JPS6247599B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to scale inhibitors produced in steam desalination equipment. More specifically, the present invention relates to a scale inhibitor having the effect of suppressing the formation of scale deposited on the heat transfer surface of various evaporative desalination devices and dispersing the formed scale in an aqueous system. In order to solve the shortage of fresh water, various methods of desalinating seawater, natural saltwater, wastewater, etc. have been researched and developed in many parts of the world for many years.
The desalinated water thus obtained can be used as drinking water or industrial water, and can also be safely discharged into natural waters. BACKGROUND ART Various types of evaporative desalination apparatuses, such as multistage flash evaporators, thin film evaporators, and submerged evaporators, have been used to obtain fresh water by heating and evaporating seawater and then concentrating it. However, when seawater, natural salt water, etc. is evaporated and desalinated using various evaporative desalination equipment, as it is concentrated to a high concentration, the calcium ions, magnesium ions, etc. contained in it are converted into salts, hydroxides, etc. This deposits as scale on the heat exchange surfaces of the evaporative desalination equipment. As a result, the heat exchange coefficient decreases significantly, the desalination efficiency gradually decreases, and the plant ultimately has to be shut down for scale removal, which causes serious damage. The main scales deposited on the heat exchange surfaces of evaporative desalination equipment, such as seawater, are of two types: alkaline scale (calcium carbonate and magnesium hydroxide) and calcium sulfate scale. This alkaline scale can be suppressed by adjusting the pH by adding acids such as sulfuric acid, but in order to decompose the scale components, the amount of acid added must be increased, and moreover, the corrosion of equipment materials etc. However, there are also problems with the handling of normally used acids such as sulfuric acid, and it cannot be said that this method is necessarily satisfactory in practice. On the other hand, no effective method has yet been found for suppressing the formation of calcium sulfate scale. A method of adding scale inhibitors such as polyphosphates and polycarboxylate salts has been proposed, but polyphosphates easily hydrolyze at high temperatures and lose their scale prevention ability, causing calcium ions and It forms an insoluble salt with magnesium ions and becomes a factor in scale formation. Furthermore, although polycarboxylate salts are recognized to have a certain degree of scale prevention ability, the scale that is generated is hard and adherent eggshell-like scale. For this reason, scale formation in evaporative desalination equipment is currently avoided by appropriately controlling the concentration degree and concentration temperature, which is inefficient and is an important factor hindering the development of seawater desalination. It's summery. As described above, a satisfactory scale prevention method has not yet been developed for desalination of seawater, etc. using evaporative desalination equipment, and there is currently a need for the development of an effective scale prevention method in this field. be. In view of the current situation, the present inventors have conducted intensive research to develop an excellent scale inhibitor that is effective for suppressing scale precipitation in evaporative desalination equipment and dispersing the precipitated scale. The inventors have discovered that the water-soluble polymer has particularly excellent effects as a scale inhibitor for evaporative demineralization equipment, and have completed the present invention. Therefore, an object of the present invention is to provide an excellent scale inhibitor effective for suppressing scale precipitation and dispersing precipitated scale for use in evaporative desalination equipment. That is, the scale inhibitor for evaporative demineralization equipment of the present invention has the general formula (However, in the formula, m and n are 0 or positive integers, and m+n=
1 to 100, and the (-C ₂ H ₄ O)- and (-C ₃ H ₆ O)- units may be bonded in any order. ) Polyalkylene glycol monoallyl ether () represented by the general formula (However, in the formula, R ₁ represents hydrogen or a methyl group, and
represents hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. ) (meta)
Copolymerizing the acrylic acid monomer () using a polymerization initiator at a ratio such that () is 0.1% by weight or more and less than 5.0% by weight with respect to the total of () and (),
It consists of a water-soluble polymer obtained by further neutralizing with an alkaline substance if necessary. The polyalkylene glycol monoallyl ether () used in the present invention is represented by the above general formula, and has an added mole number m+n of 1 to 100 of alkylene oxide. Number of moles added m
If +n is 0, the resulting copolymer will not have sufficient performance as a scale inhibitor for evaporative demineralization equipment;
When it exceeds 100, the copolymerization reactivity of such polyalkylene glycol monoallyl ether is low, and a polymer effective as a scale inhibitor for an evaporative desalination apparatus of the present invention cannot be obtained. Polyalkylene glycol monoallyl ether () can be synthesized by a known method of directly adding ethylene oxide and/or propylene oxide to allyl alcohol using an alkali such as KOH or NaOH as a catalyst. The (meth)acrylic acid monomer () is represented by the general formula above, and specifically includes acrylic acid, methacrylic acid, their monovalent metal salts, divalent metal salts, ammonium salts, and organic amines. Salt can be mentioned. One or more of these can be used. Water-soluble polymer used as a scale inhibitor for evaporative desalination equipment of the present invention by copolymerizing polyalkylene glycol monoallyl ether () and (meth)acrylic acid monomer () using a polymerization initiator can be manufactured. Copolymerization can be carried out by methods such as polymerization in a solvent or bulk polymerization. Polymerization in a solvent can be carried out either batchwise or continuously, and the solvents used in this case include water,
Examples include lower alcohols, mixed solvents of water and lower alcohols, aromatic hydrocarbons, aliphatic hydrocarbons, ketone compounds, and ethyl acetate. Depending on the solvent used, various water-soluble polymerization initiators, peroxides,
Hydroperoxides, combinations of these with polymerization accelerators, azo compounds, etc. are used. The polymerization temperature is appropriately determined depending on the solvent and polymerization initiator used, but it is usually carried out within the range of 0 to 120°C. When water is used as a solvent, sodium hydrogen sulfite-oxygen may be used as a polymerization catalyst. In this case, the polymerization is carried out by blowing oxygen gas or a mixed gas of oxygen and an inert gas into the solvent while adding sodium hydrogen sulfite to the solvent containing the raw material monomer.
This can be carried out by proceeding the polymerization reaction within a temperature range of ~80°C. Bulk polymerization uses peroxide as a polymerization initiator,
It is carried out using hydroperoxide or an azo compound, etc., within a temperature range of 50 to 150°C. When producing a water-soluble polymer in this way, the charging ratio of polyalkylene glycol monoallyl ether () and (meth)acrylic acid monomer (), the amount of polymerization initiator used, the polymerization temperature,
In the case of polymerization in a solvent, the molecular weight of the resulting water-soluble polymer can be adjusted as appropriate by adjusting the type and amount of the solvent. The molecular weight of the water-soluble polymer used as the scale inhibitor for the evaporative desalination equipment of the present invention is not particularly limited, and a wide range of molecular weights can be used, but those in the range of 500 to 50,000 are particularly effective. ing. The water-soluble polymer thus obtained can be used as it is as a scale inhibitor for the evaporative desalination apparatus of the present invention, but it may be further neutralized with an alkaline substance if necessary. Preferred examples of such alkaline substances include hydroxides, chlorides, and carbonates of monovalent metals and divalent metals, ammonia, and organic amines. The scale inhibitor for evaporative desalination equipment of the present invention is sufficiently effective when used alone, but it may also be used in combination with an acid such as sulfuric acid, and if necessary, it may be used in combination with other water treatment agents known in the art. May be used together.
Such other water treatment agents include dispersants or limiting agents such as polyacrylic acid or its salts, hydrolyzed polyacrylonitrile, polymethacrylic acid or its salts, polyacrylamide, acrylic acid or methacrylic acid and acrylamide. copolymers with ligninsulfonic acid or its salts, tannins, naphthalenesulfonic acid-formaldehyde condensation products, starch or its derivatives, cellulose derivatives such as carboxymethyl cellulose, polymaleic acid or its salts, alkylphosphonic acids, 1-
(aminoalkyl 1,1-diphosphonic acids or their salts, alkali metal phosphates, etc.); precipitants (e.g., alkali metal orthophosphates, alkali metals, carbonates, alkali metal hydroxides, etc.); oxygen scavengers (e.g., alkali metal phosphates, etc.); metal sulfite, alkali metal hydrazine, etc.);
Sequestering agents (e.g. nitrilotriacetic acid or its salts, ethylenediaminetetraacetic acid or its salts, etc.); Corrosion inhibitors (e.g. cyclohexylamine, morpholine, distearylamine-ethylene oxide condensate, stearylamine, sodium sulfate, magnesium sulfate, etc.) ); anti-foaming agents (for example, distearylsebamide, distearyl adipamide, etc.); or aliphatic alcohols such as caprylic alcohol or condensates of aliphatic alcohols and ethylene oxide. In order to use the water-soluble polymer used as a scale inhibitor for evaporative desalination equipment in the present invention, it may be added continuously or at appropriate times to seawater or natural salt water. The amount added can be used over a wide range, but it is usually 0.1~
A range of 100ppm (weight basis) is recommended. By using the scale inhibitor for evaporative desalination equipment of the present invention, the generation of scale in evaporative desalination equipment can be suppressed over a long period of time, and even when scale is precipitated due to long-term operation, it can be prevented from forming. Since the scale is made soft by the action of the scale inhibitor for evaporative desalination equipment of the present invention, it can be easily dispersed and removed by a water stream. In addition, in water-soluble polymers, the polyalkylene glycol moiety in the molecule is bonded to the main chain of the polymer through an ether bond, so it is difficult to use water-soluble polymers for long periods of time at high temperatures, in boiling water, or in high pH ranges. It also has the feature that hydrolysis does not occur at all, and its performance is not affected in any way. The present invention will be described below with reference to Reference Examples and Examples, but the present invention is not limited to these Examples. Further, in the examples, unless otherwise specified, all parts are by weight, and all percentages are by weight. In addition, all water-soluble polymer aqueous solution viscosities in the examples were measured using a Bismethron viscometer (manufactured by Seiki Kogyo Kenkyusho).
Measurement was performed at ℃ and 60 rpm. Furthermore, the molecular weight was measured using gel permation chromatography (Model 244 manufactured by Waters). Reference Example 1 Polyethylene glycol monoallyl ether (containing an average of 5 ethylene oxide units per molecule) was placed in a glass reaction vessel equipped with a thermometer, stirrer, dropping funnel, gas introduction tube, and reflux condenser.
7.5 parts and 389.9 parts of water were charged, and the inside of the reaction vessel was purged with nitrogen while stirring, and heated to 95°C in a nitrogen atmosphere. Then, 38% sodium acrylate aqueous solution
506.6 parts and 80 parts of 5% ammonium persulfate aqueous solution were each added over 120 minutes. After addition, further
16 parts of 5% ammonium persulfate aqueous solution was added over 20 minutes. 120 minutes after completion of addition of monomer aqueous solution
The temperature was maintained at 95°C to complete the polymerization reaction, and a water-soluble polymer (1) was obtained. A 40% aqueous solution of this water-soluble polymer (1) obtained by concentrating under reduced pressure has a pH of 7.3 and a viscosity of
It was 267cps. Moreover, the molecular weight was 4100. Reference Example 2 In the same reaction vessel as Reference Example 1, add 9.8 parts of polyethylene glycol monoallyl ether (containing an average of 10 ethylene oxide units per molecule) and water.
After charging 441.7 parts, the inside of the reaction vessel was purged with nitrogen while stirring, and heated to the boiling point in a nitrogen atmosphere. after that
500.5 parts of 38% sodium acrylate aqueous solution and 5%
40 parts of ammonium persulfate aqueous solution and 120 parts each
After the addition was complete, 8 parts of 5% ammonium persulfate aqueous solution was added over 20 minutes. After the addition of the monomers was completed, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction, yielding a water-soluble polymer (2). A 40% aqueous solution of this water-soluble polymer (2) has a pH of 7.5 and a viscosity of
It was 348cps. Moreover, the molecular weight was 4700. Reference Example 3 In the same reaction vessel as in Reference Example 1, an azeotropic composition of 1 part of polypropylene glycol monoallyl ether (containing on average 2 propylene oxide units per molecule), isopropyl alcohol (hereinafter abbreviated as IPA), and water. (IPA/water = 87.4/12.6 (weight ratio))
495.5 parts were charged, and the inside of the reaction vessel was purged with nitrogen while stirring, and heated to the boiling point. then acrylic acid 199
1 part, 6 parts of benzoyl peroxide and 298.5 parts of IPA-water azeotrope was added over 120 minutes. After the addition was complete, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction. Then 40% caustic soda aqueous solution
Neutralization was performed using 276.2 parts, and IPA was distilled off to obtain a water-soluble polymer (3). A 45% aqueous solution of this water-soluble polymer (3) had a pH of 8.5 and a viscosity of 830 cps. Moreover, the molecular weight was 2800. Reference Example 4 In the same reaction vessel as in Reference Example 1, 285 parts of isopropyl alcohol (hereinafter abbreviated as IPA) was charged, the inside of the reaction vessel was purged with nitrogen while stirring, and the mixture was heated to the boiling point in a nitrogen atmosphere. Then, a mixture of 4.5 parts of polyalkylene glycol monoallyl ether (containing on average 18 ethylene oxide units and 2 propylene oxide units per molecule), 295.5 parts of acrylic acid, 3 parts of benzoyl peroxide and 300 parts of IPA was added over 120 minutes. After the addition was completed, 0.6 parts of benzoyl peroxide dispersed in 11.4 parts of IPA was added in two portions every 30 minutes. After the addition of the monomer mixture was completed, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction. Thereafter, it was neutralized with 410.1 parts of a 40% caustic soda aqueous solution. Next, IPA was distilled off to obtain a water-soluble polymer (4). This water-soluble polymer
The 45% aqueous solution of (4) had a pH of 8.5 and a viscosity of 1920 cps. Moreover, the molecular weight was 3000. Reference Example 5 438.8 parts of water was charged into the same reaction vessel as in Reference Example 1, and while stirring, the reaction vessel was purged with nitrogen and heated to 95°C. Then, 63 parts of a 10% aqueous solution of polyethylene glycol monoallyl ether (containing on average 30 ethylene oxide units per molecule) and partially neutralized sodium acrylate (80 mol% neutralization) were added.
378.2 parts of a 38% aqueous solution and 120 parts of a 5% ammonium persulfate aqueous solution were each added over 120 minutes. After the addition was complete, the temperature was maintained at 95° C. for 120 minutes to complete the polymerization reaction. Thereafter, it was completely neutralized with a caustic soda aqueous solution to obtain a water-soluble polymer (5). A 40% aqueous solution of this water-soluble polymer (5) had a pH of 9.0 and a viscosity of 403 cps. Moreover, the molecular weight was 4800. Example 1 Put 700ml of seawater into the beaker 1, add the water-soluble polymer (1) obtained in Reference Example 1 to 5.0ppm, and add a pipe heater (100V, 500W) as a heat source to this seawater. was immersed in the solution and evaporated and concentrated under stirring. Water-soluble polymer (1) is evaporated and concentrated.
Seawater added at 5.0 ppm was sequentially replenished. While performing such operations, the amount of scale attached to the pipe heater was determined at the time when the concentration ratio increased to 4 times. The results are shown in Table 1. Examples 2 to 5 The same procedure as in Example 1 was carried out except that the water-soluble polymers (2) to (5) obtained in Reference Examples 2 to 5 were used instead of the water-soluble polymer (1). It was tested. The results are shown in Table 1. Comparative Example 1 A test was carried out in the same manner as in Example 1, except that commercially available sodium polyacrylate (molecular weight 5000) was used in place of the water-soluble polymer (1). The results are shown in Table 1. Comparative Example 2 In Example 1, a test was conducted in which the water-soluble polymer (1) was not used. The results are shown in Table 1.

[Table] As is clear from the results shown in Table 1, the scale inhibitor for evaporative desalination equipment of the present invention has an excellent effect on preventing scale precipitation.

Claims (1)

[Claims] 1. General formula (However, in the formula, m and n are 0 or positive integers, and m+n
= 1 to 100, and (-C ₂ H ₄ O)- unit and (-C ₃ H ₆ O)-
Units may be combined in any order. ) Polyalkylene glycol monoallyl ether () represented by the general formula (However, in the formula, R ₁ represents hydrogen or a methyl group, and
represents hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. ) (meta)
A water-soluble polymer obtained by copolymerizing acrylic acid monomer () using a polymerization initiator at a ratio such that () is 0.1% by weight or more and less than 5.0% by weight with respect to the total of () and (). A scale inhibitor for evaporative desalination equipment consisting of a combination of 2 General formula (However, in the formula, m and n are 0 or positive integers, and m+n
= 1 to 100, and (-C ₂ H ₄ O)- unit and (-C ₃ H ₆ O)-
Units may be combined in any order. ) Polyalkylene glycol monoallyl ether () represented by the general formula (However, in the formula, R ₁ represents hydrogen or a methyl group, and
represents hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. ) (meta)
Acrylic acid monomer () is copolymerized using a polymerization initiator at a ratio such that () is 0.1% by weight or more and less than 5.0% by weight based on the total of () and (), and further copolymerized with an alkaline substance. A scale inhibitor for evaporative desalination equipment made of a water-soluble polymer obtained by