JP2016193427A - Hollow fiber membrane and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a module filled with a hollow fiber membrane excellent in permeability, usable in an outside pressure system, especially when being used in an anti-pressure osmosis method or in a forward osmosis method, and capable of suppressing inside solute residence.SOLUTION: A hollow fiber membrane module includes a housing, and a hollow fiber membrane filled in the housing, which is a membrane having the outer diameter of 15 μm or more and 290 μm or less, and having a hollow rate of 43% or more and 60% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hollow fiber membrane mainly for water treatment that has excellent permeation performance.

  In recent years, water treatment and gas purification using membranes have been put into practical use. In particular, separation by reverse osmosis is used for the purpose of removing ions that are solutes from water.

  Patent Document 1 describes a hollow reverse osmosis membrane having a semi-permeable layer that is a substantial separation active layer in the vicinity of the outer surface. That is, in Patent Document 1, the membrane includes a layer having substantially no separation activity and a separation active layer outside the layer.

  Further, as a separation method using a semipermeable membrane, forward osmosis and pressure osmosis have been studied. This is a separation method using the fact that two liquids having different concentrations are separated by a semipermeable membrane and water permeates from a low concentration side to a high concentration side due to a difference in osmotic pressure. Since these are performed at a lower pressure than reverse osmosis, fresh water may be obtained at low cost. Furthermore, a power generation method using forward osmosis has been studied.

  For example, in Patent Document 2, the concentrated seawater discharged as a by-product when seawater is desalinated by the reverse osmosis method is concentrated from the brine side by bringing it into contact with brine through a semipermeable membrane. It has been proposed to generate electricity using the phenomenon of water permeating into the seawater side.

  At present, reverse osmosis membranes are often used also in forward osmosis and pressure osmosis.

JP 2012-115835 A WO2012-002263

  In addition, when a conventional reverse osmosis membrane is used for the forward osmosis method or the pressure osmosis method, there is a problem that the amount of water permeation decreases while being used, and it cannot be used in a short period of time, which is not suitable for practical use. .

  An object of the present invention is to provide a separation membrane module that is excellent in water permeability and can be suitably used for the anti-pressure osmosis method or the forward osmosis method.

  In the anti-pressure osmosis method or the forward osmosis method, the present inventors supply a solution containing a solute on both the supply water side and the permeate side of the membrane because the cause of the decrease in the water permeability of the reverse osmosis membrane is In the membrane used conventionally, the solute stays on one side (support layer side), the salt concentration rises, and the osmotic pressure difference serving as a driving force for permeating the ion-blocking (semi-permeable) layer fluctuates. Because of that.

  Therefore, the present inventors examined a membrane structure that does not cause salt retention that causes fluctuations in the osmotic pressure difference and a method for producing the membrane structure, and has a hollow fiber shape, an outer diameter of 15 μm or more and 290 μm or less, and a hollow ratio of 43%. As described above, a module having a hollow fiber membrane was invented in which a solute does not stay in the membrane and a filtration operation can be performed in a practical period. The conventional reverse osmosis membrane module has a shape optimized for use in the reverse osmosis method, but in the reverse osmosis method, only the generated water that has passed through the semipermeable membrane is supplied to the support layer side. Therefore, there has been no invention in which the water permeability on the support layer side is small and the hollow portion of the hollow fiber membrane is improved. The present invention focuses on an excessive amount of water permeation on the support layer side (permeation side) of the filled separation membrane in order to embody a membrane module suitable for a new water production method such as a pressure osmosis method or a forward osmosis method. , Research is repeated.

  In the semipermeable membrane of the present invention, both the membrane area in contact with the supply water and the hollow portion through which the permeated water passes are high. A compatible separation membrane module is provided.

It is sectional drawing which shows the outline of a hollow fiber membrane module.

1. Separation Membrane Module A case for a module for a reverse osmosis membrane has a hole for supplying a mixed solution, a nozzle for passing purified water passing through the membrane, and a nozzle for passing concentrated drainage.

  In the case of the module for the anti-pressure osmosis method and the forward osmosis method, at least one nozzle that supplies the mixed solution to the outside of the hollow fiber membrane and one nozzle that discharges the mixed solution are provided so that crossflow filtration can be performed. At least one nozzle for supplying solutions having different concentrations to the hollow part of the hollow fiber membrane and one for discharging the solution from the hollow part are provided.

  A module for the anti-pressure osmosis method and the forward osmosis method is shown in FIG. The module includes a cylindrical case 3 having side nozzles 1 and 2 provided on the side surfaces, and a plurality of hollow fiber membranes 4 accommodated in the case. A plurality of hollow fiber membranes are bundled, and both ends 5 and 6 thereof are fixed in the case with polyurethane, epoxy resin or the like, and are connected to end face nozzles 7 and 8, respectively.

  In this embodiment, each of the side nozzles 1 and 2 can supply a fluid to the space between the outside of the hollow fiber membrane and the case 3, and can discharge the fluid in this space to the outside of the case 3. .

  Moreover, in this embodiment, the end surface nozzles 7 and 8 can each supply a fluid to the hollow part inside a hollow fiber membrane, and can discharge the fluid in this hollow part out of a case.

  In the module of this embodiment, when an aqueous solution is supplied from the nozzle 1 or 2, and an aqueous solution having a different solute concentration is supplied from the nozzle 7 or 8, water moves from an aqueous solution having a low solute concentration to an aqueous solution having a high solute concentration.

2. Hollow fiber membrane A hollow fiber membrane has an outer diameter of 15 μm or more and 290 μm or less and a hollow ratio of 43% or more and 60% or less. Here, the hollow fiber membrane is a filamentous membrane having a hollow.

2-1. Shape of hollow fiber membrane (1) Outer diameter It is important that the hollow fiber membrane filled in the module of the present invention has an outer diameter of 290 μm or less, more preferably 130 μm or less, and less than 80 μm. Is more preferable. If the outer diameter of the hollow fiber membrane is thin, the membrane area when the maximum amount of the membrane is filled in the module is increased, so that the permeation amount is increased.

    In order to spread the reverse osmosis method, anti-pressure osmosis method and forward osmosis method of low pressure operation, it is necessary to increase the water permeability compared to conventional membranes, but it is already difficult to increase the water permeability per unit area, and the membrane area Increasing the value is an important means for increasing the amount of transmission. The hollow fiber membrane filled in the module of the present invention has a thin outer diameter and a thick inner diameter by controlling the thickness ratio of a layer having a semipermeable layer (hereinafter referred to as a semipermeable layer) and a support layer. The diameter can be increased (increase in the hollow ratio).

  On the other hand, the larger the outer diameter of the hollow fiber membrane, the more the folding and breaking of the hollow fiber membrane can be suppressed. Therefore, it is important that the outer diameter of the hollow fiber membrane is 15 μm or more, and more preferably 45 μm or more. More preferably, it is 65 μm or more.

(2) Hollow rate It is important that the hollow fiber membrane filled in the module of the present invention has a hollow rate of 43% or more, more preferably 45% or more, and even more preferably 49% or more. . As described above, it is preferable that the hollow fiber membrane has a small outer diameter. However, if the outer diameter is reduced, the inner diameter is also reduced. Therefore, in the hollow fiber membrane used in the present invention, the amount of water coming out from the inside due to pressure loss, that is, Water permeability is reduced. In this case, the solute tends to stay in the hollow portion, which further promotes the reduction of the water permeability. Therefore, the hollow ratio needs to be increased in order to reduce the pressure loss of the water flowing through the hollow portion. However, in the conventional hollow fiber membrane production method, when the outer diameter is small, it is difficult to make the hollow ratio larger than 40%, and a suitable method for making the hollow ratio 43% or more will be described later. On the other hand, as an upper limit that the hollow fiber membrane is not crushed, it is important that the hollow ratio is 60% or less, more preferably less than 56%, and still more preferably less than 53%. The module of the present invention is suitable for use in applications where the differential pressure between the external pressure and the internal pressure generated in the filled hollow fiber membrane is small. Basically, priority is given to reducing the outer diameter, and as necessary within that range. It is better to design so as to increase the hollow ratio. Here, the hollow ratio was calculated by measuring the total area Sa of the radial cross section of the hollow fiber membrane and the area Sb of the hollow portion, and using the following equation.

Hollow ratio (%) = (Sb / Sa) × 100
(3) Thickness ratio between semipermeable layer and support layer The hollow fiber membrane filled in the module of the present invention is composed of a semipermeable layer and a support layer even if it is a uniform membrane composed only of a semipermeable layer. A composite film may be used.

  In the case of a composite membrane, the thickness ratio of the semipermeable layer and the support layer (support layer thickness / semipermeable layer thickness) is preferably 8 or less, more preferably less than 6, and less than 4. More preferably it is. Although the minimum of thickness ratio is not specifically limited, In order to acquire the strength reinforcement effect of a support layer, it is preferable that thickness ratio is 1 or more, for example, and it is more preferable that it is 2 or more.

  Here, the homogeneous membrane composed only of the semipermeable layer is one in which the entire membrane has a structure capable of blocking salt and allowing water to pass through. With such a structure, even if the structure such as pore size or shape differs depending on the position in the thickness direction of the film, it is included in the homogeneous film.

  A conventional hollow fiber membrane is formed into a layer having a semi-permeable property by forming a porous membrane by containing more than 40% by weight of an organic liquid at the time of production, and densifying only the membrane surface after the process. The support layer is thicker than necessary because it has an asymmetric structure in which a semipermeable layer is laminated on a porous support layer. (Thickness / thickness of semipermeable layer) is about 19, and is about 9 even if the ratio is low.

  In contrast, by producing a hollow fiber membrane by melt spinning, a homogeneous membrane can be obtained, and a membrane in which two different layers (a semipermeable layer and a support layer) are combined has an arbitrary thickness. Ratio. The structure of the two layers is not particularly limited, but is usually designed so that the membrane permeation flux of the support layer is higher than that of the semipermeable layer. Although these details will be described later, the performance of the membrane permeation flux can be designed according to the type and amount of the organic liquid added to the raw material at the time of manufacture, and since it has a higher extensional viscosity than that at the time of manufacture, it is homogeneous in the processing process. In addition, it is possible to achieve both the fineness of the outer shape and the high hollowness ratio.

  As a homogeneous membrane suitable for the reverse osmosis method, the pressure osmosis method, and the forward osmosis method of low pressure operation, the positron annihilation lifetime obtained by the positron annihilation lifetime measurement method is preferably 1.5 ns to 4 ns, and preferably 2 ns to 3 ns. More preferably, it is more preferably less than 2.5 ns and less than 2.5 ns. When the positron annihilation lifetime is 1.5 ns or more, there are vacancies capable of passing water, and when the positron annihilation lifetime is 4 ns or less, salt permeation can be easily prevented and the film has semi-permeability.

  Here, the positron annihilation lifetime measurement method is a method of measuring the time (in the order of several hundred picoseconds to several tens of nanoseconds) from when a positron is incident on a sample until it disappears. This is a technique for nondestructively evaluating information such as the size of holes of 1 to 10 nm, the number density, and the distribution of the sizes. Details of such a measurement method are described in, for example, “Fourth Edition Experimental Chemistry Course” Vol. 14, page 485, edited by The Chemical Society of Japan, Maruzen Co., Ltd. (1992). Specifically, it is a positron beam method using a positron beam emitted from an electron beam accelerator as a positron beam source, and this method is useful for evaluation of thin film vacancies. A more specific measuring method will be described in Examples.

(4) Inner Diameter The inner diameter of the hollow fiber membrane filled in the module of the present invention is preferably 10 μm or more, more preferably 20 μm or more, and more preferably 30 μm or more in order to reduce the pressure loss of water passing through the hollow portion. More preferably. On the other hand, in order to make it hard to crush, it is preferable that it is 200 micrometers or less, It is more preferable in it being less than 50 micrometers, It is further more preferable in it being less than 35 micrometers. As described above in the section of the hollowness ratio, it is preferable to basically prioritize the reduction of the outer diameter and to design the inner diameter (and the hollowness ratio) to be larger within that range.

(5) Membrane Thickness The hollow fiber membrane filled in the module of the present invention preferably has a thickness of less than 30 μm, more preferably 10 μm or less, and more preferably less than 5 μm in order to increase the water permeability. preferable. On the other hand, from the viewpoint of film strength, it is preferably 0.1 μm or more, more preferably 1 μm or more, and further preferably 2 μm or more. The module of the present invention can be preferably used for reverse osmosis with a low operating pressure, anti-pressure osmosis for supplying a solution to both inside and outside, and forward osmosis.

  The thickness is the distance from the outer surface to the inner surface of the membrane, and is the sum of the thicknesses when both the semipermeable layer and the support layer are provided.

(6) Roundness The hollow fiber membrane filled in the module of the present invention preferably has a higher roundness. The higher the roundness, the higher the pressure because it affects the pressure loss of the fluid passing through the hollow portion, preferably 0.85 or more, more preferably 0.98 or more, and even more preferably 0.99 or more.

(7) Tensile modulus The hollow fiber membrane filled in the module of the present invention preferably has a tensile modulus in the longitudinal direction (axial direction) of 500 to 7,500 MPa, and 1,000 to 6,500 MPa. It is more preferable that the pressure is 1,500 MPa to 5,000 MPa. When the tensile elastic modulus in the longitudinal direction is 500 MPa or more, and further 1,000 MPa or more, it can be used without breaking even if the hollowness is high. In addition, when the tensile modulus in the longitudinal direction is 7,500 MPa or less, flexibility suitable for incorporating the separation membrane into the membrane module is realized.

2. Composition of Hollow Fiber Membrane The hollow fiber membrane filled in the module of the present invention may contain a liquid such as water in order to maintain its shape. However, in the following description, these liquids for maintaining the shape are not considered as components of the hollow fiber membrane.

  There is no restriction | limiting in the composition which comprises the hollow fiber membrane with which the module of this invention is filled, As a compound used as a main component, compounds with high hydrophilicity, such as a cellulose and nylon, are preferable, and it is preferable that it is a cellulose ester. Furthermore, specific examples of cellulose ester include cellulose acetate, cellulose propionate, cellulose butyrate, and cellulose mixed ester in which three hydroxyl groups present in cellulose glucose unit are blocked with two or more acyl groups. Is mentioned.

  The preferable content is 60% by weight or more. As described above, when calculating this ratio, the weight of the liquid such as water is excluded from the weight of the hollow fiber membrane. The hollow fiber membrane preferably contains a cellulose ester in a proportion of 80% by weight or more, and more preferably is substantially composed only of the cellulose ester. When the content of the cellulose ester is 60% by weight or more, a high water permeability, a desalting rate, and a high durability can be achieved when used as a water treatment membrane. In the case of cellulose mixed ester, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate laurate, cellulose acetate oleate, cellulose acetate stearate and the like can be mentioned.

Each illustrated cellulose mixed ester has an acetyl group and another acyl group (propionyl group, butyryl group, lauryl group, oleyl group, stearyl group, etc.). The average degree of substitution between the acetyl group and other acyl groups in the cellulose mixed ester preferably satisfies the following formula.
1.0 ≦ (average degree of substitution of acetyl group + average degree of substitution of acyl group) ≦ 3.0
0.1 ≦ (Average degree of substitution of acetyl group) ≦ 2.6
0.1 ≦ (Average substitution degree of acyl group) ≦ 2.6
The average degree of substitution refers to the number of chemically bonded acyl groups among the three hydroxyl groups present per glucose unit of cellulose. When this equation is satisfied, the separation performance and permeation performance of the water treatment membrane are compatible, and the thermal fluidity during melt spinning is good, so that the hollow ratio can be easily increased during film formation.

  The hollow fiber membrane may contain at least one cellulose ester. That is, the hollow fiber membrane may contain only one type of compound as the cellulose ester, or may contain two or more types of cellulose ester.

  Moreover, it is preferable that a hollow fiber membrane contains a cellulose acetate propionate and / or a cellulose acetate butyrate among the compounds mentioned as a specific example as a cellulose ester. As a result, the fluidity during the film forming process is increased, and the hollowness is easily increased. The number average molecular weight (Mw) of the cellulose ester is preferably 50,000 to 255,000. When the number average molecular weight is 50,000 or more, thermal decomposition during melt spinning can be suppressed, and the membrane strength of the hollow fiber membrane can reach a practical level. When the number average molecular weight is 255,000 or less, it is possible to suppress the melt viscosity from becoming too high and perform stable melt spinning. Mw is more preferably 60,000 to 22 million, and further preferably 80,000 to 20 million.

  Containing other than cellulose ester includes hydrophilic polymer, hydrophobic polymer, plasticizer residue, organic lubricant, crystal nucleating agent, organic particles, inorganic particles, terminal blocker, chain extender, ultraviolet absorber, infrared absorber , Anti-coloring agent, matting agent, antibacterial agent, antistatic agent, deodorant, flame retardant, weathering agent, antistatic agent, antioxidant, ion exchange agent, antifoaming agent, coloring pigment, fluorescent whitening agent, Dyes etc. are mentioned and these can be included in the range which does not impair the effect of this invention.

3. Method for Producing Hollow Fiber Membrane A preferred embodiment as a method for producing the hollow fiber membrane described above will be described below. However, the hollow fiber membrane filled in the module of the present invention is not limited to the following manufacturing method.

The production method preferably includes three steps: a step of producing a resin composition (pellet), a step of producing a hollow fiber, and a step of producing a hollow fiber membrane. Even if a high draft is applied while injecting gas into the center pipe (described later) to form a hollow part, the injected gas does not pulsate in the hollow of the melt. Therefore, it is easy to achieve an outer diameter of 290 μm or less and a hollowness of 43% or more.
Below, the manufacturing method using a cellulose ester and an organic liquid as a main component of a hollow fiber membrane is demonstrated as a specific example.

(3-1) Manufacture of pellets First, pellets containing cellulose ester and an organic liquid are manufactured.

  Cellulose ester is charged into a twin-screw kneading extruder equipped with a vent. When mixing powdery additives, they may be mixed with cellulose ester and charged, using a method of mixing and charging in advance, or using multiple feeders each set with a discharge rate. Any method can be used such as a method of charging.

  Next, the cellulose ester is heated. The temperature is preferably (Tm + 5 ° C.) to (Tm + 50 ° C.), more preferably (Tm + 6 ° C.) to (Tm + 15 ° C.), and (Tm + 7 ° C.) to (Tm + 10), where Tm is the crystal melting temperature of the cellulose ester. Is more preferred. The DSC measurement conditions will be described in detail in Examples.

  Subsequently, an organic liquid is added from the vent and melt-kneaded until it is uniformly mixed, and then discharged into a gut shape and cut into pellets. As an organic liquid, an organic liquid generally refers to a compound having a number average molecular weight of less than 2000, which is called a plasticizer or a solvent, and plasticizes or dissolves a cellulose ester in a hollow fiber manufacturing process, and is hollow. It plays a role in affecting the water permeability and desalination performance of the thread membrane. A compound having a number average molecular weight of more than 2000 is not preferable because the plasticizing / dissolving effect cannot be obtained. When the cellulose ester is cellulose acetate propionate, a polyhydric alcohol compound, triacetin, formic acid, N-methylpyrrolidone (hereinafter referred to as NMP), dimethylacetamide (hereinafter referred to as DMAc), dimethylformamide (hereinafter referred to as DMF) ), Sulfolane, dimethyl sulfone, dimethyl sulfoxide, and the like, and mixtures thereof. Among them, polyhydric alcohol compounds are preferable, and the polyhydric alcohol is polyethylene glycol (hereinafter referred to as PEG), polypropylene glycol, polybutylene. Examples include polyalkylene glycols such as glycols and glycerin. Among these, polyalkylene glycol is more preferable, and PEG is more preferable. In the case of polyalkylene glycol, the number average molecular weight is preferably 100 or more, more preferably 300 or more, and further preferably 500 or more. As the number average molecular weight is higher, volatilization and elution during the production process can be suppressed, and deterioration can be suppressed. On the other hand, the number average molecular weight is preferably 1800 or less, more preferably less than 1600, and even more preferably less than 900. The lower the number average molecular weight, the higher the plasticizing effect, and the easier it is to mold. The mixing ratio of the organic liquid is preferably 40% by weight or less of the total raw material, more preferably less than 35% by weight, and further preferably less than 27% by weight. On the other hand, when the cellulose ester is cellulose triacetate, the polyhydric alcohol is a non-solvent that does not plasticize or dissolve.

  In conventional hollow fiber membrane production methods, a polymer and an organic liquid cause heat-induced phase separation or non-solvent-induced phase separation, resulting in the formation of a porous layer. When the organic liquid to be mixed is mixed at 40% by weight or less, a porous layer is not formed, and a homogeneous film having only a separation function layer capable of water permeation can be formed. Furthermore, a film in which a semipermeable layer and a support layer are laminated by a composite extrusion of a resin composition containing 40% by weight or less of an organic liquid and a resin composition containing 40% by weight or more can be formed.

  In addition, if the mixing ratio of the organic liquid is too large, it will not be homogeneous, so the gas in the hollow will pulsate at the point where the ratio of the polymer decreases when the draft ratio is increased by introducing gas into the hollow part in the film forming process. It becomes impossible to achieve a thin outer diameter and a high hollow ratio at which thread breakage occurs. In addition, the higher the mixing ratio of the organic liquid, the higher the water permeability of the hollow fiber membrane obtained by washing, and the desalination rate tends to be low, and the addition amount may be changed according to the required properties, Basically, it is preferable that the amount added is small in order to increase the desalting rate. On the other hand, if the amount of the organic liquid is too small, the yarn may be deteriorated due to insufficient plasticization in the production process. Therefore, the amount is preferably 5% by weight or more, more preferably 10% by weight or more. More preferably, it is at least wt%.

Moreover, it is preferable to contain a phosphorus antioxidant, and a pentaerythritol compound (hereinafter referred to as PEP) is particularly preferable. When a phosphorus-based antioxidant is contained, thermal decomposition during melt spinning is suppressed, and as a result, film strength can be improved and coloring of the film can be prevented. The content of the antioxidant is preferably 0.005 to 0.500% by weight with respect to the composition to be melt-spun. This antioxidant is also considered to be substantially eluted by water.
Moreover, when it is set as the laminated body of a semipermeable layer and a support layer, the pellet by the side of a support material layer is manufactured similarly. Examples of pellets on the support layer side include polyvinylpyrrolidone (hereinafter referred to as PVP), PVP-containing copolymers such as PVP / vinyl acetate copolymer and PVP / methyl methacrylate copolymer, polyvinyl alcohol, number average molecular weight Mixing 10,000 or more PEG or polyester compounds and eluting them after processing into hollow fibers increases the membrane permeation flow rate. These can be used alone or in combination. PVP has a relatively low molecular weight with a molecular weight of 20,000 or less that can be easily eluted even after cross-linking, since elution described later is difficult when thermal cross-linking occurs. Used. It is also preferable to use a copolymer such as vinyl pyrrolidone and vinyl acetate because thermal crosslinking is suppressed.

(3-2) Production of hollow fiber Next, the obtained pellet is made into a hollow fiber by a melt spinning method. Specifically, the pellets are fed into an extruder and heated while being melted, supplied to the spinning pack, discharged from the outer slit of the spinneret, and simultaneously injected with gas from the central pipe at the center of the spinneret.

  The melting and spinning temperature (spinning pack temperature) is preferably (Tm + 5 ° C.) to (Tm + 20 ° C.), where Tm is the crystal melting temperature in the temperature rise measurement of the pellet using a differential scanning calorimeter (DSC). , (Tm + 6 ° C.) to (Tm + 15 ° C.) are more preferable, and (Tm + 7 ° C.) to (Tm + 10 ° C.) are more preferable.

  As the spinneret, a tube-in-orifice type spinneret of a double pipe or a triple pipe or more can be preferably applied. Here, the spinneret of the double pipe includes a base in which a pipe is inserted into a base nozzle having a circular hole. In the case of a triple pipe, the pipe may be a two-layer pipe. Here, the outermost slit of the base is the outer layer slit, the innermost pipe is the center pipe, and in the case of a triple pipe, the middle slit is the middle slit. The intermediate slit is shorter than the central pipe and the discharge surface, and the pellet melts that have passed through the outer slit and the intermediate slit in the die are joined and stacked. The width of the outer layer slit and the intermediate slit can be arbitrarily set in consideration of the melt viscosity of the raw material to be used, but considering pressure loss, it is preferably 40 μm or more, more preferably 70 μm or more, and 120 μm or more. More preferably it is. On the other hand, considering the cooling efficiency after ejection, it is preferably 600 m or less, more preferably less than 450 μm, and even more preferably less than 150 μm.

  In addition, as a suitable method for reducing the thickness ratio of the semipermeable layer and the support layer to 8 or less, two types of resin compositions having different ratios of the polymer and the organic liquid are supplied to the outer slit and the intermediate slit, and the triple tube A method of confluence and compounding in the base is conceivable. At this time, the shape of the channel gap of the resin composition constituting each layer in the spinneret is appropriately changed according to the melt viscosity of the resin composition and the desired cross-sectional shape of the composite hollow fiber membrane to be produced. Further, the discharge amount of the resin composition constituting each layer from the die is appropriately changed depending on the desired cross-sectional shape of the composite hollow fiber membrane to be manufactured, for example, by the number of revolutions of the gear pump. By this method, compared with the conventional method of separating a single layer into a semipermeable layer and a support layer by phase separation, the thickness ratio can be controlled, and a thickness ratio of 8 or less can be easily achieved. While gas is supplied from the center pipe, molten pellets are pushed downward from the outer slit.

  The hollow fiber discharged from the spinneret is cooled and solidified with cooling air or a water bath. The temperature is preferably 5 to 25 ° C. The cooled hollow fiber is wound up by a winding device. The draft ratio that can be calculated by the winding speed / discharge speed is preferably 50 or more, more preferably 200 or more, and even more preferably 600 or more when cooled with cold air. On the other hand, the draft ratio is preferably 1000 or less, less than 8500, or less than 700. Since the conventional technology contains a large amount of water-soluble polyhydric alcohol and organic solvent, the gas in the hollow pulsates at the point where the ratio of the polymer is not uniform and the ratio of the polymer is reduced. Even if the ratio is high, it is about 10 and it is difficult to reduce the outer diameter to less than about 130 μm. Moreover, even if the orifice diameter and slit width of the die of the base are reduced in order to reduce the outer diameter, it is difficult to achieve both the increase in the outer diameter and the hollowness because of the occurrence of swaying when gas is injected. is there. On the other hand, by melting and discharging pellets with an organic liquid of 40% by weight or less, the melt viscosity is increased, and even if the draft ratio is increased by injecting gas, there is little fluctuation and the hollow portion is suppressed from becoming smaller. The outer shape can be made thinner. In addition, increasing the draft ratio also has the effect of improving productivity because the film forming speed increases. On the other hand, by setting the draft ratio to 1000 or less, the possibility of yarn breakage can be reduced.

(3-3) Stretching The manufacturing method may include a step of stretching the hollow fiber.

  The stretching method is not particularly limited. For example, the temperature is raised to a temperature at which stretching is performed by conveying the hollow fiber on a heating roll, and stretching is performed in one or more stages using a difference in peripheral speed between the heating rolls. I do. The preferable range of the temperature of the hollow fiber in the drawing step is 25 to 80 ° C, more preferably 25 to 70 ° C, and further preferably 25 to 60 ° C.

  The length of the hollow fiber after drawing relative to the length of the hollow fiber before drawing (after the final drawing in the case of multistage drawing) is referred to as “stretch ratio”. The draw ratio is preferably 1.05 to 1.50, more preferably 1.10 to 1.45, and even more preferably 1.15 to 1.40.

  Moreover, you may heat-process a hollow fiber as needed or during extending | stretching. The heat treatment temperature is preferably 80 to 140 ° C. By performing the heat treatment in this range, the molecular chain is fixed, so that deterioration with time due to thermal relaxation can be suppressed.

  In this step, preferably, the outer diameter is 15 μm or more and 290 μm or less, the hollow ratio is 43% or more, the cellulose ester is contained in a proportion of 60% by weight or more and 95% by weight or less, and the polyalkylene glycol is 5% by weight. A hollow fiber containing at a rate of 40% by weight or less is obtained.

(3-4) Elution of organic liquid The production method includes a step of eluting the organic liquid from the hollow fiber thus obtained. As a result, a hollow fiber membrane is obtained.

  When the organic liquid is a highly hydrophilic substance such as PEG, this step is performed simply by immersing in water and / or alcohol. Water is inexpensive and alcohol is preferable in that the surface of the membrane can be hydrophilized. Further, since the molecular interval changes when the membrane is dried, it is preferable to store the organic liquid in a state in which alcohol or water is contained after the organic liquid is eluted. Here, this step can also be performed after making the module. In the manufacturing process of the hollow fiber membrane so far, the content of the organic liquid is large, and it is difficult for the organic liquid to remain in the membrane, and it is replaced with alcohol and / or water simultaneously with the manufacturing. However, since the hollow fiber membrane of the present invention can be produced with a content of 40% by weight or less that allows the organic liquid to remain without replacement, it can be transported before the organic liquid is eluted and processed into a module. Can be handled easily.

5. Use of Module The module of the present invention can be recovered by, for example, pressurizing a liquid containing a solute and supplying it to the module, and selectively allowing a solvent (mainly fresh water) to permeate the semipermeable layer. Further, by supplying mixed liquids having different solute concentrations from both sides of the semipermeable layer, the solvent can be selectively permeated and collected using the concentration difference as a driving force. That is, the hollow fiber membrane in the module is used in a method for producing a concentrated fluid that selectively permeates a solvent by supplying a mixed fluid at different operating pressures and solute concentrations from one or both of the outside and inside thereof.

  When used for selective separation utilizing reverse osmosis, the higher the difference in operating pressure, the faster the permeation flow rate, so the differential pressure between the side that supplies the mixed liquid and the side that is selectively separated and recovered by the membrane is Generally, it is 5 MPa or more. However, in recent years, there has been a demand for a module that can be operated with a small differential pressure, such as operation with a small pump drive, and further a household water purifier, in order to reduce running costs. The module of the present invention can be preferably used for reverse osmosis, anti-pressure osmosis, and forward osmosis with a low operating pressure.

  When the module of the present invention is operated, the differential pressure applied to both surfaces of the membrane is preferably 0.1 MPa or more, more preferably 0.3 MPa or more, and further preferably 0.5 MPa or more. In general, the greater the operating pressure, the greater the membrane permeation flux and the desalination rate. On the other hand, it is preferably 3 MPa or less, more preferably less than 1.5 MPa, and even more preferably less than 0.8 MPa. When the operating pressure is increased and the hollow fiber membrane is crushed, the membrane permeation flux decreases.

  The module of the present invention can be preferably used particularly for pressure penetration and forward penetration. Since these are driven by solute concentration differences, it is necessary to supply solutions containing different solutes, such as seawater, on both the outside and inside of the membrane. Since the solute stays in the support layer made of, it can be used only for a short time and is not practical.

  The module of the present invention is suitable for applications in which the differential pressure applied to both sides of the membrane is lower than the conventional reverse osmosis method, and in this range, the collapse resistance of the membrane can be adequately handled by the diameter design, Depending on the operating pressure, the inner diameter may be 120 μm or less, less than 30 μm, or less than 18 μm. However, if it is used continuously at a high pressure, the membrane is crushed and the amount of water passing through the inner diameter side is reduced, so that it is not preferable to use it at a pressure higher than 3 MPa for a long time.

  When the module of the present invention is used for liquid desalination, the temperature of the supplied liquid is preferably 45 ° C. or less, more preferably less than 40 ° C. in order to achieve a high desalting rate. More preferably, it is less than 35 ° C. On the other hand, in order to obtain a high membrane permeation flux, the temperature of the feed water is preferably 5 ° C. or higher, more preferably 10 ° C. or higher.

  In addition, when the pH of the liquid to be supplied becomes high, scales such as magnesium may be generated in the case of high salt concentration supply water such as seawater, and there is a concern about deterioration of the membrane due to high pH operation. Operation in the sex region is preferred.

When the module of the present invention is used for removing a solute from a solution, a 500 ppm NaCl aqueous solution adjusted to a temperature of 25 ° C. and a pH of 6.5 is permeated from outside to inside of the membrane at an operating pressure of 0.75 MPa. The membrane permeation flux is preferably 1.5 L / m ² / day, more preferably 2.1 L / m ² / day, and even more preferably 5.5 L / m ² / day. The desalting rate is preferably 50% or more, preferably 90% or more, and more preferably 94% or more. Moreover, it can be said that this performance has a performance that can be suitably used not only for pressure difference driving but also for density difference driving.

  The module membrane of the present invention can be used for separating and removing gases and liquids, but can be used for producing beverages and industrial water, particularly by removing solutes in an aqueous solution. In particular, as described above, it can be preferably used in reverse osmosis, anti-pressure osmosis, and forward osmosis under conditions of a low operating pressure.

  The upper and lower limits of the numerical ranges described above can be arbitrarily combined.

  The present invention can also be expressed as follows.

  (1) A hollow fiber membrane module comprising a housing and a hollow fiber membrane filled in the housing, the outer diameter of which is 15 μm or more and 290 μm or less, and the hollow ratio is 43% or more and 60% or less.

(2) The hollow fiber membrane has a support layer and a semipermeable layer,
The hollow fiber membrane module according to (1), including a membrane having a ratio of the thickness of the semipermeable layer to the thickness of the support layer of 8 or less.

  (3) The hollow fiber membrane module according to (1) or (2), wherein the hollow fiber membrane has a positron annihilation lifetime of 1.5 ns to 4.0 ns.

(4) The roundness of the hollow fiber membrane is 0.85 or more,
The hollow fiber membrane module according to any one of (1) to (3).

  (5) The hollow fiber membrane module according to any one of (1) to (4), wherein a tensile elastic modulus of the hollow fiber membrane is 500 to 7,500 MPa.

(6) While including at least one nozzle capable of supplying fluid to the outside of the hollow fiber membrane and one nozzle capable of discharging,
The hollow fiber membrane module according to any one of (1) to (5), wherein the hollow fiber membrane module includes at least one nozzle capable of supplying a fluid to a hollow portion of the hollow fiber membrane and one nozzle capable of being discharged.

  (7) The hollow fiber membrane module according to any one of (1) to (6), wherein a main component of the hollow fiber membrane is a cellulose ester.

  (8) A fresh water generation method including a step of supplying an aqueous solution containing salt to the module according to any one of (1) to (7) at a pressure of 0.1 MPa to 3.0 MPa.

  (9) The fresh water generation method according to (8), including a step of preparing solutions having different concentrations and supplying the solutions to the outside and the inside of the hollow fiber membrane at a pressure of 0.1 MPa to 3.0 MPa.

(10) Prepare solutions having different concentrations from each other, and supply a solution having a high concentration inside the hollow fiber membrane and a solution having a low concentration outside, thereby allowing water to pass from the outside to the inside of the hollow fiber membrane. 8) or the fresh water generation method as described in (9).

(11) A resin composition preparation step of preparing a resin composition by kneading at least 60% by weight to 95% by weight cellulose ester and 5% by weight to 40% by weight polyalkylene glycol;
A step of taking out the resin composition from the outer slit with a base of a double pipe or more while injecting gas from the central pipe into the hollow part, and drawing with a draft ratio of 200 or more while cooling with cold air;
A process for producing a hollow fiber membrane having
A method for producing a hollow fiber membrane module, comprising a modularization step of modularizing the obtained hollow fiber.

(12) The double pipe or more base is a triple pipe base,
Production of a hollow fiber membrane module comprising the steps of laminating the resin composition of the outer slit and the intermediate slit inside the triple tube cap, and discharging the resin composition of the laminated outer / intermediate slit and the gas of the center pipe Method.

(13) The hollow fiber according to (11) or (12), wherein the manufacturing process of the hollow fiber membrane further includes an elution step of eluting polyalkylene glycol from the hollow fiber that has passed through the step of drawing at the draft ratio of 200 or more. A method for producing a membrane.

  (14) The outer diameter is 15 μm or more and 290 μm or less, the hollowness is 43% or more, the cellulose ester is contained in a proportion of 60% by weight to 95% by weight, and the polyalkylene glycol is 5% by weight or more and 40% by weight. A hollow fiber characterized by being contained in the following ratio.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited thereto.

[Measurement and evaluation method]
Hereinafter, the present invention will be described in more detail with reference to examples. In addition, each characteristic value in an Example is calculated | required with the following method. The present invention is not limited to these examples.

1. Measuring method (1) Average substitution degree of cellulose ester The calculation method of the average substitution degree of cellulose fatty acid ester in which acetyl group and acyl group are bonded to cellulose is as follows.

  0.9 g of cellulose ester dried at 80 ° C. for 8 hours was weighed, 35 ml of acetone and 15 ml of dimethyl sulfoxide were added and dissolved, and then 50 ml of acetone was further added. While stirring, 30 ml of 0.5N sodium hydroxide aqueous solution was added and saponified for 2 hours. After adding 50 ml of hot water and washing the side of the flask, it was titrated with 0.5N sulfuric acid using phenolphthalein as an indicator. Separately, a blank test was performed in the same manner as the sample. The supernatant of the solution after titration was diluted 100 times, and the composition of the organic acid was measured using an ion chromatograph. From the measurement result and the acid composition analysis result by ion chromatography, the substitution degree was calculated by the following formula.

TA = (B−A) × F / (1000 × W)
DSace = (162.14 × TA) / [{1− (Mwace− (16.00 + 1.01)) × TA} + {1− (Mwacy− (16.00 + 1.01)) × TA} × (Acy / Ace)]
DSacy = DSace × (Acy / Ace)
TA: Total organic acid amount (ml)
A: Sample titration (ml)
B: Blank test titration (ml)
F: titer of sulfuric acid W: sample weight (g)
DSace: average substitution degree of acetyl group DSacy: average substitution degree of acyl group Mwash: molecular weight of acetic acid Mwacy: molecular weight of other organic acids Acy / Ace: molar ratio of acetic acid (Ace) to other organic acids (Acy) 162 .14: Molecular weight of cellulose repeating unit 16.00: Atomic weight of oxygen 1.01: Atomic weight of hydrogen (2) Outer diameter of hollow fiber membrane (μm)
The hollow fiber membrane was vacuum dried at 25 ° C. for 8 hours.

  A sample was cut in a direction (radial direction) perpendicular to the long axis of the hollow fiber membrane. The cut cross section was photographed using an optical microscope so that the entire cross section of the film could be displayed at about 100 to 1000 times. Between the outer surfaces of the hollow fiber membranes, 10 straight lines crossing the membrane were arbitrarily drawn so as to pass through the center of the cross section. The distances between the outer surfaces of the membrane were measured for 10 straight lines and totaled, and divided by 10 to obtain the outer diameter.

(3) Roundness of inner diameter Using the above-mentioned sample in which the outer diameter of the hollow fiber membrane was measured, the sample was observed and photographed with an optical microscope. The longest major axis was measured and calculated using the following formula. A sample having a roundness of 0.85 or more was marked as ◯.
Roundness = total minor axis / total major axis (4) Hollow ratio of hollow fiber membrane (%)
Using the sample in which the outer diameter of the hollow fiber membrane was measured, the sample was observed and photographed with an optical microscope, the total area Sa of the cross section and the area Sb of the hollow part were measured, and calculated using the following formula. The hollow ratio was calculated using 10 hollow fibers, and the average was obtained.
Hollow ratio (%) = (Sb / Sa) × 100
(5) Hollow fiber crystallization exothermic peak Using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc., about 5 mg of a hollow fiber membrane sample that had been vacuum-dried at 25 ° C. for 8 hours was set in an aluminum pan. Based on the peak area of heat generated by crystallization observed when the temperature is raised from −50 ° C. to 350 ° C. at a rate of temperature increase of 20 ° C./minute and kept at 350 ° C. for 5 minutes, / G) was determined according to the method defined in JIS K 7121 (1987). When a plurality of exothermic peaks due to crystallization appeared, the total crystallization exotherm was calculated by summing up. The presence or absence of a crystallization exothermic peak was determined based on whether the crystal melting crystallization exotherm ΔHc was 3 J / g or more.

(6) Positron Annihilation Lifetime Measurement Method by Positron Beam Method Measurement was performed using the positron beam method. The hollow fiber membrane is dried at room temperature under reduced pressure, and wound around a sample table to obtain a test sample. A thin film positron annihilation lifetime measuring device equipped with a positron beam generator (this device is described in detail in Radiation Physics and Chemistry, 58, 603, Pergamon (2000), for example), beam intensity of 3 keV, room temperature Under vacuum, a test sample was measured at a total count of 5 million using a barium difluoride scintillation counter using a photomultiplier tube, and analyzed by POSITRONFIT to obtain an average lifetime τ of the third component.

(7) A sodium chloride aqueous solution adjusted to a permeation performance concentration of 500 ppm, a temperature of 25 ° C., and a pH of 6.5 was supplied to the outside of the hollow fiber membrane at an operating pressure of 0.75 MPa, and membrane filtration was performed. From the obtained permeated water amount and the sampling time, the membrane permeation flux was determined by the following formula.
Membrane permeation flux (L / m ² / day) = Amount of permeate per day / membrane area (8) Separation performance (desalting rate (%))
Membrane filtration was performed under the same conditions as the membrane permeation flux, and the salt concentration of the resulting permeated water was measured. From the salt concentration of the obtained permeated water and the salt concentration of the feed water, the desalting rate was determined based on the following formula. In addition, the salt concentration of permeated water was calculated | required from the measured value of the electrical conductivity using the Toa Denpa Kogyo Co., Ltd. electrical conductivity meter.
Desalination rate (%) = 100 × {1− (sodium chloride concentration in permeated water / sodium chloride concentration in feed water)}
In addition, in said (7) and (8), the small module was created as follows and the membrane filtration process was performed.

The hollow fibers were bundled and bent at the center and inserted into a polycarbonate pipe having holes on the side surfaces, and then a thermosetting resin was injected into the pipe end, cured and sealed. A small module for evaluation in which the opening surface of the hollow fiber membrane is obtained by cutting the thermosetting resin sealing the hollow fiber membrane in a cross-sectional direction perpendicular to the long axis, and the membrane area on the basis of the outer diameter is about 0.1 m ² Was made. The membrane was hydrophilized while the organic liquid and the average pore radius adjusting agent were eluted by immersing in a 10% by weight aqueous solution of isopropyl alcohol in a small modular hollow fiber for 1 hour.

2. Sample preparation (1) Synthesis of cellulose acetate propionate (CAP) To 100 parts by weight of synthetic cellulose (cotton linter), 240 parts by weight of acetic acid and 67 parts by weight of propionic acid were added and mixed at 50 ° C. for 30 minutes.

  After cooling the mixture to room temperature, 172 parts by weight of acetic anhydride and 168 parts by weight of propionic anhydride cooled in an ice bath are added as an esterifying agent, and 4 parts by weight of sulfuric acid is added as an esterification catalyst, followed by stirring for 150 minutes. Then, an esterification reaction was performed. In the esterification reaction, when it exceeded 40 ° C., it was cooled in a water bath.

  After the reaction, a mixed solution of 100 parts by weight of acetic acid and 33 parts by weight of water was added as a reaction terminator over 20 minutes to hydrolyze excess anhydride. Thereafter, 333 parts by weight of acetic acid and 100 parts by weight of water were added, and the mixture was heated and stirred at 80 ° C. for 1 hour.

  After completion of the reaction, an aqueous solution containing 6 parts by weight of sodium carbonate was added, the precipitated CAP was filtered off, washed with water, and dried at 60 ° C. for 4 hours. The average substitution degree of the acetyl group and propionyl group of the obtained CAP was 1.9 and 0.7, respectively, and the number average molecular weight was 178,000.

(2) Production of hollow fiber membrane (Example 1)
82 wt% of CAP obtained by the above procedure, 17.9 wt% of PEG having a number average molecular weight of 600 and 0.1 wt% of PEP as an antioxidant were melt-kneaded at 240 ° C in a twin screw extruder and homogenized. Pellets were obtained.

  The pellets were vacuum dried at 80 ° C. for 8 hours. Subsequently, the dried pellets were supplied to a twin screw extruder and melted at 230 ° C. The melt was introduced into a melt spinning pack with a spinning temperature of 240 ° C. The spinning pack has a double pipe cap with a discharge hole radius of 1 mm and a slit width of 0.1 mm. The melt is spun from the outer slit at a speed of 3 m / m, and from the center pipe. Nitrogen gas was discharged into the hollow portion of the melt. The distance L from the lower surface to the upper end of the cooling device (chimney) was adjusted to be 30 mm.

The melt guided to the cooling device was cooled by cooling air at 25 ° C. and a wind speed of 1.5 m / sec, and an oil agent was applied to converge. Then, the hollow fiber was obtained by winding with a winder at the speed of 1500 m / min.
After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

(Comparative Examples 1-4)
Using the pellets obtained in Example 1, Comparative Example 1 formed a film without injecting gas into the double tube die, and Comparative Examples 2 to 4 were a C-type die, a 3-slit die, and a 4-slit die, respectively. Was used to form a hollow fiber membrane with air around the slit. In all cases, the membrane had a low hollow ratio.

  After producing these modules with hollow fibers, the hollow fibers were washed with a 10 wt% aqueous solution of isopropyl alcohol to produce modules with hollow fiber membranes, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

(Comparative Example 5)
In order to increase the hollow ratio using a 4-slit die, it is cooled by cooling air at 15 ° C. and a wind speed of 3.5 m / second, and the hollow fiber is wound by winding with a winder at a winding speed of 40 m / min. Obtained. The outer diameter was 340 μm, the hollowness was 44%, and since the draft ratio could not be increased, the outer diameter was thick.

  After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

(Example 2)
66% by weight of CAP obtained by the above procedure, 33.9% by weight of PEG having a number average molecular weight of 600 and 0.1% by weight of PEP as an antioxidant were melt-kneaded at 230 ° C. in a twin-screw extruder and homogenized. Pellets were obtained.

  Using this pellet, a cellulose ester hollow fiber was obtained in the same manner as in Example 1 except that the spinning temperature was 230 ° C. and the winder winding speed was 1000 m / min. After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

Example 3
78% by weight of CAP obtained by the above procedure, 17.9% by weight of PEG having a number average molecular weight of 600, 4% by weight of PEG having a number average molecular weight of 8300, and 0.1% by weight of PEP as an antioxidant at 230 ° C. in a twin screw extruder. Melt-kneaded and homogenized pellets for melt spinning were obtained.

  Cellulose ester was produced in the same manner as in Example 1 except that a double pipe cap having a discharge hole radius of 2.3 mm, a slit width of 0.45 mm was used, and the spinning temperature was 230 ° C. A hollow fiber was obtained. After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

Example 4
74% by weight of CAP obtained by the above procedure, 17.9% by weight of PEG having a number average molecular weight of 600, 8% by weight of PEG having a number average molecular weight of 3400, and 0.1% by weight of PEP as an antioxidant at 230 ° C. in a twin screw extruder. Melt-kneaded and homogenized pellets for melt spinning were obtained.

  Using this pellet, a cellulose ester hollow fiber was obtained in the same manner as in Example 3 except that it was wound with a winder at a speed of 600 m / min. After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

(Example 5)
66% by weight of CAP obtained by the above procedure, 17.9% by weight of PEG having a number average molecular weight of 600, 18% by weight of PVP (K17 manufactured by BASF) and 0.1% by weight of PEP as an antioxidant were 230 ° C. in a twin screw extruder. And kneaded to obtain a homogenized pellet for melt spinning.

  Using this pellet, a cellulose ester hollow fiber was obtained in the same manner as in Example 3. After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

(Comparative Example 6)
56% by weight of CAP obtained by the above procedure, 43.9% by weight of PEG having a number average molecular weight of 600 and 0.1% by weight of PEP as an antioxidant were melt-kneaded at 220 ° C. in a twin-screw extruder and homogenized. Pellets were obtained.

  Using this pellet, an attempt was made to obtain a cellulose ester hollow fiber by the same method as in Example 4. However, the membrane was shaken by the injected gas because of its low melt viscosity, and could not be collected. Therefore, the injection of gas was stopped and the hollow fiber was collected. After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

(Example 6)
78% by weight of CAP obtained by the above procedure, 17.9% by weight of PEG having a number average molecular weight of 600, 4% by weight of PEG having a number average molecular weight of 8300, and 0.1% by weight of PEP as an antioxidant at 230 ° C. in a twin screw extruder. Melt-kneaded and homogenized pellets for melt spinning (A) were obtained. In the same procedure, 64 wt% CAP, 17.9 wt% PEG having a number average molecular weight of 600, 18 wt% PVP (BASF K17) and 0.1 wt% PEP as an antioxidant were melt kneaded at 230 ° C. in a twin screw extruder. Thus, a homogenized melt spinning pellet (B) was obtained.

  Each of the pellets (A) and (B) was vacuum-dried at 80 ° C. for 8 hours. The pellets (A) and (B) are supplied to separate twin screw extruders, and melted by adjusting the extrusion amount of the pellet (A) melt and the pellet (B) melt to 1: 3 with a gear pump. Introduced into spinning pack. The spin pack is provided with a triple tube cap that discharges with a radius of 2.3 mm and a slit width of 0.45 mm after the outer slit and the intermediate slit merge in the cap. After the pellet (A) melt and the pellet (B) melt passed through the intermediate slit, they were merged in the die and laminated. The laminated melt was spun and discharged at a speed of 3 m / m, and nitrogen gas was discharged from the center pipe into the hollow portion of the melt. Thereafter, a cellulose ester hollow fiber was obtained in the same manner as in Example 3. After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

(Example 7)
82% by weight of CAP obtained by the above procedure, 17.9% by weight of PEG having a number average molecular weight of 600, and 0.1% by weight of PEP as an antioxidant were melt-kneaded at 230 ° C. in a twin-screw extruder and homogenized. A spinning pellet (A) was obtained. In the same procedure, 78 wt% CAP, 17.9 wt% PEG having a number average molecular weight of 600, 4 wt% PEG having a number average molecular weight of 20000, and 0.1 wt% PEP as an antioxidant were melt kneaded at 230 ° C. in a twin screw extruder. A homogenized melt spinning pellet (B) was obtained.
Using these pellets (A) and (B), the extrusion rate of the gear pump was set to 1: 7, and the cellulose ester hollow fiber was formed in the same manner as in Example 6 except that it was wound with a winder at a speed of 600 m / min. Obtained. After producing a module comprising this hollow fiber, the hollow fiber was washed with a 10 wt% aqueous solution of isopropyl alcohol to produce a module comprising a hollow fiber membrane, and the membrane permeation flux and separation performance were evaluated. Moreover, it was confirmed that the organic liquid was completely eluted by the change in weight of the hollow fiber and the hollow fiber membrane.

1, 2: Side nozzle 3: Cylindrical case 4: Hollow fiber membrane 5, 6: Fixed part 7, 8: End face nozzle

  The present invention is a water treatment module excellent in separation performance and permeation performance. The module of the present invention can be preferably used for reverse osmosis membranes, anti-pressure osmosis membranes, forward osmosis membranes and the like having a low operating pressure.

Claims (14)

  A hollow fiber membrane module comprising a housing and a hollow fiber membrane filled in the housing, the outer diameter of which is 15 μm or more and 290 μm or less, and the hollow ratio is 43% or more and 60% or less. The hollow fiber membrane has a support layer and a semipermeable layer,
The hollow fiber membrane module of Claim 1 provided with the film | membrane whose ratio of the thickness of the said semipermeable layer and the thickness of the said support layer is 8 or less. The hollow fiber membrane module of Claim 1 or 2 whose positron annihilation lifetime of the said hollow fiber membrane is 1.5 ns or more and 4.0 ns or less. The roundness of the hollow fiber membrane is 0.85 or more,
The hollow fiber membrane module in any one of Claim 1 to 3. The hollow fiber membrane module according to any one of claims 1 to 4, wherein the hollow fiber membrane has a tensile elastic modulus of 500 to 7,500 MPa. While including at least one nozzle that can supply fluid to the outside of the hollow fiber membrane and one that can discharge,
The hollow fiber membrane module in any one of Claim 1 to 5 provided with the nozzle which can supply a fluid to the hollow part of the said hollow fiber membrane, and the nozzle which can be discharged | emitted 1 each.   The hollow fiber membrane module in any one of Claim 1 to 6 whose main component of the said hollow fiber membrane is a cellulose ester.   A fresh water generation method comprising a step of supplying an aqueous solution containing salt to a module according to any one of claims 1 to 7 at a pressure of 0.1 MPa to 3.0 MPa. The fresh water generation method according to claim 8, comprising preparing solutions having different concentrations from each other and supplying the solutions to the outside and the inside of the hollow fiber membrane at a pressure of 0.1 MPa to 3.0 MPa. A solution having different concentrations is prepared, and a solution having a high concentration is supplied to the inside of the hollow fiber membrane and a solution having a low concentration is supplied to the outside, thereby allowing water to pass from the outside to the inside of the hollow fiber membrane. The fresh water generation method as described in. A resin composition preparation step of preparing a resin composition by kneading at least 60% by weight to 95% by weight cellulose ester and 5% by weight to 40% by weight polyalkylene glycol;
A step of taking out the resin composition from the outer slit with a base of a double pipe or more while injecting gas from the central pipe into the hollow part, and drawing with a draft ratio of 200 or more while cooling with cold air;
A process for producing a hollow fiber membrane having
A method for producing a hollow fiber membrane module, comprising a modularization step of modularizing the obtained hollow fiber. The base of the double pipe or more is a triple pipe base,
Production of a hollow fiber membrane module comprising the steps of laminating the resin composition of the outer slit and the intermediate slit inside the triple tube cap, and discharging the resin composition of the laminated outer / intermediate slit and the gas of the center pipe Method. The method for producing a hollow fiber membrane according to claim 11 or 12, wherein the production process of the hollow fiber membrane further comprises an elution step of eluting polyalkylene glycol from the hollow fiber that has undergone the step of drawing at the draft ratio of 200 or more. The outer diameter is 15 μm or more and 290 μm or less, the hollow ratio is 43% or more, the cellulose ester is contained in a proportion of 60% by weight or more and 95% by weight or less, and the polyalkylene glycol is contained in a proportion of 5% by weight or more and 40% by weight or less. A hollow fiber characterized by comprising:

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