Separation method and separation device

Abstract

A method for separating a fluorocarbon mixed gas includes a gas separation step in which a mixed gas (x) containing two or more fluorocarbon gases having different molecular diameters is brought into contact with a molecular sieve membrane (20) which is formed by a chemical vapor deposition method and contains amorphous silica, thereby separating the mixed gas into gases (a, b) having a mixing ratio different from that of the mixed gas. A separation device which has a porous membrane that is formed by chemical vapor deposition and contains amorphous silica, and through the porous membrane, separates a gas composition or a single gas, in which the mixing ratio of one fluorocarbon gas has been increased, from a mixed gas containing two or more fluorocarbon gases having different molecular diameters.

Description

Technical Field

[0001] This invention relates to a method and apparatus for separating fluorocarbon mixed gases. Background Technology

[0002] Distillation is a technique for separating a specific refrigerant gas from a mixture of multiple refrigerant gases. However, distillation is energy-intensive and requires significant equipment investment. Therefore, a low-cost technique is desired to separate the mixed refrigerant gas into various refrigerants for recycling.

[0003] For example, Patent Document 1 discloses a method for separating and recovering Freon from a gas mixture containing Freon, characterized in that the gas mixture containing Freon is contacted with a selectively permeable composite membrane, allowing Freon to selectively permeate through the membrane and be separated. The selectively permeable composite membrane is formed of an active film formed by crosslinking a crosslinked organosilicon resin on a porous support membrane, and the porous support membrane is formed of polyimide or polysulfone.

[0004] Furthermore, Non-Patent Literature 1 reports the use of a fluorinated amorphous polymer membrane containing polydimethylsiloxane, 5 mol% perfluorinated (butenyl vinyl ether) and 95 mol% perfluorinated (2,2-dimethyl-1,3-m-dioxane) to separate a mixture R410A consisting of 50% difluoromethane (HFC-32, CH2F2) and 50% pentafluoroethane (HFC-125, CHF2CF3), with the results showing that the permeability of HFC-32 was higher than that of HFC-125.

[0005] Patent Document 1: Japanese Patent Application Publication No. 1-42444;

[0006] Non-patent literature 1: Abby N. Harders et al., J.Membr.Sci., 652, 120467 (2022). Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Although fluorocarbons are used in refrigerants and other applications as mixed gases, they are difficult to separate due to azeotropy and other factors. Furthermore, due to the small difference in molecular diameter, even membrane separation is difficult to efficiently separate and regenerate them.

[0009] In the separation technologies for fluorocarbon gases disclosed in Patent Document 1 and Non-Patent Document 1, the ratio of the permeability of each fluorocarbon gas is about several times to about 20 times, and a separation technology with higher selectivity is desired.

[0010] The purpose of this invention is to provide a new method and apparatus for separating fluorocarbons.

[0011] Solution for solving the problem

[0012] The methods used to solve the above problems include the following approaches.

[0013] <1> A method for separating a fluorocarbon mixture, comprising:

[0014] The molecular sieve membrane preparation process involves preparing a molecular sieve membrane containing amorphous silica, which is deposited by chemical vapor deposition; and

[0015] The gas separation process involves contacting a mixture of two or more fluorocarbon gases with different molecular diameters with the aforementioned molecular sieve membrane to separate gases into those with a different mixing ratio than the mixture ratio in the original mixture before contact with the molecular sieve membrane.

[0016] <2> The method for separating fluorocarbon mixed gases according to <1>, wherein the molecular sieve membrane is an amorphous silica membrane having a structure containing -Si-O-Si- bonds.

[0017] <3> The method for separating fluorocarbon mixed gases according to <1> or <2>, wherein the above gas separation process is carried out in an environment of 20℃ to 300℃.

[0018] <4> The method for separating fluorocarbon mixed gas according to any one of <1> to <3>, wherein the above gas separation step is carried out in an environment of 0.1 MPa or higher.

[0019] <5> The method for separating fluorocarbon mixed gas according to any one of <1> to <4>, wherein the molecular sieve membrane is a molecular sieve membrane formed by using dimethoxydiphenylsilane as the chemical vapor deposition material in the above chemical vapor deposition method.

[0020] <6> The method for separating fluorocarbon mixed gas according to any one of <1> to <5>, wherein the above-mentioned chemical vapor deposition method is a counter diffusion method.

[0021] <7> A method for separating fluorocarbon mixed gases according to any one of <1> to <6>, wherein the molecular sieve membrane is formed on a porous ceramic support.

[0022] <8> A method for separating a fluorocarbon mixed gas according to any one of <1> to <7>, wherein the fluorocarbon mixed gas is a mixture of difluoromethane and pentafluoroethane.

[0023] <9> A separation device having a porous membrane containing amorphous silica deposited by chemical vapor deposition.

[0024] Through the aforementioned porous membrane, a gas composition or single gas with an increased mixing ratio of one fluorocarbon gas can be separated from a mixture of two or more fluorocarbon gases with different molecular diameters.

[0025] Invention Effects

[0026] According to the present invention, a new method and apparatus for separating fluorocarbons can be provided. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating an example of the structure of the molecular sieve membrane used in the separation method and separation apparatus for fluorocarbon mixed gases according to the present invention.

[0028] Figure 2 This is a schematic structural diagram of a gas separator, a key component of an embodiment of an apparatus for implementing the fluorocarbon gas separation method of the present invention.

[0029] Figure 3 To indicate Figure 2 A schematic cross-sectional view of the molecular sieve membrane and shell along the CC line.

[0030] Figure 4 This is a schematic diagram illustrating the structure of the film-forming apparatus and gas permeation test apparatus used in the embodiments.

[0031] Figure 5 A graph showing the Arrhenius curves of each single-component gas in the examples.

[0032] Figure 6 This is a graph illustrating the temperature dependence of the ideal selectivity in the embodiments.

[0033] Figure 7 A graph showing the pressure dependence of the permeability of each component gas of HFC-32 and HFC-125 at 200°C.

[0034] Figure 8 A graph showing the pressure dependence of the permeability of each component gas of HFC-32 and HFC-125 at 100°C.

[0035] Figure 9 A graph showing the pressure dependence of the permeability of each component gas of HFC-32 and HFC-125 at 25°C. Detailed Implementation

[0036] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0037] In addition, in this specification, the numerical range indicated by “~” refers to the range including the values ​​recorded before and after “~” as the lower and upper limits.

[0038] Furthermore, the term "process" in this specification is not only used for independent processes, but also for processes that cannot be clearly distinguished from other processes, as long as the desired purpose of the process is achieved.

[0039] In this invention, a combination of two or more preferred methods is a more preferred method.

[0040] Furthermore, structural elements indicated by the same reference numerals in various figures are considered to be the same structural element. Reference numerals for components with the same function in the figures are sometimes omitted. Additionally, reference numerals are sometimes omitted in the following description. Furthermore, the scales of the dimensions in the figures do not necessarily represent actual scales.

[0041] The inventors of this invention have repeatedly studied and experimented with methods for highly selectively separating refrigerant gases composed of a mixture of two or more fluorocarbon gases with different molecular sizes (sometimes referred to as "fluorocarbon mixed gas" in this invention). The results showed that by utilizing the differences in the physical properties (size, etc.) of various gases and using a molecular sieve membrane containing amorphous silica formed by chemical vapor deposition (also known as chemical vapor deposition, hereinafter sometimes referred to as CVD), highly selective separation can be achieved.

[0042] For example, the active membrane formed by cross-linking of cross-linked organosilicon resin disclosed in Patent Document 1 and the fluorine-based amorphous polymer membrane disclosed in Non-Patent Document 1 are not porous membranes, but separate gases by utilizing the dissolution-diffusion effect of the difference in solubility and diffusivity of the gas on the membrane. On the other hand, the CVD amorphous silica membrane used in this invention mainly utilizes the difference in size of each gas molecule to separate gases through the molecular sieve effect brought about by pore size control.

[0043] For example, although the mixed refrigerant R410A, consisting of difluoromethane (sometimes denoted as HFC-32 or R32) and pentafluoroethane (sometimes denoted as HFC-125 or R125), is currently used in air conditioning and refrigeration, there is a shift towards R32, which has a lower global warming potential. It is clearly understood that the CVD amorphous silica membrane used in this invention has a transmittance of difluoromethane (R32, molecular diameter: 0.363 nm) that is more than 100 times greater than that of pentafluoroethane (R125, molecular diameter: 0.447 nm). Furthermore, it has been confirmed that the transmittance ratio is temperature-dependent within the range of room temperature (e.g., 25°C) to 200°C, and the transmittance ratio is even greater at high temperatures, making it more suitable for separation. Additionally, pressure dependence of the transmittance is almost undetectable.

[0044] That is, the separation method of the fluorocarbon mixed gas (sometimes simply referred to as "mixed gas" in this invention) of the present invention includes: a molecular sieve membrane preparation step, preparing a molecular sieve membrane containing amorphous silica formed by chemical vapor deposition; and a gas separation step, separating a mixed gas containing two or more fluorocarbon gases with different molecular diameters into gases with a different mixing ratio of the two or more fluorocarbon gases than the mixing ratio of the mixed gas before contacting the molecular sieve membrane.

[0045] <Molecular sieve membrane>

[0046] First, the molecular sieve membrane used in the separation method of the fluorocarbon mixed gas of the present invention will be described. Figure 1 A cross-sectional view is shown to schematically illustrate one embodiment of a gas separation component using a molecular sieve membrane in the separation method for fluorocarbon mixed gases of the present invention. Figure 1 The gas separation component 30 shown includes a porous support 10 and an amorphous silica layer (amorphous silica membrane) 20 formed as a molecular sieve membrane on one surface of the porous support 10. The amorphous silica layer 20 has the function of selectively or preferentially allowing the fluorocarbon gas with a relatively smaller molecular diameter among the two or more fluorocarbon gases contained in the fluorocarbon mixture to pass through the molecular sieve.

[0047] The molecular sieve membrane of the present invention can be composed solely of a CVD amorphous silica layer. From the viewpoints of strength and ease of film formation of the molecular sieve membrane, it is preferable to use a CVD amorphous silica layer. Figure 1 The diagram shows the configuration of the gas separation member 30, which has a structure in which an amorphous silica layer 20, serving as a molecular sieve membrane, is supported by a porous support 10. Furthermore, as described later, the amorphous silica layer 20 can be formed not only on the surface of the porous support 10 but also within the pores of the porous support 10.

[0048] (porous support)

[0049] As a porous support 10 supporting the amorphous silica layer 20, a porous support with pores can be used, wherein the pores are permeable to the fluorocarbon gas to be separated.

[0050] exist Figure 1 In the illustrated embodiment, the porous support 10 has a double-layer structure consisting of a support layer 12 and an intermediate layer 14, each of which is porous. From the viewpoint of more stably fixing the amorphous silica layer 20 and stabilizing the amorphous silica layer 20 for a longer period of time, it is preferable to use a porous structure. Figure 1As shown in the double-layer structure, a porous support 10 with a support layer 12 and an intermediate layer 14 is used. The support layer 12 has good strength and gas permeability and is more cost-effective. The intermediate layer 14 has better retention of the amorphous silicon dioxide layer 20 and has smaller pores than the support layer 12. In this invention, the surface of the intermediate layer 14 opposite to the side that contacts the support layer 12 is sometimes referred to as the "surface of the intermediate layer".

[0051] In the porous support 10 with a double-layer structure, an amorphous silica layer 20 is present at least on the surface of the intermediate layer 14. The amorphous silica layer 20 may be formed only on the surface of the intermediate layer 14, or it may be formed not only on the surface of the intermediate layer 14 but also inside the pores of the intermediate layer 14. Preferably, in the porous support 10 with a double-layer structure, the amorphous silica layer 20 is present both inside the pores of the intermediate layer 14 and on the surface of the intermediate layer 14. By having the amorphous silica layer 20 inside the pores of the intermediate layer 14, the amorphous silica layer 20 exists more densely and stably in a state of filling the pores. Therefore, the function of the amorphous silica layer 20 as a molecular sieve is considered to be further enhanced, and the amorphous silica layer 20 functions as a highly active separation region for separating fluorocarbon mixed gases. The separation active region will be described later.

[0052] Here, "having an amorphous silica layer inside the pore" refers to two states: either an amorphous silica layer formed on the inner wall of the pore, or a state in which the pore is filled with amorphous silica in a manner that allows a portion of a fluorocarbon gas mixture to permeate. In the case of forming an amorphous silica layer using the chemical vapor deposition method described later, the gaseous silica precursor penetrates into the pores of the porous support and transforms into amorphous silica on the inner wall of the pore. If chemical vapor deposition continues further, the thickness of the amorphous silica layer formed on the inner wall of the pore may increase, and the pores of the porous support may become filled with an amorphous silica layer. Both of these situations are referred to as having an amorphous silica layer inside the pore.

[0053] As a preferred embodiment of the molecular sieve membrane used in the separation method of the fluorocarbon mixed gas of the present invention, the following embodiment is provided: an amorphous silica layer is provided inside the pores of the intermediate layer and on the surface of the intermediate layer, the thickness of the fluorocarbon gas separation active region in the amorphous silica layer is 5 nm to 15 nm, and the membrane length (length in the longitudinal direction) of the amorphous silica layer is 6 cm or more.

[0054] From the viewpoint of pore size and ease of acquisition, porous ceramics can be cited as materials for porous supports. From the viewpoint of heat resistance, metal oxides and metal nitrides are preferred. More specifically, porous supports such as alumina, silicon dioxide, titanium dioxide, zirconium oxide, and magnesium oxide are more preferred, and α-alumina supports are particularly preferred.

[0055] In the case of a tubular porous support, there is no particular limitation on the size. Examples of porous tubular supports include those with an outer diameter of about 3 mm to 20 mm, an inner diameter of about 1 mm to 15 mm, and a wall thickness of about 1 mm to 3 mm.

[0056] The average pore size of the porous support is preferably in the range of 30 nm to 1000 nm, more preferably in the range of 50 nm to 500 nm, and even more preferably in the range of 80 nm to 180 nm.

[0057] As a porous support with a two-layer structure, the following porous support is preferred: a tubular α-alumina layer with an average pore size of 20nm to 1000nm, preferably 80nm to 180nm, is used as the support layer 12, and a γ-alumina layer with an average pore size of 1nm to 20nm, preferably 3nm to 5nm, is used as the intermediate layer 14 on the outer surface of the tubular support layer 12.

[0058] The average pore size of a porous support can be determined, for example, by using a through-pore size evaluation device based on, for example, the bubble point method of ASTM F316-86 (JIS K 3832) to measure the pore size distribution. Examples of such devices include Shiwa Digital Imaging Co., Ltd., and a pore size distribution measuring instrument (PermPorometer).

[0059] The thickness of the support layer 12 can be arbitrarily selected according to the purpose. From the viewpoint of balancing strength and gas permeability, the thickness of the support layer 12 can be, for example, 0.5 mm to 3 mm, preferably in the range of 1 mm to 2 mm.

[0060] The thickness of the intermediate layer 14 can be, for example, 0.5 μm to 10 μm, preferably in the range of 1 μm to 5 μm.

[0061] The thicknesses of the support layer 12 and intermediate layer 14 in the porous support 10 can be determined by platinum sputtering of the cross-section and observation using a field emission scanning electron microscope (FE-SEM). An example FE-SEM device is the JSM-6701F (manufactured by Nippon Electron Ltd.). The accelerating voltage of the FE-SEM can be set to, for example, 10.0 kV.

[0062] There are no particular limitations on the method of providing the intermediate layer 14 on the support layer 12, which serves as a porous support, and known manufacturing methods for porous layers can be appropriately applied.

[0063] In the case where the support layer 12 is made of a material with good heat resistance, such as alumina, the method described later, of coating the support layer 12 with an intermediate layer forming material containing boehmite sol and then sintering it, is preferred. According to the method for forming the intermediate layer 14 using the intermediate layer forming material containing boehmite sol, an intermediate layer 14 of arbitrary thickness can be formed by varying the amount of intermediate layer forming material applied, the sintering temperature, and by performing multiple coatings and sintering processes.

[0064] As a method for manufacturing a porous support with a two-layer structure, an example is to dip and coat the outer surface of a tubular porous support layer made of α-alumina with boehmite sol, which serves as an intermediate layer forming material, two to three times, and then sinter it to form an γ-alumina intermediate layer with an average pore size of 3 nm to 5 nm. When coating the intermediate layer forming material onto the tubular support layer, it is preferable to perform sealing treatments at the ends of the tubular body in a manner that prevents the intermediate layer forming material from penetrating into the interior of the tubular body serving as the support layer 12.

[0065] Boehmite sol can be manufactured using, for example, aluminum sec-butoxide (sometimes simply ALSB), 2-propanol and gallium(III) octahydrate, or using aluminum sec-butoxide (ALSB), 2-propanol and nitric acid by conventional methods.

[0066] (Amorphous silicon dioxide layer)

[0067] The amorphous silica layer 20 functions as a molecular sieve, selectively separating the fluorocarbon gases contained in the fluorocarbon mixture based on molecular diameter (molecular size). The amorphous silica layer 20 preferably has an amorphous structure with a three-dimensional network of siloxane bonds represented by -Si-O-Si-. The mesh structure of the three-dimensional silica can be considered to act as a molecular sieve.

[0068] There is no particular limitation on the thickness of the amorphous silica layer 20. When the thickness of the amorphous silica layer, which serves as a molecular sieve membrane, is relatively thick, the separation efficiency of fluorocarbon gases becomes better, but there is a tendency for gas permeability to decrease. From this point of view, the thickness of the separation active region in the amorphous silica layer is, for example, 5 nm to 100 nm, preferably in the range of 5 nm to 15 nm.

[0069] Here, the separation-active region in the amorphous silica layer refers to a dense region within the amorphous silica layer that facilitates the separation of fluorocarbon gases. It can be inferred that, compared to the silica film formed on the surface of the intermediate layer, regions with a denser structure within the pores of the intermediate layer of the amorphous silica layer are more likely to function as highly active separation regions for fluorocarbon gases; these regions are termed the separation-active region in the amorphous silica layer. The separation-active region in the amorphous silica layer can be identified based on the results of analysis using X-ray photoelectron spectroscopy (XPS), described later, according to the elemental composition along the depth direction of the formed amorphous silica layer, in the form of regions with increased Al2p and decreased Si2p.

[0070] The thickness of the amorphous silica layer and the thickness of the separation active region within the amorphous silica layer can be determined by elemental composition analysis of the amorphous silica layer in the gas separation component from the surface opposite to the porous support along the depth direction of the film using X-ray photoelectron spectroscopy (XPS). In this invention, an XPS VG ESCALAB250 spectrometer (Thermo Fisher Scientific) equipped with an Al Kα ray source can be used at a chamber pressure of less than 10... -8 The values ​​were determined under conditions of Pa and an etching rate of 0.05 nm / s. The elements and electron orbitals used in the XPS-based analysis were Si: 2p, Al: 2p, O: 1s, and C: 1s.

[0071] When the fluorocarbon mixture to be separated contains two fluorocarbon gases with different molecular diameters, it is preferable that the average pore size of the amorphous silica layer 20 is larger than that of the fluorocarbon gas with a relatively smaller molecular diameter, but smaller than that of the fluorocarbon gas with a relatively larger molecular diameter. For example, when separating a mixture of R32 (molecular diameter: 0.363 nm) and R125 (molecular size: 0.447 nm), if the average pore size of the pores formed by the silica mesh structure in the amorphous silica layer 20 is set to about 0.38 to 0.42 nm, R32 can easily pass through, while R125 cannot pass through, thus enabling efficient separation of the fluorocarbon mixture with high gas selectivity.

[0072] Furthermore, even if the average pore size of the amorphous silica layer 20 is larger than the molecular diameter of R125, the average pore size of the amorphous silica layer 20 can be larger than the molecular diameter of R125 because R32 is more permeable than R125.

[0073] Furthermore, the amorphous silica film used in this invention has a pore size distribution and the pore size is less than 1 nm. Therefore, there is no quantitative method for measuring the pore size distribution. However, the pore size can be analytically inferred using the normalized Knudsen-based permeance (NKP) method using permeation data of a single-component gas. Specifically, in this invention, an amorphous silica film with an average pore size of 0.3 to 0.6 nm can be inferred using the NKP method (200°C) described in the following documents.

[0074] <Literature on NKP Method>

[0075] Evaluation and fabrication of pore-size-tuned silica membranes withtetraethoxydimethyl disiloxane for gas separation

[0076] Hye Ryeon Lee,Masakoto Kanezashi,Yoshihiro Shimomura,TomohisaYoshioka,Toshinori Tsuru

[0077] AIChE Journal,57(10)2755-2765(2011)

[0078] <Methods for Manufacturing Molecular Sieve Membranes>

[0079] The molecular sieve membrane used in the separation method of the fluorocarbon mixed gas of the present invention can be manufactured by chemical vapor deposition (CVD). According to the CVD method, an amorphous silica layer 20 with high durability can be formed on the porous support 10.

[0080] The CVD method used in the formation of the amorphous silica layer 20 includes, for example, unidirectional diffusion CVD, in which a silica precursor from a silica source and an oxidant preferably oxygen are supplied to one side of a porous support to form an amorphous silica layer; and counter-directional diffusion CVD, in which a silica precursor from a silica source is supplied to one side of a porous support, and an oxidant is supplied to the other side of the porous support.

[0081] According to the counter-diffusion CVD method, by maintaining the same pressure on both sides of a porous support, silica precursors and oxidants diffuse into the pores of the porous support, contacting each other within the pores to generate amorphous silica. An amorphous silica layer is formed on the pore walls within the pores of the porous support, and the pores are filled with the silica layer, thereby automatically terminating the reaction. On the other hand, in the pores of the porous support not filled with the silica layer, the reaction between the silica precursor and oxygen continues. Thus, the reaction continues until the pores are filled with the amorphous silica layer, easily yielding a reproducible and high-performance amorphous silica layer. In other words, by using the counter-diffusion CVD method, an amorphous silica layer can be easily fabricated not only on the surface of the intermediate layer of a porous support with a double-layer structure as the preferred embodiment described above, but also inside the pores of the intermediate layer.

[0082] Regarding the formation of the amorphous silica layer 20, taking the counter-diffusion CVD method as an example, a porous support 10 is disposed within a housing. On the other hand, a silicon compound serving as a silica source is disposed within a bubbler, and nitrogen gas is supplied while heating to supply the silicon compound vapor into the housing. The temperature inside the housing is set to 300°C to 650°C. The silicon compound vapor, serving as a silica source, is supplied to one side (e.g., the outer peripheral side) of the porous support, while oxygen flows through the other side (e.g., the inner peripheral side), allowing both to react within the porous support. For example, when forming an amorphous silica layer on the outer surface of a tubular porous support with a length of 10 mm to 100 mm, if the concentration of the silicon compound vapor is approximately 0.93 mol / m³... 3 If the oxygen flow rate is approximately 200 mL / min, then a sufficient amount of amorphous silica layer can be formed in about 60 minutes.

[0083] Then, the silicon compound vapor was stopped, the shell was purged with oxygen, the oxygen supply was stopped, and nitrogen was supplied to the interior of the porous support for purging to obtain an amorphous silicon dioxide layer.

[0084] Examples of chemical vapor deposition materials (silicon dioxide sources) that can be used in the manufacture of the amorphous silicon dioxide layer 20 include: dimethoxydimethylsilane (DMDMS), tetraethyl silicate (TEOS), hexamethyldisiloxane (HMDS), tetramethyl silicate (TMOS), trimethoxy(methyl)siloxane (TMMS), methoxytrimethylsiloxane (MTMS), phenyltrimethoxysilane (PTMS), dimethoxydiphenylsilane (DMDPS), triethoxyethylsilane, diethoxydiethylsilane, ethoxytriethylsilane, and methoxytriphenylsilane. Furthermore, the abbreviation of the compound is given in parentheses after its name; these abbreviations are sometimes used to refer to the compounds listed below.

[0085] As a silica source, DMDMS, TMOS, HMDS, TEOS, TMMS, MTMS, DMDPS, etc. are preferred, and DMDPS are more preferred. That is, the amorphous silica layer is more preferably an amorphous silica layer from a silica source containing DMDPS.

[0086] As a method for manufacturing the molecular sieve membrane used in the separation method of the fluorocarbon mixed gas of the present invention, a method having, for example, the following steps is preferred: on an alumina porous support with an average pore size of 30 nm to 1000 nm, an amorphous silica layer with an average pore size of 0.3 nm to 0.6 nm, for example, by means of the NKP method (200 °C), is formed by CVD using a silica source containing dimethoxydiphenylsilane (DMDPS).

[0087] As a porous support, as described above, it is preferable to have a double-layer structure with at least a support layer 12 and an intermediate layer 14, wherein the support layer 12 is a porous body with an average pore size of 50 nm to 200 nm, and the intermediate layer 14 is a porous body with an average pore size of 3 nm to 5 nm. More preferably, for the intermediate layer 14 of the double-layer porous support 10, an amorphous silicon dioxide layer 20 is formed not only on the surface of the intermediate layer 14 but also in the pores by a counter-diffusion CVD method.

[0088] <Separation Methods for Fluorocarbon Gas Mixtures>

[0089] Next, the method for separating fluorocarbon mixed gases using the separation method of the present invention will be described with reference to the accompanying drawings.

[0090] Figure 2 This is a schematic structural diagram of a gas separator, a key component of an embodiment of an apparatus for implementing the fluorocarbon gas separation method of the present invention. Figure 3 Briefly Figure 2 The cross-section of the CC line.

[0091] Figure 2 The gas separator 50 shown has a tubular gas separation member 30 disposed inside a tubular housing 32, with both ends sealed by sealing members 33A and 33B. At the center of the sealing member 33A, a conduit 28 is connected to the inner side A of the gas separation member 30 for introducing the mixed gas x. Conversely, at the center of the sealing member 33B, a conduit 28A is connected to the inner side A of the gas separation member 30 for discharging gas that has not passed through the gas separation member 30. Near the outer periphery of the sealing member 33B, a conduit 28B is connected to the space B between the gas separation member 30 and the housing 32 for discharging gas that has passed through the gas separation member 30. Furthermore, the gas separation member 30 has… Figure 1The layered structure shown has a CVD amorphous silica layer (silica membrane) 20 formed on the outermost layer as a molecular sieve membrane.

[0092] Gas permeation through the molecular sieve membrane 20 can be facilitated by connecting a vacuum pump (not shown) to pipe 28B for suction. Furthermore, gas flow rate and pressure can be adjusted by installing valves (not shown) on each of pipes 28, 28A, and 28B. The diameter of pipe 28A, which exits from the gas separation member 30, can also be made smaller than that of pipe 28, which introduces the mixed gas, thereby increasing the internal pressure of the gas separation member 30 while simultaneously promoting gas permeation through the molecular sieve membrane 20.

[0093] Using a gas separation device equipped with a gas separator 50 having such a structure, in the case of separating, for example, a fluorocarbon mixture of R125 and R32, the mixed gas x is supplied to the interior (inner A) of the gas separation member 30 through pipe 28. During the passage of the mixed gas x through the gas separation member 30, it passes through the porous support 10 and comes into contact with the amorphous silica layer 20. At least a portion of the R32 molecules, with relatively small diameters, permeates through the amorphous silica layer 20 and moves into the space B between the gas separation member 30 and the housing 32. Thus, gas a, with a lower R32 concentration than the mixed gas x before introduction, is discharged from pipe 28A, and gas b, with a higher R32 concentration than the mixed gas x before introduction, is discharged from pipe 28B.

[0094] For example, by configuring the gas separation device to have multiple gas separators 50, the mixed gas x can pass through the gas separators 50 multiple times, thereby improving the separation efficiency. The gas separation device of the present invention can also perform multi-stage separation of the mixed gas x. If the gas separation device of the present invention is used, a gas composition or single gas with an increased mixing ratio of one fluorocarbon gas can be separated from a mixed gas containing two or more fluorocarbon gases with different molecular diameters.

[0095] Alternatively, the following structure can be used: the mixed gas x is supplied to the outside (space B) of the gas separation member 30, so that at least a portion of the R32 with a relatively small molecular diameter passes through the inside (inner side A) of the gas separation member 30, thereby discharging a gas with a higher R32 concentration than the mixed gas x before introduction from the pipe 28A, and discharging a gas with a lower R32 concentration from the pipe 28B.

[0096] Furthermore, the environment in which gas separation is performed using the fluorocarbon mixed gas separation method of the present invention is not particularly limited. Since the gas separation component 30 used in the present invention is made of inorganic material, it has high heat resistance. In addition, according to the permeation experiment of the fluorocarbon gas in the present invention described later, it exhibits a higher gas selectivity at 100°C to 200°C than at room temperature (e.g., 25°C). Therefore, it is preferable to perform gas separation in an environment of, for example, 20°C to 300°C.

[0097] On the other hand, based on the permeation experiments of fluorocarbon gas described later, almost no pressure dependence of the permeability was confirmed. Therefore, gas separation is preferably performed under an environment with a pressure of 0.1 MPa or higher.

[0098] Furthermore, the permeation rate of the gas being separated is not particularly limited and can be set according to the type of gas, etc. For example, the permeation rate of R32 ([mol / (m 2 The preferred value is 1.0 × 10⁻⁶. -4 ~1.0×10 -10 More preferably 1.0×10 -5 ~1.0×10 -9 More preferably 1.0×10 -6 ~1.0×10 -8 .

[0099] Example

[0100] The following examples further illustrate the method for separating fluorocarbon mixed gases according to the present invention. However, the following examples do not limit the method for separating fluorocarbon mixed gases according to the present invention.

[0101] [Formation of amorphous silica films]

[0102] The following steps are followed to form an amorphous silica film.

[0103] A Ga-added γ-alumina interlayer is coated onto the outer peripheral surface of a tubular α-alumina substrate using a sol-gel method. Next, amorphous silica is deposited inside the pores of the Ga-added γ-alumina interlayer using counter-diffusion CVD, thereby forming an amorphous silica film (hereinafter sometimes referred to as "silica film"). This will be explained in detail below.

[0104] (1) Fabrication of porous support

[0105] (Substrate)

[0106] As the substrate serving as the support layer, a tubular α-alumina substrate (manufactured by Noritake Co., Ltd.) is used. Specifications of the α-alumina substrate are shown in Table 1. Additionally, "pore size" refers to the average pore size.

[0107] [Table 1]

[0108] shape full length outer diameter inner diameter aperture tubular 400mm 6mm 4mm 150nm

[0109] Using a diamond cutting tool, the α-alumina substrate was cut into pieces 120 mm in length, with the two ends sealed with glass for 20 mm. The length of the amorphous film formed on the substrate was 80 mm, excluding the glass-sealed portion.

[0110] (γ-alumina coating)

[0111] The γ-alumina coating is applied only to the outer surface of the substrate. The process is carried out in three stages as described below: preparation of Ga-added boehmite sol (hereinafter, sometimes referred to as "boehmite sol"), preparation of the coating solution, dip coating, and sintering.

[0112] (Preparation of Boehmite sol with added Ga)

[0113] Prepare the following reagents.

[0114] • Aluminum sec-butoxide (ALSB) 500g, manufactured by Fujifilm and Koh Genuine Chemicals Co., Ltd.

[0115] ·2-Propanol 500mL, manufactured by Fujifilm and Koh Genuine Chemicals Co., Ltd.

[0116] Gallium(III) nitrate octahydrate 25g, manufactured by Fujifilm and Koko Pure Chemical Industries Co., Ltd.

[0117] <Production Steps>

[0118] Place ALSB, 2-propanol, a 50 mL beaker, stir bar, Pasteur pipette, a 100 mL dropping bottle, a nitrogen bladder, an electronic balance, and a stirrer into a glove box (manufactured by AS ONE Corporation) and close it. Also, prepare the nitrogen bladder before closing the glove box.

[0119] Replace the glove box with nitrogen for 15 minutes.

[0120] After nitrogen replacement, add 3.60 g (0.06 mol) of 2-propanol to the beaker to wet the inner wall of the beaker.

[0121] Add 24.6 g (0.10 mol) of ALSB directly from the reagent bottle to a beaker whose walls have been moistened with 2-propanol, and stir for 1 hour.

[0122] Add 360 mL of pure water to a 500 mL beaker and heat to 90°C on a stirrer. Prepare 90°C pure water beforehand to adjust the liquid level, and add more pure water to the 500 mL beaker as needed. Additionally, cover the mouth of each beaker with aluminum foil when not in use.

[0123] Inside the glove box, transfer the mixture of ALSB and 2-propanol into a 100 mL dropper bottle, and attach a nitrogen bladder to the top of the dropper bottle.

[0124] Remove the dropper bottle with the nitrogen bladder from the glove box, vigorously stir the 90°C pure water prepared on a heated stirrer, and add dropwise a mixture of ALSB and 2-propanol.

[0125] Without covering the mouth of the beaker with aluminum foil, stir continuously at 90°C until the 2-propanol evaporates (until the alcohol odor disappears). Maintain the liquid volume at 340 mL.

[0126] Add 17.14 g (0.04 mol) of gallium(III) octahydrate to 108 g (6 mol) of pure water, cover the mouth of the beaker with parafilm and stir for more than 1 hour to prepare an aqueous solution of gallium nitrate.

[0127] After evaporating the 2-propanol, transfer it to a 500 mL Erlenmeyer flask. If a white precipitate forms, remove it as well. Cover the mouth of the flask with aluminum foil and allow it to cool. After cooling, slowly add an aqueous solution of gallium nitrate while stirring vigorously. Stir for at least 12 hours to obtain boehmite sol, which is then stored in a plastic bottle.

[0128] (Preparation of the coating solution)

[0129] In addition to the boehmite sol prepared above, the following reagents are also prepared.

[0130] • 1 mol / L nitric acid, 500 mL, manufactured by Fujifilm and Koukou Pure Chemicals Co., Ltd.

[0131] • Polyvinyl alcohol 500 fully saponified type, 500g, manufactured by Fujifilm and Koh Genuine Chemicals Co., Ltd.

[0132] <Production Steps>

[0133] 1) Add 47.5 mL of pure water and 2.5 mL of 1 M HNO3 to a 50 mL graduated cylinder. Transfer the solution to a 100 mL Erlenmeyer flask and add a stir bar.

[0134] 2) While gently stirring to avoid foaming, add 1.75g ​​of fully saponified polyvinyl alcohol 500 (PVA) to a 100mL Erlenmeyer flask.

[0135] 3) Since PVA is not easily soluble, the 100mL Erlenmeyer flask was transferred to a heating stirrer, and the mouth of the flask was sealed with aluminum foil. The mixture was heated to 90°C while stirring. After 40 minutes, it was allowed to cool while still stirring to prepare a PVA solution.

[0136] 4) Add 20 mL of the prepared PVA solution and 30 mL of boehmite sol to a 50 mL beaker, add a stir bar, cover the mouth of the beaker with sealing film, and stir for 15 minutes to prepare the coating solution.

[0137] (Dipping and sintering)

[0138] <Operating Steps>

[0139] 1) Since only the outer surface of the substrate is coated, the opening on one side (the lower side during immersion) of the substrate is sealed with sealing tape to prevent the coating solution from penetrating the inside of the substrate.

[0140] 2) Pour the coating solution into the test tube in a manner that prevents air bubbles from entering, and retain the remaining coating solution while stirring. Immerse the 120mm long substrate in the coating solution from the side sealed with sealing tape for 5 seconds. Take care to avoid touching the test tube wall when removing and placing the substrate.

[0141] 3) Place the impregnated substrate into an electric muffle furnace KM-600 (manufactured by Advantec Co., Ltd.), and dry and sinter it according to the prescribed temperature program (hold at 60°C for 3 hours, then raise the temperature to 600°C for 6 hours and hold for another 6 hours, then cool down to room temperature for 6 hours). When placing the substrate into the electric muffle furnace, place the glass-sealed part of the substrate on the base to avoid contact with the film-forming part.

[0142] 4) Repeat the dip coating and sintering steps (2) to 3) above to create a porous support (hereinafter, sometimes referred to as "γ / α-alumina substrate" or simply "substrate") with a Ga-added γ-alumina layer (intermediate layer) formed on the outer peripheral surface of the tubular α-alumina substrate (substrate layer).

[0143] (2) Formation of amorphous silica layer (silicon dioxide film)

[0144] An amorphous silica layer (silica film) is formed on the outer peripheral surface of a porous support (γ / α-alumina substrate) with a double-layer structure as described above by a counter-diffusion CVD method.

[0145] A schematic structure of the apparatus 100 used in the formation of the silica film is shown in Figure 4 . Figure 4The apparatus 100 shown, in addition to the gas tank 24 containing oxygen used in film formation, also includes gas tanks 13, 16, 18, 22, etc., containing various gases such as R125, R32, H2, and N2, configured to perform various gas permeation tests by adjusting valves 38, etc., installed in each pipeline 28. MFC is an abbreviation for mass flow controller. SUS tubing is used in pipeline 28.

[0146] Gas separator 40 and Figure 3 The configuration shown is the same, with a space B provided on the outside of the gas separation member 30 for the gas to pass through the gas separation member 30, and a glass tube shell 32 disposed thereon. An electric furnace 34 equipped with a thermocouple 36 is disposed on the outside of the shell 32.

[0147] The substrate 10 is joined to the SUS pipe fitting by using graphite sealing rings (manufactured by GL Sciences Co., Ltd.) and connectors (manufactured by Swagelok) 31A and 31B at the glass sealing portions exposed at both ends of the housing 32.

[0148] In addition, pressure gauges 44 and 48, soap film flow meter 52, pressure sensor 54, and vacuum pump 58 are connected to each pipeline 28.

[0149] When forming an amorphous silica layer on a porous support (γ / α-alumina substrate) 10 using the apparatus 100 with this structure, the silica precursor (precursor) is bubbled by supplying nitrogen to the bubbler 26 at a flow rate of 200 mL / min, thereby supplying silica precursor vapor to the housing 32. A wrapped strip heater 42 is used to prevent the precursor from condensing in the line 28, maintaining the line temperature at 180°C. Furthermore, unreacted precursor is recovered via an ice-water cooling trap 46. The temperature of the bubbler 26 is controlled by wrapping it with a mantle heater (not shown).

[0150] The silica precursor vapor concentration was determined before film formation using a gas pipeline that did not pass through the housing 32. The silica precursor in the nitrogen carrier gas was captured for a certain period using an ice-water cooling trap 46, and the silica precursor vapor concentration (mol / m³) was calculated. 3 ).

[0151] (Silica film formation using counter-diffusion CVD)

[0152] As a precursor, DMDPS (dimethoxydiphenylsilane, manufactured by Tokyo Chemical Industry Co., Ltd.) as shown in the following structural formula is used.

[0153] [Chemical Formula 1]

[0154]

[0155] The physical properties of DMDPS are shown in Table 2.

[0156] [Table 2]

[0157] Molecular formula molecular weight proportion boiling point <![CDATA[C 14 H 16 O2Si]]> 244.37 1.08 110℃

[0158] <Film Formation Steps>

[0159] Turn on the power to the temperature control of the electric furnace 34, the strip heater 42, and the bubbler 26 located on the outside of the housing. Heat the furnace 34 from room temperature to 600°C over 1.5 hours, and set the strip heater 42 to 180°C.

[0160] After all temperatures have stabilized, prepare the ice-water cooling trap 46. Use a gas line that does not pass through the casing 32 to measure the DMDPS vapor concentration, with a DMDPS vapor concentration of approximately 0.08 mol / m³. 3 Adjust the bubbler temperature left and right.

[0161] After adjusting the bubbler temperature, DMDPS vapor is supplied to the housing 32 (outer side of the substrate B). After 2 minutes, oxygen is allowed to flow into the inner side A of the substrate at 200 mL / min to begin film formation.

[0162] After 60 minutes, the supply of DMDPS vapor was stopped, and nitrogen was supplied to the outer side B of the substrate at a fully open flow rate, while oxygen flowed to the inner side A of the substrate at 200 mL / min to purge the inside of the housing 32.

[0163] One hour later, the oxygen supply was stopped, and nitrogen was purged into the inner side A of the substrate at full flow for several minutes to complete the film formation.

[0164] <Gas Permeability Evaluation>

[0165] (Single-component gas permeation test 1)

[0166] After the silica film is formed, it is used Figure 4 The apparatus 100 shown is used to conduct a gas permeation test.

[0167] Gas is supplied to the supply side (outside the substrate), and valve 38B at the membrane outlet is closed, applying pressure to the supply side. The supply side pressure is 0.20–0.40 MPa. Gas is allowed to permeate through the membrane in a dead-end manner with a pressure difference of 0.20–0.40 MPa between the membranes. The flow rate of the permeate gas from the permeate side is measured using a bubble flowmeter (BFM) 52 (manufactured by Horiba Co., Ltd.). Typically, the BFM 52 is used for measurement when the permeate side gas flow rate is high. When the permeate side gas flow rate is too low to be measured using the BFM, the pressure variation method is used to measure the permeate side gas flow rate. The pressure variation method involves setting the supply side pressure to 0.20 MPa, evacuating the permeate side for 2 hours using an oil rotary vacuum pump 58 (manufactured by ULVAC Co., Ltd.), and applying a membrane differential pressure of approximately 0.35 MPa. When gas is supplied to the supply side, permeation occurs, and the pressure on the permeate side begins to rise. The rate of pressure rise is determined by measuring the pressure over time, and the flow rate of the permeated gas is calculated based on the permeated side volume.

[0168] (Temperature dependence)

[0169] Figure 5 The temperature dependence of the transmittances of H2, N2, HFC-32, and HFC-125 for an 80 mm long silica film deposited on a Ga-added γ / α-alumina substrate is shown. Furthermore, in... Figure 5 The "E" on the vertical axis refers to powers of 10, for example, "E-10" means "10 -10 ".also, Figure 6 The temperature dependence of the ideal selectivity is shown. Based on the NKP method (200℃) described above, the average pore size of the silica film can be considered to be around 0.40–0.55 nm, indicating that it is suitable for the separation of HFC-32 and HFC-125.

[0170] The transmittance and transmittance ratio of HFC-32 and HFC-125 at 200℃, 100℃ and 25℃ are shown in Table 3 below.

[0171] [Table 3]

[0172]

[0173] The ideal selectivity, calculated by dividing the transmittance of HFC-32 by the transmittance of HFC-125, is 1026 at 200°C, 1623 at 100°C, and 617 at 25°C.

[0174] Furthermore, for reference, the ideal selectivity calculated using the H2 transmittance / N2 transmittance is approximately 10 at any temperature. This also indicates that it is particularly suitable for the separation of HFC-32 and HFC-125.

[0175] (Single-component gas permeation test 2)

[0176] After the silica film is formed, it is used Figure 4 The apparatus 100 shown is used for gas permeation testing. Gas is supplied to the supply side (outside the substrate), the valve 38B at the membrane outlet is closed, and pressure is applied to the supply side. The supply side pressure is 0.20–0.60 MPa. Gas is permeated through the membrane in a dead-end manner with a pressure difference of 0.10–0.50 MPa. The flow rate of the permeated gas from the permeation side is measured using a bubble flowmeter (BFM) 52 (manufactured by HORIBA Co., Ltd.). Typically, the BFM 52 is used for measurement when the permeation side gas flow rate is high. When the permeation side gas flow rate is too low to be measured using the BFM, the pressure variation method is used to measure the permeation side gas flow rate. The pressure variation method involves setting the supply side pressure to 0.20–0.60 MPa, evacuating the permeation side for 2 hours using an oil rotary vacuum pump 58 (manufactured by Nippon Vacuum Technology Co., Ltd.), and applying a membrane differential pressure of approximately 0.20–0.60 MPa. When gas is supplied to the supply side, permeation occurs, and the pressure on the permeation side begins to rise. The rate of pressure rise is determined by measuring the pressure over time, and the flow rate of the permeated gas is calculated based on the permeated side volume.

[0177] Figure 7 , Figure 8 , Figure 9 The relationship between supply-side pressure and transmittance of HFC-32 and HFC-125 at 200℃, 100℃, and 25℃ is shown. At any temperature during the test, no significant difference (pressure dependence) was found in the transmittance of HFC-32 and HFC-125 due to different pressures.

[0178] Industrial availability

[0179] The method for separating fluorocarbon mixed gases according to the present invention achieves energy-saving separation compared to separation using distillation, and is expected to bring significant economic benefits. Furthermore, it helps to limit refrigerant gases that are indicated to have a strong greenhouse effect more than 100 times greater than carbon dioxide.

[0180] The inventions of Japanese Patent Application No. 2023-059439, filed on March 31, 2023, and Japanese Patent Application No. 2023-112649, filed on July 7, 2023, are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as each document, patent application, and technical standard is specifically and separately shown.

[0181] Explanation of reference numerals in the attached figures

[0182] 10: Porous support;

[0183] 13, 16, 18, 22: Gas cylinders;

[0184] 12: Support layer;

[0185] 14: Intermediate layer;

[0186] 20: Amorphous silica layer (molecular sieve membrane);

[0187] 24: Gas cylinder;

[0188] 26: Bubble maker;

[0189] 28, 28A, 28B: Piping;

[0190] 30: Gas separation components;

[0191] 32: Shell;

[0192] 33A, 33B: Sealing components;

[0193] 34: Electric furnace;

[0194] 36: Thermocouple;

[0195] 38, 38B: Valves;

[0196] 40: Gas separator;

[0197] 42: Strip heater;

[0198] 44: Pressure gauge;

[0199] 46: Ice-water cooling trap;

[0200] 50: Gas separator;

[0201] 52: Soap film flow meter;

[0202] 54: Pressure sensor;

[0203] 58: Vacuum pump;

[0204] 100: Film-forming device and gas permeation test device.

Claims

1. A method for separating a fluorocarbon mixture, comprising: The molecular sieve membrane preparation process involves preparing a molecular sieve membrane containing amorphous silica, which is formed by chemical vapor deposition. as well as The gas separation process involves contacting a mixture of two or more fluorocarbon gases with different molecular diameters with the molecular sieve membrane to separate the gases into gases with a different mixing ratio than the mixture in the original gas mixture before contact with the molecular sieve membrane.

2. The method for separating fluorocarbon mixed gases according to claim 1, wherein, The molecular sieve membrane is an amorphous silica membrane with a structure containing -Si-O-Si- bonds.

3. The method for separating fluorocarbon mixed gases according to claim 1, wherein, The gas separation process is carried out in an environment of 20℃ to 300℃.

4. The method for separating fluorocarbon mixed gases according to claim 1, wherein, The gas separation process is carried out in an environment with an pressure of 0.1 MPa or higher.

5. The method for separating fluorocarbon mixed gases according to claim 1, wherein, The molecular sieve membrane is formed using dimethoxydiphenylsilane as the chemical vapor deposition material in the chemical vapor deposition method.

6. The method for separating fluorocarbon mixed gases according to claim 1, wherein, The chemical vapor deposition method is a counter-diffusion method.

7. The method for separating fluorocarbon mixed gases according to claim 1, wherein, The molecular sieve membrane is formed on a porous ceramic support.

8. The method for separating fluorocarbon mixed gases according to any one of claims 1 to 7, wherein, The fluorocarbon mixture is a mixture of difluoromethane and pentafluoroethane.

9. A separation device comprising a porous membrane containing amorphous silica, formed by chemical vapor deposition. The porous membrane allows for the separation of a gas composition or single gas with an increased mixing ratio of one fluorocarbon gas from a mixture of two or more fluorocarbon gases with different molecular diameters.

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