Separation filter and method for producing separation filter

Abstract

This separation filter has an inorganic material layer which is a sintered body of a mixture including dolomite, kaolin, and a binder and has pores each having an opening diameter of 0.1-100 μm. The content of dolomite with respect to all components constituting the inorganic material layer is more than 0 mass% but not more than 50 mass%, and the content of kaolin with respect to said all components constituting the inorganic material layer is not less than 50 mass% but less than 100 mass%. The present invention also relates to a method for producing the separation filter.

Description

Separation filter and method for manufacturing separation filter

[0001] The present disclosure relates to a separation filter and a method for manufacturing a separation filter.

[0002] The amount of wastewater generated from oil or gas fields is estimated at 32 million tons per day, and a method for separating oil and water from this wastewater is needed. In addition, a method for extracting oil from oil shells and oil sands using steam has been developed, and the wastewater discharged during processing also needs to be separated into oil and water. Not only wastewater from oil fields, but also wastewater discharged from mines, for example, may contain various heavy metals that vary depending on the region, making treatment more difficult. Even in urban areas, wastewater generated from car wash stations, gas stations, etc., requires the removal of oil from the wastewater before discharge for environmental reasons. Therefore, a technology for separating oil and water from the above-mentioned various types of wastewater and removing heavy metals is desired.

[0003] As a method for removing heavy metals and the like, for example, a method for manufacturing an adsorbent, which includes a step of adsorbing a phosphorus compound onto dolomite and then calcining the dolomite to immobilize the phosphorus component, has been proposed (see Japanese Patent No. 7164884 (Patent Document 1)). Also, a harmful substance insolubilizing material containing dolomite hydroxide, a phosphate compound, and a raw material containing allophane has been proposed (see Japanese Patent Laid-Open No. 2014-084744 (Patent Document 2)). However, while both Patent Documents 1 and 2 describe powder-like adsorbents that can adsorb and remove heavy metals by mixing with a liquid containing heavy metals, they do not focus on oil-water separation using adsorbents. Regarding oil-water separation membranes, for example, a porous alumina microsheet membrane obtained by forming a membrane from polysulfone in which a high concentration of alumina powder is dispersed using a phase separation method and then calcining the membrane has been proposed (see Membrane, Vol. 45, No. 1, pp. 35-40, 2020 (Non-Patent Document 1)). However, the above-mentioned alumina microsheet membrane does not address the removal of heavy metals, and there are still issues to be resolved, such as the suppression of oil-induced fouling during long-term use. Furthermore, a technology has been disclosed in which a mixture containing kaolin, coal fly ash, and dolomite is sintered to form a low-cost ceramic membrane for use in oil-water separation (see Ceramics International Vol. 46 (2020), pp. 6889-6898 (Non-Patent Document 2)). However, because coal fly ash contains a non-negligible amount of iron due to its raw materials, the inventors' studies have shown that the resulting ceramic membrane contains a large amount of iron. Furthermore, because coal fly ash is recovered from industrial waste, it is unsuitable for use in the food industry or water purification. Furthermore, the ceramic membrane described in Non-Patent Document 2 does not address the removal of heavy metals.

[0004] Japanese Patent No. 7164884 Japanese Patent Application Laid-Open No. 2014-084744

[0005] H Nagasawa, “Treatment of Oily Wastewater by Ceramic Membranes” MEMBRANE, Vol. 45, No. 1, pp35-40 (2020) Nisha Malik et al. , "Preparation of novel porous ceramic microfiltration membranes from fly ash, kaolin and dolomite mixtures" Ceramics International Vol. 46 (2020), pp6889-6898

[0006] An object of one embodiment of the present disclosure is to provide a separation filter that can separate water and oil in wastewater and remove heavy metals contained in the wastewater.An object of another embodiment of the present disclosure is to provide a method for manufacturing a separation filter that can separate water and oil in wastewater and remove heavy metals contained in the wastewater.

[0007] The present disclosure includes the following embodiments: <1> A separation filter comprising an inorganic material layer that is a fired product of a mixture containing dolomite, kaolin, and a binder, and that has pores with an average pore size of 0.1 μm to 100 μm, wherein the content of the dolomite relative to all components constituting the inorganic material layer is greater than 0 mass% and not more than 50 mass%, and the content of the kaolin relative to all components constituting the inorganic material layer is 50 mass% or more and less than 100 mass%. <2> A separation filter comprising: an inorganic material layer that is a fired product of a mixture containing dolomite, kaolin, and a binder, and that has pores with an average pore size of 0.1 μm to 100 μm; and a functional separation layer provided on at least a part of the inorganic material layer, wherein the content of the dolomite relative to all components constituting the inorganic material layer is greater than 0 mass% and less than 50 mass%, and the content of the kaolin relative to all components constituting the inorganic material layer is 50 mass% or more and less than 100 mass%, and the functional separation layer contains at least one compound selected from the group consisting of fluorine compounds and silicon-based compounds. <3> A separation filter according to <1> or <2>, wherein, when the content of the dolomite is D and the content of the kaolin is K, the ratio of D to K in the inorganic material layer (D / K) satisfies the following formula: Formula: 1>D / K>0.01

[0008] <4> The separation filter according to at least one of <1> to <3>, which is in the form of a membrane having a thickness of 10 μm to 10 mm. <5> The separation filter according to at least one of <1> to <3>, which is in the form of particles having an average particle diameter of 10 μm to 10 mm. <6> The separation filter according to at least one of <1> to <5>, wherein the dolomite includes at least one kind selected from the group consisting of burnt dolomite, semi-burnt dolomite, and dolomite.

[0009] <7> The separation filter according to any one of <1> to <6>, wherein the fluorine compound comprises at least one fluororesin selected from the group consisting of polytetrafluoroethylene, perfluoroalkoxyalkane, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride. <8> The separation filter according to any one of <2> to <7>, wherein the silicon-based compound comprises at least one silicon-based compound selected from the group consisting of silicon nanoparticles, silicon oxide nanoparticles, and silicone resins.

[0010] <9> The separation filter according to <1> or <2>, wherein the inorganic material layer further contains a phosphorus component. <10> The separation filter according to <1> or <2>, wherein the inorganic material layer further contains silver ions and is for removing bromine.

[0011] <11> A method for producing a separation filter, comprising the steps of: (I) preparing a mixture containing more than 0% by mass and not more than 50% by mass of dolomite, at least 50% by mass and less than 100% by mass of kaolin, and a binder; (II) shaping and drying the resulting mixture to obtain an inorganic material layer precursor; and (III) sintering the resulting inorganic material layer precursor at a temperature of 650° C. to 1250° C. to obtain an inorganic material layer. <12> A method for producing a separation filter, comprising the steps of: (I) preparing a mixture containing more than 0% by mass and not more than 50% by mass of dolomite, at least 50% by mass and less than 100% by mass of kaolin, and a binder; (II) shaping and drying the resulting mixture to obtain an inorganic material layer precursor; and (III) sintering the resulting inorganic material layer precursor at a temperature of 650° C. to 1250° C. to obtain an inorganic material layer; and (IV) forming a functional separation layer containing at least one compound selected from the group consisting of a fluorine compound and a silicon-based compound on at least a portion of the surface of the inorganic material layer. <13> The method for producing a separation filter according to <11> or <12>, wherein, when the content of dolomite in the mixture is D and the content of kaolin in the mixture is K, the ratio of K to D contained in the mixture (D / K) satisfies the following formula: 1>D / K>0.01. <14> The mixture is molded at a molding pressure of 1900 N / cm ２ ~5000N / cm ２The method for producing a separation filter according to <11> or <12>, wherein the separation filter is produced under a pressure of 0.15 or less.

[0012] <15> The method for producing a separation filter according to any one of <11> to <14>, further comprising a step (V) of immersing the inorganic material layer obtained in the step (III) in a silver ion-containing solution, followed by drying and sintering to adsorb silver ions onto the inorganic material layer.

[0013] According to one embodiment of the present disclosure, there is provided a separation filter capable of separating water and oil in wastewater and removing heavy metals contained in the wastewater. According to another embodiment of the present disclosure, there is provided a method for manufacturing a separation filter capable of separating water and oil in wastewater and removing heavy metals contained in the wastewater.

[0014] 1 is a SEM photograph at 500x magnification showing an example of a separation filter of the present disclosure, which is a sintered body of a mixture containing 75% by mass of kaolin, 20% by mass of dolomite, and 5% by mass of methylcellulose as a binder. 2 is a SEM photograph at 500x magnification showing an example of a comparative separation filter, which is a sintered body of a mixture containing 95% by mass of kaolin and 5% by mass of methylcellulose as a binder, but no dolomite. 3 is a graph showing the relationship between the kaolin and dolomite contents in an inorganic material layer, and the strength and water permeation flux of the resulting separation filter. 4 is a graph showing the relationship between the sintering temperature and the membrane strength and water permeation flux of an inorganic material layer obtained by sintering an inorganic material layer precursor obtained from a mixture containing kaolin, dolomite, and a binder for 4 hours. 5 is a graph showing the relationship between the sintering temperature and the average pore size of pores formed in the inorganic material layer and the water absorption rate of an inorganic material layer obtained by sintering an inorganic material layer precursor obtained from a mixture containing kaolin, dolomite, and a binder at a sintering temperature of 1100°C to 1250°C for 4 hours. 1 is a graph showing XRD patterns of kaolin, dolomite, and the inorganic material layers of Examples 1 to 4. FIG. 1 is a graph showing the removal rates of heavy metals and metals by adsorption and the permeation flux of the liquid to be treated of the separation filters of Example 1 and Comparative Example 1. FIG. 2 is a graph showing the oil removal rates and the permeation flux of the liquid to be treated of the separation filters of Examples 1 to 4. FIG. 3 is a graph showing the As removal rate when the liquid to be treated is passed through the separation filter of Example 1 at each As content. FIG. 4 is a graph showing the Br removal rate by separation filter permeation when the liquid to be treated containing Br is passed through the separation filters of Examples 5 to 7.

[0015] The separation filter and the manufacturing method thereof according to the present disclosure will be described in detail below with reference to embodiments. The following embodiments are merely examples, and the present disclosure is not limited to the following embodiments.

[0016] In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In the numerical ranges described in this disclosure, the upper or lower limit of the numerical range may be replaced with a value shown in the examples. In this disclosure, the content of each component means the total amount of the corresponding multiple substances, unless otherwise specified, when there are multiple substances corresponding to each component. In this disclosure, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0017] [Separation filter] A first embodiment of the separation filter of the present disclosure is a sintered body of a mixture containing dolomite, kaolin, and a binder, and has an inorganic material layer having pores with an average pore size of 0.1 μm to 100 μm, in which the content of dolomite relative to all components constituting the inorganic material layer is more than 0 mass% and not more than 50 mass%, and the content of kaolin relative to all components constituting the inorganic material layer is 50 mass% or more and less than 100 mass%.

[0018] A second embodiment of the separation filter of the present disclosure is a sintered body of a mixture containing dolomite, kaolin, and a binder, and has an inorganic material layer having pores with an average pore size of 0.1 μm to 100 μm, and a functional separation layer provided on at least a part of the inorganic material layer, wherein the content of dolomite relative to all components constituting the inorganic material layer is greater than 0 mass% and less than 50 mass%, and the content of kaolin relative to all components constituting the inorganic material layer is 50 mass% or more and less than 100 mass%, and the functional separation layer contains at least one compound selected from the group consisting of fluorine compounds and silicon-based compounds.

[0019] The separation filter of the present disclosure has an inorganic material layer that is a sintered body of a mixture containing a predetermined amount of dolomite and kaolin, resulting in an inorganic material layer that exhibits good heavy metal removal properties, good water permeability, and low oil permeability. Therefore, the separation filter of the present disclosure can pass a liquid (liquid to be treated) containing a mixture of oil and water, such as an emulsion, through the inorganic material layer to obtain water from the liquid to be treated from which heavy metals and oil have been removed. Furthermore, as in the second embodiment, by providing a functional separation layer on at least a portion of the inorganic material layer, the water and oil permeability can be controlled according to the purpose. Furthermore, according to the inventors' studies, although the mechanism of action is unclear, it has been found that a filter containing kaolin and a predetermined amount of dolomite exhibits improved separation filter strength and water flux through the separation filter compared to a filter containing only kaolin. Therefore, the separation filter of the present disclosure can simultaneously remove oil or water and heavy metals contained in a liquid simply by passing the liquid through it, and can be effectively used in fields such as the treatment of oil-containing wastewater, etc. The above-mentioned dolomite and kaolin contents and the average pore size of the inorganic material layer define optimal embodiments, and the inventors believe that a separation filter having an inorganic material layer that is a sintered body of a mixture containing both dolomite and kaolin and has a pore size that allows water permeability can be expected to achieve a certain degree of separation of water and oil in wastewater and removal of heavy metals contained in wastewater.

[0020] <Inorganic Material Layer> A first embodiment of the separation filter of the present disclosure has an inorganic material layer, and a second embodiment of the separation filter of the present disclosure has an inorganic material layer and a functional separation layer provided on at least a part of the inorganic material layer. Hereinafter, in the description of matters common to the first and second embodiments, they will be collectively referred to simply as "the inorganic material layer according to the present invention" or simply as "embodiment." Below, each component contained in the inorganic material layer according to the present disclosure will be described.

[0021] [Kaolin] The inorganic material layer according to the present disclosure contains kaolin. Specifically, the inorganic material layer is a sintered body of a mixture containing kaolin. Kaolin is a type of clay mineral also known as kaolinite, and is mainly composed of Si and Al. It also contains aluminum hydroxide and silicon oxide, and has the property of adsorbing pollutants. Kaolin has the chemical formula Al ４ SiO １０ (OH) ３ and further contains K, Mg, etc. The kaolin that can be used in the inorganic material layer is not particularly limited, and commercially available products may be used. The kaolin contained in the inorganic material layer is preferably a powdered solid. From the viewpoint of uniformity of the resulting inorganic material layer, the particle size of the kaolin is preferably an average particle size of 100 μm or less, more preferably an average particle size of 50 μm or less, and even more preferably an average particle size of 10 μm or less. The particle size of the kaolin can be determined, for example, from a scanning electron microscope (SEM) photograph. In the present disclosure, the particle sizes of 200 kaolin particles within the viewing angle of the SEM photograph are measured, and the arithmetic average is taken as the average particle size. Kaolin has a particle size distribution, and particles with a particle size exceeding 15 μm may exist. However, as long as the number of particles exceeding 15 μm is 10% or less, it is considered highly unlikely that the performance of the resulting inorganic material layer will be affected.

[0022] The kaolin content of the mixture used to form the inorganic material layer relative to the total components of the mixture that is the raw material for the sintered body is 50% by mass or more and less than 100% by mass, preferably 65% ​​by mass or more and 95% by mass or less, more preferably 70% by mass or more and 90% by mass or less, and even more preferably 75% by mass or more and 80% by mass or less. When the kaolin content in the mixture used to form the inorganic material layer is within the above range, the inorganic material layer has good mechanical strength and good removability of heavy metals.

[0023] [Dolomite] The inorganic material layer contains dolomite. Specifically, the inorganic material layer is a sintered body of a mixture containing dolomite. Dolomite contains calcium carbonate and magnesium carbonate as main components and has the chemical formula CaMg(CO ３ ) ２and is a mineral further containing Si, Al, Fe, etc. There are no particular limitations on the dolomite that can be used in the inorganic material layer, and commercially available products may be used. The dolomite in the present disclosure may include at least one selected from the group consisting of calcined dolomite, semi-calcined dolomite, and dolomite. Dolomite is a powdered solid, and from the viewpoint of the uniformity of the resulting inorganic material layer, the average particle size of dolomite measured in the same manner as kaolin is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less. Dolomite has a particle size distribution, and particles with a particle size exceeding 10 μm may exist. However, as long as the number of particles exceeding 10 μm is 10% or less, the formation of the inorganic material layer is unlikely to be affected.

[0024] The content of dolomite relative to the total components of the mixture that is the raw material for the sintered body that constitutes the inorganic material layer is more than 0 mass% and 50 mass% or less, preferably 10 mass% to 35 mass% and more preferably 18 mass% to 25 mass%. When the content of dolomite in the mixture used to form the inorganic material layer is within the above range, the inorganic material layer has good mechanical strength and water permeability.

[0025] [Ratio of Dolomite and Kaolin Content] When the content of dolomite is D and the content of kaolin is K, it is preferable that the ratio of K to D (D / K) in the mixture that is the raw material for the inorganic material layer satisfies the following formula: 1 > D / K > 0.01.

[0026] [Binder] The inorganic material layer contains a binder. Specifically, the inorganic material layer is a sintered body of a mixture containing the binder. The binder is used to mold a mixture of powdered kaolin and dolomite into the inorganic material layer. As the binder, any known binder that has good binding properties between inorganic powders and can improve moldability can be used without limitation. Examples of binders include methyl cellulose, ethyl cellulose, methoxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc., and from the viewpoints of environmental compatibility and removability during molding of the inorganic material layer, cellulose-based polymer compounds such as methyl cellulose and ethyl cellulose are preferred.

[0027] The content of the binder in the mixture that is the raw material for the inorganic material layer is not particularly limited, as long as it is an amount that gives the mixture sufficient shape retention when the powdered kaolin and dolomite mixture is compression-molded and fired. Specifically, for example, the content of the binder is preferably 1% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and even more preferably 3% by mass or more and 7% by mass or less, based on the total components of the inorganic material layer before sintering.

[0028] 1(A) is a 500x SEM photograph showing an example of a separation filter of the present disclosure, which is a sintered body of a mixture containing 75% by mass of kaolin, 20% by mass of dolomite, and 5% by mass of methylcellulose as a binder. FIG. 1(B) is a 500x SEM photograph showing an example of a comparative separation filter, which is a sintered body of a mixture containing 95% by mass of kaolin and 5% by mass of methylcellulose as a binder, but does not contain dolomite. Comparing FIG. 1(A) and FIG. 1(B), a separation filter that is a sintered body of a mixture containing kaolin and dolomite has many pores that contribute to liquid permeation, while a separation filter that is a sintered body of a mixture consisting only of kaolin and a binder, without dolomite, has almost no pores. From this, it can be seen that by using a sintered body of a mixture containing dolomite as the inorganic material layer, the formation of pores that contribute to the liquid permeability of the separation filter is improved, and the resulting separation filter can be expected to have better water permeability.

[0029] [Other Components] In addition to the kaolin, dolomite, and binder, the mixture serving as the raw material for the inorganic material layer according to the present disclosure may further contain other components depending on the purpose, as long as the effects of the present disclosure are not impaired. Examples of other components include P (phosphorus) compounds, Ag ions, and Fe ions.

[0030] The separation filter of the present disclosure, which has an inorganic material layer that is a sintered body of a mixture containing dolomite, kaolin, and a binder, is useful for oil-water separation and for removing heavy metals such as Pb (lead), Cu (copper), Zn (zinc), and Cd (cadmium).

[0031] As an additional component, the mixture serving as the raw material for the inorganic material layer preferably further contains a phosphorus component. By including a phosphorus component in the inorganic material layer, the separation filter of the present disclosure can efficiently adsorb and remove, in addition to the above-mentioned heavy metals, elements such as As (arsenic) and F (fluorine). When the inorganic material layer contains a phosphorus component, dolomite adsorbed with the phosphorus component can be used to prepare the mixture. The phosphorus component can be adsorbed onto the dolomite by contacting the dolomite with an aqueous solution of a phosphorus compound. Examples of phosphorus compounds include phosphoric acid and its salts (e.g., ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and calcium dihydrogen phosphate), phosphorous acid and its salts, peroxomonophosphoric acid and its salts, phosphonic acid and its salts, phosphinic acid and its salts, phosphorus oxides such as diphosphorus pentoxide, phosphorus halides such as phosphorus pentachloride, phosphoryl halides such as phosphoryl chloride, and calcium phosphides such as calcium monophosphide and calcium diphosphide. The amount of phosphorus adsorbed onto dolomite is preferably 0.1 parts by mass or more and 10 parts by mass or less of phosphate ions per 100 parts by mass of dolomite. Dolomite with adsorbed phosphorus can be obtained, for example, by the method described in paragraph

[0007] of Japanese Patent No. 7164884.

[0032] As another component, the inorganic material layer preferably further contains silver ions. By further containing silver ions, the separation filter of the present disclosure can efficiently adsorb and remove Br (bromine) in addition to the heavy metals exemplified above. A method for incorporating silver ions into the inorganic material layer includes preparing an aqueous solution of a silver compound that generates silver ions in water, applying the aqueous solution of the silver compound to the sintered inorganic material layer, drying, and sintering. In this manner, silver ions can be adsorbed into the inorganic material layer. Methods for applying silver ions to the inorganic material layer include coating, spraying, and immersion. From the perspective of uniform application, immersing the inorganic material layer in an aqueous solution of a silver compound is preferred. Silver ion adsorption is performed after the formation of the inorganic material layer. In the inorganic material layer of the second embodiment of the present disclosure, it is preferable to perform the adsorption after the formation of the inorganic material layer and before the formation of the functional separation layer. The adsorption amount of silver ions is preferably 0.01 to 7 parts by mass of silver ions per 100 parts by mass of dolomite.

[0033] [Average pore size of the inorganic material layer] The inorganic material layer has pores with an average pore size of 0.1 μm to 100 μm. The liquid to be treated passes through the pores of the inorganic material layer, thereby separating oil from water and removing heavy metals from the liquid to be treated. The average pore size of the inorganic material layer can be measured from an electron microscope photograph using ImageJ software, as described below.

[0034] The average pore size of the inorganic material layer is appropriately selected depending on the intended use of the separation filter. For example, when separating oil components and water from large volumes of wastewater generated from oil fields, etc., from the viewpoint of processing efficiency, the average pore size is preferably 10 μm to 100 μm, more preferably 30 μm to 90 μm. Furthermore, when used with wastewater discharged from mines, etc., removal of heavy metals is important, so the average pore size is preferably, for example, 0.5 μm to 50 μm, more preferably 1 μm to 10 μm. For wastewater generated from gas stations in urban areas, the treatment volume is small, so the average pore size can be set to 1 μm to 10 μm in consideration of oil removal. The above-mentioned preferred average pore size is a guideline and may be appropriately selected taking into consideration the amount of liquid to be treated per unit time, oil-water separation performance, heavy metal removal performance, etc.

[0035] The inorganic material layer can be obtained by mixing the kaolin, dolomite, and binder, compression molding, drying, and then firing. If the inorganic material layer contains other components as desired, the other components may be adsorbed onto the dolomite or kaolin, or the formed inorganic material layer may be coated or immersed in the other components to incorporate them. The shape of the inorganic material layer is not particularly limited, but it can be, for example, a film or particles. The method for manufacturing the inorganic material layer will be described in detail in the section on the method for manufacturing the separation filter.

[0036] <Functional Separation Layer> The separation filter according to the second embodiment of the present disclosure has a functional separation layer in at least a portion of the inorganic material layer. Here, the functional separation layer is a layer that is provided in at least a portion of the inorganic material layer and that imparts water repellency or oil repellency to at least a portion of the inorganic material layer. The functional separation layer may be provided in a portion of the inorganic material layer, or may be provided over the entire surface of the inorganic material layer. Each component contained in the functional separation layer will be described below.

[0037] The inclusion of a functional separation layer improves the oil-water separation of the separation filter of the present disclosure. That is, when the functional separation layer is a water-repellent layer, water contained in the treatment liquid quickly passes through the separation filter without adhering to the surface of the separation filter. On the other hand, oil is prevented from passing through the separation filter by splashing up or adhering to the functional separation layer. Furthermore, when the functional separation layer is an oil-repellent layer, oil contained in the treatment liquid quickly passes through the separation filter without adhering to the surface of the separation filter. On the other hand, water is prevented from passing through the separation filter by being repelled by the functional separation layer or adhering to the surface of the separation filter. For this reason, the functional separation layer is thought to contribute to improving the oil-water separation ability of the separation filter. The functional separation layer includes at least one compound selected from the group consisting of fluorine compounds and silicon-based compounds.

[0038] Examples of fluorine compounds contained in the functional separation layer include fluorine resins capable of forming a water-repellent film. Specific examples include at least one fluorine resin selected from the group consisting of polytetrafluoroethylene, perfluoroalkoxyalkane, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride. Among these, from the viewpoint of good water repellency and durability, polytetrafluoroethylene, perfluoroalkoxyalkane, etc. are preferred as the fluorine compound, with polytetrafluoroethylene being more preferred. The functional separation layer may contain only one of the above fluorine resins, or may contain two or more types. When the functional separation layer contains two or more types of fluorine resins, they may be contained as a mixture of two or more types of fluorine resins, for example, as a copolymer such as a copolymer of tetrafluoroethylene and perfluoroalkoxyalkane (PFA).

[0039] Commercially available fluorine compounds may be used. Examples of commercially available products that impart water repellency and oil repellency include fluorine coating agents such as Fluorosurf (registered trademark) FG-5084EX-0.1 and FG-5093S135-0.5 manufactured by Fluorotechnology Co., Ltd. Furthermore, examples of commercially available products that impart hydrophilic and oil repellency include the Efrontier (registered trademark) series manufactured by Mitsubishi Materials Corporation.

[0040] The silicon-based compound contained in the functional separation layer can be any compound capable of forming a water-repellent film, without particular limitations. Examples of the silicon-based compound include at least one silicon-based compound selected from the group consisting of silicon nanoparticles, silicon oxide nanoparticles, and silicone resins. The silicon-based compound may be solid particles such as nanoparticles. The silicone resin may be silicone resin nanoparticles. As described below, a water-repellent functional separation layer may be formed by applying a composition containing a silicone resin and a solvent to an inorganic material layer and then removing the solvent.

[0041] Known methods can be used to provide a functional separation layer on an inorganic material layer. Examples of methods for forming a functional separation layer include applying a fluorine compound or silicone resin dissolved in a solvent to at least a portion of the surface of the inorganic material layer and drying to remove the solvent, immersing the inorganic material layer in a solution of a fluorine compound, removing excess solution, and drying, and applying a fluorine coating agent to at least a portion of the surface of the inorganic material layer and drying. When the silicon-based compound is in the form of nanoparticles, they may be fixed to the inorganic material layer with an appropriate binder to form a functional separation layer. Here, "nanoparticles" refers to particles with an average particle size on the nanometer order, specifically in the range of 1 nm to 100 nm.

[0042] The separation filter of the present disclosure, which has a functional separation layer in at least a portion of the inorganic material layer, can be formed into various shapes depending on the purpose and conditions of use of the separation filter.

[0043] (Shape of Separation Filter) When the separation filter of the present disclosure is used as a membrane filter, it can be in the form of a membrane with a thickness of 10 μm to 10 mm. Here, "membrane" refers to a flat plate-like shape having at least two flat surfaces, with a thickness of 2 or less, where the maximum length constituting the flat surfaces is 10. The shape of the membrane-shaped separation filter can be, for example, a shape depending on the location where the separation filter is to be installed. For example, when the separation filter is installed in a flow path for the liquid to be treated, the separation filter can be in the form of a membrane with a thickness of 10 μm to 10 mm. When the separation filter is placed in a cylindrical flow path (pipe) through which the liquid to be treated passes, it can be a cylindrical membrane with a thickness of 10 μm to 10 mm that matches the inner diameter of the flow path. A cylindrical membrane separation filter may be fixed to a predetermined position within the cylindrical flow path using a liquid-permeable mesh or the like. Fixing the separation filter using a liquid-permeable mesh or the like suppresses deformation of the separation filter, further improving the durability of the separation filter.

[0044] As another example, the separation filter may be particulate with an average particle diameter of 10 μm to 10 mm. The particulate separation filter may be filled into a liquid-permeable holding container. The liquid to be treated passes through the holding container filled with the particulate separation filter, thereby removing oil or water and heavy metals from the liquid to be treated.

[0045] Furthermore, a particulate separation filter having an average particle size of 10 μm to 10 mm can be molded into any shape using, for example, a polymeric compound capable of forming a water-repellent layer as a binder, and used as a separation filter having a water-repellent functional separation layer as a whole. For example, a particulate separation filter having an average particle size of 10 μm to 10 mm can be molded using a polymeric compound capable of forming a water-repellent functional separation layer as a binder, and processed into a plate of any thickness to form a separation filter, or processed into plates of various shapes to form a separation filter. During molding, it is preferable to adjust the content ratio of the polymeric compound to the particulate separation filter under conditions such that the open pores in the particulate separation filter are not blocked by the polymeric compound. These separation filters can be machined into a shape that matches the shape of the flow path and then attached to the flow path. As the liquid to be treated passes through the flow path, oil or moisture and heavy metals contained in the liquid to be treated are removed.

[0046] When the liquid to be treated passes through the separation filter, separated oil adheres to and accumulates on the inlet side of the separation filter for the liquid to be treated, for example, if the inorganic material layer has a water-repellent functional separation layer. Therefore, it is preferable to check the separation ability of the separation filter and the amount of the liquid to be treated that has passed through in advance, and to replace the separation filter after treating a predetermined amount of the liquid to be treated.

[0047] FIG. 2 is a graph showing the relationship between the content of kaolin and dolomite in the inorganic material layer and the strength and water permeation flux of the resulting separation filter. In FIG. 2, kaolin is represented as KA and dolomite as DO. In FIG. 2, "wt%" is synonymous with "mass%." As shown in FIG. 2, adding dolomite to kaolin improved the water permeation flux compared to a separation filter that did not contain dolomite. On the other hand, the strength of the separation filter did not change significantly due to the inclusion of dolomite, and it can be seen that the separation filter exhibited strength that was sufficient for practical use at any ratio.

[0048] The separation filter of the present disclosure has the above-described configuration, and therefore has good oil-water separation and heavy metal removal performance. When formed into a membrane, the water permeation flux is good, and the membrane itself has high strength, so it can be applied to various liquids to be treated. In particular, because the water permeation flux is good, it is useful when treating large amounts of wastewater containing oil, and its applications are wide.

[0049] Although there are no particular limitations on the method for manufacturing the separation filter of the present disclosure, it is preferable to manufacture the separation filter by the following method for manufacturing the separation filter of the present disclosure from the viewpoint of separation filter properties and manufacturing efficiency.

[0050] [Method for manufacturing separation filter] A first embodiment of the method for manufacturing a separation filter according to the present disclosure includes the steps of: (I) preparing a mixture containing more than 0 mass % and not more than 50 mass % dolomite, 50 mass % or more and less than 100 mass % kaolin, and a binder; (II) molding and drying the obtained mixture to obtain an inorganic material layer precursor; and (III) sintering the obtained inorganic material layer precursor at a temperature of 650°C to 1250°C to obtain an inorganic material layer.

[0051] A second embodiment of the method for producing a separation filter of the present disclosure includes the steps of: (I) preparing a mixture containing more than 0% by mass and not more than 50% by mass of dolomite, 50% by mass or more and less than 100% by mass of kaolin, and a binder; (II) molding and drying the resulting mixture to obtain an inorganic material layer precursor; (III) sintering the resulting inorganic material layer precursor at a temperature of 650 ° C to 1250 ° C to obtain an inorganic material layer; and (IV) forming a functional separation layer containing a fluorine compound on at least a portion of the surface of the inorganic material layer. In the method for producing a separation filter of the present disclosure, the production method according to the second embodiment has the same steps (I), (II), and (III) as the production method according to the first embodiment, and further includes the step (VI) described below. The first and second embodiments of the method for producing a separation filter of the present disclosure may be collectively referred to as the production method of the present disclosure.

[0052] [Step (I)] Step (I) is a step of preparing a mixture containing more than 0 mass% and not more than 50 mass% dolomite, 50 mass% or more and less than 100 mass% kaolin, and a binder. In a preferred embodiment of the mixture, when the content of the dolomite in the mixture is D and the content of the kaolin is K, the ratio of K to D contained in the mixture (D / K) satisfies the following formula: 1 > D / K > 0.01

[0053] The dolomite, kaolin, and binder used here are the same as those described in the separation filter of the present disclosure, and the contents of each component in the mixture are also the same, so detailed description will be omitted. The mixture can be prepared by adding pre-measured powdered kaolin, powdered dolomite, and binder to a mixer and mixing them. There are no particular limitations on the mixer, and known devices such as mixers with stirring blades and rotary mixers can be used. During mixing, a solvent such as water or an aqueous solvent may be added to ensure uniform mixing and moldability of the mixture. Alternatively, the binder may be dissolved in a solvent such as water and mixed with the dolomite and kaolin. When the mixture contains a solvent (dispersion medium), a kneader may be used to prepare the mixture. When the inorganic material layer contains an optional phosphorus component, dolomite to which the phosphorus component has been previously adsorbed may be used as the dolomite used in step (I). The mixing time can be set to 10 to 60 minutes, preferably 20 to 40 minutes, from the viewpoint of uniform mixing and workability.

[0054] [Step (II)] Step (II) is a step of forming the mixture obtained in step (I) and drying it to obtain an inorganic material layer precursor. When the mixture is formed into a film, it can be formed using a press. The mixture is sandwiched between a pair of press plates of the press and pressure-formed to obtain a film-like inorganic material layer precursor. The pressure conditions can be appropriately selected depending on the size of the film-like inorganic material layer precursor, i.e., the area of ​​the flat portion, the thickness of the film, etc. Generally, the mixture is formed at a pressure of 1900 N / cm from the viewpoint of good formability and easy formation of necessary pores in the obtained inorganic material layer.２ ~5000N / cm ２ Preferably, the pressure is 2000 N / cm ２ ~4000N / cm ２ More preferably, the pressure is 3000 N / cm ２ ~3500N / cm ２ It is more preferred that the reaction is carried out under a pressure of 0.1 to 1000 kJ / min.

[0055] The molding method for forming the particulate inorganic material layer is not particularly limited, and any known method can be used, such as a method of filling a predetermined mold with the mixture and molding it, or a method of molding using a granulator.

[0056] The molded mixture is dried to obtain an inorganic material layer precursor. Drying is preferably performed by heating, from the viewpoint of removing the solvent contained in the mixture and easily maintaining the shape as designed in the subsequent sintering. Heating conditions can be a temperature of 90°C to 150°C and a drying time of 1 hour to 48 hours, and preferably a temperature of 100°C to 130°C and a drying time of 20 hours to 30 hours. The mixture is molded and dried to obtain an inorganic material layer precursor.

[0057] [Step (III)] Step (III) is a step of sintering the inorganic material layer precursor obtained in step (II) at a temperature of 650°C to 1250°C to obtain an inorganic material layer. Sintering can be performed in a temperature-controllable heating device such as a heating furnace. As for sintering conditions, from the viewpoint of easily obtaining the water permeation flux required for the separation filter, the heating temperature is in the range of 650°C to 1250°C, preferably in the range of 1100°C to 1250°C, and more preferably in the range of 1150°C to 1250°C. From the viewpoint of removing moisture from the inorganic material layer and forming pores, the sintering time can be 1 hour to 10 hours, preferably 2 hours to 5 hours, and more preferably 3.5 hours to 4 hours. By sintering the inorganic material layer precursor under the above temperature range and sintering time conditions, an inorganic material layer having appropriate pores and a good water permeation flux can be obtained.

[0058] 3 is a graph showing the relationship between the sintering temperature and the membrane strength and water permeation flux of an inorganic material layer obtained by sintering for 4 hours an inorganic material layer precursor obtained from a mixture containing 75% by mass of kaolin, 20% by mass of dolomite, and 5% by mass of methyl cellulose as a binder. The measurement method is described below. As is clear from FIG. 3, at a sintering temperature of 950°C, the membrane strength and water permeation flux were 300 L / h m. ２ As the sintering temperature increases, the permeation flux and membrane strength increase.

[0059] (Method for measuring water permeation flux) A 3 mm thick inorganic material layer was set in a stainless steel vacuum filtration filter holder (Advantec, KSF-47, manufactured by Toyo Roshi Kaisha Ltd.), and the liquid to be measured was passed through it at a reduced pressure of 0.015 MPa. When separating oil and the like, the amount of water permeating the inorganic material layer per unit time was measured, and the calculated value was taken as the water permeation flux. The liquid to be measured was an emulsion-like liquid prepared by stirring and mixing 25 ml of water, 25 ml of kerosene, and 0.5% by mass of an anionic surfactant in kerosene.

[0060] (Method for measuring film strength of inorganic material layer (thickness: 3 mm)) The film strength of the inorganic material layer (thickness: 3 mm) was measured using a tabletop precision universal testing machine (manufactured by Shimadzu Corporation; AGS-X, a device capable of measuring up to 10 kN) as the equipment used, and cubes (2 cm x 2 cm x 2 cm) were prepared as experimental samples for each experimental condition. Using a tabletop precision universal testing machine equipped with an ESA-CU200 as an external amplifier, the force at which the sample breaks when compressed was determined, and this force was divided by the cross-sectional area of ​​the sample. In each case, measurements were performed using three samples, and the arithmetic average was used as the measured value.

[0061] 4 is a graph showing the relationship between the sintering temperature (sintering time: 4 hours) and the average pore size and water absorption rate of pores formed in an inorganic material layer obtained by sintering an inorganic material layer precursor obtained from a mixture containing 75% by mass of kaolin, 20% by mass of dolomite, and 5% by mass of methyl cellulose as a binder for 4 hours at the optimum sintering temperature of 1100°C to 1250°C. The measurement method is shown below.

[0062] According to FIG. 4, sintering at a sintering temperature of 1100° C. to 1250° C. for 4 hours forms pores in the inorganic material layer having an average pore size of 2 μm to 7 μm, which is useful for improving the water permeation flux, and this is consistent with the good water permeation flux results shown in FIG. 3.

[0063] (Method for measuring average pore diameter) The average pore diameter is measured from an electron microscope (SEM) photograph using ImageJ software. In the present disclosure, the electron microscope used is an SEM (JCM-6000, manufactured by JEOL Ltd.). In the present disclosure, unless otherwise specified, the average pore diameter is a value measured by the above measurement method.

[0064] When measuring the pore size inside the inorganic material layer, the pore distribution and pore size can be measured from the BET specific surface area. The BET specific surface area can be measured using, for example, a specific surface area measuring device (Microtrackbell Co., Ltd.).

[0065] (Water absorption rate of inorganic material layer) A dry inorganic material layer with a diameter of 38.5 mm and a thickness of 3 mm was prepared and its mass was measured. The inorganic material layer was then immersed in ion-exchanged water (25°C) for at least 1 hour to allow it to fully absorb water, after which the water on the surface was removed and the mass was measured. The amount of water contained in the inorganic material layer was calculated from the difference between the two masses to determine the water absorption rate. In each case, measurements were performed using three film-like inorganic material layers as samples, and the arithmetic average was used as the measured value.

[0066] (Change in composition due to sintering) When the change in composition during firing of a mixture of kaolin and dolomite was confirmed using XRD patterns obtained by X-ray diffraction, it was found that decomposition of dolomite occurred and mullite was produced at a sintering temperature of around 950°C, anort was produced at 1100°C, and cordierite was produced at 1200°C. It is estimated that the following reactions occur during sintering:

[0067]

[0068] [Step (IV)] Step (IV) is a step of forming a functional separation layer containing a fluorine compound on at least a part of the surface of the inorganic material layer obtained in step (III). By having a functional separation layer containing a fluorine compound, the separation filter of the present disclosure has better oil-water separation performance. Fluorine compounds that can be used to form the functional separation layer are as described in the separation filter section of the present disclosure. Methods for forming the functional separation layer include immersing the inorganic material layer obtained in step (III) in a liquid (hereinafter also referred to as a fluorine solution) in which the above-mentioned preferred fluorine compound, preferably a fluorine-based resin, is dissolved in a solvent, and applying the fluorine solution to the surface of the inorganic material layer by spraying, brushing, etc.

[0069] The fluorine solution is prepared by dissolving at least one fluororesin selected from the group consisting of polytetrafluoroethylene, perfluoroalkoxyalkane, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride in an appropriate solvent. Examples of the solvent include n-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), and dimethyl sulfoxide (DMSO). The solution may contain one or more of these solvents. The concentration of the fluorine compound in the fluorine solution is preferably 0.01% to 10% by mass. It is preferably 0.02% to 0.5% by mass, and more preferably 0.02% to 0.3% by mass. The fluorine solution may be prepared or a commercially available product may be used. Examples of commercially available coating agents include Fluorosurf (registered trademark) FG-5084EX-0.1 and FG-5093S135-0.5 manufactured by Fluorotechnology Co., Ltd., and the Efrontier (registered trademark) series manufactured by Mitsubishi Materials Corporation (manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.). When a commercially available product is used, the commercially available coating agent may be applied directly to the inorganic material layer, for example, by immersion.

[0070] In the case of the immersion method, the fluorine solution adheres to the surface of the inorganic material layer, and further, depending on the conditions, the fluorine solution penetrates into the pores of the inorganic material layer, and from the viewpoint that a functional separation layer is easily formed on the surface of the inorganic material layer and in the pores, the immersion time is preferably 1 hour or more, and more preferably 10 hours or more. There are no particular restrictions on the immersion time condition, but from the viewpoint of efficiently producing a separation filter, it can be 50 hours or less. The immersion time is preferably 1 hour or more and 50 hours or less.

[0071] After immersion, excess fluorine solution is removed and the substrate is dried to fix the functional separation layer. Drying is preferably performed by natural drying at room temperature or by heating. Heating conditions can be a temperature of 20°C to 150°C and a drying time of 0.1 to 48 hours, and preferably a temperature of 30°C to 100°C and a drying time of 0.2 to 30 hours.

[0072] According to the manufacturing method of the present disclosure, a separation filter useful for oil-water separation and heavy metal removal can be efficiently manufactured.

[0073] [Other Steps] The production method of the present disclosure may include other steps in addition to the above steps (I), (II), (III), and (IV).

[0074] Other steps include a pretreatment step of allowing the dolomite used in step (I) to adsorb a phosphorus compound in advance, and step (V) of immersing the inorganic material layer obtained in step (III) in a silver ion-containing solution, followed by drying and sintering to adsorb silver ions onto the inorganic material layer.

[0075] Step (V) is a step performed after step (III) and prior to step (IV), in which a silver ion-containing solution is applied to the inorganic material layer, followed by drying and sintering to adsorb silver ions onto the inorganic material layer. By adsorbing silver ions onto the inorganic material layer in step (V), the separation filter of the present disclosure further possesses the ability to remove Br from a Br-containing liquid to be treated. Step (V) preferably includes immersing the inorganic material layer obtained in step (III) in a silver ion-containing liquid to adsorb silver ions onto the inorganic material layer, removing the silver ion solution, and drying and sintering the inorganic material layer with the adsorbed silver ions to fix the silver ions onto the inorganic material layer. The silver ion solution can be obtained by dissolving a silver compound that generates silver ions upon dissolution in a solvent. From the viewpoint of allowing silver ions to be sufficiently adsorbed onto the inorganic material layer, the silver ion concentration of the silver ion solution can be 800 ppm to 2000 ppm, and preferably 1000 ppm to 1500 ppm. The silver ion solution may be applied to the inorganic material layer at room temperature (25°C). For example, when the inorganic material layer is immersed in the silver ion solution, the silver ion solution may be heated to 30°C to 90°C before immersion. From the viewpoint of allowing silver ions to be sufficiently adsorbed onto the inorganic material layer, the immersion time is preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more. There is no particular upper limit to the immersion time, but from the viewpoint of production efficiency, it can be 30 hours or less.

[0076] The inorganic material layer that has adsorbed silver ions in step (V) is subjected to step (IV) to form a functional separation layer, thereby obtaining the separation filter of the present disclosure that can adsorb and remove not only heavy metals but also Br.

[0077] According to the method for producing a separation filter of the present disclosure, a separation filter having good oil-water separation and heavy metal removal performance can be efficiently produced.

[0078] The present invention will be described in detail below based on specific examples, but the present invention is not limited to these examples.

[0079] [Example 1] (Production of inorganic material layer) 75% by mass of kaolin, 20% by mass of dolomite, and 5% by mass of methyl cellulose as a binder (total 100% by mass) were weighed and stirred for 30 minutes in a mixer equipped with stirring blades to obtain a mixture in which the components were uniformly mixed (step (I)). Next, the mixture was pressed in a press molding machine at 3000 N / cm ２ The area was 0.522 × 10 －３ m ２ A disk-shaped inorganic material layer precursor having a thickness of 3 mm was obtained (step (II)). The obtained disk-shaped inorganic material layer precursor was dried at 100°C for 24 hours and then sintered at 1100°C for 4 hours to obtain an inorganic material layer (step (III)).

[0080] (Evaluation of inorganic material layer) The water permeation flux and strength of the obtained inorganic material layer were evaluated by the above-mentioned method. ２ The compressive strength was 1.1 MPa. The average pore size of the inorganic material layer of Example 1 (sintering temperature 1100°C) determined from an SEM photograph based on the measurement results of the graph in Figure 4 was 2.2 µm. The pore size determined from the BET specific surface area was 18.5 nm.

[0081] (Formation of Functional Separation Layer) Next, the obtained inorganic material layer was immersed in a fluorine solution (Fluorosurf (registered trademark) FG-5084, manufactured by Fluoro Technology Co., Ltd.) for 12 hours and dried to form a water-repellent functional separation layer containing a fluorine compound on the surface of the inorganic material layer, thereby obtaining the separation filter of Example 1 (step (IV)).

[0082] [Examples 2 to 4] Separation filters of Example 2 (firing temperature: 1150°C), Example 3 (firing temperature: 1200°C), and Example 4 (firing temperature: 1250°C) were obtained in the same manner as Example 1, except that the sintering temperature of the inorganic material layer precursor in step (III) was changed to 1150°C, 1200°C, and 1250°C, respectively.

[0083] (Confirmation of XRD Pattern) Figure 5 is a graph showing XRD patterns of the inorganic material layer of Example 1, which is a sintered body obtained by firing a mixture containing (a) kaolin, (b) dolomite, (c) (a) 75% by mass of kaolin, (b) 20% by mass of dolomite, and 5% by mass of methyl cellulose as a binder at 1100 ° C. for 4 hours, (d) the inorganic material layer of Example 2, which is a sintered body obtained by firing at 1150 ° C. for 4 hours, (e) the inorganic material layer of Example 3, which is a sintered body obtained by firing at 1200 ° C. for 4 hours, and (f) the inorganic material layer of Example 4, which is a sintered body obtained by firing at 1250 ° C. for 4 hours. As shown in Figure 5, it was confirmed that decomposition of the dolomite and kaolin occurred and the composition changed by sintering the mixture.

[0084] [Comparative Example 1] In preparing the mixture, an inorganic material layer and a functional separation layer were formed in the same manner as in Example 1, except that a mixture containing kaolin of 95 mass% and no dolomite was used, to obtain a separation filter of Comparative Example 1. When the inorganic material layer used in the separation filter of Comparative Example 1 was evaluated in the same manner as in Example 1, the water permeation flux was 50 L / hm ２ The compressive strength was 0.8 MPa, and both the water permeation flux and the compressive strength were inferior to those of the separation filter of Example 1.

[0085] [Evaluation of Heavy Metal Removal Ability of Separation Filter] A liquid containing the following heavy metals and metals was passed through the separation filters of Comparative Example 1 and Example 1. A liquid to be treated, having a pH of 5 and containing 10 ppm each of Pb(II), Cu(II), Zn(II), and Cd(II), was prepared as the heavy metals and metals. The liquid to be treated was passed through the separation filter at an operating pressure of 0.015 MPa. The contents of the heavy metals and metals contained in the liquid to be treated before and after passing through the separation filter were measured, and the removal rate of heavy metals by passing through the separation filter was measured from the measurement results. The permeation flux of the liquid to be treated through the separation filter was also measured. The results are shown in Figure 6. Figure 6 is a graph showing the removal rate of heavy metals and metals by adsorption and the permeation flux of the liquid to be treated for the separation filters of Example 1 and Comparative Example 1.

[0086] As is clear from Figure 6, in a comparison between the separation filter of Comparative Example 1 and the separation filter of Example 1, the removal rates of Pb(II) were both good, but the separation filter of Example 1 had higher removal rates of Cu(II), Zn(II), and Cd(II) than the separation filter of Comparative Example 1, and it was found that the separation filter of Example 1 had particularly high removal rates of Zn(II) and Cd(II). In addition, the permeation flux of the treated liquid was about 20 L / h m for the separation filter of Comparative Example 1. ２ In contrast, the separation filter of Example 1 had a flow rate of about 150 L / h m ２ The separation filter of Example 1 had a Pb(II) removal rate of 99.12%, a Cu(II) removal rate of 99.82%, a Zn(II) removal rate of 85.62%, and a Cd(II) removal rate of 65.94%, demonstrating that the simple method effectively removes even harmful Cd.

[0087] [Evaluation of oil-water separation performance of separation filters] For the separation filters of Examples 1 to 4, an oil-containing emulsion liquid was passed through the filters, and the oil-water separation performance was evaluated based on the amount of oil before and after passing through the separation filter. The amount of oil in the emulsion liquid after passing through the separation filter was measured to evaluate the oil-water separation performance. Kerosene was used as the oil contained in the liquid to be treated. The liquid to be treated for measurement was prepared by adding an anionic surfactant at 0.2% by mass of water to a mixture of equal volumes of oil and water, and stirring for 1 hour to form an emulsion. The flux of the oil-containing liquid to be treated was also measured.

[0088] The results are shown in Figure 7. Figure 7 is a graph showing the oil removal rate and permeation flux of the treated liquid of the separation filters of Example 1 (sintering temperature: 1100°C), Example 2 (sintering temperature: 1150°C), Example 3 (sintering temperature: 1200°C), and Example 4 (sintering temperature: 1250°C). As is clear from Figure 7, the permeation flux of the treated liquid was 200 L / h m ２ Up to 250 L / h m ２The average pore size determined from the SEM photograph of the pores in the inorganic material layer of Example 2 (sintering temperature 1150°C) based on the measurement results of the graph in Figure 4 was 2.4 μm, and the pore size determined from the BET specific surface area was 19.2 nm. Similarly, the average pore size determined from the SEM photograph of the pores in the inorganic material layer of Example 3 (sintering temperature 1200°C) was 3.8 μm, and the pore size determined from the BET specific surface area was 15.4 nm. The average pore size determined from the SEM photograph of the pores in the inorganic material layer of Example 4 (sintering temperature 1250°C) was 6.8 μm, and the pore size determined from the BET specific surface area was 15.2 nm. The oil-water separation performance was excellent with a removal rate of 90% or more in Examples 1 and 2, where the sintering temperatures were 1100°C and 1150°C. It was found that the oil-water separation performance was slightly reduced in Examples 3 and 4, where the sintering temperatures were 1200°C to 1250°C.

[0089] [Evaluation of arsenic removal ability of separation filter] Using the separation filter of Example 1, a pH 4 solution containing initial As concentrations of 1 ppm, 10 ppm, 30 ppm, and 50 ppm was passed through the separation filter at an operating pressure of 0.015 MPa, and the As removal rate was measured. The results are shown in Figure 8. Figure 8 is a graph showing the As removal rate when the solution to be treated was passed through the separation filter of Example 1 for each initial As content (initial concentration). As is clear from Figure 8, for example, the As removal rate after passing the separation filter for a solution to be treated containing 1 ppm As was about 20%, and the permeation flux was 100 L / h m ２ Up to 150 L / h m ２ It was possible to remove As from low to high concentrations using activated carbon. It showed a more effective removal rate than the As removal rate of 5% when the same amount of activated carbon was used.

[0090] [Examples 5 to 7] In Examples 2 to 4, the inorganic material layer obtained in step (III) was immersed in an ionic solution containing 1000 ppm of silver ions for 24 hours, then dried, sintered at 100°C for 1 hour, and further re-sintered at 300°C for 4 hours to obtain a silver ion-adsorbed inorganic material layer (step (V)). Step (IV) was performed on the obtained silver ion-adsorbed inorganic material layer in the same manner as in Example 1 to form a functional separation layer, and separation filters of Example 5 (sintering temperature: 1150°C), Example 6 (sintering temperature: 1200°C), and Example 7 (sintering temperature: 1250°C), which were separation filters adsorbing silver ions, were obtained.

[0091] [Evaluation A of Separation Filter Bromine Removal] Using a separation filter having a silver ion-adsorbing inorganic material layer, a pH 7 solution containing 100 ppm of Br was passed through the separation filter at an operating pressure of 0.015 MPa, and the Br removal rate was measured. The results are shown in FIG. 9 . FIG. 9 is a graph showing the Br removal rate calculated from the Br content in the Br-containing solution before and after passing the Br-containing solution through the separation filters of Examples 5 to 7. As is clear from FIG. 9 , the separation filters of Examples 5 and 6 had Br removal rates of 90% and 34%, respectively. However, the separation filter of Example 7 (inorganic material layer baked at 1250°C) only achieved a removal rate of approximately 10%. This confirms that, from the perspective of Br removal rate, it is effective to adsorb silver ions to an inorganic material layer baked at 1150°C or 1200°C.

[0092] [Evaluation of Bromine Removal Ability of Separation Filter of Example 2: Reference Example] A similar evaluation was performed using the separation filter of Example 2, which did not adsorb a silver ion solution. As described above, it was confirmed that the oil-water separation performance and heavy metal removal ability were good, but that the Br removal ability was not good. This confirmed that adsorption of silver ions into the inorganic material layer is effective for Br removal.

[0093] [Comparison of Bromine Removal Performance Evaluation B of Separation Filter with Activated Carbon] Bromine removal performance evaluation B was performed using the separation filter of Example 5-2, in which silver ions were adsorbed onto the inorganic material layer of Example 1 in the same manner as in Example 5, and the separation filter of Example 7. The evaluation method for bromine removal performance evaluation B was to add 200 mL of a pH 7 solution containing 100 ppm Br to 8.55 × 10 －４ m ２ The Br removal rate after filtration for 12 minutes using a separation filter with a membrane area of ​​0.314 Ls －１ m －２ ) was measured. In addition, 200 mL of the treated liquid containing 10 ppm Br and having a pH of 7 was used to measure the Br removal rate of the treated liquid after filtration in the same manner. The results are shown in Table 1 below.

[0094] Next, the bromine removal efficiency using activated carbon was evaluated. The evaluation method was to add 0.1 g, 0.5 g, or 1.0 g of activated carbon to 50 mL of the liquid to be treated containing 100 ppm Br, and measure the Br removal rate after adsorption for one day. The Br removal rate was also measured in the same manner for the liquid to be treated with a Br content of 10 ppm. The results are shown in Table 1 below.

[0095]

[0096] As is clear from Table 1, the separation filters of Examples 5-2 and 7 exhibited good bromine removal properties, and it was confirmed that they exhibited better bromine removal properties than the filters using activated carbon, which is commonly used for adsorbing bromine.

[0097] [Example 8] Next, in Example 5, which had a good Br removal rate, the adsorption conditions of the silver ion solution were changed and evaluation was performed. In Example 5, the inorganic material layer obtained in step (III) was immersed in an ionic solution containing 1000 ppm of silver ions for 24 hours, then dried and sintered at 300 ° C for 4 hours to obtain a silver ion-adsorbed inorganic material layer (step (V)). The obtained silver ion-adsorbed inorganic material layer was subjected to step (IV) in the same manner as in Example 1 to form a functional separation layer, thereby obtaining the separation filter of Example 8. When the Br removal rate of the separation filter of Example 8 was measured in the same manner as in Example 5, the removal rate was 80%, indicating good Br removal properties. It was confirmed that good Br removal properties were obtained regardless of the sintering conditions after silver ion addition.

[0098] [Examples 9 and 10] The inorganic material layer (baking temperature 1100°C) used in Example 1 and the inorganic material layer (baking temperature 1250°C) used in Example 4 were immersed in a water and oil repellent agent (Efrontier A0111, manufactured by Mitsubishi Materials Corporation (Mitsubishi Materials Electronic Chemicals Co., Ltd.) for 12 hours and dried at room temperature for 24 hours to form an oil and water repellent functional separation layer, thereby obtaining the separation filters of Examples 9 and 10. The BET specific surface area of ​​the separation filter of Example 9 was 2.9394 (m ２ / g), and the pore volume is 0.013591 (cm ３ The BET specific surface area of ​​the separation filter of Example 10 was 0.5005 (m ２ / g), and the pore volume is 0.001899 (cm ３ / g) and the average pore size was 15.180 (nm).

[0099] (Evaluation of oil-water separation ability) Kerosene as oil and an aqueous solution containing each heavy metal at the concentration shown in Table 2 below were mixed in a 1:1 ratio by mass, and an anionic surfactant was added to the mixed solution in an amount to give a concentration of 0.1 mass%, and the mixture was shaken to prepare an emulsion, which was used as the test solution. The test solution was cloudy when visually observed.

[0100] The obtained test liquid was subjected to suction filtration through a separation filter using a suction filtration device. The separation filter had an area of ​​0.855 × 10 －３ m２ The flux was calculated using the following formula: Flux = (filtration volume: mL) / [membrane area (m ２ ) × filtration time (s)] The calculated flux of each separation filter is shown in Table 2 below.

[0101]

[0102] In the above test, the average flux of Example 9 was 155.2, and the average flux of Example 10 was 298.4. The volume of the oil-water emulsion before filtration was 50 mL, but the volume decreased after filtration. This is thought to be due to separation of oil and water.

[0103] After suction filtration, a visually transparent separated liquid was obtained. The heavy metal content of the separated liquid was analyzed by ICP-AES. The results are shown in Table 3 below. The removal rate was calculated using the following formula: Removal rate (%) = [1 - (heavy metal concentration after removal / initial heavy metal concentration)] x 100

[0104]

[0105] The results in Tables 2 and 3 show that the separation filters having functional separation layers with oil and water repellency in Examples 9 and 10 also have good oil-water separation properties and heavy metal removal, just like separation filters having functional separation layers with water repellency.

[0106] The disclosure of Japanese Patent Application No. 2024-009042, filed on January 24, 2024, is incorporated herein by reference. All documents, patent applications, and technical standards mentioned in this disclosure are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A fired product of a mixture containing dolomite, kaolin, and a binder, having an inorganic material layer with pores having an average open pore diameter of 0.1 μm to 100 μm, wherein the content of the dolomite with respect to all components constituting the inorganic material layer exceeds 0% by mass and is 50% by mass or less, and the content of the kaolin with respect to all components constituting the inorganic material layer is 50% by mass or more and less than 100% by mass, a separation filter.

2. A fired product of a mixture containing dolomite, kaolin, and a binder, having an inorganic material layer with pores having an average open pore diameter of 0.1 μm to 100 μm, and a functional separation layer provided on at least a part of the inorganic material layer, wherein the content of the dolomite with respect to all components constituting the inorganic material layer exceeds 0% by mass and is 50% by mass or less, and the content of the kaolin with respect to all components constituting the inorganic material layer is 50% by mass or more and less than 100% by mass, and the functional separation layer contains at least one selected from the group consisting of a fluorine compound and a silicon-based compound, a separation filter.

3. The separation filter according to claim 1 or claim 2, wherein when the content of the dolomite is D and the content of the kaolin is K, the ratio (D / K) of K to D in the inorganic material layer satisfies the following formula: Formula: 1 > D / K > 0.01 4. The separation filter according to claim 1 or claim 2, which is in the form of a film with a thickness of 10 μm to 10 mm.

5. The separation filter according to claim 1 or claim 2, which is in the form of particles with an average particle diameter of 10 μm to 10 mm.

6. The separation filter according to claim 1 or claim 2, wherein the dolomite contains at least one selected from the group consisting of calcined dolomite, semi-calcined dolomite, and dolomite.

7. The separation filter according to claim 2, wherein the fluorine compound contains at least one fluororesin selected from the group consisting of polytetrafluoroethylene, perfluoroalkoxyalkane, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride.

8. The separation filter according to claim 2, wherein the silicon-based compound contains at least one silicon-based compound selected from the group consisting of silicon nanoparticles, silicon oxide nanoparticles, and silicone resins.

9. The separation filter according to claim 1 or claim 2, wherein the inorganic material layer further contains a phosphorus component.

10. The separation filter according to claim 1 or claim 2, wherein the inorganic material layer further contains silver ions and is for bromine removal.

11. A method for manufacturing a separation filter, comprising: step (I) of preparing a mixture containing 0% by mass or more and 50% by mass or less of dolomite, 50% by mass or more and less than 100% by mass of kaolin, and a binder, based on a total amount of 100% by mass; step (II) of molding and drying the obtained mixture to obtain a precursor of the inorganic material layer; and step (III) of sintering the obtained precursor of the inorganic material layer under the condition of a temperature of 650°C to 1250°C to obtain the inorganic material layer.

12. A method for manufacturing a separation filter, comprising: step (I) of preparing a mixture containing 0% by mass or more and 50% by mass or less of dolomite, 50% by mass or more and less than 100% by mass of kaolin, and a binder, based on a total amount of 100% by mass; step (II) of molding and drying the obtained mixture to obtain a precursor of the inorganic material layer; step (III) of sintering the obtained precursor of the inorganic material layer under the condition of a temperature of 650°C to 1250°C to obtain the inorganic material layer; and step (IV) of forming a functional separation layer containing a fluorine compound or a silicon-based compound on at least a part of the surface of the inorganic material layer.

13. The method for manufacturing a separation filter according to claim 11 or claim 12, wherein when the content of dolomite in the mixture is D and the content of kaolin is K, the ratio (D / K) of K to D contained in the mixture satisfies the following formula: Formula: 1 > D / K > 0.01 14. The molding of the mixture is carried out under a pressure of 1900 N / cm ２ to 5000 N / cm ２ The method for manufacturing a separation filter according to claim 11 or claim 12.

15. The method for manufacturing a separation filter according to claim 11 or claim 12, further comprising step (V) of applying a silver ion-containing solution to the inorganic material layer obtained in step (III), followed by drying and sintering to adsorb silver ions to the inorganic material layer.

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