Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Reexamination Certificate
2000-02-23
2001-05-22
Ogden, Necholus (Department: 1751)
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
C252S079000
Reexamination Certificate
active
06235217
ABSTRACT:
BACKGROUND OF THE INVENTION
Technical Field
This invention relates to an acid based antifreeze formulation for inhibition and prevention erosion and corrosion of aluminum and the corrosion of other metals exposed to an aqueous liquid in automotive coolant systems. The formulation further inhibits mineral scale. Traditionally antifreeze/coolant is sold at nearly one-hundred percent glycol content. This concentrated packaging allows for flexibility so that the user can dilute the antifreeze/coolant, as needed, with available water to obtain the required freeze/boil protection. However, corrosion protection is needed over the entire dilution range.
In modern automotive engineering, many engine components are fabricated from aluminum. Engine coolants, primarily ethylene glycol or propylene glycol based solutions, must transfer heat from operating aluminum engines while inhibiting corrosion. Older automotive engines did not have aluminum components and thus, the traditional antifreeze/coolant compositions may produce corrosion in heat rejecting aluminum or aluminum alloy components. The cavitation erosion-corrosion of aluminum water pumps upon exposure to aqueous systems such as water-cooled internal combustion engine coolants is a relatively new development.
DESCRIPTION OF THE PRIOR ART
Automotive engine cooling systems consist of many metals including aluminum, steel, cast iron, brass, copper and solder. Engine coolants must not only provide freeze protection but corrosion inhibition as well. Often the components are thin walled for improved heat transfer making them more vulnerable to corrosive attack and subsequent failure. Corrosion products and deposits can interfere with heat transfer. Ultimately overheating and engine failure from thermal related stresses are possible.
Traditionally engine coolants based on inorganic components like silicates, phosphates, nitrates, borates and nitrites have been used. Concerns due to inhibitor depletion, particularly silicates have lead to concerns about lifetime. Also, high solids loading from inorganic salts presents potential deposit issues. Amine and nitrite compounds, which are often employed as corrosion inhibitors in antifreeze formulations may form potentially dangerous nitroso compounds when used together. Antifreeze formulations containing phosphates are often diluted with hard water which results in precipitation of insoluble alkali earth phosphate salts from the aqueous antifreeze solution. The precipitation may cause depletion of the phosphate in solution and a decrease in corrosion protection with the antifreeze solution. The precipitating solids may scale and plug passages within the engine coolant system. Moreover, several European automobile manufacturers have banned the use of phosphate-containing antifreeze based on silicate formulations due to hard water compatibility problems.
Recently the automotive industry has developed engine coolants based primarily on carboxylic acid technology. Many U.S. and foreign patent references disclose the use of various monobasic or dibasic acids or salts as corrosion inhibitors. For example, in U.S. Pat. No. 4,647,392, Darden teaches a synergistic combination of 0.1 to 15 weight percent of C
5
to C
6
aliphatic monobasic acid with the same amount of C
5
to C
6
dicarboxylic acid and 0.1 to 0.5 weight percent of a hydrocarbonyl triazole. The triazole is typically tolytriazole or benzotriazole. The acids are present as salts in an alkaline solution. In U.S. Pat. No. 4,946,616, Falla teaches a mixture of two aliphatic dicarboxylic acids with a hydrocarbyl triazole. In U.S. Pat. No. 4,587,028, Darden discloses two to five weight percent of an aromatic monocarboxylic acid, benzoic acid, with 0.5 to 1.5 weight percent of a C
8
to C
12
aliphatic carboxylic acid and an alkali metal nitrate. British military specification TS 10177 (Al39), March of 1978, call for 4 to 4.5 weight percent of sebacic acid(aliphatic dicarboxylate) and 0.25 to 0.30 weight percent of benzlytriazole. In U.S. Pat. No. 4,382,008, Boreland has combined an aromatic monocarboxylic acid with C
7
to C
13
dibasic organic acids and conventional inhibitors such as borate and silicate to prepare formulations. However, the use of these additives increase the overall cost of the formulation.
U.S. Pat. No. 5,366,651 by Maes et al. emphasizes that imidazole serves as a buffer to assist in pH control and serve as the buffer in carboxylic acid based antifreeze formulations. Imidazole is an unsubstituted triazole containing two nitrogen molecules providing a very active triazole molecule to combine with hydrogen providing a neutralizing or buffering capability.
In summary, a wide number of organic acids have been successfully used in various combinations among themselves and with more common components. Typically acids are used at the several percent level if common inhibitors are not present. The presence of hydrocarbyl triazoles indicates that yellow metals such as copper and brass, and solder must be protected separately. The carboxylates are primarily inhibiting ferrous metals and aluminum in these formulations. Despite the successful lab data reported, questions remain about the ability of full acid technologies like Darden and Falla to protect solder and prevent cavitation erosion-corrosion on aluminum in engine applications. Further, the addition of large quantities of inorganic salts to correct these deficiencies negates the low solids benefit.
SUMMARY OF THE INVENTION
The present invention has met the above-described need by providing an antifreeze/coolant composition using a combination of an aliphatic carboxylic acid, hydrocarbyl tolytriazole, and low levels of molybdate additives which reduce corrosion over the entire dilution range without creating precipitates. This composition is soluble in water, alcohol, and alcohol/water mixtures, is compatible with other commonly used antifreeze/coolant components, does not corrode or damage automotive cooling systems and is effective at relatively low concentrations. In addition, the present corrosion inhibition formulations are effective in reducing corrosion in the entire range of cooling system metals, including heat rejecting aluminum, aluminum alloys, copper, steel, cast iron, brass, solder and the like.
The instant antifreeze formulation having a mixture of ethylene or propylene glycol, monobasic aliphatic organic acid, azoles, and low levels of molybdates may also provide a protective effect against the cavitation corrosion of aluminum in aqueous liquids reducing the corrosion rate which is effective at relatively low concentrations and varying pH ranges. The combination of monobasic aliphatic organic acid, hydrocarbyl tolytriazole, and low levels of molybdates not only significantly reduces glycol based coolant cavitation erosion-corrosion, heat rejecting aluminum corrosion, and hard water precipitates and scale, it has been discovered that the combination leads to improvement in aluminum corrosion protection and coolant life when utilized with selected amounts of the above-identified additives. Thus, the formulation is particularly suitable for automotive gasoline and diesel engine coolant applications.
It is an object of the present invention to provide corrosion inhibition formulations for antifreeze/coolant compositions for reducing glycol based coolant cavitation erosion-corrosion.
It is another object of the present invention to provide corrosion inhibition formulations for antifreeze/coolant compositions utilizing an acid based formula for enhancing coolant stability providing an improvement in coolant life.
It is another object of the present invention to provide corrosion inhibition formulations which reduce corrosion over the entire dilution range of antifreeze/coolant compositions without creating precipitates.
It is an additional object of the present invention to provide corrosion inhibition formulations which are effective in reducing corrosion in the entire range of cooling system metals.
It is an additional object of the present invention to provide corro
Coffey, Jr. Arnold L.
Dituro Michael A.
Olsen Alden W.
Stephens Carl R.
Turcotte David E.
Ashland Inc.
Carrithers David W.
Carrithers Law Office
Ogden Necholus
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