JP7840786B2 - Membrane module - Google Patents

Description

This invention relates to a membrane module that is also suitably used for processing high-temperature fluids.

In technologies for separating or filtering specific components from fluids, membrane modules using various membranes tailored to the target components, such as reverse osmosis membranes, ultrafiltration membranes, microfiltration membranes, and gas separation membranes, have been put into practical use.

In particular, hollow fiber membrane modules are widely used because they allow for a high surface area per unit volume and enable compact construction of the module-equipped device. The basic structure of a hollow fiber membrane module consists of a bundle of numerous hollow fiber membranes, a housing that contains the bundle, and a fixing section that secures the bundle and housing with a resin-based potting material (or adhesive) while leaving the end faces of the hollow fiber membranes open. In separation operations using a hollow fiber membrane module, pressure is applied from one side of the module to supply fluid to the hollow fiber membranes, selectively allowing a predetermined component of the fluid to permeate through the membrane to the other side, thereby concentrating the impermeable component of the fluid.

In recent years, from an energy-saving perspective, a method of membrane separation using high-temperature fluids that directly supplies the fluid to the membrane module without cooling or other operations has attracted attention. This method reduces the energy required for reheating the fluid, achieving significant energy savings in membrane separation. Examples of applications requiring separation using high-temperature fluids include ultrapure water production processes and manufacturing processes in the pharmaceutical or food sectors. Generally, the upper temperature limit of the fluids used in such membrane separation is often around 80°C. In addition, the operating pressure of the membrane module is usually in the range of 100 kPa to 200 kPa, but can sometimes reach nearly 300 kPa. Therefore, a membrane module capable of withstanding a maximum differential pressure of 300 kPa is required.

To provide membrane modules with the heat resistance necessary to directly supply such high-temperature fluids, not only components such as membrane bundles (e.g., hollow fiber membrane bundles) and housings must possess heat resistance, but also the potting material forming the fixed section must itself. In particular, the potting material forming the fixed section is used to isolate the raw fluid side from the filtrate side. Therefore, when using high-temperature fluids, the potting material is constantly subjected to high temperatures and pressure during the operation of the membrane module, and thus requires excellent heat resistance.

Conventionally, in membrane modules used at such high temperatures, epoxy resin has often been used as the potting material to fix the membrane, due to its high elastic modulus and excellent heat resistance. Furthermore, in recent years, efforts have been made to improve the heat resistance performance when other candidate materials, such as urethane resin and unsaturated esters, are used as potting materials.

As examples of membrane modules with heat-resistant potting materials, Patent Document 1 describes a filtration membrane module in which one or both ends of a hollow fiber membrane are fixed with urethane resin (corresponding to the potting material), with a specified blending ratio of urethane resin raw materials and the hardness (durometer hardness) of the resin in a temperature range of 10°C to 80°C. Furthermore, Patent Document 2 describes a hollow fiber membrane module that prevents strength reduction and thermal deformation of the membrane, housing, etc., due to the heat generated during curing of the adhesive, by specifying the glass transition temperature of the adhesive within a specific range and selecting the Vicat softening temperature (VST) of the hollow fiber membrane to satisfy a predetermined formula. Additionally, Patent Document 3 describes a hollow fiber membrane module that can withstand multiple thermal loads by setting the glass transition temperature of the sealing material (corresponding to the potting material) to a temperature lower than the lower limit of the test temperature range in a leak durability test against thermal loads.

Patent No. 4780738 Patent No. 6543693 Japanese Patent Publication No. 2017-29885

However, it is assumed that using such conventional performance indicators for potting materials does not accurately evaluate the durability of membrane modules during long-term operation in temperature ranges including high temperatures.

Specifically, indicators such as the elastic modulus of epoxy resins and other resins used as potting materials, and the hardness (durometer hardness) of the potting material (see Patent Document 1), which have been widely proposed to date, are indicators that focus solely on the storage modulus E', which evaluates the static durability of the cured potting material. Therefore, using only such indicators fails to predict the deformation of the fixed part made of potting material, and the resulting damage to the membrane module (e.g., delamination between the membrane and the fixed part), which are caused by stresses generated when the membrane module is operated for extended periods, especially at high temperatures.

Furthermore, even when using the glass transition temperature of a resin as an indicator, it is not possible to accurately evaluate the durability of the fixing part made of potting material in the temperature range below the glass transition temperature (see Patent Documents 2-3). In other words, the glass transition temperature is an indicator that shows the temperature range in which the motion state of molecules in the resin changes and the crystallinity changes; therefore, it does not accurately represent the resin properties in the temperature range below the glass transition temperature. For this reason, when using the glass transition temperature as an indicator, one method is to consider a temperature a certain temperature (e.g., 10-20°C) lower than the glass transition temperature as the practical operating temperature limit. However, it is difficult to say that such a method can accurately guarantee durability in the operating temperature range.

Therefore, a membrane module is required that takes into account deformation of fixed parts due to stress during long-term operation of the membrane module, and that can more reliably ensure durability in the practical operating temperature range, including high temperatures.

Therefore, the present invention aims to provide a membrane module that exhibits superior durability and reliability during long-term operation in a temperature range including high temperatures.

The inventors of this invention have conducted diligent studies to solve the above problems and have arrived at the present invention. That is, the present invention encompasses the following preferred embodiments.

The membrane module according to this aspect of the present invention is a membrane module in which at least one end of the membrane is fixed with a potting material, and the tanδ of the potting material, calculated from the formula: loss tangent tanδ = loss modulus E'' / storage modulus E'', is 0.3 or less in a temperature range of 80°C or below.

In the aforementioned membrane module, it is preferable that the tanδ of the potting material is 0.2 or less in the temperature range of 80°C or below.

In the aforementioned membrane module, it is more preferable that the tanδ of the potting material is 0.3 or less in the temperature range of 90°C or below.

In the aforementioned membrane module, a hollow fiber membrane module is even more preferable.

According to the present invention, it is possible to provide a membrane module with superior durability that can be reliably maintained during long-term operation in a temperature range including high temperatures.

Figure 1 is a schematic diagram showing an example of the configuration of a hollow fiber membrane module in an embodiment of the present invention. Figure 2 is a schematic diagram showing the apparatus used in the durability test in the example.

As a result of diligent research by the inventors, it was found that the durability of a membrane module during long-term operation in a temperature range including high temperatures, particularly its resistance to deformation of the fixed part, depends not only on the storage modulus E' of the potting material used in the fixed part, but also on the loss modulus E'' and the loss tangent tanδ (hereinafter simply referred to as "tanδ") calculated from these values. Specifically, by forming the fixed part using a potting material in which tanδ is below a predetermined value in a temperature range including high temperatures, the membrane module will have more reliably superior durability during long-term operation in that temperature range.

In this specification, "high temperature," "high-temperature fluid," or "under high temperature conditions" generally refers to approximately 80°C, which is the upper limit temperature of a fluid when performing membrane separation, filtration, etc., in a membrane module.

The embodiments of the present invention will be described in detail below. However, the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without impairing the spirit of the invention.

(Membrane module configuration)
First, the membrane module in the embodiment of the present invention will be described.

The membrane module in this embodiment is a membrane module in which at least one end of the membrane, i.e., one end or both ends, is fixed with a potting material (specifically, a hardened potting material).

The type and shape of the membrane module are not particularly limited, as long as they are any membrane module known to those skilled in the art and having the above-described configuration. Examples include hollow fiber membrane modules, flat membrane modules, spiral membrane modules, and tubular membrane modules. Of these, hollow fiber membrane modules are preferred from the viewpoint of achieving a high membrane surface area per unit volume, i.e., enabling a compact device.

Below, an example of the configuration of a hollow fiber membrane module in an embodiment of the present invention will be briefly described with reference to the drawings.

Figure 1 is a schematic diagram showing an example of the configuration of a hollow fiber membrane module in an embodiment of the present invention. As shown in Figure 1, the hollow fiber membrane module 1 comprises a hollow fiber membrane bundle 3 in which a plurality of hollow fiber membranes 2 are bundled together, a fixing part 4 made of potting material that fixes the hollow fiber membrane bundle 3 at its upper end, a cylindrical housing 5 in which an internal space S1 is formed to house the hollow fiber membrane bundle 3, a water conduit 6 for introducing the raw liquid into the housing 5, and an aeration member 7 for dispersing the gas supplied into the housing 5.

The hollow fiber membrane module 1 in Figure 1 is an external pressure filtration type hollow fiber membrane module that supplies the raw liquid to the outer surface side of the hollow fiber membrane 2 and extracts the filtrate from the inner surface side. With the hollow fiber membrane module 1, high-temperature fluids up to approximately 80°C can be supplied directly as the raw liquid, and then the raw liquid is filtered.

The hollow fiber membrane bundle 3 is of the free-end type. That is, the upper ends of multiple hollow fiber membranes 2 are fixed by the fixing part 4 with open ends, while the lower ends of each hollow fiber membrane 2 are sealed without being fixed.

The fixing part 4 is made of a hardened potting material. The fixing part 4 liquid-tightly partitions the space within the housing 5 into an internal space S1 for the raw liquid and a space S2 for the filtrate, in order to allow the hollow fiber membrane 2 to function as a filtration membrane. The fixing part 4 can be molded to fix the hollow fiber membrane bundle 3 within the housing 5 by placing the hollow fiber membrane bundle 3 in the space within the housing 5, injecting a potting material (e.g., the main component of the resin and a hardening agent), and applying any method known to those skilled in the art, such as centrifugal bonding or static bonding. The physical properties of the potting material in this embodiment will be described in detail later.

The material of the hollow fiber membrane 2 is not particularly limited, and any material known to those skilled in the art may be used. For example, the material of the hollow fiber membrane 2 preferably contains polyethylene, polypropylene, polyacrylonitrile, polyvinylidene fluoride, etc. Of these, polyvinylidene fluoride is more preferably included from the viewpoint of excellent heat resistance and chemical resistance.

The number of hollow fiber membranes 2 bundled by the hollow fiber membrane bundle 3 is not particularly limited and can be adjusted as appropriate depending on the application.

A filtrate pipe 8 for extracting the filtrate is connected to the upper side of the housing 5, and this filtrate pipe 8 is provided with a filtrate outlet 9 and a filtrate-side gas inlet 10. A gas vent 11 for discharging gas from the internal space S1 to the outside of the system is provided on the side of the housing 5. A drain outlet 12 for discharging liquid from the internal space S1 to the outside of the system is provided near the lower side of the housing 5. A diffuser gas inlet 13 for supplying gas into the internal space S1 is provided near the center of the lower side of the housing 5.

The material of the housing 5 is not particularly limited and may be any material known to those skilled in the art. Examples include SUS, modified PPE, polyvinyl chloride, polysulfone, polycarbonate, polyolefin, and ABS resin.

The water conduit 6 penetrates the lower center of the housing 5, extends upwards, and its upper end is connected to the fixing part 4. A raw liquid inlet 14 is provided at the lower end of the water conduit 6 for supplying the raw liquid before filtration into the housing 5.

The aeration member 7 disperses the gas supplied into the housing 5 from the aeration gas inlet 13 so that it spreads radially across the hollow fiber membrane bundle 3. A water conduit 6 passes through the center of the aeration member 7.

The hollow fiber membrane module shown in Figure 1 above is merely one example of a membrane module in this embodiment. For example, the membrane module in this embodiment may be a hollow fiber membrane module with both ends fixed with potting material and having fixing parts at both ends.

Furthermore, the membrane module in this embodiment is not limited to an external pressure filtration type membrane module, but may be any type of filtration membrane module known to those skilled in the art. For example, depending on the conditions of the membrane separation process and/or the desired processing performance, it may be a membrane module of an external pressure total filtration type, an external pressure circulation filtration type, an internal pressure circulation filtration type, etc.

(Physical properties of potting material)
Next, the physical properties of the potting material in the embodiment of the present invention will be described.

In this embodiment, the loss tangent tanδ of the potting material is 0.3 or less in the temperature range of 80°C or below. The loss tangent tanδ can be calculated using the formula: Loss tangent tanδ = Loss modulus E'' / Storage modulus E''.

Based on the function of the potting material, which hardens to form a fixed portion, the potting material has a storage modulus E' > 0 and a loss modulus E'' > 0. Therefore, the loss tangent tanδ of the potting material is defined as 0 > 0. That is, in this specification, the lower limit of the loss tangent tanδ of the potting material at a given temperature or a given temperature range only needs to be greater than 0.

In this specification, the lower limit of the temperature range in which the tanδ value of the potting material is calculated is not particularly limited. This is because, in the temperature range below the glass transition point, the loss tangent tanδ tends to approach 0 as the temperature decreases. On the other hand, practically speaking, the temperature at which the fluid to be filtered freezes can be considered as the lower limit. Given that most fluids filtered by membrane modules are mainly composed of water, it is preferable that the temperature at which the tanδ value of the potting material is calculated is, for example, 0°C or higher.

By using a potting material with a tanδ of 0.3 or less in the temperature range below 80°C, the membrane module will exhibit superior durability even during long-term operation in temperature ranges including high temperatures (i.e., around 80°C), without deformation or other damage to the fixed parts made of the potting material.

Specifically, it was found that when operating a membrane module for a long period at a specific operating temperature (or fluid temperature), if the tanδ of the potting material used for the fixing part exceeds 0.3 at that specific operating temperature, damage to the membrane module may occur, such as deformation of the fixing part or delamination between the fixing part and the membrane. Therefore, for example, when operating a membrane module for a long period at a high temperature of around 80°C, if the tanδ of the potting material at 80°C exceeds 0.3, damage to the membrane module may occur.

In this specification, the loss tangent tanδ, loss modulus E'', and storage modulus E'' of the potting material at a predetermined temperature or temperature range are specifically the values measured using a solid dynamic viscoelasticity measuring device, which will be described in detail in later examples.

The tanδ of the potting material in the temperature range below 80°C is preferably 0.25 or less, and more preferably 0.2 or less. A smaller tanδ value in the temperature range including high temperatures makes the fixed portion less prone to deformation and reduces the likelihood of damage to the membrane module. Therefore, it is possible to obtain a membrane module with more reliable and superior long-term durability in the temperature range including high temperatures.

Furthermore, in this embodiment, the tanδ of the potting material in the membrane module is preferably 0.3 or less, more preferably 0.25 or less, and even more preferably 0.2 or less in the temperature range of 90°C or below. By having a tanδ of 0.3 or less or smaller in the temperature range including higher temperatures, the fixing portion is less likely to deform and the membrane module is less likely to be damaged, even at higher temperatures. Therefore, a membrane module with even more reliable and superior long-term durability can be obtained in the temperature range including higher temperatures.

Furthermore, the storage modulus E' of the potting material is preferably 1 × ^10⁸ N/ ^m² or higher, and more preferably 1 × ^10⁹ N/ ^m² or higher, in the temperature range of 80°C or below. By controlling the tanδ of the potting material in the temperature range of 80°C or below to within a range of 0.3 or less, and by setting the storage modulus E' within such a range, it is possible to obtain a membrane module that has superior durability even when operated for a long period of time, while ensuring the static durability of the fixed part made of potting material in a temperature range that includes high temperatures.

In this specification, "potting material" means an adhesive used to fix a film or film bundle to a component such as a housing, as is generally known to those skilled in the art, and refers to a resin that hardens to form a fixed part, or a resin composition containing a main component and a hardener. The potting material may also contain additives as needed.

The type of resin used in the potting material is not particularly limited, as long as the tanδ of the potting material in the temperature range of 80°C or below is 0.3 or less. Examples of such resins include thermosetting resins such as urethane resins, epoxy resins, and unsaturated polyester resins. Of these, it is preferable that the potting material contains one or more resins selected from urethane resins and epoxy resins, as these resins exhibit excellent heat resistance, water resistance, and durability against various chemicals such as acids, alkalis, and oxidizing agents used in cleaning the membrane module.

One example of such a potting material is the heat-resistant urethane resin described below.

The urethane resin used as a potting material consists, for example, of a main component containing an isocyanate component (I) and a curing agent containing an active hydrogen component (H). Furthermore, the urethane resin contains a polyfunctional polyether polyol and/or polyfunctional amine polyol (hereinafter referred to as "polyol (A)") as a constituent component.

When incorporating polyol (A) as a constituent component, polyol (A) itself may be included as the active hydrogen component (H). Alternatively, a compound produced using polyol (A) may be included as a component of the active hydrogen component (H) and/or the isocyanate component (I). From the viewpoint of system viscosity, it is preferable to include polyol (A) itself as the active hydrogen component (H).

The mass of polyol (A) relative to the total mass of the urethane resin is preferably 20% to 100% by mass, and more preferably 30% to 90% by mass.

From the viewpoint of heat resistance and viscosity, the hydroxyl value of polyol (A) is preferably 200 mg KOH/g to 900 mg KOH/g, and more preferably 300 mg KOH/g to 800 mg KOH/g.

Examples of isocyanate component (I) include polyisocyanates having two or more isocyanate groups in one molecule, isocyanate-terminated urethane prepolymers obtained by the reaction of such polyisocyanates with active hydrogen compounds (such as polyols) having two or more active hydrogens in one molecule, and mixtures thereof.

Examples of polyisocyanates having two or more isocyanate groups in one molecule include aliphatic polyisocyanates with 2 to 18 carbon atoms (excluding carbon atoms in the isocyanate groups; the same applies hereinafter), alicyclic polyisocyanates with 4 to 15 carbon atoms, aromatic polyisocyanates with 6 to 20 carbon atoms, aromatic aliphatic polyisocyanates with 8 to 15 carbon atoms, compounds obtained by modifying some or all of the isocyanate groups of these polyisocyanates with isocyanurates, burettes, allophanates, uretdiones, uretonimines, carbodiimides, oxazolidones, amides, or imides, and mixtures thereof.

From the viewpoint of having good reactivity, the polyisocyanate is preferably an aromatic polyisocyanate, a modified version thereof, or a mixture thereof. Specifically, 4,4'-, 2,4'-, or 2,2'-diphenylmethane diisocyanate, a modified version thereof, and mixtures thereof are more preferable.

Examples of active hydrogen compounds having two or more active hydrogens constituting the isocyanate-terminated urethane prepolymer include the aforementioned polyol (A) and/or other polyols excluding polyol (A) (hereinafter referred to as "polyol (B)"). Examples of polyol (B) include low molecular weight polyols, polyether polyols, natural oil-based polyols, natural oil-based polyol derivatives, polyester polyols, polyolefin polyols, amine polyols, etc. The hydroxyl value of polyol (B) is preferably 20 mg KOH/g to 1850 mg KOH/g.

Isocyanate-terminated urethane prepolymers are obtained by reacting polyisocyanate and polyol with an equivalent ratio of isocyanate groups to OH groups (NCO/OH) typically between 1.01/1 and 100/1.

Examples of the active hydrogen component (H) include the aforementioned polyol (A), polyol (B), polyamines, and polymer captans containing active hydrogen, active hydrogen-terminated urethane prepolymers obtained by the reaction of these with the aforementioned polyisocyanates, and mixtures of two or more of these.

In the reaction between the main component containing isocyanate component (I) and the curing agent containing active hydrogen component (H) in a urethane resin, the NCO/OH equivalent ratio is preferably 0.5/1 to 2/1, more preferably 0.7/1 to 1.5/1, and even more preferably 0.8/1 to 1.2/1, from the viewpoint of reducing unreacted materials.

The viscosity at 25°C of the main component containing the isocyanate component (I) and/or the curing agent containing the active hydrogen component (H) in the urethane resin is usually between 100 mPa·s and 100,000 mPa·s. Furthermore, from the viewpoint of curability and moldability, the viscosity is preferably between 200 mPa·s and 50,000 mPa·s, and more preferably between 500 mPa·s and 30,000 mPa·s.

Urethane resin may contain additives commonly used in polyurethane resins, such as urethane catalysts, foaming agents, flame retardants, fillers, hydrolysis inhibitors, antioxidants, UV absorbers, mold inhibitors, mold release agents, dehydrating agents, and foaming inhibitors.

In a urethane resin with excellent heat resistance as described above, the storage modulus E' and loss modulus E'' of the urethane resin in the temperature range of 80°C or below can be controlled to an appropriate ratio by appropriately selecting and adjusting the types of isocyanate component (I), active hydrogen component (H), and polyol (A) used as starting materials, their blending ratios, the NCO/OH equivalent ratio, and the viscosity of the resin. This allows for obtaining a urethane resin potting material with a tanδ of 0.3 or less in the temperature range of 80°C or below.

Furthermore, another example of a potting resin is the heat-resistant epoxy resin described below.

Epoxy resins used as potting materials are typically a combination of an epoxy resin as the main component and an amine-based curing agent or imidazole as the hardening agent.

The type of epoxy resin used as the main component is not particularly limited, but it is preferably a bisphenol-type epoxy resin, and more preferably a bisphenol F-type epoxy resin. The epoxy equivalent of the epoxy resin is not particularly limited, but is preferably, for example, 150 to 250. Furthermore, the epoxy resin used as the main component may be used in combination with any material known to those skilled in the art, such as monofunctional reactive diluents like butyl glycidyl ether, allyl glycidyl ether, or phenyl glycidyl ether, or polyfunctional reactive diluents like ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, or dipropylene glycol diglycidyl ether.

Amine-based curing agents can be aromatic amine-based curing agents, aliphatic amine-based curing agents, or combinations thereof.

Examples of aromatic amine curing agents include monocyclic aromatic diamines such as 2,4-diaminotoluene, p-phenylenediamine, m-phenylenediamine, p-xylylenediamine, m-xylylenediamine, and tetrachloro-p-xylylenediamine; diaminodiphenylmethanes such as 3,5-diamino-4-chlorobenzoate alkyl esters, 4,4'-diaminodiphenylmethane, 3,3'-dichloro-4,4'-diaminodiphenylmethane, and 3,3'-diethyl-4,4'-diaminodiphenylmethane; diaminodiphenyl sulfones such as 4,4'-diaminodiphenyl sulfone and 3,3'-dimethyl-4,4'-diaminodiphenyl sulfone; and 4,4'-diaminodiphenyl ether. Furthermore, modified aromatic amines obtained by modifying these may also be used. These aromatic amines may be used individually or in combination of two or more.

Examples of aliphatic amine-based curing agents include linear aliphatic diamines such as hexamethylenediamine, diethylenetriamine, triethylenetetramine, and diproprendiamine, and cyclic aliphatic diamines such as mensendiamine and isophoronediamine. These aliphatic amines may be used individually or in combination of two or more.

The mixing ratio of the epoxy resin as the main component to the amine-based curing agent is preferably such that the equivalent ratio of amino groups to epoxy groups is 0.3 to 1.1, and more preferably 0.5 to 1.1.

The epoxy resin used as a potting material may optionally contain organic solvents, such as aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, esters, ketones, ethers, or mixtures thereof.

The viscosity of the epoxy resin at 25°C is preferably, for example, 1000 mPa·s to 10000 mPa·s, and more preferably 2000 mPa·s to 8000 mPa·s.

In epoxy resins exhibiting excellent heat resistance as described above, the storage modulus E' and loss modulus E'' of the epoxy resin in the temperature range of 80°C or below can be controlled to an appropriate ratio by appropriately selecting and adjusting the type of epoxy resin and amine-based curing agent used as starting materials, their mixing ratio, the equivalent ratio of amino groups to epoxy groups, and the viscosity of the resin. This allows for the production of an epoxy resin potting material with a tanδ of 0.3 or less in the temperature range of 80°C or below.

In this embodiment, the membrane module is fixed at at least one end with a potting material possessing the physical properties described above. Therefore, even when operating the membrane module for extended periods in a temperature range including high temperatures, for example, when filtering a high-temperature fluid at 80°C for a long period, the hardened potting material does not deform, and consequently, the membrane module does not suffer damage. This ensures that the membrane module exhibits superior durability.

Such membrane modules are suitably used for applications involving the separation, concentration, or filtration of specific components from fluids, particularly high-temperature fluids. Specifically, the membrane module in this embodiment, particularly in the form of a hollow fiber membrane module, is suitably used in a wide range of manufacturing processes, such as ultrapure water production processes and pharmaceutical or food manufacturing processes, for the separation, concentration, or filtration of specific components from high-temperature fluids like boiler water.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

In this embodiment, hollow fiber membrane modules for testing (hereinafter also simply referred to as "test membrane modules") were fabricated using various types of potting materials, and durability tests were conducted.

First, the specific method for durability testing of the test membrane modules, as well as the measurement methods for the loss tangent tanδ and durometer hardness (hereinafter also referred to as "D hardness") of the potting materials used in each example and comparative example, will be described in detail.

[Durability testing of test membrane modules]
In the durability test, the long-term durability of the test membrane module was evaluated by repeatedly switching between pressurized and depressurized states at various test temperatures from 20°C to 90°C. Generally, even at high temperatures, membrane modules use 80°C as their upper temperature limit; therefore, the 90°C test was conducted solely as a reference test to ensure superior safety during high-temperature operation of the membrane module. Figure 2 schematically shows the apparatus used in the durability test. As shown in Figure 2, the durability test apparatus 15 consisted of a water tank 16, a pump 17 for supplying water from the water tank 16, a pressurized valve 18 installed between the pump 17 and the test membrane module 19, the test membrane module 19, an air vent valve 20 for releasing air from the test membrane module 19, a pressure relief valve 21 installed between the test membrane module 19 and the water tank 16, and a pressure adjustment valve 22 for adjusting the pressure applied to the test specimen.

The test temperatures were adjusted by controlling the fluid temperature in the water tank 16. In the pressurization process, the pressurizing valve 18 was opened and the pressure relief valve 21 was closed, pressurizing the test membrane module 19 with water pressurized by the pump. In the subsequent depressurization process, the pressurizing valve 18 was closed and the pressure relief valve 21 was opened, releasing the pressure on the test membrane module 19. One cycle consisted of one pressurization and one depressurization process, and durability was evaluated by repeating the pressurization and depressurization processes alternately. The pump 17 was also operating during both the pressurization and depressurization processes, and the pressure adjustment valve 21 was kept open. The water pressure during the test was set to 0.3 MPa in the pressurized state and 0 MPa in the depressurized state by appropriately adjusting the pressurizing valve 18, pressure relief valve 21, and pressure adjustment valve 22. After repeating 1000 cycles, the test membrane module 19 was inspected to check for any damage such as deformation or peeling around the fixed part and membrane. For evaluation purposes, "○" was used if no damage was observed, "△" if deformation was observed in the fixing part, and "×" if delamination occurred between the fixing part and the membrane.

[Measurement of loss tangent tanδ of potting material]
The loss tangent tanδ of the potting material at each test temperature was measured as follows. First, the potting material to be measured was formed into a thin plate with a thickness of approximately 1 mm, and test specimens were prepared by cutting the formed material into pieces measuring 30 mm in length and 5 mm in width. The prepared test specimens of the potting material were placed on a solid dynamic viscoelasticity analyzer (DVE-V4FT, manufactured by Rheology Co., Ltd.), and the loss tangent tanδ of the potting material at temperatures from 20°C to 90°C (loss tangent tanδ = loss modulus E'' / storage modulus E') was analyzed to determine the values at each temperature.

[Measurement of D hardness of potting material]
The hardness (D hardness) of the potting material at each test temperature was measured by the following method. First, the main component and hardener of the resin used as the potting material were degassed under reduced pressure at 20°C (1000 Pa x 2 hours). Next, the main component and hardener of each potting material, according to the mixing ratio described later, were mixed using a rotary stirrer at 300 rpm for 30 seconds. After that, this mixture was centrifuged and degassed at 1500 rpm for 60 seconds using a centrifuge, and then poured into a square container (50 mm x 50 mm x 10 mm (height)). The mixture in this container was cured in a constant temperature bath at 20°C for 72 hours to prepare the test specimen. After the test specimen was left to stand for 1 hour in a constant temperature bath adjusted to each test temperature, the D hardness (10-second value) was measured using a Shore D hardness tester ("Rubber Hardness Tester Type D" manufactured by Polymer Instruments Co., Ltd.).

Next, the preparation methods for the potting materials used in each example and comparative example, as well as the methods for fabricating the test membrane modules, will be described in detail.

(Method for preparing urethane resin potting material A)
Urethane resin potting material A was prepared as follows: First, 28 parts by mass of a 1:1 mixture of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MI") and 40 parts by mass of 4,4'-diphenylmethane diisocyanate (Tosoh Corporation, "Millionate MT") were added to 12 parts by weight of polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix GP-250"), and the mixture was reacted at 70°C for 3 hours. Next, 20 parts by mass of carbodiimide-modified 4,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MM103") was added to the reaction product and stirred for 30 minutes to prepare isocyanate component A (NCO content: 22.5%, viscosity (25°C): 5500 mPa·s). In addition, 64 parts by mass of polyfunctional polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix SP-750") and 36 parts by mass of natural oil-based polyol (Toyokuni Oil Co., Ltd., "ELA-DR") were added and stirred to prepare active hydrogen component A (hydroxyl value: 371 mg KOH/g, viscosity (25°C): 5200 mPa·s). The isocyanate component A and active hydrogen component A prepared in this way were combined in a mixing ratio of 56:44 to obtain urethane resin potting material A.

(Method for preparing urethane resin potting material B)
Urethane resin potting material B was prepared as follows. First, 30.2 parts by weight of polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix PP-1000") was added to 48.5 parts by mass of 4,4'-diphenylmethane diisocyanate (Tosoh Corporation, "Millionate MT"), and the mixture was reacted at 70°C for 3 hours. Next, 21.3 parts by mass of carbodiimide-modified 4,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MM103") was added to the reactant, and the mixture was stirred for 30 minutes to prepare isocyanate component B (NCO content: 18.1%, viscosity (25°C): 2700 mPa·s). In addition, 100 parts by mass of a polyfunctional polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix SP-750") was prepared as the active hydrogen component B (hydroxyl value: 477 mg KOH/g, viscosity (25°C): 34,000 mPa·s). The isocyanate component B and the active hydrogen component B prepared in this way were combined in a mixing ratio of 67:33 to obtain urethane resin potting material B.

(Method for preparing urethane resin potting material C)
The urethane resin potting material C was prepared as follows: 20.5 parts by weight of a natural oil-based polyol (manufactured by Toyokuni Oil Co., Ltd., "ELA-DR") and 5 parts by weight of a polyether polyol (manufactured by Sanyo Chemical Industries, Ltd., "Sannix GP-250") were added to 74.4 parts by weight of a 1:1 mixture of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate (manufactured by BASF INOAC Polyurethane Co., Ltd., "Luplanate MI"), and the mixture was reacted at 70°C for 3 hours to prepare isocyanate component C (NCO content: 18.0%, viscosity (25°C): 1900 mPa·s). In addition, 100 parts by mass of a polyfunctional polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix HS-209") was prepared as the active hydrogen component C (hydroxyl value: 450 mg KOH/g, viscosity (25°C): 6000 mPa·s). The isocyanate component C and the active hydrogen component C prepared in this way were combined in a mixing ratio of 63:37 to form the urethane resin potting material C.

(Method for preparing urethane resin potting material D)
The urethane resin potting material D was prepared as follows: First, 28 parts by mass of a 1:1 mixture of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MI") and 40 parts by mass of 4,4'-diphenylmethane diisocyanate (Tosoh Corporation, "Millionate MT") were added to 12 parts by weight of polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix GP-250"), and the mixture was reacted at 70°C for 3 hours. Next, 20 parts by mass of carbodiimide-modified 4,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MM103") was added to the reaction product and stirred for 30 minutes to prepare isocyanate component D (NCO content: 22.5%, viscosity (25°C): 5500 mPa·s). In addition, 54 parts by mass of polyfunctional polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix HS-209") and 46 parts by mass of natural oil-based polyol (Toyokuni Oil Co., Ltd., "ELA-DR") were added and stirred to prepare active hydrogen component D (hydroxyl value: 307 mgKOH/g, viscosity (25°C): 4200 mPa·s). The isocyanate component D and active hydrogen component D thus prepared were combined in a mixing ratio of 51:49 to obtain urethane resin potting material D.

(Method for preparing urethane resin potting material E)
The urethane resin potting material E was prepared as follows: First, 36.4 parts by weight of a natural oil-based polyol derivative ("HS2P-080" manufactured by Toyokuni Oil Co., Ltd.) was added to 30.6 parts by mass of 4,4'-diphenylmethane diisocyanate ("Millionate MT" manufactured by Tosoh Corporation), and the mixture was reacted at 70°C for 3 hours. Next, 10.3 parts by mass of a 1:1 mixture of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MI") and 22.7 parts by mass of carbodiimide-modified 4,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MM103") were added to the reaction product, and the mixture was stirred for 30 minutes to prepare isocyanate component E (NCO content: 18.1%, viscosity (25°C): 520 mPa·s). Furthermore, 55 parts by mass of polyfunctional polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix SP-750"), 23 parts by mass of polyether polyol (Sanyo Chemical Industries, Ltd., "Sannix GP-1000"), and 22 parts by mass of natural oil-based polyol (Toyokuni Oil Co., Ltd., "ELA-DR") were added and stirred to prepare active hydrogen component E (hydroxyl value: 336 mg KOH/g, viscosity (25°C): 3800 mPa·s). The isocyanate component E and active hydrogen component E prepared in this way were combined in a blending ratio of 59:41 to obtain urethane resin potting material E.

(Method for preparing urethane resin potting material F)
The urethane resin potting material F was prepared as follows: 17 parts by mass of isophorone diisocyanate (Evonik Japan Co., Ltd., "VESTANAT IPDI") was added to 53 parts by mass of polyether polyol (AGC Inc., "Exsenol 230") and reacted at 90°C for 3 hours. Then, 4 parts by mass of carbodiimide-modified 4,4'-diphenylmethane diisocyanate (BASF INOAC Polyurethane Co., Ltd., "Luplanate MM103") was added to the reactant to prepare isocyanate component F (NCO content: 8.7%, viscosity (25°C): 7000 mPa·s). Polytetramethylene oxydose-P-aminobenzoate (Kumiai Chemical Industry Co., Ltd., "Elasmer 250P") was used as the active hydrogen component F (amine value: 230 mg KOH/g, waxy solid). The isocyanate component F and the active hydrogen component F prepared in this manner were combined in a ratio of 64:30 to obtain a urethane resin potting material F.

(Method for preparing epoxy resin potting material A)
Epoxy resin potting material A was prepared as follows: As the main epoxy resin component, bisphenol F type epoxy resin (DIC Corporation, "EPICLON 830") was used. As the amine-based curing agent, an imidazole-based epoxy resin curing agent (DIC Corporation, "2E4MZ") was used. These main epoxy resin components and amine-based curing agents were combined in a mixing ratio of 100:2 to obtain epoxy resin potting material A.

(Method for preparing epoxy resin potting material B)
Epoxy resin potting material B was prepared as follows: As the main epoxy resin component, bisphenol A type epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., "ST-3000") was used. As the amine-based curing agent, a modified aliphatic polyamine (manufactured by Daito Sangyo Co., Ltd., "Daitoclar I-5682") was used. These main epoxy resin components and amine-based curing agents were combined in a mixing ratio of 100:23 to obtain epoxy resin potting material B.

(Example 1)
In Example 1, a hollow fiber membrane made of hydrophilically treated polyvinylidene fluoride resin was used, with an average pore size of 0.02 μm and an effective length of 1035 mm. The above-mentioned urethane resin potting material A was used as the potting material. 15,000 hollow fiber membranes were inserted into a module case with an inner diameter of 154 mm, and isocyanate component A and active hydrogen component A from the urethane resin potting material A, heated to 25°C, were injected and mixed in the aforementioned mixing ratio, centrifugal molding was performed, and then curing was carried out at 25°C for 24 hours. After curing, a one-end free type test membrane module with a membrane area of 42 ^m² was obtained. The thickness of the fixed part of the obtained test membrane module was 40 mm.

(Examples 2 to 7 and Comparative Example 1)
In Examples 2 to 7 and Comparative Example 1, test membrane modules were obtained in the same manner as in Example 1, except that, as shown in Table 1 below, one of the aforementioned urethane resin potting materials B to E, epoxy resin potting materials A to B, and urethane resin potting material F was used as the potting material.

The types and properties of the potting materials used in each example and comparative example, as well as the results of the durability tests of the test membrane modules in each example and comparative example, are summarized in Table 1 below. A "-" indicates that the test was not performed.

As shown in Table 1 above, the test membrane modules of Examples 1 to 6, using urethane resin potting materials A to E or epoxy resin potting material A, showed no damage in the entire temperature range of 20°C to 90°C. Furthermore, urethane resin potting materials A to C and epoxy resin potting material A exhibited a tanδ of 0.2 or less in the entire temperature range of 20°C to 90°C. Urethane resin potting materials D and E exhibited a tanδ of 0.2 or less in the entire temperature range of 20°C to 80°C, and a tanδ of 0.3 at 90°C.

Furthermore, as shown in Table 1 above, the test membrane module in Example 7 using epoxy resin potting material B showed no damage in the temperature range of 20°C to 80°C. However, in the reference test at 90°C, delamination occurred between the fixed part and the membrane. In the temperature range of 20°C to 80°C, where no deformation of the fixed part or damage to the membrane module was observed, the tanδ of epoxy resin potting material B was 0.2 or less. On the other hand, at the test temperature of 90°C, where deformation of the fixed part and damage to the membrane module were observed, the tanδ of epoxy resin potting material B exceeded 0.3.

As shown in Table 1 above, the test membrane module of Comparative Example 1, using urethane resin potting material F, showed no damage in the temperature range of 20°C to 60°C. However, deformation of the fixing part was observed in the 70°C test. In the 80°C test, delamination occurred between the fixing part and the membrane. In Comparative Example 1, since damage was already observed in the test membrane module in the 80°C durability test, the 90°C durability test was not performed. Furthermore, in the temperature range of 20°C to 60°C, where no deformation of the fixing part or damage to the membrane module was observed, the tanδ of urethane resin potting material F was 0.2 or less. On the other hand, at the test temperatures of 70°C and 80°C, where deformation of the fixing part and damage to the membrane module were observed, the tanδ of urethane resin potting material F exceeded 0.3.

[Consideration]
From the results of Examples 1 to 7 and Comparative Example 1, it was found that satisfying the condition that the tanδ of the potting material at the test temperature is 0.3 or less (preferably 0.2 or less) allows the membrane module to exhibit excellent durability even when operated at the test temperature for a long period of time. Therefore, when operating a membrane module for a long period of time in a temperature range including high temperatures (i.e., about 80°C), it is expected that by selecting a potting material that satisfies the condition that the tanδ in the temperature range below 80°C is 0.3 or less (preferably 0.2 or less) and forming the fixing part, the membrane module will exhibit excellent durability, and as a result, deformation of the fixing part and the resulting damage to the membrane module can be prevented.

Furthermore, it was found that using only the D hardness of the cured potting material as a performance indicator for the durability of the membrane module, as has been conventionally proposed (see, for example, Patent Document 1), does not necessarily allow for accurate durability evaluation. Specifically, as shown in Table 1 above, the D hardness of urethane resin potting material A in the 90°C test of Example 1 is lower than that of urethane resin potting material F in the 70°C test of Comparative Example 1. However, in the 90°C test of Example 1, the membrane module demonstrated sufficient durability.

The embodiments and examples disclosed herein should be understood in all respects to be illustrative and not restrictive. The scope of the present invention is defined by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended.

1 Hollow fiber membrane module 2 Hollow fiber membrane 3 Hollow fiber membrane bundle 4 Fixing part 5 Housing 6 Water conduit 7 Aeration member 8 Filtrate piping 9 Filtrate outlet 10 Filtrate side gas inlet 11 Gas vent 12 Drain outlet 13 Aeration gas inlet 14 Raw liquid inlet S1 Internal space S2 Filtrate side space 15 Durability test apparatus 16 Water tank 17 Pump 18 Pressure valve 19 Test membrane module 20 Air vent valve 21 Pressure relief valve 22 Pressure regulating valve

Claims (4)

A membrane module in which at least one end of the membrane is fixed with a potting material, wherein the tanδ of the potting material, calculated from the formula: loss tangent tanδ = loss modulus E'' / storage modulus E', is 0.3 or less in a temperature range of 80°C or less.
The storage modulus E' of the potting material is 1 × 10⁹ ^N /m² ^or more in the temperature range of 0°C to 80°C.
The potting material is a membrane module containing urethane resin. The film module according to claim 1, wherein the tanδ of the potting material is 0.2 or less in a temperature range of 80°C or less. The film module according to claim 1, wherein the tanδ of the potting material is 0.3 or less in a temperature range of 90°C or less. A membrane module according to any one of claims 1 to 3, which is a hollow fiber membrane module.