Membrane module for membrane distillation and method for manufacturing same

Abstract

Provided is a membrane module 100 for membrane distillation, the membrane module 100 comprising a porous hydrophobic hollow fiber membrane bundle and a container 10 for accommodating the membrane bundle. The membrane bundle is formed of a plurality of porous hollow fiber membranes 20, each having one end and the other end, by bundling together the one ends and the other ends. A hydrophobic polymer is adhered to at least a portion of the porous hollow fiber membranes 20. In each surface layer on both surfaces of the porous hollow fiber membranes 20, when the adhesion amount of the hydrophobic polymer on the porous hollow fiber membranes at the center of the membrane bundle is denoted as A1, and the adhesion amount of the hydrophobic polymer on the porous hollow fiber membranes at the outermost layer of the membrane bundle is denoted as A2, the relationship of |log10(A1 / A2)|≤0.75 is satisfied.

Description

Membrane distillation membrane module and its manufacturing method

[0001] The present invention relates to a membrane module for membrane distillation and a method for manufacturing the same. More specifically, the present invention relates to a membrane module for membrane distillation and a method for manufacturing the same, in which a bundle of a plurality of porous hollow fiber membranes having through holes is housed in a cylindrical container, and a hydrophobic polymer is attached to at least a portion of the hollow fiber membranes, and a liquid to be treated is passed inside the hollow fiber membranes and a liquid to be removed, the vapor pressure of which is lower than that of the liquid to be treated, is passed outside the hollow fiber membranes, thereby transferring the liquid to be removed to the liquid outside the hollow fiber membranes.

[0002] There are many raw material liquids in the industry that require concentration and contain water and an organic solvent as the solvent.

[0003] One example is the pharmaceutical manufacturing process. In recent years, the development of pharmaceuticals and the like having a polymer structure with a molecular weight of 10,000 or more, such as medium-molecular-weight peptides with a molecular weight of 1,000 or more, has progressed in the field of pharmaceutical manufacturing. These pharmaceuticals and the like are often synthesized and purified in an organic solvent or a mixed solvent containing water and an organic solvent. However, in order to commercialize the resulting synthesized product or product, it is necessary to remove the organic solvent.

[0004] Removal of organic solvents from raw materials containing valuable substances such as pharmaceuticals as solutes has traditionally been performed by vacuum distillation, thin-film distillation, etc. However, vacuum distillation and thin-film distillation require the raw material to be heated to high temperatures. Therefore, if the valuable substances (solutes) contained in the raw material have low heat resistance, there is a risk that the valuable substances may be altered or deactivated.

[0005] In recent years, membrane distillation has attracted attention as a method for removing organic solvents from a feed solution containing water and an organic solvent as solvents without heating the feed solution. In membrane distillation, the feed solution is contacted with an absorption solution, the vapor pressure of which is lower than that of the feed solution, through a hydrophobic porous membrane that does not allow water to pass through. The difference in the vapor pressure of the organic solvent between the feed solution and the absorption solution is used as a driving force, and only the vapor of the organic solvent in the feed solution passes through the hydrophobic porous membrane and moves to the absorption solution. By applying this principle, the organic solvent can be preferentially removed from the feed solution. For example, Patent Documents 1 and 2 propose removing organic solvents from a feed solution using a membrane distillation membrane module, which is formed by attaching a hydrophobic polymer to a membrane module containing a hollow fiber porous membrane to hydrophobize the porous membrane.

[0006] International Publication No. 2021 / 070955 International Publication No. 2023 / 249115

[0007] When applying membrane distillation to the manufacture of pharmaceuticals, a large amount of raw material liquid needs to be concentrated for mass production, and a long membrane distillation module, for example, 40 cm in length, is required to ensure the membrane area. On the other hand, the membrane distillation membrane modules for removing organic solvents described in Patent Documents 1 and 2 are both short, having lengths of 15 cm or less.

[0008] Therefore, the present inventors fabricated a long module using the same hydrophobic polymer attachment method as in Patent Document 2, and found that the surface of the porous hollow fiber membrane became wet with the raw material solution, resulting in a "wetting" phenomenon in which the raw material solution itself, rather than the organic solvent vapor, passes through the membrane. This wetting phenomenon is problematic because it can cause loss of pharmaceutical ingredients in the raw material due to leakage. While the wetting phenomenon can be suppressed by increasing the amount of attached hydrophobic polymer, the increased amount of attached polymer narrows the flow path of the porous membrane, reducing the amount of organic solvent vapor that permeates, which increases the time required to remove the organic solvent from the raw material solution.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for efficiently removing an organic solvent from a raw material solution containing water and an organic solvent as solvents, without causing loss of valuable materials due to deterioration, deactivation, leakage, etc., even in a long module, for example, one having a length exceeding 40 cm.

[0010] As a result of extensive research and experiments to solve the above problems, the present inventors discovered that it is possible to improve anti-wetting properties while maintaining the permeate volume per unit volume of the module by optimizing the state of adhesion of the hydrophobic polymer to the porous hollow fiber membrane, the method of applying and drying the hydrophobic polymer solution, etc., and thus completed the present invention.

[0011] [1] A membrane module for membrane distillation comprising a hydrophobic porous hollow fiber membrane bundle and a container accommodating the hydrophobic porous hollow fiber membrane bundle, wherein the container comprises a main body, a liquid to be treated inlet section having a flow path for introducing the liquid to be treated, a water to be treated outlet section having a flow path for extracting the water to be treated, an absorbing liquid inlet section having a flow path for introducing the absorbing liquid, and an absorbing liquid outlet section having a flow path for extracting the absorbing liquid, wherein the hydrophobic porous hollow fiber membrane bundle is a membrane bundle formed by bundling a plurality of porous hollow fiber membranes, each having one end and the other end, end-to-end and end-to-end, wherein a hydrophobic polymer is adhered to at least a portion of the porous hollow fiber membranes, and wherein, in the surface layers on both sides of the porous hollow fiber membranes, when the amount of the hydrophobic polymer adhered to the porous hollow fiber membrane at the center of the membrane bundle is A1 and the amount of the hydrophobic polymer adhered to the porous hollow fiber membrane in the outermost layer of the membrane bundle is A2, the following formula (1) is satisfied: |log10(A1 / A2)| {where | to | indicate absolute values, and log10( to ) indicates common logarithms} are each 0.75 or less. [2] The membrane distillation membrane module according to [1], wherein the amount of the hydrophobic polymer attached has a distribution in the thickness direction of the porous hollow fiber membrane, and the amount of the attached hydrophobic polymer in the surface layer of at least one side of the porous hollow fiber membrane of the membrane distillation membrane module is greater than the amount of the attached hydrophobic polymer in the interior. [3] The membrane distillation membrane module according to [1] or [2], wherein the hydrophobic polymer contains a fluorine atom. [4] The membrane distillation membrane module according to [1] or [2], wherein the hydrophobic polymer has a CF ３-(CF ２ )m-(CH ２ ) ２

[0013]

[0014] The membrane distillation membrane module according to [3], comprising a structure represented by the molecular formula: -- {where m is an integer of 3 or more and 7 or less}. [5] The membrane distillation membrane module according to any of [1] to [4], wherein the porous hollow fiber membrane comprises, as a raw material, at least one polymer selected from the group consisting of polyvinylidene fluoride, polyethylene, polyolefin, polysulfone, and polyacrylamide. [6] The membrane distillation membrane module according to any of [1] to [5], wherein the total length of the membrane distillation membrane module is 40 cm or more. [7] The method for producing a membrane distillation membrane module according to any of [1] to [6], comprising a coating and drying step of the hydrophobic polymer, wherein after the hydrophobic polymer solution is applied to the membrane distillation membrane module, air is blown through the membrane distillation membrane module to dry the solvent, and air is blown against both sides of the porous hollow fiber membrane to dry the solvent. [8] A method for producing a membrane distillation membrane module according to [7], which includes a drying step of the hydrophobic polymer solution, and wherein a value obtained by dividing the linear airflow speed toward the inner surface of the porous hollow fiber membrane by the linear airflow speed toward the outer surface of the porous hollow fiber membrane is equal to or greater than 2. [9] A method for producing a membrane distillation membrane module according to [8], which includes a drying step of the hydrophobic polymer solution, and wherein a total linear airflow speed toward the porous hollow fiber membrane is 9 m / min or more and 100 m / min or less.

[0012] The membrane distillation module of the present invention suppresses and prevents loss of valuable materials and efficiently removes organic solvents from the raw material liquid, even in long modules, for example, those having a length of more than 40 cm, and can maintain high anti-wetting properties while maintaining the amount of permeated liquid per unit volume of the module, thereby realizing low-cost and space-saving membrane distillation apparatuses that use the membrane module for membrane distillation of the present invention as a main component.

[0013] Fig. 1 is a schematic diagram of an example of a membrane module for membrane distillation according to the present invention. Fig. 2 is a conceptual diagram for explaining an example of an embodiment of membrane distillation using the raw material liquid concentration system according to the present invention. Fig. 3 is a conceptual diagram for explaining an example of an embodiment of measurement of liquid intrusion pressure applied to the raw material liquid concentration system according to the present invention.

[0014] Hereinafter, a detailed description will be given of an embodiment of the present invention (hereinafter also referred to as "the present embodiment"). The present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention. In this disclosure, the same reference numerals in the drawings indicate similar elements.

[0015] [Membrane distillation membrane module] The membrane distillation membrane module of this embodiment comprises a hydrophobic porous hollow fiber membrane bundle and a container for accommodating the hollow fiber membrane bundle. The container has a main body, a liquid to be treated inlet having a flow path for introducing the liquid to be treated, a water to be treated outlet having a flow path for extracting the water to be treated, an absorbing liquid inlet having a flow path for introducing the absorbing liquid, and an absorbing liquid outlet having a flow path for extracting the absorbing liquid.

[0016] The hydrophobic porous hollow fiber membrane bundle is a membrane bundle formed by bundling a plurality of hydrophobic porous hollow fiber membranes, each having one end and the other end, with their one ends facing each other and their other ends facing each other.

[0017] The shape of the container is not limited and may be cylindrical, polygonal prism, other polyhedral shapes, etc. Preferably, a hollow fiber membrane bundle is housed in a cylindrical or polygonal prism container so that the longitudinal direction of the hollow fibers coincides with the axial direction of the container, and both ends of the hollow fiber membrane bundle are fixed to the inside of the container with an appropriate adhesive resin. In this case, it is preferable to fix the hollow fiber membrane bundle with the adhesive resin in a liquid-tight manner so that the flow paths inside and outside the hollow fiber membranes do not mix.

[0018] FIG. 1 is a schematic diagram showing an example of a membrane distillation membrane module according to the present embodiment. The membrane distillation membrane module 100 of FIG. 1 contains a plurality of hollow fiber membranes 20 for membrane distillation in a housing (container) 10, and both ends of the hollow fiber membranes are bonded and fixed with an adhesive resin 30, such as a hydrophobic thermoplastic resin, a thermosetting resin, or an adhesive. Here, both ends of the membrane distillation membrane may be open and not blocked. The hydrophobic adhesive is preferably composed of a silicone resin and / or a fluororesin, and more preferably composed of a silicone resin or a fluororesin. The hydrophobic thermoplastic resin is preferably polyethylene or polypropylene, which is melted and bonded. As the thermosetting resin, for example, an epoxy resin or the like may be used.

[0019] The side of the housing 10 has an absorption liquid inlet section having a first housing side pipe 11 for introducing the absorption water AW and an absorption liquid introduction flow path, and an absorption liquid outlet section having a second housing side pipe 12 for discharging the absorption water AW and an absorption liquid outlet flow path, which allow the absorption water AW to circulate in the external space of the membrane distillation membrane.

[0020] At both ends of the housing 10 in the axial direction (left and right direction in Figure 1), there are a treated liquid inlet section having an opening for introducing raw material liquid a and a treated liquid inlet flow path, and a treated water outlet section having an opening for discharging raw material liquid b after organic solvent removal and a treated water outlet flow path, which allow raw material liquid a, the treated liquid, and the treated water to flow through the hollow part of the membrane distillation membrane.

[0021] The interior of the membrane distillation membrane module 100 is divided into a space on the hollow side of the membrane distillation membrane and a space on the external space side of the membrane distillation membrane by the membrane distillation hollow fiber membrane 20. These two spaces are fluidically isolated except that a predetermined solvent can pass through the outer wall of the membrane distillation membrane.

[0022] The hollow fiber membrane 20 for membrane distillation is, for example, hollow fiber-shaped, and its outer wall is preferably highly hydrophobic and porous, but does not allow liquid to penetrate inside, and only allows gas to pass through the outer wall.Furthermore, since high vapor permeability is required even at room temperature, it is preferable that the membrane has a high porosity and an appropriate average pore size.

[0023] [Hydrophobic porous hollow fiber membrane] The hydrophobic porous hollow fiber membrane of this embodiment preferably has through-holes and continuous pores extending from the outside to the inside of the hollow fiber membrane. The continuous pores may be included in the network of the membrane material, such as a hydrophobic polymer, that constitutes the hollow fiber membrane, and may be branched or straight pores. The pores may be permeable to vapor but not liquid.

[0024] From the viewpoint of achieving both vapor permeability and mechanical strength of the membrane, the membrane thickness of the hydrophobic porous hollow fiber membrane is preferably 10 μm to 1,000 μm, more preferably 20 μm to 500 μm. A membrane thickness of 1,000 μm or less can achieve high vapor permeability, and a membrane thickness of 10 μm or more can be used for a long period of time without deformation.

[0025] The outer diameter of the hydrophobic porous hollow fiber membrane is preferably 300 μm to 5,000 μm, more preferably 350 μm to 4,000 μm, and the inner diameter of the hydrophobic porous hollow fiber membrane is preferably 200 μm to 4,000 μm, more preferably 250 μm to 1,500 μm. Adjusting the outer or inner diameter of the hydrophobic porous hollow fiber membrane to a size within this range provides a good balance between membrane strength and the effective area of ​​the membrane.

[0026] The average pore size of the hydrophobic porous hollow fiber membrane is preferably in the range of 0.02 μm to 0.5 μm, more preferably in the range of 0.03 μm to 0.3 μm. When the average pore size is 0.02 μm or more, the vapor permeation resistance is not too large, and the concentration rate of the raw material liquid is increased. When the average pore size is 0.5 μm or less, the effect of suppressing membrane wetting is good. The average pore size is a value measured by the half-dry method in accordance with ASTM: F316-86.

[0027] From the viewpoint of achieving both vapor permeability and wetting suppression, the pore size distribution of the membrane is preferably narrow. Specifically, the pore size distribution, which is the ratio of the maximum pore size to the average pore size, is preferably in the range of 1.2 to 2.5, more preferably in the range of 1.2 to 2.0. The maximum pore size is a value measured using the bubble point method.

[0028] The porosity of the hydrophobic porous hollow fiber membrane is preferably in the range of 60% to 90% in order to achieve both high vapor permeability and long-term durability. To achieve high vapor permeability, the porosity of the hydrophobic porous hollow fiber membrane is preferably 60% or more, more preferably 70% or more. To maintain the strength of the membrane itself well and prevent problems such as breakage during long-term use, the porosity of the hydrophobic porous hollow fiber membrane is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less. The porosity is a value calculated from the true specific gravity and apparent specific gravity of the material constituting the hydrophobic porous hollow fiber membrane.

[0029] The surface opening ratio of the hydrophobic porous hollow fiber membrane is preferably 15% or more, more preferably 18% or more, and even more preferably 20% or more on each of the two surfaces of the hydrophobic porous hollow fiber membrane from the viewpoint of efficiently removing volatile organic solvents, and is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less from the viewpoint of maintaining good strength of the membrane itself and making it less likely to cause problems such as breakage during long-term use. The surface opening ratio is a value determined by detecting pores using image analysis software in an image of the membrane surface observed with a scanning electron microscope (SEM).

[0030] Examples of materials constituting the hydrophobic porous hollow fiber membrane of this embodiment include polysulfone, polyethersulfone, polyolefin, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylamide, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, etc., and materials containing one or more resins selected from these include. The hydrophobic porous hollow fiber membrane of this embodiment preferably contains at least one polymer selected from the group consisting of polyvinylidene fluoride, polyethylene, polyolefin, polysulfone, and polyacrylamide as a raw material. Among these, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, or polychlorotrifluoroethylene is preferred from the viewpoint of being able to produce a membrane excellent in hydrophobicity, mechanical durability, and thermal durability with high membrane formability.

[0031] [Hydrophobic Polymer] At least a portion of the hydrophobic porous hollow fiber membrane is coated with a hydrophobic polymer different from the hydrophobic polymer itself that is the material of the porous hollow fiber membrane. In the membrane distillation membrane module of this embodiment, the raw material liquid passes through the inside of the hollow fiber membrane, and the organic solvent is expected to permeate the inside of the hollow fiber membrane. Therefore, wetting can be suppressed by not only being hydrophobic but also by coating at least a portion of the inner surface of the hollow fiber membrane that comes into contact with the raw material liquid and the surface of the through holes with a hydrophobic polymer. In this specification, "hydrophobic polymer" refers to a polymer with low affinity for water, and may be, for example, a polymer with a hydrophobic structure. Examples of hydrophobic structures include non-polar or low-polarity groups, non-polar or low-polarity skeletons, etc. Examples of non-polar or low-polarity groups include hydrocarbon groups and fluorine-containing groups, and examples of non-polar or low-polarity skeletons include hydrocarbon main chains and siloxane main chains.

[0032] Examples of hydrophobic polymers include polymers having siloxane bonds and fluorine atom-containing polymers, and more specifically, the following can be mentioned: (a) Examples of polymers having siloxane bonds include dimethylsilicone gel, methylphenylsilicone gel, reactive modified silicone gels having organic functional groups (amino groups, fluoroalkyl groups, etc.), silicone polymers that form crosslinked structures by reacting with silane coupling agents, and polymer gels that are crosslinked products thereof; (b) Examples of fluorine atom-containing polymers include polymers having fluorine atom-containing groups in their side chains, where the fluorine atom-containing groups are (per)fluoroalkyl groups, (per)fluoropolyether groups, alkylsilyl groups, fluorosilyl groups, etc.

[0033] In particular, from the viewpoint of hydrophobicity and thermal stability, the hydrophobic polymer is ３ -(CF ２ )m-(CH ２ ) ２ Preferably, the compound contains a structure represented by the molecular formula - in a side chain, and more preferably is a polymer of a (meth)acrylate monomer and / or a vinyl monomer containing the structure represented by the above molecular formula, where m in the molecular formula is an integer of 3 or more and 7 or less.

[0034] The hydrophobic polymer may be attached to the entire pores of the porous hollow fiber membrane. However, from the viewpoint of preventing liquid penetration into the pores and ensuring vapor permeability, it is preferable that the amount of hydrophobic polymer attached has a distribution in the thickness direction of the porous hollow fiber membrane, with a large amount of hydrophobic polymer attached to the surface layer of the membrane that comes into contact with the liquid and a small amount attached to the interior of the membrane in the thickness direction, thereby maintaining the pore structure. The resistance to liquid penetration into the pores can be evaluated using a measurement method called liquid penetration pressure, which will be described later. From this viewpoint, it is preferable that the amount of hydrophobic polymer attached to the surface layer on at least one side of the porous hollow fiber membrane is greater than the amount attached to the interior, and it is more preferable that the amount of hydrophobic polymer attached decreases from the surface layer on one side to the surface layer on the opposite side of the porous hollow fiber membrane.

[0035] As a result of repeated experiments, the present inventors have found that, in order to ensure vapor permeability while preventing liquid from entering the pores, it is preferable that the amount of hydrophobic polymer attached to the surface layer of each porous hollow fiber membrane bundle is uniform, particularly in long modules with a total length of 40 cm or more or more. The reason for this is unclear, but is presumed to be as follows.

[0036] As described above, membrane distillation membrane modules include a membrane bundle consisting of hollow fiber membranes. Considering the vapor permeability and wetting resistance of the entire membrane module, rather than the vapor permeability and wetting resistance of a single porous hollow fiber membrane, vapor permeability depends on the average vapor permeability of all hollow fibers included in the membrane bundle. In contrast, wetting resistance is determined by the liquid penetration pressure of the hollow fiber with the lowest liquid penetration pressure in the membrane bundle, because wetting of even one membrane in the membrane bundle causes leakage of pharmaceutical ingredients in the raw material. Long modules require higher liquid penetration pressure than short modules due to their long flow paths and large pressure loss. According to the present disclosure, we have newly discovered that in short modules with low liquid penetration pressure, even hollow fibers with low liquid penetration pressure due to non-uniformity in the surface adhesion amount of the membrane bundle do not cause leakage due to the low pressure, whereas in long modules with high liquid penetration pressure, hollow fibers with low liquid penetration pressure due to non-uniformity can cause leakage.

[0037] For the above reasons, it is estimated that the more uniform the amount of hydrophobic polymer attached to the surface layer of all hollow fibers in a porous hollow fiber membrane bundle, the more likely it is that both a high liquid entry pressure and a high vapor permeability can be achieved.

[0038] The uniformity of the amount of hydrophobic polymer attached to the surface layer of the porous hollow fiber membrane bundle provided in the membrane distillation membrane module can be determined by the value shown in the following formula (1): |log10(A1 / A2)| ... (1) (in formula (1), | to | indicates an absolute value, and log10( to ) indicates a common logarithm), where A1 is the amount of hydrophobic polymer attached to the porous hollow fiber membrane in the center of the membrane bundle, and A2 is the amount of hydrophobic polymer attached to the porous hollow fiber membrane in the outermost layer of the membrane bundle, in the surface layers on both sides of the porous hollow fiber membranes constituting the membrane bundle.

[0039] From the viewpoint of achieving both high liquid penetration pressure and high vapor permeability, as estimated from the above reasons, if the value of the above formula (1) is 0.75 or less in each surface layer on both sides of the porous hollow fiber membranes constituting the membrane bundle, it is possible to ensure vapor permeability while preventing liquid penetration into the pores. The value of the above formula (1) is preferably 0.50 or less, and particularly preferably 0.30 or less.

[0040] In this specification, "a porous hollow fiber membrane at the center of a membrane bundle" refers to a hollow fiber membrane located in the center of a cross section obtained by cutting the membrane bundle from the side. More specifically, when the radius of the entire membrane bundle is taken as 100%, it refers to any one hollow fiber membrane contained within a range equivalent to 20% from the center. In this specification, "a porous hollow fiber membrane in the outermost layer of a membrane bundle" refers to any one hollow fiber membrane located at the outermost periphery of a cross section obtained by cutting the membrane bundle from the side. Furthermore, "cutting the membrane bundle from the side" refers to cutting in a direction perpendicular to the longitudinal direction of the membrane bundle.

[0041] Alternatively, the constituent material of the porous hollow fiber membrane can be identified using an appropriate bulk analysis device, followed by analysis of the porous hollow fiber membrane with the hydrophobic polymer attached using an appropriate surface analysis device. The amount of hydrophobic polymer attached can be determined from the signal intensity ratio between the constituent material of the porous hollow fiber membrane and the hydrophobic polymer. Since a surface analysis device can analyze any portion of the porous hollow fiber membrane, the distribution of hydrophobic polymer attachment can be determined by comparing the signal intensity ratios for each portion of the membrane. Examples of bulk analysis devices in this case include IR (infrared spectroscopy) devices, transmission Raman spectroscopy devices, and NMR (nuclear magnetic resonance) devices. Examples of surface analysis devices in this case include IR (infrared spectroscopy) devices, XPS (X-ray photoelectron spectroscopy) devices, and TOF-SIMS (time-of-flight secondary ion spectroscopy) devices.

[0042] [Method for Adhering a Hydrophobic Polymer to a Porous Hollow Fiber Membrane and Method for Manufacturing a Membrane Module for Membrane Distillation] A hydrophobic polymer can be attached to a porous hollow fiber membrane by applying a coating solution in which the hydrophobic polymer is dissolved in a good solvent for the hydrophobic polymer to the membrane module and drying it. Therefore, the method for manufacturing a membrane distillation membrane module according to this embodiment may include, for example, a step of forming a porous hollow fiber membrane by a known method; a step of forming a membrane bundle from multiple porous hollow fiber membranes; a step of housing the membrane bundle in a housing (container); and a step of applying and drying the hydrophobic polymer. The order of these steps can be arbitrarily reversed. To obtain a desired hydrophobic polymer distribution, the coating location, the volatility (boiling point) of the solvent in the coating solution, the concentration of the hydrophobic polymer in the coating solution, and the drying conditions after coating can be appropriately adjusted.

[0043] To obtain a structure in which the amount of hydrophobic polymer attached to the surface layer of the porous hollow fiber membrane is greater than the amount of hydrophobic polymer attached inside the porous hollow fiber membrane, it is preferable to apply a solution of the hydrophobic polymer to a membrane distillation membrane module, a porous hollow fiber membrane, or a membrane bundle, and then blow air through the membrane distillation membrane module to dry the solvent, and then blow air on both sides of the porous hollow fiber membrane (in one embodiment, the outer surface of the porous hollow fiber membrane and the inner surface of the porous hollow fiber membrane) to dry the solvent. The total linear air speed on both sides is preferably 9 m / min or more and 100 m / min or less, more preferably 10 m / min or more and 100 m / min or less. If the total linear air speed on both sides is 9 m / min or more, the drying of the solvent occurs preferentially on the surface layer of the porous hollow fiber membrane, and the hydrophobic polymer accumulates on the surface layer, which is preferable. On the other hand, if the total linear airflow speed on both sides is 100 m / min or less, the coating liquid is not pushed into the hollow fiber membrane due to pressure loss, the solvent dries preferentially on the surface layer of the porous hollow fiber membrane, and the hydrophobic polymer accumulates on the surface layer, which is preferable. From this perspective, the total linear airflow speed on both sides is more preferably 10 m / min or more and 50 m / min or less, and particularly preferably 20 m / min or more and 50 m / min or less. The drying temperature is not particularly limited and can be appropriately set as needed from the viewpoint of preventing deterioration of the hollow fiber substrate and saving on equipment costs.

[0044] To obtain a structure in which the value of the above formula (1) is 0.75 or less, it is preferable that the linear air velocity toward the inner surface of the porous hollow fiber membrane is greater than the linear air velocity toward the outer surface. Specifically, for example, in the drying process of a hydrophobic polymer solution, it is preferable that the linear air velocity toward the inner surface of the porous hollow fiber membrane divided by the linear air velocity toward the outer surface of the porous hollow fiber membrane is 2 or more. The reason for this is unclear, but is presumed to be as follows.

[0045] The space on the inner surface side of the porous hollow fiber membrane in the membrane module is a space in which the hollow fibers are aligned in the longitudinal direction, and the blown air travels linearly. Therefore, if the airflow linear velocity toward the inner surface of the porous hollow fiber membrane is higher than that toward the outer surface, uniform drying is possible. In contrast, the outer surface side space has a complex shape as shown in Figure 1, and linear speed distribution is likely to occur during airflow. Therefore, it is believed that when the airflow linear velocity toward the outer surface of the porous hollow fiber membrane is higher than that toward the inner surface, even if the total airflow linear velocity is sufficient, at 10 m / min or more, regions of low linear speed will exist due to the linear speed distribution, resulting in regions where the amount of hydrophobic polymer attached to the surface layer is reduced.

[0046] To obtain a structure in which the value of the above formula (1) is 0.50 or less, it is preferable that the value obtained by dividing the linear air velocity toward the inner surface of the porous hollow fiber membrane by the linear air velocity toward the outer surface of the porous hollow fiber membrane is 5 or more.

[0047] To obtain a porous hollow fiber membrane with a desired hydrophobic polymer attachment amount, the concentration of the hydrophobic polymer solution can be appropriately adjusted. Furthermore, if the viscosity of the solution increases at the desired hydrophobic polymer concentration, which deteriorates the handleability during application, the desired hydrophobic polymer attachment amount can be obtained by applying the hydrophobic polymer to the porous hollow fiber membrane multiple times or by applying the hydrophobic polymer to the porous hollow fiber membrane at a stage prior to the formation of the membrane module for membrane distillation.

[0048] [Feedstock liquid concentration system and membrane distillation] The membrane distillation according to this embodiment can be performed by a feedstock liquid concentration system equipped with a membrane distillation membrane module according to this embodiment. The feedstock liquid concentration system uses a membrane distillation method in which a feedstock liquid containing a solvent and a solute is contacted with absorption water AW via a membrane distillation membrane, and the solvent in the feedstock liquid passes through the membrane distillation membrane in a vapor state and moves to the absorption water AW side. The feedstock liquid concentration system according to this embodiment will be described below with reference to Figures 1 and 2.

[0049] To concentrate a raw material liquid by membrane distillation, the raw material liquid is passed through one side of a membrane distillation membrane (in Figure 1, the hollow space of the hollow fiber membrane for membrane distillation), and absorption water AW, which is at a lower temperature than the raw material liquid, is passed through the other side (in Figure 1, the external space side of the hollow fiber membrane for membrane distillation). The pores communicating with both spaces inside the membrane wall come into contact with the raw material liquid and absorption water AW through the membrane wall. As a result, the vapor generated from the raw material liquid, which has a high vapor pressure, passes through the membrane wall and moves to the absorption water AW, which has a low vapor pressure, where it is cooled and liquefied, thereby concentrating the raw material liquid.

[0050] FIG. 2 shows an example of a feedstock liquid concentration system according to this embodiment. In the concentration system of FIG. 2, a means (piping system) for circulating the feedstock solution a is provided at both axial ends of the membrane distillation membrane module (MD Membrane) 100 shown in FIG. 1. The piping system for circulating the feedstock solution a includes a feedstock solution storage tank 200, a pump P for circulating the feedstock solution, and a temperature controller TC for maintaining the temperature of the feedstock solution at a set temperature. This concentration system may, as necessary, be equipped with a flow meter FM for indicating the circulation flow rate, a flow rate regulator (not shown) for adjusting the circulation flow rate, and a pressure gauge PG for displaying the liquid pressure when supplying the feedstock solution to the membrane distillation membrane module. In addition, by providing a weight scale, a liquid level gauge LG, etc. in the feedstock solution storage tank, the membrane performance and concentration rate can be estimated based on the degree of decrease in the liquid level, weight, etc.

[0051] Meanwhile, a means (piping system) for circulating the absorption water AW is provided in the housing side pipe of the membrane distillation membrane module. This piping system is equipped with an absorption water storage tank 300, a pump P for circulating the absorption water AW, a flow meter FM indicating the circulation flow rate, a flow rate regulator (not shown) for adjusting the circulation flow rate, and a temperature regulator TC for maintaining the temperature of the absorption water AW at a set temperature. The volume of the absorption water AW increases over time as the solvent moves from the raw material solution to the AW during membrane distillation. Therefore, the storage volume of the absorption water storage tank 300 increases as membrane distillation continues. If the absorption water AW can be disposed of at this time, an overflow port can be installed in the absorption water storage tank to maintain a constant storage volume of the absorption water AW.

[0052] In a raw material liquid concentration system for manufacturing pharmaceuticals, chemicals, etc., the raw material liquid must be kept at a low temperature (for example, 50°C or below) in order to handle raw material liquids containing substances that can be decomposed by heating, such as peptides and proteins. In addition, liquids with low surface tension, such as acetonitrile, methanol, ethanol, and isopropanol, are used as solvents for the raw material liquid.

[0053] For these reasons, membranes for membrane distillation are required to have strong hydrophobicity so that they do not get wet even with low surface tension liquids, and high vapor permeability so that solvent vapor can be efficiently extracted from the raw material liquid at room temperature. Therefore, the hollow fiber membrane for membrane distillation used in this embodiment is preferably strong hydrophobic, and more preferably has a water contact angle of 90° or more. Furthermore, from the viewpoint of ensuring high vapor permeability, it is preferable that the hollow fiber membrane for membrane distillation has high interconnectivity.

[0054] By performing membrane distillation of the liquid to be treated using the porous hollow fiber membranes according to this embodiment and a membrane distillation membrane module comprising a membrane bundle and a container, it is possible to perform water production / dehydration and concentration operations with high efficiency.

[0055] The configuration and effects of the present invention will be further described below with reference to examples, but the present invention is not limited to the following examples.

[0056] [Physical Properties of Porous Hollow Fiber Membrane] In the present examples, the physical properties of the porous hollow fiber membrane were determined by the various measurement methods described below.

[0057] [Outer diameter, inner diameter, and membrane thickness of hollow fiber membrane] The outer diameter and inner diameter of the hollow fiber membrane distillation membrane were determined by microscopic observation. Specifically, the hollow fiber membrane was thinly sliced ​​in a direction perpendicular to the longitudinal direction with a razor or the like, a microscopic image of the cross section was obtained, and the outer diameter and inner diameter of the cross section were measured and determined. The membrane thickness of the hollow fiber membrane was calculated using the following formula (2): membrane thickness [mm] = (outer diameter [mm] - inner diameter [mm]) ÷ 2 (2)

[0058] [Average pore diameter of porous hollow fiber membrane] The average pore diameter of the porous hollow fiber membrane was measured by the average pore diameter measurement method (also known as the half-dry method) described in ASTM: F316-86. For a hollow fiber membrane approximately 10 cm long, ethanol was used as the liquid, and the standard measurement conditions were 25°C and a pressure increase rate of 0.01 atm / sec. The average pore diameter was calculated using the following formula (3): Average pore diameter [μm] = 2,860 × (s [mN / m]) / (p [Pa]) (3) (In the above formula, s is the surface tension of the liquid used, and p is the half-dry air pressure.) Here, the surface tension s of the liquid used, ethanol, at 25°C is 21.97 mN / m, so 2,860 × s = 62,834 is used, and equation (3) is transformed to the following equation (4), and the value of the half-dry air pressure p is substituted into equation (4) to determine the average pore diameter of the hollow fiber membrane. Average pore diameter [μm] = 62,834 / (p [Pa]) ... (4)

[0059] [Maximum pore diameter of hollow fiber membrane] The maximum pore diameter of the porous hollow fiber membrane was measured by the bubble point method using ethanol as the immersion liquid. One end of an 8 cm long hollow fiber membrane was blocked, and a nitrogen gas supply line was connected to the other end via a pressure gauge. Nitrogen gas was supplied in this state to replace the inside of the line with nitrogen, and then the hollow fiber membrane was immersed in ethanol. At this time, the hollow fiber membrane was immersed in ethanol under a very slight nitrogen pressure to prevent ethanol from flowing back into the line. With the hollow fiber membrane immersed in ethanol, the nitrogen gas pressure was gradually increased until the pressure P (kg / cm) at which nitrogen gas bubbles began to stably emerge from the hollow fiber membrane was measured. ２ ) was recorded. The maximum pore diameter d of the hollow fiber membrane was calculated by substituting this P into the following equation (5): d = C1γ / P (5) {where d is the maximum pore diameter of the hollow fiber, C1 is a constant, γ is the surface tension of the immersion liquid, and P is the pressure.} In this case, the maximum pore diameter d (μm) was calculated by setting the value of C1γ when ethanol was used as the immersion liquid to 0.632 (kg / cm).

[0060] [Porosity of hollow fiber membrane] The porosity of the porous hollow fiber membrane was calculated from the mass of the hollow fiber membrane and the density (true density) of the material constituting the hollow fiber membrane. That is, the hollow fiber membrane was cut to a certain length, the mass was measured, and the following formula (6): The porosity of the hollow fiber membrane was calculated using the following formula: {In the above formula, d is the true density of the raw polymer of the hollow fiber membrane, and π is the constant of the circumference of the circumference.}

[0061] [Hydrophobic Polymer Surface Adhesion Amount] IR and ATR Methods Comparison of the hydrophobic polymer adhesion amount on the porous hollow fiber membrane surface was performed using IR spectrum analysis and ATR (total reflection, internal reflection) methods, using a diamond crystal as a prism. The measurement device used was a PerkinElmer Spectrum 2, and the crystal pressing pressure was measured with a pressure contour value of approximately 12. The amount of hydrophobic polymer attached to the membrane surface was calculated by calculating the ratio of the peak intensity derived from the hydrophobic polymer to the peak intensity derived from the hollow fiber membrane's constituent material from the obtained IR spectrum. The hollow fiber membrane sample was cut out from the module and cut open in the longitudinal direction. In the examples, the hollow fiber membrane was made of polyvinylidene fluoride resin (PVDF), and the hydrophobic polymer was an acrylate polymer having a perfluoroalkyl group in the side chain. Therefore, the peak intensity derived from the hydrophobic polymer was calculated as 1,734 cm. －１ ν(C=O), and a peak intensity of 1,180 cm due to the constituent material of the hollow fiber membrane －１ The peak intensity (ν(C-F) + ν(C-O)) near the hydrophobic polymer was obtained, and the value of ν(C=O) / (ν(C-F) + ν(C-O)) was calculated as the ratio of the peak intensity derived from the hydrophobic polymer to the peak intensity derived from the constituent material of the hollow fiber membrane, and this value was used as an index of the amount of hydrophobic polymer attached.

[0062] [Linear Drying Airflow Speed ​​of Hydrophobic Polymer] The linear drying airflow speed to the porous hollow fiber membrane was determined by the following method. A gas flow meter was connected to each of the inner and outer flow channel inlet / outlet nozzles of the hollow fiber membrane of the membrane distillation membrane module, and drying was performed at a desired flow rate. The linear drying speed on the inner side was calculated using the following formula (7): Therefore, the outer surface linear speed is calculated by the following formula (8): was calculated by

[0063] [Evaluation of Liquid Entry Pressure of Membrane Module] The liquid entry pressure, which indicates the level of wetting resistance of a membrane distillation membrane module, was measured using the apparatus shown in Figure 3. First, 500 mL of a 50% by mass aqueous ethanol solution was placed in a tank and pressurized to fill the inner surface of the hollow fibers of the membrane distillation membrane module with the aqueous ethanol solution. Next, the outer surface of the hollow fiber membrane of the membrane distillation membrane module was filled with the aqueous ethanol solution. Thereafter, the pressure applied to the tank was gradually increased until the water level on the outer surface of the hollow fiber membrane of the module rose (the aqueous solution passed through the membrane). The applied pressure when the water level on the outer surface of the hollow fiber membrane of the module began to rise was defined as the liquid entry pressure (LEP).

[0064] Example 1 (1) Preparation of porous hollow fiber membrane module A porous hollow fiber membrane made of PVDF and having an inner diameter of 0.7 mm, an outer diameter of 1.3 mm, an average pore size of 0.20 μm determined in accordance with ASTM-F316-86, a maximum pore size of 0.26 μm, and a porosity of 72% was immersed in a fluororesin-based water repellent agent "FS1610-TH" (polymer concentration: 1.00% by mass) manufactured by FluoroTechnologies, Inc., removed, drained, and air-dried at room temperature.

[0065] 800 of the above porous hollow fiber membranes were bundled together to form a membrane bundle, which was then placed in a container. A thermosetting epoxy resin was used as the adhesive resin, and the porous hollow fiber membrane bundle was adhered and fixed in the container by centrifugal adhesion to prepare a membrane module.

[0066] The interior of the prepared membrane module was completely filled with a fluororesin-based water repellent agent "FS1610-TH" (polymer concentration: 1.00% by mass) manufactured by FluoroTechnologies, and then excess water repellent agent was removed from the membrane module. The volume of air flowing through the membrane module was then controlled so that the linear speed on the inner surface of the porous hollow fiber membrane was 10.3 m / min and the linear speed on the outer surface was 2.2 m / min, and the membrane module was air-dried at room temperature. The air-dried membrane module was then left in a dryer at 90°C for 5 hours to completely dry out the solvent.

[0067] By the above operation, the module length was 50 cm and the membrane area was 0.72 m ２Four membrane distillation modules were fabricated. One of the four modules was disassembled, and |log10(A1 / A2)| was calculated. |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.72, and |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.23. The average LEP of the membrane module was 69.8 kPa.

[0068] (2) Implementation of Membrane Distillation As shown in FIG. 2, membrane distillation was performed using one membrane module (100) prepared. A solution of the following composition was used as a simulated liquid of the raw material solution (FS) containing pharmaceutical ingredients, etc. Solvent: 50% by mass ethanol aqueous solution Solute: 1,000 ppm dipeptide and 1,000 ppm NaCl Amount of solution: 50 L NaCl was added to the raw material solution (FS) as a means of checking if the membrane distillation membrane was wetting. The raw material solution (FS) was filled into the raw material solution storage tank (200). The raw material solution (FS) was circulated through the inside of the hollow fiber membrane of the membrane distillation membrane module (100) at a flow rate of 12 L / min using a pump (P). At this time, the temperature of the raw material solution (FS) was adjusted using a temperature controller (TC) so that it was maintained at 23 ° C. at the inlet side of the membrane distillation membrane module (100).

[0069] Meanwhile, an absorption water storage tank (300) holding approximately 50 L of absorption water (AW) was provided, and the water was flowed to the outside of the hollow fiber membrane of the membrane distillation membrane module (100) at a flow rate of 12 L / min using a pump (P). At this time, the temperature of the absorption water (AW) was adjusted using a temperature controller (TC) so that it was maintained at 23 ° C. In addition, the conductivity of the absorption water (AW) leaving the membrane distillation membrane module (100) was constantly measured. If the conductivity of the absorption water (AW) rose to 500 μS / cm or more, it was considered that NaCl added to the raw material solution (FS) had become mixed into the absorption water (AW). Therefore, in this case, it was determined that the membrane distillation membrane had become wet.

[0070] Every hour from the start of operation, 10 mL of the raw material liquid was withdrawn from the raw material liquid withdrawal port, and the refractive index was measured. When the ethanol concentration calculated from the refractive index became 30.0 mass percent or less, the concentration was stopped. Measurement every hour allows for an advantageous measurement of concentration changes.

[0071] In Example 1, the concentration progressed as shown in Figure 2, and it took 23 hours to concentrate the ethanol to a concentration of 30.0 mass percent or less. The conductivity of the absorbed water (AW) was always 5 μS / cm or less, and wetting of the membrane distillation membrane did not occur.

[0072] Example 2 (1) Preparation of Porous Hollow Fiber Membrane Module A membrane distillation membrane module was prepared in the same manner as in Example 1, except that a fluororesin-based water repellent agent "FS1610-TH73" (polymer concentration 0.70% by mass) manufactured by FluoroTechnologies Corporation was used as the hydrophobic polymer solution applied before and after adhesively fixing the porous hollow fiber membrane bundle in the container, and the linear speed during drying of the hydrophobic polymer solution applied to the membrane module after adhesive fixing was 24.1 m / min on the inner surface and 2.9 m / min on the outer surface. |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.45, and |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.02. The average LEP of the membrane module was 76.1 kPa.

[0073] (2) Implementation of membrane distillation Membrane distillation was carried out using the same raw material solution, absorption water, and operating conditions as in Example 1. The time required to concentrate the ethanol to a concentration of 30.0 mass percent or less was 22 hours. The conductivity of the absorption water (AW) was always 5 μS / cm or less, and wetting of the membrane distillation membrane did not occur.

[0074] Example 3 (1) Preparation of Porous Hollow Fiber Membrane Module A fluororesin-based water repellent agent "FS1610-TH73" (polymer concentration 0.85% by mass) manufactured by FluoroTechnologies was used as the hydrophobic polymer solution applied before and after adhesively fixing the porous hollow fiber membrane bundle in the container. A membrane distillation membrane module was prepared in the same manner as in Example 1, except that the linear speed during drying of the hydrophobic polymer solution applied to the membrane module after adhesive fixing was 31.0 m / min on the inner surface and 1.4 m / min on the outer surface. The |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.26, and the |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.23. The average LEP of the membrane module was 80.4 kPa.

[0075] (2) Implementation of membrane distillation Membrane distillation was carried out using the same raw material solution, absorption water, and operating conditions as in Example 1. The time required to concentrate the ethanol to a concentration of 30.0 mass percent or less was 21 hours. The conductivity of the absorption water (AW) was always 5 μS / cm or less, and wetting of the membrane distillation membrane did not occur.

[0076] Example 4 (1) Preparation of Porous Hollow Fiber Membrane Module A membrane distillation membrane module was prepared in the same manner as in Example 1, except that a fluororesin-based water repellent "FS1610-TH73" (polymer concentration 1.00% by mass) manufactured by FluoroTechnologies Corporation was used as the hydrophobic polymer solution applied before and after adhesively fixing the porous hollow fiber membrane bundle in the container, and the linear speed during drying of the hydrophobic polymer solution applied to the membrane module after adhesive fixing was 34.4 m / min on the inner surface and 0.7 m / min on the outer surface. |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.15, and |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.07. The average LEP of the membrane module was 83.4 kPa.

[0077] (2) Implementation of membrane distillation Membrane distillation was carried out using the same raw material solution, absorption water, and operating conditions as in Example 1. The time required to concentrate the ethanol to a concentration of 30.0 mass percent or less was 22 hours. The conductivity of the absorption water (AW) was always 5 μS / cm or less, and wetting of the membrane distillation membrane did not occur.

[0078] Comparative Example 1 (1) Preparation of Porous Hollow Fiber Membrane Module A membrane distillation membrane module was prepared in the same manner as in Example 1, except that a fluororesin-based water repellent agent "FS1610-TH73" (polymer concentration 0.85% by mass) manufactured by FluoroTechnologies was used as the hydrophobic polymer solution applied before and after adhesively fixing the porous hollow fiber membrane bundle in the container, and the linear speed during drying of the hydrophobic polymer solution applied to the membrane module after adhesive fixing was 3.4 m / min on the inner surface and 7.2 m / min on the outer surface. The |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.77, and that of the outer surface was 0.47. The average LEP of the membrane module was 68.6 kPa.

[0079] (2) Implementation of membrane distillation Membrane distillation was carried out using the same raw material solution, absorption water, and operating conditions as in Example 1. The time required to concentrate the ethanol to a concentration of 30.0 mass percent or less was 28 hours. The conductivity of the absorption water (AW) was always 5 μS / cm or less, and wetting of the membrane distillation membrane did not occur.

[0080] Comparative Example 2 (1) Preparation of Porous Hollow Fiber Membrane Module The hydrophobic polymer solution was not applied before the porous hollow fiber membrane bundle was adhered and fixed in the container. Instead, the hydrophobic polymer solution applied after the porous hollow fiber membrane bundle was adhered and fixed was a fluororesin-based water repellent agent "FS-392B" (polymer concentration 0.50% by mass) manufactured by FluoroTechnologies. Furthermore, the linear speed during drying of the hydrophobic polymer solution applied to the membrane module after the porous hollow fiber membrane bundle was adhered and fixed was 10.3 m / min on the inner surface and 0 m / min on the outer surface. A membrane distillation membrane module was prepared in the same manner as in Example 1. The |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.82, and the |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.54. The average LEP of the membrane module was 50.0 kPa.

[0081] (2) Implementation of Membrane Distillation Membrane distillation was carried out using the same raw material liquid, absorption water, and operating conditions as in Example 1. One hour after the start of operation, the conductivity of the absorption water (AW) exceeded 500 μS / cm, and wetting of the membrane occurred.

[0082] Comparative Example 3 (1) Preparation of Porous Hollow Fiber Membrane Module Before adhesively fixing the porous hollow fiber membrane bundle in the container, no hydrophobic polymer solution was applied. Instead, the hydrophobic polymer solution applied after adhesively fixing the porous hollow fiber membrane bundle was a fluororesin-based water repellent "DP02H" (polymer concentration 2.00% by mass) manufactured by AGC Seimi Chemical Co., Ltd. The linear speed during drying of the hydrophobic polymer solution applied to the membrane module after adhesively fixing the porous hollow fiber membrane bundle was 120 m / min on the inner side and 120 m / min on the outer side. A membrane distillation membrane module was prepared in the same manner as in Example 1. The |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.84, and the |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.57. The average LEP of the membrane module was 76.2 kPa.

[0083] (2) Implementation of membrane distillation Membrane distillation was carried out using the same raw material solution, absorption water, and operating conditions as in Example 1. The time required to concentrate the ethanol to a concentration of 30.0 mass percent or less was 28 hours. The conductivity of the absorption water (AW) was always 5 μS / cm or less, and wetting of the membrane distillation membrane did not occur.

[0084] Comparative Example 4 (1) Preparation of Porous Hollow Fiber Membrane Module The hydrophobic polymer solution was not applied before the porous hollow fiber membrane bundle was adhered and fixed in the container. Instead, the hydrophobic polymer solution applied after the porous hollow fiber membrane bundle was adhered and fixed was a fluororesin-based water repellent "FS1610-TH" (polymer concentration 1.00% by mass) manufactured by FluoroTechnologies. Furthermore, the linear speed during drying of the hydrophobic polymer solution applied to the membrane module after the porous hollow fiber membrane bundle was adhered and fixed was 10.3 m / min on the inner surface and 0 m / min on the outer surface. A membrane distillation membrane module was prepared in the same manner as in Example 1. The |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.78, and the |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.42. The average LEP of the membrane module was 56.6 kPa.

[0085] (2) Implementation of Membrane Distillation Membrane distillation was carried out using the same raw material liquid, absorption water, and operating conditions as in Example 1. Two hours after the start of operation, the conductivity of the absorption water (AW) exceeded 500 μS / cm, and wetting of the membrane occurred.

[0086] Comparative Example 5 (1) Preparation of Porous Hollow Fiber Membrane Module A membrane distillation membrane module was prepared in the same manner as in Example 1, except that the hydrophobic polymer solution applied to the porous hollow fiber membrane bundle before adhesively fixing it in the container was a fluororesin-based water repellent "FS1610-TH" (polymer concentration 1.00% by mass) manufactured by FluoroTechnologies, Inc., the hydrophobic polymer solution was not applied to the membrane module after adhesively fixing the porous hollow fiber membrane bundle, and air drying was not performed. The |log10(A1 / A2)| of the inner surface of the porous hollow fiber membrane was 0.49, and the |log10(A1 / A2)| of the outer surface of the porous hollow fiber membrane was 0.80. The average LEP of the membrane module was 52.3 kPa.

[0087] (2) Implementation of Membrane Distillation Membrane distillation was carried out using the same raw material liquid, absorption water, and operating conditions as in Example 1. One hour after the start of operation, the conductivity of the absorption water (AW) exceeded 500 μS / cm, and wetting of the membrane occurred.

[0088] The preparation conditions, measurement results, and evaluation results for each example are shown in Table 1 below.

[0089]

[0090] The abbreviations in Table 1 have the following meanings: <Hydrophobic polymers> FS1610-TH: Fluoropolymer water repellent "FS1610-TH" manufactured by Fluorotechnology Co., Ltd. FS1610-TH73: Fluoropolymer water repellent "FS1610-TH73" manufactured by Fluorotechnology Co., Ltd. DP02H: Fluoropolymer water repellent "DP02H" manufactured by AGC Seimi Chemical Co., Ltd. FS392B: Fluoropolymer water repellent "FS-392B" manufactured by Fluorotechnology Co., Ltd.

[0091] REFERENCE SIGNS LIST 10 Housing (container) 11 First housing side pipe 12 Second housing side pipe 20 Hollow fiber membrane for membrane distillation 30 Adhesive resin a Raw material liquid b Raw material liquid after removal of organic solvent 100 Membrane module for membrane distillation 200 Raw material liquid storage tank 300 Absorption water storage tank AW Absorption water FM Flow meter LG Liquid level gauge P Pump PG Pressure gauge TC Temperature controller

Claims

1. A membrane module for membrane distillation comprising a hydrophobic porous hollow fiber membrane bundle and a container for accommodating the hydrophobic porous hollow fiber membrane bundle, wherein the container comprises a main body, a liquid to be treated inlet section having a flow path for introducing the liquid to be treated, a water to be treated outlet section having a flow path for extracting the water to be treated, an absorbing liquid inlet section having a flow path for introducing the absorbing liquid, and an absorbing liquid outlet section having a flow path for extracting the absorbing liquid, wherein the hydrophobic porous hollow fiber membrane bundle is a membrane bundle formed by bundling a plurality of porous hollow fiber membranes, each having one end and the other end, end-to-end and end-to-end, wherein a hydrophobic polymer is adhered to at least a portion of the porous hollow fiber membranes, and wherein, on each surface layer on both sides of the porous hollow fiber membranes, when the amount of the hydrophobic polymer adhered to the porous hollow fiber membrane at the center of the membrane bundle is A1 and the amount of the hydrophobic polymer adhered to the porous hollow fiber membrane in the outermost layer of the membrane bundle is A2, the following formula (1) can be expressed: |log10(A1 / A2)| {where | to | indicates an absolute value, and log10( to ) indicates a common logarithm}, wherein each of the values ​​shown in is 0.75 or less.

2. The membrane distillation membrane module according to claim 1, wherein the amount of the hydrophobic polymer attached has a distribution in the thickness direction of the porous hollow fiber membrane, and the amount of the hydrophobic polymer attached on the surface layer of at least one side of the porous hollow fiber membrane of the membrane distillation membrane module is greater than the amount of the hydrophobic polymer attached inside.

3. The membrane distillation membrane module according to claim 1 or 2, wherein the hydrophobic polymer contains fluorine atoms.

4. The hydrophobic polymer has CF in the side chain. ３ -(CF ２ )m-(CH ２ ) ２ The membrane module for membrane distillation according to claim 3, comprising a structure represented by the molecular formula: {wherein m is an integer of 3 or more and 7 or less}.

5. The membrane distillation membrane module according to claim 1 or 2, wherein the porous hollow fiber membrane contains, as a raw material, at least one polymer selected from the group consisting of polyvinylidene fluoride, polyethylene, polyolefin, polysulfone, and polyacrylamide.

6. The membrane distillation membrane module according to claim 1 or 2, wherein the total length of the membrane distillation membrane module is 40 cm or more.

7. A method for manufacturing a membrane distillation membrane module according to claim 1 or 2, comprising a step of applying and drying the hydrophobic polymer, wherein after applying a solution of the hydrophobic polymer to the membrane distillation membrane module, air is blown through the membrane distillation membrane module to dry the solvent, and air is blown over both sides of the porous hollow fiber membrane to dry the solvent.

8. A method for producing a membrane distillation module according to claim 7, comprising a drying step of the hydrophobic polymer solution, wherein the linear airflow speed on the inner surface of the porous hollow fiber membrane divided by the linear airflow speed on the outer surface of the porous hollow fiber membrane is 2 or more.

9. A method for producing a membrane distillation membrane module according to claim 8, comprising a drying step of the hydrophobic polymer solution, and wherein the total linear airflow speed of the porous hollow fiber membrane is 9 m / min or more and 100 m / min or less.

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