite film obtained under the same conditions as in Example 2, except that the high frequency output was increased to 50 W, exhibited the following characteristics.

Claims (1)

[Claims] 1. By applying a siloxane compound onto a smooth flat surface, overlaying a porous polymer membrane thereon, applying a constant pressure to the entire surface, and then peeling off the porous polymer membrane from the smooth flat surface. Then,
A method for producing a gas selectively permeable composite membrane, comprising transferring a coating film of a siloxane compound onto the surface of a porous polymer membrane, and laminating a plasma polymerized membrane using a polymerizable gas on the surface of the transferred coating film of the siloxane compound. . 2. The manufacturing method according to claim 1, wherein the polymerizable gas is a compound containing tertiary carbon. 3 Polymerizable gas is tertiary organosilicon▲mathematical formula, chemical formula,
The manufacturing method according to claim 1, which is a compound containing ▼. 4. The manufacturing method according to claim 1, 2 or 3, wherein the porous polymer membrane is a tetrafluoroethylene resin having a porous structure consisting of fibers and nodules.