Use of a combination of additives for improving the oxidation stability of a lubricant composition for a gas engine

Abstract

The present invention relates to the use of the combination of at least one first additive selected from bisdithiocarbamates and at least one second additive selected from diphenylamines substituted with one or more aromatic groups for improving the oxidation stability of a lubricant composition intended to lubricate a powertrain system comprising a gas engine, the lubricant composition comprising at least one base oil selected from oils belonging to Groups I, II, III and IV of the API classification and mixtures thereof. The present invention further relates to the use of such a lubricant composition for lubricating a powertrain system comprising a gas engine. The present invention also relates to a method for lubricating a gas engine, the method comprising a step of bringing at least one internal part of the engine into contact with such a lubricant composition.

Description

[0001] DESCRIPTION

[0002] TITLE: Use of a combination of additives to improve the oxidation stability of a lubricating composition for gas engines

[0003] The present invention relates to the use of a particular combination of additives to improve the oxidation stability of a lubricating composition intended to lubricate a motorization system comprising a gas engine.

[0004] The present invention further relates to the use of a lubricating composition containing these additives to lubricate a motorization system comprising a gas engine.

[0005] The present invention also relates to a method of lubricating a gas engine, comprising a step of bringing at least one internal part of the engine into contact with a lubricating composition containing the particular combination of additives.

[0006] The present invention finally relates to a method of operating a motorization system, mobile or stationary, comprising a gas engine and consisting of supplying said engine with a gaseous fuel and lubricating at least one part of said engine by means of a lubricating composition containing the particular combination of additives.

[0007] PREVIOUS STATE OF THE ART

[0008] In order to reduce greenhouse gas emissions generated by the combustion of hydrocarbon-based fuels, the international community is studying the use of alternative fuels with lower carbon dioxide emissions. In this context, gaseous fuels are of particular interest.

[0009] A specific, but not exhaustive, example of such a fuel is hydrogen, which is considered a promising solution, particularly for the transport sector and electricity generation in gas turbines. Hydrogen offers multiple advantages, including, but not limited to: - It is a completely decarbonized fuel that can be produced using various technologies, including electricity from renewable sources;

[0010] - Its combustion does not generate emissions of carbon dioxide (CO2), sulfur gases (SOx), unburned hydrocarbons, or particles;

[0011] - It can be used in existing engines and heating devices, with some adaptations.

[0012] Gaseous fuels have a higher specific heat capacity than liquid hydrocarbons, and gas engines therefore generate higher combustion temperatures than hydrocarbon-powered engines. This places particularly stringent demands on the lubricants used in these engines, necessitating the development of dedicated lubricants with improved performance, especially in terms of oxidation stability.

[0013] Indeed, oxidation is a chemical process accelerated by the combined effect of contact with oxygen and high temperatures. During the oxidation process, the components of the lubricant composition oxidize, transforming into a series of oxygenated products that can, for example, polymerize, leading to more or less acidic products, etc.

[0014] 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 and, more generally, a degradation of the performance of the lubricating composition.

[0015] The oxidation stability performance of a lubricant composition reflects the composition's ability to resist oxidation phenomena, particularly chemical degradation at high temperatures and in the presence of oxygen.

[0016] Therefore, there is a particular need to protect the mechanical parts of gas engines from wear and an underlying need to reduce friction between these parts. It is thus necessary to have access to lubricating compounds that offer very high lubrication efficiency for the parts of these gas engines.

[0017] In particular, there is a need for these gas engines to have lubricating compositions with particularly high and durable oxidation stability performance, given the operating conditions of these engines.

[0018] The present invention aims to remedy the problems described above.

[0019] DESCRIPTION OF THE INVENTION

[0020] The Applicant has now discovered that the use of a combination of two particular additives as defined below formulated in at least one base oil belonging to API Groups I, II, III and / or IV, in particular Groups II and / or III, unexpectedly improves the oxidation stability of a lubricating composition intended to lubricate a drive system including a gas engine.

[0021] The present invention thus relates to the use, for improving the oxidation stability of a lubricating composition, in particular intended to improve the oxidation stability of a lubricating composition intended to lubricate a motorization system comprising a gas engine, of the combination of at least one first additive chosen from bisdithiocarbamates and at least one second additive chosen from diphenylamines substituted by one or more aromatic groups.

[0022] The present invention relates more particularly to the use of the combination of at least one first additive chosen from bisdithiocarbamates and at least one second additive chosen from diphenylamines substituted by one or more aromatic groups to improve the oxidation stability of a lubricating composition intended to lubricate a powertrain system comprising a gas engine and comprising at least one base oil chosen from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III. The combination of said first and second additives in combination with the use of a base oil chosen from oils belonging to groups I, II, III and IV of the API classification and their mixtures, preferably to groups II and / or III, makes it possible to obtain excellent oxidation stability performance of the lubricating composition.The level of performance provided by this combination of additives is, unexpectedly, particularly high and even synergistic.

[0023] Thus, the use of said first and second additives in a lubricating composition comprising a base oil chosen from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III, makes it possible to avoid the oxidation of this lubricating composition.

[0024] Its particular properties make the combination of additives particularly suitable for use in a lubricating composition intended for an engine powered by a gaseous fuel (also referred to hereafter as "gas engine").

[0025] The invention therefore also relates to the use in a gas engine of a lubricating composition comprising at least one base oil chosen from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III, as well as the combination of these two additives.

[0026] The present invention thus relates to the use, for lubricating a motorization system comprising a gas engine, of a lubricating composition comprising at least one base oil chosen from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III, at least one first additive chosen from bisdithiocarbamates and at least one second additive chosen from diphenylamines substituted by one or more aromatic groups.

[0027] For the purposes of this invention, "engine system" means a system comprising all the mechanical parts necessary for the intended mobile or stationary application and including at least one gas engine. The use of this lubricant composition provides excellent lubricating properties, which are sustained due to its very good oxidation resistance. This allows for a lasting reduction in friction, ensures proper lubrication of the moving mechanical parts in the gas engine, reduces the risk of mechanical part degradation, and consequently improves the gas engine's lifespan.

[0028] The present invention also relates to a method of lubricating moving parts in a motorization system including a gas engine, comprising a step of bringing at least one of said parts into contact with a lubricating composition comprising at least one base oil chosen from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III, at least one first additive chosen from bisdithiocarbamates and at least one second additive chosen from diphenylamines substituted by one or more aromatic groups.

[0029] The present invention also relates to a method of operating a motorization system, mobile or stationary, comprising a gas engine and consisting of supplying said engine with a gaseous fuel and lubricating at least one part of said motorization system by means of a lubricating composition comprising at least one base oil selected from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III, at least one first additive selected from bisdithiocarbamates and at least one second additive selected from diphenylamines substituted by one or more aromatic groups.

[0030] A "stationary" motorization system, as defined in the invention, is a motorization system that includes a stationary motor. It can, for example, find applications in electrical power generation devices.

[0031] A "mobile" motorization system is more specifically a motorization system implemented in vehicles, including for example light vehicles, heavy goods vehicles, mobile machines known as "off road". A mobile motorization system can thus be a vehicle propulsion system.

[0032] For the purposes of this invention, "propulsion system" means a system comprising the mechanical parts necessary for the propulsion of a vehicle. The propulsion system more specifically includes at least one gas engine.

[0033] Other objects, features, aspects and advantages of the invention will become even clearer upon reading the description that follows.

[0034] In what follows, and unless otherwise indicated, the boundaries of a range of values ​​are included in that range, in particular in the expressions "between" and "ranging from ... to .".

[0035] Furthermore, the expressions "at least one" and "at least" used in this description are respectively equivalent to the expressions "one or more" and "greater than or equal to".

[0036] Finally, in a manner known in itself, a compound or group in CN is designated as a compound or group containing in its chemical structure N carbon atoms.

[0037] DETAILED DESCRIPTION

[0038] The first additives

[0039] The first additive(s) are chosen from among the bisdithiocarbamates.

[0040] Bisdithiocarbamates can more specifically be chosen from compounds with the following general formula (I):

[0041]

[0042] in which:

[0043] - R3 and R4 represent, independently of each other, hydrocarbon groups, possibly substituted, comprising from 1 to 30 carbon atoms, preferably from 2 to 24 carbon atoms, more preferably from 3 to 8 carbon atoms; and

[0044] - R5 represents a hydrocarbon group comprising 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms.

[0045] Preferably:

[0046] - R3 and R4 represent, independently of each other, alkyl groups, branched or unbranched, comprising from 2 to 24 carbon atoms, more preferably from 3 to 8 carbon atoms and even better 4 carbon atoms;

[0047] - R5 represents an alkylene group comprising 1 to 4 carbon atoms, preferably 1 or two carbon atoms and even better one carbon atom.

[0048] In this application, the term "alkylene group" means a divalent alkyl group, also known as an "alkanediyl group". This group corresponds to a saturated hydrocarbon chain with the formula -CnU2n-.

[0049] A particularly preferred compound is that in which R3 and R4 denote a butyl group and R5 denotes a methylene group, namely methylene bis(dibutyldithiocarbamate) of formula (II):

[0050]

[0051] The first additive(s) may be present at a content within the range of 0.1% to 10% by mass, preferably 0.2% to 5% by mass, more preferably 0.5% to 2% by mass, even more preferably 0.8% to 1.5% by mass, relative to the total mass of the lubricating composition.

[0052] The second set of additives

[0053] The second additive(s) are chosen from among the diphenylamines substituted by one or more aromatic groups.

[0054] Substituted diphenylamines can be chosen from the compounds of the following formula (III):

[0055]

[0056] in which

[0057] - RI is an aromatic group comprising at least one benzene ring;

[0058] - R2, identical or different from RI, is chosen from the group consisting of hydrogen and saturated or unsaturated hydrocarbon groups. Preferably, RI is chosen from alkylphenyl groups comprising from 1 to 22 carbon atoms, more preferably from 1 to 12 carbon atoms. These groups advantageously have the formula -R-Ph, in which R is an alkylene group comprising from 1 to 8, and preferably from 1 to 4, carbon atoms, and Ph is a phenyl group, substituted or not by one or more ethyl or methyl groups.

[0059] Preferably, RI is a group of formula -R-Ph in which R is an alkylene group comprising 1 to 4 carbon atoms and Ph is a phenyl group.

[0060] Preferably, R2 designates an alkyl group or an aromatic group. Alkyl groups may have from 1 to 22 carbon atoms, more preferably from 1 to 12 carbon atoms, and may be branched or straight-chain, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, isomers of these, for example, t-butyl, 2-ethylhexyl, and analogues, and mixtures thereof.

[0061] When R2 is an aromatic group, it comprises at least one benzene ring. Preferably, R2 is chosen from alkylphenyl groups comprising from 1 to 22 carbon atoms, more preferably from 1 to 12 carbon atoms. These groups advantageously have the formula -R-Ph, in which R is an alkylene group comprising from 1 to 8, and preferably from 1 to 4, carbon atoms, and Ph is a phenyl group, substituted or not by one or more ethyl or methyl groups. Preferably, R2 is a group of the formula -R-Ph, in which R is an alkylene group comprising from 1 to 4 carbon atoms, and Ph is a phenyl group.

[0062] In a preferred embodiment, RI and R2 both denote an aromatic group and, more preferably, a group of the formula -R-Ph as described above. More preferably, the groups RI and R2 are identical.

[0063] A particularly preferred compound is 4-(l-methyl-l-phenylethyl)-N-[4-(1-methyl-l-phenylethyl)phenyl]aniline of formula (IV):

[0064]

[0065] The second additive(s) may be present at a content within the range of 0.1% to 10% by mass, preferably 0.2% to 5% by mass, more preferably 0.5% to 2% by mass, even more preferably 0.8% to 1.5% by mass, relative to the total mass of the lubricating composition.

[0066] The weight ratio between the mass content of the first additive(s) and the mass content of the second additive(s) may advantageously be within the range of 0.1 to 10, preferably 0.2 to 5, more preferably 0.5 to 2, even more preferably 1.

[0067] The use of additives

[0068] According to the invention, the combination of said first and second additives is used to improve the oxidation stability of a lubricating composition.

[0069] The combination of the aforementioned first and second additives unexpectedly confers antioxidant properties to the lubricating composition, preferably synergistic ones.

[0070] The oxidation stability performance of the composition can be evaluated by differential vacuum scanning calorimetry (PDSC), which determines the oxidation induction time for the lubricant composition under study. This is a standard procedure in the lubricating oil industry based on CEC L-85 T-99.

[0071] This test is particularly suitable for evaluating the oxidation stability of the lubricating composition at high temperatures.

[0072] The lubricating composition in which the combination of said first and second additives is used typically includes one or more base oil(s).

[0073] It may also include one or more additives as described below.

[0074] According to a preferred embodiment, said lubricating composition comprises (in addition to said first and second additives described above):

[0075] - one or more base oil(s);

[0076] - at least one phosphosulfur additive; and

[0077] - at least one dispersing additive chosen from polyisobutylene succinimides and their borated derivatives.

[0078] The base oils

[0079] The lubricating composition comprises one or more base oil(s) selected from oils belonging to groups I, II, III and IV of the API classification and their mixtures, preferably to groups II and / or III.

[0080] It can be a single base oil or a mixture of several base oils, for example a mixture of two, three or four base oils.

[0081] Base oils are specifically oils of mineral or synthetic origin belonging to groups I to IV according to the classes defined in the API classification (or their equivalents according to the ATIEL classification). The API (American Petroleum Institute) classification is a standardized system that classifies base oils for lubricants into five groups presented in Table A below.

[0082] [Table A] Sulfur content Saturated content Viscosity index (VI) Group I < 90% >0.03% 80 <VI< 120 Huiles

[0083] minerals

[0084] Group II >90% <0.03% 80 <VI<120 Huiles

[0085] hydrocracked

[0086] Group III >90% <0.03% >120 Oils

[0087] hydrocracked

[0088] or hydro-isomerized

[0089] Group IV Polyalphaolefins (PAO) Group V Esters and other bases not included in the groups

[0090]

[0091] I to IV

[0092] 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, desalpha removal, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

[0093] Synthetic base oils can be polyalphaolefins. Polyalphaolefins used as base oils are obtained, for example, 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 mm 2.sl according to ASTM D445. Their average molecular weight is generally between 250 and 3000 according to ASTM D5296.

[0094] Mixtures of synthetic and mineral oils, which may be bio-based, can also be used.

[0095] The base oil(s) may be chosen from oils that are at least partially re-refined, also known as "regenerated oils" or "recycled oils." Such oils are derived, at least in part, from a used lubricating composition that has undergone one or more re-refining treatment steps. Examples of such re-refined base oils are described in application WO2024 / 126554.

[0096] There are no limitations on the use of different base oils in the lubricating composition, except that they must have properties, including viscosity, viscosity index, sulfur content or oxidation resistance, suitable for use in engine systems operating with a gaseous fuel such as hydrogen.

[0097] Preferably, the lubricating composition includes at least one base oil selected from API Group II, III and IV oils, and their mixtures.

[0098] Preferably, the lubricating composition includes at least one base oil chosen from the oils of group II and III of the API classification, and their mixtures.

[0099] According to a preferred embodiment, the lubricating composition comprises at least one Group II base oil.

[0100] According to a more preferred embodiment, the lubricating composition may include at least one Group III base oil.

[0101] In particular, such a lubricating composition may include at least one Group II base oil and at least one Group III base oil.

[0102] Base oils can have a kinematic viscosity measured at 40 °C according to ASTM D445 (KV40) ranging from 10 to 100 mm 2 / s, in particular from 12 to 50 mm 2 / s, more specifically from 15 to 40 mm 2 The base oils suitable for the invention may have a kinematic viscosity measured at 100 °C according to ASTM D445 (KV100) ranging from 1 to 15 mm 2 / s, in particular from 2 to 10 mm 2 / s, more specifically from 4 to 8 mm 2 / s.

[0103] The base oil(s) may be present in the lubricating composition at a content of at least 50% by mass, relative to its total mass, in particular at least 60% by mass, more particularly ranging from 60 to 99% by mass and preferably from 70 to 90% by mass, relative to the total mass of the composition. The lubricating composition may advantageously be of grade XW-Y according to the SAE J 300 classification, X being equal to 0, 5, 10 or 20, and Y being between 20 and 60, preferably between 20 and 40.

[0104] Phosphosulfur additives

[0105] In a preferred embodiment, the lubricating composition further comprises at least one phosphosulfur additive. Phosphosulfur additives may be selected from metallic and non-metallic phosphosulfur additives.

[0106] Preferably, the lubricating composition includes at least one metallic phosphosulfur additive, as described below.

[0107] The metallic phosphosulfur additive(s) can be chosen from metallic alkyldithiophosphates, preferably metallic dialkyldithiophosphates, more preferably zinc dialkyldithiophosphates or DTPZn.

[0108] Preferably, the zinc dialkyldithiophosphate(s) are chosen from compounds of formula Zn((SP(S)(OR5)(OR6))2, in which R5 and R6, identical or different, independently represent alkyl groups, linear or branched, especially branched, in Cl to C18, preferably in C2 to C12, and more preferably in C3 to C8.

[0109] Zinc dialkyldithiophosphates of formula Zn((SP(S)(OR5)(OR6))2 can be obtained for example from secondary alcohols of formulas R5OH and R6OH, in which R5 and R6 represent alkyl groups, linear or branched, preferably branched, in C3 to C8, for example R5 represents an alkyl group in C3 or C4, especially in C3, for example an isopropyl group, and R6 represents an alkyl group in C5 or C6, especially in C6, for example a 1,3-dimethylbutyl group.

[0110] The non-metallic phosphosulfur additive(s) can be chosen from among the non-metallic dithiophosphates.

[0111] Non-metallic dithiophosphates can be selected from compounds derived from 3-dithiophosphorylpropionic acid of the following formula (V):

[0112]

[0113] in which R7 and R8, whether identical or different, independently represent an alkyl group at C3 to C18, a cycloalkyl group at C5 to C12, in particular a cycloalkyl group at C9 to C10, a bicycloalkylmethyl group at C9 to C10, a tricycloalkylmethyl group at C9 to C10, a phenyl group or an alkylphenyl group at C7 to C24, or

[0114] R7 and R8 together form a formula group:

[0115] H3C^ CH 2

[0116] H3C CH2— ,

[0117]

[0118] ET

[0119] R9 represents a hydrogen atom or a methyl group.

[0120] Preferably, R7 and R8 independently represent an alkyl group at C3 to C18, more particularly an isopropyl, isobutyl or 2-ethylhexyl group.R7 and R8 can also represent other groups including an n-propyl group, an n-butyl group, a tert-butyl group, an n-pentyl group, an isoamyl group, a neopentyl group, a 2-ethylbutyl group, an n-hexyl group, a 1-methylpentyl group, a 1,3-dimethylbutyl group, an n-heptyl group, an isoheptyl group, an n-octyl group, a 1,4,4-trimethyl-2-pentyl group, a 3,4-dimethyl-1-hexyl group, a 3,5-dimethyl-1-hexyl group, a 4,5-dimethyl-1-hexyl group, a 3-methylheptyl group, a 5-methylheptyl group, a 1,1 ,3,3-tetramethylbutyl, a branched octyl group as obtained from an isobutylene dimer, an n-nonyl group, a 1,1,3-trimethylhexyl group, a branched nonyl group as obtained from a tripropylene trimer.

[0121] Preferred compounds of formula (V) are those in which R7 and R8 represent an alkyl group at C3 to C18, for example a 2-methylpropyl group, and R9 represents a methyl group.

[0122] A preferred derivative of 3-dithiophosphorylpropionic acid is 3-[[bis(2-methylpropoxy)phosphinothioyl]thio]-2-methylpropanoic acid.

[0123] Non-metallic dithiophosphates can also be selected from the ammonium salts of dithiophosphoric acid of formula (VI):

[0124]

[0125] in which R7 and R8 are as defined previously, Ra, Rb, Rc and Rd, identical or different, represent a hydrogen atom or a hydrocarbon group in C6 to C20.

[0126] Preferably, R7 and R8 of formula (VI) independently represent a phenyl group or an alkyl group at C3 to C8, and in particular an isopropyl group.

[0127] Preferably, Ra, Rb, Rc and Rd independently represent a hydrogen atom or an alkyl group in C12 to C20.

[0128] The phosphosulfur additive(s) may be present at a concentration ranging from 0.1 to 1.5% by mass, relative to the total mass of the lubricating composition. Preferably, the phosphosulfur additive(s) are present at a concentration ranging from 0.1% to 0.9% by mass, more preferably from 0.2% to 0.8% by mass, and even more preferably from 0.3% to 0.6% by mass, relative to the total mass of the lubricating composition.

[0129] According to a preferred embodiment, the composition comprises at least one metallic phosphosulfur additive preferably selected from zinc dialkyldithiophosphates, at a content in the range of 0.1 to 1.5% by mass, preferably 0.1% to 0.9% by mass, more preferably 0.2% to 0.8% by mass, even more preferably 0.3% to 0.6% by mass, relative to the total mass of the lubricating composition.

[0130] Dispersive additives

[0131] According to a preferred embodiment, the lubricating composition further comprises at least one dispersing additive selected from polyisobutylene succinimides and their borated derivatives.

[0132] In particular, the lubricating composition may include at least one phosphosulfur additive as described above and at least one dispersing additive selected from polyisobutylene succinimides and their borated derivatives.

[0133] Such dispersing additives can be chosen from borated succinimide polyisobutylenes.

[0134] Such dispersing additives can also be selected from polyisobutylene succinimides-polyamines. These dispersing additives are typically obtained by reacting a polyisobutylene-substituted succinic acid or anhydride with a polyalkylene polyamine.

[0135] Such dispersing additives may be chosen from among the substituted succinimides corresponding to formulas (VII) and (VIII) below:

[0136] •3

[0137] (VII)

[0138]

[0139] (VIII)

[0140] in which:

[0141] • x represents an integer from 1 to 10, preferably 2, 3, 4, 5 or 6; • y represents an integer from 2 to 10;

[0142] • RI represents a hydrogen atom, a linear or branched alkyl group comprising from 2 to 20 carbon atoms, a heteroalkyl group comprising from 2 to 20 carbon atoms and at least one heteroatom selected from the group formed by O, N and S, a hydroxyalkyl group comprising from 2 to 20 carbon atoms or a -(CH2) group X -O-(CH2) X -OH ;

[0143] • R2 represents a polyisobutylene group comprising 8 to 400 carbon atoms, preferably 50 to 200 carbon atoms;

[0144] • R3 and R4, whether identical or different, independently represent a hydrogen atom, a linear or branched alkyl group comprising 1 to 25 carbon atoms, an alkoxy group comprising 1 to 12 carbon atoms, an alkylene group comprising 2 to 6 carbon atoms, a hydroxylated alkylene group comprising 2 to 12 carbon atoms, or an amine alkylene group comprising 2 to 12 carbon atoms.

[0145] Advantageously, the dispersing additive(s) are compounds of formula (VIII).

[0146] Even more advantageously, the dispersing additive(s) are compounds of formula (VIII) in which:

[0147] • RI represents a grouping -(CH2) X -O-(CH2) X -OH,

[0148] • R2 represents a polyisobutylene group,

[0149] • x represents 2,

[0150] • y represents 5.

[0151] Advantageously, the dispersing additive(s) have an average molecular mass by weight ranging from 2000 to 15000 g / mol, preferably ranging from 2500 to 10000 g / mol, advantageously from 3000 to 7000 g / mol.

[0152] Also advantageously, the dispersing additive(s) furthermore have a number molecular mass greater than or equal to 1000 g / mol, preferably from 1000 to 5000 g / mol, more preferably from 1800 to 3500 g / mol, advantageously from 1800 to 3000 g / mol.

[0153] The molecular weight by number of dispersing additive(s) is / are evaluated according to ASTM D5296. The lubricating composition may include the dispersing additive(s) at a content in the range of 0.5% to 3.5% by mass, preferably 1% to 3% by mass, relative to the total mass of the lubricating composition.

[0154] Anti-foaming additives

[0155] According to a preferred embodiment, the lubricating composition further comprises at least one anti-foaming additive.

[0156] In particular, the lubricating composition may include at least one phosphosulfur additive as described above and at least one antifoaming additive. It may further include at least one dispersing additive as described above.

[0157] Anti-foaming additives help prevent the lubricating fluid from foaming.

[0158] This could be, for example, an antifoaming additive based on polysiloxanes or acrylate polymers. Preferably, the antifoaming additive is chosen from among three-dimensional siloxanes.

[0159] Antifoaming additives can also be polar polymers such as polymethylsiloxanes or polyacrylates.

[0160] The composition may include a content in the range of 0.01% to 3% by mass of at least one antifoaming additive(s) as described above, preferably 0.01% to 1% by mass, more preferably 0.02% to 0.1% by mass, relative to the total mass of the lubricating composition.

[0161] Detergent additives

[0162] The lubricating composition may also include at least one detergent additive.

[0163] Detergent additives usable in a lubricating composition implemented according to the invention are generally known to those skilled in the art. These detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head group. The associated cation may be a metallic cation of an alkali or alkaline earth metal. Detergent additives are preferably selected from alkali or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, and phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium, or barium.

[0164] These metallic salts generally contain the metal in stoichiometric quantities or in excess, i.e., in a quantity greater than the stoichiometric amount. These are then called over-basic detergent additives; the excess metal, which gives the detergent additive its over-basic character, is then generally in the form of a metallic salt insoluble in oil, for example, a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate.

[0165] According to an advantageous embodiment, the composition includes at least one detergent additive selected from substituted salicylic acid salts.

[0166] Salicylic acid, as is well known, refers to 2-hydroxybenzoic acid. The salicylic acid salts used are substituted, meaning they have at least one group (or substituent) on the benzoic ring.

[0167] Preferably, the substituent(s) of said substituted salicylic acid salts are chosen from linear or branched alkyl groups comprising from 4 to 100 carbon atoms, preferably from 10 to 80 carbon atoms.

[0168] Preferably, the detergent additive(s) are chosen from the salts of alkali metals or alkaline earth metals, superbased or not, of substituted salicylic acid, in particular from the salts of calcium, magnesium, sodium, barium acid and mixtures thereof.

[0169] Preferably, the detergent additive(s) are chosen from among the neutral salts of salicylic acid.

[0170] According to a preferred embodiment, the detergent additive(s) are selected from among substituted calcium salts of salicylic acid, in particular from among substituted neutral calcium salts of salicylic acid.

[0171] According to another preferred embodiment, the detergent additive(s) are selected from among substituted magnesium salts of salicylic acid, more preferably from among substituted neutral magnesium salts of salicylic acid. Advantageously, the use of such magnesium-based detergents makes it possible to reduce the particulate matter content in the exhaust gases of the engine system, whether mobile or stationary.

[0172] Examples of suitable detergent additives are described in application EP 2 308 953.

[0173] The lubricating composition may include at least one detergent additive as described above at a content in the range of 0.5% to 10% by mass, preferably 0.8% to 5% by mass, more preferably 1% to 2% by mass relative to the total mass of the composition.

[0174] Corrosion inhibitor additives

[0175] The lubricating composition may also include at least one corrosion inhibitor additive.

[0176] Such additives can be chosen, for example, from among succinic anhydride polyisobutenes, thiadiazole sulfonates or mercaptobenzothiazoles.

[0177] The corrosion inhibitor(s) can also be chosen from substituted naphthalene sulfonic acid salts, such as substituted naphthalene sulfonic acid calcium salts. A preferred example is the dinonylnaphthalene sulfonic acid calcium salt.

[0178] The composition may include the corrosion inhibitor additive(s) at a content in the range of 0.05% to 1% by mass, preferably 0.1% to 0.5% by mass, relative to the total mass of the composition.

[0179] Phenolic antioxidant additives

[0180] The lubricating composition may further comprise at least one phenolic-type antioxidant additive, preferably selected from sterically hindered phenols, sterically hindered phenol esters, and sterically hindered phenols comprising a thioether bridge, more preferably from sterically hindered phenols. The presence of such an antioxidant additive provides the composition with additional low-temperature oxidation resistance properties.

[0181] Preferably, sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon bearing the alcohol function is substituted by at least one alkyl group in Cl to C10, preferably an alkyl group in Cl to C6, preferably an alkyl group in C4, preferably a tert-butyl group.

[0182] Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

[0183] Preferably, the phenolic-type antioxidant additive(s) are present in the lubricating composition at a content in the range of 0.5% to 3% by mass, preferably 1% to 2% by mass, relative to the total mass of the lubricating composition.

[0184] Pour point depressant additives

[0185] The lubricating composition may also include at least one pour point depressant additive (also known as PPD agents). By slowing the formation of paraffin crystals, pour point depressants generally improve the cold-weather performance of the lubricating composition.

[0186] Examples of such additives include polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylated polystyrenes and preferably, preferably alkyl polymethacrylates.

[0187] The composition may include pour point lowering additive(s) at a concentration of up to 1% by mass, preferably in the range of 0.05 to 0.8%, more preferably 0.1 to 0.5% by mass, relative to the total mass of the composition. Viscosity index improving additives

[0188] The lubricating composition may further include at least one viscosity index (VI) improving additive.

[0189] Viscosity index (VI) improving additives, particularly viscosity index improving polymers, ensure good cold stability and minimal viscosity at high temperatures. Examples of viscosity index improving polymers include polymer esters, hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene, and isoprene, olefin homopolymers or copolymers such as ethylene or propylene, polyacrylates, and polymethacrylates.

[0190] Advantageously, a lubricating composition includes at least one viscosity index improving additive selected from hydrogenated polyisoprene-styrene (PISH), linear, grafted, comb or star, preferably star.

[0191] Preferably, the viscosity index improving additive(s) are present in the lubricating composition at a content of 5 to 10% by mass, more preferably 6 to 8% by mass, relative to the total mass of the lubricating composition.

[0192] Applications

[0193] The invention also relates to the use for lubricating a motorization system comprising a gas engine, of a lubricating composition comprising one or more base oil(s) belonging to groups I, II, III and IV of the API classification and their mixtures, in particular chosen from group II and III oils of the API classification and their mixtures, at least one first additive chosen from bisdithiocarbamates and at least one second additive chosen from diphenylamines substituted by one or more aromatic groups.

[0194] The lubricating composition, its ingredients and their contents are as described above.

[0195] In a preferred embodiment, said lubricating composition further comprises:

[0196] - at least one phosphosulfur additive as described above; - optionally, at least one dispersing additive chosen from polyisobutylene succinimides and their borated derivatives, and

[0197] - optionally, at least one anti-foaming additive.

[0198] The lubricating composition may also include one or more additional additives, such as those described above and in particular chosen from:

[0199] - detergent additives preferably chosen from substituted salicylic acid salts;

[0200] - corrosion inhibitor additives;

[0201] - pour point lowering additives;

[0202] - additives improving the viscosity index (VI);

[0203] - and their mixtures.

[0204] In particular, the lubricating composition may also include one or more additional additives, such as those described above and specifically chosen from:

[0205] - detergent additives preferably chosen from substituted salicylic acid salts;

[0206] - corrosion inhibitor additives;

[0207] - pour point lowering additives;

[0208] - additives improving the viscosity index (VI);

[0209] - anti-foaming additives;

[0210] - and their mixtures.

[0211] Advantageously, this composition is used for its lubricating properties, which notably reduce friction between moving parts within the gas engine. This lubricating composition is also used to reduce wear on these parts. The engine part(s) lubricated by this composition are advantageously selected from among: pistons, piston rings, cylinders, connecting rods, piston pins, bearings, crankshafts, oil pumps, turbochargers, camshafts, and valve train systems (including, in particular, cams, tappets, rocker arms, and oil pumps).

[0212] The lubricating composition is intended to lubricate a drive system comprising a gas engine. Gas engines according to the invention include, in particular: - stationary gas engines; and

[0213] - mobile gas engines, in particular gas engines for vehicles including in particular heavy goods vehicles, construction equipment or agricultural machinery such as for example tractors, public transport vehicles (buses, trains, etc.) and light vehicles such as cars.

[0214] A "gas engine" is defined as an engine that runs on a fuel that is in a gaseous state under normal temperature and pressure conditions. Examples of such fuels include natural gas, including liquefied natural gas (LNG) or compressed natural gas (CNG), biogas, and hydrogen.

[0215] In a preferred embodiment, the gas engine is a hydrogen engine (i.e., an engine operating by combustion of hydrogen). It may, in particular, be a piston engine or a gas turbine.

[0216] As is well known, a gas turbine, also called a combustion turbine, is a rotating thermodynamic machine of the family of internal combustion engines and can be used for propulsion, electricity production, or as a stationary engine (for example to drive pumps, compressors, etc.).

[0217] Preferably, the hydrogen engine is a piston engine. The present invention also relates to a method of lubricating moving parts in a motorization system including a gas engine, comprising a step of bringing at least one of said parts into contact with a lubricating composition comprising at least one base oil chosen from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III, at least one first additive chosen from bisdithiocarbamates and at least one second additive chosen from diphenylamines substituted by one or more aromatic groups.

[0218] The present invention also relates to a method of operating a motorization system, mobile or stationary, comprising a gas engine and consisting of supplying said engine with a gaseous fuel and lubricating at least one part of said motorization system by means of a lubricating composition comprising at least one base oil selected from oils belonging to groups I, II, III and IV of the API classification and their mixtures, in particular to groups II and / or III, at least one first additive selected from bisdithiocarbamates and at least one second additive selected from diphenylamines substituted by one or more aromatic groups.

[0219] The lubricating composition, its ingredients and their contents are as described above.

[0220] The engine can be any gas engine, including but not limited to those described above. Preferably, said engine is a hydrogen engine.

[0221] The engine part(s) lubricated by means of the composition are advantageously as described above.

[0222] The examples below are intended solely to illustrate the invention, and should not be interpreted as limiting its scope.

[0223] EXAMPLES

[0224] Example 1: Preparation of lubricating compositions

[0225] Four lubricating compositions were formulated, by mixing the components in the quantities (expressed as mass percentages) detailed in Table I below.

[0226] [Table I]

[0227] Al Cl C2 C3 First additive (1) 1 0 1 2 Second additive (2) 1 1 0 0 Phosphosulfur additive (3) 0.5 0.5 0.5 0.5 Dispersive additive (4) 2 2 2 2 Detergent additive (5) 1 1 1 1 Antioxidant additive (6) 0.5 0.5 0.5 0.5 PPD additive (7) 0.3 0.3 0.3 0.3 Antifoam additive (8) 0.03 0.03 0.03 0.03 Improver additive VI (9) 7.05 7.05 7.05 7.05

[0228]

[0229] Base oil (10) Qsp 100 Qsp 100 Qsp 100 Qsp 100 (1) First additive: methylene bis(dibutyldithiocarbamate)

[0230] (2) Second additive: 4-(l-methyl-l-phenylethyl)-N-[4-(l-methyl-l-phenylethyl)phenyl]aniline

[0231] (3) Metallic phosphosulfur additive: DTPZn of formula Zn((SP(S)(OR5)(OR6))2 with R5 designating an alkyl group at C4 and R6 designating an alkyl group at C6.

[0232] (4) Dispersive additive: polyisobutylene succinimide.

[0233] (5) Detergent additive: neutral calcium salicylic acid salt.

[0234] (6) Antioxidant additive: sterically hindered phenol.

[0235] (7) Pour point lowering additive known as PPD additive: alkyl polymethacrylate (PMA).

[0236] (8) Antifoam additive: three-dimensional siloxane.

[0237] (9) Additive improving viscosity index (VI), called improver VI: hydrogenated polyisoprene-styrene polymer (PISH).

[0238] (10) Group III base oil of kinematic viscosity measured at 100°C, according to ADTM D445, of 6 cSt.

[0239] Composition Al conforms to the invention while compositions Cl to C3 are comparative.

[0240] Example 2: Evaluation of oxidation stability:

[0241] Oxidation stability measurement protocol:

[0242] Oxidation stability is evaluated in accordance with CEC L-85 T-99 by differential pressure scanning calorimetry (PDSC), which determines the oxidation induction time, known as OIT (for "Oxidation Induction Time" in Anglo-Saxon terminology) for the tested lubricant compositions.

[0243] According to this protocol, the lubricant composition to be tested is heated to a high temperature (in this case, isothermal at 50°C for 5 minutes, then raised to 210°C at a rate of 40°C / min), and the time at which the lubricant begins to decompose is measured. The longer the time, expressed in minutes, before the onset of degradation (induction time), the better the lubricant's oxidation stability. Results:

[0244] The results obtained in terms of oxidation induction time (OIT) are gathered in the following Table II.

[0245] [Table II]

[0246] Al Cl C2 C3

[0247]

[0248] ILO (min) 261 117 73 98

[0249] These tests demonstrate a synergistic effect of the combination of the first and second additives on the oxidation stability of the lubricating composition. The lubricating composition Al, comprising the combination of the two additives according to the invention, surprisingly exhibits significantly greater stability than the lubricating compositions Cl, C2, and C3, which do not conform to the invention.

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