JP7732225B2 - Method for adding chemicals to treated water - Google Patents

Description

The present invention relates to a method for adding chemicals to water to be treated, and in particular to a method for adding a carboxylic acid polymer-containing chemical to water to be treated in water treatment equipment.

Heat source equipment such as boilers and open cooling towers require scaling control in the boiler body and cooling system to minimize various problems caused by water used in the boiler and circulating cooling water, and to maintain stable operation. It is also necessary to prevent corrosion and slime formation in each part. Therefore, water quality management of water used in the operation of heat source equipment is essential.

Known methods for water quality control include physical methods such as filtering the water, as well as chemical methods that involve adding chemicals to the water. The chemicals added to water include a variety of agents with different effects depending on the desired water quality control objectives, such as scale inhibitors, pH adjusters, anticorrosive agents, oxygen absorbers, and disinfectants. However, adding these agents individually to water is cumbersome both in terms of the work involved and chemical management. Therefore, composite agents that combine multiple agents have been developed as chemicals to be added to water. For example, Patent Document 1 discloses a composite boiler compound to be added to boiler water, consisting of an aqueous solution containing both sodium polyacrylate as a scale inhibitor and sulfite as an oxygen absorber.

Combining agents, such as the composite boiler compound described in Patent Document 1, are typically kept on hand at the installation site of heat source equipment and added to service water as needed. However, because the complexing agent is an aqueous solution, 70 to 80% by mass of which is water as a solvent, its weight and bulk require laborious transportation to the installation site of the heat source equipment, as well as the need to secure storage space. Quality maintenance and other inventory management are also required. While the issues of weight and bulk can be resolved to some extent by using concentrated complexing agents, such complexing agents can be classified as deleterious or hazardous substances depending on their ingredients, or can have poor storage stability. This requires careful consideration of safety when using and storing the agent, as well as advanced quality control, which places a significant burden on the management at the site of use.

Japanese Unexamined Patent Publication No. 166981/1981

The present invention aims to improve the handleability of chemicals containing carboxylic acid polymers, which are often used as scale inhibitors for water treated in water treatment equipment such as heat source equipment.

The present invention relates to a method for adding a chemical containing a carboxylic acid polymer to water to be treated in a water treatment device. This chemical addition method includes step 1 of preparing a chemical solution containing a carboxylic acid polymer-containing chemical, and step 2 of adding the chemical solution prepared in step 1 to the water to be treated. In step 1, the chemical solution is prepared by dissolving the carboxylic acid polymer-containing chemical in a solvent, freeze-drying or spray-drying the solution, and then redissolving the solid agent in the solvent to prepare the chemical solution.

In the chemical addition method of the present invention, for example, the chemical solution is prepared at the site where it is to be added to the water to be treated.

In another aspect, the present invention relates to a method for producing a solid agent for preparing a chemical solution containing a carboxylic acid polymer to be added to water to be treated in a water treatment device. This production method includes the steps of dissolving a chemical containing a carboxylic acid polymer in a solvent to prepare a solution, and freeze-drying or spray-drying the prepared solution.

In yet another aspect, the present invention relates to a method for producing a chemical solution containing a carboxylic acid polymer to be added to water to be treated in a water treatment device. This method for producing a chemical solution includes a step of dissolving a solid agent for preparing a chemical solution containing a carboxylic acid polymer, produced by the production method of the present invention, in a solvent.

In yet another aspect, the present invention relates to a solid agent for preparing a chemical solution containing a carboxylic acid polymer to be added to water to be treated in a water treatment device. This solid agent contains a carboxylic acid polymer and is sealed together with water in a 133 mL container so that the converted mass of the carboxylic acid polymer is 10 g and the total mass with the water is 100 g. When this solid agent is shaken at 200 times per minute at 25°C using a shaker set to orbit with a diameter of 2 cm to 3 cm, the time for complete dissolution is at least 200 seconds.

The chemical addition method of the present invention involves dissolving a carboxylic acid polymer-containing chemical in a solvent to prepare a solution, freeze-drying or spray-drying the resulting solution, and then redissolving the resulting solid in a solvent to prepare a chemical solution to be added to water being treated in water treatment equipment.This makes it easy to handle the carboxylic acid polymer-containing chemical in terms of transportation, storage, quality control, and handling safety.

The method for producing a solid formulation according to the present invention can produce a solid formulation that can be used to quickly prepare a chemical solution containing a carboxylic acid polymer to be added to water to be treated in water treatment equipment.

The method for producing a chemical solution according to the present invention involves dissolving the solid agent produced by the production method of the present invention in a solvent, making it possible to quickly prepare a chemical solution containing a carboxylic acid polymer for addition to water to be treated in water treatment equipment.

The solid agent of the present invention allows for the rapid preparation of a carboxylic acid polymer-containing chemical solution to be added to water being treated in water treatment equipment, and is easy to handle in terms of transportation, storage, and quality control.

FIG. 1 shows the evaluation results of the solid preparations of the examples and the mixed preparations of the comparative examples.

The chemical addition method of the present invention is a method for adding a carboxylic acid polymer-containing chemical to water being treated in water treatment equipment. This chemical addition method is applicable to water treatment equipment such as heat source equipment like boilers and open-type cooling towers, as well as filtration equipment like reverse osmosis membrane filtration systems and wastewater filtration systems, where scale formation due to concentration of water containing hardness (calcium ions and magnesium ions) is a concern. The water being treated in a typical heat source equipment, i.e., boiler water, is the feedwater supplied to the boiler to generate steam. Boiler water is concentrated by heating within the boiler, increasing the hardness concentration and forming scale within the boiler that impairs thermal conductivity. The water being treated in an open-type cooling tower is circulating cooling water. The circulating cooling water is concentrated by evaporation and cooling, increasing the hardness concentration and forming scale within the cooling tower and heat exchangers that reduces heat exchange efficiency. The water to be treated in filtration devices such as reverse osmosis membrane filtration devices and wastewater filtration devices is raw water or wastewater used to produce pure water, and the concentration of dissolved components, especially hardness, increases on the filtration membrane surface, causing scale to form on the filtration surface.

In the addition method of the present invention, first, a drug solution containing a drug containing a carboxylic acid polymer is prepared (Step 1). Here, the target drug solution is prepared by dissolving a solid agent containing a carboxylic acid polymer in a solvent. The solid agent used here is obtained in advance by freeze-drying or spray-drying a solution prepared by dissolving the drug containing a carboxylic acid polymer in a solvent.

The carboxylic acid polymer-containing agent used to obtain the solid agent contains a carboxylic acid polymer and, if necessary, other agents. The carboxylic acid polymer used here functions as a scale inhibitor, and examples include carboxylic acid homopolymers such as polyacrylic acid and its salts, polymethacrylic acid and its salts, and polymaleic acid and its salts; carboxylic acid copolymers such as acrylic acid/2-acrylamido-2-methylpropanesulfonic acid binary copolymer, acrylic acid/maleic acid binary copolymer, maleic acid/methyl vinyl ether binary copolymer, acrylic acid/hydroxypropyl acrylate binary copolymer, and sulfonated styrene/maleic anhydride binary copolymer; and terpolymers such as maleic acid/acrylic acid alkyl ester/vinyl acetate terpolymer, acrylic acid/sulfonic acid/sodium styrenesulfonate terpolymer, and acrylic acid/sulfonic acid/substituted acrylamide terpolymer. Two or more of these carboxylic acid polymers may be used in combination.

Examples of other components contained in agents containing carboxylic acid polymers include tracer substances, as well as active ingredients other than carboxylic acid polymers, such as scale inhibitors, anticorrosive agents, stabilizers, and bactericides. There may be two or more types of other components.

Examples of scale inhibitors other than carboxylic acid polymers include chelating agents, such as phosphonic acid and its salts (usually alkali metal salts), and phosphonocarboxylic acids or phosphonocarboxylates such as tetrasodium phosphonoethane-1,2-dicarboxylate, hexasodium phosphonobutane-1,2,3,4-tetracarboxylate, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

Anticorrosion agents are used to inhibit corrosion that may occur due to the concentration of salts in the water being treated in heat exchangers in heat source equipment through which the water being treated flows, in pipes made of metals such as copper or iron, and in other water systems. Examples of anticorrosion agents for copper-based pipes include azole compounds such as pyrrole, diazole, triazole, tetrazole, benzazole, benzodiazole, and benzotriazole, phosphorus compounds, zinc compounds, and lignin. Examples of anticorrosion agents for iron-based pipes include silica, amine compounds such as diethylhydroxylamine and 2-amino-2-methyl-1-propanol, phosphorus compounds, zinc compounds, lignin, and alkaline agents such as potassium hydroxide and sodium hydroxide.

Stabilizers are used to increase the stability of the desired solid formulation, and examples include pH adjusters such as sodium hydroxide, potassium hydroxide, sulfuric acid, and hydrochloric acid, magnesium compounds such as magnesium nitrate and magnesium chloride, and surfactants.

Bactericides are used to prevent the proliferation of Legionella and other bacteria and the generation of slime in water supplies. Examples include 2-bromo-2-nitro-1,3-propanediol, 2,2-dibromo-2-nitro-1-ethanol, 1,5-pentanedial, 2,2-dibromo-3-nitrilopropionamide, 1-bromo-3-chloro-5,5-dimethylhydantoin, N-decyl-N-isononyl-N,N-dimethylammonium chloride, hydrazine, 2-pyrilthio-1-oxide sodium, zinc pyrithione, methylene bisthiocyanate, and 3-(3,4-dichlorophenyl)-1,1-dimethyl Examples include thiazoline compounds such as thiourea, 2-(4-thiazolyl)-benzimidazole, 1,2-benzisothiazolin-3-one, 2,3,3-triiodoallyl alcohol, poly[oxyethylene(dimethylimino)ethylene(dimethylimino)ethylene chloride], and 2-methyl-3-isothiazolone, 2-ethyl-3-isothiazolone, 2-octyl-4-chloro-isothiazolone, 2-benzyl-4,5-dichloro-3-isothiazolone, 2-allyl-3-isothiazolone, 2-propynyl-3-isothiazolone, 5-chloro-2-methyl-3-isothiazolone, and 1,2-benzothiazolone.

The tracer substance is used to indirectly measure the concentration of carboxylic acid polymers and other active ingredients derived from the agent, contained in the treated water to which a carboxylic acid polymer-containing agent has been added, by fluorometry. Examples of such tracer substances include sulfonated pyrene compounds such as pyrenesulfonic acid or alkali metal salts such as its sodium salt, fluorescein, molybdic acid or its salts, vanadic acid or its salts, or sodium naphthalenedisulfonic acid.

When preparing a solid dosage form, the carboxylic acid polymer and other necessary ingredients are mixed uniformly, and this mixed drug is dissolved in a solvent to prepare a solution. At this time, the carboxylic acid polymer and other ingredients can also be added separately to the solvent, and the components can be mixed uniformly in the solvent. The proportion of the carboxylic acid polymer in the total amount of the carboxylic acid polymer and other ingredients is usually preferably set to 10 to 70% by mass, and more preferably set to 20 to 60% by mass.

The solvent used to prepare the mixed drug solution is usually purified water such as distilled water, pure water, or ion-exchanged water. However, various organic solvents that can dissolve the components can also be used, such as water-soluble organic solvents such as methanol, ethanol, or 2-propanol. Two or more solvents may be used in combination. When preparing the solution, stirring or heating may be performed to mix the components uniformly, and bubbling or ultrasonic vibration may also be applied.

The resulting solution is then freeze-dried or spray-dried to prepare a solid formulation, preferably with a solvent content controlled to 20% by mass or less. Here, "solvent content" refers to the mass ratio of the solvent to the solid formulation. Note that when the solvent is water (i.e., the purified water described above), the solvent content may hereinafter be referred to as "water content." When preparing a solid formulation by freeze-drying, it is preferable to set the pressure to 600 Pa or less (particularly 100 Pa or less), the initial temperature (pre-freezing temperature) to -30°C or higher (particularly -15°C or higher), and the freezing time to within two days. While freeze-drying produces a solid formulation in chunks, this solid formulation may be pulverized into powder. When preparing a solid formulation by spray-drying, the spraying method may be a two-fluid, one-fluid, ultrasonic, or rotary method. It is preferable to set the inlet temperature to 100-300°C and the outlet temperature to 70-200°C. It is particularly preferable to select a two-fluid spraying method, set the inlet temperature to 250°C or lower, and the outlet temperature to 150°C or lower. Furthermore, the target droplet diameter during spray drying is preferably set to 500 μm or less, and particularly 300 μm or less. Spray drying produces a powdered solid formulation. To improve handleability, the solid formulation obtained by freeze drying or spray drying may be further processed into tablets, granules, flakes, or fine particles using a tablet press or grinder.

The solid formulation obtained by freeze-drying or spray-drying is a dried product that is resistant to deterioration during storage. Furthermore, because it is porous, it exhibits a unique solubility in water, i.e., rapid solubility. Specifically, the solid formulation is sealed together with water in a 133 mL container so that the equivalent mass of the carboxylic acid polymer is 10 g and the total mass with water is 100 g. When the solid formulation is shaken at 200 rpm at 25°C using a shaker set to orbit with a diameter of 2 cm to 3 cm, the time to complete dissolution is no longer than 200 seconds. The solvent content of the solid formulation is preferably 20% by mass or less, and more preferably 15% by mass or less. Here, the solvent content is a value determined based on the mass loss rate before and after freeze-drying and the solids concentration of the mixed drug solution in the case of freeze-drying. In the case of spray-drying, the solvent content is a value determined from the mass loss rate after 60 minutes in a thermostatic chamber maintained at 105°C.

When preparing a chemical solution, the solid agent is dissolved in the solvent by adding the solid agent to the solvent or by adding the solvent to the solid agent. To prepare a homogeneous chemical solution, the solvent may be stirred or heated, or may be subjected to bubbling or ultrasonic vibration. The solvent used to dissolve the solid agent is typically water or a water-soluble organic solvent. Examples of water that can be used include tap water, well water, ion-exchanged water, and purified water such as reverse osmosis membrane-treated water or forward osmosis membrane-treated water, with purified water being particularly preferred. Water to be treated, such as boiler feedwater, boiler water, or cooling water, to which the chemical solution is to be added, can also be used. Examples of water-soluble organic solvents that can be used include methanol, ethanol, and 2-propanol, with ethanol being particularly preferred. Water and water-soluble organic solvents may also be used in combination. Because solid agents exhibit the unique solubility described above and dissolve rapidly in water, the desired chemical solution can be quickly prepared.

In the addition method of the present invention, the prepared chemical solution is then added to the water to be treated (Step 2). Because the added chemical solution contains a carboxylic acid polymer, it can suppress scale formation in water treatment equipment, and if it contains active ingredients other than the carboxylic acid polymer, it can further impart the benefits of those ingredients to the water to be treated.

The water to be treated to which the chemical solution is added can be selected depending on the type of water treatment equipment. If the water treatment equipment is a boiler, the water to be treated to which the chemical solution is added is the boiler feedwater or boiler water. In the case of an open cooling tower, the water to be treated to which the chemical solution is added is the circulating cooling water. In the case of filtration equipment such as a reverse osmosis membrane filtration system or wastewater filtration system, the water to be treated to which the chemical solution is added is the raw water or wastewater being filtered.

The solid agent used in step 1 of the addition method of the present invention is a dry product, so it is lightweight and small in volume, and is stable and safe. Therefore, it can be easily transported to and from a storage location to a chemical preparation location, and can be stored efficiently and safely in a limited space. Therefore, in step 1 of the addition method of the present invention, the chemical can be prepared at the site where the chemical will be added to the water to be treated, for example, at the location of a boiler or cooling tower, and the required amount of this chemical can be added to the water to be treated.

In the addition method of the present invention, the solid agent is brought into contact with the water to be treated in a water flow pipe for the water to be treated, such as a water supply pipe for a water treatment device (e.g., a water supply pipe to a boiler) or a circulation pipe (e.g., a circulating cooling water pipe for a cooling tower), or in a bypass line installed in the circulation pipe, thereby dissolving the solid agent in the water to be treated to prepare a chemical solution, which can then be supplied to the water to be treated. For example, if a cylindrical container with an exposed bottom is placed in the circulation pipe or the bypass line and the solid agent is filled in this container, the solid agent will gradually come into contact with the water to be treated flowing through the circulation pipe or the bypass line, and the chemical solution can be gradually supplied to the water to be treated in accordance with the flow rate of the water to be treated.

Example 1
440 g of a 50% by mass aqueous solution of polymaleic acid used for calcium scale prevention, 80 g of a phosphonocarboxylic acid chelating agent, 110 g of sodium hydroxide, 110 g of potassium hydroxide, and trace components such as metal salts were dissolved in pure water to prepare 2.2 kg of an aqueous solution, which was then freeze-dried to produce a solid block.

To freeze-dry the prepared aqueous solution, the aqueous solution was placed in a container to a liquid thickness of 13 mm, and the container was placed in a freeze-dryer (Tokyo Rikakikai Co., Ltd., Model No. FDU-1110, combined with a dry chamber (Model No. DRC-1000) manufactured by the same company) and pre-frozen to -30°C. The pressure inside the dry chamber was then reduced to 3-15 Pa, and the temperature was maintained at -10°C for 24 hours for primary drying. The temperature was then changed to 30°C and maintained at this temperature for at least 20 hours for secondary drying. During the drying process, the ultimate vacuum was set to 0.7 Pa, the actual vacuum at the end of drying to 3 Pa, and the trap temperature was set to -60°C. The resulting solid formulation had a polymaleic acid content of 37% by mass and a water content of 1.5% by mass.

<Examples 2 and 3>
The same aqueous solution as prepared in Example 1 was prepared, and this aqueous solution was spray-dried to produce a powdery solid preparation. The aqueous solution was spray-dried using a spray dryer (Buchi model number "B-290") under the conditions shown in Table 1. At this time, air dehumidified using a dehumidifier (Buchi model number "B-296") was used as the drying gas. The obtained solid preparation had a polymaleic acid content of 37% by mass, and the water content was 5.8% by mass in Example 2 and 7.7% by mass in Example 3.

<Comparative Example 1>
A mixture in the form of a paste was prepared by kneading 500 g of sodium polyacrylate used for calcium scale prevention, 180 g of a phosphonocarboxylic acid chelating agent, 170 g of sodium hydroxide, trace components such as metal salts, and pure water. The concentration of sodium polyacrylate contained in this mixture was 41% by mass (31% by mass in terms of polyacrylic acid).

<Comparative Example 2>
The same aqueous solution as in Example 1 was prepared, and this aqueous solution was evaporated to dryness by placing it in an environment of 50°C for 6 days to prepare a solid mixed drug. The water content of this mixed drug was 40% by mass. This water content was determined based on the mass loss rate before and after evaporation to dryness and the solids concentration of the mixed drug solution.

<Evaluation>
The solubility in water was evaluated for the solid preparations obtained in Examples 1 to 3, the paste-like mixed preparation obtained in Comparative Example 1, and the solid mixed preparation obtained in Comparative Example 2. Here, the preparation to be evaluated and city water from Matsuyama City, Ehime Prefecture, were enclosed in a transparent polypropylene bottle (product name "Good Boy 100 mL 110172" by AS ONE Corporation, actual volume 133 mL) so that the total mass was 100 g. The amount of the preparation to be evaluated was set so that the concentration of the carboxylic acid polymer after dissolution in the city water would be 10% by mass (the concentration was polymaleic acid for the solid preparations in Examples 1 to 3 and the mixed preparation in Comparative Example 2, and the concentration was sodium polyacrylate for the mixed preparation in Comparative Example 1). The transparent polypropylene bottle was then fixed sideways on a shaker (Tokyo Rikakikai Co., Ltd., model number "MMS-3010") and orbitally shaken at 200 rpm at 25°C with a diameter of 2 cm to 3 cm. The shaking time until complete dissolution was measured. The complete dissolution of the solid preparation or mixed preparation was confirmed by visual inspection to ensure that no undissolved solid preparation or mixed preparation remained. The results are shown in Figure 1.

As shown in Figure 1, the solid formulations of Examples 1 to 3 were completely dissolved in approximately 100 seconds, enabling the medicinal solution to be prepared quickly in approximately 1/2 to 1/3 of the time required when preparing the medicinal solution using the mixed pharmaceutical formulations of Comparative Examples 1 and 2.

The solid mixed agent of Comparative Example 2 dissolves in water more quickly than the paste-like mixed agent of Comparative Example 1, but the aqueous solution used to prepare it takes time to evaporate and dry. This is thought to be because polymaleic acid, a carboxylic acid polymer used to prevent calcium scale, has a high affinity for water molecules, making it difficult to remove water from the aqueous solution. While the efficiency of water removal can be increased by heating the aqueous solution to a higher temperature, this can lead to thermal decomposition of components in the aqueous solution, such as polymaleic acid. Furthermore, the mixed agent of Comparative Example 2 begins to become viscous during the drying process and ultimately becomes a gel-like solid with a small specific surface area. This is thought to result in a slower dissolution rate in water than the solid agents of Examples 1 to 3. As a result, preparation of the solution takes time, making it difficult to prepare the required amount of solution when needed.

Claims (5)

A method for adding a carboxylic acid polymer-containing agent to water to be treated in a water treatment device, comprising:
Step 1: preparing a drug solution containing the carboxylic acid polymer-containing drug;
Step 2 of adding the chemical solution to the water to be treated,
The drug containing a carboxylic acid polymer comprises one carboxylic acid polymer selected from the group consisting of polymethacrylic acid and its salts, polymaleic acid and its salts, acrylic acid/maleic acid binary copolymer, acrylic acid/hydroxypropyl acrylate binary copolymer , sulfonated styrene/maleic anhydride binary copolymer, maleic acid/acrylic acid alkyl ester/vinyl acetate terpolymer, acrylic acid/sulfonic acid/ sodium styrene sulfonate terpolymer, and acrylic acid/sulfonic acid/substituted acrylamide terpolymer;
In step 1, the drug solution is prepared by dissolving the carboxylic acid polymer-containing drug in a solvent, freeze-drying or spray-drying the solution to obtain a solid drug, and then dissolving the solid drug in the solvent again to prepare the drug solution.
A method for adding chemicals to the water to be treated. The method for adding a chemical to water to be treated described in claim 1, wherein the chemical solution is prepared at the site where the chemical solution is to be added to the water to be treated. A method for producing a solid agent for preparing a chemical solution containing a carboxylic acid polymer to be added to water to be treated in a water treatment device, comprising:
a step of dissolving a drug containing one carboxylic acid polymer selected from the group consisting of polymethacrylic acid and its salts, polymaleic acid and its salts, acrylic acid/maleic acid binary copolymer, acrylic acid /hydroxypropyl acrylate binary copolymer, sulfonated styrene/maleic anhydride binary copolymer, maleic acid/acrylic acid alkyl ester/vinyl acetate terpolymer, acrylic acid/sulfonic acid/sodium styrene sulfonate terpolymer, and acrylic acid/sulfonic acid/ substituted acrylamide terpolymer in a solvent to prepare a solution;
freeze-drying or spray-drying the solution;
A method for producing a solid preparation for preparing a medicinal solution containing a carboxylic acid polymer, comprising: A method for producing a carboxylic acid polymer-containing chemical solution to be added to water to be treated in a water treatment device, comprising:
The method comprises dissolving the carboxylic acid polymer-containing solid preparation for preparing a medicinal solution, which is produced by the method according to claim 3, in a solvent.
A method for producing a chemical solution containing a carboxylic acid polymer. A solid agent for preparing a carboxylic acid polymer-containing chemical solution to be added to water to be treated in a water treatment device,
The polymer comprises one carboxylic acid polymer selected from the group consisting of polymethacrylic acid and its salts, polymaleic acid and its salts, acrylic acid/maleic acid binary copolymers, acrylic acid /hydroxypropyl acrylate binary copolymers, sulfonated styrene/maleic anhydride binary copolymers, maleic acid/acrylic acid alkyl ester/vinyl acetate terpolymers, acrylic acid/sulfonic acid/sodium styrene sulfonate terpolymers, and acrylic acid/sulfonic acid/ substituted acrylamide terpolymers;
the polymer is sealed together with water in a 133 mL container so that the converted mass of the carboxylic acid polymer is 10 g and the total mass with water is 100 g, and the container is shaken at 25°C at 200 rpm using a shaker set to orbitally shake with a diameter of 2 cm to 3 cm, and the time required for complete dissolution is 200 seconds at the latest;
A solid formulation containing a carboxylic acid polymer for preparing medicinal solutions.