JP2008080187A - Composite semipermeable membrane and use thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite semipermeable membrane having high durability, high separation capacity and high water permeability, and a use thereof. <P>SOLUTION: The composite semipermeable membrane prepared by first forming a layer having a separation function on a microporous support-membrane and subsequently allowing the resulting layer to contact with an aqueous solution containing chlorine is characterized in that the layer having a separation function is comprised of a cross-linked polyamide prepared by interfacial condensation polymerization of a polyfunctional amine and a polyfunctional acid halide and the ratio of the polyfunctional amine component and the polyfunctional acid halide component each constituting the cross-linked polyamide satisfies the equation: [molarity of polyfunctional amine component/morality of ployfunctional acid halide component ≥1.2]. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite semipermeable membrane for selectively separating various mixed solutions, and relates to a semipermeable membrane excellent in water permeability, durability, and selective permeability and a method for producing the same.

  Conventionally, semi-permeable membranes used industrially include asymmetric membrane type cellulose acetate membranes (Patent Documents 1 and 2). However, this membrane did not have sufficient salt rejection and water permeability. For this reason, the cellulose acetate asymmetric membrane has been used in some applications, but has not yet been put to practical use in a wide range of applications.

  In order to compensate for these disadvantages, a composite semipermeable membrane was devised as a semipermeable membrane that has a different form from the asymmetric membrane, and on which a separation functional layer that substantially controls membrane separation performance was coated with a different material on a microporous support membrane. It was. In the composite semipermeable membrane, it is possible to select an optimal material for each of the separation functional layer and the microporous support membrane, and various methods can be selected for the membrane formation technique. Most of the commercially available composite semipermeable membranes are those obtained by interfacial polycondensation of monomers on a microporous support membrane. Polyamide is used for the separation functional layer, and higher desalination performance than the cellulose acetate asymmetric membrane. Is obtained (patent documents 3 to 8).

  Further, as one means for improving the water permeability of the composite semipermeable membrane, a method of treating the composite semipermeable membrane with a chlorine-containing aqueous solution (Patent Document 9) has been disclosed. Is still inadequate because of the deterioration of desalination performance and selective separation performance when treated with chlorine, hydrogen peroxide, etc., used for membrane sterilization. In this case, it is necessary to restrict operating conditions.

US Pat. No. 3,133,132 US Pat. No. 3,133,137 US Pat. No. 3,744,942 U.S. Pat. No. 3,926,798 US Pat. No. 4,277,344 JP-A-55-147106 JP 58-24303 A JP 62-121603 A JP-A 63-54905

  Thus, until now, no composite semipermeable membrane satisfying high durability, high separability and high water permeability has been obtained. An object of the present invention is to provide a composite semipermeable membrane having high durability and high separability and high water permeability.

To achieve the above object, the present invention has the following configuration. That is,
(1) A composite semipermeable membrane produced by forming a separation functional layer on a microporous support membrane and then bringing it into contact with a chlorine-containing aqueous solution, wherein the separation functional layer comprises a polyfunctional amine and a polyfunctional acid halogen. A composite semipermeable membrane comprising a cross-linked polyamide by interfacial polycondensation with a fluoride, wherein the abundance ratio of the polyfunctional amine component and polyfunctional acid halide component constituting the cross-linked polyamide satisfies the relationship of the following formula: .
Number of moles of polyfunctional amine component / number of moles of polyfunctional acid halide component ≧ 1.2
(2) A membrane filtration element comprising the composite semipermeable membrane as described in (1) above as a filtration membrane.
(3) A fluid separator provided with the membrane filtration element according to (2) above.
(4) A water treatment method characterized by subjecting water to membrane filtration using the composite semipermeable membrane according to (1).

  According to the present invention, a composite semipermeable membrane satisfying high durability, high separability, and high water permeability can be produced. Desalination of seawater and brine, recovery of valuable materials, reuse of wastewater, production of ultrapure water It can be used in a wide range of fields such as energy saving, cost reduction, and space saving.

  The composite semipermeable membrane according to the present invention is a composite semipermeable membrane produced by forming a separation functional layer on a microporous support membrane and then bringing it into contact with a chlorine-containing aqueous solution. A cross-linked polyamide comprising interfacial polycondensation of a functional amine and a polyfunctional acid halide, wherein the abundance ratio of the polyfunctional amine component and polyfunctional acid halide component constituting the cross-linked polyamide satisfies the relationship of the following formula: And

Number of moles of polyfunctional amine component / number of moles of polyfunctional acid halide component ≧ 1.2
The separation functional layer is preferably composed only of a crosslinked polyamide having high chemical stability with respect to acids and alkalis, but may be composed mainly of the crosslinked polyamide. The crosslinked polyamide is preferably formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide, and at least one of the polyfunctional amine component or the polyfunctional acid halide component preferably contains a trifunctional or higher functional compound.

  The separation functional layer may be provided on both surfaces of the microporous support membrane, or a plurality of separation functional layers may be provided. However, it is usually sufficient to have one separation functional layer on one surface. 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 are preferred in view of selective separation, permeability, and heat resistance of the membrane. Examples of such polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, 1, 3,5-triaminobenzene is 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 difunctional acid such as adipoyl chloride, sebacoyl chloride Mention may be made of alicyclic bifunctional acid halides such as halides, cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, tetrahydrofuran dicarboxylic acid dichloride. 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, the polyfunctional aromatic acid chloride is preferable. Preferably there is. 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.

  The composite semipermeable membrane of the present invention is a composite semipermeable membrane formed by coating a separation functional layer on a microporous support membrane, and the abundance ratio of the polyfunctional amine component and the polyfunctional acid halide component constituting the crosslinked polyamide. However, the production method is not particularly limited as long as the relationship of the number of moles of polyfunctional amine component / number of moles of polyfunctional acid halide component ≧ 1.2 is satisfied and the separation functional layer is in contact with the chlorine-containing aqueous solution. For example, after contacting a polyfunctional amine aqueous solution on a microporous support membrane, contacting with a water-immiscible organic solvent solution containing a polyfunctional acid halide, and microporous support by interfacial polycondensation After forming the separation functional layer containing the crosslinked polyamide on the membrane, it is preferable to employ a method in which the polyfunctional amine remains before the separation functional layer is brought into contact with the chlorine-containing aqueous solution. Before bringing the separation functional layer into contact with the chlorine-containing aqueous solution, the polyfunctional amine remains, so that the polyfunctional amine can be reacted with the polyfunctional acid halide for a sufficiently long time. Can be formed. As a result, the abundance ratio of the polyfunctional amine component and the polyfunctional acid halide component constituting the cross-linked polyamide is polyfunctional amine component moles / polyfunctional acid halide component moles ≧ 1.2. Composite semi-permeable that is resistant to deterioration such as desalting performance and selective separation performance degradation when treated with chlorine, hydrogen peroxide, etc. used for sterilization of membranes because it can form polyamide with high degree of durability. A membrane can be obtained.

  Before bringing the separation functional layer into contact with the chlorine-containing aqueous solution, the polyfunctional amine remains, for example, after the separation functional layer is formed on the microporous support membrane, the composite semipermeable membrane is washed. Without contact with a chlorine-containing aqueous solution, or after forming a separation functional layer on a microporous support membrane and again with a polyfunctional amine aqueous solution.

  The abundance ratio of the polyfunctional amine component and polyfunctional acid halide component constituting the crosslinked polyamide is hydrolyzed by heating the separation functional layer separated from the microporous support membrane with a strong alkaline aqueous solution. The sample can be measured by 1H-NMR measurement.

  In the present invention, the microporous support membrane is intended to give strength to a separation functional layer that substantially does not have separation performance of ions or the like and has substantial separation performance. The size and distribution of the pores are not particularly limited. For example, the pores have uniform and fine pores or gradually have large pores from the surface on the side where the separation functional layer is formed to the other surface, and the separation functional layer has A support film having a micropore size of 0.1 nm or more and 100 nm or less on the surface to be formed is preferable. The material used for the microporous support membrane and the shape thereof are not particularly limited. For example, polysulfone, cellulose acetate, polyvinyl chloride reinforced with a fabric mainly composed of at least one selected from polyester or aromatic polyamide, or those A mixture of these is preferably used. As a 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 repeating units represented by the following chemical formula because the pore diameter is easy to control and the dimensional stability is high.

  For example, an N, N-dimethylformamide (DMF) solution of the above polysulfone is cast on a densely woven polyester cloth or non-woven fabric to a certain thickness, and wet coagulated in water, thereby increasing the size of the surface. A microporous support membrane having fine pores with a diameter of several tens of nm or less can be obtained.

  The thickness of the microporous support membrane and the substrate affects 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, it 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 microporous support membrane exists in the range of 10-200 micrometers, More preferably, it exists in the range of 30-100 micrometers.

  The form of the microporous support film can be observed with a scanning electron microscope, a transmission electron microscope, or an atomic microscope. For example, when observing with a scanning electron microscope, the microporous support film is peeled off from the base material, and then cut by a freeze cleaving method to obtain a sample for cross-sectional observation. The sample is thinly coated with platinum, platinum-palladium, or ruthenium tetrachloride, preferably ruthenium tetrachloride, and observed with a high-resolution field emission scanning electron microscope (UHR-FE-SEM) at an acceleration voltage of 3 to 6 kV. A Hitachi S-900 electron microscope or the like can be used as the high-resolution field emission scanning electron microscope. The film thickness and surface pore diameter of the microporous support membrane are determined from the obtained electron micrograph. In addition, the thickness and the hole diameter in this invention mean an average value.

  Next, the manufacturing method of the composite semipermeable membrane of this invention is demonstrated.

  The 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. The skeleton can be formed by interfacial polycondensation on the surface of the support membrane.

  Here, the concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 0.1 to 10% by weight, and more preferably in the range of 0.5 to 5.0% by weight. If the concentration is less than 0.1% by weight, the progress of the reaction tends to be slow, and if it exceeds 10% by weight, the ultrathin film layer becomes thick and water permeability tends to be insufficient. As long as the polyfunctional amine aqueous solution does not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide, a surfactant, an organic solvent, an alkaline compound, an antioxidant, or the like may be contained. The surfactant has the effect of improving the wettability of the microporous support membrane surface and reducing the interfacial tension between the polyfunctional amine aqueous solution and the nonpolar solvent, and the organic solvent acts as a catalyst for the interfacial polycondensation reaction. In some cases, the interfacial polycondensation reaction can be efficiently carried out 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. The 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 within a range of 1 to 10 minutes, and more preferably within a range of 1 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. If the droplets remain, the remaining portion of the droplets after the film formation tends to be a film defect, which tends to deteriorate the film performance. As a method for draining, for example, as described in JP-A-2-78428, the microporous support membrane after the contact with the polyfunctional amine aqueous solution is vertically gripped to allow the excess aqueous solution to flow down naturally. A method or a method of forcibly draining liquid 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 microporous support membrane after contact with the polyfunctional amine aqueous solution, and a skeleton of the crosslinked polyamide separation functional layer is formed by interfacial polycondensation.

  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. If it is less than 0.01% by weight, the progress of the reaction tends to be slow, and if it exceeds 10% by weight, a side reaction tends to occur. 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.

  Organic solvents that are immiscible with water and desirably dissolve polyfunctional acid halides and do not destroy microporous support membranes and are inert to polyfunctional amines and polyfunctional acid halides If it is. Preferable examples include hydrocarbon compounds such as n-hexane, n-octane, and n-decane.

  The method for contacting the organic solvent solution of the polyfunctional acid halide with the polyfunctional amine aqueous solution phase may be performed in the same manner as the method for coating the polyfunctional amine aqueous solution on the microporous support membrane.

  As described above, after interfacial polycondensation is performed by contacting an organic solvent solution of a polyfunctional acid halide to form a separation functional layer made of a crosslinked polyamide on a microporous support membrane, excess solvent is drained off. Good. 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. In this case, the time for gripping in the vertical direction is preferably 1 to 5 minutes, more preferably 1 to 3 minutes.

  After draining, it is usually dried. As the drying method, for example, as shown in JP-A-5-76740, the wind speed at the film surface is 2 to 20 m / sec, particularly preferably 3 to 10 m / sec, and the temperature is 10 to 80 ° C., particularly preferably 20 It is preferable to blow a gas of ˜40 ° C. onto the film. When a gas having a time longer than that shown above or at a high temperature is used, the microporous support membrane contracts due to excessive evaporation of moisture, and the performance tends to deteriorate.

  And after drying the organic solvent solution of the excess polyfunctional acid halide, before bringing the separation functional layer into contact with the chlorine-containing aqueous solution, the composite semipermeable membrane was not washed and the polyfunctional amine component remained. By making it into a state, it is possible to form a polyamide having a high water permeability and a high degree of crosslinking, and a composite semipermeable membrane having excellent durability can be obtained. Also, a separation functional layer can be formed on the microporous support membrane and brought into contact with the polyfunctional amine aqueous solution again, or the polyfunctional amine component can be left before the separation functional layer is brought into contact with the chlorine-containing aqueous solution. This is preferable.

Here, the remaining amount of the polyfunctional amine before bringing the separation functional layer into contact with the chlorine-containing aqueous solution is preferably in the range of 0.01 to 1 g / m ² , and is preferably 0.05 to 0.5 g / m. More preferably, it is within the range of ² . If it is less than 0.01 g / m ² , the reaction with the polyfunctional acid halide tends to be slow, and if it exceeds 0.5 g / m ² , a side reaction tends to occur.

  The contact of the chlorine-containing aqueous solution is preferably performed uniformly and continuously on the composite semipermeable membrane surface. Specifically, for example, a method of coating a chlorine-containing aqueous solution on the composite semipermeable membrane and a method of immersing the composite semipermeable membrane in the chlorine-containing aqueous solution can be mentioned. The contact time between the composite semipermeable membrane and the chlorine-containing aqueous solution is preferably in the range of 1 to 10 minutes, and more preferably in the range of 1 to 3 minutes. After bringing the chlorine-containing aqueous solution into contact with the multi-composite semipermeable membrane, it is preferable to immerse in a sulfite aqueous solution to reduce and remove the remaining chlorine-containing aqueous solution.

  Examples of the chlorine generating reagent include chlorine gas, salicy powder, sodium hypochlorite, chlorine dioxide, chloramine B, chloramine T, chlorinated isocyanuric acid and salts thereof, but an aqueous sodium hypochlorite aqueous solution is easily available. It can be preferably employed from the viewpoint of the property and the handleability.

  The effective chlorine concentration in the chlorine-containing aqueous solution is preferably in the range of 0.001 to 1% by weight, and more preferably in the range of 0.005 to 0.5% by weight. If the amount is less than 0.001% by weight, the progress of the reaction tends to be slow, and if it exceeds 1% by weight, a side reaction tends to occur.

  The contact time between the composite semipermeable membrane and the chlorine-containing aqueous solution is preferably within a range of 1 to 10 minutes, and more preferably within a range of 1 to 3 minutes.

  The composite semipermeable membrane obtained by the above-described method includes a step of hydrothermal treatment in a range of 50 to 150 ° C., preferably in a range of 70 to 130 ° C. for 1 to 10 minutes, more preferably 2 to 8 minutes. By adding, the exclusion performance and water permeability of the composite semipermeable membrane can be further improved.

  The composite semipermeable membrane of the present invention formed in this way has a large number of pores together 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. Is wound around a 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.

  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 the raw water, and water suitable for the purpose can be obtained.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Measurements in Examples and Comparative Examples were performed as follows.

(Desalination rate)
By measuring the permeated water salt concentration when a 1500 ppm sodium chloride aqueous solution adjusted to a temperature of 25 ° C. and pH 6.5 was supplied to the composite semipermeable membrane at an operating pressure of 1.5 MPa, it was obtained from the following equation.
Desalination rate = 100 × {1− (salt concentration in permeated water / salt concentration in feed water)}

(Membrane permeation flux)
A 1500 ppm sodium chloride aqueous solution was used as the feed water, and the membrane permeation flux (m ³ / m ² · day) was determined from the daily water permeability (cubic meter) per square meter of membrane surface.

(Example 1)
15.7 weight of polysulfone on a plain fabric made of polyester fiber, taffeta (both warp and weft multifilament yarns of 166 dtex were used. Weave density was 90 / inch in length, 67 / inch in width, and 160 μm in thickness) A microporous support membrane composed of a fiber-reinforced polysulfone support membrane was prepared by casting a% dimethylformamide (DMF) solution with a thickness of 200 μm at room temperature (25 ° C.), and immediately immersing in pure water and allowing to stand for 5 minutes. .

  The microporous support membrane (thickness 210 to 215 μm) thus obtained was 1.5% by weight of the total polyfunctional amine, and m-phenylenediamine / 1,3,5-triaminobenzene = 70 / Immerse in an aqueous polyfunctional amine solution with 1,3,5-triaminobenzene added to a 30 molar ratio for 2 minutes, slowly pull up the support film in the vertical direction, blow nitrogen from an air nozzle, and support film surface After removing the excess aqueous solution, an n-decane solution containing 0.06% by weight 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, and dried by blowing a gas at 20 ° C. using a blower.

  After that, the composite semipermeable membrane was not washed and immersed in an aqueous solution having a sodium hypochlorite concentration of 500 mg / l adjusted to pH 7 for 2 minutes and immersed in an aqueous solution having a sodium bisulfite concentration of 1,000 mg / l. Thus, excess sodium hypochlorite was reduced and removed. Furthermore, this membrane was rewashed with hot water at 95 ° C. for 2 minutes.

  The separation functional layer of the composite semipermeable membrane obtained in this way was subjected to 1H-NMR measurement of a sample hydrolyzed by heating with a strong alkaline aqueous solution, which was peeled from the microporous support membrane, When the abundance ratio of the polyfunctional amine component and the polyfunctional acid halide component constituting the crosslinked polyamide was measured, it was found that polyfunctional amine component moles / polyfunctional acid halide component moles = 1.4.

When the membrane performance of this composite semipermeable membrane was evaluated, the salt rejection was 99.4%, and the membrane permeation flux was 1.0 m ³ / m ² · day. When this membrane was immersed in a 50 ppm sodium hypochlorite aqueous solution adjusted to pH 7 for 24 hours and then evaluated, the rejection rate was 99.2% and the membrane permeation flux was 1.1 m ³ / m ² · day. No deterioration was observed.

(Comparative Example 1)
Example 1 except that the sample was drained and dried in Example 1, washed with water for 5 minutes, and then immersed in an aqueous solution having a sodium hypochlorite concentration of 500 mg / l adjusted to pH 7 for 2 minutes. A composite semipermeable membrane was prepared in the same manner as described above. The abundance ratio of the polyfunctional amine component and the polyfunctional acid halide component constituting the crosslinked polyamide of the composite semipermeable membrane was polyfunctional amine component moles / polyfunctional acid halide component moles = 1.1.

When the membrane performance of this composite semipermeable membrane was evaluated, the salt rejection was 99.4% and the membrane permeation flux was 1.1 m ³ / m ² · day. When this membrane was immersed in a 50 ppm sodium hypochlorite aqueous solution adjusted to pH 7 for 24 hours and then evaluated, the rejection rate was 97.0% and the membrane permeation flux was 1.5 m ³ / m ² · day. The salt permeability was 5 times, and the membrane permeation flux was 1.4 times.

  The composite semipermeable membrane of the present invention can produce a composite semipermeable membrane with high desalination performance and high chlorine resistance, desalination of seawater and brine, recovery of valuable materials, reuse of wastewater, production of ultrapure water It can be used in a wide range of fields such as energy saving, cost reduction, and space saving.

Claims (4)

A composite semipermeable membrane produced by forming a separation functional layer on a microporous support membrane and then contacting with a chlorine-containing aqueous solution, wherein the separation functional layer comprises a polyfunctional amine and a polyfunctional acid halide. A composite semipermeable membrane comprising a cross-linked polyamide by interfacial polycondensation, wherein the abundance ratio of a polyfunctional amine component and a polyfunctional acid halide component constituting the cross-linked polyamide satisfies the relationship of the following formula:
Number of moles of polyfunctional amine component / number of moles of polyfunctional acid halide component ≧ 1.2 A membrane filtration element comprising the composite semipermeable membrane according to claim 1 as a filtration membrane. A fluid separator provided with the membrane filtration element according to claim 2. A water treatment method comprising subjecting water to membrane filtration using the composite semipermeable membrane according to claim 1.