WO2012114953A1 - 逆浸透膜用スケール防止剤及びスケール防止方法 - Google Patents
逆浸透膜用スケール防止剤及びスケール防止方法 Download PDFInfo
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- WO2012114953A1 WO2012114953A1 PCT/JP2012/053490 JP2012053490W WO2012114953A1 WO 2012114953 A1 WO2012114953 A1 WO 2012114953A1 JP 2012053490 W JP2012053490 W JP 2012053490W WO 2012114953 A1 WO2012114953 A1 WO 2012114953A1
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- maleic acid
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/025—Reverse osmosis; Hyperfiltration
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/04—Feed pretreatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
- B01D65/08—Prevention of membrane fouling or of concentration polarisation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2311/00—Details relating to membrane separation process operations and control
- B01D2311/04—Specific process operations in the feed stream; Feed pretreatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2311/00—Details relating to membrane separation process operations and control
- B01D2311/12—Addition of chemical agents
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/16—Use of chemical agents
- B01D2321/168—Use of other chemical agents
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2303/00—Specific treatment goals
- C02F2303/22—Eliminating or preventing deposits, scale removal, scale prevention
Definitions
- the present invention relates to a scale inhibitor for reverse osmosis membranes and a scale prevention method. More specifically, the present invention relates to a scale inhibitor and a scale prevention method for preventing the adhesion of calcium carbonate scale generated in film treatment.
- the scale generated in the heat exchange section causes heat transfer inhibition
- the scale attached to the pipe causes a decrease in flow rate
- the scale attached to the film causes a decrease in flux.
- the generated scale is peeled off, it circulates in the system and causes the pump, the piping and the heat exchanging section to be blocked. Further, along with the blockage, the scaling in the pipe and the heat exchanging section is promoted.
- a similar phenomenon can occur in the reduction well of a geothermal power plant.
- Scale species generated in these aqueous systems include calcium carbonate, calcium sulfate, calcium sulfite, calcium phosphate, calcium silicate, magnesium silicate, magnesium hydroxide, zinc phosphate, zinc hydroxide, and basic zinc carbonate.
- inorganic polyphosphoric acids such as sodium hexametaphosphate and sodium tripolyphosphate
- phosphonic acids such as hydroxyethylidene diphosphonic acid and phosphonobutanetricarboxylic acid
- maleic acid acrylic acid and itaconic acid
- vinyl monomers having sulfonic acid groups such as vinyl sulfonic acid, allyl sulfonic acid and 3-allyloxy-2-hydroxypropane sulfonic acid, and nonionic vinyl monomers such as acrylamide are included
- Copolymers combined according to water quality are used as scale inhibitors.
- examples of the scale species generated in the reverse osmosis membrane (RO membrane) treatment include calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, calcium phosphate, and magnesium hydroxide.
- the scale inhibitor generally has a relatively low molecular weight and a high scale prevention effect. Therefore, inorganic polyphosphates such as sodium hexametaphosphate and sodium tripolyphosphate, aminomethylphosphonic acid, hydroxyethylidene diphosphonic acid and phosphonobu Materials containing phosphorus such as phosphonic acids such as tantricarboxylic acid are used.
- the scale inhibitor includes a copolymer produced from an unsaturated carboxylic acid and an unsaturated sulfonic acid, and an unsaturated compound having an unsaturated carboxylic acid and a polyalkylene oxide side chain. Copolymers to be produced are used in combination. Furthermore, in the method described in Patent Document 3, a polymer of an ethylenically unsaturated dibasic carboxylic acid and a quaternary dialkyl diallylammonium monomer is used as a scale inhibitor.
- Patent Document 6 proposes a scale inhibitor using a specific carboxyl group-containing water-soluble copolymer.
- Patent Document 7 discloses that a number average molecular weight obtained by aqueous solution polymerization of at least one monomer selected from maleic acid, maleic anhydride, fumaric acid and itaconic acid and other water-soluble monomers is 400 to 400%. Scale inhibitors containing 1000 copolymers have been proposed.
- Japanese Patent Laid-Open No. 02-075396 Japanese Patent Laid-Open No. 01-063098 Japanese Patent Laid-Open No. 02-059099 Japanese Patent Laid-Open No. 02-115384 (Patent No. 2942991) Japanese Patent Laid-Open No. 04-222697 (Japanese Patent No. 3196031) JP-T-09-504043 (Patent No. 3571343) JP 2001-252692 A
- scales generated in cooling water, evaporative concentration, boilers, etc. adhere to the surface of a heat exchanger or the like with a certain thickness, thereby causing heat transfer inhibition or affecting the stabilization of equipment.
- the scale attached to the surface acts as an anticorrosion coating, and therefore some scale generation is allowed.
- a scale inhibitor such as a cooling water system is required to have the ability to suppress the generated scale growth, and can be applied as long as it has a certain precipitation suppressing effect and gelation resistance.
- the range of physical properties (molecular weight, composition, etc.) applicable as a scale inhibitor is wide.
- RO membrane treatment has a small water flow path, and when fine precipitates such as scales and coexisting ions and scale inhibitor gels are formed, the membrane surface is clogged, affecting membrane treatment performance. .
- the scale inhibitor for RO membrane treatment is required not to generate fine precipitates, and even if it is a material that can be applied in cooling water, evaporative concentration, etc., further limited physical property conditions are required. It is necessary to have.
- the temperature at the location where scale should be prevented is lower, the residence time of water is shorter, and generally the concentration of the scale inhibitor added is lower than in the cooling water system.
- the temperature at the place where scale should be prevented is about 10 to 40 ° C. in the RO membrane treatment, whereas it is 50 to 90 ° C. in the cooling water system or the like.
- the residence time of water is about 15 minutes for the RO membrane treatment, whereas it is about 20 to 100 hours for the cooling water system.
- the concentration of the scale inhibitor added is about 1 to 10 mg / L for the RO membrane treatment, whereas it is about 5 to 50 mg / L for the cooling water system.
- the scale inhibitor for RO membrane treatment is different from the scale inhibitor used in other systems such as cooling water system, the processing conditions and required characteristics are different, the scale inhibitor such as cooling water system is treated with RO membrane treatment. Even if it is used, the same effect cannot be obtained.
- the present invention is for an osmotic membrane that can suppress the precipitation of calcium carbonate scale generated in the osmotic membrane treatment without increasing the phosphorus concentration in the waste water, and does not produce a fine precipitate such as a gelled product.
- the main object is to provide a scale inhibitor and a scale prevention method.
- the scale inhibitor for reverse osmosis membrane according to the present invention is a scale inhibitor that suppresses the precipitation of calcium carbonate scale in reverse osmosis membrane treatment, and the main component has a mass average molecular weight of 1.2 ⁇ 10 3 to 1.8. It is ⁇ 10 3 and is a phosphorus-free maleic acid water-soluble polymer having a maleic acid unit of 50 mol% or more. In the present invention, since the phosphorus-free maleic acid water-soluble polymer is a main component, the phosphorus concentration in the waste water is not increased.
- the main component water-soluble polymer has a mass average molecular weight of 1.2 ⁇ 10 3 to 1.8 ⁇ 10 3 and contains 50 mol% or more of maleic acid units.
- the “mass average molecular weight” in the present invention is a value measured by gel permeation chromatography using sodium polyacrylate as a standard substance.
- the maleic acid unit of the water-soluble polymer may be 60 mol% or more.
- the water-soluble polymer for example, polymaleic acid, a copolymer of maleic acid and isobutylene, and a terpolymer of maleic acid, ethyl acrylate and vinyl acetate can be used.
- the reverse osmosis membrane scale prevention method comprises a phosphorus-free maleic acid water-soluble polymer having a mass average molecular weight of 1.2 ⁇ 10 3 to 1.8 ⁇ 10 3 and having a maleic acid unit of 50 mol% or more.
- a scale inhibitor as a main component is added to the reverse osmosis membrane treated water system.
- a scale inhibitor mainly composed of a phosphorus-free maleic acid water-soluble polymer having a molecular weight within a specific range and having a maleic acid unit of 50 mol% or more is used.
- the phosphorus concentration does not increase, and fine precipitates such as gelled products are not generated.
- the water-soluble polymer that is the main component of the scale inhibitor may have a maleic acid unit of 60 mol% or more.
- the main component of the scale inhibitor is a phosphorus-free maleic acid water-soluble polymer having a molecular weight and a maleic acid content within a specific range, without increasing the phosphorus concentration in the wastewater. Further, precipitation of calcium carbonate scale generated in the osmotic membrane treatment can be suppressed, and further, fine precipitates such as gelled products are not generated.
- the scale inhibitor of the present embodiment suppresses the precipitation of calcium carbonate scale that occurs in the reverse osmosis membrane treatment, and prevents the scale from adhering to the RO membrane and the like.
- It is a maleic acid water-soluble polymer.
- the “maleic acid water-soluble polymer” is a homopolymer of maleic acid or a copolymer of maleic acid and other monomers not containing phosphorus, which is water-soluble.
- a maleic acid water-soluble polymer having a molecular weight of 1.2 ⁇ 10 3 to 1.8 ⁇ 10 3 is used.
- the molecular weight defined here is a mass average molecular weight measured by gel permeation chromatography using sodium polyacrylate as a standard substance, and the same applies to the following description.
- the gelation resistance can be improved by reducing the molecular weight.
- a maleic acid water-soluble polymer having a small molecular weight it is necessary to stop the polymerization by reacting a polymerization initiator or a chain transfer agent with a monomer. For this reason, if the molecular weight of the maleic acid water-soluble polymer is too small, the number of carboxyl groups decreases, and the number of anionic groups exhibiting a dispersion effect decreases, so that gelation tends to occur.
- a maleic acid water-soluble polymer having a molecular weight of less than 1.2 ⁇ 10 3 tends to gel even in an environment where the cation concentration is low because maleic acid units in the polymer are reduced.
- the molecular weight of the maleic acid water-soluble polymer is less than 1.2 ⁇ 10 3 , a polymerization initiator and a chain transfer agent remain in the polymer, but this also reduces the number of carboxyl groups which are anionic groups. It becomes a factor.
- the scale inhibitor described in Patent Document 7 which uses a copolymer having a number average molecular weight of 400 to 1000, includes fine precipitates such as gelled substances even in an environment where the cation concentration is low. Is easy to generate.
- the molecular weight of the maleic acid water-soluble polymer is too large, a plurality of carboxyl groups in the polymer molecule act on one cation, especially a polyvalent cation, and the molecular chain is bent. , Easily gelled.
- a maleic acid water-soluble polymer having a molecular weight exceeding 1.8 ⁇ 10 3 tends to gel even in an environment where the cation concentration is low, and when such a water-soluble polymer is used, minute precipitates are formed. It tends to occur.
- the amount of maleic acid units in the maleic acid water-soluble polymer is 50 to 100 mol%.
- a maleic acid water-soluble polymer having a maleic acid unit of less than 50 mol% is easily gelled because of a small number of carboxyl groups which are anionic groups.
- the amount of maleic acid units in the maleic acid water-soluble polymer is preferably 60 mol% or more, more preferably 75 mol% or more, from the viewpoint of improving the calcium carbonate precipitation suppression effect.
- the maleic acid water-soluble polymer blended in the scale inhibitor of the present embodiment may be a maleic acid homopolymer such as polymaleic acid or a copolymer of maleic acid and another monomer.
- the monomer copolymerized with maleic acid may be a nonionic monomer containing no phosphorus, such as monoethylenically unsaturated hydrocarbons, alkyl esters of monoethylenically unsaturated acids, monoethylenic monomers. Examples include vinyl esters of unsaturated acids and substituted acrylamides.
- the monoethylenically unsaturated hydrocarbon may be linear (including branched) or cyclic having 3 to 8 carbon atoms. Specific examples thereof include isobutylene and styrene. There is.
- As the alkyl ester of monoethylenically unsaturated acid one having 1 to 8 carbon atoms can be used. Specific examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl acrylate, N-butyl. Examples include acrylate and 2-ethylhexyl acrylate.
- vinyl ester of monoethylenically unsaturated acid those having 1 to 8 carbon atoms can be used, and specific examples thereof include vinyl acetate and vinyl propionate.
- Substituted acrylamides having 1 to 4 carbon atoms can be used, and specific examples thereof include acrylamide, propylacrylamide, N-isopropylacrylamide, dimethylacrylamide, and diethylacrylamide.
- Acrylic acid is easier to polymerize than maleic acid, but it is difficult to control it to a low molecular weight.
- a method for improving the gelation resistance there is a method of copolymerizing with sulfonic acid.
- the number of carboxyl groups decreases, and conversely, the ability to suppress precipitation decreases. Therefore, it is difficult for acrylic acid to find physical properties with high performance of both precipitation suppression ability and gelation resistance compared to maleic acid.
- maleic acid has a higher number of carboxyl groups in the monomer than acrylic acid, and exhibits high ability to suppress precipitation even when copolymerized. Further, since maleic acid has a slower polymerization reaction than acrylic acid, the molecular weight can be controlled to be small.
- the method for producing the maleic acid water-soluble polymer described above is not particularly limited, and solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization, and the like can be applied, but polymerization having a maleic acid unit.
- the product is preferably a polymerization method using toluene or xylene.
- a known peroxide initiator can be appropriately selected and used as the initiator. Specifically, dibenzoyl peroxide, tert-butyl perpenzoate, dicumyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxide, and the like can be used.
- the polymerization mode in this case may be either a batch type or a continuous type.
- a maleic acid water-soluble polymer is obtained by heating to a temperature of 100 to 200 ° C., polymerizing for 2 to 6 hours, and then allowing to cool. be able to.
- aqueous polymerization for example, an aqueous monomer solution or aqueous dispersion is prepared, the pH is adjusted as necessary, the atmosphere is replaced with an inert gas, and then heated to 50 to 100 ° C., A water-soluble polymerization initiator may be added.
- water-soluble polymerization initiator examples include 2,2′-azobis (2-amidinopropane) dihydrochloride, azobis-N, N′-dimethyleneisobutylamidine dihydrochloride, and 4,4′- Use azo compounds such as azobis (4-cyanovaleric acid) -2-sodium, persulfates such as ammonium persulfate, sodium persulfate, potassium persulfate, peroxides such as hydrogen peroxide and sodium periodate. Can do.
- the polymerization conditions in that case are not particularly limited. For example, after polymerizing for 2 to 6 hours and then allowing to cool, an aqueous polymer solution or an aqueous dispersion can be obtained.
- the polymerization of the maleic acid water-soluble polymer is not limited to an aqueous medium, and can be performed by solution polymerization, suspension polymerization, emulsion polymerization, or the like in a general organic solvent.
- the scale inhibitor of the present embodiment includes a slime control agent, an enzyme, a disinfectant, a colorant, a fragrance, and a water-soluble organic solvent as long as the object of the present invention is not impaired. And an antifoamer etc. may be mix
- the slime control agent include quaternary ammonium salts such as alkyldimethylbenzylammonium chloride, chloromethyltrithiazoline, chloromethylisothiazoline, methylisothiazoline, ethylaminoisopropylaminomethylthiatriazine, hypochlorous acid, hypochlorous acid, and hypochlorous acid. Bromic acid, a mixture of hypochlorous acid and sulfamic acid, and the like can be used.
- the scale inhibitor of this embodiment is mainly composed of a phosphorus-free maleic acid water-soluble polymer, precipitation of calcium carbonate scale can be achieved without increasing the phosphorus concentration in the waste water. Can be suppressed.
- the water-soluble polymer has a molecular weight of 1.2 ⁇ 10 3 to 1.8 ⁇ 10 3, it is difficult to form a fine precipitate such as a gelled product.
- the scale inhibitor of this embodiment can stably suppress the precipitation of scale with a small amount of addition. For this reason, the scale inhibitor of this embodiment is suitable for reverse osmosis membrane treatment.
- the scale prevention method of the present embodiment is a method for suppressing the precipitation of calcium carbonate scale in the reverse osmosis membrane treatment using the scale inhibitor of the first embodiment described above. That is, the scale prevention method of the present embodiment is mainly composed of a phosphorus-free maleic acid water-soluble polymer having a molecular weight of 1.2 ⁇ 10 3 to 1.8 ⁇ 10 3 and maleic acid units of 50 mol% or more. A scale inhibitor is added to the reverse osmosis membrane treated water system.
- the addition method of the scale inhibitor is not particularly limited, and may be added at a place where scale adhesion is to be prevented or just before the place.
- the amount of addition is not particularly limited and can be appropriately selected according to the water quality of the aqueous system, but it is added so that the concentration of the maleic acid water-soluble polymer is 0.01 to 100 mg / L. In particular, from the viewpoint of prevention of blockage of the membrane surface, it is more preferable to add so as to be 0.1 to 10 mg / L.
- the scale prevention method of this embodiment can also use together the scale inhibitor of 1st Embodiment mentioned above and another scale inhibitor.
- the scale inhibitor used in combination include polyacrylic acid, a copolymer of maleic acid and acrylic acid, a copolymer of maleic acid and sulfonic acid, a copolymer of acrylic acid and sulfonic acid, and an acrylic acid and nonionic group Examples thereof include copolymers of monomers, terpolymers of acrylic acid, sulfonic acid, and nonionic group-containing monomers.
- Examples of the sulfonic acid constituting the copolymer described above include, for example, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, isoprene sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, 2-acrylamido-2-methyl.
- Examples thereof include propanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, -4-sulfobutyl methacrylate, allyloxybenzenesulfonic acid and methallyloxybenzenesulfonic acid, or metal salts thereof.
- Nonionic group-containing monomers include, for example, alkyl amides having 1 to 5 carbon atoms, hydroxyethyl methacrylate, (poly) ethylene / propylene oxide mono (meth) acrylates having 1 to 30 addition moles, and addition moles. Examples thereof include 1 to 30 monovinyl ether ethylene / propylene oxide.
- the scale prevention method of this embodiment since the scale inhibitor mainly composed of a phosphorus-free maleic acid-soluble water-soluble polymer having a molecular weight within a specific range is used, phosphorus in wastewater is used. Without increasing the concentration, precipitation of calcium carbonate scale generated in the osmotic membrane treatment can be suppressed, and fine precipitates such as gelled products are not generated. Moreover, the scale prevention method of this embodiment can suppress the precipitation of scale stably only by adding a small amount of a scale inhibitor to the aqueous system.
- the water quality condition and operation condition of the water system to which the scale prevention method of this embodiment is applied are not particularly limited.
- the configuration and effects other than those described above in the scale prevention method of the present embodiment are the same as those of the first embodiment described above.
- ⁇ Flat membrane test> First, in order to measure the initial performance of the membrane, a 500 mg / L NaCl aqueous solution was passed through a polyamide reverse osmosis membrane (ES20 manufactured by Nitto Denko Corporation) at an operating pressure of 0.75 MPa and a recovery rate of 50%. (Flux) was measured for a predetermined time.
- ES20 polyamide reverse osmosis membrane manufactured by Nitto Denko Corporation
- aqueous solution containing calcium chloride 250 mg CaCO 3 / L, Examples 1 to 7 and Comparative Examples 1 to 9 scale inhibitors (polymers): 1 mg / L, sodium bicarbonate: 250 mg CaCO 3 / L was prepared. Furthermore, the pH was adjusted to 8.5 with a small amount of aqueous sodium hydroxide or sulfuric acid solution to prepare a test solution. Each test solution was passed through a polyamide reverse osmosis membrane (ES20 manufactured by Nitto Denko Corporation) at an operating pressure of 0.75 MPa and a recovery rate of 50%, and flux was measured for a predetermined time.
- ES20 polyamide reverse osmosis membrane
- FIGS. 1 and 2 are graphs showing changes with time in the ratio (flux ratio) to the flux measured with the test solution, where the flux in a 500 mg / L NaCl aqueous solution is 1.
- FIG. Moreover, the blank (Blank) shown in FIG.1 and FIG.2 is a flux ratio when a chemical
- ⁇ Desktop test> (1) Precipitation suppression test Into a 500 ml conical beaker, 500 ml of ultrapure water is added, and an aqueous solution containing calcium chloride: 500 mg CaCO 3 / L, scale inhibitor: 2 mg / L, sodium bicarbonate: 500 mg CaCO 3 / L is prepared. Furthermore, the pH was adjusted to 8.5 with an aqueous sodium hydroxide solution or an aqueous sulfuric acid solution to obtain a test solution. Then, the beaker was sealed and each test solution was stirred for 3 hours in a thermostatic bath at 30 ° C. Thereafter, the calcium hardness of the filtrate was quantified by an EDTA method using a filter paper having a pore diameter of 0.1 ⁇ m.
- Table 1 and Table 2 show details of the scale inhibitors of Examples 1 to 7 and Comparative Examples 1 to 9.
- the monomers shown in Tables 1 and 2 below are MA: maleic acid, IB: isobutylene, VA: vinyl acetate, EA: ethyl acrylate, AA: acrylic acid, and SA: sulfonic acid.
- the scale inhibitor of Example 1 using polymaleic acid the scale inhibitor of Examples 2, 4, 5 and 7 using a copolymer of maleic acid and isobutylene, maleic acid, ethyl acrylate and vinyl acetate.
- the scale inhibitor of Examples 3 and 6 using a polymer was able to suppress the precipitation of calcium carbonate.
- these polymers (polymers) have a molecular weight of 1.2 ⁇ 10 3 to 1.8 ⁇ 10 3 and a high gel point, so that the gelled product is less than the scale inhibitors of Comparative Examples 1 to 4. It was confirmed that it was difficult to produce and the membrane could be operated stably.
- the scale inhibitors of Examples 1 to 7 were excellent in calcium carbonate precipitation inhibiting ability because the maleic acid unit of the phosphorus-free maleic acid water-soluble polymer was 50 mol% or more.
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Abstract
Description
本発明においては、リン非含有マレイン酸水溶性重合物を主成分としているため、排水中のリン濃度を増加させることがない。また、主成分の水溶性重合物は、質量平均分子量が1.2×103~1.8×103であり、かつ、マレイン酸単位を50mol%以上含有しているため、ゲル化物などの微小な析出物を生成しにくい。
なお、本発明における「質量平均分子量」は、ポリアクリル酸ナトリウムを標準物質として用い、ゲル浸透クロマトグラフィにより測定した値である。
このスケール防止剤では、前記水溶性重合物のマレイン酸単位を60mol%以上としてもよい。
また、水溶性重合物として、例えば、ポリマレイン酸、マレイン酸とイソブチレンとのコポリマー、並びにマレイン酸、エチルアクリレート及び酢酸ビニルのターポリマーなどを使用することができる。
本発明においては、分子量が特定の範囲内にあり、マレイン酸単位が50mol%以上のリン非含有のマレイン酸水溶性重合物を主成分とするスケール防止剤を使用しているため、排水中のリン濃度が増加せず、ゲル化物などの微小な析出物も生成しない。
このスケール防止方法では、前記スケール防止剤の主成分である水溶性重合物を、マレイン酸単位が60mol%以上のものにしてもよい。
先ず、本発明の第1の実施形態に係るスケール防止剤について説明する。本実施形態のスケール防止剤は、逆浸透膜処理で発生する炭酸カルシウムスケールの析出を抑制し、RO膜などにスケールが付着することを防止するものであり、その主成分は、リン非含有のマレイン酸水溶性重合物である。ここで、「マレイン酸水溶性重合物」とは、マレイン酸の単独重合体又はマレイン酸とリンを含有しない他の単量体の共重合体で、水溶性のものである。
次に、本発明の第2の実施形態に係るスケール防止方法について説明する。本実施形態のスケール防止方法は、前述した第1の実施形態のスケール防止剤を使用して、逆浸透膜処理において炭酸カルシウムスケールの析出を抑制する方法である。即ち、本実施形態のスケール防止方法は、分子量が1.2×103~1.8×103で、マレイン酸単位が50mol%以上のリン非含有マレイン酸水溶性重合物を主成分とするスケール防止剤を、逆浸透膜処理水系に添加する。
先ず、膜の初期性能を測定するため、500mg/LのNaCl水溶液を、ポリアミド逆浸透膜(日東電工社製 ES20)に、操作圧を0.75MPa、回収率を50%として通水し、フラックス(Flux)を所定時間測定した。
(1)析出抑制試験
500mlのコニカルビーカーに、超純水:500mlを入れ、塩化カルシウム:500mgCaCO3/L、スケール防止剤:2mg/L、炭酸水素ナトリウム:500mgCaCO3/Lを含有する水溶液を調整し、更に、水酸化ナトリウム水溶液又は硫酸水溶液でpHを8.5に調製して試験溶液とした。そして、ビーカーを密栓し、30℃の恒温槽中で、各試験溶液を3時間撹拌した。その後、孔径0.1μmの濾紙を用いて、EDTA法により、濾液のカルシウム硬度を定量した。
500mlのコニカルビーカーに、超純水:500mlを入れ、これにホウ酸塩緩衝液(Buffer)、スケール防止剤及び塩化カルシウムを加えた後、水酸化ナトリウム水溶液又は硫酸水溶液でpHを8.5に調製して試験溶液とした。そして、ビーカーを密栓し、90℃の恒温槽中で、1時間静置した。その後、50mmのセルを使用して、波長380nmの吸光度を測定した。そして、カルシウム硬度を変化させて、急激に吸光度が大きくなるカルシウム硬度を、ゲル化点とした。
Claims (7)
- 逆浸透膜処理において炭酸カルシウムスケールの析出を抑制するスケール防止剤であって、
主成分が、質量平均分子量が1.2×103~1.8×103で、マレイン酸単位が50mol%以上のリン非含有マレイン酸水溶性重合物である逆浸透膜用スケール防止剤。 - 前記水溶性重合物のマレイン酸単位が60mol%以上であることを特徴とする請求項1に記載の逆浸透膜用スケール防止剤。
- 前記水溶性重合物は、ポリマレイン酸であることを特徴とする請求項1又は2に記載の逆浸透膜用スケール防止剤。
- 前記水溶性重合物は、マレイン酸とイソブチレンのコポリマーであることを特徴とする請求項1又は2に記載の逆浸透膜用スケール防止剤。
- 前記水溶性重合物は、マレイン酸と、エチルアクリレートと、酢酸ビニルのターポリマーであることを特徴とする請求項1又は2に記載の逆浸透膜用スケール防止剤。
- 質量平均分子量が1.2×103~1.8×103で、マレイン酸単位が50mol%以上のリン非含有マレイン酸水溶性重合物を主成分とするスケール防止剤を、逆浸透膜処理水系に添加するスケール防止方法。
- 前記スケール防止剤の主成分である水溶性重合物は、マレイン酸単位が60mol%以上であることを特徴とする請求項6に記載のスケール防止方法。
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