JP2010099549A - Manufacturing method of composite semi-permeable membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a composite semi-permeable membrane having high solute removability and high water permeability. <P>SOLUTION: The manufacturing method of the composite semi-permeable membrane having a polyamide separation functional layer includes: a step A of forming the polyamide separation functional layer by the interfacial polycondensation of a polyfunctional amine with a polyfunctional acid halide on a microporous support membrane; a step B of bringing the polyamide separation functional layer into contact with ammonia; and a step C of bringing into contact with an isocyanating reagent. <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 a treatment method 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. However, these treatment methods have a problem that water permeability is improved while solute removal properties such as boron are lowered.
JP 63-175604 A (Claims) JP 63-54905 A (Claims)

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

To achieve the above object, the present invention has the following configuration.
(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 method for producing a composite semipermeable membrane, comprising A, a step B in which the polyamide separation functional layer is brought into contact with ammonia, and a step C in which the polyamide separation functional layer is brought into contact with an isocyanate reagent.
(2) The method for producing a composite semipermeable membrane as described in (1) above, wherein the isocyanate reagent is an alkaline aqueous solution of halogen.
(3) The method for producing a composite semipermeable membrane according to the above (1) or (2), comprising the step D of hydrolyzing the isocyanate after the step C.

  According to the present invention, a composite semipermeable membrane having both high solute removal properties and high water permeability can be obtained.

  The present invention relates to 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 step, a step of bringing the polyamide separation functional layer into contact with ammonia, and a step of bringing into contact with an isocyanate reagent.

  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, a porous support reinforced with a base material that is a fabric mainly composed of at least one selected from polyester or aromatic polyamide is used. . As the material for the porous support, polysulfone, cellulose acetate, polyvinyl chloride, or a mixture thereof is preferably used, and 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 microporous support membrane 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 microporous support membrane 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, after peeling off the microporous support from the base material, it is 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.

  In the present invention, the polyamide constituting the separation functional layer can be formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. Here, 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, 3,5-diaminobenzoic acid, etc. Aliphatic amines such as ethylenediamine, propylenediamine, alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 1,3-bispiperidylpropane, 4-aminomethylpiperazine, etc. Can be mentioned. 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 bifunctional 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 microporous support membrane surface and reducing the interfacial tension between the aqueous amine solution and the nonpolar solvent, and the organic solvent can act as a catalyst for the interfacial polycondensation reaction. In some cases, the interfacial double reaction can be carried out efficiently 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. Specific examples include 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. 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 bringing the polyfunctional amine aqueous solution into contact with the microporous 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 for draining, for example, as described in JP-A-2-78428, the microporous support membrane after contacting 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 an air stream such as nitrogen from an air nozzle can be used. 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 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. 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 the polyfunctional acid halide and does not break the microporous support membrane, and is inert to the polyfunctional amine compound and the polyfunctional acid halide. If there is something. Preferred examples include hydrocarbon compounds such as n-hexane, n-octane, and n-decane.

  The method for contacting the polyfunctional acid halide organic solvent solution with the polyfunctional amine compound aqueous solution phase may be the same 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 containing 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. If it is too short, the separation functional layer will not be completely formed, and if it is too long, the organic solvent will be overdried and defects will easily occur and performance will be deteriorated.

  Next, the formed polyamide separation functional layer is brought into contact with ammonia. By this step, the functional group that did not react during polymerization with the carbonyl halide group of the polyfunctional acid halide is converted to a primary amide. Ammonia is used as a solution using water and / or alcohol as a solvent. The concentration of the ammonia solution is preferably in the range of 0.1 to 30% by weight. If the concentration is lower than 0.1%, a sufficient effect cannot be obtained, and if the concentration is higher than 30%, it becomes difficult to handle the solution. The contact time between the polyamide separation functional layer and ammonia is preferably in the range of 1 second to 10 minutes. If it is too short, the reaction does not proceed sufficiently.

  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.

  Subsequently, the polyamide separation functional layer is brought into contact with a reagent that reacts with a primary amide to produce an isocyanate. A chemical reaction for converting a primary amide to an isocyanate is generally known as a Hofmann rearrangement reaction, and the method for producing an isocyanate in the present invention is based on this. That is, an alkaline aqueous solution of halogen is used as a reagent for generating an isocyanate, and bromine, hypozinc acid salt, hypochlorous acid, or the like is preferably used as the halogen.

  It is also effective to improve the performance to further treat the obtained composite semipermeable membrane with an acidic aqueous solution. By this step, isocyanate having a relatively unstable chemical structure can be hydrolyzed, and the polyamide separation functional layer can be stabilized. In order to carry out the hydrolysis efficiently, it is appropriate to bring the polyamide separation functional layer into contact with an acidic aqueous solution having a pH of 1 to 3 for 1 to 30 minutes from the viewpoint of handling of chemicals and production efficiency. As the acid, a mineral acid such as hydrochloric acid or sulfuric acid whose pH is easily controlled is preferably used.

  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 higher the salt 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 rises, the salt removal rate decreases, but as the feed water temperature decreases, the membrane permeation flux also decreases. 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.

  Examples of raw water treated by the composite semipermeable membrane according to the present invention include liquid mixtures containing 500 mg / L to 100 g / L TDS, such as seawater, brine, and waste water. In general, TDS refers to the total dissolved solid content, and is expressed as “mass ÷ volume” or “weight ratio”. According to the definition, the solution 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., but more simply converted from practical salt (S) To do.

  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)}
(Boron removal rate)
The boron concentration in the feed water and the permeated water was analyzed with an ICP emission analyzer, and obtained from the following equation.
Boron removal rate (%) = 100 × {1− (boron concentration in permeated water / boron 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 day (m ³ / m ² / d) per square meter of membrane surface (m ³ / m ² / d).

Example 1
A 15.3 wt% DMF solution of polysulfone was cast on a polyester nonwoven fabric (air permeability 0.5 to 1 cc / cm ² / sec) at a room temperature (25 ° C.) to a thickness of 200 μm, 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. Subsequently, the composite semipermeable membrane was immersed in an aqueous solution containing 5.0 wt% ammonia and 10.0 wt% isopropyl alcohol for 2 minutes. Then, it was immersed in a 1.0 mmol / L bromine aqueous solution adjusted to pH 12 with sodium hydroxide for 1 minute and washed with hot water at 90 ° C. for 2 minutes.

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

(Comparative Example 1)
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 the ammonia solution and the bromine 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 the ammonia solution. The evaluation results are shown in Table 1.

(Comparative Example 3)
A membrane was prepared in the same manner as in Example 1 except that the polyamide separation functional layer was not brought into contact with the bromine solution. The evaluation results are shown in Table 1.

(Comparative Example 4)
A membrane was prepared by the same process as in Example 1 except that the bromine solution brought into contact with the polyamide separation functional layer did not contain bromine. The evaluation results are shown in Table 1.

(Comparative Example 5)
A porous support membrane formed by the same process as in Example 1 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 nitrogen was removed from the air nozzle. After removing the excess aqueous solution from the surface of the spray supporting film, an n-decane solution containing 0.15% by weight of TMC 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 vertically held for 1 minute to drain, air-dried at room temperature for 30 seconds, and then washed with hot water at 90 ° C. for 2 minutes. Finally, it was immersed in a 2000 ppm sodium nitrite aqueous solution adjusted to pH 3 with sulfuric acid for 35 seconds to obtain a polyamide composite semipermeable membrane. The evaluation results are shown in Table 1.

(Comparative Example 6)
A porous support membrane formed by the same process as in Example 1 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 nitrogen was removed from the air nozzle. After removing the excess aqueous solution from the surface of the spray supporting film, an n-decane solution containing 0.15% by weight of TMC 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 vertically held for 1 minute to drain, and air dried at room temperature for 30 seconds. Subsequently, the membrane was washed with hot water at 90 ° C. for 2 minutes, and then immersed in a 200 ppm sodium hypochlorite aqueous solution adjusted to pH 7 for 2 minutes. Finally, it was washed with hot water at 95 ° C. for 2 minutes to obtain a polyamide composite semipermeable membrane. The evaluation results are shown in Table 1.

  As described above, the composite semipermeable membrane obtained by the production method of the present invention has high solute removability and high water permeability that could not be achieved by existing production methods.

  Especially the manufacturing method of this invention can be used suitably for manufacture of the 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 ammonia; and a step C in which the polyamide separation functional layer is brought into contact with an isocyanate reagent. 2. The method for producing a composite semipermeable membrane according to claim 1, wherein the isocyanate reagent is an alkaline aqueous solution of halogen. The manufacturing method of the composite semipermeable membrane of Claim 1 or 2 including the process D which hydrolyzes an isocyanate after the process C.