CH668975A5 - TARTAR INHIBITOR FOR AQUEOUS SYSTEM. - Google Patents

Description

DESCRIPTION

This invention relates to a scale inhibitor for aqueous systems. More particularly, it relates to a scale inhibitor for an aqueous system, which essentially consists of a specific polymer of maleic acid comprising a homopolymer and a copolymer thereof.

Many aqueous systems including natural water, tap water and industrial water contain dissolved metal salts such as magnesium and calcium salts, as well as silica. When the water is heated in a boiler or in a condenser, or when sea water is desalinated by distillation, the dissolved salts are then likely to become hardly soluble and are fixed on the surface of the heat exchanger or of the heating surface by forming tartar.

The scale thus formed not only significantly reduces the effect of transfer of cold or heat, but also brings various drawbacks such as corrosion of the tubes or heating surfaces.

Various scale inhibitors have been used in order to prevent the formation of it. Conventional scale inhibitors include inorganic and organic phosphate compounds of polysodium (meth) acrylate and homopolymers and copolymers of maleic acid.

However, the phosphate compounds are undesirable, since they are capable of producing eutrophication when they are eliminated from the system, for example by blowing which tends to bring about pollution of the environment. In addition, they tend to be hydrolyzed in water, making it difficult to apply them in a system with an extended residence time or a high temperature. On the other hand, polysodium (meth) acrylate has an insufficient effect.

A well-known example of a scale inhibitor comprising a maleic acid homopolymer is that obtained by polymerization of maleic anhydride with the use of toluene or xylene as solvent, followed by the hydrolysis of polymethyl anhydride -leique obtained (see Japanese patent published N ° 20475/1978). Taking into account decarbonization and the catalyst groups and the solvent as terminal groups, the aforementioned publication suggests that the polymaleic anhydride has the following structure:

R-

-ch-

-CH-

-CH2

-ch-

-R '

COOM COOM

COOM

40

in which R and R 'each represent a hydrogen atom or a group derived from the solvent or from the catalyst used for the polymerization, such as a group C6HSCH2 - coming from toluene as solvent, a group CH3C6H4CH2 - coming from xylene as solvent , a C6HS group - originating from benzene as solvent or a benzoyl peroxide as catalyst or a group (CH3) 3C - originating from tert.-butyl peroxide as catalyst; and m + n is between 2 and 50.

Such a homopolymer of maleic acid has an excellent scale-inhibiting effect. However, it is necessary to use not only an organic solvent as described above, but also a large amount of an expensive initiator for polymerization, which makes the product very expensive. Therefore, there has been an urgent need to develop an excellent scale inhibitor which can be prepared easily and economically in an aqueous solvent system.

We have therefore studied how to overcome the disadvantages described above, and have therefore found that a polymer having a specific structure represented by formula (I) and containing a large amount of maleic acid is an excellent scale inhibitor, reaching thus the aim of the present invention.

A scale inhibitor according to the invention comprises a polymer or copolymer of maleic acid represented by formula (I) or a salt thereof:

R3 -n

Ri-

-CH-I

-ch-I

-ch2

-R?

(I)

COOM COOM

3

668975

in which Rx and R2 are hydrogen, a hydroxyl group, an alcohol residue having from 1 to 4 carbon atoms or a ketone group having 3 or 4 carbon atoms, R! and R2 is not at the same time hydrogen or a hydroxyl group, M is a hydrogen atom, NH4, an alkali metal or an alkaline earth metal, m is 2 to 40, n is 0 or a positive number, the total of m and n being from 3 to 80 when n is positive, the ratio of n to m being from 0/100 to 100/100, R3 is a hydrogen atom or a methyl group, A is -COOM, -C0NH2 , -CH2OH, -CH2S03M, - S03M, phenyl, —COOR4 or

<o> -

so3m,

Ri-

-CH-

-ch-

-CH,

-R,

(I)

COOM COOM

in which R! and R2 each represent —h or —oh, an alcohol residue having from 1 to 4 carbon atoms such as ch3 I

ch2-, ch3-ch-, ch3-ch2-ch-, ch3-c-, Il II

oh oh oh oh ch3 ch3

I I

ch3-ch2-ch2-ch-, ch3 ~ ch2-c-, ch3-ch-ch-

ch3

OH

I

Oh oh

OH

or a ketone residue having 3 or 4 carbon atoms such as o o o

He II II

CH3-C-CH2-, CH3-CH2-C-CH2- or CH3 — C — CH—

I

CH.

with the condition that Rj and R2 do not represent -Hou -OH at the same time;

R3 represents —H or - CH3;

A represents -COOM, -C0NH2, -CH2-OH, -CH2S03M,

-so3m,

<Ö> -SO3M, - <ö>

and R4 is a saturated hydrocarbon group having from 1 to 6 carbon atoms.

The polymer or copolymer will be designated below by the term "polymer".

The polymer is characterized in that it has an alcohol group or a ketone group at one or both ends thereof, preferably in an amount of 20 mol% or more.

The polymer to be used in the invention comprises three groups of examples. The first is the homopolymer. The second is a copolymer containing up to 5% by weight of a vinyl comonomer. The third is a copolymer of maleic acid or a salt thereof and a vinylic comonomer with a monomer ratio of 100/5 to 100/100.

The polymer and the invention will now be illustrated. The description relating to the polymer applies to the three types thereof.

The fact that the polymaleic acid or the salt thereof according to the present invention has the structure illustrated by the general formula (I) is proven by 1 H NMR- For example, an 1 H NMR spectrum thereof, obtained using a water / isopropanol mixture as solvent, exhibits a signal of the methylene group hydrogen in the terminal carboxyl group at 2.5 to 3.0 ppm (S) and that of the methyl group hydrogen at 1.0 at 1.5 ppm (8). As for the homopolymer, it has no peak around 1.6 ppm (8), which clearly indicates that maleic acid has not been decarbonated and that no acrylic acid group is present. is present in the homopolymer. The copolymer with acrylic acid has such a peak.

Consequently, the present invention provides a scale inhibitor comprising a polymaleic acid polymer of general formula:

or - COOR4, where R4 is a saturated hydrocarbon having from 1 to 10 to 6 carbon atoms; M represents H, NH4, an alkali metal such as Na or K, or an alkaline earth metal such as Ca or Mg, and m and n represent a molar copolymerization ratio in combination as defined above.

The polymer of maleic acid according to the present invention can be obtained by polymerization of maleic acid with a copolymerizable monomer in a solvent mixture comprising water and a monohydric alcohol having from 1 to 4 carbon atoms or a ketone having 3 or 4 carbon atoms.

Examples of the alcohol which can be used are methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec.-butanol and tert.-butanol, while examples of the ketone to be used are acetone and methyl ethyl ketone.

Preferably, the weight ratio of water to alcohol or acetone and from 1: 1 to 5: 1.

As will be shown in the reference examples below, the polymaleic acid polymer according to the present invention can be prepared by adding 0 to 120 moles of an alkali metal hydroxide or ammonia to a solution of maleic acid (100 moles) in a mixture of water and an alcohol or a ketone, addition of a monomer corresponding to the nucleus of

R,

"f ~ ch2

35

in the general formula (I) to the mixture, and dropwise addition of an initiator by heating to 50-120 ° C. so as to polymerize the mixture.

A comonomer to be used in the invention comprises those 40 which can form the patterns defined above. A water-soluble comonomer is preferred for this purpose.

In the example of the copolymer containing up to 5% by weight of a vinyl comonomer, this comonomer comprises unsaturated carboxylic acids, such as acrylic acid, methacrylic acid 45 and itaconic acid; unsaturated amides such as acrylamide; unsaturated (meth) acrylates such as methyl acrylate and ethyl acrylate; allyl alcohol; unsaturated allyl ethers such as the EO adduct of allyl alcohol; an unsaturated sulfonic acid such as styrenesulfonic acid or vinylsulfonic acid; 50 vinyl esters such as vinyl acetate; unsaturated nitriles such as acrylonitrile and vinyl aromatic compounds such as styrene.

The monomers mentioned above for the copolymerization can be applied to the example of the copolymer having a monomer ratio 55 of 100/5 to 100/100.

A water soluble initiator such as a persulfate or hydrogen peroxide or a mixture thereof is particularly suitable as polymerization initiators. The initiator can be used in an amount of 0.5 to 200 moles per 100 moles of the monomer. The reaction time can be between 2 and 12 hours.

The polymaleic acid polymer according to the present invention preferably has a molecular weight from 200 to 5000, more particularly from 300 to 1500. The term "molecular weight" as used herein means that which has been determined as follows. The polymer obtained is transformed into an acid form with an ion exchange resin and transformed into a methyl ester using, for example, diazomethane, then the determination is carried out.

668,975

4

killed in a solvent such as chloroform by vapor phase osmometry. In the case of a copolymer having a sulfonic acid group in the molecule, the sulfonic acid is chlorinated with, for example, thionyl chloride, then methylesterified, for example with diazomethane, and then determined.

The polymaleic acid polymer according to the present invention contains an alcohol having 1 to 4 carbon atoms or a ketone having 3 or 4 carbon atoms as a solvent in the polymerization. Since these solvents are reactive and affect the propagation of the chain and the interruption of the polymer, the polymer contains end groups chosen from —H, —OH, alcohol residues having from 1 to 4 carbon atoms and ketone residues having 3 or 4 carbon atoms, as illustrated in the general formula (I).

The mechanism of the formation of the polymaleic acid polymer according to the present invention can be summarized as follows. The a-proton of the alcohol or ketone solvent is firstly torn off by the initiator and the alcohol or ketone radical thus obtained initiates the polymerization of maleic acid so as to form a polymaleic acid polymer having one or more alcohol or ketone at one or its ends. When hydrogen peroxide is used as the initiator, a polymer having a —OH group derived from hydrogen peroxide at a termination is further formed by the above reaction. Next, the α-hydroxycarboxylic acid at the end of the polymer is oxidized and decarbonization through the a-keto acid transforms the terminal group into a carboxymethyl group.

Thus, the polymer obtained is presumed to be a mixture of those having different end groups such as one or more alcohol or ketone residues and carboxymethyl groups having a hydrogen atom at the end.

The polymer according to the invention is different from the conventional polymer obtained with an organic solvent such as toluene and xylene as regards the end groups. The scale inhibiting effect is based on the specific end groups in the invention. It should be noted that the scale inhibiting effect is provided according to the invention when the polymer has a low degree of polymerization, due to the fact that the function of the end groups increases. This is produced by the fact that the —H and —OH groups, the alcohol radicals having 1 to 4 carbon atoms and the ketone radicals having 3 or 4 carbon atoms are more hydrophilic than the terminal groups of the polymers prepared with the use organic solvents such as groups C6H5CH2—,

CH3C6H4CH2-, C6H5— or (CH3) 3C—.

In the case of the polymaleic acid polymer according to the present invention, it is particularly desirable that it contains at least 20 mol% of alcohol or ketone residue at the end or ends from the point of view of the gelation stability of the polymer vis -to versatile metals.

The scale inhibitor according to the present invention can be added to a system in an amount of 0.5 to 100 ppm, preferably 2 to 50 ppm relative to this system. A lower amount of the inhibitor only brings about an insufficient effect, while a larger amount of it is not desirable from an economic point of view. Thus, the above area is preferable.

The scale inhibitor according to the present invention exerts a sufficient effect when used alone. Alternatively, it can be combined with conventional water treatment agents such as rust inhibitors, corrosion inhibitors, chelating agents or dispersants.

Examples of chemicals which can be used simultaneously with the scale inhibitor according to the present invention include nitrogen-containing compounds such as amines, imidazolines and amides, phosphates, hydroxycarboxylates, lignin sulfonates , formalin condensates (salts) of aromatic sulfonates, formalin condensates (salts) of melamine sulfonates, polymers of acrylic or methacrylic acid (polycarboxylic acids), copolymers of olefins with maleic acid, inorganic salts such as nitrites, sulfates and phosphates, aromatic carboxylates, carboxylates

aliphatics, aminopolycarboxylates, thiourea, sulphosuccinic acid, polyethylene glycol, thioglycolates, polyethylenimine, polyethyleneimide and benzotriazole.

The tartar inhibitor according to the present invention has an excellent effect regardless of the type of tartar. For example, it is highly effective on tartars of calcium carbonate, calcium phosphates, magnesium hydroxide and silica. The scale inhibitor according to the present invention is highly useful for inhibiting the formation of scale in a water feed boiler, a condenser, a seawater desalination system by evaporation, in the geothermal hot water and oil recovery.

The present invention will now be illustrated by the following examples:

Reference example 1:

196 g of maleic anhydride and 300 g of water were introduced into a container equipped with a thermometer, a stirrer, a tap funnel, a nitrogen inlet and a reflux condenser , and the mixture was heated to 60 ° C with stirring. After the interruption of the heating, 138 g of 30% caustic soda were added to the mixture, then 140 g of isopropanol were also added to it. Subsequently, the system temperature was raised to the reflux point, and 0.25 g of a 1% aqueous solution of FeSO4 (as Fe) was added. Then, 40 g of 60% aqueous hydrogen peroxide was added dropwise to the mixture over a period of 6 hours. After the addition was complete, the reaction mixture was heated for a further 2 hours. The residual isopropanol was removed in vacuo, and the moisture content of the mixture was adjusted to give an aqueous solution of a polymer having a solid content of 40% (pH = 3.8), which will be designated as being the polymer (1).

Reference example 2:

The procedure of reference example 1 was followed, except that the isopropanol was replaced by n-propanol in order to give an aqueous solution of a polymer having a solid content of 40% (pH = 3 , 7), which will be designated as the polymer mother (2).

Reference example 3:

The procedure of reference example 1 was followed, except that the isopropanol was replaced by ethanol to give an aqueous solution of a polymer having a solid content of 40% (pH = 3 , 7), which will be designated as the polymer (3).

Reference example 4:

196 g of maleic anhydride and 300 g of water were introduced into a container equipped with a thermometer, a stirrer, a tap funnel, a nitrogen inlet and a reflux condenser and the mixture was heated to 60 ° C with stirring. After the interruption of the heating, 138 g of 30% caustic soda were added to the mixture, then 200 g of methyl ethyl ketone were also added to it. Subsequently, the system temperature was raised to the reflux point, and 0.25 g of a 1% FeSO4 solution (as Fe) was added. Then, 40 g of 60% aqueous hydrogen peroxide was added dropwise to the mixture over a period of 6 hours. After the addition was complete, the reaction mixture was heated for an additional 2 hours. After removal of the residual methyl ethyl ketone under vacuum, the moisture content of the mixture was adjusted so as to give a polymer solution with a solid content of 40% (pH = 3.8), which will be designated as the polymer ( 4).

Reference example 5:

The procedure of Reference Example 4 was followed, except that 100 g of methyl ethyl ketone was used to give a

5

10

15

20

25

30

35

40

45

50

55

60

65

5

668975

aqueous solution of a polymer having a solid content of 40% (pH = 3.6), which will be designated as the polymer (5).

Reference example 6:

Polymaleic acid was prepared using toluene s as the solvent for comparison.

50 g of maleic anhydride and 100 g of toluene were introduced into a container equipped with a stirrer, a thermometer and a reflux condenser, and the mixture was dissolved by heating to 70 ° C. 10 g benzoyl peroxide dissolved in 50 g of toluene was added dropwise to the maleic anhydride / toluene solution over 15 minutes. Then the mixture was reacted at 90-95 ° C for 5 hours and cooled to 30 ° C. After decantation of the upper phase comprising toluene, the polymer obtained in the form of a precipitate was dissolved in 100 g of water at 50-60 ° C. i5

Then, it was purified under vacuum so as to remove the residual toluene and give an aqueous solution of hydro-lysed polymaleic acid, which will be designated as the polymer (6).

Example 1:

r 20

The following scale inhibition test was carried out in order to examine the scale inhibition effect of the aqueous solutions containing the polymers according to the present invention as prepared in the reference examples 1 to 3.

300 μl of an aqueous solution 1% of each polymer as prepared in the reference examples 1 to 3 were added to 150 g of an aqueous solution of calcium chloride dihydrate 0.178% and 150 g of a solution 0.168% aqueous sodium hydrogencarbonate was further added to the mixture. After adjusting the pH to 8.0, the mixture was introduced into a glass bottle, sealed and allowed to stand at 50 ° C for 6 hours. The mixture was then cooled and the precipitate formed was filtered through a 0.1 µm membrane filter. Then, the calcium concentration in the filtrate was determined by titration with EDTA. Table 1 presents the results obtained.

In addition, the results obtained without using a scale inhibitor and those obtained using polymaleic acid synthesized by an organic method and a commercially available polysodium acrylate are also presented in Table 1, for comparison.

Table 1

Tartar inhibitor

Quantity (ppm)

pH of the aqueous solution after test

CaCO3 in the filtrate (ppm)

M-alkalinity of the filtrate (ppm)

Inhibition rate "(%)

Sample according to the invention

Polymer (1)

10

8.1

595

495

98

Polymer (2)

10

8.1 '

590

490

97

Polymer (3)

10

8.1

580

480

94

Sample for comparison

Commercial polysodium acrylate *

10

7.9

505

390

72

No

0

7.1

260

135

0

Polymer (6)

10

8.0

570

465

91

*: Molecular weight = 3000.

**: Inhibition rate = (B — C) / (A — C) x 100 A: Ca concentration before heating,

B: Concentration of Ca in the filtrate after examination,

C: Concentration of Ca in the filtrate after examination without using an additive.

Example 2:

The following scale inhibition test was carried out in order to examine the scale inhibition effect of aqueous solutions containing the polymers according to the invention as prepared in reference examples 4 and 5.

300 (of a 1% aqueous solution of each polymer as prepared in reference examples 4 and 5 were added to 150 g of a 0.264% aqueous sodium chloride dihydrate solution, and 150 g of a 0.168% aqueous sodium hydrogencarbonate solution was also added to the mixture After adjusting the pH value to 8.0, the mixture was introduced into a glass bottle, sealed and allowed to stand at 50 ° C for 6 hours then the mixture was cooled and the precipitate formed was filtered through a 0.1 membrane filter then the concentration of calcium in the filtrate was determined by titration with EDTA. The obtained results.

In addition, the results obtained without the use of a scale inhibitor and those obtained using polymaleic acid synthesized with a solvent method and commercially available polysodium acrylate 55 are also presented in Table 2 for comparison.

Table 2

Tartar inhibitor

Quantity (ppm)

pH of the aqueous solution after test

CaCO3 in the filtrate (ppm)

M-alkalinity of the filtrate (ppm)

Inhibition rate (%)

Sample according to the invention

Polymer (4)

10

8.1

884

482

96

Polymer (5)

10

8.0

875

470

94

668,975

6

Table 2 (continued)

*: Molecular weight = 3000.

**: Inhibition rate = (B-C) / (A-C) x 100 A: Ca concentration before heating,

B: Concentration of Ca in the filtrate after examination,

C: Concentration of Ca in the filtrate after examination without using an additive.

Example 3:

The following test was carried out in order to examine the scale inhibition effect of the polymers according to the present invention as prepared in the reference examples 1 to 3 on a seawater heating system.

Twice concentrated artificial seawater has been circulated in a device in which this seawater passes through a stainless steel pipe with an internal diameter of 6 mm while being heated to 110 ° C, with a flow rate from 3201 / h for 20 hours. The scale adhering to the surface of the pipe in the heater was dissolved by washing with an acid and determined by atomic absorption spectroscopy so as to examine the scale inhibiting effect of each of the inhibitors. Table 3 presents the results obtained.

Table 3

Tartar inhibitor

Quantity (ppm)

Fixed scale * (mg / m2)

Sample according to the invention

Polymer (1)

10

380

Polymer (2)

10

425

Polymer (3)

10

450

Sample for comparison

Commercial polysodium acrylate

10

1280

No

0

6300

Polymer (6)

10

530

* Total amount of CaCO3 and Mg (OH) 2 per unit area of the heat transfer tube.

Example 4:

The following test was carried out in order to examine the scale inhibition effect of the polymers according to the present invention as prepared in reference examples 4 and 5 on a seawater heating system.

Twice concentrated artificial seawater has been circulated in a device in which this seawater passes through a stainless steel tube with an internal diameter of 6 mm, while being heated to 110 ° C., with a flow rate of 3201 / h for 10 hours. The scale adhering to the surface of the pipe in the heater was dissolved by washing with an acid and determined by atomic absorption spectroscopy so as to examine the scale inhibiting effect of each of the inhibitors. Table 4 presents the results obtained.

20

25

30

* Total amount of CaCO3 and Mg (OH) 2 per unit area of the heat transfer tube.

Reference example 7:

35 196 g of maleic anhydride and 300 g of water were introduced into a container equipped with a thermometer, a stirrer, a tap funnel, a nitrogen inlet and a condenser. reflux and the mixture was heated to 60 ° C with stirring. After heating was stopped, 138 g of 30% caustic soda was added to the mixture. Then 140 g of isopropanol were added to the mixture, as well as 63.2 g of sodium methallylsulfonate. The system temperature was then raised to the reflux point, and 0.25 g of a 1% FeSO4 solution (as Fe) was added to the mixture. Then 40 g of 60% aqueous hydrogen peroxide was added dropwise to the dropper over a period of 6 hours. After this addition was complete, the reaction mixture was heated for an additional 2 hours. The residual isopropanol was removed in vacuo and the moisture content of the mixture was adjusted to give an aqueous solution of a polymer having a solid content of 40% 50 (pH = 3.8), which will be designated as the polymer (7).

Reference examples 8 and 9:

Polymers (8) and (9) were prepared in the same manner as described in reference example 7, except that the sodium methallyl-55 sulfonate was replaced by the copolymerizable monomers as presented in Table 5 below.

Table 5

60

65

Tartar inhibitor

Quantity (ppm)

pH of the aqueous solution after test

CaCO3 in the filtrate (ppm)

M-alkalinity of the filtrate (ppm)

Inhibition rate (%)

Sample for comparison

Commercial polysodium acrylate *

10

7.8

814

410

79

No

0

7.2

491

91

0

Polymer (6)

10

8.1

867

462

92

Tartar inhibitor

Quantity (ppm)

Fixed scale * (mg / m2)

Sample according to the invention

Polymer (4)

10

220

Polymer (5)

10

250

Sample for comparison

Commercial polysodium acrylate

10

710

No

0

4000

Polymer (6)

10

285

Example of ref. No.

Monomer composition (moles)

Molecular weight

Polymer No

Maleic acid

Copolymerizable monomer

7

100

Methallylsulfonate

sodium 20

770

(7)

8

100

Acrylic acid 25

900

(B)

9

100

Acrylamide 40

1050

(9)

7

668,975

Reference example 10:

196 g of maleic anhydride and 300 g of water were introduced into a container equipped with a thermometer, a stirrer, a tap funnel, a nitrogen inlet and a reflux condenser , and the mixture was heated to 60 ° C with stirring. After heating was stopped, 138 g of 30% caustic soda was added to the mixture. Then 100 g of methyl ethyl ketone were added thereto, as well as 63.2 g of sodium methallylsulfonate. Then, the system temperature was raised to the reflux point, and 0.25 g of a 1% aqueous solution of FeSO4 (as Fe) was added. Then 40 g of 60% aqueous hydrogen peroxide were added dropwise over a period of 6 hours. After the addition was complete, the reaction mixture was heated for an additional 2 hours. After removal of the residual methyl ethyl ketone under vacuum, the moisture content of the mixture was adjusted so as to give a polymer solution having a solid content of 40% (pH = 3.8) which will be designated as the polymer (10 ).

Reference examples 11 and 12:

The polymers (11) and (12) were prepared in the same manner as described in reference example 10, except that the sodium methallylsulfonate was replaced by the copolymerizable monomers presented in table 6 below. after. ->

Example 5:

The following scale inhibition test was performed to examine the scale inhibition effect of aqueous solutions containing the

- »Table 6

Example of ref. No.

Monomer composition (moles)

Molecular weight

Polymer No

Maleic acid

Copolymerizable monomer

10

100

Methallylsulfonate

sodium 20

770

(10)

11

100

Acrylic acid 25

900

(H)

12

100

Acrylamide 40

1050

(12)

polymers according to the present invention as prepared in the reference examples 7 to 9.

300 (of an aqueous solution 1% of each of the polymers as prepared in the reference examples 7 to 9 were added to 150 g of an aqueous solution of sodium chloride dihydrate 0.176%, and 150 g of a further 0.168% aqueous sodium hydrogencarbonate solution was added to the mixture, after adjusting the pH to a value of 8.0, the mixture was introduced into a glass bottle, sealed and allowed to stand at 50 ° C for Then the mixture was cooled and the precipitate formed was filtered through a 0.1 μm membrane filter. The calcium concentration in the filtrate was then determined by titration with EDTA. results obtained.

In addition, the results obtained without the use of a scale inhibitor and those obtained using polymaleic acid synthesized by an organic method and a commercially available polysodium acrylate are also presented in Table 7 for comparison.

Table 7

Tartar inhibitor

Quantity (ppm)

pH of the aqueous solution after test

CaCO3 in the filtrate (ppm)

M-alkalinity of the filtrate (ppm)

Inhibition rate (%)

Sample according to the invention

Polymer (7)

10

8.0

580

480

94

Polymer (8)

10

8.1

585

475

95

Polymer (9)

10

8.0

575

475

93

Sample for comparison

Commercial polysodium acrylate *

10

7.9

505

390

72

No

0

7.1

260

135

0

Polymer (6)

10

8.0

570

465

91

*: Molecular weight = 3000.

**: Inhibition rate = (B — C) / (A — C) x 100 A: Ca concentration before heating,

B: Ca concentration in the filtrate after examination, C: Ca concentration in the filtrate after examination without using an additive.

Example 6:

The following test was carried out in order to examine the scale inhibition effect of the polymers according to the present invention prepared in reference examples 7 to 12 on a seawater heating system.

Twice concentrated artificial seawater has been circulated in a device in which this seawater passes through a stainless steel pipe with an internal diameter of 6 mm while being heated to 110 ° C, with a flow of 3201 / h for 20 hours. The scale adhering to the surface of the pipe in the heater was dissolved by washing with an acid and determined by atomic absorption spectroscopy to examine the scale inhibiting effect of each of the inhibitors.

Table 8 presents the results obtained.

Table 8

Tartar inhibitor

Quantity (ppm)

Fixed scale * (mg / m2)

Sample according to the invention

Polymer (7)

10

480

Polymer (8)

10

470

Polymer (9)

10

490

Polymer (10)

10

490

Polymer (11)

10

480

Polymer (12)

10

480

Sample for comparison

Commercial polysodium acrylate

10

1280

No

0

6300

Polymer (6)

10

530

* Total amount of CaCO3 and Mg (OH) 2 per unit area of the heat transfer tube.

r

Claims (8)

668,975 2 1. Scale inhibitor comprising a polymer or copolymer of maleic acid represented by formula (I) or a salt thereof: Ri- -CH- -CH-I COOM COOM R, -ch, -R, (I) in which R 1 and R 2 are a hydrogen atom, a hydroxyl group, an alcohol residue having from 1 to 4 carbon atoms or a ketone group having 3 or 4 carbon atoms, R 1 and R 2 not being simultaneously hydrogen or a hydroxyl group, M is a hydrogen atom, NH4, an alkali metal or an alkaline earth metal, m is 2 to 40, n is 0 or a positive number, the total of m and n being 15 3 to 80 when n is positive, the ratio of n to m being from 0/100 to 100/100, R3 is a hydrogen atom or a methyl group, A is a group chosen from —COOM, - CONH2, - CH2OH, —CH2S03M, - so3m, phenyl, - COOR4 or - <ô> - so3m, OH OH OH OH CH, -CH2-CH, -CH- OH CH, ch3 I ch3 ch3-ch2-c-, ch3-ch-ch-, ch3-c-ch2- OH OH I OH 20 R4 is a saturated hydrocarbon group having 1 to 6 carbon atoms. 2. Scale inhibitor according to claim 1, characterized in that the said copolymer has a molecular weight of 200 to 5000 on average. 3. Scale inhibitor according to claim 1, characterized in that the alcohol residue is one or more of the following groups: ch3 30 ch2-, ch3-ch-, ch3-ch2-ch-, ch3-c-, 4. Scale inhibitor according to claim 1, characterized in that the said ketone group is one or more of the following groups: O OO He II II ch3-c-ch2-, ch3-ch2-c-ch2-, ch3-c-ch- I ch3 5. Scale inhibitor according to claim 1, characterized in that the said copolymer has 20 mol% or more of alcohol residue and / or of ketone group in Rx and / or R2. 6. Scale inhibitor according to claim 1, characterized in that the said copolymer comprises up to 5% by weight of other vinyl monomer units. 7. Scale inhibitor according to claim 1, characterized in that n is 0. 8. Scale inhibitor according to claim 1, characterized in that the ratio of n to m is from 5/100 to 100/100.