JP2003038940A - Selective separating membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a selective separating membrane which is a cleaning membrane for blood containing protein existing therein at a high concentration and a treating membrane for waste water and city water containing suspended components existing therein at a high concentration, lessens the degradation in performance during treatment with lapse of time and permits the easy restoration of the once degrade performance. SOLUTION: In the selective separating membrane, the water permeation rate in a physiological salt solution increases by >=1.07 times than the water permeation rate in pure water. The membrane is swollen by liquid, such as blood, containing ions, by which the adsorption and deposition of the protein on the membrane surface are suppressed and the degradation in the permeation performance with lapse of time is suppressed. The membrane is shrunk and the membrane structure is changed by cleaning the membrane with a solution not containing the ions, by which the adsorbed and deposited protein is made easily peelable and the degraded membrane performance is recovered.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention provides a separation membrane capable of maintaining and recovering stable separation characteristics. In particular,
There is little performance deterioration over time during treatment with blood purification membranes used for treatment of liquids with high protein concentration or selective separation membranes such as wastewater and water purification membranes with high concentration of suspended components. The present invention also provides a selective separation membrane capable of easily recovering the once lowered performance.

[0002]

2. Description of the Related Art Selective separation membranes are currently widely used for wastewater treatment, seawater desalination, water purification treatment, gas separation, blood purification and the like. In selective separation membranes used for wastewater treatment, drinking water production, blood treatment, etc., when solutes, suspension components, and insoluble components contained in the treatment liquid are adsorbed, deposited and deposited on the membrane surface, This results in clogging and formation of a cake layer on the surface of the membrane, which results in deterioration of membrane performance over time, such as a reduction in water permeation rate or solute permeation rate.

Therefore, it is necessary to provide a means for recovering the lowered performance of the selective separation membrane used in such applications. For example, microfiltration membranes (MF membranes) and ultrafiltration membranes (UF membranes) used for wastewater treatment and drinking water production.
Is regularly backwashed (flowing water or gas in the opposite direction of filtration to destroy the cake layer deposited on the surface of the membrane to remove the substances clogged in the pores) and chemical treatment of the membrane. To wash.
In the case of blood treatment membranes, for example, in the United States, it is possible to recover the membrane performance by using a chemical to clean the hemodialyzer (dialyzer) whose performance has deteriorated due to blood cell components and proteins adhering to the membrane surface after use. It is widely practiced.

From the standpoint of producing a membrane, the membrane material has been improved from the viewpoint of preventing deterioration of membrane performance over time. For example, since proteins in blood are easily adsorbed on a hydrophobic surface, the hemodialysis membrane material is actively hydrophilized.

[0005]

However, with respect to the deterioration resistance of performance over time and the recoverability of degraded performance,
The present situation is that a selective separation membrane that is sufficiently satisfactory has not yet been obtained.

[0006]

Means for Solving the Problems As a result of intensive investigations by the present inventors, the present invention has been made with respect to the deterioration resistance of the selective separation membrane over time and the recoverability of the deteriorated performance. That is, the present invention is: 1) A selective separation membrane characterized in that the ratio of the water permeation rate in physiological saline (UFR (S)) and the water permeation rate in pure water (UFR (P)) satisfies the following formula: , UFR (S) / UFR (P) ≧ 1.072 2) The film structure is a substantially uniform film in which macrovoids are not substantially observed, and the film thickness is in the range of 10 to 50 μm). Is a selective separation membrane of.

The water permeation rate means the volume of the liquid to be treated per unit time, unit pressure, and unit membrane area when the liquid to be treated (in pure water or physiological saline) is filtered through a selective separation membrane. Represent Generally, the water permeation rate depends on the viscosity of the liquid to be treated. At 37 ° C, the viscosity of pure water is 0.70 cP, the viscosity of physiological saline is 0.71 cP, and the viscosity of physiological saline is higher than that of about 1% pure water. In the case of a common membrane, the water permeation rate in saline is lower than that in pure water. However, as a result of investigations by the present inventors, it was surprisingly found that a certain type of membrane has a water permeation rate higher than that in pure water and a ratio of 1.07 or more. It has been found that the membrane maintains stable separation properties and can easily recover once degraded membrane performance.

Although the mechanism of this phenomenon is not clear, in the case of a selective separation membrane having positive and negative charges in the molecular chain forming the selective separation membrane and keeping contraction by electrostatic attraction, ions are In the saline solution containing the ions, the charged ions in the membrane molecules are canceled by the charged ions, the contraction is alleviated, the membrane swells, and the pore size increases. It is believed that speed will increase.

When such a selective separation membrane having an increased water permeation rate in physiological saline is used for a blood purification membrane such as hemodialysis, since blood contains ions, the membrane swells and protein is adsorbed or deposited on the membrane surface. Is suppressed, and there is an advantage that performance deterioration with time is small. Furthermore, by washing with a solution containing no ions, the membrane is contracted and the membrane structure is changed, so that the adsorbed and deposited proteins are easily peeled off, and the lowered membrane performance can be easily recovered.

The selective membrane of the present invention is reduced due to clogging of impurities and solutes in a liquid to be treated and formation of a cake layer even when used in a liquid to be treated containing almost no ions such as in waste water treatment and tap water production. The above performance is useful in that it is possible to swell the membrane and eliminate clogging and the cake layer by flowing an aqueous solution having strong ionic strength. Examples of the aqueous solution having a strong ionic strength include saline.
Saline is safer than the detergents and chemicals that are commonly used at present because of environmental pollution even if it is discarded as it is.

In the present invention, the ratio of the water permeation rate in physiological saline to the water permeation rate in pure water is 1.07 or more. This changes the membrane structure in the liquid to be treated containing ions such as blood, prevents deterioration of the membrane performance over time due to adsorption or deposition of proteins and blood cell components, and maintains the performance of the membrane over time. This is to restore the membrane performance. When the ratio of the water permeation rate in physiological saline to the water permeation rate in pure water is less than 1.07,
The change in the film structure is small, and the effects described above cannot be obtained.
Of course, when the membrane structure does not change at all, the water permeation rate depends on the viscosity of the liquid to be treated, so in the prior art membrane, the ratio of the water permeation rate in physiological saline to pure water is about 0.99. When the ratio of the water permeation rate in physiological saline to the water permeation rate in pure water is 1.07 or more, the larger the water permeation rate, the larger the change in the membrane structure and the greater the effect. 10 or more is preferable, and 1.15 or more is more preferable.

In the present invention, it is preferable that the changes in the water permeation rate in physiological saline and the water permeation rate in pure water are reversible. If it changes reversibly, the membrane performance can be reused any number of times by repeatedly performing the membrane performance recovery after use, and as a result, the running cost of the membrane module can be reduced.

The structure of the selective separation membrane of the present invention is not particularly limited, but is preferably a substantially uniform membrane in which macrovoids are not substantially observed. In the structure having a dense skin layer on the inner surface or outer surface of the film and a supporting layer containing voids in the middle portion, the effect of the present invention is difficult to obtain, probably because the structure change of the skin layer is hard to occur. Further, if macrovoids are present in the selective separation membrane, the distance between the membrane-constituting molecules is large, and the membrane contraction due to electrostatic attraction between the membrane-constituting molecules is difficult to work. Here, a substantially uniform film in which macrovoids are not substantially observed means that the cross section of the film is 1
It shows a uniform structure in which voids having a diameter of 0.5 μm or more and voids derived from the sponge structure are not observed when observed at a magnification of 000. Depending on the material, voids and voids having a diameter of less than 0.5 μm are observed by observation at a higher magnification (5000 times or more). When the voids or voids have a diameter of less than 0.5 μm, even if they exist, the ratio of the water permeation rate in physiological saline to the water permeation rate in pure water can be 1.07 or more. On the other hand, even though the film is substantially uniform, defects during film formation (for example, inclusion of foreign matter or bubbles)
As a result, voids and voids having a size of 0.5 μm or more are observed, and when the defects are a very small portion of the entire film, the ratio is 1.0
It is possible to achieve 7 or more. Therefore, macrovoids existing in a very small portion of the selective separation film due to such defects may be observed.

The selective separation membrane of the present invention has a thickness of 10 to 50.
The range of μm is preferable because the film structure is likely to change. When the film thickness is larger than 50 μm, the film structure becomes too strong, and the film shrinkage due to electrostatic attraction due to the charge of the film structure is less likely to occur, so that the effect of the present invention is considered to be difficult to obtain. On the other hand, it is considered that when the thickness of the selective membrane is smaller than 10 μm, the distribution of electric charges in the membrane structure is narrow, and the difference in water permeation rate between pure water and physiological saline is less likely to occur.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the material for the selective separation membrane is not particularly limited, and includes regenerated cellulose, cellulose acetate, polysulfone, polyacrylonitrile, polymethylmethacrylate, ethylene vinyl alcohol copolymer, polyvinyl alcohol and the like. In particular, a polyacrylonitrile-based polymer having a negative or positive charge in the molecule, or a polymethyl methacrylate or ethylene vinyl alcohol copolymer having a polarity in the molecule can be preferably used.

The method for producing the separation membrane of the present invention is not particularly limited, and it may be produced in the form of a hollow fiber membrane or a flat membrane. Especially, in the case of a hollow fiber membrane, the following conditions are satisfied: It can be suitably obtained. -The hollow fiber membrane-forming polymer solution contains 1 wt% or more of an electrolyte having a high dissociation degree such as lithium chloride or sodium chloride in the solution.・ During hollow fiber membrane molding, the draft ratio of the polymer solution at the die (the linear velocity of the coagulation bath entry / the ejection linear velocity of the die) is 5 or more, and the draft ratio of the core liquid discharged as a hollow forming material is 1.5. Do the following: -The polymer concentration in the polymer solution should be 15% by weight or more. Due to the above three points, the selective separation membrane of the present invention can be suitably obtained.

Here, the discharge linear velocity of the die is the amount of discharge of the polymer solution or the core liquid divided by the area of the die discharge part. Since the coagulation bath entry linear velocity cannot be actually measured, it refers to the initial roller velocity at which the hollow fiber discharged from the die is guided. Further, in the case of the tube-in-orifice type die, the area of the discharge portion of the polymer solution is the area of the gap between the outside of the slit and the inside of the slit. The tube-in-orifice type mouthpiece has a hole for discharging the core liquid, but since the discharged core liquid immediately expands to the inside of the slit, the area of the core liquid mouthpiece discharge part is the area inside the slit. .

Although the detailed mechanism is unknown, by incorporating an electrolyte in the polymer solution, electrostatic repulsion between the polymer molecules in the solution can be suppressed, and further, the draft ratio of the polymer solution in the die part is 5 or more. When the draft ratio of the core liquid is 1.5 or less and the concentration of the polymer in the polymer solution is 15% by weight or more, it is considered that there is an effect of strongly entangling polymer molecules with each other during hollow fiber molding. .

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples.

(Example 1) (Production of hollow fiber and module) 21% by weight of polyacrylonitrile-based copolymer (molecular weight 170,000: acrylonitrile 90% by weight, methallylsulfonic acid 10% by weight) Lithium chloride was dissolved in a mixed solvent having a composition of N-methyl-2-pyrrolidone (NMP) / dimethylacetamide (DMAc) / triethylene glycol (TEG): 45/45/10 weight ratio so as to be 2% by weight, A polymer solution for forming a hollow fiber membrane was obtained. This was discharged at a rate of 2.0 cc / min from a tube-in-orifice type mouthpiece having a slit inner diameter of 200 μm, a slit outer diameter of 800 μm, and a core liquid discharge diameter of 100 μm. The cross-sectional area of the polymer solution discharge part of this tube-in-orifice type nozzle is 4.
The cross-sectional area of the core fluid discharge part is 7 × 10 ⁻⁷ m ² and is 3.1 × 10.
^-8 m ² . Core fluid is NMP / DMAc / TEG: 4
An 85 wt% aqueous solution of 5/45/10 was discharged at a rate of 1.6 cc / min. The polymer solution discharge linear velocity at this time was 4.3 m / min, and the core liquid discharge linear velocity was 50.9 m.
/ Min. NMP / D with an air gap of 2 cm
It was led to a coagulation bath of 40 ° C., which was composed of a coagulation liquid of a 40 wt% aqueous solution of MAc / TEG = 45/45/10, and was guided to a roller outside the coagulation bath at a speed of 50 m / min. The draft ratio of the polymer solution mouthpiece at this time was 11.6 (= 50/4.
3), and the core liquid draft ratio is 0.98 (= 50/5).
It was 0.9). Then, wash with water and wind up, 50
After immersing in a wt% glycerin aqueous solution, it was dried to obtain a hollow fiber membrane. The obtained hollow fiber membrane had an inner diameter of 200 μm and a thickness of 40 μm, and was a uniform membrane in which macrovoids were not observed. 10800 hollow fiber membranes obtained were bundled to produce a module having an effective membrane area of 1.5 m ² .

(Measurement of water permeation rate) The water permeation rate was measured by a dialyzer performance evaluation standard (Japan Society for Artificial Organs, Showa 5).
It was performed in accordance with the C method (STOP method) of September, 7). The water penetration rate (UFR) is expressed by the following equation. UFR = QF / A / TMP In the above formula, QF is the filtration flow rate (mL / hour), A is the membrane area (m ² ), and TMP is the transmembrane pressure difference (mmHg). However, the transmembrane pressure difference (TMP) was calculated by the following formula. TMP = (PBi + PBo) / 2 PBi is the inlet side pressure of the dialyzer blood or stock solution, and PBo is the outlet side pressure of the dialyzer blood or stock solution. The TMP was changed at 4 points and the filtration flow rate (QF) at that time was measured. The relationship between QF and TMP was plotted, and the water permeation rate was calculated from the slope. The temperature was 37 ± 1 ° C. The water permeation rate (UFR (P)) in pure water was measured for an unused hollow fiber membrane module using ion-exchanged water as pure water. Permeability rate in physiological saline (UFR)
(S)) was measured using physiological saline in which 0.9 wt% of salt was dissolved in ion-exchanged water after UFR (P) measurement. The water permeation rate (UFR (P)) in pure water of the hollow fiber membrane module produced in Example 1 was 180 mL / hour / m ² / m ² .
mmHg, water permeation rate in physiological saline (UFR)
(S)) is 215 mL / hour / m ² / mmHg, UFR
The (S) / UFR (P) ratio was 1.19.

(Evaluation of reversibility of water permeation rate) The above UFR
After measuring (P) and UFR (S), the water permeation rate UFR (P) in pure water was measured again by the above method. The second measured value of UFR (P) is 180 mL / hour / m ² / m
It was mHg and the water permeation rate reversibly returned to the first measured value.

(Evaluation of time-dependent deterioration and recovery of water permeability using bovine blood) Bovine blood (hematocrit 30%, total protein concentration 6.5 g / dL) was used at a temperature of 37 ± 1 ° C.
Blood side flow rate 200mL / min, filtration flow rate 40mL / min,
A hemofiltration experiment was performed for 120 minutes. From the transmembrane pressure difference TMP (15) after 15 minutes from the start of hemofiltration and the transmembrane pressure difference TMP (120) after 120 minutes, C% shown in the following formula
The value of was calculated. C% = TMP (120) × 100 / TMP (15) When the hollow fiber membrane module does not deteriorate with time, the value of C% is 100%. The larger the C% value, the greater the deterioration over time. Regarding the hollow fiber membrane module of Example 1, TMP (15) 15 minutes after the start of hemofiltration was 47.
mmHg, TMP (120) after 120 minutes is 52 mmH
The g and C% were 111%. After the blood filtration experiment was completed, the dialyzer was removed from the circuit, and the dialysate was directed from the blood side to ion-exchanged water at a rate of 500 mL / min for 10 minutes for backwashing. When the water permeation rate of pure water after backwashing was determined, the UFR (P) was 172 mL / hour / m ² / mmHg, which was a recovery rate of 95.5% compared with that before the blood treatment.

Comparative Example 1 Polyacrylonitrile-based copolymer (molecular weight 170,000: acrylonitrile 90% by weight, methallyl sulfonic acid 10% by weight) was used in 2 parts.
The hollow fiber was dissolved in a mixed solvent having a composition of N-methyl-2-pyrrolidone (NMP) / dimethylacetamide (DMAc) / triethylene glycol (TEG): 45/45/10 weight ratio so as to be 1% by weight. A film-forming polymer solution was obtained. This was discharged at a rate of 2.0 cc / min from a tube-in-orifice type mouthpiece having a slit inner diameter of 250 μm, a slit outer diameter of 400 μm, and a core liquid discharge diameter of 150 μm. The cross-sectional area of the polymer solution discharge part of this tube-in-orifice type nozzle is 7.7 × 10 ⁻⁸ m ² , and the cross-sectional area of the core liquid discharge part is 4.9 × 10 ⁻⁸ m ² . The core fluid is NMP /
An 85 wt% aqueous solution of DMAc / TEG = 45/45/10 was discharged at a rate of 1.6 cc / min. The polymer solution discharge linear velocity at this time was 26.1 m / min, and the core liquid discharge linear velocity was 32.6 m / min. NMP / DMAc / TEG = 45/45/10 with an air gap of 2 cm
Was introduced into a coagulation bath of 40 ° C. consisting of a coagulation liquid of a 40 wt% aqueous solution of, and led to a roller outside the coagulation bath at a speed of 50 m / min. The draft ratio of the polymer solution mouthpiece at this time was 1.
92 (= 50 / 26.1), the draft ratio of the core liquid was 1.
It was 53 (= 50 / 32.6). Then, it was washed with water, wound up, immersed in a 50% by weight glycerin aqueous solution, and then dried to obtain a hollow fiber membrane. The obtained hollow fiber membrane had an inner diameter of 200 μm and a thickness of 40 μm, and was a uniform membrane in which macrovoids were not observed. Obtained hollow fiber membrane 10800
The books were bundled into a module having an effective film area of 1.5 m ² .

The obtained hollow fiber membrane module was evaluated in the same manner as in Example 1, and as a result, UFR (P) was 205 mL / min,
UFR (S) is 203 mL / min, UFR (S) / UFR
The (P) ratio was 0.99. UFR (S) / UFR
The (P) ratio was a change depending on the viscosity of the liquid to be treated, and it was considered that the film structure did not change. The UFR (P) measured the second time was 205 mL / hour / m ² / mmHg. In hemofiltration experiment, TMP (15) was 52 mmHg
And, TMP (120) is 90mmHg, C% is 1
It was 73%. Higher TMP than in the first embodiment
It also has a large value, and C% is also a large value, and it can be seen that the performance of the membrane is deteriorated and deteriorated with time due to components in blood. The water permeation rate (UFR (P)) in pure water measured after backwashing in the same manner as in Example 1 was 131 mL / hour / m ² / mm.
Hg, recovery rate was 63.9% compared to before blood treatment
And the recovery rate of the performance of the hollow fiber membrane was lower than that in Example 1.

[0026]

EFFECTS OF THE INVENTION The selective separation membrane of the present invention has little performance deterioration over time during treatment, and can easily recover the once deteriorated performance. Therefore, it is useful as a blood purification membrane used for treating a liquid containing a high concentration of protein, a selective separation membrane such as a waste water and tap water treatment membrane containing a high concentration of suspended components.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4C077 AA01 AA05 BB01 BB02 EE01                       KK12 LL02 LL05 PP03 PP04                       PP09 PP10 PP15                 4D006 GA06 GA07 MA01 MA03 MA11                       MA21 MA31 MB02 MC12 MC18                       MC33 MC34 MC37 MC39X                       MC62 NA05 PB08 PB15 PC47

Claims (2)

[Claims] 1. A water permeation rate (UFR) in physiological saline.
(S)) and the water permeation rate in pure water (UFR (P)),
A selective separation membrane characterized by satisfying the following formula. UFR (S) / UFR (P) ≧ 1.07 2. The film structure is a substantially uniform film in which substantially no macrovoids are observed, and the film thickness is 10 to 5.
The selective separation membrane according to claim 1, which is in a range of 0 μm.