JPWO2012114953A1 - Reverse osmosis membrane scale inhibitor and scale prevention method - Google Patents

Abstract

Without increasing the concentration of phosphorus in the wastewater, it is possible to prevent the adhesion of calcium carbonate scale generated in osmotic membrane treatment, and to prevent the formation of fine precipitates such as gelled products, and scale inhibitors for osmotic membranes and scale prevention Provide a method. A scale inhibitor containing a phosphorus-free maleic acid water-soluble polymer having a weight average molecular weight of 1.2 × 103 to 1.8 × 103 and containing 50 mol% or more of maleic acid units as a main component in a reverse osmosis membrane treated water system Add. In this case, as the water-soluble polymer, for example, polymaleic acid, a copolymer of maleic acid and isobutylene, or a terpolymer of maleic acid, ethyl acrylate and vinyl acetate is used.

Description

  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.

  In cooling water systems, boiler water systems, membrane treatment, or reduction wells of geothermal power plants, scale obstacles occur on heat transfer surfaces, piping, or membrane surfaces that come into contact with water. In particular, when highly concentrated operation is performed from the viewpoint of saving resources and energy, and when the recovery rate is increased in the case of membranes, the salt dissolved in water is concentrated to form a sparingly soluble salt. Turn into.

  For example, the scale generated in the heat exchange section causes heat transfer inhibition, the scale attached to the pipe causes a decrease in flow rate, and the scale attached to the film causes a decrease in flux. Further, if 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.

  Examples of 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.

  In general, for calcium-based scales, 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 If necessary, 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.

  On the other hand, 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. In addition, 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.

  However, in recent years, with the regulation of phosphorus concentration in wastewater, scale inhibitors that do not contain phosphorus are desired. Thus, conventionally, calcium carbonate scale inhibitors that do not contain phosphorus have been studied (for example, see Patent Documents 1 to 7). For example, in the method described in Patent Document 1, a copolymer of maleic acid and allyl sulfonic acid is used as a scale inhibitor.

  In addition, in the method described in Patent Document 2, 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.

  On the other hand, in the treatment method described in Patent Document 4, a terpolymer of maleic acid, ethylene acrylate, and styrene having a mass average molecular weight of 600 to 10,000 is used as a scale inhibitor. In the aqueous treatment composition described in Patent Document 5, a polymaleic acid having a mass average molecular weight of 400 to 800 and an acrylic copolymer having a molecular weight of 800 to 9500 are used in combination.

  Furthermore, Patent Document 6 proposes a scale inhibitor using a specific carboxyl group-containing water-soluble copolymer. Furthermore, Patent Document 7 discloses that the number average molecular weight obtained by aqueous 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 Application Laid-Open No. 01-063098 Japanese Patent Laid-Open No. 02-059099 JP 02-115384 A (Patent No. 2942991) Japanese Patent Laid-Open No. 04-222697 (Patent No. 3196031) JP-T-09-504043 (Patent No. 3571343) JP 2001-252692 A

  However, the conventional techniques described above have the following problems. That is, conventional scale inhibitors as described in Patent Documents 1 to 7 have been reported as materials having a relatively high scale prevention effect in various systems such as cooling water and evaporative concentration. It is hard to say that it is suitable for use.

  For example, scales generated in cooling water, evaporative concentration, boilers, etc. adhere to a surface of a heat exchanger or the like with a certain thickness, thereby causing heat transfer inhibition or affecting the stabilization of equipment. On the other hand, in a cooling water system or the like, the scale attached to the surface acts as an anticorrosion coating, and therefore some scale generation is allowed. For this reason, 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. . Further, in a cooling water system or the like, the range of physical properties (molecular weight, composition, etc.) applicable as a scale inhibitor is wide.

  On the other hand, 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. . For this reason, 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.

  Furthermore, the RO membrane treatment has a lower temperature at a location where scale should be prevented, a shorter water residence time, and generally a lower concentration of the scale inhibitor compared to a cooling water system or the like. Specifically, the temperature at the place where scale should be prevented is about 10 to 40 ° C. for RO membrane treatment, whereas it is 50 to 90 ° C. for a cooling water system or the like. Moreover, the residence time of water is about 20 to 100 hours in the cooling water system or the like while the RO membrane treatment is about 15 minutes. Furthermore, the addition concentration of the scale inhibitor is about 1 to 10 mg / L for RO membrane treatment, whereas it is about 5 to 50 mg / L for a cooling water system or the like.

  Thus, since 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.

  Therefore, 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. It is difficult to produce fine precipitates.
The “mass average molecular weight” in the present invention is a value measured by gel permeation chromatography using sodium polyacrylate as a standard substance.
In this scale inhibitor, the maleic acid unit of the water-soluble polymer may be 60 mol% or more.
Further, as 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.

According to the reverse osmosis membrane scale prevention method of the present invention, a phosphorus-free maleic acid water-soluble polymer having a weight average molecular weight of 1.2 × 10 ^{3 to} 1.8 × 10 ³ and having a maleic acid unit of 50 mol% or more is used. A scale inhibitor as a main component is added to the reverse osmosis membrane treated water system.
In the present invention, 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.
In this scale prevention method, the water-soluble polymer that is the main component of the scale inhibitor may have a maleic acid unit of 60 mol% or more.

  According to the present invention, since 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.

It is a figure which shows the result of the flat film test of the scale inhibitor of the Example of this invention. It is a figure which shows the result of the flat film test of the scale inhibitor of the comparative example of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

(First embodiment)
First, the scale inhibitor according to the first embodiment of the present invention will be described. 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. Here, 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.

In the scale inhibitor of the present embodiment, 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.

  In general, since the water-soluble polymer is easily gelled as the molecular weight increases, the gelation resistance can be improved by reducing the molecular weight. On the other hand, in order to obtain 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.

Specifically, 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. Moreover, when 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.

  For these reasons, the scale inhibitor described in Patent Document 7 using a copolymer having a number average molecular weight of 400 to 1000 is a fine precipitate such as a gelled substance even in an environment where the cation concentration is low. Is easy to generate.

On the other hand, if 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. Specifically, 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. In this case, 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 a straight chain (including branched ones) having 3 to 8 carbon atoms or a cyclic one. Specific examples thereof include isobutylene and styrene. There is. As the alkyl ester of monoethylenically unsaturated acid, those 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.

  As the vinyl ester of monoethylenically unsaturated acid, one having 1 to 8 carbon atoms can be used, and specific examples thereof include vinyl acetate and vinyl propionate. As the substituted acrylamide, those having 1 to 4 carbon atoms can be used, and specific examples thereof include acrylamide, propylacrylamide, N-isopropylacrylamide, dimethylacrylamide, and diethylacrylamide.

  In addition, although acrylic acid is easy to superpose | polymerize compared with maleic acid, it is difficult to control to low molecular weight. On the other hand, as a method for improving the gelation resistance, there is a method of copolymerizing with sulfonic acid. However, when copolymerized 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.

  On the other hand, maleic acid has a larger 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.

  Further, 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. In the case of this polymerization method, 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. For example, 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.

  On the other hand, in the case of aqueous polymerization, for example, an aqueous monomer solution or aqueous dispersion is prepared, 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. Examples of the water-soluble polymerization initiator used here 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.

  In addition, the polymerization conditions in that case are not particularly limited. For example, after polymerization for 2 to 6 hours, the polymer aqueous solution or the aqueous dispersion can be obtained by cooling. 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.

  In addition to the above-described maleic acid water-soluble polymer, 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 | blended. In this case, examples of 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.

As described above in detail, the scale inhibitor of the present embodiment is mainly composed of a maleic acid water-soluble polymer that does not contain phosphorus, so that the calcium carbonate scale is deposited without increasing the phosphorus concentration in the waste water. Can be suppressed. Moreover, since this water-soluble polymer has a molecular weight of 1.2 × 10 ^{3 to} 1.8 × 10 ^3, it is difficult to produce fine precipitates such as gelled products. Furthermore, 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. In addition, there is no restriction | limiting in particular in the water quality condition in the case of applying the scale inhibitor of this embodiment, and the operating condition of water system.

(Second Embodiment)
Next, a scale prevention method according to the second embodiment of the present invention will be described. 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 this 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.

  In the scale prevention method of the present embodiment, the addition method of the scale inhibitor is not particularly limited, and may be added at a place where it is desired to prevent the scale from being attached or immediately before that. Further, the amount of addition is not particularly limited and can be appropriately selected according to the water quality of the aqueous system, but 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.

  Moreover, the scale prevention method of this embodiment can also use together the scale inhibitor of 1st Embodiment mentioned above, and another scale inhibitor. Examples of 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, methallyloxybenzenesulfonic acid, and metal salts thereof.

  Examples of the nonionic group-containing monomer include alkylamides 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 1-30 monovinyl ether ethylene / propylene oxide.

  Thus, in 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.

  In addition, the water quality conditions and operation conditions of the water system to which the scale prevention method of this embodiment is applied are not particularly limited. In addition, 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.

  Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention. In this example, the performance of the scale inhibitors of Examples 1 to 7 within the scope of the present invention and the scale inhibitors of Comparative Examples 1 to 9 deviating from the scope of the present invention was evaluated by the method described below. .

<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.

Next, an 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.

  The results are shown in FIGS. 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 | medical agent is not added.

<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. Further, 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 μm.

(2) Gelation performance test Into a 500 ml conical beaker, 500 ml of ultrapure water: 500 ml is added, and after adding borate buffer (Buffer), scale inhibitor and calcium chloride, sodium hydroxide aqueous solution or sulfuric acid aqueous solution The pH was adjusted to 8.5 to prepare a test solution. Then, the beaker was sealed and left in a constant temperature bath at 90 ° C. for 1 hour. Thereafter, the absorbance at a wavelength of 380 nm was measured using a 50 mm cell. And the calcium hardness which changes a calcium hardness and a light absorbency increases rapidly was made into the gel point.

  The results of these desktop tests are summarized in Table 1 and Table 2 below. In addition, in the following Table 1 and Table 2, the detail of the scale inhibitor of Examples 1-7 and Comparative Examples 1-9 is also shown collectively. 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.

  As shown in FIG. 1, in the blank to which no chemical was added, a decrease in flex was observed, but in the case where the scale inhibitors of Examples 1 to 7 were added, no decrease in flex was observed. Thereby, in the system which added the scale inhibitor of Examples 1-7, precipitation of a scale was suppressed and it turned out that the stable film | membrane process is possible. Moreover, as shown in the said Table 1, the scale inhibitor of Examples 1-7 was high in the carbonate carbonate precipitation inhibitory effect also in the desk test, and was excellent also in the gelation ability.

  On the other hand, as shown in FIG. 2, in the system using the scale inhibitors of Comparative Examples 1 to 9, a decrease in flux was observed. The rate of decrease was in the order of Examples 1 to 7 <Comparative Example 6 <Comparative Example 7 <Comparative Examples 5, 8, 9 <Comparative Examples 1, 3 and Blank <Comparative Examples 2 and 4. Moreover, as shown in the said Table 2, in the desk test, although the scale inhibitor of the comparative example 6 is inferior to the scale inhibitor of Examples 1-7, the scale inhibitor of Comparative Examples 1-5, 7-9 In comparison with, the calcium carbonate precipitation inhibitory effect and gelation resistance were high.

  Although the scale inhibitors of Comparative Examples 1 to 4 and 7 were able to maintain the calcium concentration of the filtrate in the precipitation suppression test, it was considered that the gelation product was generated and the flux was reduced because the gelation resistance was low. It is done. In addition, the scale inhibitors of Comparative Examples 5, 8, and 9 were excellent in gelation resistance performance, but in the precipitation suppression test, the calcium concentration of the filtrate could not be maintained, so that calcium carbonate precipitated and the flux increased. It is thought that it decreased.

  Here, when the scale inhibitor of Example 2 using a copolymer of maleic acid and isobutylene was compared with the scale inhibitor of Comparative Example 5, the scale inhibitor of Comparative Example 5 had less than 50 mol% of maleic acid units. Compared to the scale inhibitor of Example 2, the number of carboxyl groups having calcium carbonate precipitation inhibiting ability is small. For this reason, even if the scale inhibitor of Comparative Example 5 has the same gel point as the scale inhibitor of Example 2, precipitation of calcium carbonate could not be sufficiently suppressed and the membrane could not be operated stably. it is conceivable that.

That is, 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. In addition, 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 smaller 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. Furthermore, since the scale inhibitors of Examples 1 to 7 contained 50 mol% or more of the maleic acid unit of the phosphorus-free maleic acid water-soluble polymer, they were excellent in calcium carbonate precipitation inhibiting ability.

  From the above results, according to the present invention, without increasing the phosphorus concentration in the wastewater, it is possible to suppress the precipitation of calcium carbonate scale generated in the osmotic membrane treatment without adding at a high concentration, and It was confirmed that a scale inhibitor for osmotic membranes in which fine precipitates such as gelled products are not generated can be realized.

Claims (7)

A scale inhibitor that suppresses the precipitation of calcium carbonate scale in reverse osmosis membrane treatment,
A scale inhibitor for reverse osmosis membranes, wherein the main component is 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 maleic acid units of 50 mol% or more.   The scale inhibitor for reverse osmosis membrane according to claim 1, wherein the water-soluble polymer contains 60 mol% or more of maleic acid units.   The scale inhibitor for reverse osmosis membrane according to claim 1 or 2, wherein the water-soluble polymer is polymaleic acid.   The scale inhibitor for reverse osmosis membrane according to claim 1 or 2, wherein the water-soluble polymer is a copolymer of maleic acid and isobutylene.   The scale inhibitor for reverse osmosis membrane according to claim 1 or 2, wherein the water-soluble polymer is a terpolymer of maleic acid, ethyl acrylate, and vinyl acetate. Reverse osmosis membrane treatment with a scale inhibitor mainly composed of 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 maleic acid units of 50 mol% or more A scale prevention method added to water systems.   The method for preventing scale according to claim 6, wherein the water-soluble polymer as a main component of the scale inhibitor has a maleic acid unit of 60 mol% or more.

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