Method for improving the coking resistance of a lubricating composition

Method of lubrication which comprises a step of lubricating a machine with a lubricating composition, the lubricating composition comprising, in mass with respect to the total mass of said lubricating composition, from 20% to 100% of an ionic liquid or of a mixture of several ionic liquids,

• wherein said ionic liquid or said mixture of ionic liquids is selected from an ionic liquid or a mixture of ionic liquids comprising 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+ comprising 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 from 1 to 3 carbon atoms, on condition that when the cation is a quaternary ammonium, at least two of these substituents are a methyl group,
• the deposition start temperature (TDD) in thin film, determined by the MCT method according to the standard GFC Lu-27 A-13, of the ionic liquid or of the mixture of ionic liquids being at least equal to 330° C.,
• said lubricating composition being suitable to reduce the deposits formed in said machine.

Method for reducing the deposits formed in a machine by using a lubricating composition, in which said lubricating composition comprises, by mass with respect to its total mass, from 20% to 100% of an ionic liquid or of a mixture of several ionic liquids,

• said ionic liquid or said mixture of ionic liquids being selected from an ionic liquid or a mixture of ionic liquids comprising at least:
• an anion A− chosen from sulfonylimides, the substituent(s) of which is (are) independently chosen from a fluoroalkyl, fluoroether, perfluorinated alkyl, perfluoroether or perfluorosulfonyl group, and
• a cation C+ comprising 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 from 1 to 3 carbon atoms, on condition that when the cation is a quaternary ammonium, at least two of these substituents are a methyl group,
• the deposition start temperature (TDD) in thin film, determined by the MCT method according to the standard GFC Lu-27 A-13, of the ionic liquid or of the mixture of ionic liquids is at least equal to 330° C.