EP4004168A1

EP4004168A1 - Lubricant composition for gas turbines

Info

Publication number: EP4004168A1
Application number: EP20742762.6A
Authority: EP
Inventors: Frédéric Michel; Florence Bredon
Original assignee: Total Marketing Services SA
Current assignee: TotalEnergies Onetech SAS
Priority date: 2019-07-26
Filing date: 2020-07-24
Publication date: 2022-06-01
Also published as: FR3099176B1; US20220315856A1; WO2021018768A1; CN114174481A; FR3099176A1; JP2022541338A

Abstract

The present invention relates to a lubricant composition, in particular for a gas or steam turbine, comprising: - at least one base oil; - at least one phenylnaphthylamine (PAN) compound, preferably alkylphenyl-α-naphthylamine (APAN ) compound; - at least one diphenylamine (DPA) compound, preferably dialkyl-diphenylamine compound; and - at least one phosphite ester compound, preferably triaryl phosphite ester compound; in which the ratio by weight between said diphenylamine compound(s) and said phosphite ester compound(s) is strictly greater than 1.0.

Description

LUBRICANT COMPOSITION FOR GAS TURBINES

Technical area

The present invention relates to the field of lubricating compositions, more particularly the field of lubricating compositions for turbines. It relates more specifically to a lubricating composition for turbines using a combination of three types of specific antioxidant additives, in specific proportions.

Prior art

Gas or steam turbines are typically used in the fields of aeronautics, naval, rail transport and power generation.

In particular, gas or steam turbines have the advantages of lightness, high specific power and density, lending themselves particularly well to aeronautical propulsion, in particular on airplanes and helicopters, but also to naval propulsion, in particular for high speed ships. Also, in recent electricity production installations, gas turbines using high temperature combustion gases such as liquefied natural gas are used, or energy production installations combining a gas turbine and a steam turbine.

Industrial lubricating compositions, also known as “lubricating oils” or “lubricants”, and more particularly lubricants for gas or steam turbines, can be subjected to extreme conditions, and in particular to operating temperatures which can range up to - above 250 ° C. This is the case, for example, for lubricating oils for aviation jet turbines.

Subjected to such high temperature conditions, lubricating oils can degrade and oxidize. This degradation can result in the formation of deposits, such as varnishes, in the presence of sludge and / or in an increase in the viscosity of the composition.

The oxidative stability of lubricating oils is further reduced due to the dissolution of metals in these oils, under the extreme conditions of use described above. Indeed, dissolved metals are capable of catalyzing the degradation by oxidation of lubricants. Such degradation greatly reduces the life of the oils, forcing the oil change intervals to be shortened and causing significant operating losses. At the present time, some manufacturers consequently impose very strict specifications concerning the properties of oxidation stability and thermal stability, at high temperature, of lubricating compositions intended in particular to be used in gas turbines or in gas turbines. steam.

To increase oxidative stability, most lubricants contain additives to inhibit their oxidation. Various antioxidant additives have thus been proposed in lubricants, such as, for example, sterically hindered phenolic compounds, aromatic organic amines, diphenylamine derivatives (denoted by DPA) or else phenyl-naphthylamine (PAN) derivatives.

By way of example, document WO 2008/009704 proposes a lubricating composition, in particular for turbines, comprising a succinate ester and a sarcosinic acid as anti-rust agents. The compositions described therein may also include various aromatic amine antioxidants, such as phenyl-α-naphthylamine and dialkyl-α-diphenylamine compounds. The lubricating compositions proposed in this document do not, however, make it possible to achieve the desired performance levels in terms of thermal stability and resistance to oxidation at high temperature.

Consequently, there remains a need for a lubricating composition, in particular for turbines, exhibiting improved properties in terms of thermal stability and resistance to oxidation, while retaining good properties of resistance to corrosion, and helping to reduce the formation of unwanted deposits when using the lubricant, especially in high temperature conditions.

Summary of the invention

The present invention aims precisely to meet this need.

More particularly, the present invention relates, according to a first of its aspects, to a lubricating composition, in particular for a gas or steam turbine, comprising:

- at least one base oil;

- at least one phenyl-naphthylamine (PAN) compound, preferably alkylphenyl-a-naphthylamine (AP AN);

- at least one diphenylamine (DPA) compound, preferably dialkyl-diphenylamine; and - at least one phosphite ester compound, preferably triaryl phosphite ester;

wherein the mass ratio between said diphenylamine compound (s) and said phosphite ester compound (s) is strictly greater than 1.0.

Against all expectations, the inventors have discovered that the implementation of a combination of the three specific antioxidant additives mentioned above, at least one phenyl-naphthylamine compound (PAN), at least one diphenylamine compound (DPA) and at least one ester compound of phosphite, with a mass ratio of DPA compounds / phosphite ester (s) strictly greater than 1.0, provides access to a lubricating composition exhibiting improved properties in terms of thermal stability, oxidation stability and resistance to corrosion, under high temperature conditions.

In particular, as illustrated in the examples, it is not possible to achieve such performance in terms of thermal stability, oxidation stability and corrosion resistance, by using only one, or even two antioxidants. among the three considered according to the invention.

Thus, the specific combination of antioxidant additives according to the invention makes it possible to give the lubricant excellent properties for reducing the phenomena of oxidation and the formation of undesirable deposits which take place during the use of the lubricant, very particularly in high temperature conditions and in the presence of oxygen.

Advantageously, a lubricating composition according to the invention thus has an increased service life.

As detailed in the following examples, the performance of corrosion resistance, oxidation stability and thermal stability can be evaluated according to various tests.

More particularly, a lubricating composition according to the invention advantageously exhibits stability to oxidation, evaluated by the RPVOT test (for “Rotating Pressure Vessel Oxidation Test”), according to the ASTM D2272 standard, greater than or equal to 2200 minutes, advantageously greater than or equal to 2500 minutes. Advantageously, it presents a residual RPVOT, measured according to the test called "dry TOST

- 1000 hours ”adapted from standard ASTM D7873, and detailed below in the examples, greater than or equal to 70%, advantageously greater than or equal to 75% and more particularly greater than or equal to 80%. A lubricating composition according to the invention advantageously exhibits an amount of insolubles after 48 hours at 180 ° C. of less than 30 mg / kg, preferably less than 25 mg / kg, more preferably less than or equal to 20 mg / kg.

It also exhibits excellent resistance to oxidation and corrosion, rated by ASTM D4636.

These improved performances in terms of thermal stability, resistance to oxidation and corrosion make it possible to reduce the content, or even to eliminate the presence of additional additives, in particular anti-wear and / or extreme additives. -pressure, or pour point depressant additives (PPD).

The present invention also relates to the use, in a lubricating composition, in particular for a gas or steam turbine, comprising at least one base oil, of at least one phenyl-naphthylamine (PAN) compound, preferably alkylphenyl-a - naphthylamine (AP AN); of at least one compound diphenylamine (DPA), preferably dialkyl-diphenylamine; and at least one phosphite ester compound, preferably triaryl phosphite ester, said phosphite ester compound (s) being used in a DPA / phosphite ester (s) ratio strictly greater than 1.0 in order to improve performance thermal stability and resistance to oxidation of the composition.

The lubricating composition according to the invention thus proves to be particularly suitable for its use as a lubricant for a gas or steam turbine.

The present invention thus relates, according to another of its aspects, to the use of a composition as described above, as a lubricant for a gas or steam turbine.

It also relates to a method of lubricating at least one mechanical part of an organ, such as the bearings, of a gas or steam turbine, comprising at least one step in which said mechanical part is brought into contact with a lubricating composition according to the invention.

Other characteristics, variants and advantages of the lubricating compositions according to the invention will emerge more clearly on reading the description and the examples which follow, given by way of illustration and without limitation of the invention. In the remainder of the text, the expressions "between ... and ...", "ranging ... to ..." and "varying from ... to ..." are equivalent and are intended to mean that the limits are included, unless otherwise noted.

Unless specified otherwise, the expression "comprising a" should be understood as "comprising at least one".

detailed description

In the context of the invention, and in the absence of an indication to the contrary, by:

- "alkyl", a saturated, linear or branched aliphatic group; for example, a C _x to C _z alkyl represents a saturated carbon chain of x to z carbon atoms, linear or branched;

- "alkenyl", an unsaturated, linear or branched aliphatic group; for example, a C _x to C _z alkenyl group represents an unsaturated carbon chain of x to z carbon atoms, linear or branched;

- "cycloalkyl", a cyclic alkyl group, for example a C _x to C _z cycloalkyl represents a cyclic carbon group of x to z carbon atoms, for example a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl;

- "aryl", a mono- or polycyclic aromatic group, in particular comprising between 6 and 10 carbon atoms. By way of example of an aryl group, mention may be made of phenyl or naphthyl groups.

PHENYL-NAPHTHYLAMINE COMPOUND (PAN)

As mentioned above, according to one of its essential characteristics, a lubricating composition according to the invention comprises at least one phenyl-naphthylamine compound, denoted "PAN".

The term “phenyl-naphthylamine” compound is intended to denote a compound chosen from N-phenyl-a-naphthylamine, N-phenyl-B-naphthylamine and their derivatives, preferably having one or more alkyl groups as substituents of the phenyl ring.

More particularly, the compound of phenyl-naphthylamine type, preferably alkylphenyl-a-naphthylamine (denoted "AP AN") used according to the invention corresponds to the following formula (I):

in which :

n is an integer ranging from 1 to 5; and

R 1 represents an alkyl group, linear or branched, preferably C 1 to C 22, in particular C 2 to C 12.

Preferably, the compound of phenyl-naphthylamine type, in particular alkylphenyl-a-naphthylamine, is of the following formula (I-a):

in which Ri and n are as defined above.

Preferably, the phenyl-naphthylamine compound is an alkylphenyl-a-naphthylamine compound, in particular corresponds to the above formula (I-a), in which n is an integer ranging from 1 to 3, in particular n is 1.

According to a particular embodiment, the phenyl-naphthylamine compound has the following formula (I-b):

in which R 1 is as defined above, preferably R 1 represents a C2 to C12 alkyl group.

Preferably, the group R 1 is in the para position of the amino group. The phenyl-naphthylamine compounds can be commercially available or prepared according to synthetic methods known to those skilled in the art.

Preferably, a lubricating composition according to the invention comprises between 0.05 and 5% by mass of phenyl-naphthylamine compound (s), in particular between 0.1 and 3% by mass, preferably between 0.15 and 1% by mass and more particularly between 0.2 and 0.5% by weight of phenyl-naphthylamine compound (s), relative to the total weight of the composition.

DIPHENYLAMINE COMPOUND (DPA)

As indicated above, a lubricating composition according to the invention further comprises at least one diphenylamine compound (denoted by DPA).

The term "diphenylamine compound" is intended to denote diphenylamine and its derivatives, preferably in which at least one, or even both, phenyl groups are substituted by one or more groups chosen from linear or branched alkyl groups. More particularly, the compound of diphenylamine type, preferably dialkyldiphenylamine, used according to the invention, corresponds to the following formula (II):

in which :

P2 and P3 are, independently of each other, integers ranging from 1 to 5; and

R2 and R3 represent, independently of each other, a linear or branched alkyl group, preferably C1 to C22, in particular C4 to C8.

Preferably, the compound of diphenylamine type, preferably dialkyldiphenylamine, used according to the invention is of the following formula (II- a):

in which R2 and R3 are as defined above.

Preferably, the R2 and R3 groups are in the para position of the amino group. Thus, according to a particular embodiment, the diphenylamine compound is chosen from p, p'-dialkyldiphenylamine compounds.

Diphenylamine compounds may be commercially available or prepared according to synthetic methods known to those skilled in the art.

Preferably, a lubricating composition according to the invention comprises between 0.05 and 5% by mass of diphenylamine compound (s), in particular between 0.1 and 3% by mass, preferably between 0.15 and 1% by mass and more particularly between 0.2 and 0.5% by mass, of diphenylamine compound (s) relative to the total mass of the composition.

According to a particularly preferred embodiment, the said phenylnaphthylamine compound (s) are chosen from the compounds of formula (I-b) above, in particular in which R 1 represents a C 2 to C 12 alkyl group; and said diphenylamine compound (s) are chosen from the compounds of formula (II-a) above, in particular in which R2 and R3 represent, independently of one another, a linear or branched alkyl group, preferably C2 to C12.

According to a particular embodiment, the said phenyl-naphthylamine (PAN) compound (s), in particular as defined above, and the said diphenylamine (DPA) compound (s), in particular as defined above, are used in a mass ratio N-phenyl-a-naphthylamine compound (s) / diphenylamine compound (s) between 0.8 and 1.0, in particular about 1.

PHOSPHITE ESTER

As indicated above, a lubricating composition according to the invention further comprises at least one phosphite ester compound.

More particularly, the phosphite ester compounds can be of the following formula (III):

in which each R ₄ , R ₅ and Rr represents, independently of one another, a hydrocarbon group, preferably having 1 to 24 carbon atoms.

The hydrocarbon groups in the aforementioned formula (III) can be more particularly chosen, independently of one another, from:

- alkenyl groups, linear or branched, preferably C ₂ to Cis;

- alkoxy-alkyl groups, preferably C 1 to C ₂₄ ;

- cycloalkyl groups, preferably C ₃ to Cs;

- aryl groups, preferably C _Ô Cio;

said groups possibly themselves being optionally substituted by one or more hydrocarbon groups, in particular by one or more alkenyl, alkoxyalkyl, cycloalkyl and / or aryl groups.

Preferably, R ₄ , R ₅ and R ₆ are chosen, independently of each other, from cycloalkyl groups, preferably C ₃ to C ₅ ; and aryl groups, preferably C _Ô Cio; said cycloalkyl and aryl groups possibly being optionally substituted by one or more alkyl groups, linear or branched. According to a particular embodiment, the phosphite ester compound used according to the invention is of the above formula (III), in which R ₄ , R ₅ and R ₆ are identical, preferably as defined above.

According to this embodiment, the phosphite ester compounds according to the invention can be advantageously chosen from esters of triaryl phosphite, and in particular esters of tri (alkyl-aryl) phosphite, preferably from esters of triphenyl phosphite and more particularly. tri (alkylphenyl) phosphite esters.

Preferably, a phosphite ester compound according to the invention corresponds to the following formula (III-a):

in which the groups R represent, independently of one another, alkyl groups, linear or branched in C1 to Cio, in particular from C3 to Cs, and n represent, independently of one another, 0, 1 or 2, in particular 1 or 2.

Preferably, n is 1 or 2, preferably n is 2.

Preferably, n is 2, and R represent groups, in particular in ortho and para positions, preferably alkyl groups, preferably branched, in C3 to

C _Ô , such as a tert-butyl group.

Preferably, a phosphite ester compound according to the invention is of formula (III-a) in which the groups - (R) _n are identical.

Advantageously, a phosphite ester compound according to the invention is tris (2,4-ditert-butylphenyl) phosphite (CAS 31570-04-4).

According to a particular embodiment, it is tris (2,4-ditert-butylphenyl) phosphite (CAS 31570-04-4).

The phosphite ester compounds may be commercially available or prepared according to synthetic methods known to those skilled in the art.

Preferably, a lubricating composition according to the invention comprises between 0.01 and 3% by weight of phosphite ester compound (s), in particular between 0.02 and 1% by weight, preferably between 0.05 and 0.5% by mass and more particularly between 0.1 and 0.3% by mass, of phosphite ester compound (s), relative to the total mass of the composition.

According to a particular embodiment, said diphenylamine compound (s) are chosen from the compounds of formula (II-a) above, in particular in which R2 and R3 represent, independently of one another, a linear or branched alkyl group , preferably C2 to C12; and said phosphite ester compound (s) are chosen from the compounds of formula (III-a) above, in particular in which n is 2, and R represent groups, in particular in ortho and para positions, preferably alkyl groups, preferably branched, C3 to C6, such as a tert-butyl group.

As indicated above, the said diphenylamine (DPA) compound (s), in particular as defined above and the said phosphite ester compound (s), in particular as defined above, are used in a compound (s) DPA / ester mass ratio (s) of phosphite strictly greater than 1.0, in particular greater than or equal to 1.5; in particular greater than or equal to 2.0 and more particularly between 2.0 and 3.0.

Advantageously, said phenyl-naphthylamine (PAN) compound (s), in particular as defined above and said phosphite ester compound (s), in particular as defined above, are used in a PAN / ester compound (s) mass ratio (s) of phosphite strictly greater than 1.0, in particular greater than or equal to 1.5; in particular strictly greater than 2.0 and more particularly between 2.1 and 3.0.

It is understood that the various aforementioned embodiments, in particular as regards the nature of the said phenyl-naphthylamine compound (s), of the said diphenylamine compound (s) and of the said phosphite ester compound (s), can be combined.

In particular, a lubricating composition according to the invention advantageously comprises at least the combination:

- one or more phenyl-naphthylamine compounds, in particular alkylphenyl-a-naphthylamine, as defined above, preferably chosen from the compounds of above-mentioned formula (Ib), in which R 1 preferably represents a C2 to C12 alkyl group ;

- one or more diphenylamine compounds, in particular dialkyl-diphenylamine as defined above, preferably chosen from the compounds of formula (II-a) above, in which R2 and R3 preferably represent, independently, one of the other, a linear or branched alkyl group, preferably C2 to C12; and

- one or more phosphite ester compounds, in particular triaryl phosphite esters as defined above, preferably chosen from the compounds of formula (III-a) above, in particular in which n is 2, and the Rs represent groups, in particular in ortho and para positions, preferably alkyl groups, preferably branched, C3 to C6, such as a tert-butyl group;

the said diphenylamine compound (s) and the said phosphite ester compound (s) being used in a weight ratio of the diphenylamine compound (s) / phosphite ester compound (s) strictly greater than 1.0.

According to a particular embodiment, a lubricating composition according to the invention comprises:

- from 0.05 to 5% by weight, in particular from 0.1 to 3% by weight, preferably from 0.15 to 1% by weight and more particularly from 0.2 to 0.5% by weight, of one or more phenyl-naphthylamine compounds, preferably alkylphenyl-a-naphthylamine, in particular as defined above, preferably chosen from the compounds of formula (Ia) above, in which R preferably represents a C2 to C12 alkyl group;

- from 0.05 to 5% by weight, in particular from 0.1 to 3% by weight, preferably from 0.15 to 1% by weight and more particularly from 0.2 to 0.5% by weight, of one or more diphenylamine compounds, preferably dialkyl-diphenylamine, in particular as defined above, preferably chosen from the compounds of formula (II-a) above, in which R2 and R3 preferably represent, independently of one another, a linear or branched alkyl group, preferably C2 to C12; and

- from 0.01 to 3% by weight, in particular from 0.02 to 1% by weight, preferably from 0.05 to 0.5% by weight and more particularly from 0.1 to 0.3% by weight, of a or more phosphite ester compounds, preferably triaryl phosphite ester, in particular as defined above, preferably chosen from the compounds of formula (III-a) above, in particular in which n is 2, and the R represent groups , in particular in ortho and para positions, preferably alkyl groups, preferably branched, C3 to C6, such as a tert-butyl group;

the contents being expressed relative to the total mass of said lubricating composition, with the proviso that the mass ratio of diphenylamine compound (s) / phosphite ester compound (s) is strictly greater than 1.0.

BASE OIL (S)

As indicated above, a lubricating composition according to the invention comprises at least one base oil. Said base oil (s) present in a lubricating composition according to the invention are suitably chosen, in particular with regard to their compatibility with the phenyl-naphthylamine, diphenylamine and phosphite ester compounds used according to the invention.

It can be a mixture of several base oils, for example a mixture of two, three or four base oils.

These base oils can be chosen from the base oils conventionally used in the field of lubricating oils, such as mineral, synthetic or natural, animal or vegetable oils or their mixtures.

The base oils used in the lubricating compositions according to the invention can in particular be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (Table 1), or their equivalents according to the classification. ATIEL, or their mixtures.

TABLE 1

Mineral base oils include all types of bases obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, dealphating, solvent dewaxing, hydrotreatment, hydrocracking, hydroisomerization and hydrofinishing. Synthetic base oils can be esters of carboxylic acids and alcohols, polyalphaolefins (PAO) or even polyalkylene glycols (PAG) obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms. , in particular from 2 to 4 carbon atoms. The polyalphaolefins used as base oils are for example obtained from monomers comprising 4 to 32 carbon atoms, for example from decene, octene or dodecene, and whose viscosity at 100 ° C is between 1, 5 and 15 mrhks ¹ according to ASTM D445. Their average molecular mass is generally between 250 and 3000 according to the ASTM D5296 standard.

Mixtures of synthetic and mineral oils can also be used.

There is generally no limitation as to the use of different lubricating bases to produce the lubricating compositions according to the invention, except that they must have properties, in particular of viscosity, viscosity index, sulfur content. , anti-corrosion suitable for use in gas and / or steam turbines.

Preferably, the base oil is selected from API classification Group II and III oils, and mixtures thereof. Advantageously, the base oils of group II and

III further improve the oxidation stability properties of the lubricating composition.

Preferably, the base oil is selected from group III oils.

The kinematic viscosity, measured at 40 ° C according to standard ASTM D445, of the base oil or mixture of base oils can advantageously be between 20 mm ² / s and 100 mm ² / s, preferably between 25 mm ² / s and 50 mm ² / s.

Advantageously, a lubricating composition according to the invention comprises at least 40% by mass of base oil (s) relative to the total mass of the composition, in particular at least 50% by mass of base oil (s) , and in particular between 60 and 99.5% by mass and more particularly between 70 and 99% by mass, of base oil (s).

ADDITIONAL ADDITIVES

A lubricating composition according to the invention can also comprise additional additives, suitable for use in a lubricant for turbines, such as gas and / or steam turbines. Advantageously, a lubricating composition according to the invention comprises one or more additives chosen from antioxidants other than the compounds used in the context of the present invention, viscosity index improvers (VI), additives lowering the point d flow (PPD), defoamers, thickeners, corrosion inhibitors, copper passivators, and mixtures thereof.

It is understood that the nature and the amount of additives used are chosen so as not to affect the properties of the lubricating composition, in particular the performances, discussed above, conferred by the combination of the three antioxidants used according to l 'invention.

A lubricating composition according to the invention may further comprise one or more corrosion inhibitors.

Corrosion inhibitors are known to those skilled in the art of lubricants, in particular lubricants for turbines.

They can be more particularly chosen from organic acid esters, triazole derivatives, N-acyl sarcosines or else imidazoline derivatives.

According to a particular embodiment, a lubricating composition according to the invention comprises one or more corrosion inhibitors chosen from triazole type derivatives and organic acid esters, in particular alkylated organic acid esters.

Preferably, the triazole type compound is a benzotriazole or one of its derivatives, preferably a benzotriazole derivative, more preferably a tolyltriazole derivative. The tolyltriazole derivatives can more particularly be of the following formula (IV):

in which :

- R ⁴ and R ⁵ represent, independently of one another, a hydrogen atom, a linear or branched, preferably branched, C ₃ to C ₁₄ , preferably C6 to C12 alkyl group; and -A- represents a linear or branched alkylene group, preferably linear, C1 to C6, preferably C1 to C3 and more preferably a methylene group (-CH2-), in particular, said tolyltriazole derivative being 2- ethyl-N- (2-ethylhexyl) -N - [(4-methylbenzotriazol-1 -yl) methyl] hexan-1 -amine.

According to a particular embodiment, the compound of triazole type is of formula (IV), in which R ⁴ and R ⁵ represent branched C-C12 alkyl groups and -A- represents a C 1 -C 3 alkylene group, preferably a methylene group.

As an example of corrosion inhibitors of the alkylated organic acid ester type, there may be mentioned esters of succinic acid.

The corrosion inhibitor additive (s), in particular of the type derived from tolyltriazole and / or alkylated organic acid ester, can be used in a lubricating composition according to the invention, in an amount of 0.01 to 5% by mass. , in particular from 0.1 to 3% by mass, and more particularly from 0.1 to 2% by mass, relative to the total mass of the lubricating composition.

A lubricating composition according to the invention may further comprise at least one anti-foam additive. The anti-foam additives can, for example, be chosen from polar polymers such as polymethylsiloxanes or polyacrylates. In particular, a lubricating composition according to the invention may comprise from 0.01 to 3% by mass of anti-foam additive (s), relative to the total weight of the lubricating composition.

A lubricating composition according to the invention can also comprise one or more antioxidant additive (s), distinct from the phenyl-naphthylamine, diphenylamine and phosphite ester compounds, described above.

As examples of additional antioxidant additives may be mentioned, for example, sterically hindered phenols, esters of sterically hindered phenols and sterically hindered phenols comprising a thioether bridge. Preferably, the sterically hindered phenols are chosen from compounds comprising a phenol group of which at least one carbon vicinal of the carbon carrying the alcohol function is substituted by at least one C 1 -C 10 alkyl group, preferably a C 1 -C alkyl group. _Ô , of preferably a C4 alkyl group, preferably by the tert-butyl group. As examples of antioxidant additives of sterically hindered phenol type, mention may be made of di-t-butyl-2,6-methyl-4-phenol (B HT), t-butyl hydroquinone (TBHQ), 2,6 and 2,4-di-t-butyl phenol, 2,4-dimethyl-6-t-butyl phenol, pyrogallol, and octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate.

According to a particular embodiment, a lubricating composition according to the invention does not comprise an antioxidant additive distinct from the compounds phenyl-naphthylamine, diphenylamine and phosphite ester, described above.

A lubricating composition according to the invention can also comprise at least one pour point depressant additive (also called "PPD" agent for "Pour Point Depressant" in English). By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricant composition according to the invention. Examples of pour point reducing agents include polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes. A lubricating composition according to the invention can comprise from 0.1% to 2%, preferably from 0.2% to 1% by mass of additive (s) reducing the pour point (s), relative to the total weight of the composition.

According to a particular embodiment, a lubricating composition according to the invention comprises less than 200 ppm, in particular less than 100 ppm, in particular less than 50 ppm and more particularly less than 10 ppm by mass, or even is completely free of additive. Pour point depressor (s).

A lubricating composition according to the invention can also comprise at least one additive improving the viscosity index (VI). Viscosity index improvers, in particular polymers which improve the viscosity index, make it possible to guarantee good resistance to cold and minimum viscosity at high temperature. As examples of polymer improving the viscosity index, mention may be made of polymer esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, of styrene, butadiene and isoprene, olefin homopolymers or copolymers, such as than ethylene or propylene, polyacrylates and polymethacrylates (PMA), preferably homopolymers or copolymers of olefin, such as ethylene or propylene.

In particular, a lubricating composition according to the invention may comprise from 1 to 15% by mass of additive (s) improving the viscosity index, preferably from 5% to

10% by mass, relative to the total weight of the lubricating composition.

Advantageously, a lubricating composition according to the invention comprises a mass content of less than or equal to 200 ppm, in particular less than or equal to

100 ppm, in particular less than or equal to 50 ppm and more particularly less than or equal to 10 ppm, or even is completely free, of anti-wear and / or extreme pressure additives of the phosphate ester type, such as tri (isopropylphenyl) phosphate.

100 ppm, in particular less than or equal to 50 ppm and more particularly less than or equal to 10 ppm, or even is completely free, of antiwear additives and / or extreme pressure of the amine phosphate salt type.

More preferably, a lubricating composition according to the invention comprises less than 200 ppm, in particular less than 100 ppm, in particular less than 50 ppm and more particularly less than 10 ppm by mass, or even is completely free, of antiwear additives and / or extreme pressure phosphorus containing sulfur or zinc.

In fact, the inventors have observed that the presence of such phosphorus compounds containing sulfur or zinc is liable to induce the formation of unwanted deposits when using the lubricating composition for turbines.

More preferably, a lubricating composition according to the invention comprises less than 200 ppm, in particular less than 100 ppm, in particular less than 50 ppm and more particularly less than 10 ppm by mass, or even is completely free, of antiwear additives and / or extreme pressure phosphorus and / or sulfur.

In terms of formulation of a lubricating composition according to the invention, the antioxidants considered according to the invention, phenyl-naphthylamine, diphenylamine and phosphite ester compounds, as described above, can be added to an oil or mixture of oils of base, then the other additional additives added. Alternatively, the antioxidants considered according to the invention, phenylnaphthylamine, diphenylamine and phosphite ester compounds, can be added to a pre-existing lubricating formulation, comprising in particular one or more base oils, and optionally additional additives.

Alternatively, the antioxidants considered according to the invention, phenyl-naphthylamine, diphenylamine and phosphite ester compounds, can be combined with one or more additional additives, and the "package" of additives thus formed is added to an oil or mixture of. base oils.

Advantageously, the use of the three antioxidant compounds according to the invention, N-phenyl-naphthylamine compound (s), diphenylamine compound (s) and phosphite ester compound (s), makes it possible to dispense with the use of use of anti-wear and / or extreme pressure additives.

Thus, according to a particular embodiment, a lubricating composition according to the invention comprises less than 200 ppm, in particular less than 100 ppm, in particular less than 50 ppm and more particularly less than 10 ppm by mass, or even is completely free, of 'anti-wear and / or extreme pressure additives.

According to a particularly preferred embodiment, a lubricating composition according to the invention comprises, or even consists of:

- a base oil or mixture of base oils, preferably chosen from base oils of group II and III, preferably of group III;

- one or more phenyl-naphthylamine (PAN) compounds, in particular alkylphenyl-a-naphthylamine, as defined above, preferably chosen from the compounds of formula (Ia) above, in which R preferably represents a C2 to alkyl group to C12;

- one or more diphenylamine (DPA) compounds, in particular diakyl-diphenylamine, as defined above, preferably chosen from the compounds of formula (II-a) above, in which R2 and R3 preferably represent, independently one of the other, a linear or branched alkyl group, preferably C2 to C12;

- one or more phosphite ester compounds, in particular triaryl phosphite esters, as defined above, preferably chosen from the compounds of formula (III-a) above, in particular in which n is 2, and R represent groups, in particular in ortho and para positions, preferably alkyl groups, preferably branched, C3 to C6, such as a tert-butyl group;

the mass ratio of DPA compound (s) / phosphite ester (s) being strictly greater than 1; and

- optionally one or more additional additives, preferably chosen from corrosion inhibitor additives, in particular from tolyltriazole derivatives, and alkylated organic acid esters; and anti-foam additives.

In particular, a lubricating composition according to the invention can comprise, or even consist of:

- from 50% to 99.5% by weight, preferably from 70% to 99% by weight of base oil (s), preferably chosen from base oils of group II and III, preferably of group III ;

- from 0.05 to 5% by weight, in particular from 0.1 to 3% by weight, preferably from 0.15 to 1% by weight and more particularly from 0.2 to 0.5% by weight, of one or more phenyl-naphthylamine compounds, in particular alkylphenyl-a-naphthylamine, as defined above, preferably chosen from the compounds of formula (Ia) above, in which R1 preferably represents a C2 to C12 alkyl group;

- from 0.05 to 5% by weight, in particular from 0.1 to 3% by weight, preferably from 0.15 to 1% by weight and more particularly from 0.2 to 0.5% by weight, of one or more diphenylamine compounds, in particular dialkyl-diphenylamine, as defined above, preferably chosen from the compounds of formula (II-a) above, in which R2 and R3 preferably represent, independently of one another, an alkyl group linear or branched, preferably C2 to C12; and

- from 0.01 to 3% by weight, in particular from 0.02 to 1% by weight, preferably from 0.05 to 0.5% by weight and more particularly from 0.1 to 0.3% by weight, of a or more phosphite ester compounds, in particular triaryl phosphite esters as defined above, preferably chosen from the compounds of formula (III-a) above, in particular in which n is 2, and the R represent groups, in particular of ortho and para positions, preferably alkyl groups, preferably branched, C3 to C6, such as a tert-butyl group;

- optionally from 0.01 to 5% by mass, in particular from 0.1 to 3% by mass, and more particularly from 0.1 to 2% by mass, of additive (s) inhibitor (s) of corrosion, in particular of the type derived from tolyltriazole and / or ester of alkylated organic acid; and

- optionally from 0.01% to 3% by weight of anti-foam additive (s),

with the proviso that the mass ratio of diphenylamine compound (s) / phosphite ester compound (s) is strictly greater than 1.0

the contents being expressed relative to the total mass of said lubricating composition.

A lubricating composition according to the invention can have a kinematic viscosity, measured at 40 ° C according to the ISO 3104 standard, of between 20 mm ² / s and 100 mm ² / s, in particular between 25 mm ² / s and 50 mm ^2. / s.

A lubricating composition according to the invention advantageously exhibits a viscosity index, measured according to the ASTM D2270-93 standard, of between 100 and 300, in particular between 100 and 150.

In particular, it has an acid number, measured according to the ASTM D664 standard, of between 0.08 and 0.2.

As mentioned above, a lubricating composition according to the invention exhibits excellent properties in terms of oxidation stability, thermal stability and corrosion resistance.

More particularly, a lubricating composition according to the invention advantageously exhibits an oxidation stability "RPVOT", measured according to the ASTM D2272 standard, greater than or equal to 2200 minutes, advantageously greater than or equal to 2500 minutes.

Advantageously, it exhibits a residual RPVOT, measured according to the so-called “dry TOST - 1000 hours” test according to a method adapted from standard ASTM D7873, greater than or equal to 70%, advantageously greater than or equal to 75% and more particularly greater than or equal at 80%.

A lubricating composition according to the invention advantageously exhibits an amount of insolubles after 48 hours at 180 ° C. of less than 30 mg / kg, preferably less than 25 mg / kg, more preferably less than or equal to 20 mg / kg. It also exhibits excellent resistance to oxidation and corrosion, evaluated according to the ASTM D4636 test.

The invention will now be described by means of the following examples, given by way of illustration and not limiting the invention.

Example

Measurement protocols

Corrosion resistance evaluation

Corrosion resistance can be quantified by measuring the corrosion of steel in the presence of seawater after 24 hours at 60 ° C, according to ISO 7120B.

The object of this method is to verify the ability of the compositions to provide protection against the corrosion of ferrous metals in the presence of water. It consists of stirring a mixture of 300 ml of test oil with 30 ml of synthetic seawater, at a temperature of 60 ± 1 ° C, in the presence of a cylindrical steel test tube immersed in the oil. After contact with the oil-water mixture, the test piece is examined with a view to verifying the presence or absence of rust. The test usually lasts 24 hours.

Evaluation of oxidation resistance - RPVOT (ASTM D2272)

A first method for measuring the oxidation stability of a composition is the RPVOT test (for "Rotating Pressure Vessel Oxidation Test") carried out according to the ASTM D2272 standard.

This method involves placing a 50g sample of oil in a rotating chamber, under oxygen pressure, in the presence of water and a copper catalyst to assess its resistance to oxidation.

The conditions are as follows:

- Temperature: 150 ° C;

- Oxygen pressure: 620 kPa;

- Rotation speed: 100 revolutions per minute;

- Angle of rotation: 30 °.

The result expresses the service life of the tested oil, expressed in minutes. The longer the life of the oil thus determined, the more its resistance to oxidation is increased.

Evaluation of resistance to oxidation - residual RPVOT according to the "Dry TOST - 1000 hours" test (adapted from ASTM D7873)

A second method for measuring the oxidation stability of a composition consists in evaluating the residual RPVOT after artificial aging of the oil in accordance with the oxidation stability test for a dry matter turbine, called "dry TOST -" 1000 hours ”for“ Dry Turbine Oxidative Stability Test ”in English, adapted from standard ASTM D7873, in order to be carried out over a period of 1000 hours.

This method involves heating a tube containing 360 mL of oil sample to 120 ° C under oxygen and in the presence of an Fe / Cu catalyst, for a total period of 1000 hours.

The tube is then removed to be analyzed by measuring the RPVOT (ASTM D2272 method described above).

The residual RPVOT is calculated by dividing the RPVOT value of the oil that has undergone dry TOST - 1000 hours aging by that of the so-called “new” oil, that is to say that has not undergone any aging, and determined according to the first method defined above.

The higher the residual RPVOT, the more resistant the oil to oxidation.

Stability to oxidation and corrosion at high temperature (ASTM D 4636-procedure 25 and non-standardized test)

This method of measuring oxidation and corrosion applies in particular to hydraulic oils, aviation turbine oils and more generally to oils subjected to high temperatures.

There is a standardized method for measuring oxidation and corrosion of lubricating compositions according to ASTM D4636 - procedure 25.

The method consists in oxidizing for 72 hours at 175 ° C a volume of 100 mL of oil in the presence of an air flow of 5 L / h and copper, steel, aluminum, magnesium and cadmium metallic specimens. Between the start and the end of the test, the following are evaluated:

- the variation in kinematic viscosity at 40 ° C,

- the loss of mass of the Cadmium specimen, and

- the loss of mass of the magnesium specimen.

The smaller the variations thus evaluated, the better the performance of the oil with respect to oxidation and corrosion.

The Applicant has also developed a method for quantifying the oxidation and corrosion of lubricating compositions at high temperature.

This non-standardized method consists in oxidizing for 24 h at 175 ° C a volume of 40 mL of oil in the presence of a flow of 5 L / h of air and of copper and cadmium metallic specimen. Between the start and the end of the test, the variation in kinematic viscosity at 40 ° C. is evaluated.

The thermal stability of an oil can be evaluated by measuring the amount of insoluble matter after 48 hours at 180 ° C.

The mass of insoluble in an oil is determined gravimetrically by filtering a 100 g sample through a membrane filter having a pore size of 0.45 µm.

The higher the amount of insoluble matter, the less thermally stable the oil.

Example 1

Preparation of lubricating compositions.

A lubricating composition in accordance with the invention (II), comprising a combination of additives required according to the invention, namely an alkylphenyl-a-naphthylamine, an alkyldiphenylamine and a phosphite ester with a strictly higher ratio of alkyldiphenylamine / phosphite ester to 1.0, and comparative compositions (C1 to C4), not comprising such a specific combination, have been formulated.

The lubricating compositions were prepared by simple mixing, at room temperature, of the following components, in the proportions by mass indicated in Tables 2 and 3 below.

TABLE 2

The physicochemical characteristics of the compositions thus prepared are summarized in Table 3 below.

⁽¹⁾ Kinematic viscosity measured at 40 ° C according to ISO 3104 standard

⁽²⁾ viscosity index measured according to standard ASTM D2270-93.

TABLE 3 Example 2

Evaluation of the properties of lubricating compositions

The various properties of the lubricating compositions prepared according to Example 1 were evaluated in accordance with the measurement protocols detailed above. The results are compiled in Table 4 below.

P emerges from these examples that the composition in accordance with the invention (composition II) combines excellent properties in terms of resistance to oxidation, thermal stability and resistance to corrosion, at high temperatures, unlike compositions which do not not comprising a combination of the three antioxidants specifically considered according to the invention (Cl, C2 and C4), and / or not satisfying the diphenylamine / phosphite ester mass ratio strictly greater than 1.0 (composition C3).

Claims

1. Lubricating composition, in particular for a gas or steam turbine, comprising:

- at least one base oil;

- at least one diphenylamine (DPA) compound, preferably dialkyl-diphenylamine; and

- at least one phosphite ester compound, preferably triaryl phosphite ester;

2. Lubricating composition according to the preceding claim, in which said phenyl-naphthylamine compound (s) are of formula (I):

in which :

n is an integer ranging from 1 to 5; and

Ri represents an alkyl group, linear or branched, preferably C1 to C22, in particular C2 to C12;

in particular of formula (I-b) below:

3. A lubricating composition according to any one of the preceding claims, in which the said diphenylamine compound (s) are of formula (II):

in which :

m and P3 are, independently of each other, integers ranging from 1 to 5; and

R2 and R3 represent, independently of one another, a linear or branched alkyl group, preferably C 1 to C ₂₂ , in particular C ₄ to Cx.

4. A lubricating composition according to any one of the preceding claims, in which said phosphite ester compound (s) is of the following formula (III):

R ₆ - O -P - O - R ₄

O

R 5 (III)

in which each R4, R5 and Rr represents, independently of one another, a hydrocarbon group, preferably having 1 to 24 carbon atoms,

in particular are of the following formula (III-a):

in which the groups R represent, independently of one another, alkyl groups, linear or branched in C1 to Cio, in particular from C3 to Cx, and n represent, independently of one another, 0, 1 or 2, in particular 1 or 2.

5. Composition according to any one of the preceding claims, in which the said diphenylamine compound (s) (DPA), in particular as defined in claim 3 and the said phosphite ester compound (s), in particular as defined in claim 4, are used in a compound (s) DPA / phosphite ester (s) mass ratio greater than or equal to 1.5; in particular greater than or equal to 2.0 and more particularly between 2.0 and 3.0.

6. Composition according to any one of the preceding claims, comprising: - from 0.05 to 5% by weight, in particular from 0.1 to 3% by weight, preferably from 0.15 to 1% by weight and more particularly from 0.2 to 0.5% by weight, of one or more phenyl-naphthylamine compounds, preferably alkylphenyl-a-naphthylamine, in particular as defined in claim 2;

- from 0.05 to 5% by weight, in particular from 0.1 to 3% by weight, preferably from 0.15 to 1% by weight and more particularly from 0.2 to 0.5% by weight, of one or more diphenylamine compounds, preferably dialkyl-diphenylamine, in particular as defined in claim 3; and

- from 0.01 to 3% by weight, in particular from 0.02 to 1% by weight, preferably from 0.05 to 0.5% by weight and more particularly from 0.1 to 0.3% by weight, of a or more phosphite ester compounds, preferably triaryl phosphite ester, in particular as defined in claim 4;

7. Composition according to any one of the preceding claims, further comprising at least one additive chosen from antioxidants other than the compounds defined in claims 1 to 4, viscosity index improvers (VI), point-lowering additives. anti-foaming agents, thickeners, corrosion inhibitors, copper passivators, and mixtures thereof.

8. Use of a composition as defined according to any one of claims 1 to 7, as a lubricant for a gas or steam turbine

9. Use, in a lubricating composition, in particular for a gas or steam turbine, comprising at least one base oil, of at least one compound phenyl-naphthylamine (PAN), preferably alkylphenyl-a-naphthylamine (AP AN); of at least one compound diphenylamine (DPA), preferably dialkyl-diphenylamine; and at least one phosphite ester compound, preferably triaryl phosphite ester, and said phosphite ester compound (s) being used in a DPA / phosphite ester (s) ratio strictly greater than 1.0 in order to improve the thermal stability and oxidation resistance performance of the composition.

10. Use according to the preceding claim, in which said phenyl-naphthylamine compound or compounds are as defined in claim 2; and / or said Diphenylamine compounds are as defined in claim 3 and / or said phosphite ester compound (s) are as defined in claim 4.