JP7798494B2 - Gas separation material manufacturing method and gas separation material manufacturing apparatus - Google Patents

Description

This disclosure relates to a method for manufacturing a gas separation material, a gas separation material manufacturing apparatus, and a gas separation material.

Gas separation technology is known that separates mixed gases based on the size of the gas molecules. This technology uses ceramic gas separation materials with sub-nanosized pores. Patent documents 1-3, for example, disclose counter-diffusion chemical vapor deposition (counter-diffusion CVD) as a method for manufacturing gas separation materials.

Japanese Patent Application Laid-Open No. 2007-216106 Japanese Patent Application Laid-Open No. 2009-202096 International Publication No. 2014/007140

However, gas separation materials produced by conventional production methods do not necessarily have sufficient gas permeability, and further improvement in gas permeability has been desired.
The present disclosure has been made in view of the above circumstances, and aims to improve gas permeability, and can be realized in the following forms.

A raw material gas containing a vaporized silica-forming substance and an inert gas is supplied to one surface side of the porous substrate;
An active gas serving as a reactive species is supplied to the other surface side of the porous substrate;
A method for producing a gas separation material, comprising counter-diffusing the raw material gas and the activated gas to form a gas separation layer containing silica in pores of the porous substrate by chemical vapor deposition at a reaction temperature of 300°C or higher and 800°C or lower,
The method for producing a gas separation material further comprises heat-treating the gas separation layer formed by the chemical vapor deposition at a temperature lower than the reaction temperature and not lower than 200°C.

The manufacturing method for the gas separation material disclosed herein removes organic matter derived from the source gas remaining in the gas separation layer, thereby improving gas permeability.

FIG. 1 is a schematic diagram of a gas separation material manufacturing apparatus. FIG. 2 is a chemical formula showing an example of the raw material of the gas separation layer. FIG. 3 is a conceptual diagram of the counter-diffusion chemical vapor deposition method. FIG. 4 is a conceptual diagram of the chemical vapor infiltration method. FIG. 5 is a diagram showing the evaluation of the gas separation layer by FT-IR. FIG. 6 is a schematic diagram illustrating a state in which steric hindrance occurs due to impurities (organic substances). FIG. 7 is a schematic diagram illustrating a state in which impurities (organic substances) have been removed and steric hindrance has been eliminated. FIG. 8 is a graph showing the relationship between the heat treatment and the gas permeability. FIG. 9 is a graph showing the effect of various atmospheres.

Here, a preferred example of the present disclosure will be described.
The method for producing a gas separation material, wherein organic matter derived from the raw material gas remaining in the gas separation layer is removed by the heat treatment.
The method for producing a gas separation material, wherein the heat treatment is carried out in an atmosphere of a gas containing one or more gases selected from the group consisting of oxygen, helium, hydrogen, argon, and nitrogen.
- A method for producing a gas separation material, wherein during the heat treatment, the gas pressure difference between the gas pressure on one side of the porous substrate and the gas pressure on the other side of the porous substrate is 10 kPa or more and 980 kPa or less.
a raw material gas supply unit that supplies a raw material gas containing a vaporized silica-forming substance and an inert gas to one surface side of the porous substrate;
An active gas supply unit that supplies an active gas that becomes a reactive species to the other surface side of the porous substrate,
A gas separation material manufacturing apparatus for forming a gas separation layer containing silica in pores of the porous substrate by chemical vapor deposition at a reaction temperature of 300°C or higher and 800°C or lower by counter-diffusing the raw material gas and the activated gas,
The gas separation material manufacturing apparatus further comprises a heat treatment section for heat-treating the gas separation layer formed by the chemical vapor deposition at a temperature lower than the reaction temperature and not lower than 200°C.
The gas separation material manufacturing apparatus, wherein organic matter derived from the raw material gas remaining in the gas separation layer is removed by the heat treatment.
A gas separation material manufacturing apparatus, wherein the heat treatment is carried out in an atmosphere of a gas containing one or more gases selected from the group consisting of oxygen, helium, hydrogen, argon, and nitrogen.
- A gas separation material manufacturing apparatus wherein, during the heat treatment, the gas pressure difference between the gas pressure on one side of the porous substrate and the gas pressure on the other side of the porous substrate is 10 kPa or more and 980 kPa or less.
A gas separation material having a gas separation layer containing silica formed by counter diffusion chemical vapor deposition using a raw material gas containing a silica-forming substance and an inert gas and an active gas,
A gas separation material, wherein the carbon content in the gas separation layer is less than 0.3 mass%.

The present disclosure is explained in detail below. In this specification, when a numerical range is indicated using "-", it is considered to include both the lower limit and the upper limit unless otherwise specified. For example, the expression "10-20" includes both the lower limit of "10" and the upper limit of "20". In other words, "10-20" has the same meaning as "10 or more and 20 or less."

1. Manufacturing Method of Gas Separation Material In the manufacturing method disclosed herein, a source gas containing a vaporized silica-forming substance and an inert gas is supplied to one side of a porous substrate. In this manufacturing method, an active gas serving as a reactive species is supplied to the other side of the porous substrate. For example, when the porous substrate is cylindrical, the source gas is supplied to the outer peripheral surface of the porous substrate and the active gas is supplied to the inner peripheral surface, or the source gas is supplied to the inner peripheral surface of the porous substrate and the active gas is supplied to the outer peripheral surface. This manufacturing method then produces a gas separation layer containing silica by chemical vapor deposition in the pores of the porous substrate at a reaction temperature of 300°C to 800°C by counter-diffusion of the source gas and the active gas. In this manufacturing method, the gas separation layer formed by chemical vapor deposition is further heat-treated at a temperature lower than the reaction temperature but not lower than 200°C.

(1) Porous substrate The porous substrate as the film-forming material is not particularly limited. The porous substrate has a film-forming portion consisting of a porous portion having a plurality of pores. The film-forming portion is preferably a porous body having linear or network-like pores (communicating holes) penetrating therethrough to allow the source gas and the active gas (counter gas) to diffuse in opposite directions. However, in chemical vapor deposition, the temperature around the porous substrate may also become high when the source gas and the active gas are reacted, so it is preferable to use a thermally stable inorganic porous substrate.

The inorganic porous substrate preferably comprises at least one porous support substrate selected from the group consisting of α-alumina, mullite, cordierite, zirconia, and silicon carbide, with an inorganic porous membrane as an intermediate layer. Because the average pore diameter of interconnected pores in porous support substrates is typically 50-1000 nm, they are unsuitable for forming a thin film inside the pores by blocking the pores with reaction products using counter-diffusion CVD. Therefore, in order to form a thin film inside the pores, it is preferable that the inorganic porous substrate has an intermediate layer formed as an inorganic porous membrane with an average pore diameter of approximately 4-8 nm.

In particular, when forming a gas separation layer (separation active layer) primarily composed of silica, it is preferable to use an inorganic porous substrate having a membrane-forming portion formed on its surface, which is a gamma-alumina intermediate layer with pores having an average pore diameter of preferably 12 nm or less, more preferably 10 nm or less, and particularly preferably 8 nm or less. Here, "main component" refers to a substance with a content (mass %) of 50% or more. A gamma-alumina intermediate layer containing nickel (Ni) is suitable from the perspective of the moisture resistance required for gas separation materials. The lower limit of the average pore diameter of the pores in the gamma-alumina intermediate layer is not particularly limited, but is preferably 1 nm, more preferably 2 nm, and even more preferably 3 nm. Such a gamma-alumina intermediate layer is preferably formed on the surface of a porous support substrate having pores with an average pore diameter of preferably 40 nm to 300 nm, more preferably 60 nm to 200 nm. The thickness of the intermediate layer is not particularly limited. The thickness of the intermediate layer is preferably 1 μm to 6 μm, and more preferably 2 μm to 5 μm.

In this specification, the average pore diameter of the inorganic porous substrate is the 50% permeation flux diameter in the pore distribution measured by the bubble point method and half-dry method using a commercially available pore distribution measuring device. The average pore diameter of the intermediate layer is the 50% permeation flux diameter in the pore distribution measured using a pore size distribution measuring device "Nanoperm Porometer" manufactured by Seika Sangyo Co., Ltd.

The shape of the membrane-forming portion is selected appropriately depending on the purpose and application. The shape of the membrane-forming portion may be columnar, cylindrical, semi-cylindrical, rod-shaped, block-shaped, etc. The size of the membrane-forming portion is also selected depending on the purpose and application. If the membrane-forming portion has a cylindrical shape suitable for gas separation materials, its outer diameter is preferably φ3mm-φ16mm, and more preferably φ6mm-φ12mm.

(2) Source Gas The source gas contains a vaporized silica-forming substance and an inert gas.

(2.1) Silica-forming substance The silica-forming substance is a precursor of silica. As the silica-forming substance, either an organic silicon compound or an inorganic silicon compound can be used.
As the silica-forming substance, it is preferable to use an organosilicon compound from the viewpoint of film-forming properties and pore size control.
Examples of organosilicon compounds include siloxane compounds such as hexamethyldisiloxane (HMDS), tetraethylsiloxane, tetramethylcyclotetrasiloxane, and trimethyldisiloxane, and silane compounds such as CH ₃ SiH ₃ , dimethylsilane, tripropylsilane, tetramethoxysilane, tetraethoxysilane, phenyltrimethoxysilane, and diphenyldimethoxysilane.
Examples of inorganic silicon compounds include inorganic silane compounds such as monosilane, disilane, SiH ₂ Cl ₂ and SiF ₄ .
It is desirable to vaporize one or more of these silica-forming substances and use them in a gaseous state.
Since many of the silica-forming substances are liquid at room temperature, they may be gasified by a bubbling method in which the liquid is placed in a bubbler maintained at a constant temperature and vaporized by the action of a carrier gas. Alternatively, a gas mixer may be used to mix multiple types of gases or to mix a gas containing an additive element.

(2.2) Inert Gas The inert gas is at least one selected from the group consisting of nitrogen gas, helium gas, argon gas, krypton gas, and xenon gas. The inert gas is used as a carrier gas. The content of the inert gas is preferably 70% by volume or more and 95% by volume or less, and more preferably 80% by volume or more and 90% by volume or less, when the entire source gas is taken as 100% by volume.

(3) Active Gas As the active gas (counter gas), oxygen gas, ozone gas, hydrogen gas, etc., can be used. The active gas is preferably at least one selected from the group consisting of oxygen gas containing oxygen element, which has good reactivity with the silica-forming substance, and ozone gas.

(4) Counter-diffusion chemical vapor deposition method In this manufacturing method, a raw material gas is supplied to one side of a porous substrate, and an active gas is supplied to the other side of the porous substrate, causing counter-diffusion of the raw material gas and the active gas. The concept of counter-diffusion chemical vapor deposition is shown in FIG. 3. Reference numeral 101 indicates a porous substrate (an inorganic porous membrane serving as an intermediate layer). Reference numeral 101A indicates one side, reference numeral 101B indicates the other side, and reference numeral 101C indicates pores. Reference numeral 103 indicates a raw material gas, and reference numeral 105 indicates an active gas. Reference numeral 107 indicates a gas separation layer containing silica. The upper arrows schematically indicate the flow of the raw material gas, and the lower arrows schematically indicate the flow of the active gas. In the counter-diffusion chemical vapor deposition method, the raw material gas 103 and the active gas 105 come into contact with each other inside the pores 101C of the porous substrate 101, and a gas separation layer 107 is formed in the pores 101C.

Figure 4 shows the chemical vapor infiltration (CVI) method. The symbols in Figure 4 are the same as those in Figure 3. In chemical vapor infiltration, the source gas 103 and the active gas 105 enter the pores 101C from the same side (one surface 101A) of the porous substrate 101. In chemical vapor infiltration, the thickness of the gas separation layer 107 up to the sealing pores is several times the diameter of the pores 101C, resulting in a gas separation material with low gas permeability and low separation performance. In contrast to chemical vapor infiltration, in the counter-diffusion chemical vapor deposition method shown in Figure 3, when the gas separation layer 107 blocks the pores 101C, the source gas 103 and the active gas 105 are not in contact with each other. This reduces the thickness of the silica-containing gas separation layer 107, resulting in a gas separation material with high gas permeability and high performance.

From the viewpoint of decomposition of the raw materials and control of the amorphous network diameter, the reaction temperature is 300°C or higher and 800°C or lower, preferably 300°C or higher and 750°C or lower, and more preferably 550°C or higher and 725°C or lower.

The position where the reaction product, which is the gas separation layer, is formed depends on the balance of the flow rates of the raw material gas and the active gas (counter gas). When depositing the reaction product inside the pores of the porous substrate, the flow rate (sccm) ratio of the raw material gas to the active gas is preferably 1:1-1:10, and more preferably 1:2-1:8. The volume ratio of the raw material gas and the counter gas that come into contact within the pores of the film formation area, assuming the total of both to be 100 volume percent, is preferably 20-80 volume percent of the raw material gas, and even more preferably 30-70 volume percent.

The average pore diameter of the gas separation layer is not particularly limited. From the perspective of hydrogen separation, an average pore diameter of 0.29 nm to 0.32 nm is preferred. The pore diameter of the gas separation layer is a value estimated from the gas permeability obtained by a gas permeation method using pure gases with known molecular diameters.

(5) Heat Treatment of Gas Separation Layer In the production method of the present disclosure, the gas separation layer formed by chemical vapor deposition is further subjected to a heat treatment.
The heat treatment temperature is lower than the reaction temperature and is 200°C or higher, preferably 250°C or higher, and more preferably 300°C or higher. By setting the heat treatment temperature within this range, organic substances derived from the raw material gas remaining in the gas separation layer are removed, thereby improving the gas permeability. The organic substances are not particularly limited. For example, the organic substances are hydrocarbons, and are represented by the general _{formula CmHn} .
For example, when the reaction temperature is 550°C or higher and 700°C or lower, the heat treatment temperature is preferably 250°C or higher and 500°C or lower.
The heat treatment time is not particularly limited, but is preferably from 1 hour to 10 hours, more preferably from 3 hours to 7 hours, from the viewpoint of sufficiently removing organic substances while suppressing production costs.

Figures 6 and 7 are schematic diagrams of an example of a gas separation layer before and after heat treatment. Figure 6 shows the gas separation layer before heat treatment. Figure 6 shows how the presence of organic _{matter CmHn} as an impurity in the pores of a silica-containing gas separation membrane causes steric hindrance, hindering gas permeation. Figure 7 shows the gas separation layer after heat treatment. The gas separation layer in Figure 7 shows how the organic matter has been removed, the steric hindrance has been eliminated, and the gas permeability has improved.

The heat treatment is preferably performed in a gas atmosphere containing one or more gases selected from the group consisting of oxygen, helium, hydrogen, argon, and nitrogen. The gas pressure in the heat treatment is not particularly limited. The gas atmosphere may be a reduced pressure atmosphere. Even in the reduced pressure atmosphere, it is preferable that the atmosphere contains a gas containing one or more gases selected from the group consisting of oxygen, helium, hydrogen, argon, and nitrogen.
Oxygen is presumed to be suitable for removing organic matter because it can burn organic matter.
It is presumed that helium has a small molecular size and therefore easily penetrates into the pores of the gas separation layer, resulting in an excellent effect in removing organic matter.
Hydrogen has the ability to etch carbon, and is presumed to be highly effective in removing organic matter.

In the heat treatment, it is preferable that gas is present on both sides of the porous substrate, and the difference in gas pressure between the gas on one side of the porous substrate and the gas on the other side of the porous substrate is preferably 10 kPa or more and 980 kPa or less.
For example, the gas pressure difference may be adjusted by increasing the gas supply flow rate on one side of the porous substrate relative to the gas supply flow rate on the other side, or by decreasing the gas supply flow rate on one side relative to the gas supply flow rate on the other side.
The gas pressure difference may also be adjusted by reducing the pressure on one side of the porous substrate below atmospheric pressure or by reducing the pressure on the other side of the porous substrate below atmospheric pressure.
The gas pressure difference may also be adjusted by pressurizing one surface of the porous substrate to a pressure higher than atmospheric pressure or by pressurizing the other surface to a pressure higher than atmospheric pressure.

When this gas pressure difference creates a gas pressure gradient from one side of the porous substrate to the other, the gas becomes more likely to come into contact with the remaining organic matter, resulting in efficient removal of the organic matter.

2. Gas separation material manufacturing device 1
FIG. 1 shows an example of an embodiment of a gas separation material manufacturing apparatus 1. The gas separation material manufacturing apparatus 1 includes a raw material gas supply unit 20, an opposing gas supply unit 30 (corresponding to an "active gas supply unit"), and a heat treatment unit 60. The raw material gas supply unit 20 supplies a raw material gas containing a vaporized silica-forming substance and an inert gas to one side of a porous substrate S. The opposing gas supply unit 30 supplies an active gas, which serves as a reactive species, to the other side of the porous substrate S. The gas separation material manufacturing apparatus 1 forms a gas separation layer containing silica by chemical vapor deposition in the pores of the porous substrate S at a reaction temperature of 300°C to 800°C by counter-diffusion of the raw material gas and the opposing gas (active gas). The heat treatment unit 60 heats the gas separation layer formed by chemical vapor deposition at a temperature lower than the reaction temperature and equal to or higher than 200°C.
In the gas separation material manufacturing apparatus 1, the descriptions such as "(1) porous substrate,""(2) raw material gas,""(3) activated gas,""(4) counter-diffusion chemical vapor deposition method,""(5) heat treatment of gas separation layer," and "(6) gas separation material" explained in the section "1. Gas separation material manufacturing method" are applied as is, and these descriptions are omitted.

The gas separation material manufacturing apparatus 1 includes a film formation chamber 10 , a raw material gas exhaust mechanism 40 , and an opposing gas exhaust mechanism 50 .
The film formation chamber 10 is, for example, a cylindrical reactor made of, for example, stainless steel. Vacuum joints are fixed to both axial ends of the film formation chamber 10 via a pair of O-rings. A counter gas supply unit 30 is connected to a counter gas supply port 11 at one axial end of the film formation chamber 10, and a counter gas exhaust mechanism 50 is connected to a counter gas exhaust port 12 at the other axial end of the film formation chamber 10. A source gas supply pipe serving as a source gas supply port 13 and a source gas exhaust pipe serving as a source gas exhaust port 14 are also provided on the outer circumferential surface of the film formation chamber 10. A source gas supply unit 20 is connected to the source gas supply port 13, and a source gas exhaust mechanism 40 is connected to the source gas exhaust port 14. The source gas supply port 13 is also connected to the counter gas supply unit 30. During the heat treatment, atmospheric gas during the heat treatment is supplied into the film formation chamber 10 from a third gas cylinder 34 of the counter gas supply unit 30 via the counter gas supply port 11 and the source gas supply port 13. The third gas cylinder 34 contains an active gas during chemical vapor deposition and an atmospheric gas during heat treatment, which is preferably a gas containing at least one selected from the group consisting of oxygen, helium, hydrogen, argon, and nitrogen.
The film formation chamber 10 has a storage space for storing a porous substrate S as a material to be treated.

The source gas supply unit 20 includes a source gas supply pipe 21 (e.g., stainless steel), a first bubbler 22a, a first mass flow controller (hereinafter, "MFC"), a first MFC 23a, a first gas cylinder 24a, a second bubbler 22b, a second MFC 23b, a second gas cylinder 24b, a first on-off valve 71, a second on-off valve 72, a third on-off valve 73, a fourth on-off valve 74, on-off valves α and β. One end of the source gas supply pipe 21 is connected to the source gas supply port 13 of the deposition chamber 10, and the other end branches off and is connected to the first bubbler 22a and the second bubbler 22b, respectively. The first bubbler 22a and the second bubbler 22b each have a mantle heater that maintains a constant temperature inside the bubbler. A first on-off valve 71 is disposed at one branch of the raw gas supply pipe 21 connecting the raw gas supply port 13 and the first bubbler 22a, and a second on-off valve 72 is disposed at the other branch of the raw gas supply pipe 21 connecting the raw gas supply port 13 and the second bubbler 22b. The first bubbler 22a is connected to the first gas cylinder 24a via a first pipe 25a. A third on-off valve 73 and a first MFC 23a are disposed in this order from the first bubbler 22a side in the first pipe 25a connecting the first bubbler 22a and the first gas cylinder 24a. The second bubbler 22b is connected to the second gas cylinder 24b via a second pipe 25b. A fourth on-off valve 74 and a second MFC 23b are disposed in this order from the second bubbler 22b side in the second pipe 25b connecting the second bubbler 22b and the second gas cylinder 24b. Furthermore, the source gas supply pipe 21 and the counter gas supply pipe 31 are connected by a third pipe 25c, and a ninth opening/closing valve 80 is disposed on the third pipe 25c.

The counter gas supply unit 30 includes a counter gas supply pipe 31 made of, for example, stainless steel, a third MFC 33, a third gas cylinder 34, a fifth on-off valve 75, and an on-off valve γ. One end of the counter gas supply pipe 31 is connected to the counter gas supply port 11 and source gas supply port 13 of the film formation chamber 10, and the other end of the counter gas supply pipe 31 is connected to the third gas cylinder 34. The on-off valve γ, the fifth on-off valve 75, and the third MFC 33 are arranged on the counter gas supply pipe 31, in this order from the counter gas supply port 11 side.

The source gas exhaust mechanism 40, which serves as an exhaust mechanism for exhausting the inside of the film formation chamber 10, includes a source gas exhaust pipe 41 made of, for example, stainless steel, a cold trap 42, a first pressure gauge 43, and a sixth on-off valve 76. One end of the source gas exhaust pipe 41 is connected to the source gas exhaust port 14 of the film formation chamber 10, and the other end of the source gas exhaust pipe 41 is connected to the cold trap 42. The exhaust side of the cold trap 42 is open to the atmosphere. The source gas exhaust pipe 41 is equipped with the first pressure gauge 43 and the sixth on-off valve 76, arranged in this order from the source gas exhaust port 14 side.

The opposing gas exhaust mechanism 50, which serves as an exhaust mechanism for exhausting the interior of the deposition chamber 10, includes an opposing gas exhaust pipe 51 made of, for example, stainless steel, a second pressure gauge 52, a rotary pump 53 serving as a vacuum pump, a first flow control valve 54a, a seventh on-off valve 77, and an eighth on-off valve 79. One end of the opposing gas exhaust pipe 51 is connected to the opposing gas exhaust port 12 of the deposition chamber 10, and the other end of the opposing gas exhaust pipe 51 is open to the atmosphere via the eighth on-off valve 79. A second pressure gauge 52 is disposed on the opposing gas exhaust pipe 51 on the opposing gas exhaust port 12 side, and a first branch opposing gas exhaust pipe 51a branches off from the opposing gas exhaust pipe 51 between the eighth on-off valve 79 and the second pressure gauge 52. The opposing gas exhaust pipe 51 is connected to the rotary pump 53. The first flow control valve 54a and the seventh on-off valve 77 are disposed on the opposing gas exhaust pipe 51, in that order from the branch point from the opposing gas exhaust pipe 51.

For example, an electric tubular furnace having a heating element made of a cylindrical module heater and a heat insulating material made of Al ₂ O ₃ —SiO ₂ ceramic fiber housed in an aluminum housing can be used as the heating processing unit 60. The electric tubular furnace is configured to be axially divided into two parts so as to be openable and closable, and has two sets of semicircular grooves in its cross section that sandwich a raw material gas supply pipe serving as the raw material gas supply port 13 and a raw material gas exhaust pipe serving as the raw material gas exhaust port 14. Furthermore, the film formation chamber 10 may be housed coaxially in the hollow portion of the heating element.

Here, the production of a gas separation material using the gas separation material manufacturing apparatus 1 will be described. First, a porous substrate S is placed in the film formation chamber 10. The raw material gas supply unit 20 supplies raw material gas to one side (outer peripheral side) of the porous substrate S in the film formation chamber 10. The counter gas supply unit 30 supplies active gas to the other side (inner peripheral side) of the porous substrate S. In this manner, the raw material gas and the active gas are counter-diffused to form a gas separation layer containing silica in the pores of the porous substrate S by chemical vapor deposition at a reaction temperature of 300°C to 800°C. Thereafter, the heat treatment unit 60 heats the gas separation layer formed by chemical vapor deposition at a temperature lower than the reaction temperature and equal to or higher than 200°C. During the heat treatment, it is preferable to perform the heat treatment with atmospheric gas supplied to at least one of the one side and the other side of the porous substrate S. The atmospheric gas is supplied using a third gas cylinder 34. When the atmospheric gas is supplied to one side of the porous substrate S, it is supplied from the third gas cylinder 34 via the raw material gas supply port 13. When the atmospheric gas is supplied to the other side of the porous substrate S, it is supplied from the third gas cylinder 34 via the opposing gas supply port 11.
By using the gas separation material manufacturing apparatus 1 of the present disclosure, the heat treatment unit 60 heats the gas separation layer formed by chemical vapor deposition at a temperature lower than the reaction temperature and not lower than 200°C, thereby removing organic matter derived from the raw material gas, thereby making it possible to manufacture a gas separation material with high gas permeability.

The heat treatment of the gas separation layer does not have to be performed in the film formation chamber 10 where chemical vapor deposition was performed. In other words, after chemical vapor deposition, the porous substrate S may be removed from the film formation chamber 10 and heat-treated in a separate container.

3. Gas Separation Material The gas separation material comprises a gas separation layer containing silica formed by counter-diffusion chemical vapor deposition using a source gas containing a silica-forming substance and an inert gas and an active gas. The gas separation material preferably comprises a porous substrate having a plurality of pores and a gas separation layer that blocks at least the inside of the pores of the porous substrate.
From the viewpoint of improving gas permeability, the gas separation layer of the gas separation material preferably has a carbon content of less than 0.3 mass %, although the carbon content may be 0 mass %.
The carbon content in the gas separation layer can be determined by measurement under the following conditions using a fully automatic elemental analyzer (organic trace element analysis: CHN analysis) (product name "vario MACRO cube", manufactured by Elementor Japan Co., Ltd.).
Combustion temperature: 1150°C
Reduction temperature: 850°C
Standard substance: sulfanilamide standard (Elementar Japan Co., Ltd.)

In the section "3. Gas separation material," the descriptions of "(1) porous substrate," "(2) feed gas," "(3) activated gas," "(4) counter-diffusion chemical vapor deposition method," "(5) heat treatment of gas separation layer," "(6) gas separation material," etc., explained in the section "1. Manufacturing method of gas separation material" will be applied as is, and these descriptions will be omitted.

The present invention will be explained in more detail below with reference to examples.
1. Effect of heat treatment temperature (evaluation by FT-IR)
It was confirmed by FT-IR that the organic matter was removed by the heat treatment.
(1) Sample Preparation (1.1) Formation of Gas Separation Layer An asymmetric α-alumina porous tube having an outer diameter of 12 mm, an axial length of 500 mm, a thickness of 1.6 mm, and communicating pores with an average pore diameter of 170 nm was prepared. After glass sealing both ends of the outer surface of this porous tube, Ni-doped γ-alumina was coated in the center and fired in air at 800 ° C. As a result, a glass seal portion S1 was formed on the outer surface of both axial ends, and a film-forming portion S2 consisting of a Ni-doped γ-alumina intermediate layer was formed on the outer surface of the axial center, and a porous substrate S was prepared as a treated material. The film-forming portion S2 had an axial length of 50 mm, a thickness of 2.5 μm, and an average pore diameter of 8 nm.

Using the gas separation material manufacturing apparatus 1, a gas separation layer containing silica was formed on the membrane formation portion S2 of the porous substrate S in the following manner.
First, the porous substrate S was inserted from one end to the other end of the film formation chamber 10. Then, both ends of the porous substrate S were fixed with vacuum fittings via a pair of O-rings, making the inside of the film formation chamber 10 airtight. The inside of the film formation chamber 10 was partitioned by the porous substrate S into a source gas supply section 15 located on the outer circumferential surface side and an opposing gas supply section 16 located on the inner circumferential surface side. The source gas exhaust port 14 was located near one end of the film formation section S2, and the source gas supply port 13 was located near the other end of the film formation section S2.

Next, the film formation chamber 10 was placed inside the heating element of an electric tubular furnace serving as the heating processing unit 60. In this state, the vacuum fitting on the opposing gas supply port 11 side was connected to the opposing gas supply pipe 31, the vacuum fitting on the opposing gas exhaust port 12 side was connected to the opposing gas exhaust pipe 51, the raw gas supply pipe serving as the raw gas supply port 13 was connected to the raw gas supply pipe 21, and the raw gas exhaust pipe 41 serving as the raw gas exhaust port 14 was connected.

Nitrogen was prepared as a carrier gas in the first gas cylinder 24a, and hexamethyldisiloxane (HMDS) was prepared as a source gas in the first bubbler 22a. Oxygen gas was prepared as a counter gas (active gas) in the third gas cylinder 34. Nitrogen was prepared as a carrier gas in the second gas cylinder 24b, and zirconium isopropoxide (ZDTH) was prepared as a source gas in the second bubbler 22b. The chemical formulas of HMDS and ZDTH are shown in Figure 2.

In the initial state, all on-off valves were closed. First, the rotary pump 53 was operated to open the seventh on-off valve 77 located on the first branched opposing gas exhaust pipe 51a, thereby reducing the pressure inside the film formation chamber 10. When the pressure inside the film formation chamber 10 reached 20 Pa, the heating unit 60 was operated to raise the temperature inside the film formation chamber 10 to 625°C. At this time, both ends of the film formation chamber 10 were cooled by cooling fans (not shown).

Next, the seventh on-off valve 77 was closed to stop the rotary pump 53, and on-off valve α was opened to introduce nitrogen gas from the first gas cylinder 24a into the film formation chamber 10, replacing the atmosphere inside the film formation chamber 10 with nitrogen gas. The temperature (reaction temperature) inside the film formation chamber 10 was maintained at 625°C. On-off valve α was closed, and the first on-off valve 71 and third on-off valve 73 were opened. The HMDS in the first bubbler 22a was bubbled with nitrogen gas to vaporize it, and the ZDTH in the second bubbler 22b was bubbled with nitrogen gas to vaporize it, and the source gases were introduced into the source gas supply port 13 of the film formation chamber 10. The sixth on-off valve 76 located on the source gas exhaust pipe 41 was opened to release excess source gas outside the film formation chamber 10.

Then, the fifth on-off valve 75 and on-off valve γ, located on the counter gas supply pipe 31, were opened to start the supply of counter gas from the third gas cylinder 34. Counter gas was supplied from the third gas cylinder 34 and the third MFC 33 to the counter gas supply section 16 of the film formation chamber 10 at a predetermined flow rate. The eighth on-off valve 79, located on the counter gas exhaust pipe 51, was opened to release excess counter gas outside the film formation chamber 10. In this way, the source gas and the counter gas were counter-diffused to form a gas separation layer by chemical vapor deposition. The reaction time was 5 minutes. The gas flow ratio (sccm) of the source gas to the counter gas was 1:5.

(1.2) Heat Treatment In a He atmosphere, the porous substrate S on which the gas separation layer was formed was heat treated at various temperatures. The heat treatment temperatures were room temperature (RT), 200°C, 300°C, 400°C, and 500°C. The treatment time was 5 hours in each case.

(2) Evaluation Method FT-IR measurement was carried out on the gas separation layer treated at each temperature.

(3) Results The results are shown in Figure 5. As the temperature increased, the absorption peaks of hydrocarbon groups (-CH ₃ , -CH ₂ -) decreased.

2. Relationship between heat treatment temperature and transmittance The relationship between heat treatment temperature and transmittance was investigated.
(1) Preparation of Samples (1.1) Formation of Gas Separation Layer A gas separation layer was formed in the same manner as described above in the section "1. Effect of Heat Treatment Temperature (1.1) Formation of Gas Separation Layer."

(1.2) Heat Treatment In an _O2 atmosphere, the porous substrate S on which the gas separation layer was formed was heat treated at various temperatures. The heat treatment temperatures were 300°C, 400°C, and 500°C. The treatment time was 5 hours in each case.

(2) Evaluation Method: For the gas separation layers treated at each heating temperature, reduced pressure permeability measurements were performed using pure gases. Reduced pressure permeability measurements are a method of calculating the gas permeability of the gas separation layer by measuring the amount of permeation from the time required for the pressure change that occurs when the gas that has permeated the gas separation layer is stored in a container with a constant volume. For the measurements, a single-component gas permeation test was performed at 50°C using a gas permeation tester based on the constant volume pressure change method. The single-component gases used were helium, hydrogen, carbon dioxide, argon, and nitrogen.
The permeation amount [mol·s ⁻¹ ·Pa ⁻¹ ] was calculated from the pressure change amount and the measured change time, and then the permeability per unit area [mol·m ⁻² ·s ⁻¹ ·Pa ⁻¹ ] was calculated. The hydrogen/argon permeability ratio (H ₂ /Ar) was calculated from the permeability values of argon gas and hydrogen gas. The hydrogen/nitrogen permeability ratio (H ₂ /N ₂ ) was calculated from the permeability values of nitrogen gas and hydrogen gas.

(3) Results The results are shown in Figure 8. As the heat treatment temperature increased, the hydrogen permeability increased. This result confirms that the higher the temperature, the better the removal of unreacted materials. It was confirmed that both the hydrogen/argon permeability ratio and the hydrogen/nitrogen permeability ratio increased as the temperature increased. In this way, the heat treatment also improved the gas selectivity of the gas separation layer.

3. Relationship between Heat Treatment Atmosphere and Transmittance The relationship between heat treatment atmosphere and transmittance was investigated. The gases for which transmittance was measured were He gas, _H2 gas, _CO2 gas, Ar gas, and _N2 gas, in order of decreasing molecular dynamic diameter.
(1) Preparation of Samples (1.1) Formation of Gas Separation Layer A gas separation layer was formed in the same manner as described above in the section "1. Effect of Heat Treatment Temperature (1.1) Formation of Gas Separation Layer."

(1.2) Heat Treatment The porous substrate S on which the gas separation layer was formed was heat treated in various atmospheres. The types of atmosphere were He atmosphere, _H2 atmosphere, _CO2 atmosphere, Ar atmosphere, _O2 atmosphere, and _N2 atmosphere. The heat treatment temperature was 400°C in all cases. The treatment time was 5 hours in all cases.

(2) Results Figure 9 shows the ratio of (transmittance after heat treatment) / (transmittance before heat treatment). In all atmospheres, the ratio value exceeded 1 for He gas, _H2 gas, and _CO2 gas, confirming the improvement in transmittance due to heat treatment. In the _O2 atmosphere, He atmosphere, and _H2 atmosphere, the improvement in transmittance was significant. _O2 is capable of burning organic matter, so it is presumed to be suitable for removing organic matter. He has a small molecular size, so it easily enters the pores of the gas separation layer, and is presumed to have an excellent effect on removing organic matter. _H2 has the effect of etching carbon, so it is presumed to have an excellent effect on removing organic matter.

4. Measurement of Carbon Content in Gas Separation Layer (1) Measurement Sample As a measurement sample, the gas separation layer heat-treated at 500° C. obtained in the above section "2. Relationship between Heat Treatment Temperature and Transmittance" was used.
(2) Measurement Method CHN analysis was performed on the measurement sample.
(3) Measurement Results The carbon content of the measured sample was less than 0.3% by mass. Organic matter was well removed from the measured sample.

The present disclosure is not limited to the embodiments detailed above, and various modifications and variations are possible within the scope of the claims.

REFERENCE SIGNS LIST 1 ...gas separation material manufacturing apparatus 10 ...film formation chamber 11 ...counter gas supply port 12 ...counter gas exhaust port 13 ...raw material gas supply port 14 ...raw material gas exhaust port 15 ...raw material gas supply section 16 ...counter gas supply section 20 ...raw material gas supply unit 21 ...raw material gas supply piping 22a ...first bubbler 22b ...second bubbler 24a ...first gas cylinder 24b ...second gas cylinder 25a ...first piping 25b ...second piping 25c ...third piping 30 ...counter gas supply unit 31 ...counter gas supply piping 34 ...third gas cylinder 40 ...raw material gas exhaust mechanism 41 ...raw material gas exhaust piping 42 ...cold trap 43 ...first pressure gauge 50 ...counter gas exhaust mechanism 51 ...counter gas exhaust piping 51a ...first branched counter gas exhaust piping 52 ...second pressure gauge 53 ...rotary pump 54a ...first flow rate adjustment valve 60 ...heat treatment unit 71 ...first opening/closing valve 72 ...second opening/closing valve 73 ...third on-off valve 74 ...fourth on-off valve 75 ...fifth on-off valve 76 ...sixth on-off valve 77 ...seventh on-off valve 79 ...eighth on-off valve 80 ...ninth on-off valve α ...on-off valve β ...on-off valve γ ...on-off valve δ ...on-off valve 101 ...porous substrate 101A ...one surface side 101B ...other surface side 101C ...pores 103 ...raw material gas 105 ...active gas 107 ...gas separation layer 23a ...first MFC
23b...Second MFC
33...3rd MFC

Claims (8)

In the deposition chamber,
A raw material gas containing a vaporized silica-forming substance, a compound represented by the following formula (1), and an inert gas is supplied to one surface side of the porous substrate,
An active gas serving as a reactive species is supplied to the other surface side of the porous substrate;
A method for producing a gas separation material, comprising: diffusing the raw material gas and the activated gas in a counter-diffusion manner, setting the temperature inside the film formation chamber at 300°C or higher and 800°C or lower, and forming a gas separation layer containing silica in the pores of the porous substrate by chemical vapor deposition,
The gas separation layer formed by the chemical vapor deposition is further heated at a temperature lower than the temperature in the film formation chamber during the chemical vapor deposition and at 200°C or higher to remove organic matter derived from the raw material gas remaining in the gas separation layer.
During the chemical vapor deposition, the temperature inside the film formation chamber is set to 550° C. or higher and 750° C. or lower,
The method for producing a gas separating material according to claim 1 , wherein the heat treatment for removing hydrocarbons derived from the raw material gas remaining in the gas separation layer is carried out at a temperature of 250° C. or higher and 500° C. or lower. The method for producing a gas separation material according to claim 1 or 2, wherein the heat treatment is carried out in an atmosphere of a gas containing one or more selected from the group consisting of oxygen, helium, hydrogen, argon, and nitrogen. The method for producing a gas separation material according to claim 3, wherein during the heat treatment, the gas pressure difference between the gas pressure on one side of the porous substrate and the gas pressure on the other side of the porous substrate is 10 kPa or more and 980 kPa or less. a raw material gas supply unit that supplies a raw material gas containing a vaporized silica-forming substance, a compound represented by the following formula (1), and an inert gas to one surface side of the porous substrate in the film formation chamber;
an active gas supply unit that supplies an active gas that serves as a reactive species to the other surface side of the porous substrate in the film formation chamber;
a gas separation material manufacturing apparatus in which the raw material gas and the activated gas are diffused in opposite directions, the temperature inside the film formation chamber is set to 300°C or higher and 800°C or lower, and a gas separation layer containing silica is formed in the pores of the porous substrate by chemical vapor deposition,
A gas separation material manufacturing apparatus further comprising a heating element that heats the gas separation layer formed by the chemical vapor deposition at a temperature lower than the temperature in the film formation chamber during the chemical vapor deposition and at 200°C or higher, thereby removing organic matter derived from the raw material gas remaining in the gas separation layer.
During the chemical vapor deposition, the temperature inside the film formation chamber is set to 550° C. or higher and 750° C. or lower,
6. The gas separation material manufacturing apparatus according to claim 5, wherein the heat treatment for removing hydrocarbons derived from the raw material gas remaining in the gas separation layer is carried out at a temperature of 250°C or higher and 500°C or lower. The gas separation material manufacturing apparatus according to claim 5 or 6, wherein the heat treatment is carried out in an atmosphere of gas containing one or more selected from the group consisting of oxygen, helium, hydrogen, argon, and nitrogen. The gas separation material manufacturing apparatus of claim 7, wherein during the heat treatment, the gas pressure difference between the gas pressure on one side of the porous substrate and the gas pressure on the other side of the porous substrate is 10 kPa or more and 980 kPa or less.