JP2009220023A - Method for manufacturing composite semi-permeable membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a composite semi-permeable membrane having high solute removability, high water permeability, and high durability. <P>SOLUTION: The manufacturing method includes the step A of forming a polyamide separating function layer by an interfacial polycondensation of a multifunctional amine and multifunctional acid halide on a microporous support membrane, the step B of allowing the polyamide separating function layer to contact hydrazine to produce hydrazide, and the step C of allowing hydrazide to contact with and react with a reagent to produce acid azide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a composite semipermeable membrane useful for selective separation of a liquid mixture. The composite semipermeable membrane obtained by the present invention can be suitably used for desalination of seawater and brine, for example.

  Regarding the separation of mixtures, there are various techniques for removing substances (eg, salts) dissolved in a solvent (eg, water), but in recent years, the use of membrane separation methods has expanded as a process for saving energy and resources. is doing. Membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes can be used for beverages such as seawater, brine, and water containing harmful substances. It is used to obtain water, to manufacture industrial ultrapure water, to treat wastewater, to recover valuable materials.

  The majority of currently marketed reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes, which have an active layer in which a gel layer and a polymer are crosslinked on a porous support membrane, and monomers on the porous support membrane. There are two types, one having an active layer obtained by polycondensation. Among these, composite semipermeable membranes obtained by coating a porous support membrane with a separation functional layer made of a crosslinked polyamide obtained by polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide have permeability and selective separation. It is widely used as a highly reliable separation membrane. However, from the viewpoints of resource depletion and soaring and environmental conservation, a simple membrane treatment method and manufacturing method that realizes high water permeability intended for further energy saving are desired.

As processing methods for improving water permeability, for example, a post-treatment method using nitrous acid (Patent Document 1) and a post-treatment method using chlorine (Patent Document 2) are known.
JP-A-63-175604 JP-A 63-54905

  An object of this invention is to provide the manufacturing method of the composite semipermeable membrane which has high durability with high solute removal property and high water permeability.

To achieve the above object, the present invention has the following configuration. That is,
(1) A method for producing a composite semipermeable membrane having a polyamide separation functional layer, wherein a polyamide separation functional layer is formed on a microporous support membrane by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. A composite semi-transparent material comprising: A; a step B in which the polyamide separation functional layer is brought into contact with hydrazine to form a hydrazide; and a step B in which the polyamide separation functional layer is brought into contact with a reagent that reacts with the hydrazide to form an acid azide. A method for producing a membrane.

  (2) The method for producing a composite semipermeable membrane according to (1), wherein the reagent that reacts with hydrazide to produce acid azide is an aqueous solution containing nitrous acid and / or a salt thereof.

  (3) The method for producing a composite semipermeable membrane according to (1) or (2), comprising a step D of performing hydrothermal treatment at a temperature of 40 ° C. or higher and 100 ° C. or lower after the step C.

  According to the present invention, a composite semipermeable membrane having high solute removability and high water permeability and also having high durability can be obtained.

  The composite semipermeable membrane according to the present invention is a composite semipermeable membrane formed by forming a polyamide separation functional layer on a microporous support membrane.

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 membrane in which the size of the micropores is 0.1 nm or more and 100 nm or less on the surface on the side to be formed is preferable. The material used for the microporous support membrane and the shape thereof are not particularly limited. For example, polyester or aromatic Polysulfone, cellulose acetate, polyvinyl chloride, or a mixture thereof reinforced with a cloth mainly composed of at least one selected from polyamide 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 (hereinafter referred to as DMF) solution of the above polysulfone is cast on a densely woven polyester cloth or nonwoven fabric to a certain thickness, and wet coagulated in water. Thus, a microporous support membrane having most of the surface with fine pores having a diameter of several tens of nm or less can be obtained.

  The thickness of the porous support and the substrate described above 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 100 to 250 μm. Moreover, it is preferable that the thickness of a porous support body exists in the range of 10-200 micrometers, More preferably, it exists in the range of 30-100 micrometers.

  The form of the porous 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 porous support is peeled off from the substrate, 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 porous support are determined from the obtained electron micrograph. In addition, the thickness and the hole diameter in this invention mean an average value.

  The polyamide constituting the separation functional layer can be formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. It is preferable that at least one of the polyfunctional amine or the polyfunctional acid halide component contains a trifunctional or higher functional compound.

  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. Among them, in view of selective separation, permeability, and heat resistance of the membrane, it is preferably an aromatic polyfunctional amine having 2 to 4 primary and / or secondary amino groups in one molecule. As the polyfunctional 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 of two or more.

  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, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalene dicarboxylic acid chloride, aliphatic difunctional acid halides such as adipoyl chloride, sebacoyl chloride, cyclopentane Examples thereof include alicyclic difunctional acid halides such as dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, and 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, 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 of two or more.

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

  The separation functional layer in the composite semipermeable membrane uses, for example, an aqueous solution containing the aforementioned polyfunctional amine and a water-immiscible organic solvent solution containing a polyfunctional acid halide, and a microporous support membrane. The skeleton can be formed by interfacial polycondensation on the surface.

  Here, the concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 0.1 to 20% by weight, more preferably in the range of 0.5 to 15% by weight. In this range, sufficient salt removal performance and water permeability can be obtained. 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 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 porous support membrane, first, the above-mentioned polyfunctional amine aqueous solution is brought into contact with the porous support membrane. The contact is preferably performed uniformly and continuously on the porous support membrane surface. Specific examples include a method of coating a porous support membrane with a polyfunctional amine aqueous solution and a method of immersing the porous support membrane in a polyfunctional amine aqueous solution. The contact time between the porous support membrane and the polyfunctional amine 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 polyfunctional amine aqueous solution into contact with the porous support membrane, the solution is sufficiently drained so that no droplets remain on the membrane. 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 of draining, for example, as described in JP-A-2-78428, a method of allowing an excess aqueous solution to naturally flow down by vertically gripping a porous support membrane after contacting a polyfunctional amine aqueous solution. Alternatively, it is possible to use a method of forcibly removing liquid by blowing an air stream such as nitrogen from an air nozzle. In addition, after draining, the membrane surface can be dried to partially remove water from the aqueous solution.

  Next, an organic solvent solution containing a polyfunctional acid halide is brought into contact with the support film after contact with the polyfunctional amine aqueous solution, and a skeleton of a 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. This is because a sufficient reaction rate can be obtained when the content is 0.01% by weight or more, and the occurrence of side reactions can be suppressed when the content is 10% by weight or less. Further, it is more preferable to include an acylation catalyst such as DMF in the organic solvent solution, since interfacial polycondensation is promoted.

  The organic solvent is preferably immiscible with water and dissolves acid halides and does not destroy the microporous support membrane, and may be any one that is inert to amino compounds and acid halides. . Preferred examples include hydrocarbon compounds such as n-hexane, n-octane, and n-decane.

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

  As described above, after the interface polycondensation is performed by bringing the acid halide organic solvent solution into contact with each other and the separation functional layer containing the crosslinked polyamide is formed on the porous support membrane, the excess solvent may be drained. 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. If it is too short, the separation functional layer is not completely formed, and if it is too long, the organic solvent is excessively dried and defects are likely to occur, and performance may be deteriorated.

  Next, the formed polyamide separation functional layer is brought into contact with hydrazine to form hydrazide. Since anhydrous hydrazine is a toxic substance, it is preferable to use a hydrate from the viewpoint of safety. Hydrazine may be used as a solution of water or alcohol. The contact time with hydrazine is preferably in the range of 1 second to 10 minutes, more preferably 10 seconds to 5 minutes. If it is too short, the reaction does not proceed sufficiently, and if it is too long, the production efficiency may decrease.

  Next, a reagent that reacts with hydrazide to produce an acid azide is brought into contact with the polyamide separation functional layer formed as hydrazine.

  Examples of the reagent of the present invention that reacts with hydrazide to produce an acid azide include aqueous solutions of nitrous acid and its salts, nitrosyl compounds and the like. Since an aqueous solution of nitrous acid or a nitrosyl compound easily generates gas and decomposes, it is preferable to sequentially generate nitrous acid by, for example, a reaction between nitrite and an acidic solution. In general, nitrite reacts with hydrogen ions to produce nitrous acid, but in an aqueous solution at 20 ° C., it is efficiently produced at a pH of 7 or less, preferably 5 or less, more preferably 4 or less. Among these, an aqueous solution of sodium nitrite reacted with hydrochloric acid or sulfuric acid in an aqueous solution is particularly preferable because of easy handling.

  The concentration of nitrous acid or nitrite in the reagent that reacts with hydrazide to produce acid azide is preferably in the range of 0.01 to 1% by weight at 20 ° C. If the concentration is lower than 0.01%, a sufficient effect cannot be obtained, and if the concentration is higher than 1%, it may be difficult to handle the solution.

  The composite semipermeable membrane obtained by the above method is subjected to a hydrothermal treatment step in the range of 40 to 100 ° C., preferably in the range of 60 to 100 ° C. for 1 to 10 minutes, more preferably 2 to 8 minutes. By adding, the solute blocking performance and water permeability of the composite semipermeable membrane can be further improved.

  It is also effective to improve the performance to further treat the obtained composite semipermeable membrane with an acidic aqueous solution. It may be brought into contact with an acidic aqueous solution of pH 1 to 3 for 1 to 30 minutes, more preferably 1 to 10 minutes.

  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, raw water can be separated into permeated water such as drinking water and concentrated water that has not permeated through the membrane, and water suitable for the purpose can be obtained.

  The higher the operating pressure of the fluid separator, the better the boron removal rate, 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 at the time of permeation is preferably 1.0 MPa or more and 10 MPa or less. As the feed water temperature increases, the boron removal rate may decrease. However, as the supply water temperature decreases, the membrane permeation flux also decreases. Therefore, it is preferably 5 ° C. or higher and 45 ° C. or lower. Further, when the pH of the feed water becomes high, boron in the feed water is dissociated into borate ions, so that the boron removal rate is improved. However, in the case of feed water with a high salt concentration such as sea water, scales such as magnesium may be generated. In addition, since there is a concern about membrane deterioration due to high pH operation, operation in a neutral region is preferable.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

  The membrane characteristics in the examples and comparative examples are membrane filtration treatment by supplying seawater (TDS concentration of about 3.5%) adjusted to a temperature of 25 ° C. and pH 6.5 to the composite semipermeable membrane at an operating pressure of 5.5 MPa. And the quality of permeated water and feed water was measured.

(Desalination rate (TDS removal rate))
TDS removal rate (%) = 100 × {1- (TDS concentration in permeated water / TDS concentration in feed water)}
(Membrane permeation flux)
The amount of water that the feed water (seawater) permeated through the membrane was expressed as the amount of water per cubic meter (m ³ / m ² · day) per square meter of membrane surface.

(TDS transmission coefficient)
It calculated | required from the following calculation formulas of "Membrane processing technology large series", the first volume, p171, the supervision of Masayuki Nakagaki, and the Fuji techno system (1991).
TDS permeability coefficient (m / s) = {(100−TDS removal rate) / TDS removal rate} × membrane permeation flux × 115.7 × 10 ⁻⁷
(Film composition evaluation method)
The presence of the substituent represented by the above formula (1) in the separation functional layer is obtained by measuring a solid NMR spectrum or heating with a strong alkaline aqueous solution for the separation functional layer peeled from the support membrane. The sample can be analyzed by performing HPLC measurement or ¹ H-NMR spectrum measurement of the hydrolyzed sample.

Example 1
A 15.3% by weight DMF solution of polysulfone was cast on a polyester non-woven fabric (air permeability 0.5 to 1 cc / cm ² · sec) to a thickness of 200 μm at room temperature (25 ° C.) and immediately immersed in pure water 5 A microporous support membrane was prepared by leaving for a minute.

  The microporous support membrane (thickness 210 to 215 μm) thus obtained was immersed in a 3.4 wt% aqueous solution of m-PDA for 2 minutes, the support membrane was slowly pulled up in the vertical direction, and air Nitrogen was blown from the nozzle to remove excess aqueous solution from the surface of the support membrane, and then an n-decane solution containing 0.15% by weight of trimesic acid chloride (hereinafter referred to as TMC) was applied so that the surface was completely wetted and allowed to stand for 1 minute. I put it. Next, in order to remove excess solution from the membrane, the membrane was held vertically for 1 minute and drained. Thereafter, an isopropyl alcohol solution containing 10% of hydrazine monohydrate was applied so that the surface was completely wet and allowed to stand for 2 minutes, and nitrogen was blown to remove excess solution. Subsequently, it was immersed in an aqueous solution containing 0.3% by weight of sodium nitrite adjusted to pH 3 with sulfuric acid for 1 minute and treated with hot water at 90 ° C. for 2 minutes to obtain a composite semipermeable membrane.

  When the obtained composite semipermeable membrane was evaluated, the membrane permeation flux and the TDS removal rate were the values shown in Table 1, respectively.

(Comparative Example 1)
A membrane was prepared in the same manner as in Example 1 except that the polyamide separation functional layer was not contacted with hydrazine and was not contacted with an aqueous sodium nitrite solution. The evaluation results are shown in Table 1.

(Comparative Example 2)
A membrane was prepared by the same process as in Example 1 except that the polyamide separation functional layer was not brought into contact with sodium nitrite. The evaluation results are shown in Table 1.

(Comparative Example 3)
A membrane was prepared by the same process as in Example 1 except that the polyamide separation functional layer was not contacted with hydrazine. The evaluation results are shown in Table 1.

  The treatment method and the production method of the present invention can be suitably used particularly for the production of a semipermeable membrane useful for desalination of brine or seawater.

Claims (3)

A method for producing a composite semipermeable membrane having a polyamide separation functional layer, which comprises forming a polyamide separation functional layer by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide on a microporous support membrane; A method for producing a composite semipermeable membrane, comprising: a step B in which the polyamide separation functional layer is brought into contact with hydrazine to form hydrazide; and a step C in which the polyamide separation functional layer is brought into contact with a reagent that reacts with hydrazide to produce an acid azide. . The method for producing a composite semipermeable membrane according to claim 1, wherein the reagent that reacts with hydrazide to produce an acid azide is an aqueous solution containing nitrous acid and / or a salt thereof. The manufacturing method of the composite semipermeable membrane of Claim 1 or 2 including the process D of hydrothermally treating at the temperature of 40 to 100 degreeC after the process C.