JPH04260424A - Manufacture of porous polysulfone hollow fiber membrane having high strength - Google Patents

Abstract

PURPOSE:To obtain a polysulfone hollow fiber membrane having a network structure whose inside comprises three-dimensionally continuous, thick branches and satisfying a high strength and a high rate of filtration at the same time. CONSTITUTION:A polysulfone hollow fiber membrane is manufactured from a spinning stock solution which is prepared by dissolving polysulfone in a solution of polyethylene glycol having a number-average molecular weight of 150,000-2,000,000 according to the dry and wet spinning.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polysulfone hollow fiber membranes. More specifically, the present invention relates to a method for producing a high-strength, porous polysulfone hollow fiber membrane having uniformly shaped pores on the inner and outer surfaces of the hollow fibers.

0002

BACKGROUND OF THE INVENTION Polysulfone hollow fiber membranes are widely used in industrial precision filtration or ultrafiltration because of their excellent heat resistance and chemical resistance.

Conventional polysulfone hollow fiber membranes are manufactured by a so-called dry-wet spinning method. This method basically consists of a step in which a homogeneous or nearly homogeneous solution of polysulfone is extruded into the air together with a core liquid through a double nozzle, and then immersed in a coagulation liquid.

[0004] Up to now, many improvements have been made to each of the above steps, mainly for the purpose of improving the permeation performance of the membrane.

[0005] The conventional technology related to polysulfone hollow fiber membranes having relatively large pores, which is related to the present invention, will be explained below.

[0006] In the conventional technology, the spinning dope is as follows:
A solution in which aromatic polysulfone is dissolved in a mixture of its good solvent and additives is usually used.

As the good solvent, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc., which are water-soluble and have a high boiling point, are used.

The additives include polysulfone non-solvents, such as polyhydric alcohols having 2 to 4 carbon atoms (see JP-A-56-15270 and JP-A-60-222112), and water-soluble pore-forming agents. , for example, polyethylene glycol (JP-A-54-26283, JP-A-57-35906)
JP-A-61-93801, JP-A No. 61-23)
No. 8306 and No. 63-97205) are used.

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

[0010] The temperature of the spinning dope is kept constant within a range where the spinning dope becomes uniform or almost uniform.

[0011] The traveling distance in the air is usually set to several cm/several tens of cm.

As with 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 set in a range from room temperature to about 70°C.

[0013] The spinning speed is usually 20 to 70 m/min.

[0014] In order to further stabilize the structure of the hollow fiber membrane produced by such a method and to prevent the membrane from losing its filtration performance even when dried, a process of soaking it in hot water of 80° C. or higher is added. There are also (see Japanese Patent Application Laid-open No. 71606/1983).

[0015] The outline of the conventional techniques particularly related to the present invention is as above, and the problems of these will be discussed next.

[0016]

As mentioned above, aromatic polysulfone hollow fiber membranes have excellent heat resistance and chemical resistance, and are widely used industrially for everything from ultrafiltration to precision filtration. As a result, there is a growing demand for filters that can withstand rapid temperature changes such as hot water sterilization and steam sterilization, and that can be used in applications that are subjected to harsh handling like conventional pleated cartridge filters. There is.

[0017] However, because the conventional manufacturing method was developed with emphasis on improving the filtration performance of the membrane, the breaking strength and especially the elongation at break of the hollow fiber membrane are low, and the rapid increase as described above is low. It has been pointed out that polysulfone hollow fiber membranes often break in applications where they are subjected to temperature changes or harsh handling.

For example, in JP-A-57-35906 and JP-A-58-114702, in order to increase the filtration rate, a solution of polysulfone such as dimethylformamide is The average molecular weight is so large that it phase separates and becomes cloudy.
~20,000 polyethylene glycol was added,
A uniform solution obtained by cooling this is used as a spinning dope. As shown in Figure 6 of JP-A-58-114702, the hollow fiber membrane produced from this spinning dope has a network structure with many discontinuous thin branches, so it is difficult to Both the strength and the elongation at break are low, especially the elongation at break does not reach 25%.

Furthermore, Japanese Patent Application Laid-Open No. 60-222112 discloses that in order to increase the pore diameter, a solution of polysulfone such as N-methyl-2-pyrrolidone is added as a spinning stock solution.
A non-solvent such as propylene glycol is added so that the solution phase separates at temperatures below room temperature, and this is heated to form a homogeneous solution. As shown in Figure 9 of the same publication, the hollow fiber membrane produced from this spinning dope has a highly developed network structure with uninterrupted branches, so the elongation at break is large and can reach 100%. Some even reach.

However, when the polysulfone concentration in the spinning dope is increased and the thickness of the hollow fibers is also 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 decreases significantly. .

[0021] Therefore, even with this method, a film having satisfactory tensile strength cannot be obtained.

On the other hand, JP-A-61-93801 and JP-A-61-238 using polyvinylpyrrolidone as an additive
The hollow fiber membranes described in JP-A No. 306 and JP-A No. 63-97205 also have the same problems as those described in JP-A-57-35906 and the like when polyethylene glycol is added.

[0023] Furthermore, hollow fiber membranes having macrovoids inside, which are generally used for ultrafiltration, have lower strength than those without macrovoids.

Another problem with the prior art is that the pores on the inner or outer surface of the hollow fiber membrane are irregular in shape and lack uniformity. For example, the hollow fiber membranes described in JP-A-57-35906 and JP-A-58-114702 have slit-like holes with irregular lengths and widths on their inner surfaces.
The holes on the outer surface are also irregular in shape (for example, in JP-A-58-1
(Figures 4 and 5 of Publication No. 14702). In hollow fiber membranes having such irregularly shaped pores, when the pore diameter is increased, the reproducibility of filtration performance such as molecular weight cutoff and filtration rate becomes poor.

[0025] JP-A-61-23806 and JP-A-63-97205 using polyvinylpyrrolidone as an additive
This publication also has the same problem as above.

The present invention has been made to solve the above-mentioned problems, and has significantly greater tensile strength and elongation at break than conventional hollow fiber membranes, and has a uniform shape on the inner and outer surfaces. The purpose of this invention is to obtain a hollow fiber membrane having large pores.

[0027]

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the inventors have arrived at the following idea.

That is, as mentioned above, regarding the relationship between the structure, strength, and filtration rate of hollow fiber membranes, ① Hollow fiber membranes with a network structure consisting of thin branches, some of which are not continuous inside, have a high filtration rate. The speed is high, but the tensile strength and especially the elongation at break are low. ■Hollow fiber membranes with a cellular structure inside are
Both the tensile strength and the elongation at break are high, but the filtration rate is low.Therefore, it is thought that a hollow fiber membrane with a high strength and filtration rate exists between the structures (1) and (2).

Regarding the uniformity of the pore shapes on the inner and outer surfaces, conventional methods use polysulfone with a relatively small degree of polymerization of several tens of degrees, and polysulfone molecules with a low degree of polymerization are removed from the nozzle. As a result of being highly oriented when extruded, when it comes into contact with the core liquid, which has a strong coagulating force, the orientation state is almost fixed as it is, and as shown in Figure 4 of JP-A-58-114702, a slit-like shape is formed. On the other hand, when polysulfone comes into contact with a core liquid that has weak coagulation power, intermolecular cohesion is strong between nearby molecules, but because the molecular weight is small, aggregation does not extend over long distances and is localized. It is thought that an agglomerated state (an irregular state in which the shape of the pores is not constant) is formed, as shown in Fig. 6 of JP-A No. 60-222112. In order to achieve this, it is considered necessary to prepare a spinning stock solution that does not orient the polysulfone molecules when exiting from the nozzle and prevents the polysulfone from locally aggregating.

[0030] In all of the above conventional methods, polysulfone with a relatively small degree of polymerization of several tens of degrees is used, and the concentration and composition of the solution are also explained in detail. Although the phase separation temperature and common sense viscosity are also explained, there is no other explanation or suggestion regarding the relationship between the characteristics of the hollow fiber membrane and the characteristics of the spinning dope. .

[0031] In accordance with the above-mentioned concept, the present inventor has conducted repeated studies to create a hollow fiber membrane that solves the above-mentioned two problems at the same time.As a result, the present inventor has developed a method using a spinning dope in which the molecular weight of polyethylene glycol as an additive is varied over a wide range. When producing hollow fiber membranes, they discovered that the above two problems could be solved at the same time by selecting a spinning dope with specific solution properties based mainly on the molecular weight of polyethylene glycol, and completed the present invention. I ended up doing it.

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

[0033]

[Function] In the conventional method, polysulfone molecules were oriented in the fiber axis direction because they were oriented only in the fiber axis direction, but a spinning dope using a solution of polyethylene glycol with a number average molecular weight of 150,000 to 2 million When extruded from a nozzle, the polysulfone molecules expand rapidly in the radial direction (having a normal stress effect), so the polysulfone molecules become oriented not only in the fiber axis direction but also in the circumferential direction, and the polysulfone molecules are oriented in a specific direction. It becomes unoriented. Therefore, uniformly shaped pores are formed on the inner and outer surfaces of the hollow fiber membrane. In addition, the above-mentioned high molecular weight polyethylene glycol gives a normal stress effect when added in a small amount, and the inside of the hollow fiber membrane made from such a spinning dope has a network of three-dimensionally continuous thick branches. It has a structure that satisfies high strength and filtration speed at the same time.

[0034]

[Example] The polysulfone used in the present invention has the formula (1)
:

[0035]

[Chemical formula 1]

Or formula (2):

[0037]

[Case 2]

A typical example is one consisting of a repeating unit represented by the following.

The number average molecular weight of the polyethylene glycol used in the present invention is 150,000 to 2,000,000, preferably 20,000 to 2,000,000.
It is between 10,000 and 500,000. If the number average molecular weight is less than 150,000, it is necessary to add a large amount to provide a normal stress effect, and a hollow fiber membrane with a network structure of thin branches is formed from such a spinning stock solution. Strength decreases. On the other hand, 20
When it exceeds 0,000, the solubility of polyethylene glycol decreases, a hollow fiber membrane with a cellular structure is formed, and the filtration rate decreases.

The above-mentioned normal stress effect refers to a phenomenon in which when a solution of polyethylene glycol is stirred with a stirring rod, the solution crawls up to the stirring rod by exceeding the surface tension of the solution.

Solvents used to prepare the polyethylene glycol solution include dimethylformamide, dimethylacetamide, N- which is also a polysulfone solvent.
Methyl-2-pyrrolidone and the like can be used, but N-methyl-2
- Particular preference is given to pyrrolidone. Of course, it is also possible to use a mixed solvent in which a small amount of water or a low molecular weight polyhydric alcohol such as propylene glycol is added to these good solvents. The polyethylene glycol is added to these solvents in an amount of 1 to 15% (by weight, the same applies hereinafter), preferably 2 to 10%.
A solution exhibiting normal stress effects is prepared by dissolving %. The amount of dissolved polyethylene glycol is 15%
When the amount is more than 1%, the hollow fiber membrane becomes weak, and when it is less than 1%, the filtration rate becomes low.

[0042] Polysulfone is added to the polyethylene glycol solution in an amount of usually 15 to 35%, preferably 16 to 2%.
5% dissolved. Note that there is no particular limitation on the order in which the solution containing polysulfone and polyethylene glycol is prepared. If the dissolved amount of polysulfone is less than 15%, the strength of the hollow fiber membrane will be reduced, and if it exceeds 35%, the viscosity will increase and it will be difficult to prepare a solution. In this case, the strength of the hollow fiber membrane also increases, but the performance exceeds the required strength.

[0043] In the same manner as in the conventional method, the spinning stock solution having the above-mentioned characteristics is extruded from a double nozzle together with the core liquid, and after traveling an appropriate distance in the air, it is immersed in the coagulation liquid and then wound up. High strength and
A porous polysulfone hollow fiber membrane is produced.

At this time, as the coagulation effect of the core liquid becomes weaker, the pores on the inner surface become larger and more numerous. In addition, the shape of the pores changes from a circular shape with a smooth periphery, to a shape where the number of pores increases and two circles touch each other, and then to a complete net shape. There is no particular directionality in the shape of the pores in any of the shapes.

On the other hand, if the traveling distance in the air is increased or if a non-solvent is added to the spinning dope to make it easier to coagulate, the pore diameter on the outer surface becomes larger and more numerous. Also, as with the inner surface, the shape of the pores changes from a circular shape with a smooth periphery, to an increasing number of pores, to a shape where two circles touch each other, and then to a complete net shape. . In either shape, as with the inner surface, the shape of the hole has almost no specific directionality. In addition, the inner and outer conditions include
Since there is no specific directionality regardless of the hole size or shape, the manufacturing reproducibility is extremely high.

The inside of the hollow fiber membrane produced according to the present invention has strong branches that are continuously developed three-dimensionally, and has high tensile strength and elongation at break, especially elongation of 5.
It reaches 0-100%. Moreover, since it has such a structure, its filtration rate also exceeds that of conventional hollow fiber membranes.

[0047] The production method of the present invention will be explained in more detail below with reference to Examples.

The state (structure) of the hollow fiber membrane was observed using a scanning electron microscope. Furthermore, the water filtration rate was expressed as 1/m2·hr·kg/cm2, 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 difference between the membranes between the outer surface and the inner surface was used for the pressure. Furthermore, the strength of the hollow fiber membrane was measured using Autograph AG-200 manufactured by Shimadzu Corporation.
Measurement was carried out using 0A, sample length of 50 mm, and pulling speed of 50 mm/min. The tensile strength is expressed as the load (grams) at break per hollow fiber membrane, and the elongation is
It is expressed as the length (%) elongated to breakage relative to the original length.

Test Example 1 Number average molecular weight is 50,000, 100,000, 200,000, 300,000, 50
1,000,000, 2,000,000 and 4,000,000 polyethylene glycol were added to N-methyl-2-pyrrolidone at different concentrations in a 100 cc eggplant-shaped flask until the total amount was 100%.
The presence or absence of a normal stress effect was determined by observing the state in which it crawled onto a stainless steel stirring bar at 60°C. A solution of polyethylene glycol with a number average molecular weight of 100,000 or less had no normal stress effect at a concentration of 15% or less. Number average molecular weight is 200,000 to 20
Solutions of 0,000 polyethylene glycol had normal stress effects between 2 and 15%, depending on molecular weight. However, a solution of 4 million polyethylene glycol
At 2% or more, the normal stress effect was so strong that it resembled a gel state rather than a uniform solution, making it difficult to dissolve. These characteristics were similarly observed when approximately 15% propylene glycol, a non-solvent for polysulfone, was added to N-methyl-2-pyrrolidone.

Examples 1 to 3 5 parts of polyethylene glycol having a number average molecular weight of 300,000 was dissolved in a mixed solvent of 66 parts (by weight, same hereinafter) of N-methyl-2-pyrrolidone and 9 parts of propylene glycol. Prepare a solution with linear stress effect and add polysulfone (Udel Polysulfone P-3500 manufactured by Amoco) to this solution.
A spinning stock solution was prepared by dissolving 20 parts of. While maintaining this spinning stock solution at 60°C, using the core liquid listed in Table 1, it was discharged from a nozzle with an inner diameter of 0.5 mm and an outer diameter of 0.8 mm, and was placed in a warm water at 60°C located 15 cm below the nozzle. While coagulating with a spinning speed of 50 m/min,
The inner and outer diameters are approximately 450μm and 700μm.
A hollow fiber membrane of μm size was obtained. Table 1 shows the properties of the hollow fiber membrane obtained.

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

G: Glycerin N: N-methyl-2-pyrrolidone ICP: PSCP in which circular pores are independently dispersed
: A state where some circular holes are in contact with each other (as the number of holes increases, the number of holes in contact with each other also increases) SNW:
A network of strong branches

[0053]

[Table 1]

Examples 4 to 6 A number average molecular weight of 30 was added to a mixed solvent of 67.5 parts of N-methyl-2-pyrrolidone and 11.5 parts of propylene glycol.
A solution having a normal stress effect was prepared by dissolving 5 parts of polyethylene glycol, and 16 parts of polysulfone was dissolved therein to prepare a spinning dope. While keeping this at 60℃, using the core liquid listed in Table 2,
A hollow fiber membrane with inner and outer diameters of approximately 300 μm and 500 μm was produced by discharging it from a nozzle with an outer diameter of 0.6 mm and coagulating it in hot water at 60°C located 15 cm below the nozzle, and winding it up at a spinning speed of 50 m/min. I got it. Table 2 shows the properties of the obtained hollow membrane.

The meanings of the symbols in Table 2 are as follows.

P: Propylene glycol SSCP: State where many circular holes are in contact with each other NW
P: Network structure in which most of the circular pores are in contact with each other and the contact areas form continuous branches NW: Network structure

[0057]

[Table 2]

Test Example 2 Load amount on the hollow fiber membrane of Example 6 was 107 pieces/cm
2 Pseudomonas diminuta
IFO-12697 (Pseudomonas dim
Inuta IFO-12697) culture solution was filtered. This bacterium was not detected in the filtrate.

Test Example 3 A small module was made using the hollow fiber membrane of Example 6, and the effective membrane area was approximately the same as that of a small module made from a hollow fiber membrane made of polysulfone taken from a commercially available household water purifier. The filtration capacity for Kobe city tap water was compared. Filtration speed is 500 liters/m2・hr・kg/cm
The life span was defined as the time when the temperature decreased to 2. The cumulative filtration amount over the life of the hollow fiber membrane according to the present invention is 1.8 higher than that of the comparative membrane.
It had an extremely long lifespan, four times as long.

Comparative Example 1 A mixed solvent of 60.2 parts of N-methyl-2-pyrrolidone and 9.8 parts of propylene glycol had a number average molecular weight of 5.
10 parts of polyethylene glycol was dissolved. This solution had no normal stress effects. 20 parts of polysulfone was dissolved in this to prepare a spinning dope, and a hollow fiber membrane was produced in the same manner as in Example 1. Circular pores with an average pore diameter of approximately 0.8 μm were formed on the outer surface of this hollow fiber membrane.
Holes with irregular shapes were formed on the inner surface.

Comparative Example 2 A mixed solvent of 68 parts of N-methyl-2-pyrrolidone and 11 parts of propylene glycol had a number average molecular weight of 4,000.
,000 of polyethylene glycol was dissolved to create a solution with a normal stress effect. 20 parts of polysulfone was dissolved in this to prepare a spinning dope, and a hollow fiber membrane was produced in the same manner as in Example 1. This hollow fiber membrane had relatively uniformly shaped pores 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 many circular pores with an average pore diameter of approximately 0.8 μm, and the inner surface had substantially circular uniform pores with an average diameter of approximately 0.03 μm or less that were not slit-shaped. The interior had a net-like structure, with the eyes gradually increasing in size from the inner surface to the outer surface.

[0063]

Effects of the Invention In the present invention, since a polysulfone hollow fiber membrane is manufactured using a spinning stock solution in which polysulfone is dissolved in a polyethylene glycol solution having a normal stress effect, polysulfone molecules are no longer oriented in a specific direction. Holes of uniform shape 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, and satisfies high strength and filtration speed at the same time. Such an effect is not exhibited by polyvinylpyrrolidone used in conventional technology.

Claims (1)

[Claims] 1. A high-strength, porous polysulfone characterized in that the spinning dope is a solution of polysulfone having a normal stress effect and a number average molecular weight of 150,000 to 2,000,000. Manufacturing method for hollow fiber membranes.