Method for improving the coking resistance of a lubricating composition

Abstract

Disclosed is a method of lubrication including a step of lubricating a machine with a lubricating composition, the lubricating composition including 20-100% ionic liquid or of a mixture of several ionic liquids. The ionic liquid or the mixture is selected from at least: an anion A− chosen from sulfonylimides, the substituent(s) of which is (are) independently chosen from a fluoroalkyl, fluoroether, perfluorinated alkyl or perfluoroether group; and a cation C+ including a nitrogen-containing heterocycle or a quaternary ammonium, the substituent(s) of which is (are) independently chosen from: a hydrogen atom or alkyl, alkoxy, fluorinated alkyl, perfluorinated alkyl, alkylsilane, alkyl alcohol, vinyl, alkyl allyl, ether or polyether groups having a linear or branched chain having 1-3 carbon atoms. The deposition start temperature in thin film of the ionic liquid or of the mixture of ionic liquids is at least equal to 330° C. The lubricating composition reduces deposits formed in the machine.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the field of lubricating compositions, especially for gas turbines of jet engines of aircraft or further for conveyor chains.[0002]Especially, the present invention relates to a method of diminishing the thin-film coking, at very high temperatures, of a lubricating composition comprising one or a mixture of several specific ionic liquids, especially as a base oil.PRIOR ART[0003]The gas turbines of aircraft need lubricating compositions of high performance which can be used over a very wide range of temperatures. The lubricating compositions intended for civilian and military aviation have to comply with very precise specifications figuring in detail in standards such as MIL PRF 23699 set up by the military authorities or standard AS 5780 set up by the SAE International. These standards determine, among other features, the physical and chemical properties, the levels of thermal stability, the stability with respect to oxida...

AI Technical Summary

Benefits of technology

The patent text explains that the applicant selected MCT (Mobile Coking Test) for testing the resistance to coking, which is a common problem in lubricating compositions. This test is suitable, effective, and trustworthy. It demonstrates the superiority of certain oils, such as MIL-PRF 23699 of HTS grade, over standard oils. The test is fast and requires small amounts of the product being tested. The results show that the higher the temperature at which deposition starts, the better the thermal stability of the lubricating composition and its resistance to coking.

Problems solved by technology

Coking generally leads to a high reduction of the flow rate of the oil circulation in the cooling exchangers, resulting in overheating or in a defect of lubricating the roller bearings of the turbines of the engine.

The same problem of thermal resistance and of resistance to coking exists for conveyor chains.

Indeed, the lubricant is generally applied to conveyor chains on a drop by drop basis or by spraying, which results in thin films of lubricant which are then exposed to very high temperatures when the chains pass into the ovens.

Under those conditions, coke is formed when the lubricant is not sufficiently resistant, said coke accumulating until it blocks the chains with a subsequent stop of the production becoming necessary for maintenance and repair.

However, none of said studied molecules or formulae has been satisfying.

However, as will be shown further down in the experimental part, a high temperature of beginning of thermal degradation determined for an ionic liquid by TGA (under an inert atmosphere) does not necessarily indicate that this liquid has a resistance to coking at high temperature, such as a resistance to coking at high temperature in thin film.

However, those ionic liquids, used as a base, do not make it possible to solve the problems of coking at high temperature as will be shown further down in the examples.

However, according to that document, the ionic liquids which make it possible to reduce the deposits when they are used as additive in a conventional oil, cannot be used as a base since they are not resistant to oxidation and to the formation of deposits.

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