LUBRICANT COMPOSITION WITH IMPROVED OXIDATION RESISTANCE PROPERTIES

Abstract

LUBRICATING COMPOSITION WITH IMPROVED OXIDATION RESISTANCE PROPERTIES The present invention relates to the use, in a lubricating composition intended for a gas engine, of a mixture comprising at least one polyphosphate-type compound, to improve the oxidation resistance of said lubricating composition. Figure for abstract: none

Description

Title of the invention: LUBRICATING COMPOSITION WITH IMPROVED OXIDATION RESISTANCE PROPERTIES

[0001] The present invention relates to the field of gas engines. Its subject more particularly is a lubricating composition, in particular for gas engines, having improved oxidation resistance properties.

[0002] Lubricants developed specifically for the lubrication of gas engines have been known for several years.

[0003] The major characteristic of gas applications is the higher combustion temperatures than in Diesel applications. Oxidation is a natural chemical process during which the lubricant is altered and oxidation can be promoted by the combined effect of contact with oxygen and high temperature conditions. During the oxidation process, the molecules of hydrocarbons and synthetic fluids oxidize, transforming into a series of more or less polymerized oxygenated products, leading to more or less acidic products.

[0004] Following a reaction of the oil with the oxidized products, at the high temperature conditions and the pressure to which the oil is subjected during its use, it begins to saturate with the presence of both soluble and insoluble oxidized compounds.

[0005] Oxidation of the lubricating composition leads to degradation of the composition in service; this degradation can notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the composition.

[0006] The first lubricants dedicated to gas engines contained group I base oils according to the API classification. These lubricants exhibited good behavior at high temperatures, in particular they formed little or no deposits but had limited resistance to oxidation. However, as indicated above, these phenomena have a significant negative impact on the life of the lubricant and also on the oil change interval.

[0007] There is currently a need to provide lubricating compositions for gas engines having improved oxidation resistance properties.

[0008] The present invention therefore aims to provide lubricating compositions for gas engines having improved oxidation resistance properties.

[0009] Another object of the invention is to provide lubricating compositions for gas engines having improved oxidation resistance properties, allowing

[0010]

[0011]

[0012] to increase the life of the lubricant but also to increase the oil change intervals. Thus, the present invention relates to the use, in a lubricating composition intended for a gas engine, of at least one polyphosphate compound, to improve the oxidation resistance of said lubricating composition. As indicated above, by "oxidation" is meant here the contact of the lubricating composition with oxygen (02). By “polyphosphate compound” or “polyphosphate-type compound” is meant a compound comprising at least two phosphate units of the following formula: O O l .AWA*'

[0013]

[0014]

[0015] Preferably, the polyphosphate compound comprises from 2 to 10 phosphate units, in particular from 2 to 5 phosphate units. The number of phosphate units can be determined by mass spectrometry using atmospheric pressure ionization sources such as the electrospray ionization source, the atmospheric pressure chemical ionization source, or the atmospheric pressure photoionization source. In particular, the polyphosphate compound used according to the invention comprises at least one unit corresponding to the formula below: O WWW<

[0016]

[0017] in which y is an integer between 1 and 10, preferably between 1 and 5, and more particularly y is 1 or 2. Preferably, the polyphosphate compound used according to the invention has a weight-average molar mass of between 200 g.mol1 and 2,000 g.mol1, in particular between 200 g.mol1 and 1,500 g.mol1, and in particular between 300 g.mol1 and 800 g.mol1.

[0018]

[0019] The "weight-average molar mass" refers to the average of the molar masses weighted by the mass of chains of each length. This weight-average molar mass is measured in particular by size exclusion chromatography (SEC) which separates the analytes according to their size or hydrodynamic radius. In a particular embodiment, the polyphosphate compound corresponds to the following formula (I):

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] in which: - x is an integer between 1 and 10, preferably between 1 and 5, in particular is 1 or 2; - y, identical or different depending on the phosphate units, is an integer between 1 and 10, preferably between 1 and 5, and more particularly is 1 or 2; - R1 is chosen from the group consisting of: . a hydrogen atom; . a radical of formula (II) below: r "1 ?< n) O--R1 L CH^J< " y with y', identical or different to y, being between 1 and 10, preferably between 1 and 5, and in particular being 1 or 2; R3' is as defined for R3; . a linear or branched alkyl group comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl group (C8), and . a phosphate radical of formula (III) below: (HD R 1—P=O O । 2 R'

[0029] wherein R1', identical to or different from R1, is as defined for R1, and R2', identical to or different from R2, is as defined for R2;

[0030] - R2, identical to or different from R1, is as defined for R1;

[0031] - R3 is chosen from the group consisting of:

[0032] . a hydrogen atom and

[0033] . a phosphate radical of formula (III) as defined above;

[0034] it being understood that:

[0035] - the polyphosphate compound of formula (I) comprises a number of atoms of phosphorus between 2 and 10, preferably between 2 and 5; and

[0036] - the weight average molar mass of the compound of formula (I) is comprised between 200 g.mol1 and 2,000 g.mol1, in particular between 200 g.mol1 and 1,500 g.mol1, and in particular between 300 g.mol1 and 800 g.mol *.

[0037] Examples of polyphosphate type compounds that can be used according to the invention are detailed more particularly in the rest of the text.

[0038] As mentioned above, the oil in a gas engine must have a high resistance to degradation. This is mainly due to the high temperatures and corrosiveness of the gases produced during the combustion process and the contact between oxygen and the lubricant. This oxidation process must therefore be monitored regularly.

[0039] However, as is apparent from the examples which follow, the inventors have found that the use of a polyphosphate type compound according to the invention, in a lubricating composition, advantageously and surprisingly makes it possible to significantly improve the resistance to oxidation of said lubricating composition (or lubricant).

[0040] In the context of the present invention, the improvement in the oxidation resistance of a lubricant is defined by a reduction in the quantity of oxidized compounds present in said lubricant.

[0041] The quantity of oxidized compounds present in the lubricant can be evaluated by an infrared method as described later in the present application, which makes it possible to assess the level of oxidation of engine oils. This parameter is quantified by means of the infrared spectrometry technique (FT-IR), by means of the measurement of changes in the concentration of constituents of oxidized compounds in the suitable spectral range, as described later.

[0042] The improvement in resistance to oxidation is understood in relation to what is observed in the absence of polyphosphate type compound according to the invention in the lubricating composition.

[0043] The lubricating composition according to the invention is intended for a gas engine.

[0044] The gas engines according to the invention include:

[0045] - stationary gas engines; and

[0046] - mobile gas engines, in particular gas engines for vehicles including including heavy goods vehicles or public transport vehicles such as buses.

[0047] Advantageously, the lubricating composition used according to the invention is intended for a gas engine in a motor vehicle, in particular for heavy goods vehicles, or even for a stationary gas engine.

[0048] By “gas engine” is meant an engine running on natural gas, including liquefied natural gas (LNG) or compressed natural gas (CNG), but also biogas.

[0049] Other characteristics and variants of the use of polyphosphate type compounds according to the invention to improve resistance to oxidation will become more apparent on reading the description and examples which follow, given by way of illustration and not limitation of the invention.

[0050] In the rest of the text, the expressions “between ... and ...”, “ranging from ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated.

[0051] As indicated above, the present invention relates to the use, in a lubricating composition intended for a gas engine, of at least one polyphosphate type compound as defined above, to improve the oxidation resistance of said lubricating composition.

[0052] The present invention also relates to the use of a lubricating composition intended for a gas engine comprising at least one polyphosphate type compound as defined above, to improve the oxidation resistance of said lubricating composition.

[0053] The present invention also relates to a method for lubricating a gas engine by using a lubricating composition comprising at least one polyphosphate type compound as defined above, to improve the oxidation resistance of said lubricating composition.

[0054] The present invention also relates to a method for improving the oxidation resistance of a lubricating composition intended for a gas engine, comprising a step of lubricating said gas engine with a lubricating composition comprising at least one polyphosphate type compound as defined previously.

[0055] In particular, the use of a lubricating composition comprising at least one polyphosphate-type compound according to the invention makes it possible to reduce by at least 15%, in particular by at least 20%, more particularly by at least 25%, even more particularly by at least 30%, for example more than 40%, in particular more than 60%, the quantity of oxidized compounds present in said lubricating composition, in comparison with the quantity measured for the same lubricating composition without polyphosphate-type compound.

[0056] The lubricating composition used in the context of the present invention may comprise one or more polyphosphate type compound(s) as defined above and in particular as detailed in the remainder of the text.

[0057] It is understood that a lubricating composition according to the invention may comprise a mixture of two or more polyphosphate type compounds.

[0058] By “polyphosphate compound” according to the invention, it is thus understood to denote a single polyphosphate compound or a mixture of at least two polyphosphate compounds as defined above.

[0059] As indicated above, a polyphosphate type compound used according to the invention is more particularly chosen from the compounds of the following formula (I):

[0060] in which:

[0061] - x is an integer between 1 and 10, preferably between 1 and 5, in particular is worth 1 or 2;

[0062] - y, identical or different depending on the phosphate units, is an integer included between 1 and 10, preferably between 1 and 5, and more particularly is 1 or 2;

[0063] - R1 is chosen from the group consisting of:

[0064] . a hydrogen atom;

[0065] . a radical of formula (II) below:

[0066] with y', identical or different to y, being between 1 and 10, preferably between 1 and 5, and in particular being 1 or 2; R3' is as defined for R3;

[0067] . a linear or branched alkyl group comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferably from 6 to 8 carbon atoms, for example an octyl group (C8), and

[0068] . a phosphate radical of formula (III) below: R'1 <ni) OI 7 R'“

[0069] wherein R1', identical to or different from R1, is as defined for R1, and R2', identical to or different from R2, is as defined for R2;

[0070] - R2, identical to or different from R1, is as defined for R1;

[0071] - R3 is chosen from the group consisting of:

[0072] . a hydrogen atom and

[0073] . a phosphate radical of formula (III) as defined above;

[0074] it being understood that:

[0075] - the polyphosphate compound of formula (I) comprises a number of atoms of phosphorus between 2 and 10, preferably between 2 and 5;

[0076] - the weight average molar mass of the compound of formula (I) is comprised between 200 g.mol1 and 2,000 g.mol1, in particular between 200 g.mol1 and 1,500 g.mol1, and in particular between 300 g.mol1 and 800 g.mol1.

[0077] In the context of the invention, the following terms are understood to mean:

[0078] - “alkyl”, a saturated, linear or branched, aliphatic hydrocarbon group;

[0079] - “aliphatic group”, a hydrocarbon group comprising carbon atoms and hydrogen, linear or branched, saturated or unsaturated, non-aromatic, and possibly comprising one or more heteroatoms.

[0080] An aliphatic hydrocarbon group is an aliphatic group consisting only of carbon and hydrogen atoms. The aliphatic hydrocarbon group can be saturated (in which case it is called an alkyl group); it can alternatively be unsaturated (in which case it is called an alkenyl group).

[0081] Preferably, the weight-average molar mass of the compound of formula (I) is between 200 g.mol1 and 2,000 g.mol1, in particular between 200 g.mol1 and 1,500 g.mol1, in particular between 300 g.mol1 and 800 g.mol1, preferably between 450 g.mol1 and 700 g.mol1, and preferentially between 500 g.mol1 and 650 g.mol1.

[0082] Preferably, the polyphosphate type compounds of formula (I) according to the invention have a polydispersity index ranging from 1 to 3, and in particular from 1.5 to 2.5.

[0083] The polydispersity index of the polyphosphate corresponds to the ratio of the weight molar mass of the polyphosphate to the number molar mass of the polyphosphate. The polydispersity index can be measured using instruments that use light scattering (for example, using a multi-angle light scattering detector or MALS).

[0084] In formula (I) as defined above, in particular, x can be between 1 and 5, in particular x can be 2.

[0085] In the above-mentioned formula (I), in particular, y may be between 1 and 5, in particular may be 1 or 2, it being understood that y may be different in the x phosphate units. By "phosphate unit" is meant the unit repeated x times in the molecule and comprising the phosphate unit(s).

[0086] In the above-mentioned formula (I), y is identical or different depending on the phosphate units: the compound of formula (I) can therefore comprise a chain of different phosphate units, each phosphate unit being able to comprise a number of different -CH2-CH(CH3)-O- groups.

[0087] In a particular embodiment, the average number of propylene glycol units (-CH2-CH(CH3)-O- or denoted PPG) per phosphorus atom in a polyphosphate compound according to the invention, in particular in a polyphosphate compound of formula (I) mentioned above, is between 1 and 5, in particular is 1 or 2, in particular 1. The average number of PPG units per phosphorus atom of the polyphosphate compound can be evaluated by mass spectrometry.

[0088] In a particular embodiment, the average number of alkyl groups, in particular alkyl chains of 2 to 20 carbon atoms, in particular 4 to 10 carbon atoms, and preferably 6 to 8 carbon atoms, and in particular octyl chains, per phosphorus atom in a polyphosphate compound according to the invention, in particular in a polyphosphate compound of formula (I) above, is between 1 and 5, and is preferably 1 or 2. The average number of alkyl groups per phosphorus atom of the polyphosphate compound can be evaluated by mass spectrometry.

[0089] According to one embodiment, in formula (I) as defined above, R1 and R2 are not phosphate radicals.

[0090] In a particular embodiment, a polyphosphate type compound according to the invention is of formula (I) above, in which:

[0091] - R1 represents a hydrogen atom, a radical of formula (II) as defined above or a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain; preferably R1 represents an alkyl chain; and

[0092] - R2 is a hydrogen atom, a radical of formula (II) as defined above or an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain.

[0093] According to one embodiment, in formula (I) as defined above, at least one of R , R and R , in particular one or two of R , R and R , comprises a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain.

[0094] According to one embodiment, in formula (I) as defined above, R1 and / or R2 represents(s) an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain.

[0095] In particular, in formula (I) as defined above, R1 may represent a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms.

[0096] In a particular embodiment, a polyphosphate compound according to the invention can thus correspond to formula (I) in which:

[0097] - R1 is an alkyl chain, linear or branched, comprising from 2 to 20 atoms of carbon, preferably from 4 to 10 carbon atoms, and preferably from 6 to 8 carbon atoms, for example an octyl chain, and

[0098] - R2 is a hydrogen atom, a radical of formula (II) as defined above or an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain; preferably R2 is a hydrogen atom or an alkyl chain.

[0099] In particular, in formula (I) as defined above, R2 may represent a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferably from 6 to 8 carbon atoms.

[0100] In a particular embodiment, a polyphosphate compound according to the invention can thus correspond to formula (I) in which:

[0101] - R1 is a hydrogen atom, a chain of formula (II) as defined above or a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain; preferably R1 is a hydrogen atom or an alkyl chain; and

[0102] - R2 is an alkyl chain, linear or branched, comprising from 2 to 20 atoms of carbon, preferably from 4 to 10 carbon atoms, and preferably from 6 to 8 carbon atoms, for example an octyl chain.

[0103] In a particular embodiment, a polyphosphate compound according to the invention corresponds to formula (I) as defined above, in which R1 and R2, independently of one another, are linear or branched alkyl chains comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms. For example, a polyphosphate compound according to the invention corresponds to formula (I) in which R1 and R2 are octyl groups.

[0104] In a particular embodiment, in formula (I) as defined above, R3 represents a hydrogen atom.

[0105] It is understood that the different sub-modes defined above can be combined, as far as possible, to define structural variants for a polyphosphate compound according to the invention.

[0106] Thus, in a particular embodiment, a polyphosphate compound according to the invention corresponds to the abovementioned formula (I), in which:

[0107] - x is an integer ranging from 1 to 5, preferably x is 2;

[0108] - R1 represents a hydrogen atom, a radical of formula (II) as defined above or an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain;

[0109] - R2 is a hydrogen atom, a radical of formula (II) as defined above or an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain; and

[0110] - R3 represents a hydrogen atom.

[0111] Particularly suitable for the invention are the polyphosphate compounds of formula (I) in which:

[0112] - R1 and R2, identical or different, represent an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example R1 and R2 represent octyl chains;

[0113] -x is 2;

[0114] - y, identical or different, on the different phosphate units, is 1 or 2; and

[0115] - R3 is a hydrogen atom.

[0116] As indicated previously, the invention can use a mixture of polyphosphate compounds, in particular a mixture of polyphosphate compounds of formula (I).

[0117] In a particular embodiment, the present invention uses a mixture of polyphosphate compounds, in particular a mixture of polyphosphate compounds of formula (I) as defined above, said mixture comprising at least one polyphosphate compound of formula (I) in which:

[0118] - R1 and R2, identical or different, represent an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example R1 and R2 represent octyl chains;

[0119] -x is 2;

[0120] - y, identical or different, on the different phosphate units, is 1 or 2; and

[0121] - R3 is a hydrogen atom.

[0122] The polyphosphate type compounds used according to the invention, in particular of formula (I), can be prepared by methods known to those skilled in the art. Alternatively, they may be commercially available polyphosphate compounds, in particular in the form of a mixture of one or more polyphosphates, preferably comprising at least one polyphosphate of formula (I), optionally in combination with one or more monophosphate compounds.

[0123] By monophosphate compound is meant a compound comprising a single phosphate unit.

[0124] The said monophosphate compound(s) may, for example, be of the following formula (Ibis): (Ibis) 4 II R—O—P—O—R n

[0125] in which:

[0126] - y is an integer between 1 and 10, preferably between 1 and 5 and more particularly is worth 1 or 2;

[0127] - R4 is chosen from the group consisting of:

[0128] . a hydrogen atom;

[0129] . a radical of formula (Ilbis) below: Î--ch2h( CH, J;

[0130] with y', identical or different to y, being between 1 and 10, preferably between 1 and 5, and in particular being 1 or 2;

[0131] .a linear or branched alkyl group comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl group (C8), and

[0132] - R5, identical or different to R4, is as defined for R4.

[0133] In particular, the above-mentioned mixture is composed mainly of one or more polyphosphate compounds of formula (I). Preferably, the above-mentioned mixture may comprise more than 80% by mass, in particular more than 85% by mass, or even more than 90% by mass, of one or more polyphosphate compounds of formula (I) relative to the total mass of said mixture.

[0134] According to one embodiment, a lubricating composition used according to the invention contains from 0.1% to 10%, preferably from 0.5% to 5%, and preferentially from 0.7% to 3% by mass of polyphosphate compound(s) as defined above, in particular of polyphosphate compound(s) of formula (I) as defined above, relative to the total mass of said lubricating composition.

[0135] A lubricating composition used according to the invention may comprise, in addition to said polyphosphate-type compound(s) according to the invention as defined above, one or more base oils, as well as additives, in particular as defined in the remainder of the text.

[0136] These base oils can be chosen from base oils conventionally used in the field of lubricating oils, such as mineral, synthetic or natural, animal or vegetable oils or their mixtures.

[0137] The base oils used in the lubricating compositions according to the invention may in particular be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification, or their equivalents according to the ATIEL classification (table 1), or their mixtures.

[0138] [Tables 1] Saturates content Sulphur content Viscosity index (VI) Group I Mineral oils <90% > 0.03% 80 <VI < 120 Groupement II Huiles hydrocraquées >90% <0.03% 80 <VI < 120 Groupement III Huiles hydrocraquées ou hydro-isomérisées >90% <0.03% >120 Group IV Polyalphaolefins (PAO) Group V Esters and other bases not included in groups I to IV

[0139] Mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, de-alphatting, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

[0140] Mixtures of synthetic and mineral oils, which can be bio-sourced, can also be used.

[0141] In particular, a lubricating composition formulated according to the invention based on a polyphosphate compound as described above, may further comprise one or more base oils chosen from group I, II, III and IV oils of the APL classification. In particular, a lubricating composition formulated according to the invention may comprise one or more group II and / or III base oils, in particular several group II base oils.

[0142] According to a particular embodiment, a lubricating composition used according to the invention comprises at least 50% by mass, in particular from 60% to 98% by mass, and more particularly from 70% to 95% by mass, and preferably from 75% to 90% by mass of one or more base oils, relative to the total mass of said lubricating composition, said base oil(s) being more particularly chosen from group II and / or group III base oils.

[0143] Preferably, a lubricating composition used according to the invention contains one or more group II base oils.

[0144] According to a particular embodiment, a lubricating composition used according to the invention comprises at least 50% by mass, in particular from 60% to 98% by mass, and more particularly from 70% to 95% by mass, and preferentially from 75% to 90% by mass of one or more, preferably several, group II base oils, relative to the total mass of said lubricating composition.

[0145] A lubricating composition used according to the invention may further comprise all types of additives suitable for use in an engine lubricant, in particular for a gas engine.

[0146] These additives can be introduced in isolation and / or in the form of a mixture like those already available for sale for formulations of commercial lubricants for vehicle engines, with performance levels as defined by the ACEA (Association of European Automobile Manufacturers) and / or the API (American Petroleum Institute), well known to those skilled in the art.

[0147] According to one embodiment, the lubricating composition used according to the invention further comprises one or more additives chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, other than the polyphosphate type compounds according to the invention, viscosity index improvers, pour point lowering additives, dispersants, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

[0148] According to a particular embodiment, the lubricating composition used according to the invention further comprises one or more viscosity index (VI) improving polymers. Viscosity index improvers, in particular viscosity index improving polymers, make it possible to guarantee good cold resistance and minimal viscosity at high temperature. Examples of viscosity index improving polymers include polymer esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, of styrene, butadiene and isoprene, homopolymers or copolymers of olefin, such as ethylene or propylene, polyacrylates and polymethacrylates (PMA), preferably homopolymers or copolymers of olefin, such as copolymers of ethylene and / or propylene.

[0149] Preferably, the lubricating composition used according to the invention further comprises, as viscosity-improving polymer, one or more olefin copolymers, such as ethylene and / or propylene copolymers.

[0150] These olefin copolymers are traditionally copolymers based on ethylene units and propylene units, or optionally copolymers based on ethylene units, propylene units and diene units (EPDM). Preferably, the viscosity-improving polymer is an ethylene-propylene copolymer.

[0151] The amount of olefin copolymer in the lubricating composition according to the invention is for example from 0.01% to 5%, preferably from 0.05% to 3%, preferentially from 0.5% to 1%, by mass relative to the total mass of the lubricating composition. This amount is understood as the amount of dry matter of polymer. Indeed, the olefin copolymer used in the context of the present invention is sometimes found diluted in a mineral or synthetic oil, for example in a group I, II and / or III oil, in particular a group II oil.

[0152] A lubricating composition used according to the invention may also comprise at least one detergent additive.

[0153] Detergent additives generally make it possible to reduce the formation of deposits on the surface of metal parts by dissolving secondary oxidation and combustion products.

[0154] The detergent additives that can be used in a lubricating composition used according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali or alkaline-earth metal.

[0155] The detergent additives are preferably chosen from alkali metal or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, as well as phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

[0156] These metal salts generally comprise the metal in a stoichiometric quantity or in excess, therefore in a quantity greater than the stoichiometric quantity. These are then overbased detergent additives; the excess metal providing the overbased character to the detergent additive is then generally in the form of a metal salt insoluble in oil, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate.

[0157] A lubricating composition used according to the invention may, for example, comprise from 1% to 10%, in particular from 2% to 5%, by mass of detergent additive(s), relative to the total mass of the composition.

[0158] A lubricating composition used according to the invention may comprise at least one additional antioxidant additive, different from the polyphosphate compounds according to the invention.

[0159] Among the commonly used antioxidant additives, mention may be made of phenolic type antioxidant additives, amine type antioxidant additives, phosphosulfur antioxidant additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, may be ash-generating. The phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. The antioxidant additives may in particular be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C1-C12 alkyl group, N,N'-dialkyl-aryl-diamines and mixtures thereof.

[0160] Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group of which at least one vicinal carbon of the carbon carrying the alcohol function is substituted by at least one C1-C10 alkyl group, preferably a C1-C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group.

[0161] Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR4R5R6 in which R4 represents an aliphatic group or an aromatic group, optionally substituted, R5 represents an aromatic group, optionally substituted, R6 represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R7S(O)ZR8 in which R7 represents an alkylene group or an alkenylene group, R8 represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

[0162] Sulphurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

[0163] Another class of antioxidant additives is that of copper compounds, for example copper thio- or dithio-phosphates, copper salts of carboxylic acids, dithiocarbamates, sulfonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or anhydride salts can also be used.

[0164] A lubricating composition used according to the invention may comprise from 0.1% to 5% by mass, in particular from 0.5% to 2% by mass of at least one additional antioxidant additive, distinct from the polyphosphate compounds according to the invention, relative to the total mass of the composition.

[0165] According to one embodiment, the lubricating composition according to the invention does not comprise an additional antioxidant, other than the phosphate ester type compounds of formula (I) according to the present invention.

[0166] According to one embodiment, the lubricating composition according to the invention does not comprise an amine antioxidant.

[0167] A lubricating composition used according to the invention may comprise at least one anti-wear additive.

[0168] There is a wide variety of anti-wear additives. Preferably for the composition used according to the invention, the anti-wear additives are chosen from phosphosulfur additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTP. The preferred compounds are of formula Zn((SP(S)(OR2)(OR3)) 2, in which R2 and R3, identical or different, independently represent an alkyl group, preferably an alkyl group comprising from 1 to 18 carbon atoms.

[0169] Amine phosphates are also anti-wear additives that can be used in a composition implemented according to the invention. However, the phosphorus provided by these additives can act as a poison for automobile catalytic systems because these additives generate ash. These effects can be minimized by partially substituting the amine phosphates with additives that do not provide phosphorus, such as, for example, polysulfides, in particular sulfur-containing olefins.

[0170] A lubricating composition used according to the invention may comprise from 0.01% to 6% by mass, preferably from 0.05% to 4% by mass, more preferably from 0.1% to 2% by mass, of anti-wear additives, by mass relative to the total mass of composition.

[0171] A lubricating composition used according to the invention may further comprise one or more other additives chosen from friction modifying additives, extreme pressure additives, pour point lowering additives, dispersants, thickeners, corrosion inhibitors, copper passivating agents and mixtures thereof.

[0172] The friction modifying additive may be chosen from a compound providing metallic elements and an ash-free compound. Among the compounds providing metallic elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu, Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms. Ash-free friction modifying additives are generally of organic origin and may be chosen from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides; fatty amines or glycerol esters of fatty acid, and dithiocarbamates.

[0173] A lubricating composition used according to the invention may comprise from 0.01% to 2% by mass or from 0.01% to 5% by mass, preferably from 0.1% to 1.5% by mass or from 0.1% to 2% by mass of friction modifying additive, relative to the total mass of the composition.

[0174] Advantageously, a lubricating composition used according to the invention is free of friction modifying additive.

[0175] A lubricating composition used according to the invention may also comprise at least one pour point lowering additive.

[0176] By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the composition.

[0177] Examples of pour point depressant additives include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, or alkylated polystyrenes.

[0178] A lubricating composition according to the invention may also comprise at least one dispersing agent. Such dispersing agents ensure the maintenance in suspension and the evacuation of insoluble solid contaminants constituted by the secondary oxidation products which are formed when the lubricating composition is in service. They may be chosen from Mannich bases, succinimides and their derivatives, such as polyisobutylene succinic anhydride derivatives.

[0179] In particular, a lubricating composition according to the invention may comprise from 0.2% to 10% by mass of dispersing agent(s), relative to the total mass of the composition.

[0180] It may also comprise at least one anti-corrosion agent or copper passivating agent, for example compounds such as succinic polyisobutene anhydrides, thiadiazole sulfonates or mercaptobenzothiazoles. They are typically present in a lubricating composition according to the invention at contents of between 0.01% and 1% by mass, relative to the total mass of the composition.

[0181] The lubricating composition used according to the invention and as defined above is intended for a gas engine. It is in particular intended for a gas engine in a motor vehicle, in particular for heavy vehicles and light vehicles, in particular for heavy goods vehicles, or a stationary engine.

[0182] The present invention also describes the use of a lubricating composition as defined above, for lubricating the parts of a gas engine, as explained above.

[0183] The invention will now be described by means of the following examples given of course by way of illustration and not limitation of the invention. EXAMPLES

[0184] Example 1: Preparation of lubricating compositions

[0185] Two lubricating compositions, CL1 and CCI, were prepared by simple mixing, at room temperature, of the following components, in the mass proportions indicated in Table 2.

[0186] [Tables2] Components CL1 CCI Group II base oil (KV100 = 5.2 - 5.6 mm2 / s) 61.7 62.3 Group II base oil (KV100 = 10.0 - 12.0 mm2 / s) 20.8 21.0 Viscosity improver polymer (Olefin copolymer at 12.5% ​​active matter in a Group II base oil) 5.9 6 Additive package (*) 10.6 10.7 Polyphosphate compound (1) 1 -

[0187] * includes detergents, antioxidants and anti-wear additives.

[0188] KV100 corresponds to a kinematic viscosity measured at 100°C, measured according to the ASTM D445 standard.

[0189] The polyphosphate compound (1) is a mixture of polyphosphate compounds according to the invention comprising at least one compound of formula (I) according to the invention comprising two phosphorus atoms. Its weight-average molar mass (Mw), estimated by SEC, is approximately 524 g.mol1. Its polydispersity index determined by SEC is approximately 1.7. Example 2#: Evaluation of oxidation resistance

[0190] Method for evaluating resistance to oxidation

[0191] To evaluate the resistance to oxidation, the lubricant to be tested is subjected to thermal aging by catalyzed oxidation, intended to simulate the evolution of an engine oil subjected to severe conditions (high load, hot sump). The lubricant to be tested is maintained at a temperature above 150°C, in the presence of a ferric catalyst and under air flow for 3 days.

[0192] The level of oxidation of the lubricant is then evaluated by infrared spectrometry according to the ASTM D7214 standard, by calculating the PAI (PAI for Peak Area Increase).

[0193] The area of ​​the infrared peak is linked to the presence of oxidized compounds. Here, we measure the C=O band from 1650 to 1820 cm '. The more oxidized compounds the oil contains, the larger this band is. The area of ​​this band is measured using a subtraction between the spectrum of the oxidized lubricant and that of the new lubricant.

[0194] Results

[0195] Two analyses were carried out for the polyphosphate-free lubricant CCI and three analyses for the lubricant containing polyphosphates CL1. The values ​​obtained concerning the PAI (averages of the analyses) are indicated in Table 3 below.

[0196] [Tables3] CL1 CCI Mean values ​​(PAI C=O) (in A.cm '.mm ') 192,521

[0197] Significant differences are therefore observed when adding 1% of polyphosphate compound for the composition according to the invention CL1 compared to CCI.

[0198] The oxidation values ​​given by the CO band during an infrared analysis are significantly reduced for CL1 (in the presence of polyphosphate) in comparison with CCI (without polyphosphate). These results demonstrate the improvement in oxidation resistance performance due to the presence of a polyphosphate compound according to the invention.

Claims

1.

2. Claims Use, in a lubricating composition intended for a gas engine, of at least one polyphosphate compound, to improve the oxidation resistance of said lubricating composition. Use according to claim 1, wherein the polyphosphate compound comprises at least one unit of formula: O II j -O—P—O— 5 I * O

3. in which y is an integer between 1 and 10, preferably between 1 and 5, and more particularly y is 1 or 2. Use according to claim 1 or 2, in which the polyphosphate compound corresponds to the following formula (I): in which: - x is an integer between 1 and 10; preferably between 1 and 5, in particular is 1 or 2; - y, identical or different depending on the phosphate units, is an integer between 1 and 10, preferably between 1 and 5, and more particularly is 1 or 2; - R1 is chosen from the group consisting of: . a hydrogen atom; . a radical of formula (II) below: ? (II)

4. with y', identical or different to y, being between 1 and 10, preferably between 1 and 5, and in particular being 1 or 2; and R3' is as defined for R3; . a linear or branched alkyl group comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl group (C8), and . a phosphate radical of formula (III) below: R-1 (III) O s I I—P=O O wherein R1', identical to or different from R1, is as defined for R1, and R2', identical to or different from R2, is as defined for R2; - R2, identical to or different from R1, is as defined for R1; - R3 is chosen from the group consisting of: . a hydrogen atom and . a phosphate radical of formula (III) as defined above; it being understood that: - the polyphosphate compound of formula (I) comprises a number of phosphorus atoms between 2 and 10, in particular between 2 and 5; - the weight-average molar mass of the compound of formula (I) is between 200 g.mol1 and 2,000 g.mol ', in particular between 200 g.mol1 and 1,500 g.mol1, and in particular between 300 g.mol1 and 800 g.mol i Use according to claim 3, wherein the polyphosphate compound corresponds to formula (I) in which: - R1 represents a hydrogen atom, a radical of formula (II) as defined in claim 3, or a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain; preferably R1 represents an alkyl chain; and - R2 is a hydrogen atom, a radical of formula (II) as defined in claim 3, or a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain.

5. Use according to claim 3 or 4, in which the polyphosphate compound corresponds to formula (I) in which R1 and / or R2 represents(s) an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms; preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain.

6. Use according to any one of claims 3 to 5, in which the polyphosphate compound corresponds to formula (I) in which: - R1 is a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms; and - R2 is a hydrogen atom, a radical of formula (II) as defined in claim 3, or a linear or branched alkyl chain comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain; preferably R2 is a hydrogen atom or an alkyl chain;or - R1 is a hydrogen atom, a radical of formula (II) as defined in claim 3, or an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain; preferably R1 is a hydrogen atom or an alkyl chain; and; - R2 is an alkyl chain, linear or branched, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example an octyl chain.

7. Use according to any one of claims 3 to 6, wherein the polyphosphate compound corresponds to formula (I) in which R3 is a hydrogen atom.

8. Use according to any one of the preceding claims, using a mixture of polyphosphate compounds, in particular a mixture of polyphosphate compounds of formula (I) as defined in any one of claims 3 to 7, said mixture comprising at least one polyphosphate compound of formula (I) in which: - R1 and R2, identical or different, represent a linear or branched alkyl chain, comprising from 2 to 20 carbon atoms, preferably from 4 to 10 carbon atoms, and preferentially from 6 to 8 carbon atoms, for example R1 and R2 represent octyl chains; -x is 2 - y, identical or different, on the different phosphate units, is 1 or 2; and - R3 is a hydrogen atom.

9. Use according to any one of claims 1 to 8, in which the lubricating composition contains from 0.1% to 10%, preferably from 0.5% to 5%, and preferentially from 0.7% to 3% by mass of polyphosphate compound(s), in particular of formula (I) as defined in any one of claims 3 to 8, relative to the total mass of said lubricating composition.

10. Use according to any one of claims 1 to 9, in which the lubricating composition comprises at least 50% by mass, in particular from 60% to 98% by mass, and more particularly from 70% to 95% by mass, and preferentially from 75% to 90% by mass of one or more base oils, relative to the total mass of said lubricating composition, said base oil(s) being more particularly chosen from group II and / or group III base oils.

11. Use according to any one of claims 1 to 10, wherein the lubricating composition further comprises one or more viscosity index improving polymers, preferably one or more olefin copolymers, such as ethylene and / or propylene copolymers.

12. Use according to any one of claims 1 to 11, wherein the lubricating composition further comprises one or more additives selected from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, other than the compounds of formula (I), viscosity index improvers, pour point depressant additives, dispersants, thickeners, corrosion inhibitors, copper passivators and mixtures thereof.

13. Use according to any one of claims 1 to 12, wherein the lubricating composition is intended for a gas engine in a motor vehicle, in particular for heavy vehicles and light vehicles, in particular for heavy goods vehicles, or a stationary engine.