JP2675197B2 - Manufacturing method of high strength and porous polysulfone hollow fiber membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polysulfone hollow fiber membrane. More specifically, it relates to a method for producing a high-strength, porous polysulfone hollow fiber membrane having pores of uniform shape on the inner and outer surfaces of the hollow fiber.

[0002]

2. Description of the Related Art Polysulfone hollow fiber membranes are widely used for industrial precision filtration or ultrafiltration because of their excellent heat resistance and chemical resistance.

Conventional polysulfone hollow fiber membranes are manufactured by the so-called dry-wet spinning method. This method basically comprises a step of extruding a uniform or nearly uniform solution of polysulfone into the air through a double nozzle together with the core liquid, and then immersing it in a coagulating liquid.

Up to now, a number of improvements have been added to each of the above steps, mainly for the purpose of improving the permeation performance of the membrane.

The prior art relating to the polysulfone hollow fiber membrane having a relatively large pore, which is related to the present invention, will be described below.

In the prior art, as the spinning solution,
A solution in which aromatic polysulfone is dissolved in a mixed solution of a good solvent and an additive is usually used.

Examples of the good solvent include water-soluble high-boiling point dimethylformamide, dimethylacetamide, and N-methyl.
-2-Pyrrolidone is used.

As the above-mentioned additive, a non-solvent of polysulfone, for example, a polyhydric alcohol having 2 to 4 carbon atoms (Japanese Patent Laid-Open Publication No.
56-15270 and 60-222112) and water-soluble pore-forming agents such as polyethylene glycol (JP-A-54-262).
83, 57-35906, 58-114702), polyvinylpyrrolidone (JP-A 61-93801, 61-238306)
No. 63-97205).

As the core liquid, a non-solvent of polysulfone, for example, water or an aqueous solution of a good solvent is used.

The temperature of the spinning dope is kept constant within the range where the spinning dope is in a uniform or almost uniform state.

The distance traveled in the air is usually set to several cm / several tens of cm.

Similar to the core liquid, water or an aqueous solution of a good solvent is usually used as the coagulating liquid, and the temperature of the coagulating liquid is from room temperature to
It is set in the range of about 70 ℃.

The spinning speed is usually 20 to 70 m / min.

In order to further stabilize the structure of the hollow fiber membrane produced by such a method and prevent the filtration performance from being lost even when dried, a treatment of immersing in hot water at 80 ° C. or higher is added. (See Japanese Patent Laid-Open No. 57-71606).

The outline of the conventional technique which is particularly related to the present invention is as described above. Next, these problems will be described.

[0016]

As described above, the aromatic polysulfone hollow fiber membrane is excellent in heat resistance and chemical resistance, and is widely used industrially from ultrafiltration to precision filtration.
Along with this, there is a growing demand for products that can withstand rapid changes in temperature, such as hot water sterilization and steam sterilization, as well as those that can be used for applications that are subject to the same severe handling as conventional so-called pleated cartridge filters. There is.

However, since the conventional manufacturing method was developed by focusing on improving the filtration performance of the membrane, the breaking strength of the hollow fiber membrane and especially the elongation at the breaking time are small, and the above-mentioned rapid production is not possible. It has been pointed out that the polysulfone hollow fiber membrane often breaks in applications subject to temperature changes and severe handling.

For example, JP-A-57-35906 and 58-1
In the 14702 publication, in order to increase the filtration rate, a solution of polysulfone such as dimethylformamide has a large average molecular weight of 400 to 20000 so that the solution becomes phase-separated and becomes cloudy at a high temperature (for example, 80 to 130 ° C). A homogeneous solution obtained by adding polyethylene glycol and cooling it is used as a spinning dope. A hollow fiber membrane produced from this spinning dope is disclosed in JP-A-58-114702, No. 6
As shown in the figure, since it has a network structure in which many thin branches that are not continuous are seen, both the tensile strength and the elongation at break are small, and especially the elongation at break does not reach 25%.

Further, in JP-A-60-222112, in order to increase the pore diameter, polysulfone N-
A non-solvent such as propylene glycol is added to a solution of methyl-2-pyrrolidone or the like so that the solution is phase-separated at a temperature of room temperature or lower, and this is heated to form a uniform solution. As shown in FIG. 9 of the publication, the hollow fiber membrane produced from this spinning dope has a highly developed network structure without breaks in the branches, and therefore has a large elongation at break of 100%. Some can reach.

However, if the polysulfone concentration in the spinning dope is increased and the wall thickness of the hollow fiber is increased in order to further increase the strength, the inside of the membrane changes from a network structure to a cell structure, and the filtration rate remarkably decreases. .

Therefore, even with this method, a film having a satisfactory tensile strength cannot be obtained.

On the other hand, JP-A-61-93801, JP-A-61-238306 and JP-A-63-9 using polyvinylpyrrolidone as an additive.
The hollow fiber membranes described in JP-A Nos. 7205 and 7205 also have the above-mentioned disclosure.
There is the same problem as in the case of adding polyethylene glycol in Japanese Patent No. 5906.

Further, the hollow fiber membrane having a macro void inside which is generally used for ultrafiltration has a smaller strength than a hollow fiber membrane having no macro void.

Another problem of the prior art is that the shape of the pores on the inner surface or outer surface of the hollow fiber membrane is uneven and the uniformity is poor. For example, JP-A-57-35906 and JP-A-58-11470.
The inner surface of the hollow fiber membrane described in Japanese Patent Publication No. 2 has slit-shaped holes with irregular lengths and widths, and the holes on the outer surface also have irregular shapes (for example, Japanese Patent Laid-Open No. 58-114702). 4 and 5). The hollow fiber membrane having such irregularly shaped pores has poor reproducibility of filtration performance such as molecular weight cutoff and filtration rate when the pore diameter is increased.

JP-A-61-23806 and JP-A-63-97205, which use polyvinylpyrrolidone as an additive, have the same problems as described above.

The present invention has been made in order to solve the above-mentioned problems, and has significantly higher tensile strength and elongation at break than conventional hollow fiber membranes, and has a uniform inner and outer surface. The purpose is to obtain a hollow fiber membrane having various pores.

[0027]

The present inventor has arrived at the following idea as a result of extensive studies to achieve the above object.

That is, as described above, regarding the relationship between the structure of the hollow fiber membrane and the strength and the filtration rate, the hollow fiber membrane having a reticulated structure consisting of fine branches with some branches which are not continuous inside has a filtration rate. Is large, but the tensile strength and especially the elongation at break are small.
Although the tensile strength and the elongation at break are both high, the filtration rate is low. Therefore, it is considered that there is a hollow fiber membrane having both high strength and filtration rate between the structures.

Regarding the uniformity of the shape of the pores on the inner surface and the outer surface, in the conventional method, polysulfone having a relatively low degree of polymerization of several tens is used, and polysulfone molecules having a low degree of polymerization are discharged from the nozzle. As a result of being highly oriented when extruded, when it comes into contact with a core liquid having a strong coagulation force, its orientation state is almost fixed as it is.
As shown in FIG. 4 of JP-A-58-114702, while a slit-shaped hole is formed, when the polysulfone comes into contact with the core liquid having a weak coagulation force, the polysulfone has an intermolecular cohesive force between adjacent molecules. However, since the molecular weight is small, the aggregation does not reach a long distance, and an aggregated state of locally aggregated (a non-uniform state in which the shapes of pores are not uniform) is formed.
It is believed that the polysulfone molecules will not be oriented as they exit the nozzle in order to align the shapes of the pores.
It is considered necessary to prepare a spinning dope in which polysulfone does not locally aggregate.

In the above-mentioned conventional methods, polysulfone having a relatively small degree of polymerization of several tens is used, and the characteristics and concentration of the solution are described in detail. Although the phase separation temperature and common sense viscosity are also explained, there is no explanation or suggestion other than the above regarding the other explanation, that is, the relationship between the characteristics of the hollow fiber membrane and the characteristics of the spinning dope. .

According to the above idea, the present inventor has conducted extensive studies to obtain a hollow fiber membrane which solves the above two problems at the same time, and as a result, using a spinning solution containing polyethylene glycol as an additive in a wide range of molecular weights. When the hollow fiber membrane was produced, it was found that the above-mentioned two problems can be solved at the same time when a spinning dope having a specific solution property mainly based on the molecular weight of polyethylene glycol is selected, and the present invention is completed. Came to do.

That is, according to the present invention, polysulfone dissolved in a solution of polyethylene glycol having a normal stress effect and having a number average molecular weight of 150,000 to 2,000,000 is used as a spinning dope, which has a high strength. -Regarding a method for producing a porous polysulfone hollow fiber membrane.

[0033]

[Function] In the conventional method, the polysulfone molecules are oriented in the fiber axis direction only because they are oriented in the fiber axis direction. However, a spinning solution prepared by using a polyethylene glycol solution having a number average molecular weight of 150,000 to 2,000,000. Expands from the nozzle rapidly expands radially (has normal stress effect)
Therefore, the polysulfone molecules are oriented not only in the fiber axis direction but also in the circumferential direction, and the polysulfone molecules are not oriented in a specific direction. Therefore, uniform holes are formed on the inner surface and the outer surface of the hollow fiber membrane. In addition, the above-mentioned high molecular weight polyethylene glycol gives a normal stress effect even when added in a small amount, and the inside of the hollow fiber membrane made from such a spinning dope has a net-like structure in which thick branches are three-dimensionally continuous. It has a structure and satisfies high strength and filtration speed at the same time.

[0034]

EXAMPLE The polysulfone used in the present invention has the formula (1):

[0035]

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Or equation (2):

[0037]

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A typical example is a repeating unit represented by:

The number average molecular weight of polyethylene glycol used in the present invention is 150,000 to 2,000,000, preferably 200,000 to 500,000. When the number average molecular weight is less than 150,000, it is necessary to add a large amount in order to give a normal stress effect, from such a spinning stock solution, a hollow fiber membrane having a thin branch network structure is formed, Strength becomes low. On the other hand, when it exceeds 2 million, the solubility of polyethylene glycol is decreased, and a hollow fiber membrane having a cell structure is formed, and the filtration rate is decreased.

The normal stress effect means a phenomenon in which, when a polyethylene glycol solution is stirred with a stirring rod, the solution rises above the surface tension of the solution on the stirring rod.

As the solvent used for preparing the polyethylene glycol solution, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, which is also a solvent for polysulfone, may be used, but a clear normal stress effect is obtained. N-methyl-2-pyrrolidone is particularly preferable from the viewpoint of giving. It is of course possible to use a mixed solvent obtained by adding a small amount of water or a low molecular weight polyhydric alcohol such as propylene glycol to these good solvents. A solution exhibiting a normal stress effect is prepared by dissolving the polyethylene glycol in these solvents in an amount of 1 to 15% (weight%, the same applies hereinafter), preferably 2 to 10%. When the amount of polyethylene glycol dissolved exceeds 15%,
The hollow fiber membrane becomes weak, and if it is less than 1%, the filtration rate becomes small.

Polysulfone is usually dissolved in the above-mentioned polyethylene glycol solution in an amount of 15 to 35%, preferably 16 to 25%. The order of preparing the solution containing polysulfone and polyethylene glycol is not particularly limited. When the dissolved amount of polysulfone is less than 15%, the strength of the hollow fiber membrane becomes small, and when it exceeds 35%, the viscosity becomes high and it becomes difficult to prepare a solution. In this case, the strength of the hollow fiber membrane increases, but the performance exceeds the required strength, resulting in excessive performance.

The spinning dope having the above-mentioned characteristics is extruded together with the core liquid from the double nozzle in the same manner as in the conventional method, allowed to run in the air for an appropriate distance, immersed in the coagulating liquid, and then wound up. High strength that the invention aims at
A porous polysulfone hollow fiber membrane is produced.

At this time, as the coagulating action of the core liquid becomes weaker, the pore diameter on the inner surface becomes larger and larger. In addition, the shape of the holes changes from a circular shape having a smooth periphery to a shape in which the circles are in contact with each other due to an increase in the number of holes, and a perfect mesh shape. There is no specific orientation of the hole shape in either shape.

On the other hand, if the running distance in the air is increased or a non-solvent is added to the spinning dope to facilitate coagulation, the pore diameter on the outer surface becomes large and large. Also, like the case of the inner surface, the shape of the holes changes from a circular shape with a smooth periphery to a shape where the number of holes increases and the circles are in contact with each other, and a perfect mesh shape. . In any of the shapes, as in the case of the inner surface, the shape of the holes has almost no specific directionality. Also, the state of the inner surface and the outer surface,
Since there is no specific directionality regardless of the size and shape of the holes, reproducibility in manufacturing is extremely high.

In the hollow fiber membrane produced by the present invention, strong branches are continuously developed three-dimensionally, and both tensile strength and elongation at break are large, and the elongation is particularly 50.
It reaches ~ 100%. Further, because of such a structure, the filtration speed exceeds that of the conventional hollow fiber membrane.

Hereinafter, the production method of the present invention will be described more specifically with reference to Examples.

The state (structure) of the hollow fiber membrane was observed with a scanning electron microscope. The filtration rate of water was expressed as 1 / m ² · hr · kg / cm ² by using a small module and filtering from the outer surface to the inner surface of the hollow fiber membrane. However, the effective membrane area was measured on the outer surface, and the pressure was the pressure difference between the outer and inner surfaces. Furthermore, the strength of the hollow fiber membrane is
Using an autograph AG-2000A manufactured by Shimadzu Corporation, measurement was performed at a sample length of 50 mm and a pulling speed of 50 mm / min. The tensile strength is represented by the load (gram) at break per hollow fiber membrane, and the elongation is represented by the length (%) of the original length that has been extended to break.

Test Example 1 Number average molecular weight of 50,000, 100,000, 200,000, 300,000, 500,000, 200
And 4 million polyethylene glycols were dissolved in N-methyl-2-pyrrolidone to a total amount of 100 g in 100 cc eggplant-shaped flasks at different concentrations, and then put into a stainless steel stirring rod at 60 ° C. The presence of the normal stress effect was judged by observing the ascending state. Polyethylene glycol solutions with number average molecular weight less than 100,000 had no normal stress effect at concentrations less than 15%. Number average molecular weight is 20
A solution of 1 to 2 million polyethylene glycol had a normal stress effect at 2-15%, depending on the molecular weight. However, a solution of 4 million polyethylene glycols had a too strong normal stress effect at 2% or more, and was closer to a gel state than a uniform solution, and it was difficult to dissolve it. These characteristics are such that N-methyl-2-pyrrolidone contains about 15% of propylene glycol, which is a nonsolvent of polysulfone.
Similar observations were made when% was added.

Examples 1 to 3 A mixed solvent of 66 parts of N-methyl-2-pyrrolidone (parts by weight, the same applies hereinafter) and 9 parts of propylene glycol had a number average molecular weight of
A solution having a normal stress effect was prepared by dissolving 5 parts of 300,000 polyethylene glycol, and 20 parts of polysulfone (Udel Polysulfone P-3500 manufactured by Amoco) was dissolved in the solution to prepare a spinning dope. While keeping this spinning solution at 60 ° C, use the core solution listed in Table 1 and using an inner diameter of 0.5 mm.
, Discharge from a nozzle with an outer diameter of 0.8 mm, 15 cm below the nozzle
Coated in warm water at 60 ℃ at 50m / min, and the inner and outer diameters were about 450μm and 7
A hollow fiber membrane of 00 μm was obtained. The characteristics of the obtained hollow fiber membrane are shown in Table 1.

The meanings of the symbols in Table 1 are as follows.

G: Glycerin N: N-Methyl-2-pyrrolidone ICP: Circular pores are dispersed independently PSCP: Circular pores are in contact with each other (the larger the pores, the more contact SNW: Resilient mesh structure

[0053]

[Table 1]

Examples 4-6 N-methyl-2-pyrrolidone 67.5 parts and propylene glycol
5 parts of polyethylene glycol having a number average molecular weight of 300,000 was dissolved in a mixed solvent with 11.5 parts to prepare a solution having a normal stress effect, and 16 parts of polysulfone was dissolved therein to prepare a spinning dope. While maintaining this at 60 ° C, the core liquid shown in Table 2 was used to discharge from a nozzle with an inner diameter of 0.4 mm and an outer diameter of 0.6 mm, and solidified in warm water at 60 ° C 15 cm below the nozzle. It was wound at a spinning speed of 50 m / min to obtain hollow fiber membranes having inner and outer diameters of about 300 μm and 500 μm. The properties of the obtained hollow membrane are shown in Table 2.

The symbols in Table 2 have the following meanings.

P: Propylene glycol SSCP: A state in which a large number of circular holes are in contact with each other NWP: A reticulated structure in which most of the circular holes are in contact with each other to form continuous branches NW: A reticulated structure

[0057]

[Table 2]

Test Example 2 Pseudomonas diminutor IFO-12697 so that the load on the hollow fiber membrane of Example 6 would be 10 ⁷ pieces / cm ^2.
(Pseudomonas diminuta IFO-12697) culture fluid was filtered. This bacterium was not detected in the filtered liquid.

Test Example 3 A small module was prepared by using the hollow fiber membrane of Example 6 and made of a hollow fiber membrane made of polysulfone taken out from a commercially available household water purifier. We compared the filterability for Kobe city tap water. The life was defined as when the filtration speed decreased to 500 liters / m ² · hr · kg / cm ² . The cumulative filtration amount up to the life was 1.84 times that of the hollow fiber membrane of the present invention as compared with the comparative one, and the life was extremely long.

Comparative Example 1 60.2 parts of N-methyl-2-pyrrolidone and propylene glycol
Ten parts of polyethylene glycol having a number average molecular weight of 50,000 was dissolved in a mixed solvent with 9.8 parts. This solution had no normal stress effects. A hollow fiber membrane was prepared in the same manner as in Example 1 by dissolving 20 parts of polysulfone into a stock solution for spinning. The outer surface of this hollow fiber membrane has an average pore size of about 0.8 μm.
, But circular holes were formed on the inner surface.

Comparative Example 2 N-methyl-2-pyrrolidone 68 parts and propylene glycol 11
1 part of polyethylene glycol having a number average molecular weight of 4,000,000 was dissolved in a mixed solvent with 1 part to prepare a solution having a normal stress effect. A hollow fiber membrane was prepared in the same manner as in Example 1 by dissolving 20 parts of polysulfone into a spinning dope.
This hollow fiber membrane had pores of relatively uniform shape on both the inner and outer surfaces and had high tensile strength, but the filtration rate was extremely low.

Example 7 A hollow fiber membrane was prepared in the same manner as in Example 4 except that a 50% aqueous solution of polyethylene glycol having a number average molecular weight of 1000 was used as the core liquid. The outer surface of this hollow fiber membrane had a large number of circular pores with an average pore diameter of about 0.8 μm, and the inner surface had substantially circular uniform pores of about 0.03 μm or less that were not slit-like. In addition, the inside had a mesh structure in which the size of the eyes gradually increased from the inner surface to the outer surface.

[0063]

INDUSTRIAL APPLICABILITY In the present invention, since a polysulfone hollow fiber membrane is produced using a spinning dope prepared by dissolving polysulfone in a solution of polyethylene glycol having a normal stress effect, polysulfone molecules are not oriented in a specific direction.
Uniform holes are formed on both the inner and outer surfaces of the hollow fiber membrane. The hollow fiber membrane thus formed has a network structure in which thick branches are three-dimensionally continuous inside, and simultaneously satisfies high strength and filtration rate. Such an effect does not appear in the polyvinylpyrrolidone used in the prior art.

Claims (1)

(57) [Claims] 1. A high-strength, porous polysulfone, characterized in that polysulfone dissolved in a solution of polyethylene glycol having a normal stress effect and a number average molecular weight of 150,000 to 2,000,000 is used as a spinning stock solution. Hollow fiber membrane manufacturing method.