JP7420473B2 - Gas separation material and its manufacturing method - Google Patents

Description

The present invention relates to a gas separation material for separating and purifying specific gas components from a mixed gas, and a method for producing the same.

Chemical vapor deposition (CVD) is known as a technique for forming a thin film by depositing evaporated substances on the surface of a material to be treated. Chemical vapor deposition is often used to manufacture ceramic gas separation materials used to separate and purify specific gas components such as hydrogen gas from mixed gases. Ceramic gas separation materials are capable of gas separation through the sub-nano-sized pores that the material itself has, and in particular, membranes containing silicon oxide, carbon, silicon carbide, etc. as the main components are used as the separation active layer. There is. Since the gas permeation rate is inversely proportional to the membrane thickness, it is effective to use an extremely thin separation active layer because it increases the permeation rate during gas separation and increases the separation throughput. Furthermore, in order to improve gas separation characteristics, a separation active layer with fewer defects is desired.

As a method for manufacturing a silicon carbide film (SiC film) used as a separation active layer, Non-Patent Document 1 describes a chemical vapor phase impregnation method using SiH ₂ Cl ₂ as a Si source and C ₂ H ₂ as a C source. Vapor Infiltration (CVI) is disclosed. FIG. 9(A) is a schematic diagram explaining the concept of CVI. In CVI, since the raw material gas and the reaction gas that reacts with the raw material gas are supplied to the pores from the same direction, the surface of the porous base material is A reaction product is formed nearby. In Non-Patent Document 1, by further depositing SiC into the unsealed pores of a SiC film formed using polycarbosilane as a precursor by CVI, the surface of the porous base material as a whole is improved. A covering SiC film with a thickness of about 130 nm is formed. This SiC membrane can be used as a hydrogen separation membrane for steam reforming (methane is reacted with steam on a catalyst to be converted into hydrogen and carbon dioxide). The gas separation coefficient is used as an index of the gas separation characteristics of such a membrane. In particular, the gas separation coefficient expressed as the ratio of the permeability of pure gas is called the ideal separation coefficient, and according to Non- _Patent Document 1, the permeability of hydrogen gas (P The ideal separation coefficient (P _H2 /P _CO2 ) expressed as the ratio of P _H2 ) is about 15 at 600°C. In order to use a SiC membrane as a hydrogen separation membrane, it is practically desirable to manufacture a SiC membrane with a thin film thickness in order to increase the amount of permeation of the gas to be separated, and with low defects in order to improve gas separation characteristics. .

Incidentally, a SiC film is usually formed on a porous support base material made of a porous material, and α-alumina, which is often used as a support base material, has a thermal expansion coefficient of 7.2×10 ^-6 /°C ( 40 to 400°C), and the thermal expansion coefficient of SiC is 3.7×10 ⁻⁶ /°C. Therefore, as the SiC film formed on the support base material becomes thicker, the residual stress due to the difference in thermal expansion coefficient increases, and peeling of the SiC film is more likely to occur. It is possible to reduce residual stress and suppress peeling of the SiC film by making the thickness of the SiC film extremely thin. However, ultra-thin membranes are prone to defects and cannot provide high gas separation properties.

On the other hand, counter-diffusion CVD is advantageous because it can perform vapor deposition so as to seal the inside of the pores of the porous support base material, and is therefore less susceptible to differences in thermal expansion. Patent Document 1 discloses a method for manufacturing a silicon oxide film (silica film) using counter-diffusion CVD. FIG. 9(B) is a schematic diagram illustrating the concept of counter-diffusion CVD. In counter diffusion CVD, a source gas (for example, an organic silicon compound gas) and a counter gas (for example, oxygen gas) that reacts with the source gas are diffused in opposite directions from both ends of the pores of a porous base material. A silica film is formed by reaction. The reaction products are deposited on the inner walls of the pores, and as the reaction progresses, the pores are blocked by the reaction products, so that the reaction is terminated by preventing contact between the two gases. As a result, the closed portion F formed within the pore becomes an extremely thin film with few defects.

Japanese Patent Application Publication No. 2008-246295

Helium-Permselective Amorphous SiC Membrane Modified by Chemical Vapor Infiltration, Soft Materials Volume 4, 2007, Issue 2-4, 109-122

When forming a silica film by counter-diffusion CVD, the silicon adhering to the inner walls of the pores oxidizes and expands in volume, which tends to fill the pores and prevents contact between the raw material gas and the counter gas at an early stage. The closed portion F (FIG. 9(B)) is likely to be formed thin. On the other hand, no attempt has been made to use counter-diffusion CVD to form a SiC film. In the process of producing SiC, even if the thermal decomposition products of the raw material gas are deposited on the inner walls of the pores, no volumetric expansion occurs, so the pores are difficult to fill in the reaction process of counter-diffusion CVD. Therefore, it is presumed that the reaction does not end and continues, and a film similar to that deposited by CVI is formed at and around the openings of the pores. Therefore, it is considered difficult to form a low-defect and extremely thin SiC film by counter-diffusion CVD.

Furthermore, Patent Document 1 discloses that after supplying a raw material gas and a counter gas for a certain period of time and causing them to react in a counter supply manner, at least the supply of the counter gas is stopped and the supply is changed to unidirectional supply. A film forming method is disclosed in which directional supply is performed multiple times. By changing the unidirectional supply method, the gas permeability and gas separation coefficient change, but the detailed mechanism behind this phenomenon is not known.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a silicon carbide-based gas separation material with improved gas separation characteristics compared to the conventional one, and a method for manufacturing the same.

As a result of intensive research to solve this problem, the present inventors have succeeded in manufacturing a silicon carbide-based gas separation material that can be practically used as a gas separation material using counter-diffusion CVD, and have developed a new material with high gas separation properties. This led to the production of gas separation materials.

That is, the method for producing a gas separation material of the present invention is to form a gas separation layer by chemical vapor deposition in which a raw material gas and a counter gas are reacted, which are diffused in opposite directions from both ends of the pores of an inorganic porous part having a plurality of pores. In a method for producing a gas separation material forming a
The raw material gas contains a compound containing carbon (C) and silicon (Si), and the reaction step is repeatedly carried out while carrying out the raw material gas supply step of supplying the raw material gas to one end side of the pore. The process is
a counter gas supply step of supplying a counter gas that reacts with the compound to produce silicon carbide to the other end side of the pore;
a counter gas stop step of stopping the supply of the counter gas, which is performed after the counter gas supply step;
A raw material gas introducing step of drawing the raw material gas from one end side of the pore to the other end side, which is performed simultaneously with the opposing gas stopping step or after the opposing gas stopping step;
including.

As described above, in the reaction process of silicon carbide in counter-diffusion CVD, pores are difficult to fill with silicon carbide-based products. Therefore, the counter gas continues to contact and react with the source gas. In particular, when hydrogen gas with a small molecular dynamic diameter is used as the counter gas, the hydrogen gas easily permeates the product, and the permeated hydrogen gas exists in high concentration at one end where the pore opens. Easy to come into contact with raw material gas. The present inventors have noticed that such a phenomenon in the reaction process of silicon carbide promotes the formation of a thick film that covers the surface of the inorganic porous portion and, in turn, the generation of defects. According to the method for producing a gas separation material of the present invention, in the reaction step, after the counter gas is supplied, the supply of the counter gas is temporarily stopped and the raw material gas is drawn from one end of the pore to the other end. By repeating this reaction step, the raw material gas present in high concentration at one end of the pore can be moved to the other end of the pore while the reaction itself is temporarily stopped. As a result, it is presumed that silicon carbide-based products are formed on the inner walls of the pores of the inorganic porous portion, resulting in an extremely thin, low-defect film that blocks the insides of the pores. A gas separation material having such a gas separation layer has excellent gas separation properties.

Further, the gas separation material of the present invention includes an inorganic porous part having a plurality of pores, and a gas separation layer containing silicon carbide and closing at least the inside of the pores of the inorganic porous part, The gas separation layer has an external part protruding from the pores of the inorganic porous part, and the film thickness in the external part from the surface of the inorganic porous part to the surface of the external part is 100 nm or less. .

Alternatively, the gas separation material of the present invention includes an inorganic porous part having a plurality of pores, and a gas separation layer containing silicon carbide and closing at least the inside of the pores of the inorganic porous part, and It can also be considered that the ideal separation coefficient, expressed as the ratio of hydrogen permeability to carbon permeability, is 1000 or more at 400°C.

The gas separation material of the present invention has higher gas separation properties than conventional ones. Further, according to the method for producing a gas separation material of the present invention, it is possible to produce a silicon carbide-based gas separation material with improved gas separation characteristics than before by counter-diffusion CVD.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram illustrating an embodiment of the method for producing a gas separation material of the present invention, in which a counter gas supply step and a raw material gas introduction step are performed simultaneously in a reaction step. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram illustrating an embodiment of the method for producing a gas separation material of the present invention, in which a source gas introduction step is performed after a counter gas supply step in a reaction step. It is a schematic diagram of the gas separation material of an Example, and the vapor deposition processing apparatus used for its manufacturing method. FIG. 2 is a schematic diagram showing an inorganic porous part used in a gas separation material and a method for producing the same according to an example. 1 is a schematic diagram of a gas permeation test device using a constant volume pressure change method. 1 is a graph showing gas permeation characteristics of a gas separation material obtained by the method for manufacturing a gas separation material of Example 1. 1 is a scanning electron microscope image (SEM image) and energy dispersive X-ray analysis (EDS) results of a cross section of the gas separation material of Example 1. 1 is an energy dispersive X-ray analysis (EDS) result of a cross section of the gas separation material of Example 1. FIG. 2 is a schematic diagram illustrating the concepts of (A) CVI and (B) counter-diffusion CVD.

EMBODIMENT OF THE INVENTION Below, the form for implementing the gas separation material of this invention and its manufacturing method is demonstrated. Note that a numerical range can be constructed by arbitrarily combining the upper and lower limits of the numerical ranges described in this specification, as well as the numerical values listed in the examples.

<Method for producing gas separation material>
In the method for producing a gas separation material of the present invention, a gas separation layer is formed by chemical vapor deposition in which a counter gas reacts with a raw material gas which is diffused in opposite directions from both ends of the pores of an inorganic porous part having a plurality of pores. Form. Therefore, the method for producing a gas separation material of the present invention can basically be carried out using a membrane forming apparatus for opposed diffusion CVD that has been conventionally used for producing various inorganic membranes. Note that the inorganic porous portion will be explained later.

In the method for producing a gas separation material of the present invention, the reaction step is repeatedly carried out while carrying out the raw material gas supply step of supplying the raw material gas to one end side of the pores of the inorganic porous part. The raw material gas contains a compound containing carbon (C) and silicon (Si), preferably a compound containing hydrogen (H) in addition to C and Si. In other words, the raw material gas contains a compound that can be used as both a Si source and a C source for silicon carbide-based products. Such a compound includes preferably a compound having a Si--C bond, and more preferably a compound containing a C--C bond in addition to the Si--C bond. Further, a compound containing a cyclic structure is desirable. Specifically, t-butylsilane (tert-C ₄ H ₉ SiH ₃ ), silacyclobutane (H ₂ Si-(CH ₂ CH ₂ CH ₂ )-), 1,4-disilabutane (H ₃ SiC ₂ H ₄ SiH ₃ ), tris(methylamino)ethylsilane ( _C2H5Si [NH(CH) ₃ ] ₃ ), and tris(dimethylamino)silane (Si[N( _CH3 ) ₂ ] _3H ) _. It will be done. It is desirable to use one or more of these in a gaseous state. Since many of the above compounds are liquid at room temperature, it is preferable to gasify them using a bubbling method in which the liquid is stored in a bubbler maintained at a constant temperature and the liquid is vaporized by the action of a carrier gas. That is, the raw material gas may further contain one or more types of inert gases such as nitrogen gas, helium gas, argon gas, and krypton gas as a carrier gas. The temperature of the bubbler is not particularly limited, but is preferably 15 to 30°C, more preferably 20 to 25°C. Furthermore, the raw material gas may contain one or more types of inert gases such as nitrogen gas, helium gas, argon gas, and krypton gas as a diluent gas. It is practical that the carrier gas and the diluent gas are contained in an amount of 85 to 99.5% by volume, more preferably 90 to 99% by volume, when the raw material gas is 100% by volume. Furthermore, a gas mixer may be used to mix multiple types of gases or to mix gases containing additive elements. For example, C sources include hydrocarbon gases such as CH ₄ , C ₃ H ₈ , C ₄ H ₁₀ and C ₂ H ₂ , CO gas, and Si sources include silane compound gases such as SiH ₄ and SiH ₂ Cl ₂ . .

A particularly desirable compound contained in the raw material gas is a compound having an Si--C bond and a cyclic structure, and specifically, silacyclobutane. It is presumed that the presence of the network structure composed of Si and C of silacyclobutane in the silicon carbide structure as the separation active layer contributes to improving the gas separation coefficient of the gas separation material.

The counter gas is not particularly limited as long as it can react with the above-mentioned raw material gas to produce silicon carbide, but a reducing gas is preferable. By decomposing the above-mentioned raw material gas by applying energy in a reducing atmosphere, a silicon carbide-based reaction product is deposited in the inorganic porous portion. Specifically, hydrogen gas (H ₂ ) is preferable, and an inert gas may be included together with the hydrogen gas. By using a counter gas that essentially contains hydrogen gas, if the silicon carbide-based product contains an amorphous structure, the non-bond terminations that lead to defects in the amorphous structure are terminated with hydrogen. , is effective because it stabilizes the amorphous structure.

The raw material gas is decomposed and deposited in the pores in a pressure balance with the opposing gas in the reaction process described below. There is no particular limitation on the method of decomposing the raw material gas, and it is desirable to heat the raw material gas supplied into the pores of the inorganic porous part. That is, it is desirable that the source gas supply step is a step in which thermally decomposed source gas is supplied. The thermal decomposition temperature is preferably 300 to 650°C, more preferably 400 to 550°C, particularly preferably 460 to 530°C. Therefore, the compound contained in the raw material gas preferably has a decomposition temperature of 650°C or lower, more preferably 150 to 450°C, particularly preferably 180 to 400°C. By performing the reaction at a relatively low temperature of 650° C. or lower, amorphous silicon carbide is likely to be produced. A convenient method for thermal decomposition is, for example, to heat the entire inorganic porous portion from the outside using a heater or the like. Other methods include use of electromagnetic waves such as radio wave irradiation such as high frequency waves and microwaves, light irradiation such as ultraviolet rays, and laser irradiation, as well as plasma irradiation.

In the method for producing a gas separation material of the present invention, the reaction step is repeatedly carried out while carrying out the raw material gas supply step of supplying the raw material gas to one end side of the pores of the inorganic porous part. The reaction step includes a counter gas supply step, a counter gas stop step, and a raw material gas introduction step. The reaction process will be explained in detail below.

<Counter gas supply process>
The counter gas supply step is a step of supplying a counter gas that reacts with a compound to produce silicon carbide to the other end side of the pores of the inorganic porous portion. Since the counter gas supply step is performed while performing the raw material gas supply step, a more desirable silicon carbide-based gas separation layer is formed by adjusting the flow rate balance of the raw material gas and the counter gas. The flow rates of the raw material gas and the counter gas are appropriately determined depending on the volume of the inorganic porous part, the area where the gas separation layer is formed, and the volume of the processing space. /min) is preferably 1:9 to 9:1, more preferably 2:8 to 6:4.

<Opposing gas stop process>
The counter gas stopping process is a process of stopping the supply of the counter gas, which is performed after the counter gas supply process. Since it is only necessary to stop the supply of counter gas to the pores, a normal method such as blocking the gas flow path communicating from the gas supply source to the inorganic porous portion may be used. The counter gas stopping process is performed while the raw material gas supply process is being carried out, but at this time, since most of what exists around the inorganic porous part is the raw material gas, it acts in the direction of substantially stopping the reaction. .

In the reaction step, the timing of changing from the counter gas supply step to the counter gas stop step will be described later.

<Raw material gas introduction process>
The raw material gas introducing step is a step of drawing the raw material gas from one end side of the pores of the inorganic porous portion to the other end side, which is performed simultaneously with the opposing gas stopping step or after the opposing gas stopping step. The raw material gas introduction process is also performed while the raw material gas supply process is being carried out, so for example, by applying a differential pressure between one end of the pore and the other end, the raw material gas can be easily transferred to one end of the pore. from the other end. The raw material gas introduction step is preferably a raw material gas exhausting step in which the raw material gas is supplied to one end of the pores of the inorganic porous part and exhausted from the other end. With a simple configuration such as reusing a pump or adding another vacuum pump, the raw material gas can be drawn from one end of the pore to the other end.

By drawing the raw material gas from one end of the pore to the other end while the reaction is essentially stopped, the gas is present at a high concentration at one end of the pore while the reaction itself is temporarily stopped. The source gas can be moved to the other end of the pore. In this state, if the counter gas supply is restarted and the reaction process is repeated, the silicon carbide products generated in the reaction of the previous counter gas supply process will be located in the vicinity of the silicon carbide-based products, specifically in the fine areas of the inorganic porous part. Since the reaction can be restarted inside the pores, it is thought that it is possible to suppress thickening of the film and reduce defects. In particular, since the raw material gas introduction step reduces the concentration of the raw material gas present on the surface of the inorganic porous part, the generation of silicon carbide-based products that cover the surface of the inorganic porous part is suppressed. It is desirable to repeat the reaction step desirably three times or more, more desirably five times or more. It is thought that by ensuring repeated reactions inside the pores of the inorganic porous portion, it is possible to suppress the increase in thickness of the gas separation layer. Note that it is practical to carry out the reaction step desirably 5 times or less, and more desirably 10 times or less.

FIG. 1 and FIG. 2 are diagrams schematically showing one embodiment of the reaction step in the method for producing a gas separation material of the present invention. The horizontal axis shows the passage of time, and "ON" and "OFF" indicate whether each gas is supplied (indicated by a solid line) or introduced (indicated by a dotted line). While the counter gas supply step A is performed together with the raw material gas supply step that is performed continuously in the reaction process, the raw material gas and the counter gas react, and silicon carbide-based products, which are reaction products, are absorbed into the pores. is deposited on. In the embodiment shown in FIG. 1, following the counter gas supply step A, the counter gas stop step B and the raw material gas introduction step B are performed simultaneously. These steps A and B constitute one cycle. Alternatively, in the embodiment shown in FIG. 2, the counter gas supply step A is followed by the counter gas stop step C, and the counter gas stop step C is followed by the source gas introduction step D. These steps A, C, and D constitute one cycle. In steps B, C, and D, there is basically no contact between the raw material gas and the counter gas, and the reaction substantially stops. In other words, it can be said that one cycle consists of a step in which a silicon carbide-based reaction product is produced and a step in which the production is stopped.

The execution time of one cycle is not particularly limited and is appropriately determined depending on the area where the gas separation layer is formed and the pore diameter, but the execution time per cycle is preferably 25 to 180 seconds, more preferably 50 seconds. ~100 seconds. By setting the execution time per cycle to 25 seconds or more, the flow rate of the opposing gas is stabilized and the reproducibility of film formation is improved. If the execution time per cycle is 180 seconds or less, excessive consumption of the raw material gas can be suppressed and the balance between the raw material gas and the counter gas can be maintained. Further, the implementation time of process A and process B per cycle is the ratio of the implementation time of process A to the implementation time of process B, which is preferably 1:2 to 2:1, more preferably 2:3 to 3: It is 2. Note that the implementation time of process B per cycle can be regarded as the sum of the implementation times of process C and process D per cycle. Furthermore, the implementation time of Step C and Step D is the ratio of the implementation time of Step C to the implementation time of Step D, and is preferably 1:2 to 1:10, more preferably 1:3 to 1:9. Although FIGS. 1 and 2 show the same execution time for each cycle, the execution time may be changed for each cycle.

<Other processes>
The method for producing a gas separation material of the present invention may further include other steps depending on the use of the gas separation material to be produced. For example, after the reaction step described above, only a counter gas supply step may be performed. Further, depending on the material of the inorganic porous part, a reduction step for reducing the inorganic porous part may be performed before the reaction step. The reduction step is effective when the material constituting the inorganic porous portion contains an additive metal.

<Gas separation material>
The gas separation material of the present invention includes an inorganic porous portion having a plurality of pores, and a gas separation layer containing silicon carbide and closing at least the inside of the pores of the inorganic porous portion. Note that the gas separation material of the present invention can be manufactured by the method for manufacturing the gas separation material of the present invention described in detail above.

The inorganic porous part is not particularly limited as long as it has a plurality of pores. The inorganic porous portion is preferably a porous body having pores penetrating linearly or in a mesh pattern, in other words, communicating pores, in order to cause the raw material gas and the counter gas to diffuse in opposite directions. However, in chemical vapor deposition, when the source gas and counter gas are reacted, the temperature around the inorganic porous portion may become high, so it is preferable to use a thermally stable material. Specific examples include α-alumina, mullite, cordierite, and silicon carbide. However, these inorganic porous materials usually have communicating pores with an average pore diameter of 150 to 1000 nm, so counter-diffusion CVD is used to block the pores with a reaction product to form a gas separation layer inside the pores. Not suitable for forming. When forming a gas separation layer inside the pores, an inorganic porous intermediate layer having an average pore diameter of about 1 to 10 nm formed in an inorganic porous member made of the above-mentioned inorganic porous material is used as an inorganic porous intermediate layer. It is preferable to use it as a part. In particular, for a gas separation layer mainly composed of silicon carbide, an intermediate layer made of γ-alumina having pores with an average pore size of preferably 10 nm or less, more preferably 9 nm or less, particularly preferably 8 nm or less is used. Good to use. Among these, a γ-alumina intermediate layer containing nickel (Ni) as an added metal element is suitable from the viewpoint of moisture resistance required for a gas separation material. That is, the inorganic porous portion is preferably composed of an alumina-based material containing aluminum (Al), oxygen (O), and nickel (Ni). If the lower limit of the average pore diameter of the pores in the γ-alumina intermediate layer is to be defined, it is preferably 2 nm, more preferably 3 nm, and particularly preferably 4 nm. Such a γ-alumina intermediate layer is preferably formed on the surface of an inorganic porous member having pores with an average pore diameter of preferably 40 to 200 nm, more preferably 60 to 150 nm. The thickness of the intermediate layer is not limited, but is preferably 1 to 6 μm, more preferably 2 to 5 μm. The γ-alumina intermediate layer can be formed by a known method.

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

The shape of the inorganic porous member is selected depending on the purpose and use, and may be any of plate, columnar, cylindrical, semi-cylindrical, rod-like, block-like, etc. The size of the inorganic porous member is also selected depending on the purpose and use, and examples include cylindrical shapes such as square tubes and cylinders, and plate shapes such as curved plates and flat plates. When the shape of the inorganic porous member is a cylindrical shape suitable for a gas separation material, the outer diameter is preferably φ2 to 16 mm, more preferably φ5 to 13 mm.

The gas separation layer contains silicon carbide and closes at least the inside of the pores of the inorganic porous portion. It is preferable that the gas separation material is formed on the inner walls of the pores of the inorganic porous part to block the insides of the pores, and basically, it is preferable that the gas separation material exists only inside the pores. In other words, it is preferable that the gas separation layer does not include any protruding parts that protrude from the pores of the inorganic porous part. However, if the outgoing part is intentionally defined, the film thickness in the outgoing part from the surface of the inorganic porous part to the surface of the outgoing part is preferably 100 nm or less, more preferably 10 nm or more and 60 nm or less. In order to confirm the gas exit part, a cross section of the gas separation material whose surface is coated with platinum is subjected to SEM/EDS analysis using an energy dispersive X-ray analyzer attached to a scanning electron microscope. This is possible by observing the nearby outermost surface. If the film thickness of the external portion is thick, the amount of gas permeation is reduced, which lowers the processing capacity, and it is also undesirable because it causes defects such as easy cracking and leads to a reduction in gas separation characteristics.

The silicon carbide contained in the gas separation layer preferably includes amorphous silicon carbide. Since amorphous materials do not have grain boundaries, they are less likely to have defects and have excellent gas separation properties. In addition, in order to manufacture a gas separation layer containing an amorphous substance, as mentioned above, it is desirable to select a raw material gas with a low decomposition temperature and to react at a low temperature.

The gas separation material of the present invention preferably has an ideal separation coefficient (H ₂ /CO ₂ ) expressed as a ratio of hydrogen permeability to carbon dioxide permeability of 1000 or more and more preferably 2000 or more at 400°C. Note that, if the upper limit of the ideal separation coefficient is to be specified, it is preferably 20,000 or less, and more preferably 10,000 or less. The permeability of hydrogen gas and carbon dioxide gas is calculated from the measured value of permeation amount by "constant volume pressure change method".

Although the embodiments of the gas separation material and the method for producing the same of the present invention have been described above, the present invention is not limited to the above embodiments. Which embodiment is best depends on the required performance, intended use, etc., but the present invention may be implemented in various forms with changes and improvements that can be made by those skilled in the art without departing from the gist of the present invention. I can do it.

The present invention will be specifically explained below by giving examples of the gas separation material of the present invention and its manufacturing method. FIG. 3 schematically shows the vapor deposition processing apparatus used in Example 1, and FIG. 4 schematically shows the inorganic porous member used in Example 1.

<Example 1>
(1) Vapor Deposition Processing Apparatus The vapor deposition processing apparatus includes a processing chamber 10, a raw material gas supply means 20, a counter gas supply means 30, a raw material gas introduction means 40, and an energy application means 50.

The processing chamber 10 includes a cylindrical reactor 11 made of stainless steel and having both axial ends connectable to piping via vacuum joints 16 and 17. The reactor 11 has an inner diameter of 28 mm, a total length of 476 mm, and two openings 18 and 19 are formed in the outer peripheral surface.

The raw material gas supply means 20 is composed of a raw material gas supply pipe 218, a raw material gas pipe 21, a bubbler 22, mass flow controllers (hereinafter abbreviated as "MFC") 23, 23d, and gas cylinders 24, 24d, and further includes a raw material gas supply pipe 218, a raw material gas pipe 21, a bubbler 22, a mass flow controller (hereinafter abbreviated as "MFC") 23, 23d, and gas cylinders 24, 24d. A gas release pipe 219, a raw material gas release pipe 29, and a cold trap 28 are provided. The raw material gas supply pipe 218 is made of stainless steel and is welded to the opening 18 so as to extend from the opening 18 toward the outer peripheral side of the reactor 11 in the radial direction. The raw material gas pipe 21 is a stainless steel pipe, and connects the raw material gas supply pipe 218 and the bubbler 22. The gas cylinder 24 is connected to the bubbler 22 , and an MFC 23 and an opening/closing valve 25 are installed between the gas cylinder 24 and the baffler 22 to control the flow rate of gas supplied from the gas cylinder 24 to the bubbler 22 . Further, an on-off valve 25b is installed between the raw material gas supply pipe 218 and the bubbler 22. The gas cylinder 24d is connected to a branched end of the source gas pipe 21, and an MFC 23d for controlling the flow rate and an on-off valve 25d are installed between the gas cylinder 24d and the source gas supply pipe 218. Further, the raw material gas discharge pipe 219 is made of stainless steel and is welded to the opening 19 so as to extend from the opening 19 toward the radially outer peripheral side of the reactor 11 . The raw material gas discharge pipe 29 is a stainless steel pipe, and connects the raw material gas discharge pipe 219 and the cold trap 28 . The pressure gauge 27 and the on-off valve 26 are installed between the raw material gas discharge pipe 219 and the cold trap 28.

The counter gas supply means 30 includes a counter gas pipe 31, an MFC 32, and a gas cylinder 33. The counter gas pipe 31 is a stainless steel pipe, and one end of the counter gas pipe 31 is connected to one end of the reactor 11 via the vacuum joint 17, and the other end of the counter gas pipe 31 is connected to the gas cylinder 33. It is connected. An on-off valve 36 and an MFC 32 are attached to the opposing gas pipe 31. The MFC 32 controls the flow rate of gas flowing out from the gas cylinder 33 to the reactor 11 when the on-off valve 36 is opened.

The raw material gas introducing means 40 is mainly composed of an exhaust pipe 49 branching in two directions and a rotary pump 48 connected to one of the branches. The exhaust pipe 49 is made of stainless steel, and one end of the exhaust pipe 49 is connected to the other end of the reactor 11 via the vacuum joint 16, and the other branched end of the exhaust pipe 49 is connected to the on-off valve 44. and is connected to a rotary pump 48 via a flow rate adjustment valve 46. Further, an on-off valve 45 is attached to the other branched end of the exhaust pipe 49, and by alternately opening and closing the on-off valves 44 and 45, the introduction of raw material gas by the rotary pump 48 and the discharge of counter gas are switched. . The pressure gauge 47 is located before the exhaust pipe 49 branches, and measures pressure changes within the reactor 11.

The energy imparting means 50 uses a ceramic electric tubular furnace in which a cylindrical heating element 51 and a heat insulating material 52 are housed in an aluminum casing 53. The ceramic electric tubular furnace is configured to be able to be opened and closed in two parts in the axial direction, and has a semicircular groove in its cross section that can hold the raw material gas supply pipe 218 and the raw material gas discharge pipe 219 in the closed state. Further, ring-shaped heat-resistant spacers 54 and 55 are placed on both ends of the heating element 51, and the reaction tubes 11 are accommodated in the hollow portion of the heating element 51 so as to be coaxial with each other. Since the total length of the heating element 51 is shorter than the total length of the reactor 11, both ends of the reactor 11 protrude from the ceramic electric tubular furnace. Cooling fans (not shown) are attached to the outer sides of both ends of the energy applying means 50 for the purpose of cooling the vicinity of the rubber O-rings 14 and 15 used in the vacuum joints 16 and 17, respectively.

(2) Inorganic porous member The inorganic porous member S is formed by forming a γ-alumina intermediate layer S1 and a glass seal S2 on the outer surface of a tubular base material S0 made of α-alumina. The γ-alumina intermediate layer S1 formed in the longitudinal center of the inorganic porous member S is an inorganic porous part Ps on which a silicon carbide-based product is deposited.

As the base material S0, an α-alumina tube manufactured by NOK Corporation was used, which had an outer diameter of φ3 mm, a thickness of 300 μm, a length of 400 mm, had communicating pores with an average pore diameter of 150 nm, and was glass-sealed for 175 mm from both ends. . A boehmite-based mixture containing Ni was applied as an inorganic porous part Ps to the unsealed width (longitudinal length; hereinafter the same) 50 mm central part of the base material S0, and then heated to 800 °C. By firing, a γ-alumina intermediate layer S1 containing Ni as an added metal element was formed. By performing coating and baking twice, an intermediate layer S1 having a thickness of 2.4 μm (as confirmed by the SEM image in FIG. 7) and an average pore diameter of 8 nm (50% permeation flux diameter) was obtained.

(3) Preparation of gas separation material A silicon carbide-based gas separation layer was formed in the inorganic porous part Ps using the vapor deposition processing apparatus shown in FIG. The inorganic porous member S was inserted from one end of the processing chamber 10 to the other end. Both ends thereof were fixed with vacuum joints 16 and 17 via a pair of O-rings 14 and 15, so that the inside of reactor 11 was made airtight. The inside of the reactor 11 was divided by the inorganic porous member S into a raw material gas supply side 12 located on the outer peripheral surface side and a counter gas supply side 13 located on the inner peripheral surface side.

Next, the reactor 11 was housed in a heating element 51 of a ceramic electric tubular furnace. In this state, the vacuum joint 16 and the exhaust pipe 49, the vacuum joint 17 and the counter gas pipe 31, the raw material gas supply pipe 218 and the raw material gas pipe 21, and the raw material gas discharge pipe 219 and the raw material gas discharge pipe 29 were connected, respectively.

Argon gas was prepared in the gas cylinders 24 and 24d, and hydrogen gas was prepared in the gas cylinder 33, respectively. The bubbler 22 was prepared with silacyclobutane (SCB: decomposition temperature 200°C). That is, a mixed gas of SCB and argon gas was used as the raw material gas, and hydrogen gas was used as the counter gas. In the initial state, each valve 25, 25b, 25d, 26, 36, 44, 45, and 46 were all closed.

First, the rotary pump 48 was operated to open the valves 44 and 46 to reduce the pressure inside the reactor 11. When the pressure inside the reactor 11 reached 20 Pa, the heating element 51 was activated to raise the temperature inside the reactor 11 to 515°C. At this time, both ends of the reactor 11 were cooled by cooling fans (not shown). Next, the valve 44 is closed, the valves 26 and 25d are opened, and the inside of the reactor 11 is purged with argon gas from the gas cylinder 24d. After that, the valves 45 and 36 are opened, hydrogen gas is introduced into the reactor 11 from the gas cylinder 33, and the inorganic porous The mass part Ps was subjected to hydrogen reduction treatment for 2 hours. After the hydrogen reduction treatment, the valve 36 was closed and the inside of the reactor 11 was purged with argon gas from the gas cylinder 24d.

[Raw material gas supply process]
Following the hydrogen reduction treatment, the temperature inside the reactor 11 was maintained at 515°C. The temperature of the bubbler 22 was 25°C. In order to lower the raw material concentration, 64.3 mL/min of argon gas was flowed as a dilution gas from the gas cylinder 24d by the MFC 23d. Next, the valve 25 was opened and 7.2 mL/minute of argon gas was flowed through the MFC 23 to bubble the SCB in the bubbler 22. The valve 25b was opened and the raw material gas was introduced into the raw material gas supply side 12 of the reactor 11. The valve 26 was opened so that excess raw material gas was discharged outside the reactor 11.

[Reaction process]
[Opposing gas supply process]
The valve 36 was opened, and hydrogen gas was introduced into the opposing gas supply side 13 (the inner peripheral side of the inorganic porous member S) of the reactor 11 at a rate of 275 mL/min. Valve 45 was opened so that excess counter gas was discharged to the outside of reactor 11. In this state, SCB gas and hydrogen gas were counter-diffused for 90 seconds.

[Counter gas stop process and raw material gas introduction process]
The opposing gas stopping process and the source gas introducing process were performed simultaneously as shown in FIG. Close the valve 36 to stop the supply of hydrogen gas, and at the same time close the valve 45 and open the valves 44 and 46 so that the differential pressure becomes 98 kPa as indicated by the pressure gauge 47, and the inside of the reactor 11 is heated for 90 seconds. I aspirated it.

The above reaction process was repeated for a total of 5 cycles, and finally only the opposing gas supply process was performed for 90 seconds to obtain the gas separation material of Example 1.

<Gas separation performance evaluation>
Regarding the gas separation material of Example 1, vacuum transmittance measurement using pure gas was performed. Decompression type permeability measurement is a method of calculating the gas permeability of the separation membrane by measuring the amount of permeation from the time required for the pressure change that occurs when the gas that has permeated through the separation membrane is stored in a container with a constant volume. For the measurements, a single component gas permeation test was conducted at 50°C, 200°C, or 400°C based on the constant volume pressure change method using a gas permeation test device schematically shown in FIG. 5. Single component gases used were helium, hydrogen, carbon dioxide, argon, oxygen, and nitrogen. When measuring with hydrogen gas, first, a supply gas at atmospheric pressure was flowed at 500 mL/min into a permeation cell holding a gas separation material, and the pressure inside the buffer tank was reduced to 6 kPa (starting setting) using a vacuum pump. Next, a stop valve installed between the vacuum pump and the buffer tank was closed, and the time required for the pressure inside the buffer tank to rise to 10 kPa (end setting) was measured using a pressure gauge P2. Note that the start and end settings of the gas pressure in the buffer tank were changed depending on the type of gas used. For helium, it started at 6kPa and ended at 12kPa. For carbon dioxide, argon, oxygen and nitrogen, it started at 4kPa and ended at 4.01kPa. From the pressure change amount and the measured change time, the permeation amount [mol・s ⁻¹・Pa ⁻¹ ] and the permeability per unit area [mol・m ⁻²・s ⁻¹・Pa ⁻¹ ] are calculated, respectively. Calculated. The results are shown in FIG.

Furthermore, the ideal separation coefficient was determined using the permeability values of carbon dioxide gas and hydrogen gas. The results are shown in Table 1. The ideal separation coefficient tended to increase as the measurement temperature increased, but it still exceeded 300 even in the low temperature range of 50°C, and at 400°C, the average value exceeded 2500 and the maximum value was 3503. Met.

<SEM/EDX analysis>
Furthermore, the gas separation material of Example 1 was subjected to SEM/EDX analysis (acceleration voltage: 5 kV). The SEM image and EDS line analysis results of carbon (C) and platinum (Pt) are shown in Figure 7, and the EDS line analysis results of silicon (Si) and carbon (C) are shown in Figures 8(a) and 8(b). shown respectively. In the analysis, after cutting the gas separation material of Example 1, its surface was coated with 60 nm of platinum (Pt) and further coated with tungsten (W) to protect the outermost surface on the inorganic porous side. A sample processed by focused ion beam (FIB) to a thickness of 500 nm was used.

FIG. 7 shows the results of EDS line analysis of the SEM image and the positions indicated by white lines on the SEM image, and the EDS line analysis results show C and Pt superimposed. At the boundary between the base material S0 and the intermediate layer S1 (inorganic porous part Ps) seen in the SEM image, the detection intensity of C rapidly increased, and C was present inside the pores of the intermediate layer S1. Furthermore, since the position of the outermost surface of the intermediate layer S1 can be determined from the detected position of Pt, the position of the outermost surface is indicated by a dotted line in the EDS line analysis results shown in FIG. In FIG. 8(a), the detection intensity of Si appears high near the outermost surface, but it exists inside the outermost surface. The outside portion was within a range of about 50 nm at most. In other words, it can be said that C and Si, which indicate the existence of an external portion protruding from the pores of the intermediate layer S1 containing Al and O, can hardly be confirmed. In addition, what is detected at 5 μm or more in FIG. 8(a) is an overlap peak of W. Therefore, in the gas separation material of Example 1, the silicon carbide-based products are formed on the inner walls of the pores of the intermediate layer S1 and block the insides of the pores as a gas separation layer, and the gas separation function is It was assumed that this was due to the layer existing inside the pore.

<Comparative example 1>
A mixed gas of t-butylsilane (TBS: decomposition temperature 340°C) and nitrogen gas was used as the raw material gas, the reaction step was only a counter gas supply step (10 minutes), and the dimensions of the inorganic porous member S were changed. A gas separation material of Comparative Example 1 was produced in the same manner as in Example 1. With the change in raw material gas, the nitrogen gas flow rate for bubbling was set to 10 mL/min, the nitrogen gas flow rate as diluent gas was set to 90 mL/min, and the hydrogen gas flow rate was set to 150 mL/min. Further, due to the change in dimensions of the inorganic porous member S, the inner diameter of the reactor 11 was set to φ17 mm, and the total length was set to 389 mm. The inorganic porous member used in this comparative example will be explained below using FIG. 4.

The inorganic porous member S is formed by forming a γ-alumina intermediate layer S1 and a glass seal S2 on the outer surface of a tubular base material S0 made of α-alumina. As the substrate S0, an α-alumina tube manufactured by Noritake Co., Ltd., having an outer diameter of φ6 mm, a thickness of 880 μm, a length of 400 mm, and communicating pores with an average pore diameter of 150 nm was used. After applying glass powder to a width of 225 mm from both ends of the base material S0, it is melted and solidified to completely cover the surfaces of both ends of the base material S0 with glass, and the communicating holes that do not require vapor deposition treatment are closed with glass. I let it happen. In the unsealed central part of the base material S0 with a width of 50 mm, a boehmite-based mixture containing Ni is applied as an inorganic porous part Ps, and then Ni is added as an added metal element by baking at 800°C. A γ-alumina intermediate layer S1 was formed. By performing coating and baking twice, an intermediate layer S1 having a thickness of 2 μm and an average pore diameter of 8 nm (50% permeation flux diameter) was obtained.

<Gas separation performance evaluation>
Regarding the gas separation material of Comparative Example 1, similarly to the gas separation material of Example 1, vacuum permeability measurement was performed at 50° C. based on the constant volume pressure change method to evaluate the gas separation performance. The results are shown in Table 1. Since the ideal separation factor measured at 50° C. was 7, it cannot be expected to show an ideal separation factor of 1000 or more even if measured at 400° C.

<Example 2>
Using a mixed gas of 1,4-disilabutane (DSB: decomposition temperature 350°C) and nitrogen gas as the raw material gas, the bubbler temperature was 20°C, the temperature inside the reactor was 490°C, and the reaction process was carried out for 10 cycles (counter gas supply process). The gas separation material of Example 2 was produced in the same manner as in Example 1, except that the counter gas supply step after the reaction step was changed to 30 seconds, the counter gas stop step and raw material gas introduction step: 30 seconds), and the counter gas supply step after the reaction step was changed to 30 seconds. did. In addition, due to the change in raw material gas, the flow rate of nitrogen gas for bubbling was set to 12 mL/min, and the flow rate of nitrogen gas as diluent gas was set to 100 mL/min.

<Gas separation performance evaluation>
As with the gas separation material of Example 1, the gas separation material of Example 2 was evaluated for gas separation performance by performing vacuum permeability measurement at 400° C. based on the constant volume pressure change method. The results are shown in Table 1. The ideal separation coefficient measured at 400°C was 1020, indicating high gas separation properties.

Claims (8)

In a method for producing a gas separation material in which a gas separation layer is formed by chemical vapor deposition in which a counter gas is reacted with a source gas diffused in opposite directions from both ends of the pores of an inorganic porous part having a plurality of pores,
The raw material gas contains a compound containing carbon (C) and silicon (Si), and the reaction step is repeatedly carried out while carrying out the raw material gas supply step of supplying the raw material gas to one end side of the pore. The process is
a counter gas supply step of supplying a counter gas that reacts with the compound to produce silicon carbide to the other end side of the pore;
a counter gas stop step of stopping the supply of the counter gas, which is performed after the counter gas supply step;
A raw material gas introducing step of drawing the raw material gas from one end side of the pore to the other end side, which is performed simultaneously with the opposing gas stopping step or after the opposing gas stopping step;
A method for producing a gas separation material comprising: The method for producing a gas separation material according to claim 1, wherein the reaction step is repeated three or more times. The method for producing a gas separation material according to claim 1 or 2, wherein the raw material gas supplying step is a step of supplying the raw material gas thermally decomposed at 300 to 650°C. The method for producing a gas separation material according to claim 1, wherein the raw material gas contains a compound having a decomposition temperature of 150 to 450°C. The method for producing a gas separation material according to any one of claims 1 to 4, wherein the raw material gas contains a compound having an Si--C bond. The method for producing a gas separation material according to claim 1, wherein the raw material gas contains a compound having a cyclic structure. 7. The method for producing a gas separation material according to claim 6, wherein the raw material gas contains silacyclobutane. The method for producing a gas separation material according to any one of claims 1 to 7, wherein the raw material gas introduction step is a raw material gas exhausting step in which the raw material gas is supplied from one end of the pore and exhausted from the other end. .

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