JP2008036574A - Membrane module and water-treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane filtration method which enables the membrane filtration of water to be treated, such as ground water, river water, lake and marsh water, sea water and secondarily treated sewage water, to obtain filtrated water, suppresses an increase in filtration resistance for a long period of time, and makes a stable membrane filtration operation possible. <P>SOLUTION: A membrane module for water treatment employs a separation membrane, which comprises a poly(vinylidenefluoride)-based resin, as a membrane filter. In this case, a membrane, which has a filtration resistance increase degree A of 2×10<SP>12</SP>/m<SP>2</SP>or larger, back washing restorability of 50% or larger, a filtration resistance increase degree B of 2×10<SP>12</SP>/m<SP>2</SP>or smaller and an initial filtration resistance of 1×10<SP>12</SP>/m or smaller, is used as the separation membrane. Water filtration processing is carried out by using a membrane filtration device equipped with the membrane module while physical washing is periodically being carried out, thereby producing filtrated water. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a separation membrane module for water treatment used for water treatment such as water purification, industrial water production, wastewater treatment, reverse osmosis membrane pretreatment, and a water treatment method using the membrane module.

  Separation membranes such as microfiltration membranes and ultrafiltration membranes are used as filtration membranes in various fields such as the food industry, medical field, water production, and wastewater treatment field. Particularly in recent years, separation membranes are increasingly used in the field of drinking water production, that is, in the process of water purification.

  Compared with water treatment by slow filtration or rapid filtration, water treatment by membrane filtration can remove impurities in raw water reliably and stably, and the installation area of equipment is small and requires less land. It is very advantageous in that there are few. In recent years, when water shortages have become serious, it is considered that the need for water treatment by membrane filtration will increase as a method for stably producing safer water in the future.

  Especially for separation membranes used in the field of drinking water production, for the purpose of sterilizing permeate and reducing membrane fouling, an oxidizing agent such as sodium hypochlorite can be added to treated water and backwash water, It is essential to wash membranes with chemicals such as hydrochloric acid, citric acid and oxalic acid, alkalis such as aqueous sodium hydroxide, chlorine, and surfactants. High chemical durability against these chemicals The separation membrane is required. In addition, since the end of the 20th century, the problem that chlorine-resistant pathogenic microorganisms such as Cryptosporidium are mixed in drinking water has become apparent, and it is so high that the membrane is not damaged and the treated water is not mixed into the permeated water. Physical strength and physical durability are also required for the separation membrane. Against this background, in recent years, a separation membrane using a polyvinylidene fluoride resin as a material having high chemical durability, high physical strength, and physical durability has attracted attention, and the application tends to expand.

  In membrane filtration treatment, clear permeated water can be obtained by blocking various components contained in the water to be treated with the membrane, but at the same time, clogging of the membrane due to components blocked by the membrane occurs. Therefore, with the continuation of the filtration operation, the water permeability of the filtration membrane decreases, and the membrane filtration resistance increases. If this phenomenon can be prevented and the increase in filtration resistance can be suppressed, the frequency of replacement of filtration membranes in water treatment using membranes can be reduced, and power consumption can be saved by reducing filtration pressure, thus reducing water production costs and environmental impact. Connected.

  In a water treatment method using a microfiltration membrane or an ultrafiltration membrane, the membrane filtration step and the physical cleaning step are generally performed alternately. In the membrane filtration step of filtering the water to be treated with a membrane, pores are blocked by components blocked from the water to be treated, and the filtration resistance is increased. Subsequently, in the physical cleaning process, gas is brought into contact with the membrane surface, or reverse flow cleaning is performed in which water flows in the opposite direction from the filtration process from the permeate side to the treated water side. Wash away any ingredients that have been blocked from. In this physical cleaning step, a part of the blocked component is peeled off from the membrane, and the filtration resistance is restored. However, it is difficult to remove all of the blocked components, and the filtration resistance continues to increase as the operation continues due to the components remaining in the membrane, eventually leading to chemical cleaning using chemicals and replacement of the membrane module itself.

  In order to suppress such a long-term increase in filtration resistance, it has hitherto been considered that it is effective to use a membrane having a small increase in filtration resistance in a single membrane filtration step. This is because a membrane with a small increase in filtration resistance in the filtration step, that is, a membrane that is not easily clogged by filtration, is considered to be able to suppress an increase in filtration resistance over a long period of time. However, even when a membrane having a small increase in filtration resistance in one membrane filtration step is used for the membrane module, it is difficult to sufficiently suppress long-term increase in filtration resistance.

  In addition, research for membrane filtration operation stably for a long time has been conducted so far, and it is generally qualitatively said that if the membrane is hydrophilized, the stain resistance is improved. Means are disclosed. For example, Patent Document 1 discloses a method of modifying a membrane surface made of a polyvinylidene fluoride resin by hydrophilization treatment with an alkaline aqueous solution, etc., but it is superior in membrane filtration including physical cleaning, or operated for membrane filtration. No mention is made of the stability in the above, and it is difficult to sufficiently suppress long-term increase in filtration resistance with a hydrophilic membrane by this means.

  In Patent Document 2, a hollow fiber membrane made of polyvinylidene fluoride coated with an ethylene-vinyl alcohol copolymer is disclosed as a membrane having excellent contamination resistance. However, there is a discussion on improvement of water permeability retention capability in a filtration process. There is no mention of the superiority in membrane filtration including physical cleaning.

  Moreover, in patent document 3, the film | membrane with a high surface opening rate is disclosed as a film | membrane which is excellent in filtration stability, and it describes that the film | membrane with a high surface opening rate suppresses the water-permeable performance deterioration by clogging. However, in the water treatment method in which the membrane filtration operation is performed while periodically performing physical washing, particularly back-flow washing, it is important to suppress clogging that occurs in one filtration step in order to stably perform membrane filtration in the long term. However, it is difficult to sufficiently suppress long-term increase in the filtration resistance by using a membrane having a high filtration rate in continuous operation and having a large open area ratio. In the case of a membrane having a large open area ratio, it is considered that the cleaning recovery property is poor due to the components entering the inside of the membrane and it is difficult to suppress fouling in continuous operation.

  As described above, in the prior art, when water treatment is performed using a membrane module for water filtration treatment using a separation membrane, the increase in filtration resistance can be suppressed over a long period of time, and a stable membrane filtration operation can be performed. No vinylidene resin separation membrane or membrane module was found.

JP 58-93734 A Japanese Patent Application Laid-Open No. 2002-233739 Japanese Patent No. 3781679

  The object of the present invention is to suppress the increase in filtration resistance over a long period of time in a membrane filtration method for obtaining permeate by subjecting treated water such as groundwater, river water, lake water, seawater, and secondary treated water to membrane filtration. An object of the present invention is to provide a water treatment membrane module that enables a stable membrane filtration operation, and a water treatment method using the same.

In order to achieve the above-mentioned object, the membrane module for water filtration treatment of the present invention uses a separation membrane having characteristics within a specific range at the time of a membrane filtration experiment as a filtration membrane. In this membrane filtration experiment, after the filtration step of filtering to 0.06 m ³ / m ² at a filtration pressure of 50 kPa, an operation of performing a back washing step of back washing at 0.025 m ³ / m ^{2 at a} back washing pressure of 100 kPa, This is an experiment of membrane filtration repeated 5 times, and a graph is drawn in which the filtration resistance selected thereby is plotted on the vertical axis and the horizontal axis is plotted on the total filtered water amount. The separation membrane is specified by the characteristic value obtained from this graph. That is, the filtration resistance increase degree A of the separation membrane is an average value of the inclination of the filtration resistance increase in the second to fifth filtration steps. The backwash recovery property is an average value of the ratio of filtration resistance recovered (reduced) by backwashing. The filtration resistance increase degree B is an average value of the increase slope of the filtration resistance value at the start of the filtration process after backwashing.

  In order to increase the stability when the membrane filtration process is operated for a long time, the separation membrane used in the membrane module has a large filtration resistance increase in one membrane filtration step, a membrane having a high washing recovery property, and an initial filtration resistance. It is effective not to be too high, and by using a separation membrane having these characteristics at appropriate levels, it is possible to suppress an increase in filtration resistance over a long period of time and to enable stable operation.

That is, the present invention
(1) In a membrane module for water treatment using a separation membrane made of polyvinylidene fluoride resin as a filtration membrane, the separation membrane has a filtration resistance increase A of 2 × 10 ¹² / m ² or more, and has a backwash recovery property. A membrane module that is a membrane having a characteristic of 50% or more, a filtration resistance increase degree B of 2 × 10 ¹² / m ² or less, and an initial filtration resistance of 1 × 10 ¹² / m or less.
(2) The membrane module according to (1), wherein the pore size of the separation membrane used is 0.1 μm or less.
(3) The membrane module according to the above (1) or (2), wherein the separation membrane used has a porosity of less than 20%.
(4) A water treatment method for producing permeated water by performing water treatment while periodically performing physical cleaning, using a membrane filtration device comprising the membrane module according to (3) above.
(5) The water treatment method according to (4), wherein the physical washing is back-flow washing.
(6) The water treatment method according to (4), wherein the physical cleaning interval is 10 minutes or more and 60 minutes or less.
(7) The water treatment method according to (5), wherein the separation membrane used is a hollow fiber membrane.
It consists of

  When the membrane module or water treatment method of the present invention is used, in membrane filtration to obtain permeated water by membrane filtration of ground water, river water, lake water, seawater, sewage secondary treated water, etc. It can be operated stably for a long time with less. As a result, the frequency of chemical cleaning and membrane replacement can be reduced, and water production costs can be reduced. In addition, in the present invention, a polyvinylidene fluoride resin separation membrane excellent in chemical durability, physical strength and physical durability is used, so that even when chemical cleaning is repeated, deterioration of the membrane is prevented over a long period of time. In view of this, stable long-term operation can be realized.

  The membrane module for water treatment of the present invention is suitably used for membrane filtration of water to be treated consisting of at least one kind selected from groundwater, river water, lake water, seawater and sewage secondary treated water. This treated water is raw water supplied to the separation membrane arranged in the membrane module in the filtration step, and natural water represented by groundwater, river water, lake water, and seawater is treated water. In addition, secondary treated water of sewage is also used as treated water.

  Further, the polyvinylidene fluoride resin in the present invention is a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer. A plurality of types of vinylidene fluoride copolymers may be contained. The vinylidene fluoride copolymer is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. Examples of the copolymer include a copolymer of vinylidene fluoride and at least one selected from vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and trifluoroethylene chloride. As long as the effects of the present invention are not impaired, a monomer such as ethylene other than the fluorine-based monomer may be copolymerized. In addition, for the purpose of enhancing the stain resistance, it is selected from cellulose ester, fatty acid vinyl ester, vinyl pyrrolidone, ethylene oxide, acrylonitrile, vinyl alcohol, etc. within the range that does not impair the chemical durability and physical strength of the polyvinylidene fluoride resin. It may contain a hydrophilic polymer having at least one kind. The weight average molecular weight of the polyvinylidene fluoride resin may be appropriately selected depending on the required strength and water permeability of the hollow fiber membrane, but is preferably in the range of 100,000 to 800,000. In consideration of processability to a hollow fiber membrane, the range of 200,000 to 600,000 is more preferable, and the range of 250,000 to 500,000 is more preferable.

  In the separation membrane disposed in the membrane module, the surface on the side to which the water to be treated is supplied is the surface to be treated and the surface on the side from which the permeated water is obtained is the surface on the permeated water side. The filtration step in the present invention refers to an operation of supplying raw water to the treated water side surface of the separation membrane at an arbitrary pressure and obtaining permeated water from the permeated water side surface.

  Further, the physical cleaning is an operation of applying a physical force to the membrane to clean the membrane, and refers to an operation such as air cleaning, air scrubbing cleaning, back-flow cleaning, or some combination thereof. Backflow cleaning refers to an operation of supplying the distilled water to the surface of the permeate side of the separation membrane at an arbitrary pressure after the filtration step and allowing it to permeate the surface of the water to be treated to wash the separation membrane. Therefore, the filtration pressure is a pressure for supplying raw water to the surface of the separation membrane to be treated in the filtration step, and the backwash pressure is a pressure for supplying distilled water to the permeate side surface in the backwashing step.

  When the pores of the separation membrane are clogged and the water permeation amount decreases, the filtration resistance increases. For this reason, in previous studies, it was considered that the use of a membrane in which the filtration resistance hardly increases in one filtration step leads to stable operation. However, since the membrane filtration method in which the filtration step and the physical cleaning step are alternately performed in the actual operation is the mainstream, in order to enable stable operation, the increase in the filtration resistance in one filtration step is suppressed rather than the physical resistance. It is required to suppress an increase in filtration resistance in continuous operation including a washing step. That is, not the degree of clogging that occurs in the filtration step, but the behavior of the filtration resistance value including the cleaning recovery property is important. Even if the filtration resistance increases in one filtration step, the amount of water permeation increases and the filtration resistance decreases at the start of the next filtration step if the component causing clogging in the physical washing step can be removed. Therefore, regardless of the ease of increase in filtration resistance, if the membrane is highly washable, the filtration resistance in continuous operation can be kept low, and stable in the long term in membrane filtration operation that repeats filtration and backwashing. Driving is possible.

  In addition, the shape of the separation membrane in the present invention is not limited. However, since the backwashing as the physical washing is most effective for expressing the effect of the present invention, the hollow fiber membrane that can easily carry out the backwashing. It is preferable that

  By the way, it can be said that the separation membrane in which the filtration resistance is hardly increased in one filtration step is a membrane that is not easily clogged when the membrane filtration operation is performed without performing physical cleaning. However, in the case of a water treatment method in which membrane filtration operation is carried out while periodically performing physical cleaning, the recovery width of filtration resistance by physical cleaning is more than the increase width of filtration resistance in one filtration step. It proved to be important to prevent clogging in long-term membrane filtration operation. That is, it has been found that the separation membrane in which the filtration resistance is difficult to increase in one filtration step has a low washing recovery property, and as a result, the filtration resistance is likely to increase in continuous operation. This tendency is manifested because there are few components that are blocked on the membrane surface, so most of the components contained in the raw water pass through the surface and the surface pores are difficult to block, but on the other hand, they are not blocked on the membrane surface. Since the components enter the membrane and are trapped by adsorption or recesses on the pore structure, it is difficult to remove the components that have entered the inside even if physical cleaning is performed, resulting in poor cleaning recovery. It is considered that the blocked components are accumulated without being removed in the physical cleaning step, and the long-term increase in filtration resistance is increased.

  In contrast, a membrane in which filtration resistance is likely to increase in a single filtration step has high cleaning recovery, and the filtration resistance in continuous operation can be kept low. Such a membrane has a large amount of components to be blocked on the membrane surface and a large increase in filtration resistance, but since almost no components have entered the membrane, it is easy to remove components adhered to the membrane surface or inside by physical cleaning. It can be removed and the water permeability can be recovered.

  From the above, in order to make a membrane module for water treatment that enables stable operation over a long period of time, it is not always necessary to suppress an increase in filtration resistance in a single filtration step, and the whole in continuous operation. It can be said that it is important to suppress an increase in typical filtration resistance.

  From this point of view, in a membrane module for water treatment using a separation membrane made of polyvinylidene fluoride resin as a filtration membrane, the increase in filtration resistance in one filtration step is somewhat high, and in one backwash step Filtration over a long period of time can be achieved by using a separation membrane that has a certain degree of recovery of filtration resistance and that has a certain level of increase in filtration resistance in continuous membrane filtration operation that alternately performs the filtration process and the backwashing process. It was found that a stable membrane filtration operation is possible while suppressing an increase in resistance.

  Therefore, in order to quantitatively represent the degree of increase in filtration resistance and the recoverability during backwashing (backwash recoverability), experimental filtration experiments using a reagent aqueous solution were conducted. Moreover, in order to suppress the increase in filtration resistance in continuous operation, it is not a module including a separation membrane in which the filtration resistance is unlikely to increase in one filtration process, but rather the filtration resistance tends to increase in one filtration process and vice versa. It has been found that it is effective to use a film having a high washing recovery property. This is because the use of a separation membrane capable of blocking many of the components contained in the raw water on the membrane surface as described above leads to an improvement in the backwash recovery and, as a result, to obtain stability in continuous operation. .

  That is, in the membrane module of the present invention, the object of the present invention is achieved by using a separation membrane having filtration resistance increase degree A, backwash recovery property, filtration resistance increase degree B, and initial filtration resistance at specific level values. Is.

The separation resistance increase A of the separation membrane used in the present invention is 1 × 10 ¹² / m ² or more, preferably 2 × 10 ¹² / m ² or more, and more preferably 3 × 10 ¹² / m ² or more. The backwash recoverability is 50% or more, preferably 70% or more. The filtration resistance increase degree B is 2 × 10 ¹² / m ² or less, preferably 1 × 10 ¹² / m ² or less, more preferably 8 × 10 ¹¹ / m ¹¹ or less. Furthermore, the initial filtration resistance is 1 × 10 ¹² / m or less, and the separation membrane is made of a polyvinylidene fluoride resin.

  In the present invention, the filtration resistance increase A is the backwash recovery property, the filtration resistance increase B and the initial filtration resistance are membrane filtration continuous in which the filtration step and the backwashing step are alternately performed under the following conditions. It is obtained by carrying out the model operation.

The filtration process at a filtration pressure of 50 kPa was carried out until the filtered water volume was 0.06 m ³ / m ² , and then the back washing process was performed with a back washing pressure of 0.025 m ³ / m ² at a back washing pressure of 100 kPa. In addition, a membrane filtration experiment is repeated in which the filtration step and then the backwashing step are sequentially repeated. Here, an aqueous solution containing 3 mg / L of humic acid and 25 mg / L of calcium chloride is used as membrane feed water, and the filtration step and the backwashing step are repeated five times. The total filtration water amount is plotted on the horizontal axis, and the calculated filtration resistance is plotted on the vertical axis. The permeated water amount obtained per fixed time in the filtration step is recorded, and the filtration resistance value at that time is obtained by dividing the filtration pressure 50 kPa by the permeated water amount.

  A method of calculating each value will be described by taking as an example the case where the graph shown in FIG. 1 is obtained when the total filtration water amount is plotted on the horizontal axis and the calculated filtration resistance is plotted on the vertical axis. In this graph, the filtration resistance when starting the first filtration step is the initial filtration resistance.

  In the graph, from the relationship between the total amount of filtered water and the filtration resistance, the slope of the increase in filtration resistance in the second, third, fourth, and fifth filtration steps was obtained, and the average value calculated from the slope was the degree of increase in filtration resistance. A.

  In the graph, the difference (D) between the filtration resistance at the end of the nth filtration and the filtration resistance at the start of the (n + 1) th filtration is the difference between the filtration resistance at the end of the nth filtration and the filtration resistance at the start of the nth filtration. A value [(D / U) × 100] indicating what percentage of the difference (U) is obtained is calculated, and an average value of the values obtained at n = 2, 3, and 4 is calculated to obtain a backwash recovery property. .

  Moreover, the filtration resistance increase degree B refers to the slope of a straight line connecting four points of filtration resistance at the start of the second, third, fourth, and fifth filtration steps in this graph. However, when the four points do not lie on the straight line, the slope of the straight line is obtained by linear approximation and is set as the filtration resistance increase degree B.

  In order to exert the effect of the present invention, it is desirable that the separation membrane disposed in the membrane module does not have a too large pore diameter. This is because most of the raw water-containing components can be blocked on the membrane surface, and the separation membrane in which the raw water-containing components are less likely to enter the membrane has a higher filtration resistance increase A, higher backwash recovery, and filtration. This is because it tends to be a separation membrane having a low resistance increase B. Therefore, the separation membrane used in the membrane module of the present invention preferably has an average pore diameter on the surface to be treated of 0.1 μm or less, more preferably 0.08 μm or less, particularly preferably 0.06 μm or less. is there.

  In addition, a membrane having a large open area inevitably has a large pore size, so that components of raw water enter the membrane and the backwash recovery property is lowered. In the case of a separation membrane having a pore diameter in the above range, it is difficult to increase the aperture ratio to 20% or more even if the number of pores is increased in a practical range. Therefore, it is preferable that the separation membrane used in the membrane module of the present invention has a surface area of the water to be treated of less than 20%.

  What is necessary is just to measure the average pore diameter of the to-be-processed water side surface, and an opening rate about the pore grasped | ascertained by observing this surface with a scanning electron microscope etc. The average pore diameter on the surface of the water to be treated is that the surface of the water to be treated is photographed at a magnification of 10,000 times or more using a scanning electron microscope, and the number of arbitrary pores of 10 or more, preferably 20 or more. This is the value obtained by measuring the diameter and averaging the numbers. If the surface pores on the treated water side are not circular, a circle having an area equal to the area of the pores (equivalent circle) is obtained by an image processing device or the like, and the equivalent circle diameter is used as the pore diameter. It can be determined by a method. The open area ratio of the surface to be treated is determined from the average pore diameter and the pore density by the following formula.

Opening ratio (%) = π × (average pore diameter / 2) ² × (pore density) × 100

The pore density means that the surface of the water to be treated of the hollow fiber membrane is photographed with a scanning electron microscope or the like at such a magnification that the pores can be clearly confirmed, and the pores in the photograph are counted to 1 m ^The value converted into the number of pores per ² is defined as the pore density. It is preferable to count and average over a wide area such as a plurality of areas. For example, in the examples of the present invention, the number of pores per 3 μm square of a scanning electron micrograph was counted and calculated. It is also possible to analyze a photograph with an image processing apparatus.

The separation membrane used as a filtration membrane in the present invention can be produced by the following method.
For example, a method of forming a three-dimensional network structure layer composed of a fluororesin polymer solution containing a predetermined hydrophilic polymer on a fluororesin layer composed of a spherical structure, or two or more types of fluororesins A method of simultaneously forming a three-dimensional network structure layer and a spherical structure layer by simultaneously discharging a polymer solution (one type of which is a fluororesin polymer solution containing a predetermined hydrophilic polymer) from a die. It is done.

  A method for forming a three-dimensional network structure layer made of a fluororesin polymer solution containing a predetermined hydrophilic polymer on a fluororesin layer having a spherical structure will be described below.

  In the case of this manufacturing method, first, a fluororesin film (layer) having a spherical structure is manufactured. A polymer solution is prepared by dissolving a fluororesin-based polymer at a relatively high concentration of about 20 wt% to 60 wt% in a poor solvent or a good solvent of the polymer at a relatively high temperature. The solution is discharged from the die so as to be in the form of a hollow fiber membrane or a flat membrane, and phase-separated by cooling and solidifying in a cooling bath to form a spherical structure. Here, the poor solvent cannot dissolve the above polymer at 5% by weight or more at a low temperature of 60 ° C. or lower, but it is 60 ° C. or higher and below the melting point of the polymer (for example, the polymer is a vinylidene fluoride homopolymer). In the case of being constituted alone, the melting point is a solvent that can be dissolved by 5 wt% or more in a high temperature region of about 178 ° C.). On the other hand, a solvent capable of dissolving 5% by weight or more of a polymer even in a low temperature region of 60 ° C. or lower is a good solvent. A solvent that does not dissolve or swell is defined as a non-solvent.

  Examples of poor solvents for fluoropolymers include cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, and glycerol triacetate. Examples include ketones, esters, glycol esters and organic carbonates, and mixed solvents thereof. Even if it is a mixed solvent of a non-solvent and a poor solvent, what satisfies the definition of the poor solvent is treated as a poor solvent. Examples of good solvents include N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetoxide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethyl urea, trimethyl phosphate, and other lower alkyl ketones, esters, amides, and the like. These mixed solvents are mentioned. Further, non-solvents include water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentane. Aliphatic hydrocarbons such as diol, hexanediol, low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated organic liquids and mixtures thereof A solvent is mentioned.

  In the above method, first, the fluororesin polymer is dissolved at a relatively high concentration of about 20 wt% to 60 wt% in a poor solvent or a good solvent of the polymer at a relatively high temperature of about 80 to 170 ° C. Thus, it is preferable to prepare a polymer solution. The higher the concentration in the polymer solution, the higher the strength and elongation of the polymer separation membrane. However, when the concentration is too high, the porosity of the polymer separation membrane decreases and the permeation performance decreases. Moreover, it is preferable that a solution viscosity exists in an appropriate range from a viewpoint of the ease of handling of a polymer solution, and film forming property. Therefore, the concentration of the polymer solution is more preferably in the range of 30% by weight to 50% by weight.

  In order to cool and solidify the polymer solution into a predetermined shape such as a hollow fiber or a flat membrane, a method of discharging the polymer solution from the die into a cooling bath is preferable. At this time, as the cooling liquid used for the cooling bath, it is preferable to use a liquid having a temperature of 5 to 50 ° C. and a concentration of 60 to 100% by weight and containing a poor solvent or a good solvent. In the cooling liquid, in addition to the poor solvent and the good solvent, a non-solvent may be contained within a range that does not inhibit the formation of the spherical structure. Note that when a liquid mainly composed of a non-solvent is used as the cooling liquid, the phase separation due to the non-solvent intrusion takes precedence over the phase separation due to cooling and solidification, so that it becomes difficult to obtain a spherical structure. In the case of producing a polymer separation membrane by a method of quenching and solidifying a solution in which a fluororesin polymer is dissolved at a relatively high concentration in a poor solvent or a good solvent of the polymer at a relatively high temperature, Depending on the conditions, the structure of the separation membrane may not be a spherical structure but a dense network structure. In order to form a spherical structure, the concentration and temperature of the polymer solution, the composition of the solvent used, the cooling liquid Properly control the combination of composition and temperature.

  When the shape of the polymer separation membrane here is a hollow fiber membrane, the prepared polymer solution is discharged from the outer tube of the double-tube type die, and the hollow portion forming fluid is double-tube type. What is necessary is just to discharge from the pipe | tube inside a nozzle | cap | die, and to cool and solidify in a cooling bath and to make a hollow fiber membrane. At this time, a gas or a liquid can be used as the hollow portion forming fluid. However, in the present invention, a liquid containing a poor solvent or a good solvent having a concentration of 60 to 100% by weight similar to the cooling liquid is used. It is preferable to use it. The hollow portion forming fluid may be cooled and supplied. However, if the hollow fiber membrane can be solidified only by the cooling power of the cooling bath, the hollow portion forming fluid is supplied without cooling. May be.

  Further, when the shape of the polymer separation membrane is a flat membrane, the prepared polymer solution is discharged from a slit die and solidified in a cooling bath to obtain a flat membrane.

  A three-dimensional network structure made of a fluororesin polymer solution containing a predetermined hydrophilic polymer is formed (laminated) on the fluororesin film (layer) having a spherical structure obtained as described above. . The lamination method is not particularly limited, but the following method is preferable. That is, a three-dimensional network structure is formed by applying a fluororesin polymer solution containing a predetermined hydrophilic polymer on a fluororesin film (layer) having a spherical structure and then immersing it in a coagulation bath. This is a method of laminating layers.

  Here, the fluororesin polymer solution containing a predetermined hydrophilic polymer for forming a three-dimensional network structure is composed of the specific hydrophilic polymer, the fluororesin polymer and a solvent described above. As the solvent, it is preferable to use a good solvent of a fluororesin polymer. The good solvent described above can be used as the good solvent for the fluororesin-based polymer. The polymer concentration in the fluororesin polymer solution containing a hydrophilic polymer is usually preferably 5 to 30% by weight, more preferably 10 to 25% by weight. If it is less than 5% by weight, the physical strength of the three-dimensional network structure layer tends to decrease, and if it exceeds 30% by weight, the transmission performance tends to decrease.

  In addition, the fluororesin polymer solution containing this hydrophilic polymer is optimally dissolved depending on the type and concentration of the fluororesin polymer and hydrophilic polymer, the type of solvent, and the type and concentration of additives described below. The temperature will be different. In order to prepare a stable solution with good reproducibility in this fluororesin polymer solution, it is preferable to heat it for several hours while stirring at a temperature below the boiling point of the solvent so that a transparent solution is obtained. Furthermore, the temperature at which the fluororesin polymer solution is applied is also important for producing a polymer separation membrane having excellent characteristics. For example, in order to stably produce a polymer separation membrane, it is preferable to control the temperature so as not to impair the stability of the fluororesin polymer solution and to prevent the invasion of a non-solvent from outside the system. . Also, if the temperature of the fluororesin polymer solution at the time of application is too high, the fluororesin polymer on the surface of the spherical structure layer is dissolved, and a dense layer is formed at the interface between the three-dimensional network structure layer and the spherical structure layer. Are easily formed, and the water permeability of the obtained separation membrane is lowered. On the contrary, if the solution temperature at the time of application is too low, a part of the solution gels during application, a separation membrane containing many defects is formed, and the separation performance deteriorates. For this reason, the solution temperature at the time of application | coating needs to be made into optimal temperature by the composition of a solution, the target separation membrane performance, etc.

  When producing a hollow fiber polymer separation membrane, a fluororesin polymer solution containing a predetermined hydrophilic polymer is applied on the outer surface of a fluororesin hollow fiber membrane (layer) having a spherical structure. As a method, a method of immersing the hollow fiber membrane in the polymer solution or a method of dropping the polymer solution on the surface of the hollow fiber membrane is preferable. Moreover, as a method of applying a fluororesin polymer solution containing a predetermined hydrophilic polymer to the inner surface side of the hollow fiber membrane, a method of injecting the polymer solution into the hollow fiber membrane is preferable. At this time, as a method for controlling the coating amount of the polymer solution, a method for controlling the supply amount of the polymer solution to the coating itself, a method in which the polymer separation membrane is immersed in the polymer solution, After applying the polymer solution, a method of adjusting the coating amount by scraping off a part of the attached polymer solution or blowing it off using an air knife can be used.

  Moreover, it is preferable that the coagulation bath immersed after application | coating contains the non-solvent of a fluororesin type polymer. As the non-solvent, a non-solvent as described above is preferably used. By bringing the applied resin solution into contact with a non-solvent, non-solvent-induced phase separation occurs, and a three-dimensional network structure layer is formed. In the case of the present invention in which a fluororesin polymer solution containing a predetermined hydrophilic polymer is applied and then immersed in a coagulation bath, it is preferable to use a highly polar non-solvent such as water as the coagulation bath.

  The method for controlling the average pore diameter of the pores on the surface of the three-dimensional network structure layer within a desired range (for example, 1 nm or more and 1 μm or less) depends on the type and concentration of the hydrophilic polymer contained in the fluororesin polymer solution. For example, the following method can be adopted although it differs depending on the case.

  When an additive for controlling the pore size is added to a fluororesin polymer solution containing a hydrophilic polymer, it is added when forming a three-dimensional network structure or after forming a three-dimensional network structure. The agent is eluted, and the average pore diameter of the pores on the surface can be controlled.

  Examples of the pore diameter control additive include the following organic compounds and inorganic compounds. As the organic compound, those that are soluble in both the solvent used in the fluororesin polymer solution and the non-solvent that causes non-solvent-induced phase separation are preferably used. For example, polyvinyl pyrrolidone, polyethylene glycol, polyethylene imine, polyacrylic acid, Examples thereof include water-soluble polymers such as dextran, surfactants, glycerin, and saccharides. The inorganic compound is preferably one that is soluble in both the solvent used for the fluororesin polymer solution and the non-solvent that causes non-solvent-induced phase separation, such as calcium chloride, magnesium chloride, lithium chloride, and barium sulfate. Can do. Further, without using this additive, it is also possible to control the phase separation rate by adjusting the type, concentration and temperature of the non-solvent in the coagulation bath, and to control the average pore diameter of the surface. In general, when the phase separation rate is high, the average pore size on the surface becomes small, and when the phase separation rate is low, the average pore size on the surface becomes large. In addition, the phase separation rate can be controlled by adding a non-solvent to the polymer solution.

  In the above-described method for forming a three-dimensional network structure, the polymer solution for forming a three-dimensional network structure layer contains a fluororesin polymer and a cellulose ester, and the ratio of the cellulose ester to the fluororesin polymer is 20% by weight. When the content is less than 50% by weight, it is preferable to use a coagulation bath containing a good solvent for the fluororesin-based polymer. In this case, the good solvent component of the fluororesin polymer is contained in the coagulation bath in an amount of 10 wt% to 60 wt%, preferably 20 wt% to 50 wt%. By adjusting the good solvent component contained in the coagulation bath to the above range, the rate at which the non-solvent penetrates into the applied cellulose ester / fluororesin polymer solution is reduced, and the macrovoids in the three-dimensional network structure layer Formation of (major axis of 5 μm or more) can be suppressed.

  Further, when the ratio of the cellulose ester to the fluororesin polymer is 50% by weight or more and 75% by weight or less, the coagulation bath does not contain a good solvent component of the fluororesin polymer, for example, coagulation composed only of a non-solvent The inside of the bath can be used, and even when such a coagulation bath is used, a three-dimensional network structure layer free from macrovoids can be formed.

  The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples.

(1) Filtration experiment with a miniature membrane module A miniature membrane module having a length of 15 mm was prepared by housing seven hollow fiber membranes in an outer cylinder and fixing the ends (FIG. 2). In this membrane module, the hollow fiber membrane is sealed at the B end, and the hollow fiber membrane is open at the D end.

  Raw water is put into a 10 L stainless steel pressurized tank ADVANTEC PRESURE VRSSEL DV-10 with a pressure gauge installed, and Wako Pure Chemical distilled water is added to a 40 L stainless steel pressurized tank ADVANTEC PRESSURE VRSSEL DV-40 with a pressure gauge installed in the same manner. Put. Each tank was connected to a two-way cock at the water outlet. As raw water, 30 mg of humic acid (manufactured by Wako Pure Chemical Industries) and 250 mg of calcium chloride (manufactured by Nacalai Tesque) were dissolved in 10 L of Wako Pure Chemical distilled water.

  Connect the two-way cock of the pressurized tank with raw water (hereinafter referred to as raw water tank) and the point A of the miniature membrane module with a Teflon (registered trademark) tube via the three-way cock, and pressurize the tank with distilled water (hereinafter referred to as distilled water). The two-way cock of the tank) and point B of the miniature membrane module were connected with a Teflon (registered trademark) tube. The point C of the miniature membrane module was sealed with a resin cap so that permeated water was discharged from point D. In addition, you may use the miniature membrane module which does not provide the connection end like C point.

  First, 0.4 MPa compressed air was adjusted to 50 KPa with an SMC regulator (AF2000-02, AR2000-02G), pressure was applied to the raw water tank, the two-way cock was opened, and raw water was fed into the miniature membrane module. . At this time, the three-way cock between the miniature membrane module was opened only between the tank and the membrane module, and the two-way cock between the distilled water tank and point B was closed.

  The permeate weight was measured every 5 seconds with an electronic balance AND HF-6000 connected to a personal computer, and the continuous recording program AND RsCom ver. Recorded using 2.40. Since the data obtained in this experiment is the permeated water weight per 5 seconds, the filtration resistance was calculated using the following equation.

Filtration resistance = (filtration pressure) × 10 ³ × 5 × (membrane area) × 10 ⁶ / ((viscosity × (permeated water weight per 5 seconds) × (density))

After continuing the filtration step to a total filtered water amount of 0.06 m ³ / m ² , the two-way cock of the raw water tank was closed to complete the filtration step. Next, the three-way cock between the miniature membrane module was opened in all three directions, and the permeate outlet (point D) of the miniature membrane module was sealed with a resin cap.

  0.4 MPa compressed air was adjusted to 100 KPa with an SMC regulator (AF2000-02, AR2000-02G), pressure was applied to the distilled water tank, the two-way cock was opened, and distilled water was fed into the miniature module. By this operation, the backwash process was started. The backwashing process was continued until the backwashing drainage flowing out from the 3-way cock reached 100 ml, and then the backwashing process was completed by closing the 2-way cock of the distilled water tank.

  The above operation was continuously performed 5 times for one membrane module, and the total filtration water amount was plotted on the horizontal axis and the calculated filtration resistance was plotted on the vertical axis.

  Here, the plot was started 30 seconds after the start of each filtration. Moreover, since the water permeation amount decreases as the filtration resistance increases, the absolute value of the increase amount every 5 seconds decreases. Since the filtration resistance is calculated from the increase amount according to the above formula, when the increase amount decreases, the variation has a greater effect on the calculated filtration resistance. Therefore, when the decrease in water permeability was significant, the graph was corrected by taking a moving average approximation of the graph created as appropriate.

(2) Filtration resistance increase A
In the graph of total filtration water amount-filtration resistance created from the results of the filtration experiment, and in some cases, the graph obtained by taking the moving average approximation in the graph, from the relationship between the total filtration water amount and the filtration resistance, the second time, the third time, the fourth time, The average value calculated by obtaining the slope of each of the fifth filtration steps was defined as the filtration resistance increase A.

(3) Filtration resistance increase B
In the graph, the slope of the straight line connecting the four filtration resistances at the start of the second, third, fourth, and fifth filtration steps was defined as a filtration resistance increase B. However, when the four points did not lie on a straight line, the slope of the straight line was obtained by linear approximation and used as the filtration resistance increase A.

(4) Backwash recovery property The difference between the filtration resistance at the end of the nth filtration and the filtration resistance at the start of the (n + 1) th filtration is the difference between the filtration resistance at the end of the nth filtration and the filtration resistance at the start of the nth filtration. It is a value indicating what percentage of the difference, and the average value of n = 2, 3, 4 was defined as the backwash recovery property.

(5) Pore diameter and open area ratio The average pore diameter of the hollow fiber membrane is 30,000 times using a scanning electron microscope (S-800) (manufactured by Hitachi, Ltd.) on the outer surface of the hollow fiber that is the surface to be treated. Images were taken, the diameters of 30 arbitrary pores were measured, and the number average was obtained. In addition, the open area ratio is calculated by counting the number of pores per 3 μm square in the photograph for which the average pore diameter was obtained, and converting it into the number of pores per 1 m ² and the average pore diameter. And calculated by the following formula.

Opening ratio (%) = π × (average pore diameter / 2) ² × (pore density) × 100

(6) Small membrane module continuous filtration experiment A small membrane module was prepared so that the diameter was 3 cm, the length was 50 cm, and the effective membrane area was 0.3 m ^2, and Lake Biwa water was filtered at a constant flow rate and external pressure at a membrane filtration flow rate of 3 m / d. Drove. Every 60 minutes, backwashing with a 5 ppm sodium hypochlorite aqueous solution was performed for 30 seconds, and air scrubbing with air was performed for 1 minute. A one-week filtration operation was performed. The change in filtration differential pressure during one week was measured, and the daily average increase rate of filtration differential pressure (kPa / day) was calculated according to the following formula.

Filtration differential pressure increase rate (kPa / day) = (P ₁ −P ₀ ) / T

Here, the filtration differential pressure immediately after the physical cleaning at the start of the operation evaluation is P ₀ (kPa), the filtration differential pressure at the end of the operation evaluation is P ₁ (kPa), and the operation period is T (day). Here, the filtration differential pressure in the initial stage of operation is about 30 kPa, and the standard for chemical solution washing is about 100 kPa to 150 kPa of the filtration differential pressure, so the number of months from the start of operation until the filtration differential pressure exceeds 100 kPa is filtered. It was calculated from the pressure rise rate and was taken as the number of months that stable operation was possible.

<Example 1>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. This polymer solution is discharged from a base while stirring γ-butyrolactone as a hollow portion forming liquid and solidified in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure Was made.

  Next, 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 4% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), and 77% of N-methyl-2-pyrrolidone A polymer solution is prepared by mixing and dissolving 3% by weight of polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name Ionette T-20C) at a temperature of 95 ° C. at a rate of 3% by weight. did. This membrane stock solution is uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a 30% by weight aqueous solution of N-methyl-2-pyrrolidone to form a three-dimensional network structure layer on the spherical structure layer. A hollow fiber membrane was produced.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.01 μm on the surface to be treated and a porosity of 0.05%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 8.0 × 10 ¹¹ / m, the filtration resistance increase A was 4.8 × 10 ¹² / m ² , and the filtration resistance increase B was 5.3 × 10 ¹¹ / m ² . The recoverability was 92%.
A small module was made using this membrane, and a continuous filtration experiment was conducted using Lake Biwa as raw water. The rate of increase in the filtration differential pressure was 0.12 kPa / day, and it took 19 months to reach 100 kPa. It can be said that stable operation is possible.

<Example 2>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. This polymer solution is discharged from a base while stirring γ-butyrolactone as a hollow portion forming liquid and solidified in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure Was made.

  Next, 14% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 1% by weight of cellulose acetate propionate (Eastman Chemical Co., CAP482-0.5), and N-methyl-2-pyrrolidone 77% by weight, polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name Ionette T-20C) 5% by weight and water 3% by mixing and dissolving at a temperature of 95 ° C. to obtain a polymer solution It was adjusted. This membrane-forming stock solution was uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a water bath to produce a hollow fiber membrane having a three-dimensional network structure layer formed on the spherical structure layer.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.05 μm on the surface to be treated and a porosity of 12%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 5.0 × 10 ¹¹ / m, the filtration resistance increase A was 2.1 × 10 ¹² / m ² , and the filtration resistance increase B was 7.0 × 10 ¹¹ / m ² . The recoverability was 76%.
A small module was made using this membrane, and a continuous filtration experiment was conducted using Lake Biwa water as raw water. The rate of increase in the filtration differential pressure was 0.14 kPa / day, and it took 17 months to reach 100 kPa. It can be said that stable operation is possible.

<Example 3>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

  Subsequently, 14% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 3% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), and 77% of N-methyl-2-pyrrolidone A polymer solution is prepared by mixing and dissolving 3% by weight of polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name Ionette T-20C) at a temperature of 95 ° C. at a rate of 3% by weight. did. This membrane stock solution is uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a 30% by weight aqueous solution of N-methyl-2-pyrrolidone to form a three-dimensional network structure layer on the spherical structure layer. A hollow fiber membrane was produced.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.014 μm on the surface to be treated and a porosity of 0.8%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 9.0 × 10 ¹¹ / m, the filtration resistance increase A was 4.0 × 10 ¹² / m ² , the filtration resistance increase B was 4.0 × 10 ¹¹ / m ² , and backwashing. The recoverability was 95%.
A small module was made using this membrane, and a continuous filtration experiment was conducted using Lake Biwa water as raw water. The rate of increase in the filtration differential pressure was 0.1 kPa / day, and it took 23 months to reach 100 kPa. It can be said that stable operation is possible.

<Example 4>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

  Next, 12% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 3% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), and 79% of N-methyl-2-pyrrolidone A polymer solution is prepared by mixing and dissolving 3% by weight of polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name Ionette T-20C) at a temperature of 95 ° C. at a rate of 3% by weight. did. This membrane stock solution is uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a 30% by weight aqueous solution of N-methyl-2-pyrrolidone to form a three-dimensional network structure layer on the spherical structure layer. A hollow fiber membrane was produced.

The obtained polyvinylidene fluoride hollow fiber membrane had an average pore size of 0.02 μm on the surface to be treated and a porosity of 10%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 6.6 × 10 ¹¹ / m, the filtration resistance increase A was 3.8 × 10 ¹² / m ² , and the filtration resistance increase B was 5.3 × 10 ¹¹ / m ² . The recoverability was 90%.
A small module was made using this membrane, and a continuous filtration experiment was conducted using Lake Biwa water as raw water. As a result, the rate of increase in the filtration differential pressure was 0.15 kPa / day, and it took 16 months to reach 100 kPa. It can be said that stable operation is possible.

<Example 5>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

  Subsequently, 14% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 1% by weight of cellulose acetate propionate (Eastman Chemical Co., CA435-75S: cellulose triacetate), N-methyl-2- Pyrrolidone is 77% by weight, polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name Ionet T-20C) is 5% by weight, and water is 3% by weight at a temperature of 95 ° C. The solution was adjusted. This membrane stock solution is uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a 30% by weight aqueous solution of N-methyl-2-pyrrolidone to form a three-dimensional network structure layer on the spherical structure layer. A hollow fiber membrane was produced.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore size of 0.04 μm on the surface to be treated and a porosity of 10%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 5.2 × 10 ¹¹ / m, the filtration resistance increase A was 3.1 × 10 ¹² / m ² , and the filtration resistance increase B was 9.0 × 10 ¹² / m ² , backwashing. The recoverability was 70%.
A small module was made using this membrane, and a continuous filtration experiment was conducted using Lake Biwa as raw water. The rate of increase in the filtration differential pressure was 0.16 kPa / day, and it took 15 months to reach 100 kPa. It can be said that stable operation is possible.

<Example 6>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

  Then, 14% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 1% by weight of cellulose acetate propionate (Eastman Chemical Co., CAB551-0.2), and N-methyl-2-pyrrolidone 77% by weight, polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name Ionette T-20C) 5% by weight and water 3% by mixing and dissolving at a temperature of 95 ° C. to obtain a polymer solution It was adjusted. This membrane-forming stock solution was uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a water bath to produce a hollow fiber membrane having a three-dimensional network structure layer formed on the spherical structure layer.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.06 μm and a porosity of 17 on the surface to be treated. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 4.6 × 10 ¹¹ / m, the filtration resistance increase A was 2.2 × 10 ¹² / m ² , and the filtration resistance increase B was 7.2 × 10 ¹¹ / m ² . The recoverability was 84%.
A small module was made using this membrane, and a continuous filtration experiment was conducted using Lake Biwa water as raw water. As a result, the rate of increase in the filtration differential pressure was 0.15 kPa / day, and it took 16 months to reach 100 kPa. It can be said that stable operation is possible.

<Example 7>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

  Subsequently, 14% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 1.25% by weight of polyvinyl acetate (Nacalai Tesque, 75% ethanol solution, polymerization degree 500), N-methyl-2- Pyrrolidone was mixed and dissolved at a temperature of 95 ° C. at a ratio of 76.75% by weight, polyoxyethylene coconut oil fatty acid sorbitan (Sanyo Chemical Co., Ltd., trade name Ionet T-20C) at 5% by weight and water at 3% by weight. A polymer solution was prepared. This membrane-forming stock solution was uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a water bath to produce a hollow fiber membrane having a three-dimensional network structure layer formed on the spherical structure layer.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.04 μm on the surface to be treated and a porosity of 8%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 5.0 × 10 ¹¹ / m, the filtration resistance increase A was 3.4 × 10 ¹² / m ² , and the filtration resistance increase B was 1.5 × 10 ¹² / m ² . The recoverability was 63%.
Using this membrane, a small module was fabricated and a continuous filtration experiment was conducted using Lake Biwa as raw water. The rate of increase in the filtration differential pressure was 0.18 kPa / day, and it took 13 months to reach 100 kPa. It can be said that stable operation is possible.

<Comparative Example 1>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

  Next, 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 5% by weight of polyethylene glycol having a weight average molecular weight of 20,000, 79% by weight of dimethylformamide, and 3% by weight of water at 85 ° C. The polymer solution was prepared by mixing and dissolving at a temperature of. This membrane-forming stock solution was uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a water bath to produce a hollow fiber membrane having a three-dimensional network structure layer formed on the spherical structure layer.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.05 μm on the surface to be treated and a porosity of 6%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 3.0 × 10 ¹¹ / m, the filtration resistance increase A was 2.6 × 10 ¹² / m ² , and the filtration resistance increase B was 5.8 × 10 ¹² / m ² , backwashing. The recoverability was 76%.
When a small module was produced using this membrane and a continuous filtration experiment was conducted using Lake Biwa water as raw water, the rate of increase in the filtration differential pressure was 0.22 kPa / day, reaching 100 kPa in 10 months.

<Comparative example 2>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

Next, 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 5% by weight of polyoxyethylene sorbitan monooleate, and 82% by weight of dimethyl sulfoxide were mixed and dissolved at a temperature of 100 ° C. A polymer solution was prepared. This membrane-forming stock solution was uniformly applied to the surface of a hollow fiber membrane having a spherical structure, and immediately solidified in a water bath to produce a hollow fiber membrane having a three-dimensional network structure layer formed on the spherical structure layer.
The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.04 μm on the surface to be treated and a porosity of 9%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed. FIG. 4 shows a graph of total filtration water amount-filtration resistance selected by this filtration experiment.

As a result, the initial filtration resistance was 4.0 × 10 ¹¹ / m, the filtration resistance increase A was 2.7 × 10 ¹² / m ² , and the filtration resistance increase B was 9.2 × 10 ¹² / m ² . The recoverability was 81%.
A small module was produced using this membrane, and a continuous filtration experiment was conducted using Lake Biwa water as raw water. As a result, the rate of increase in the differential pressure of filtration was 0.32 kPa / day, reaching 100 kPa in only 7 months.

<Comparative Example 3>
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38% by weight and 62% by weight, respectively. The polymer solution was discharged from the base while stirring γ-butyrolactone as a hollow part forming liquid, and crushed in a cooling bath composed of an 80% by weight aqueous solution of γ-butyrolactone at a temperature of 20 ° C. to form a hollow fiber membrane having a spherical structure. Produced.

Subsequently, using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-described miniature membrane module having an effective membrane area of 0.004 m ² was prepared. What was dissolved in Wako Pure Chemical Industries distilled water so that Wako Pure Chemical Humic Acid would be 3 mg / L and Calcium Chloride 25 mg / L was used as raw water, and the filtration step was performed at a filtration pressure of 50 kPa, and the filtered water volume was 0.06 m ³ / m ² Then, an experiment for carrying out the backwashing step of backwashing 0.025 m ³ / m ² at a backwashing pressure of 100 kPa was carried out 5 times in succession.

The obtained hollow fiber membrane made of polyvinylidene fluoride had an average pore diameter of 0.3 μm on the surface to be treated and a porosity of 22%. Using the obtained hollow fiber membrane made of polyvinylidene fluoride, the above-mentioned miniature membrane module having an effective membrane area of 0.004 m ² was prepared, and a miniature membrane module filtration experiment was performed.

As a result, the initial filtration resistance was 2.0 × 10 ¹¹ / m, the filtration resistance increase A was 3.2 × 10 ¹² / m ² , and the filtration resistance increase B was 1.5 × 10 ¹³ / m ² . The recoverability was 32%.
A small module was produced using this membrane, and a continuous filtration experiment was conducted using Lake Biwa water as raw water. As a result, the rate of increase in the filtration differential pressure was 0.82 kPa / day, reaching 100 kPa in just 3 months.

The membrane module of the present invention can be used for membrane filtration of groundwater, river water, lake water, seawater, sewage secondary treated water, and the like.

An example of the graph of the total amount of filtrate water-filtration resistance by a filtration experiment is shown. It is a perspective view which shows the outline of the miniature membrane module used for filtration experiment. It is a graph of the total filtration water amount-filtration resistance which carried out filtration experiment about the separation membrane used in Example 1. FIG. It is a graph of the total filtration water amount-filtration resistance which carried out filtration experiment about the separation membrane used by the comparative example 3. FIG.

Claims (7)

In a membrane module for water treatment using a separation membrane made of a polyvinylidene fluoride resin as a filtration membrane, the separation membrane has a filtration resistance increase A of 2 × 10 ¹² / m ² or more, and a backwash recovery property of 50% or more. A membrane module characterized in that the membrane has a characteristic that the filtration resistance increase degree B is 2 × 10 ¹² / m ² or less and the initial filtration resistance is 1 × 10 ¹² / m or less. The membrane module according to claim 1, wherein the separation membrane used has a pore diameter of 0.1 µm or less. The membrane module according to claim 1 or 2, wherein the separation membrane used has a porosity of less than 20%. A water treatment method for producing permeated water by using a membrane filtration apparatus comprising the membrane module according to claim 3 to perform water treatment while periodically performing physical cleaning. The water treatment method according to claim 4, wherein the physical cleaning is backflow cleaning. 5. The water treatment method according to claim 4, wherein the physical cleaning interval is 10 minutes or more and 60 minutes or less. The water treatment method according to claim 5, wherein the separation membrane used is a hollow fiber membrane.

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