JPH05208121A - Method for making porous membrane hydrophilic - Google Patents

Abstract

PURPOSE:To simply make a hydrophobic porous membrane hydrophilic without bringing about the contamination of said membrane with a foreign substance by dipping the porous membrane in degassed water wherein the concn. of dissolved air is a definite ratio of the saturated concn. of dissolved air or less. CONSTITUTION:A hydrophobic porous membrane composed of polypropylene or polyethylene is dipped in water degassed so that the concn. of dissolved air is reduced to 80% or less, pref., 50% or less of the saturated concn. of dissolved air and the concn. of dissolved oxygen is reduced to 80% or less, pref., 50% or less of the saturated concn. of dissolved oxygen. Since the hydrophobic porous membrane can be made hydrophilic by this method without using a surfactant or an org. solvent, the remaining possibility of a foreign substance is eliminated and the removal thereof by washing is unnecessary and labor or cost can be omitted.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention can be generally applied to filtration of a liquid containing water or an aqueous solution as a medium through a porous membrane, for example, medical, pharmaceutical, food industry, chemical industry, tap water treatment, waste water treatment, etc. Used in the field of.

[0002]

2. Description of the Related Art Porous membranes such as microfiltration membranes, ultrafiltration membranes and reverse osmosis membranes are composed of a hydrophobic polymer,
There are advantages such as a decrease in change over time, an increase in biostability, a decrease in temperature change, an improvement in pressure resistance, and a decrease in performance change due to drying during manufacturing.

However, when a liquid containing water or an aqueous solution as a medium is filtered, the hydrophobic porous membrane cannot be filtered because the water or aqueous medium does not enter the pores. When water is pressurized, water is pressed into the pores and permeates, but depending on the degree of hydrophobicity and pore size, a large pressure is required, and a powerful pump may be required, or in some cases, the membrane A pressure higher than the breaking pressure is required. In addition, since the membrane has a pore size distribution, water does not still enter the small pores, and a portion that does not work for filtration occurs. Therefore, even if filtration is possible, the amount of permeated water becomes small. Therefore, when the hydrophobic membrane is used for filtering a liquid using water or an aqueous solution as a medium, a treatment for wetting the inside of the pores, that is, a hydrophilic treatment is required before use.

As the method for hydrophilizing, a method of wetting the membrane with an aqueous solution of a surfactant and then substituting with water, a method of wetting the membrane with an organic solvent such as ethanol or glycerin and then substituting with water, and the membrane with pressurized water are used. It is known to immerse the membrane in water to press the water into the pores, and as a permanent hydrophilization method, a method in which the membrane surface is made hydrophilic by a plasma treatment or other method is known. .

[0005]

However, in the method using a surfactant or an organic solvent, it is necessary to wash and remove these substances before use. It causes labor and cost increase in unfavorable applications, and the pressurizing method requires a special device, which makes it difficult to carry out on-site. Furthermore, the permanent hydrophilization method has led to an increase in membrane production cost.

[0006]

Means for Solving the Problems The present inventors have arrived at the present invention by studying a method for easily hydrophilizing a hydrophobic porous membrane without causing contamination by foreign substances.

[0007] That is, the gist of the present invention is to remove water from a porous membrane in which the dissolved air concentration is degassed to 80% or less of the saturated dissolved air concentration or to dissolve the dissolved oxygen concentration to 80% or less of the saturated dissolved oxygen concentration. Vaporized water, dissolved air concentration is deaerated to 80% or less of saturated dissolved air concentration, and dissolved oxygen concentration is saturated Deaerated to 80% or less of dissolved oxygen concentration, or dissolved air concentration is saturated Degassed to 50% or less of the dissolved air concentration, and the dissolved oxygen concentration is 50% of the saturated dissolved oxygen concentration.
In a method for making a porous membrane hydrophilic, which is characterized in that it is immersed in water that is degassed to a content of not more than 10%.

[0008]

[Constitution] The hydrophobic porous membrane which is the subject of the present invention is
The membrane has pores having a pore diameter of 5 to 10000 nanometers in the membrane, and the pores communicate from one surface of the membrane to the other surface. Such a membrane is used as a liquid filtration membrane, and its filtering ability and fractionating ability are determined by the pore size. The size of the pores may be uniform over the entire thickness of the film, or may be a distributed one, for example, an asymmetric film.

The hydrophobicity of the porous membrane can be determined by allowing water to permeate the membrane. As is well known in the capillarity, if the membrane is hydrophilic, water permeates with zero or slight pressure, but if it is hydrophobic, a large pressure difference is required. The hydrophobic membrane that is the subject of the present invention is a membrane that requires a pressure difference of 0.1 Kgf / cm ² or more in order to allow distilled water at 25 ° C. to permeate. As the hydrophobic film, for example, polypropylene, polyethylene, polyolefin such as poly 4-methylpentene-1, polyvinylidene fluoride, fluororesin such as polytetrafluoroethylene, polyvinyl chloride, chlorine-containing resin such as polyvinylidene chloride, Examples thereof include membranes mainly made of polymers such as silicone resin, polysulfone, polyethersulfone, polyphenylene sulfide, and polyetheretherketone, and membranes made of a polymer containing some of these constituent elements. Of course, these are examples, and the present invention is not limited to these. The form of the film of the present invention is not particularly limited. For example, it can be applied to flat membranes, hollow fiber membranes, tubular membranes.

In the present invention, the water for hydrophilizing the membrane is water and / or deaerated to a dissolved air concentration of 80% or less, preferably 50% or less, and more preferably 30% or less of the saturated dissolved air concentration. Alternatively, it is water deaerated to a dissolved oxygen concentration of 80% or less, preferably 50% or less, and more preferably 30% or less of the saturated dissolved oxygen concentration (such water is hereinafter referred to as deaerated water). If the dissolved air concentration or dissolved oxygen concentration exceeds this value, the effect of hydrophilization is reduced, or the time required for hydrophilization treatment becomes long. The lower limit of the dissolved air concentration or the dissolved oxygen concentration may be naturally limited in practice, but it is not necessary to limit it in the present invention because there is no inconvenience due to its low value. It is also preferable that the content is 10% or less or 1% or less in order to exert the effect of the present invention, but the degassed water production cost increases.

In the present invention, the dissolved air concentration is 80% or less, preferably 50% or less, of the saturated dissolved air concentration.
More preferably, it is degassed to 30% or less, and the dissolved oxygen concentration is 80% or less of the saturated dissolved oxygen concentration, preferably 5
It is more preferable that the water is degassed to 0% or less, further preferably 30% or less.

The dissolved air concentration referred to in the present invention means the sum of the dissolved oxygen concentration and the dissolved nitrogen concentration. The dissolved air concentration is determined by the Ostwald method (Experimental Chemistry Course 1 Basic Operation [I], 241
Page, 1975, Maruzen) or the mass spectrum method. The dissolved oxygen concentration can be measured by a simple oxygen concentration meter such as a galvanic cell type or polarographic type in addition to the above method. Saturated dissolved air (or oxygen) concentration refers to the equilibrium concentration of air (or oxygen) dissolved in water in contact with the atmosphere at 1 atm, and saturated dissolved air concentration is the sum of saturated dissolved oxygen concentration and saturated dissolved nitrogen concentration. Say. The saturated dissolved air (and oxygen) concentration depends on the water temperature, but in the present invention, it means the value at the temperature of the water used. The values of the saturated dissolved oxygen concentration and the saturated dissolved air concentration are, for example, about 25 wt.
pm (hereinafter, simply referred to as ppm), saturated dissolved nitrogen concentration is about 13.8 ppm, saturated dissolved air concentration is about 22 pp
m (according to the Chemical Handbook).

Generally, the dissolved air (oxygen) concentration of water is usually a value close to the saturated air (oxygen) concentration. However, in rare cases, the value may change due to oxygen consumption in the conduit, oxygen consumption in the groundwater vein, fluctuations in water temperature, oxygen supply by photosynthesis of algae in lakes and reservoirs, and the like. In the present invention, even naturally degassed water can be used as long as it has a predetermined dissolved air (oxygen) concentration.

The water referred to in the present invention includes so-called water, such as tap water, well water, hot water cooling, hot water, distilled water, filtered water, sterile water, and the like, as well as an aqueous solution and an aqueous dispersion. Examples of the aqueous solution include an aqueous solution of an inorganic salt such as seawater or saline solution,
An acid / base aqueous solution, a bactericide aqueous solution, an aqueous solution to be filtered can be mentioned, and an example of the dispersion liquid can be a dispersion liquid to be filtered. Although water can be arbitrarily selected, it is preferable to select water which does not require special washing and removing operations in each application. For example, physiological saline is preferably used when used for plasma separation, and distilled water, filtered water, sterile water, etc. are preferably used when used in the food industry or pharmaceuticals.

As a method for producing degassed water used in the present invention, a membrane-type vacuum degassing in which raw water is passed through one side of a membrane through which gas is permeated but liquid is not permeated and the other side is depressurized (see, for example, Japanese Patent Laid-Open Publication No. Sho. 63-258605), so-called vacuum degassing for decompressing the inside of a packed tower or a spray tower, heating degassing for heating water to or near the boiling point to utilize the decrease in solubility, bubbling of an inert gas, ultrasonic degassing. There are methods such as a method of reacting dissolved oxygen with hydrogen and other reducing agents, and any method can be adopted. Among these, the membrane-type vacuum deaeration is preferable in that the apparatus is small, easy to handle, and highly deaerated. Vacuum degassing is preferred next to membrane vacuum degassing.

Usually, dissolved oxygen and dissolved nitrogen are removed almost in parallel by degassing of water, but one is selectively removed depending on the degassing method, such as oxygen absorption by a reducing agent. Sometimes it happens. As a result of various studies, the inventors have found that even if the dissolved air has a saturated concentration, an effect can be seen if the dissolved oxygen concentration is a fixed ratio or less of the saturated dissolved oxygen concentration. The Ostwald method for measuring the concentration of dissolved air is time-consuming and time-consuming, and the mass spectrum method is difficult to measure on-site, whereas the measurement of dissolved oxygen by an oximeter is simple and quick. Since there is a merit that it can be performed, it is preferable to make the determination based on the oxygen concentration.

When deaerated water is left to stand, the air is redissolved and the rate of dissolution is increased by stirring. Therefore, it is preferable to use the degassed water immediately after the production, and it is preferable to avoid entrapment and stirring of air when handling the degassed water. That is, when the membrane after modularization is immersed in degassed water, it is preferable to introduce it from the lower side of the module.

The hydrophilic treatment of the present invention is carried out by immersing the porous membrane in degassed water. At this time, it is necessary to contact both sides of the membrane with degassed water. That is, when the membrane is a hollow fiber membrane or a tubular membrane, it is necessary that both the inner and outer surfaces of the membrane come into contact with degassed water. If one side or part of the membrane does not come into contact with degassed water, that part is not made hydrophilic. The immersion treatment can be carried out by any method. That is, there are a method of immersing the membrane in the retained deaerated water, a method of immersing the membrane in running deaerated water, and the like. In the case of the method of immersing the membrane in the retained degassed water, it is also preferable to replace the degassed water and perform the dipping treatment a plurality of times. The treatment time is not particularly limited, and can be largely changed depending on the degree of degassing and the water temperature, but the treatment can usually be performed for 1 minute to 1 hour. The higher the degree of degassing of the degassed water and the higher the water temperature, the shorter the required time. Further, when the degree of deaeration is low, the treatment time can be shortened by a method of immersing in running water or a method of replacing the deaerated water and immersing a plurality of times. The once hydrophilized membrane may be contacted with air as long as it is not dried.

There is no particular restriction on the point of time at which the hydrophilic treatment is carried out in the series of steps from the production of the membrane to the use thereof.
The treatment may be performed before or after modularization of the membrane, but it is preferable to perform the treatment after modularization. In addition, after being hydrophilized, it can be distributed / sold in a wet state, or can be distributed / sold in a dry state and hydrophilized before use, but just before use. It is preferable to perform hydrophilic treatment.

The pressure at which the hydrophilization treatment is performed is preferably atmospheric pressure or higher, and it is preferable to perform the hydrophilization treatment at atmospheric pressure because no special pressurizing device is required. However, when it is easy to apply pressure, such as when performing hydrophilic treatment after modularization, it is also preferable to perform under pressure.

[0021]

It is known that deaerated water absorbs and dissolves the air when it comes into contact with the air. When the porous membrane is immersed in degassed water, the air in the pores of the membrane dissolves in the water, and the water then enters the pores to fill the pores, forcing the surfaces of the pores to be wet. Once the pores are filled with water, water can permeate the membrane even if replaced with normal air saturated water. Even if the film is taken out into the air after the hydrophilic treatment,
The hydrophilicity is not lost unless it is dried.

[0022]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

[Example 1] (Production of a membrane module for measurement) A polypropylene porous hollow fiber membrane manufactured by Hoechst Celanese Co., Ltd. [outer diameter 400 μm, inner diameter 330 μm, pore diameter 0.4 × 0.04 μm (catalog value)] about 5000 The book was incorporated into a cylindrical housing to prepare a membrane module having a hollow fiber outer surface standard membrane area of about 1 m ² . Using this module, piping was connected as shown in FIG.

(Confirmation of Hydrophobic Membrane) Distilled water at 25 ° C. was introduced from the lower connection port 4 of the membrane module to the side in contact with the inside of the hollow fiber 2, and the valve 10 was closed to 0.1 Kgf. The measurement was performed by applying a water pressure of / cm ² G, but no water permeation was observed.

(Production of Degassed Water) JP-A-63-25860
A degassing module incorporating a heterogeneous membrane made of poly (4-methylpentene-1) was prepared in the same manner as in Example 6 of 5. Distilled water was flowed at a rate of 3 liters per minute on the side in contact with the inside of the hollow fiber of this module, and the portion in contact with the outside of the hollow fiber membrane was depressurized to about 20 torr with a water flow aspirator, at a temperature of 25 ° C. by mass spectrometry. The measured dissolved oxygen concentration is 3.5 ppm (saturation concentration of 43
%), The dissolved nitrogen concentration is 8.7 ppm (63% of the saturation concentration).
%), Dissolved air concentration 12.2 ppm (saturation concentration 55
%) Deaerated water was obtained.

(Hydrophilic treatment) Next, degassed water is introduced from the connection ports 4 and 5 of the membrane module, and the connection ports 6 and 7 are introduced.
To completely fill the inner surface side and the outer surface side of the membrane, close the valves 8 and 9 and leave them for 30 minutes for hydrophilic treatment. At this time, the connection ports 6 and 7 were opened, and the water pressure on both sides of the membrane was kept at atmospheric pressure.

(Water permeation test) Distilled water at 25 ° C. was introduced into the hydrophilically treated module from the connection port 4, the valve 10 was closed, and a pressure of 0.1 Kgf / cm ² G was applied.
Permeate at 30 l / min.

[Comparative Example 1] A temperature of 25 was used instead of degassed water.
Distilled water without degassing at ℃ (Dissolved oxygen concentration 8.2pp
m, dissolved air concentration 14.1 ppm), exactly the same test as in Example 1 was conducted, and no permeation of water was observed even after the immersion treatment.

Example 2 (Confirmation of Hydrophobic Membrane) An experimental flat membrane made of polytetrafluoroethylene and having a diameter of 47 mm (Advantech Co., Ltd., pore diameter 0.5 μm) was mounted on a filtration holder to form a membrane. Distilled water at 25 ° C was introduced to one side of 0.1kgf / c
When water pressure of m ² G was applied, water did not permeate at all.

(Production of degassed water) The dissolved oxygen concentration was 0.5 ppm (6.2% of the saturated concentration) and the dissolved nitrogen concentration was changed by changing the flow rate to the same apparatus as that used in Example 1. Degassed water having a concentration of 0.9 ppm (6.5% of saturation concentration) and a dissolved air concentration of 1.4 ppm (6.4% of saturation concentration) was prepared.

(Hydrophilic treatment) Both sides of the membrane were filled with this degassed water, and the same permeation test was conducted after standing for 15 minutes. Water permeated at 3200 l / m ² .hr.

[Example 3] As a hydrophobic membrane, a polysulfone ultrafiltration membrane having a diameter of 47 mm (Nitto Denko N
TU-3150, molecular weight cut off of 50,000) was thoroughly washed with distilled water and ethanol and then dried, and the same treatments and tests as in Example 2 were carried out. The result is that the water that had not permeated at first was 38 after the hydrophilization treatment.
It permeated at 1 / m ² .hr.

Example 4 Degassed water produced in the same manner as in Example 1 was placed in a water tank and stirred under the atmosphere while measuring with a dissolved oxygen concentration meter to obtain a dissolved oxygen concentration of 6.1 ppm (at a saturated concentration of (75%), the same treatment and test as in Example 2 were carried out except that the hydrophilization treatment was performed using this and the immersion time was 1 hour. When the deaerated water used was measured by the mass spectrum method, the dissolved nitrogen concentration was 11.1 ppm (81% of the saturated concentration), and the dissolved air concentration was 17.2 ppm (78% of the saturated concentration). As a result of the water permeability test, the permeation flux was 2180 l / m ² .hr.

[Comparative Example 2] Degassed water produced in the same manner as in Example 1 was placed in a water tank and stirred in the atmosphere while measuring with a dissolved oxygen concentration meter to obtain a dissolved oxygen concentration of 7.3 ppm (saturated concentration 90%), the same treatment and test as in Example 2 were performed except that the hydrophilic treatment was performed using this. When the degassed water used was measured by the mass spectrum method, the dissolved nitrogen concentration was 13.0 ppm (saturated concentration of 94%).
%), Dissolved air concentration is 20.3 ppm (saturated concentration 92
%)Met. As a result of the water permeability test, no water permeation was observed.

[0035]

INDUSTRIAL APPLICABILITY According to the present invention, when hydrophobizing a hydrophobic porous membrane, it can be hydrophilized without using a surfactant or an organic solvent. Therefore, these substances are washed before use. It does not need to be removed, which does not increase labor and cost. In addition, especially in applications such as medical treatment, pharmaceuticals, food industry, etc. where the contamination is disliked, there is no risk of these foreign substances remaining. Also, unlike the hydrophilization method by pressurization, it does not require a large-scale device and can be carried out on-site. Also,
Unlike the permanent hydrophilic method, it does not increase the membrane production cost.

[Brief description of drawings]

FIG. 1 is a schematic partial vertical cross-sectional view of a membrane module to which a pipe used in Example 1 is connected.

[Explanation of symbols]

 1 Membrane Module 2 Hollow Fiber Membrane 3 Resin Sealing Part 4 Connection Port 5 Connection Port 6 Connection Port 7 Connection Port 8 Valve 9 Valve 10 Valve

Claims (4)

[Claims] 1. Water obtained by degassing a porous membrane to a dissolved air concentration of 80% or less of a saturated dissolved air concentration, or water degassed to a dissolved oxygen concentration of 80% or less of a saturated dissolved oxygen concentration. A method for hydrophilizing a porous membrane, which comprises immersing in a porous membrane. 2. A porous membrane is immersed in water that has been degassed to a dissolved air concentration of 80% or less of a saturated dissolved air concentration and a dissolved oxygen concentration of 80% or less of a saturated dissolved oxygen concentration. A method for making a porous membrane hydrophilic. 3. A porous membrane is immersed in water that has been degassed to a dissolved air concentration of 50% or less of a saturated dissolved air concentration and a dissolved oxygen concentration of 50% or less of a saturated dissolved oxygen concentration. A method for making a porous membrane hydrophilic. 4. The method for hydrophilizing a porous membrane according to claim 1, wherein the porous membrane is composed of polyolefin, polytetrafluoroethylene or polysulfone.