Separation membrane unit and separation device

Abstract

The present invention provides a separation membrane unit and separation apparatus that have a good selectivity ratio relative to the selectivity ratio of the separation membrane while suppressing damage to the separation membrane. [Solution] A separation membrane unit for selectively separating carbon dioxide gas from a supply gas containing carbon dioxide gas and nitrogen gas, comprising: a porous plate having a plurality of through holes formed therein; a porous body disposed on a first surface of the porous plate; and a separation membrane comprising a resin layer disposed on the porous body and selectively permeating the carbon dioxide gas contained in the supply gas toward the porous body, wherein when the average thickness of the separation membrane is T1 and the average diameter of the plurality of through holes on the first surface is D1, T1 / D1 ≥ 0.02, and when the carbon dioxide gas permeability of the separation membrane is A, the nitrogen gas permeability of the separation membrane is B, and the gas permeability of the porous plate is C, 1 > (B + C) / (A + C) ≥ 0.8.

Description

[Technical Field]

[0001] The present invention relates to a separation membrane unit and a separation apparatus. [Background technology]

[0002] To achieve carbon neutrality, technologies for capturing and recovering carbon dioxide gas from the atmosphere are being investigated. One such technology is membrane separation, which uses a separation membrane to separate target gases such as carbon dioxide gas from a mixed gas such as the atmosphere.

[0003] For example, Patent Document 1 discloses a separation membrane comprising a porous support, a thin film of a siloxane compound disposed on the porous support and having its surface layer plasma-treated with a non-polymerizable gas, and a plasma-polymerized film disposed on the thin film. The porous support supports the thin film and the polymerized film. A mixed gas is supplied to the thin film and the polymerized film. In the thin film and the polymerized film, the permeability of the target gas in the mixed gas is higher than the permeability of the non-target gas in the mixed gas. Therefore, the separation membrane can selectively separate the target gas from the mixed gas. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 60-75320 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] When there is a pressure difference between the two surfaces of a separation membrane, the permeation of the target gas is promoted. However, this pressure difference can cause the separation membrane to deform. Therefore, the separation membrane is used as a separation membrane unit, for example, in combination with a perforated plate that supports it. The ratio of the permeability of the target gas to the permeability of the non-target gas, such as the separation membrane, is called the "selectivity ratio." Depending on the configuration of the perforated plate, the selectivity ratio of the separation membrane unit may be significantly lower than that of the separation membrane. [Means for solving the problem]

[0006] A separation membrane unit according to an application example of the present invention is a separation membrane unit that selectively separates carbon dioxide gas from a supply gas containing carbon dioxide gas and nitrogen gas, A porous plate having a first surface and a second surface that are in a front-back relationship with respect to each other, and having a plurality of through holes formed therein that extend from the first surface toward the second surface, A separation membrane comprising a porous body disposed on the first surface, and a resin layer disposed on the porous body, which selectively permeates the carbon dioxide gas contained in the supply gas toward the porous body, Equipped with, When the carbon dioxide gas permeability of the separation membrane is A, then 500,000 GPU ≥ A ≥ 1,000 GPU, When the average thickness of the separation membrane is T1, then 200 μm ≥ T1 ≥ 10 μm. When the average diameter of the plurality of through holes in the first surface is D1, T1 / D1 ≥ 0.02, When the nitrogen gas permeability of the separation membrane is B and the gas permeability of the porous plate is C, then 1 > (B + C) / (A + C) ≥ 0.8.

[0007] The separation device according to an example of the present invention is equipped with the above-described separation membrane unit. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing a separation device according to an embodiment. [Figure 2] It is a cross-sectional view showing an enlarged part of FIG. 1. [Figure 3] It is a top view showing the perforated plate of FIG. 1. [Figure 4] It is a schematic diagram showing the relationship between the deflection of the separation membrane and the diameter of the through hole on the first surface of the perforated plate. [Figure 5] It is a schematic diagram showing a method for measuring the gas permeability of the perforated plate. [Figure 6] It is a cross-sectional view showing the separation membrane unit according to Modification 1. [Figure 7] It is a cross-sectional view showing the separation membrane unit according to Modification 2. [Figure 8] Table 1 shows the configurations and evaluation results of the separation membrane units of Examples 1 to 5 and the separation membrane units of Comparative Examples 1 to 4. [Figure 9] Table 2 shows the configurations and evaluation results of the separation membrane units of Examples 6 and 7 and the separation membrane unit of Comparative Example 5.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments and modifications of the present invention will be described while referring to the drawings. Note that the following description does not limit the technical scope or the meaning of terms described in the claims. Also, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios.

[0010] <Embodiment> First, the separation device 100 according to the embodiment will be described. FIG. 1 is a cross-sectional view showing the separation device 100 according to the present embodiment. FIG. 2 is a cross-sectional view showing an enlarged part of FIG. 1. In FIG. 1, the pump 150 described later is simply shown as a circle. Also, in FIG. 1, the housing portion 120 and the pipe 140 described later are shown as end faces instead of cross-sections.

[0011] In each figure of the present embodiment, the X-axis, Y-axis, and Z-axis are set as three axes orthogonal to each other. Each axis is represented by an arrow, and the tip side of the arrow is defined as "plus" and the base side of the arrow is defined as "minus". In the following description, for example, the "X-axis direction" includes both the plus direction and the minus direction of the X-axis. The same applies to the Y-axis direction and the Z-axis direction. Further, in the following description, specifically, the plus side of the Z-axis is defined as "up" and the minus side of the Z-axis is defined as "down". The Z-axis does not necessarily have to be parallel to the vertical axis and may intersect the vertical axis. Further, in the following, the uppermost end of each member is referred to as the "upper end", and a certain range downward from the upper end in each member is referred to as the "upper end portion". Similarly, the lowermost end of each member is referred to as the "lower end", and a certain range upward from the lower end in each member is referred to as the "lower end portion".

[0012] The separation device 100, as outlined by referring to FIG. 1, includes a separation membrane unit 110, a housing portion 120, a pipe 140, and a pump 150.

[0013] The separation membrane unit 110 includes a porous plate 111 in which a plurality of through holes 111h are formed, and a separation membrane 112 disposed on the porous plate 111. A mixed gas is supplied to the separation membrane 112. Hereinafter, the mixed gas supplied to the separation membrane 112 is also referred to as "supply gas G1". The supply gas G1 includes carbon dioxide gas and nitrogen gas. The supply gas G1 is not particularly limited, but for example, it is air or the like. In the separation membrane 112, the carbon dioxide gas permeability is higher than the nitrogen gas permeability. Therefore, the separation membrane 112 can selectively permeate the carbon dioxide gas contained in the supply gas G1 toward the porous plate 111. Thereby, the separation membrane 112 can selectively separate the carbon dioxide gas from the supply gas G1. Here, "selectively permeating or separating carbon dioxide gas" does not mean that only carbon dioxide gas permeates or separates and no nitrogen gas permeates or separates at all. "Selectively permeating or separating carbon dioxide gas" means permeating or separating carbon dioxide gas with a higher permeability than nitrogen gas, that is, preferentially permeating or separating carbon dioxide gas over nitrogen gas.

[0014] The gas that permeates through the separation membrane 112 then permeates through the multiple through-holes 111h of the porous plate 111. Hereinafter, the gas that permeates through the separation membrane 112 will also be referred to as "permeate gas G2". The separation membrane 112 permeates carbon dioxide gas preferentially, while also permeating nitrogen gas. Therefore, permeate gas G2 contains both carbon dioxide gas and nitrogen gas.

[0015] The containment section 120 holds the separation membrane unit 110. The containment section 120 has a containment space 120s formed therein for containing the permeate gas G2 that has permeated through the perforated plate 111.

[0016] The piping 140 is connected to the containment section 120. The pump 150 depressurizes the containment space 120s through the piping 140. As a result, the pressure applied to the surface 112a to which the supply gas G1 is supplied in the separation membrane 112 becomes higher than the pressure applied to the surface 112b in contact with the porous plate 111 in the separation membrane 112. Consequently, the permeation of carbon dioxide gas through the separation membrane 112 is promoted. The permeated gas G2 in the containment space 120s is drawn into the pump 150 and recovered.

[0017] In this embodiment, the separation device 100 further includes a fixing member 130 for fixing the separation membrane unit 110 to the housing section 120. The parts of the separation device 100 will be described in detail below.

[0018] First, let me explain the perforated plate 111. Figure 3 is a top view showing the perforated plate 111 of Figure 1. As shown in Figure 2, in this embodiment, the perforated plate 111 is a flat plate that is generally parallel to the XY plane. As shown in Figure 3, the shape of the perforated plate 111 in a top view is, for example, circular. The surface of the perforated plate 111 has a first surface 111a and a second surface 111b, which are opposite each other and have a front-back relationship. The first surface 111a corresponds to the top surface and is the surface on which the separation membrane 112 is placed. The second surface 111b corresponds to the bottom surface. The rigidity of the perforated plate 111 is higher than the rigidity of the separation membrane 112. Therefore, the perforated plate 111 can support the separation membrane 112 well.

[0019] Each through-hole 111h formed in the perforated plate 111 extends from the first surface 111a toward the second surface 111b. That is, each through-hole 111h penetrates the perforated plate 111 in the thickness direction. In this embodiment, the thickness direction of the perforated plate 111 coincides with the Z-axis direction.

[0020] As shown in Figure 3, in this embodiment, the multiple through holes 111h are formed so as to be distributed on the XY plane, except for the outer periphery of the perforated plate 111. Specifically, in a top view, the centers 111c of the multiple through holes 111h are located on the intersections of a plurality of imaginary first lines L1 and a plurality of second lines L2. The plurality of first lines L1 are parallel to each other. The plurality of first lines L1 are arranged at equal intervals in a direction perpendicular to the direction in which the first lines L1 extend. The plurality of second lines L2 are parallel to each other and intersect with the plurality of first lines L1. The plurality of second lines L2 are arranged at equal intervals in a direction perpendicular to the direction in which the second lines L2 extend. The angle θ between the first line L1 and the second line L2 is less than 90 degrees. However, the arrangement of the plurality of through holes is not limited to the above. For example, the plurality of through holes may also be formed on the outer periphery of the perforated plate, and the angle between the first line and the second line may be 90 degrees.

[0021] The shape of each through-hole 111h in a top view is, for example, circular. However, the shape of each through-hole 111h in a top view may be a polygon such as a hexagon, an oval, or an ellipse. In this embodiment, the diameter of each through-hole 111h is generally constant and does not change in the thickness direction of the perforated plate 111. If the shape of the through-hole in a top view is a shape other than circular, the diameter of the circumscribed circle of the through-hole in a top view is taken as the diameter of the through-hole.

[0022] The average value of the diameters of the multiple through holes 111h in the first surface 111a is defined as the "average diameter D1". While not particularly limited, it is preferable that 5 mm ≥ D1 ≥ 0.1 mm, more preferably 4 mm ≥ D1 ≥ 0.1 mm, and even more preferably 2 mm ≥ D1 ≥ 0.1 mm. By setting the average diameter D1 to be above the lower limit, the gas permeability of the perforated plate 111 can be improved. By setting the average diameter D1 to be below the upper limit, the rigidity of the perforated plate 111 can be improved.

[0023] The average thickness T2 of the perforated plate 111 is defined as the average value of the thickness at multiple locations on the XY plane of the perforated plate 111. While not particularly limited, it is preferable that 30 mm ≥ T2 ≥ 0.05 mm, more preferably 30 mm ≥ T2 ≥ 0.07 mm, and even more preferably 1 mm ≥ T2 ≥ 0.07 mm. By setting the average thickness T2 of the perforated plate 111 to be above the above lower limit, the rigidity of the perforated plate 111 can be improved. This suppresses deformation of the perforated plate 111 when the pump 150 is depressurizing the containment space 120s. Furthermore, by setting the average thickness T2 of the perforated plate 111 to be below the above upper limit, the pressure loss when the permeate gas G2 flows through each through-hole 111h of the perforated plate 111 can be reduced. As a result, the gas permeability of the perforated plate 111 can be increased.

[0024] In a top view, the ratio of the total area of ​​the multiple through-holes 111h to the effective area of ​​the separation membrane 112 is called the "opening ratio" of the perforated plate 111. The "effective area of ​​the separation membrane 112" refers to the area of ​​the upper surface of the separation membrane 112 that is exposed from other parts such as the fixing member 130 and to which the supply gas G1 is supplied to the separation membrane 112. The "total area of ​​the multiple through-holes 111h" refers to the total area of ​​the multiple through-holes 111h that are located within the range of the effective area of ​​the separation membrane 112 in a top view. The opening ratio of the perforated plate 111 is preferably 5% or more and 95% or less, more preferably 20% or more and 95% or less, and even more preferably 70% or more and 95% or less. By setting the opening ratio of the perforated plate 111 to be above the lower limit, the gas permeability of the perforated plate 111 can be improved. By setting the opening ratio of the perforated plate 111 to be below the upper limit, the rigidity of the perforated plate 111 can be improved. This prevents deformation of the perforated plate 111 when the pump 150 is reducing the pressure in the containment space 120s.

[0025] The arithmetic mean roughness of the surface forming the through-holes 111h of the perforated plate 111 is defined as the "surface roughness" of the perforated plate 111. The surface roughness of the perforated plate 111 is not particularly limited, but is preferably 0.012 μm or more and 6.3 μm or less, more preferably 0.05 μm or more and 6.3 μm or less, and even more preferably 0.1 μm or more and 1.6 μm or less. By setting the surface roughness of the perforated plate 111 to be below the above upper limit, the pressure loss when the permeate gas G2 flows through the multiple through-holes 111h can be reduced. By setting the surface roughness to be above the above lower limit, the manufacturing cost of the perforated plate 111 can be suppressed. The surface roughness is measured using a contact-type or non-contact-type surface roughness measuring instrument in accordance with the provisions of JIS B 0601:2013.

[0026] The material of the perforated plate 111 is a ceramic material or a metallic material, etc. Examples of ceramic materials include alumina. Examples of metallic materials include stainless steel, titanium, and aluminum.

[0027] Next, we will describe the separation membrane 112. As shown in Figure 2, the separation membrane 112 comprises a porous body 113 disposed on the first surface 111a of the porous plate 111, and a resin layer 114 disposed on the porous body 113.

[0028] In this embodiment, the porous body 113 consists of a porous layer in which a plurality of voids 113h are formed. The porous body 113 extends in the X-axis direction and the Y-axis direction. In this embodiment, the porous body 113 covers almost the entire area of ​​the first surface 111a of the porous plate 111. Therefore, the shape of the porous body 113 in a top view is circular in this embodiment. However, the shape of the porous body in a top view is not limited to the above, and may be a polygon such as a quadrilateral.

[0029] Each void 113h penetrates the porous body 113 in the thickness direction. In this embodiment, the thickness direction of the porous body 113 coincides with the Z-axis direction. The multiple voids 113h are formed to be dispersed on the XY plane. Here, the diameter of the inscribed circle of the void 113h is defined as the "diameter" of the void 113h.

[0030] The average value of the diameters of multiple pores 113h is defined as the "average diameter" of the pores 113h. The average diameter of the pores 113h is smaller than the average diameter D1 of the porous plate 111. The average diameter of the pores 113h is preferably between 5 nm and 1,000 nm, more preferably between 50 nm and 500 nm, and even more preferably between 50 nm and 200 nm. The average diameter of the pores 113h can be measured using a through-pore diameter evaluation device after removing the resin layer 114 from the separation membrane 112 to obtain a single porous body 113. An example of a through-pore diameter evaluation device is the palm porometer manufactured by PMI. By setting the average diameter of the pores 113h to be above the lower limit, the carbon dioxide gas permeability of the porous body 113 can be improved. Furthermore, by setting the average diameter of the pores 113h to be below the upper limit, the mechanical strength of the separation membrane 112 can be improved.

[0031] The material of the porous body 113 is, for example, a polymer material, a ceramic material, or a metallic material. Examples of polymer materials include polyolefin resins such as polyethylene and polypropylene, fluororesins such as polytetrafluoroethylene, polyvinyl fluoride and polyvinylidene fluoride, polystyrene, cellulose, cellulose acetate, polyurethane, polyacrylonitrile, polyphenylene oxide, polysulfone, polyethersulfone, polyimide, polyaramid, and nylon. Examples of ceramic materials include alumina, cordierite, mullite, silicon carbide, and zirconia. Examples of metallic materials include stainless steel.

[0032] However, the structure of the porous body is not limited to the above. For example, the porous body may be composed of multiple stacked porous layers.

[0033] The resin layer 114 is a substantially dense film and has good affinity for carbon dioxide molecules. Therefore, the carbon dioxide gas permeability in the resin layer 114 is higher than that of nitrogen gas permeability. As a result, the resin layer 114 selectively permeates carbon dioxide gas from the supply gas G1. In this embodiment, the resin layer 114 covers almost the entire upper surface of the porous body 113. Therefore, the shape of the resin layer 114 in a top view is circular, similar to that of the porous body 113 in this embodiment. However, the shape of the resin layer 114 in a top view is not limited to the above and may be a polygon such as a square.

[0034] The average thickness of the resin layer 114 at multiple locations on the XY plane is defined as the "average thickness" of the resin layer 114. In this embodiment, the average thickness of the resin layer 114 is smaller than the average thickness of the porous body 113. The average thickness of the resin layer 114 is not particularly limited, but is preferably 5 nm to 1,000 nm, more preferably 10 nm to 800 nm, and even more preferably 30 nm to 500 nm. The average thickness of the resin layer 114 can be measured, for example, by a scanning electron microscope (SEM). By setting the average thickness of the resin layer 114 to be above the lower limit, defects and damage to the resin layer 114 can be suppressed. By setting the average thickness of the resin layer 114 to be below the upper limit, the carbon dioxide gas permeability of the separation membrane 112 can be improved.

[0035] The material of the resin layer 114 is a polymer material. Examples of polymer materials include polyolefin resins such as polyethylene and polypropylene, fluororesins such as polytetrafluoroethylene, polyvinyl fluoride and polyvinylidene fluoride, polystyrene, cellulose, cellulose acetate, polyurethane, polyacrylonitrile, polyphenylene oxide, polysulfone, polyethersulfone, polyimide, polyaramid, organopolysiloxane, polyethylene terephthalate (PET), polyacetal (POM), and polylactic acid (PLA). The constituent material of the resin layer 114 may be a composite material of one or more of these polymer materials. Furthermore, the polymer material may be a thermoplastic resin, a thermosetting resin, or a photocurable resin.

[0036] Of these, it is preferable to use organopolysiloxane as the constituent material of the resin layer 114. Organopolysiloxane has good affinity for carbon dioxide molecules.

[0037] The average thickness T1 of the separation membrane 112 is defined as the average of the thicknesses at multiple locations on the XY plane of the separation membrane 112. T1 is 200 μm ≥ 10 μm. While not particularly limited, it is preferably 150 μm ≥ T1 ≥ 10 μm, and more preferably 100 μm ≥ T1 ≥ 10 μm. The average thickness T1 can also be measured, for example, by SEM. By setting the average thickness T1 of the separation membrane 112 to be above the lower limit, the mechanical strength of the separation membrane 112 can be improved. By setting the average thickness T1 of the separation membrane 112 to be below the upper limit, the carbon dioxide gas permeability of the separation membrane 112 can be improved.

[0038] Next, the storage section 120 will be described. As shown in Figure 1, the containment section 120 is a chamber. In this embodiment, the containment section 120 is a hollow cylindrical shape. The central axis C1 of the containment section 120 extends in the Z-axis direction. In this embodiment, the containment space 120s is cylindrical. Specifically, the containment section 120 comprises an upper wall 121 that is generally parallel to the XY plane, a lower wall 122 located below the upper wall 121 and generally parallel to the XY plane, and a side wall 123 located between the upper wall 121 and the lower wall 122 and extending in the Z-axis direction. An inlet 120a into which the permeate gas G2 flows is formed in the upper wall 121. An outlet 120b into which the permeate gas G2 flows out is formed in the lower wall 122. The side wall 123 is cylindrical.

[0039] The intake opening 120a penetrates the upper wall 121 in the thickness direction, approximately through its center in a top view. The shape of the intake opening 120a in a top view is, for example, circular. On the upper surface of the upper wall 121, a step 120c is formed around the intake opening 120a, on which the perforated plate 111 can be placed. The perforated plate 111 is positioned on the step 120c so as to cover the intake opening 120a.

[0040] The outlet 120b penetrates the lower wall 122 in the thickness direction, approximately through its center when viewed from above. The shape of the outlet 120b when viewed from above is generally similar to the outer shape of the pipe 140, which will be described later, and is circular.

[0041] However, the specific shape of the containment section is not limited to the above. For example, the shape of the containment section may be a hollow rectangular parallelepiped. Also, for example, it is not necessary to form a step on the upper wall for arranging the perforated plate. Furthermore, the shapes of the intake port, containment space, and outlet port are not limited to the above. For example, the shape of the intake port and outlet port in a top view may be a polygon such as a square. Also, for example, the shape of the containment space may be a rectangular parallelepiped. Furthermore, the positions of the intake port and outlet port are not limited to the above, as long as the permeate gas can flow into the containment space and the permeate gas that has flowed into the containment space can be discharged into the piping.

[0042] Next, the fixing member 130 will be described. In this embodiment, the fixing member 130 is frame-shaped. The fixing member 130 covers the outer periphery of the separation membrane 112 and the perforated plate 111 from above and is fixed to the housing 120 by a plurality of fasteners 131 such as screws and bolts. In this way, the housing 120 holds the separation membrane 112 and the perforated plate 111. Although not shown in the figures, it is preferable to arrange a sealing member to prevent gas leakage from gaps between the separation membrane 112 and the fixing member 130, and gaps between the fixing member 130 and the housing 120. However, the specific shape of the fixing member is not limited to the above, as long as it can fix the separation membrane unit to the housing. Furthermore, the method of fixing the separation membrane unit to the housing is not limited to the method using a fixing member.

[0043] Next, we will explain piping 140. The pipe 140 is cylindrical and, in this embodiment, extends linearly in the Z-axis direction. Therefore, the internal space 141 of the pipe 140 also extends linearly in the Z-axis direction. The pipe 140 is connected to the housing 120 with its upper end inserted into the outlet 120b of the housing 120. The internal space 141 of the pipe 140 communicates with the housing space 120s. However, the specific shape of the pipe is not limited to the above. For example, the pipe may be bent. Alternatively, instead of inserting the upper end of the pipe into the outlet, the pipe may be connected to the housing with its upper end in contact with the lower surface of the lower wall of the housing.

[0044] Next, I will explain pump 150. Pump 150 is connected to the lower end of piping 140. Pump 150 depressurizes the containment space 120s through piping 140. Pump 150 is, for example, a dry vacuum pump. However, the type of pump is not particularly limited as long as it can depressurize the containment space.

[0045] Next, we will explain the flow of supply gas G1 and permeate gas G2. First, supply gas G1 is supplied to the separation membrane 112. When the containment space 120s is depressurized by the pump 150, some of the carbon dioxide and nitrogen gas in the supply gas G1 permeates through the separation membrane 112. The permeate gas G2, which contains the carbon dioxide and nitrogen gas that has permeated through the separation membrane 112, permeates through the multiple through-holes 111h of the perforated plate 111. Next, the permeate gas G2 flows into the internal space 141 of the piping 140 via the containment space 120s. Then, the permeate gas G2 is drawn into the pump 150 and recovered.

[0046] The separation device 100 equipped with the separation membrane unit 110 has been described above, but the configuration of the separation device is not limited to the above. For example, a single separation device may be equipped with multiple separation membrane units. In this case, one housing may hold multiple separation membrane units, or the separation device may be provided with a number of housings corresponding to the number of separation membrane units.

[0047] Next, we will describe the parameters of the separation membrane unit 110. Let A be the carbon dioxide gas permeability of separation membrane 112. Let B be the nitrogen gas permeability of separation membrane 112. "Permeability" refers to the amount of gas permeating per unit area, unit time, and unit pressure. The carbon dioxide gas permeability A and the nitrogen gas permeability B are measured using a gas permeability measuring device in accordance with the gas permeability test method (Part 1: Differential pressure method) specified in JIS K 7126-1:2006. Examples of gas permeability measuring devices include the GTR-11A / 31A manufactured by GTR Tech Co., Ltd. The units for carbon dioxide gas permeability A and nitrogen gas permeability B are, for example, GPU. Note that 1 GPU is equal to 3.35 × 10⁻¹⁶ -10 mol·m -2 ·s -1 ·Pa -1 Thus, the carbon dioxide gas permeability A and nitrogen gas permeability B represent the performance of the separation membrane 112 alone, when the separation membrane 112 is not incorporated into the separation membrane unit 110 and the separation device 100.

[0048] In this embodiment, 500,000 GPU ≥ A ≥ 1,000 GPU. Preferably, 400,000 GPU ≥ A ≥ 5,000 GPU, and more preferably, 300,000 GPU ≥ A ≥ 7,000 GPU. By setting the carbon dioxide gas permeability A to be above the above lower limit, the amount of energy required for separation can be reduced. Specifically, the amount of energy required for separation is the difference between the pressure applied to the surface 112a to which the supply gas G1 is supplied in the separation membrane 112 and the pressure applied to the surface 112b in contact with the porous plate 111 in the separation membrane 112. Furthermore, in the separation membrane 112 including a resin layer 114 made of polymer material, there is a trade-off relationship between the carbon dioxide gas permeability A and the selectivity ratio of the separation membrane 112. Therefore, if the carbon dioxide gas permeability A exceeds the above upper limit, it may become difficult to maintain a balance with the selectivity ratio of the separation membrane 112.

[0049] The carbon dioxide gas permeability A of the separation membrane 112 can be controlled by adjusting the material of the resin layer 114, the average thickness of the resin layer 114, the average diameter of the pores 113h of the porous body 113, and the average thickness T1 of the separation membrane 112. Specifically, the carbon dioxide gas permeability A of the separation membrane 112 can be increased by using a material with high affinity for carbon dioxide molecules for the resin layer 114. The carbon dioxide gas permeability A of the separation membrane 112 can also be increased by reducing the average thickness of the resin layer 114. The carbon dioxide gas permeability A of the separation membrane 112 can also be increased by using a material with high gas permeability for the porous body 113. The carbon dioxide gas permeability A of the separation membrane 112 can also be increased by increasing the average diameter of the pores 113h of the porous body 113. The carbon dioxide gas permeability A of the separation membrane 112 can also be increased by reducing the average thickness T1 of the separation membrane 112.

[0050] As shown in (Equation 1) below, the ratio of carbon dioxide gas permeability A to nitrogen gas permeability B is defined as the selectivity ratio of the separation membrane 112. Selectivity ratio of separation membrane 112 = A / B (Equation 1)

[0051] Hereinafter, the selectivity of the separation membrane 112 will also be referred to as "selectivity ratio A / B". The carbon dioxide gas permeability A is greater than the nitrogen gas permeability B. Therefore, the selectivity ratio A / B of the separation membrane 112 is greater than 1.

[0052] Figure 4 is a schematic diagram showing the relationship between the deflection δ of the separation membrane 112 and the diameter d of the through-hole 111h in the first surface 111a of the porous plate 111.

[0053] When the containment space 120s is depressurized by the pump 150, the pressure applied to the surface 112a of the separation membrane 112 to which the supply gas G1 is supplied becomes higher than the pressure applied to the surface 112b of the separation membrane 112 that is in contact with the porous plate 111. Therefore, a force is applied to the separation membrane 112 in the direction from the separation membrane 112 toward the porous plate 111, i.e., downward. As a result, depending on the rigidity of the separation membrane 112 and the pressure difference, the separation membrane 112 will bend so as to fall into the through-hole 111h, as shown in Figure 4. Furthermore, the larger the diameter d of the through-hole 111h on the first surface 111a of the porous plate 111, the greater the deflection δ of the separation membrane 112.

[0054] Furthermore, the smaller the thickness of the separation membrane 112, the lower its rigidity. The lower the rigidity of the separation membrane 112, the greater the deflection δ of the separation membrane 112. The more the separation membrane 112 deflects, the more easily it is damaged. Therefore, in order to suppress damage to the separation membrane 112, it is important to adjust the average thickness T1 of the separation membrane 112 and the average diameter D1 of the multiple through holes 111h in the first surface 111a of the perforated plate 111. As will be described in detail later, according to the inventors' studies, if the average thickness T1 of the separation membrane 112 and the average diameter D1 of the multiple through holes 111h satisfy the following equation (Equation 2), damage to the separation membrane 112 can be suppressed. T1 / D1≧0.02 (Formula 2)

[0055] From the above explanation, it can be seen that the smaller the average diameter D1 of the multiple through holes 111h, the easier it is to suppress damage to the separation membrane 112. However, the smaller the average diameter D1 of the multiple through holes 111h, the lower the gas permeability of the porous plate 111. In addition, the gas permeability of the porous plate 111 changes depending on other components such as the average thickness T2 and the aperture ratio of the porous plate 111. When the gas permeability of the porous plate 111 decreases, the selectivity ratio of the separation membrane unit 110 decreases relative to the selectivity ratio A / B of the separation membrane 112. Therefore, the inventors of this application considered that in order to realize a separation membrane unit 110 that has a good selectivity ratio relative to the selectivity ratio A / B of the separation membrane 112 while suppressing damage to the separation membrane 112, it is important to consider not only T1 / D1 but also the gas permeability of the porous plate 111.

[0056] Figure 5 is a schematic diagram showing a method for measuring the gas permeability of the perforated plate 111. In the figure, some of the piping is simplified and shown with solid lines.

[0057] A gas permeability measuring device 10 is used to measure the gas permeability of the perforated plate 111. The gas permeability measuring device 10 comprises a gas supply unit 11, a chamber 12, an upstream pressure gauge 13, a downstream pressure gauge 14, a flow meter 15, a vacuum pump 16, and a concentration meter 17. First, the perforated plate 111 is placed inside the chamber 12. The internal space of the chamber 12 is divided into an upstream space 12a and a downstream space 12b, with the perforated plate 111 as the boundary. The gas supply unit 11 and the upstream space 12a are connected by piping, etc. The downstream space 12b and the vacuum pump 16 are also connected by piping, etc.

[0058] The gas supply unit 11 is composed of, for example, a gas tank and a mass flow controller. The gas supplied by the gas supply unit 11 is the main component of the permeate gas G2. In this embodiment, the supply gas G1 is the atmosphere, and the concentration and partial pressure of nitrogen gas in the supply gas G1 are much higher than the concentration and partial pressure of carbon dioxide gas. Therefore, although the carbon dioxide gas permeability A of the separation membrane 112 is higher than the nitrogen gas permeability B, the amount of nitrogen gas permeation is greater than the amount of carbon dioxide gas permeation. In other words, in this embodiment, the main component of the permeate gas G2 is nitrogen gas. Therefore, the gas supply unit 11 supplies single-gas nitrogen gas. However, if the supply gas is not the atmosphere, and the concentration and partial pressure of carbon dioxide gas in the supply gas are higher than the concentration and partial pressure of nitrogen gas, the main component of the permeate gas will be carbon dioxide gas. In this case, the gas supply unit should supply carbon dioxide gas.

[0059] To measure the gas permeability of the perforated plate 111, first, the internal space of the chamber 12 is reduced to 3 kPa using a vacuum pump 16. Next, gas is supplied at 103 kPa to the space 12a upstream of the chamber 12 by the gas supply unit 11. This causes gas to begin flowing through the multiple through-holes 111h of the perforated plate 111. Then, the vacuum pump 16 sucks up the gas that has permeated through the perforated plate 111. At this time, the absolute pressure of the gas supplied to the perforated plate 111 is measured by the upstream pressure gauge 13. The absolute pressure of the gas that has permeated through the perforated plate 111 is measured by the downstream pressure gauge 14. The volume of gas permeated through the perforated plate 111 per unit time is measured by the flow meter 15. The amount of substance per unit volume of gas recovered by the vacuum pump 16 is measured by the concentration meter 17. Other test conditions, such as the test temperature, shall, as far as possible, follow JIS K 7126-1:2006.

[0060] Immediately after gas supply, the flow rate and absolute pressure of the gas permeating through the perforated plate 111 gradually increase, and then stabilize to a state where the flow rate and absolute pressure remain approximately constant. In the stable state, the absolute pressure on the upstream side of the perforated plate 111 is denoted as P3, and the absolute pressure on the downstream side of the perforated plate 111 is denoted as P4. Furthermore, in the stable state, the amount of gas permeating through the perforated plate 111 per unit time is calculated from the volume of gas permeating through the perforated plate 111 per unit time and the amount of gas per unit volume. This amount of gas per unit time is denoted as n. Also, the area of ​​the perforated plate 111 to which the gas is supplied, i.e., the area of ​​the upper surface of the perforated plate 111, is denoted as s1.

[0061] Let C be the gas permeability of the perforated plate 111. By substituting the above values ​​into the following equation (Equation 3), the gas permeability C of the perforated plate 111 can be calculated. C=n / {(P3-P4)·s1} (Equation 3)

[0062] The unit of the gas permeability C above is mol·m -2 ·s -1 ·Pa -1The gas permeability C is used, along with the carbon dioxide gas permeability A and nitrogen gas permeability B, in the calculation of the parameters described later. Therefore, the units of gas permeability C must be the same as the units of carbon dioxide gas permeability A and nitrogen gas permeability B. When using GPU as the unit for carbon dioxide gas permeability A and nitrogen gas permeability B, the value calculated in (Equation 3) is 3.35 × 10⁻¹⁰. -10 Divide by . Since the gas permeability C is measured using the main component gas of the permeate gas G2, it can be considered as the gas permeability of the permeate gas G2 through the perforated plate 111. The gas permeability measuring device 10 may also be used to measure the carbon dioxide gas permeability A and nitrogen gas permeability B.

[0063] Theoretically, when two gas permeators are arranged in a continuous manner, if the gas permeability of the upstream gas permeator is x and the gas permeability of the downstream gas permeator is y, then the total gas permeability z of the two gas permeators combined can be expressed by the following equation (4). 1 / z = 1 / x + 1 / y (Equation 4)

[0064] Transforming (Equation 4) yields the following (Equation 5). z = (xy) / (x + y) (Equation 5)

[0065] The separation membrane 112 can be considered as an upstream gas permeator, and the porous plate 111 can be considered as a downstream gas permeator. Therefore, when the carbon dioxide gas permeability of the separation membrane unit 110 is z1, the carbon dioxide gas permeability z1 of the separation membrane unit 110 is considered to be expressed by the following equation (Equation 6) as a combination of the carbon dioxide gas permeability A of the separation membrane 112 and the gas permeability C of the porous plate 111. z1=(AC) / (A+C) (Equation 6)

[0066] Similarly, when the nitrogen gas permeability of the separation membrane unit 110 is denoted as z2, the nitrogen gas permeability z2 of the separation membrane unit 110 is considered to be expressed by the following equation (7). z2=(BC) / (B+C) (Equation 7)

[0067] Let α be the selectivity ratio of the separation membrane unit 110. Based on (Equation 6) and (Equation 7), the selectivity ratio α of the separation membrane unit 110 is considered to be expressed by (Equation 8) below. α=z1 / z2={(B+C) / (A+C)}·(A / B) (Equation 8)

[0068] Based on (Equation 8), the selectivity ratio α of the separation membrane unit 110 can be determined by multiplying the selectivity ratio A / B of the separation membrane 112 by (B+C) / (A+C). Therefore, (B+C) / (A+C) can be considered as a multiplier of the selectivity ratio.

[0069] Hereinafter, (B+C) / (A+C) will also be referred to as the "selectivity ratio (B+C) / (A+C)". In the selectivity ratio (B+C) / (A+C), the carbon dioxide gas permeability A and nitrogen gas permeability B are determined by the performance of the separation membrane 112 incorporated into the separation membrane unit 110. The nitrogen gas permeability B is smaller than the carbon dioxide gas permeability A. Therefore, regardless of the value of the gas permeability C of the perforated plate 111, the selectivity ratio (B+C) / (A+C) should be less than 1. Furthermore, the larger the value of the gas permeability C of the perforated plate 111, the less influence the magnitude of the values ​​of carbon dioxide gas permeability A and nitrogen gas permeability B can be reduced, and the selectivity ratio (B+C) / (A+C) approaches 1.

[0070] Therefore, it is clear that increasing the gas permeability C of the porous plate 111 is important in order to increase the selectivity ratio α of the separation membrane unit 110. Furthermore, considering only the effect of gas permeability C, it is thought that the selectivity ratio α of the separation membrane unit 110 can be made to less than 100% of the selectivity ratio A / B of the separation membrane 112, but 80% or more, by designing the porous plate 111 to satisfy the following equation (9). 1>(B+C) / (A+C)≧0.8 (Formula 9)

[0071] However, in reality, due to other factors such as insufficient pressure reduction in pump 150, even if equation (9) above is satisfied, the selectivity ratio α of the separation membrane unit 110 may not be 80% or more of the selectivity ratio A / B of the separation membrane 112. Thus, (B+C) / (A+C) is not necessarily a multiple of the selectivity ratio, but (B+C) / (A+C) is considered to have a certain correlation with the selectivity ratio α of the separation membrane unit 110.

[0072] The gas permeability C of the perforated plate 111 can be increased by reducing the pressure loss in the perforated plate 111. The pressure loss in the perforated plate 111 can be adjusted by, for example, the average thickness T2 of the perforated plate 111, the average diameter D1 of the multiple through holes 111h, the aperture ratio of the perforated plate 111, and the surface roughness of the perforated plate 111. The smaller the average thickness T2 of the perforated plate 111, the smaller the pressure loss. The larger the average diameter D1 of the multiple through holes 111h, the smaller the pressure loss. The larger the aperture ratio of the perforated plate 111, the smaller the pressure loss. The smaller the surface roughness of the perforated plate 111, the smaller the pressure loss.

[0073] As mentioned above, damage to the separation membrane 112 can be suppressed when T1 / D1 ≥ 0.02. On the other hand, the larger the average thickness T1 of the separation membrane 112, or the smaller the average diameter D1 of the multiple through holes 111h, the lower the carbon dioxide gas permeability of the separation membrane unit 110. Therefore, it is preferable that 1.5 ≥ T1 / D1 ≥ 0.02, and more preferably that 0.1 ≥ T1 / D1 ≥ 0.02.

[0074] Thus, the inventors of this application have clarified that in order to suppress damage to the separation membrane 112 and to ensure that the selectivity ratio α of the separation membrane unit 110 is good relative to the selectivity ratio A / B of the separation membrane 112, it is important to consider both T1 / D1 and the gas permeability C of the perforated plate 111.

[0075] Next, we will explain the design method for the separation membrane unit 110 based on the above. The design method for the separation membrane unit 110 comprises the steps of selecting the separation membrane 112 and designing the perforated plate 111. Each step is described in detail below.

[0076] In the step of selecting the separation membrane 112, a separation membrane having 500,000 GPU ≥ A ≥ 1,000 GPU and 200 μm ≥ T1 ≥ 10 μm is selected as the separation membrane 112 to be incorporated into the separation membrane unit 110.

[0077] In the process of designing the perforated plate 111, the perforated plate 111 is designed such that T1 / D1 ≥ 0.02 and 1 > (B+C) / (A+C) ≥ 0.8.

[0078] Thus, based on the average thickness T1, carbon dioxide gas permeability A, and nitrogen gas permeability B of the selected separation membrane 112, the values ​​of average diameter D1 and gas permeability C that yield a separation membrane unit 110 with a good selectivity ratio α while suppressing damage to the separation membrane 112 are clearly defined. Therefore, the design of the separation membrane unit 110 becomes easier. As a result, a separation membrane unit 110 with a good selectivity ratio α relative to the selectivity ratio A / B of the separation membrane 112 can be easily obtained while suppressing damage to the separation membrane 112.

[0079] Next, the effects of this embodiment will be described. The separation membrane unit 110 according to this embodiment is a separation membrane unit 110 that selectively separates carbon dioxide gas from a supply gas G1 containing carbon dioxide gas and nitrogen gas. The separation membrane unit 110 comprises a porous plate 111 and a separation membrane 112. The porous plate 111 has a first surface 111a and a second surface 111b that are in a front-back relationship with each other, and a plurality of through holes 111h are formed thereon that extend from the first surface 111a toward the second surface 111b. The separation membrane 112 includes a porous body 113 disposed on the first surface 111a and a resin layer 114 disposed on the porous body 113 that selectively permeates carbon dioxide gas contained in the supply gas G1 toward the porous body 113. When the carbon dioxide gas permeability of the separation membrane 112 is A, 500,000 GPU ≥ A ≥ 1,000 GPU. When the average thickness of the separation membrane 112 is T1, then 200 μm ≥ T1 ≥ 10 μm. When the average diameter of the multiple through holes 111h in the first surface 111a is D1, then T1 / D1 ≥ 0.02. When the nitrogen gas permeability of the separation membrane 112 is B and the gas permeability of the porous plate 111 is C, then 1 > (B + C) / (A + C) ≥ 0.8.

[0080] As mentioned above, T1 / D1 ≥ 0.02. Therefore, when the pressure applied to the surface 112a to which the supply gas G1 is supplied in the separation membrane 112 is higher than the pressure applied to the surface 112b in contact with the porous plate 111 in the separation membrane 112, damage to the separation membrane 112 can be suppressed. Also, 1 > (B+C) / (A+C) ≥ 0.8. Therefore, a separation membrane unit 110 with a good selectivity ratio α relative to the selectivity ratio A / B of the separation membrane 112 can be realized. In other words, it is possible to achieve both the suppression of damage to the separation membrane 112 and the improvement of the selectivity ratio α of the separation membrane unit 110.

[0081] Furthermore, 1.5 ≥ T1 / D1. This prevents the average thickness T1 of the separation membrane 112 from becoming excessively large, and the average diameter D1 of the multiple through-holes 111h of the porous plate 111 from becoming excessively small. As a result, a decrease in the carbon dioxide gas permeability of the separation membrane unit 110 can be suppressed.

[0082] Furthermore, 5mm ≥ D1 ≥ 0.1mm. By setting the average diameter D1 of the multiple through holes 111h in the perforated plate 111 to be less than or equal to the above upper limit, the rigidity of the perforated plate 111 can be improved. This suppresses deformation of the perforated plate 111 when the pressure applied to the first surface 111a of the perforated plate 111 is higher than the pressure applied to the second surface 111b. In addition, by setting the average diameter D1 of the multiple through holes 111h in the perforated plate 111 to be greater than or equal to the above lower limit, the gas permeability C of the perforated plate 111 can be improved.

[0083] Furthermore, when the average thickness of the perforated plate 111 is T2, 30mm ≥ T2 ≥ 0.05mm. By setting the average thickness T2 of the perforated plate 111 to be less than or equal to the above upper limit, the gas permeability C of the perforated plate 111 can be improved. Also, by setting the average thickness T2 of the perforated plate 111 to be greater than or equal to the above lower limit, the rigidity of the perforated plate 111 can be improved. As a result, deformation of the perforated plate 111 can be suppressed when the pressure applied to the first surface 111a of the perforated plate 111 is higher than the pressure applied to the second surface 111b.

[0084] Furthermore, the aperture ratio of the perforated plate 111 is between 5% and 95%. By setting the aperture ratio of the perforated plate 111 to be above the lower limit, the gas permeability C of the perforated plate 111 can be improved. By setting the aperture ratio of the perforated plate 111 to be below the upper limit, the rigidity of the perforated plate 111 can be improved. As a result, deformation of the perforated plate 111 can be suppressed when the pressure applied to the first surface 111a of the perforated plate 111 is higher than the pressure applied to the second surface 111b.

[0085] Furthermore, the porous body 113 has multiple pores 113h formed therein, and the average diameter of the multiple pores 113h is between 5 nm and 1,000 nm. By setting the average diameter of the multiple pores 113h of the porous body 113 to be above the lower limit, the carbon dioxide gas permeability of the porous body 113 can be improved. Also, by setting the average diameter of the multiple pores 113h of the porous body 113 to be below the upper limit, the mechanical strength of the porous body 113 can be improved. As a result, the porous body 113 can properly support the resin layer 114.

[0086] Furthermore, the perforated plate 111 may contain a metallic or ceramic material. This can increase the rigidity of the perforated plate 111.

[0087] Furthermore, the resin layer 114 contains organopolysiloxane. This increases the carbon dioxide gas permeability of the resin layer 114.

[0088] Furthermore, the porous body 113 may include a polymer material, a ceramic material, or a metallic material. If the porous body 113 includes a polymer material, the gas permeability of the porous body 113 can be increased. If the porous body 113 includes a ceramic material or a metallic material, the mechanical strength of the porous body 113 can be increased.

[0089] Furthermore, the separation device 100 according to this embodiment is equipped with the separation membrane unit 110 described above. Therefore, it is possible to realize a separation device 100 that has a good selectivity ratio relative to the selectivity ratio A / B of the separation membrane 112 while suppressing damage to the separation membrane 112.

[0090] <Example 1> Next, a separation membrane unit 210 according to modified example 1 will be described.

[0091] Figure 6 is a cross-sectional view showing the separation membrane unit 210 according to this modified example. The separation membrane unit 210 differs from the separation membrane unit 110 according to the previously described embodiment in the shape of the multiple through holes 211h formed in the perforated plate 211. Below, the differences between this modified example and the embodiment will be mainly described, and descriptions of configurations similar to the embodiment will be omitted as appropriate. The same applies to the description of Modified Example 2, which will be described later.

[0092] The perforated plate 211 has a first surface 211a and a second surface 211b that are in a front-back relationship with each other. The separation membrane 112 is placed on the first surface 211a. The perforated plate 211 has a plurality of through holes 211h that extend from the first surface 211a toward the second surface 211b.

[0093] The diameter d of each through-hole 211h decreases in a stepwise direction from the first surface 211a to the second surface 211b. This increases the area in which the separation membrane 112 is exposed from the perforated plate 211. As a result, the carbon dioxide gas permeability of the separation membrane unit 210 can be increased. Furthermore, by gradually decreasing the diameter d of each through-hole 211h from the first surface 211a to the second surface 211b, the solid portion of the perforated plate 111 can be increased, thereby increasing the rigidity of the perforated plate 211.

[0094] In this modified example, the diameter d of the through-hole 211h changes once in the direction from the first surface 211a to the second surface 211b, but it may change two or more times.

[0095] <Modification 2> Next, a separation membrane unit 310 according to modified example 2 will be described.

[0096] Figure 7 is a cross-sectional view showing the separation membrane unit 310 according to this modified example. The separation membrane unit 310 differs from the separation membrane unit 110 according to the embodiment in the shape of the multiple through holes 311h formed in the porous plate 311.

[0097] The perforated plate 311 has a first surface 311a and a second surface 311b that are in a front-back relationship with each other. The separation membrane 112 is placed on the first surface 311a. The perforated plate 311 has a plurality of through holes 311h that extend from the first surface 311a toward the second surface 311b.

[0098] The diameter d of each through-hole 311h decreases continuously in the direction from the first surface 311a to the second surface 311b. In this embodiment, the shape of each through-hole 311h is frustoconical. Even with this configuration, the same effects as the separation membrane unit 210 according to Modification 1 can be obtained. Note that "the diameter d decreases continuously" does not strictly mean that the diameter d gradually decreases, but rather allows for surface roughness of the through-hole 311h formation surface due to the manufacturing precision of the perforated plate 111, etc. [Examples]

[0099] Next, examples will be described. Figure 8 is Table 1 showing the configurations and evaluation results of the separation membrane units of Examples 1 to 5 and Comparative Examples 1 to 4.

[0100] First, it was examined whether the separation membrane was damaged according to the value of T1 / D1 and how the selection ratio of the separation membrane unit changed depending on the structure of the porous plate. This will be described in detail below.

[0101] As shown in Table 1, separation membrane units according to Examples 1 to 5 and Comparative Examples 1 to 4 were prepared. Each separation membrane unit includes a porous plate and a separation membrane.

[0102] The method for preparing each separation membrane will be described. First, on one surface of a porous body made of alumina (A l2 O3), an organopolysiloxane film was formed by a plasma polymerization method. Thereby, a separation membrane, which is a composite membrane of a porous body and a resin layer, was obtained. Note that octamethyltrisiloxane was used as the source gas, and the constituent material of the obtained resin layer was organopolysiloxane. Also, the average diameter of the pores of the porous body was 100 nm, and the porosity was about 50%. The average thickness T1 of the separation membranes and the average thickness of the resin layer in each example and each comparative example were measured by SEM. The results are shown in Table 1.

[0103] Using the gas permeability measuring device 10, the carbon dioxide gas permeability A and nitrogen gas permeability B of each separation membrane were measured. When measuring the carbon dioxide gas permeability A of each separation membrane, the gas supply unit 11 was set to supply a single gas of carbon dioxide gas. When measuring the nitrogen gas permeability B of each separation membrane, the gas supply unit 11 was set to supply a single gas of nitrogen gas. Then, the selection ratio A / B of each separation membrane was calculated from the carbon dioxide gas permeability A and nitrogen gas permeability B. The results are shown in Table 1.

[0104] Furthermore, perforated metal made of stainless steel was used for each perforated plate. The average diameter D1 of the multiple through holes in each perforated plate was measured using calipers or a measuring microscope. The average thickness T2 of each perforated plate was also measured using calipers. The shape of each through hole was cylindrical, as in the embodiment. The aperture ratio of the perforated plate was calculated from the total area of ​​the average diameter D1 of the multiple through holes. In addition, T1 / D1 was calculated from the average thickness T1 of the separation membrane and the average diameter D1 of the multiple through holes. The results are shown in Table 1.

[0105] Furthermore, the gas permeability C of each perforated plate was measured using the gas permeability measuring device 10. When measuring the gas permeability C of each perforated plate, the gas supply unit 11 was set to supply only nitrogen gas. (B+C) / (A+C) was calculated from the carbon dioxide gas permeability A, nitrogen gas permeability B, and gas permeability C. The results are shown in Table 1.

[0106] Next, each of the prepared separation membranes was placed on each perforated plate. Then, the carbon dioxide gas permeability and nitrogen gas permeability of each separation membrane unit were measured using the gas permeability measuring device 10. At this time, the gas supplied by the gas supply unit 11 was a mixture of carbon dioxide gas and nitrogen gas. The concentration of carbon dioxide gas was set to 400 ppm. The test temperature was set to 20°C. The selectivity ratio α of the separation membrane unit was calculated from the measured carbon dioxide gas permeability and nitrogen gas permeability. The decrease rate of the selectivity ratio α of the separation membrane unit relative to the selectivity ratio A / B of the separation membrane was also calculated. Furthermore, the presence or absence of damage to the separation membrane was confirmed by SEM. The separation membrane units were then evaluated according to the following evaluation criteria. The results are shown in Table 1.

[0107] S: No damage to the separation membrane, and the decrease in selectivity is 20% or less. T: The separation membrane is damaged, or the decrease in selectivity exceeds 20%.

[0108] In the separation membrane units of Examples 1 to 5, T1 / D1 ≥ 0.02 was observed in all cases, and no damage to the separation membrane was observed. Furthermore, in the separation membrane units of Examples 1 to 5, (B+C) / (A+C) ≥ 0.8, and the decrease in selectivity was 20% or less in all cases. Therefore, a separation membrane unit with a good selectivity α relative to the selectivity A / B of the separation membrane was realized while suppressing damage to the separation membrane.

[0109] Furthermore, among the perforated plates of Examples 1 to 5, the perforated plates of Examples 2 and 5 had the highest gas permeability C. Compared to the perforated plates of Examples 1, 3, and 4, the perforated plates of Examples 2 and 5 had a smaller average diameter D1 of multiple through holes and a smaller aperture ratio, but the average thickness T2 of the perforated plates was smaller. Therefore, it was found that reducing the average thickness T2 of the perforated plate is particularly effective in increasing the gas permeability C.

[0110] In the separation membrane unit of Comparative Example 1, 0.02 > T1 / D1, indicating damage to the separation membrane. The average thickness T1 of the separation membrane in Comparative Example 1 is approximately the same as the average thickness T1 of the separation membrane in Example 2, but the average diameter D1 of the multiple through-holes in the perforated plate of Comparative Example 1 is larger than the average diameter D1 of the multiple through-holes in the perforated plate of Example 2. Furthermore, in Comparative Example 1, the separation membrane was deflected as if falling into the through-holes of the perforated plate. Therefore, in Comparative Example 1, the average diameter D1 of the multiple through-holes in the perforated plate was too large relative to the average thickness T1 of the separation membrane, resulting in excessive deflection of the separation membrane and subsequent damage.

[0111] In the separation membrane unit of Comparative Example 2, T1 / D1 ≥ 0.02, and no damage to the separation membrane was observed. However, 0.8 > (B+C) / (A+C), and the rate of decrease in selectivity exceeded 20%. The perforated plate of Comparative Example 2 is the same as the perforated plate of Example 1, and the gas permeability C is the same. However, the carbon dioxide gas permeability A and nitrogen gas permeability B of the separation membrane of Comparative Example 2 are higher than those of the separation membrane of Example 1. Therefore, even though the same perforated plate was used, in Comparative Example 2, the gas permeability C of the perforated plate was insufficient, and (B+C) / (A+C) decreased. As a result, it is considered that the rate of decrease in selectivity exceeded 20%.

[0112] In the separation membrane unit according to Comparative Example 3, the separation membrane failed to stand on its own and was damaged. This is thought to be because, despite the average thickness T1 of the separation membrane being 8 μm, which is smaller than that of Examples 1 to 5, the average thickness of the resin layer was made too large, and the porous material could not support the resin layer, causing the separation membrane to be damaged. In Examples 1 to 5, the average thickness T1 of the separation membrane was 10 μm or more, and the self-supporting ability of the separation membrane was ensured even with a large average thickness of the resin layer. Therefore, in order to ensure the self-supporting ability of the separation membrane regardless of the average thickness of the resin layer, it is considered preferable for the thickness of the separation membrane to be 10 μm or more.

[0113] In the separation membrane unit according to Comparative Example 4, A > 500,000 GPU. In such a separation membrane, the decrease in selectivity rate exceeded 20%. This is thought to be because if the carbon dioxide gas permeability A of the separation membrane is too high, the concentration of carbon dioxide gas directly above the separation membrane decreases, and as a result, the carbon dioxide gas permeability of the separation membrane unit decreases. Therefore, it is preferable that 500,000 GPU ≥ A.

[0114] Furthermore, the selectivity ratio α of the separation membrane units in Examples 1-5 and Comparative Examples 1-4 shown in the table was obtained experimentally, as described above, but it showed a trend that was generally similar to that of the theoretical formula (Equation 8). Therefore, it was confirmed that designing the perforated plate using (B+C) / (A+C) is appropriate.

[0115] In summary, it was found that when 500,000 GPU ≥ A ≥ 1,000 GPU, 200 μm ≥ T1 ≥ 10 μm, T1 / D1 ≥ 0.02, and 1 > (B+C) / (A+C) ≥ 0.8, a separation membrane unit can be realized that has a good selectivity α relative to the selectivity ratio A / B of the separation membrane while suppressing the damage to the separation membrane.

[0116] Figure 9 is Table 2, which shows the configuration and evaluation results of the separation membrane units of Examples 6 and 7 and Comparative Example 5.

[0117] Next, we investigated whether the separation membrane was damaged depending on the shape of the through-holes in the perforated plate, and how the selectivity ratio of the separation membrane unit changed depending on the shape of the through-holes in the perforated plate. Details are described below.

[0118] First, separation membrane units according to Examples 6 and 7 and Comparative Example 5 were prepared. Each separation membrane unit comprises a perforated plate and a separation membrane. The method for preparing each separation membrane is the same as described above, so the explanation is omitted. The material for each perforated plate is stainless steel perforated metal.

[0119] The shape of each through-hole in the perforated plate of Example 6 was the same as the shape of the through-hole in the perforated plate of Modified Example 1. That is, the diameter of each through-hole was made progressively smaller in the direction from the separation membrane toward the perforated plate.

[0120] The shape of each through-hole in the perforated plate of Example 7 was the same as the shape of the through-hole in the perforated plate of Modified Example 2. That is, the diameter of each through-hole was made to decrease continuously in the direction from the separation membrane toward the perforated plate.

[0121] In Comparative Example 5, the shape of each through-hole in the porous plate was designed so that the diameter of each through-hole remained generally constant in the direction from the separation membrane toward the porous plate.

[0122] Then, using the same method as described above, the average thickness T1 of the separation membrane, the average thickness of the resin layer, the carbon dioxide gas permeability A of the separation membrane, the nitrogen gas permeability B of the separation membrane, and the selectivity ratio A / B of the separation membrane were determined. Also, using the same method as described above, the average diameter D1 of the through holes on the first surface of the perforated plate, the average thickness T2 of the perforated plate, the aperture ratio T1 / D1 of the perforated plate, and the gas permeability C of the perforated plate were determined. Furthermore, using the same method as described above, (B+C) / (A+C), the selectivity ratio α of the separation membrane unit, and the rate of decrease in selectivity were determined. In addition, the presence or absence of damage to the separation membrane was investigated using the same method as described above. The results are shown in Table 2.

[0123] In Examples 6 and 7, T1 / D1 ≥ 0.02, and no damage to the separation membrane was observed. Therefore, it was found that the evaluation method using T1 / D1 ≥ 0.02 can be applied even to porous plates in which the shape of the through-holes changes in the thickness direction of the porous plate, as in Examples 6 and 7.

[0124] Furthermore, in Examples 6 and 7, 1 > (B+C) / (A+C) ≥ 0.8, and the decrease in selectivity was 20% or less. Therefore, it was found that even with perforated plates where the shape of the through-holes changes in the thickness direction of the perforated plate, as in Examples 6 and 7, sufficient gas permeability C can be secured. In addition, since the gas permeability C of the perforated plate in Example 7 was higher than that of the perforated plate in Example 6, it was also found that continuously changing the diameter of the through-holes can further increase the gas permeability C.

[0125] In Comparative Example 5, T1 / D1 ≥ 0.02, and no damage to the separation membrane was observed. However, 0.8 > (B+C) / (A+C), and the rate of decrease in selectivity exceeded 20%. This is thought to be because the gas permeability C of the porous plate in Comparative Example 5 was lower than the gas permeability C of the porous plates in Examples 6 and 7.

[0126] Although the separation membrane unit and separation apparatus according to the present invention have been described above based on the illustrated embodiments and several modifications, the present invention is not limited thereto.

[0127] For example, the separation membrane unit and separation apparatus according to the present invention may be such that each part of the above-described embodiment and modified example is replaced with any component having a similar function, or any component may be added to the above-described embodiment and modified example. [Explanation of Symbols]

[0128] 10...Gas permeability measuring device, 11...Gas supply unit, 12...Chamber, 12a...Upstream space, 12b...Downstream space, 13...Upstream pressure gauge, 14...Downstream pressure gauge, 15...Flow meter, 16...Vacuum pump, 17...Concentration meter, 100...Separation device, 110...Separation membrane unit, 111...Perforated plate, 111a...First surface, 111b...Second surface, 111c...Center, 111h...Through hole, 112...Separation membrane, 112a...Surface, 112b...Surface, 113...Porous body, 113h...Vacuum, 114...Resin layer, 120...Housing section, 120a...Intake port, 120b ...Discharge port, 120c...Step, 120s...Accommodation space, 121...Upper wall, 122...Lower wall, 123...Side wall, 130...Fixing member, 131...Fixing tool, 140...Piping, 141...Internal space, 150...Pump, 210...Separation membrane unit, 211...Perforated plate, 211a...First surface, 2 11b...Second surface, 211h...Through hole, 310...Separation membrane unit, 311...Perforated plate, 311a...First surface, 311b...Second surface, 311h...Through hole, C1...Central axis, G1...Supply gas, G2...Permeate gas, L1...First straight line, L2...Second straight line, d...Diameter, δ...Deflection, θ...Angle

Claims

1. A separation membrane unit for selectively separating carbon dioxide gas from a supply gas containing carbon dioxide gas and nitrogen gas, A porous plate having a first surface and a second surface that are in a front-back relationship with respect to each other, and having a plurality of through holes formed therein that extend from the first surface toward the second surface, A separation membrane comprising a porous body disposed on the first surface, and a resin layer disposed on the porous body, which selectively permeates the carbon dioxide gas contained in the supply gas toward the porous body, Equipped with, When the carbon dioxide gas permeability of the separation membrane is A, then 500,000 GPU ≥ A ≥ 1,000 GPU. When the average thickness of the separation membrane is T1, then 200 μm ≥ T1 ≥ 10 μm. When the average diameter of the plurality of through holes in the first surface is D1, T1 / D1 ≥ 0.02, When the nitrogen gas permeability of the separation membrane is B and the gas permeability of the porous plate is C, then 1 > (B + C) / (A + C) ≥ 0.

8. A separation membrane unit characterized by the following features.

2. The separation membrane unit according to claim 1, wherein 1.5 ≥ T1 / D1.

3. A separation membrane unit according to claim 1 or 2, wherein 5 mm ≥ D1 ≥ 0.1 mm.

4. The separation membrane unit according to claim 1 or 2, wherein when the average thickness of the perforated plate is T2, 30 mm ≥ T2 ≥ 0.05 mm.

5. The separation membrane unit according to claim 1 or 2, wherein the aperture ratio of the porous plate is 5% or more and 95% or less.

6. The separation membrane unit according to claim 1 or 2, wherein the diameter of the through-hole decreases continuously or stepwise in the direction from the first surface to the second surface.

7. The porous body has a plurality of pores formed therein. The separation membrane unit according to claim 1 or 2, wherein the average diameter of the plurality of pores is 5 nm or more and 1,000 nm or less.

8. The separation membrane unit according to claim 1 or 2, wherein the porous plate comprises a metal material or a ceramic material.

9. The separation membrane unit according to claim 1 or 2, wherein the resin layer comprises an organopolysiloxane.

10. The separation membrane unit according to claim 1 or 2, wherein the porous body comprises a polymer material, a ceramic material, or a metallic material.

11. A separation apparatus equipped with the separation membrane unit described in claim 1 or 2.

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