JPS6152760B2 - - Google Patents

Description

[Detailed description of the invention]

The formation of scale and sludge deposits on heating surfaces is the most important problem occurring in industrial boiler operations. To combat the scale-forming tendency of entrained impurities such as calcium and magnesium salts and iron, boiler water is commonly treated with precipitants and sludge conditioners to retain the sludge in the fluid, thereby reducing its Prevents it from adhering to the boiler surface. Precipitating agents commonly used for calcium salts are soda ash (sodium carbonate) and sodium phosphates, such as disodium phosphate, trisodium phosphate or sodium metaphosphate. Magnesium precipitates as magnesium hydroxide due to the alkalinity of the boiler water. The resulting precipitate or sludge, which is made non-sticky and easily handleable by the addition of a sludge conditioner, is "blowdown".
removed from the boiler by (“blowdown”). (“Blowdown” is the operation of draining boiler water, including fluid sludge, from a boiler by rapidly reducing the pressure within the boiler). So far, tannins, lignins,
Starches, polyacrylates and polymethacrylates have been used as sludge conditioners. However, they did not give completely satisfactory results. Although no complete solution to this problem has been found in the prior art, the Applicant has developed a method for satisfactorily controlling and preventing scale formation in steam-generating boilers and for scale build-up in aqueous systems in general. We have fortunately discovered an improved sludge conditioning composition based on the synergistic action of two components that is useful in preventing sludge conditioning. The composition of the present invention comprises (a) a copolymer of styrene sulfonic acid and maleic anhydride or maleic acid, or a water-soluble salt thereof, and (b) a water-soluble organic phosphonic acid having a carbon-phosphorous bond or a water-soluble salt thereof. contains. The present invention provides a method for preventing scale formation in an aqueous medium, particularly water in a boiler, in which the above-mentioned components (a) and (b) are added in an amount of 0.01 to 500 ppm in the medium.
(weight). The components can be added sequentially or as a composition. The most preferred organic phosphonic acid is 1-hydroxyethylidene-1,1-diphosphonic acid (simply referred to as
HEDP). Water-soluble salts thereof are also preferred. A preferred general class of organic phosphonic acids for use in the present invention are those of formulas A, B and C below: In the above formula, m is an integer from 1 to 10, R ₁ is hydrogen or an alkyl group having 1 to 4 carbon atoms, and R ₂ is hydroxyl, hydrogen, or an alkyl group having 1 to 4 carbon atoms. (When m is 2 to 10, each R ₁ does not necessarily have the same meaning, and each R ₂ does not necessarily have the same meaning. ), R ₃ is an alkyl group having 1 to 10 carbon atoms, benzyl or phenyl, and R' is an alkylene group having 1 to 10 carbon atoms. Mixtures of two or more of any of these acids or their water-soluble salts can be used. HEDP falls within formula A. Other specific examples of organic phosphonic acids that can be used in the present invention are those described in the Examples below, including polyalkylene polyamine poly(methylene) phosphonic acids and all of the formulas A, B and C Other types of organic phosphonic acids which are not necessarily within the scope of are included. Copolymers of styrene sulfonic acid and maleic anhydride are well known and commercially available. They contain a copolymer of styrene and maleic anhydride dissolved in an inert organic solvent such as methylene chloride or dichloroethane with sulfuric acid trioxide.
It can be produced by a general method of reacting with an organic phosphorus compound adduct. The resulting copolymer of styrene sulfonic acid and maleic anhydride is insoluble in organic solvents and precipitates from solution. A method for sulfonating copolymers of styrene and maleic anhydride using sulfur trioxide-organophosphorous compound adducts is described in US Pat. No. 3,072,618. The main advantage of the present invention is that the copolymer is approximately
Molecular weight in the range 800-7000000, preferably about 4000
It has a molecular weight of The proportion of styrene sulfonic acid units in the polymer generally ranges from 2 to 98% of the copolymer, more usually and more preferably about 75%. The preferred weight ratio of copolymer or salt thereof: water-soluble organic phosphonic acid or salt thereof is 1:10 to 10:1, particularly 1:1. In use, the concentration of the additive is established in the boiler water at a level approximately 10 times the level in the feed water. Therefore, feed water concentrations of approximately 2 ppm (see Table 2) and 5 ppm (see Table 3) are approximately
It will increase to 20ppm and 50ppm. A particularly preferred range of concentration in the boiler is approximately 0.2~
50 ppm, most preferably about 20 ppm. For either feed water or boiler water, the wide range is approximately
Additives from 0.01 to 500 ppm. US Pat. No. 3,671,448 describes the use of mixtures of amino alcohols and organic phosphonic acids or salts thereof to prevent scale formation. The comparative experiments presented here show that at both high and low temperatures 1-hydroxyethylidene-1,1-diphosphonic acid is not effective for very long. Applicant's US Pat. No. 4,048,066 describes the use to prevent scale formation prior to the addition of various polymers, including styrene sulfonic acid-maleic anhydride copolymerization, among others. There is no suggestion that these copolymers are advantageous over the many other additives proposed, and no suggestion is made of the combination of any of the disclosed polymeric additives with an organic phosphonic acid or its salt. I haven't. As illustrated in Tables 2 and 3 in the Examples below, especially when compared to Examples 2 and 4 and Examples 6 and 8, the additive combinations used in the present invention contain the same amount of styrene sulfonic acid-anhydride. Provides greater scale reduction than can be obtained from maleic acid copolymers alone. The present invention, in particular the synergistic effect of components (a) and (b), is illustrated by the following examples. EXAMPLES Test Methods Used Tests were conducted in a small laboratory boiler with three removable tubes. A small laboratory boiler was used at the Fifteenth Annual Mizawaki Meeting.
Proceedings of the Water Conference, Engineers Society of Western Pennsylvania
Pennsylvania), pp. 87-102 (1954). Upon completion of the test, the unheated boiler tubes are removed from the boiler and any scale or deposits present on the 6 inch (15 cm) center length tubes are removed (by scraping), collected and weighed. . The boiler supply water is from Lake Zurich Illinois, United States.
of America) tap water was diluted with distilled water as CaCO ₃ to 40 ppm total hardness, followed by adjusting the elemental calcium to magnesium ratio to 6:1 using calcium chloride. The boiler feed water is treated with a chemical treatment solution (containing treatment agents consisting of sodium sulfate, sodium sulfite, sodium hydroxide, sodium chloride, phosphates and sludge conditioning reagents except for the blank test). The feed water is supplied to the boiler at a ratio of 3 volumes to 1 volume of feed water to obtain feed water with a total hardness of 30 ppm as CaCO ₃ . All scale formation tests with and without sludge conditioning reagent (blank) were performed in a manner similar to the following: Boiler blowdown was adjusted to 10% of the boiler feed water, thereby The salt in the boiler water was concentrated by about 10 times. Using the feed water described in the previous section, the composition of the chemical treatment solution was adjusted to give boiler water (after concentration 10 times) with the following composition: Table 1 Sodium hydroxide as NaOH 258 ppm Carbonic acid as Na ₂ CO _{3 Sodium} 120ppm Sodium Chloride as _NaCl 681ppm Sodium Sulfite as _Na2SO3 50ppm Sodium Sulfate as _Na2SO4 819ppm Silica as _SiO2 Iron as less than 1ppm Fe as less than 1ppm Phosphate as less than _1ppm PO4 10-20ppm All scale formation tests is 220 psig (15.5
Each test was carried out for 45 hours at a boiler pressure of Kg/cm ² gauge). Examples 1-4 2 ppm in feed of synergistic mixture of styrene sulfonic acid and maleic anhydride copolymer and HEDP
The boiler water sludge adjustment characteristics in Table 2 below are explained below.

[Table] Copolymers ()
3 HEDP() 0.094 86.3
4 + (1:1 weight) 0.000 100.0
Examples 5-8 Experiments were conducted on in-service cleaning of boilers on high iron content scales. The laboratory boiler is
First run for 24 hours to form a hydroxyapatite-type scale on the heated tube using feed water containing 45 ppm total hardness (as _CaCO3 ), 10 ppm (as Fe) ferric chloride and phosphate ions. did. Over a 24-hour period, the average boiler scale formed on the 6-inch (15 cm) center of the three heating tubes was 4.64 hydroxyapatite, which contains a large amount of iron.
It was hot at g. The above pre-scaling (pre-
After scaling), low hardness feed water (0.6 ppm as CaCO ₃ total hardness) and 5 ppm of treatment additives to be tested
A laboratory boiler test was carried out for 45 hours using No phosphate or iron was added. The experimental results are shown in the table below.

[Table] Combine ()
7 HEDP() (0.15) 3.2
8 + (1:1 weight, (0.90) 19.4
i.e. 2.5ppm each)
The additive effect of the compositions of the invention in scale prevention is evident from Tables 2 and 3. Examples 9-22 The following compositions according to the present invention are also compatibly effective in preventing scale formation when tested by the method described above. Example 9 90% copolymer of sodium styrene sulfonate and maleic anhydride (9:1 by weight) with a molecular weight of 500,000 and nitrilotri(methylenephosphonic acid)
10% copolymer. Example 10 Copolymer of potassium styrene sulfonate and maleic anhydride (1:5 by weight) with a molecular weight of 1200
Example 11 80% copolymer of styrene sulfonic acid and maleic acid (2:1 by weight) with a molecular weight of 6000 and 20% hydroxypropylidene diphosphonic acid. Example 12 15% copolymer of ammonium styrene sulfonate and maleic anhydride (1:15 by weight) with a molecular weight of 2,000,000 and 85% of the potassium salt of HEDP. Example 13 10% copolymer of sodium styrene sulfonate and sodium maleate (1:2 by weight) with a molecular weight of 15000 and 90% hexamethylenediaminetetra (methylenephosphonic acid). Example 14 75% copolymer of styrene sulfonic acid and maleic anhydride (20:1 by weight) with a molecular weight of 2000 and 25% sodium salt of diethylenetriaminebenta (methylenephosphonic acid). Example 15 20% copolymer of sodium styrene sulfonate and maleic anhydride (1:1 by weight) with a molecular weight of 250,000 and aminoethylidene diphosphonic acid 80%
%. Example 16 8% copolymer of styrene sulfonic acid and maleic anhydride (8:1 by weight) with a molecular weight of 9000 and
HEDP92%. Example 17 70% copolymer of styrene sulfonic acid and maleic anhydride (4:1 by weight) with a molecular weight of 50,000 and 30% n-butylaminodi(ethylphosphonic acid). Example 18 55% copolymer of styrene sulfonic acid and maleic anhydride (8:1 by weight) with a molecular weight of 3000 and 45% isopropylphosphonic acid. Example 19 Copolymer of potassium styrene sulfonate and maleic anhydride (1:8 by weight) with a molecular weight of 250000
40% and 2-phosphono-butanetricarboxylic acid-
1, 2, 4 60%. Example 20 68% copolymer of styrene sulfonic acid and maleic anhydride (1:20 by weight) with a molecular weight of 5000, 2-
Aminoethylphosphonic acid 32%. Example 21 40% copolymer of styrene sulfonic acid and maleic anhydride (5:1 by weight) with a molecular weight of 2500, 60% tetraethylenepentamine hepta (methylenephosphonic acid). Example 22 25% copolymer of styrene sulfonic acid and maleic anhydride (1:9 by weight) with a molecular weight of 700,000 and 75% methylene diphosphonic acid.

Claims (1)

[Scope of Claims] 1. A composition containing a water-soluble organic phosphonic acid having a carbon-phosphorus bond or a water-soluble salt thereof, which is added to water to prevent scale formation in an aqueous medium, wherein styrene sulfonic acid and maleic anhydride, a copolymer of maleic acid, or a water-soluble salt thereof. 2 The organic phosphonic acid has the following formula A, B or C In the above formula, m is an integer from 1 to 10, R ₁ is hydrogen or an alkyl group having 1 to 4 carbon atoms, and R ₂ is hydroxyl, hydrogen, or an alkyl group having 1 to 4 carbon atoms. (and when m is 2 to 10, each R ₁ does not necessarily have the same meaning, or each R ₂ does not necessarily have the same meaning) ), _R3 is 1~
A composition according to claim 1, having the following: an alkyl group having 10 carbon atoms, benzyl or phenyl, and R' is an alkylene group having 1 to 10 carbon atoms. 3. The composition according to claim 1, wherein the organic phosphonic acid is 1-hydroxyethylidene-1,1 diphosphonic acid. 4. The composition according to any one of claims 1 to 3, wherein the weight ratio of the copolymer or its salt to the water-soluble organic phosphonic acid or its salt is 10:1 to 1:10. 5. The composition according to any one of claims 1 to 4, wherein the copolymer or water-soluble salt thereof contains about 75% by weight of styrene sulfonic acid units and has a molecular weight of about 4,000. 6. Preventing the formation of scale in an aqueous medium by maintaining the total amount of a scale-inhibiting additive containing a water-soluble organic phosphonic acid having a carbon-phosphorus bond or a water-soluble salt thereof at 0.01 to 500 ppm by weight in the aqueous medium. 1. A method for preventing the occurrence of styrene sulfonic acid and maleic anhydride or a copolymer of maleic acid or a water-soluble salt thereof in the aqueous medium. 7. A composition consisting essentially of a copolymer of styrene sulfonic acid and maleic anhydride and 1-hydroxyethylidene-1,1-diphosphonic acid is added to the water, and the additive is added to the aqueous medium at about
7. The method of claim 6, wherein the total concentration is maintained at 20 ppm by weight. 8. The method according to any one of claims 6 to 7, wherein the additive is introduced into boiler water. 9. A method according to any of claims 6 to 8, wherein the additive is maintained in an aqueous medium containing a scale-forming iron salt.