LUBRICANT COMPOSITION WITH IMPROVED NITROXIDATION RESISTANCE PROPERTIES

Abstract

LUBRICANT COMPOSITION WITH IMPROVED NITROXIDATION RESISTANCE PROPERTIES The present invention relates to the use, in a lubricating composition intended for a gas engine, of a dithiocarbamate compound, to improve the nitroxidation resistance of said lubricating composition. Figure for abstract: none

Description

Title of the invention: LUBRICATING COMPOSITION WITH IMPROVED PROPERTIES OF RESISTANCE TO NITROXIDATION

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

[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. The high operating temperatures of gas engines can cause the reaction of atmospheric nitrogen (N2) and oxygen (O2), which forms nitrogen oxides (NOx). Thus, in gas engines, NOx emissions are higher.

[0004] These characteristics result in faster deterioration and degradation of the lubricant through nitroxidation phenomena. Nitroxidation (or nitration) means oxidation through contact with nitrogen oxides (NOx). Nitration is thus a form of degradation of the lubricating oil occurring in gas engines, and caused by a reaction of the oil with the nitrogen oxides produced during combustion. Due to the reactions with the nitrogen oxides, the oil begins to become saturated with both soluble and insoluble nitrogen oxide compounds. The presence of these nitrating compounds is likely to cause corrosion on the engine surfaces. They also contribute to an increase in the viscosity of the oil, and to the formation of sludge which can ultimately lead to a reduction in engine performance and damage to its components.

[0005] Therefore, it is important to reduce oil degradation by nitroxidation.

[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 exhibited limited resistance to nitroxidation. However, as indicated above, these phenomena have a significant negative impact on the service life of the lubricant and, therefore, on the oil change interval.

[0007] Usually, to date, to reduce these negative nitroxidation phenomena, lubricating compositions are added with additives of the amine and / or phenolic antioxidant type.

[0008] There is currently a need to provide lubricating compositions for gas engines having improved nitroxidation resistance properties.

[0009] The present invention specifically aims to provide lubricating compositions for gas engines having improved nitroxidation resistance properties.

[0010] Another object of the invention is to provide lubricating compositions for gas engines having improved nitroxidation resistance properties, making it possible to increase the service life of the lubricant and thereby increase oil change intervals.

[0011] Thus, the present invention relates to the use, in a lubricating composition intended for a gas engine, of a dithiocarbamate compound, to improve the resistance to nitroxidation of said lubricating composition.

[0012] As indicated above, by “nitroxidation” (or nitration) is meant here the phenomena of oxidation of the lubricant by contact with nitrogen oxides (NOx).

[0013] 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 increase in nitrogen oxides. This nitroxidation process (or nitration of the oil) must therefore be monitored regularly.

[0014] However, as is apparent from the examples which follow, the inventors have found that the use of a dithiocarbamate compound according to the invention in a lubricating composition advantageously and surprisingly makes it possible to improve the resistance to nitroxidation of said lubricating composition (or lubricant).

[0015] In the context of the present invention, the improvement in the resistance to nitroxidation of a lubricant is manifested by a reduction in the quantity of nitrogen oxide compounds (or nitration compounds) present in said lubricant.

[0016] The amount of nitrogen oxide 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 nitroxidation of engine oils. This parameter is quantified by means of the infrared spectrometry technique (FT-IR), by means of measuring the changes in the concentration of the constituents of the nitrogen oxides in the appropriate spectral range, as described later.

[0017] The improvement in resistance to nitroxidation is understood in relation to what is observed in the absence of dithiocarbamate compound according to the invention in the lubricating composition.

[0018] According to one embodiment, the lubricating composition used according to the invention contains at least one base oil.

[0019] According to one embodiment, the lubricating composition used according to the invention further comprises one or more polymers improving the viscosity index, preferably olefin copolymers, such as ethylene and propylene copolymers.

[0020] The lubricant composition according to the invention is intended for a gas engine.

[0021] The gas engines according to the invention include:

[0022] - stationary gas engines;

[0023] - mobile gas engines, in particular gas engines for vehicles including including heavy goods vehicles or public transport vehicles such as buses.

[0024] 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.

[0025] By “gas engine” is meant an engine running on natural gas, including liquefied natural gas (LNG) or compressed natural gas (CNG), but also biogas.

[0026] Other characteristics and variants of the use of dithiocarbamate compounds according to the invention to improve resistance to nitroxidation will become more apparent on reading the description and examples which follow, given by way of illustration and not limitation of the invention.

[0027] In the rest of the text, the expressions “between ... and ...”, “ranging ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated.

[0028] Unless otherwise indicated, the expression “comprising a(n)” must be understood as “comprising at least one(n)”.

[0029] As indicated above, the present invention relates to the use, in a lubricating composition intended for a gas engine, of a dithiocarbamate compound, to improve the resistance to nitroxidation of said lubricating composition.

[0030] The present invention also relates to the use of a lubricating composition intended for a gas engine comprising a dithiocarbamate compound, to improve the resistance to nitroxidation of said lubricating composition.

[0031] The present invention also relates to a method for lubricating a gas engine by using a lubricating composition comprising a dithiocarbamate compound, to improve the resistance to nitroxidation of said lubricating composition.

[0032] The present invention also relates to a method for improving the nitroxidation resistance of a lubricating composition intended for a gas engine, comprising a step of lubricating said gas engine with a lubricating composition comprising a dithiocarbamate compound.

[0033] In particular, the use of a lubricating composition comprising a dithiocarbamate compound makes it possible to reduce by at least 15%, in particular by at least less than 20%, more particularly at least 25%, even more particularly at least 30%, or even more than 35%, the quantity of nitrogen oxide compounds (or nitrating compounds) present in said lubricating composition, in comparison with the quantity measured for the same lubricating composition without dithiocarbamate compound.

[0034] The lubricating composition used in the context of the present invention may comprise one or more dithiocarbamate compounds.

[0035] Preferably, the dithiocarbamate compound is chosen from metal dithiocarbamates, bisdithiocarbamates and their mixtures, preferably is chosen from bisdithiocarbamates.

[0036] Metal dithiocarbamates can more particularly be defined according to the following general formula (I):

[0037] in which the groups R 1 and R 2 represent, independently of one another, hydrocarbon groups, optionally substituted, comprising from 1 to 30 carbon atoms, preferably from 4 to 18 carbon atoms, M represents a metal cation and n is the valence of this metal cation.

[0038] Preferably, M is molybdenum.

[0039] The metal dithiocarbamates that can be used according to the present invention are compounds well known to those skilled in the art and can be obtained by any process also known to those skilled in the art. An example of a process for preparing these compounds is described in particular in US patent 2,492,314.

[0040] Metal dithiocarbamates are particularly known for their use in lubricating compositions as friction modifying additives.

[0041] The metal dithiocarbamate compound MoDTC used according to the invention can be chosen from compounds whose nucleus comprises two molybdenum atoms (dimeric MoDTC) and compounds whose nucleus comprises three molybdenum atoms (trimeric MoDTC).

[0042] The trimeric MoDTC compounds are generally of formula Mo3SkLm in which k represents an integer at least equal to 4, preferably ranging from 4 to 10, advantageously from 4 to 7; m represents an integer ranging from 1 to 4; and L represents an alkyl dithiocarbamate group comprising from 1 to 100 carbon atoms, preferably from 1 to 40 carbon atoms, advantageously from 3 to 20 carbon atoms.

[0043] Examples of trimeric MoDTC compounds include the compounds and their preparation processes described in application WO 98 / 26030.

[0044] An example of a trimeric MoDTC compound is that marketed under the name Infineum® C9455B by the company Infineum International Ltd.

[0045] Preferably, the MoDTC compound in the lubricating composition used according to the invention is a dimeric MoDTC compound. Examples of dimeric MoDTC compounds include the compounds and their preparation processes described in patent application EP 0 757 093. According to a particular embodiment of the invention, the metal dithiocarbamate compound is a molybdenum dithiocarbamate (MoDTC) of the following formula (Ia):

[0046] in which:

[0047] the groups Ri and R2 are, independently of each other, as defined above,

[0048] X1, X2, X3 and X4, identical or different, independently represent an atom of oxygen or a sulfur atom.

[0049] Advantageously, X1 and X2 can represent an oxygen atom and X3 and X4 can represent a sulfur atom.

[0050] Advantageously, the MoDTC compound is chosen from the compounds of formula (Ia) in which:

[0051] X1 and X2 represent an oxygen atom,

[0052] X3 and X4 represent a sulfur atom,

[0053] Ri represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms,

[0054] R2 represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms.

[0055] Thus, advantageously, the MoDTC compound can be chosen from the compounds of formula (la'):

[0056]

[0057]

[0058]

[0059] in which Ri and R2 are as defined for formula (I) above. Specific examples of MoDTC compounds include the products Molyvan L®, Molyvan 807® or Molyvan 822® marketed by RT Vanderbilt Company or the products Sakuralube 200®, Sakuralube 165®, Sakuralube 525® or Sakuralube 600® marketed by Adeka. The lubricating composition used according to the invention can also be implemented with an organomolybdenum compound chosen from the MoDTC compounds described in patent application WO 2012 / 141855. Bisdithiocarbamates can more particularly be defined according to the following general formula (II):

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066] in which: - the groups R3 and R4 represent, independently of each other, hydrocarbon groups, optionally substituted, comprising from 1 to 30 carbon atoms, preferably from 2 to 24 carbon atoms, more preferably from 3 to 8 carbon atoms; and - the R5 group represents a hydrocarbon group comprising from 1 to 8 carbon atoms, preferably from 1 to 4 carbon atoms. The bisdithiocarbamate compounds which can be used according to the present invention are compounds well known to those skilled in the art and can be obtained by any method also known to those skilled in the art. Bisdithiocarbamates are particularly known for their use in lubricating compositions as antioxidant additives. It may advantageously be methylene bis(dibutyldithiocarbamate). Examples of commercial products that may be cited are Vanlube® 7723 sold by the company Vanderbilt or Additin® RC 6340 sold by the company Rhein Chemie. According to one embodiment, a lubricating composition implemented according to the present invention comprises a mixture of at least one metal dithiocarbamate and at least one bisdithiocarbamate, in particular as defined above. Thus, the dithiocarbamate compound used in a composition according to the invention may be more particularly chosen from dithiocarbamate of molybdenum (MoDTC), methylene bis(dibutyldithiocarbamate) (mDTC), and mixtures thereof.

[0067] According to a preferred embodiment, the lubricating composition used according to the invention comprises a bisdithiocarbamate.

[0068] Preferably, the use according to the present invention relates to a lubricating composition comprising at least one bisdithiocarbamate compound, in particular of formula (II) as defined above.

[0069] According to an advantageous embodiment, the dithiocarbamate compound used according to the present invention is 4,4'-methylene bis(dibutyldithiocarbamate).

[0070] The lubricating composition used according to the invention may contain from 0.1% to 10%, in particular from 0.5% to 5%, in particular from 0.7% to 3% by mass of dithiocarbamate compound(s), relative to the total mass of said lubricating composition.

[0071] Preferably, the content of dithiocarbamate compound(s) in the lubricating composition used according to the invention is greater than or equal to 1% by mass relative to the total mass of said lubricating composition.

[0072] A lubricating composition used according to the invention may comprise, in addition to the dithiocarbamate compound 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.

[0073] 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.

[0074] 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.

[0075] [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

[0076] 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.

[0077] Mixtures of synthetic and mineral oils, which can be bio-sourced, can also be used.

[0078] In particular, a lubricating composition formulated according to the invention based on a dithiocarbamate compound as described above, may further comprise one or more base oils chosen from group I, II, III and IV oils of the API 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.

[0079] According to a particular embodiment, the 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 75% to 95% 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.

[0080] Preferably, the lubricating composition used according to the invention contains one or more group II base oils.

[0081] According to a particular embodiment, the 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 75% to 95% by mass, of one or more, preferably several, group II base oils, relative to the total mass of said lubricating composition.

[0082] 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.

[0083] 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.

[0084] Such additives may be chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index improvers, pour point depressants, dispersants, thickeners, corrosion inhibitors, copper passivators, and mixtures thereof.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] A lubricating composition used according to the invention may also comprise at least one detergent additive.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] A lubricating composition used according to the invention may comprise at least one antioxidant additive.

[0096] The antioxidant additive generally makes it possible to delay the 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.

[0097] Antioxidant additives act in particular as radical inhibitors or hydroperoxide destroyers. 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. 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.

[0098] 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 Cr-Cio alkyl group, preferably a C1-C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group.

[0099] 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.

[0100] Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

[0101] A lubricating composition used according to the invention may contain any type of antioxidant additives known to those skilled in the art.

[0102] Advantageously, a lubricating composition used according to the invention comprises at least one ash-free antioxidant additive.

[0103] A lubricating composition used according to the invention may comprise from 0.1% to 5% by mass, in particular 0.5 to 2% by mass of at least one antioxidant additive, relative to the total mass of the composition.

[0104] A lubricating composition used according to the invention may comprise at least one anti-wear additive.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] A lubricating composition used according to the invention may further comprise one or more other additives, distinct from the dithiocarbamate compounds, chosen from friction modifying additives, extreme pressure additives, pour point lowering additives, dispersants, thickeners, corrosion inhibitors, copper passivating agents and mixtures thereof.

[0109] 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. The 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 fatty acid glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

[0110] 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.

[0111] Advantageously, a lubricating composition used according to the invention is free of friction modifying additive.

[0112] A lubricating composition used according to the invention may also comprise at least one pour point lowering additive.

[0113] By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the composition.

[0114] Examples of pour point lowering additives include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylated polystyrenes.

[0115] 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 form when the lubricating composition is in service. They can be chosen from Mannich bases, succinimides and their derivatives, such as polyisobutylene succinic anhydride derivatives.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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

[0121] Example 1: Preparation of lubricating compositions

[0122] 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.

[0123] [Tables2] Components CL1 CCI Group II base oil (KV100 = 5.2 - 5.6 mm2 / s) 61.3 61.8 Group II base oil (KV100 = 10.0 - 12.0 mm2 / s) 21 21.5 Viscosity improver polymer (Olefin copolymer at 12.5% ​​active matter in a Group II base oil) 6 6 Additive package (*) 10.7 10.7 Dithiocarbamate compound 1 - (4,4'-methylene bis(dibutyldithiocarbamate))

[0124] * includes detergents, antioxidants and anti-wear additives.

[0125] KV100 corresponds to a kinematic viscosity measured at 100°C according to the ASTM D445 standard.

[0126] Example 2: Evaluation of resistance to nitroxidation

[0127] Method for evaluating resistance to nitroxidation

[0128] To evaluate the resistance to nitroxidation, the lubricant to be tested is maintained under a flow of an air / NO2 mixture for a period of at least 3 days at a temperature above 130°C.

[0129] 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).

[0130] The area of ​​the infrared peak is linked to the presence of oxidized compounds. Here, we measure the N=O band from 1,580 to 1,650 cm1. The more NOx compounds the oil contains, the larger this band is. The area of ​​this band is measured using a subtraction between the spectrum of the nitroxidized lubricant and that of the new lubricant.

[0131] Results

[0132] Four analyses were carried out for each of the CCI and CL1 lubricants. The values ​​obtained concerning the PAI (averages of the 4 analyses) are indicated in Table 3 below.

[0133] [Tables3] CL1 CCI Mean values ​​(PAI N=O) (in A.cm '.mm ') 77 120

[0134] Significant differences are therefore observed when adding 1% of dithiocarbamate compound for the composition according to the invention CL1.

[0135] The nitroxidation values ​​given by the NO band during an infrared analysis are systematically lower for CL1 (in the presence of dithiocarbamate) in comparison with CCI (without dithiocarbamate). These results demonstrate the improvement in nitroxidation resistance performance due to the presence of a dithiocarbamate compound according to the invention.

Claims

Claims

1. Use, in a lubricating composition intended for a gas engine, of a dithiocarbamate compound, to improve the resistance to nitroxidation of said lubricating composition.

2. Use according to claim 1, wherein the dithiocarbamate compound is selected from metal dithiocarbamates, bisdithiocarbamates and mixtures thereof.

3. Use according to claim 1 or 2, wherein the dithiocarbamate compound is selected from bisdithiocarbamates.

4. Use according to any one of claims 1 to 3, wherein the dithiocarbamate compound is 4,4'-methylene bis(dibutyldithiocarbamate).

5. Use according to any one of claims 1 to 3, 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 dithiocarbamate compound, relative to the total mass of said lubricating composition.

6. Use according to any one of claims 1 to 5, in which the lubricating composition comprises at least 50% by mass, in particular from 60% to 98% by mass, and more particularly from 75% to 95% 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 I, II and / or III, group II and / or group III base oils.

7. Use according to any one of claims 1 to 6, wherein the lubricating composition contains one or more Group II base oils.

8. Use according to any one of claims 1 to 7, wherein the lubricating composition further comprises one or more viscosity index improving polymers, preferably olefin copolymers, in particular ethylene and propylene copolymers.

9. Use according to any one of claims 1 to 8, wherein the lubricating composition further comprises one or more additives chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents,

10. antioxidants, pour point depressants, dispersants, thickeners, corrosion inhibitors, copper passivators and mixtures thereof. Use according to any one of claims 1 to 9, in which the lubricating composition is intended for a gas engine in a motor vehicle, in particular heavy goods vehicles, or in a stationary gas engine.