JP5131027B2 - Manufacturing method of composite semipermeable membrane - Google Patents

Description

  The present invention is a composite semipermeable membrane that can be used for selective separation of a liquid mixture, and particularly has a high ion removal property and a high water permeability, and is useful for seawater desalination treatment. The present invention relates to an improvement of a composite semipermeable membrane having a polyamide separation functional layer formed thereon.

  In recent years, seawater desalination using a composite semipermeable membrane has been put to practical use in water treatment plants around the world. In general, a composite semipermeable membrane is formed by coating a separation functional layer on a microporous support membrane. When the separation functional layer is formed of a crosslinked aromatic polyamide, it is rich in rigidity by including a benzene ring. It has the advantage that it can be easily formed by interfacial polycondensation between an aromatic polyfunctional amine and an aromatic polyfunctional acid halide, and is also known to have high desalting properties and high permeability (Patent Documents) 1 and 2).

  In order to further improve the high desalting property and high water permeability of the composite semipermeable membrane, it is known to treat the polyamide separation functional layer with various chemical solutions. For example, contact treatment or immersion treatment with ammonia, alkylamine, alcohols, hydrochloric acid, organic acid, inorganic salt, etc. has been proposed (see Patent Documents 3 to 7). However, in these treatments, the TDS removal rate is lowered even if high water permeability is obtained, or the water permeability is lowered even if the TDS removal rate is improved. Especially for semi-permeable membranes for seawater desalination, membranes with high water permeability and high TDS removal rate are required, but among the conventional membrane treatment methods, treatment methods that solve this problem have been reported. It wasn't.

That is, the semipermeable membrane used in seawater desalination has a TDS removal rate of 99.25 when seawater having a TDS concentration of 3.5% by weight at 25 ° C., pH = 6.5 is permeated at an operating pressure of 5.5 MPa. It is necessary to be 5% or more, and a processing technique for further improving the performance of the semipermeable membrane for seawater desalination has been demanded.
JP-A-1-180208 Japanese Patent Laid-Open No. 2-115027 Special Table 2000-504270 JP-A-6-327953 JP 2000-237559 A JP 2003-117360 A JP 2003-117361 A

An object of the present invention is to provide a method capable of producing a composite semipermeable membrane having superior decalcification performance, water permeability performance, and deTDS performance for seawater desalination semipermeable membranes compared to the conventional methods described above. It is to provide. That is, when seawater having a temperature of 25 ° C., pH = 6.5, and a TDS concentration of 3.5% by weight is permeated at an operating pressure of 5.5 MPa, the TDS removal rate is 99.5% or more and the water permeability is 0.9 m. ^{The present} invention provides a method capable of producing a semipermeable membrane for seawater desalination having a high water permeability and high ion removability, which is ³ / m ² · day or more and a calcium permeability is 0.05% or less.

The present invention for solving the above-described problems is characterized by the following (1) to (4) .
(1) A polyamide separation functional layer formed by polycondensation of a polyfunctional amine and a polyfunctional acid halide is formed on a microporous support membrane, and is 25 ° C., pH = 6.5, TDS concentration 3.5 wt. Organic compound having the structure represented by the following general formula (1) or an organic compound thereof having a TDS removal rate of 99.5% or more when 1% of seawater is permeated at an operating pressure of 5.5 MPa The manufacturing method of the composite semipermeable membrane characterized by performing the process made to contact the solution of the salt of a compound and an acid .

(In general formula (1), X represents an oxygen atom, a sulfur atom, or an NH group, and R1 to R4 represent any one of a hydrogen atom, a hydrocarbon group, and an oxyalkyl group.)
(2) The method for producing a composite semipermeable membrane according to (1), wherein the organic compound has a molecular weight of 59 to 1,000.
(3) said organic compound is urea, guanidine and Chionyo fluorinated et al method for producing a composite semipermeable membrane according to at least one (1) to be selected.
(4) The method for producing a composite semipermeable membrane according to (1), wherein the organic compound is urea.

  According to the present invention, a semipermeable membrane used in a seawater desalination apparatus has a high water permeability and a high solute removal performance, and is particularly excellent in a bivalent cation removal performance and has a high durability. A permeable membrane can be manufactured with high productivity.

  The composite semipermeable membrane in the present invention is a composite semipermeable membrane in which a polyamide separation functional layer is formed on a microporous support membrane, and seawater having a temperature of 25 ° C., a pH = 6.5, and a TDS concentration of 3.5% by weight. This is a separation membrane for seawater desalination having a TDS removal rate of 99.5% or more when it is permeated at an operating pressure of 5.5 MPa.

Here, the microporous support membrane has substantially no separation performance and is intended to give strength to the separation functional layer having the separation performance substantially. The size and distribution of the micropores are not particularly limited. For example, the micropores have uniform and fine pores, or gradually have large micropores from the surface on the side where the separation functional layer is formed to the other surface, and the separation function. A support membrane in which the size of the micropores is 0.1 nm or more and 100 nm or less on the surface on which the layer is formed is preferable. The material used for the microporous support membrane and the shape thereof are not particularly limited. It is a resin film reinforced with a fabric (base fabric) containing at least one selected from aromatic polyamide as a main component. As this resin, polysulfone, cellulose acetate, polyvinyl chloride, or a resin obtained by mixing them is preferably used. Is done. As the resin material to be used, it is particularly preferable to use polysulfone having high chemical, mechanical and thermal stability. Specifically, it is preferable to use polysulfone composed of a repeating unit represented by the following chemical formula (2) because the pore diameter is easy to control and the dimensional stability is high.

  For example, the N, N-dimethylformamide (DMF) solution of the above polysulfone is cast on a densely woven polyester woven fabric or non-woven fabric (base fabric) to a certain thickness, and wet coagulated in water. Examples thereof include a microporous support membrane in which fine pores having a diameter of several tens of nm or less are formed in most of the polysulfone porous layer on the surface.

  The thickness of the microporous support membrane and the thickness of the base fabric affect the strength of the composite semipermeable membrane and the packing density when it is used as an element. In order to obtain sufficient mechanical strength and packing density, the thickness of the microporous support membrane is preferably in the range of 50 to 300 μm, more preferably in the range of 75 to 200 μm. Moreover, it is preferable that the thickness of a polysulfone porous layer exists in the range of 10-200 micrometers, More preferably, it exists in the range of 30-100 micrometers.

  The polyamide separation functional layer formed on the microporous support membrane may be composed only of a crosslinked polyamide having high chemical stability against acids and alkalis, or may be composed of a resin mainly composed of the crosslinked polyamide. preferable. The crosslinked polyamide is formed by interfacial polycondensation between a polyfunctional amine and a polyfunctional acid halide, and is a compound having three or more functional groups in at least one monomer component of the polyfunctional amine or polyfunctional acid halide before polycondensation. Is preferably included.

  The thickness of the separation functional layer is usually in the range of 0.01 to 1 μm, preferably in the range of 0.1 to 0.5 μm, in order to obtain sufficient separation performance and permeated water amount.

  Here, the polyfunctional amine refers to an amine having at least two primary and / or secondary amino groups in one molecule. For example, two amino groups are any of ortho, meta, and para positions. Aromatic polyfunctional amines such as phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene and 3,5-diaminobenzoic acid bonded to benzene in the positional relationship of Aliphatic amines such as ethylenediamine and propylenediamine, alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 1,3-bispiperidylpropane and 4-aminomethylpiperazine be able to. Of these, aromatic polyfunctional amines having 2 to 4 primary and / or secondary amino groups in one molecule are preferred in consideration of selective separation, permeability, and heat resistance of the membrane. As the functional aromatic amine, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used. Among these, it is more preferable to use m-phenylenediamine (hereinafter referred to as m-PDA) from the standpoint of availability and ease of handling. These polyfunctional amines may be used alone or in combination.

  The polyfunctional acid halide refers to an acid halide having at least two carbonyl halide groups in one molecule. Examples of trifunctional acid halides include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride, and bifunctional acid halides include biphenyl dicarboxylic acid. Aromatic difunctional acid halides such as acid dichloride, biphenylene carboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalene dicarboxylic acid chloride, aliphatic such as adipoyl chloride, oxalyl chloride, sebacoyl chloride Cycloaliphatic difunctional acid halides such as difunctional acid halides, cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, tetrahydrofuran dicarboxylic acid dichloride, etc. It can gel. Considering the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride, and considering the selective separation property and heat resistance of the membrane, 2 to 4 per molecule. The polyfunctional aromatic acid chloride having a carbonyl chloride group is preferred. Among them, it is more preferable to use trimesic acid chloride from the viewpoint of easy availability and easy handling. These polyfunctional acid halides may be used alone or in combination.

  Seawater for evaluating membrane performance such as TDS removal rate is seawater at a temperature of 25 ° C., pH = 6.5, a TDS concentration of 3.5% by weight, and a calcium concentration of 400 ppm. If necessary, use seawater diluted with pure water and prepared by adjusting the ingredients.

  Here, TDS generally indicates the total amount of dissolved solids and is expressed by “(mass) ÷ (volume)” or by weight ratio. According to the definition, water filtered through a 0.45 micron filter can be calculated from the weight of the residue by evaporating at a temperature of 39.5 to 40.5 ° C. Calculated from

  The TDS removal rate (salt removal rate) is the measurement of the permeate salt concentration when seawater at a temperature of 25 ° C., pH 6.5, and TDS 3.5 wt% is supplied to the composite semipermeable membrane at an operating pressure of 5.5 MPa. From the following equation:

  In the case of a semipermeable membrane for seawater desalination, the TDS removal rate needs to be 99.5% or more, preferably 99.7% or more.

  The calcium permeability is the permeated water calcium concentration when supplying seawater prepared at a temperature of 25 ° C., pH 6.5, TDS 3.5 wt%, calcium concentration 400 ppm to the composite semipermeable membrane at an operating pressure of 5.5 MPa. By measuring, it is obtained from the following equation.

  Here, the calcium concentration was determined from the emission intensity at a wavelength of 396.847 nm of an inductively coupled plasma (ICP) measuring device.

  According to the present invention, the calcium permeability can be reduced by performing the treatment with the solution of the organic compound having the structure represented by the general formula (1) according to the present invention. The composite semipermeable membrane can have a calcium permeability of 0.05% or less. This is considered to be because the charge on the membrane surface was changed by treating the polyamide separation functional layer with the organic compound having the structure of the general formula (1), and as a result, it was assumed that the calcium removal performance was improved.

The water permeability of the semipermeable membrane is to use the above-mentioned seawater as supply water, and obtain the membrane permeation flux (m ³ / m ² · day) from the amount of water per day (cubic meter) per square meter of membrane surface. It was expressed by. The water permeation performance is preferably 0.5 m ³ / m ² · day or more. If it is less than 0.5 m ³ / m ² · day, it is not practical because water production efficiency deteriorates.

  As a result of examining the treatment means for modifying the polyamide separation functional layer in the composite semipermeable membrane, it was found that treatment with the organic compound solution having the structure of the general formula (1) is effective.

The organic compound having the structure of the general formula (1) has a function as a protein denaturant and is considered to have an effect of cleaving hydrogen bonds between / in the amide molecules. When the polyamide becomes dilute in the solution and the intermolecular or intramolecular hydrogen bond interaction becomes weak, the amide I absorption band (1600 to 1700 cm ⁻¹ ) of the infrared absorption spectrum shifts to the high wavenumber side, and the amide II absorption. It is known that the band (1500 to 1550 cm ⁻¹ ) shifts to the low wavenumber side. In order to confirm the modification effect of the polyamide separation functional membrane and improve the membrane performance, the polyamide separation functional layer is treated by treating the polyamide separation functional layer with an organic compound having a structure represented by the general formula (1). In the infrared absorption spectrum, the amide I and II absorption bands may be shifted by ¹ cm ⁻¹ or more, preferably 3 cm ⁻¹ or more.

  In the general formula (1), the functional group X is any one of oxygen, sulfur, and NH groups having a double bond with carbon. Examples of the organic compound having the structure of the general formula (1) include urea, thio Mention may be made of urea, guanidine, and derivatives thereof.

The substituent for R _{1 to} R ₄ is any one of a hydrogen atom, a hydrocarbon group, and an oxyalkyl group. The hydrocarbon group is preferably a hydrocarbon group having 1 to 6 carbon atoms. When the number of carbon atoms is 7 or more, handling becomes difficult and productivity is lowered. Here, as a C1-C6 hydrocarbon group, alkyl groups, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a vinyl group, an allyl group, a phenyl group, etc. can be mentioned. The oxyalkyl group refers to an alkyl group modified with a hydroxyl group and / or a substituent having a structure in which an oxygen atom is inserted into a carbon-carbon bond of the alkyl group. The oxyalkyl group preferably has 1 to 6 carbon atoms. When the number of carbon atoms is 7 or more, handling becomes difficult and productivity is lowered. Here, the oxyalkyl group having 1 to 6 carbon atoms includes an ether group such as a methoxymethyl group, an ethoxymethyl group, a propoxymethyl group, and an isopropoxymethyl group, an ester group such as an acetoxymethyl group and an acetoxyethyl group, a hydroxy group Examples thereof include hydroxyalkyl groups such as a methyl group and a hydroxyethyl group. Moreover, the substituents of R _{1 to} R ₄ may be accompanied by chemical bonds.

  Specific examples of the organic compound having the structure of the general formula (1) include urea, dimethylurea, diethylurea, dibutylurea, 1-phenyl-3methylurea, dimethylphenylurea, dicyclohexylurea, dimethoxymethylurea, Urea organic compounds such as diethoxymethylurea, dimethylolethyleneurea, dimethyloldihydroxyethyleneurea, dimethylolpropyleneurea, tetramethylolacetyleneurea; thiourea, dimethylthiourea, diethylthiourea, dibutylthiourea, diphenylthiourea, 1- Examples include thiourea-based organic compounds such as butyl-3phenylthiourea; and guanidine-based organic compounds such as guanidine, dimethylguanidine, diethylguanidine, and diphenylguanidine. Further, hydrochlorides, sulfates, nitrates, thiocyanates and the like of these organic compounds can be used. Among these, urea and guanidine are more preferable from the viewpoint of easy availability and ease of handling.

  This organic compound has a molecular weight of 59 or more, which is the minimum molecular weight of the organic compound having the above structure, and preferably 1000 or less. This is because when the molecular weight exceeds 1000, the performance improvement effect is reduced.

  Next, a method for producing a composite semipermeable membrane by forming a polyamide functional layer on a microporous support membrane will be described.

  The polyamide separation functional layer constituting the composite semipermeable membrane is microporous using, for example, an aqueous solution containing the aforementioned polyfunctional amine and an organic solvent solution immiscible with water containing the polyfunctional acid halide. It is a layer whose skeleton is formed by interfacial polycondensation on the surface of the conductive support membrane.

  Here, the concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 2.5 to 10% by weight, more preferably in the range of 3 to 5% by weight. In this range, sufficient salt removal performance and water permeability can be obtained. The polyfunctional amine aqueous solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant, or the like as long as it does not inhibit the reaction between the polyfunctional amine and the polyfunctional acid halide. The surfactant has the effect of improving the wettability of the porous support membrane surface and reducing the interfacial tension between the aqueous amine solution and the nonpolar solvent, and the organic solvent may act as a catalyst for the interfacial polycondensation reaction. In some cases, the interfacial double reaction can be efficiently performed by adding them.

  In order to perform interfacial polycondensation on the microporous support membrane, first, the above-mentioned polyfunctional amine aqueous solution is brought into contact with the microporous support membrane. This contact is preferably performed uniformly and continuously on the surface of the microporous support membrane. Specifically, for example, a method of coating a polyfunctional amine aqueous solution on a microporous support membrane and a method of immersing the microporous support membrane in a polyfunctional amine aqueous solution can be mentioned. The contact time between the microporous support membrane and the polyfunctional amine aqueous solution is preferably in the range of 1 second to 10 minutes, and more preferably in the range of 10 seconds to 3 minutes.

  After the polyfunctional amine aqueous solution is brought into contact with the microporous support membrane, the solution is sufficiently drained so that no droplets remain on the membrane surface. By sufficiently draining the liquid, it is possible to prevent the remaining portion of the liquid droplet from becoming a film defect after the film is formed and deteriorating the film performance. As a method for draining, for example, as described in JP-A-2-78428, a method of allowing an excess aqueous solution to naturally flow by gripping a porous support membrane in a vertical direction after contacting with a polyfunctional amine aqueous solution. Alternatively, a method of forcibly draining by blowing air such as nitrogen from an air nozzle can be used. In addition, after draining, the membrane surface can be dried to remove part of the water in the aqueous solution.

  Next, an organic solvent solution containing a polyfunctional acid halide is brought into contact with the surface of the support membrane after the contact with the polyfunctional amine aqueous solution, and a skeleton of the crosslinked polyamide separation functional layer is formed by interfacial polycondensation of both components.

  The concentration of the polyfunctional acid halide in the organic solvent solution is preferably in the range of 0.01 to 10% by weight, and more preferably in the range of 0.02 to 2.0% by weight. Within this range, a sufficient reaction rate can be obtained, and the occurrence of side reactions can be suppressed. Further, it is more preferable that an acylation catalyst such as N, N-dimethylformamide is contained in the organic solvent solution because interfacial polycondensation is promoted.

  Here, as the organic solvent for dissolving the polyfunctional acid halide, it is desirable to use an organic solvent that is immiscible with water and that dissolves the acid halide and does not destroy the microporous support membrane. Any material that is inert to the acid halide may be used. Preferable examples include hydrocarbon compounds such as n-hexane, n-octane, and n-decane.

  The method of bringing the polyfunctional acid halide organic solvent solution into contact with the amino compound aqueous solution adhesion layer on the microporous support membrane may be performed in the same manner as the method of coating the microporous support membrane with the polyfunctional amine aqueous solution. .

  As described above, after contacting the organic halide solution of the acid halide to cause interfacial polycondensation between the amine and the halide and forming the separation functional layer containing the crosslinked polyamide on the microporous support membrane, Drain excess solvent. As a method for draining, for example, a method in which a film is held in a vertical direction and excess organic solvent is allowed to flow down and removed can be used.

  The step of subjecting the composite semipermeable membrane obtained by the above method to hydrothermal treatment in the range of 50 to 150 ° C., preferably in the range of 70 to 130 ° C. for 1 second to 10 minutes, more preferably 1 minute to 8 minutes. By adding the above, it is possible to further improve the exclusion performance and water permeability of the composite semipermeable membrane.

  It is also preferable to improve the performance of the membrane by contacting it with a chlorine-containing aqueous solution having a pH in the range of 5 to 13 at normal pressure.

  In the present invention, a crosslinked polyamide separation functional layer formed by interfacial polycondensation of an aqueous polyfunctional amine solution and an organic solvent solution containing a polyfunctional acid halide is used as a solution of an organic compound having the structure of the general formula (1). The performance of the composite semipermeable membrane is improved by performing the treatment of contacting with the membrane. The method for bringing the solution of the organic compound into contact with the crosslinked polyamide separation functional layer is not particularly limited. Examples thereof include a method of immersing the entire semipermeable membrane in an organic compound solution, a method of applying an organic compound solution to the surface of the separation functional layer, and a method of allowing the organic compound solution to permeate the membrane by pressurization.

  In the solution of the organic compound having the structure of the general formula (1), it is desirable to use a solvent that can dissolve the organic compound and does not destroy the microporous support membrane. Examples thereof include water, alcohols such as methanol and ethanol, and hydrocarbons such as normal decane.

  The concentration of the solution of the organic compound having the structure of the general formula (1) is preferably 1M or more. More preferably, it is 4M or more and 8M or less. By setting it to 4M or more, contact is sufficient and the effects of the present invention can be exerted. By setting it to 8M or less, sufficient solubility in a solvent is exhibited and the cost is reduced. .

  In order to sufficiently obtain the effect of contact, it is preferable to perform contact in an atmosphere of 0 ° C. or higher and 100 ° C. or lower. More preferably, it is 20 ° C. or higher. When the reaction is performed at 100 ° C. or higher, the membrane undergoes thermal shrinkage and the amount of permeated water tends to be low.

  The contact time is not particularly limited. When the contact time is 1 day or less, it is difficult to obtain membrane performance with high water permeability and high calcium removability, and when it is 14 days or more, production efficiency is remarkably deteriorated and it is difficult to maintain high TDS removability. .

The composite semipermeable membrane obtained by the treatment in this manner was allowed to permeate seawater having a TDS concentration of 3.5% by weight and a calcium concentration of 400 ppm at an operating pressure of 5.5 MPa at 25 ° C. Further, the water permeability is 0.74 m ³ / m ² · day or more, more preferably 0.9 m ³ / m ² · day or more, and the calcium permeability is 0.05% or less, more preferably 0.03% or less. The TDS removal rate (salt removal rate) is as high as 99.5% or more, more preferably 99.6% or more.

  The composite semipermeable membrane thus obtained has a large number of holes along with a raw water channel material such as a plastic net, a permeate channel material such as tricot, and a film for increasing pressure resistance if necessary. It is wound around a provided cylindrical water collecting pipe and is suitably used as a spiral composite semipermeable membrane element.

  Furthermore, a composite semipermeable membrane module in which these elements are connected in series or in parallel and accommodated in a pressure vessel can be obtained.

  The treatment in the present invention is a treatment of a compound semipermeable membrane element (for example, an envelope-like membrane connected to a water collecting pipe and wound in a spiral) with an organic compound having the structure of the above general formula (1) at normal pressure. You may carry out by the method of immersing in a solution. The immersion time in this case varies depending on the temperature, but is preferably 1 day to 30 days. If it is less than 1 day, it is difficult to satisfactorily achieve the above-described effect of decreasing the calcium permeability. If it exceeds 30 days, the decrease in the calcium permeability reaches saturation, and it takes a longer time than necessary. In the present invention, the treatment with the organic compound aqueous solution can also be carried out by assembling the reverse osmosis membrane module and then passing the organic compound aqueous solution under pressure.

  In addition, the above-described composite semipermeable membrane, its elements, and modules can be combined with a pump that supplies raw water to them, a device that pretreats the raw water, and the like to form a fluid separation device. By using this separation device, permeated water such as drinking water and concentrated water that has not permeated through the membrane can be separated from raw water to obtain water having a desired quality.

  When the operating pressure of the fluid separation device is higher, the calcium permeability decreases, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane, water to be treated is added to the composite semipermeable membrane. The operating pressure during permeation is preferably 1.0 MPa or more and 10 MPa or less. As the feed water temperature increases, the calcium permeability improves, but as the feed water temperature decreases, the membrane permeation flux also decreases. Therefore, it is preferably 5 ° C. or higher and 45 ° C. or lower. In addition, when the pH of the feed water becomes high, scales such as magnesium may be generated in the case of feed water with a high salt concentration such as seawater, and there is a concern about deterioration of the membrane due to high pH operation. Is preferred.

In Examples and Comparative Examples, the amount of water permeation, calcium permeability, and salt removal rate were measured by the measurement methods described above.
(Comparative Example 1)
A dimethylformamide (DMF) solution having a polysulfone concentration of 15.3% by weight is cast on a polyester nonwoven fabric (air permeability 0.5 to 1 cc / cm ² · sec) at room temperature (25 ° C.) so as to have a thickness of 200 μm. The microporous support membrane was prepared by immediately immersing in pure water and allowing to stand for 5 minutes.

  The microporous support membrane (thickness 210 to 215 μm) thus obtained was immersed in a 4.6% aqueous solution of metaphenylenediamine for 2 minutes, the support membrane was slowly pulled up in the vertical direction, and an air nozzle After removing excess aqueous solution from the surface of the supporting membrane by blowing nitrogen, an n-decane solution containing 0.165 wt% of trimesic acid chloride was applied so that the surface was completely wetted and allowed to stand for 1 minute. Next, in order to remove excess solution from the membrane, the membrane was held vertically for 2 minutes to drain the solution. Then, after washing with hot water at 90 ° C. for 2 minutes, it was immersed in an aqueous solution of sodium hypochlorite adjusted to pH 7 and a chlorine concentration of 200 mg / l for 2 minutes, and in an aqueous solution having a sodium bisulfite concentration of 1,000 mg / l. By dipping, excess sodium hypochlorite was reduced and removed. Furthermore, this membrane was rewashed with hot water at 95 ° C. for 2 minutes.

When the obtained composite semipermeable membrane was evaluated with seawater having a temperature of 25 MPa, a pH of 6.5, a TDS concentration of 3.5% by weight and a calcium concentration of 400 ppm at an operating pressure of 5.5 MPa, the water permeability (m ³ / m ² · day), calcium permeability (%), and salt removal rate (%) were the values shown in Table 1, respectively.

(Examples 1-4)
The film obtained in Comparative Example 1 was immersed in a 4M urea aqueous solution at room temperature for various times as shown in Table 2. The membrane was immersed for a predetermined time and then washed with water at room temperature. When the obtained membrane was evaluated, the water permeability (m ³ / m ² · day), calcium permeability (%), and salt removal rate (%) were values shown in Table 2.

In addition, infrared absorption spectrum measurement (ATR-FT-IR method) was performed using Avatar 360 manufactured by ThermoNicolet, using Ge45 ° as an internal reflection element. The composite semipermeable membranes of Comparative Example 1 and Example 3 were vacuum-dried for 24 hours, and the difference spectrum of the infrared absorption spectrum of the polyamide separation functional layer was analyzed. As a result, the peak near 1660 cm ⁻¹ observed in Comparative Example 1 was observed. example 3 shifted to ^{5 cm -1} higher wave number side in the peak around 1545 cm ^-1 is shifted to ^{5 cm -1} wave number side lower in example 3.

(Examples 5 to 9)
The film obtained in Comparative Example 1 was immersed in a 1M urea aqueous solution at room temperature for various times as shown in Table 3. When the obtained membrane was immersed in water at room temperature and evaluated, the water permeability (m ³ / m ² · day), calcium permeability (%), and salt removal rate (%) were as shown in Table 3. .

  The composite semipermeable membrane produced by the production method of the present invention can achieve a high calcium removal rate, a high TDS removal rate, and a high water permeability, and can be used for the treatment of cooling water and plating waste water of a nuclear power plant, In particular, it can be suitably used for drinking water production by desalination of seawater.

Claims (4)

A polyamide separation functional layer formed by polycondensation of a polyfunctional amine and a polyfunctional acid halide is formed on a microporous support membrane, and seawater having a TDS concentration of 3.5% by weight at 25 ° C., pH = 6.5. A compound semipermeable membrane having a TDS removal rate of 99.5% or more when allowed to pass through at an operating pressure of 5.5 MPa, an organic compound having a structure represented by the following general formula (1), or an organic compound thereof and an acid A method for producing a composite semipermeable membrane, comprising performing a treatment with a salt solution.

(In general formula (1), X represents an oxygen atom, a sulfur atom, or an NH group, and R _{1 to} R ₄ represent a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms.) The method for producing a composite semipermeable membrane according to claim 1, wherein the organic compound has a molecular weight of 59 to 1,000. The method for producing a composite semipermeable membrane according to claim 1, wherein the organic compound is at least one selected from urea, guanidine and thiourea. The method for producing a composite semipermeable membrane according to claim 1, wherein the organic compound is urea.