JP2012024756A5 - - Google Patents

Description

Manufacturing method of composite semipermeable membrane

  The present invention relates to a method for producing a composite semipermeable membrane that selectively separates its components from a liquid mixture. More specifically, the present invention relates to a method for producing a composite semipermeable membrane having a high salt removal rate and a high water permeability, comprising a thin film (separation active layer) mainly composed of polyamide on a porous support membrane.

  The composite semipermeable membranes currently on the market mainly include those having an active layer obtained by crosslinking a gel layer and a polymer layer on a porous support membrane, and an active layer obtained by polycondensing monomers on the porous support membrane. There are two types of things you have. Among them, a composite semipermeable membrane obtained by coating a porous support membrane with a separation functional layer made of polyamide obtained by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide is widely used.

  However, although the conventional composite semipermeable membrane has high water permeability and salt removal rate, it is not yet sufficient, and it is possible to improve water permeability while maintaining a higher salt removal rate. It is requested from. Further, when used as a reverse osmosis membrane, it is required that the above membrane performance can be maintained even during long-time operation at high pressure.

In response to these requirements, a method of performing an interfacial polycondensation reaction using an acylation catalyst (Patent Document 1) and a solubility parameter of 8 to 14 (cal / cm ³ ) ^1/2 when performing an interfacial polycondensation reaction. A method in which a certain compound is present (Patent Document 2), a method in which an aqueous solution of persulfate is brought into contact with the formed composite semipermeable membrane (Patent Document 3), and a method in which an aqueous sodium hypochlorite solution is brought into contact (Patent Document 4) However, since these methods use a large amount of chemicals during film formation, there is a problem that the burden on the global environment increases.

  Patent Documents 5 and 6 propose a method for improving the film performance by applying polyfunctional acid halide solutions having different concentrations in two stages during the interfacial polycondensation reaction to form polyamide. The present condition is that the composite semipermeable membrane of the level which reaches | attains a request is not obtained.

JP 63-12310 A Japanese Patent No. 3023300 Japanese Patent No. 3111539 JP 2005-246207 A WO99 / 01208 pamphlet JP 63-178805 A

  An object of the present invention is to provide a method for producing a composite semipermeable membrane having a high salt removal rate and water permeability while reducing the burden on the economy and waste liquid treatment.

  In order to achieve the above object, the present invention provides a method for forming a polyamide separation functional layer by bringing a polyfunctional amine and a polyfunctional acid halide into contact with each other on a porous support membrane. After the contact with the aqueous solution, the liquid A containing no polyfunctional acid halide is brought into contact with the solution containing the polyfunctional acid halide before contacting with the solution containing the polyfunctional acid halide.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the composite semipermeable membrane which has a high salt removal rate and water permeability can be provided.

  The present invention is a method for improving water permeability while maintaining a high salt removal rate.

  In the present invention, the composite semipermeable membrane is formed by bringing a separation functional layer having substantially separation performance into contact with a porous support membrane having substantially no separation performance. The separation functional layer is made of polyamide obtained by a reaction between a polyfunctional amine and a polyfunctional acid halide. Here, the polyfunctional amine comprises at least one component of an aliphatic polyfunctional amine and an aromatic polyfunctional amine.

  The aliphatic polyfunctional amine is an aliphatic amine having two or more amino groups in one molecule, and preferably a piperazine-based amine and a derivative thereof. For example, piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, 2,6-dimethylpiperazine, 2,3,5-trimethylpiperazine, 2,5-diethylpiperazine, 2,3,5-triethylpiperazine, 2- Examples thereof include n-propylpiperazine and 2,5-di-n-butylpiperazine, and piperazine and 2,5-dimethylpiperazine are particularly preferable from the viewpoint of the stability of performance expression.

  The aromatic polyfunctional amine is an aromatic amine having two or more amino groups in one molecule, and is not particularly limited, but includes metaphenylenediamine, paraphenylenediamine, 1,3,5 -N-alkylaminophenylene, N, N-diethylmetaphenylenediamine, N, N-dimethylparaphenylenediamine, N, N-diethylparaphenylenediamine, etc. Metaphenylenediamine and 1,3,5-triaminobenzene are particularly preferable from the viewpoint of stability of performance expression.

  The polyfunctional acid halide is an acid halide having two or more halogenated carbonyl groups in one molecule, and is not particularly limited as long as it gives a polyamide by reaction with the polyfunctional amine. Examples of the polyfunctional acid halide include oxalic acid, malonic acid, maleic acid, fumaric acid, glutaric acid, 1,3,5-cyclohexanetricarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid. 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,3-benzenedicarboxylic acid, and acid halides of 1,4-benzenedicarboxylic acid can be used. Among acid halides, acid chlorides are preferred, and are acid halides of 1,3,5-benzenetricarboxylic acid, particularly in terms of economy, availability, ease of handling, and ease of reactivity. Trimesic acid chloride is preferred. Although the said polyfunctional acid halide can also be used independently, you may use it as a mixture.

  The solvent that dissolves the polyfunctional acid halide is preferably immiscible with water and does not destroy the porous support membrane, and any solvent that does not inhibit the formation reaction of the crosslinked polyamide. Typical examples include halogenated hydrocarbons such as liquid hydrocarbons and trichlorofluoroethane, but they are substances that do not destroy the ozone layer, are easily available, are easy to handle, and are safe for handling. , Cyclohexane, cyclooctane, ethylcyclohexane, and other linear aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, etc. Unsaturated aliphatic hydrocarbons such as 1-octene and 1-decene are preferred, and these simple substances or mixtures are preferably used.

  Next, the preferable manufacturing method of a composite semipermeable membrane is demonstrated. The separation functional layer having substantially separation performance in the composite semipermeable membrane is, for example, an aqueous solution containing the aforementioned polyfunctional amine and an aqueous solution immiscible with water containing the aforementioned polyfunctional acid halide. And is contacted on a porous support membrane described later to cause interfacial polycondensation.

Here, the concentration in the aqueous solution containing the polyfunctional amine is preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight. When the content is less than 0.1% by weight, the formation of the separation functional layer is not observed, and when the content exceeds 20% by weight , the produced polyamide becomes bulky and the desired membrane performance cannot be obtained.

  For aqueous solutions containing polyfunctional amines and solutions containing polyfunctional acid halides, acylation catalysts, polar solvents, acid scavengers, interfaces, etc., are necessary as long as they do not interfere with the reaction between the two components. Compounds such as activators and antioxidants may be included.

  In the present invention, the porous support membrane is intended to give strength to the separation functional layer that has substantially no separation performance such as ions and substantially has the 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 which the separation functional layer is formed to the other surface, and the separation functional layer has A supporting membrane in which the size of the micropores is 0.1 nm or more and 100 nm or less on the surface to be formed is preferable.

  The porous support membrane used in the present invention can be selected from various commercially available materials such as “Millipore Filter VSWP” (trade name) manufactured by Millipore and “Ultra Filter UK10” (trade name) manufactured by Toyo Roshi Kaisha. Can be produced according to the method described in “Office of Saleen Water Research and Development Progress Report” No. 359 (1968).

The material used for the porous support membrane and the shape thereof are not particularly limited. For example, polysulfone, cellulose acetate, and polyvinyl chloride reinforced with a fabric (base material) mainly composed of at least one selected from polyester or aromatic polyamide. Or a mixture thereof (porous support) is preferably used. As the material for the porous support to be used, it is particularly preferable to use polysulfone having high chemical, mechanical and thermal stability. Specifically, a solution of polysulfone in dimethylformamide ( hereinafter referred to as DMF) is applied on a densely woven polyester cloth or non-woven fabric to a substantially constant thickness, and 0.5% by weight of sodium dodecyl sulfate and 2% by weight of DMF are added. By wet coagulation with the aqueous solution containing it, it is possible to obtain a suitable porous support membrane having most of the surface having fine pores with a diameter of several tens of nm or less.

The thickness of the porous 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, the thickness of the porous support membrane is preferably in the range of 50 to 300 μm , more preferably in the range of 100 to 250 μm . The thickness of the porous support of which, preferably in the range of 10 to 200 mu m, more preferably in the range of 30 to 100 mu m.

  The form of the porous 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, 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. Hitachi's S-900 electron microscope 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 aqueous solution containing the polyfunctional amine may be brought into contact with the surface of the porous support membrane as long as the aqueous solution is brought into contact with the surface uniformly and continuously. The coating method may be performed by the method of immersing the porous support membrane in the aqueous solution. Next, the excessively applied aqueous solution is removed by a liquid draining step. As a method for draining liquid, for example, there is a method in which the film surface is allowed to flow naturally while being held in a vertical direction. After draining, the membrane surface may be dried to remove all or part of the water in the aqueous solution.

  The method of the present invention involves applying a liquid A that does not contain a polyfunctional acid halide prior to contacting and reacting the solution containing the polyfunctional acid halide. The method for applying the liquid A is not particularly limited, and for example, a method using a bar coater, a die coater, a gravure coater, a spray, or the like can be appropriately employed. Here, the coating thickness of the liquid A is not particularly limited, but the coating thickness immediately before contacting with the solution containing the polyfunctional acid halide is preferably 0.1 mm or less. When the coating thickness immediately before is increased, when the solution containing the polyfunctional acid halide is brought into contact, the polyfunctional acid halide at the reaction interface is diluted with the liquid A, and the progress of the interfacial polycondensation reaction becomes insufficient. As a result, the membrane performance is degraded.

  The liquid A is not particularly limited as long as it does not contain a polyfunctional acid halide and does not destroy the porous support membrane. Representative examples include liquid hydrocarbons, halogenated hydrocarbons, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters and the like having the predetermined properties. Among them, considering that it is a substance that does not destroy the ozone layer, availability, ease of handling, and safety in handling, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, Tetradecane, cyclohexane, cyclooctane, ethylcyclohexane, 1-octene, 1-decene, benzene, toluene, xylene, ethylbenzene, styrene, naphthalene, ethanol, propanol, butanol, pentanol, isopropyl alcohol, isobutyl alcohol, ethylene glycol, diethylene glycol, Allyl alcohol, benzyl alcohol, methyl benzyl alcohol, cresol, diethyl ether, ethyl methyl ether, methyl propyl ether, ethyl propyl ether, aniso , Ethyl benzyl ether, dibenzyl ether, oxetane, oxolane, oxane, dioxolane, dioxane, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, vinyl aldehyde, methacrylamide, benzaldehyde, acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl Ketone, diacetone alcohol, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, formic acid, acetic acid, propionic acid, butyric acid, methyl formate, ethyl formate, propyl formate, butyl formate, isobutyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate And isobutyl acetate. Among these, the hydrocarbons, the alcohols, and the ketones are particularly preferable. These compounds may be used alone or in combination of two or more. Among these, it is more preferable to use the same liquid as the solvent used in the polyfunctional acid halide solution because it leads to a reduction in the types of chemicals used. If necessary, compounds such as an acylation catalyst, an acid scavenger, a surfactant, and an antioxidant may be contained.

  In the present invention, the term “not containing a polyfunctional acid halide” means that, for example, liquid A is subjected to a known hydrolysis treatment for converting a polyfunctional acid halide into a polyfunctional carboxylic acid, followed by high performance liquid chromatography or When the concentration of polyfunctional carboxylic acid in liquid A is quantified using ion chromatography or the like, it indicates that the concentration is below the detection limit (that is, 1 ppm).

  Thereafter, a solution containing the above-mentioned polyfunctional acid halide is applied to the porous support membrane coated with the above-mentioned liquid A, and a separation functional layer of crosslinked polyamide is formed by reaction.

  The concentration of the polyfunctional acid halide in the 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. Furthermore, it is more preferable to include an acylation catalyst such as N, N-dimethylformamide in this solution because interfacial polycondensation is promoted.

  After interfacial polycondensation is performed by contacting a solution of a polyfunctional acid halogen compound to form a separation functional layer containing a crosslinked polyamide on the porous support membrane, 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 solvent is allowed to flow down and removed can be used. In this case, the time for gripping in the vertical direction is preferably between 1 and 5 minutes, more preferably between 1 and 3 minutes. If it is too short, the separation functional layer will not be completely formed, and if it is too long, the solvent will be overdried and defects will easily occur and performance will be deteriorated.

  The composite semipermeable membrane obtained by the above method is subjected to 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 solute blocking 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, 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 present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, all n-decane used was “n-decane” special grade manufactured by Wako Pure Chemical Industries, Ltd.

  The characteristics of the membrane are that the seawater (salt concentration of about 3.5%) adjusted to a temperature of 25 ° C and pH 6.5 is supplied to the composite semipermeable membrane at an operating pressure of 5.5 MPa, and membrane filtration is performed. Was determined from the following equation.

(Salt removal rate)
Salt removal rate (%) = 100 x {1-(salt concentration in permeated water / salt concentration in feed water)}
(Membrane permeation flux)
Membrane permeation flux (m ³ / m ² / day) was expressed in terms of the permeate flow rate of the supplied water (seawater) per square meter of the membrane surface with the permeate flow rate per cubic meter (cubic meter).

(Example 1)
A fabric-reinforced polysulfone support membrane (ultrafiltration membrane), which is a porous support membrane, was produced by the following method. That is, a wet non-woven fabric composed of a mixed yarn of polyester fiber having a single yarn fineness of 0.5 dtex and 1.5 dtex polyester fiber, having an air permeability of 0.7 cm ³ / cm ² / sec and an average pore diameter of 7 μm or less, and having a length of 30 A sample having a size of cm and a width of 20 cm is fixed on a glass plate, and a solution of dimethylformamide (DMF) solvent in a polysulfone concentration of 15% by weight (20 ° C.) is added to the total thickness of 210 to 215 μm. And then immediately immersed in water to produce a polysulfone porous support membrane. The obtained porous support membrane is referred to as a PS support membrane.

The PS support membrane thus obtained was immersed in a 6.5% by weight aqueous solution of metaphenylenediamine (hereinafter referred to as mPDA) at room temperature for 2 minutes, and the support membrane was slowly pulled up in the vertical direction to remove excess from the surface of the support membrane. After removing the aqueous solution, n-decane was coated as liquid A on the surface of the membrane using a die coater and allowed to stand for 60 seconds. (The coating thickness at this time was 0.064 mm.) Then, an n-decane solution containing 0.175% by weight of trimesic acid chloride (hereinafter referred to as TMC) was applied so that the surface was completely wetted. Next, after removing the excess solution by draining the membrane vertically, in order to evaporate the solvent remaining on the membrane surface, the temperature of 30 ° C was set so that the wind speed on the membrane surface was 8 m / s. Was blown for 1 minute. When the obtained composite semipermeable membrane was evaluated under the above conditions, the salt removal rate was 99.8%, and the membrane permeation flux was 0.86 m ³ / m ² / day.

(Examples 2 to 10)
In Example 1, the composite semipermeable membrane was the same as Example 1 except that the concentration of mPDA to be immersed, the liquid A to be applied thereafter, and the concentration of the TMC solution to be applied were changed as shown in Table 1 below. Was made. The evaluation results of the composite semipermeable membrane thus obtained are shown in Table 1 below. The mixing ratio in the mixed solvent (that is, liquid A) is a volume ratio.

(Comparative Example 1)
In Example 1, a composite semipermeable membrane was prepared in the same manner as in Example 1 except that the liquid A was not used and an n-decane solution containing 0.175% by weight of TMC was immediately applied. The evaluation results of the composite semipermeable membrane thus obtained are shown in Table 1 below.

(Comparative Examples 2-6)
In Comparative Example 1, a composite semipermeable membrane was prepared in the same manner as in Example 1 except that the concentration of mPDA to be immersed and the concentration of the TMC solution to be applied thereafter were changed as described in Table 1 below. The evaluation results of the composite semipermeable membrane thus obtained are shown in Table 1 below.

From the results of Examples and Comparative Examples, in the method of forming a polyamide separation functional layer, after contacting an aqueous solution containing a polyfunctional amine with a porous support membrane, and before contacting a solution containing a polyfunctional acid halide, By contacting the liquid A containing no polyfunctional acid halide, a composite semipermeable membrane with improved water permeability can be obtained while maintaining a high salt removal rate.