Carbon film composite and method for producing carbon film composite

Abstract

This carbon film composite is provided with: a porous support (11); and a carbon film (12) provided on a surface of the support (11). A carbon-rich layer (35) having a larger amount of carbon than the surrounding portions is provided inside the support (11). The carbon-rich layer (35) is disposed at a position separated from the surface of the support (11). As a result, a decrease in the permeation flux of the carbon film composite (1) can be limited while the separation coefficient thereof can be improved.

Description

Carbon membrane composite and method for producing the carbon membrane composite

[0001] The present invention relates to a carbon membrane composite and a method for manufacturing the same. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2024-052143, filed on March 27, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] Conventionally, carbon membrane composites, in which a carbon membrane is provided on the surface of a porous support, have been used as filters having excellent chemical stability and heat resistance. JP 2010-509035 A (Document 1) and WO 2012 / 111792 (Document 2) propose techniques for improving the permeation flux and separation factor of carbon membrane composites.

[0003] Literature 1 discloses a technique for improving the permeation flux of a carbon membrane composite by forming a composite layer having a thickness of 1 mm or less (i.e., a layer in which a carbon membrane material has permeated into a dense layer of the support) at the interface between the support and the carbon membrane of the carbon membrane composite. Furthermore, as a method for producing the carbon membrane composite, the literature discloses a technique for thinning and uniforming the thicknesses of the carbon membrane and the composite layer by applying a carbon membrane precursor solution to the surface of the support and pressurizing the inside of the pores of the support, thereby making it difficult for the precursor solution to permeate from the surface of the support into the pores.

[0004] Literature 2 proposes providing a layer having a pore size smaller than that of the support at the interface between the carbon membrane and the support of a carbon membrane composite, and providing carbon so as to cover the inner surfaces of the pores of the layer and the inner surfaces of the pores of the support. According to Literature 2, a fluid (i.e., gas, liquid, etc.) that has permeated the carbon membrane quickly moves through the pores of the layer and the support via the carbon and is discharged to the outside of the system, thereby improving the permeation flux and separation factor of the carbon membrane composite.

[0005] However, the carbon membrane composite of Document 1 has limitations in reducing pressure drop in the composite layer and in improving permeation flux.

[0006] In the carbon membrane composite of Literature 2, carbon permeates the entire layer and the portion of the support adjacent to the layer. Therefore, the carbon present in the pores over a relatively wide area may inhibit fluid permeation, resulting in a risk of a decrease in the permeation flux of the carbon membrane composite. Furthermore, the carbon content in the layer with a small particle size is greater than the carbon content in the support. Because the layer with a high carbon content is in direct contact with the carbon membrane, the fluid that has permeated the carbon membrane may be less likely to permeate the layer, further reducing the permeation flux of the carbon membrane composite.

[0007] The present invention is directed to a carbon membrane composite, and aims to improve the separation factor while suppressing a decrease in permeation flux of the carbon membrane composite.

[0008] A first aspect of the present invention is a carbon membrane composite comprising a porous support and a carbon membrane provided on a surface of the support. A carbon-rich layer is provided inside the support, the carbon-rich layer being spaced apart from the surface of the support and having a higher carbon content than the surrounding area.

[0009] This makes it possible to improve the separation factor while suppressing a decrease in the permeation flux of the carbon membrane composite.

[0010] A second aspect of the invention is the carbon membrane composite of the first aspect, wherein the support includes a first layer extending from the surface of the support toward the inside of the support, and a second layer extending from the first layer toward the inside of the support and having a larger average pore diameter than the first layer, and the carbon-rich layer is located closer to the surface of the support than the interface between the first layer and the second layer.

[0011] A third aspect of the present invention is the carbon membrane composite of the second aspect, wherein the carbon-rich layer is in contact with the interface between the first layer and the second layer.

[0012] A fourth aspect of the invention is the carbon membrane composite of the second aspect (or may be either the second or third aspect), wherein the sum of the thickness from the surface of the support to the carbon-rich layer and the thickness of the carbon-rich layer in a thickness direction perpendicular to the surface of the support is 0.1 μm or more and 30 μm or less.

[0013] A fifth aspect of the invention is the carbon membrane composite of the second aspect (which may be any one of the second to fourth aspects), wherein the thickness from the surface of the support to the carbon-rich layer in a thickness direction perpendicular to the surface of the support is 1.0 to 20.0 times the thickness of the carbon-rich layer.

[0014] A sixth aspect of the present invention is the carbon membrane composite of the first aspect, wherein the support includes a first layer extending from the surface of the support toward the interior of the support, and a second layer extending from the first layer toward the interior of the support and having a larger average pore diameter than the first layer, and the carbon-rich layer is located on the opposite side of the surface of the support with respect to the interface between the first layer and the second layer.

[0015] A seventh aspect of the invention is the carbon membrane composite of the sixth aspect, wherein the sum of the thickness from the surface of the support to the carbon-rich layer and the thickness of the carbon-rich layer in a thickness direction perpendicular to the surface of the support is 1 μm or more and 1000 μm or less.

[0016] An eighth aspect of the invention is the carbon membrane composite of any one of the first to seventh aspects, wherein the maximum carbon amount in the carbon-rich layer is 1.1 to 4.0 times the average carbon amount in a region between the surface of the support and the carbon-rich layer.

[0017] A ninth aspect of the invention is the carbon membrane composite of the eighth aspect, wherein the maximum carbon content in the carbon-rich layer is 1.2 to 2.0 times the average carbon content in the region between the surface of the support and the carbon-rich layer.

[0018] A tenth aspect of the invention is the carbon membrane composite according to any one of Aspects 1 to 7 (or any one of Aspects 1 to 5), wherein the maximum carbon amount in the carbon-rich layer is 0.05 to 0.25 times the maximum carbon amount in the carbon membrane.

[0019] An eleventh aspect of the invention is the carbon membrane composite according to any one of the first to seventh aspects (or any one of the first to sixth aspects), wherein the carbon-rich layer has a thickness of 0.01 μm or more and 15 μm or less in a thickness direction perpendicular to the surface of the support.

[0020] A twelfth aspect of the invention is a method for producing a carbon membrane composite, comprising: a) applying a first precursor solution containing a first precursor from a surface side of a porous support and allowing the solution to penetrate the surface, thereby forming a first precursor layer containing the first precursor inside the support; b) removing a part of the first precursor layer from the surface side of the support; c) applying a second precursor solution containing a second precursor from the surface side of the support, thereby forming a second precursor layer containing the second precursor inside the support, thereby forming a second precursor film that is a film containing the second precursor on the surface of the support; and d) carbonizing the first precursor layer, the second precursor layer, and the second precursor film to form a carbon film on the surface of the support, and to form a carbon-rich layer inside the support that is located at a position spaced from the surface of the support and has a higher carbon amount than surrounding regions.

[0021] A thirteenth aspect of the invention is the method for producing a carbon membrane composite according to the twelfth aspect, further comprising, between the b) step and the c) step, a step of curing the first precursor layer remaining inside the support.

[0022] A fourteenth aspect of the invention is a method for producing a carbon membrane composite, comprising: a) applying a first precursor solution containing a first precursor from a surface side of a porous support while reducing the pressure on the side of the support opposite to the surface to cause the first precursor solution to permeate the support, thereby forming a first precursor layer containing the first precursor inside the support; b) applying a second precursor solution containing a second precursor from the surface side of the support, thereby forming a second precursor layer containing the second precursor inside the support, and forming a second precursor film that is a film containing the second precursor on the surface of the support; and c) carbonizing the first precursor layer, the second precursor layer, and the second precursor film to form a carbon film on the surface of the support, and to form a carbon-rich layer inside the support that is located at a position spaced from the surface of the support and has a higher carbon amount than surrounding regions.

[0023] A fifteenth aspect of the invention is the method for producing a carbon membrane composite according to the fourteenth aspect, further comprising a step of curing the first precursor layer between the step a) and the step b).

[0024] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention, which proceeds with reference to the accompanying drawings.

[0025] 1 is a side view of a carbon membrane composite according to a first embodiment. FIG. 1 is a longitudinal sectional view of a carbon membrane composite. FIG. 1 is a sectional view showing an enlarged portion of the carbon membrane composite. FIG. 2 is a sectional view showing an enlarged portion of the carbon membrane composite. FIG. 3 is a sectional view showing an enlarged portion of the carbon membrane composite. FIG. 4 is a diagram showing the relationship between measured depth and carbon amount. FIG. 5 is a diagram showing the relationship between measured depth and carbon amount. FIG. 6 is a diagram showing the relationship between measured depth and carbon amount. FIG. 7 is a diagram showing the relationship between measured depth and carbon amount. FIG. 8 is a diagram showing the relationship between measured depth and carbon amount. FIG. 9 is a diagram showing the relationship between measured depth and carbon amount. FIG. 10 is a diagram showing the relationship between measured depth and carbon amount. FIG. 11 is a diagram showing the relationship between measured depth and carbon amount. FIG. 12 is a diagram showing the relationship between measured depth and carbon amount. FIG. 13 is a diagram showing the relationship between measured depth and carbon amount. 1A and 1B are cross-sectional views of a carbon membrane composite in the process of being manufactured, and FIG. 1C are cross-sectional views of a carbon membrane composite in the process of being manufactured, and FIG. 1D are cross-sectional views showing an enlarged portion of another carbon membrane composite.

[0026] Fig. 1 is a side view showing an end face of a carbon membrane composite 1 according to a first embodiment of the present invention. Fig. 2 is a longitudinal cross-sectional view of the carbon membrane composite 1. The carbon membrane composite 1 is a substantially columnar member extending in the left-right direction in Fig. 2. In the following description, the left-right direction in Fig. 2 will also be referred to as the "longitudinal direction." Fig. 1 shows an end face on one side in the longitudinal direction of the carbon membrane composite 1, but the end face on the other side has the same shape as that shown in Fig. 1.

[0027] The carbon membrane composite 1 includes a support 11 and a carbon membrane 12. The support 11 is a porous member that is permeable to gases and liquids. The support 11 illustrated in FIGS. 1 and 2 has a monolithic structure in which a single, continuous columnar body is provided with a plurality of through-holes 111 (hereinafter also referred to as "cells 111") that extend in the longitudinal direction of the body. The monolithic structure is a concept that includes a honeycomb structure. The outer shape of the support 11 is, for example, approximately cylindrical. The multiple cells 111 are arranged, for example, in a substantially concentric pattern in a cross section of the support 11 perpendicular to the longitudinal direction. The cross section of each cell 111 perpendicular to the longitudinal direction has, for example, an approximately circular shape. Note that "approximately circular" includes not only a perfect circle but also an ellipse or a distorted circle. In FIG. 2, the diameter of the cells 111 is larger than the actual diameter, and the number of cells 111 is smaller than the actual number. Note that the number, cross-sectional shape, and arrangement of the cells 111 are not limited to the above example and may be variously modified.

[0028] The length of the support 11 (i.e., the length in the left-right direction in FIG. 2) is, for example, 10 cm to 200 cm. The outer diameter of the support 11 is, for example, 0.5 cm to 30 cm. The distance between the central axes of adjacent cells 111 is, for example, 0.3 mm to 10 mm. The inner diameter of the cells 111 is, for example, 0.5 mm to 25 mm. The shape of the support 11 may be, for example, a honeycomb shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal columnar shape. When the shape of the support 11 is tubular or cylindrical, the thickness of the support 11 is, for example, 0.1 mm to 10 mm.

[0029] A carbon film 12 is provided on the inner surface of each cell 111. The carbon film 12 is preferably provided so as to cover substantially the entire inner surface of each cell 111. The support 11 is used to support the carbon film 12. In Figures 1 and 2, the carbon film 12 is depicted by a thick line.

[0030] Fig. 3 is an enlarged cross-sectional view of a portion of the carbon membrane composite 1 shown in Fig. 2. In Fig. 3, the carbon membrane 12 is shown with hatched lines to make the thickness of the carbon membrane 12 appear thicker than it actually is. In addition, the diameter of the cells 111 is shown smaller than it actually is. In Fig. 3, the particles constituting the support 11 are schematically depicted as circles, but the particles may have various shapes.

[0031] In the example shown in FIG. 3 , the support 11 includes a substrate 31, an intermediate layer 32, and a surface layer 33. The substrate 31, the intermediate layer 32, and the surface layer 33 are each porous. The substrate 31 has the monolith structure described above. In the support 11, the intermediate layer 32 and the surface layer 33 are provided on the inner surface of each through-hole of the substrate 31 (i.e., the through-hole that will become the cell 111), thereby forming the cell 111. The intermediate layer 32 is provided on the inner surface of each through-hole of the substrate 31 so as to be in direct contact with the inner surface and cover substantially the entire inner surface. The intermediate layer 32 is a substantially cylindrical portion that is relatively thin in thickness in the radial direction (hereinafter simply referred to as the "radial direction") about the central axis of the cell 111.

[0032] The surface layer 33 is provided on the inner surface of the intermediate layer 32 so as to be in direct contact with the inner surface and to cover substantially the entire inner surface. That is, the surface layer 33 is provided indirectly on the substrate 31 via the intermediate layer 32. The surface layer 33 is a substantially cylindrical portion with a relatively thin radial thickness. When viewed from the inside of the cells 111, the surface layer 33 is the innermost portion of the support 11. That is, the inner surface of the surface layer 33 is the inner surface of the cells 111. A carbon film 12 is provided on the inner surface of the surface layer 33 so as to cover substantially the entire inner surface. The carbon film 12 is in direct contact with an inner surface 331 of the surface layer 33. That is, the inner surface of the surface layer 33 is the surface of the support 11 on which the carbon film 12 is formed.

[0033] The region near the inner surface of the cell 111 has a laminated structure in which the surface layer 33, the intermediate layer 32, and the substrate 31 are laminated in the thickness direction (i.e., in the radial direction about the central axis of the cell 111). In this laminated structure, the surface layer 33 is a first layer that extends from the surface of the support 11 toward the inside of the support 11 (i.e., from the inner surface of the cell 111 toward the radially outward direction). The intermediate layer 32 is a second layer that extends from the surface layer 33 toward the inside of the support 11 and is provided between the surface layer 33 and the substrate 31. The substrate 31 is a third layer that extends from the intermediate layer 32 toward the inside of the support 11.

[0034] The thickness of the surface layer 33 in the thickness direction (i.e., the direction perpendicular to the surface of the support 11) is, for example, 1 μm or more and 100 μm or less. The thickness of the intermediate layer 32 in the thickness direction is, for example, 100 μm or more and 500 μm or less. The thickness of the surface layer 33 in the thickness direction (hereinafter simply referred to as "thickness") can be determined, for example, by observing the polished cross section of the sample with a scanning electron microscope (SEM). The thickness of the intermediate layer 32 can also be determined similarly, for example, by observing the polished cross section of the sample with an SEM.

[0035] In this embodiment, the material of the support 11 (i.e., the base material 31, the intermediate layer 32, and the surface layer 33) is a ceramic that is chemically stable during the process of forming the carbon film 12. The support 11 is formed, for example, of a ceramic sintered body. Examples of ceramic sintered bodies selected as the material of the support 11 include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide. Preferably, the support 11 is formed of alumina, mullite, zirconia, or titania. In this embodiment, alumina is used as the material of the support 11 in consideration of its high corrosion resistance, small change in pore size due to temperature changes, and relatively high strength. The materials of the base material 31, the intermediate layer 32, and the surface layer 33 may be the same or different.

[0036] The support 11 (i.e., the base material 31, the intermediate layer 32, and the surface layer 33) contains, for example, an inorganic binder for binding aggregate particles of the ceramic sintered body. The inorganic binder can be at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite.

[0037] The support 11 may also contain an alkali metal and / or alkaline earth metal, such as sodium (Na), potassium (K), calcium (Ca), or magnesium (Mg).

[0038] The average pore diameter of the surface layer 33 is smaller than the average pore diameter of the intermediate layer 32 and the average pore diameter of the substrate 31. The average pore diameter of the intermediate layer 32 is smaller than the average pore diameter of the substrate 31. In other words, the average pore diameter of the substrate 31 is larger than the average pore diameter of the intermediate layer 32, and the average pore diameter of the intermediate layer 32 is larger than the average pore diameter of the surface layer 33. The average pore diameter of the substrate 31 is, for example, 0.01 μm or more and 70 μm or less, and preferably 0.05 μm or more and 25 μm or less. The average pore diameter of the intermediate layer 32 is, for example, 0.01 μm or more and 10 μm or less. The average pore diameter of the surface layer 33 is, for example, 0.005 μm or more and 2.0 μm or less, and preferably 0.05 μm or more and 0.5 μm or less. The average pore diameters of the substrate 31, intermediate layer 32 and surface layer 33 can be measured by, for example, a mercury porosimeter, a perm porometer or a nanoperm porometer.

[0039] The porosity of the surface layer 33, the intermediate layer 32, and the substrate 31 is, for example, approximately the same. Note that the porosity of the surface layer 33, the intermediate layer 32, and the substrate 31 may be different. The porosity of the support 11 near the surface on which the carbon film 12 is formed is, for example, 20% or more and 60% or less. The porosity can be determined as the proportion of the area where voids exist in an SEM image of a cross section of the support 11.

[0040] The average particle size of the aggregate particles in the surface layer 33 (i.e., the median diameter in the volume-based particle size distribution (D ５０ )) is smaller than the average particle size of the aggregate particles in the intermediate layer 32. The average particle size of the aggregate particles in the intermediate layer 32 is also smaller than the average particle size of the aggregate particles in the base material 31. The average particle size of the aggregate particles in the base material 31 is, for example, 5 μm to 200 μm. The average particle sizes of the aggregate particles in the base material 31, intermediate layer 32, and surface layer 33 can be measured, for example, by laser diffraction.

[0041] As described above, the carbon membrane 12 is formed on the inner surface of each cell 111 (i.e., on the inner surface of the surface layer 33) and covers the inner surface over substantially the entire surface. In this embodiment, the carbon membrane 12 has a substantially cylindrical shape centered on a central axis extending in the longitudinal direction of the cell 111. The carbon membrane 12 is a porous membrane having micropores formed almost entirely of carbon or carbide. The carbon membrane 12 separates a specific substance from a mixture containing multiple substances by using the molecular sieve effect. For example, when a mixture of water and ethanol is introduced into the cell 111 of the carbon membrane composite 1, the water is selectively separated from the mixture by the carbon membrane 12, permeates the support 11, and is discharged from the outer surface of the carbon membrane composite 1.

[0042] The average pore diameter of the carbon membrane 12 is smaller than the average pore diameter of the surface layer 33 of the support 11. The average pore diameter of the carbon membrane 12 is, for example, 0.2 nm or more and 1.0 nm or less. By setting the average pore diameter of the carbon membrane 12 to 0.2 nm or more, it is possible to suppress a decrease in the permeation flux of the substance to be separated. Furthermore, by setting the average pore diameter of the carbon membrane 12 to 1.0 nm or less, it is possible to suppress a decrease in the separation factor (i.e., selectivity) of the carbon membrane 12. The average pore diameter of the carbon membrane 12 can be measured, for example, by gas permeation analysis.

[0043] The thickness of the carbon membrane 12 (i.e., the thickness in the thickness direction) is, for example, 0.1 μm or more and 5.0 μm or less, preferably 0.2 μm or less and 2.5 μm or less, and more preferably 0.3 μm or more and 1.5 μm or less. Increasing the thickness of the carbon membrane 12 improves the separation factor. Increasing the thickness of the carbon membrane 12 increases the permeation flux.

[0044] Fig. 4 is an enlarged cross-sectional view showing a region in the vicinity of the carbon film 12 in Fig. 3. As indicated by the hatched area different from that of the carbon film 12 in Fig. 4, a carbon-rich layer 35 is provided inside the support 11. The carbon-rich layer 35 is a layer-like region in the support 11 that has a higher carbon content than the region surrounding the carbon-rich layer 35.

[0045] The carbon-rich layer 35 is disposed inside the support 11 at a position spaced radially outward from the inner surface 331 of the surface layer 33 (i.e., the surface of the support 11). The carbon-rich layer 35 extends substantially parallel to the inner surface 331 of the surface layer 33 (i.e., the inner surface of the cell 111). The thickness of the carbon-rich layer 35 in the thickness direction (i.e., the direction perpendicular to the surface of the support 11) is substantially constant over substantially the entire circumferential direction centered on the central axis of the cell 111. The carbon-rich layer 35 is a substantially cylindrical portion centered on the central axis of the cell 111.

[0046] In the example shown in FIG. 4 , substantially the entire carbon-rich layer 35 is provided inside the surface layer 33. In other words, substantially the entire carbon-rich layer 35 is located between the interface 332 between the surface layer 33 and the intermediate layer 32 and the inner surface 331 of the surface layer 33. In other words, substantially the entire carbon-rich layer 35 is located closer to the inner surface 331 of the surface layer 33 than the interface 332 between the surface layer 33 and the intermediate layer 32 (i.e., radially inward, which is closer to the inner surface 331 in the thickness direction). Furthermore, a substantially cylindrical interface 352 of the carbon-rich layer 35 farther from the inner surface 331 of the surface layer 33 (i.e., radially outward) is located on the interface 332 between the surface layer 33 and the intermediate layer 32. In other words, the carbon-rich layer 35 is in contact with the interface 332 between the surface layer 33 and the intermediate layer 32.

[0047] A portion of the support 11 closer to the inner surface 331 of the surface layer 33 than the carbon-rich layer 35 (i.e., radially inward) has a lower carbon content than the carbon-rich layer 35, and will be referred to hereinafter as the "low carbon layer 36." The low carbon layer 36 is a region between the inner surface 331 of the surface layer 33 (i.e., the surface of the support 11) and the carbon-rich layer 35. The low carbon layer 36 is disposed adjacent to the carbon film 12 and the carbon-rich layer 35 between the carbon film 12 and the carbon-rich layer 35, and is in direct contact with the carbon film 12 and the carbon-rich layer 35. A substantially cylindrical interface 351 on the side of the carbon-rich layer 35 closer to the inner surface 331 of the surface layer 33 (i.e., radially inward) is the interface between the carbon-rich layer 35 and the low carbon layer 36.

[0048] 5 , the carbon-rich layer 35 may be disposed in the surface layer 33 at a distance radially inward from the interface 332 between the surface layer 33 and the intermediate layer 32. In this case, the radially outer interface 352 of the carbon-rich layer 35 is located radially inward of and spaced apart from the interface 332 between the surface layer 33 and the intermediate layer 32. In other words, the radially outer interface 352 of the carbon-rich layer 35 is located between the interface 351 between the low carbon layer 36 and the carbon-rich layer 35 and the interface 332 between the surface layer 33 and the intermediate layer 32. In this case, the carbon amount in the portion of the surface layer 33 from the radially outer interface 352 of the carbon-rich layer 35 to the interface 332 between the surface layer 33 and the intermediate layer 32 is smaller than the carbon amount in the carbon-rich layer 35.

[0049] The thickness of the carbon-rich layer 35 is, for example, 0.01 μm or more and 15 μm or less, and preferably 0.01 μm or more and 10 μm or less. The thickness of the low-carbon layer 36 is, for example, 1.0 times or more and 20.0 times or less, and preferably 1.5 times or more and 15 times or less, the thickness of the carbon-rich layer 35. The sum of the thickness of the low-carbon layer 36 and the thickness of the carbon-rich layer 35 (i.e., the sum of the thickness from the inner surface 331 of the surface layer 33 to the carbon-rich layer 35 and the thickness of the carbon-rich layer 35) is, for example, 0.1 μm or more and 30 μm or less, and preferably 5 μm or more and 25 μm or less.

[0050] The thickness of the carbon-rich layer 35 and the thickness of the low-carbon layer 36 are determined as follows: First, a cross section of a sample of the carbon film composite 1 is polished by ion polishing, and then an elemental mapping analysis is performed on the cross section using a field emission electron probe microanalyzer (FE-EPMA).

[0051] Next, within the mapping field of view, the carbon-derived mass concentrations are obtained at multiple positions at the same distance in the thickness direction from the surface 121 of the carbon film 12 (hereinafter also referred to as "measurement depths"), and the arithmetic mean of the obtained multiple mass concentrations is obtained as the carbon amount at that measurement depth. In other words, the arithmetic mean of the carbon-derived mass concentrations at one measurement depth within the mapping field of view is obtained as the carbon amount at that measurement depth. The carbon-derived mass concentration is a value obtained by normalizing the signal intensity of the characteristic X-rays derived from carbon with the signal intensity of the standard sample. Then, the carbon amount at each measurement depth within the mapping field of view is obtained in the same manner as above, thereby obtaining the relationship between the measurement depth and the carbon amount.

[0052] Fig. 6A is a diagram showing an example of the relationship between the measurement depth and the carbon amount in a cross section of a sample of the carbon membrane composite 1. In the graph shown in Fig. 6A, the horizontal axis represents the measurement depth, and the vertical axis represents the carbon amount. Measurement depth 0 corresponds to the surface 121 of the carbon film 12. In Fig. 6A, a broken line 8 shown as a solid line represents the relationship between the measurement depth and the carbon amount. In Fig. 6A, a portion of the cross section of the carbon membrane composite 1 is also shown below the graph to facilitate understanding of the correlation between the measurement depth and the structure of the carbon membrane composite 1.

[0053] Once the relationship between the measurement depth and the carbon amount described above has been obtained, the positions of the interfaces 351, 352 of the carbon-rich layer 35 in the thickness direction can be determined based on this relationship as follows. First, in FIG. 6A , in order to approximate the broken line 8 with a plurality of straight lines, a plurality of boundary lines 60 are set based on the outline of the broken line 8, and the horizontal axis is divided into a plurality of regions. Each boundary line 60 is a straight line extending in the vertical direction in FIG. 6A and is indicated by a dashed line. The positions of the boundary lines 60 shown in FIG. 6A are tentative, and these positions are variable as described below. The boundary lines 60 are tentatively set near positions where the slope of the broken line 8 changes significantly in the outline of the broken line 8.

[0054] In the example shown in Figure 6A, the horizontal axis is divided into six regions 61 to 66 by five boundary lines 60. In Figure 6A, the ranges corresponding to the regions 61 to 66 are indicated by arrows extending in the left-right direction in the figure. The regions 61 to 66 are arranged consecutively in order from left to right in Figure 6A. In the example shown in Figure 6A, the regions 61 and 62 roughly correspond to the carbon film 12, the region 63 roughly corresponds to the low carbon layer 36, the regions 64 and 65 roughly correspond to the carbon-rich layer 35, and the region 66 roughly corresponds to the intermediate layer 32.

[0055] 6A , the carbon amount in the carbon film 12 is substantially constant from the surface 121 of the carbon film 12 to a predetermined measurement depth, and decreases as the measurement depth increases near the inner surface 331 of the surface layer 33, which is the interface between the carbon film 12 and the support 11. Note that, as will be described later, the carbon amount in the carbon film 12 may increase as the measurement depth increases from the surface 121 of the carbon film 12 to the predetermined measurement depth.

[0056] 6A , the carbon content in the low carbon layer 36 decreases from the inner surface 331 of the surface layer 33 toward the interface 351 between the low carbon layer 36 and the carbon-rich layer 35. As will be described later, the carbon content in the low carbon layer 36 may be substantially constant. Alternatively, the carbon content in the low carbon layer 36 may increase from the inner surface 331 of the surface layer 33 toward the interface 351 between the low carbon layer 36 and the carbon-rich layer 35.

[0057] 6A , the carbon content in the carbon-rich layer 35 increases with increasing distance from an interface 351 between the low carbon layer 36 and the carbon-rich layer 35 toward the radially outer side, and decreases near an interface 352 on the radially outer side of the carbon-rich layer 35 (i.e., an interface 332 between the surface layer 33 and the intermediate layer 32) toward the interface 352. As will be described later, the carbon content in the carbon-rich layer 35 may be substantially constant in the central portion of the carbon-rich layer 35 in the thickness direction.

[0058] 6A, the carbon amount in the intermediate layer 32 is substantially constant regardless of the measurement depth. As will be described later, the carbon amount in the intermediate layer 32 may decrease as the measurement depth increases.

[0059] When the above-described plurality of boundary lines 60 are provisionally set, the portions of the polygonal line 8 corresponding to the respective regions 61 to 66 are approximated by straight lines as shown in FIG. 6B. In FIG. 6B, the approximate straight lines 81 to 86 in the respective regions 61 to 66 are indicated by two-dot chain lines. The coefficients of determination R of the approximate straight lines 81 to 86 are then calculated. ２ are obtained, and the coefficient of determination R ２ The sum of these (hereinafter also referred to as the "total coefficient of determination") is obtained as an index indicating the appropriateness of the positions of the plurality of boundary lines 60. The appropriateness of the positions of the plurality of boundary lines 60 improves as the total coefficient of determination increases.

[0060] Next, the positions of the plurality of boundary lines 60 are changed and the total coefficient of determination is repeatedly obtained. The position of the boundary line 60 where the total coefficient of determination is greatest is determined as the appropriate position of the boundary line 60. Once the position of the boundary line 60 is determined, as shown in FIG. 6C , an intersection 801 between an approximated line 83 in the region 63 corresponding to the low carbon layer 36 and an approximated line 84 in the region 64 corresponding to the carbon rich layer 35 is determined. Then, the measurement depth corresponding to the intersection 801 is determined as the distance in the thickness direction between the radially inner interface 351 of the carbon rich layer 35 and the surface 121 of the carbon film 12. That is, the position in the thickness direction of the interface 351 of the carbon rich layer 35 is determined from the measurement depth corresponding to the intersection 801. Furthermore, an intersection 802 between the approximated line 85 in the region 65 corresponding to the carbon rich layer 35 and the approximated line 86 in the region 66 corresponding to the intermediate layer 32 is determined. Then, the measurement depth corresponding to the intersection 802 is determined as the distance in the thickness direction between the radially outer interface 352 of the carbon rich layer 35 and the surface 121 of the carbon film 12. That is, the position of the interface 352 of the carbon-rich layer 35 in the thickness direction can be determined from the measured depth corresponding to the intersection 802 .

[0061] The distance in the thickness direction between the interface 351 and the interface 352 of the carbon-rich layer 35 is obtained as the thickness in the thickness direction of the carbon-rich layer 35 (hereinafter simply referred to as "thickness"). The thickness of the low-carbon layer 36 is obtained as the distance in the thickness direction between the interface 351 of the carbon-rich layer 35 and the inner surface 331 of the surface layer 33, using the position in the thickness direction of the inner surface 331 of the surface layer 33 obtained by a method described below.

[0062] The thickness of the surface layer 33 is determined based on an SEM image of the cross section of the sample. Specifically, the thickness of the surface layer 33 is determined at any number of (e.g., five) measurement positions on the SEM image, and the arithmetic average of the thicknesses at the plurality of measurement positions is defined as the thickness of the surface layer 33. The thickness of the surface layer 33 at each measurement position is determined from the thickness direction positions of the inner surface 331 and the radially outer interface 332 of the surface layer 33, which are determined based on the contrast difference in the SEM image, etc.

[0063] Like the thickness of the surface layer 33, the thickness of the carbon film 12 is also determined based on an SEM image of the cross section of the sample. Specifically, the thickness of the carbon film 12 is determined at any number of measurement positions (for example, five) on the SEM image, and the arithmetic average of the thicknesses at the plurality of measurement positions is defined as the thickness of the carbon film 12. The thickness of the carbon film 12 at each measurement position is determined from the position in the thickness direction of the surface 121 of the carbon film 12 and the radially outer interface (i.e., the inner surface 331 of the surface layer 33) determined based on the contrast difference or the like in the SEM image.

[0064] The relationship between the measurement depth and the carbon content in the carbon membrane composite 1 is not necessarily limited to that shown in Fig. 6A and varies in various ways. For example, in the example shown in Fig. 7A , the carbon content indicated by the broken line 8a is approximately constant in the low carbon layer 36. The carbon content in the carbon-rich layer 35 increases with increasing radial distance from the interface 351 between the low carbon layer 36 and the carbon-rich layer 35, is approximately constant at the center in the thickness direction of the carbon-rich layer 35, and decreases with increasing distance from the interface 352 on the radially outer side of the carbon-rich layer 35 (i.e., the interface 332 between the surface layer 33 and the intermediate layer 32). The carbon content in the intermediate layer 32 decreases with increasing measurement depth.

[0065] 7A with a plurality of straight lines, six boundary lines 60 are provisionally set, and the horizontal axis is divided into seven regions 61 a to 67 a. In the example shown in FIG. 7A, the regions 61 a and 62 a approximately correspond to the carbon film 12, the region 63 a approximately corresponds to the low carbon layer 36, the regions 64 a, 65 a, and 66 a approximately correspond to the carbon-rich layer 35, and the region 67 a approximately corresponds to the intermediate layer 32.

[0066] 6A, the portions of the broken line 8a corresponding to the regions 61a to 67a are linearly approximated by approximation lines 81a to 87a as shown in FIG. 7B, and the total coefficient of determination is obtained. The positions of the multiple boundary lines 60 are then changed and the total coefficient of determination is obtained repeatedly, and the position of the boundary line 60 that maximizes the total coefficient of determination is determined as the appropriate position of the boundary line 60.

[0067] 7C , an intersection 801a is determined between an approximate line 83a in the region 63a corresponding to the low carbon layer 36 and an approximate line 84a in the region 64a corresponding to the carbon rich layer 35. Then, from the measurement depth corresponding to the intersection 801a, the position in the thickness direction of the radially inner interface 351 of the carbon rich layer 35 is determined. Also, an intersection 802a is determined between an approximate line 86a in the region 66a corresponding to the carbon rich layer 35 and an approximate line 87a in the region 67a corresponding to the intermediate layer 32. Then, from the measurement depth corresponding to the intersection 802a, the position in the thickness direction of the radially outer interface 352 of the carbon rich layer 35 is determined. Thereafter, the thicknesses of the carbon rich layer 35 and the low carbon layer 36 are determined in substantially the same manner as above.

[0068] 8A , the carbon content indicated by broken line 8b in the low carbon layer 36 generally decreases as the measurement depth increases, but has multiple peaks 831 along the way. In this case, to avoid confusing these peaks 831 with peak 841 of the carbon content in the carbon-rich layer 35, the peak located outermost in the radial direction among the multiple peaks 831, 841 is regarded as peak 841 in the carbon-rich layer 35, and the other peaks are regarded as peaks in the low carbon layer 36. Five boundary lines 60 are provisionally set so that peak 841 is included in regions 84b to 85b corresponding to the carbon-rich layer 35 and the other peak 831 is included in region 83b corresponding to the low carbon layer 36, and the horizontal axis is divided into six regions 61b to 66b, substantially similar to FIG. 6A .

[0069] 6A, the portions of the broken line 8b corresponding to the regions 61b to 66b are linearly approximated by approximation lines 81b to 86b as shown in FIG. 8B, and the total coefficient of determination is obtained. The positions of the multiple boundary lines 60 are then changed and the total coefficient of determination is obtained repeatedly, and the position of the boundary line 60 that maximizes the total coefficient of determination is determined as the appropriate position of the boundary line 60.

[0070] 8C , an intersection 801b is determined between an approximate line 83b in the region 63b corresponding to the low carbon layer 36 and an approximate line 84b in the region 64b corresponding to the carbon rich layer 35. Then, from the measurement depth corresponding to the intersection 801b, the position in the thickness direction of the radially inner interface 351 of the carbon rich layer 35 is determined. Also, an intersection 802b is determined between an approximate line 85b in the region 65b corresponding to the carbon rich layer 35 and an approximate line 86b in the region 66b corresponding to the intermediate layer 32. Then, from the measurement depth corresponding to the intersection 802b, the position in the thickness direction of the radially outer interface 352 of the carbon rich layer 35 is determined. Thereafter, the thicknesses of the carbon rich layer 35 and the low carbon layer 36 are determined in substantially the same manner as above.

[0071] 9A, the carbon content indicated by the broken line 8c in the carbon film 12 increases as the measurement depth from the surface 121 of the carbon film 12 increases, and decreases as the measurement depth increases in the vicinity of the inner surface 331 of the surface layer 33. In this case, five boundary lines 60 are provisionally set, and the horizontal axis is divided into six regions 61c to 66c, substantially similar to the example shown in FIG.

[0072] 6A, the portions of the broken line 8c corresponding to the regions 61c to 66b are linearly approximated by approximation lines 81c to 86c as shown in FIG. 9B, and the total coefficient of determination is obtained. The positions of the multiple boundary lines 60 are then changed and the total coefficient of determination is obtained repeatedly, and the position of the boundary line 60 that maximizes the total coefficient of determination is determined as the appropriate position of the boundary line 60.

[0073] 9C , an intersection 801c is determined between an approximate line 83c in the region 63c corresponding to the low carbon layer 36 and an approximate line 84c in the region 64c corresponding to the carbon rich layer 35. Then, from the measurement depth corresponding to the intersection 801c, the position in the thickness direction of the radially inner interface 351 of the carbon rich layer 35 is determined. Also, an intersection 802c is determined between an approximate line 85c in the region 65c corresponding to the carbon rich layer 35 and an approximate line 86c in the region 66c corresponding to the intermediate layer 32. Then, from the measurement depth corresponding to the intersection 802c, the position in the thickness direction of the radially outer interface 352 of the carbon rich layer 35 is determined. Thereafter, the thicknesses of the carbon rich layer 35 and the low carbon layer 36 are determined in substantially the same manner as above.

[0074] The maximum carbon amount in the carbon-rich layer 35 is, for example, 1.1 to 4.0 times the average carbon amount in the low carbon layer 36 (i.e., the region between the surface of the support 11 and the carbon-rich layer 35). Preferably, the maximum carbon amount in the carbon-rich layer 35 is 1.2 to 2.0 times the average carbon amount in the low carbon layer 36. Furthermore, the maximum carbon amount in the carbon-rich layer 35 is, for example, 0.05 to 0.25 times the maximum carbon amount in the carbon film 12. Preferably, the maximum carbon amount in the carbon-rich layer 35 is 0.05 to 0.21 times the maximum carbon amount in the carbon film 12.

[0075] The above-mentioned maximum carbon amount in the carbon-rich layer 35 is the largest carbon amount in the carbon-rich layer 35. Specifically, the peak values ​​in the carbon-rich layer 35 of the polygonal lines 8, 8a, 8b, and 8c shown in FIGS.

[0076] The average carbon content in the low carbon layer 36 is the average carbon content in the central portion in the thickness direction of the low carbon layer 36. The average carbon content in the low carbon layer 36 is determined as follows. First, on the above-mentioned broken line 8 (the same applies to broken lines 8a to 8c), a point radially inward and a point radially outward from the center in the thickness direction of the portion included in the low carbon layer 36 are identified at a distance equal to 10% of the thickness of the low carbon layer 36. Then, the arithmetic average of the carbon content between these two points is determined, and this arithmetic average is set as the average carbon content in the low carbon layer 36.

[0077] The maximum carbon amount in the carbon film 12 is the largest carbon amount in the carbon film 12. Specifically, the maximum values ​​in the carbon film 12 of the polygonal lines 8, 8a, 8b, and 8c shown in FIGS.

[0078] Next, the production of the carbon membrane composite 1 will be described with reference to Fig. 10 and Fig. 11A to Fig. 11D. Fig. 10 is a diagram showing an example of the flow of producing the carbon membrane composite 1. Fig. 11A to Fig. 11D are diagrams schematically showing a partial cross section of the carbon membrane composite 1 in the process of production.

[0079] When the carbon membrane composite 1 is manufactured, first, the support 11 is prepared (step S11). In step S11, for example, the raw material of the substrate 31 is molded by extrusion molding or the like and fired to form the substrate 31 having a monolith structure. Next, the intermediate layer 32 and the surface layer 33 are formed on the inner surfaces of the through holes of the substrate 31 by a filtration membrane formation method or the like and fired to form and prepare the support 11.

[0080] Next, a first precursor solution is applied to the support 11 from the inner surface of the cell 111 (i.e., the inner surface 331 of the surface layer 33). The first precursor solution contains a first precursor that will become carbon in the carbon-rich layer 35. The first precursor solution permeates the support 11 from the surface layer 33 side. As a result, as shown in FIG. 11A, a first precursor layer 71 containing the first precursor is formed inside the support 11 (step S12). In FIG. 11A, the first precursor layer 71 is indicated by hatching (the same applies to FIGS. 11B to 11D). The support 11 with the first precursor layer 71 formed therein is dried, for example, by air blowing or using a dryer. The support 11 is dried, for example, at room temperature (25°C) to 90°C for 5 to 120 minutes.

[0081] The first precursor may be, for example, a thermosetting resin such as a phenolic resin, a melamine resin, a urea resin, a furan resin, a polyimide resin, or an epoxy resin; a thermoplastic resin such as polyethylene, polyphenylene oxide, or polyetherimide; a cellulose-based resin; or an intrinsically microporous polymer (PIM). Alternatively, the first precursor may be a precursor material of these resins. In this embodiment, a phenolic resin is used as the first precursor.

[0082] The first precursor solution is obtained by mixing or dissolving the first precursor in a solvent. The solvent is, for example, an organic solvent such as methanol, ethanol, acetone, tetrahydrofuran, NMP (N-methyl-2-pyrrolidone), or toluene, or water. In this embodiment, ethanol is used as the solvent. Note that the first precursor and the solvent contained in the first precursor solution are not limited to the above examples and may be variously changed.

[0083] The application of the first precursor solution in step S12 is performed by, for example, a flow-down method, an immersion method, dip coating, spin coating, drip coating, spray coating, or filtration coating. In the present embodiment, the application of the first precursor solution is performed by a flow-down method. Specifically, the support 11 is placed so that the longitudinal direction of the support 11 is approximately parallel to the direction of gravity, and the first precursor solution is poured into the upper openings of each cell 111 to contact the inner surfaces of each cell 111, thereby applying the first precursor solution to the support 11.

[0084] The first precursor solution that has permeated into the surface layer 33 from the inner surface of the cell 111 stops permeating at an interface 332 between the surface layer 33 and the intermediate layer 32 due to, for example, the difference in average pore size between the surface layer 33 and the intermediate layer 32, and does not substantially enter the intermediate layer 32. Therefore, as shown in Fig. 11A , the radially outer end of the first precursor layer 71 is located at approximately the same radial position as the interface 332. In the example shown in Fig. 11A , the radially inner end of the first precursor layer 71 is located at approximately the same radial position as the inner surface 331 of the surface layer 33.

[0085] 11A , the first precursor layer 71 is formed over substantially the entire surface layer 33, but this is not limiting. For example, by adjusting the amount of the first precursor solution applied to the support 11, it is also possible to position the radially outer end of the first precursor layer 71 radially inward of the interface 332 between the surface layer 33 and the intermediate layer 32.

[0086] After step S12 is completed, a portion of the first precursor layer 71 provided inside the support 11 is removed (step S13). Specifically, for example, the support 11 is placed so that the longitudinal direction of the support 11 is approximately parallel to the direction of gravity, and a removal treatment liquid is poured into the upper openings of each cell 111 to contact the inner surface of each cell 111. The removal treatment liquid permeates the support 11 from the inner surface of the cell 111 (i.e., the inner surface 331 of the surface layer 33). As a result, as shown in FIG. 11B , a radially inner portion of the first precursor layer 71 is dissolved by the removal treatment liquid and removed from the support 11. In other words, the first precursor layer 71 is partially removed from the inner surface of the cell 111 (i.e., the surface of the support 11).

[0087] The removal processing liquid is a liquid capable of dissolving the first precursor. The removal processing liquid is preferably a liquid having a low boiling point and high volatility. The removal processing liquid is, for example, an organic solvent such as methanol, ethanol, acetone, tetrahydrofuran, NMP (N-methyl-2-pyrrolidone), or toluene. For example, the solvent of the first precursor solution (ethanol in this embodiment) is used as the removal processing liquid. Note that the removal processing liquid is not limited to the solvent of the first precursor solution, and may be various liquids capable of removing the first precursor layer 71.

[0088] In step S13, the radially outer portion of the first precursor layer 71 formed in step S12 is not removed by the removal treatment liquid and remains inside the support 11. The radially inner end of the first precursor layer 71 remaining inside the support 11 is located radially between the inner surface 331 of the surface layer 33 and the interface 332 between the surface layer 33 and the intermediate layer 32. The radially outer end of the first precursor layer 71 remaining inside the support 11 is located radially at approximately the same position as the interface 332 between the surface layer 33 and the intermediate layer 32. The support 11 with the first precursor layer 71 remaining inside is dried, for example, by air blowing or a dryer. The support 11 is dried, for example, at room temperature (25°C) to 90°C for 5 to 120 minutes.

[0089] After step S13 is completed, the dried support 11 is subjected to a heat treatment, and the first precursor layer 71 remaining inside the support 11 is cured (step S14). Specifically, for example, the support 11 is heated to 90°C to 500°C using a dryer and held at that temperature for 0.5 to 72 hours, thereby curing the first precursor layer 71. The curing of the first precursor layer 71 in step S14 may be performed by other methods.

[0090] After step S14 is completed, the second precursor solution is applied to the support 11 from the inner surface of the cell 111 (i.e., the inner surface 331 of the surface layer 33). The second precursor solution contains a second precursor that will become the carbon of the carbon film 12. The second precursor solution permeates the support 11 from the surface layer 33 side. As a result, as shown in FIG. 11C , a second precursor layer 72 containing the second precursor is formed inside the support 11. In FIG. 11C , the second precursor layer 72 is indicated by hatched lines, which are different from the first precursor layer 71 (the same applies to FIG. 11D ).

[0091] The second precursor may be, for example, a thermosetting resin such as a phenolic resin, a melamine resin, a urea resin, a furan resin, a polyimide resin, or an epoxy resin; a thermoplastic resin such as polyethylene, polyphenylene oxide, or polyetherimide; a cellulose-based resin; or an intrinsically microporous polymer (PIM). Alternatively, the second precursor may be a precursor material of these resins. In this embodiment, a phenolic resin is used as the second precursor.

[0092] The second precursor solution is obtained by mixing or dissolving the second precursor in a solvent. The solvent is, for example, an organic solvent such as methanol, ethanol, acetone, tetrahydrofuran, NMP (N-methyl-2-pyrrolidone), or toluene, or water. In this embodiment, ethanol is used as the solvent. The second precursor and solvent contained in the second precursor solution are not limited to the above examples and may be variously changed. Furthermore, the second precursor and solvent contained in the second precursor solution may be the same substances as the first precursor and solvent contained in the first precursor solution, or may be different substances.

[0093] The second precursor solution is applied by, for example, a flow-down method, an immersion method, dip coating, spin coating, drip coating, spray coating, or filtration coating. In this embodiment, the second precursor solution is applied by a flow-down method. Specifically, the support 11 is placed so that the longitudinal direction of the support 11 is approximately parallel to the direction of gravity, and the second precursor solution is poured into the upper openings of each cell 111 to bring the second precursor solution into contact with the inner surfaces of each cell 111, thereby applying the second precursor solution to the support 11. The application of the second precursor solution may be performed by the same method as the application of the first precursor solution described above, or by a different method.

[0094] 11C , the radially outer end of the second precursor layer 72 is in contact with the radially inner end of the first precursor layer 71. As described above, the first precursor layer 71 has been cured in step S14. Therefore, even if the second precursor solution comes into contact with the first precursor layer 71, mixing of the second precursor solution with the first precursor layer 71 and dissolution of the first precursor layer 71 do not substantially occur. Note that even if the first precursor layer 71 has not been cured because the solvent of the second precursor solution is different from the solvent of the first precursor solution, if mixing of the second precursor solution with the first precursor layer 71 and dissolution of the first precursor layer 71 do not substantially occur, curing of the first precursor layer 71 in step S14 does not have to be performed.

[0095] The first precursor layer 71 and the second precursor layer 72 are intended to become the carbon-rich layer 35 and the low-carbon layer 36, respectively, in the carbon membrane composite 1. Therefore, when the first precursor contained in the first precursor solution and the second precursor contained in the second precursor solution are the same substance (e.g., phenolic resin), the concentration of the second precursor in the second precursor solution is lower than the concentration of the first precursor in the first precursor solution. Furthermore, when the first precursor contained in the first precursor solution and the second precursor contained in the second precursor solution are different substances, for example, the residual carbon rate of the second precursor is lower than the residual carbon rate of the first precursor. The residual carbon rate is the ratio of the amount of carbon remaining after the carbonization process to the amount of precursor (i.e., the first precursor or the second precursor) before the carbonization process in step S16, which will be described later. The second precursor solution may contain a second precursor having a higher residual carbon rate than the first precursor, but at a lower concentration than the concentration of the first precursor in the first precursor solution.

[0096] The support 11 with the second precursor layer 72 formed therein is dried, for example, by air blowing or a dryer. The support 11 is dried, for example, at room temperature (25°C) to 90°C for 5 to 120 minutes. The dried support 11 is then heat-treated, and the second precursor layer 72 inside the support 11 is hardened. This heat treatment is performed, for example, in substantially the same manner as the heat treatment in step S14. Specifically, the support 11 is heated to 90°C to 500°C using a dryer and held at that temperature for 0.5 to 72 hours, thereby hardening the second precursor layer 72.

[0097] 11C , the second precursor layer 72 is formed over substantially the entire portion of the surface layer 33 that is radially inward of the first precursor layer 71. In other words, the radially inner end of the second precursor layer 72 is located at substantially the same radial position as the inner surface 331 of the surface layer 33, which is the interface between the surface layer 33 and the carbon film 12 to be formed. If the second precursor layer 72 shown in FIG. 11C cannot be formed by applying the second precursor solution and performing the heat treatment only once (i.e., if the radial thickness of the second precursor layer 72 is insufficient), the second precursor layer 72 shown in FIG. 11C may be formed by repeating the application of the second precursor solution and the heat treatment multiple times.

[0098] Next, the second precursor solution is again applied to the support 11 from the inner surface of the cell 111 (i.e., the inner surface 331 of the surface layer 33). The second precursor solution adheres to the inner surface 331 of the surface layer 33, inside which the second precursor layer 72 has been formed. As a result, as shown in FIG. 11D , a second precursor film 73, which is a thin film containing the second precursor, is formed on the inner surface 331 of the surface layer 33 (i.e., the surface of the support 11) (step S15). In FIG. 11D , the second precursor film 73 is indicated by the same hatched lines as the second precursor layer 72.

[0099] The support 11 on which the second precursor film 73 is provided is dried, for example, by air blowing or a dryer. The support 11 is dried, for example, at room temperature (25°C) for 5 to 120 minutes. The dried support 11 is then heat-treated, and the second precursor film 73 on the surface of the support 11 is hardened. This heat treatment is performed, for example, in substantially the same manner as the heat treatment performed on the second precursor layer 72. For example, the support 11 is heated to 90°C to 500°C and maintained at this temperature for 0.5 to 72 hours, thereby hardening the second precursor film 73.

[0100] 11D , if the second precursor film 73 does not reach the desired thickness by applying the second precursor solution and performing the heat treatment only once, the application of the second precursor solution and the heat treatment may be repeated multiple times to form the second precursor film 73 shown in FIG. 11D . Alternatively, if the second precursor layer 72 and the second precursor film 73 can be formed by applying the second precursor solution and performing the heat treatment once, the drying treatment and the heat treatment are not performed between the formation of the second precursor layer 72 and the formation of the second precursor film 73.

[0101] After step S15 is completed, the support body 11 provided with the first precursor layer 71, the second precursor layer 72, and the second precursor film 73 is subjected to a carbonization treatment. As a result, inside the support body 11, the carbon-rich layer 35 is formed from the first precursor layer 71, and the low-carbon layer 36 is formed from the second precursor layer 72. Furthermore, the carbon film 12 is formed from the second precursor film 73 on the surface of the support body 11. As a result, a carbon membrane composite 1 including the carbon-rich layer 35, the low-carbon layer 36, and the carbon film 12 is obtained (step S16).

[0102] In the carbonization treatment in step S16, for example, the support 11 provided with the first precursor layer 71, the second precursor layer 72, and the second precursor film 73 is placed in an electric furnace, heated to 400°C to 1200°C, and maintained at that temperature for 0.5 hours to 200 hours. By setting the temperature during the carbonization treatment to 400°C or higher, the second precursor film 73 is suitably carbonized, pores are formed, and the separation factor of the carbon film 12 falls within a suitable range. By setting the temperature during the carbonization treatment to 1200°C or lower, the carbon film 12 is prevented from becoming excessively dense, and the separation factor of the carbon film 12 falls within a suitable range. Note that the temperature during the carbonization treatment is preferably 600°C to 900°C.

[0103] The carbonization treatment is preferably carried out in a non-oxidizing atmosphere. The non-oxidizing atmosphere means an atmosphere in which the first precursor and the second precursor are not oxidized when carbonized in the above-mentioned temperature range. Specifically, the non-oxidizing atmosphere is an inert gas atmosphere such as nitrogen or argon, or a vacuum atmosphere.

[0104] Next, separation of a mixed substance using the carbon membrane composite 1 will be described with reference to Fig. 12. Fig. 12 is a cross-sectional view showing a separation device 2. In Fig. 12, the cross section of the carbon membrane composite 1 is shown conceptually in a simplified form in order to facilitate understanding of the drawing.

[0105] In the separation device 2, a mixed substance containing multiple types of fluids (i.e., gas or liquid) is supplied to the carbon membrane composite 1, and highly permeable substances in the mixed substance are separated from the mixed substance by permeating the carbon membrane composite 1. Separation in the separation device 2 may be performed, for example, for the purpose of extracting highly permeable substances (hereinafter also referred to as "highly permeable substances") from the mixed substance, or for the purpose of concentrating lowly permeable substances (hereinafter also referred to as "lowly permeable substances").

[0106] The mixed substance (i.e., mixed fluid) may be a mixed gas containing multiple types of gases, a mixed liquid containing multiple types of liquids, or a gas-liquid two-phase fluid containing both gas and liquid.

[0107] The mixture may include, for example, hydrogen (H ２ ), helium (He), nitrogen (N ２ ), oxygen (O ２ ), water (H ２ O), carbon monoxide (CO), carbon dioxide (CO ２ ), nitrogen oxides, ammonia (NH ３ ), sulfur oxides, hydrogen sulfide (H ２ S), sulfur fluoride, mercury (Hg), arsine (AsH ３ ), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1-C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes. ２ , N.H. ３ and H ２ The mixed substance and the highly permeable substance may be one or more of the substances listed above.

[0108] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of the nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO ２ ), nitrous oxide (also called dinitrogen monoxide) (N ２ O), dinitrogen trioxide (N ２ O ３ ), dinitrogen tetroxide (N ２ O ４ ), dinitrogen pentoxide (N ２O ５ ) etc. Ｘ It is a substance called NOX.

[0109] Sulfur oxides are compounds of sulfur and oxygen. Examples of the sulfur oxides include sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ) and other SOs Ｘ It is a substance called SOXI.

[0110] Sulfur fluoride is a compound of fluorine and sulfur. The above-mentioned sulfur fluoride is, for example, disulfur difluoride (FS-SF, S=SF ２ ), sulfur difluoride (SF ２ ), sulfur tetrafluoride (SF ４ ), sulfur hexafluoride (SF ６ ) or disulfur decafluoride (S ２ F １０ ) etc.

[0111] C1-C8 hydrocarbons are hydrocarbons with one or more carbon atoms and eight or less. C3-C8 hydrocarbons may be straight-chain compounds, branched-chain compounds, or cyclic compounds. C2-C8 hydrocarbons may be either saturated hydrocarbons (i.e., those without double and triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those with double and / or triple bonds in the molecule). C1-C4 hydrocarbons include, for example, methane (CH ４ ), ethane (C ２ H ６ ), ethylene (C ２ H ４ ), propane (C ３ H ８ ), propylene (C ３ H ６ ), normal butane (CH ３ (CH ２ ) ２ CH ３ ), isobutane (CH(CH ３ ) ３ ), 1-butene (CH ２ =CHCH ２ CH ３ ), 2-butene (CH ３ CH=CHCH ３) or isobutene (CH ２ =C(CH ３ ) ２ )

[0112] The organic acid is a carboxylic acid or a sulfonic acid. The carboxylic acid is, for example, formic acid (CH ２ O ２ ), acetic acid (C ２ H ４ O ２ ), oxalic acid (C ２ H ２ O ４ ), acrylic acid (C ３ H ４ O ２ ) or benzoic acid (C ６ H ５ COOH), etc. Sulfonic acids include, for example, ethanesulfonic acid (C ２ H ６ O ３ S) and the like. The organic acid may be a chain compound or a cyclic compound.

[0113] The alcohols mentioned above include, for example, methanol (CH ３ OH), ethanol (C ２ H ５ OH), isopropanol (2-propanol) (CH ３ CH(OH)CH ３ ), ethylene glycol (CH ２ (OH)CH ２ (OH)) or butanol (C ４ H ９ OH) and the like.

[0114] Mercaptans are organic compounds with hydrogenated sulfur (SH) at the end, and are also called thiols or thioalcohols. Examples of the above-mentioned mercaptans include methyl mercaptan (CH ３ SH), ethyl mercaptan (C ２ H ５ SH) or 1-propanethiol (C ３ H ７ SH), etc.

[0115] The esters mentioned above are, for example, formates or acetates.

[0116] The above-mentioned ethers include, for example, dimethyl ether ((CH ３ ) ２ O), methyl ethyl ether (C ２ H ５ OCH ３ ) or diethyl ether ((C ２ H ５ ) ２ O) etc.

[0117] The above-mentioned ketones can be, for example, acetone ((CH ３ ) ２ CO), methyl ethyl ketone (C ２ H ５ COCH ３ ) or diethyl ketone ((C ２ H ５ ) ２ CO), etc.

[0118] The aldehydes mentioned above include, for example, acetaldehyde (CH ３ CHO), propionaldehyde (C ２ H ５ CHO) or butanal (butyraldehyde) (C ３ H ７ CHO) etc.

[0119] As shown in Fig. 12 , the separation device 2 includes a carbon membrane composite 1, a sealing unit 21, a housing 22, and two sealing members 23. The carbon membrane composite 1, the sealing unit 21, and the sealing members 23 are housed in the housing 22. In Fig. 12 , the support 11 and the carbon membrane 12 of the carbon membrane composite 1 are indicated by parallel diagonal lines. The internal space of the housing 22 is a sealed space isolated from the space surrounding the housing 22. A supply unit 26, a first recovery unit 27, and a second recovery unit 28 are connected to the housing 22.

[0120] As described above, the sealing portion 21 is attached to both ends of the support 11 in the longitudinal direction (i.e., the left-right direction in FIG. 12 ), and is a member that covers and seals both longitudinal end faces of the support 11 and parts of the outer surfaces near these end faces. In this embodiment, the sealing portion 21 is a glass seal with a thickness of 10 μm to 50 μm. The material and shape of the sealing portion 21 may be changed as appropriate. Note that the sealing portion 21 has multiple openings that overlap with the multiple cells 111 of the support 11, and therefore both longitudinal ends of each cell 111 are not covered by the sealing portion 21. Therefore, fluid can flow in and out of the cells 111 from these ends.

[0121] The housing 22 is a substantially cylindrical tubular member. The housing 22 is made of, for example, stainless steel or carbon steel. The longitudinal direction of the housing 22 is substantially parallel to the longitudinal direction of the carbon membrane composite 1. A supply port 221 is provided at one longitudinal end of the housing 22 (i.e., the left end in FIG. 12 ), and a first discharge port 222 is provided at the other end. A supply unit 26 is connected to the supply port 221. A first recovery unit 27 is connected to the first discharge port 222. A second discharge port 223 is provided on a side surface of the housing 22. A second recovery unit 28 is connected to the second discharge port 223. The shape and material of the housing 22 may be modified in various ways.

[0122] Two seal members 23 are disposed between the outer surface of the carbon membrane composite 1 and the inner surface of the housing 22 near both longitudinal ends of the carbon membrane composite 1. Each seal member 23 is a substantially annular member made of a material impermeable to gases and liquids. The seal members 23 are, for example, O-rings or packings made of flexible resin. The seal members 23 are in close contact with the outer surface of the carbon membrane composite 1 and the inner surface of the housing 22 around the entire circumference of the carbon membrane composite 1. In the example shown in FIG. 12 , the seal member 23 is in close contact with the outer surface of the sealing portion 21 and indirectly with the outer surface of the carbon membrane composite 1 via the sealing portion 21. The seal member 23 may also be in direct contact with the outer surface of the carbon membrane composite 1. A seal is formed between each seal member 23 and the outer surface of the carbon membrane composite 1 or the sealing portion 21, and between each seal member 23 and the inner surface of the housing 22, substantially preventing the passage of gases and liquids. The material of the seal member 23 may be carbon, metal, or other inorganic material other than resin.

[0123] Supply unit 26 supplies the mixed substance to the internal space of housing 22 via supply port 221. Supply unit 26 includes, for example, a pressure-feeding mechanism such as a blower or pump that pressure-feeds the mixed substance toward housing 22. The pressure-feeding mechanism includes, for example, a temperature adjustment unit and a pressure adjustment unit that respectively adjust the temperature and pressure of the mixed substance supplied to housing 22. First recovery unit 27 and second recovery unit 28 include, for example, a storage container that stores the substance discharged from housing 22, or a blower or pump that transports the substance.

[0124] When separating a mixed substance, first, the carbon membrane composite 1 is prepared. Specifically, the carbon membrane composite 1 is attached inside the housing 22. Then, a mixed substance containing multiple types of substances with different permeabilities to the carbon membrane 12 is supplied into the housing 22 by the supply unit 26, as indicated by the arrow 251. For example, the mixed substance is a mixed liquid in which multiple types of liquids are mixed. The main components of the mixed liquid are, for example, water and ethanol. The mixed liquid may contain liquids other than water and ethanol.

[0125] The mixed substance supplied from the supply unit 26 to the housing 22 is introduced into each cell 111 of the support 11 from the left end of the carbon membrane composite 1 in the drawing. A highly permeable substance in the mixed substance, which is a substance with high permeability, permeates through the carbon membrane 12 provided on the inner surface of each cell 111 and the support 11, and is discharged from the outer surface of the support 11. In this way, the highly permeable substance (e.g., water) is separated from a less permeable substance in the mixed substance (e.g., ethanol).

[0126] The substance discharged from the outer surface of the support 11 (hereinafter referred to as the "permeated substance") is led to the second recovery section 28 via the second discharge port 223 as indicated by the arrow 253, and is recovered by the second recovery section 28. The permeated substance may include, in addition to the above-mentioned highly permeable substance, a low-permeable substance that has permeated the carbon membrane 12.

[0127] Furthermore, of the mixed substance, substances other than those that have permeated the carbon membrane 12 and the support 11 (hereinafter referred to as "non-permeated substances") pass through each cell 111 of the support 11 from left to right in the figure and are recovered by the first recovery unit 27 via the first discharge port 222, as indicated by arrow 252. The non-permeated substances may include, in addition to the low-permeable substances described above, highly permeable substances that have not permeated the carbon membrane 12. The non-permeated substances recovered by the first recovery unit 27 may be circulated to the supply unit 26, for example, and supplied again into the housing 22.

[0128] Next, a carbon membrane composite 1a according to a second embodiment of the present invention will be described. Fig. 13 is an enlarged cross-sectional view showing a portion of the carbon membrane composite 1a near the carbon membrane 12. The carbon membrane composite 1a has substantially the same structure as the carbon membrane composite 1, except that the position of the carbon-rich layer 35 is different from that shown in Figs. 4 and 5. In the following description, the same reference numerals will be used to denote components of the carbon membrane composite 1a that correspond to those of the carbon membrane composite 1.

[0129] 13 , substantially the entire carbon-rich layer 35 is provided inside the intermediate layer 32. In other words, substantially the entire carbon-rich layer 35 is located between an interface 332 between the surface layer 33 and the intermediate layer 32 and an interface 322 between the intermediate layer 32 and the substrate 31. In other words, substantially the entire carbon-rich layer 35 is located on the opposite side of the interface 332 between the surface layer 33 and the intermediate layer 32 to the inner surface 331 of the surface layer 33 (i.e., on the radially outer side opposite the inner surface 331 in the thickness direction).

[0130] 13 , the radially inner interface 351 of the carbon-rich layer 35 is located radially outward (i.e., farther from the cells 111) than the interface 332 between the surface layer 33 and the intermediate layer 32, and at a position spaced apart from the interface 332. The radially outer interface 352 of the carbon-rich layer 35 is located radially inward than the interface 322 between the intermediate layer 32 and the substrate 31, and at a position spaced apart from the interface 322.

[0131] In the carbon membrane composite 1a, the carbon amount in a portion of the intermediate layer 32 extending from the radially inner interface 351 of the carbon-rich layer 35 to the interface 332 between the surface layer 33 and the intermediate layer 32 is smaller than the carbon amount in the carbon-rich layer 35. The carbon amount in the surface layer 33 is also smaller than the carbon amount in the carbon-rich layer 35. That is, in the example shown in FIG. 13 , the low carbon layer 36 described above is composed of the entire surface layer 33 and a portion of the intermediate layer 32 extending from the radially inner interface 351 of the carbon-rich layer 35 to the interface 332 between the surface layer 33 and the intermediate layer 32. The carbon amount in a portion of the intermediate layer 32 extending from the radially outer interface 352 of the carbon-rich layer 35 to the interface 322 between the intermediate layer 32 and the substrate 31 is also smaller than the carbon amount in the carbon-rich layer 35.

[0132] The thickness of the carbon-rich layer 35 in its thickness direction (i.e., the direction perpendicular to the surface of the support 11) is, for example, 0.01 μm or more and 15 μm or less, and preferably 0.01 μm or more and 10 μm or less. The sum of the thickness of the low-carbon layer 36 and the thickness of the carbon-rich layer 35 (i.e., the sum of the thickness from the inner surface 331 of the surface layer 33 to the carbon-rich layer 35 and the thickness of the carbon-rich layer 35) is, for example, 1 μm or more and 1000 μm or less.

[0133] Next, a method for manufacturing the carbon membrane composite 1a will be described with reference to Fig. 14 and Fig. 15A to Fig. 15C. Fig. 14 is a diagram showing an example of the flow of manufacturing the carbon membrane composite 1a. Fig. 15A to Fig. 15C are diagrams schematically showing a partial cross section of the carbon membrane composite 1a during manufacturing.

[0134] When the carbon membrane composite 1a is manufactured, first, the support 11 is prepared (step S21) in substantially the same manner as in step S11 (see FIG. 10) described above.

[0135] Next, the pressure around the outer surface of the support 11 (i.e., the space radially outward from the outer surface of the support 11) is reduced. Specifically, for example, a substantially cylindrical casing made of stainless steel or the like covers substantially the entire outer surface of the support 11. Because the inner diameter of the casing is larger than the outer diameter of the support 11, a substantially cylindrical space (hereinafter also referred to as the "outer peripheral space") exists between the inner surface of the casing and the outer surface of the support 11 over the entire circumference. At both longitudinal ends of the support 11, O-rings or the like are provided between the inner surface of the casing and the outer surface of the support 11, and the outer peripheral space is airtightly sealed. The outer peripheral space is reduced in pressure by a vacuum pump or the like connected to the casing. As a result, the pressure in the surface layer 33 and intermediate layer 32 of the support 11 decreases from the inner surface 331 of the surface layer 33 toward the radially outward direction. The pressure in the outer peripheral space is, for example, 0 kPa to 90 kPa.

[0136] Then, in substantially the same manner as in step S12, the first precursor solution is applied to the support 11 with the peripheral space decompressed from the inner surface of the cell 111 (i.e., the inner surface 331 of the surface layer 33). As described above, the first precursor solution contains the first precursor that will become the carbon of the carbon-rich layer 35. The first precursor solution permeates the support 11 from the surface layer 33 side. As a result, as shown in FIG. 15A, a first precursor layer 71 containing the first precursor is formed inside the support 11 (step S12). In FIG. 15A, the first precursor layer 71 is indicated by hatching (the same applies to FIGS. 15B to 15C).

[0137] The first precursor solution that has soaked into the surface layer 33 from the inner surface of the cell 111 moves from the surface layer 33 to the intermediate layer 32 due to the reduced pressure in the outer peripheral space, and is positioned inside the intermediate layer 32 (i.e., between the interface 332 and the interface 322), radially inward of the substrate 31. The support 11 with the first precursor layer 71 formed on the intermediate layer 32 is dried, for example, by blowing air or using a dryer. The support 11 is dried, for example, at room temperature (25°C) to 90°C for 5 to 120 minutes. The radial position of the first precursor layer 71 in the intermediate layer 32 can be adjusted by adjusting the degree to which the outer peripheral space is reduced in pressure.

[0138] After step S22 is completed, the dried support 11 is heated in substantially the same manner as step S14, and the first precursor layer 71 remaining inside the support 11 is cured (step S23). Specifically, for example, the support 11 is heated to 90°C to 500°C using a dryer and held there for 0.5 to 72 hours, thereby curing the first precursor layer 71. The curing of the first precursor layer 71 in step S23 may be performed by other methods.

[0139] After step S23 is completed, the second precursor solution is applied to the support 11 from the inner surface of the cell 111 (i.e., the inner surface 331 of the surface layer 33), in substantially the same manner as step S15. As described above, the second precursor solution contains a second precursor that will become the carbon of the carbon film 12. The second precursor solution permeates the support 11 from the surface layer 33 side. As a result, as shown in FIG. 15B , a second precursor layer 72 containing the second precursor is formed inside the support 11. In FIG. 15B , the second precursor layer 72 is indicated by hatched lines, which are different from those used for the first precursor layer 71 (the same applies to FIG. 15C ).

[0140] 15B , the radially outer end of the second precursor layer 72 contacts the radially inner end of the first precursor layer 71 in the intermediate layer 32 (i.e., radially outer than the interface 332 between the surface layer 33 and the intermediate layer 32). As described above, since the first precursor layer 71 is cured in step S23, even if the second precursor solution comes into contact with the first precursor layer 71, mixing of the second precursor solution with the first precursor layer 71 and dissolution of the first precursor layer 71 do not substantially occur. Note that even if the first precursor layer 71 has not been cured because the solvent of the second precursor solution is different from the solvent of the first precursor solution, if mixing of the second precursor solution with the first precursor layer 71 and dissolution of the first precursor layer 71 do not substantially occur, curing of the first precursor layer 71 in step S23 does not have to be performed.

[0141] The support 11 with the second precursor layer 72 formed therein is dried, for example, by air blowing or a dryer. The support 11 is dried, for example, at room temperature (25°C) to 90°C for 5 to 120 minutes. The dried support 11 is then heat-treated, and the second precursor layer 72 inside the support 11 is hardened. This heat treatment is performed, for example, in substantially the same manner as the heat treatment in step S23. Specifically, the support 11 is heated to 90°C to 500°C using a dryer and held at that temperature for 0.5 to 72 hours, thereby hardening the second precursor layer 72.

[0142] 15B , the second precursor layer 72 is formed over substantially the entire surface layer 33 and over substantially the entire portion of the intermediate layer 32 that is radially inward from the first precursor layer 71. In other words, the radially inner end of the second precursor layer 72 is located at substantially the same radial position as the inner surface 331 of the surface layer 33, which is the interface between the surface layer 33 and the carbon film 12 to be formed. If the second precursor layer 72 shown in FIG. 15B cannot be formed by applying the second precursor solution and performing the heat treatment only once (i.e., if the radial thickness of the second precursor layer 72 is insufficient), the second precursor layer 72 shown in FIG. 15B may be formed by repeating the application of the second precursor solution and the heat treatment multiple times.

[0143] Next, the second precursor solution is again applied to the support 11 from the inner surface of the cell 111 (i.e., the inner surface 331 of the surface layer 33). The second precursor solution adheres to the inner surface 331 of the surface layer 33, inside which the second precursor layer 72 has been formed. As a result, as shown in FIG. 15C , a second precursor film 73, which is a thin film containing the second precursor, is formed on the inner surface 331 of the surface layer 33 (i.e., the surface of the support 11) (step S24). In FIG. 15C , the second precursor film 73 is indicated by the same hatched lines as the second precursor layer 72.

[0144] The support 11 on which the second precursor film 73 is provided is dried, for example, by air blowing or a dryer. The support 11 is dried, for example, at room temperature (25°C) for 5 to 120 minutes. The dried support 11 is then heat-treated, and the second precursor film 73 on the surface of the support 11 is hardened. This heat treatment is performed, for example, in substantially the same manner as the heat treatment performed on the second precursor layer 72. For example, the support 11 is heated to 90°C to 500°C and maintained at this temperature for 0.5 to 72 hours, thereby hardening the second precursor film 73.

[0145] 15C 。 Alternatively, if the second precursor layer 72 and the second precursor film 73 can be formed by applying the second precursor solution and performing the heating treatment once, the second precursor film 73 does not reach the desired thickness.

[0146] After step S24 is completed, substantially similar to step S16, the support body 11 provided with the first precursor layer 71, the second precursor layer 72, and the second precursor film 73 is subjected to a carbonization treatment. As a result, inside the support body 11, the carbon-rich layer 35 is formed from the first precursor layer 71, and the low-carbon layer 36 is formed from the second precursor layer 72. Furthermore, the carbon film 12 is formed from the second precursor film 73 on the surface of the support body 11. As a result, a carbon membrane composite 1a including the carbon-rich layer 35, the low-carbon layer 36, and the carbon film 12 is obtained (step S25).

[0147] 13 , the carbon-rich layer 35 is substantially entirely provided inside the intermediate layer 32. However, the carbon-rich layer 35 is not limited to this. For example, the carbon-rich layer 35 may be provided across both the intermediate layer 32 and the substrate 31, straddling the interface 322 between the intermediate layer 32 and the substrate 31 (i.e., including the interface 322).

[0148] Alternatively, the carbon-rich layer 35 may be provided only inside the substrate 31, as in the carbon membrane composite 1b illustrated in Fig. 16. In other words, the carbon-rich layer 35 is located on the opposite side of the surface of the support 11 (i.e., the inner surface 331 of the surface layer 33) with respect to the interface 322 between the intermediate layer 32 and the substrate 31. In the carbon membrane composite 1b, the carbon-rich layer 35 is also located on the opposite side of the surface of the support 11 with respect to the interface 332 between the surface layer 33 and the intermediate layer 32. The carbon membrane composite 1b can be manufactured by the manufacturing method shown in steps S21 to S25 described above, in a manner similar to that of the carbon membrane composite 1a.

[0149] Next, Examples 1 to 6 of carbon membrane composite 1, Example 7 of carbon membrane composite 1a, Example 8 of carbon membrane composite 1b, and Comparative Example 1 of the carbon membrane composite will be described with reference to Tables 1 and 2. Table 1 shows the conditions for producing the carbon membrane composites. Table 2 shows the carbon amounts in the carbon membrane composites and the performance of the carbon membrane composites.

[0150]

[0151]

[0152] The carbon membrane composites 1 of Examples 1 to 6 were manufactured by the manufacturing method shown in steps S11 to S16 described above. In Examples 1 to 6, the concentrations of the first precursor in the first precursor solution applied to the support 11 in step S12 were different. In Examples 1 to 6, the drying of the support 11 in steps S12, S13, and S15 was performed at room temperature (25°C) for 20 minutes. In Examples 1 to 6, the curing of the first precursor layer 71 in step S14 and the curing of the second precursor layer 72 and the second precursor film 73 in step S15 were performed by heating the support 11 to 200°C in an air atmosphere and holding the temperature for 5 hours. Furthermore, the carbonization treatment in step S16 was performed by heating the support 11 to 850°C in a vacuum atmosphere and holding the temperature for 5 hours. The thicknesses of the carbon films 12 in Examples 1 to 6 were the same. The thicknesses of the low-carbon layers 36 in Examples 1 to 6 were also the same. The thicknesses of the carbon-rich layers 35 in Examples 1 to 6 were also the same. The carbon-rich layer 35 in Examples 1 to 6 is located in the surface layer 33 .

[0153] The carbon membrane composites 1a and 1b of Examples 7 and 8 were manufactured by the manufacturing method shown in steps S21 to S25 described above. That is, in Examples 7 and 8, depressurization was performed in step S22, and the application of the removal treatment liquid in step S13, as in Examples 1 to 6, was not performed. On the other hand, depressurization was not performed in Examples 1 to 6. In Examples 7 and 8, drying of the support 11 in steps S22 and S24 was performed at room temperature (25°C) for 20 minutes. In Examples 7 and 8, curing of the first precursor layer 71 in step S23 and curing of the second precursor layer 72 and second precursor film 73 in step S24 were performed by heating the support 11 to 200°C in an air atmosphere and maintaining the temperature for 5 hours. In addition, carbonization in step S25 was performed by heating the support 11 to 850°C in a vacuum atmosphere and maintaining the temperature for 5 hours. The thickness of the carbon film 12 in Examples 7 and 8 was the same as that of the carbon film 12 in Examples 1 to 6. The thickness of the carbon rich layer 35 in Examples 7 and 8 is also the same as the thickness of the carbon rich layer 35 in Examples 1 to 6. The carbon rich layer 35 in Example 7 is located in the intermediate layer 32. The carbon rich layer 35 in Example 8 is located in the substrate 31.

[0154] In Comparative Example 1, among the above-described steps S11 to S16, the application of the removal treatment liquid in step S13 and the application of the second precursor solution in step S15 are omitted. In Comparative Example 1, by repeatedly applying the first precursor solution to the support 11 and curing it, a first precursor layer 71 is formed over substantially the entire interior of the surface layer 33, and a first precursor film, which is a thin film formed from the first precursor solution, is formed on the inner surface 331 of the surface layer 33 (i.e., on the surface of the support 11). Then, by performing the carbonization treatment in step S16, the above-described low carbon layer 36 and carbon-rich layer 35 are not formed, and the carbon amount within the surface layer 33 is substantially the same as the carbon amount in the carbon-rich layer 35 in Examples 1 to 6 throughout substantially the entire surface layer 33. Furthermore, the carbon film 12 is formed by carbonizing the first precursor contained in the first precursor film. The thickness of the carbon film 12 in Comparative Example 1 is substantially the same as the thickness of the carbon films 12 in Examples 1 to 6 and Examples 7 and 8.

[0155] In Examples 1 to 6 and Comparative Example 1, the carbon amounts in the carbon film 12, the low-carbon layer 36, the carbon-rich layer 35, and the like were obtained by the above-described method. Measurement of signal intensity when determining the mass concentration was performed using a JXA-8500F FE-EPMA manufactured by JEOL Ltd. at an acceleration voltage of 5 kV, a field of view of 38 μm×50 μm, and a magnification of 2000 times. Carbon (C) with 100% purity was used as the standard sample. The thickness of the low-carbon layer 36, etc., required for determining the carbon amount in the low-carbon layer 36, was also determined by the above-described method. Measurement of the position of the interface 332 between the surface layer 33 and the intermediate layer 32, and measurement of the thicknesses of the carbon film 12 and the surface layer 33 were performed using an SEM manufactured by Hitachi High-Technologies Corporation at an acceleration voltage of 15 kV, a field of view of 36 μm×50 μm, and a magnification of 50 times to 20,000 times. In Examples 7 and 8, the carbon amounts in the carbon film 12, the low carbon layer 36, the carbon rich layer 35, etc. were obtained in a substantially similar manner.

[0156] The separation coefficients and permeation fluxes in Table 2 were measured using the separation device 2 (see FIG. 12 ). Specifically, a mixed liquid of water and ethanol was first supplied to the carbon membrane composite 1, 1a from the supply section 26 of the separation device 2, and the liquid separated by pervaporation (PV) (i.e., the liquid that permeated the carbon membrane 12 and the support 11; hereinafter, also referred to as the “permeated liquid”) was recovered in the second recovery section 28. The mass ratio of water to ethanol in the mixed liquid was 50:50, and the temperature of the mixed liquid supplied from the supply section 26 was 50°C. The permeation-side pressure, which is the pressure on the second recovery section 28 side, was 6.67 kPa (i.e., 50 Torr). Next, the mass and density of the permeated liquid recovered in the second recovery section 28 were measured, and the mass ratio of water to ethanol in the permeated liquid was calculated. The density of the permeated liquid was measured using a density specific gravity meter. Then, from the mass of the permeated liquid and the mass ratio of water to ethanol in the permeated liquid, the separation coefficient of water for ethanol in the carbon membrane composite 1 and the permeation flux of water (kg / m ２ h) was obtained.

[0157] In Table 2, "AA" in the column for separation factor indicates that the separation factor is 200 or more, "A" indicates that the separation factor is 140 or more and less than 200. In addition, "B" in the column for separation factor indicates that the separation factor is 100 or more and less than 140, "C" indicates that the separation factor is 80 or more and less than 100, and "D" indicates that the separation factor is less than 80.

[0158] In Table 2, "AA" in the permeation flux column indicates that the water permeation flux is 1.3 kg / m ２ h or more, and "A" indicates that the water permeation flux is 1.0 kg / m ２ h or more and 1.3 kg / m ２ In addition, "B" in the permeation flux column indicates that the water permeation flux is 0.7 kg / m ２ h or more and 1.0 kg / m ２ h, and "C" indicates that the water permeation flux is less than 0.3 kg / m ２ h or more and 0.7 kg / m ２ h, and "D" indicates that the water permeation flux is less than 0.3 kg / m ２ This indicates that the value is less than h.

[0159] In the strength column of Table 2, "AA" indicates that the strength of the carbon membrane composite 1, 1a is 60 MPa or more, and "A" indicates that the strength of the carbon membrane composite 1, 1a is less than 60 MPa. The strength of the carbon membrane composite 1, 1a was measured in accordance with "JIS R1601:2008." For the measurement, a flat test piece having a length of 20 mm, a width of 20 mm, and a thickness of 1.5 mm was used. The test piece was cut out from a partition wall forming the cell 111 of the support 11. The test piece contained the intermediate layer 32 over substantially the entire surface in a plan view (i.e., when viewed along the thickness direction).

[0160] In Example 1, the concentration of the first precursor in the first precursor solution applied to the support 11 in step S12 was 7.5 mass %. The first precursor was a phenolic resin (Bellpearl (registered trademark) S899, manufactured by Air Water Inc.), and the solvent of the first precursor solution was ethanol (manufactured by Amakasu Chemical Industry Co., Ltd.). The first precursor solution was produced by weighing and mixing the first precursor and the solvent so that the concentration of the first precursor was the above-mentioned concentration, stirring the mixture with a magnetic stirrer at room temperature for four days, and then filtering the mixture using a 20 μm sieve.

[0161] In Example 1, a removal treatment liquid was applied in step S13. The removal treatment liquid was the same as the solvent in the first precursor solution. The concentration of the second precursor in the second precursor solution applied to the support 11 in step S15 was 2 mass%. The second precursor was a phenolic resin (Bellpearl (registered trademark) S899, manufactured by Air Water Inc.), and the solvent of the second precursor solution was ethanol (manufactured by Amakasu Chemical Industry Co., Ltd.). The second precursor solution was produced by mixing 12 g of the phenolic resin as the second precursor with 588 g of the ethanol solvent, stirring the mixture at room temperature with a magnetic stirrer for four days, and then filtering the mixture using a 20 μm sieve.

[0162] In Example 1, as described above, the carbon-rich layer 35 was located in the surface layer 33. In Example 1, the value obtained by dividing the maximum carbon amount in the carbon-rich layer 35 by the average carbon amount in the low carbon layer 36 (hereinafter also referred to as the "carbon amount ratio (carbon-rich layer / low carbon layer)") was 1.2. In other words, the maximum carbon amount in the carbon-rich layer 35 was 1.2 times the average carbon amount in the low carbon layer 36. Furthermore, the value obtained by dividing the maximum carbon amount in the carbon-rich layer 35 by the maximum carbon amount in the carbon membrane 12 (hereinafter also referred to as the "carbon amount ratio (carbon-rich layer / carbon membrane)") was 0.07. In other words, the maximum carbon amount in the carbon-rich layer 35 was 0.07 times the maximum carbon amount in the carbon membrane 12. In Example 1, the separation coefficient was "A", the permeation flux was "A", and the intensity was "A".

[0163] Example 2 is similar to Example 1, except that the concentration of the first precursor in the first precursor solution was 10 mass %. In Example 2, the carbon amount ratio (carbon-rich layer / low carbon layer) was 2.0. The carbon amount ratio (carbon-rich layer / carbon membrane) was 0.12. In Example 2, the separation factor was "A", the permeation flux was "A", and the strength was "A".

[0164] Example 3 is similar to Example 1, except that the concentration of the first precursor in the first precursor solution was 5 mass %. In Example 3, the carbon amount ratio (carbon-rich layer / low carbon layer) was 1.1. The carbon amount ratio (carbon-rich layer / carbon membrane) was 0.06. In Example 3, the separation factor was "B", the permeation flux was "AA", and the strength was "A".

[0165] Example 4 is similar to Example 1, except that the concentration of the first precursor in the first precursor solution was 12 mass%. In Example 4, the carbon mass ratio (carbon-rich layer / low carbon layer) was 3.6. The carbon mass ratio (carbon-rich layer / carbon membrane) was 0.21. In Example 4, the separation factor was "AA", the permeation flux was "B", and the intensity was "A".

[0166] Example 5 is similar to Example 1, except that the concentration of the first precursor in the first precursor solution was 14% by mass. In Example 5, the carbon mass ratio (carbon-rich layer / low carbon layer) was 4.4. The carbon mass ratio (carbon-rich layer / carbon membrane) was 0.26. In Example 5, the separation factor was "AA", the permeation flux was "C", and the strength was "A".

[0167] Example 6 is similar to Example 1, except that the concentration of the first precursor in the first precursor solution was 3 mass%. In Example 6, the carbon amount ratio (carbon-rich layer / low-carbon layer) was 1.05. The carbon amount ratio (carbon-rich layer / carbon membrane) was 0.06. In Example 6, the separation factor was "C", the permeation flux was "AA", and the strength was "A".

[0168] Example 7 is similar to Example 1, except that it was produced by the production method according to the second embodiment, rather than the production method according to the first embodiment. In Example 7, the carbon-rich layer 35 was located in the intermediate layer 32. In Example 7, the carbon amount ratio (carbon-rich layer / low carbon layer) was 1.2. The carbon amount ratio (carbon-rich layer / carbon membrane) was 0.07. In Example 7, the separation factor was "A", the permeation flux was "B", and the strength was "AA".

[0169] Example 8 is similar to Example 7, except that the carbon-rich layer 35 is located on the substrate 31. In Example 8, the carbon amount ratio (carbon-rich layer / low carbon layer) was 1.2. The carbon amount ratio (carbon-rich layer / carbon membrane) was 0.07. In Example 8, the separation factor was "A", the permeation flux was "B", and the strength was "AA".

[0170] In Comparative Example 1, as described above, the removal treatment liquid and the second precursor solution were not applied. The concentration of the first precursor in the first precursor solution in Comparative Example 1 was 7.5 mass%, similar to Example 1. In Comparative Example 1, the separation factor was "A", the permeation flux was "D", and the intensity was "A". In Comparative Example 1, unlike Examples 1 to 8, carbon was present over almost the entire thickness direction of the surface layer 33, with approximately the same carbon amount as that of the carbon-rich layer 35 in Examples 1 to 8. Therefore, in Comparative Example 1, when water that permeated the carbon membrane 12 permeated the support 11, permeation was inhibited by carbon present in a relatively high carbon amount over almost the entire thickness direction of the surface layer 33 that is in contact with the carbon membrane 12 (i.e., carbon present in a relatively high carbon amount continuously from the surface of the support 11), which is considered to have reduced the water permeation flux.

[0171] In contrast, in Examples 1 to 8, the carbon-rich layer 35 having a relatively high carbon content was disposed at a position separated from the surface of the support 11 (i.e., the inner surface 331 of the surface layer 33), and therefore, when water that had permeated the carbon membrane 12 permeated the support 11, the permeation was prevented from being hindered by the carbon in the surface layer 33. As a result, the permeation flux in Examples 1 to 8 was "C" or higher (i.e., "AA", "A", "B", or "C").

[0172] Comparing Example 4 and Example 5, in order to achieve a permeation flux of "B" or higher (i.e., "AA," "A," or "B"), the carbon amount ratio (carbon-rich layer / low-carbon layer) is preferably 4.0 or less. Also, the carbon amount ratio (carbon-rich layer / carbon membrane) is preferably 0.25 or less.

[0173] Comparing Example 2 and Example 4, in order to achieve a permeation flux of "A" or higher (i.e., "AA" or "A"), the carbon amount ratio (carbon-rich layer / low carbon layer) is preferably 2.0 or less.

[0174] Comparing Example 3 and Example 6, in order to achieve a separation factor of "B" or higher (i.e., "AA", "A", or "B"), the carbon amount ratio (carbon-rich layer / low-carbon layer) is preferably 1.1 or higher.

[0175] Comparing Example 1 and Example 3, in order to achieve a separation factor of "A" or higher (i.e., "AA" or "A"), the carbon amount ratio (carbon-rich layer / low-carbon layer) is preferably 1.2 or higher.

[0176] Comparing Example 1 with Examples 7 and 8, it is clear that by positioning carbon-rich layer 35 in intermediate layer 32 or substrate 31, the strength of carbon membrane composites 1 a and 1 b is increased compared to when carbon-rich layer 35 is positioned in surface layer 33.

[0177] As described above, the carbon membrane composites 1, 1a, and 1b include the porous support 11 and the carbon membrane 12 provided on the surface of the support 11 (in the above example, the inner surface of the cell 111). A carbon-rich layer 35 having a higher carbon content than the surrounding region is provided inside the support 11. The carbon-rich layer 35 is disposed at a position spaced apart from the surface of the support 11.

[0178] In this way, by providing the carbon-rich layer 35 inside the support 11, separation of mixed substances is preferably performed not only in the carbon membrane 12 but also inside the support 11. Therefore, the separation factor of the carbon membrane composite 1, 1a, 1b can be improved. Furthermore, in the carbon membrane composites 1, 1a, 1b, a low-carbon layer 36 having a low carbon content is provided between the surface of the support 11 and the carbon-rich layer 35, preventing the carbon-rich layer 35 having a high carbon content from contacting the carbon membrane 12. This prevents the carbon-rich layer 35 from interfering with the permeation of substances that have permeated the carbon membrane 12 when they flow into and permeate the support 11. As a result, a decrease in the permeation flux of the carbon membrane composite 1, 1a, 1b can be suppressed. In other words, the above-mentioned carbon membrane composites 1, 1a, 1b can improve the separation factor while suppressing a decrease in the permeation flux.

[0179] Preferably, the maximum carbon amount in the carbon-rich layer 35 is 1.1 to 4.0 times the average carbon amount in the region between the surface of the support 11 and the carbon-rich layer 35 (i.e., the low-carbon layer 36). In other words, the carbon amount ratio (carbon-rich layer / low-carbon layer) is preferably 1.1 to 4.0. This makes it possible to preferably achieve both suppression of a decrease in the permeation flux and an improvement in the separation factor of the carbon membrane composites 1, 1a, and 1b, as described above.

[0180] More preferably, the maximum carbon amount in the carbon-rich layer 35 is 1.2 to 2.0 times the average carbon amount in the region between the surface of the support 11 and the carbon-rich layer 35 (i.e., the low-carbon layer 36). In other words, the carbon amount ratio (carbon-rich layer / low-carbon layer) is preferably 1.2 to 2.0. This makes it possible to more suitably achieve both suppression of a decrease in the permeation flux and an improvement in the separation factor of the carbon membrane composites 1, 1a, and 1b, as described above.

[0181] Preferably, the maximum carbon amount in the carbon-rich layer 35 is 0.05 to 0.25 times the maximum carbon amount in the carbon membrane 12. In other words, the carbon amount ratio (carbon-rich layer / carbon membrane) is preferably 0.05 to 0.25. This makes it possible to preferably achieve both suppression of a decrease in the permeation flux and improvement of the separation factor of the carbon membrane composites 1, 1a, and 1b, as described above.

[0182] As described above, the thickness of the carbon-rich layer 35 in the thickness direction perpendicular to the surface of the support 11 is preferably 0.01 μm or more and 15 μm or less. By setting the thickness of the carbon-rich layer 35 to 0.01 μm or more, a suitable separation factor of the carbon membrane composite 1, 1a, 1b is realized. Furthermore, by setting the thickness of the carbon-rich layer 35 to 15 μm or less, a decrease in the permeation flux of the carbon membrane composite 1, 1a, 1b is suitably suppressed. Therefore, it is possible to suitably achieve both suppression of a decrease in the permeation flux of the carbon membrane composite 1, 1a, 1b and an improvement in the separation factor.

[0183] As shown in the first embodiment, the support 11 preferably includes a first layer (i.e., a surface layer 33) and a second layer (i.e., an intermediate layer 32). The surface layer 33 extends from the surface of the support 11 (in the above example, the inner surface of the cell 111) toward the inside of the support 11. The intermediate layer 32 extends from the surface layer 33 toward the inside of the support 11. The intermediate layer 32 has a larger average pore diameter than the surface layer 33. In addition, the carbon-rich layer 35 is preferably located closer to the surface of the support 11 than the interface 332 between the surface layer 33 and the intermediate layer 32.

[0184] In this way, by providing the carbon-rich layer 35 on the surface layer 33, separation of mixed substances in the carbon-rich layer 35 is more favorably performed than when the carbon-rich layer 35 is provided on the intermediate layer 32, which has a relatively large average pore size. As a result, it is possible to favorably improve the separation factor of the carbon membrane composite 1. Furthermore, by providing the carbon-rich layer 35 at a position relatively close to the surface of the support 11, it is possible to facilitate the formation of the carbon-rich layer 35.

[0185] As shown in the first embodiment, it is more preferable that the carbon-rich layer 35 contacts the interface 332 between the surface layer 33 and the intermediate layer 32. This makes it possible to increase the radial thickness (i.e., the radial direction about the central axis of the cell 111) of the low-carbon layer 36, which is the region between the surface of the support 11 (i.e., the inner surface 331 of the surface layer 33) and the carbon-rich layer 35. As a result, the separation factor can be further improved while suppressing a decrease in permeation flux. Furthermore, when producing the carbon membrane composite 1, it is easy to stop the penetration of the first precursor solution at the interface 332 between the surface layer 33 and the intermediate layer 32, which have different average pore diameters, and this makes it easy to form the carbon-rich layer 35 having a desired radial thickness.

[0186] As shown in the first embodiment, in the thickness direction perpendicular to the surface of the support 11, the sum of the thickness from the surface of the support 11 to the carbon-rich layer 35 (i.e., the thickness of the low-carbon layer 36) and the thickness of the carbon-rich layer 35 is preferably 0.1 μm or more and 30 μm or less. By setting the total thickness to 0.1 μm or more, the thickness of the carbon-rich layer 35 can be increased to a certain extent. This achieves a favorable separation factor for the carbon membrane composite 1. Furthermore, by setting the total thickness to 30 μm or less, it is possible to prevent the distance in the thickness direction between the carbon membrane 12 and the carbon-rich layer 35 from becoming excessively large, and to prevent the thickness of the carbon-rich layer 35 from becoming excessively large. This effectively prevents a decrease in the permeation flux of the carbon membrane composite 1. Therefore, it is possible to effectively achieve both the suppression of a decrease in the permeation flux of the carbon membrane composite 1 and an improvement in the separation factor.

[0187] As shown in the first embodiment, in the thickness direction perpendicular to the surface of the support 11, the thickness from the surface of the support 11 to the carbon-rich layer 35 (i.e., the thickness of the low carbon layer 36) is preferably 1.0 to 20.0 times the thickness of the carbon-rich layer 35. By making the thickness of the low carbon layer 36 1.0 times or more the thickness of the carbon-rich layer 35, the distance in the thickness direction between the carbon membrane 12 and the carbon-rich layer 35 can be increased to a certain extent. This suitably suppresses a decrease in the permeation flux of the carbon membrane composite 1. Furthermore, by making the thickness of the low carbon layer 36 20.0 times or less the thickness of the carbon-rich layer 35, it is possible to prevent the distance in the thickness direction between the carbon membrane 12 and the carbon-rich layer 35 from becoming excessively large. This allows a suitable separation factor of the carbon membrane composite 1 to be achieved. Therefore, it is possible to suitably achieve both suppression of a decrease in the permeation flux of the carbon membrane composite 1 and an improvement in the separation factor.

[0188] The method for producing the carbon membrane composite 1 according to the first embodiment includes the steps of: applying a first precursor solution containing a first precursor from the surface side (in the above example, the inner surface of the cell 111) of the porous support 11 and allowing it to soak into the surface, thereby forming a first precursor layer 71 containing the first precursor inside the support 11 (step S12); removing a part of the first precursor layer 71 from the surface side of the support 11 (step S13); applying a second precursor solution containing a second precursor from the surface side of the support 11 to form a second precursor layer 72 containing the second precursor inside the support 11, thereby forming a second precursor film 73 that is a film containing the second precursor on the surface of the support 11 (step S15); and carbonizing the first precursor layer 71, the second precursor layer 72, and the second precursor film 73 to form a carbon membrane 12 on the surface of the support 11, and to form a carbon-rich layer 35 inside the support 11 that is positioned at a distance from the surface of the support 11 and has a higher carbon amount than surrounding regions (step S16).

[0189] This makes it possible to suitably produce a carbon membrane composite 1 having a carbon-rich layer 35 spaced apart from the surface of the support 11. In the carbon membrane composite 1, as described above, the separation factor can be improved while suppressing a decrease in permeation flux.

[0190] The method for manufacturing the carbon membrane composite 1 according to the first embodiment preferably further includes, between step S13 and step S15, a step (step S14) of curing the first precursor layer 71 remaining inside the support body 11. This makes it possible to suitably prevent the second precursor solution from mixing with the first precursor layer 71 and the first precursor layer 71 from dissolving when the second precursor solution comes into contact with the first precursor layer 71.

[0191] As shown in the second embodiment, the support 11 preferably includes a first layer (i.e., a surface layer 33) and a second layer (i.e., an intermediate layer 32). The surface layer 33 extends from the surface of the support 11 (in the above example, the inner surface of the cell 111) toward the inside of the support 11. The intermediate layer 32 extends from the surface layer 33 toward the inside of the support 11. The intermediate layer 32 has a larger average pore diameter than the surface layer 33. In addition, the carbon-rich layer 35 is preferably located on the opposite side of the surface of the support 11 with respect to the interface 332 between the surface layer 33 and the intermediate layer 32.

[0192] Thus, in the carbon membrane composites 1a and 1b, the carbon-rich layer 35 is provided in the intermediate layer 32 and / or the substrate 31. The average particle size of the aggregate particles in the intermediate layer 32 and the substrate 31 is larger than that in the surface layer 33, and the bonding strength between the aggregate particles is relatively weak. The carbon-rich layer 35 can favorably bond the aggregate particles in the intermediate layer 32 and / or the substrate 31, thereby increasing the strength of the intermediate layer 32 and / or the substrate 31. As a result, the strength of the carbon membrane composites 1a and 1b can be increased.

[0193] As shown in the second embodiment, in the thickness direction perpendicular to the surface of the support 11, the sum of the thickness from the surface of the support 11 to the carbon-rich layer 35 (i.e., the thickness of the low-carbon layer 36) and the thickness of the carbon-rich layer 35 is preferably 1 μm or more and 1000 μm or less. By making the total thickness 1 μm or more, the thickness of the carbon-rich layer 35 can be increased to a certain extent. This achieves a favorable separation factor for the carbon membrane composites 1a and 1b, and favorably increases the strength of the intermediate layer 32. Furthermore, by making the total thickness 1000 μm or less, it is possible to prevent the distance in the thickness direction between the carbon membrane 12 and the carbon-rich layer 35 and the thickness of the carbon-rich layer 35 from becoming excessively large, and to prevent the decrease in the permeation flux of the carbon membrane composites 1a and 1b from becoming excessively large. This favorably achieves the suppression of a decrease in the permeation flux of the carbon membrane composites 1a and 1b, the improvement in the separation factor, and the increase in the strength of the intermediate layer 32.

[0194] The method for manufacturing the carbon membrane composites 1 a and 1 b according to the second embodiment includes the following steps: a step of applying a first precursor solution containing a first precursor from the surface side of the porous support 11 (in the above example, the inner surface of the cell 111) and reducing the pressure on the side opposite to the surface of the support 11 to cause the first precursor solution to permeate the support 11, thereby forming a first precursor layer 71 containing the first precursor inside the support 11 (step S22); a step of applying a second precursor solution containing a second precursor from the surface side of the support 11, thereby forming a second precursor layer 72 containing the second precursor inside the support 11, and forming a second precursor film 73 that is a film containing the second precursor on the surface of the support 11 (step S24); and a step of carbonizing the first precursor layer 71, the second precursor layer 72, and the second precursor film 73, thereby forming a carbon membrane 12 on the surface of the support 11, and forming a carbon-rich layer 35 inside the support 11 that is positioned at a distance from the surface of the support 11 and has a higher carbon amount than surrounding regions (step S25).

[0195] This makes it possible to suitably produce the carbon membrane composites 1 a and 1 b having the carbon-rich layer 35 spaced apart from the surface of the support 11. In the carbon membrane composites 1 a and 1 b, as described above, the separation factor can be improved while suppressing a decrease in permeation flux. In addition, the strength of the intermediate layer 32 can also be increased.

[0196] The method for manufacturing the carbon membrane composites 1 a and 1 b according to the second embodiment preferably further includes, between steps S22 and S24, a step (step S23) of curing the first precursor layer 71. This makes it possible to suitably prevent the second precursor solution from mixing with the first precursor layer 71 and the first precursor layer 71 from dissolving when the second precursor solution comes into contact with the first precursor layer 71.

[0197] The above-described carbon membrane composites 1, 1a, and 1b and the method for manufacturing the carbon membrane composites 1, 1a, and 1b can be modified in various ways.

[0198] For example, the carbon-rich layer 35 may be provided across both the surface layer 33 and the intermediate layer 32, straddling (i.e., including) the interface 332 between the surface layer 33 and the intermediate layer 32. In this case, the maximum carbon content in the carbon-rich layer 35 (i.e., the boundary between region 64 and region 65 in FIG. 6A , region 65 a in FIG. 7A , the boundary between region 64 b and region 65 b in FIG. 8A , and the boundary between region 64 c and region 65 c in FIG. 9A ) may be located, for example, in the surface layer 33, in the intermediate layer 32, or on the interface 332 between the surface layer 33 and the intermediate layer 32. Furthermore, the interface 332 between the surface layer 33 and the intermediate layer 32 may be located, for example, in a region in the carbon-rich layer 35 where the carbon content decreases from the maximum carbon content (i.e., region 65 in FIG. 6A , region 66 a in FIG. 7A , region 65 b in FIG. 8A , and region 65 c in FIG. 9A ).

[0199] The thickness of the carbon-rich layer 35 may be less than 0.01 μm and may be greater than 15 μm.

[0200] The maximum carbon content in the carbon-rich layer 35 may be less than 0.05 times the maximum carbon content in the carbon film 12, or may be more than 0.25 times.

[0201] The maximum carbon content in the carbon-rich layer 35 may be more than 1.0 times the average carbon content in the low carbon layer 36, but may be less than 1.2 times or less than 1.1 times. The maximum carbon content in the carbon-rich layer 35 may be more than 2.0 times or more than 4.0 times the average carbon content in the low carbon layer 36.

[0202] In the carbon membrane composite 1, the thickness of the low carbon layer 36 may be less than 1.0 times the thickness of the carbon rich layer 35, and may be more than 20.0 times the thickness of the carbon rich layer 35.

[0203] In the carbon membrane composite 1, the sum of the thickness of the low carbon layer 36 and the thickness of the carbon rich layer 35 may be less than 0.1 μm or may be greater than 30 μm.

[0204] In the carbon membrane composites 1a and 1b, the sum of the thickness of the low carbon layer 36 and the thickness of the carbon rich layer 35 may be less than 1 μm or may be greater than 1000 μm.

[0205] In the carbon membrane composites 1, 1a, and 1b, the support 11 (i.e., the substrate 31, the intermediate layer 32, and the surface layer 33) does not necessarily have to be made of ceramics, and may be made of other materials such as metal.

[0206] In the support 11 of the carbon membrane composites 1, 1a, and 1b, either the surface layer 33 or the intermediate layer 32 may be omitted, or both the surface layer 33 and the intermediate layer 32 may be omitted. When both the surface layer 33 and the intermediate layer 32 are omitted, the substrate 31 functions alone as the support 11, and the carbon membrane 12 is provided directly on the surface of the substrate 31. Alternatively, in the carbon membrane composites 1, 1a, and 1b, in addition to the surface layer 33 and the intermediate layer 32, another layer having an average pore diameter smaller than that of the substrate 31 may be provided directly or indirectly on the substrate 31. The other layer is laminated on the substrate 31 together with the surface layer 33 and the intermediate layer 32.

[0207] The partial removal of the first precursor layer 71 in step S13 described above does not necessarily have to be performed by applying the removal treatment liquid, but may be performed by other methods.

[0208] The method for manufacturing the carbon membrane composites 1, 1a, and 1b is not limited to the above, and the carbon membrane composites 1, 1a, and 1b may be manufactured by other manufacturing methods.

[0209] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0210] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention.

[0211] The present invention can be used for separating various substances using a carbon membrane.

[0212] 1, 1a, 1b Carbon membrane composite 11 Support 12 Carbon membrane 32 Intermediate layer 33 Surface layer 35 Carbon-rich layer 36 Low-carbon layer 71 First precursor layer 72 Second precursor layer 73 Second precursor membrane 332, 352, 351 Interface 331 Inner surface S11 to S16 Steps

Claims

1. A carbon membrane composite comprising: a porous support; and a carbon membrane provided on a surface of the support, wherein a carbon-rich layer is provided inside the support, the carbon-rich layer being spaced apart from the surface of the support and having a higher carbon content than surrounding regions.

2. A carbon membrane composite according to claim 1, wherein the support comprises: a first layer extending from the surface of the support toward the inside of the support; and a second layer extending from the first layer toward the inside of the support and having a larger average pore diameter than the first layer, and the carbon-rich layer is located closer to the surface of the support than the interface between the first layer and the second layer.

3. A carbon membrane composite according to claim 2, wherein the carbon-rich layer is in contact with the interface between the first layer and the second layer.

4. A carbon membrane composite according to claim 2, wherein the sum of the thickness from the surface of the support to the carbon-rich layer and the thickness of the carbon-rich layer in the thickness direction perpendicular to the surface of the support is 0.1 μm or more and 30 μm or less.

5. A carbon membrane composite according to claim 2, wherein the thickness from the surface of the support to the carbon-rich layer in the thickness direction perpendicular to the surface of the support is 1.0 to 20.0 times the thickness of the carbon-rich layer.

6. A carbon membrane composite according to claim 1, wherein the support comprises: a first layer extending from the surface of the support toward the inside of the support; and a second layer extending from the first layer toward the inside of the support and having a larger average pore diameter than the first layer, and the carbon-rich layer is located on the opposite side of the surface of the support with respect to the interface between the first layer and the second layer.

7. A carbon membrane composite according to claim 6, wherein the sum of the thickness from the surface of the support to the carbon-rich layer and the thickness of the carbon-rich layer in the thickness direction perpendicular to the surface of the support is 1 μm or more and 1000 μm or less.

8. A carbon membrane composite according to any one of claims 1 to 7, wherein the maximum carbon content in the carbon-rich layer is 1.1 times or more and 4.0 times or less the average carbon content in the region between the surface of the support and the carbon-rich layer.

9. A carbon membrane composite according to claim 8, wherein the maximum carbon content in the carbon-rich layer is 1.2 times or more and 2.0 times or less the average carbon content in the region between the surface of the support and the carbon-rich layer.

10. A carbon film composite according to any one of claims 1 to 7, wherein the maximum carbon content in the carbon-rich layer is 0.05 to 0.25 times the maximum carbon content in the carbon film.

11. A carbon membrane composite according to any one of claims 1 to 7, wherein the thickness of the carbon-rich layer in the thickness direction perpendicular to the surface of the support is 0.01 μm or more and 15 μm or less.

12. A method for producing a carbon membrane composite, comprising: a) applying a first precursor solution containing a first precursor from the surface side of a porous support and allowing it to soak into the support, thereby forming a first precursor layer containing the first precursor inside the support; b) removing a portion of the first precursor layer from the surface side of the support; c) applying a second precursor solution containing a second precursor from the surface side of the support, thereby forming a second precursor layer containing the second precursor inside the support, and forming a second precursor film that is a film containing the second precursor on the surface of the support; and d) carbonizing the first precursor layer, the second precursor layer, and the second precursor film to form a carbon film on the surface of the support, and to form a carbon-rich layer inside the support that is positioned at a distance from the surface of the support and has a higher carbon content than surrounding regions.

13. A method for producing a carbon membrane composite according to claim 12, further comprising, between step b) and step c), a step of curing the first precursor layer remaining inside the support.

14. A method for producing a carbon membrane composite, comprising: a) applying a first precursor solution containing a first precursor from a surface side of a porous support while reducing the pressure on the side of the support opposite to the surface to allow the first precursor solution to permeate the support, thereby forming a first precursor layer containing the first precursor inside the support; b) applying a second precursor solution containing a second precursor from the surface side of the support, thereby forming a second precursor layer containing the second precursor inside the support, and forming a second precursor film that is a film containing the second precursor on the surface of the support; and c) carbonizing the first precursor layer, the second precursor layer, and the second precursor film to form a carbon film on the surface of the support, and to form a carbon-rich layer inside the support that is positioned at a distance from the surface of the support and has a higher carbon content than surrounding regions.

15. A method for producing a carbon membrane composite according to claim 14, further comprising a step of curing the first precursor layer between steps a) and b).

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