JP6888940B2 - Method for manufacturing fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane - Google Patents

Description

The present invention relates to a method for producing a fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane. More specifically, the present invention relates to a method for producing a fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane that is effectively used as a treatment membrane for water purification treatment and wastewater treatment, a humidification membrane for a fuel cell, a dehumidification membrane, and the like.

In recent years, with increasing interest in the environment and stricter water quality regulations in the water treatment field such as wastewater and purified water, research and development and practical use of separation membranes, especially hollow porous membranes, from the viewpoint of high separability and energy saving. The conversion is being greatly promoted.

Compared with conventional coagulation sedimentation filtration methods, water purification treatment by membrane filtration and wastewater treatment are easier to maintain and manage in operation, and the quality of treated water is also good, so membrane filtration is widely used in the water treatment field. It is used. Here, from the viewpoint of securing water resources in recent years, a porous hollow fiber membrane module having high strength and a large membrane area per unit volume is often used. For example, in the case of waste water treatment, ^{a porous hollow fiber membrane module having a membrane area of about 50 to 100 m 2} per unit volume is generally used, and the amount of such a membrane module is tens to hundreds of liters per minute. Water will be supplied. In that case, the porous hollow fiber membrane may be broken due to the influence of the generated load. Further, when the porous hollow fiber membrane module is used for industrial purposes, it is usually used for a long period of several years to 10 years, so that it is necessary to avoid breakage of the porous hollow fiber membrane due to fatigue.

Polyvinylidene fluoride (PVDF) is used as a hollow fiber membrane material having excellent chemical stability. Applicants first used PVDF as the hollow fiber membrane material and triethyl phosphate as the solvent to be added to the coagulation bath (and core liquid), and further slowed the replacement rate of the solvent to cause the skin layer and voids. We have proposed a method for producing a layerless and homogeneous PVDF porous membrane (Patent Document 1). However, in such a manufacturing method, there are cases where it is not easy to form a hollow thread due to a slow solidification rate.

For physical stability, Applicants also passed the cylindrical braid through the inner nozzle of the double annular spinning nozzle and doubled on the outer surface of the cylindrical braid that passed through the inner nozzle of the double annular spinning nozzle. In a method for producing a fiber-reinforced porous hollow fiber membrane, which is produced by applying a film-forming stock solution discharged from an outer nozzle of an annular spinning nozzle, impregnating it, coagulating it in a coagulating solution, and drying it.
As the film-forming stock solution, a solution prepared by dissolving polyvinylidene fluoride in triethyl phosphate at a concentration of 16 to 27% by weight is used, and the hollow fiber obtained after spinning is prepared from an aqueous solution of triethyl phosphate having a concentration of 10 to 90% by weight. We have proposed a method for producing a porous hollow fiber membrane that is coagulated in a coagulating solution for 40 to 120 seconds (Patent Document 2).

The porous hollow fiber membrane module obtained by such a manufacturing method has high permeation characteristics by slowing the coagulation rate and forming a homogeneous film depending on the composition of the membrane stock solution and the coagulation liquid, and has high load resistance and fatigue resistance. On the other hand, it has an excellent effect of suppressing breakage of the porous hollow fiber membrane due to a fluid such as a high-flow gas or liquid or breakage due to fatigue.

However, if the spinning speed is increased in the process of manufacturing the hollow yarn film at low cost and in order to improve productivity, the starting point of cracking along the axial direction of the porous film coated on the cylindrical braid is formed, and the film dries and shrinks. As a result, the phenomenon of cracking in the axial direction will occur.

The following two points can be considered as factors that cause the origin of cracks that occur in the axial direction.
(1) Weld line formed at the confluence of resins, which is a problem in hollow fiber formation
(2) By slowing the solidification rate, the film-forming stock solution permeates the inside of the braid to improve the peeling strength. On the other hand, the film-forming stock solution permeates too much and the outer diameter shape becomes unstable and the film thickness becomes uneven. As a result, the stress due to shrinkage during membrane drying is concentrated in a part.

Japanese Patent No. 3,261,761 Japanese Unexamined Patent Publication No. 2012-179603 JP-A-2016-010792

An object of the present invention is to improve load resistance and fatigue resistance without causing defects such as cracks in the porous hollow fiber membrane obtained even when the spinning speed is increased, and to have high permeation characteristics. Another object of the present invention is to provide a method for producing a porous hollow fiber membrane capable of suppressing breakage of the porous hollow fiber membrane due to a fluid such as a gas or liquid having a high flow rate or breakage due to fatigue.

An object of the present invention is to allow a cylindrical braid to pass through the inner nozzle of the double annular spinning nozzle and to the outer surface of the cylindrical braid that has passed through the inner nozzle of the double annular spinning nozzle to the outer nozzle of the double annular spinning nozzle. A method for producing a fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane, which is produced by applying a film-forming stock solution discharged from the sheet, impregnating it, coagulating it in a coagulating solution, and winding it on a winder. In
This is achieved by using a cylindrical braid with a knitting density of 70 / inch (25.4 mm) or more, or a yarn fineness of 360 to 500 decitex and a number of filaments of 48 to 76.

The method for producing a fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane according to the present invention makes it possible to control the amount of permeation of the membrane-forming stock solution into the cylindrical braid, so that the outer fiber-reinforced porous hollow fiber membrane can be obtained. The diameter shape is stabilized and the film thickness can be made uniform. As a result, the starting point of cracking in the axial direction of the hollow fiber membrane is not formed, and the film cracking can be eliminated, which is an excellent effect.

It is a side view of the polyester sleeve used in Example 1. 3 is an SEM photograph showing a cross section of the fiber-reinforced porous hollow fiber membrane obtained in Example 1. It is an SEM photograph which shows the membrane surface in the long axis direction of the fiber-reinforced porous hollow fiber membrane obtained in Example 1. It is a side view of the polyester sleeve used in Example 2. It is an SEM photograph which shows the cross section of the fiber-reinforced porous hollow fiber membrane obtained in Example 2. It is an SEM photograph which shows the membrane surface in the long axis direction of the fiber-reinforced porous hollow fiber membrane obtained in Example 2. It is a side view of the polyester sleeve used in the comparative example. It is an SEM photograph which shows the cross section of the fiber-reinforced porous hollow fiber membrane obtained in the comparative example. It is an SEM photograph which shows the membrane surface in the long axis direction of the fiber-reinforced porous hollow fiber membrane obtained in the comparative example.

In the method for producing a fiber-reinforced porous hollow fiber membrane according to the present invention, a cylindrical braid is passed through the inner nozzle of the double annular spinning nozzle, and the outer surface of the cylindrical braid is passed through the inner nozzle of the double annular spinning nozzle. The fiber-reinforced polyvinylidene fluoride produced by applying the film-forming stock solution discharged from the outer nozzle of the double cyclic spinning nozzle, impregnating it, coagulating it in the coagulating solution, and winding it on a bobbin. In the method for producing a porous hollow fiber membrane,
The fiber-reinforced porous hollow fiber membrane obtained by using a cylindrical braid having a knitting density of 70 / inch (25.4 mm) or more, a yarn fineness of 360 to 500 decitex, and a filament number of 48 to 76 can be obtained. The outer diameter shape can be stabilized, the film thickness can be made uniform, and the origin of cracks in the axial direction of the hollow fiber membrane is not formed, so that film cracks can be eliminated.

As a cylindrical braid, a multifilament having a knitting density of 70 / inch (25.4 mm) or more, preferably 70 to 100 / inch (25.4 mm) , or a yarn fineness of 360 to 500 decitex and a filament number of 48 to 76 is used. , As shown in FIGS. 1 and 4, rounded ones are used so as to have a cylindrical shape. Examples of the fiber base material include organic fiber base materials such as polyphenylene sulfide, polyester, polypropylene, polyethylene, rayon, vinylon, polyamide, polyimide, and aramid, and polyphenylene sulfide and polyester are preferably used. If the knitting density, yarn fineness, etc. are outside this range, the outer diameter shape of the hollow fiber membrane is not stable and the film thickness is not uniform, so that the starting point of cracking in the axial direction of the hollow fiber membrane is formed. There is a risk of film cracking.

A film-forming stock solution for forming a porous hollow fiber membrane is adhered to the outer peripheral surface of the cylindrical braid. To adhere the film-forming stock solution to the outer peripheral surface of the cylindrical braid, apply the film-forming stock solution discharged from the outer nozzle of the double annular spinning nozzle to the outer surface of the cylindrical braid that has passed through the inner nozzle of the double annular spinning nozzle. Method is used. Here, when the cylindrical braid is passed through the inner nozzle of the double annular spinning nozzle, a tension of about 4 to 50 N is generally applied to the cylindrical braid.

As the film-forming stock solution, a solution in which polyvinylidene fluoride is dissolved in a soluble solvent of polyvinylidene fluoride resin so as to have a concentration of about 16 to 27% by weight, preferably about 18 to 25% by weight is used. If the concentration of polyvinylidene fluoride is lower than this, the membrane pore size becomes too large, while if the concentration is higher than this, it becomes difficult to dissolve polyvinylidene fluoride. As the soluble solvent of the polyvinylidene fluoride resin, various alcohols, aprotic polar solvents such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, dimethylsulfoxide, N-methyl-2-pyrrolidone, triethyl phosphate and the like are used.

The cylindrical braid to which the membrane-forming stock solution for forming a porous hollow fiber membrane is attached is coagulated using a coagulating liquid by a dry-wet spinning method or a wet spinning method, and after washing and drying, a fiber-reinforced porous hollow fiber A film is formed.

Although Patent Document 3 discloses that a cylindrical braid having a yarn fineness of 200 to 600 decitex (dtex) and a stroke number of 16 to 48 is used, the polyester sleeve used in the examples (Example 1). Has a thread fineness of 280 decitex (dtex) and a number of strokes of 24, and a polyphenylene sulfide sleeve (Example 2) has a thread fineness of 280 decitex (dtex) and a number of strokes of 24. Is used, and no effect is shown when the cylindrical braid specified in the present invention is selectively used.

The coagulation is carried out by immersing in the coagulation liquid for, for example, about 20 to 120 seconds, preferably about 20 to 90 seconds. If the solidification time is shorter than this, the film does not solidify and becomes irregularly shaped, and even if the solidification time is longer than this, the production time is only lengthened, and no further effect can be obtained.

As the coagulating liquid, an aqueous solution of triethyl phosphate of about 10 to 90% by weight, preferably about 60 to 90% by weight, more preferably about 70 to 80% by weight is used. When an aqueous solution of triethyl phosphate having a concentration lower than this is used as the coagulating liquid, a porous membrane cannot be obtained.

Next, the present invention will be described with respect to Examples.

Example 1
A membrane-forming stock solution was prepared by dissolving 100 g of polyvinylidene fluoride resin (Kureha product KF-1550) in 400 g of dimethyl sulfoxide. Next, a polyester tetron sleeve (knitting density 70 to 75 / inch (25.4 mm) , yarn fineness 280 decitex, number of filaments 24), which is a cylindrical braid, is attached to the inner nozzle of a double annular spinning nozzle with an inner tube diameter of 2.0 mm. To the support that has passed through the inside and passed through the inner nozzle of the double annular spinning nozzle, the film-forming stock solution that has been pumped and discharged from the outer nozzle of the double annular spinning nozzle is applied to the outer surface thereof. The mixture was impregnated with the mixture, spun at a spinning speed of 5 m / min, extruded into a coagulating solution consisting of an 80 wt% triethyl phosphate aqueous solution, and coagulated for 24 seconds.

In the produced hollow fiber membrane, polyvinylidene fluoride penetrates up to about 50% inside the Tetron sleeve, and the outer diameter shape is a circular shape that is not particularly distorted or dented, as shown in FIG. there were. Moreover, when the film surface after washing and drying was observed by SEM, no axial cracking was confirmed as shown in FIG.

Example 2
In Example 1, a Tetron sleeve (knitting density 35-40 / inch (25.4 mm) , yarn fineness 360 decitex, number of filaments 48) was used as the cylindrical braid. In the obtained hollow fiber membrane, polyvinylidene fluoride penetrates up to about 50% inside the Tetron sleeve, and the outer diameter shape is a circular shape with no particular distortion or dent as shown in FIG. there were. Moreover, when the film surface after washing and drying was observed by SEM, no axial cracking was confirmed as shown in FIG.

Comparative Example In Example 1, a Tetron sleeve (knitting density 45 to 50 / inch (25.4 mm) , yarn fineness 280 decitex, number of filaments 24) was used as the cylindrical braid. In the obtained hollow fiber membrane, polyvinylidene fluoride penetrated to 100% inside the Tetron sleeve, and as shown in FIG. 8, the outer diameter shape was not circular, and a dent was confirmed in the cross section. .. Moreover, when the film surface after washing and drying was observed by SEM, cracks in the axial direction were confirmed as shown in FIG.

Since the fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane produced by the production method according to the present invention has high permeation characteristics and mechanical strength, it is used in water treatment fields such as wastewater and water purification, and as a humidifying membrane for fuel cells. It is effectively used as a dehumidifying film.

Claims (3)

A film-forming stock solution in which a cylindrical braid is passed through the inner nozzle of the double annular spinning nozzle and discharged from the outer nozzle of the double annular spinning nozzle to the outer surface of the cylindrical braid that has passed through the inner nozzle of the double annular spinning nozzle. In the method for producing a fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane, which is produced by coating, impregnating, and then coagulating in a coagulating liquid and winding it on a winder.
As a cylindrical braid, a fiber-reinforced polyvinylidene fluoride porous hollow fiber having a knitting density of 70 / inch (25.4 mm) or more, a yarn fineness of 360 to 500 decitex, and a filament number of 48 to 76 is used. Method of manufacturing a thread film. The method for producing a fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane according to claim 1, wherein a polyester sleeve is used as the cylindrical braid. The method for producing a fiber-reinforced polyvinylidene fluoride porous hollow fiber membrane according to claim 1 or 2, wherein triethyl phosphate is used as a coagulating liquid.

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