Scale and/or corrosion inhibiting composition

Compositions – Preservative agents – Anti-corrosion

Reexamination Certificate

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C252S390000, C252S396000, C252S387000, C210S697000, C210S700000, C210S749000

Reexamination Certificate

active

06207079

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a scale and/or corrosion inhibiting compositions for aqueous systems comprising (a) polyaspartic acid or salts thereof, and (b) a water soluble phosphonated oligomer. The compositions are effective scale inhibitors, but are also advantageous from an environmental standpoint because they are non-toxic, contain no heavy metals, and have little or no phosphorus. They also have significant calcium/hardness tolerance, are chlorine/bromine stable, and are effective corrosion inhibitors.
BACKGROUND OF THE INVENTION
Water used in industrial cooling or mining systems comes from rivers, lakes, ponds or from underground reservoirs. Such water contains dissolved inorganic salts. When this water circulates through the heat exchangers and cooling towers in a cooling system, a portion of the water is lost due to the evaporation. This increases the concentration of inorganic salts in the system. If the solubility of these salts in water is exceeded, precipitation will take place.
As the salts precipitate on the internal surface of a cooling system, they form scale or deposits. The scale inhibits effective heat transfer, restricts the flow of the water, and promotes the development of underdeposit corrosion. Consequently, it is necessary to remove the scale by cleaning. Such cleaning is expensive because equipment must be shutdown, labor costs are incurred, and production is delayed. In view of these problems, preventing scale formation is preferred to scale removal.
Scale formation can be inhibited by adding a sequestering or chelating compound to the water treatment system. The amount of a chelating/sequestering compound required is a stoichiometric amount based upon the amount of calcium and magnesium cations in the aqueous system cleaned. This method of the scale inhibition is expensive and not customarily used.
More than 50 years ago it was discovered that certain compounds performed as highly efficient scale inhibitors. Such compounds are used in significantly lower than stoichiometric amounts and are known as “threshold inhibitors”. Examples of threshold inhibitors are phosphonates and water soluble acrylic/maleic/sulfonic polymers or copolymers. Corrosion inhibitors, such as phosphonates, inorganic phosphates, azoles, zinc, and molybdate, are often used with scale inhibitors.
In addition to effective performance, water treatment chemicals must be environmentally acceptable. Environmental regulations prohibit the use of such corrosion inhibitors as chromates and restrictions are now prevalent for the use of all heavy metals. The trend is also toward water treatment chemicals that are non-toxic, have little or no phosphorus, have high calcium/hardness tolerance, are chlorine/bromine stable, and at the same time have high scale and corrosion efficacy. Because of these requirements, the cost of water has increased, causing higher reuse/higher cooling cycles which results in cooling waters with high hardness and alkalinity contents.
U.S. Pat. No. 5,523,023 relates to compositions comprising polyaspartic acid and phosphonobutane tricarboxylic acid which are used for alkaline cleaners. U.S. Pat. No. 5,386,038 discloses a water soluble mixture of phosphonated oligomers having the general formula:
H[CHRCHR]
n
—PO
3
M
2
wherein at least one R group in each unit is a COOM, CH
2
OH, phosphono sulphono, sulphato, or phosphono group and the other R group which may be the same as, or different from, the first R group, is hydrogen or a COOM, hydroxyl, phosphono sulphono, sulphato, C
1-7
alkyl, C
1-7
alkenyl group or a carboxylate, phosphono, sulphono, sulphato, and/or hydroxyl C
1-7
alkyl, C
1-7
alkenyl group, and each M is a cation such that the phosphonated oligomer is water soluble and n is 1 to 6, preferably>1 and <6. These compositions inhibit scale formation and/or the corrosion of metal exposed to aqueous systems.
SUMMARY OF THE INVENTION
This invention relates to scale inhibitor compositions for aqueous systems such as cooling waters, mining waters and geothermal waters having high levels of hardness and alkalinity. The compositions comprise:
(a) a water soluble polyaspartic acid or salt thereof; and
(b) a water soluble phosphonated oligomer having the general formula (I):
H[CHRCHR]
n
—PO
3
M
2
wherein at least one R group in each unit is a COOM, CH
2
OH, sulphono, or phosphono group and the other R group which may be the same as, or different from, the first R group, is hydrogen or a COOM, hydroxyl, phosphono, sulphono, sulphato, C
1-7
alkyl, C
1-7
alkenyl group or a carboxylate, phosphono, sulphono, sulphato, and/or hydroxyl substituted C
1-7
alkyl or C
1-7
alkenyl group, and each M is a cation such that the phosphonated oligomer is water soluble and n is 1 to 6, preferably >1 and <6.
The scale inhibiting compositions are synergistic because they inhibit scale to a greater extent than was expected in view of the scale inhibition activity of the individual components. The compositions are environmentally desirable because they are non-toxic, contain no heavy metals, and have low or no phosphorus. They have significant calcium/hardness tolerance, are chlorine/bromine stable, and also effectively inhibit corrosion.
BEST MODE AND OTHER MODES
Component (a) of the scale inhibitor composition is a water soluble polyaspartic acid. For purposes of this invention, the term “polyaspartic acid” shall be construed to include salts and derivatives of polyaspartic acid. Polyaspartic acid, salts thereof, and derivatives of polyaspartic acid are well known and are described in U.S. Pat. No. 5,523,023 which is hereby incorporated by reference. Preferably used is polyaspartic acid having a molecular weight, according to gel-permeation chromatographic analysis, of from 500 to 10,000, preferably 1,000 to 5,000, most preferably 2,000 to 4,000. The polyaspartic acid is preferably used as a salt, in particular as a sodium salt or potassium salt. Whether polyaspartic acid is used in the form of an acid or a salt depends upon the pH of the aqueous system treated. Preferably the salts of polyaspartic acid are sodium salts. Derivatives of polyaspartic acid, for example anhydrides of polyaspartic acid, which can convert into polyaspartic acid as a result of hydrolysis under use conditions, also can be used.
Component (b) of the scale inhibitor composition is a water soluble phosphonocarboxylic oligomer salt, preferably a sodium salt, typically found as mixture of oligomers. These oligomers are described in U.S. Pat. No. 5,386,038 which hereby is incorporated by reference. The general structural formula (I) for these water soluble phosphonocarboxylic oligomer salts is set forth previously under the Summary of the Invention. Preferably used as the water soluble phosphonocarboxylic oligomer salts are salts having the following specific version of the above general structural formula:
H[CH(CO
2
Na)—CH(CO
2
Na)]
n
PO
3
Na
2
where “n”<5. Specific examples of water soluble phosphonocarboxylic oligomer salts include an aqueous mixture of phosphonocarboxylic acid oligomeric salts known as BRICORR 288, manufactured by Albright&Wilson Inc. The weight ratio of phosphonated oligomer to polyaspartic acid to is from 8:1 to 1:12, preferably 4:1 to 1:9, more preferably from 1:4 to 1:9.
For some applications it is preferable to add a water soluble copolymer to the scale inhibiting composition, for instance phosphinocarboxylic polymer, maleic acid or maleic anhydride polymer, acrylic polymer, methacrylic polymer and their copolymers with sulfonic and/or phosphino functionalities, preferably acrylic/sulfonic copolymers or acrylic/maleic copolymers.
Other optional components include phosphonobutane tricarboxylic acid, tolyltriazole, orthophosphate, polyphosphates, hydroxyethylidene diphosphonic acid, amino tri(methylene phosphonic acid).
The scale inhibiting compositions inhibit the formation of calcium carbonate, calcium phosphate, calcium sulfate, and other scale forming substances. They are particularly useful in the pH range of 8.0

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