JPH0712416B2 - Hollow fiber type substance separation membrane - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hollow fiber type substance separation membrane having a fine pore structure, and in particular, there is no deterioration in performance over time, so-called clogging or fouling. The present invention relates to a hollow fiber type substance separation membrane having stable membrane performance.

(Prior Art) Conventionally, the concept of removing a specific component has been generally used for material separation by a membrane. That is, the main purpose is to remove inorganic ions, endotoxins, fine particles, etc. contained in water such as desalination of seawater by the reverse osmosis method, production of ultrapure water in the field of electronic component production, and production of pyrogen-free water for medical use. Thus, little emphasis was placed on the fractionation of substances.

However, today, the separation of substances by membranes is also focused on this point. For example, membrane systems are being used as biocatalyst recycling systems in fermentation or enzymatic reactions. The role of the membrane in this system is to separate the biocatalyst from the product, and unlike the conventional concept of removal, biocatalyst that is not excluded from the membrane is reused. Further, the role of the membrane in collecting plasma from a healthy person is to fractionate the blood cell component, and the blood cell component is returned to the blood donor again.
In this way, separation and fractionation are the two
Although there are two concepts, most of the fine filtration (MF) membranes that have been developed and used in the past were intended for removal, and were not suitable for fractionation of substances. This is due to the large variation in the pore size distribution of the conventional MF membrane, but from the viewpoint of the membrane structure, the conventional MF membrane has a sponge-like or three-dimensional network structure. ing. Such pores are those that pass through the gaps of the membrane material in a zigzag manner, and the smallest gap portion in the passage of the pores is the portion that determines the passage performance of the membrane. What has this minimum gap part uniformly distributed over the entire film is considered to be a film with excellent removal characteristics.
If the minimum gap has a uniform size, it can be said that a substance having a size larger than the minimum gap does not leak out of the membrane and is excellent in terms of removal. However, the size of the gap of the membrane material in the part other than the minimum pore size is ignored, and the greater the variation in the size of the gap in this part is,
That is, the larger the standard deviation value σ of the pore size distribution of the entire membrane, the larger the size of the substance entering the membrane material gap,
The substance that cannot pass through the minimum gap remains in the gap as it is. For this reason, in such a sponge-like or three-dimensional network structure membrane, a change in membrane permeation performance due to clogging or fouling, a change in membrane performance such as a decrease in overspeed, etc. are caused. As described above, the conventional MF membrane shows excellent performance in removing substances in a dilute system, but the performance during use of the membrane is superior in the substance fractionation of a rich system or a system containing substances of various sizes. However, there was a problem in that stable fractionation performance could not be obtained.

(Problems to be solved by the invention) The stability of the performance over time, which is difficult in the conventional precision membrane, that is, the membrane separation structure required for a precision membrane without clogging or fouling Another object of the present invention is to provide a hollow fiber type substance separation membrane, which has an advantage and can be advantageously used for fractionation of concentrated substances.

(Means for solving the problem) As a means for preventing the performance of the membrane from changing over time when using the membrane, a structure should be adopted in which a substance having a size that blocks the pores of the membrane is not taken into the membrane. It is basically necessary to do. Rather than uniformizing only the minimum gap as in conventional MF membranes, if the pore size of the entire membrane wall is made uniform and substances that block the membrane pores on the membrane surface can be eliminated, the pores inside the membrane will be It is possible to obtain a stable MF membrane that is free from clogging and does not change with time when the membrane is used. That is, in the present invention, the average pore diameter P of the pore size distribution of the pores existing on the entire membrane wall and the standard deviation value σ of the distribution are 0.01 (μ
m) ≦ P ≦ 0.6 (μm) and σ / P ≦ 1.0, and the porosity ε of the membrane is 0.6 ≦ ε ≦ 0.8. It has stable film performance that does not change with time. The pore size distribution here refers to all pores existing in the entire membrane wall, and the average pore size P and standard deviation value σ are calculated by parameters obtained by approximating the pore size distribution to a lognormal distribution. It The pore size distribution of the membrane was measured by the generally used mercury intrusion method. In the mercury injection method, the relationship between the injection pressure and the injection amount of mercury can be obtained.
The number of pores can be determined from the amount of press fit. Further, the porosity of the film can be calculated from the total amount of mercury injected. In approximating the pore size distribution to a lognormal distribution, it is found by linear approximation by plotting the pore size and the integrated press-fit amount on a lognormal probability paper. The lognormal distribution is shown by the following equation.

γ: Pore diameter [μm] (γ): Probability of existence of pore diameter γ [-] θ ₁ , θ ₂ : Parameter average pore size P and standard deviation value σ are And in the lognormal distribution From this, P and σ can be obtained. P represents the average pore size of the pores, but P is 0.01 (μm) to 0.6 (μm)
In the region where P is less than 0.01 μm, the meaning is defined as the ultrafiltration (UF) membrane region rather than the MF membrane region, and these separation characteristics are more important than the pores in the membrane than the MF membrane region. This is because it is dominated by the gel layer or the concentration polarization layer formed on the surface, and the pore size distribution is hardly a problem. In the region where P exceeds 0.6 μm, the size of the MF membrane is very close to the size of microorganisms, cell components in blood, etc., which is the target of fractionation, and the particles of the MF membrane are separated into pores on the membrane surface. Due to the biting and the clogging that accompanies it, the overperformance is significantly reduced. In the hollow fiber membrane,
Due to the relationship with spinning, it becomes a very difficult area for film formation in terms of strength, which is not realistic. For these reasons, it is necessary that the average pore size P of the microstructure of the membrane be between 0.01 μm and 0.6 μm. When the standard deviation value σ of the pore size distribution is σ / P ≦ 1 in relation to the average pore size P, it can be said that the pore size distribution is extremely uniform. Therefore σ / P
In a film satisfying the relationship of ≦ 1, not only are the pores present in the film of uniform size, but there is little change in the size even in one interstitial passage, and the pores enter the pores from the film surface. The substance will pass through the membrane without any obstacles. That is, when such a relationship is satisfied, it can be said that the structure is such that clogging inside the film and fouling do not easily occur. In fact, when observing the membrane with a uniform pore size distribution with an electron microscope, the membrane material is not a sponge-like or three-dimensional network structure of the conventional MF membrane, but the membrane material becomes a particle-filled structure. Is observed. Further, in such a structure, the porosity of the film takes a value slightly smaller than that of the conventional MF film. However, the porosity ε is 0.6
If the ratio is less than the above, the number of pores on the membrane surface will decrease, and as a result, the efficiency of the membrane surface will decrease. Therefore, as a result of increasing the amount of the substance passing through the pore gaps, the probability of causing clogging and fouling increases. Therefore, the value of ε needs to be 0.6 or more. On the other hand, if ε is too high, the strength becomes very weak in the particle packing structure due to the membrane structure, so that it is difficult to form a hollow fiber membrane. Further, when the film is formed with a high ε, the film structure changes to a sponge-like or three-dimensional network structure, and it is difficult to obtain a film having a uniform pore size distribution. For these reasons, it is necessary to select the porosity of the film from the range of 0.6 ≦ ε ≦ 0.8.

As described above, the hollow fiber type substance separation membrane according to the present invention is a novel MF membrane having a pore size distribution membrane structure different from that of the conventional MF membrane, and has excellent substance fractionation characteristics with almost no clogging or fouling during use. It is an MF membrane with.

Such a hollow fiber type substance separation membrane according to the present invention is produced, for example, by the following method. That is, a polymer concentration is 20% by weight or more, and a spinning stock solution is prepared using an aprotic polar solvent and a non-solvent, and then the spinning stock solution and the inner solution are discharged from a double tube nozzle, It is manufactured by coagulating under controlled conditions and controlling the membrane pore size.

Solidification conditions: O <T ₁ −T ₂ ≦ 40 (℃) (where T ₁ is the discharge temperature,
T ₂ is the coagulation bath temperature), and the concentration of the solvent and the non-solvent in the coagulation bath and the internal solution ≧ 50% by weight.

Preparation of spinning solution A polymer concentration of 20% by weight or more and a solvent of 150%
A spinning stock solution is prepared by using an aprotic polar solvent having a boiling point of not lower than 0 ° C. and the non-solvent. As the aprotic polar solvent, N-methylpyrrolidone (bp202 ° C), dimethylformamide (bp153 ° C), dimethylacetamide (bp1)
64 ° C), dimethylsulfoxide (bp189 ° C), etc., and as nonsolvents, polyhydric alcohols compatible with water such as ethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polypropylene glycol, etc., and alcohols such as methanol, ethanol, etc. However, it is not limited to these.

In this way, the polymer is mixed and dissolved in the solvent and the non-solvent to prepare a spinning dope. At this time, the important point is the polymer concentration. That is, in the past, in order to form a separation membrane, it was general to set the polymer concentration to a low value to increase the water permeation rate, but the present invention, contrary to the conventional method, uses a high polymer concentration at a later time. It is intended to produce a film that is clogged with the film and does not cause fouling.

Thus, in the present invention, it is necessary to adjust the polymer concentration to 20% by weight or more. If it is less than 20% by weight, a film having desired performance cannot be formed, which is not preferable.

Discharging and coagulation process The spinning solution prepared as described above is subjected to defoaming treatment, heat treatment,
Over-process and discharge from a double tube nozzle. It is important to let the internal liquid flow down into the hollow portion of the hollow fiber at the time of discharging. The internal liquid is a water-soluble coagulating liquid which uses the above-mentioned solvent and non-solvent, and it is necessary to set the concentration of these solvent and non-solvent to 50% by weight or more.

The hollow fibers after discharge are solidified in a coagulation bath. In this case also, it is necessary to set the concentration of the solvent and the non-solvent to 50% by weight or more as in the case of the above inner liquid.

That is, by using a high concentration solvent and non-solvent system in the coagulation bath and internal solution, the particle size of the polymer formed at the time of coagulation is made as large as possible to form the membrane structure as a granular aggregate structure and excellent in permeability. A separation membrane was obtained. In other words, if the concentration of the solvent and non-solution (total concentration of solvent and non-solvent) in the coagulation bath and the internal liquid is less than 50% by weight, the coagulation rate for forming the porous membrane is too fast and the outer surface of the hollow fiber is very dense. In addition, the above-mentioned granular aggregate structure is not formed on the inner surface of the hollow fiber.

Further, an important point in forming this granular aggregate structure is O <T ₁ −T ₂ ≦ 40 (where the coagulation bath temperature (T ₂ ) during coagulation regeneration and the discharge temperature (T ₁ ) of the double tube nozzle are ℃) to satisfy the relationship. In other words, if there is no temperature difference of (T ₁ −T ₂ ), coagulation is insufficient and no membrane pores are formed, and if the temperature of (T ₁ −T ₂ ) exceeds 40 ° C, the above coagulation conditions are not met. Similarly, since the solidification rate at the time of forming the porous film is too fast, the desired film structure of the present invention cannot be obtained, which is not preferable.

Water Washing and Winding Steps The hollow fibers that have undergone the coagulation step described above are subsequently subjected to a water washing step to remove excess solvent and non-solvent, and then subjected to an appropriate heat treatment to be wound up. Further or thereafter, it is desirable to perform a hydrophilic treatment with a polyhydric alcohol such as glycerin to give a so-called wettability.

By adopting the above-mentioned steps, a hollow fiber type separation membrane having a pore structure in which the permeability can be remarkably enhanced and which is clogged with time and has no fouling was obtained. The polymer used in the present invention is preferably a cellulose thread polymer such as cellulose acetate or cellulose triacetate, or a synthetic polymer, but is not limited thereto.

The hollow fiber type material separation membrane thus obtained is made into a module by a usual method with a urethane adhesive or the like,
Used as a final product.

Next, a concrete description of the hollow fiber type substance separation membrane of the present invention will be described by way of Examples.

Example Cellulose triacetate (CTA) was used as the polymer of the membrane material, N-methylpyrrolidone (NMP) was used as the solvent, and polyethylene glycol (PEG, molecular weight 40 was used as the micropore-forming agent.
The three components of 0) were mixed and dissolved at 140 ° C. to prepare a stock solution for spinning a hollow fiber membrane. This spinning solution was discharged from a double-tube nozzle together with water, an internal solution consisting of three components of NMP and PEG.
A hollow fiber membrane is formed by a (dry) wet spinning method by discharging into a coagulating liquid composed of three components of NMP and PEG. In order to obtain a uniform pore size distribution of the hollow fiber type substance separation membrane of the present invention, the coagulation conditions are such that the spinning dope temperature is lowered to 90 ° C or lower, and the coagulation liquid temperature is 70 ° C or higher, and coagulation is performed under very mild conditions. . Furthermore, in order to control the strength and porosity of the membrane, the polymer concentration in the spinning dope was increased (27%) to obtain a hollow fiber type membrane.
(No. 1 in Table 1) Furthermore, as a comparative example, a hollow fiber type substance separation membrane of a conventional MF membrane was also formed. (Nos. 2 to 4 in Table 1) When these hollow fiber type substance separation membranes were used as plasma collection membranes for collecting plasma components from blood, changes in performance during use were investigated. Moreover, in order to investigate the permeation performance of the membrane, the permeation performance of the fine particles was investigated. Bovine blood was used as the blood thread evaluation method, and the permeation performance was determined by plasma collection 15,30
It was evaluated by the sieving coefficient of total cholesterol at two points. In addition, Dow Dnifor
Sieving coefficient was calculated using m Latex 380Å and compared. The sieving coefficient is a numerical value representing the mass permeation performance of the membrane, and is represented by the ratio of the concentration Cin in the undiluted solution before passing through the membrane and the concentration Cf in the perfusate. SC = Cf / Cin (Table 2) No. 2
As shown in the table, in the hollow fiber type substance separation membrane (No. 1) of the present invention, the separation performance of the membrane is almost unchanged, whereas in other comparative examples (No. 2 to 4). In, the remarkable change is seen with time. Also, in the permeation performance of fine particles, the hollow fiber type substance separation membrane of the present invention shows high permeation performance. In the pores of the hollow fiber membrane of the present invention, there is almost no change in the pore size from the inlet to the outlet, and there is no hindrance to the passage of particles having a size of half or less of the average pore size. Although the average pore size is apparently large in this type of membrane, the variation in pore size distribution over the entire membrane wall causes the size of the pores to change in various ways, resulting in the formation of fine particles within the membrane. As a result of being trapped, it is considered that there is only a low transmission amount. As a means to increase the permeation of fine particles, it is possible to increase the average pore size in the conventional MF membrane. Comparative example
It is true that a large average pore size such as No. 4 will improve the permeation performance in a single system of fine particles, but in a system containing dense and various sizes such as blood, the pore size of the membrane will be large. As a result of the increased dispersion in distribution, good transmission performance is not always obtained. Thus, it can be seen that the hollow fiber type substance separation membrane of the present invention has a high substance permeation performance without clogging or fouling over time when the membrane is used.

Claims (1)

[Claims] 1. A hollow fiber type substance separation membrane having a fine pore structure, wherein the average pore diameter P of the pore diameter distribution of the pores existing on the entire membrane wall and the standard deviation value σ of the distribution are 0.01 (μm) ≦ P, respectively.
Satisfies the relationship of ≦ 0.6 (μm) and σ / P ≦ 1.0, and
A hollow fiber type substance separation membrane, characterized in that the relation of 0.8 ≧ ε ≧ 0.6 (ε: porosity of membrane) is satisfied.