Membrane distillation membrane, method for manufacturing the same, membrane distillation module, and method for producing liquid

Abstract

To provide a membrane distillation membrane high in permeation flux and removal ratio and high in alkali resistance and howling resistance when membrane distillation is carried out, a method for manufacturing the same, a membrane distillation module provided with the membrane distillation membrane, and a method for producing a liquid refined through membrane distillation using the membrane distillation membrane.SOLUTION: This membrane distillation membrane is configured such that a porous layer, a carbon material layer, and a water repellent layer are laminated with the porous layer in contact with the carbon material layer and the carbon material layer in contact with the water repellent layer, a water contact angle of a hydrophilic main surface which is a main surface of the porous layer not in contact with the carbon material layer is over 0° to lower than 10°, a water contact angle of a hydrophobic main surface which is a main surface of the water repellent layer is over 100°, and in a Raman spectrum of the carbon material layer measured by Raman spectroscopy, a ratio (ID / IG) of a peak area (ID) of a D band derived from a sp3 hybrid track component to a peak area (IG) of a G band derived from a sp2 hybrid track component is 0.1-10.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a membrane distillation membrane used in membrane distillation, a method for manufacturing the membrane distillation membrane, a membrane distillation module including the membrane distillation membrane, and a method for manufacturing a purified liquid by membrane distillation using the membrane distillation membrane. [Background technology]

[0002] Membrane distillation is a method for purifying a crude liquid by allowing vapor to pass through a porous membrane due to the vapor pressure generated by the temperature difference between two liquids separated by the porous membrane. Membrane distillation does not require high pressure for purifying a crude liquid, as does reverse osmosis. Therefore, membrane distillation is expected to contribute to reducing the cost of purifying a crude liquid (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-200770 Summary of the Invention [Problem to be solved by the invention]

[0004] When alkaline water such as sewage or industrial wastewater discharged from factories is purified as a crude liquid, the porous membrane (membrane distillation membrane) used in the membrane distillation method is required to have alkali resistance. It is also desirable that the crude liquid has a high removal rate of components other than water (for example, alkali, organic matter, and microorganisms).

[0005] In addition, a high permeation flux is also desired in order to increase the amount of crude liquid purified (processed). In the membrane distillation method, if organic matter, microorganisms, etc. contained in the crude liquid adhere to the porous membrane (membrane distillation membrane) and cause fouling, the purification amount (processing amount) decreases. Therefore, it is also desirable for the porous membrane (membrane distillation membrane) used in the membrane distillation method to be able to suppress fouling, which is the adhesion of organic matter, microorganisms, etc. to the porous membrane, i.e., to have excellent fouling resistance.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a membrane distillation membrane that has a high permeation flux and removal rate and is excellent in alkali resistance and fouling resistance when performing membrane distillation, a method for manufacturing the membrane distillation membrane, a membrane distillation module including the membrane distillation membrane, and a method for manufacturing a purified liquid by membrane distillation using the membrane distillation membrane. [Means for solving the problem]

[0007] The present inventors have discovered a method for producing a porous carbon film in which a porous layer, a carbon material layer, and a water-repellent layer are laminated together such that the porous layer is in contact with the carbon material layer and the carbon material layer is in contact with the water-repellent layer, the hydrophilic main surface of the porous layer that is not in contact with the carbon material layer has a water contact angle of more than 0° and less than 10°, and the hydrophobic main surface that is the main surface of the water-repellent layer has a water contact angle of more than 100°, and the Raman spectrum of the carbon material layer measured by Raman spectroscopy shows that 3 The peak area of ​​the D band due to the hybrid orbital component (I D ) and sp 2 The peak area of ​​the G band due to the hybrid orbital component (I G ) and the ratio (I D / I G The present inventors have found that the above problems can be solved by using a membrane distillation membrane in which the ratio (ratio) of the total mass of the membrane to the total mass of the distillation membrane is 0.1 or more and 10 or less, and have arrived at the present invention. Specifically, the present invention provides the following.

[0008] [1] In a membrane distillation method, a membrane distillation membrane is used to obtain a purified liquid by passing vapor of a crude liquid to be purified, In the membrane distillation membrane, a porous layer, a carbon material layer, and a water-repellent layer are laminated in a state in which the porous layer is in contact with the carbon material layer and the carbon material layer is in contact with the water-repellent layer, a hydrophilic main surface of the porous layer that is not in contact with the carbon material layer has a water contact angle of more than 0° and less than 10°; the contact angle of water on the hydrophobic main surface, which is the main surface of the water-repellent layer, is greater than 100°; In the Raman spectrum of the carbon material layer measured by Raman spectroscopy, sp 3 The peak area of ​​the D band due to the hybrid orbital component (I D ) and sp 2 The peak area of ​​the G band due to the hybrid orbital component (I G ) and the ratio (I D / I G ) is 0.1 or more and 10 or less.

[0009] [2] The carbon material layer is a diamond-like carbon layer, The membrane distillation membrane according to [1] above, wherein the water-repellent layer is formed by treating the carbon material layer with plasma derived from a gas containing a fluorinated hydrocarbon or a silicon-containing compound.

[0010] [3] The membrane distillation membrane according to [1] or [2] above, wherein the element ratio of fluorine atoms is 10 atm% or more, or the element ratio of silicon atoms is 10 atm% or more, in the ratio of elements constituting the surface of the water-repellent layer.

[0011] [4] The membrane distillation membrane according to any one of [1] to [3] above, wherein the membrane distillation membrane has a Gurley air permeability of 20 seconds or more and 150 seconds or less.

[0012] [5] The membrane distillation membrane according to any one of the above [1] to [4], wherein the thickness of the water-repellent layer is 10 nm or more and 1 μm or less.

[0013] [6] The membrane distillation membrane according to any one of the above [1] to [5], wherein the surface tension of the water-repellent layer is 73 mN / m or less.

[0014] [7] The membrane distillation membrane according to any one of [1] to [6] above, wherein the porous layer is made of at least one resin material selected from the group consisting of polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, nylon, polypropylene, and polysulfone.

[0015] [8] The membrane distillation membrane according to any one of the above [1] to [7], wherein the crude liquid is an alkaline liquid having a pH of 11 or more at 20°C.

[0016] [9] When the crude liquid is purified by membrane distillation, The permeation flux, which is the amount of the purified liquid per unit area and unit time that permeates the membrane distillation membrane and is recovered, is 15 kg / m 2 The membrane distillation membrane according to any one of the above [1] to [8], wherein the membrane distillation membrane has a viscosity of more than 1000 sq m.

[0017]

[10] A method for producing a membrane distillation membrane according to any one of [1] to [9] above, a carbon material layer forming step of forming the carbon material layer on a surface of the untreated porous film that is the porous layer; and a water-repellent layer forming step of treating the surface of the carbon material layer with plasma derived from a gas containing a fluorinated hydrocarbon or a silicon-containing compound to form the water-repellent layer.

[0018]

[11] A membrane distillation module comprising the membrane distillation membrane according to any one of [1] to [5] above.

[0019]

[12] A high-temperature tank into which a crude liquid to be purified is introduced and a liquid receiving tank for recovering the purified liquid; The high-temperature tank and the receiving tank are separated by the membrane distillation membrane,

[11] The membrane distillation module according to the above

[11] , wherein the purified liquid obtained by condensing the vapor derived from the crude liquid while the vapor is passing through the membrane distillation membrane or after the vapor has passed through the membrane distillation membrane is recovered in the liquid receiving tank.

[0020]

[13] A heating device is provided to heat the crude liquid introduced into the high-temperature tank or the crude liquid introduced into the high-temperature tank. The membrane distillation module according to

[12] above, further comprising a cooling device that lowers the internal temperature of the receiver tank.

[0021]

[14] Contacting a crude liquid to be purified with the membrane distillation membrane according to any one of [1] to [9] above; A method for producing a purified liquid by membrane distillation, comprising condensing the vapor derived from the crude liquid while the vapor is permeating through the membrane distillation membrane or after the vapor has permeated through the membrane distillation membrane to obtain a purified liquid.

[0022]

[15] A method for producing a purified liquid according to

[14] above, comprising membrane distilling the crude liquid using the membrane distillation module according to any one of

[11] to

[13] above.

[0023]

[16] The method for producing a purified liquid according to

[14] or

[15] above, wherein the crude liquid is brought into contact with the hydrophilic main surface of the membrane distillation membrane.

[0024]

[17] The method for producing a purified liquid according to any one of

[14] to

[16] above, wherein the crude liquid is an alkaline liquid having a pH of 11 or higher at 20°C. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide a membrane distillation membrane that has a high permeation flux and removal rate and is excellent in alkali resistance and fouling resistance when performing membrane distillation, a method for producing the membrane distillation membrane, a membrane distillation module including the above-mentioned membrane distillation membrane, and a method for producing a purified liquid by membrane distillation using the above-mentioned membrane distillation membrane. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram showing an example of a membrane distillation membrane of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] <Membrane distillation membrane> In a membrane distillation method, a membrane distillation membrane is used to obtain a purified liquid by passing the vapor of a crude liquid to be purified through the membrane distillation membrane. The membrane distillation membrane will be described below with reference to Figure 1. Figure 1 is a schematic diagram showing an example of a membrane distillation membrane of the present invention. As shown in FIG. 1, the membrane distillation membrane 1 has a porous layer 11, a carbon material layer 12, and a water-repellent layer 13. In the membrane distillation membrane 1, a porous layer 11, a carbon material layer 12, and a water-repellent layer 13 are laminated in a state in which the porous layer 11 is in contact with the carbon material layer 12 and the carbon material layer 12 is in contact with the water-repellent layer 13. The hydrophilic main surface 11a of the porous layer 11, which is the main surface not in contact with the carbon material layer 12, has a water contact angle of more than 0° and less than 10°. The hydrophobic main surface 13a of the water-repellent layer 13 has a water contact angle of more than 100°. In the Raman spectrum of the carbon material layer 12 measured by Raman spectroscopy, sp 3 The peak area of ​​the D band due to the hybrid orbital component (I D ) and sp 2 The peak area of ​​the G band due to the hybrid orbital component (I G ) and the ratio (I D / I G ) is between 0.1 and 10.

[0028] When membrane distillation is performed, the membrane distillation membrane 1 has a high permeation flux and a high removal rate, and is excellent in alkali resistance and fouling resistance. For example, when a crude liquid is purified by membrane distillation, the permeation flux, which is the amount of purified liquid per unit area and unit time that is recovered through the membrane distillation membrane 1, is 15 kg / m 2 ·h and 20 kg / m 2 It can also be more than 1 / h. The permeation flux can be calculated by the following formula by measuring the recovered amount of the purified liquid obtained by membrane distillation using an electronic balance. Permeation flux (kg / m 2 h) = Liquid recovery amount (kg) / (Membrane area (m 2 ) × collection time (h) Furthermore, when a crude liquid is purified by membrane distillation, the removal rate of components other than water contained in the crude liquid (e.g., alkali, organic matter, and microorganisms) is, for example, 95% or more, and can also be 97% or more. The removal rate can be calculated from the electrical conductivity of the crude liquid to be purified and the electrical conductivity of the purified liquid using the following formula. Removal rate (%) = (electrical conductivity of crude liquid to be purified - electrical conductivity of purified liquid) / (electrical conductivity of crude liquid to be purified) x 100

[0029] The crude liquid to be purified is not particularly limited, but is preferably an alkaline liquid, which is an alkaline liquid. The above-mentioned membrane distillation membrane has excellent alkali resistance and is therefore suitable for purifying alkaline liquids by membrane distillation. The alkaline solution may be water containing ammonia. Specific examples of the alkaline solution include sewage, industrial wastewater discharged from factories, and concentrated or diluted solutions of these. The alkaline solution as the crude liquid preferably has a pH value of 11 or more at 20°C.

[0030] Here, the contact angle of water is a static contact angle, which can be measured, for example, using a Dropmaster 700 (manufactured by Kyowa Interface Science Co., Ltd.) by dropping a 2.0 μL droplet of pure water onto the surface of the object to be measured (the hydrophilic or hydrophobic main surface), and then measuring the contact angle 10 seconds after the dropping. The water contact angle of the hydrophilic main surface 11a may be greater than 0° and less than 10°. The water contact angle of the hydrophobic main surface 13a may be more than 100°. There is no particular upper limit to the water contact angle, but it is, for example, 110° or less.

[0031] In the Raman spectrum of the carbon material layer 12 measured by Raman spectroscopy, sp 3 The peak area of ​​the D band due to the hybrid orbital component (I D ) and sp 2 The peak area of ​​the G band due to the hybrid orbital component (I G ) and the ratio (I D / IG ) should be between 0.1 and 10. D / I G ) is preferably 0.2 or more and 5.0 or less, and more preferably 0.5 or more and 2.5 or less. In this specification, the D band is defined as 1310 cm -1 The G band is at 1580 cm -1 This is the peak.

[0032] The above ratio (I D / I G A diamond-like carbon (DLC) layer is a specific example of the carbon material layer 12 in which the value of ρ is 0.1 or more and 10 or less. The carbon material layer 12 is preferably a diamond-like carbon layer. Diamond-like carbon has a diamond structure and a graphite structure. In the Raman spectrum of diamond-like carbon measured by Raman spectroscopy, sp 3 Hybrid orbitals and sp 2 Hybrid orbitals are observed. 3 The peak area of ​​the D band due to the hybrid orbital component (I D ) and sp 2 The peak area of ​​the G band due to the hybrid orbital component (I G ) and the ratio (I D / I G ) is between 0.1 and 10. In addition, when the carbon material layer 12 is made of graphite or the like that does not have a diamond structure, the above ratio (I D / I G ) is less than 0.1.

[0033] The thickness of the carbon material layer 12 in the membrane distillation membrane 1 is not particularly limited, but is preferably 30 nm or more and 1 μm or less. The thickness of the carbon material layer 12 can be determined by, for example, measuring the thickness at multiple locations with a micrometer or the like and averaging the measurements, or by observing the cross section of the film with a scanning electron microscope (SEM) and averaging the measurements.

[0034] The water-repellent layer 13 is not particularly limited as long as it satisfies the above conditions, but is preferably formed by treating the carbon material layer 12 with plasma derived from a gas containing a fluorinated hydrocarbon or a silicon-containing compound. Fluorinated hydrocarbons include CF4 and C4F8. An example of the silicon-containing compound is polydimethylsiloxane.

[0035] The thickness of the water-repellent layer 13 in the membrane distillation membrane 1 is not particularly limited, but is preferably 10 nm or more and 1 μm or less, and more preferably 30 nm or more and 2.0 μm or less. The film thickness of the water-repellent layer 13 can be determined, for example, by measuring the thickness at multiple locations with a micrometer or the like and averaging the measurements, or by observing the cross section of the film with a scanning electron microscope (SEM) and averaging the measurements.

[0036] The surface tension of the water-repellent layer 13 is not particularly limited, but is preferably 73 mN / m or less, more preferably 60 mN / m or less, and is preferably 20 mN / m or more. In this specification, the surface tension (surface free energy) of the water-repellent layer 13 is determined by measuring the contact angle of various liquid droplets on the surface of the water-repellent layer 13 (the hydrophobic main surface 13a, which is the main surface of the water-repellent layer 13). Note that the surface tension ([mN / m]) is calculated based on the surface free energy [mJ / m 2 ]) has the same absolute value as

[0037] When the water-repellent layer 13 contains fluorine atoms, the atomic ratio of fluorine atoms in the ratio of elements constituting the surface of the water-repellent layer 13 is preferably 10 atm% or more, more preferably 15 atm% or more, and even more preferably 20 atm% or more. The upper limit of the atomic ratio of fluorine atoms may be, for example, 70 atm% or less, or 51 atm% or less.

[0038] When the water-repellent layer 13 contains silicon atoms, the elemental ratio of silicon atoms in the ratio of elements constituting the surface of the water-repellent layer 13 is preferably 10 atm% or more, more preferably 15 atm% or more, and even more preferably 20 atm% or more. The upper limit of the elemental ratio of silicon atoms may be, for example, 70 atm% or less, or 51 atm% or less.

[0039] The ratio of elements constituting the surface of the water-repellent layer 13 can be determined by measuring the amount of fluorine atoms, silicon atoms, etc. by X-ray photoelectron spectroscopy.

[0040] The Gurley air permeability of the membrane distillation membrane 1 is preferably 20 seconds or more and 150 seconds or less, more preferably 25 seconds or more and 100 seconds or less, and particularly preferably 30 seconds or more and 50 seconds or less.

[0041] The shape of the pores in the membrane distillation membrane 1 is not particularly limited as long as the membrane distillation membrane 1 allows the vapor of the crude liquid to be purified to pass through. The porous layer 11 constituting the membrane distillation membrane 1 can be a porous membrane manufactured by a known method, such as a phase separation method such as a water vapor absorption method or a thermally induced phase separation method, a stretching method, or a method of removing fine particles from a membrane containing fine particles, which will be described later. The pores in the porous layer 11 (and thus the membrane distillation membrane 1) may be spherical or non-spherical. The pores present in the porous membrane may form a structure in which the pores are interconnected (hereinafter referred to as interconnected pores). When the porous layer 11 is a laminate, the same applies to each porous layer included in the laminate.

[0042] The shape of the pores in the porous layer 11 may be spherical or non-spherical. The sphere with respect to the shape of the pores is a concept that includes a perfect sphere, but is not necessarily limited to a perfect sphere. The sphere may be substantially a perfect sphere, and also includes a shape that can be recognized as approximately a perfect sphere when a magnified image of the pore is visually observed. Specifically, in the case of a spherical hole, the surface defining the hole portion is a curved surface, and the curved surface may define a hole having a perfect sphere or a nearly perfect sphere. When the porous layer 11 is a laminate, the porosity and the diameter of the spherical pores of each porous layer constituting the laminate may be the same or different.

[0043] The diameter of the pores contained in the porous layer 11 is not particularly limited. Typically, the preferred range of the pore diameter is adjusted appropriately to 30 nm or more, preferably 30 nm or more to 2000 nm or less, depending on the type of material of the porous layer 11, the type of surface treatment method, etc. For example, when the material of the porous layer 11 is polyethersulfone, it is also preferable that the pore diameter is more than 150 nm. When the cross-sectional shape of the hole is a shape other than a circle, the diameter of the hole can be the equivalent circle diameter of the cross-section of the hole.

[0044] When the porous layer 11 has interconnected pores made of spherical pores, the individual spherical pores are typically formed by removing individual particles present in the resin-particle composite film in a later step, as will be described later. Furthermore, the interconnected pores are formed by removing, in a later step, a plurality of particles present in contact with each other in the resin-particle composite film in the manufacturing method of the porous layer 11 (untreated porous film), as will be described later. The locations where the interconnected spherical pores are present are derived from the locations where the plurality of particles contact each other before being removed.

[0045] When a membrane distillation membrane 1 having a porous layer 11, a carbon material layer 12, and a water-repellent layer 13 has internal communicating holes that penetrate the membrane distillation membrane 1 in the thickness direction as a fluid flow path, the fluid can pass from one main surface of the membrane distillation membrane 1 to the other main surface.

[0046] The porous layer 11 may be a single layer film made of only one type of film, or a laminated film in which two or more types of films are laminated in two or more layers.

[0047] When the porous layer 11 is a laminated film, the laminated film can be formed by a conventional method such as lamination. Alternatively, the porous film included in the laminated film may be sequentially formed on one of the porous films constituting the outermost layers of the laminated film. Alternatively, a precursor film for the porous layer 11 may be laminated by lamination, coating, or the like, and then the laminated film on which the precursor film is laminated may be made porous to form the porous layer 11, which is a laminated film. Examples of the precursor film include a layer containing fine particles in a resin matrix that can be removed by thermal decomposition or treatment with an organic solvent, water, acid, alkali, or the like.

[0048] There are no particular limitations on the thickness of the porous layer 11. The thickness of the porous layer 11 is determined appropriately depending on the type of liquid to be purified by membrane distillation, etc. Typically, the thickness of the porous membrane is preferably 20 μm or more, more preferably 20 μm or more and 200 μm or less, and even more preferably 30 μm or more and 150 μm or less.

[0049] The film thickness of the porous layer 11, or, if the porous layer 11 is a laminated film, the film thickness of each porous film included in the laminated film, can be determined, for example, by measuring the thickness at multiple locations using a micrometer or the like and averaging the results, or by observing the film cross section using a scanning electron microscope (SEM) and averaging the results.

[0050] The material for forming the porous layer 11 may be an organic material or an inorganic material. Polymer materials are typically preferred because of their excellent processability and flexibility. The material of the porous layer 11 is not particularly limited. The porous layer 11 is preferably made of at least one resin material selected from the group consisting of polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, nylon, polypropylene, and polysulfone. Suitable examples of materials for forming the porous film include solutions of various resins, thermosetting resin compositions, and photosensitive resin compositions. Photosensitive resin compositions include positive-type photosensitive resin compositions in which exposed areas are soluble in a developer, and negative-type photosensitive resin compositions in which exposed areas are insoluble in a developer, and both can be used to form the porous layer 11. As a material for forming the porous layer 11, a thermosetting resin composition that is cured by heating is preferred because it can form a thin film with excellent strength.

[0051] <Varnish for producing porous layer> Hereinafter, a description will be given of a varnish for producing a porous layer that is suitably used for producing a porous layer 11 (untreated porous film) having continuous pores. For manufacturing the porous layer 11 described above, it is preferable to use a porous layer manufacturing varnish (hereinafter also referred to simply as "varnish") that contains predetermined fine particles, a resin material, and a solvent, with the resin material dissolved in the solvent. The varnish is typically produced by a step of preparing a fine particle dispersion by dispersing fine particles in a solvent, a step of preparing a resin solution, and a step of kneading the fine particle dispersion and the resin solution together to adjust the concentration. Polyethersulfone is preferred as the resin used in preparing the varnish.

[0052] For kneading the varnish, a rotation-revolution mixer (for example, trade name: Awatori Rentaro, manufactured by Thinky Corporation), a planetary mixer, a bead mill, or the like can be used.

[0053] [Resin material] As mentioned above, the resin contained in the varnish is preferably polyethersulfone. The polyethersulfone is not particularly limited as long as it is soluble in the solvent used to form the varnish. The polyethersulfone can be appropriately selected depending on the application of the porous layer to be produced. It may be an aliphatic polyethersulfone or an aromatic polyethersulfone. The weight-average molecular weight of the polyethersulfone is not particularly limited as long as the desired effect is not impaired. The weight-average molecular weight is, for example, 5,000 to 1,000,000, and preferably 10,000 to 300,000.

[0054] [Fine particles] The material of the particles is not particularly limited, and any known material can be used as long as it is insoluble in the solvent contained in the varnish and can be subsequently removed from the resin-particle composite film. For example, inorganic materials include metal oxides such as silica (silicon dioxide), titanium oxide, and alumina (Al2O3), and organic materials include organic polymer particles such as high-molecular-weight olefins (polypropylene, polyethylene, etc.), polystyrene, epoxy resins, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, and polyether.

[0055] Specific examples of fine particles include colloidal silica. Among them, monodispersed spherical silica particles are preferred because they can form uniform pores.

[0056] Furthermore, it is preferable that the microparticles have a high sphericity and a small particle size distribution index. Microparticles that meet these conditions have excellent dispersibility in the varnish and can be used without agglomerating together. The average particle size of the microparticles used is, for example, preferably 15 nm to 1800 nm, more preferably 20 nm to 1500 nm, and even more preferably 30 nm to 1200 nm. By satisfying these conditions, the pore size of the porous layer obtained by removing the microparticles can be made uniform. The average particle size of the microparticles is D50. D50 refers to the particle size at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction / scattering. The fine particles may be used alone or in combination of two or more kinds.

[0057] 〔solvent〕 The solvent is not particularly limited as long as it can dissolve the resin and does not dissolve the fine particles. Examples of the solvent include nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea; lactone-based polar solvents such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; dimethyl sulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellosolve acetate, and ethyl cellosolve acetate; and phenolic solvents such as cresols and xylene-based mixed solvents. The solvents may be used alone or in combination of two or more. In the case of polyethersulfone, examples of the solvent include the nitrogen-containing polar solvents described above, as well as polar solvents such as diphenylsulfone, dimethylsulfone, dimethylsulfoxide, benzophenone, tetrahydrothiophene-1,1-dioxide, and 1,3-dimethyl-2-imidazolidinone.

[0058] [Dispersant] A dispersant may be added together with the fine particles to uniformly disperse the fine particles in the varnish. Adding a dispersant allows the fine particles to be mixed more uniformly in the varnish and to be uniformly distributed in the film formed from the varnish. As a result, dense openings can be formed on the surface of the finally obtained porous layer, and the front and back surfaces can be efficiently connected, thereby improving the air permeability of the porous layer. Furthermore, adding a dispersant tends to improve the drying properties of the varnish and the peelability of the formed unfired composite film from the substrate, etc.

[0059] The dispersant is not particularly limited, and known dispersants can be used. For example, anionic surfactants such as coconut fatty acid salts, castor sulfated oil salts, lauryl sulfate salts, polyoxyalkylene allyl phenyl ether sulfate salts, alkyl benzene sulfonic acid, alkyl benzene sulfonate salts, alkyl diphenyl ether disulfonate salts, alkyl naphthalene sulfonate salts, dialkyl sulfosuccinate salts, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salts, and polyoxyethylene allyl phenyl ether phosphate salts; cationic surfactants such as oleylamine acetate, lauryl pyridinium chloride, cetyl pyridinium chloride, lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, and didecyl dimethyl ammonium chloride; amphoteric surfactants such as coconut alkyl dimethyl amine oxide, fatty acid amidopropyl dimethyl amine oxide, alkyl polyaminoethyl glycine hydrochloride, amido betaine surfactants, alanine surfactants, and lauryliminodipropionic acid; Nonionic surfactants of polyoxyalkylene primary alkyl ethers or polyoxyalkylene secondary alkyl ethers, such as ethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxyethylene polystyrylphenyl ether, and polyoxyalkylene polystyrylphenyl ether; other polyoxyalkylene-based nonionic surfactants, such as polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylenated castor oil, polyoxyethylenated hydrogenated castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, and fatty acid diethanolamides; fatty acid alkyl esters, such as octyl stearate and trimethylolpropane tridecanoate; and polyether polyols, such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether, and trimethylolpropane tris(polyoxyalkylene) ether, but are not limited to these.The above dispersants can also be used in combination of two or more.

[0060] In the varnish, the content of the dispersant is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less, relative to the mass of the microparticles, for example, from the viewpoint of film-forming properties.

[0061] <Suitable method for producing porous layer> A preferred example of a method for producing the porous layer 11 using the above-mentioned varnish will be described below, but the method for producing the porous layer 11 is not limited to the method described below.

[0062] [Unfired composite film formation process] In the green composite film forming step, for example, the green composite film can be formed by applying the above-mentioned varnish onto a substrate and drying it under normal pressure or in vacuum at a temperature of 0° C. to 100° C., preferably at normal pressure and 10° C. to 100° C. Examples of the substrate include a PET film, a SUS substrate, and a glass substrate.

[0063] Furthermore, when peeling the unfired composite film from the substrate, a substrate pre-formed with a release layer can be used to further enhance the film's releasability. When a release layer is pre-formed on the substrate, a release agent is applied to the substrate and dried or baked before applying the varnish. The release agent used here can be any known release agent, such as an alkyl ammonium phosphate salt, a fluorine-based agent, or a silicone-based agent, without any particular restrictions. When peeling the dried unfired composite film from the substrate, a small amount of release agent remains on the peeled surface of the unfired composite film, which can cause discoloration during firing and adversely affect the electrical properties, so it is preferable to remove it as much as possible. To remove the release agent, a cleaning step can be introduced in which the unfired composite film peeled from the substrate is washed with an organic solvent.

[0064] On the other hand, when the substrate is used as is without providing a release layer for forming the green composite film, the above-mentioned release layer forming step and the above-mentioned cleaning step can be omitted. Furthermore, in the production of the green composite film, the following optional steps may be provided before the firing step described below: a step of immersing in a solvent containing water, a pressing step, and a drying step after the immersion step.

[0065] [Firing process] The unsintered composite film is subjected to post-treatment (sintering) by heating to form a composite film (resin-particle composite film) consisting of resin and particles. The baking temperature in the baking step varies depending on the structure of the unsintered composite film and the presence or absence of a condensing agent, but is preferably 120°C to 450°C, more preferably 150°C to 400°C. Furthermore, when an organic material is used for the particles, the temperature must be set lower than their thermal decomposition temperature. When an unsintered composite film is formed on a substrate and then peeled off from the substrate, the ends of the unsintered composite film can be fixed to a SUS mold or the like to prevent deformation.

[0066] [Particle removal process] By selecting an appropriate method to remove the particles from the resin-particle composite film formed as described above, a porous layer having a desired structure can be produced with good reproducibility. When silica is used as the material of the fine particles, for example, the silica can be dissolved and removed by treating the resin-fine particle composite film with low-concentration hydrogen fluoride water or the like. When the fine particles are organic fine particles, the fine particles can also be removed from the resin-particle composite film by thermally decomposing the organic fine particles. Furthermore, when the fine particles are organic fine particles, a treatment liquid that dissolves the fine particles but does not dissolve the resin is selected, and the organic fine particles can be removed by treatment with the treatment liquid. Typically, an organic solvent is used as the treatment liquid. When the organic fine particles are soluble in an acid or an alkali, an acidic aqueous solution or an alkaline aqueous solution can also be used as the treatment liquid.

[0067] [Resin removal process] The method for producing a porous layer may include a resin removal step of removing at least a portion of the resin portion of the resin-particle composite film before the particle removal step, or a resin removal step of removing at least a portion of the porous film after the particle removal step. By removing at least a portion of the resin portion of the resin-particle composite film before the particle removal step, or by removing at least a portion of the porous layer after the particle removal step, it is possible to improve the porosity of the porous layer compared to when removal is not performed.

[0068] The step of removing at least a portion of the resin portion or the step of removing at least a portion of the porous layer can be carried out by a common chemical etching method, a physical removal method, or a combination of these methods.

[0069] Chemical etching methods include treatment with chemical etching solutions such as inorganic alkaline solutions or organic alkaline solutions. Inorganic alkaline solutions are preferred. Examples of inorganic alkaline solutions include hydrazine solutions containing hydrazine hydrate and ethylenediamine; solutions of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate, and sodium metasilicate; ammonia solutions; and etching solutions containing alkali hydroxides, hydrazine, and 1,3-dimethyl-2-imidazolidinone as main components. Examples of organic alkaline solutions include alkaline solutions of primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; alcohol amines such as dimethylethanolamine and triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; and cyclic amines such as pyrrole and piheridine.

[0070] The solvent for each of the above solutions can be selected appropriately from pure water or alcohols. Solvents containing an appropriate amount of surfactant can also be used. The alkali concentration is, for example, 0.01% by mass or more and 20% by mass or less.

[0071] Physical methods that can be used include, for example, dry etching using plasma (oxygen, argon, etc.) or corona discharge, and a surface treatment method in which an abrasive (e.g., alumina (hardness 9)) is dispersed in a liquid and irradiated onto the surface of the film at a speed of 30 m / s to 100 m / s.

[0072] The above-mentioned method is preferable because it can be applied to the resin removal step either before or after the fine particle removal step.

[0073] On the other hand, a physical method applicable only to the resin removal process performed after the particle removal process can be used, in which the target surface is pressed against a wetted mount film (e.g., a polyester film such as a PET film) and then the porous layer is peeled off from the mount film, either before or after drying. Due to the surface tension or electrostatic adhesion of the liquid, the porous membrane is peeled off from the mount film, leaving only the surface layer of the porous layer on the mount film.

[0074] <Membrane distillation membrane manufacturing method> a carbon material layer forming step of forming a carbon material layer on the surface of the untreated porous film, which is the porous layer; The membrane distillation membrane can be produced by a method for producing a membrane distillation membrane, the method including a water-repellent layer formation step of treating the surface of the carbon material layer with plasma derived from a gas containing a fluorinated hydrocarbon or a silicon-containing compound to form a water-repellent layer. Each step will be explained below.

[0075] [Carbon material layer formation process] In the carbon material layer forming step, a carbon material layer 12 is formed on the surface of the untreated porous film, which is the porous layer 11.

[0076] The method for forming the carbon material layer 12 is not particularly limited. For example, a diamond-like carbon layer serving as the carbon material layer 12 can be manufactured by, for example, a plasma CVD method or a PVD method. In the plasma CVD method, for example, a hydrocarbon gas such as acetylene is used as a raw material, and the raw material gas is converted into plasma in a chamber, and the hydrocarbon synthesized in the vapor phase is deposited on the surface of the untreated porous film. In the PVD method, the raw material graphite is exposed to an ion beam, arc discharge, glow discharge, or the like in a vacuum by a sputtering method or an ion plating method, and the scattered carbon atoms are attached to the untreated porous film.

[0077] [Water-repellent layer formation process] In the water-repellent layer forming step, the surface of the carbon material layer 12 is treated with plasma derived from a gas containing a fluorinated hydrocarbon or a silicon-containing compound to form the water-repellent layer 13 .

[0078] The plasma treatment can be easily carried out in a plasma generating device using a fluorinated hydrocarbon or a silicon-containing compound as a process gas. The fluorinated hydrocarbon and the silicon-containing compound are as described above in the section <<Membrane Distillation Membrane>>.

[0079] In addition, when the membrane distillation membrane 1 is manufactured using an untreated porous membrane whose water contact angle is outside the range of more than 0° and less than 10°, the main surface of the untreated porous membrane may be subjected to oxygen plasma treatment, water vapor plasma treatment, deep ultraviolet irradiation, or the like to form a hydrophilic main surface 11a whose water contact angle is more than 0° and less than 10°.

[0080] <Membrane distillation module and method for producing purified liquid> The membrane distillation membrane can be used as a membrane for membrane distillation, and is preferably used as a membrane distillation module. A purified liquid can be produced by performing membrane distillation of a crude liquid using the membrane distillation module. The membrane distillation module includes a high-temperature tank into which the crude liquid to be purified is introduced and a receiver tank for collecting the purified liquid. The membrane distillation membrane is installed to separate the high-temperature tank from the receiver tank. In this case, the hydrophilic main surface of the membrane distillation membrane of the membrane distillation module is preferably installed so as to be in contact with the crude liquid. That is, the membrane distillation membrane of the membrane distillation module is preferably installed so that the hydrophilic main surface of the membrane distillation membrane faces the high-temperature tank and the hydrophobic main surface of the membrane distillation membrane faces the receiving tank. In such a membrane distillation module, the crude liquid to be purified is brought into contact with a membrane distillation membrane, and the purified liquid obtained by condensing the vapor derived from the crude liquid while it is passing through the membrane distillation membrane or after it has passed through is recovered in a receiving tank.

[0081] The membrane distillation module is equipped with a heating device that heats the crude liquid introduced into the high-temperature tank or the crude liquid introduced into the high-temperature tank, or a cooling device that lowers the internal temperature of the receiving tank. It is preferable to use the heating device or the cooling device to maintain a temperature difference between the crude liquid and the internal temperature of the liquid receiving tank of 20°C or more. This allows the vapor that has permeated the porous membrane to be efficiently condensed, improving the recovery efficiency of the purified liquid.

[0082] <Membrane distillation method> The membrane distillation membrane can be used in any membrane distillation method, such as direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), sweeping gas membrane distillation (SGMD), vacuum membrane distillation (VMD), and permeation gap membrane distillation (PGMD). [Example]

[0083] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0084] Comparative Example 1 As the membrane distillation membrane of Comparative Example 1, a porous membrane (pore diameter: 30 nm, thickness: 135 μm) manufactured by GVS and having a resin material of polyethersulfone (PES) was used.

[0085] Comparative Example 2 As the membrane distillation membrane of Comparative Example 2, a porous membrane manufactured by Merck (product name: Durapore, pore size: 220 nm, thickness: 120 μm) whose resin material was PVDF was used.

[0086] Comparative Example 3 Slurry A containing 70 parts by mass of silica fine particles, 0.35 parts by mass of a nonionic surfactant as a dispersant, and 70 parts by mass of dimethylacetamide was stirred in a 200 mL container at 400 rpm with a stirring blade for 15 minutes. The stirred slurry A was then subjected to five dispersion treatments at 200 MPa using a dispersing device (Yoshida Kikai Kogyo Co., Ltd., NVL-S008). Silica with an average particle diameter of 100 nm was used as the silica fine particles.

[0087] The dispersed slurry A was mixed with 30 parts by mass of polyamic acid to obtain slurry B. The polyamic acid was used as a dimethylacetamide solution with a solids concentration of 20% by mass. The polyamic acid used was a polymer obtained by polymerizing equimolar amounts of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (hereinafter referred to as 6FDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (hereinafter referred to as HFBAPP)). Slurry B contained dimethylacetamide and gamma-butyrolactone as organic solvents so that the solid content concentration was 29 mass %. The mass ratio of dimethylacetamide to gamma-butyrolactone in Slurry B was 90:10 (dimethylacetamide:gamma-butyrolactone).

[0088] The obtained slurry B was dispersed in a 200 mL container by stirring with a stirring blade at 400 rpm for 30 minutes to prepare a varnish for producing a porous membrane. The varnish for producing a porous membrane was applied to a PET film, which was then heated at 90°C for 300 seconds to remove the solvent, forming a coating film with a thickness of approximately 40 μm.

[0089] The formed coating film was peeled off from the PET film and imidized by heat treatment (baking) at 380°C for 15 minutes to obtain a polyimide resin-particle composite film. The obtained polyimide resin-particle composite film was immersed in a 10% HF solution for 10 minutes to remove the silica particles contained in the film. After removing the silica particles, the film was washed with water and dried to obtain a porous film with spherical pores and interconnected pores, which was used as the membrane distillation membrane of Comparative Example 3. The resulting porous membrane had a pore size of 300 nm and a thickness of 39 μm.

[0090] Comparative Example 4 A diamond-like carbon (DLC) layer was formed on the main surface of the porous membrane (porous layer) of Comparative Example 1 opposite the side that came into contact with the crude liquid using acetylene gas plasma to obtain the membrane distillation membrane of Comparative Example 4. The acetylene plasma treatment was carried out using a TCA3822 interdigitated electrode (Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 300 W, time: 120 seconds, pressure: 40 Pa, and flow rate: 100 sccm.

[0091] Comparative Example 5 For the porous membrane of Comparative Example 1, polydimethylsiloxane (PDMS: Dow SYLGARD 184 base) diluted to 1% by mass with n-heptane was sprayed onto the main surface opposite the side contacted with the crude liquid, and the membrane was dried at 60°C for 2 minutes. After that, a water-repellent layer was formed by plasma treatment in Ar gas, and a membrane distillation membrane of Comparative Example 5 was obtained. The PDMS plasma treatment was performed using a TCA3822 comb electrode (Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 150 W, time: 60 seconds, pressure: 40 Pa, flow rate: 100 sccm.

[0092] Comparative Example 6 The membrane distillation membrane of Comparative Example 6 was obtained by carrying out the same operation as in Comparative Example 4, except that the acetylene plasma treatment time was changed to 60 seconds as the DLC layer formation conditions.

[0093] Comparative Example 7 Regarding the conditions of the PDMS plasma treatment, the same operation as in Comparative Example 5 was performed except that the concentration of polydimethylsiloxane diluted with n-heptane was changed to 0.5 mass %, to obtain a membrane distillation membrane of Comparative Example 7.

[0094] Comparative Example 8 In the porous membrane of Comparative Example 1, a water-repellent layer was formed on the main surface opposite to the side that came into contact with the crude liquid by performing CF4 plasma treatment, thereby obtaining a membrane distillation membrane of Comparative Example 8. The CF4 plasma treatment was performed using a TCA3822 interdigitated electrode (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 150 W, time: 120 seconds, pressure: 40 Pa, and flow rate: 100 sccm.

[0095] Comparative Example 9 The porous membrane obtained in the same manner as in Comparative Example 3 was hydrophilized by oxygen plasma treatment on the main surface that came into contact with the crude liquid. The oxygen plasma treatment was carried out using a TCA3822 interdigitated electrode (Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 300 W, time: 10 seconds, pressure: 40 Pa, and flow rate: 100 sccm. Next, a water-repellent layer was formed on the main surface opposite to the side that came into contact with the crude liquid by performing a CF4 plasma treatment, thereby obtaining a membrane distillation membrane of Comparative Example 9. The CF4 plasma treatment was performed using a TCA3822 interdigitated electrode (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 500 W, time: 120 seconds, pressure: 40 Pa, and flow rate: 100 sccm.

[0096] Example 1 A diamond-like carbon (DLC) layer was formed on the main surface opposite to the side contacted with the crude liquid of the porous film (porous layer) of Comparative Example 1 by acetylene plasma treatment (carbon material layer formation step). The acetylene plasma treatment was performed using a TCA3822 comb-shaped electrode (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 300 W, time: 120 seconds, pressure: 40 Pa, and flow rate: 100 sccm. Next, a water-repellent layer was formed on the surface of the diamond-like carbon (DLC) layer by performing CF4 plasma treatment (water-repellent layer formation step), thereby obtaining the membrane distillation membrane of Example 1. The CF4 plasma treatment was performed using a TCA3822 interdigitated electrode (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 150 W, time: 120 seconds, pressure: 40 Pa, and flow rate: 100 sccm.

[0097] Example 2 The membrane distillation membrane of Example 2 was obtained by the same procedure as in Example 1, except that instead of CF4 plasma treatment, a 1% by mass solution of polydimethylsiloxane (PDMS: Dow SYLGARD 184 base material) diluted with n-heptane was sprayed onto the membrane, dried at 60°C for 2 minutes, and then plasma treated in Ar gas to form a water-repellent layer. PDMS plasma treatment was performed using a TCA3822 comb electrode (Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 25°C, RF (power): 150 W, time: 60 seconds, pressure: 40 Pa, flow rate: 100 sccm.

[0098] Example 3 The membrane distillation membrane of Example 3 was obtained by performing the same operations as in Example 2, except that the DLC layer formation conditions were changed to 60 seconds for the acetylene plasma treatment time and the PDMS plasma treatment conditions were changed to 0.5 mass% for the concentration of polydimethylsiloxane diluted with n-heptane.

[0099] Example 4 The membrane distillation membrane of Example 4 was obtained by performing the same operations as in Example 2, except that a porous membrane (pore size: 200 nm, thickness: 135 μm) manufactured by GVS and having a resin material of polyethersulfone (PES) was used instead of the porous membrane (porous layer) of Comparative Example 1.

[0100] [Production of purified liquids using membrane distillation] A purified liquid was obtained by performing permeation gap membrane distillation under the following conditions using a membrane distillation apparatus equipped with a membrane distillation module having a high-temperature tank and a liquid receiving tank separated by the membrane distillation membrane obtained in Examples 1 to 4 and Comparative Examples 1 to 9. [High temperature tank] Crude liquid: Concentrated sewage (pH at 20°C: 11.5, electrical conductivity: 200 μs / cm) ·Temperature: 50℃ ·Circulation flow rate: 4.0L / min [Liquid receiving tank (low temperature tank)] Refrigerant: Tap water ·Temperature: 20℃

[0101] The membrane distillation membranes of Examples 1 to 4 and Comparative Examples 1 to 9 obtained as described above were analyzed for the water contact angles of the hydrophilic and hydrophobic main surfaces, the surface tension of the water-repellent layer, the film thickness of the water-repellent layer and / or the DLC layer, and the above ratio (I D / I G The electrical conductivity of the purified liquids obtained by membrane distillation under the above-mentioned conditions using the membrane distillation membranes of Examples 1 to 4 and Comparative Examples 1 to 9 was also measured. However, for Comparative Example 1, the removal rate and permeation flux could not be measured due to leakage of the crude liquid. Surface tension, the ratio (I D / I G The water contact angle, the film thickness of the water-repellent layer and the DLC layer, and the permeation flux were measured by the methods described above. Furthermore, the membrane distillation membranes of Examples 1 to 4 and Comparative Examples 1 to 9 were observed after membrane distillation under the above-mentioned conditions, and their fouling resistance was evaluated according to the following method. These results are shown in Table 1. In Table 1, "<0.1" means less than 0.1, and "<10" means less than 10. For electrical conductivity, the removal rate calculated using the above formula is shown in Table 1.

[0102] [Measurement of surface tension (surface free energy)] Using a contact angle meter ("Dropmaster 700" manufactured by Kyowa Interface Science Co., Ltd.), droplets of pure water and methylene iodide were dropped onto the surface of the water-repellent layer of each membrane distillation membrane produced in the Examples and Comparative Examples at a temperature of 25°C and a relative humidity of 50%, and the contact angle was measured 1 second after the droplet adhered to the surface. The surface tension (surface free energy) was calculated from each of the obtained contact angles according to the Owens-Wendt method.

[0103] [Ratio(I D / I G ) Measurement For the carbon material layer (DLC layer) of the membrane distillation membrane, a 632.8 nm He-Ne excitation laser light source was used, and the wavelength range was 800 to 2000 cm -1 The Raman spectrum was measured in the range of In the obtained Raman spectrum, sp 3 The peak area of ​​the D band due to the hybrid orbital component (I D ) and sp 2 The peak area of ​​the G band due to the hybrid orbital component (I G ) and calculate the ratio (I D / I G ) was calculated. The D band is at 1310 cm -1 The G band is at 1580 cm -1 This is the peak.

[0104] [Air permeability measurement] Using a 5 cm x 5 cm sample of membrane distillation membrane, the time it took for 100 mL of air to pass through the sample was measured using a Gurley densometer (manufactured by Toyo Seiki Seisaku-sho) in accordance with JIS P 8117. The smaller the air permeability value, the shorter the time it took for 100 mL of air to pass through, and the faster the gas passing through the sample.

[0105] [Measurement of the elemental ratio of fluorine atoms and the elemental ratio of silicon atoms] Using a K-Alpha (registered trademark) XPS system (manufactured by Thermo Fisher Scientific), an X-ray photoelectron spectrometer, the amount of each atom on the surface of the water-repellent layer of the membrane distillation membrane sample was measured, and the elemental ratio of fluorine atoms and the elemental ratio of silicon atoms were determined.

[0106] [Measurement of electrical conductivity] The electrical conductivity was measured at 50°C using an AC two-electrode electrical conductivity meter in accordance with JIS K 0130.

[0107] [Evaluation of fouling resistance] After carrying out the above membrane distillation for 200 hours, the membrane distillation membrane was visually observed and evaluated for fouling resistance according to the following criteria. A: No deposits were observed. B: Some adhesion was observed. C: A large amount of adhesion was observed.

[0108] [Evaluation of alkaline resistance] The membrane distillation membranes of Examples 1 to 4 and Comparative Examples 1 to 9 were each immersed in a 12% by mass aqueous solution of sodium hypochlorite (pH: 12.6) for 2.5 hours at room temperature (20° C.) After immersion, the membrane distillation membranes were visually observed and evaluated for alkali resistance according to the following criteria. A: There was no change in the membrane distillation membrane before and after immersion. B: After immersion, the membrane distillation membrane was partially dissolved.

[0109] [Table 1]

[0110] [Table 2]

[0111] According to Table 1, the porous layer, the carbon material layer, and the water-repellent layer are laminated in a state in which the porous layer is in contact with the carbon material layer and the carbon material layer is in contact with the water-repellent layer, the hydrophilic main surface of the porous layer, which is the main surface not in contact with the carbon material layer, has a water contact angle of more than 0° and less than 10°, the hydrophobic main surface, which is the main surface of the water-repellent layer, has a water contact angle of more than 100°, and the Raman spectrum of the carbon material layer shows sp 3 The peak area of ​​the D band due to the hybrid orbital component (I D ) and sp2 The peak area of ​​the G band due to the hybrid orbital component (I G ) and the ratio (I D / I G ) is 0.1 or more and 10 or less, the membrane distillation membranes of Examples 1 to 4 have high permeation flux and removal rate, and are excellent in alkali resistance and fouling resistance. On the other hand, the porous layer, the carbon material layer, and the water-repellent layer are laminated in a state in which the porous layer is in contact with the carbon material layer and the carbon material layer is in contact with the water-repellent layer, and the water contact angle of the hydrophilic main surface, which is the main surface of the porous layer not in contact with the carbon material layer, is more than 0° and less than 10°, and the water contact angle of the hydrophobic main surface, which is the main surface of the water-repellent layer, is more than 100°, and the above ratio (I D / I G ) does not satisfy the condition of 0.1 or more and 10 or less, the membrane distillation membranes of Comparative Examples 1 to 9 have low permeation flux or removal rate, and poor alkali resistance and fouling resistance. [Explanation of symbols]

[0112] 1. Membrane distillation membrane 11 Porous layer 11a Hydrophilic main surface 12 Carbon material layer 13 Water-repellent layer 13a Hydrophobic main surface

Claims

1. In a membrane distillation method, a membrane distillation membrane is used to obtain a purified liquid by passing vapor of a crude liquid to be purified, In the membrane distillation membrane, a porous layer, a carbon material layer, and a water-repellent layer are laminated in a state in which the porous layer is in contact with the carbon material layer and the carbon material layer is in contact with the water-repellent layer, a hydrophilic main surface of the porous layer that is not in contact with the carbon material layer has a water contact angle of more than 0° and less than 10°; the contact angle of water on the hydrophobic main surface, which is the main surface of the water-repellent layer, is greater than 100°; In the Raman spectrum of the carbon material layer measured by Raman spectroscopy, ３ The peak area of ​​the D band due to the hybrid orbital component (I Ｄ ) and sp ２ The peak area of ​​the G band due to the hybrid orbital component (I Ｇ ) and the ratio (I Ｄ / I Ｇ ) is 0.1 or more and 10 or less.

2. the carbon material layer is a diamond-like carbon layer, The membrane distillation membrane according to claim 1 , wherein the water-repellent layer is formed by treating the carbon material layer with plasma derived from a gas containing a fluorinated hydrocarbon or a silicon-containing compound.

3. 3. The membrane distillation membrane according to claim 2, wherein the element ratio of fluorine atoms is 10 atm% or more, or the element ratio of silicon atoms is 10 atm% or more, in the ratio of elements constituting the surface of the water-repellent layer.

4. The membrane distillation membrane according to claim 1, wherein the Gurley air permeability of the membrane distillation membrane is 20 seconds or more and 150 seconds or less.

5. The membrane distillation membrane according to claim 1, wherein the water-repellent layer has a thickness of 10 nm or more and 1 μm or less.

6. The membrane distillation membrane according to claim 1 , wherein the surface tension of the water-repellent layer is 73 mN / m or less.

7. 2. The membrane distillation membrane according to claim 1, wherein the porous layer is made of at least one resin material selected from the group consisting of polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, nylon, polypropylene, and polysulfone.

8. The membrane distillation membrane according to claim 1, wherein the crude liquid is an alkaline liquid having a pH of 11 or more at 20°C.

9. When the crude liquid is purified by membrane distillation, The permeation flux, which is the amount of the purified liquid per unit area and unit time that permeates the membrane distillation membrane and is recovered, is 15 kg / m ２ The membrane distillation membrane of claim 1, wherein the membrane distillation membrane has a viscosity of more than h.

10. The method for producing a membrane distillation membrane according to any one of claims 1 to 9, a carbon material layer forming step of forming the carbon material layer on a surface of the untreated porous film that is the porous layer; and a water-repellent layer forming step of treating the surface of the carbon material layer with plasma derived from a gas containing a fluorinated hydrocarbon or a silicon-containing compound to form the water-repellent layer.

11. A membrane distillation module comprising the membrane distillation membrane according to any one of claims 1 to 9.

12. The system includes a high-temperature tank into which a crude liquid to be purified is introduced, and a liquid receiving tank for recovering the purified liquid, The high-temperature tank and the receiving tank are separated by the membrane distillation membrane, The purified liquid obtained by condensing the vapor derived from the crude liquid while the vapor is permeating through the membrane distillation membrane or after the vapor has permeated through the membrane distillation membrane is recovered in the receiver tank. The membrane distillation module according to claim 11.

13. a heating device for heating the crude liquid to be introduced into the high-temperature tank or the crude liquid introduced into the high-temperature tank; The membrane distillation module according to claim 12, further comprising a cooling device that lowers the internal temperature of the receiver tank.

14. Contacting a crude liquid to be purified with the membrane distillation membrane according to any one of claims 1 to 9; A method for producing a purified liquid by membrane distillation, comprising condensing the vapor derived from the crude liquid while the vapor is permeating through the membrane distillation membrane or after the vapor has permeated through the membrane distillation membrane to obtain a purified liquid.

15. The method for producing a purified liquid according to claim 14, wherein the crude liquid is subjected to membrane distillation using the membrane distillation module according to claim 11.

16. The method for producing a purified liquid according to claim 14, wherein the crude liquid is contacted with the hydrophilic major surface of the membrane distillation membrane.

17. The method for producing a purified liquid according to claim 14, wherein the crude liquid is an alkaline liquid having a pH of 11 or more at 20°C.

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