Lubricating oil composition for gas engines

Abstract

To provide a lubricant composition for a gas engine, that has low ash content and has excellent long drain property and heat resistance.SOLUTION: A lubricant composition for a gas engine comprises: a base oi; a metal detergent; a dispersant including a boron-based dispersant and a boron-free ashless dispersant; a phenol based antioxidant; an amine based antioxidant containing an aromatic amine-based antioxidant A with a pKa of 0.1 or more to 2 or less and an aromatic amine-based antioxidant B with a pKa of more than 2 to 8 or less; and an anti-wear agent, wherein metal element content, boron element content, nitrogen element content and zinc element content derived from a metal-based cleaning agent satisfy a predetermined range based on a total amount of the lubricant composition, and sulfated ash content is 0.45 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, cogeneration systems have been attracting attention from the perspective of energy conservation measures and the diversification of power sources. Gas cogeneration systems, in particular, are seen as promising environmentally friendly systems that use clean fuels. However, the lubricating oil used in gas engines tends to be susceptible to chemical thermal oxidation when exposed to high-temperature environments during long periods of continuous operation. Gas engines have high combustion temperatures, which means that the NOx concentration in the blow-by gas is relatively high, which can easily cause sludge to form in the lubricating oil. This requires periodic replacement of the lubricating oil, but increasing the number of replacements leads to higher maintenance costs, so there is a demand for longer-lasting lubricating oil (i.e., long-drain properties).

[0003] Recent gas cogeneration systems have been pursuing energy conservation through the optimization of fuel combustion to minimize emissions of carbon dioxide, nitrogen oxides, and sulfur oxides, and through the high efficiency of power generation and heat utilization. Therefore, lubricating oil compositions used in gas engines are also required to maintain excellent high-temperature stability without reducing power generation efficiency.

[0004] Gas cogeneration systems often use relatively large gas engines, which require high maintenance costs, making reducing the frequency of maintenance inspections an important issue. However, when using lubricating oil in gas engines, the ash contained in the lubricating oil accumulates on the top of the pistons and on the exhaust valves, reducing the cleanliness of the engine. As a result, the engine itself must be overhauled multiple times periodically, which requires a great deal of maintenance effort. Therefore, a lubricating oil with low ash content is necessary to improve maintainability.

[0005] 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 specific metallic detergents, amine compounds, and molybdenum compounds for the purpose of maintaining a residual base number, heat resistance, etc. while having a low ash content. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-511410 [Patent Document 2] Japanese Patent Publication No. 2020-164747 [Patent Document 3] Japanese Patent Publication No. 2020-164746 Summary of the Invention [Problem to be solved by the invention]

[0007] Ash generated during combustion of a lubricating oil composition for gas engines can accumulate near the top of the piston in the gas engine, potentially causing damage to the ring liner. Because the ash in a lubricating oil composition is primarily metal components derived from metal-based detergents, it is conceivable to reduce the amount of metal-based detergent blended to reduce ash content. However, simply reducing the amount of metal detergent blended directly leads to a decrease in the residual base number and a shortened service life of the lubricating oil composition itself. Furthermore, in gas engines that are prone to NOx generation, it is necessary to ensure detergency at high temperatures. However, it is generally difficult to ensure sufficient detergency (i.e., high-temperature detergency) within a composition range in which the amount of metal detergent blended is low.

[0008] An object of one embodiment of the present disclosure is to provide a lubricating oil composition for gas engines that has a low ash content and is excellent in long drain properties and heat resistance. [Means for solving the problem]

[0009] Specific means for solving the above problems include the following embodiments. [1] A lubricating oil composition comprising a base oil, a metal-based detergent, a dispersant including a boron-based dispersant and a boron-free ashless dispersant, a phenol-based antioxidant, an amine-based antioxidant including an aromatic amine-based antioxidant A having an acid dissociation constant (pKa) of 0.1 or more and 2 or less, and an aromatic amine-based antioxidant B having an acid dissociation constant (pKa) of more than 2 and 8 or less, and an antiwear agent; The content of metal elements derived from the metallic detergent is 300 ppm by mass or more and 1000 ppm by mass or less based on the total amount of the lubricating oil composition, The boron element content is 80 ppm by mass or more and 470 ppm by mass or less based on the total amount of the lubricating oil composition, The nitrogen element content is 1800 ppm by mass or more and 2900 ppm by mass or less based on the total amount of the lubricating oil composition, The zinc element content is 150 ppm by mass or more and 1500 ppm by mass or less based on the total amount of the lubricating oil composition, The sulfated ash content according to JIS K2272 (1998) is 0.45 mass% or less based on the total amount of the lubricating oil composition. A lubricating oil composition for gas engines. [2] The lubricating oil composition for gas engines according to [1], wherein the metallic detergent comprises an alkaline earth metal detergent. [3] The lubricating oil composition for gas engines according to [2], wherein the metallic detergent comprises at least one selected from the group consisting of calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, and magnesium sulfonate. [4] The lubricating oil composition for gas engines according to any one of [1] to [3], wherein the boron-based dispersant comprises a boron-containing imide-based dispersant. [5] The lubricating oil composition for gas engines according to any one of [1] to [4], wherein the total content of dispersants is 6 mass % or more based on the total amount of the lubricating oil composition. [6] The lubricating oil composition for gas engines according to any one of [1] to [5], wherein the total content of the phenolic antioxidant and the amine antioxidant is 1 mass % or more and 4 mass % or less, based on the total amount of the lubricating oil composition. [7] The lubricating oil composition for gas engines according to any one of [1] to [6], wherein the aromatic amine-based antioxidant B is an aromatic amine-based antioxidant having an acid dissociation constant (pKa) of more than 2 and not more than 7. [8] The lubricating oil composition for gas engines according to any one of [1] to [7], wherein the amine-based antioxidant further comprises an amine-based antioxidant C having an acid dissociation constant (pKa) of 7 or more and 12 or less. [9] The lubricating oil composition for gas engines according to any one of [1] to [8], wherein the antiwear agent comprises one or more selected from zinc dialkyldithiophosphates having two identical or different alkyl groups selected from primary or secondary alkyl groups having 4 to 12 carbon atoms.

[10] The lubricating oil composition for gas engines according to any one of [1] to [9], which is for use in a hydrogen engine or a dual-fuel engine for a ship. [Effects of the Invention]

[0010] According to one embodiment of the present disclosure, there is provided a lubricating oil composition for gas engines which has a low ash content and excellent long drain properties and heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0013] In the present disclosure, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, it means the total amount of the multiple components present in the composition, unless otherwise specified.

[0014] In the present disclosure, "mass %" and "weight %" are synonymous. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, "JIS" is used as an abbreviation for Japanese Industrial Standards.

[0015] In the present disclosure, a lubricating oil composition having a "low ash content" means that the sulfated ash content according to JIS K2272 (1998) is 0.45 mass % or less.

[0016] In this disclosure, "long drain properties" refers to the property of suppressing deterioration of a lubricating oil composition in a gas engine, thereby extending the replacement interval of the lubricating oil composition. In this disclosure, "long drain properties" are evaluated based on thermal oxidation stability and NOx degradation suppression. Specifically, long drain properties are evaluated by the Internal Combustion Engine Lubrication Oxidation Stability Test (ISOT test) and NOx degradation test described in the Examples below. Details of the ISOT test and NOx degradation test are described in the Examples below.

[0017] <Lubricating oil composition for gas engines> The lubricating oil composition for gas engines according to the present disclosure comprises: The oil composition contains a base oil, a metal-based detergent, a dispersant including a boron-based dispersant and a boron-free ashless dispersant, a phenol-based antioxidant, an amine-based antioxidant including an aromatic amine-based antioxidant A having an acid dissociation constant (pKa) of 0.1 or more and 2 or less, and an aromatic amine-based antioxidant B having an acid dissociation constant (pKa) of more than 2 and 8 or less, and an antiwear agent, The content of metal elements derived from the metallic detergent is 300 ppm by mass or more and 1000 ppm by mass or less based on the total amount of the lubricating oil composition, The boron element content is 80 ppm by mass or more and 470 ppm by mass or less based on the total amount of the lubricating oil composition, The nitrogen element content is 1800 ppm by mass or more and 2900 ppm by mass or less based on the total amount of the lubricating oil composition, The zinc element content is 150 ppm by mass or more and 1500 ppm by mass or less based on the total amount of the lubricating oil composition, The sulfated ash content according to JIS K2272 (1998) is 0.45 mass % or less based on the total amount of the lubricating oil composition.

[0018] The lubricating oil composition for gas engines according to the present disclosure preferably further contains a viscosity index improver, and may contain other additives as desired. The lubricating oil composition for gas engines according to the present disclosure may contain metal components or non-metal components other than those mentioned above, as long as the low ash content is not impaired.

[0019] Due to the above-described configuration, the lubricating oil composition for gas engines according to the present disclosure has a low ash content and exhibits excellent long-drain properties and heat resistance. The lubricating oil composition for gas engines according to the present disclosure also exhibits excellent wear properties, metal corrosion resistance, and demulsibility.

[0020] (base oil) The base oil is not particularly limited, and any base oil used in the field of lubricants can be used, including, for example, mineral base oils and synthetic base oils.

[0021] Examples of mineral oil-based 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 combining the processes of hydrocracking, catalytic dewaxing, etc.; and base oils classified as API Group III, which are obtained by combining the processes of advanced hydrotreating, such as hydrocracking and hydroisomerization dewaxing. The mineral base oil may be refined paraffinic mineral oil, naphthenic mineral oil, and aromatic base oil, which may be used alone or in combination.

[0022] As the base oil, it is preferable to mainly use a mineral base oil classified as API Group III from the viewpoint of oxidation stability at high temperatures.

[0023] 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.

[0024] From the viewpoint of oxidation stability at high temperatures, 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 prevent sufficient dissolution of the additives.

[0025] The kinematic viscosity at 40°C of the base oil is not particularly limited, but from the viewpoint of high temperature stability and wear resistance, it is preferably 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 even more preferable.

[0026] 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 9.0mm2 / s or less is more preferable, and 7.0 mm 2 / s or more 8.0mm 2 / s or less is more preferable.

[0027] The kinematic viscosity at 40°C and the kinematic viscosity at 100°C of the base oil are preferably within the above ranges whether the base oil is a single base oil or a mixed base oil.

[0028] The kinematic viscosity at 40°C and the kinematic viscosity at 100°C of the base oil are measured in accordance with JIS K2283 (2000).

[0029] 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.

[0030] The viscosity index of the base oil is measured in accordance with JIS K2283 (2000).

[0031] (Metallic detergents) The lubricating oil composition for gas engines according to the present disclosure contains a metal-based detergent. The metal-based detergent may be one type or two or more types.

[0032] Examples of metal-based detergents include alkali metal-based detergents and alkaline earth metal-based detergents, and alkaline earth metal-based detergents are preferred from the viewpoint of detergency effects. The alkali metals include alkali metals such as sodium, etc. The alkaline earth metals include alkaline earth metals such as calcium and magnesium, etc. Alkaline earth metal detergents include alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates, and the like.

[0033] From the viewpoint of extending the life of the lubricating oil composition, the metal detergent is preferably at least one selected from the group consisting of calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, and magnesium sulfonate, and calcium salicylate is more preferred.

[0034] The calcium salicylate may be in the form of a neutral salt, a basic salt, or an overbased salt. The method for producing calcium salicylate is not limited.

[0035] The base number of calcium salicylate is preferably 200 mgKOH / g to 250 mgKOH / g, and more preferably 210 mgKOH / g to 240 mgKOH / g.

[0036] The base number of calcium salicylate is measured by the perchloric acid method in accordance with JIS K2501 (2003).

[0037] In the lubricating oil composition for gas engines according to the present disclosure, the content of metal elements derived from the metallic detergent is 300 ppm by mass or more and 1000 ppm by mass or less, and preferably 340 ppm by mass or more and 660 ppm by mass or less, based on the total amount of the lubricating oil composition. When two or more elements are derived from the metallic detergent, the above metal element content is the total content of the two or more elements.

[0038] The metal element derived from the metal-based detergent is, for example, calcium element or magnesium element.

[0039] When the content of metal elements derived from the metallic detergent is 300 ppm by mass or more, the lubricating oil composition will have good life characteristics in high-temperature environments and in the presence of NOx, and when it is 1000 ppm by mass or less, significant deposition of metal elements derived from the metallic detergent on pistons in gas engines can be suppressed.

[0040] The content of metal elements derived from metallic detergents is the analytical value obtained by ICP atomic emission spectrometry in accordance with JPI-5S-38-92.

[0041] From the viewpoint of realizing low ash content, the content of the metallic detergent is preferably 0.01 mass % or more and 1.5 mass % or less, more preferably 0.1 mass % or more and 1.0 mass % or less, and even more preferably 0.4 mass % or more and 0.8 mass % or less, based on the total amount of the lubricating oil composition.

[0042] (dispersant) The lubricating oil composition for gas engines according to the present disclosure contains a dispersant, which includes boron-based dispersants and boron-free ashless dispersants.

[0043] The boron-based dispersant and the boron-free ashless dispersant may each be one or more selected from the corresponding dispersants.

[0044] <Boron-based dispersant> By boron-based dispersant is meant a dispersant that contains boron. As the boron-based dispersant, a boron-based dispersant used in the field of lubricating oils can be used.

[0045] As the boron-based dispersant, a boron-containing imide-based dispersant is preferred. The boron-containing imide-based dispersant refers to a dispersant that is a compound containing boron and has an imide bond. Examples of the boron-containing imide-based dispersant include monoimides of alkyl or alkenyl succinic acid and boron-modified bisimides thereof. Among these, as the boron-containing imide-based dispersant, boron-modified bisimides of alkyl or alkenyl succinic acid are preferred from the viewpoints of extending the life, wear resistance, and dispersibility of the lubricating oil composition.

[0046] The boron-based dispersant may be either a low molecular weight compound or a polymer, but from the viewpoint of clean dispersibility, a polymer is preferred. In the present disclosure, a polymer refers to a compound having a weight average molecular weight (Mw) of 1,000 or more in terms of polystyrene.

[0047] From the viewpoint of clean dispersibility, the boron-based dispersant preferably has a weight average molecular weight (Mw) of 2,000 to 7,000. In the present disclosure, the weight average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC).

[0048] In this disclosure, the weight-average molecular weight (Mw) is measured using a Shodex GPC-101 (Showa Denko K.K.) measuring instrument, three Shodex GPC LF-804 (Showa Denko K.K.) measuring columns, a differential refractive index detector, THF (tetrahydrofuran) mobile phase, a flow rate of 1 ml / min, a sample concentration of 1.0 mass% / vol, and an injection volume of 100 μL. The weight-average molecular weight is calculated from the measurement results using a molecular weight distribution curve prepared using a monodisperse polystyrene standard sample.

[0049] The boron-containing succinimide dispersant is preferably a boron-modified bisimide of alkyl or alkenyl succinic acid, which has a weight average molecular weight (Mw) of 3,000 to 8,000 in terms of polystyrene.

[0050] The boron content in the lubricating oil composition for gas engines according to the present disclosure may be the content of boron derived from a boron-based dispersant, i.e., the boron content in the lubricating oil composition for gas engines according to the present disclosure may be adjusted by the type and / or content of the boron-based dispersant. The boron element content will be described later.

[0051] <Boron-free ashless dispersion> The boron-free ashless dispersant refers to a dispersant that does not contain boron and is included in the category of ashless dispersants.

[0052] As the boron-free ashless dispersant, an ashless dispersant used in the field of lubricating oils that does not contain boron can be used.

[0053] Examples of boron-free ashless dispersants include compounds in which a polar group is directly bonded to the side chain of a polyolefin that does not have a polar group in its main chain or to the side chain of a polyamine that has a polar group in its main chain. Examples of the polar group include an alcoholic hydroxy group, an amide group, and an ester group.

[0054] As the boron-free ashless dispersant, for example, polyamines containing one or more alkyl or alkenyl groups in the molecule, and acid-modified products thereof can be used. As boron-free ashless dispersants, for example, succinimides represented by general formula (1) or general formula (2) described in paragraphs 0029 to 0032 of JP-A-2018-048220 (excluding boron-modified compounds) and dispersant B described in paragraph 0048 can also be suitably used. A specific example of a suitable boron-free ashless dispersant is a boron-free polyisobutenyl succinimide compound.

[0055] From the viewpoint of long drain properties and heat resistance, the total content of dispersants may be 5% by mass or more, preferably 6% by mass or more, and more preferably 6% by mass or more and 10% by mass or less, based on the total amount of the lubricating oil composition.

[0056] (antioxidant) The lubricating oil composition for gas engines according to the present disclosure contains, as an antioxidant, a combination of a phenol-based antioxidant and multiple types of amine-based antioxidants. The multiple types of amine-based antioxidants include aromatic amine-based antioxidants and aliphatic amine-based antioxidants.

[0057] The lubricating oil composition for gas engines according to the present disclosure preferably contains a phenolic antioxidant, an aromatic amine-based antioxidant A having an acid dissociation constant (pKa) of 0.1 or more and 2 or less, and an aromatic amine-based antioxidant B having an acid dissociation constant of more than 2 and 8 or less, and further contains an amine-based antioxidant C having an acid dissociation constant (pKa) of 7 or more and 12 or less. The phenolic antioxidant and the amine antioxidant will be described in detail below.

[0058] <Phenol-based antioxidant> The antioxidant includes at least one selected from phenol-based antioxidants.

[0059] Examples of phenolic antioxidants include alkylphenolic compounds such as 2,6-di-tert-p-cresol, bisphenolic compounds such as 4,4'-methylenebis-(2,6-di-tert-butylphenol), and hindered phenolic compounds such as esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with alcohols having 8 or more carbon atoms. These compounds may be isomers differing in the number of carbon atoms or structure of the alkyl group.

[0060] <Amine-based antioxidants> The antioxidant includes a plurality of types of amine-based antioxidants. The multiple types of amine antioxidants include at least one selected from aromatic amine antioxidants A having an acid dissociation constant (pKa) of 0.1 or more and 2 or less (hereinafter also simply referred to as "aromatic amine antioxidant A"), and at least one selected from aromatic amine antioxidants B having an acid dissociation constant (pKa) of more than 2 and 8 or less (hereinafter also simply referred to as "aromatic amine antioxidant B"). The multiple types of amine antioxidants may include an amine antioxidant other than the aromatic amine antioxidants A and B.

[0061] By combining amine-based antioxidants with different acid dissociation properties, it becomes possible to inhibit oxidation of the lubricating oil composition in stages from the initial to final stages of the deterioration process, and the effects of a reduced content of metal-based detergents can be effectively compensated for.

[0062] In the present disclosure, the acid dissociation constant (pKa) of the amine antioxidant is a value in water at 20°C measured by potentiometric titration.

[0063] Examples of the amine antioxidant include amine compounds such as diphenylamine, 4-benzylamine, 2-aminobiphenyl, naphthylamine, allylaniline, 4-aminobinephenyl, o-toluidine, m-toluidine, p-toluidine, aniline, allylamine, alkylated derivatives thereof, hindered amine compounds, and alkenylated derivatives thereof. These compounds may be isomers having different carbon atoms or structures in the alkyl group.

[0064] Examples of aromatic amine antioxidants include amine compounds that contain one or more amines selected from primary amines, secondary amines, primary diamines, and secondary diamines in their chemical structure, contain one or more aromatic rings, and have an acid dissociation constant of 8 or less for the one or more amines.

[0065] As the aromatic amine-based antioxidant, from the viewpoint of making the antioxidant effect of the amine moiety more effective, it is preferable to select and contain one or more types of compounds represented by the following formula (1) and formula (2).

[0066] [ka]

[0067] In formula (1), R1 to R6 each independently represent an alkyl group or an alkoxy group, and n and m each independently represent an integer of 0 to 4. The alkyl group represented by R1 to R6 is preferably an alkyl group having 1 to 16 carbon atoms, more preferably an alkyl group having 1 to 14 carbon atoms. The alkyl group may be a linear or branched alkyl group. Examples of the alkyl group include a methyl group, an ethyl group, and an octyl group. The alkoxy group represented by R1 to R6 is preferably an alkoxy group having 1 to 16 carbon atoms, more preferably an alkoxy group having 1 to 14 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, and an octoxy group. The alkyl or alkoxy groups represented by R1 to R6 may further have a substituent, for example, an alkylamino group, an alkanonyl group, or an alkyl ester group. n is preferably 0 to 2, and more preferably 0 to 1. m is preferably 0 to 2, and more preferably 0 to 1.

[0068] [ka]

[0069] In formula (2), R 21 ~R 28 each independently represents a hydrogen atom, an alkyl group, an alkoxy group, or a phenyl group. R 21 ~R 28 The alkyl group represented by the formula (I) is preferably an alkyl group having 1 to 16 carbon atoms, and more preferably an alkyl group having 1 to 12 carbon atoms. The alkyl group may be a linear or branched alkyl group. Examples of the alkyl group include a methyl group, an ethyl group, an octyl group, and a dodecyl group. R 21 ~R 28 The alkoxy group represented by the formula (I) is preferably an alkoxy group having 1 to 16 carbon atoms, and more preferably an alkoxy group having 1 to 12 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, and an octoxy group. R 21 ~R 28 The alkyl group, alkoxy group, or phenyl group represented by the formula (I) may further have a substituent, such as an alkylamino group, an alkanonyl group, or an alkyl ester group.

[0070] Aromatic amine antioxidants A and B The aromatic amine antioxidant A is an aromatic amine antioxidant having an acid dissociation constant (pKa) of 0.1 or more and 2 or less, and is preferably selected from the compounds represented by the above formula (1) as a compound having an acid dissociation constant (pKa) of 0.1 or more and 2 or less. The acid dissociation constant (pKa) of the aromatic amine antioxidant A is more preferably 0.1 or more and 1.8 or less.

[0071] When the aromatic amine antioxidant A is a compound selected from the compounds represented by the above formula (1), examples include compounds in which R1 to R6 are each independently a branched-chain alkyl group having 3 to 12 carbon atoms, n is 0 to 2, and m is 0 to 2.

[0072] The aromatic amine antioxidant B is an aromatic amine antioxidant having an acid dissociation constant (pKa) of more than 2 and not more than 8, and it is preferable to select a compound having an acid dissociation constant (pKa) of more than 2 and not more than 8 from the compounds represented by the above formula (2). The acid dissociation constant (pKa) of the aromatic amine antioxidant B is more preferably more than 2 and not more than 7.

[0073] When the aromatic amine antioxidant B is a compound selected from the compounds represented by the above formula (2), for example, 1-naphthylamine (R 21 ~R 28 : hydrogen atom), R 21 ~R 28 and each independently represents an alkyl group or an alkoxy group having a branched chain and having 4 to 16 carbon atoms.

[0074] Amine-based antioxidant C The lubricating oil composition for gas engines according to the present disclosure preferably further contains an amine-based antioxidant C. Examples of the amine-based antioxidant C include amine-based compounds containing, in their chemical structure, one or more amines selected from primary amines, secondary amines, primary diamines, and secondary diamines, wherein the one or more amines have an acid dissociation constant (pKa) of at least 7. The acid dissociation constant (pKa) of the amine-based antioxidant C is preferably 7 or more and 12 or less. The amine-based antioxidant C does not include the aromatic amine-based antioxidant B described above.

[0075] One embodiment of the amine antioxidant C is an aliphatic amine compound having, in its chemical structure, one or more amines selected from a primary amine, a secondary amine, a primary diamine, and a secondary diamine, and containing no aromatic ring, wherein the one or more amines have an acid dissociation constant of 7 or more.

[0076] Another embodiment of the amine antioxidant C is a compound represented by the above formula (1) and having an acid dissociation constant (pKa) of 7 or more and 12 or less.

[0077] As the amine-based antioxidant C, in order to effectively utilize the antioxidant effect of the amine moiety, it is preferable to contain one or more compounds selected from the compounds represented by the following formula (3A) and formula (3B).

[0078] [ka]

[0079] In formulas (3A) and (3B), R 31 and R 32 each independently represents an alkyl group or an alkoxy group. R 31 and R 32 The alkyl group represented by the formula (I) is preferably an alkyl group having 1 to 18 carbon atoms, more preferably an alkyl group having 1 to 16 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, an octyl group, and a dodecyl group. R 31 and R 32 The alkoxy group represented by the formula (I) is preferably an alkoxy group having 1 to 18 carbon atoms, more preferably an alkoxy group having 1 to 16 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, and an octoxy group. R 31 and R 32The alkyl group or alkoxy group represented by the formula (I) may further have a substituent, for example, an alkenyl group, an alkylamino group, an alkanonyl group, or an alkyl ester group.

[0080] Specific examples of the amine-based antioxidant C include, but are not limited to, the following. Examples of the compound represented by formula (3A) include R 31 However, examples of the 2,2,6,6-tetramethylpiperidin-4-yl hexadecanoate and 2,2,6,6-tetramethylpiperidin-4-yl octadecanoate include those having 8 carbon atoms. Examples of the compound represented by formula (3B) include R 31 and R 32 wherein each independently has 12 carbon atoms, such as didodecylamine.

[0081] The total content of the phenolic antioxidant and the amine antioxidant is preferably 1 mass % or more and 4 mass % or less, and more preferably 2 mass % or more and 3.5 mass % or less, based on the total mass of the lubricating oil composition.

[0082] The lubricating oil composition for gas engines according to the present disclosure contains 1.0 mass% or more of a phenolic antioxidant and an amine antioxidant, which effectively promotes radical scavenging reactions during the thermal oxidative degradation process of the base oil and efficiently stops oxidation reactions. On the other hand, by containing 4 mass% or less of the antioxidant, a significant decrease in metal corrosion resistance and a significant color change can be suppressed.

[0083] The lubricating oil composition for gas engines according to the present disclosure may contain antioxidants other than the phenol-based antioxidant and the amine-based antioxidant, as long as the effects of the present disclosure can be obtained. Examples of other antioxidants include sulfur-based antioxidants and phosphorus-based antioxidants. The content of other antioxidants is preferably 4 mass% or less based on the total mass of the lubricating oil composition.

[0084] [Anti-wear agent] The lubricating oil composition for gas engines according to the present disclosure contains an antiwear agent.

[0085] Examples of the anti-wear agent include zinc compounds such as zinc dialkyldithiophosphate (i.e., zinc-based antioxidants), amide-based molybdenum compounds, molybdate amine compounds, molybdenum dithiocarbamate, molybdenum dithiophosphate, and derivatives thereof.

[0086] The lubricating oil composition for gas engines according to the present disclosure preferably contains a zinc compound (i.e., a zinc-based antiwear agent) as an antiwear agent, and zinc dialkyldithiophosphate (ZnDTP) is preferred as the zinc-based antiwear agent.

[0087] The zinc dialkyldithiophosphate is preferably, for example, a zinc dialkyldithiophosphate having a primary or secondary alkyl group. The primary or secondary alkyl group in the zinc dialkyldithiophosphate is preferably an alkyl group having 4 to 12 carbon atoms. That is, one suitable embodiment of the antiwear agent is at least one selected from zinc dialkyldithiophosphates having two identical or different alkyl groups selected from primary or secondary alkyl groups having 4 to 12 carbon atoms.

[0088] Specific examples of zinc dialkyldithiophosphates include, but are not limited to, zinc dialkyldithiophosphates having a primary alkyl group with 8 carbon atoms and zinc alkyldithiophosphates having a secondary alkyl group with 4 carbon atoms.

[0089] The zinc content in the lubricating oil composition for gas engines according to the present disclosure may be the zinc content derived from the zinc compound agent described above, i.e., the zinc content in the lubricating oil composition for gas engines according to the present disclosure may be adjusted by the type and / or content of the zinc compound described above.

[0090] The content of the zinc-based antioxidant is preferably 0.1 to 2 mass%, more preferably 0.2 to 1.5 mass%, and even more preferably 0.3 to 0.5 mass%, based on the total amount of the lubricating oil composition. By having the content of the zinc-based antioxidant in the range of 0.1 to 2 mass%, based on the total amount of the lubricating oil composition, friction and wear properties can be efficiently maintained without significantly increasing the ash content. When the lubricating oil composition for gas engines according to the present disclosure contains, as antiwear agents, a zinc-based antioxidant and an antiwear agent other than the zinc-based antioxidant, the content of the antiwear agent other than the zinc-based antioxidant is preferably 2 mass % or less based on the total mass of the lubricating oil composition.

[0091] (Viscosity index improver) The lubricating oil composition for gas engines according to the present disclosure preferably contains one or more viscosity index improvers.

[0092] Viscosity index improvers include non-dispersant type viscosity index improvers and dispersant type viscosity index improvers described in JASO M355:2021.

[0093] Non-dispersant type viscosity index improvers include olefin copolymers. Examples of olefin copolymers include polymers such as polyisobutylene and ethylene-propylene copolymers.

[0094] Dispersant-type viscosity index improvers include polymers such as 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.

[0095] When the above-mentioned polymer (olefin copolymer, polymethacrylate, etc.) that is the viscosity index improver is an alkylated derivative having a side chain alkyl group, the side chain alkyl group preferably has 1 to 50 carbon atoms.

[0096] In this disclosure, a viscosity index improver is a polymer that contributes to improving the viscosity index and has a weight-average molecular weight of 10,000 or more, and the content of the polymer is 1 mass% or more based on the total amount of the lubricating oil composition. The weight average molecular weight of the viscosity index improver is preferably 50,000 or more and 1,000,000 or less, and more preferably more than 100,000 and 800,000 or less. The weight average molecular weight of the viscosity index improver is determined by gel permeation chromatography and calculated using polystyrene as a standard.

[0097] (Other additives) The lubricating oil composition for gas engines according to the present disclosure may contain other additives as required.

[0098] Other additives include pour point depressants, corrosion inhibitors, demulsifiers, antifoaming agents, and the like.

[0099] Pour point depressants include, for example, olefin copolymers, polyalkyl methacrylates, copolymers thereof, alkylated derivatives thereof, and the like. The pour point depressant has a weight average molecular weight of 100,000 or less. The weight average molecular weight of the pour point depressant is determined by gel permeation chromatography and calculated using polystyrene as a standard. In the present disclosure, the pour point depressant is contained in an amount of less than 1 mass % based on the total amount of the lubricating oil composition.

[0100] 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.

[0101] 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.

[0102] (Physical Properties of Lubricating Oil Composition for Gas Engines) -Kinematic viscosity- The kinematic viscosity of the lubricating oil composition for gas engines 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 at 100°C of the lubricating oil composition for gas engines is preferably 10.0 mmHg. 2 / s or more 20.0mm 2 / s or less, preferably 12.5 mm 2 / s or more 16.3mm 2 / s or less. 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).

[0103] -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. The viscosity index of a lubricating oil composition for gas engines is measured in accordance with JIS K2283 (2000). 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.

[0104] -Base number- The base number of the lubricating oil composition for gas engines is preferably 1.5 mgKOH / g to 7 mgKOH / g, and more preferably 2 mgKOH / g to 6 mgKOH / g. 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 1.5 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.

[0105] The sulfated ash content of the lubricating oil composition for gas engines is preferably 0.45 mass % or less, and more preferably 0.40 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.

[0106] -Boron element content- The boron element content in the lubricating oil composition for gas engines is 80 ppm by mass or more and 470 ppm by mass or less, based on the total amount of the lubricating oil composition, preferably 100 ppm by mass or more and 470 ppm by mass or less, and more preferably 250 ppm by mass or more and 470 ppm by mass or less. If the boron content is 80 ppm by mass or more, the dispersibility of the sludge produced at high temperatures is effectively improved, and if it is 470 ppm by mass or less, a significant deterioration in the demulsibility against water vapor can be suppressed.

[0107] The boron may come from, for example, a component of a boron-based dispersant. The boron element content is the analytical value obtained by ICP atomic emission spectrometry in accordance with JPI-5S-38-92.

[0108] -Nitrogen element content- The nitrogen element content in the lubricating oil composition for gas engines is 1800 ppm by mass or more and 2900 ppm by mass or less based on the total amount of the lubricating oil composition, from the viewpoints of sludge dispersancy and metal corrosiveness. The nitrogen is derived from nitrogen-containing components such as dispersants, antioxidants, and viscosity index improvers. That is, the nitrogen element content in the lubricating oil composition for gas engines according to the present disclosure may be adjusted by the type and / or content of components such as dispersants, antioxidants, viscosity index improvers, and the like. The nitrogen element content is the analytical value obtained by ICP atomic emission spectrometry in accordance with JPI-5S-38-92.

[0109] -Zinc element content- From the viewpoints of low ash content, wear properties, and antioxidant properties, the zinc element content in the lubricating oil composition for gas engines is from 150 ppm by mass to 1500 ppm by mass, preferably from 200 ppm by mass to 1000 ppm by mass, and more preferably from 280 ppm by mass to 480 ppm by mass, based on the total amount of the lubricating oil composition. The zinc may come from, for example, a zinc-based antiwear agent. The zinc element content is the analytical value obtained by ICP atomic emission spectrometry in accordance with JPI-5S-38-92.

[0110] (Use of lubricating oil composition for gas engines) 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). The gas engine lubricating oil composition according to the present disclosure has low ash content and excellent long-drain properties and heat resistance. The gas engine lubricating oil composition according to the present disclosure also has excellent wear properties, metal corrosion resistance, and demulsification properties. Therefore, the gas engine lubricating oil composition according to the present disclosure is suitable for hydrogen engines and dual-fuel marine engines.

[0111] (Manufacturing method) The method for producing a lubricating oil composition for gas engines is not particularly limited, and it is sufficient to appropriately mix the base oil and other components contained in the lubricating oil composition. The lubricating oil composition for gas engines can be prepared, for example, by mixing the base oil, detergent, dispersant, antioxidant, antiwear agent, viscosity index improver, and other additives. The mixing method and mixing order are not particularly limited, and the other components may be mixed sequentially with the base oil. [Example]

[0112] Examples will be described below, but the present disclosure is not limited to these examples in any way.

[0113] <Examples 1 to 6 and Comparative Examples 1 to 10> Lubricating oil compositions for gas engines were prepared by mixing base oils, metal-based detergents, dispersants, antioxidants (phenolic antioxidants and amine-based antioxidants), antiwear agents, viscosity index improvers, and other additives in the types and blending ratios (mass%) shown in Tables 1, 2, and 3 below, and dissolving and dispersing the mixture at 60°C.

[0114] <Evaluation> The lubricating oil compositions for gas engines of Examples 1 to 6 and Comparative Examples 1 to 10 were evaluated by the following test methods. For Examples 4 to 6 and Comparative Examples 9 and 10, only the neutralization number of the new oil, the residual content (sulfated ash content) and the elements in the oil were measured, and NOx degradation tests (after 24 hours, 72 hours and 144 hours) were conducted. The results of Examples 1 to 3 and Comparative Examples 1 to 8 are shown in Tables 1 and 2. For Examples 2, 4 to 6 and Comparative Examples 7, 9 to 10, the measurement results of the neutralization number, residual content (sulfated ash content), and elements in the oil of the new oil, as well as the results of the NOx degradation test, are shown in Table 3. Note that Example 2 and Comparative Example 7 listed in Table 3 are the same as Example 2 listed in Table 1 and Comparative Example 7 listed in Table 2, respectively.

[0115] 1.Kinematic viscosity The kinematic viscosity and density of the gas engine lubricating oil compositions were measured at 40°C and 100°C using a capillary viscometer in accordance with JIS K2283 (2000), and the viscosity index was calculated.

[0116] 2.Neutralization value 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.

[0117] 3.Residual content (sulfated ash content, residual carbon content) In accordance with JIS K2272 (1998), the gas engine lubricating oil composition was precisely weighed in a porcelain crucible, sulfuric acid was added to the burned carbonaceous material, and the residual ash content was measured as sulfated ash by heating to a constant weight. In accordance with JIS K2270-1 (2009), the lubricating oil composition for gas engines was precisely weighed in a porcelain crucible, burned to form a carbonaceous substance, and then repeatedly heated in an electric furnace until the carbonaceous substance disappeared. The mass of the residue measured at room temperature was determined as the residual carbon content.

[0118] 4.Elements in oil The amounts of elements (ppm by mass) in the oil of the lubricating oil composition for gas engines were measured by ICP emission spectroscopy in accordance with JPI-5S-38-92. The amount of an element means the mass of the element to be measured relative to the total mass of the lubricating oil composition for gas engines.

[0119] 5.ISOT Test The oxidation stability of gas engine lubricating oil compositions was tested in accordance with JIS K2514-1 (2013). Copper and steel catalysts were added to 250 mL of each gas engine oil composition, and the test was carried out at 165.5°C, 1300 rpm (revolutions per minute, hereinafter the same) for 72 hours. After the test, the base number (hydrochloric acid method) of the gas engine oil composition was measured in accordance with JIS K2501 (2003).

[0120] 6.NOx degradation test Copper and steel catalysts were added to 40 mL of each gas engine lubricating oil composition, and a mixture of nitrogen gas containing 0.8% by volume of NO gas at 50 mL / min and humidified air at 150 mL / min was blown into the test oil at 140°C. 2 mL of measurement samples were taken every 24 hours, and the test was continued for up to 144 hours.

[0121] 7. Anti-emulsification test A 72-hour oxidation stability test of a gas engine lubricating oil composition was conducted in accordance with JIS K2514-1 (2013). After the test, the deteriorated oil and new oil were each transferred to a 50 mL glass container, and steam was blown into each container at a rate of 5.0 g / min for 1 minute. The amount of highly viscous sludge (mL) remaining after 72 hours was measured.

[0122] 8. Shell 4-ball wear test Using the gas engine lubricating oil composition (new oil), a Shell 4-ball wear resistance test was conducted 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 (μm) on the steel ball after the test was measured.

[0123] 9.Metal Corrosion Test Using 50 g of oil from a 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, and lead as a catalyst, and the amount of lead and copper components eluted from the oil was measured using ICP atomic emission spectroscopy in accordance with JPI-5S-38-92. The amounts of eluted copper and eluted lead refer to the mass ppm of lead atoms or copper atoms relative to the total mass of the lubricating oil composition for gas engines after the test.

[0124] 10.Hot tube test The high-temperature detergency of gas engine oil compositions was evaluated in accordance with JPI-5S-55-99. A glass test tube was placed in a heating furnace set at 300°C, and 5 mL of test oil was dispensed from the bottom of the tube using a syringe at a flow rate of 0.31 mL / min. After 16 hours, the color of the test tube was evaluated using a rating system.

[0125] (Evaluation criteria) In the present disclosure, low ash content, long drain property, heat resistance, wear properties, metal corrosion resistance, and demulsibility were evaluated according to the following criteria.

[0126] =Low ash= Gas engine lubricating oil compositions for which the measured value obtained in "3. Sulfated ash content" was "0.45 mass % or less" were evaluated as having a low ash content.

[0127] =Long drainage= 6. A lubricating oil composition for gas engines having a base number retention rate (base number retention rate) of 20% or more obtained from the test results obtained in a NOx deterioration test relative to the base number of new oil was evaluated as having excellent long drain properties.

[0128] =Heat resistance= A lubricating oil composition for gas engines that received a rating of 3 to 10 in the test results obtained in "10. Hot tube test" was evaluated as having excellent heat resistance.

[0129] =Wear characteristics= In the test results of "8. Shell 4-ball wear test," lubricating oil compositions for gas engines that have a wear scar diameter of 500 μm or less were evaluated as having excellent wear properties.

[0130] =Metal corrosion resistance= In the test results of "9. Metal Corrosion Test," gas engine lubricating oil compositions having an amount of copper elution of 170 mass ppm or less and an amount of lead elution of 100 mass ppm or less were evaluated as having excellent metal corrosion resistance.

[0131] =Demulsifying property= In the test results for new oil and aged oil (oil after 72 hours of ISOT) obtained in "7. Anti-emulsification test," gas engine lubricating oil compositions with a high-viscosity sludge amount of 10 mL or less were evaluated as having excellent anti-emulsification properties. The high-viscosity sludge amount is shown as "Sludge amount" in Tables 1 and 2.

[0132] [Table 1]

[0133] [Table 2]

[0134] [Table 3]

[0135] Details of the abbreviations in Tables 1, 2 and 3 are given below.

[0136] (base oil) Base oil (Gr III): A mineral oil-based refined base oil that belongs to API Group III and has been hydrotreated through an advanced hydrogenation process, and has the following general properties: Kinematic viscosity (100℃): 7.6mm 2 / s, viscosity index: 130, flash point: 240℃ or higher

[0137] (Metallic detergents) Calcium-based detergent: A calcium salicylate-based metal detergent with a base number of 228 mg KOH / g measured according to JIS K2501 (2003) and a density of 1.05 g / cm 3 (15°C), kinematic viscosity at 100°C of 81 cSt, flash point of 194°C, and calcium content of 7.9%.

[0138] (dispersant) Boron-based dispersant 1: A succinimide-based dispersant with a density of 0.94 g / cm 3 (15°C), kinematic viscosity at 100°C of 512 cSt, boron content of 0.95%, nitrogen content of 1.7%, base number of 33 mg KOH / g, and weight average molecular weight of 5,500 g / mol. Boron-based dispersant 2: A succinimide-based dispersant with a density of 0.93 g / cm 3 (15°C), kinematic viscosity at 100°C of 140 cSt, boron content of 0.52%, nitrogen content of 1.5%, base number of 32 mg KOH / g, and weight average molecular weight of 4400 g / mol as measured by gel permeation chromatography in polystyrene equivalent. Ashless dispersant (boron-free ashless dispersant): Density 0.92 g / cm 3 (15°C), kinematic viscosity at 100°C of 404 cSt, nitrogen content of 1.8%, base number of 41 mg KOH / g, and weight average molecular weight of 4,910.

[0139] (antioxidant) Phenolic antioxidants The phenolic antioxidant is a hindered phenolic antioxidant that prevents oxidative deterioration of base oils by converting it to a quinoid structure, and has a density of 0.97 g / cm 3It is a phenolic compound (octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate) classified under CAS No. 125643-61-0, with a flammability temperature of 20°C, a flash point of 152°C, and a boiling point of 240°C.

[0140] Amine antioxidants The amine antioxidants are aromatic amine compounds having a conjugated amine structure with a phenylamine main skeleton having a pKa of 0.1 or more and 2 or less (amine antioxidant 1), aromatic amine compounds having a naphthalene skeleton having a pKa of more than 2 and 8 or less (amine antioxidant 2), and amine compounds having a pKa of 7 or more and 12 or less (amine antioxidants 3 to 5).

[0141] Amine antioxidant 1; density 0.97g / cm 3 (20°C), kinematic viscosity at 40°C of 401 cSt, flash point of 154°C, and basic nitrogen of 4.5%. An aromatic amine compound classified under CAS No. 68411-46-1 (aromatic amine antioxidant A, the compound represented by formula (1)) Amine antioxidant 2: an aromatic amine compound classified as CAS No. 68259-36-9. (Aromatic amine antioxidant B is a compound represented by formula (2)) Amine antioxidant 3: an aliphatic amine compound classified as CAS No. 106-20-7. (Amine antioxidant C is a compound represented by formula (3B)) Amine antioxidant 4: an amine compound classified as CAS No. 103-49-1 (a compound represented by formula (1) which is an amine antioxidant C) Amine antioxidant 5; flash point 184°C, density 0.90g / cm 3 (20°C), a kinematic viscosity at 40°C of 13.2 cSt, and a melting point of 7°C. A hindered amine compound having a 2,2,6,6-tetramethylpiperidine structure (a compound represented by formula (3A), which is an amine antioxidant C).

[0142] (anti-wear agent) Zinc dialkyldithiophosphate is a zinc compound having primary and secondary alkyl groups with 3 to 5 carbon atoms, and 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%.

[0143] (Viscosity index improver) Viscosity index improver: a copolymer of polyalkyl methacrylate and olefin copolymer diluted with mineral oil, having a density of 0.885 g / cm 3 (15℃), 100℃ kinematic viscosity 1750mm 2 It is a dispersant-type viscosity index improver with a weight average molecular weight of 140,000 g / mol.

[0144] (Other additives) Other additives used were the pour point depressant, corrosion inhibitor and antifoaming agent shown below. Pour point depressant: a pour point depressant which is a polymethacrylate dissolved in mineral oil and has a molecular weight of 65,000 g / mol. · Corrosion inhibitor: Corrosion inhibitor which is alkyldimethylamine. · Defoamer: A silicone-based defoamer that is polydimethylsilicone.

[0145] As shown in Tables 1 and 2, the lubricating oil compositions of the Examples had lower ash content and were excellent in long drain properties, wear characteristics, heat resistance, metal corrosion resistance, and demulsification properties compared to the lubricating oil compositions for gas engines of the Comparative Examples.

[0146] Compared with Comparative Examples 4 to 8, which contain a high content of calcium-based detergent, Examples 1 to 3 have significantly lower sulfated ash contents, and it is clear that, despite their low ash content, they are good in all aspects of long drain properties, wear characteristics, heat resistance, metal corrosion resistance, and demulsification properties.

[0147] In Comparative Example 1, the sulfated ash content was sufficiently low at 0.16 mass%, but the nitrogen element content was 1300 mass ppm and the zinc element content was 90 mass ppm, and the residual base number after the NOx degradation test and the heat resistance in the hot tube test were insufficient.In Comparative Example 2, the nitrogen element content was 1600 mass ppm and the heat resistance was insufficient. Comparative Example 3 had a zinc content of 100 ppm, and was poor in long drain properties and wear properties. Comparative Example 4 did not achieve low ash content and had a boron content of 70 ppm, and was poor in wear properties. None of Comparative Examples 4 to 10 achieved a low ash content.

[0148] All of the examples in which the amount of zinc element was 150 ppm by mass or more were excellent in wear properties, and it is clear that a zinc element amount of 150 ppm by mass or more is also suitable from the standpoint of wear properties.

[0149] As shown in Table 3, Examples 4 to 6, in which amine-based antioxidants 3 to 5 (amine-based antioxidant C) having acid dissociation constants of 8 or more were added, respectively, showed a higher base number from the early stage (after 24 hours) of the NOx degradation test than Example 2, which did not contain amine-based antioxidant C. This result shows that, from the viewpoint of further extending the life, it is also preferable to further add an amine-based antioxidant having a pKa of 8 or more (an antioxidant equivalent to amine-based antioxidant C). Furthermore, from the viewpoint of low ash content, it is expected that simply reducing the content of calcium-based detergent will directly lead to a decrease in the residual base number and a shortened service life of the lubricating oil composition itself. However, it can be seen that in Examples 2 and 4 to 6, the residual base number was maintained at a retention rate similar to that of Comparative Example 9, which contains a sufficiently high content of calcium-based detergent (i.e., calcium element amount of 1,300 ppm by mass), even 144 hours after the NOx deterioration test.

[0150] From the above, it can be seen that the lubricating oil composition for gas engines of this Example can provide a lubricating oil composition for gas engines that has low ash content, excellent life characteristics (long drain properties) and heat resistance, and also has an excellent balance of properties such as wear characteristics, metal corrosion resistance, and demulsification properties.

Claims

1. A base oil, A metal-based detergent; a dispersant comprising a boron-based dispersant and a boron-free ashless dispersant; a phenolic antioxidant, an amine-based antioxidant comprising an aromatic amine-based antioxidant A having an acid dissociation constant (pKa) of 0.1 or more and 2 or less, and an aromatic amine-based antioxidant B having an acid dissociation constant (pKa) of more than 2 and 8 or less; and an anti-wear agent, the content of metal elements derived from the metallic detergent is 300 ppm by mass or more and 1000 ppm by mass or less based on the total amount of the lubricating oil composition; The boron element content is 80 ppm by mass or more and 470 ppm by mass or less based on the total amount of the lubricating oil composition, The nitrogen element content is 1800 ppm by mass or more and 2900 ppm by mass or less based on the total amount of the lubricating oil composition, The zinc element content is 150 ppm by mass or more and 1500 ppm by mass or less based on the total amount of the lubricating oil composition, The sulfated ash content according to JIS K2272 (1998) is 0.45 mass% or less based on the total amount of the lubricating oil composition. A lubricating oil composition for gas engines.

2. 2. The gas engine lubricating oil composition of claim 1, wherein the metallic detergent comprises an alkaline earth metal detergent.

3. 3. The lubricating oil composition for gas engines according to claim 2, wherein the metallic detergent comprises at least one selected from the group consisting of calcium salicylate, calcium phenate, calcium sulfonate, magnesium salicylate, and magnesium sulfonate.

4. 2. The gas engine lubricating oil composition of claim 1, wherein the boron-based dispersant comprises a boron-containing imide-based dispersant.

5. 2. The lubricating oil composition for gas engines according to claim 1, wherein the total content of the dispersants is 6 mass % or more based on the total amount of the lubricating oil composition.

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

7. 2. The lubricating oil composition for gas engines according to claim 1, wherein the aromatic amine-based antioxidant B is an aromatic amine-based antioxidant having an acid dissociation constant (pKa) of more than 2 and not more than 7.

8. 2. The lubricating oil composition for gas engines according to claim 1, wherein the amine-based antioxidant further comprises an amine-based antioxidant C having an acid dissociation constant (pKa) of 7 or more and 12 or less.

9. 2. The lubricating oil composition for gas engines according to claim 1, wherein the antiwear agent comprises one or more selected from zinc dialkyldithiophosphates having two identical or different alkyl groups selected from primary or secondary alkyl groups having 4 to 12 carbon atoms.

10. The gas engine lubricating oil composition according to any one of claims 1 to 9, which is for use in a hydrogen engine or a dual-fuel engine for a ship.

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