JPH0258970B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a member that separates gases by utilizing differences in gas permeation rates, and particularly to a member that selectively separates hydrogen or helium from other gases.

Hydrogen is attracting attention as a future energy source because it can be easily obtained through water electrolysis or water gas. However, in any production process, it is necessary to separate hydrogen from other by-product gases, and it is a very important issue to carry out this process in an energy-saving manner. There are various separation methods such as absorption method, adsorption method, diffusion method, cryogenic separation method, etc., but the diffusion method that applies membrane separation technology is considered to be promising from the viewpoint of energy saving.

In particular, palladium diffusion methods using palladium-based alloy membranes are attracting attention for hydrogen separation.
It is true that palladium is expensive and has the drawback of being degraded by hydrogen.

On the other hand, since helium is a gas with poor reactivity, it is used for various purposes such as scientific experiments, but it is extremely expensive because its production areas are limited. It is advantageous to perform recovery and purification when used on a large scale, but since the equipment for this becomes large-sized, it is usually not a good idea to perform recovery when used on a laboratory scale. It would be beneficial if a small-scale recovery and purification device that could be used on a laboratory scale could be developed, so attempts have been made to develop methods that apply membrane separation technology. However, the membranes currently produced have poor performance, such as low separation ability from other gases or a small amount of recovery per unit time.
This type of device is not common.

The present invention provides a gas separation member that has higher performance than conventional gas separation members, and is particularly excellent in separating hydrogen and helium from other gases.

The gas separation member of the present invention consists of a membrane-like or wall-like porous substrate, and two or more kinds of polymer thin films with different chemical compositions formed in a layered manner on the surface of the substrate by plasma polymerization. The first layer of polymer thin film formed in direct contact with the surface of the substrate is a resin thin film made of an organic silicon compound, and the second layer of polymer thin film formed on the first layer of polymer thin film is saturated. Hydrocarbons, unsaturated hydrocarbons, aromatic hydrocarbons, carboxylic acids, carboxylic acid esters, nitrile compounds,
Alternatively, it is characterized by being formed of at least one layer formed by plasma polymerizing a heterocyclic compound.

The porous substrate herein refers to a porous film or a porous wall having pores ranging from several tens of angstroms (Å) to several micrometers in diameter, and is responsible for the mechanical strength of the gas separation member. Specifically, sintered bodies obtained by sintering metal, ceramic, or polymer particles; fibrous bodies formed by knitting, weaving, or stacking fibers in the form of felt;
Porous polymer films and other porous hollow fibers such as porous polypropylene hollow fibers and porous glass hollow fibers are used as the substrate. The shape of the substrate may be flat, tubular, or other shapes. In the method of the present invention, since the polymer thin film is formed by plasma polymerization, the polymer thin film can be formed relatively easily even on objects with relatively complex shapes such as tubular surfaces or uneven surfaces. Can be formed. In order to form a stable first-layer thin polymer film in the pores on the substrate surface, when the pores are circular in shape, the diameter is preferably several thousand angstroms or less. Further, when the hole is rectangular or elliptical, it is preferable that the short diameter thereof is 1000 angstroms or less. As such a substrate, a porous cellulose acetate membrane in which many pores of several tens to several hundred angstroms are uniformly formed, a porous polycarbonate membrane, or a porous polypropylene membrane in which pores of several hundred angstroms are formed by stretching are advantageously used. can.

Plasma polymerization, which forms a thin polymer film on the surface of a substrate, is a polymerization method in which an electric field is applied to an organic monomer under low pressure to activate the organic monomer and convert it into radicals or ions, causing polymerization. As a method of applying an electric field, an internal electrode method or a non-electrode method is possible. In the internal electrode method, direct current, alternating current, and high frequency electric fields can be applied. In the electrodeless method, a high-frequency electric field can be applied. Furthermore, the method generally known as reverse sputtering is the same as the internal electrode method described above, and the plasma polymerization of the present invention can be performed by reverse sputtering.

In the present invention, the first layer of the polymer thin film formed on the surface of the substrate by plasma polymerization is characterized by being composed of a resin made of an organic silicon compound (hereinafter referred to as organosilane resin). As organic monomers for plasma polymerization for this purpose, organosilanes such as hexamethyldisiloxane, diethoxydimethylsilane, octamethylcyclotetrasiloxane, tetraethoxysilane, triethoxyvinylsilane, and tetramethylsilane can be used. In a composite membrane in which a first layer of polymer thin film is supported on the surface of a substrate, the surface of fine pores existing on the surface of the substrate is coated with a polymer thin film made of organosilane resin formed by plasma polymerization, and the pores are Gas separation is performed by a thin polymer film formed in the area. For this reason, it is important to know the properties of the thin polymer film formed on the surface of the pores, but because the pore diameter is so small as to be less than 1,000 angstroms, the properties cannot be determined using current physical property measurement methods. Based on current knowledge of plasma polymerization, it is assumed that polymers are formed around the pores of the substrate, grow toward the center, and finally close the pores in the center and form a thin film. Seem. For this reason, it is assumed that the first polymer thin film formed on the surface of the hole is not of uniform thickness, but is thicker at the periphery and thinner at the center. In addition, since reactions of various reaction modes are thought to occur simultaneously in the plasma state, the resulting polymer thin film itself may have a different chemical composition from that obtained by ordinary polymerization methods. It is thought that there are. For example, conventional silicone thin films consisting of dimethylpolysiloxane skeletons have weak mechanical strength and have low separation rates of hydrogen, helium, and oxygen relative to nitrogen (H ₂ /N ₂ , He/N ₂ , and
O ₂ /N ₂ ) are about 2.1, 1.1, and 2.0, respectively, but the composite membrane supporting the silicone thin film obtained by plasma polymerization of the present invention has high mechanical strength and separation rate (H ₂ /N ₂ , It is also inferred that the chemical compositions are different from the fact that the He/N ₂ and O ₂ /N ₂ ) values are as high as 6.0, 4.0, and 2.3 or higher, respectively. Conventional silicone thin films made of a dimethylpolysiloxane skeleton are characterized by a gas permeation rate that is about 100 times higher than thin films of the same thickness made of other polymers such as polyethylene. On the other hand, when comparing the nitrogen permeation rate of the composite film supporting the organosilane resin thin film obtained by plasma polymerization of the present invention and a commercially available silicone thin film with the same thickness, it is found that the nitrogen permeation rate is about the same or slightly inferior. In polymerization, an extremely thin organosilane resin film is produced, so the amount of gas permeation per unit time is about 100 times greater. As described above, a composite membrane supporting an organosilane resin thin film is extremely superior in separation ability and gas permeation rate compared to conventional gas separation members. However, the separation ability of this composite membrane is not sufficient for use in the separation and purification of hydrogen or helium. On the other hand, the inventors have developed a composite membrane in which a thin polymer film is formed by plasma polymerization on the surface of a porous substrate using olefinic hydrocarbons such as 1-hexene and cyclohexene as organic monomers, which has a high separation rate of hydrogen and helium relative to nitrogen. I found out that it is expensive. However, when this composite membrane was made to have a thickness comparable to that of an organosilane resin thin film, it did not have sufficient mechanical strength and was also inferior in gas permeation rate. In the present invention, a thin polymer film other than the organosilane resin is formed as a second layer on the surface of a composite film having a thin organosilane resin film supported on the surface of the substrate. As the second layer of polymer thin film, a thin film obtained by plasma polymerization of olefinic hydrocarbons, aromatic hydrocarbons, or derivatives thereof can be employed. Examples of saturated hydrocarbons include methane and ethane; examples of unsaturated hydrocarbons include 1-hexene, cyclohexene, 1,3-pentadiene,
1,3-cyclohexadiene, dicyclopentadiene, acetylene, etc., aromatic hydrocarbons include benzene, toluene, xylene, styrene, divinylbenzene, etc., and derivatives thereof include acrylic acid, ethyl acrylate, furan, Carboxylic acids such as benzonitrile, carboxylic esters, nitrile compounds, heterocyclic compounds, etc. are advantageously used.

The second layer of polymer thin film may be a single layer or a multilayer consisting of two or more of the above compounds. Further, each layer may be made of a homopolymer of the above-mentioned compounds, or a copolymer of two or more of the above-mentioned compounds, or may be made of a mixture of homopolymers or copolymers.

The polymer thin film as the second layer has high mechanical strength because it is reinforced by the porous substrate and the organosilane resin thin film, and its performance in separating hydrogen and helium is superior to that of the composite supporting only the organosilane resin thin film. Separation rate of hydrogen and helium relative to nitrogen (H ₂ /N ₂ , He/N ₂ ) compared to membranes
increases significantly to about 30 and 25, respectively. On the other hand, the reduction in permeation amount is at most one-tenth of that of a composite membrane supporting only an organosilane resin thin film, and the permeation rate is significantly higher than that of conventional gas separation members. Here, the performance of the gas separation member of the present invention will be estimated.

The permeation rate of the gas separation member of the present invention for various gases has approximately the following values. H ₂ permeation rate is 9.4×10 ^-5 cm ³ /sec, cm ² , cmHg, He permeation rate is
8.1×10 ^-5 cm ³ /sec, cm ² , cmHg, N ₂ permeation rate is 3.1
×10 ^-6 cm ³ /sec, cm ² , cmHg, O ₂ permeation rate is 1.3×
10 ^-5 cm ³ /sec, cm ² , cmHg. Assuming that the air contains 50% hydrogen or helium, this gas mixture is brought to one side of the gas separation member of the present invention at 1 atmosphere, the other side is brought into a vacuum state, and the other side is brought into a vacuum state. Shows the total amount and composition of the mixed gas that permeates.

The following values were calculated based on the assumption that a gas separation member of 1 square meter was used and permeation was performed for 1 minute. First, if the air contains 50% hydrogen, the total amount of the mixed gas that permeates is 2.3 liters, and the composition is 95% hydrogen and 2.5% nitrogen.
%, oxygen is 2.8%. Also, if the air contains 50% helium, the total amount of permeated gas is 2.0
The composition is 94% helium and 2.9% nitrogen.
%, oxygen is 3.3%. '' Thus, it can be seen that the gas separation member of the present invention is extremely excellent in the separation and purification of hydrogen and helium.

Furthermore, since the gas separation member of the present invention forms a thin polymer film on the surface of the substrate by plasma polymerization, a strong thin polymer film can be easily formed on the surface of the substrate regardless of the shape of the substrate. It is possible. Therefore, a hollow system-like gas separation member can also be easily obtained by the method of the present invention.

The amount of gas permeation and the separation rate were determined based on the ASTM method (pressure method) by separating, detecting, and quantifying the components of the permeated gas using a gas chromatograph.

More specifically, after sandwiching the membrane in a permeation cell and evacuating the space on both sides of the membrane using a vacuum pump,
Air, hydrogen, or helium pressurized to 1.1 Kg/cm ² is introduced into one side of the membrane, and the gas that permeates through the membrane within a predetermined period of time is temporarily trapped, then guided to a gas chromatograph and then transferred to a molecular sieve type. Separate each component using a column, and calculate the amount of each component using a pre-prepared calibration curve.H2 permeation rate, _He permeation rate,
The O ₂ permeation rate and N ₂ permeation rate were calculated.

Examples will be explained below.

A schematic cross-sectional view of the plasma generator used in this example is shown in the figure. This plasma generator has a height of about 50 cm and a protrusion 11 with a diameter of about 7 cm on the top.
A glass jar 1 with a bottom diameter of about 30 cm, a metal base 2 forming the bottom of the jar 1, and copper plate electrodes 3 wrapped around the upper and lower parts of the projections 11.
It becomes more. The stand 2 includes a passage 21 for introducing monomer gas and a passage 2 for discharging the gas in the jar 1.
2, and inside the jar 1 there is a metal sample stage 4.
is provided. The substrate 5 on which a thin polymer film is formed by plasma polymerization is placed on the sample stage 4 inside the jar 1 (this is the A position), between the electrodes 3.3 of the protrusion 11 (this is the B position), It was placed on either the shoulder of the jar 1 (this is the C position), the center of the jar 1 (this is the D position), or the bottom of the jar 1 (this is the E position). The size of the substrate 5 was 7 cm x 10 cm, and two substrates were placed side by side at the same position.

In plasma polymerization, the substrate is first treated with the above A, B, C,
placed in at least one of the positions D and E;
Air in the jar 1 was evacuated through passage 22 by a vacuum pump (not shown). Next, while degassing was continued using a vacuum pump, a predetermined organosilane compound was introduced as an organic monomer through passage 21, and the pressure inside the jar was maintained at about 0.1 to 0.3 Torr. In this state, a high frequency voltage of a predetermined input was applied between the electrodes 3 and 3 to cause plasma polymerization, which continued for a predetermined period of time to form an organosilane resin thin film on the surface of the substrate 5.
Next, the composite membrane supporting the organosilane resin thin film is placed in at least one of the positions A, B, C, D, and E in the plasma generator, and the membrane is heated in the jar 1 using a vacuum pump (not shown). Air was vented through passage 22. While degassing is continued using a vacuum pump, a predetermined olefin hydrocarbon, aromatic hydrocarbon, or a derivative thereof is introduced as an organic monomer through the passage 21, and the pressure inside the jar is reduced to approx.
Keep it at 0.1-0.3 Torr. In this state, electrode 3.3
During this period, a high frequency voltage of a predetermined input was applied to cause plasma polymerization, and a thin polymer film was formed on the surface of the composite membrane for a predetermined period of time. The substrate used in the examples was a porous polypropylene membrane 25 micrometers thick, having a large number of rectangular pores measuring 200 x 2000 angstroms. In the Examples, only the types of monomers and plasma polymerization conditions are described.

Example 1 The substrate was sampled at position A using hexamethyldisiloxane as the organic monomer, and the monomer pressure was 0.2.
The reaction was carried out for 20 minutes at a power of 50 watts between the electrodes to form an organosilane resin thin film on the substrate. This composite membrane was reacted at sample position A using cyclohexene as an organic monomer at a monomer pressure of 0.2 torr and an interelectrode input of 50 watts for 20 minutes to form a polymer thin film on the composite membrane. The gas permeation rate and separation rate of this gas separation member were measured using the ASTM method described above. The results were as follows.

_H2 permeation rate: 3.3 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 3.0 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 2.3 x ^{10-6 cm3} / sec, cm ² , cmHg N ₂ permeation rate: 6.7×10 ^-7 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 49 He/N ₂ separation rate: 44 Example 2 Same as Example 1 The composite membrane supporting the organosilane resin thin film prepared by the above method was reacted at sample position C using 1-hexene as an organic monomer at a monomer pressure of 0.2 Torr and an interelectrode input of 50 W for 20 minutes to form a polymer thin film on the composite membrane. formed. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 9.4 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 8.1 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 1.3 x ^{10-5 cm3} / sec, cm ² , cmHg N ₂ transmission rate: 3.1×10 ^-6 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 31 He/N ₂ separation rate: 26 Example 3 Place the substrate at sample position A Using octamethylcyclotetrasiloxane as an organic monomer, the reaction was carried out for 30 minutes at a monomer pressure of 0.2 Torr and an interelectrode input of 50 W.
An organosilane resin thin film was formed on the substrate.
This composite membrane was reacted at sample position C using cyclohexene as an organic monomer at a monomer pressure of 0.2 torr and an interelectrode input of 50 watts for 5 minutes to form a polymer thin film on the composite membrane. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 9.1 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 7.5 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 1.1 x ^{10-5 cm3} / sec, cm ² , cmHg N ₂ transmission rate: 3.4×10 ^-6 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 27 He/N ₂ separation rate: 22 Example 4 Place the substrate at sample position A using hexamethyldisiloxane as the organic monomer at a monomer pressure of 0.2
A reaction was carried out for 30 minutes at a power input of 50 W between the electrodes to form an organosilane resin thin film on the substrate. This composite membrane was reacted at sample position D using toluene as an organic monomer at a monomer pressure of 0.2 torr and an interelectrode input of 50 watts for 5 minutes to form a polymer thin film on the composite membrane. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 8.1 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 7.2 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 8.4 x ^{10-6 cm3} / sec, cm ² , cmHg N ₂ transmission rate: 3.1×10 ^-6 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 26 He/N ₂ separation rate: 23 Example 5 Same as Example 4 The composite membrane supporting the organosilane resin thin film prepared by the method was placed at sample position D using styrene as an organic monomer, and the monomer pressure was
A thin polymer film was formed on the composite membrane by reacting for 5 minutes at an input power of 50 watts between the electrodes of 0.2 torr. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 3.2 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 3.2 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 2.9 x ^{10-6 cm3} / sec, cm ² , cmHg N ₂ transmission rate: 7.5×10 ^-7 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 43 He/N ₂ separation rate: 43 Example 6 Same as Example 4 The composite membrane supporting the organosilane resin thin film prepared by the above method was reacted at sample position E using ethyl acrylate as an organic monomer at a monomer pressure of 0.2 Torr and an interelectrode input of 50 W for 20 minutes to form a polymer thin film on the composite membrane. formed. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 9.8 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 9.4 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 9.7 x ^{10-6 cm3} / sec, cm ² , cmHg N ₂ permeation rate: 3.9×10 ^-6 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 26 He/N ₂ separation rate: 25 Example 7 Same as Example 4 The composite membrane supporting the organosilane resin thin film prepared by the method was placed at sample position A using furan as an organic monomer, and the monomer pressure was 0.2.
A thin polymer film was formed on the composite membrane by reacting for 20 minutes at a power of 50 watts between the electrodes. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 8.8 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 7.6 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 7.8 x ^{10-6 cm3} / sec, cm ² , cmHg N ₂ transmission rate: 2.0×10 ^-6 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 44 He/N ₂ separation rate: 39 Example 8 Same as Example 4 The composite membrane supporting the organosilane resin thin film prepared by the method was placed at sample position E using acetylene as an organic monomer, and the monomer pressure was
A thin polymer film was formed on the composite membrane by reacting for 2 minutes at a 0.2 torr interelectrode input of 50 watts. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 9.5 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 9.3 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 4.4 x ^{10-6 cm3} / sec, cm ² , cmHg N ₂ transmission rate: 1.8×10 ^-6 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 54 He/N ₂ separation rate: 53 Example 9 Same as Example 4 The composite film supporting the organosilane resin thin film prepared by the above method was reacted at sample position D using benzonitrile as an organic monomer at a monomer pressure of 0.2 Torr and an interelectrode input of 50 W for 1 minute to form a polymer thin film on the composite film. I let it happen. The gas permeation rate and separation rate of this gas separation member were as follows.

_H2 permeation rate: 4.6 x ^{10-5 cm3} /sec, ^cm2 , cmHg He permeation rate: 5.5 x ^{10-5 cm3} /sec, ^cm2 , cmHg _O2 permeation rate: 2.8 x ^{10-6 cm3} / sec, cm ² , cmHg N ₂ permeation rate: 1.2×10 ^-6 cm ³ /sec, cm ² , cmHg H ₂ /N ₂ separation rate: 38 He/N ₂ separation rate: 45

[Brief explanation of the drawing]

The figure is a cross-sectional view of a plasma polymerization apparatus used in an example of the present invention. In the figure, reference numeral 1 indicates a jar, 2 a stand, 3 an electrode, 4 a sample stand, and 5 a substrate or a composite film supporting a thin resin film made of an organic silicon compound.

Claims (1)

[Scope of Claims] 1. Consisting of a porous substrate in the form of a film or wall, and at least two types of polymer thin films formed in a layered manner on the surface of the substrate by plasma polymerization, which are directly applied to the surface of the substrate. The first layer of polymer thin film formed in contact is a resin thin film made of an organosilicon compound,
The second layer of polymer thin film formed on the first layer of polymer thin film contains saturated hydrocarbons, unsaturated hydrocarbons, aromatic hydrocarbons, carboxylic acids, carboxylic acid esters, nitrile compounds, or heterocyclic compounds. A gas separation member characterized in that it is formed of at least one layer subjected to plasma polymerization. 2. Gas separation according to claim 1, wherein when the pores in the substrate are circular, the diameter thereof is several thousand angstroms or less, and when the pores are rectangular or elliptical, the minor axis is 1000 angstroms or less. Element.