JPH0310368B2 - - Google Patents

Description

Detailed Description of the Invention (Objective of the Invention) (Industrial Application Field) The present invention relates to a hydrogen selectively permeable composite membrane having excellent heat resistance, chemical resistance, and mechanical properties, and more specifically,
The present invention relates to a hydrogen selectively permeable composite membrane formed by depositing a plasma polymerized thin film on the surface of a polymer support.

(Prior Art) In recent years, gas separation and purification technology using polymer membranes has been actively developed from the viewpoint of energy conservation. Among these, expectations are high for hydrogen selectively permeable membranes. For example, large-scale industrial technology research “C1 Chemistry”
One development goal is the separation and purification of hydrogen, carbon monoxide, methane, etc. Hydrogen is also attracting attention as a future energy source, and the separation and purification of hydrogen obtained from water electrolysis and water gas has become an important issue.

It is useful for the selectively permeable hydrogen membrane to not only have high selective permselectivity and high permeability for hydrogen, but also to have excellent heat resistance, chemical resistance, and mechanical properties. High selective permeability here means
When the permeation rate of hydrogen is Q _H2 and the permeation rate of other gases such as carbon monoxide is Q _CO , the separation coefficient defined by α=Q _H2 /Q _CO is large. Furthermore, high transparency means that the absolute value of Q _H2 is large.

Various membrane forming methods are being considered for the development of hydrogen selectively permeable membranes that meet these required characteristics, and among them, a membrane forming method using plasma polymerization is noteworthy.

Plasma polymerization is operated under reduced pressure, so there is no problem with dust contamination during film formation, and there is no need for the use of solvents or heating methods that are found in wet film formation, and there is no need for extremely thin pinholes on the surface of the support. It is possible to create a film that is free of oxidation. The application of plasma polymerization to hydrogen permselective membranes is described, for example, in the literature J.of
APPI.Polym.Sci.1505, Volume 16 (1972) reports research mainly using compounds containing cyano groups. However, polymer films obtained from these compounds are rigid and brittle, have defects in mechanical properties, and are difficult to handle because these compounds are highly toxic. Further, JP-A No. 57-30528 presents an example in which two types of plasma polymerized thin films are formed in layers on a porous body. Here, a polymer film using organosilane is formed as the first layer, and then a second layer is laminated by plasma polymerizing saturated hydrocarbons, unsaturated hydrocarbons, aromatic hydrocarbons, or derivatives thereof. The organosilane polymer of the first layer is
Although it has excellent permeability and mechanical properties, it has insufficient permselectivity, while the second layer polymer membrane has high permselectivity, but has insufficient mechanical strength and low permeability. ing. As described above, one type of plasma polymerized membrane cannot satisfy all the required characteristics, and a frequent operation of laminating two types of plasma polymerized membranes is performed.

(Objective of the Invention) The object of the present invention is to use one type of organic silane compound that is easy to handle, and to perform a simple plasma polymerization operation.
The object of the present invention is to provide a hydrogen selective permeability composite membrane that has extremely high hydrogen selective permeability and permeability, and has excellent heat resistance, chemical resistance, and mechanical properties.

(Structure of the Invention) (Means) The hydrogen permselective composite membrane according to the present invention is a composite membrane formed by depositing a plasma polymerized membrane using ethynyltrimethylsilane on the surface of a polymer support.
At this time, the polymer support may be either a nonporous material or a porous material, and may be a nonporous material or a 0.1μ
For porous materials with an average pore size of: A plasma-polymerized film is then deposited onto the composite structure.

The operating procedure for plasma polymerization using ethynyltrimethylsilane is detailed below.

(1) Set the polymer support inside the reactor of the plasma polymerization device.

(2) The inside of the reactor is vacuum pumped to at least 0.01
Exhaust below toll.

(3) While continuing to evacuation, feed ethynyltrimethylsilane monomer vapor into the reactor through a flow meter. At this time, an inert gas such as helium or argon, or nitrogen gas may be used as a carrier gas. Further, the total gas flow rate (total flow rate of monomer vapor and carrier gas) is set so that the pressure inside the reactor after gas supply is 5 torr or less, preferably 1 torr or less. If the pressure is high, the discharge becomes unstable and the energy required for the reaction is insufficient.

(4) Apply power and perform glow discharge. Power depends on equipment factors (electrode structure, reactor volume, etc.)
The optimum value changes depending on the operating conditions (pressure, monomer flow rate, etc.), but if too little is applied, the polymer will have a low molecular weight and sufficient properties will not be expressed, while if too much is applied, the polymer support will deteriorate. generally operated between 10watts and 100watts.

(5) The operation is continued for a predetermined period of time to complete the operation after a plasma-polymerized thin film of the required thickness is deposited on the polymeric support. The thickness of the plasma polymerized thin film is
It is preferably 0.01μ or more and 1.0μ or less. If it is thinner than 0.01μ, the hydrogen selective permeation function will not be fully expressed. Moreover, if the thickness is more than 1.0 μm, the permeability becomes insufficient and minute defects are likely to be induced due to internal stress due to the highly crosslinked structure peculiar to plasma polymerized membranes. The characteristics of the plasma polymerized film will be explained in detail in the next (function) section.

Next, the polymer support supporting this ethynyltrimethylsilane plasma polymerized film will be explained. The polymer support may be a non-porous material, but in order to obtain a membrane with higher permeability, a porous material or a composite membrane in which a thin polymer film is laminated on a porous material is desirable. Furthermore, when depositing a plasma-polymerized thin film directly onto a porous material, the average pore diameter is preferably 0.1 μm or less. This is because if the polymer is deposited so thickly that it blocks pores exceeding 0.1 μm, micro defects will occur in the polymer membrane for the reasons mentioned above, and the selective hydrogen permeability will decrease.

Therefore, when using a porous material with an average pore diameter of more than 0.1μ as a support, a structure in which a plasma-polymerized thin film is deposited on a composite film in which a thin polymer film with excellent gas permeability is laminated on the surface of the porous material is used. It is desirable to do so.

Various polymers can be used as the polymer support depending on the purpose of the hydrogen permselective membrane, but polysulfone, polyphenylene, etc. are useful because they have good mechanical properties, heat resistance, and chemical resistance. oxide,
Polyaromatic esters and polyimides are preferable. However, tetrafluoroethylene resin is a polymer material that has the best properties as described above, and the technology for making it porous has been advanced, so it can be suitably used as a porous polymer support.

When using a porous material with an average pore diameter exceeding 0.1μ, the material for the thin film to be laminated to close the pores in the surface layer should not only have the above properties but also have excellent gas permeability or thin film forming ability. High-quality polymeric materials are desirable, such as siloxane polymers or copolymers such as polydimethylsiloxane, polyphenylsiloxane, polyvinylsiloxane, polydimethylsiloxane-carbonate block copolymers, as well as polyphenylene oxide, polyaromatic esters, etc. Resin is a typical example. Several techniques are known for forming these thin films on the surface of porous materials. For example, a method in which a porous material is dip coated in a polymer solution and then dried and cured to form a thin polymer film, or a method in which a polymer solution is spread on the surface of a liquid such as water and transferred onto a porous material. A method of coating a porous material with a roll coater, a reverse roll coater, etc. can be mentioned, and any of these techniques may be applied. An ultrathin film of ethynyltrimethylsilane plasma polymer that exhibits a substantial selective hydrogen permeation function is deposited on the polymer support thus obtained.

(Function) The substantial selective hydrogen permeation function of the hydrogen selectively permeable composite membrane in the present invention is achieved by the plasma polymerized thin film of ethynyltrimethylsilane.

Plasma polymerization is a unique polymerization method in which monomers are activated with radical ions or excited species by the action of an electric field in a reduced pressure system, and are sequentially combined to increase the molecular weight. The polymer is amorphous, has a rich branched and cross-linked molecular structure, and generally has excellent heat resistance and chemical resistance, but it also tends to generate internal stress in the direction of expansion, and when deposited thickly, Another drawback is that defects such as cracks are likely to occur. However, among various organic compounds, compounds containing silicon generally tend to form plasma polymerized films with low internal stress and excellent flexibility. As a result of extensive studies to apply plasma polymerized membranes of organic silane compounds to hydrogen selectively permeable membranes, the present inventor found that ethynyltrimethylsilane has particularly high hydrogen selective perms and permeability, and is an excellent mechanical material. The present invention was completed based on the discovery that this material has both physical properties and heat resistance.

Plasma polymerized membranes made of alkoxysilanes, siloxane compounds, and silazane compounds containing oxygen or nitrogen in their molecules have excellent permeability, but do not have sufficient selective permselectivity. In addition, for silane compounds containing double bonds such as vinyl groups and allyl groups, as the number of double bonds increases, the plasma polymerized membrane has a structure with more advanced branching and crosslinking, and the hydrogen selective permeability of the membrane also tends to increase. However, on the other hand, the permeability decreases and the membrane quality also loses its flexibility.

On the other hand, we have found that ethynyltrimethylsilane, which has a triple bond, has both high permselectivity and excellent permeability, and can provide a plasma polymerized film that is highly flexible. This is because the ethynyl group in the triple bond is extremely reactive and forms a rigid part with a highly branched and cross-linked structure, while the methyl group part with low reactivity forms a part with relatively high flexibility. The reason is considered to be to provide a membrane with excellent selective hydrogen permeability that is well-balanced as a whole. Furthermore, ethynyltrimethylsilane has a relatively low boiling point of 50°C to 52°C, and monomer vapor can be easily and stably supplied to the reactor. In addition, other silane compounds containing triple bonds have high boiling points or contain oxygen or nitrogen in their molecules, making it difficult to form membranes with excellent hydrogen permselectivity.

The excellent mechanical properties of the ethynyltrimethylsilane plasma polymerized membrane - its high flexibility - are due to its ability to block the pores and certain defects of the polymer support supporting it, resulting in stable hydrogen selective permeability. This will give a composite membrane. It also has excellent heat resistance, and by depositing it on the aforementioned polymer support, it can be heated up to 100°C.
A composite membrane exhibiting high hydrogen selective permeability with α of 20 to 50 can be obtained.

Next, examples will be shown to specifically explain the present invention.

In addition, the hydrogen permeation rate and separation coefficient shown in the examples are based on the ASTN method (pressure method), and the permeated components are separated and detected using a gas chromatograph.
It was determined by quantitative determination.

The thickness of the plasma polymer thin film was determined by measuring the weight increase of the polymer support due to polymerization and the specific gravity of the polymer, and calculating from there.

Example 1 A silicone rubber containing a phenyl group (manufactured by Toray Silicone, SE-955U) was dissolved in toluene, and a vulcanizing agent was added to prepare a 15% by weight solution.

Use a doctor knife to measure this solution.
After coating on a polytetrafluoroethylene resin porous membrane (manufactured by Sumitomo Electric Industries, Ltd., Fluoropore FP-022) having a pore size of 0.22μ, primary vulcanization was performed at 170°C for 10 minutes, and then secondary vulcanization at 200°C for 4 hours. Subsequent vulcanization was performed to cure crosslinking, and a silicone layer with a thickness of 8 μm was laminated.

The gas permeability of the resulting composite membrane was measured at a measurement temperature of 100°C and showed the following characteristics.

H ₂ permeation rate; Q _H2 = 6.2×10 ^-5 cm ³ /cm ²・sec・cmHg Co permeation rate; Q _CO =2.3×10 ⁻⁵ cm ³ /cm ²・sec・cmHg Separation coefficient; α=Q _H2 /Q _CO =2.7 This composite membrane was placed in a plasma reactor with parallel plate electrodes inside, and ethynyltrimethylsilane was applied at a flow rate of 5 while maintaining the system pressure at 0.3 Torr.
It was introduced into the system at a rate of cc/min, and glow discharged for 30 minutes at an output of 40 W from a high frequency power source of 13.56 MHz, thereby depositing an ethynyltrimethylsilane plasma polymerized film on the composite film.

The gas permeability of the resulting three-layer composite membrane was
The results measured at 100°C were as follows.

Q _H2 =4.7×10 ^-5 cm ³ /cm ²・sec・cmHg Q _CO =1.1×10 ⁻⁶ cm ³ /cm ²・sec・cmHg α=Q _H2 /Q _CO =42.7 Example 2 Aromatic polyester ( Manufactured by Unitika, U-100)
was dissolved in dichloromethane to prepare a 1% by weight solution.

This solution was casted onto a smooth and clean glass plate using a doctor knife, and after drying, it was peeled off from the glass plate in water to obtain a thin film approximately 1 μ thick. These two thin films were made of the same tetrafluoroethylene resin porous film (FP-022) used in Example 1.
It was laminated on top and heated to integrate.

The gas permeability of the obtained composite membrane at 100°C was as follows.

Q _H2 =2.4×10 ^-5 cm ³ /cm ²・sec・cmHg Q _CO =1.4×10 ⁻⁶ cm ³ /cm ²・sec・cmHg α=Q _H2 /Q _CO =17.1 Example Ar2 by the same operation as 1.
cc/min, ethynyltrimethylsilane 6c.c./
Output 30W, time 20 while flowing min mixed gas
A glow discharge was performed for 1 minute to deposit a plasma polymerized film.

The gas permeability of the resulting three-layer composite membrane is 100℃
It was as follows.

Q _H2 =1.8×10 ^-5 cm ³ /cm ²・sec・cm/Hg Q _CO =3.7×10 ⁻⁷ cm ³ /cm ² . sec・cmHg α=Q _H2 /Q _CO =48.6 Example 3 27 parts by weight of liquid lubricant (DOSB, manufactured by Ciel Chemical Co., Ltd.) was added to 100 parts by weight of tetrafluoroethylene resin fine powder (F104, manufactured by Daikin Industries, Ltd.). The mixture was mixed and formed into a plate-like product with a width of 50 mm and a thickness of 5 mm using a ram extruder, and then rolled into a film with a thickness of 0.1 mm. After immersing this film in trichlorethylene and extracting and removing the liquid lubricant,
C. and then slowly cooled to obtain a non-porous tetrafluoroethylene resin film having a thickness of 0.1 mm and a crystallinity of 72%.

This film was first stretched at a temperature of 20℃ and a stretching ratio of 1.5.
A porous tetrafluoroethylene resin film having a thickness of 0.06 mm, a porosity of 29%, and an average pore diameter of approximately 0.06 μm was obtained by stretching at a temperature of 175° C. and a stretching ratio of 4.0 times. .

By the same operation as in Example 1, while flowing a mixed gas of N _{2 2} c.c./min and ethynyltrimethylsilane 6 c.c./min,
Glow discharge was performed at 20W for 40 minutes to deposit a plasma polymerized film.

The gas permeability of the resulting two-layer composite membrane is 100℃
It was as follows.

Q _H2 =5.2×10 ^-5 cm ³ /cm ²・sec・cmHg Q _CO =2.4×10 ⁻⁶ cm ³ /cm ²・sec・cmHg α=Q _H2 /Q _CO =21.7 (Effect of the invention) The present invention Hydrogen selectively permeable composite membrane is made by depositing an ethynyltrimethylsilane plasma-polymerized membrane on a polymeric support. , mechanical properties, and chemical resistance, it is possible to obtain an excellent hydrogen selective permeability composite membrane by combining it with an appropriate polymeric support.

Claims (1)

[Claims] 1. Ethynyltrimethylsilane is plasma polymerized on the surface of a polymer support made of porous tetrafluoroethylene resin by glow discharge to increase the hydrogen permeation rate.
Q _H2 , when the permeation rate of carbon monoxide is expressed as Q _CO ,
A hydrogen selectively permeable composite membrane characterized in that the hydrogen selectivity α defined by α=Q _H2 /Q _CO is 20 to 50 at a measurement temperature of 100°C. 2. The hydrogen selectively permeable composite membrane according to claim 1, wherein the polymer support is a porous material made of tetrafluoroethylene resin having an average pore diameter of 0.1 μm or less. 3. The polymer support is a porous material made of tetrafluoroethylene resin with an average pore size exceeding 0.1μ,
2. The selectively permeable hydrogen composite membrane according to claim 1, wherein a polymeric material that closes the pores is laminated on its surface.