Lubricating oil composition for gas engines

Abstract

To provide a lubricating oil composition for a gas engine which prevents occurrence of coking, prevents corrosion of metals contained in members of the gas engine, and improves wear resistance of the members of the gas engine.SOLUTION: A lubricating oil composition for a gas engine includes: a base oil having a flash point of 240°C or more; a molybdenum friction modifier; and a viscosity modifier having a flash point of 270°C or more. In the lubricating oil composition for the gas engine, a mass of a molybdenum atom to a mass of the whole lubricating oil composition is 20 ppm or more and 800 ppm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to lubricating oil compositions for gas engines. [Background technology]

[0002] When gas engines are operated continuously for long periods of time, the lubricating oil contained in the engine is constantly exposed to high temperatures, which gradually causes thermal oxidation degradation. Furthermore, gas engines, which have higher combustion temperatures than diesel engines, tend to have higher concentrations of NOx in their blow-by gas, which can easily cause sludge formation in the lubricating oil. Therefore, while regular replacement of the lubricating oil is necessary, there is a need for both long life and coking resistance to reduce maintenance costs by extending the life of the lubricating oil itself and to prevent problems caused by localized coking in various parts of the engine. Gas cogeneration systems often use relatively large gas engines, and because they use a lot of lubricating oil, high safety standards are also required for gas engine oil.In this regard, the Fire Service Act classifies gas engine oils with a flash point of 250°C or higher as designated flammable materials from a safety perspective, and allows for simple storage, distinguishing them from Class 4 Class 4 hazardous materials that have a lower flash point. Lubricating oil compositions for gas engines are composed of base oils and additives appropriately selected according to the above requirements. For example, Patent Documents 1 to 3 disclose lubricating oil compositions containing metal detergents and phosphorus-based additives for the purpose of improving base number retention, high-temperature detergency, and friction modifier properties. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-203952 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-196695 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-052126 Summary of the Invention [Problem to be solved by the invention]

[0004] Even in conventional lubricating oil compositions for gas engines, there is room for further improvement in terms of suppressing the occurrence of coking, suppressing corrosion of metals contained in gas engine components, and improving the wear resistance of gas engine components. Therefore, an object of the embodiments of the present disclosure is to provide a lubricating oil composition for gas engines that suppresses the occurrence of coking, suppresses corrosion of metals contained in gas engine components, and improves the wear resistance of gas engine components. [Means for solving the problem]

[0005] The means for solving the above problems include the following means. <1> A base oil having a flash point of 240°C or higher; a molybdenum-based friction modifier; A viscosity modifier having a flash point of 270°C or higher, A lubricating oil composition for gas engines, in which the mass of molybdenum atoms relative to the total mass of the lubricating oil composition for gas engines is 20 ppm or more and 800 ppm or less. <2> The initial boiling point temperature (TIBP) of the base oil is 350°C or higher; <1> The lubricating oil composition for gas engines according to claim 1. <3> Contains at least one metal-based detergent selected from the group consisting of calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, magnesium sulfonate, and detergents containing alkaline earth metals, <1> or <2> The lubricating oil composition for gas engines according to claim 1. <4> Contains phenolic antioxidants, amine antioxidants and zinc antioxidants, The total content of the phenolic antioxidant and the amine antioxidant is 1% by mass or more and 4% by mass or less based on the total amount of the lubricating oil composition for gas engines. <1> ~ <3> 1. The lubricating oil composition for gas engines according to claim 1, <5> The amine antioxidant contains an aromatic amine compound having an acid dissociation constant (pKa) of 7 or less. <4> The lubricating oil composition for gas engines according to claim 1. <6> The molybdenum-based friction modifier is at least one selected from the group consisting of an amide-based molybdenum compound, an ester-based molybdenum compound, a molybdate amine compound, molybdenum dithiocarbamate, and molybdenum dithiophosphate. <1> ~ <5> 1. The lubricating oil composition for gas engines according to claim 1, <7> The viscosity modifier is at least one selected from the group consisting of an olefin copolymer, a polymethacrylate, a random copolymer of an olefin and a methacrylate, a block copolymer of an olefin and a methacrylate, and a graft copolymer of a polymethacrylate and an olefin copolymer. <1> ~ <6> 1. The lubricating oil composition for gas engines according to claim 1, <8> For gas engines, hydrogen engines, or dual-fuel engines for ships used in total energy systems <1> ~ <7> 1. The lubricating oil composition for gas engines according to claim 1, [Effects of the Invention]

[0006] According to one embodiment of the present disclosure, there is provided a lubricating oil composition for gas engines that inhibits the occurrence of coking, inhibits corrosion of metals contained in gas engine components, and improves the wear resistance of gas engine components. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0008] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0009] <Lubricating oil composition for gas engines> The lubricating oil composition for gas engines according to the present disclosure contains a base oil having a flash point of 240°C or higher, a molybdenum-based friction modifier, and a viscosity modifier having a flash point of 270°C or higher, and the mass of molybdenum atoms relative to the total mass of the lubricating oil composition for gas engines is 20 ppm or more and 800 ppm or less.

[0010] Due to the above-described configuration, the lubricating oil composition for gas engines according to the present disclosure inhibits the occurrence of coking, inhibits corrosion of metals contained in gas engine components, and improves the wear resistance of gas engine components. The reason for this is presumed to be as follows.

[0011] The inclusion of a molybdenum-based friction modifier produces molybdenum disulfide under boundary lubrication conditions, thereby reducing friction and suppressing coking at high temperatures. Furthermore, the use of a base oil with a flash point of 240°C or higher and a viscosity modifier with a flash point of 270°C or higher in combination suppresses coking of low-boiling fractions under high-temperature conditions. Furthermore, by limiting the molybdenum atom mass to between 20 ppm and 800 ppm relative to the total mass of the gas engine lubricating oil composition, coking is suppressed without impairing the above-mentioned performance.

[0012] Therefore, it is presumed that the lubricating oil composition for gas engines according to the present disclosure will suppress the occurrence of coking, suppress corrosion of metals contained in gas engine components, and improve the wear resistance of gas engine components.

[0013] (base oil) The lubricating oil composition for gas engines according to the present disclosure contains a base oil having a flash point of 240°C or higher. By adjusting the flash point of the base oil to 240°C, the flash point of the entire lubricating oil composition for gas engines becomes high, making it easier to handle. The base oil is not particularly limited, and any base oil used in the field of lubricating oils can be used. Specific examples of the base oil include mineral base oils and synthetic base oils.

[0014] Examples of mineral base oils include base oils classified as API (American Petroleum Institute) Group I, which are obtained from crude oil by combining the processes of atmospheric distillation, vacuum distillation, solvent deasphalting, solvent extraction, hydrorefining, and solvent dewaxing; base oils classified as API Group II, which are obtained by further combining processes such as hydrocracking and catalytic dewaxing; and base oils classified as API Group III, which are obtained by further combining advanced hydrotreating processes such as hydrocracking and hydroisomerization dewaxing. In order to maintain a high flash point and to use a base oil that does not contain low-boiling fractions that worsen coking when exposed to high temperatures, it is preferable to use a base oil classified as API Group III.

[0015] Examples of synthetic base oils include synthetic hydrocarbons such as α-olefin oligomers, isoparaffin oligomers, propylene oligomers, isobutylene oligomers, butene oligomers, 1-octene oligomers, 1-decene oligomers, and ethylene-propylene oligomers; aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes; esters such as di-2-ethylhexyl adipate and diisodecyl adipate; polyol esters such as trimethylolpropane oleate and pentaerythritol-2-ethylhexanoate; polyglycols such as polyoxyalkylene glycols; and polyphenyl ethers.

[0016] In order to maintain a high flash point and to obtain a base oil that contains as little low-boiling fractions as possible that cause coking, it is preferable to use a mineral base oil as the base oil, but synthetic base oils may also be used to the extent that they do not interfere with sufficient dissolution of the additives.

[0017] The base oil may include other base oils besides mineral base oils and synthetic base oils. When the base oil contains other base oils, the NOACK evaporation amount of the lubricating oil composition for gas engines is preferably 10% or less, and more preferably 8% or less. NOACK evaporation is measured in accordance with ASTM D5800-21.

[0018] The kinematic viscosity of the base oil at 40°C is not particularly limited, but from the viewpoint of evaporation performance and wear resistance, it is preferable that the kinematic viscosity be 10.0 mm 2 / s or more 60.0mm 2 / s or less is preferable, and 30.0 mm 2 / s or more 55.0mm 2 / s or less is more preferable, and 40.0 mm 2 / s or more 50.0mm 2 / s or less is more preferable.

[0019] The kinematic viscosity of the base oil at 100°C is 4.0 mm 2 / s or more 10.0mm 2 / s or less is preferable, and 6.0 mm 2 / s or more 9.0mm 2 / s or less is more preferable, and 7.0 mm 2 / s or more 8.0mm 2 / s or less is more preferable.

[0020] The kinematic viscosity of the base oil at 40°C and at 100°C is measured in accordance with JIS K2283 (2000).

[0021] The viscosity index of the base oil is not particularly limited, but is preferably 100 or greater, more preferably 110 or greater, and even more preferably 120 or greater. By having a viscosity index within the above range, the viscosity stability of the gas engine lubricating oil composition with respect to temperature is improved, and performance such as wear resistance is more likely to be stably exhibited in a variety of external environments.

[0022] The viscosity index of the base oil is measured in accordance with JIS K2283 (2000).

[0023] The flash point of the base oil is 240°C, but from the viewpoint of ease of handling, it is preferably 250°C or higher. The flash point of the base oil is measured in accordance with JIS K2265-4 (2007).

[0024] From the viewpoint of ease of handling, the initial boiling point temperature (TIBP) of the base oil is preferably 320°C or higher, more preferably 330°C or higher, and even more preferably 350°C or higher. The upper limit of the initial boiling point temperature (TIBP) of the base oil may be 470 or less.

[0025] The initial boiling point temperature (TIBP) of the base oil is measured in accordance with JIS K2254 (2018).

[0026] The content of the base oil is preferably 70% by mass or more and 95% by mass or less, more preferably 75% by mass or more and 90% by mass or less, and even more preferably 80% by mass or more and 88% by mass or less, based on the total mass of the lubricating oil composition for gas engines.

[0027] (Molybdenum-based friction modifier) The lubricating oil composition for gas engines according to the present disclosure contains a molybdenum-based friction modifier. The molybdenum-based friction modifier refers to a friction modifier that contains molybdenum. Examples of molybdenum friction modifiers include amide-based molybdenum compounds, ester-based molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamates, molybdenum dithiophosphates, and other organic molybdenum complexes.

[0028] From the viewpoint of improving wear resistance, the molybdenum-based friction modifier is preferably at least one selected from the group consisting of amide-based molybdenum compounds, ester-based molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamates, and molybdenum dithiophosphates.

[0029] The amide molybdenum compound is a compound containing an amide group and molybdenum. From the viewpoint of improving wear resistance, the amide group of the amide molybdenum compound is preferably bonded to an alkyl group. The alkyl group bonded to the amide group may be linear or branched. From the viewpoint of improving abrasion resistance, the alkyl group bonded to the amide group preferably has 4 or more and 12 or less carbon atoms, more preferably 5 or more and 11 or less carbon atoms, and even more preferably 5 or more and 10 or less carbon atoms.

[0030] The ester-based molybdenum compound is a compound containing an ester group and molybdenum. From the viewpoint of improving wear resistance, the ester group of the ester-based molybdenum compound is preferably bonded to an alkyl group. The alkyl group bonded to the ester group may be linear or branched. From the viewpoint of improving abrasion resistance, the alkyl group bonded to the ester group preferably has 4 or more and 12 or less carbon atoms, more preferably 5 or more and 11 or less carbon atoms, and even more preferably 5 or more and 10 or less carbon atoms.

[0031] The amine molybdate compound is molybdic acid having an amino group. Specific examples of the amine molybdate compound include those obtained by reacting a compound containing a hexavalent molybdenum atom with an amine by the method described in JP-A No. 2003-252887.

[0032] Other organic molybdenum complexes include, for example, the organic molybdenum complexes described in JP-A-62-108891.

[0033] From the viewpoint of improving wear resistance, the molybdenum-based friction modifier is preferably at least one selected from the group consisting of amide-based molybdenum compounds and ester-based molybdenum compounds.

[0034] From the viewpoint of improving wear resistance, the amide molybdenum compound is preferably a compound represented by the following general formula (1).

[0035] [ka]

[0036] In the general formula (1), R1 represents an alkyl group. The alkyl group represented by R1 is preferably a primary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a primary carbon) or a secondary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a secondary carbon). The alkyl group represented by R1 preferably has 3 or more and 20 or less carbon atoms, more preferably 4 or more and 18 or less carbon atoms, and even more preferably 5 or more and 16 or less carbon atoms.

[0037] From the viewpoint of improving wear resistance, the ester-based molybdenum compound is preferably a compound represented by the following general formula (2).

[0038] [ka]

[0039] In the general formula (2), R2 represents an alkyl group. The alkyl group represented by R2 is preferably a primary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a primary carbon) or a secondary alkyl group (i.e., an alkyl group in which, among the carbon atoms contained in the alkyl group, the carbon atom bonded to the amide group is a secondary carbon). The alkyl group represented by R2 preferably has 3 or more and 20 or less carbon atoms, more preferably 4 or more and 18 or less carbon atoms, and even more preferably 5 or more and 16 or less carbon atoms.

[0040] The molybdenum-based friction modifier may contain the molybdenum compound described in JP-A-2003-252887 to the extent that it does not significantly impair the longevity of the friction modifier and does not cause adverse effects such as the formation of precipitates.

[0041] The lubricating oil composition for gas engines according to the present disclosure has a molybdenum atom content of 20 ppm or more and 800 ppm or less relative to the total mass of the lubricating oil composition for gas engines.

[0042] If the specific molybdenum content is 20 ppm or more, coking inside the gas engine can be further suppressed, and if it is 800 ppm or less, the life characteristics in high temperature environments and in the presence of NOx can be maintained at the same level as when no molybdenum-based friction modifier is added.

[0043] From the viewpoint of improving wear resistance, the specific molybdenum amount is preferably 30 ppm or more and 700 ppm or less, more preferably 50 ppm or more and 500 ppm or less, even more preferably 50 ppm or more and 200 ppm or less, and particularly preferably 50 ppm or more and 100 ppm or less.

[0044] The mass of molybdenum atoms relative to the total mass of the lubricating oil composition for gas engines (hereinafter also simply referred to as "specific molybdenum amount") is an analytical value obtained by ICP atomic emission spectrometry in accordance with JPI-5S-38-92.

[0045] The content of the molybdenum-based friction modifier is preferably 0.01 mass % or more and 5 mass % or less, more preferably 0.05 mass % or more and 2 mass % or less, and even more preferably 0.08 mass % or more and 1 mass % or less, based on the total mass of the lubricating oil composition for gas engines.

[0046] (Viscosity modifier) The lubricating oil composition for gas engines according to the present disclosure contains a viscosity modifier having a flash point of 270°C or higher. By adjusting the flash point of the viscosity modifier to 270°C or higher, the flash point of the entire lubricating oil composition for gas engines becomes high, making it easier to handle.

[0047] Examples of viscosity modifiers include non-dispersant type viscosity modifiers and dispersant type viscosity modifiers described in JASO M355:2021. Here, the non-dispersant type refers to a viscosity modifier that does not have a polar group. Moreover, the dispersion type refers to a viscosity modifier having a polar group. The polar group means an atomic group having a heterocyclic ring. The polar group refers to, for example, an atomic group having a succinimide structure, an atomic group having a pyrrolidone structure, an atomic group having a pyridine structure, or the like.

[0048] The atomic group having a succinimide structure refers to an atomic group represented by the following general formula (3).

[0049] [ka]

[0050] In general formula (3), R3 and R4 each independently represent a hydrogen atom or a hydrocarbon group, and * represents a bond.

[0051] The atomic group having a pyrrolidone structure refers to an atomic group represented by the following general formula (4).

[0052] [ka]

[0053] In general formula (4), R5, R6 and R7 each independently represent a hydrogen atom or a hydrocarbon group, and * represents a bond.

[0054] Non-dispersant type viscosity modifiers include olefin copolymers. Examples of olefin copolymers include polyisobutylene and ethylene-propylene copolymers.

[0055] Examples of dispersion-type viscosity modifiers include polymethacrylate, random copolymers of olefins and methacrylates, block copolymers of olefins and methacrylates, and graft copolymers of polymethacrylates and olefin copolymers. Examples of polymethacrylates include polyalkyl methacrylates. Examples of the random copolymer of olefin and methacrylate include a random copolymer of ethylene-alkyl methacrylate, a random copolymer of propylene-alkyl methacrylate, and a random copolymer of isobutylene-alkyl methacrylate. Examples of the block copolymer of olefin and methacrylate include a block copolymer of ethylene-alkyl methacrylate, a block copolymer of propylene-alkyl methacrylate, and a block copolymer of isobutylene-alkyl methacrylate. Graft copolymers of polymethacrylate and olefin copolymer include polymers having a polymethacrylate main chain and an olefin copolymer side chain.

[0056] Specific examples of dispersion-type viscosity modifiers include those described in JP-A-2015-004055.

[0057] The weight average molecular weight of the viscosity modifier is preferably 5,000 or more and 1,000,000 or less, and more preferably 10,000 or more and 20,000 or less. The weight average molecular weight of the viscosity modifier is a value measured by gel permeation chromatography, calculated using polystyrene as a standard.

[0058] Preferably, the NOACK evaporation rate of the viscosity modifier is less than 8%, more preferably less than 5%. NOACK evaporation is measured in accordance with ASTM D5800-21. When a diluted viscosity modifier is used, the NOACK evaporation amount of the viscosity modifier is measured in the diluted state.

[0059] The flash point of the viscosity modifier is 270°C or higher, but from the viewpoint of ease of handling, it is preferably 280°C or higher, and more preferably 290°C or higher. The flash point of the viscosity modifier is measured in accordance with JIS K2265-4 (2007).

[0060] The content of the viscosity modifier is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 7% by mass or less, and even more preferably 3% by mass or more and 7% by mass or less, based on the total mass of the lubricating oil composition for gas engines.

[0061] (Metallic detergents) The lubricating oil composition for gas engines according to the present disclosure may contain a metal-based detergent as needed. Metallic detergents include alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates, and the like.

[0062] From the viewpoint of extending the service life, the metallic detergent is preferably at least one selected from the group consisting of calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, magnesium sulfonate, and detergents containing alkaline earth metals.

[0063] The content of the metallic detergent is preferably from 1 to 10 mass %, more preferably from 2 to 7 mass %, and even more preferably from 3 to 5 mass %, relative to the total mass of the lubricating oil composition for gas engines.

[0064] (antioxidant) The lubricating oil composition for gas engines according to the present disclosure may contain an antioxidant as needed. Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, and zinc-based antioxidants. Examples of phenolic antioxidants include alkylphenols such as 2,6-di-tert-butyl-p-cresol; bisphenols such as 4,4'-methylenebis-(2,6-di-t-butylphenol); and phenolic compounds such as n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenol) propionate and octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid. Examples of the amine-based antioxidant include aromatic amine compounds such as naphthylamines and dialkyldiphenylamines. Examples of zinc-based antioxidants include zinc dialkyldithiophosphate (ZnDTP).

[0065] The amine antioxidant preferably contains an aromatic amine compound having an acid dissociation constant (pKa) of 7 or less. The acid dissociation constant of the aromatic amine compound is more preferably 1 or more and 5 or less, and even more preferably 2 or more and 4 or less. Here, the acid dissociation constant is a value measured by potentiometric titration at room temperature (25° C.), at normal pressure (101.325 kPa), and in water.

[0066] From the viewpoint of extending the life, the lubricating oil composition for gas engines according to the present disclosure preferably contains a phenol-based antioxidant, an amine-based antioxidant, and a zinc-based antioxidant. The total content of the phenolic antioxidant and the amine antioxidant is preferably 5% by mass or less, and more preferably 4% by mass or less, based on the total amount of the lubricating oil composition for gas engines.

[0067] The total content of the antioxidants is preferably 1 mass % or more and 10 mass % or less, more preferably 2 mass % or more and 7 mass % or less, and even more preferably 3 mass % or more and 5 mass % or less, based on the total mass of the lubricating oil composition for gas engines.

[0068] (Other additives) The lubricating oil composition for gas engines may contain other additives in addition to the base oil, molybdenum-based friction modifier, and viscosity modifier, as required. Other additives include pour point depressants, corrosion inhibitors, demulsifiers, antifoaming agents, dispersants, and the like. Examples of pour point depressants include polyalkyl methacrylates having no polar group, copolymers thereof, and alkyl group derivatives thereof. The weight average molecular weight of the pour point depressant is determined by gel permeation chromatography and calculated using polystyrene as a standard. Examples of the corrosion inhibitor include thiadiazole derivatives, benzotriazole derivatives, and imidazole derivatives. Examples of the demulsifier include ionic polyoxyethylene alkyl ether derivatives, nonionic polyoxyethylene alkyl ether derivatives, polyoxyethylene alkyl phenyl ether derivatives, and the like. Examples of the antifoaming agent include silicone oils such as polydimethylsiloxane, alkylated polydimethylsiloxane derivatives, and halogenated alkylated polydimethylsiloxane derivatives. Examples of the dispersant include boron-based dispersants and ashless-based dispersants. As the boron-based dispersant, for example, succinimide containing boron can be used. The content of the boron-based dispersant may be 0.1 to 5% by mass based on the total mass of the lubricating oil composition for gas engines. Examples of ashless dispersants that can be used include polyamines containing at least one kind of group selected from the group consisting of alkyl groups and alkenyl groups in the molecule, and acid-modified products thereof. The total content of the boron-based dispersant and the ashless-based dispersant may be 0.1 to 5% by mass based on the total amount of the lubricating oil composition for gas engines. When other additives are used, the content of the other additives is preferably 0.1% by mass or more and 10% by mass or less based on the total mass of the lubricating oil composition for gas engines.

[0069] (Physical Properties of Lubricating Oil Composition for Gas Engines) -Kinematic viscosity- The kinematic viscosity of the gas engine lubricating oil composition at 40°C is 80.0 mm 2 / s or more 150.0mm 2 / s or less is preferable, and 90.0 mm 2 / s or more 120.0mm 2 / s or less is more preferable. The kinematic viscosity of the lubricating oil composition for gas engines at 100°C is 7mm 2 / s or more 22mm 2 / s or less, and more preferably 11 mm 2 / s or more 18mm 2 / s or less, most preferably 12.5 mm 2 / s or more 16.3mm 2 / s or less.

[0070] The kinematic viscosity at 40°C and the kinematic viscosity at 100°C of the lubricating oil composition for gas engines are measured in accordance with JIS K2283 (2000).

[0071] -Viscosity index- The viscosity index of the lubricating oil composition for gas engines is preferably 100 or greater, more preferably 110 or greater, and even more preferably 120 or greater. By having a viscosity index within the above range, the stability of the lubricating oil viscosity relative to temperature is ensured, and performance such as wear resistance is likely to be stably exhibited in a variety of external environments.

[0072] -flash point- The flash point of the lubricating oil composition for gas engines is preferably 250°C or higher, and more preferably 255°C or higher. From a safety standpoint, the Fire Service Act classifies materials with a flash point of 250°C or higher as designated flammable materials, and allows for simple storage, distinguishing them from Class 4 lubricating oils, which have a flash point below that. The flash point of the lubricating oil composition for gas engines is measured by the Cleveland open method in accordance with JIS K2265-4 (2007).

[0073] -Amount of evaporation- The NOACK evaporation amount of the lubricating oil composition for gas engines is preferably 10% or less, and more preferably 8% or less. NOACK evaporation is measured in accordance with ASTM D5800.

[0074] -Base number- The base number of the lubricating oil composition for gas engines is preferably 2 mgKOH / g or more and 7 mgKOH / g or less, and more preferably 4 mgKOH / g or more and 6 mgKOH / g or less. The base number of the lubricating oil composition for gas engines is measured by the hydrochloric acid method in accordance with JIS K2501 (2003). A base number of 2 mgKOH / g or higher can effectively inhibit oxidation of the base oil and deterioration in the presence of NOx, while a base number of 7 mgKOH / g or lower can effectively inhibit deposition of metal components on pistons.

[0075] -Sulfated ash content- The sulfated ash content of the lubricating oil composition for gas engines is preferably 1.0 mass % or less, and more preferably 0.8 mass % or less. The amount of sulfated ash is measured by a method in accordance with JIS K2272 (1998). If the sulfated ash content is high, deposits on the piston head tend to interfere with normal fuel use, so it is desirable to keep it low within a range that does not significantly reduce base number retention, which is an indicator of life characteristics.

[0076] (Application) The lubricating oil composition for gas engines according to the present disclosure is preferably used as a lubricating oil for gas engines that use gases such as hydrogen, autogas, and natural gas as fuel. Among gas engines, it is preferable to use it as a lubricant for gas engines, hydrogen engines, or dual-fuel engines for ships used in total energy systems (systems that use gas as fuel, gas engines, turbines, etc. to generate electricity, power, etc., and utilize the exhaust heat generated at the same time). Gas engines, hydrogen engines, and dual-fuel marine engines used in total energy systems tend to have higher concentrations of NOx in their blow-by gases, which makes them more susceptible to coking, corrosion of metals contained in gas engine components, and wear of gas engine components. The lubricating oil composition for gas engines according to the present disclosure inhibits the occurrence of coking, inhibits corrosion of metals contained in gas engine components, and improves the wear resistance of gas engine components, making the lubricating oil composition for gas engines according to the present disclosure suitable for hydrogen engines and dual-fuel marine engines.

[0077] (Manufacturing method) The method for producing the lubricating oil composition for gas engines is not particularly limited, and it may be prepared by appropriately mixing the base oil, the molybdenum-based friction modifier, the viscosity modifier, and, if necessary, other additives. The order of mixing the base oil, molybdenum-based friction modifier, viscosity modifier and other additives is not particularly limited, and they may be mixed into the base oil in that order. [Example]

[0078] Examples will be described below, but the present disclosure is not limited to these examples in any way.

[0079] <Examples 1 to 4 and Comparative Examples 1 to 8> A lubricating oil composition for gas engines was prepared by mixing the base oil, molybdenum-based friction modifier, viscosity modifier, antioxidant, and other additives in the proportions (mass%) shown in Table 1 below, and dissolving and dispersing the mixture at 60°C.

[0080] <Evaluation> The resulting lubricating oil compositions for gas engines were evaluated as follows, and the results are shown in Table 1.

[0081] (density) The density of each lubricating oil composition for gas engines at 15°C was measured using a capillary viscometer in accordance with JIS K2283 (2000).

[0082] (viscosity characteristics) The kinematic viscosity and viscosity index of the gas engine lubricating oil compositions at 40°C and 100°C were calculated using a capillary viscometer in accordance with JIS K2283 (2000).

[0083] (Neutralization price) The acid number and base number of the gas engine lubricating oil composition were measured by potentiometric titration using a mixed solvent of toluene / 2-propanol / water in accordance with JIS K2501 (2003). The base number was measured by the hydrochloric acid method and the perchloric acid method.

[0084] (flash point) The flash points of the lubricating oil compositions for gas engines were measured by the Cleveland open cup flash point test method (COC method) in accordance with JIS K2265-4 (2007).

[0085] (pour point) The pour point of the gas engine lubricating oil composition was measured in accordance with JIS K2269 (1987).

[0086] (Elements in oil) The amount of metal elements in the lubricating oil composition for gas engines was measured by ICP emission spectroscopy in accordance with JPI-5S-38-92. The amount of metal element means the mass of the metal element relative to the total mass of the lubricating oil composition for gas engines.

[0087] (ISOT test) An oxidation stability test (ISOT test) was conducted on gas engine lubricating oil compositions in accordance with JIS K2514-1 (2013). Copper and steel catalysts were added to 250 ml of the gas engine lubricating oil composition, and the test was conducted at 165.5°C, 1300 rpm, and for 72 hours. After the test, the acid number and base number (hydrochloric acid method) of the gas engine lubricating oil composition were measured in accordance with JIS K2501 (2003).

[0088] (NOx test) Copper and steel catalysts were added to 40 ml of the gas engine lubricating oil composition to prepare the test oil. A 72-hour test was carried out at 140°C while blowing a mixture of 0.8% NOx gas at 50 ml / min and humidified air at 150 ml / min into the test oil.

[0089] (Panel caulking test) In accordance with Federal Test Method No. 791B, Method No. 3462, 250 ml of a gas engine lubricating oil composition was placed in a test vessel, and a cycle of 15 seconds of oil splashing followed by a 45-second rest period was carried out for 3 hours at an oil temperature of 110°C and an aluminum panel temperature of 320°C. After the test, the mass of coking solids deposited on the aluminum panel surface was measured.

[0090] (Shell 4 ball test wear marks) The gas engine lubricating oil compositions were subjected to a Shell 4-ball wear resistance test in accordance with ASTM D4172 under conditions of a rotation speed of 1500 rpm, 30 minutes, 75°C, and a load of 30 kg, and the wear scar diameter on the steel ball after the test was measured.

[0091] (Metal Corrosion Test) Using 50 g of the gas engine lubricating oil composition after the ISOT test, an immersion test was carried out at 150°C for 360 hours using an alloy composed of copper-tin-lead as a catalyst, and the amount of lead and copper components eluted from the oil was measured by ICP atomic emission spectroscopy in accordance with JPI-5S-38-92. The amount of metal element means the mass of lead or copper atoms relative to the total mass of the lubricating oil composition for gas engines after the test. The amount of molybdenum atoms is shown in Table 1 in terms of mass % and ppm.

[0092] [Table 1-1]

[0093] [Table 1-2]

[0094] Details of the abbreviations in Table 1 are given below. (base oil) Base oil 1 (Gr III): A mineral refined base oil that belongs to API Group III and has been hydrotreated through an advanced hydrogenation process, and has the following general properties: Base oil 1: Kinematic viscosity (100℃): 7.6mm 2 / s, viscosity index: 130, flash point: 240℃ or higher, initial boiling point temperature (TIBP): 374℃ Base oil 2 (Gr III): A highly refined mineral oil base oil that belongs to API Group III and has been hydrotreated through an advanced hydrogenation process, and has the following general properties: Base oil 2: Kinematic viscosity (100℃): 7.6mm 2 / s, viscosity index: 130, flash point: 250℃ or higher, initial boiling point temperature (TIBP): 391℃

[0095] (Molybdenum-based friction modifier) Molybdenum friction modifier: A mixture of amide-type molybdenum compounds and ester-type molybdenum compounds. Density: 1.08 g / cm 3(15°C), kinematic viscosity at 100°C of 55 cSt, flash point of 193°C, nitrogen content of 2.8 mass%, molybdenum content of 7.9 mass%, and a mixture of a compound represented by general formula (1) in which R1 is an alkyl group having 3 to 16 carbon atoms and a compound represented by general formula (2) in which R2 is an alkyl group having 3 to 16 carbon atoms.

[0096] The density, kinematic viscosity at 100°C, and flash point of the molybdenum-based friction modifier were measured in the same manner as the density, kinematic viscosity at 100°C, and flash point of the gas engine lubricating oil composition, except that the measurement object was the molybdenum-based friction modifier. The molybdenum content was measured by ICP emission spectroscopy in accordance with JPI-5S-38-92, where the amount of molybdenum atoms in the molybdenum-based friction modifier was measured. The nitrogen content was measured according to the chemiluminescence method (JIS2609:1998). The nitrogen content means the mass of nitrogen atoms relative to the total mass of the molybdenum-based friction modifier, and the molybdenum content means the mass of molybdenum atoms relative to the total mass of the molybdenum-based friction modifier.

[0097] (Viscosity modifier) Viscosity modifier 1: Density 0.85g / cm 3 It is a non-dispersant viscosity modifier defined by CAS No. 9010-79-1 (ethylene-propylene copolymer) with a kinematic viscosity of 2000 cSt at 100°C (15°C), a flash point of 294°C, a pour point of -5°C, an acid value of 0.003 mg KOH / g, and a weight-average molecular weight of 14,600. Viscosity modifier 2: Density 0.85g / cm 3 (15°C), kinematic viscosity at 100°C of 2010 cSt, flash point of 300°C or higher, pour point of -7°C, acid value of 0.01 mg KOH / g or less, weight average molecular weight: 14,500. It is a viscosity modifier defined by CAS No. 9010-79-1 (ethylene-propylene copolymer). Viscosity modifier 3: Density 0.88g / cm 3(15°C), kinematic viscosity at 100°C of 2344 cSt, flash point of 220°C, acid number of 0.47 mg KOH / g, weight average molecular weight of 140,000, copolymer of polyalkyl methacrylate and olefin copolymer diluted with mineral oil. Viscosity modifier 4: Density 0.85g / cm 3 (15°C), kinematic viscosity at 100°C of 1288 cSt, flash point of 150°C, and weight average molecular weight of 170,000, diluted with mineral oil.

[0098] The density, kinematic viscosity at 100°C, flash point, pour point and acid number of the viscosity modifier were measured in the same manner as the density, kinematic viscosity at 100°C, flash point, pour point and acid number of the gas engine lubricating oil composition, except that the measurement object was a molybdenum-based friction modifier. The weight average molecular weight of the viscosity modifier is as described above.

[0099] (Metallic detergents and dispersants) The following metallic detergents and dispersants were used: The contents in Table 1 are the total mass of the metallic detergents and dispersants relative to the total mass of the lubricating oil composition for gas engines. Metallic detergents have a density of 1.05 g / cm 3 (15°C), kinematic viscosity at 100°C of 81 cSt, flash point of 194°C, calcium content of 7.9%, and base number of 224 mg KOH / g. The dispersant has a density of 0.94 g / cm 3 It is a boron-based dispersant with a kinematic viscosity of 512 cSt at 100°C, a boron content of 0.95%, a nitrogen content of 1.7%, a base number of 33 mg KOH / g, and a weight-average molecular weight of 5500 g / mol. It also has a density of 0.92 g / cm 3 An ashless dispersant with a kinematic viscosity of 404 cSt at 100°C, a nitrogen content of 1.8%, a base number of 41 mg KOH / g, and a weight-average molecular weight of 4,910 was also used.

[0100] The density, kinematic viscosity at 100°C, flash point and base number of the metallic detergent were measured in the same manner as the density, kinematic viscosity at 100°C, flash point and base number of the gas engine lubricating oil composition, except that the measurement object was the metallic detergent. The calcium content of the metallic detergent was measured by ICP emission spectroscopy in accordance with JPI-5S-38-92, and the amount of calcium atoms in the metallic detergent was measured. The calcium content means the mass of calcium atoms relative to the total mass of the metal-based detergent.

[0101] The density, kinematic viscosity at 100°C and base number of the dispersant were measured in the same manner as the density, kinematic viscosity at 100°C and base number of the gas engine lubricating oil composition, except that the dispersant was the object of measurement. The weight average molecular weight of the dispersant is a value measured by gel permeation chromatography and calculated using polystyrene as a standard. The boron content of the dispersant was measured by ICP emission spectroscopy in accordance with JPI-5S-38-92 to determine the amount of boron atoms in the dispersant. The nitrogen content was measured according to the chemiluminescence method (JIS2609:1998). The boron content means the mass of boron atoms relative to the mass of the entire dispersant, and the nitrogen content means the mass of nitrogen atoms relative to the mass of the entire dispersant.

[0102] (antioxidant) A phenolic antioxidant, an amine antioxidant, and a zinc dialkyldithiophosphate were used. The phenolic antioxidant has a density of 0.97 g / cm 3 (20℃), flash point 152℃, boiling point 240℃, phenolic compound (octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate) classified under CAS No. 125643-61-0. In addition, the amine-based antioxidant has a density of 0.97 g / cm 3 An aromatic amine compound classified as CAS No. 68411-46-1, which has a kinematic viscosity of 401 cSt at 40°C, a flash point of 154°C, basic nitrogen of 4.5%, and a base number of 180 mg KOH / g, and an aromatic amine compound classified as CAS No. 68259-36-9, which has a flash point of 215°C, were used in combination. All of the aromatic amine compounds used had an acid dissociation constant (pKa) of 7 or less. Furthermore, zinc dialkyldithiophosphate has a density of 1.16 g / cm 3 It is a secondary type zinc dialkyldithiophosphate compound classified as CAS No. 68649-42-3, with a kinematic viscosity of 9.7 cSt at 100°C (15°C), zinc content of 9.7%, sulfur content of 19.1%, and phosphorus content of 9.3%. The content of the phenolic antioxidant relative to the total content of antioxidants was 29 mass %. The content of the amine-based antioxidant relative to the total content of antioxidants was 57 mass %. The content of zinc dialkyldithiophosphate relative to the total content of antioxidants was 14 mass %.

[0103] The density, flash point, kinematic viscosity at 40°C, kinematic viscosity at 100°C and base number of the antioxidant were measured in the same manner as the density, flash point, kinematic viscosity at 40°C, kinematic viscosity at 100°C and base number of the gas engine lubricating oil composition, except that the measurement object was the antioxidant. The zinc, sulfur, and phosphorus contents of the antioxidant were measured by ICP emission spectroscopy in accordance with JPI-5S-38-92, where the amounts of zinc atoms, sulfur atoms, and phosphorus atoms in the antioxidant were measured. The zinc content means the mass of zinc atoms relative to the total mass of the antioxidant, the sulfur content means the mass of sulfur atoms relative to the total mass of the antioxidant, and the phosphorus content means the mass of phosphorus atoms relative to the total mass of the antioxidant. The amount of basic nitrogen in the antioxidant was measured according to the chemiluminescence method (JIS2609:1998).

[0104] (Other additives) Other additives include a pour point depressant (flash point: 193°C, weight average molecular weight: 49,000), a silicone antifoaming agent (density 0.97g / cm 3 (25°C, flash point 350°C) and an amine-based corrosion inhibitor (40°C kinematic viscosity 48 cSt, acid value 120 mg KOH / g).

[0105] As shown in Table 1, the gas engine lubricating oil compositions of the Examples exhibited significantly lower coking levels in the panel coking test than Comparative Example 1, which did not contain a molybdenum-based friction modifier. In Comparative Example 2, a decrease in coking levels was observed even when the molybdenum-based friction modifier content was 0.01% by mass. However, when the molybdenum-based friction modifier content was increased to 1% by mass, as in Comparative Example 3, the base number in the ISOT test decreased and the metal content in the metal corrosivity evaluation also increased. Therefore, it can be seen that a molybdenum-based friction modifier content in the range of 0.01% to 1% by mass, as in the Examples, is preferable. Furthermore, compared with Comparative Examples 5, 7, and 8, which contained viscosity modifiers 3 and 4, the Examples exhibited even lower coking levels in the panel coking test and even better results in the Shell 4-ball wear scar evaluation. These results also demonstrate the additive effect of the combined use of a molybdenum-based friction modifier and a high-flashpoint viscosity modifier. Furthermore, Example 4, which used high-flash point base oil 2 and viscosity modifier 2, had a higher flash point than Comparative Examples 4 and 5, which used viscosity modifier 3, demonstrating the flash point-improving effect of the lubricating oil composition for gas engines. Furthermore, it can be seen that when use in low-temperature environments is anticipated, the pour point can be lowered by using a pour point depressant as long as performance is not impaired, as in Example 2. It can be seen that the lubricating oil compositions for gas engines of the present examples show better evaluation results in the panel coking test, Shell 4-ball wear scar test, and metal corrosivity test than the lubricating oil compositions for gas engines of the comparative examples. From the above results, it can be seen that the lubricating oil composition for gas engines of this example suppresses the occurrence of coking, suppresses corrosion of metals contained in gas engine components, and improves the wear resistance of gas engine components.

Claims

1. A base oil having a flash point of 240°C or higher; a molybdenum-based friction modifier; A viscosity modifier having a flash point of 270°C or higher, the mass of molybdenum atoms relative to the total mass of the lubricating oil composition for gas engines is 20 ppm or more and 800 ppm or less; A lubricating oil composition for gas engines, wherein the base oil has an initial boiling point temperature (TIBP) of 350°C or higher.

2. 2. The lubricating oil composition for gas engines according to claim 1, further comprising at least one metallic detergent selected from the group consisting of calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, magnesium sulfonate, and detergents containing alkaline earth metals.

3. Contains phenolic antioxidants, amine antioxidants and zinc antioxidants, 3. The lubricating oil composition for gas engines according to claim 1, wherein the total content of the phenolic antioxidant and the amine-based antioxidant is 1% by mass or more and 4% by mass or less, based on the total amount of the lubricating oil composition for gas engines.

4. 4. The lubricating oil composition for gas engines according to claim 3, wherein the amine-based antioxidant comprises an aromatic amine compound having an acid dissociation constant (pKa) of 7 or less.

5. 5. The lubricating oil composition for gas engines according to claim 1, wherein the molybdenum-based friction modifier is at least one selected from the group consisting of amide-based molybdenum compounds, ester-based molybdenum compounds, molybdenum acid amine compounds, molybdenum dithiocarbamates, and molybdenum dithiophosphates.

6. The lubricating oil composition for gas engines according to any one of claims 1 to 5, wherein the viscosity modifier is at least one selected from the group consisting of an olefin copolymer, a polymethacrylate, a random copolymer of an olefin and a methacrylate, a block copolymer of an olefin and a methacrylate, and a graft copolymer of a polymethacrylate and an olefin copolymer.

7. The lubricating oil composition for gas engines according to any one of claims 1 to 6, which is for use in gas engines, hydrogen engines, or dual-fuel engines for ships used in total energy systems.

8. A lubricating oil composition for gas engines according to any one of claims 1 to 7, wherein the viscosity modifier has a flash point of 290°C or higher and a NOACK evaporation amount of less than 8%.

Images