FR2533549A1 - COMPOSITION AND METHOD FOR INHIBITING TARTAR FORMATION - Google Patents

Abstract

The invention relates to a composition for inhibiting the formation of tartar in an aqueous system. ACCORDING TO THE INVENTION, A COMPOSITION IS ADDED COMPRISING A COPOLYMER OF MALEIC ACID OR ANHYDRIDE AND VINYL SULPHONIC ACID AND AN ORGANIC PHOSPHONATE SUCH AS AMINOTRI ACID (METHYLENE PHOSPHONIC), HYDROXYETHOSELPHONIC ACID, SULPHONIC ACID, OR DIPHELPHONIC ACID. THE WATER. THE INVENTION APPLIES IN PARTICULAR TO THE TREATMENT OF WATER FROM BOILERS, WATER HEATERS, HEAT EXCHANGERS, COOLING TOWERS, DESALINATION SYSTEMS, CLEANING SYSTEMS, PIPELINES, GAS PURIFYING SYSTEMS .

Description

The present invention relates to the treatment of aqueous systems and

  in particular, the inhibition and removal of solid deposits in

  industrial heating and cooling.

  Water used in aqueous industrial systems such as steam generating boilers, hot water heaters, heat exchangers, cooling towers, desalting systems, cleaning systems, pipelines, scrubber systems gas and associated equipment contains various impurities

  impurities typically comprise alkaline

  earth-like calcium, barium and magnesium and various anions such as bicarbonate, carbonate, sulphate, oxalate, phosphate, silicate and fluoride These anions and cations combine and form

  precipitates due to their pH, pressure or temperature

  in the system or the presence of additional ions

  with which they form insoluble products.

  The most common impurities in industrial water sources are water-hardening ions such as calcium, magnesium, and carbonate ions. In addition to precipitating as carbonates, calcium and magnesium as well as any iron or copper present can also react with the phosphate, sulphate and silicate ions and form the respective insoluble complexes These solid reaction products accumulate on the surfaces of the system and form scale. Water can also contain various solids such as mud, clay, iron oxides, silt,

  sand and other mineral matter and micro debris.

  that accumulate as sludge deposits in the system Iron oxides may be present in the feedwater and may be produced by

  corrosion of metal surfaces in contact with water.

  * Sludge may be incorporated into scale deposits and precipitates tend to cement

  mud particles and to form a strongly adherent scale.

  Sludge and scale deposits greatly reduce the efficiency of heat transfer by depositing at low flow points in the system and by limiting the flow of water and isolating it from heating surfaces. In addition to interfering with With heat transfer and fluid flow, corrosion of the metal surfaces beneath the deposits is facilitated because corrosion control agents can not effectively contact surfaces. Deposits also harbor bacteria Removal of deposits may cause corrosion

  costly delays and shutdown of the system

  high temperatures in generator boilers

  steam and hard water are particularly

  Tartar Extremely large scale deposits can cause overheating

  localized and a break in boilers.

  Since external treatments such as softening, coagulation and filtration do not adequately remove solids and solids, various internal chemical treatments have been used to prevent and remove scale and sludge in aqueous systems. The chemical treatment for boilers generally includes the combined use of a precipitating agent and a solids conditioner to maintain the solids in the boiler water in a suspended state for effective removal with the drained water of the boiler. boiler by purging The precipitating chemicals commonly used for calcium salts are anhydrous sodium carbonate and sodium phosphates. Alkalinity of boiler water

  precipitates magnesium as magnesium hydroxide.

  A wide variety of polycarboxylates and other water-soluble polar polymers such as acrylate polymers have been used as solids conditioners in industrial water systems. The presence of small amounts of these polymers improves the fluidity of the sludge and has the effect of result in the formation of amorphous, brittle and serrated precipitates instead of hard, dense crystals that form scale on the surfaces The finely dispersed solid particles remain in suspension and are driven out of the system by the flow of water or by purging . Phosphonates are used intensively in the treatment of water as precipitation inhibitors and are effective in threshold quantities.

  significantly lower than the stoichiometric

  metric required to chelate or sequester the cation

forming scale.

  The scale inhibitor for aqueous systems of Greaves and Ingham UK Patent Publication No. 2 061 249 comprises a water-soluble phosphonate and a vinyl addition copolymer or its water-soluble salts. The phosphonates contain at least one carboxylic acid group and at least one phosphonic acid group and have at least three groups

  acids that are attached to the carbon atom

  polymers are generally derived from ethylenically unsaturated acids such as maleic acid (or anhydride), acrylic acid and methacrylic acid and they have carboxylic or carboxylic anhydride groups and sulfonate groups. A particularly preferred phosphonate is the acid 2-Phosphonobutane-1,2,4-tricarboxylic acid The preferred copolymers comprise a copolymer of methacrylic acid and 2-acrylamido-2-methylpropanesulphonic acid and a copolymer of styrene sulfonic acid and maleic acid when R 2 is hydrogen and that Y is a sulfonic acid radical in the formula disclosed for the sulfonate-containing copolymer unit and that the ethylenically unsaturated unit is maleic anhydride, the copolymer is a vinyl sulfonic acid copolymer and In the examples, it is shown that combinations of a copolymer of methacrylic acid and 2-acrylamido-2-methylpropane and phosphonobutane carboxylic acids have a synergistic effect and that the polymer combinations with

  other phosphonates including nitrolotris-

  methylene phosphonic acid, hydroxyethylidene acid

  and hexamethylene diamine tetra-

  methylene phosphonic, do not have it. U.S. Patent Nos. 4,255,259 and 4,306,991 to Hwa and Cuisia disclose a composition for inhibiting scale in aqueous systems which comprises a copolymer of styrene sulfonic acid and maleic anhydride or maleic acid and a phosphonic acid soluble in water or its salts Various phosphonic acids including hydroxyethylidene diphosphonic acid and

  amino methylene phosphonic acid can be used.

  The composition for inhibiting scale formation in an aqueous system of the present invention comprises (a) a copolymer of maleic acid or anhydride and vinyl sulfonic acid or its water-soluble salt; and (b) an organic phosphonate of the general formula: R Nt (CH CH t

R R

o R is he

-CH 2-P-OH

  OH 1 n is 0 to 6, and x is 1 to 6; or of general formula: O R O 0 R O

HO-P-C-4-OH

III

HO X OH

  X is -OH cu -NH 2 and R is an alkyl group of 1 to 5 carbon atoms; or its water-soluble salt The method of inhibiting scale formation in an aqueous system of the present invention comprises adding to the system a quantity of the composition

inhibiting scale.

  The present invention produces unexpectedly superior inhibition of scale deposition and scale formation, particularly those containing calcium and magnesium phosphates and silicates and iron oxide, on the metal structures of the catalyst systems. industrial water The composition and the process are effective

  when used in water at high temperatures

  The invention exhibits the threshold effect of inhibition of the formation of metal salt crystals and the copolymer remains soluble in water of high hardness and high alkalinity. and preventing their adhesion to heat transfer surfaces at low

treatment levels.

  In the present invention, water-soluble aminoalkylenephosphonic, hydroxy or aminoalkylidene phosphonic acids or their soluble salts are employed

  in water The preferred compounds are amino acid

  tri (methylene phosphonic) hydroxyethylidene-1, 1-

  Diphosphonic acid and their water-soluble salts This alkylidene diphosphonic acid is marketed and its preparation as well as that of such phosphonic acids is described for example in US Pat. Nos. 3,214,454 and 3,297,578. Aminophosphonic acid altogether. The preferred method is commercialized and its preparation as well as that of other such phosphonic acids is described in US Pat. Nos. 3,234,124 and 3,298,956. Other suitable phosphonic acids having these formulas include ethylenediamine tetra (methylene phosphonic acid). diethylenetriamine penta (methylene phosphonic acid), triethylenetetraamine hexa (methylene phosphonic acid), hexamethylenediamine tetra (methylene phosphonic acid), aminoethylidene diphosphonic acid, aminopropylidene diphosphonic acid, hydroxypropylidene diphosphonic acid, hydroxybutylidene diphosphonic acid and

hydroxyhexylidene diphosphonic acid.

  The composition according to the present invention additionally contains an aliphatic copolymer of maleic acid or anhydride and of vinyl sulphonic acid or its water-soluble salts. The polymers can be prepared by copolymerization of maleic acid or anhydride with vinyl sulphonic acid or its salt

  alkaline metal Conventional methods of polymeric

  In general, the copolymerization can be carried out at a temperature of from about 30 to about 120 ° C. using a peroxide catalyst such as hydrogen peroxide or hydrogen peroxide. benzoyl peroxide in an inert medium

  copolymer can be derived, for example, by polymerisation

  in solution of maleic acid and vinyl sulphonate

  sodium in the presence of hydrogen peroxide.

  Another method of producing the copolymers is to copolymerize a polymerizable monoethylenic compound such as methyl vinyl ether, ethyl vinyl ether or vinyl acetate; resolubilizing the polymer by alkaline or acid hydrolysis to substitute the ether or ester groups with hydroxyl groups;

  and to sulfonate the polymer according to conventionally

  as described in US Patent No. 2,764,576.

  The degree of sulfonation may vary, but a

substantially complete sulfonation.

  The relative proportions of vinyl sulfonate and maleic anhydride depend on the degree of scale inhibition that is required. The copolymer contains

  generally from about 10 to about 90 mole percent of the sulfonate.

  Preferably, the ratio of moles of vinyl sulfonate moieties to maleic acid derivative moieties is from about 0.5: 1 to about 4: 1 and

  particularly from about 1: 1 to about 2: 1.

  The average molecular weight of the copolymer is

  not critical as long as the polymer is soluble in water.

  In general, the molecular weight is from about 500 to about 100,000. The molecular weight is preferably from about 1,000 to about 25,000 and more.

  particularly from about 6,000 to about 10,000.

  Copper acid forms of particular copolymers

  the most preferred are :-

H H H H

H -CC C C H

I I I I

C = O C = O H SO 3 H

  ## STR1 ## are in statistical order and m is from about 20 to about 70 mole%, N is from about 30 to about 80 mole%, and

  molecular weight is from about 10,000 to about 25,000.

  Phosphonates and copolymers are generally

  These are used in the form of an alkali metal salt and usually in the form of the sodium salt. Other suitable water-soluble salts include the salts

  of potassium, ammonium, zinc and lower amine.

  Free acids can also be used and not all acidic hydrogens need to be replaced and the cation need not be the same for those that are replaced. Thus, the cation can be taken from NH 4, H, Na, K and Other or their mixture The copolymer is converted to soluble salts

  in water by conventional methods.

  While it is possible to add, separately, in an aqueous system, the phosphonate and the copolymer, it is generally more convenient to add them together in the form of a composition. The composition of the present invention generally contains about 0, 1 to about 100, preferably about 2 to 6 parts by weight of the copolymer and about 0.1 to about 100, preferably about 0.5 to 5 parts by weight of the phosphonate.

  polymer and phosphonate are used in

  generally from about 10: 1 to about 1:10, preferably from about 4: 1 to about 1: 4 and more

especially about 1: 1.

  The compositions can be added as dry powders and allowed to dissolve during use, but normally they are used in the form of aqueous solutions. The solutions generally contain from about 0.1 to about 70% by weight of the composition and preferably contain from about 1 to about 40% by weight The solutions can be formed

  adding the ingredients to water in any order.

  The amount of the composition added to the water is a substoichiometric amount which is effective in inhibiting scale and sludge and which depends on the nature of the aqueous system to be treated The phosphonate dosage depends at some point on the amounts of compounds causing the hardness and tartar which are present in the system In general, the quantity is calculated from the calcium concentration and the consequent hardness of the water The dosage of the copolymer depends at a certain point on the concentration of the solids in suspension and existing levels of solid build-up in the system The composition is generally added to the aqueous system in an amount of from about 0.01 to about 500 parts per million (ppm) and preferably about 0, 1 to about 50 parts per million of water

of the system.

  The composition according to the invention may contain or be added to water containing other ingredients usually employed in the treatment of water such as alkalis, lignin derivatives, other polymers, tannins, other phosphonates, biocides and corrosion inhibitors The composition may be introduced at any location where it will be rapidly and efficiently mixed with the system water. Treatment chemicals are usually added to make-up or water lines. Water supply water enters the system Typically, a calibrated injector for periodically or continuously dispensing a predetermined amount into makeup water is employed. The present invention is particularly useful for treating feed or make-up water in a steam generating boiler. Such boiler systems generally operate at a temperature of about 148 to about 3360 ° C.

  pressure from about 3.44 to about 138 bar.

  The composition and method of use of the invention are illustrated by the following examples where all parts are by weight unless

not indicated otherwise.

  EXAMPLES 1 and 2 Aqueous solutions of a composition containing one part of hydroxyethylidene diphosphonic acid or of aminotri (methylenephosphonic acid) and one part of a copolymer of sodium vinylsulphonate were prepared.

  and maleic anhydride having a molecular weight of

  8,000 and a molar ratio of sodium vinyl sulfonate

  to maleic anhydride of 1.5: 1.

  also contained sodium phosphate, sodium sulfate, sodium sulfite, sodium hydroxide, and sodium chloride in amounts sufficient to produce the boiler water composition shown below in Table I 1 Solutions containing the identical amounts of the process chemicals except for the composition of the present invention and solutions containing identical amounts of the process chemicals and a portion of each component of the process

  composition were also prepared.

  The sludge conditioning and scale inhibiting properties of these solutions were evaluated

  in a small laboratory boiler that had three-

  removable tubes as described in Proceedings of the Fifteenth Annual Water Conference, Engineers Society of Western Pennsylvania, USA pages 87-102 (1954) The feed water for the laboratory boiler was prepared by diluting tap water Lake Zurich, Illinois, United States of America, with distilled water up to a total hardness of 40 ppm as CaCO 3 and adding calcium chloride to produce a ratio

  elemental calcium to elemental magnesium from 6 to 1.

  Feedwater and chemical solutions of -

  treatment were fed to the boiler at the rate of 3 volumes of feed water per 1 volume of the solution, giving a total hardness of the feed water of ppm Ca CO 3 The descaling tests for all the solutions treatment was undertaken by adjusting the boiler purge to 10% of the boiler feed water, giving approximately 10 concentrations of the boiler's salt water and adjusting the composition of the treatment solution to give boiler water after the concentrations having the indicated composition

in table I.

TABLE I

  Sodium hydroxide as NaOH 258 ppm Sodium carbonate as Na 2 C 03 120 ppm Sodium chloride as Na Cl 681 ppm Sodium sulphite as Na 2503 50 ppm Sodium sulphate as Na 2504 819 ppm Silica as Si O 2 less than 1 ppm Fe iron less than 1 ppm Ph as P 04 10-20 ppm The descaling tests were carried out for 45 hours, each at boiler pressure At the end of one test, the boiler tubes were individually removed from the boiler and the tartar or deposit was scraped off 15.24 cm from the center length of each tube. , it was collected in a test results Test N

  2

  Additive None (white) Copolymer of sodium vinyl sulfonate and maleic anhydride (I)

Hydroxy acid

ethylidene

diphosphonic

(II)

Amino acid

tri (methylene phosphonic (III)

I + II

I + III

flask weighed and weighed.

are shown in Table II.

TABLE II

  Rate of reduction of additive detar of tif in trag 9 tartar ali (g / m / h (%) mentation (E Pfi 2.02 0.31 1.56 0.796

O, 021

  0.161 84.6 22.9, 6.98.9 92.0 The comparison results on scale formation in Table II demonstrate that the composition and method of the present invention produce scale-scale inhibition which is very substantially

  greater than the added components alone.

R E V E N D I C A T IO N S

  A composition for inhibiting scale formation in an aqueous system, characterized by comprising a) a copolymer of maleic acid or anhydride and vinyl sulfonic acid or its water-soluble salt ; and b) an organic phosphonate of the general formula R ## STR2 ##

-CH 2-P-0 H,

  OH n is 0 to 6 and x is I to 6; or of general formula 0 R O O R O il 1 il I

HO-P-C-P-OH

III

HO X OH

  where x is -OH or NH 2 and R is an alkyl group having

  from 1 to 5 carbon atoms; or its salt soluble in water.

  2. Composition according to claim 1, characterized in that the copolymer and the phosphonate are present at a weight ratio of about 4: 1 to

about 1: 4.

  Composition according to Claim 1, characterized in that the copolymer and the phosphonate

  are present at a weight ratio of about 1: 1.

  4. Composition according to any one of

  preceding claims, characterized in that the

  phosphonate is a smino alkylene phosphonic acid or

its salt soluble in water.

  5. Composition according to claim 4, characterized in that the phosphonate is aminotri (methylenephosphonic acid). Composition according to any one of the

  1, 2 or 3, characterized in that the

  phosphonate is a hydroxy acid or amino-alkylidene phosphonic acid. 7. The composition of claim 6, wherein the phosphonate is hydroxyethylidene-1,1-diphosphonic acid. 8. Composition according to any one of

  1, 2 or 3, characterized in that the

  The molar ratio of vinyl sulfonate moieties to maleic acid derived moieties is from about 5: 1 to about 4: 1. 9. Composition according to any one of

  Claims 1, 2 and 3, characterized in that the

  molar ratio of the vinyl sulfonate moieties to the maleic acid derived moieties is between

about 1: 1 and about 2: 1.

  10. Composition according to any one of

  1, 2 or 3, characterized in that the weight

  molecular weight of the copolymer is between about 1 000

and about 25,000.

  11-Composition according to any one of

  1, 2 or 3, characterized in that the weight

  molecular weight of the copolymer is about 6,000 to about

10,000.

  Composition for inhibiting scale formation in an aqueous system, characterized in that it comprises an aqueous solution of a composition comprising: (a) a sodium salt of a copolymer of maleic anhydride and vinyl acid sulfonic acid, said copolymer having a molecular weight of about 6000 to about 10,000 and a molar ratio of vinyl sulfonate to maleic anhydride of about 1: 1 to about 2: 1; and

  (b) a sodium salt of hydroxyethylidene-11-

  diphosphonic acid or aminotri (methylene phosphonic acid); said copolymer and said phosphonic acid being present in a weight ratio of about 1: 1. Method for inhibiting scale formation in an aqueous system, characterized by adding to said system a scale inhibiting amount of a composition according to any one of

claims I to 11.

  Process according to claim 13, characterized in that the composition is added to the aqueous system in an amount of about 0.01 to about

  500 parts per million of the system water.

  15. Process for inhibiting the formation of scale in a steam generating boiler, characterized in that it consists in adding, in the water of the boiler, an aqueous solution according to claim 12 in an amount of about 0.1. at about 50 parts per

million of water in the boiler.