JP5138572B2 - Hollow fiber membrane manufacturing method and hollow fiber membrane drying apparatus - Google Patents

Description

  The present invention relates to a method for producing a hollow fiber membrane suitably used for a filtration membrane and the like, and a hollow fiber membrane drying apparatus suitably used for this production method.

  Concentrating and collecting useful components in the fields of food industry, medical field, electronics industry, etc., removal of unnecessary components, fresh water, etc. are composed of cellulose acetate, polyacrylonitrile, polysulfone, fluororesin, etc. Porous hollow fiber membranes produced by dry and wet spinning are frequently used for microfiltration membranes, ultrafiltration membranes, reverse osmosis filtration membranes and the like.

In the case of producing a hollow fiber membrane by wet or dry wet spinning, first, a membrane forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is prepared. Next, a hollow fiber membrane is formed by a coagulation step in which the membrane-forming stock solution is discharged in a ring shape and coagulated in the coagulation solution. In addition, the film-forming stock solution may be introduced into the coagulating liquid through a free running portion that is in contact with air (dry wet spinning method) or directly into the coagulating liquid (wet spinning method).
Since the hydrophilic polymer usually remains in a solution state in the porous part of such a hollow fiber membrane, the hydrophilic polymer is usually removed by washing or the like, and then the hollow fiber membrane is dried.

Here, in order to dry the hollow fiber membrane, for example, as described in paragraph 0049 of Patent Document 1, a hot air circulation type drying apparatus is often used. Specifically, hot air is blown to the outer peripheral side of the hollow fiber membrane by continuously running the hollow fiber membrane in a drying device in which hot air circulates in the drying device at a wind speed of about several meters per second. The method of drying is used.
JP-A-2005-220202

  However, in order to sufficiently dry the hollow fiber membrane using such a hot air circulation type drying device, the hollow fiber membrane is reciprocated several times by the drying device, and the staying time is set to about several minutes. Needed and took drying time. In addition, since such a drying apparatus is large, a large installation space is required and a large amount of hot air is required. Thus, with the conventional drying method, it was difficult to dry the hollow fiber membrane in a short time and at a low cost.

    The present invention has been made in view of the above circumstances, and a method for producing a hollow fiber membrane that can dry the hollow fiber membrane in a short time and at a low cost without requiring a large facility, and suitable for this production method. It is an object to provide a drying apparatus to be used.

The method for producing a hollow fiber membrane of the present invention comprises: a coagulation step for coagulating a membrane forming raw solution in a coagulation solution to form a hollow fiber membrane; and a method for producing a hollow fiber membrane having a drying step for drying the hollow fiber membrane. In the drying step, the drying gas is permeated from the outer peripheral side of the hollow fiber membrane to the inner peripheral side, introduced into the hollow portion, passed through the hollow portion, and then from the inner peripheral side to the outer peripheral side. It is transmitted to have a drying gas injection step of discharging said at drying gas injection process, with passing the hollow fiber membrane inside the drying cylinder member, which is formed on a side surface of the drying cylinder member supply and supplying the drying gas into the mouth.
The drying step preferably includes a preliminary drying step before the drying gas press-fitting step.
The preliminary drying process preferably includes one or more of a hot air drying process and a reduced pressure drying process.
The hollow fiber membrane drying apparatus according to the present invention has a drying cylinder connected to the supply port, and a drying cylinder member through which the hollow fiber membrane passes and the supply port to which a drying gas is supplied is formed on the side surface. And a supply means.
The clearance between the hollow fiber membrane and the drying cylinder member is preferably 0.4 mm to 1.6 mm.
The ratio of the length of the drying cylinder member to the clearance between the hollow fiber membrane and the drying cylinder member is preferably 2000: 1 to 1000: 1.
The supply pressure of the drying gas is preferably 0.1 to 0.3 MPa as the gauge pressure of the drying gas at the supply port of the drying cylinder member.

  According to the present invention, there is provided a method for producing a hollow fiber membrane capable of drying the hollow fiber membrane in a short time and at a low cost without requiring a large facility, and a drying apparatus suitably used for this production method. be able to.

  Hereinafter, regarding the present invention, a film-forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is coagulated in a coagulation liquid to form a hollow fiber membrane, and a hydrophilic polymer remaining in the formed hollow fiber membrane A method for producing a hollow fiber membrane having a hydrophilic polymer removing step for removing water and a drying step for drying the hollow fiber membrane from which the hydrophilic polymer has been removed will be described in detail as an embodiment.

[Coagulation process]
In the method for producing a hollow fiber membrane of the present embodiment, first, a membrane forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is prepared. Subsequently, the hollow fiber membrane is usually formed by a coagulation step in which the membrane-forming solution is discharged from a nozzle having an annular discharge port into the coagulation solution and coagulated in the coagulation solution.
The coagulation step may be performed by either a dry-wet spinning method in which the film-forming stock solution is introduced into the coagulating solution through an idle running portion in contact with air or a wet spinning method that is directly guided to the coagulating solution. The structure of the hollow fiber membrane produced here is not particularly limited. For example, the hollow fiber membrane may be provided with a porous base material or may have a multilayer structure and be durable against rubbing during handling. .
Examples of the porous substrate are not particularly limited, but include hollow knitted or braided strings made of various fibers, and various materials can be used alone or in combination. it can. Examples of the fiber used for the hollow knitted string and braid include synthetic fiber, semi-synthetic fiber, regenerated fiber, natural fiber, and the like, and the form of the fiber may be any of monofilament, multifilament, and spun yarn.

    The hydrophobic polymer is not particularly limited as long as it can form a hollow fiber membrane by a coagulation step, and can be used without particular limitation as long as it is such as polysulfone resin such as polysulfone or polyethersulfone, polyvinylidene fluoride, etc. And fluororesin, polyacrylonitrile, cellulose derivatives, polyamide, polyester, polymethacrylate, polyacrylate, and the like. Further, copolymers of these resins may be used, and those having a substituent introduced into a part of these resins and copolymers can also be used. Further, the same type of polymers having different molecular weights may be blended and used, or two or more different types of resins may be mixed and used. Among these, fluororesins, especially polyvinylidene fluoride and copolymers made of vinylidene fluoride and other monomers have excellent durability against oxidizing agents such as hypochlorous acid. Therefore, for example, in the case of producing a hollow fiber membrane that is treated with an oxidizing agent in the hydrophilic polymer removal step described later, it is preferable to select a fluororesin as the hydrophobic polymer.

The hydrophilic polymer is added to adjust the viscosity of the membrane-forming stock solution to a range suitable for the formation of the hollow fiber membrane and stabilize the membrane-forming state. Polyethylene glycol, polyvinyl pyrrolidone, etc. are preferable. used. Among these, polyvinylpyrrolidone and a copolymer obtained by copolymerizing other monomers with polyvinylpyrrolidone are preferable from the viewpoint of controlling the pore diameter of the hollow fiber membrane and the strength of the hollow fiber membrane.
Moreover, 2 or more types of resin can also be mixed and used for a hydrophilic polymer. For example, when a higher molecular weight hydrophilic polymer is used, a hollow fiber membrane having a good membrane structure tends to be formed. On the other hand, the low molecular weight hydrophilic polymer is suitable in that it is more easily removed from the hollow fiber membrane in the hydrophilic polymer removing step described later. Therefore, the same kind of hydrophilic polymers having different molecular weights may be appropriately blended depending on the purpose.

A film-forming stock solution can be prepared by mixing the above-described hydrophobic polymer and hydrophilic polymer in a solvent in which they are soluble (good solvent). Other additive components may be added to the film-forming stock solution as necessary.
There is no particular limitation on the type of solvent, but when performing the coagulation process by dry and wet spinning, the pore diameter of the hollow fiber membrane is adjusted by absorbing the membrane forming stock solution in the idle running section, so that it is mixed uniformly with water. It is preferable to select a solvent that can be easily treated. Examples of such a solvent include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, N-methylmorpholine-N-oxide, and the like. Can be used. Moreover, you may mix and use the poor solvent of a hydrophobic polymer or a hydrophilic polymer in the range which does not impair the solubility of the hydrophobic polymer or hydrophilic polymer to a solvent. The temperature of the film-forming stock solution is not particularly limited, but is usually 20 to 40 ° C.

If the concentration of the hydrophobic polymer in the membrane forming stock solution is too thin or too thick, the stability at the time of membrane formation tends to be reduced, and it is difficult to form a suitable hollow fiber membrane structure. % By mass is preferable, and 15% by mass is more preferable. Further, the upper limit is preferably 30% by mass, and more preferably 25% by mass.
On the other hand, the lower limit of the concentration of the hydrophilic polymer is preferably 1% by mass and more preferably 5% by mass in order to make the hollow fiber membrane easier to form. The upper limit of the concentration of the hydrophilic polymer is preferably 20% by mass, and more preferably 12% by mass from the viewpoint of the handleability of the film-forming stock solution.

    As the coagulation liquid, water, alcohols, glycerin, ethylene glycol or the like can be used alone or in combination. The temperature of the coagulation liquid is not particularly limited, but is usually 60 to 90 ° C.

[Hydrophilic polymer removal step]
The hollow fiber membrane formed by the above-mentioned coagulation process generally has a large pore diameter and potentially has high water permeability, but a large amount of hydrophilic polymer remains in the hollow fiber membrane in a solution state. Therefore, sufficient high water permeability cannot be exhibited as it is. Therefore, after the coagulation step, it is preferable to perform a hydrophilic polymer removal step of removing the hydrophilic polymer remaining in the hollow fiber membrane.

Although there is no restriction | limiting in particular as a specific method of a hydrophilic polymer removal process, For example, the process provided with the preliminary | backup process, the pressure reduction process, and the washing | cleaning liquid supply process is suitable.
In the hollow fiber membrane obtained in the coagulation step, the hydrophilic polymer remains in the membrane (porous portion) in a high concentration solution state. Such a high concentration of the hydrophilic polymer is relatively easily removed to some extent by immersing the hollow fiber membrane in a cleaning solution. Therefore, as a preliminary process, first, the hollow fiber membrane is first immersed and washed in a cleaning solution (i) a hollow fiber membrane cleaning step is performed, and then (ii) a hydrophilic polymer low molecular weight reduction step using an oxidizing agent. (Iii) A method of sequentially performing the washing step of the hydrophilic polymer having a reduced molecular weight.

(I) The washing liquid used in the washing step of the hollow fiber membrane is not particularly limited as long as it is a clear liquid in which the hydrophilic polymer is dispersed or dissolved, but water is preferable because of its high washing effect. Examples of water to be used include tap water, industrial water, river water, well water, and the like, and alcohols, inorganic salts, oxidizing agents, surfactants, and the like may be mixed and used. In addition, as the cleaning liquid, a mixed liquid of a good solvent for the hydrophobic polymer and water can be used.
The washing temperature is preferably high, preferably 50 ° C. or higher, more preferably 80 ° C. or higher, in order to keep the viscosity of the hydrophilic polymer solution low and prevent a decrease in diffusion transfer rate. Further, when cleaning is performed while boiling the cleaning liquid, the outer surface of the hollow fiber membrane can be scraped off by bubbling due to boiling, so that efficient cleaning is possible.

    (I) The hydrophilic polymer remaining in the hollow fiber membrane is in a relatively low concentration state by the washing process of the hollow fiber membrane. In order to obtain a higher cleaning effect at such a low concentration, it is preferable to perform (ii) a step of lowering the molecular weight of the hydrophilic polymer using an oxidizing agent. Specifically, it is preferable to first hold a chemical solution containing an oxidizing agent in the hollow fiber membrane, and then heat the hollow fiber membrane holding the chemical solution in a gas phase. As the oxidizing agent, ozone, hydrogen peroxide, permanganate, dichromate, persulfate, etc. can be used, but it has strong oxidizing power and excellent decomposition performance, excellent handling properties, and low cost. Of these, hypochlorite is particularly preferable. Examples of hypochlorite include sodium hypochlorite and calcium hypochlorite, with sodium hypochlorite being particularly preferred.

  At this time, the temperature of the chemical solution is preferably 50 ° C. or less, and more preferably 30 ° C. or less. When the temperature is higher than 50 ° C., oxidative decomposition is promoted during the immersion of the hollow fiber membrane, and the hydrophilic polymer that has fallen into the chemical solution is further oxidatively decomposed, leading to waste of the oxidant. On the other hand, when the temperature is excessively low, the oxidative decomposition is suppressed, but the cost for controlling the temperature to a low temperature tends to increase as compared with the case of carrying out at normal temperature. Therefore, from this point, the temperature of the chemical solution is preferably 0 ° C. or higher, more preferably 10 ° C. or higher.

    After the chemical solution is held in the hollow fiber membrane, the hydrophilic polymer is oxidatively decomposed by heating the hollow fiber membrane in the gas phase. By heating in the gas phase, the chemical liquid retained in the hollow fiber membrane is hardly diluted and the chemical liquid is hardly dropped and eluted into the heating medium, so that the oxidizing agent in the chemical liquid is the hollow fiber membrane. It is preferable because it is efficiently used for decomposing the hydrophilic polymer remaining therein.

As a specific heating method, it is preferable to heat the hollow fiber membrane using a heating fluid under atmospheric pressure. It is preferable to use a fluid having a high relative humidity as the heating fluid, that is, heating under humid heat conditions, because drying of an oxidizing agent such as hypochlorite is prevented and efficient decomposition treatment is possible. At that time, the relative humidity of the fluid is preferably 80% or more, more preferably 90% or more, and most preferably in the vicinity of 100%.
The lower limit of the heating temperature is preferably 50 ° C., more preferably 80 ° C., because the treatment time can be shortened when continuous treatment is performed. The upper limit of the temperature is preferably 100 ° C. in the atmospheric pressure state.

  As described above, after the (ii) step of lowering the molecular weight of the hydrophilic polymer using the oxidizing agent, the hollow fiber membrane is again formed under the same conditions as in the above-described (i) hollow fiber membrane washing step. It is preferable to perform a washing step of the hydrophilic polymer having a reduced molecular weight by removing the hydrophilic polymer having a reduced molecular weight to some extent by immersing in a cleaning solution for cleaning.

After performing a preliminary process as needed as mentioned above, a pressure reduction process is performed. According to the decompression step, even a hydrophilic polymer that remains even after the preliminary step can be effectively removed.
The depressurization step is a step of depressurizing the outer peripheral side of the hollow fiber membrane and discharging the hydrophilic polymer remaining in the hollow fiber membrane to the outer peripheral side of the hollow fiber membrane. The hydrophilic polymer is moved to the outer peripheral side of the hollow fiber membrane and removed by the pressure difference at that time so as to be lower than the peripheral side (hollow part).

  Although there is no particular limitation on the specific method of the decompression step, for example, as shown in FIG. 1, a connection port 11a for connecting decompression means such as a decompression pump is formed on the side surface (circumferential surface), Use of the cylindrical member 11 provided with both ends 11b and 11c is provided with a sealing mechanism having a clearance enough to allow the hollow fiber membrane 10 to pass therethrough and capable of keeping the inside in a reduced pressure state or a pressurized state from the outside. preferable. Such a cylindrical member 11 is disposed in a gas phase such as the atmosphere, and the hollow fiber membrane 10 that has undergone a solidification step and a preliminary step as necessary is continuously introduced into the cylindrical member 11 from its one end 11b. By operating the decompression means, the outer peripheral side of the hollow fiber membrane 10 is decompressed in the cylindrical member 11, and the hydrophilic polymer remaining in the hollow fiber membrane 10 is entrained in the gas phase to the outer peripheral side of the hollow fiber membrane 10. And sucked and removed.

As a more preferable method, as shown in FIG. 2, a cleaning tank 12 containing a cleaning liquid is prepared, the hollow fiber membrane 10 is immersed in the cleaning tank 12, and the hollow fiber membrane 10 is immersed in the cleaning liquid. On the other hand, the method of performing a pressure reduction process as mentioned above is mentioned.
When the pressure reducing step is performed in this way, if the pressure difference between the inner peripheral side and the outer peripheral side of the hollow fiber membrane 10 is large, the hollow member 10 comes out of the cylindrical member 11 and is hollow in the portion immersed in the cleaning liquid. In the thread membrane 10, the cleaning liquid in the cleaning tank 12 passes through the membrane and is introduced to the inner peripheral side of the hollow fiber membrane 10. Then, the introduced cleaning liquid passes through the membrane again and is discharged to the outer peripheral side by the operation of the decompression means. As a result, the hydrophilic polymer remaining in the hollow fiber membrane 10 is removed from the connection port 11a together with the cleaning liquid.
According to the method of passing the cleaning liquid from the inner peripheral side to the outer peripheral side of the hollow fiber membrane 10 by such a decompression step, the hydrophilic polymer separated from the hollow fiber membrane 10 is dispersed or dissolved in the cleaning liquid, and together with the cleaning liquid Since suction and removal are performed, the concern of re-adhering to the hollow fiber membrane 10 is reduced, and a high removal effect is obtained.
In addition, as a washing | cleaning liquid, what was illustrated at the washing process of (i) hollow fiber membranes can be used.
The temperature of the cleaning liquid is not particularly limited but is preferably 30 to 80 ° C. When the temperature is high, the hydrophilic polymer is easily dispersed and dissolved in the cleaning liquid. However, since the saturated vapor pressure of the cleaning liquid increases, there is a concern that a high degree of vacuum cannot be secured. On the contrary, when the temperature is low, a high degree of decompression can be secured and water can be easily extracted, but there is a concern that the dispersion / solubility of the hydrophilic polymer in the cleaning liquid is lowered.

Further, in order to enhance the effect of removing the hydrophilic polymer, a cleaning liquid supply process for forcibly supplying a cleaning liquid from the outer peripheral side to the inner peripheral side of the hollow fiber membrane 10 is combined with the hydrophilic step after the decompression step. The polymer removal effect may be enhanced.
Specifically, two cylindrical members 11 described above are prepared, installed in series in the cleaning tank 12 with a space therebetween, and a decompression means is connected to the connection port 11a of the upstream cylindrical member 11 A supply means such as a pressurized supply pump for supplying the cleaning liquid is connected to the connection port 11a of the cylindrical member 11 on the rear stage side.
Then, the hollow fiber membrane 10 is sequentially introduced into the two cylindrical members 11 from the front side, and the decompression means and the supply means are operated. Then, the cleaning liquid is supplied from the outer peripheral side of the hollow fiber membrane 10 to the inner peripheral side in the cylindrical member 11 on the rear stage side (cleaning liquid supply step), and the inner peripheral side of the hollow fiber membrane 10 in the cylindrical member 11 on the front stage side. The cleaning liquid can be passed from the outer periphery to the outer peripheral side (decompression step).
As described above, when the cleaning liquid supply process is provided after the decompression process, the amount of the cleaning liquid flowing from the inner periphery side to the outer periphery side of the hollow fiber membrane 10 in the decompression process increases, and as a result, the effect of removing the hydrophilic polymer is large. Become.

The conditions of the decompression step and the cleaning liquid supply step are as follows: the type (material, membrane structure) of the hollow fiber membrane 10, the hydrophilic polymer concentration remaining in the hollow fiber membrane 10, and the pressure resistance of each cylindrical member 11 For this reason, it is necessary to consider the equipment cost and the pressure resistance performance of the hollow fiber membrane 10 itself, and to make the hollow fiber membrane 10 difficult to shake in the decompression step and the cleaning liquid supply step. From these points, the pressure in the decompression step is preferably -0.05 to -0.1 MPa, more preferably -0.08 to -0.1 MPa as the gauge pressure of the decompression means, and the supply pressure in the cleaning liquid supply step Is preferably more than 0 and not more than 0.4 MPa, more preferably more than 0 and not more than 0.3 MPa. Further, within such a range, the higher the difference in gauge pressure between the decompression step and the cleaning liquid supply step, the higher the hydrophilic polymer removal effect tends to be obtained.
If each staying time of the hollow fiber membrane 10 in the decompression step and the cleaning liquid supply step (staying time in each cylindrical member) is 2 to 10 seconds, respectively, a sufficient hydrophilic polymer removing effect can be obtained efficiently. it can.

[Drying process]
Next, the hollow fiber membrane 10 having been subjected to the hydrophilic polymer removing step in this way is dried (drying step).
In the drying step, the drying gas is permeated from the outer peripheral side to the inner peripheral side of the hollow fiber membrane 10 and introduced into the hollow portion, and after passing through the hollow portion, the drying gas is permeated from the inner peripheral side to the outer peripheral side and discharged. At least a gas injection step is performed.

The specific method of the drying gas press-in step is not particularly limited. For example, a hollow fiber membrane provided with a pressure-resistant drying cylinder member 20 as shown in FIG. 3 and a drying gas supply means (not shown). A method using a drying apparatus and using a high-temperature gas such as hot air (high-temperature air) or a high-temperature inert gas as the drying gas can be used.
The drying cylinder member 20 in this example has an inner diameter that allows the hollow fiber membrane 10 to pass through the inside, and the drying gas is placed inside the drying cylinder member 20 on the side surface (circumferential surface) of the central portion in the longitudinal direction. The supply port 21 for supplying to is formed.
The hollow fiber membrane is continuously introduced into and passed through the drying cylinder member 20 from one end 20a thereof, and the drying gas supply means (not shown) is connected to the supply port 21 to operate it. Gas is supplied into the drying cylinder member 20. Then, the pressure on the outer peripheral side of the hollow fiber membrane 10 in the drying cylinder member 20 becomes higher than that on the inner peripheral side by supplying the drying gas. Due to such a pressure difference, the drying gas passes through the membrane of the hollow fiber membrane 10 and is introduced from the outer peripheral side to the inner peripheral side of the hollow fiber membrane 10 as indicated by an arrow A in the figure.

The drying gas thus introduced into the inner peripheral side of the hollow fiber membrane 10, that is, the hollow portion, then passes through the hollow portion of the hollow fiber membrane 10 passing through the drying cylindrical member 20 as indicated by an arrow B in the figure. The flow reaches the positions of both ends 20a and 20b of the drying cylinder member 20. Then, outside the drying cylinder member 20, the pressure on the outer peripheral side of the hollow fiber membrane 10 is lower than that on the inner peripheral side. Therefore, as shown by the arrow C in FIG. The membrane 10 passes through the membrane and is discharged from the inner peripheral side of the hollow fiber membrane 10 to the outer peripheral side.
The moisture contained in the hollow fiber membrane 10 is accompanied by such a drying gas and is discharged from the inner peripheral side of the hollow fiber membrane 10 to the outer peripheral side.

  In this way, the drying gas is permeated from the outer peripheral side to the inner peripheral side of the hollow fiber membrane 10 to be introduced into the hollow portion, and then passed through the hollow portion of the hollow fiber membrane 10, and then discharged from the inner peripheral side to the outer peripheral side. According to the drying gas press-fitting step to be performed, for example, as in the prior art, the hollow fiber membrane 10 is caused to reciprocate several times in a hot air circulation type drying apparatus, and hot air is blown to the outer peripheral side of the hollow fiber membrane 10 to be dried. Compared with the method, the hollow fiber membrane 10 can be efficiently dried in a short time and with a very small amount of hot air, and the cost is very low. Further, such a drying gas press-in step can be easily performed by a drying apparatus including a small drying cylinder member 20 through which the hollow fiber membrane 10 passes, and does not require a large facility. It is also preferable in terms of space.

  The conditions of the drying gas press-in process may be set as appropriate depending on the type (material, membrane structure) of the hollow fiber membrane 10 and the amount of water remaining in the hollow fiber membrane 10. The temperature is preferably 90 to 110 ° C, more preferably 95 to 105 ° C. At such a temperature, although depending on the material of the hollow fiber membrane 10, the hollow fiber membrane 10 can be effectively dried without adversely affecting the hollow fiber membrane 10 due to heat. Moreover, the energy cost for heating the drying gas can be moderately suppressed. The temperature of the drying gas was measured at the supply port 21 of the drying cylinder member 20.

  As the supply pressure of the drying gas, the gauge pressure of the drying gas at the supply port 21 of the drying cylinder member 20 is preferably in the range of 0.1 to 0.3 MPa, more preferably 0.1 to 0.2 MPa. is there. When the supply pressure is in the above range, the hollow fiber membrane 10 can be efficiently dried, the equipment cost for making the drying cylinder member 20 pressure resistant can be moderately suppressed, and the hollow fiber membrane 10 oscillates. Problems are less likely to occur. Further, within such a range, the supply pressure of the dry gas does not exceed the pressure resistance performance of the hollow fiber membrane 10 itself.

In order to make the supply pressure within such a range, it is necessary to appropriately determine the inner diameter and length of the drying cylinder member 20 according to the outer diameter of the hollow fiber membrane 10.
That is, if the inner diameter of the drying cylinder member 20 is too large, a sufficient pressure difference between the outer peripheral side and the inner peripheral side of the hollow fiber membrane 10 in the drying cylinder member 20 cannot be secured, and as a result, the supply pressure is obtained. There is a tendency to become difficult to be. On the other hand, if the inner diameter of the drying cylinder member 20 is too small, the hollow fiber membrane 10 and the inner peripheral surface of the drying cylinder member 20 may come into contact with each other in the drying gas press-fitting step, causing damage to the hollow fiber membrane 10. There is a possibility that. Further, as the length of the drying cylinder member 20 is increased, a sufficient supply pressure tends to be easily obtained. However, when the length is excessively long, there are concerns such as an increase in equipment size and a decrease in workability.
From these viewpoints, the clearance between the hollow fiber membrane 10 and the drying cylinder member 20 is preferably 0.4 mm to 1.6 mm, and more preferably 0.6 mm to 1.2 mm. Here, the clearance is a difference between 1/2 of the inner diameter of the drying cylinder member 20 and 1/2 of the outer diameter of the hollow fiber membrane 10. At that time, the ratio of the length of the drying cylinder member 20 to the clearance is preferably 2000: 1 to 1000: 1, more preferably 1800: 1 to 1200: 1.
In addition, the outer diameter of the hollow fiber membrane 10 here is a value measured by an outer diameter measuring device (manufactured by KEYECE, model LS-3030).

In the case of such supply pressure, if the stay time of the hollow fiber membrane 10 in the drying gas press-in step (the time in which the hollow fiber membrane 10 stays in the drying gas press-in step) is 20 to 40 seconds Can be dried efficiently and sufficiently.
The traveling speed of the hollow fiber membrane 10 in the drying cylinder member 20 may be determined so that the staying time is in the above range, but is usually the same speed as the spinning speed and is 8 to 15 m / min. . Further, it is preferable that the length of the drying cylinder member 20 is determined in consideration of not only the clearance between the hollow fiber membrane 10 and the drying cylinder member 20 but also the staying time.

  In order to increase the drying effect, as shown in FIG. 4, a plurality (two in FIG. 4) of drying cylinder members 20 are installed in series at intervals, and each drying cylinder member 20 is used for drying. While introducing the gas, the drying gas press-fitting step may be performed by a method in which the hollow fiber membrane 10 is sequentially passed through the drying cylinder member 20. For example, when two drying cylinder members 20 having a length of α are installed in series at intervals, a drying gas press-fitting step is performed, and one drying cylinder member 20 having a length of 2α is used. In comparison with the case where the drying gas press-fitting step is performed, when two drying cylinder members 20 are installed in series, the introduction and discharge of the drying gas into the hollow portion of the hollow fiber membrane 10 are performed twice. If one drying cylinder member 20 is used, it is only once. Thus, the drying effect is considered to be affected by the number of times of introduction and discharge of the drying gas. Moreover, in the hollow part of the hollow fiber membrane 10 between the drying cylinder members 20 installed in series as shown in FIG. 4, the drying gases introduced from the adjacent drying cylinder members 20 collide with each other, and thus more effective. Thus, the drying gas is discharged outside. Therefore, a higher drying effect can be expected by arranging a plurality of drying cylinder members 20 in series at intervals.

In order to perform the drying gas press-in step more efficiently, it is preferable to provide a preliminary drying step before the drying gas press-in step in the drying step. Thus, by providing a preliminary drying step and removing a certain amount of moisture from the hollow fiber membrane 10, the drying effect by the drying gas press-in step can be further enhanced.
As a specific method, for example, a method of blowing high-temperature drying gas to the outer peripheral side of the hollow fiber membrane 10 and drying it (hot air drying step), or a method of drying the hollow fiber membrane 10 under reduced pressure (vacuum drying step). Etc., and these methods may be combined.

  When the hot air drying step is performed as the preliminary drying step, as a specific method, as shown in FIG. 5, for example, circulating hot air drying in which hot air of 95 to 115 ° C. is circulated at a wind speed of about several meters per second. There is a method in which the hollow fiber membrane 10 is continuously run in the machine 30 and the hollow fiber membrane 10 is dried from the outer peripheral side. After passing through the hot air dryer 30 in this way, the hollow fiber membrane 10 may be passed through the drying cylinder member 20 for the drying gas press-fitting step to perform the drying gas press-fitting step. If the staying time of the hollow fiber membrane 10 in the hot air drying process (the time of staying in the hot air dryer 30 in the hot air drying process) is 5 to 90 seconds, the effect of preliminary drying is sufficiently obtained.

  When performing the vacuum drying step, as shown in FIG. 6, a pressure-resistant drying cylinder member 40 similar to that used in the dry gas press-in step is disposed in the previous stage of the dry gas press-in step, and this drying is performed. After performing the vacuum drying process using the cylinder member 40, the drying gas press-in process may be performed. The drying cylinder member 40 used in the reduced-pressure drying process needs to be able to maintain the inside of the drying cylinder member 40 in a reduced pressure state from the outside. Therefore, a labyrinth seal or the like that can maintain the inside of the drying cylinder member 40 in a reduced pressure state from the outside while having a clearance that allows the hollow fiber membrane 10 to pass through at both ends of the drying cylinder member 40 is not illustrated. It is preferable that a sealing mechanism is provided.

Then, the hollow fiber membrane 10 is first continuously introduced from one end 40a of the drying cylinder member 40 for the reduced pressure drying process, and a decompression pump or the like is illustrated in the opening 41 formed on the side surface of the drying cylinder member 40. An approximately decompression means is connected and operated to decompress the inside of the drying cylinder member 40. Thereby, in the drying cylinder member 40, the outer peripheral side of the hollow fiber membrane 10 is decompressed, and the water in the hollow fiber membrane 10 is entrained in the gas phase and sucked and removed to the outer peripheral side of the hollow fiber membrane 10. The pressure at this time is preferably -0.05 to -0.1 MPa, more preferably -0.08 to -0.1 MPa as the gauge pressure of the decompression means. Further, if the staying time of the hollow fiber membrane 10 in the decompression step (the time in which the hollow fiber membrane 10 stays in the drying cylinder member 40 in the decompression step) is 5 to 30 seconds, the effect of preliminary drying is sufficiently obtained.
Thereafter, the hollow fiber membrane 10 may be passed through the drying cylinder member 20 for the drying gas press-fitting process to perform the drying gas press-fitting process.

  When the preliminary drying step is performed by combining the hot air drying step and the reduced pressure drying step, these steps may be simply performed sequentially. For example, as shown in FIG. It is also possible to install a drying cylinder member 40 for the process so that the drying effect by hot air and the drying effect by reduced pressure drying can be obtained synergistically.

  As described above, in the drying process, the drying gas is permeated from the outer peripheral side of the hollow fiber membrane 10 to the inner peripheral side and introduced into the hollow portion, and after passing through the hollow portion, from the inner peripheral side to the outer peripheral side. The hollow fiber membrane 10 can be dried at a low cost in a short time and with a very small amount of hot air by performing at least the drying gas press-fitting step for permeating and discharging. Further, such a drying gas press-fitting step is suitable from the viewpoint of installation space because it does not require a large facility.

Hereinafter, the present invention will be specifically described with reference to examples.
[Example 1]
Polyvinylidene fluoride A (manufactured by Atofina Japan, trade name Kyner 301F), polyvinylidene fluoride B (manufactured by Atofina Japan, trade name Kyner 9000LD), polyvinylpyrrolidone (manufactured by ISP, Trade name K-90) and N, N-dimethylacetamide were mixed to prepare a film-forming stock solution (1) and a film-forming stock solution (2).
Next, a hollow portion is formed at the center, and a nozzle in which an annular discharge port is sequentially formed on the outside so that two kinds of liquids can be sequentially applied (see FIG. 1 of JP-A-2005-42074). ) Is prepared, and this is kept at 30 ° C., and a polyester multifilament single filament braid (multifilament; 830T / 96F, 16 beats) is introduced into the hollow portion as a porous base material, and the outer periphery thereof is introduced. The film-forming stock solution (2) and the film-forming stock solution (1) were applied sequentially from the inside and coagulated in a coagulation liquid (mixed solution of 5 parts by mass of N, N-dimethylacetamide and 95 parts by mass of water) kept at 80 ° C. I let you. In this way, a hollow fiber membrane was obtained in which the braid was coated with a porous layer having an inclined structure having one fractional layer near the outer surface and increasing the pore diameter toward the inside. Of the applied film-forming stock solutions (1) and (2), the main stock solution forming the membrane structure of the hollow fiber membrane is the film-forming stock solution (1) applied to the outside.
In addition, a hollow portion having an inner diameter larger than the outer diameter of the hollow fiber membrane is formed in the center, and a nozzle having an annular discharge port formed in order so that two kinds of liquids can be sequentially applied to the outer side ( 1 is prepared, and the hollow fiber membrane obtained as described above is introduced into the hollow portion while keeping this at 30 ° C. Glycerin (first grade manufactured by Wako Pure Chemical Industries, Ltd.) and a film-forming stock solution (1) were sequentially applied from the inside and coagulated in the same coagulating liquid kept at 80 ° C. as previously used. In this way, a hollow fiber membrane having a braid support in a two-layer structure coated with a porous layer was obtained.
The spinning speed (running speed of the hollow fiber membrane) at this time was 8.8 m / min.

(Hydrophilic polymer removal step)
About the hollow fiber membrane obtained in this way, the hydrophilic polymer removal process was implemented as follows.
(1) Preliminary process The following processes (i) to (iii) were repeated twice as a preliminary process.
(I) Washing process of hollow fiber membrane The hollow fiber membrane was immersed in a washing tank containing boiling water at 100 ° C under the condition of staying time of 5 minutes for washing.
(Ii) Step of lowering the molecular weight of the hydrophilic polymer using an oxidizing agent Next, the hollow fiber membrane was placed in a water tank in which an aqueous solution of hypochlorite having a temperature of 30 ° C. and a concentration of 60000 mg / L was placed. Immersion was performed under conditions of minutes. Thereafter, the hydrophilic polymer was heated in a heat of 85 ° C. and a relative humidity of 100% under the condition of a residence time of 3 minutes to lower the molecular weight of the hydrophilic polymer.
(Iii) Step of washing hydrophilic polymer with reduced molecular weight Next, this hollow fiber membrane was washed again under the same conditions as in (i).
(2) Depressurization step-Cleaning liquid supply step-Depressurization step A cleaning tank containing water at a temperature of 74 ° C. is prepared as a cleaning liquid, and three cylinder members 11 shown in FIG. Arranged. And while introducing the hollow fiber membrane 10 into these cylinder members 11 sequentially from the front | former stage side, it connects to the connection port 11a of the cylinder member 11 of the foremost stage among three, and the connection port 11a of the cylinder member 11 of the last stage among three. The pressure reducing means were connected to each other, and the pressure was reduced so that the gauge pressure of the pressure reducing means was -0.06 MPa in the pressure reducing step on the front side and -0.05 MPa in the pressure reducing step on the rear side. Among the three, 74 ° C. water was supplied as a cleaning liquid from the supply means connected to the connection port 11a of the central cylindrical member 11 so that the gauge pressure was 0.1 MPa.
In addition, the time during which the hollow fiber membrane 10 stays in each of the three cylindrical members 11 (stay time) was about 3 seconds.

(Drying process)
Subsequently, the drying process was performed about the hollow fiber membrane 10 after the hydrophilic polymer removal process. Specifically, six drying cylinder members (made of stainless steel, inner diameter: 4 mm, length: about 780 mm) 20 shown in FIG. 3 are prepared, and these are installed in series at intervals, and a drying gas injection step Went.
A drying gas supply means was connected to the supply ports 21 in each of the six drying cylinder members 20 used in the drying gas press-fitting step, and hot air at 95 ° C. was introduced as the drying gas. At this time, the supply pressure of the drying gas (the gauge pressure of the drying gas at the supply port 21) was set to 0.2 MPa. At this time, the specific amount of hot air supplied was 1140 (190 per drying cylinder member) L / min. The traveling speed of the hollow fiber membrane 10 in the drying cylinder member 20 was 8.8 m / min, which is the same as the spinning speed. Further, the residence time of the hollow fiber membrane 10 in the drying cylinder member 20 (total time spent in the six drying cylinder members 20 in the drying gas press-fitting step) was 30 seconds.
As a result of measuring the moisture content of the hollow fiber membrane 10 after such a drying step, it was 0.8%.
Here, the moisture content is a moisture content based on the dry weight indicating the ratio of the remaining moisture mass to the dry mass of the hollow fiber membrane 10. In addition, an infrared moisture meter manufactured by Kett Science Laboratory Co., Ltd. was used for measuring the moisture content.
The hollow fiber membrane 10 having a braided support with a two-layer structure finally obtained in this manner had an outer diameter of 2.8 mm and an inner diameter of 1.0 mm.
Further, from the outer diameter of the hollow fiber membrane 10 and the inner diameter of the drying cylinder member 20, the clearance between the hollow fiber membrane 10 and the drying cylinder member 20 is 0.6 mm, and the length of the drying cylinder member 20 and the clearance are the same. Is 780: 0.6 = 1300: 1.
In addition, the outer diameter of the hollow fiber membrane 10 was measured using the outer diameter measuring device (the product made by KEYECE, model LS-3030). Specifically, two such outer diameter measuring devices are prepared, and these measuring devices are respectively attached so that the measured diameters are shifted from each other by 90 ° about the axis of the hollow fiber membrane 10, and the outer diameters in two directions are set. It was measured. The measurement results were all 2.8 mm.

[Example 2]
After carrying out the hydrophilic polymer removing step in the same manner as in Example 1, a drying step was carried out. Example 1 except that the temperature of hot air introduced as a drying gas is 90 ° C., the supply pressure of the drying gas is 0.3 MPa, and the supply amount of hot air is 1350 (225 per cylinder member for drying) L / min. Drying was performed under the same conditions.
As a result, a hollow fiber membrane 10 having the same moisture content as in Example 1 could be obtained.

[Example 3]
After carrying out the hydrophilic polymer removing step in the same manner as in Example 1, a drying step was carried out. Example 1 except that the temperature of hot air introduced as the drying gas is 110 ° C., the supply pressure of the drying gas is 0.15 MPa, and the supply amount of hot air is 1050 (175 per cylinder member for drying) L / min. Drying was performed under the same conditions.
As a result, a hollow fiber membrane 10 having the same moisture content as in Example 1 could be obtained.

[Comparative example]
The hollow fiber membrane 10 was dried using a hot-air circulating dryer until the moisture content of the hollow fiber membrane 10 after the drying step was approximately the same as in Example 1. The hot air temperature was 115 ° C.
As a result, the drying time, that is, the residence time of the hollow fiber membrane 10 in the circulation type hot air dryer was 200 seconds, which required a very long time.

It is a schematic block diagram which shows an example of a hydrophilic polymer removal process. It is a schematic block diagram which shows another example of a hydrophilic polymer removal process. It is a schematic block diagram which shows an example of a dry gas injection process. It is a schematic block diagram which shows another example of a dry gas injection process. It is a schematic block diagram which shows an example which implemented the dry gas injection process after the preliminary drying process. It is a schematic block diagram which shows another example which implemented the dry gas injection process after the preliminary drying process. It is a schematic block diagram which shows another example which implemented the dry gas injection process after the preliminary drying process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hollow fiber membrane 20 Drying cylinder member 21 Supply port

Claims (9)

In a method for producing a hollow fiber membrane comprising a coagulation step of coagulating a membrane-forming stock solution in a coagulation solution to form a hollow fiber membrane, and a drying step of drying the hollow fiber membrane,
In the drying step, a drying gas is permeated from the outer peripheral side to the inner peripheral side of the hollow fiber membrane and introduced into the hollow portion, and after passing through the hollow portion, is allowed to permeate from the inner peripheral side to the outer peripheral side. have a drying gas injection step of discharging Te,
In the drying gas press-fitting step, the hollow fiber membrane is allowed to pass through the inside of the drying cylinder member, and the drying gas is supplied to the inside from a supply port formed on a side surface of the drying cylinder member. A method for producing a hollow fiber membrane. The method for producing a hollow fiber membrane according to claim 1, wherein the drying step includes a preliminary drying step before the gas injection step for drying. The method for producing a hollow fiber membrane according to claim 2, wherein the preliminary drying step includes one or more of a hot air drying step and a reduced pressure drying step. The clearance between the hollow fiber membrane and the drying cylinder member is 0.4 mm to 1.6 mm. The method for producing a hollow fiber membrane according to any one of claims 1 to 3. The hollow fiber according to any one of claims 1 to 4, wherein the ratio of the length of the drying cylinder member to the clearance between the hollow fiber membrane and the drying cylinder member is 2000: 1 to 1000: 1. A method for producing a membrane. The supply pressure of the drying gas is 0.1 to 0.3 MPa as a gauge pressure of the drying gas at the supply port of the drying cylinder member, according to any one of claims 1 to 5. A method for producing a hollow fiber membrane.   A supply port to which a drying gas is supplied is formed on a side surface, and includes a drying cylinder member through which a hollow fiber membrane passes, and a drying gas supply unit connected to the supply port. Hollow fiber membrane drying equipment. The apparatus for drying a hollow fiber membrane according to claim 7, wherein a clearance between the hollow fiber membrane and the drying cylinder member is 0.4 mm to 1.6 mm. The hollow fiber membrane drying apparatus according to claim 7 or 8, wherein a ratio of a length of the drying cylinder member to a clearance between the hollow fiber membrane and the drying cylinder member is 2000: 1 to 1000: 1.

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