JP5333124B2 - Method for improving rejection of permeable membrane and permeable membrane - Google Patents

Description

The present invention relates to a method for improving the rejection rate of a permeable membrane, and in particular, effectively improves the rejection rate of a permeable membrane without significantly reducing the permeation flux of the permeable membrane and without requiring high-temperature treatment. Regarding the method.
The present invention also relates to a permeable membrane that has been subjected to a rejection improvement process by the method for improving the rejection of the permeable membrane, a water treatment method using the permeable membrane, a permeable membrane device, and a water treatment device.

  In recent years, in order to effectively use water resources, the introduction of a process for collecting, regenerating and reusing wastewater and a process for desalinating seawater has been progressing. Under these circumstances, in order to obtain treated water with high water quality, it is essential to use selective permeation membranes such as nanofiltration membranes and reverse osmosis membranes (RO membranes) that can remove electrolytes and medium and small molecules. It is.

  Conventionally, permselective membranes used for water treatment, particularly nanofiltration membranes, RO membranes and other selective permeable membranes are generally polyamide membranes, more specifically, at least two primary grades in an aromatic nucleus. A crosslinked aromatic polyamide film is used which is a reaction product of an aromatic polyamine having an amine and an aromatic polyfunctional acyl halide having an average of more than two acyl halide groups in the aromatic nucleus. Usually, this crosslinked aromatic polyamide membrane is formed as a dense layer on the surface of the porous support membrane.

  Such a selective permeable membrane, particularly an ultrapure water production system for RO membrane applications, includes an RO membrane device and an electrically regenerative deionization device or other ion exchange for advanced treatment of the permeated water of this RO membrane device. The device is built in.

  With recent advances in semiconductor circuit formation technology, it has become possible to create circuits with a line width of 65 nm or less. Along with this, the required water quality for ultrapure water as semiconductor cleaning water has also increased, and it is hoped to develop a pure water production device and a pure water production method that will reduce the burden of post-treatment and realize pure water production at a higher level. It is rare. In particular, there is a particular concern about the influence of the organic component on the device, and water that eliminates the organic component as much as possible is required. For this reason, RO membranes having high removability of substances having lower molecular weight such as methanol and ethanol as well as isopropanol (IPA) are required as organic components. Furthermore, with respect to the RO membrane, the pressure during operation is decreasing, and an RO membrane capable of obtaining a high rejection at low pressure and ultra-low pressure is demanded. In addition, RO membranes having high boron removal performance are required for RO membranes used for seawater desalination.

  However, the blocking rate of permeable membranes such as RO membranes against separation targets such as inorganic electrolytes and water-soluble organic substances is due to the effects of oxidizing substances and reducing substances present in water, and deterioration of polymer materials due to other causes. The required quality of treated water cannot be obtained. This deterioration may occur little by little during long-term use, or it may occur suddenly due to an accident. In some cases, the rejection rate of the permeable membrane as a product does not reach the required level.

  In view of this, various methods have been proposed in the past for improving the blocking rate of a permeable membrane having a reduced blocking rate or a permeable membrane having a low blocking rate.

For example, in Patent Document 1 (Japanese Patent No. 2762358), in order to improve the blocking rate of a polyamide reverse osmosis membrane in a method for producing a water softening membrane, the permeation membrane is made compatible with phosphoric acid, phosphorous acid, sulfuric acid and the like. A method is described in which the temperature is raised by contacting with an aqueous solution of strong mineral acid having a property, and then contacting with a blocking rate improver. The rejection enhancing agent, hydrolyzable tannic acid, and styrene / maleamic acid copolymer, C ₅ to C ₇ hydroxyalkyl methacrylate polymer, copolymer or terpolymer, a first polymer having a plurality of sulfonium or quaternary ammonium groups Coacervates made from a second polymer having a plurality of carboxylate groups, branched polyamidoamines with optional other substituents, vinyl acetate copolymers, hydroxyethyl methacrylate and methacrylic acid or methacrylamide (optionally Copolymers with other miscible monomers), styrene / maleamic acid copolymers and the like are shown.

  Further, Patent Document 2 (Japanese Patent Publication No. 7-114941) discloses that the organic compound removal rate is obtained by hydrothermal treatment of a polyamide composite reverse osmosis membrane composed of a microporous support membrane and an ultrathin film covering the support membrane. A way to improve it has been proposed.

  In Patent Document 3 (Patent No. 3862184), a permeable membrane comprising a polyamide composite film in which a polyamide thin film is formed on a porous support membrane is contained at 40 ° C. to 100 ° C. containing at least one of an organic substance and a salt. A method for producing a composite reverse osmosis membrane excellent in water permeation performance, organic matter blocking performance and salt blocking performance by contacting with an aqueous solution at 0 ° C. has been proposed. Examples of the organic substance include polyhydric alcohols such as propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, and polyvinyl alcohol. Examples of the salts include salts made of a mixture of a trialkylamine and an organic acid.

  Patent Document 4 (Japanese Patent Application Laid-Open No. 2006-110520) discloses an ionic polymer having a weight average molecular weight of 100,000 or more as a blocking rate improver for improving the blocking rate of a permeable membrane used for water treatment. The containment improver contained is shown. Examples of such ionic polymers include polyvinylamidine or derivatives thereof, cationic polymers such as cationic polymers having a heterocyclic ring, and anionic polymers such as polyacrylic acid or derivatives thereof, polystyrene sulfonic acid or derivatives thereof, and the like. The molecule is shown.

  Furthermore, Patent Document 5 (Japanese Patent Application Laid-Open No. 2009-56406) discloses that a permeable membrane is brought into contact with an aqueous solution containing a hydrophilic organic compound having a molecular weight of 65 or less, and heat treatment is performed at a temperature of 35 to 98 ° C. Alternatively, after the permeable membrane is cooled, a method of improving the rejection of the permeable membrane by reheating at a temperature of 35 to 98 ° C. has been proposed. Examples of the hydrophilic organic compound having a molecular weight of 65 or less used herein include methanol, ethanol, formic acid, formaldehyde, acetaldehyde, acetone, formamide, acetamide, ethylene glycol, and monomethylamine.

Japanese Patent No. 2762358 Japanese Patent Publication No.7-114941 Japanese Patent No. 3862184 JP 2006-110520 A JP 2009-56406 A

  Each of the conventional methods for improving the rejection rate has the following drawbacks, and each method has a problem that the permeation flux of the permeable membrane tends to be greatly reduced by the rejection rate improvement process.

  The method of Patent Document 1 aims to improve the rejection rate for salts, mainly hardness components, and has not been recognized for improving the rejection rate for organic matter. The reduction rate of permeation flux is reduced to reduce the rejection rate for organic matter. It has not been shown to improve. Moreover, since a strong mineral acid is used, processing operation is difficult.

  The permeation flux is remarkably reduced in the permeable membrane that has been subjected to the rejection improvement process by the method of Patent Document 2.

  In the method of Patent Document 3, the effect of improving the rejection with respect to IPA is shown, but the effect of improving the rejection with respect to other substances is unclear, and it is sufficient after suppressing a decrease in the permeation flux. It cannot be said that the method is sufficiently satisfactory in that the effect of improving the rejection rate is obtained.

  Further, as in Patent Document 4, the method of treating the permeable membrane surface with an organic substance such as an ionic polymer improves the blocking rate by reducing the molecular gap of the adsorption layer formed by this organic substance. There is a problem that the permeation flux decreases greatly as the rejection rate increases.

  Furthermore, the method of Patent Document 5 also tends to reduce the permeation flux, and in the method that requires heating, such as the methods of Patent Documents 2, 3, and 5, the permeable membrane, its supporting member, piping, etc. Due to the heat resistance, the processing temperature is limited, and for this reason, there is a case where a sufficient rejection rate improvement effect cannot be obtained.

  For this reason, there is a need for a method that can effectively improve the rejection of the permeable membrane while suppressing a decrease in the permeation flux of the permeable membrane and without requiring high-temperature heat treatment.

The present invention solves the above-mentioned conventional problems, and suppresses the decrease in permeation flux of permeation membranes such as RO membranes and nanofiltration membranes, and prevents inorganic and organic substances without requiring high-temperature treatment. It aims at providing the method of improving a rate effectively.
The present invention also provides a permeable membrane that has been subjected to rejection rate improvement processing by such a permeable membrane rejection rate improving method, a water treatment method using the permeable membrane, a permeable membrane device including the permeable membrane, and a water treatment device. The purpose is to provide.

  As a result of intensive studies to solve the above problems, the present inventor forms a water-insoluble substance (hereinafter, sometimes referred to as “slightly soluble substance”) in the permeable layer of the permeable membrane. Thus, the rejection rate can be improved by narrowing the water passage gap of the permeation layer, and this method is different from the conventional method in which an adsorption layer is formed on the membrane surface. It is possible to suppress the decrease, and furthermore, by using the solubility product of the hardly soluble substance and the behavior of the hardly soluble substance in the permeation layer, water in which the substance capable of forming the hardly soluble substance by the reaction is dissolved. It has been found that such a blocking rate improving process can be easily performed by simply passing water through the permeable membrane without requiring a high temperature process or a complicated process.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] A method for improving a rejection rate of a permeable membrane including a step of forming a poorly water-soluble substance in the permeable layer of the permeable membrane (hereinafter referred to as a “poorly soluble substance forming step”) , wherein The substance forming step is a step of passing through the permeable membrane water having improved rejection rate formed by dissolving in water two or more substances that form a hardly soluble substance in the water by reaction, and the rejection rate The concentration of the two or more substances in the improved treated water is not more than the solubility product of the hardly soluble substance formed in the water, and the hardly soluble substance is calcium oxalate and / or magnesium oxalate. A method for improving the rejection of a permeable membrane, which is characterized by the following .

[2] Oite to [1], rejection enhancing method of the permeable membrane, wherein the pH of the rejection enhancing treatment water is 1-7.

[3] Oite to [1] or [2], the hardly soluble before or after material forming step or sparingly soluble in the material forming process, to include flame-soluble substance forming process other than the rejection enhancing treatment step A method for improving the rejection of a permeable membrane.

[ 4 ] The method for improving the rejection rate of a permeable membrane according to [ 3 ], wherein the rejection rate improving treatment step other than the hardly soluble substance forming step is a heat treatment step and / or a treatment step with a polymer compound.

[ 5 ] A permeable membrane, which has been subjected to a rejection rate improving process by the method for improving a rejection rate of the permeable membrane according to any one of [1] to [ 4 ].

[ 6 ] A water treatment method using the permeable membrane according to [ 5 ].

[ 7 ] A permeable membrane device comprising the permeable membrane according to [ 5 ].

[ 8 ] A water treatment device comprising the permeable membrane device according to [ 7 ].

  In the present invention, the blocking rate is improved by forming a poorly soluble substance in the permeable layer of the permeable membrane and narrowing the water flow gap in the permeable layer of the permeable membrane by this hardly soluble substance.

  That is, for example, as described above, the RO membrane has a structure in which a dense layer made of a polyamide thin film is formed on the porous support membrane, and the separation target that cannot permeate the water flow gap of the dense layer. Membrane separation is performed by preventing the above. This dense layer is formed by, for example, entanglement of polyamide polymer chains. When a poorly soluble substance is deposited on this polymer chain, the entanglement of the polymer chains will be the same as the volume of the precipitated hardly soluble substance. The gap is narrowed, apparently the dense layer is further densified, and the flow gap of the water to be treated is narrowed, so that the rejection rate of the separation object in the water to be treated is improved. Further, the place where the hardly soluble substance is deposited is a space where the original substance forming the hardly soluble substance can enter. That is, a large space that has contributed to a decrease in the rejection rate in the dense layer is preferentially filled with the hardly soluble substance.

  Thus, even if a poorly soluble substance is deposited in the dense layer of the permeable membrane, the water passage is narrowed only in a large space in the dense layer of the permeable membrane, and the water flow path itself is secured. The permeation flux is not greatly reduced unlike the formation of the adsorption layer on the membrane surface.

Specifically, the formation of the hardly soluble substance in the dense layer is specifically made of two or more kinds of substances capable of forming a hardly soluble substance by reaction (hereinafter, these substances are referred to as “slightly soluble substance forming substances”). the rejection enhancing treatment water obtained by dissolving in water, it row by Rohm permeable membrane. The principle of depositing a poorly soluble substance in the dense layer of the permeable membrane by this method is as follows.

That is, as shown in FIG. 1 (a), the dense layer of the permeable membrane is formed by the entanglement of the polymer chain 1, and this dense layer is formed by reaction as shown in FIG. 1 (b). When water in which a poorly soluble substance, for example, oxalic acid ((COOH) ₂ ) and calcium ions (Ca ²⁺ ) that generate calcium oxalate is dissolved, the concentration of oxalic acid and calcium ions in the water is increased. Even if it is below the solubility product of calcium and remains in the dissolved state before permeating the dense layer, the water passage gap is narrow when passing through the entangled gap of the polymer chain 1 of the dense layer. Then, oxalic acid and calcium ions come close to each other, and the collision frequency is high and an apparently high concentration state is reached, and calcium oxalate is deposited on the polymer chain 1 as shown in FIG.
As a result, a hardly soluble substance can be formed in the dense layer of the permeable membrane, and the rejection rate of the permeable membrane can be improved.

As described above, the hardly soluble substance-forming substance in the treated water with improved rejection rate has an apparently high level in the process of passing through the dense layer of the permeable membrane, even if its concentration is lower than the solubility product of the hardly soluble substance. Since the poorly soluble substance precipitates in the concentration state, the concentration of the hardly soluble substance forming substance in the treated water with improved rejection rate should be less than the solubility product of the hardly soluble substance before and after passing through the dense layer of the permeable membrane. without precipitation of soluble substances, you as sparingly soluble material is deposited only in the dense layer.

In the present invention, the sparingly soluble substance forming the transparent film, sparingly soluble in water, also have difficulty redissolved upon passed through the acidic or alkaline water to be treated, calcium oxalate, oxalic acid magnesium It is.

  In addition, when the rejection rate improving treatment is performed by passing water for improving the rejection rate, the anionicity of the permeable membrane increases and the oxalic acid is completely dissociated at a high pH, so that the oxalic acid becomes dense in the permeable membrane. This treatment is preferably performed on the acidic side having a pH of 1 to 7 because it is difficult to enter the layer.

  The rejection improvement process by the formation of the hardly soluble substance of the present invention can be performed in combination with a conventional rejection improvement process, and thereby an even higher rejection improvement effect can be obtained. In this case, heat treatment, polymer treatment, etc. are mentioned as other inhibition rate improvement processing combined with the hardly soluble substance formation processing by this invention.

It is a schematic diagram explaining the precipitation principle of the hardly soluble substance in the dense layer of the permeable film in this invention.

  Hereinafter, embodiments of the present invention will be described in detail.

  The method for improving the rejection rate of a permeable membrane according to the present invention forms a hardly water-soluble substance (slightly soluble substance) in the permeable layer of the permeable membrane, and the poorly soluble substance causes a water flow gap in the permeable layer of the permeable membrane. It is characterized in that the rejection rate is improved by narrowing.

  The poorly soluble substance is not particularly limited as long as it has a low solubility in water and is hardly soluble or insoluble in water, and even if the water to be treated supplied to the permeable membrane is acidic or alkaline. In addition, a stable substance that does not elute even under acidic or alkaline conditions is preferable so that it does not elute by passing water to be treated. Specifically, calcium oxalate, magnesium oxalate, calcium fluoride, silver chloride, Examples of the water-insoluble salt include barium sulfate and silver bromide. Of these, calcium and magnesium are common cations, and oxalic acid is a chemical that is relatively used as a cleaning agent. Therefore, calcium oxalate and magnesium oxalate are easy to handle and easy to obtain. Is preferred. Only one kind of hardly soluble substance may be formed in the permeable membrane, or two or more kinds may be formed.

To form such a poorly soluble substance in the transmissive layer of the permeable membrane, specifically, 2 or more substances capable of forming a sparingly soluble substance (poorly soluble substance-forming material) is dissolved in water by the reaction the rejection enhancing treatment water comprising Te, by Rohm permeable membrane, in the above-described principle, Ru precipitating sparingly soluble substance in the dense layer of the permeable membrane.

  In this method, the hardly soluble substance-forming substance is selected and used depending on the kind of the hardly soluble substance, and examples thereof include the following combinations.

When the poorly soluble substance is calcium oxalate: oxalic acid, sodium oxalate or potassium oxalate and calcium compounds such as calcium chloride, calcium nitrate, calcium hydroxide When the poorly soluble substance is magnesium oxalate: oxalic acid, oxalic acid Sodium or potassium oxalate and magnesium compounds such as magnesium chloride, magnesium nitrate, and magnesium sulfate When the poorly soluble substance is calcium fluoride: hydrofluoric acid, sodium fluoride or potassium fluoride, calcium chloride, calcium nitrate, calcium hydroxide When the sparingly soluble substance is barium sulfate: sulfuric acid, sodium sulfate or potassium sulfate and barium compounds such as barium chloride, barium sulfate, barium hydroxide, etc. When the sparingly soluble substance is silver chloride, hydrochloric acid, sodium chloride or chloride Cali And silver compounds such as silver nitrate When the poorly soluble substance is silver bromide: hydrobromic acid, sodium bromide or potassium bromide, and silver compounds such as silver nitrate

Such sparingly soluble substances forming material, water, preferably an aqueous electrolyte solution, sparingly soluble substances forming substance concentration of rejection enhancing treatment water dissolved organic matter aqueous solution state, and are less than the solubility product of the sparingly soluble substances formed whereby, as the feed water supplied to the permeable membrane, without deposition of poorly soluble substances, the apparent flame-soluble substance-forming material between the rejection dense layer enhancement water permeable membrane approaches high When the concentration state is formed, therefore, it is possible to efficiently deposit the hardly soluble substance only in the dense layer of the permeable membrane, and therefore, the permeation of the permeable membrane is suppressed while suppressing the decrease of the permeation flux. The rate can be improved effectively.
Use of an aqueous electrolyte solution increases ionic strength and generally increases solubility. When the electrolyte is blocked by the membrane, the ionic strength is lowered and a hardly soluble salt is likely to precipitate in the membrane. In addition, examples of the organic substance in the organic substance aqueous solution include alcohols such as ethanol and isopropyl alcohol, glycols such as ethylene glycol and propylene glycol, and ketones such as acetone. These organic substances swell the film and temporarily form a dense layer. Has the effect of facilitating the entry of the hardly soluble substance-forming substance.

In addition, according to the Chemical Society of Japan “Chemical Handbook Basic Edition 2nd revised edition”, the solubility and solubility product of the aforementioned poorly soluble substances are as shown in Table 1. In Table 1, although the solubility product of magnesium oxalate has various theories of 1 × 10 ⁻⁴ to 1 × 10 ⁻⁸ (mol / L) ² (reference: Lange's Handbook of Chemistry, Chemical Handbook), detailed description According to the reviewed literature (Inafuku et al., Chemistry and Education, Vol. 36, No. 4, pp. 406-409 (1988)), it is 1.1 × 10 ⁻⁵ (mol / L) ^2. .

  When treated water containing a poorly soluble substance-forming substance is passed through a permeable membrane, the hardly soluble substance-forming substance is concentrated according to the recovery rate under the water flow conditions, and theoretically poorly soluble on the concentrated water side. In some cases, the concentration of the substance-forming substance may be higher than the solubility product of the hardly soluble substance, but increase the flow rate of the feed water and do not increase the concentration factor, and add other electrolytes to increase the ionic strength in the feed water. By paying attention to the increase, it is precipitated and removed as a hardly soluble substance in the dense layer of the permeable membrane, and even if it precipitates in the supply water, it is discharged as fine particles, so there is no problem.

  However, it is necessary to prevent precipitation of poorly soluble substances outside the dense layer of the permeable membrane by passing the treated water with improved rejection rate, and to efficiently use the poorly soluble substances within the dense layer of treated water with improved rejection rate. Therefore, the concentration of the hardly soluble substance-forming substance in the treated water with improved rejection rate is about 1/1 to 1/5 of the concentration determined from the solubility and solubility product of the hardly soluble substance to be formed. Preferably there is.

  For example, the following conditions are preferably adopted as the blocking rate improving treatment conditions for allowing such a blocking rate improving treated water to pass through the permeable membrane and depositing a hardly soluble substance.

<PH>
A hardly soluble substance-forming substance, for example, oxalic acid is a substance that dissociates in multiple stages. At low pH, the anionicity is reduced and the permeation membrane is easily transmitted. Moreover, since the ratio of the completely dissociated body which reacts with calcium reduces, solubility also increases. Therefore, it is desirable to pass the treated water with improved rejection rate at an acidic pH of 1 to 7, preferably 2 to 5. The RO membrane rejection is greatly reduced when the pH is lowered, particularly at pH 5 or lower. Therefore, not only oxalic acid but also a hardly soluble substance-forming substance can easily enter the dense layer.
When the pH after dissolving the hardly soluble substance-forming substance in water at a predetermined concentration is out of this range, the pH may be adjusted as appropriate by adding an acid such as HCl or an alkali such as NaOH.

<Pressure>
If the water flow pressure of the treated water with too high rejection is too high, the concentration rate will increase and the rejection with poorly soluble substance-forming substances will increase. If it is too low, the permeation amount of poorly soluble substance-forming substances including water will decrease. In addition, since the opportunity for formation of the hardly soluble substance in the dense layer is reduced, the water passage pressure to the permeation membrane of the water with improved rejection rate is in the range of 30 to 160% of the pressure at which the permeation membrane is normally used. It is desirable that For example, if the permeable membrane is an ultra-low pressure RO membrane (usually operating pressure of 0.75 MPa), the pressure is preferably about 0.225 to 1.2 MPa.

<Recovery rate>
The recovery rate when the treated water with improved rejection rate is passed through the permeable membrane is preferably 60% or less, because if it is too high, it may be concentrated on the feed water side and a hardly soluble substance may be deposited. .
However, if the recovery rate is too low, the chance of forming a hardly soluble substance in the dense layer is reduced, and therefore it is preferably 10% or more.

<Water temperature>
When the water temperature of the treated water with improved rejection rate that passes through the permeable membrane is low, the solubility of the hardly soluble material is lowered, and precipitation of the hardly soluble material on the feed water side is likely to occur, and the slightly soluble property of the treated water with improved rejection rate. It is necessary to reduce the concentration of substance forming substances. At high temperatures, the solubility of poorly soluble substances increases and it becomes difficult to form poorly soluble substances in the dense layer of the permeable membrane. It is efficient to raise the temperature and increase the concentration of the hardly soluble substance-forming substance in the water with improved rejection rate, which increases the chance of forming the hardly soluble substance in the dense layer. However, since the operation at a high temperature affects the RO membrane itself, it is preferable that the water flow temperature of the rejection rate improving treated water is 10 to 40 ° C, particularly 20 to 35 ° C.

<Time>
As the water passing time of the rejection-improving treated water, the poorly soluble substance-forming substance existing at a low concentration below the solubility product in the rejection-improving treated water is usually reacted for 1 to 100 hours in the dense layer of the permeable membrane. Preferably, 5 to 50 hours is appropriate.

By passing the blocking rate improving treatment water through the permeable membrane, there is no particular limitation on the amount of the hardly soluble substance to be precipitated in the dense layer of the permeable membrane, and it may be enough to obtain a desired blocking rate improving effect. That is, it is difficult to accurately grasp the amount of the hardly soluble substance precipitated in the dense layer of the permeable membrane by such treatment, and in general, the treatment water with improved rejection rate containing the hardly soluble substance forming substance at a high concentration. If the water is passed for a long time, more hardly soluble substances can be precipitated, and conversely, if the treated water containing the poorly soluble substance forming substance at a low concentration is passed for a short time, the hardly soluble substances are passed. The amount of precipitation becomes small.
Further, by depositing more hardly soluble substances in the dense layer of the permeable membrane, the effect of improving the rejection rate is increased, but the permeation flux tends to be lowered. On the contrary, when the amount of the hardly soluble substance deposited is small, the permeation flux decrease is small, but the effect of improving the rejection is low.

  Therefore, a permeation membrane having a desired rejection rate and permeation flux is obtained from the relationship between the water flow conditions of the treated water with improved rejection rate, the effect of improving the rejection rate of the permeable membrane after treatment, and the degree of decrease in permeation flux. What is necessary is just to perform the process by the rejection rate improvement treated water on such a water flow condition.

  In the present invention, it is possible to sufficiently improve the rejection rate by simply depositing a poorly soluble substance in the dense layer of the permeable membrane by passing the treated water with improved rejection rate as described above. It is also possible to perform the rejection rate improvement process in combination, thereby further improving the rejection rate improvement effect.

  In this case, the rejection rate improving process used in combination with the rejection rate improving process due to the formation of a hardly soluble substance includes the rejection rate improving process described in Patent Documents 1 to 5 mentioned above. For example, heat treatment (for example, hot water) And an aqueous solution of a compound having a polyalkylene glycol chain, a polymer treatment for passing an aqueous solution containing a cationic polymer and an anionic polymer, a method for passing an aqueous tannic acid solution, and the like.

  Among these, specific examples of the method for passing an aqueous solution of a compound having a polyalkylene glycol chain include the following methods.

The polyalkylene glycol of the compound having a polyalkylene glycol chain used here has a structure that is considered to be formed by dehydration polycondensation of alkylene glycol. Can be manufactured. Examples of the polyalkylene glycol chain that the compound having a polyalkylene glycol chain has include a polyethylene glycol chain, a polypropylene glycol chain, a polytrimethylene glycol chain, and a polytetramethylene glycol chain. These glycol chains can be formed by, for example, ring-opening polymerization of ethylene oxide, propylene oxide, oxetane, tetrahydrofuran or the like.
As the compound having a polyalkylene glycol chain, a multi-branched structure compound such as a multi-branched polyerythritol obtained by ring-opening polymerization of tetrahydrofuran-3,4-diol, a multi-branched polyglycerol obtained by ring-opening polymerization of glycidol, etc. Can be mentioned.

  The weight average molecular weight of this polyalkylene glycol chain is usually 2,000 to 6,000, preferably 3,000 to 5,000. If the weight average molecular weight of the polyalkylene glycol chain is less than 2,000, the blocking rate of the permeable membrane may not be sufficiently improved, and the fixability after processing may be lowered. If the weight average molecular weight of the polyalkylene glycol chain exceeds 6,000, the permeation flux of the permeable membrane may be greatly reduced. The weight average molecular weight can be obtained by analyzing an aqueous solution of a compound having a polyalkylene glycol chain by gel permeation chromatography (GPC) and converting the obtained chromatogram into the molecular weight of a polyethylene oxide standard product.

  The polyalkylene glycol chain is preferably a polyethylene glycol chain. Since the compound having a polyethylene glycol chain is excellent in water solubility, it is easy to handle and has high affinity for the surface of the permeable membrane, so that there is little deterioration in performance over time after treatment.

  The compound having a polyalkylene glycol chain is preferably passed through the permeable membrane as an aqueous solution having a concentration of 0.01 to 10 mg / L, more preferably 0.1 to 5 mg / L. It is preferable that the water flow pressure in that case is a pressure comparable to the pressure at the time of actual use of the permeable membrane. If the concentration of the compound having a polyalkylene glycol chain is less than 0.01 mg / L, the adsorption layer formed on the permeable membrane may be incomplete and the blocking rate may not be sufficiently improved. If the concentration of the compound having a polyalkylene glycol chain exceeds 10 mg / L, the adsorption layer may become too thick, and the permeation flux may be greatly reduced.

As the compound having a polyalkylene glycol chain, a compound in which an ionic group is introduced into the polyalkylene glycol chain can also be used. Examples of the ionic group include a sulfo group (—SO ₃ H), a carboxyl group (—COOH), an amino group (—NH ₂ ), a quaternary ammonium group (—N ⁺ R ₃ X ⁻ ), and the like. be able to. In order to prevent the generation of scale, the permeable membrane is often subjected to a filtering operation under weakly acidic conditions. In that case, it becomes anion-rich, and biological metabolites, colloids, and fine particles often have negative charge, Introduction of a strong anionic sulfo group is effective.

  Other blocking ratio improving treatments such as a method of passing an aqueous solution of a compound having a polyalkylene glycol chain may be performed in two or more types, and may be performed before or after the hardly soluble substance forming step according to the present invention. It may be done at the same time.

  However, as described above, these rejection rate improving processes generally tend to lower the permeation flux. Therefore, these processes should be performed by shortening the processing time or reducing the processing temperature. It is preferable to suppress a decrease in the permeation flux due to.

  The method for improving the rejection of the permeable membrane of the present invention is suitably applied to selective permeable membranes such as nanofiltration membranes and RO membranes. The nanofiltration membrane is a liquid separation membrane that blocks particles and polymers having a particle size of about 2 nm. Examples of the membrane structure of the nanofiltration membrane include inorganic membranes such as ceramic membranes, polymer membranes such as asymmetric membranes, composite membranes, and charged membranes. The RO membrane is a liquid separation membrane that applies a pressure higher than the osmotic pressure difference between solutions through the membrane to the high concentration side to block the solute and permeate the solvent. Examples of the membrane structure of the RO membrane include polymer membranes such as asymmetric membranes and composite membranes. Examples of the material of the nanofiltration membrane or RO membrane to which the method for improving the rejection rate of the permeable membrane of the present invention is applied include, for example, aromatic polyamides, aliphatic polyamides, polyamide materials such as composite materials thereof, and cellulose acetate. Examples thereof include cellulosic materials. Among these, the method for improving the rejection of the permeable membrane of the present invention can be particularly suitably applied to the membrane of the aromatic polyamide material.

The method for improving the rejection rate of the permeable membrane of the present invention can be applied to either an unused permeable membrane or a used permeable membrane with reduced performance.
There is no restriction | limiting in particular in the module form of the permeable membrane to apply, For example, a tubular membrane module, a plane membrane module, a spiral membrane module, a hollow fiber membrane module etc. can be mentioned.

  The permeable membrane of the present invention is a permeable membrane that has been subjected to the rejection rate improving process by the method of improving the rejection rate of the permeable membrane of the present invention, specifically, a selective permeable membrane such as an RO membrane or a nanofiltration membrane. In addition, the rejection rate is improved with the permeation flux of the permeable membrane being increased, and the high state can be maintained for a long time.

  In the water treatment method of the present invention in which water to be treated is permeated by the permeable membrane of the present invention, the rejection rate is improved with the permeation flux of the permeable membrane being increased, and the high state is lengthened. As a result, the removal effect of a substance to be removed such as an organic substance is high, and a stable treatment is possible for a long period of time. The treatment water can be supplied and permeated in the same way as normal permeable membrane treatment. However, when treating water containing hardness components such as calcium and magnesium, the raw water contains dispersants and scale prevention. Agents and other agents may be added.

  Further, the permeable membrane device of the present invention having such a permeable membrane of the present invention preferably has a permeable membrane module for passing water to be treated on the primary side and taking out the permeable water from the secondary side, And means for supplying the above-described blocking rate improving treated water to the primary side.

  The permeable membrane apparatus of the present invention is a water treatment for recovering and reusing wastewater containing high or low concentration TOC discharged in the electronic device manufacturing field, semiconductor manufacturing field, and other various industrial fields, or industrial water or city. It is effectively applied to ultrapure water production from water and water treatment in other fields. The water to be treated is not particularly limited, but can be suitably used for organic substance-containing water. For example, TOC = 0.01 to 100 mg / L, preferably about 0.1 to 30 mg / L. It is suitably used for the treatment of organic substance-containing water. Examples of such organic substance-containing water include, but are not limited to, wastewater from electronic device manufacturing factories, transportation machinery manufacturing factories, organic synthesis factories, printing plate making / painting factories, or the primary treatment water thereof. .

  In addition, the water treatment device of the present invention having such a permeable membrane of the present invention is an activated carbon tower, an ion as a pretreatment device of the permeable membrane device for the purpose of preventing clogging and fouling of the permeable membrane, particularly the RO membrane. It is preferable to provide an exchange resin tower, a coagulation sedimentation device, a coagulation pressure flotation device, a filtration device or a decarboxylation device. As the filtration device, a sand filtration device, an ultrafiltration device, a microfiltration device, or the like can be used. A prefilter may be further provided as a pretreatment device. Further, since the RO membrane is susceptible to oxidative degradation, it is preferable to provide a device for removing the oxidant (oxidation degradation inducing substance) contained in the raw water as necessary. As an apparatus for removing such an oxidative degradation inducing substance, an activated carbon tower, a reducing agent injection apparatus, or the like can be used. In particular, the activated carbon tower can also remove organic substances and can also be used as a fouling prevention means as described above. The pH of the raw water is not particularly limited, but when it contains a lot of hardness components, it is preferable to take measures such as adjusting to an acidic range of pH 5 to 7 or using a dispersant.

  In addition, when ultrapure water is produced by the water treatment method and the water treatment apparatus of the present invention, a decarbonation means, an ion exchange apparatus, an electric regeneration deionization apparatus, an ultraviolet oxidation is provided in the subsequent stage of the permeable membrane apparatus of the present invention. An apparatus, a mixed bed type ion exchange resin apparatus, an ultrafiltration apparatus, and the like are provided.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

  In the following, the RO membrane supply water used for the RO membrane rejection rate improving process was as follows. The pH of each aqueous solution below was adjusted by adding acid (HCl) or alkali (NaOH).

<Inhibition rate improved treated water No. 1 (oxalic acid / calcium chloride aqueous solution)>
Oxalic acid dihydrate concentration: 2.8 mg / L (Molar concentration of oxalic acid: 2.2 × 10 ⁻⁵ mol / L)
Calcium chloride concentration: 2.5 mg / L (Ca molar concentration: 2.25 × 10 ⁻⁵ mol / L)
pH: 3
This rejection improvement water No. 1 [oxalic acid] [Ca] is 5.0 × 10 ⁻¹⁰ (mol / L) ² , which is sufficiently more than the aforementioned solubility product of calcium oxalate: 4 × 10 ⁻⁹ (mol / L) ² This small, improved rejection rate treated water No. Even when 1 is concentrated twice by RO membrane treatment with a recovery rate of 50%, it is below the solubility product of calcium oxalate and is a concentration at which calcium oxalate does not precipitate.

<Inhibition rate improved treated water No. 2 (oxalic acid / magnesium chloride aqueous solution)>
Oxalic acid dihydrate concentration: 140 mg / L (molar concentration of oxalic acid: 1.1 × 10 ⁻³ mol / L)
Magnesium chloride concentration: 190 mg / L (Molar concentration of Mg: 2.0 × 10 ⁻³ mol / L)
pH: 3
This rejection improvement water No. 2 [oxalic acid] [Mg] is 2.2 × 10 ⁻⁶ (mol / L) ² , and the solubility product of magnesium oxalate described above: 1.1 × 10 ⁻⁵ (mol / L) ² The treatment water No. Even if 2 is concentrated twice by RO membrane treatment with a recovery rate of 50%, it is below the solubility product of magnesium oxalate and does not precipitate magnesium oxalate.

<Inhibition rate improved treated water No. 3 (oxalic acid / magnesium chloride aqueous solution)>
Oxalic acid dihydrate concentration: 700 mg / L (Molar concentration of oxalic acid: 5.56 × 10 ⁻³ mol / L)
Magnesium chloride concentration: 760 mg / L (Molar molar concentration of Mg: 8.0 × 10 ⁻³ mol / L)
pH: 3
This rejection improvement water No. 3 [oxalic acid] [Mg] is 4.45 × 10 ⁻⁵ (mol / L) ² , and the solubility product of the aforementioned magnesium oxalate: 1.1 × 10 ⁻⁵ (mol / L) ² Although slightly larger, precipitation of magnesium oxalate did not occur in the state of RO membrane feed water.

<Oxalic acid aqueous solution>
Oxalic acid dihydrate concentration: 2.8 mg / L
pH: 3

<Calcium chloride aqueous solution>
Calcium chloride concentration: 2.5mg / L
pH: 3

<PEG aqueous solution>
Polyethylene glycol (weight average molecular weight 3000) concentration: 2 mg / L

[Examples 1 to 4, Comparative Examples 1 to 5]
Using the following test apparatus and RO membrane, the rejection rate improving treatment was performed by passing the rejection rate improved treated water shown in Table 2 for the time shown in Table 2 under the following water flow conditions. However, Comparative Example 1 did not perform the rejection improvement process, and Comparative Example 4 performed a process of immersing the RO membrane in hot water at 80 ° C. for 2 hours.
Test apparatus: Small flat membrane test cell with a membrane area of 8 cm ² (inside the cell is stirred by a stirrer)
RO membrane: Ultra-low pressure RO membrane ES-20 (manufactured by Nitto Denko Corporation, normal operating pressure 0.75 MPa)
Water flow conditions: operating pressure 0.75 MPa, water temperature 25 ° C., recovery rate 50%

  The following performance evaluation was performed on the treated RO membrane, and the results are shown in Table 2.

<Performance evaluation>
A 100 mg / L isopropyl alcohol (IPA) aqueous solution is passed through under the above-mentioned water passing conditions, and the permeation flux and the TOC rejection are measured.
The rejection rate is calculated by the following formula.
Rejection rate = 1-permeated water TOC value / concentrated water TOC value

As is apparent from Table 2, according to the present invention, the rejection rate can be effectively improved without significantly reducing the permeation flux as compared with the conventional heat treatment and polymer treatment.
Moreover, the effect can be further improved by using together other blocking rate improvement processes, such as a polymer processing.

1 Polymer chain

Claims (8)

A method for improving the rejection rate of a permeable membrane, including a step of forming a poorly soluble substance in water (hereinafter referred to as a “slightly soluble substance forming step”) in the permeable layer of the permeable membrane,
The hardly soluble substance forming step is a step of passing through the permeable membrane water for improving the rejection rate obtained by dissolving in water two or more substances that form a hardly soluble substance in the water by reaction.
The concentration of the two or more substances in the rejection improvement treatment water is not more than the solubility product of the hardly soluble substance formed in the water,
The method for improving the rejection of a permeable membrane, wherein the water-insoluble substance is calcium oxalate and / or magnesium oxalate . The method for improving the rejection of a permeable membrane according to claim 1 , wherein the pH of the treated water for improving the rejection is 1 to 7. 3. The permeation of a permeable membrane according to claim 1, further comprising a blocking rate improving treatment step other than the hardly soluble substance forming step before or after the hardly soluble substance forming step or in the hardly soluble substance forming step. Rate improvement method. 4. The method for improving the rejection rate of a permeable membrane according to claim 3 , wherein the rejection rate improving treatment step other than the hardly soluble substance forming step is a heat treatment step and / or a treatment step with a polymer compound. A permeable membrane, which has been subjected to a rejection improvement process by the method for improving a rejection of a permeable membrane according to any one of claims 1 to 4 . A water treatment method using the permeable membrane according to claim 5 . A permeable membrane device comprising the permeable membrane according to claim 5 . A water treatment device comprising the permeable membrane device according to claim 7 .

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