KR100460011B1 - Post Treatment Process of Polyamide Reverse Osmosis Membrane - Google Patents

Abstract

The present invention relates to a post-treatment process of a polyamide reverse osmosis membrane used for precision filtration or water purification, and is intended to improve the amount of purified water, in particular, compared to existing products.

The present invention is to prepare a polyamide reverse osmosis composite membrane obtained by immersing a mixture of a polyfunctional amine aqueous solution on the surface of a non-porous substrate coated with a microporous polysulfone and removing the water layer on the surface, and then interfacial polymerization under a polyfunctional acid halide compound solution. In performing the post-treatment process, the unreacted amine monomer, acyl halide monomer, etc. deposited on the surface layer formed in the coating process are washed off and then treated with pure water containing sodium hypochloride. Polyamide-based reverse osmosis membrane prepared through the same post-treatment process shows a significantly improved performance compared to conventional products.

Description

Post Treatment Process of Polyamide Reverse Osmosis Membrane

The present invention relates to a post-treatment process, especially in the polyamide-based composite reverse osmosis membrane manufacturing process excellent salt rejection rate and water purification amount compared to the conventional membrane.

Reverse osmosis membranes have been actively studied since Loeb and Sourirajan developed the first reverse osmosis membrane, an asymmetric cellulose diacetate membrane. Cellulose diacetate membranes have the advantages of low cost, but they are vulnerable to microorganisms, easily hydrolyzed under strong bases, and have a narrow range of operating temperature and pH, which leads to the modification of cellulose and alloys of various celluloses. Although it is being used through, it has not completely overcome these disadvantages. Since then, research has been actively conducted on polyamides, polyurethanes, aromatic polysulfones, aromatic polyamides, and the like to compensate for the disadvantages of cellulose membranes.

Among them, a composite membrane having an aromatic polysulfone as a porous support membrane and a polyamide-based support layer has been developed and put into practical use. Such a composite membrane consists of a support layer for maintaining mechanical strength and an active layer with selective permeability. The manufacturing method of the composite membrane includes a thin layer dispersion method, an immersion coating method, a vapor deposition method, a Langmuir-Biodgett method, an interfacial polymerization method, and especially in the recently developed nano or reverse osmosis composite membrane in US Pat. No. 4,277,344. The interfacial polymerization method disclosed is mainly used for manufacture of a composite film. The start of the composite membrane by the interfacial polymerization method is NS-100 manufactured by reacting a polyethylene polyamine solution with toluene diasocyanate in hexane to a porous polysulfone support. Aliphatic amines, aromatic amines were used to prepare membranes of various properties. However, NS-300 with polypiperazineamide active layer came out by Cadette, the developer of NS-100, and finally the composite film by the interfacial polymerization method was started. The NS-300 membrane has a specific selective separation ability for nanometer solutes. At the time of NS-300 development, polypyrazineamide had a high rejection rate of over 95% for divalent ions and monosaccharides and 40-95 for sodium chloride. Membranes with a relatively broad range of rejection rates have been developed, which are mainly impregnated with polysulfone microporous substrates in a polyfunctional amine solution mixed with piperazine and an alkaline catalyst and on the substrate a polyfunctional acid halogenated compound. It is obtained by apply | coating an interpolymerization by apply | coating this. The main method of controlling the rejection rate of these membranes is to use a mixture of acid halide compounds with terephthaloyl chloride, isophthaloyl chloride, and trimezoyl chloride in an appropriate ratio, and the exclusion ratio is proportional to the mixing ratio. US Pat. No. 4,259,138 of the method for preparing a nanocomposite membrane uses N, N'-dimethylpiperazine, sodium hydroxide as a piperazine and a catalyst, and performs interfacial polymerization by mixing isophthaloyl chloride and trimezoyl chloride. N-hexane is used as a solvent of a compound. On the other hand, US Patent 4,619,767 first coated polyvinyl alcohol on polysulfone, and then interfacially polymerized with a mixture of diamine and trimesoyl chloride / isophthaloyl chloride containing piperazine or piperazine structure, and n-hexane as a solvent. I use it.

In addition, a reverse osmosis membrane was developed, which has a lower flow rate than that of the nano-membrane but has the ability to separate almost 98% of ionic minerals. The reverse osmosis membrane is a semi-permeable membrane in one direction of an aqueous solution in which salts are dissolved. It uses the principle that separation of solution and solute occurs in a certain direction when pressurized. It is a high-performance separator made of a material that withstands high pressure and has excellent durability and chemical resistance. Important characteristics of reverse osmosis membranes include salt rejection (SALT REJECTION), and flux (FLUX: flow rate of solvent exiting the membrane at constant pressure for a certain period of time). As the reverse osmosis membrane of the thin film composite material, polyamide obtained by interfacial polymerization is generally used. Interfacial polymerization is achieved by submerging the micropolymer support layer (primarily polysulfone) in a water-soluble amine, and then submerging the obtained layer in a solution layer in which the acyl chloride of the organic layer is dissolved. Solvents which do not affect the reaction and which can dissolve an appropriate amount of substrate are preferred.

The most widely used solvent so far is 1,1,2-trichlorotrifluoroethane (1,1,2-TRICHLOROTRIFLUOROETHANE), which is generally called CFC-113, but is expensive and adversely affects the environment such as destruction of the ozone layer. It is known to give.

As a result, studies on the use of environmentally friendly solvents have been actively conducted in recent years, including US Patent 4,005,012, US Patent 4,259,813, US Patent 4,360,434, US Patent 4,606,943, US Patent 4,737,325, US Patent 4,282,708, US Patent 5,258,203, and the like. A method of preparing a separator by using an aliphatic hydrocarbon solvent without using 2-trichlorotrifluoroethane is provided. However, the use of aliphatic reaction solvents such as hexane has been suggested for commercial use as a result of lowering the flow rate. Because of this, studies have been conducted to obtain a good salt rejection rate and sufficient flow rate, a study of developing materials to be added to the crude liquid (US Pat. No. 5,234,598, US Pat. No. 5,258,203), and a study of changing the structure of the monomers added to the polyamide reaction (US Patents 4,761,234, U.S. Patents 4,643,829, U.S. Patents 5,019,264, U.S. Patents 5,160,619, U.S. Patents 5,271,843, U.S. Patents 5,336,409, and studies on increasing the flow rate through post-treatment (U.S. Patent 4,938,872, U.S. Patent 4,927,540) are proposed. At this time, the aliphatic hydrocarbon solvent used is a mixture of an aliphatic hydrocarbon complex solution and several additives, and the additive is added to the aqueous solution solvent or the aliphatic hydrocarbon solvent phase. As a method of increasing the salt excretion rate and flow rate through post-treatment, US Patent 4,277,344 proposes a method of preparing a membrane and then treating the membrane with a water treatment solution containing sodium hypochloride (NaOCl). There is a problem that the increase in flow rate is insufficient.

Examples of the invention that improve the performance of the membrane by adding a small amount of glycols as an additive to the polyfunctional amine aqueous solution layer, as illustrated in US Patent 4,830,885, ethylene glycol, propylene glycol, polyethylene glycol, glycerin and the like and mixtures thereof to improve the properties Getting results. As another example, NMP, DMF, Prydine, DMAC, Sufolane, Dioxane, and mixtures thereof are added to the polyfunctional amine aqueous solution layer as illustrated in US Pat. No. 4,950,404 to obtain improved physical properties. A method of improving the physical properties by adding an organic additive to the polyfunctional acyl halide organic solution layer is described in US Pat. No. 5,258,203 to benzene, xylene, heptane, dimethyl ether, methyl ether, diethyl ether or the like. A method of adding a mixture thereof is illustrated.

The present invention is to prepare a reverse osmosis membrane composed of a composite material using an aliphatic hydrocarbon solvent, and effectively remove the by-products remaining on the surface of the membrane during the preparation of the membrane and the monomer used in the preparation of the membrane and then post-treatment to perform the post-treatment Its purpose is to provide a way to improve this.

The present invention is to immerse a polyfunctional amine solution on the surface of the non-woven substrate coated with a microporous polysulfone, and then remove the water layer of the surface and interfacial polymerization under a polyfunctional acid halide compound solution to prepare a polyamide reverse osmosis composite membrane, and then post-treatment Reverse osmosis membrane by washing with unreacted amine monomer, acyl halide monomer and oligomer reacted with amine monomer and acyl halide deposited on the surface layer formed in the coating process, and then treating with pure water containing sodium hypopochloride and ion removal It relates to a post-treatment process of a polyamide reverse osmosis composite membrane, characterized in that to improve the performance of.

The porous support layer, which is composed of the surface of the membrane and the layer just below the surface prepared by the conventional method, has an unreacted polyfunctional amine monomer, unreacted polyfunctional acyl halide monomer, hydrolyzed unreacted polyfunctional which are inevitably buried in the membrane manufacturing process. It is contaminated with acyl halide monomers and reaction by-products of the reaction between the polyfunctional amine monomer and the polyfunctional acyl halide monomer. Such contaminants interfere with the inherent properties of the membranes produced and therefore inevitably lead to degradation of the membrane properties. The present invention relates to a method for effectively removing such by-products and will be described in detail below.

In the present invention, the first step to remove the foreign matter on the surface of the membrane effectively after the preparation of the membrane to remove foreign substances such as unreacted monomers on the surface of the membrane under conditions of 0 ~ 10 psig micropressure, recovery rate less than 15% with pure water removed. The longer the time is, the better the effect is, but a small time of about 10 to 15 minutes is enough to see the effect. The pressure and recovery are very important here at high pressures of 50 psig or higher, for example, at 225 psig, which is a commonly assessed pressure, unreacted monomers and other byproduct impurities on the membrane surface are forced into the pores of the membrane. This is because there is a high possibility of clogging. In this way, the impurities on the surface of the membrane are washed off, and then the membrane is treated by a second washing process, that is, washing is performed for 1 hour or more with deionized water at a pressure of 50 to 350 psig and a recovery rate of 5 to 80%. A process for removing unreacted dispersions and monomers from the porous support layer located directly below the surface layer of the membrane and the nonwoven fabric underneath it. This process is a process to effectively carry out the third process, the chemical treatment process, to remove impurities as much as possible from the surface of the film, the back of the film, and the space of the film itself, thereby enhancing the effect of the subsequent chemical treatment. The third process is a liquid consisting of 5 to 100 ppm of residual sodium phosphate (as Cl ₂ ) in pure water from which sodium hypopochloride is deionized under pressure of 50 to 300 psig, recovery of 5 to 60%, and room temperature. Do it. The membrane treated as described above has an absolute increase in salt rejection rate of 0.3% to 5.0% compared to the untreated membrane, and the amount of purified water is rarely reduced by about 5%. However, in most cases, the usefulness can be improved by 10% to 80%. have.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In this case, the module refers to a material made of a membrane to make it convenient to use by adding other necessary subsidiary materials. The amount of purified water is passed through the membrane when processing various raw water (or feed water) using the membrane or a module. The amount of water that has been treated. In addition, salt rejection rate is a percentage value of how much the salt concentration of raw water to be treated is filtered, and recovery rate is a numerical value indicating how many percent of raw water obtained through a membrane or a module comes out as an integer.

Example 1

The reverse osmosis composite membrane was manufactured by using a known method of immersing the multifunctional amine aqueous solution mixture on the surface of the nonwoven substrate coated with the microporous polysulfone, removing the water layer on the surface, and then interfacially polymerizing the solution under the polyfunctional acid halogenated compound. After washing for 15 minutes with deionized water at a pressure of 5 psig, a recovery rate of 5%, and a temperature of 25 ° C., the unreacted monomers and other impurities on the surface were washed, and again, the pressure was 150 psig, a recovery rate of 15%, and a temperature of 25 ° C. It was washed for 60 minutes at the condition of ℃. Sodium sodium chloride was added to pure water from which ions were removed, and the residual chlorine concentration was adjusted to 15 ppm based on chlorine (as Cl ₂ ), and then treated for 25 minutes under conditions of 300 psig and 15% recovery.

The performance of the membrane thus prepared and washed and post-treated was evaluated under conditions of 2000 ppm NaCl, pressure 225 psig, temperature 25 ° C., recovery rate 15 ± 5%, and the results are shown in Table 1.

Comparative Example 1

In Example 1, the treatment was performed simply with pure water containing sodium hypochloride, and the performance of the post-treatment membrane was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

TABLE 1

Water purification amount (gfd) Salt Exclusion Rate (%) Example 1 26 99.0 Comparative Example 1 20 98.9

As can be seen from the above results, the membrane was first treated with sodium hypophosphate immediately after the preparation of the membrane, according to the present invention. Equivalent to the same level, but the availability of water purification is greatly improved.

Claims (1)

After preparing a polyamide reverse osmosis composite membrane obtained by immersing a mixture of a polyfunctional amine solution on the surface of a non-porous substrate coated with a microporous polysulfone, removing the water layer on the surface, and interfacially polymerizing the solution under a polyfunctional acid halide compound. In carrying out the post-treatment process, the membrane and the module were mounted in the post-treatment process, and washed 5 to 60 minutes with deionized water under conditions of 0 to 10 psig and 0 to 5% recovery, followed by a pressure of 50 to 350 psig. After washing for more than 1 hour with deionized water at a recovery rate of 5 to 60%, finally pressurized at 50 to 300 psig, recovery rate of 5 to 75%, and sodium hypophosphate as an aqueous solution containing 5 to 100 ppm based on the amount of residual chlorine. A post-treatment step of the polyamide reverse osmosis membrane, characterized in that the treatment for 1 to 30 minutes.