JP2014133225A - Method for removing urea within pure water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a TOC component in pure water sufficiently by a conventional pure water production process because it contains urea as a main component and is nonionic. Although it can be removed by biological treatment or oxidant treatment, not only the apparatus becomes complicated, but also the number of contamination sources increases, making it difficult to obtain pure water with a sufficiently reduced TOC.
A cation exchanger is formed in a desalting chamber of an electric desalting apparatus so that adsorption and elution by urea cationization can be performed. The cation exchanger is preferably a strongly acidic sulfonic acid group and the shape is fibrous. Urea in pure water can be reduced only by changing the ion exchanger filling structure of the desalting chamber of the conventional electric desalting apparatus.
[Selection] Figure 1

Description

  The present invention relates to a method for treating an organic urea compound that can remove an organic urea compound such as urea or thiourea contained in water, in particular, water.

  In the precision industry such as a semiconductor manufacturing factory and a liquid crystal manufacturing factory, and in the pharmaceutical and food industry fields, pure water with extremely high cleanliness is required. Among them, the TOC component is mainly composed of urea, and is difficult to remove by a reverse osmosis membrane treatment apparatus or an ion exchange treatment apparatus in a pure water production process. In the field where high-purity pure water is required, in order to remove further TOC components, TOC mainly composed of urea is decomposed with an oxidizing agent and removed with an ion exchange resin in the subsequent stage. Here, the oxidizing agent to be used is ultraviolet rays, ozone, hydrogen peroxide, etc., and it is necessary to install an ultraviolet ray irradiation facility or an oxidant injection facility. In addition, a detoxification treatment facility such as a reducing agent injection facility is required for the detoxification treatment of the remaining oxidizing agent (Japanese Patent Laid-Open No. 2011-183245). For this reason, large-scale equipment is required, resulting in an increase in cost.

  Biological treatment has long been used for organic matter treatment. However, biological treatment is effective in treating wastewater and sewage with a large amount of water and high biochemical oxygen demand (BOD), but in pure water production, it is often a source of contamination.

  Although there are adsorbent treatments with activated carbon and organic polymer resins, these adsorbents exhibit adsorption performance for relatively high molecular organic substances, but adsorption capacity for organic substances with a small molecular weight such as urea. And requires a very large amount of activated carbon and resin to be adsorbed. Moreover, since activated carbon and resin discharge many organic substances from the adsorbent itself, it has been avoided to use them for organic substance removal in the production of pure water.

However, these conventional devices are very large, very expensive when producing pure water, and become a facility that occupies a considerable installation area, so far semiconductors that require very high purity. It has been limited to use in the field of ultrapure water used in production equipment.
JP2011-183245

  In recent years, ultra-pure water with ultra-high purity of TOC 1ppb or less has been required in the manufacturing factory of 256MB to 1GB VLSI, but TOC mainly composed of urea is a conventional reduction technology. The system configuration is complicated, the water recovery rate is lowered, the equipment cost is increased, and the running cost is further increased. The present invention has been made in order to solve the conventional problems, and by improving the electric desalination apparatus often proposed as a resource-saving / energy-saving pure water production process, the equipment cost, running An object of the present invention is to provide an electric desalination apparatus for an ultrapure water production process capable of reducing the TOC concentration mainly composed of urea without increasing the cost, and an ultrapure water production process using the same.

The present invention is (1) in an electric desalination apparatus partitioned by an anion exchange membrane and a cation exchange membrane, and filled with an ion exchanger in the compartment, and at least a strong acid in contact with the cation exchange membrane and the anion exchange membrane. An electric desalination apparatus for urea removal characterized by the ion exchanger structure of the desalting chamber in which the cationic cation exchanger layer is formed. (2) The cation exchanger constituting the cation exchanger layer is obtained by a radiation graft polymerization method. Electric demineralizer for urea removal according to (1), wherein a sulfonic acid group is introduced (3) The base material employed in the radiation graft polymerization method is a single fiber, a twisted yarn that is an aggregate of fibers, Electric demineralization apparatus (4) (1), (2) for removing urea as described in (1) and (2), which is a porous polymer material such as woven fabric, nonwoven fabric and cut fiber, net, sponge, etc. (3) Cation exchanger layer as described The layer containing an anion exchanger described in the electric desalting apparatus for removing urea (5) and (4) in which an ion exchanger layer containing at least an anion exchanger is formed upstream is an anion exchanger alone, an anion exchanger and a cation Electric demineralization apparatus for removing urea as described in (6) (1), (2), (3), (4) and (5), comprising a mixed layer or laminate of exchangers Pure water production method for obtaining a liquid with reduced urea concentration by passing water through the apparatus (7) Primary desalination process selected from solid-liquid separation device, reverse osmosis device, ion exchange resin tower or electric desalination device (1), (2), (3), (4), (5) and (6) described in the present invention The electric demineralizer for removing urea according to the present invention is disposed. Pure water with reduced TOC Production method

  The inventors have been working on the development of air cleaning filters by radiation graft polymerization for many years. Among these developments were the theme of tobacco odor removal and the development of formaldehyde removal materials that cause sick house syndrome. In the former theme, the three components ammonia, acetic acid, and acetaldehyde must be removed simultaneously. There was an urgent need to develop a filter that could efficiently remove aldehydes common to both.

It is well known that aldehydes react with amines (especially primary and secondary amines). Urea has _two primary amines in the molecule as represented by the chemical structural formula CO (NH ₂ ) ₂ and adsorbs aldehydes. Therefore, it is expected that the material carrying urea is an aldehyde removing material. Since urea is a neutral molecule, it was thought that it was difficult to support it on various substrates. However, in an experiment in which urea was impregnated and supported on a material into which an ion exchange group or a hydrophilic group was introduced, a cation exchanger was used. The knowledge that it is very easy to carry was obtained.

  Therefore, because urea in water can be adsorbed with a strong acidic cation exchanger, and ionic components in water can be removed with an electric desalting device, the adsorbed urea has excellent adsorption performance in the desalting chamber of the electric desalting device. The present invention was reached on the assumption that urea could be removed by filling a cation exchanger that can be easily moved.

  As a cation exchanger filled in the desalination chamber partitioned by the cation exchange membrane and anion exchange membrane of the electric desalination apparatus, it has excellent urea adsorption performance and the cation exchange path to the cation exchange membrane is continuous. Various materials are available that meet certain requirements. A desalting chamber structure filled with a commercially available cation exchange resin alone can be used. In the case of a cation exchange fiber, the surface area is large and more preferable. A cation exchange fiber produced by a radiation graft polymerization method is more preferred.

  As the shape of the fiber, a single fiber, a non-woven fabric or a woven fabric which is an aggregate of fibers, a fiber obtained by cutting them can be suitably used. In the radiation graft polymerization method, since the shape of the substrate can be freely selected, a porous material such as a sponge can be selected in addition to the fibers. A net inserted as a spacer can also be selected.

  The radiation graft polymerization method is a method of irradiating a substrate with ionizing radiation such as γ-rays or electron beams and utilizing a radical generated on the surface of the substrate or inside the substrate (hereinafter referred to as “monomer”). Is a method of growing a graft chain from a substrate. Since the graft chain is firmly bonded by a covalent bond, there is little eluate, and it is optimal for use in the production of pure water or ultrapure water, which is an application of the present invention.

  A characteristic of the radiation graft polymerization method is that radicals can be easily generated not only on the surface of the substrate but also inside the substrate by irradiation with radiation. Therefore, since the monomer can be polymerized not only on the substrate surface but also inside the substrate, the number of graft chains introduced into the substrate increases, and thus the number of functional groups introduced into the substrate also increases. .

  Graft means “grafting” and represents a state where one end of the graft chain is fixed to the base material and the other end is a free end that is not fixed. Since the graft chains have such morphological characteristics, small ions to large molecules can easily enter between the graft chains. This is a feature that is greatly different from that of an ion exchange resin having a crosslinked structure.

  The radiation graft polymerization method will be described in more detail. First, the fiber material to be grafted is irradiated with radiation. Although there is no limitation on irradiation conditions, in order to obtain sufficient graft efficiency, 5 to 200 kGy, particularly 30 to 100 kGy is preferable in a deoxygenated state. The oxygen concentration may be a concentration at which graft polymerization can be achieved at a required polymerization rate, and is preferably 1% or less, more preferably 100 ppm or less. Examples of radiation that can be suitably used for the purpose of the present invention include, but are not limited to, α rays, β rays, γ rays, electron beams, and ultraviolet rays. Industrially, γ rays or electron beams are suitable.

  Examples of the fiber material useful as a base material for the radioactive material collection material of the present invention include synthetic fibers, cellulose fibers such as cotton, animal fibers, mineral fibers, regenerated fibers, or mixed fibers thereof. . Synthetic fibers include polyester, polyamide, acrylic, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polyurethane, polyvinyl alcohol, fluorine, and the like. Cellulosic fibers include natural cellulose fibers such as cotton and hemp, viscose rayon, copper ammonia rayon, regenerated cellulose fibers such as polynosic, purified cellulose fibers such as tencel, and semi-synthetic fibers such as acetate and diacetate. It is. Among these, a material with less eluate can be selected as appropriate according to the application. Polyolefin-based materials such as polyethylene-based and polypropylene-based materials are easy to use for graft polymerization in terms of radical preservation.

  The next step is a graft polymerization step. Here, the graft polymerization is divided into a pre-irradiation graft polymerization method and a simultaneous irradiation graft polymerization method according to the timing of irradiation, and the present invention can employ either irradiation method. The pre-irradiation graft polymerization method is a polymerization method in which a substrate is irradiated with radiation in advance and then contacted with a monomer. The simultaneous irradiation graft polymerization method is a graft polymerization method in which radiation is irradiated in the presence of a substrate and a monomer. In the present invention, it is possible to use both the pre-irradiation graft polymerization method and the simultaneous irradiation graft polymerization method. However, since the pre-irradiation graft polymerization method generates a small amount of homopolymer, the pure irradiation which is an application of the present invention is used. It is suitable for the manufacturing method of the separation material used in the water manufacturing field.

  Depending on whether the monomer to be contacted is liquid or gas, it is divided into a liquid phase graft polymerization method and a gas phase graft polymerization method, respectively. In the present invention, any of the graft polymerization methods of liquid phase or gas phase graft polymerization can be used. Further, there is an impregnation polymerization method as a graft polymerization method located between the liquid phase and the gas phase graft polymerization method. This method is a graft polymerization method in which the amount of monomer is controlled so as to obtain a predetermined graft ratio in advance and the substrate is immersed in the base material. The present invention can also be used for this graft polymerization method.

  Examples of the polymerizable vinyl monomer that can be introduced into the fiber by the radiation graft polymerization method of the present invention include a polymerizable vinyl monomer having various functional functional groups, or a secondary reaction after grafting the polymerizable vinyl monomer. A polymerizable vinyl monomer which can introduce a functional functional group by performing can be used.

  In addition to a monomer having a cation exchange group or a chelate group, a monomer that can be converted into an ion exchange group or a chelate group by performing a secondary reaction can be suitably used. Examples of the monomer having a cation exchange group include acrylic acid, methacrylic acid, styrene sulfonic acid, vinyl sulfonic acid, methacryl sulfonic acid, allyl sulfonic acid, and alkali metal salts thereof. Examples of the chelate group having a cation exchange group include an iminodiacetic acid group.

  Monomers that can be converted into ion exchange groups or chelate groups by performing a secondary reaction include acrylonitrile, acrolein, vinylpyridine, styrene, chloromethylstyrene, glycidyl methacrylate, glycidyl acrylate, and derivatives thereof. In the case of glycidyl methacrylate, various functional groups such as a sulfonic acid group and a carboxyl group as well as a chelating group such as an iminodiacetic acid group can be easily introduced. In addition, styrene and chloromethylstyrene can be easily used because ion exchange groups and chelate groups can be easily introduced.

  Crosslinking agents such as divinylbenzene, triallyl isocyanate and ethylene glycol dimethacrylate, which are crosslinking agents, can also be used.

  The amount of the cation exchange group introduced into the fiber can be arbitrarily determined depending on the graft ratio. When the graft ratio is large, the physical strength becomes small.

  When styrene is graft-polymerized, it can be sulfonated using sulfuric acid or chlorosulfonic acid. When glycidyl methacrylate is graft polymerized, sulfonation can be performed using an aqueous sodium sulfite solution and an appropriate solvent. An ion exchange capacity of about 2 meq / g can be easily obtained.

  The ion exchanger filling structure of the desalting chamber in the electric desalination apparatus of the present invention may be a packed bed filled with a cation exchanger alone as shown in FIG. 1, but is filled with a cation exchanger alone as shown in FIG. An anion exchanger or a mixed packed bed of anions and cation exchangers may exist upstream of the packed bed. By disposing these ion exchanger packed beds upstream, the ion components in the water are almost removed. For this reason, the sulfonic acid group of the cation exchanger layer is maintained in the H-type convenient for urea adsorption.

  The ion exchanger packing structure in the desalting chamber is formed of a cation exchanger alone, an anion exchanger layer, an anion / cation exchanger mixed layer, and a cation / anion exchanger multilayer upstream of the packed bed of the cation exchanger alone. Also good. In addition, as shown in FIG. 3, when water is passed through a series of compartments of an electrical desalting apparatus or when a plurality of electrical desalting apparatuses are used, as long as the above technical idea is maintained, any ion exchange can be performed. Body filling structures can also be used.

  By passing water containing urea through the electric desalting apparatus of the present invention, water having a reduced urea concentration can be obtained. Then, as shown in the basic flow diagram of pure water production in FIG. 4, a solid-liquid separation device and a reverse osmosis membrane device are arranged in the previous stage, and the TOC is produced by the pure water production apparatus comprising the electric desalination apparatus of the present invention in the subsequent stage. Can be obtained.

  Urea in water is low in molecular weight and nonionic, so it is difficult to remove it by coagulation sedimentation, reverse osmosis and ion exchange equipment. In order to remove this, measures such as installing a biological treatment apparatus and an oxidative decomposition apparatus have been considered, but the apparatus has become complicated and has led to an increase in cost. The present invention can reduce the urea concentration only by making a slight change to the electric desalination apparatus incorporated in the existing pure water production apparatus, and it meets the social demands of resource saving and energy saving. Contributing to industrial development is extremely important.

Basic configuration diagram of an electrical desalination system packed solely with a cation exchanger Desalination chamber structure with a mixed layer of cation and anion exchanger upstream of the cation exchanger Example of passing water through multiple desalination chambers in series Basic flow diagram of general pure water production

  Examples of the present invention will be described below. However, the examples of the present invention are shown, and the scope of the claims of the present invention is not limited.

(1) Production of Strong Acid Cation Exchange Fiber A 1 kg of 6-nylon fiber twisted yarn having a diameter of about 25 μm was put in a polyethylene bag, and the nitrogen substitution operation of evacuation and introduction of nitrogen gas was repeated three times. This bag was put in a foamed polystyrene box together with 5 kg of dry ice and irradiated with gamma rays of 50 kGy under cooling. The irradiated nylon fiber was taken out and placed in a glass ampoule for graft polymerization. A 10% methanol solution of glycidyl methacrylate that had been deoxygenated in advance by bubbling with nitrogen gas was introduced into a glass ampoule. Then, graft polymerization was performed in a constant temperature water bath at 40 ° C. for 5 hours. The fiber after completion of polymerization was immersed in acetone and washed for 1 hour. This operation was repeated twice. The washed fiber was vacuum dried and the weight increase rate was measured to obtain a graft rate of 86%. Further, this fiber was immersed in a solution of 10% sodium sulfite, 10% isopropyl alcohol and 80% water, and subjected to sulfonation reaction at 80 ° C. for 8 hours.

  After collecting 0.5 g of this fiber, it was regenerated by dipping in 100 ml of 1N hydrochloric acid. The PH test paper was washed with pure water until it showed no acidity. Next, it was immersed in 100 ml of 3% aqueous solution of sodium chloride for 30 minutes and stirred. A portion of the acidified solution was titrated with a 1N aqueous sodium hydroxide solution to determine the neutral salt decomposition capacity. As a result, a strongly acidic cation exchange fiber of 1.94 meq / g was obtained.

(2) Urea removal test An experimental electrodialysis apparatus having a desalting chamber partitioned by a vertical and horizontal cation exchange membrane of 50 mm and a thickness of 5 mm and an anion exchange membrane was used. About 2 g of the above-mentioned strongly acidic cation exchange fiber was uniformly filled in this desalting chamber. Urea was added to laboratory pure water (electric conductivity 0.5 μS / cm, TOC 15 ppb) to prepare urea-containing pure water having a TOC concentration of 160 ppb. A 15 V, 0.2 A direct current was applied to the electrodialyzer, and the previous synthetic raw water was passed through at 0.5 L / h. When the TOC concentration of the treated water was measured after 1 hour, it showed a low value of about 35 ppb and showed a stable TOC concentration continuously. It was clear from the removal performance of the TOC concentration that urea was removed.

(1) Production of Strong Acid Cation Exchange Fiber A nonwoven fabric having a basis weight of 80 g / m ² and a thickness of about 1 mm made of a core / sheath (polyethylene terephthalate / polyethylene) composite fiber having a diameter of about 15 μm was cut. Five large A4 sheets were put in a polyethylene bag, and glycidyl methacrylate was graft polymerized in the same manner as in Example 1 to obtain a graft ratio of 116%. Further, this fiber was immersed in a solution of 10% sodium sulfite, 10% isopropyl alcohol and 80% water, and subjected to sulfonation reaction at 80 ° C. for 8 hours.

  A sample of 5 cm × 10 cm was taken from this nonwoven fabric and then regenerated by dipping in 100 ml of 1N hydrochloric acid. The PH test paper was washed with pure water until it showed no acidity. Next, it was immersed in 100 ml of 3% aqueous solution of sodium chloride for 30 minutes and stirred. A portion of the acidified solution was titrated with a 1N aqueous sodium hydroxide solution to determine the neutral salt decomposition capacity. As a result, a strongly acidic cation exchange nonwoven fabric of 2.33 meq / g was obtained.

(2) Urea removal test Using the experimental electrodialysis apparatus of Example 1, the same urea removal test was conducted. At this time, the strongly acidic cation exchange nonwoven fabric was cut into 5 mm × 50 mm, and 40 sheets were laminated and filled in the desalting chamber. The thickness of the non-woven fabric after introduction of the sulfonic acid group was about 1.5 mm, an increase of 50% compared to the thickness of the base material, but the portion that protruded from the desalting chamber was pushed in by hand. When the same synthetic raw water was passed under the same conditions, the TOC concentration was about 30 ppb, and urea was clearly removed.

DESCRIPTION OF SYMBOLS 1 Anode 2 Concentration chamber 3 Anion exchange membrane 4 Desalination chamber 5 Cation exchange membrane 6 Cathode 7 Cation exchanger 8 Cation and anion exchanger mixed packing layer 9 Water flow path to be treated 10 Coagulation sedimentation 11 Sand filtration 12 Reverse osmosis 13 Electric type Desalination equipment

Claims (7)

  In an electric desalination apparatus that is partitioned by an anion exchange membrane and a cation exchange membrane, and the compartment is filled with an ion exchanger, at least the strongly acidic cation exchanger layer is in contact with the cation exchange membrane and the anion exchange membrane. Electric desalination apparatus having a structure for filling a formed desalting chamber ion exchanger   2. The electric desalting apparatus according to claim 1, wherein the cation exchanger constituting the cation exchanger layer is one in which a sulfonic acid group is introduced by a radiation graft polymerization method.   The base materials employed in the radiation graft polymerization method are single fibers, twisted fibers that are aggregates of fibers, woven fabrics, nonwoven fabrics, cut fibers, and porous polymer materials such as sponges. Electric desalination equipment   An electric desalination apparatus in which an ion exchanger layer containing at least an anion exchanger is formed upstream of the cation exchanger layer according to claim 1, 2 and 3.   5. An electric desalting apparatus comprising a layer containing an anion exchanger according to claim 4, comprising an anion exchanger alone, a mixed layer or a laminate of an anion exchanger and a cation exchanger.   A pure water production method for obtaining a liquid having reduced urea concentration by passing water through the electric desalting apparatus according to claim 1, 2, 3, 4 and 5.   A method for producing pure water with reduced TOC, in which the electrical desalting apparatus of the present invention is arranged downstream of a primary desalting apparatus selected from a solid-liquid separator, reverse osmosis, ion exchange resin tower or electrodialysis apparatus

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