Lubricating oil composition

Abstract

The present invention provides a lubricating oil composition comprising, based on the total weight of the lubricating oil composition, at least 80% by mass of base oil, wherein the base oil is selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof; one or more additives other than citric acid, selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants; and one or more of citric acid and its derivatives. This invention also provides the use of an additive selected from one or more citric acid and its derivatives in a lubricating oil composition comprising at least 80% by weight of a base oil, based on the total weight of the lubricating oil composition, wherein the base oil is selected from at least 80% by mass of a base oil selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof, as measured by ASTM D3427, in order to improve the air-releasing properties of the lubricating oil composition, and one or more additives other than citric acid, selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants.

Description

Technical Field

[0001] The present invention relates to industrial lubricant compositions and to the improvement of air release in industrial lubricant compositions.

Background Art

[0002] Lubricant compositions are used to protect and lubricate contacting surfaces and can also be used to transmit power. Lubricant compositions are required in all industrial equipment having moving parts. Thus, industrial lubricant compositions include hydraulic oils, gear oils, compressor oils, circulating oils, and turbine oils, among others. Such industrial lubricant compositions generally include one or more base oils and one or more additives. Typically, the additive treatment rate of industrial lubricant compositions is considerably lower than that of engine oil compositions, with an additive treatment rate of less than 10 wt% being common and an additive treatment rate of less than 5 wt% being usually preferred.

[0003] Air entrainment is known to be able to reduce the effectiveness of lubricant compositions, and particularly those used as industrial lubricant compositions. Air entrainment is the phenomenon in which air bubbles (typically having a diameter of less than 1 mm) are dispersed throughout the lubricant. Entrained air can be distinguished from free air (pockets of air trapped in part of the system), dissolved air (lubricants can contain 6 - 12 volume percent dissolved air), and foam (bubbles that collect on the surface of the oil, typically having a diameter greater than 1 mm). Air entrainment can have several negative consequences, including loss of lubricity, the potential for oxidation of the lubricant composition, noisy operation, lower efficiency, and higher oil temperatures.

[0004] Particularly relevant are industrial lubricant compositions used in hydraulic systems. Current trends in the design of hydraulic systems are towards smaller reservoirs, shorter oil residence times, and higher outputs. These changes have led to an increase in the problem of air entrainment.

[0005] The air entrainment properties of a lubricating oil are typically measured using the ASTM D3427 air release test. This test measures the time required for the volume of air entrained in the oil to decrease to 0.2% under test conditions and at a specific temperature.

[0006] International Publication No. 2017 / 089354 describes a method for improving air release, comprising mixing an alkyl acrylate additive into a lubricating oil using a high-shear mixer. International Publication No. 2017 / 089357 teaches an improvement in air release properties in a lubricating oil suitable for use as a hydraulic fluid, wherein at least 70% by mass of the base oil is GTL.

[0007] Citric acid is known to be a deemulsifier / demetallizer for crude oil; see, for example, U.S. Patent No. 4,439,345 and European Patent No. 0612,548. [Overview of the Initiative]

[0008] The inventors have attempted to improve the air-entraining properties of lubricating oil compositions, particularly those used in hydraulic systems. The present invention provides a lubricating oil composition comprising, based on the total weight of the lubricating oil composition, at least 80% by mass of base oil, wherein the base oil is selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof; one or more additives other than citric acid, selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants; and one or more of citric acid and its derivatives.

[0009] The present invention also provides the use of an additive selected from one or more citric acid and its derivatives in a lubricating oil composition comprising at least 80% by weight of a base oil, based on the total weight of the lubricating oil composition, wherein the base oil is selected from at least 80% by mass of a base oil selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof, as measured by ASTM D3427, in order to improve the air-releasing properties of the lubricating oil composition, and one or more additives other than citric acid, selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants. [Modes for carrying out the invention]

[0010] One or more specific embodiments of the present disclosure are described below. These embodiments described are examples of compositions and methods of the present disclosure. Furthermore, in order to provide a concise description of these embodiments, not all features of actual implementations may be described herein.

[0011] When describing elements of the various embodiments of this disclosure, the articles “a,” “an,” and “the” are intended to indicate that one or more of the elements exist. The terms “equip,” “include,” and “have” are intended to be inclusive and mean that additional elements other than those listed may exist. In addition, it should be understood that any reference in this disclosure to “one embodiment” or “embodiment” is not intended to be construed as excluding the existence of additional embodiments that also incorporate the listed features.

[0012] The inventors have found that the addition of one or more citric acid and its derivatives to a lubricating oil composition containing at least 80% by weight of base oil, based on the total weight of the lubricating oil composition, provides an unexpected improvement in the air-releasing properties of the lubricating oil composition. The base oil is selected from at least 80% by mass of base oil selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof, in order to improve the air-releasing properties of the lubricating oil composition as measured by ASTM D3427, and one or more additives selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants.

[0013] The lubricating oil composition is preferably an industrial lubricating oil composition. Examples of industrial lubricating oil compositions include, but are not limited to, those used as hydraulic oil, gear oil, compressor oil, circulating oil, and turbine oil. In preferred embodiments of the present invention, the lubricating oil is formulated for use in a hydraulic fluid. Hydraulic fluids are used in many different types of hydraulic machinery, not only to lubricate the machinery but also to transmit pressure. Air entrainment can be a significant problem in hydraulic systems, causing spongy or unstable hydraulic operation.

[0014] The lubricating oil composition according to the present invention comprises at least one base oil, at least one additive, and citric acid or a derivative thereof. Industrial lubricant compositions contain less additives compared to, for example, engine oil. Therefore, a lubricant composition contains at least 80% by weight of base oil. Preferably, a lubricant composition contains at least 85% by weight, more preferably at least 90% by weight of base oil, based on the total weight of the lubricant composition. Preferably, a lubricant composition contains 99.5% by weight or less of base oil, based on the total weight of the lubricant composition.

[0015] The base oil used in the present invention is preferably a Group I or Group III base oil containing Fischer-Tropsch derivatives, according to the API base oil categories. Preferably, the base oil contains one or more Fischer-Tropsch derivatives. Fischer-Tropsch derivatives are synthesized, for example, by converting natural gas or biomass into liquid fuels. Compared to mineral oil base oils refined from crude oil, these have very low sulfur and aromatic content and a very high paraffin content.

[0016] The kinematic viscosity of the Fischer-Tropsch derivative base oil at 100°C is preferably 2 to 20 mm². 2 / s, more preferably 3-15mm 2 / s, most preferably 3-10mm 2 The viscosity is expressed as / s. Viscosity is preferably measured using ASTM D445.

[0017] Preferably, the total amount of additives in the industrial lubricant composition is less than 20% by weight, more preferably less than 10% by weight, and even more preferably less than 5% by weight, based on the total weight of the industrial lubricant composition. Preferably, the total amount of additives in the industrial lubricant composition is at least 0.5% by weight, based on the total weight of the industrial lubricant composition. Additives may be incorporated into the industrial lubricant composition alone or as part of one or more additive packages. Whether added alone or in an additive package, diluent oil may be included with the additive and form part of the finished lubricant composition.

[0018] The lubricating oil composition contains one or more additives selected from the group consisting of wear-resistant additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants, in addition to citric acid. Such additives are known in many types of lubricant compositions. The typical total amount of these one or more additives is in the range of 0.001% to 10.0% by weight, based on the total weight of the lubricating oil composition.

[0019] Suitable wear-resistant additives may be selected from zinc salts such as zinc dialkyldithiophosphate or zinc diaryldithiophosphate, borates, substituted thiadiazoles, high molecular weight nitrogen / phosphorus compounds produced by reacting, for example, dialkoxyamines with substituted organophosphate esters, phosphate amines, sulfurized oils, sulfurized lards, sulfurized esters, sulfurized fatty acid esters, and similar sulfurized materials, organophosphate esters, and triphenylphosphorothionates of natural or synthetic origin.

[0020] Examples of rust inhibitors and corrosion inhibitors include zinc dithiophosphate, metal phenolates, calcium or magnesium sulfonates, and amines. The dispersant additive may be a reaction product of polyisobutenyl succinic anhydride and an amine or ester.

[0021] Extreme pressure additives are typically selected from sulfur-based additives, such as DMTD derivatives, sulfurized olefins, sulfurized oils or dithiocarbamates, and molybdenum-based additives, such as dithiocarbamates or dithiophosphates.

[0022] The friction modifier is typically selected from organic molybdenum compounds, such as molybdenum dithiocarbamate and molybdenum dithiophosphate, or from ashless esters or amides, such as oleylamide or glycerol monooleate.

[0023] Examples of viscosity index improvers include, but are not limited to, olefin polymers such as polyisobutylene, methacrylate, diene, and alkylated styrene. Examples of pour point depressants include alkylated naphthene products, polymethacrylates, and phenolic polymers.

[0024] The antioxidant can be a so-called hindered phenol-based or amine-based antioxidant, for example, naphthol, sterically hindered monohydric, dihydric, and trihydric phenols, sterically hindered dinuclear, trinuclear, and polynuclear phenols, alkylated or styrenated diphenylamine or hindered phenols derived from ionol.

[0025] Preferably, the lubricating oil composition does not contain any additives classified as demulsifiers or antifoaming agents other than citric acid. More preferably, the lubricating oil composition does not contain a demulsifier selected from the list consisting of polyalkylene derivatives of alkylphenols, fatty alcohols, fatty acids, fatty amines, fatty amides, and / or polyols (including crosslinked polyols). Also more preferably, the lubricating oil composition does not contain an antifoaming agent selected from the list consisting of polydimethylsiloxane, organomodified siloxanes, polyacrylates, and / or nonionic / anionic surfactants.

[0026] The lubricating oil composition contains one or more of citric acid and its derivatives. Citric acid has the chemical formula HOC(CO2H)(CH2CO2H)2 and may also be known by the IUPAC name of 2-hydroxypropane-1,2,3-tricarboxylic acid. The derivatives of citric acid are preferably citrate salts, including salts and esters of citric acid. Such salts and esters can include mono-, di-, and tri-esters and / or salts of tricarboxylic acids and mixtures thereof. A mixture of citric acid and its derivatives may be present in the finished lubricating oil composition. However, the preferred additive is citric acid. This is typically available in solid form but can be more suitably used in a diluted form in a non-aqueous carrier fluid. Typically, such a diluted form contains citric acid in the range of 40 to 60% by weight.

[0027] Preferably, citric acid and / or its derivatives are present in or added to the lubricating oil composition in an amount in the range of 0.005% to 0.1% by weight, preferably in the range of 0.02% to 0.08% by weight, based on the total weight of the lubricating oil composition.

[0028] The kinematic viscosity (KV40) of the lubricating oil composition at 40°C is preferably 20 to 75 mm². 2 The range of / s, more preferably 30 to 75 mm 2 The range of / s, most preferably 40-75 mm 2 It is within the range of / s.

[0029] The present invention also provides the use of an additive selected from one or more citric acid and its derivatives in a lubricating oil composition comprising at least 80% by weight of a base oil, based on the total weight of the lubricating oil composition, wherein the base oil is selected from at least 80% by mass of a base oil, selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof, as measured by ASTM D3427, in order to improve the air-releasing properties of the lubricating oil composition, and one or more additives other than citric acid, selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants.

[0030] ASTM D3247 is a standard test method for the air release characteristics of hydrocarbon oils. It measures the time it takes for air entrained in the oil to be released and for the oil's density to return to 99.8% of its initial density.

[0031] The air release characteristics are improved compared to those achieved using a lubricating oil composition that does not contain one or more of citric acid and its derivatives. Preferably, the air release characteristics are improved without degrading foaming performance when measured by ASTM D892. Also preferably, the air release characteristics are improved without degrading demulsification performance when measured by ASTM D1401. Most preferably, the air release characteristics are improved without degrading foaming performance when measured by ASTM 892 and without degrading demulsification performance as measured by ASTM D1401.

[0032] The present invention will be further described here by reference to the following non-limiting embodiments. [Examples]

[0033] Several hydraulic oil compositions shown in Table 1 were blended according to a standard procedure. The base oil used was a Fischer-Tropsch derivative group III base oil. The additive package was a standard hydraulic oil additive package containing detergents, anti-wear agents, antioxidants, and corrosion inhibitors, but without deemulsifiers or citric acid. Acrylic copolymer additives were supplied at a concentration of 1-2% active content. Citric acid additives were supplied in liquid form at a concentration of 40-60% active content.

[0034] [Table 1]

[0035] Table 1 All examples were tested for demulsification and air release characteristics as shown in Table 2.

[0036] [Table 2]

[0037] As can be seen from the data reported in Table 2, the addition of citric acid-containing additives increased the rate of air release from the tested hydraulic oil formulations and did not significantly affect the foaming or deemulsification performance of the hydraulic oil. In some cases, foaming performance was slightly improved.

[0038] When measured at 50°C according to ASTM D3427, the time required to release air from the tested hydraulic fluid decreases with the addition of a citric acid additive. Hydraulic oils with 25 ppm and 100 ppm citric acid additives can release air in 1.7 minutes and 1.4 minutes, respectively, which is faster than Comparative Example 1 (hydraulic oil with deemulsifier) ​​and Comparative Example 2 (hydraulic oil with acrylic copolymer).

Claims

1. A lubricating oil composition comprising, based on the total weight of the lubricating oil composition, at least 80% by mass of base oil, wherein the base oil comprises at least 80% by mass of base oil selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof, one or more additives other than citric acid selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants, and one or more of citric acid and its derivatives.

2. The lubricating oil composition according to claim 1, wherein the lubricating oil composition is formulated for use in a hydraulic fluid.

3. The lubricating oil composition according to claim 1 or 2, wherein the lubricating oil composition comprises at least 85% by weight, more preferably at least 90% by weight, and 99.5% by weight or less of base oil, based on the total weight of the lubricating oil composition.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the base oil comprises at least one Fischer-Tropsch derivative base oil.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein one or more additives selected from the group consisting of wear-resistant additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants, other than citric acid, are present in the lubricating oil composition in an amount ranging from 0.001% by weight to 10.0% by weight, based on the total weight of the lubricating oil composition.

6. The lubricating oil composition according to any one of claims 1 to 5, wherein one or more citric acid and its derivatives are present in the lubricating oil composition in an amount ranging from 0.005% by weight to 0.1% by weight relative to the total weight of the lubricating oil, or are added to the lubricating oil composition.

7. The lubricating oil composition is 20 to 75 mm at 40°C. ２ The range of / s, more preferably 30 to 75 mm ２ The range of / s is most preferably 40 to 75 mm ２ A lubricating oil composition according to any one of claims 1 to 6, having a kinematic viscosity in the range of / s.

8. The use of an additive selected from one or more citric acid and its derivatives in a lubricating oil composition comprising at least 80% by weight of a base oil based on the total weight of the lubricating oil composition, wherein, when the base oil is measured by ASTM D3427, the use of at least 80% by mass of a base oil selected from Group II, Group III, and Fischer-Tropsch derivative base oils and mixtures thereof, and one or more additives other than citric acid selected from the group consisting of anti-wear additives, rust inhibitors and corrosion inhibitors, dispersants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and antioxidants, in order to improve the air release characteristics of the lubricating oil composition.

9. The use according to claim 8, wherein the air release characteristics are improved without degrading the foaming performance when measured by ASTM D892.

10. The use according to claim 8 or 9, wherein the air release characteristics are improved without degrading the demulsification performance when measured by ASTM D1401.

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