Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Maintaining environment nondestructive to metal
Reexamination Certificate
1999-10-18
2002-06-11
McKane, Elizabeth (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Maintaining environment nondestructive to metal
C422S017000, C252S389210, C252S180000, C252S390000
Reexamination Certificate
active
06403028
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an all-organic corrosion inhibiting composition comprising (a) 6,6′,6″-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid; and (b) a water-soluble phosphonated oligomer salt. The invention also relates to a process for inhibiting corrosion in a closed recirculating cooling water system.
BACKGROUND OF THE INVENTION
Chemicals are added to recirculating closed and semi-closed cooling water systems, e.g. hot water boilers, chilled water systems, sweet water, free cooling tempered water, process condensate waer, desalter water, geothermal brine, lithium bromide refrigerant brines, automotive engine coolant jacket systems, water pumps and engine jackets, etc. to prevent the corrosion of metal surfaces, particularly corrosion of steel, brass, aluminum, and copper, that are in contact with water. A closed system recirculates water without evaporative cooling and usually has a low level of water loss.
For years, inorganic chemicals, such as heavy metals (chromate and molybdate) or nitrite containing corrosion inhibitors, were typically used in closed systems. When chromate was banned from use in many recirculating cooling water systems and regulations were enacted restricting the discharge of other inorganic chemicals, interest developed in using corrosion inhibitor formulations containing only organic chemicals for closed cooling water systems.
One of the widely used closed system organic corrosion inhibitors is 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid which is available from FMC Corporation under the trademark “BELCOR 590”. BELCOR 590 is a 49% solids wet cake of 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid. It is known to use BELCOR 590 as a corrosion inhibitor in formulations for closed recirculating cooling water systems.
U.S. Pat. No. 5,386,038 discloses that a mixture of water-soluble phosphonated oligomer salts is effective as corrosion inhibitors in formulations for both open and closed recirculating cooling water systems. BRICORR 288, available from Albright & Wilson, is a 40% solids mixture of water-soluble phosphonated oligomer salts.
Although many organic formulations were developed to inhibit the corrosion of metals in recirculating cooling water systems, these formulations were more expensive than the inorganic formulations they replaced. In order to make these all-organic formulations cost competitive, formulators search for blends which are synergistic. Organic synergistic blends can compete with inorganic corrosion inhibitors because they are effective at significantly lower dosages. The prior art does not disclose blends of 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid and water soluble phosphonated oligomer salts to inhibit the corrosion of metal exposed to closed recirculating aqueous systems.
SUMMARY OF THE INVENTION
This invention relates to all-organic corrosion inhibiting compositions comprising:
(a) 6,6′,6″-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid; and
(b) water-soluble phosphonated oligomer salts.
The invention also relates to a process for inhibiting corrosion in a closed recirculating cooling water system. The corrosion inhibiting compositions are particularly effective at inhibiting the corrosion of metal surfaces made of mild steel where steel is found alone in the components of the cooling system, or where there are components present made of other metals, such as brass, copper, aluminum, and or alloys. The blends are synergistic because they inhibit corrosion to a greater extent than was expected in view of the corrosion inhibition activity of the individual components. Because the blends exhibit synergism, they are more cost effective. The compositions are environmentally desirable because they are relatively non-toxic, contain no heavy metals, and have low or no phosphorus. The compositions may also contain an azole compound and/or a water-soluble, anionic polymeric dispersant, silicates, and other components known in the art for use in corrosion inhibiting compositions.
BEST MODE AND OTHER MODES
Component (a) of the corrosion inhibitor composition is 6,6′, 6″-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid. A commercially available product containing this component is BELCOR 590 sold by FMC as a 49% solids wet cake.
Component (b) of the corrosion inhibitor composition is a water-soluble phosphonated oligomer salt, preferably a sodium salt, and typically found as a mixture of oligomers. These oligomers are described in U.S. Pat. No. 5,386,038 which is incorporated by reference. The general structural formula for these water-soluble phosphonated oligomer salts is:
H[CHRCHR]
n
—PO
3
M
2
wherein at least one R group in each unit is a COOM, CH
2
OH, phosphono, sulphono, or sulphato group. 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, carboxylate, hydroxyl C
1-7
alkyl, or a C
1-7
alkenyl group. M is a cation such that the phosphonated oligomer is water soluble and n is 1 to 6, preferably >1 and <6.
Preferably used as the water-soluble phosphonated oligomer salt 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.
The weight ratio of active 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid to active phosphonated oligomer is from 9:1 to 1:9, preferably from 4:1 to 1:1. It has been found that a synergy exists between the 6,6,6-(1,3,5-triazine-2,4,6-triyltriimino) tris hexanoic acid and the water-soluble phosphonated oligomer salts if used in these amounts in a closed recirculating cooling water system.
Azoles can also be used in the corrosion inhibiting compositions to improve corrosion inhibition for copper and copper alloys. Examples of azoles that can be used in the corrosion inhibiting compositions include thiazoles and triazoles, for instance mercaptobenzothiazole, tolyltriazole, benzotriazole and 5-methylbenzotriazole. Active azole levels in the corrosion inhibitor systems range from 0.1 to 15 parts, preferably from 2 to 3 parts by weight of azole, based upon the total weight of the composition.
It may also be useful to use water soluble, low molecular weight, anionic polymeric dispersants when treating waters that contain high levels of impurities such as hardness salts (calcium carbonate, calcium phosphate) or suspended solids (iron or corrosion products). Examples of water soluble, low molecular weight, anionic polymeric dispersants that can be used in the corrosion inhibiting compositions include, but are not limited to, polyacrylates, acrylic acid copolymers, polymethacrylates, polymaleic anhydrides, maleic anhydride copolymers and sulfonated polymers and copolymers with molecular weights typically ranging from 500 to 20,000. These water soluble, low molecular weight, anionic polymeric dispersants exhibit deposit control efficacy using general dispersancy for suspended solids and corrosion products as well as sequestration, crystal lattice distortion and threshold inhibition for mineral scale deposits. The addition of a polymeric dispersant to the formulation is optional and may be unnecessary in waters with low levels of impurities. The water-soluble, low molecular weight, anionic polymeric dispersants are used in the corrosion inhibitor systems in the amount of 0.1 to 5 parts, preferably from 0.4 to 0.6 parts by weight of polymer, based upon the total weight of the composition.
A preferred closed recirculating cooling water corrosion inhibitor formulation of the present invention includes BELCOR 590 and BRICORR 288 at an actives ratio from 1:9 to 9:1 with total active BELCOR 590/BRICORR 288 solids in the formulation ranging from 1 to 25 parts, an azole compound with total active solids in the formulation ranging from 0.1 to 15 parts and a water soluble, a low molecular weight, anionic polymeric dispersant for mineral scale, and corrosion produc
Beardwood Edward S.
Colby Steven J.
Emerich Dwight E.
Ashland Inc.
Hedden David L.
McKane Elizabeth
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