JPH10305219A - Performance recovering method of porous separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of times of exchange of a membrane by allowing a porous separation membrane lowered in separation performance by the damage of the membrane surface to contact with a gas to hydrophobe, then with a oxidizing agent and after that, repeating the penetration and the flow back of a fluid to recover opening ratio and to prolong the service life of the membrane. SOLUTION: The porous separation membrane lowered in the performance by the damage of the membrane surface is brought into contact with the gas to be hydrophobed. The gas used for hydrophobing is not restricted, but air is suitably used. Next, the membrane is brought into contact with an oxidizing agent. The oxidizing agent to be used is not restricted, but particularly a sodium hypochlorite aq. solution less in malodor and easy in handling and waste water disposal is suitably used. In the separation membrane brought into contact with the oxidizing agent, a process for passing the fluid through the membrane from one side and a process for making the fluid to flow back from another side of the membrane are repeated. As the fluid to be used, a single or mixed liquid of water, methanol, ethanol, isopropyl alcohol and the like and a gas such as air are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for restoring the performance of a porous separation membrane. More specifically, the present invention relates to a method for recovering the performance of a porous separation membrane used for wastewater treatment or the like for solid-liquid separation and having reduced performance due to damage to the membrane surface.

[0002]

2. Description of the Related Art Microfiltration (MF) membranes and ultrafiltration (U)
F) Porous separation membranes, such as membranes, select specific substances by passing molecules smaller than a certain size using the sieving effect of the pores physically formed in the membrane. It is something that is separated. When such a porous separation membrane is used, all the pores function effectively when used and exhibit the expected performance, but as the use continues, the membrane surface is damaged and the pores are crushed. , Performance decreases. For example, when water is passed at a high flow rate of 1 to 2 m / sec to the circulating fluid side (drainage side) of an internal pressure type cross flow membrane made of polypropylene, the membrane surface is gradually damaged by long-term use,
The separation performance of the membrane decreases. In order to maintain and recover the performance of the separation membrane, in addition to removing the membrane contaminants by daily water flushing cleaning, periodically or with the increase of the differential pressure at the entrance and exit of the membrane separation device as a guide, Cleaning using a chemical is performed as necessary. However, even if such cleaning is performed, the performance of the film is inevitably reduced. In particular, the effect of chemical cleaning is limited to the performance deterioration due to physical damage of the film surface. When the porous separation membrane is used for a long period of several months or years, the performance of the membrane is reduced, and one operation time for collecting a predetermined amount of water is reduced. It is necessary to exchange part or all of However, various factors such as the burden of chemicals due to the frequency of chemical cleaning, the cost of new separation membranes for membrane replacement, the number of man-hours for membrane replacement, and the reduction in the operating rate of equipment for membrane replacement are increasing. Economic problems and operational difficulties occur.
Therefore, it is possible to easily recover the performance of the porous separation membrane whose performance has deteriorated, extend the life of the membrane, and continue the operation of the membrane separation device without replacing the membrane for a long period of time. There is a need for a performance recovery method.

[0003]

SUMMARY OF THE INVENTION According to the present invention, a porous separation membrane having a reduced porosity due to damage to the membrane surface due to its use can recover the porosity by a simple treatment, extend the life of the membrane, An object of the present invention is to provide a method for restoring the performance of a porous separation membrane, which can reduce the number of replacements of the separation membrane in the membrane separation device.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the porous separation membrane whose membrane surface has been damaged and the separation performance has been lowered is brought into contact with a gas. After being subjected to hydrophobization treatment and then contact with an oxidizing agent, it was found that the porosity and the separation performance were restored by repeating the permeation and backflow of the fluid, and based on this finding, the present invention was completed. Was. That is, the present invention provides (1) a method in which a porous separation membrane whose separation performance is reduced by use is subjected to a hydrophobic treatment by contacting with a gas and then an oxidizing agent; A method of recovering the performance of the porous separation membrane, characterized by repeating the step of permeating the membrane and the step of backflowing the porous separation membrane from the other side,
Is provided. Further, as a preferred embodiment of the present invention, (2) the method for recovering performance of a porous separation membrane according to the above (1), wherein the gas is pressurized air, and (3) the oxidizing agent is an aqueous sodium hypochlorite solution. (1) The method for restoring the performance of a porous separation membrane according to (1), (4) after contacting the separation membrane with an oxidizing agent, and subjecting the separation membrane to a hydrophilizing treatment using a hydrophilizing agent.
The method for restoring the performance of a porous separation membrane described in the above item and the method for restoring the performance of a porous separation membrane according to the item (1), wherein the fluid is water (5).

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention can be suitably applied to a porous separation membrane in which the membrane surface is damaged by use, and in particular, the pore opening ratio is reduced and the separation performance is reduced. Such a porous separation membrane has, for example, a pore diameter of 0.1.
Examples thereof include a microfiltration (MF) membrane having a pore size of 0.05 to 1 μm, and an ultrafiltration (UF) membrane having a pore size of 0.002 to 0.1 μm. The material of the separation membrane is not particularly limited, and examples thereof include polyethylene, polypropylene, cellulose acetate, polyamide, polycarbonate, and polyacrylonitrile. These separation membranes may be hydrophobic membranes having the intrinsic properties of the material or membranes obtained by subjecting the hydrophobic membrane to a hydrophilic treatment. There is no particular limitation on the membrane separation apparatus to which the method of the present invention can be applied. For example, any of a cross flow and a dead end type, an internal pressure type and an external pressure type, and a pressure type and a suction type It can be applied to any of them. Further, there is no particular limitation on the membrane shape to be used, and any of a flat membrane, a tubular membrane, and a hollow fiber membrane can be used according to the method of the present invention as long as the porous separation membrane has a damaged surface as a result of use. Performance can be restored. If a porous separation membrane is used for a long time in solid-liquid separation for separating fine particles in a liquid, the surface of the membrane comes into contact with and collides with the particles and is damaged. The membrane has many pores and water permeates through the pores, but if the membrane surface is damaged, the pores on the membrane surface are closed and the membrane surface is opened. The porosity decreases, and as a result, the desired amount of permeated water cannot be obtained even when used for solid-liquid separation. ADVANTAGE OF THE INVENTION According to the method of this invention, the covering part which closes the opening part of a pore can be removed, an opening rate can be recovered, and separation performance can be recovered.

In the method of the present invention, a porous separation membrane whose membrane surface has been damaged and whose performance has been reduced is brought into contact with a gas and subjected to a hydrophobic treatment. The gas used for the hydrophobic treatment is not particularly limited, and examples thereof include air, nitrogen gas, oxygen gas, hydrogen gas, and steam. Among these gases,
Air can be used particularly preferably. The method of the hydrophobization treatment is not particularly limited. For example, gas can be permeated and contacted with the membrane by pressurization or decompression. In the method of the present invention, it is not necessary to completely remove the water inside the film to make the film hydrophobic. By making the membrane hydrophobic enough to allow gas to permeate the membrane, instead of completely removing water, the oxidizing agent can easily come into contact with the degraded part, easily drop off in subsequent processing, and open the closed pores. The part can be restored. In the method of the present invention, the separation membrane subjected to the hydrophobic treatment by contact with a gas is then contacted with an oxidizing agent. There is no particular limitation on the oxidizing agent used, for example, chlorine gas,
Examples thereof include aqueous solutions of hypochlorite, persulfate, hydrogen peroxide, ozone and the like. Among them, an aqueous solution of sodium hypochlorite which has a low odor and is easy to handle and dispose of effluent can be particularly preferably used. The concentration of the oxidizing agent and the contact load are not particularly limited, and can be appropriately selected. By contacting the separation membrane, whose membrane surface has been damaged and its performance has been reduced, with an oxidizing agent, the deteriorated portion closing the opening of the pores is further fragile and deteriorated by oxidation,
It can be easily dropped off.

In the method of the present invention, the separation membrane after contact with the oxidizing agent can be subjected to a hydrophilic treatment. The hydrophilizing agent is not particularly limited, and examples thereof include methanol, ethanol, and isopropyl alcohol. One of these hydrophilizing agents may be used alone, two or more thereof may be used in combination, or may be used as a water diluent. The hydrophilization treatment is not necessarily required. By setting the transmembrane pressure difference to about ² to 5 kg / cm ² , the air in the membrane is washed away and the water permeability is improved. It is preferable to perform a hydrophilization treatment since there is a risk of deformation. By performing the hydrophilization treatment, when water is used as the fluid, the permeation and backflow of water to the separation membrane are facilitated. In the method of the present invention, for the separation membrane that has been brought into contact with the oxidizing agent, the steps of allowing the fluid to permeate the membrane from one side and the steps of flowing the fluid back to the membrane from the other side are repeated. By repeating the permeation and backflow of the fluid, the brittle and degraded portion closing the opening of the pore is dropped and removed, and the opening of the pore recovers. Since the fluid physically removes the fragile and deteriorated portion, it is possible to use water, methanol, ethanol, isopropyl alcohol, etc., a single or mixed liquid, a gas such as air, or the like. The use of water as the fluid is particularly preferred because permeation and backflow can be performed using a device attached to the membrane separation device. When gas is used as a fluid, it is better to vent the gas while keeping it as hydrophobic as possible without performing hydrophilization treatment after contacting with an oxidizing agent. It is preferable because it is possible.

When water is used as the fluid, a step of applying pressure from the circulating water side of the membrane separation device to permeate the water and a step of applying pressure to the permeated water side and flowing back to the circulating water side are repeated. By repeating the permeation and the backflow, the brittle and degraded portion closing the opening of the pore can be removed, and the opening ratio can be recovered. There is no particular limitation on the water used,
For example, pure water, industrial water, waste water and the like can be mentioned. There is no particular limitation on the time for repeating the permeation and the backflow, and for example, it can be performed in a cycle of several seconds to several minutes. There is no particular limitation on the number of repetitions of permeation and backflow,
Usually, the performance of the separation membrane can be recovered by repeating the process several hundred times. Although there is no particular limitation on the liquid used for the backflow, it is preferable to use a permeated liquid since there is no risk of contaminating the membrane. Observation of the membrane surface of the separation membrane, whose separation performance has deteriorated due to long-term use, and the membrane surface of a new unused separation membrane using an electron microscope, revealed that many pores were formed on the membrane surface of the new separation membrane. The pores on the membrane surface of the separation membrane whose performance has deteriorated are small in size and the number of pores is small. Also,
When the cross section of the separation membrane is observed with an electron microscope, it is recognized that the pores of the separation membrane having deteriorated performance are crushed and closed in the vicinity of the membrane surface. When the separation membrane with reduced separation performance is treated by the method of the present invention and observed with an electron microscope, the opening of the closed pore is restored, and the size of the opening and the number of existing pores are changed to a new separation membrane. It is recognized that they are approaching. According to the method of the present invention, the performance of the porous separation membrane can be easily recovered in the mounted state by using the membrane separation apparatus itself, and the frequency of chemical cleaning of the separation membrane and the compatibility with a new membrane can be improved. The number of replacements can be reduced.

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In Examples and Comparative Examples, the porosity of the film was determined by the following method. That is,
The membrane was cut, an electron microscope photograph of the membrane surface on the circulating water side was taken at a magnification of 3,500 times, and the photograph was further magnified 4 times by color copying. The ratio of the weight of the cut portion to the weight was defined as the porosity. Example 1 A polypropylene microfiltration (MF) membrane with an inner diameter of 5.5 mm and a pore size of 0.2 μm was taken out of a membrane separation device used for three years for solid-liquid separation of silicon polishing wastewater in a semiconductor manufacturing process. Performance recovery processing.
The membrane separation device is of a cross-flow internal pressure type, in which water having a concentration of 5% by weight of a suspended solid (SS) in a circulation tank is supplied at a flow rate of 2.0 m /
This was used under the conditions of second, permeated water amount of 5 m ³ / m ² · day, water sampling for 15 minutes, and back washing with permeated water for 5 seconds. The porosity of the polypropylene microfiltration membrane used for the last three years was 9.
2%. The pore rate of the same new polypropylene microfiltration membrane that was not used at all was 26%. Air was pushed into the polypropylene microfiltration membrane used for 3 years at a pressure of 1.5 kg / cm ² for 30 minutes to make it hydrophobic, and then a 0.1% by weight aqueous solution of sodium hypochlorite was circulated for 17 hours. Furthermore, pure water is applied to the membrane at a pressure of 5
The operation of permeating at kg / cm ² for 1 minute and backflowing at a pressure of 5 kg / cm ² for 5 seconds was repeated 500 times. This treatment restored the porosity of the membrane to 21%. Example 2 Hydrophobic treatment was performed by injecting air at a pressure of 1.5 kg / cm ² for 30 minutes into a polypropylene microfiltration membrane used for 3 years as in Example 1, and then a 0.1% by weight aqueous solution of sodium hypochlorite was used. For 17 hours and then immersed in isopropyl alcohol for 10 minutes. Further, the operation of permeating pure water through the membrane at a pressure of 0.8 kg / cm ² for 1 minute and flowing backward at a pressure of 1.5 kg / cm ² for 5 seconds was repeated 500 times. This treatment restored the porosity of the membrane to 22%. Comparative Example 1 The same polypropylene microfiltration membrane used for 3 years as in Example 1 was dried at 60 ° C. for 24 hours, and then a 0.1% by weight aqueous solution of sodium hypochlorite was circulated for 17 hours. Soak for minutes. The porosity of the membrane after this treatment was 9.6%. Comparative Example 2 The same polypropylene microfiltration membrane used for 3 years as in Example 1 was dried at 60 ° C. for 24 hours, and then a 0.1% by weight aqueous sodium hypochlorite solution was circulated for 17 hours. Soak for minutes. Further, the operation of permeating pure water through the membrane at a pressure of 0.8 kg / cm ² for 1 minute and flowing backward at a pressure of 1.5 kg / cm ² for 5 seconds was repeated 500 times. The porosity of the film after this treatment was 12%. Comparative Example 3 Hydrophobic treatment was performed by injecting air at a pressure of 1.5 kg / cm ² for 30 minutes into a polypropylene microfiltration membrane used for the same three years as in Example 1 and then treated with isopropyl alcohol for 10 minutes.
Soak for minutes. Further, the operation of permeating pure water through the membrane at a pressure of 0.8 kg / cm ² for 1 minute and flowing backward at a pressure of 1.5 kg / cm ² for 5 seconds was repeated 500 times. The porosity of the membrane after this treatment was 9.5%. Comparative Example 4 Hydrophobic treatment was performed by injecting air at a pressure of 1.5 kg / cm ² for 30 minutes into the same polypropylene microfiltration membrane used for 3 years as in Example 1, and then a 0.1% by weight aqueous solution of sodium hypochlorite was used. For 17 hours and then immersed in isopropyl alcohol for 10 minutes. The porosity of the membrane after this treatment was 9.3%. The operations and results of Examples 1 and 2 and Comparative Examples 1 to 4 are collectively shown in Table 1.

[0010]

[Table 1]

From the results shown in Table 1, it is found that a step of making the surface water-hydrophobized by contacting with air and then contacting it with an aqueous solution of sodium hypochlorite and then allowing pure water to permeate from one side and flowing back from the other side. The membranes of Examples 1 and 2 treated by the method of the present invention in which the steps are repeated are all restored to the porosity of 80% or more of the porosity of the unused fresh membrane. On the other hand, the hydrophobic treatment is performed by heating and drying,
In Comparative Example 1 in which the backflow of pure water was not performed, the porosity was hardly recovered. Further, as compared with Example 2, Comparative Example 2 was different in that the hydrophobizing treatment was performed by heating and drying, Comparative Example 3 was different in that the contact with the aqueous solution of sodium hypochlorite was not performed, and pure water was different. In Comparative Example 4, which is different in that the permeation and the backflow were not performed, the recovery of the porosity was small and none of the Comparative Examples 4 reached a state where the microfiltration membrane could be reused continuously.

[0012]

According to the method of the present invention, since the porous separation membrane can be regenerated and reused, the life of the separation membrane is extended, the number of times of replacement with a new separation membrane is significantly reduced, and the operation rate is reduced. And the amount of use of the separation membrane can be reduced.

Claims (1)

[Claims] 1. A porous separation membrane, whose separation performance has been reduced by use, is subjected to a hydrophobic treatment by contacting with a gas and then an oxidizing agent, and then a fluid is permeated through the porous separation membrane from one side. A method for recovering performance of a porous separation membrane, comprising repeating a step and a step of flowing back to the porous separation membrane from the other side.