Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Reexamination Certificate
2001-01-09
2002-07-02
Green, Anthony (Department: 1755)
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
C252S070000, C252S071000, C252S077000
Reexamination Certificate
active
06413445
ABSTRACT:
The present invention relates to novel antifreeze concentrates based on alkylene glycols and to ready-to-use aqueous coolant compositions which comprise said concentrates and are intended for cooling circuits in internal combustion engines.
Coolants for the cooling circuits of internal combustion engines, such as in motor vehicles, generally include alkylene glycols, especially ethylene glycol or propylene glycol, or else corresponding glycol ethers. For use in the cooling system they are diluted with water and are intended not only to provide frost protection by lowering the freezing point of water but also to contribute toward good heat dissipation. Alkylene glycol/water mixtures, however, are extremely corrosive at the operating temperatures of internal combustion engines and so the various metals used to construct cooling systems must be protected against corrosion.
As far as thermal loading of the heat transfer areas, pressure, flow rate, and the selection of materials are concerned, the operating conditions in modern internal combustion engines nowadays place much greater demands on the corrosion prevention capacity of the coolant than was hitherto the case. In addition to the known materials such as copper, brass, soft solder, steel, and grey cast iron, there is also increasing use of alloys of aluminum for the purpose, in particular, of weight reduction. Consequently, there is increased occurrence in more recent literature of descriptions of specific combinations of long-known active substances, each claimed to have a specific spectrum of action.
In particular, alkali metal silicates have been found excellent for protecting aluminum against corrosion. In glycol-based radiator protectants, however, they tend to form gels or even to precipitate, so creating a need for special silicate stabilizers.
Examples of constituents of such combinations of active substances include salts of organic acids which, especially in the form of their alkali metal salts, are efficient corrosion inhibitors, whereas the free acids are less effective or may even be corrosive. The incidence of free acids in radiator protectant formulations as a possible result, for example, of oxidation processes or the ingress of nitrous gases into the cooling system is therefore highly undesirable. It is for this reason that radiator protectant formulations contain small amounts of agents known as reserve alkalinity donors which have a buffer action in the relevant pH range and so prevent the formation of free acids. Examples of compounds employed as reserve alkalinity donors are amines and phosphates and, in particular, the less expensive borax. Such corrosion inhibitor compositions are described, for example, in EP-B-0 229 440 and EP-A-0 308 037.
Because of the above-described disadvantages associated with the use of silicates as corrosion inhibitors for aluminum, in recent developments a trend has been noted to omit them and instead use other active substances. Under these conditions, however, the reserve alkalinity donor, borax, is highly corrosive, and so can no longer be used. The use of phosphates in modern-day radiator protectant formulations is likewise undesirable. This applies to an even greater extent to amines, on the basis of their characterization as potential nitrosamine formers.
WO-A-96/18757 describes anticorrosion compositions for temporarily protecting metallic surfaces, especially those comprising iron, against corrosion. Said compositions are aqueous solutions comprising a combination of a carboxylic acid anion of 6 to 44 carbon atoms with an aromatic hydroxy compound having a pK
a
for the hydroxyl group in the range from 7.0 to 11, in a weight ratio of from 1:2 to 20:1. Corrosion inhibitor systems of that kind, however, are not intended for use in alkylene glycol-containing coolant systems for internal combustion engines. Instead, it is proposed that they be used in aqueous treatment baths in which the articles to be treated—for example, steel sheets—are dipped.
Consequently, there continues to be a need for improved antifreeze concentrates.
It is an object of the present invention to provide silicate-free antifreeze concentrates which comprise new reserve alkalinity donors and are unhampered by the disadvantages described above. The antifreeze concentrates should in particular exhibit enhanced corrosion inhibition on aluminum or its alloys.
We have found that this object is achieved by taking conventional silicate-free inhibitor systems for alkylene glycol-containing radiator protectant formulations and replacing the customary reserve alkalinity donors, such as borates, phosphates and amines, by a mono- or polycyclic aromatic compound which has at least one hydroxyl group and a high buffer capacity in the pH range from about 6 to 10.
The present invention therefore provides, in particular, antifreeze concentrates which comprise
a) at least one water-miscible alcohol which lowers the freezing point, preferably selected from alkylene glycols and alkylene glycol ethers;
b) at least one corrosion inhibitor; and
c) as reserve alkalinity donor, at least one mono- or polycyclic aromatic compound which has at least one hydroxyl group and a high buffer capacity in the pH range from about 6 to 10.
Such antifreeze concentrates and the ready-to-use coolant compositions prepared with them have the surprising advantage over conventional formulations of a markedly better corrosion-inhibiting effect. In particular, an improvement is observed in the corrosion stability of aluminum materials, as used in engine construction.
In one preferred embodiment the antifreeze concentrates of the invention comprise as reserve alkalinity donor at least one compound of the formula I
Ar—X (I)
where
Ar is a radical of the formula II
where
n is an integer from 0 to 4 and
R
1
is hydrogen or an alkali metal ion, and the substituents
R
2
independently of one another are a hydroxyl, alkyl, hydroxyalkyl, heteroalkyl or hydroxyheteroalkyl group, and
X is —COOH, —SO
3
H or —SO
2
Ar, where Ar is as defined above.
Preferred compounds of the formula I include Ar radicals of the formula II where n is 0, 1 or 2. The ring substituents R
2
, where present, are preferably and independently of one another hydroxyl or hydroxyalkyl groups. The radical X is preferably —SO
2
Ar, where Ar can be as defined above.
A reserve alkalinity donor which is particular preferred in accordance with the invention is selected from compounds of the formula III
where R
1
, R
2
and n independently of one another are as defined above. In compounds of formula III R
1
is preferably hydrogen, n is preferably 0, 1 or 2 and R
2
, if present, is preferably hydroxy or hydroxyalkyl. Compounds of the formula III are preferably symmetrical; that is, the two aromatic rings are substituted mirror-symmetrically starting from the central SO
2
-group.
Particular preference is given to compounds of the formula III where the radicals R
1
are identical and are hydrogen or an alkali metal and n in each case is 0. Specific examples of such compounds are 4,4′-dihydroxydiphenyl sulfone (bisphenol S) and the corresponding positional isomers, and also mixtures of these compounds.
Where R
1
in the abovementioned compounds of the formula I is not hydrogen, it is a preferably monovalent metal cation, especially an alkali metal cation such as, for example, a sodium or potassium cation. Where two or more radicals R
1
are present, they are preferably the same alkali metal cation.
Alkyl radicals suitable in accordance with the invention are straight-chain or branched carbon chains having 1 to 10, preferably 1 to 6 and, in particular 1 to 4 carbon atoms. Examples that may be mentioned include the following radicals: methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, i-butyl, t-butyl, n-pentyl, sec-pentyl, isopentyl, n-hexyl, 1-, 2- or 3-methyl-pentyl, and long chain alkyl radicals, such as unbranched heptyl, octyl, nonyl and decyl, as well as the singly or multiply branched analogs thereof. Hydroxyalkyl radicals suitable in accordance with the invention ar
Gillich Michael
Günther Wolfgang
Meszaros Ladislaus
Oppenländer Knut
Pfitzner Klaus
BASF - Aktiengesellschaft
Green Anthony
LandOfFree
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