Antifreeze concentrates based on dicarboxylic acids,...

Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components

Reexamination Certificate

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C252S076000, C252S079000, C252S088100, C252S182280, C252S180000, C252S396000

Reexamination Certificate

active

06802988

ABSTRACT:

The present invention relates to novel antifreeze concentrates based on a mixture of at least two different dicarboxylic acids, molybdate and a mixture of at least two different triazoles or thiazoles. Furthermore, the present invention relates to ready-to-use aqueous coolant compositions which comprise said antifreeze concentrates.
Radiator protection compositions for the coolant circulations of internal combustion engines, for example in automobiles, generally contain alkylene glycols, especially ethylene glycol or propylene glycol, as the main component. For use in the cooling system, they are diluted with water and, in addition to protection from freezing, should also ensure good heat removal. Alkylene glycol/water mixtures are however very corrosive at the operating temperatures of internal combustion engines, and it is for this reason that the various metals, for example copper, brass, iron, steel, cast iron (gray cast iron), lead, tin, chromium, zinc, aluminum, magnesium and the alloys thereof, and solder metals, such as tin solder (soft solder), which may occur in the cooling system, have to be adequately protected from the various types of corrosion, for example pitting, crevice corrosion, erosion or cavitation. The prior art has disclosed a large number of individual chemical substances for use as corrosion inhibitors in such cooling systems.
Antifreezes based on ethylene glycol and containing carboxylic acids, alkali metal molybdate and triazoles or thiazoles are disclosed in EP-B 552 988 (1), DE-A 34 13 416 (2), U.S. Pat. No. 4,561,990 (3) and DE-A 195 47 499 (4).
The operating conditions in modern internal combustion engines mean that today the corrosion protection capability and in particular the high-temperature stability of the coolant have to meet very much higher requirements than in the past with regard to thermal stress on the heat transfer surfaces, pressure and flow rate as well as the choice of a material. The known prior art compositions are unsatisfactory in this respect.
It is an object of the present invention to provide appropriate antifreeze concentrates which do not have the disadvantages of the prior art.
We have found that this object is achieved by antifreeze concentrates based on alkylene glycols or derivatives thereof, which contain
(a) from 0.05 to 10, preferably from 0.1 to 5, % by weight, based on the total amount of the concentrate, of a mixture of at least two different dicarboxylic acids, each of 3 to 16 carbon atoms, in the form of their alkali metal, ammonium or substituted ammonium salts,
(b) from 0.01 to 5, preferably from 0.05 to 2, % by weight, based on the total amount of the concentrate, of one or more alkali metal, ammonium or substituted ammonium molybdates and
(c) from 0.01 to 3, preferably from 0.05 to 1, % by weight, based on the total amount of the concentrate, of a mixture of at least two different corrosion inhibitors selected from the group consisting of the hydrocarbon-triazoles and the hydrocarbon-thiazoles.
The novel antifreeze concentrates can be used wherever the protection of water-containing systems from freezing (as a rule for the range from 0 to −40° C., in particular from −20 to −35° C.) and simultaneously the corrosion protection of the metal housings of water-containing containers are to be ensured. The cooling circulations of internal combustion engines, in particular in automobiles, such as cars and trucks, are of particular interest here. However, the novel antifreeze concentrates can also be used for said purpose in stationary engines, in hot water circulations of central heating systems, in radiators heated by electrical resistors and in solar heating circulations.
In a preferred embodiment, the component (a) is a mixture of two different saturated aliphatic dicarboxylic acids, each of 3 to 16, preferably each of 4 to 12, carbon atoms.
Typical examples of such dicarboxylic acids are malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, dicyclopentadienedicarboxylic acid, phthalic acid and terephthalic acid. Corresponding imides, e.g. succinimide, may be also be used here.
A mixture of succinic acid and sebacic acid is particularly preferred for the component (a).
In a further preferred embodiment, the component (c) is a mixture of two different hydrocarbon-triazoles, in particular of benzotriazole and toluotriazole. However, a mixture of two hydrocarbon-thiazoles or of one hydrocarbon-triazole and one hydrocarbon-thiazole may also be used. Examples of suitable hydrocarbon-thiazoles are benzothiazole and 2-mercaptobenzothiazole.
In a further embodiment, the novel antifreeze concentrates additionally contain
(d) from 0.05 to 5, preferably from 0.1 to 3, % by weight, based on the total amount of the concentrate, of one or more aliphatic or aromatic monocarboxylic acids, each of 5 to 18 carbon atoms, in the form of their alkali metal, ammonium or substituted ammonium salts.
Examples of suitable such linear or branched aliphatic monocarboxylic acids are pentanoic acid, hexanoic acid, octanoic acid, 2-ethylhexanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid and linolenic acid.
Suitable such aromatic monocarboxylic acids are in particular benzoic acid, as well as, for example, C
1
-C
8
-alkylbenzoic acids, such as o-, m- or p-methylbenzbic acid or p-tert-butylbenzoic acid, and hydroxyl-containing aromatic monocarboxylic acids, such as o-, m- or p-hydroxybenzoic acid or o-, m- or p-(hydroxymethyl)benzoic acid.
Aromatic monocarboxylic acids of 6 to 10 carbon atoms which may contain hydroxyl groups are particularly preferred as component (d).
All stated carboxylic acids are present as alkali metal salts, especially as sodium or potassium salts, as ammonium salts or as substituted ammonium salts (amine salts), for example trialkylamines or trialkanolamines.
Furthermore, the novel antifreeze concentrates may additionally contain one or more corrosion inhibitors selected from the group consisting of the alkali metal borates, alkali metal phosphates, alkali metal chromates, alkali metal silicates, alkali metal nitrites, alkali metal nitrates and magnesium nitrate in amounts of, in each case, up to 1, in particular from 0.01 to 0.8, % by weight, based on the total amount of the concentrate.
Examples of such additional corrosion inhibitors are sodium tetraborate (borax), disodium hydrogen phosphate, trisodium phosphate, sodium metasilicate, sodium nitrite and sodium nitrate.
When alkali metal silicates are present, they are expediently stabilized by conventional organosilicosulfonates in conventional amounts.
In addition to said inhibitor components, for example, soluble magnesium salts of organic acids, e.g. magnesium benzenesulfonate, magnesium methanesulfonate, magnesium acetate or magnesium propionate, hydrocarbazoles or quaternized imidazoles, as described in DE-A 196 05 509, may also be used in conventional amounts as further inhibitors.
Furthermore, the novel antifreeze concentrates may additionally contain up to 1, in particular from 0.01 to 0.5, % by weight, based on the total amount of the concentrate, of hard water stabilizers based on polyacrylic acid, polymaleic acid, acrylic acid/maleic acid copolymers, polyvinylpyrrolidone, polyvinylimidazole, vinylpyrrolidone/vinylimidazole copolymers and/or copolymers of unsaturated carboxylic acids and olefins.
However, low molecular weight compounds, for example polycarboxylic acids, such as 2-phosphonobutane-1,2,4-tricarboxylic acid, may also be used as hard water stabilizers or sequestering agents.
The pH of the novel antifreeze concentrates is usually from 6 to 11, preferably from 7 to 10, in particular from 7.5 to 9, especially from 7.5 to 8.3. The desired pH is as a rule established by adding alkali metal hydroxide, ammonia or amines to the formulation; solid sodium hydroxide or potassium hydroxide and aqueous sodium hydroxide or potassium hydroxide solution are particularly suitable for this purpose. Carboxylic acids wh

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