JPH029880B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a scale inhibitor for aqueous systems. More specifically, the present invention relates to an aqueous scale inhibitor containing a specific polymaleic acid or a salt thereof as a main component. Natural water, tap water, industrial water, and many other water systems generally contain dissolved salts of metals such as magnesium and calcium, and silica. When heating water in a boiler water system or cooling water system, or when desalinating seawater by heated distillation,
Dissolved salts become poorly soluble salts that adhere as scales on heat exchangers and heating surfaces. The formation of such scale not only significantly reduces the cooling or heat transfer effect, but also causes various problems such as corrosion of the tubes and heat transfer surfaces. [Prior Art] Conventionally, various scale inhibitors have been used to suppress the formation of such scales, and scale inhibitors include inorganic and organic phosphoric acid compounds, sodium poly(meth)acrylate, Examples include maleic acid homopolymers and copolymers. [Problems to be Solved by the Invention] However, when phosphoric acid compounds are discharged from the system by blowing or the like, they cause eutrophication and cause environmental pollution, which is not preferable. Furthermore, it has the property of being hydrolyzed in water, and there is a problem in suppressing scale in systems with long residence times or high temperatures. Sodium poly(meth)acrylate is insufficiently effective. As the maleic acid homopolymer, after hydrolyzing polymaleic anhydride obtained by polymerizing maleic anhydride using toluene or xylene solvent,
The method of using it as a scale inhibitor is well known (Japanese Patent Publication No. 53-20475). As the structure of the hydrolyzed polymaleic anhydride produced by this method, the above publication proposes a structure represented by the following formula, taking into account the decarboxylation reaction and the catalyst and solvent groups as terminal groups. [In the formula, R and R' are hydrogen or a group derived from the solvent in which the polymerization is carried out or a group derived from the catalyst used, and C ₆ H ₅ CH ₂ - group (derived from the solvent toluene) ), _CH3C6H4CH2- groups (derived from the solvent xylene ₎ , _C6H5- groups (derived from _the solvent benzene _{or the} catalyst beyzoyl peroxide),
or (CH ₃ ) ₃ C- group (derived from catalytic tertiary butyl peroxide), m+n is a value of 2 to 50] Although such a maleic acid homopolymer has an excellent scale inhibiting effect, As shown above, during polymerization, organic solvents are used as solvents, large amounts of expensive polymerization initiators are used, etc.
Due to the high cost, there is a need for a superior inhibitor that can be easily and inexpensively produced in an aqueous solvent system. [Means for Solving the Problems] As a result of intensive research in order to solve these conventional problems, the present inventors have found that maleic acid or a salt thereof is polymerized in an aqueous solvent in the presence of a polymerization initiator. The present invention was completed by discovering that the specific polymaleate salt obtained is excellent as a scale inhibitor. That is, the present invention is based on the general formula ( _R1 , _R2 : -H, -OH or _-OSO3M , M:H,
Alkali metals such as Na, K, _NH4 and Ca, Mg
The present invention provides a scale inhibitor whose main component is polymaleic acid or a salt thereof represented by one or more selected from the group consisting of alkaline earth metals such as (m: 3 to 80). . The polymaleic acid or its salt according to the present invention can be prepared by adding an alkali metal hydroxide such as caustic soda or aqueous ammonia to an aqueous solution of maleic acid at a ratio of 0 to 150 moles per 100 moles of maleic acid, and then adding the aqueous solution to the aqueous solution. It is produced by heating the aqueous solution to a temperature range of 50 to 160°C, and then polymerizing it while dropping a polymerization initiator into the aqueous solution. More preferably, an alkali metal hydroxide such as caustic soda or aqueous ammonia is added to an aqueous solution of maleic acid at a ratio of 0 to 80 moles per 100 moles of maleic acid, and then the aqueous solution is heated in a temperature range of 50 to 160°C. After heating, polymerization is carried out while dropping a polymerization initiator, and then the polymerization is completed by adding the alkali metal hydroxide or aqueous ammonia all at once or dropping the polymerization initiator dropwise. The final amount of alkali metal hydroxide or aqueous ammonia added is preferably 100 to 130 moles per 100 moles of maleic acid. As the polymerization initiator, water-soluble initiators such as persulfate and hydrogen peroxide, each alone or in combination, are particularly suitable. The appropriate amount to be used is 0.5 to 200 moles per 100 moles of the monomer. It is optimal to use only water as the polymerization solvent, but from the viewpoint of monomer solubility and economic efficiency, it is recommended to produce the polymer in a solvent containing 60% by weight or more, preferably 90% by weight or more of water. Appropriate. Alcohols such as ethanol and isopropanol, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and the like may be added as solvents other than water without impairing the effects of the present invention. A suitable reaction time is 2 to 12 hours. The molecular weight of such polymaleic acid or its salt is 200 to 5000, preferably 300 to 1500, as measured by vapor pressure osmosis in a chloroform solution after methyl esterification. The present invention also includes a polymer containing 5% or less of a vinyl monomer polymerizable with maleic acid (salt) in the polymaleic acid or its salt of the present invention represented by the general formula (). Examples of vinyl monomers that can be polymerized with maleic acid (salt) include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid; unsaturated amides such as acrylamide; ) Unsaturated allyl ethers such as acrylic acid esters, allyl alcohol, allyl alcohol EO adducts, unsaturated sulfonic acids such as styrene sulfonic acid and vinyl sulfonic acid,
Examples include vinyl esters such as vinyl acetate, unsaturated nitriles such as acrylonitrile, and aromatic vinyl compounds such as styrene. Although the polymaleic acid or its salt according to the present invention undergoes a decarboxylation reaction during polymerization, it has a structure of maleic acid units, and the polymer terminal groups are hydrogen groups, hydroxyl groups, and/or sulfuric acid groups as shown below. It has an ester group. (In the formula, R ₁ and R ₂ are respectively -H group, -OH group (derived from catalytic hydrogen peroxide), or -OSO ₃ M
group (derived from the catalytic persulfate), M is H,
Alkali metals such as Na, K, _NH4 and Ca, Mg
one or more selected from the group consisting of alkaline earth metals such as, m is 3 to 80). For having H groups as polymer end groups, the polymer is passed through a cation exchange resin with M
After setting it to H, NMR measurement shows that the methylene hydrogen of the terminal carboxymethyl group is
This is clear from its appearance at 2.5 to 3.0 ppm (δ). The formation mechanism is that a polymer whose terminal group is -OH group derived from the catalyst hydrogen peroxide is first formed, and then the terminal α-oxycarboxylic acid structure of this polymer is further oxidized by hydrogen peroxide, and α-keto A possible mechanism is that decarboxylation occurs via acid and the polymer ends become carboxymethyl groups. polymer end Furthermore, the absence of an acrylic acid structure in the polymer is clear from the fact that no peak is observed around 1.6 ppm (δ) corresponding to an acrylic acid structure in the NMR chart shown in FIG. The polymaleic acid or its salt of the present invention has a terminal group different from that of a polymer produced using a toluene or xylene solvent, and the scale suppression effect also differs depending on the terminal group. In particular, the polymaleic acid or its salt according to the present invention exhibits an excellent scale-inhibiting effect in a range where the degree of polymerization is small, so the influence of the terminal group is very large. -H, -OH groups and -OSO ₃ M groups are more likely to form terminal groups in polymers produced in organic solvents.
CH ₃ C ₆ H ₄ CH ₂ − group, C ₆ H ₅ CH ₂ − group, C ₆ H ₅ − group,
It is thought that the scale suppressing effect becomes stronger due to the strong hydrophilicity due to the (CH ₃ ) ₃ C- group and the like. The amount of the scale inhibitor of the present invention added to the system is
It is 0.5 to 100 ppm, preferably 2 to 50 ppm. If the amount added is too small, the effect will be insufficient, and if the amount added is too high, it will be economically disadvantageous, so the above amount is the preferred range. The scale inhibitor of the present invention is effective when used alone, but it may be used in combination with chemicals conventionally used as water treatment agents, such as rust preventives, anticorrosive agents, chelating agents, dispersants, etc. It is also possible to do so. Concomitant drugs include amines, imidazolines,
N-containing compounds such as amides, phosphoric esters, hydroxycarboxylic acids, lignin sulfonates,
Aromatic sulfonic acid formalin condensate (salt), melamine sulfonic acid formalin condensate (salt), acrylic acid or methacrylic acid polymer (polycarboxylic acid), copolymer of olefin and maleic acid,
Inorganic salts such as nitrites, sulfates, phosphates, aromatic carboxylates, aliphatic carboxylates, aminopolycarboxylates, thiourea, sulfosuccinic acids, polyethylene glycol, thioglycolic acid esters, polyethyleneimine, polyethylene Examples include imide and benzotriazole. [Effects of the Invention] The scale inhibitor of the present invention exhibits excellent performance regardless of the type of scale. For example, it shows excellent effects on scales such as calcium carbonate, calcium phosphate, magnesium hydroxide, and silica.
The scale inhibitor of the present invention can be used, for example, in boiler feed water, cooling water, seawater desalination (evaporation method), geothermal hot water,
Shows excellent performance in scale control such as oil recovery. [Examples] Hereinafter, the present invention will be explained in more detail in Examples, but the present invention is not limited to these Examples. Reference Example 1 196 g (2.0 mol) of maleic anhydride and 75 g of water were added to a flask equipped with a thermometer, stirrer, dropping funnel, nitrogen inlet tube, and reflux condenser, and the mixture was heated to 110 g with stirring.
Heat to ℃. After stopping the heating, 68 g of 60% hydrogen peroxide solution was gradually added dropwise over 2 hours. The temperature of the dropping system rose to 128°C. After dropping, age under reflux for 30 minutes, then add 48% caustic soda under reflux.
167 g (2 mol) was added over 2 hours, and 35 g of 30% sodium persulfate aqueous solution and 50 g of 60% hydrogen peroxide solution were added to
Drop simultaneously over time. After the addition was completed, the system was further aged for 1 hour, and then the system was cooled to below 40°C, and the solid content was reduced to 48°C.
%, PH4.91 was obtained (this was
(1)). Reference Example 2 173.4 g of maleic anhydride was placed in a flask equipped with a thermometer, stirrer, dropping funnel, and reflux condenser.
(1.77 mol) and 92 g of water were added and heated to 110°C while stirring. Stop heating and add 60% hydrogen peroxide solution 150%
g, 28 g of 30% sodium persulfate and 259.7 g (2.65 mol) of maleic anhydride dissolved at 60° C. are added dropwise over 4 hours. During the dropping, the temperature of the system rose to 124°C. After the dropwise addition was completed, the mixture was aged under reflux for 30 minutes.
Next, while the temperature of the system was kept at 100 DEG C. to 110 DEG C., 368.5 g (4.42 mol) of 48% caustic soda was added dropwise over 4 hours, and 112.8 g of 60% hydrogen peroxide solution and 42 g of 30% sodium persulfate were added dropwise over 5 hours. After the completion of the dropwise addition, the system was further heated for 1 hour, and then cooled to below 40℃, and the solid content was reduced to 50.8℃.
%, PH4.72 was obtained (this was
(2)). Reference Example 3 196 g of maleic anhydride was placed in a flask equipped with a thermometer, stirrer, dropping funnel, and reflux condenser.
(2.0 mol) and 100 g of water were added, and 133.4 g (1.6 mol) of 48% caustic soda was added dropwise while stirring. Then, the temperature of the system is heated to 108°C. Stop heating, then
Add 158 g of 30% sodium persulfate dropwise over 3 hours.
After completion of the dropwise addition, after aging for 30 minutes, 100.3 g (1.2 mol) of 48% caustic soda and 30% sodium persulfate were added under reflux.
Drop 79g over 4 hours. After completion of the dropwise addition, the polymerization was further aged for 1 hour to complete the polymerization. When the resulting solution is left at 5°C overnight, Glauber's salt crystals precipitate, but after crystal filtration, the solid content is 41% and the pH is
An aqueous polymer solution of 4.70 was obtained (this is referred to as polymer (3)). Reference Example 4 Next, as a comparative example, an example of producing polymaleic acid using a toluene solvent will be shown. Put 50 g of maleic anhydride and 100 g of toluene into a flask equipped with a stirrer, thermometer, and reflux condenser, and raise the temperature to 70°C to dissolve. Then, 10 g of benzoyl peroxide was dissolved in 50 g of toluene, and this was added to the maleic anhydride/toluene solution at 70°C for 15 min.
Drips in minutes. After reacting for 5 hours at a temperature of 90-95°C, it is cooled to 30°C. Since the polymer was obtained as a precipitate, the toluene in the upper layer was decanted and then dissolved in 100 g of water at 50 to 60°C. The remaining toluene was then removed by stripping under vacuum to obtain a hydrolyzed polymaleic acid aqueous solution (referred to as polymer (4)). Example 1 In order to examine the effectiveness of the aqueous solutions containing the polymers of the present invention obtained in Reference Examples 1 to 3 as scale inhibitors, the following inhibition test was conducted. To 150g of calcium chloride dihydrate 0.191% aqueous solution,
A 1% aqueous solution of the polymer obtained in Reference Examples 1 to 3 was
Added 300μ and further added 0.185% sodium bicarbonate.
150g of aqueous solution was added. After adjusting the pH to 8.0, it was placed in a glass bottle, tightly capped, and left at 50°C for 6 hours. After cooling, the precipitate was filtered through a 0.1μ membrane filter, and the calcium concentration in the filtrate was determined.
Analyzed by EDTA titration. The results obtained are shown in Table 1. For comparison, Table 1 also shows the results for polymaleic acid synthesized by the solvent method and commercially available sodium polyacrylate when no scale inhibitor is used.
Shown below.

【table】

[Table] Example 2 The following test was conducted to investigate the scale suppression effect of the polymer of the present invention on a seawater heating system. Using a testing machine that can steam-heat seawater circulating in a stainless steel pipe with an inner diameter of 6mm to 110℃,
Artificial seawater with a concentration factor of 2 was circulated at 320/hr for 10 hours. After dissolving the scale adhering to the pipes in the heater by acid washing, quantitative measurements were performed using atomic absorption spectroscopy to examine the inhibitory effects of each scale inhibitor. The results are shown in Table 2.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a ¹ H-NMR spectrum of polymaleic acid according to the present invention with H terminals.

Claims (1)

[Claims] 1. General formula ( _R1 , _R2 : -H, -OH or _-OSO3M , M:H,
One or more selected from the group consisting of alkali metals, NH ₄ and alkaline earth metals,
m: 3 to 80) A scale inhibitor containing polymaleic acid or a salt thereof as a main component. 2. The scale inhibitor according to claim 1, wherein the molecular weight of the polymaleic acid or its salt is 200 to 5000 as measured by vapor pressure osmosis in a chloroform solution after methyl esterification.