Separation membrane, membrane separation device, and separation method

Abstract

A separation membrane 10 according to the present invention is provided with a separation function layer 1 containing Si, O, and C, wherein, in the analysis of the chemical bonding state of C by the C1s spectrum on a first principal surface 1a of the separation function layer 1 using X-ray photoelectron spectroscopy, at least one selected from the group consisting of the ratio of the peak area derived from the C=O bond and the ratio of the peak area derived from the COO bond, to the total peak areas derived from C-H, C-O, C=O, and COO bonds is 1 area% or more.

Description

Separation membrane, membrane separation device, and separation method

[0001] The present invention relates to a separation membrane, a membrane separation device, and a separation method.

[0002] Currently, there is a demand for a carbon-neutral society, and the development of products with various functions is accelerating. For example, in industries such as semiconductors and alcohol production, large amounts of water are used in the manufacture of products. Therefore, with the aim of water reuse, separation technologies are being developed to separate water from mixed liquids containing water and organic solvents such as alcohol. Furthermore, in relation to the issue of global warming, technology is being developed to separate and capture carbon dioxide from exhaust gases in thermal power plants, cement plants, steelworks blast furnaces, etc.

[0003] Membrane separation methods using separation membranes have been developed as methods for separating target substances from mixed fluids such as mixed liquids and mixed gases. For example, in liquid separation, which separates a target liquid from a mixed liquid, membrane separation methods require less energy than separation by distillation, which requires a heating step, and can also suppress the generation of carbon dioxide. Thus, membrane separation methods are excellent as a separation technology that uses less energy and has a small environmental impact.

[0004] For gas or liquid separation, separation membranes in which the portion having the separation function is made of an organic material such as polyimide are usually used. On the other hand, separation membranes in which the portion having the separation function is made of an inorganic material, such as separation membranes using zeolite and hollow fiber membranes, have been proposed.

[0005] Conventionally, separation membranes of various materials and configurations have been proposed to improve the separation function for separating a target substance from a mixed fluid (e.g., improving fluid permeability or separation selectivity) or to improve mechanical strength such as bending resistance. For example, Patent Document 1 discloses a gas separation membrane with excellent gas permeability, abrasion resistance, and bending resistance. Specifically, the separation membrane disclosed in Patent Document 1 has a configuration in which a resin layer having a specific configuration is formed by subjecting a resin layer precursor containing a compound having a siloxane bond to plasma treatment, and a protective layer containing a silicone resin and a porous layer are further disposed on the resin layer.

[0006] Patent No. 6652575

[0007] Conventional separation membranes, such as those disclosed in Patent Document 1, which exhibit separation performance through plasma treatment, have room for improvement in separation performance. Therefore, the present invention provides a separation membrane having a configuration suitable for improving separation performance. Furthermore, the present invention also provides a membrane separation device equipped with a separation membrane having a configuration suitable for improving separation performance, and a separation method using such a separation membrane.

[0008] The present invention provides a separation membrane comprising a separation functional layer containing Si, O, and C, wherein, in an analysis of the chemical bonding state of C by C1s spectrum on a first main surface of the separation functional layer by X-ray photoelectron spectroscopy, at least one selected from the group consisting of a ratio of the peak area derived from a C=O bond and a ratio of the peak area derived from a COO bond to the total area of ​​peaks derived from C-H, C-O, C=O, and COO bonds is 1 area% or more.

[0009] Furthermore, the present invention provides a membrane separation device comprising the above separation membrane.

[0010] Furthermore, the present invention provides a separation method using the above separation membrane, comprising bringing a mixed fluid containing two or more fluids including a fluid to be separated into a first fluid containing the fluid to be separated and a second fluid, by contacting one side of the separation membrane.

[0011] According to the present invention, a separation membrane having a configuration suitable for improving separation performance can be provided. Furthermore, according to the present invention, a membrane separation device including a separation membrane having a configuration suitable for improving separation performance, and a separation method using such a separation membrane can also be provided.

[0012] FIG. 1 is a cross-sectional view schematically showing a separation membrane according to one embodiment of the present invention. FIG. 2 is a structural diagram showing an example of organosilica having a cyclic structure that can be included in a separation functional layer in a separation membrane according to one embodiment of the present invention. FIG. 3 is a cross-sectional view showing a modified example of a porous support in a separation membrane according to one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a membrane separation device including a separation membrane of the present invention. FIG. 5 is a perspective view schematically showing a modified example of a membrane separation device including a separation membrane of the present invention. FIG. 6 is a perspective view showing the positional relationship between a low inductance antenna and an object to be plasma treated in a plasma treatment chamber used in the examples. FIG. 7 is a cross-sectional view showing the positional relationship between a low inductance antenna and an object to be plasma treated in a plasma treatment chamber used in the examples.

[0013] A separation membrane according to a first aspect of the present invention comprises a separation functional layer containing Si, O, and C, and in an analysis of the chemical bonding state of C by C1s spectrum on a first main surface of the separation functional layer by X-ray photoelectron spectroscopy, at least one selected from the group consisting of a ratio of the peak area derived from the C=O bond and a ratio of the peak area derived from the COO bond to the total peak area derived from C-H, C-O, C=O, and COO bonds is 1 area% or more.

[0014] In a second aspect of the present invention, for example, in the separation membrane according to the first aspect, in an analysis of the chemical bonding state of C by C1s spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area derived from the C=O bond to the total peak area derived from C-H, C-O, C=O, and COO bonds is 1 area% or more.

[0015] In a third aspect of the present invention, for example, in a separation membrane according to the first or second aspect, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area derived from Si(-O)4 bonds to the total peak area derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds is 3 area% or more.

[0016] In a fourth aspect of the present invention, for example, in the separation membrane according to the third aspect, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area derived from Si(-O)3 bonds to the total peak area derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds is 15 area% or more.

[0017] In a fifth aspect of the present invention, for example, in the separation membrane according to the fourth aspect, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area derived from Si(-O)2 bonds to the total peak area derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds is 80 area% or less.

[0018] In a sixth aspect of the present invention, for example, in the separation membrane according to the third aspect, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area derived from Si(-O)4 bonds to the total peak area derived from Si(-O)2 and Si(-O)3 bonds is 0.1 or more.

[0019] In a seventh aspect of the present invention, for example, the separation membrane according to any one of the first to sixth aspects further comprises a porous support supporting the separation functional layer, the porous support being arranged on a second main surface side opposite the first main surface of the separation functional layer.

[0020] In an eighth aspect of the present invention, for example, in the separation membrane according to any one of the first to seventh aspects, the separation functional layer contains a compound containing a siloxane bond.

[0021] In a ninth aspect of the present invention, for example, in the separation membrane according to the eighth aspect, the first main surface of the separation functional layer contains organosilica having a siloxane bond, a Si—C bond, and a C—O bond.

[0022] In a tenth aspect of the present invention, for example, in a separation membrane according to any one of the first to ninth aspects, the first main surface of the separation functional layer contains a second compound obtained by modifying a first compound constituting the interior of the separation functional layer by plasma treatment.

[0023] In an eleventh aspect of the present invention, for example, in the separation membrane according to the tenth aspect, the first compound contains a siloxane bond.

[0024] In a twelfth aspect of the present invention, for example, in the separation membrane according to the eleventh aspect, the first compound is a silicone resin.

[0025] In a thirteenth aspect of the present invention, for example, in the separation membrane according to the tenth or eleventh aspect, the plasma treatment is a treatment by inductively coupled plasma using a low-inductance antenna.

[0026] In a fourteenth aspect of the present invention, for example, in the separation membrane according to any one of the first to thirteenth aspects, at least a part of the first main surface of the separation functional layer is exposed on the surface of the separation membrane.

[0027] A membrane separation device according to a fifteenth aspect of the present invention comprises the separation membrane according to any one of the first to fourteenth aspects.

[0028] A separation method according to a sixteenth aspect of the present invention is a separation method using the separation membrane according to any one of the first to fourteenth aspects, comprising bringing a mixed fluid containing two or more fluids including a fluid to be separated into a first fluid containing the fluid to be separated and a second fluid, by contacting one side of the separation membrane.

[0029] In a seventeenth aspect of the present invention, for example, in the separation method according to the sixteenth aspect, the mixed fluid is a mixed gas containing two or more kinds of gases including a gas to be separated.

[0030] In an eighteenth aspect of the present invention, for example, in the separation method according to the seventeenth aspect, the gas to be separated is H2, and H2 of the mixed gas is preferentially allowed to permeate the separation membrane.

[0031] In a nineteenth aspect of the present invention, for example, in the separation method according to the sixteenth aspect, the mixed fluid is a mixed liquid containing two or more kinds of liquids including a liquid to be separated.

[0032] In a twentieth aspect of the present invention, for example, in the separation method according to the nineteenth aspect, the liquid to be separated is H2O, and H2O in the mixed liquid is preferentially allowed to permeate the separation membrane.

[0033] The present invention will be described in detail below, but the following description is not intended to limit the present invention to a specific embodiment.

[0034] <Embodiment of Separation Membrane> As shown in FIG. 1 , the separation membrane 10 of this embodiment includes a separation functional layer 1. The separation functional layer 1 contains Si, O, and C. The separation functional layer 1 further has a specific configuration in which, in an analysis of the chemical bonding state of C by C1s spectrum on the first main surface 1a of the separation functional layer 1 using X-ray photoelectron spectroscopy (XPS), at least one selected from the group consisting of the ratio of the peak area derived from C═O bonds and the ratio of the peak area derived from COO bonds to the total peak area derived from C—H, C—O, C═O, and COO bonds is 1 area% or more. By providing the first main surface 1a with such a specific configuration, the separation functional layer 1 can improve its separation performance. For example, by having the above-described specific configuration, the separation functional layer 1 can have pores on the first main surface 1a that are miniaturized to a size appropriate for molecular sieving, thereby improving its separation performance.

[0035] Here, in the analysis of the chemical bonding state of C in the separation functional layer 1 by XPS, the C1s spectrum obtained by XPS analysis using monochrome AlKα radiation as the X-ray source is subjected to waveform analysis to analyze the chemical bonding state of C. At this time, the peak derived from the C—H bond in the C1s spectrum is charge-corrected to 284.6 eV.

[0036] The separation membrane 10 further includes, for example, a porous support 2. The porous support 2 is disposed on the second main surface 1b side opposite the first main surface 1a of the separation function layer 1, and supports the separation function layer 1. The porous support 2 may be disposed in direct contact with the second main surface 1b of the separation function layer 1 as shown in FIG. 1 , or another layer (an intermediate layer) may be further provided between the separation function layer 1 and the porous support 2. In some cases, the separation membrane 10 may not include the porous support 2, and may be a free-standing membrane (single-layer membrane) having only the separation function layer 1.

[0037] At least a portion of the first main surface 1a of the separation functional layer 1 may be exposed on the surface of the separation membrane 10. This configuration allows the separation membrane 10 to effectively exhibit the separation performance of the separation functional layer 1. Substantially the entire first main surface 1a of the separation functional layer 1 may be exposed on the surface of the separation membrane 10. In this case, substantially the entire first main surface 1a means 90% or more of the area of ​​the first main surface 1a, and may be 95% or more. The entire first main surface 1a of the separation functional layer 1 may be exposed on the surface of the separation membrane 10.

[0038] For example, a resin layer functioning as a protective layer may be provided on the first main surface 1a of the separation functional layer 1. It is desirable that such a protective layer not interfere with the separation performance of the separation functional layer 1 as much as possible, and it is more desirable that it be provided partially on the first main surface 1a in areas where protection is desired. The separation membrane 10 may be installed in the device in a folded or rolled state, for example. Therefore, taking such installation conditions into consideration, a protective layer may be provided only in areas where reinforcement is desired.

[0039] (Separation functional layer) The separation functional layer 1 is a layer that separates a substance to be separated (hereinafter referred to as "fluid to be separated") from a mixed fluid such as a mixed liquid and a mixed gas. The separation functional layer 1 may be a layer that preferentially allows the fluid to be separated contained in the mixed fluid to permeate, or may be a layer that does not allow the fluid to be separated to permeate but allows fluids other than the fluid to be separated to permeate.

[0040] For example, when the mixed fluid is a mixed liquid containing water (H2O) and an organic solvent, and H2O is to be separated from the mixed liquid as the liquid to be separated, the separation function layer 1 can separate H2O from the mixed liquid by preferentially allowing H2O to permeate.

[0041] For example, when the mixed fluid is a mixed gas containing hydrogen (H2) and other gases such as carbon dioxide (CO2), and H2 is to be separated from the mixed gas as the target gas to be separated, the separation functional layer 1 can separate H2 from the mixed gas by preferentially allowing H2 to permeate.

[0042] The separation functional layer 1 contains Si, O, and C, and as described above, in an analysis of the chemical bonding state of C on the first main surface 1a by C1s spectrum using XPS, at least one selected from the group consisting of the ratio of the peak area derived from a C=O bond to the total peak area derived from C-H, C-O, C=O, and COO bonds and the ratio of the peak area derived from the COO bond is 1 area% or more. Hereinafter, "the ratio of the peak area derived from a C=O bond to the total peak area derived from C-H, C-O, C=O, and COO bonds in an analysis of the chemical bonding state of C on the first main surface 1a by C1s spectrum using XPS" will be referred to as "C=O ratio on the first main surface 1a of the separation functional layer 1" or simply "C=O ratio." Furthermore, "the ratio of the peak area attributable to COO bonds to the total peak area attributable to C-H, C-O, C=O, and COO bonds in an analysis of the chemical bonding state of C by C1s spectrum of the first main surface 1a by XPS" is referred to as "COO ratio on the first main surface 1a of the separation functional layer 1" or simply "COO ratio."

[0043] The C═O ratio in the first main surface 1a of the separation functional layer 1 may be 1 area % or more.

[0044] The upper limit of the C=O ratio on the first main surface 1a of the separation functional layer 1 is not particularly limited, but the C=O ratio is, for example, 20 area% or less, or may be 15 area% or less, or 10 area% or less. Furthermore, the upper limit of the COO ratio on the first main surface 1a of the separation functional layer 1 is not particularly limited, but the COO ratio is, for example, 20 area% or less, or may be 15 area% or less, or 10 area% or less.

[0045] In the separation functional layer 1, in an analysis of the chemical bonding state of Si by XPS using a Si2p spectrum on the first main surface 1a, the ratio of the peak area derived from the Si(-O)4 bond to the total peak area derived from the Si(-O)2, Si(-O)3, and Si(-O)4 bonds is preferably 3 area% or more, more preferably 5 area% or more, and even more preferably 10 area% or more. Hereinafter, "the ratio of the peak area derived from the Si(-O)4 bond to the total peak area derived from the Si(-O)2, Si(-O)3, and Si(-O)4 bonds in an analysis of the chemical bonding state of Si by XPS using a Si2p spectrum on the first main surface 1a" will be referred to as "Si(-O)4 ratio on the first main surface 1a of the separation functional layer 1" or simply "Si(-O)4 ratio." When the first main surface 1a of the separation function layer 1 satisfies the above-mentioned Si(-O)4 ratio, the separation function layer 1 is more likely to have pores that are miniaturized to a size appropriate for a molecular sieve, for example, thereby achieving higher separation performance.

[0046] The upper limit of the Si(--O)4 ratio in the first main surface 1a of the separation functional layer 1 is not particularly limited, but the Si(--O)4 ratio is, for example, 90 area % or less, and may be 80 area % or less.

[0047] Here, in the analysis of the chemical bonding state of Si in the separation functional layer 1 by XPS, the chemical bonding state of Si is analyzed by performing waveform analysis on the Si2p spectrum acquired by XPS analysis using monochrome AlKα radiation as the X-ray source. At this time, the peak derived from the C-H bond in the C1s spectrum is charge-corrected to 284.6 eV.

[0048] In an XPS analysis of the chemical bonding state of Si on the first main surface 1a using a Si2p spectrum, the ratio of the peak area derived from Si(-O)3 bonds to the total peak area derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds is preferably 15 area% or more, and more preferably 20 area% or more. Hereinafter, "the ratio of the peak area derived from Si(-O)3 bonds to the total peak area derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds in an XPS analysis of the chemical bonding state of Si on the first main surface 1a using a Si2p spectrum" will be referred to as "Si(-O)3 proportion in the first main surface 1a of the separation functional layer 1" or simply "Si(-O)3 proportion." When the first main surface 1a of the separation function layer 1 satisfies the above-mentioned Si(-O)3 ratio, the separation function layer 1 is more likely to have pores that are miniaturized to a size appropriate for a molecular sieve, for example, thereby achieving higher separation performance.

[0049] The upper limit of the Si(--O)3 ratio in the first main surface 1a of the separation functional layer 1 is not particularly limited, but the Si(--O)3 ratio is, for example, 90 area % or less, and may be 85 area % or less.

[0050] In an analysis of the chemical bonding state of Si on the first main surface 1a by XPS using a Si2p spectrum, the ratio of the peak area derived from Si(-O)2 bonds to the total peak area derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds in the separation functional layer 1 is preferably 80 area% or less, more preferably 70 area% or less, and even more preferably 50 area% or less. Hereinafter, "the ratio of the peak area derived from Si(-O)2 bonds to the total peak area derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds in an analysis of the chemical bonding state of Si on the first main surface 1a by XPS using a Si2p spectrum" will be referred to as "Si(-O)2 proportion in the first main surface 1a of the separation functional layer 1" or simply "Si(-O)2 proportion." When the first main surface 1a of the separation function layer 1 satisfies the above-mentioned Si(-O)2 ratio, the separation function layer 1 is more likely to have pores that are miniaturized to a size appropriate for a molecular sieve, for example, thereby achieving higher separation performance.

[0051] The lower limit of the Si(--O)2 ratio in the first main surface 1a of the separation functional layer 1 is not particularly limited, but the Si(--O)2 ratio is, for example, 1 area % or more.

[0052] In the separation functional layer 1, when the chemical bonding state of Si is analyzed by XPS using the Si2p spectrum of the first main surface 1a, the ratio of the peak area attributable to the Si(-O)4 bond to the sum of the peak areas attributable to the Si(-O)2 and Si(-O)3 bonds is preferably 0.1 or greater, and more preferably 0.15 or greater. Hereinafter, the "ratio of the peak area attributable to the Si(-O)4 bond to the sum of the peak areas attributable to the Si(-O)2 and Si(-O)3 bonds in the analysis of the chemical bonding state of Si by XPS using the Si2p spectrum of the first main surface 1a" will be referred to as the "Si(-O)4 ratio at the first main surface 1a of the separation functional layer 1" or simply as the "Si(-O)4 ratio." When the first main surface 1a of the separation functional layer 1 satisfies the above-described Si(-O)4 ratio, the separation functional layer 1 is more likely to have pores that are miniaturized to a size appropriate for, for example, a molecular sieve, thereby achieving higher separation performance.

[0053] The upper limit of the Si(—O)4 ratio on the first main surface 1a of the separation functional layer 1 is not particularly limited, but the Si(—O)4 ratio is, for example, 30 or less, or may be 5 or less, or may be 4 or less.

[0054] In an XPS analysis of the chemical bonding state of C on the first main surface 1a using a C1s spectrum, the ratio of the peak area attributable to C-H bonds to the total peak area attributable to C-H, C-O, C=O, and COO bonds is preferably 92 area% or less, and more preferably 90 area% or less. Hereinafter, "the ratio of the peak area attributable to C-H bonds to the total peak area attributable to C-H, C-O, C=O, and COO bonds in an XPS analysis of the chemical bonding state of C on the first main surface 1a using a C1s spectrum" will be referred to as "the C-H ratio on the first main surface 1a of the separation functional layer 1" or simply "the C-H ratio." By providing the first main surface 1a with such a specific configuration, i.e., a specific C-H ratio, the separation functional layer 1 can achieve improved separation performance.

[0055] The lower limit of the C-H ratio on the first main surface 1a of the separation functional layer 1 is not particularly limited, but the C-H ratio is, for example, 50 area% or more, or may be 60 area% or more, or 70 area% or more, or may be 75 area% or more.

[0056] In an XPS analysis of the chemical bonding state of C on the first main surface 1a of the separation functional layer 1 using a C1s spectrum, the ratio of the peak area attributable to C-O bonds to the total peak area attributable to C-H, C-O, C=O, and COO bonds is preferably 5 area% or more, more preferably 6 area% or more. Hereinafter, "the ratio of the peak area attributable to C-O bonds to the total peak area attributable to C-H, C-O, C=O, and COO bonds in an XPS analysis of the chemical bonding state of C on the first main surface 1a using a C1s spectrum" will be referred to as "C-O ratio on the first main surface 1a of the separation functional layer 1" or simply "C-O ratio." When the first main surface 1a of the separation functional layer 1 satisfies the above-described C-O ratio, the separation functional layer 1 is more likely to have pores that are miniaturized to a size appropriate for a molecular sieve, for example, thereby achieving higher separation performance.

[0057] The upper limit of the C—O ratio on the first main surface 1a of the separation functional layer 1 is not particularly limited, but the C—O ratio is, for example, 40 area% or less, or may be 30 area% or less, or may be 20 area% or less.

[0058] In the first main surface 1a of the separation functional layer 1, the ratio of the number of O atoms to the number of Si atoms, O / Si, is preferably 1.2 or more, more preferably 1.4 or more, and even more preferably 1.7 or more. When the value of O / Si in the first main surface 1a of the separation functional layer 1 satisfies the above range, the separation functional layer 1 can achieve higher separation performance.

[0059] The O / Si value on the first main surface 1a of the separation functional layer 1 can be determined by a composition analysis of the first main surface 1a of the separation functional layer 1 by XPS.

[0060] The upper limit of O / Si on the first main surface 1a of the separation functional layer 1 is not particularly limited, but O / Si is, for example, 3.0 or less, and may be 2.5 or less.

[0061] In the first main surface 1a of the separation functional layer 1, the ratio of the number of C atoms to the total number of C atoms, N atoms, O atoms, and Si atoms is preferably 17 at. % or more, and more preferably 20 at. % or more. When the ratio of the number of C atoms in the first main surface 1a of the separation functional layer 1 satisfies the above range, the separation functional layer 1 can achieve higher separation performance.

[0062] The upper limit of the ratio of the number of C atoms in the first main surface 1a of the separation functional layer 1 is not particularly limited, but may be, for example, 52 at. % or less, or 50 at. % or less.

[0063] In the first main surface 1a of the separation functional layer 1, the ratio of the number of O atoms to the total number of C atoms, N atoms, O atoms, and Si atoms is preferably 54 at. % or less. When the ratio of the number of O atoms in the first main surface 1a of the separation functional layer 1 satisfies the above range, the separation functional layer 1 can achieve higher separation performance.

[0064] The lower limit of the proportion of the number of O atoms in the first main surface 1 a of the separation functional layer 1 is not particularly limited, but may be, for example, 25 at. % or more, 30 at. % or more, or 35 at. % or more.

[0065] As described above, the separation functional layer 1 is made of a material containing Si, O, and C. The material containing Si, O, and C includes, for example, an organosilicon compound containing Si, O, and C. Examples of the organosilicon compound containing Si, O, and C include alkoxysilanes such as alkylsilicon alkoxides, and compounds containing a siloxane bond (Si—O—Si). Examples of alkylsilicon alkoxides include methyltriethoxysilane (MTES), dimethyldiethoxysilane, and the like.

[0066] The separation functional layer 1 preferably contains a compound containing a siloxane bond (Si—O—Si).

[0067] The first main surface 1a of the separation functional layer 1 may contain organosilica having a siloxane bond, a Si—C bond, and a C—O bond. That is, on the first main surface 1a of the separation functional layer 1, the compound containing the siloxane bond may be, for example, organosilica having a siloxane bond, a Si—C bond, and a C—O bond. By including the organosilica on the first main surface 1a of the separation functional layer 1, it becomes easier to form pores on the first main surface 1a of the separation functional layer 1 that are miniaturized to a size appropriate for a molecular sieve. This allows the separation functional layer 1 to have higher separation performance.

[0068] The organosilica may further have a C═O bond and / or a COO bond. The inclusion of such organosilica makes it easier to form pores on the first main surface 1 a of the separation functional layer 1 that are miniaturized to a size suitable for molecular sieving. This allows the separation functional layer 1 to have higher separation performance.

[0069] The organosilica may include, for example, organosilica having a cyclic structure.

[0070] 2 is a structural diagram showing an example of organosilica having the above-mentioned cyclic structure that can be contained in the first main surface 1a of the separation functional layer 1. However, the structure of the organosilica contained in the first main surface 1a of the separation functional layer 1 is not limited to the structure shown in FIG.

[0071] In the separation functional layer 1, a portion excluding the first main surface 1a, or a portion excluding the first main surface 1a and the region adjacent to the first main surface 1a, the separation functional layer 1 may contain a silicone resin as a compound containing a siloxane bond. In this specification, the portion excluding the first main surface 1a, or the portion excluding the first main surface 1a and the region adjacent to the first main surface 1a, is referred to as the interior of the separation functional layer 1. Silicone resins have various excellent properties, such as heat resistance, water resistance, acid resistance, and flexibility, and can impart these excellent properties to the separation functional layer 1. The silicone resin contained in the separation functional layer 1 is not particularly limited, and various silicone resins can be used. The reaction type of the silicone resin is not particularly limited, and it may be an addition reaction type silicone resin or a condensation reaction type silicone resin. The organic substituent contained in the silicone resin is also not particularly limited, and a silicone resin having a substituent that can exhibit appropriate properties depending on the application of the separation membrane 10 can be appropriately selected.

[0072] The first main surface 1a of the separation functional layer 1 includes, for example, a second compound obtained by modifying a first compound constituting the interior of the separation functional layer 1 through plasma treatment. That is, in a precursor layer of the separation functional layer 1 including the first compound, the first compound contained in the precursor layer's main surface may be modified by plasma treating the main surface of the precursor layer corresponding to the first main surface 1a of the separation functional layer 1, and the material of the first main surface 1a of the separation functional layer 1 may be the second compound formed thereby. The plasma treatment here may be, for example, treatment using inductively coupled plasma using a low-inductance antenna. Details of treatment using inductively coupled plasma using a low-inductance antenna will be described later.

[0073] The first compound may contain a siloxane bond, for example, a silicone resin. When the first compound is a silicone resin, the second compound is a compound formed by modifying the silicone resin by plasma treatment.

[0074] The thickness of the separation functional layer 1 is not particularly limited and may be, for example, 200 μm or less, 100 μm or less, 50 μm or less, 10 μm or less, 4 μm or less, 2 μm or less, or even 1.5 μm or less. The thickness of the separation functional layer 1 may be 0.05 μm or more, or 0.1 μm or more.

[0075] (Porous Support) The porous support 2 is a member that supports the separation function layer 1. Examples of the porous support 2 include nonwoven fabrics, porous polytetrafluoroethylene, aromatic polyamide fibers, porous metals, sintered metals, porous ceramics, porous polyesters, porous nylons, activated carbon fibers, latex, silicone, silicone rubber, polyvinyl fluoride, polyvinylidene fluoride (PVDF), polyurethane, polypropylene, polyethylene, polycarbonate, polysulfone, polyether ether ketone, polyacrylonitrile, polyimide, polyolefins, and polyphenylene oxides. Permeable (porous) polymers containing at least one selected from the group consisting of metal foams having open or closed cells, polymer foams having open or closed cells, silica, porous glass, and mesh screens. The porous support 2 may be a combination of two or more of these.

[0076] The porous support 2 has an average surface pore diameter of, for example, 5 to 100 nm. The thickness of the porous support 2 is not particularly limited and is, for example, 10 μm or more, preferably 20 μm or more, and more preferably 50 μm or more. The thickness of the porous support 2 is, for example, 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0077] 3 is a cross-sectional view showing a modified example of a porous support body 2A. As shown in FIG. 3, the modified porous support body 2A may be, for example, a laminate including a main body portion 3 and a microporous layer 4.

[0078] The main body 3 is, for example, a fiber structure such as a woven fabric or a nonwoven fabric, and is typically a nonwoven fabric. Examples of fibers contained in the fiber structure include natural fibers such as wood pulp, cotton, and hemp (e.g., Manila hemp); and chemical fibers (synthetic fibers) such as polyester fiber, rayon, vinylon, acetate fiber, polyvinyl alcohol (PVA) fiber, polyamide fiber, polyolefin fiber, and polyurethane fiber. The main body 3 is, for example, a nonwoven fabric made of polyester fiber. The main body 3 has an average pore size of, for example, 1 μm to 50 μm.

[0079] Examples of materials for the microporous layer 4 include fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, polyarylethersulfones such as polysulfone and polyethersulfone, and polyimides. The microporous layer 4 has an average pore size of, for example, 0.01 μm to 0.4 μm.

[0080] The thickness of the porous support 2 and the porous support 2A is not particularly limited and may be, for example, 10 μm or more, 50 μm or more, or even 100 μm or more. The thickness of the porous support 2 and the porous support 2A may be, for example, 300 μm or less, or 200 μm or less.

[0081] (Shape of Separation Membrane) In this embodiment, the separation membrane 10 is typically a flat membrane. However, the separation membrane 10 may have a shape other than a flat membrane, for example, a hollow fiber membrane. As an example, the separation membrane 10 as a hollow fiber membrane includes a separation function layer 1 and a porous support 2 (or a porous support 2A).

[0082] (Method for Producing Separation Membrane) The separation membrane 10 can be produced, for example, by the following method.

[0083] First, a precursor (precursor layer) of the separation functional layer 1 is prepared. For example, a coating liquid containing a material containing Si, O, and C is prepared, and the coating liquid is applied to a substrate to form a coating film, and the coating film is dried. If necessary, this coating film is subjected to, for example, a heat treatment. The materials constituting the coating liquid are not particularly limited, as they can be selected appropriately taking into account the material of the separation functional layer 1 to be prepared. For example, when preparing a separation functional layer 1 containing a silicone resin, a precursor layer may be prepared by using a coating liquid containing a silicone resin composition containing polyorganosiloxane and a curing catalyst, and heating and curing the coating film. The silicone resin composition and curing catalyst are not particularly limited and can be selected appropriately. In this way, a precursor layer is prepared. When the separation functional layer 1 is supported by a porous support 2 (or a porous support 2A), the porous support 2 (or a porous support 2A) may be used as the substrate.

[0084] Next, plasma treatment is performed on the surface of the precursor layer. This allows the formation of a separation functional layer 1 having a first main surface 1a. This plasma treatment is, for example, treatment using inductively coupled plasma (ICP). The ICP used is preferably an ICP using a low-inductance antenna. That is, the plasma treatment performed on the surface of the precursor layer is preferably treatment using an ICP generated by applying high-frequency power to a low-inductance antenna. The method of plasma treatment is not particularly limited, but the plasma treatment may be performed while the precursor layer is being transported using a roll-to-roll method, or may be performed using a batch method.

[0085] Here, the term "low-inductance antenna" refers to an antenna that has a low inductance of 7.5 μH or less and that can generate inductively coupled plasma by applying high-frequency power. The high-frequency power is power from a high-frequency power source (RF power source) used to excite plasma discharge.

[0086] ICP plasma treatment using a low-inductance antenna can easily form a first main surface 1a of the separation functional layer 1 having a specific configuration, i.e., a configuration in which at least one selected from the group consisting of the C=O ratio and the COO ratio described above is 1 area % or more. Furthermore, ICP plasma treatment using a low-inductance antenna can also achieve other configurations described above for the first main surface 1a (e.g., Si(-O)4 ratio, Si(-O)3 ratio, and Si(-O)2 ratio, etc.). For example, when the precursor layer contains a compound with a siloxane bond, such as a silicone resin, ICP plasma treatment using a low-inductance antenna, compared to general plasma treatment, does not cleave many Si-C bonds, but cleaves C-H bonds, and is more likely to generate C-O bonds, C=O bonds, and COO bonds. By modifying such compounds, it is possible to form organosilica having siloxane bonds, Si—C bonds, and C—O bonds, as described above, and preferably organosilica further having C═O bonds and / or COO bonds, while preventing excessive damage to the first main surface 1 a of the separation functional layer 1. Note that the general plasma treatment refers to treatment using capacitively coupled plasma (CCP).

[0087] The frequency of the high-frequency power applied during plasma treatment is preferably 1 MHz or higher, more preferably 5 MHz or higher, and even more preferably 10 MHz or higher, and preferably 100 MHz or lower, more preferably 80 MHz or lower, and even more preferably 60 MHz or lower. When the frequency is above the lower limit, the plasma current density can be increased while stabilizing the plasma discharge. When the frequency is below the upper limit, the antenna potential can be suppressed, thereby suppressing damage to the separation membrane 1 caused by the plasma. Furthermore, the high-frequency power is preferably 0.1 kW or higher, more preferably 0.3 kW or higher, and even more preferably 1.0 kW or higher, and is preferably 10 kW or lower, more preferably 8 kW or lower, and even more preferably 6 kW or lower. When the high-frequency power is above the lower limit, a high-density plasma environment can be formed in the plasma treatment chamber during ICP plasma treatment. When the high-frequency power is below the upper limit, excessive damage to the separation membrane 1 caused by the plasma can be suppressed.

[0088] The plasma treatment gas for forming the first main surface 1a of the separation functional layer 1 is, for example, at least one selected from the group consisting of argon, oxygen, and nitrogen. The plasma treatment gas preferably contains argon, and more preferably further contains oxygen (i.e., a mixed gas containing argon and oxygen). This effectively modifies the compounds contained in the precursor layer, allowing the formation of a separation functional layer 1 with higher separation performance.

[0089] In the plasma treatment for forming the first main surface 1a of the separation functional layer 1, the pressure in the plasma treatment chamber is preferably 0.05 Pa or more, more preferably 0.1 Pa or more, even more preferably 0.2 Pa or more, and preferably 10 Pa or less, more preferably 7 Pa or less, even more preferably 5 Pa or less, particularly preferably 3 Pa or less, and even more preferably 1 Pa or less. When the pressure is above the above-mentioned lower limit, a plasma environment of sufficient density for the surface modification treatment for forming the first main surface 1a of the separation functional layer 1 can be formed in the plasma treatment chamber. When the pressure is below the above-mentioned upper limit, thermal damage to the first main surface 1a of the separation functional layer 1 caused by excessively high-density plasma can be suppressed, and thermal deformation of the separation functional layer 1 can also be suppressed. The pressure can be adjusted, for example, by the amount of gas supplied to the plasma treatment chamber.

[0090] In the plasma treatment for forming the first main surface 1a of the separation functional layer 1, the plasma treatment time is preferably 5 seconds or more, more preferably 10 seconds or more, even more preferably 30 seconds or more, particularly preferably 40 seconds or more, even more preferably 50 seconds or more, and preferably 200 seconds or less, more preferably 150 seconds or less, and even more preferably 120 seconds or less. When the plasma treatment time is equal to or greater than the above-mentioned lower limit, sufficient surface modification for forming the first main surface 1a of the separation functional layer 1 by plasma treatment can be achieved. When the plasma treatment time is equal to or less than the above-mentioned upper limit, thermal damage to the first main surface 1a of the separation functional layer 1 caused by excessively high-density plasma can be suppressed, and thermal deformation of the separation functional layer 1 can be suppressed.

[0091] (Uses of Separation Membrane) The separation membrane 10 of this embodiment is suitable for use in separating a mixed fluid containing two or more fluids, including a fluid to be separated, into a first fluid containing the fluid to be separated and a second fluid. The fluid may be a liquid or a gas. The separation method to which the separation membrane 10 is applied is not particularly limited. The separation membrane 10 can be used in various separation methods, such as reverse osmosis (RO), nanofiltration (NF), pervaporation (PV), and vapor permeation (VP).

[0092] (Separation method using separation membrane) A separation method using the separation membrane 10 includes, for example, contacting a mixed fluid containing two or more fluids including a fluid to be separated with one surface of the separation membrane 10 (for example, the surface of the separation membrane 10 on the first main surface 1a side of the separation functional layer 1 (the first main surface of the separation membrane 10)), and separating the mixed fluid into a first fluid containing the fluid to be separated and a second fluid. The first fluid may consist only of the fluid to be separated. Note that the second fluid may contain a small amount of the fluid to be separated. The mixed fluid is separated into a first fluid containing a larger amount of the fluid to be separated, or a first fluid consisting of the fluid to be separated, and a second fluid having a small content of the fluid to be separated, or a second fluid not containing the fluid to be separated. The first fluid may be a fluid that has permeated the separation membrane 10, and the second fluid may not have permeated the separation membrane 10, or the first fluid may be a fluid that has not permeated the separation membrane 10, and the second fluid may be a fluid that has permeated the separation membrane 10.

[0093] When the separation membrane 10 is used for gas separation, the mixed fluid is a mixed gas containing two or more gases including a gas to be separated. For example, when the gas to be separated is H, the H in the mixed gas is preferentially permeated through the separation membrane 10. This allows H to be separated from the mixed gas. In this way, the separation membrane 10 of this embodiment can separate H from, for example, a mixed gas of H and another gas (e.g., CO).

[0094] When the separation membrane 10 is used for liquid separation, the mixed fluid is a mixed liquid containing two or more liquids, including a liquid to be separated. For example, when the liquid to be separated is HO, the HO in the mixed liquid is preferentially permeated through the separation membrane 10. This allows HO to be separated from the mixed liquid. In this way, the separation membrane 10 of this embodiment can separate HO from, for example, a mixed liquid of HO and another liquid (e.g., an organic solvent such as alcohol).

[0095] <Embodiment of Membrane Separation Apparatus> As shown in Figure 4, the membrane separation apparatus 100 of this embodiment includes a separation membrane 10 and further includes a tank 20. The tank 20 includes a first chamber 21 and a second chamber 22. The first chamber 21 functions as a supply space to which a supply fluid L (i.e., a mixed fluid L containing two or more fluids including a fluid to be separated) is supplied. The second chamber 22 functions as a permeation space to which a permeated fluid L1 is supplied. The permeated fluid L1 is obtained by the permeation of the mixed fluid L through the separation membrane 10.

[0096] The separation membrane 10 is disposed inside the tank 20. Inside the tank 20, the separation membrane 10 separates a first chamber 21 and a second chamber 22. The separation membrane 10 extends from one of a pair of wall surfaces of the tank 20 to the other.

[0097] The first chamber 21 has an inlet 21a and an outlet 21b. The second chamber 22 has an outlet 22a. The inlet 21a is an opening for supplying the mixed fluid L to the supply space (first chamber 21). The outlet 22a is an opening for discharging the permeated fluid L1 from the permeated space (second chamber 22). The outlet 21b is an opening for discharging the mixed fluid L that has not permeated the separation membrane 10 (non-permeated fluid L2) from the supply space (first chamber 21). The inlet 21a, the outlet 21b, and the outlet 22a are each formed, for example, on a wall surface of the tank 20.

[0098] The membrane separation apparatus 100 is suitable for a continuous membrane separation method, but may also be used for a batch membrane separation method.

[0099] (Method of Operating Membrane Separation Apparatus) The method of operating the membrane separation apparatus 100 is carried out, for example, as follows. First, the mixed fluid L is supplied to the first chamber 21 of the membrane separation apparatus 100 through the inlet 21 a. This allows the mixed fluid L to come into contact with one surface of the separation membrane 10 (for example, the first main surface of the separation membrane 10).

[0100] The temperature of the mixed fluid L is, for example, 25° C. or higher, preferably 40° C. or higher, and more preferably 60° C. or higher. The temperature of the mixed fluid L may be 75° C. or lower.

[0101] Next, with the mixed fluid L in contact with one surface of the separation membrane 10, the space adjacent to the other surface of the separation membrane 10 (for example, the second main surface of the separation membrane 10) is depressurized. Specifically, the pressure inside the second chamber 22 is reduced through the outlet 22a. The membrane separation device 100 may further include a pump (not shown) for reducing the pressure inside the second chamber 22. The pressure inside the second chamber 22 is reduced, for example, by 10 kPa or more, preferably 50 kPa or more, and more preferably 100 kPa or more, relative to the atmospheric pressure in the measurement environment.

[0102] By reducing the pressure inside the second chamber 22, a permeated fluid L1 can be obtained on the other side of the separation membrane 10. In other words, the permeated fluid L1 is supplied to the second chamber 22. The permeated fluid L1 is discharged to the outside of the membrane separation device 100 through the outlet 22a.

[0103] On the other hand, the mixed fluid L (non-permeated fluid L2) treated in the first chamber 21 is discharged to the outside of the membrane separation device 100 through the outlet 21b.

[0104] <Modifications of Membrane Separation Device> The membrane separation device 100 may be a spiral-type membrane element, a hollow fiber membrane element, a disk-tube-type membrane element in which multiple separation membranes are stacked, a plate-and-frame-type membrane element, or the like. Fig. 5 shows a spiral-type membrane element. The membrane separation device 110 in Fig. 5 includes a central tube 41 and a stack 42. The stack 42 includes separation membranes 10.

[0105] The central tube 41 has a cylindrical shape. A plurality of holes or slits are formed on the surface of the central tube 41 to allow the permeating fluid L1 to flow into the interior of the central tube 41. Examples of materials for the central tube 41 include resins such as acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. The inner diameter of the central tube 41 is, for example, in the range of 20 to 100 mm.

[0106] The laminate 42 further includes a feed-side channel material 43 and a permeate-side channel material 44 in addition to the separation membrane 10. The laminate 42 is wound around a central tube 41. The membrane separation device 110 may further include an exterior material (not shown).

[0107] As the feed-side flow path material 43 and the permeate-side flow path material 44, for example, a resin net made of polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0108] The membrane separation device 110 can be operated, for example, by the following method. First, the mixed fluid L is supplied to one end of the wound stack 42, and the space inside the central tube 41 is depressurized. As a result, the permeated fluid L1 that has permeated the separation membranes 10 of the stack 42 moves into the central tube 41. The permeated fluid L1 is discharged to the outside through the central tube 41. The mixed fluid L (non-permeated fluid L2) that has been treated in the membrane separation device 110 is discharged to the outside from the other end of the wound stack 42.

[0109] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0110] (Preparation of Separation Membrane) (Example 1) First, RS-50 (a laminate of a PVDF microporous layer and a PET nonwoven fabric) manufactured by Nitto Denko Corporation was prepared as a porous support. Next, 2 g of a curing catalyst (SRX212 manufactured by Dow Toray) was added to 100 g of a silicone resin composition (LTC-1051L manufactured by Dow Toray) to prepare an addition reaction type silicone resin composition as a coating liquid. This coating liquid was a solventless type that did not contain a solvent. Next, a coating film was obtained by applying the coating liquid onto the microporous layer of the porous support. Next, the coating film was heated at 150°C for 10 minutes and cured to prepare a precursor layer, which is a precursor of the separation functional layer. At this time, the precursor layer was prepared so that its dry thickness was 15 μm or less.

[0111] Next, the surface of the prepared precursor layer was plasma-treated. In this example, a laminate (plasma-treated object) in which a precursor layer was formed on a porous support was transported by roll-to-roll, while a plasma treatment was performed on the surface of the precursor layer by ICP using a low-inductance antenna. Specifically, an apparatus capable of performing a roll-to-roll process on the laminate was used. The apparatus included a payout chamber, a plasma treatment chamber, and a winding chamber, which were arranged in this order and connected to each other. The payout chamber was equipped with a payout roller. A roll of general-purpose PET film was set on the payout roller as a carrier film for transporting the laminate. The plasma treatment chamber was equipped with a temperature-adjustable transport roller and four low-inductance antennas. Figure 6 is a perspective view showing the positional relationship between the low-inductance antenna and the plasma-treated object in the plasma treatment chamber used in this example. Figure 7 is a cross-sectional view showing the positional relationship between the low-inductance antenna and the plasma-treated object in the plasma treatment chamber used in this example. Each low-inductance antenna 71 had an extension 71a parallel to the object 70 to be plasma processed. The four low-inductance antennas 71 had an extension length d1 of 88 mm, a maximum length d2 (length of the extension) of 100 mm, a separation distance d3 of 112 mm, a center-to-center distance d4 of 290 mm, and a center-to-center distance d5 of 280 mm. Each low-inductance antenna 71 was electrically connected to a high-frequency power source (RF power source, frequency 13.56 MHz) via an impedance matching box outside the plasma processing chamber. In FIGS. 6 and 7 , 72 denotes a fixture, 74 denotes a feedthrough, and the low-inductance antenna 71 was fixed to the fixture 72 via the feedthrough 74.

[0112] The laminate of the porous support and the precursor layer, which was the object to be plasma treated, was cut to A4 size and attached using tape so that the porous support was in contact with a general-purpose PET film, which was the carrier film. This raw roll was set in a feeding chamber, and while the carrier film was transported from the feeding chamber to the winding chamber by a roll-to-roll method, the surface of the precursor layer was plasma treated in the plasma treatment chamber.

[0113] The plasma treatment conditions were as follows: the ultimate vacuum of the plasma treatment chamber was 1.0×10 -4 After evacuating the apparatus until the pressure reached 0.2 Pa, argon (Ar) gas was introduced into the plasma treatment chamber, and the pressure in the plasma treatment chamber was set to 0.2 Pa. An inductively coupled plasma of argon-containing gas was formed around the four low-inductance antennas by applying 5.0 kW of power to the four low-inductance antennas using a 13.56 MHz high-frequency power source (RF power source). The running speed of the carrier film was changed according to the treatment time (80 seconds in Example 1). The temperature of the temperature-adjustable transport roller was set to 20°C. Table 2 shows the plasma treatment conditions.

[0114] The surface of the precursor layer that had been subjected to the above plasma treatment became the first main surface of the separation functional layer, and the separation membrane of Example 1 was produced.

[0115] Example 2 A separation membrane of Example 2 was produced in the same manner as in Example 1, except that the plasma treatment conditions were changed as shown in Table 2.

[0116] (Example 3) First, a Nitto Denko SWC (a laminate of a polysulfone microporous layer and a PET nonwoven fabric) was prepared as a porous support and dried overnight in a draft. Next, 3 g of a crosslinker (Wacker, CROSSLINKER V 24) and 0.6 g of a curing catalyst (Wacker, CATALYST OL) were added to 30 g of a silicone resin composition (Wacker, DEHESIVE (registered trademark) 944), and dissolved in 100 mL of a hydrocarbon solvent (Wacker, EXXSOL D40) and stirred for 30 minutes to prepare a condensation reaction type silicone resin composition as a coating liquid. Next, the coating liquid was applied onto the microporous layer of the porous support to obtain a coating film. After drying the coating film for 2 hours in a draft, the coating liquid was again applied onto the microporous layer of the porous support. Next, the coating film was dried overnight in a draft and then heated at 100° C. for 30 minutes to be cured, thereby producing a precursor layer, which is a precursor of the separation functional layer. At this time, the precursor layer was produced so that its dry thickness was 15 μm or less.

[0117] The plasma treatment of the surface of the precursor layer was carried out in the same manner as in Example 1, except that the plasma treatment conditions were changed as shown in Table 2.

[0118] The separation membrane of Example 3 was produced by the above method.

[0119] Example 4 A separation membrane of Example 4 was produced in the same manner as in Example 1, except that the plasma treatment conditions were changed as shown in Table 2. In Example 4, a mixed gas of argon gas and oxygen gas was used, and the flow rates of the argon gas and oxygen gas were adjusted so that the volume ratio of the argon gas to the oxygen gas was 1:1.

[0120] Example 5 A separation membrane of Example 5 was produced in the same manner as in Example 3, except that the plasma treatment conditions were changed as shown in Table 2.

[0121] Example 6 A separation membrane of Example 6 was produced in the same manner as in Example 3, except that the plasma treatment conditions were changed as shown in Table 2.

[0122] Example 7 A separation membrane of Example 6 was produced in the same manner as in Example 3, except that the plasma treatment conditions were changed as shown in Table 2.

[0123] Comparative Example 1 The precursor layer produced in Example 3 was used as a separation functional layer without being subjected to plasma treatment. That is, the laminate of the porous support and the precursor layer produced in Example 3 was used as the separation membrane of Comparative Example 1.

[0124] Comparative Example 2 The precursor layer produced in Example 1 was used as a separation functional layer without being subjected to plasma treatment. That is, a laminate of the porous support and the precursor layer produced in Example 1 was used as a separation membrane of Comparative Example 2.

[0125] (Comparative Example 3) A separation membrane of Comparative Example 3 was produced in the same manner as in Example 1, except that the plasma treatment using ICP was changed to plasma treatment using CCP. The plasma treatment using CCP performed in Comparative Example 3 was as follows.

[0126] Instead of a plasma treatment chamber equipped with a low-inductance antenna, a cathode electrode and an anode electrode (rectangular electrodes made of SUS304) were installed as flat plate electrodes and used as a plasma treatment chamber. The pair of planar electrodes were spaced 50 mm apart and positioned parallel to a laminate (plasma treatment target) consisting of a porous support and a precursor layer formed thereon. The anode electrode was positioned 35 mm away from the laminate and grounded outside the plasma treatment chamber. The cathode electrode was positioned facing the surface of the precursor layer (the plasma treatment surface) and was electrically connected to an RF power source (13.56 MHz) via an impedance matcher. Argon gas was introduced into the plasma treatment chamber and the flow rate was adjusted to a pressure of 0.5 Pa. CCP was generated by applying 0.2 kW from the RF power source between the planar electrodes, and treatment was performed. The surface size of each planar electrode facing the laminate was 110 mm x 430 mm.

[0127] (Analysis of the first principal surface of the separation functional layer) For the separation membranes of Examples 1 to 7 and Comparative Examples 1 to 3, XPS analysis was performed on the first principal surface of the separation functional layer. Wide scan measurement was performed on the first principal surface of the separation functional layer, i.e., the outermost surface of the separation functional layer, and qualitative analysis was performed. Narrow scan measurement was performed on each element, and the element ratio (atomic%) was calculated. The chemical bond state was analyzed by performing waveform analysis on the Si2p and C1s spectra. At this time, the peak derived from the C-H bond in the C1s spectrum was charge corrected to 284.6 eV (see Table 1). The apparatus used was a "Quantera SXM" manufactured by ULVAC-PHI, and a monochromatic AlKα was used as the X-ray source. The results of the XPS analysis of the first principal surface of the separation functional layer are shown in Tables 3 and 4.

[0128]

[0129] (Evaluation of Liquid Separation) Liquid separation was evaluated for the separation membranes of Examples 1 to 4 and Comparative Examples 1 to 3. Specifically, the separation coefficient α (α=HO / IPA) of water relative to isopropanol (IPA) was measured by the following method.

[0130] First, the separation membrane was cut into a size of 74 mm in diameter to prepare a flat membrane test piece. This test piece was set in a batch-type membrane separation device (cell). A mixed liquid consisting of IPA and water was supplied to the supply space of this cell. The IPA content in the mixed liquid was 50% by mass.

[0131] Next, the cell was immersed in a water bath, and the temperature of the mixed liquid was adjusted to 40° C. Next, the pressure in the permeation space was reduced to 15 hPa while stirring the mixed liquid using a stirrer placed in the cell. As a result, the mixed liquid permeated the separation membrane, and a gas permeated fluid was obtained.

[0132] The gaseous permeate was cooled and condensed using a cold trap using liquid nitrogen. The composition of the liquid permeate was analyzed using gas chromatography, and the separation factor α was calculated based on the results. The results are shown in Table 3.

[0133] (Evaluation of Gas Separation) Gas separation was evaluated for the separation membranes of Examples 3 to 7 and Comparative Examples 1 to 3. Specifically, the separation factor α of H2 relative to CO2 (α = H2 / CO2) was measured by the following method.

[0134] First, the separation membrane was cut into a size of 64 mm in diameter to prepare a flat membrane-shaped test piece. This test piece was set in a batch-type membrane separation device (cell). H gas and CO gas were simultaneously supplied to the supply space of this cell. Next, the cell was set in an oven chamber, and the temperature was adjusted to 150°C. This allowed the mixed gas to permeate the separation membrane, and permeated gas was obtained.

[0135] The composition of the permeated gas was analyzed using gas chromatography, and the permeation rate [GPU] of each gas was determined based on the results obtained. The gas separation factor α was calculated from the permeation rate [GPU] of each gas using the following formula: Gas separation factor α = H [GPU] / CO [GPU]

[0136]

[0137]

[0138]

[0139] As shown in Tables 3 and 4, the separation membranes of the examples had improved separation performance in both liquid separation and gas separation.

[0140] The separation membrane of this embodiment has improved separation performance and is particularly suitable for separating water from a liquid mixture and hydrogen from a gas mixture.

Claims

1. A separation membrane comprising a separation functional layer containing Si, O, and C, wherein, in an analysis of the chemical bonding state of C by C1s spectrum on a first main surface of the separation functional layer by X-ray photoelectron spectroscopy, at least one selected from the group consisting of the ratio of the peak area derived from the C=O bond and the ratio of the peak area derived from the COO bond to the total peak area derived from C-H, C-O, C=O, and COO bonds is 1 area% or more.

2. The separation membrane according to claim 1, wherein, in an analysis of the chemical bonding state of C by C1s spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area derived from the C=O bond to the total peak area derived from C-H, C-O, C=O, and COO bonds is 1 area% or more.

3. The separation membrane according to claim 1, wherein, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area attributable to Si(-O)4 bonds to the total peak areas attributable to Si(-O)2, Si(-O)3, and Si(-O)4 bonds is 3 area% or more.

4. The separation membrane according to claim 3, wherein, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area attributable to Si(-O)3 bonds to the total peak areas attributable to Si(-O)2, Si(-O)3, and Si(-O)4 bonds is 15 area% or more.

5. The separation membrane according to claim 4, wherein, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area derived from Si(-O)2 bonds to the total peak areas derived from Si(-O)2, Si(-O)3, and Si(-O)4 bonds is 80 area% or less.

6. The separation membrane according to claim 3, wherein, in an analysis of the chemical bonding state of Si by Si2p spectrum on the first main surface of the separation functional layer by X-ray photoelectron spectroscopy, the ratio of the peak area attributable to Si(-O)4 bonds to the total peak area attributable to Si(-O)2 and Si(-O)3 bonds is 0.1 or more.

7. The separation membrane according to claim 1, further comprising a porous support for supporting the separation functional layer, the porous support being disposed on a second main surface side opposite the first main surface of the separation functional layer.

8. The separation membrane according to claim 1, wherein the separation functional layer contains a compound containing a siloxane bond.

9. The separation membrane according to claim 8, wherein the first main surface of the separation functional layer contains organosilica having a siloxane bond, a Si—C bond, and a C—O bond.

10. The separation membrane according to claim 1, wherein the first main surface of the separation functional layer contains a second compound obtained by modifying a first compound constituting the interior of the separation functional layer by plasma treatment.

11. The separation membrane according to claim 10, wherein the first compound contains a siloxane bond.

12. The separation membrane according to claim 11, wherein the first compound is a silicone resin.

13. The separation membrane according to claim 10, wherein the plasma treatment is an inductively coupled plasma treatment using a low inductance antenna.

14. The separation membrane according to claim 1, wherein at least a portion of the first main surface of the separation functional layer is exposed on the surface of the separation membrane.

15. A membrane separation device comprising the separation membrane according to any one of claims 1 to 14.

16. A separation method using the separation membrane according to any one of claims 1 to 14, comprising bringing a mixed fluid containing two or more fluids including a fluid to be separated into a first fluid containing the fluid to be separated and a second fluid, by contacting one side of the separation membrane.

17. The separation method according to claim 16, wherein the mixed fluid is a mixed gas containing two or more gases including the gas to be separated.

18. The separation method according to claim 17, wherein the gas to be separated is H2, and H2 in the mixed gas is preferentially allowed to permeate through the separation membrane.

19. The separation method according to claim 16, wherein the mixed fluid is a mixed liquid containing two or more liquids including the liquid to be separated.

20. The separation method according to claim 19, wherein the liquid to be separated is H2O, and H2O in the mixed liquid is preferentially allowed to permeate through the separation membrane.

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