Lubricating oil composition

Abstract

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

Description

Technical Field

[0001] This invention relates to industrial lubricating oil compositions and improvements in air release from industrial lubricating oil compositions. Background Technology

[0002] Lubricating oil compositions are used to protect and lubricate contacting surfaces and can also be used to transmit power. Lubricating oil compositions are required in all industrial equipment with moving parts. Therefore, industrial lubricating oil compositions include hydraulic oils, gear oils, compressor oils, circulating oils, and turbine oils, etc. Such industrial lubricating oil compositions typically contain one or more base oils and one or more additives. Generally, the additive treatment rate of industrial lubricating oil compositions is significantly lower than that of engine oil compositions, where an additive treatment rate of less than 10% by weight is conventional, and less than 5% by weight is generally preferred.

[0003] Air entrainment is known to reduce the effectiveness of lubricating oil compositions, particularly those used in industrial applications. Air entrainment is the phenomenon where air bubbles (typically less than 1 mm in diameter) are dispersed throughout the lubricating oil. Entrained air can be distinguished from free air (cavitation trapped in a portion of the system), dissolved air (lubricating oils may contain between 6% and 12% dissolved air by volume), and foam (bubbles typically larger than 1 mm in diameter that aggregate on the surface of the oil). Air entrainment can have numerous negative consequences, including loss of lubricity, potential oxidation of the lubricating oil composition, increased operating noise, lower efficiency, and higher oil temperatures.

[0004] Of particular relevance are industrial lubricant compositions used in hydraulic systems. Current trends in hydraulic system design are toward smaller reservoirs, lower oil residence times, and higher power output. These changes have led to an increase in air entrainment problems.

[0005] The air entrainment properties of lubricating oils 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 specified temperature.

[0006] WO2017089354 describes a method comprising incorporating an alkyl acrylate additive into a lubricating oil using a high-shear mixer to improve air release. WO2017089357 teaches the improvement of 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 demulsifier / demetallizer for crude oil, see, for example, US4439345 and EP0612548.

[0008] The inventors have attempted to improve the air entrainment properties of lubricating oil compositions (particularly those used in hydraulic systems). Summary of the Invention

[0009] The present invention provides 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 Group II base oils, Group III base oils and Fischer-Tropsch derived base oils and mixtures thereof; one or more additives other than citric acid, wherein the one or more additives are 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.

[0010] The present invention also provides the use of additives selected from one or more of citric acid and its derivatives in a lubricating oil composition for improving the air release properties of said lubricating oil composition, as measured by ASTM D3427, wherein the lubricating oil composition comprises 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 Group II base oils, Group III base oils and Fischer-Tropsch-derived base oils and mixtures thereof; and one or more additives other than citric acid, said one or more additives being 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. Detailed Implementation

[0011] One or more specific embodiments of this disclosure will now be described. These described embodiments are examples of the compositions and methods currently disclosed. Additionally, for the purpose of providing a concise description of these embodiments, not all features of the actual embodiments can be described in the specification.

[0012] When describing elements of various embodiments of this disclosure, the articles “a,” “an,” and “the” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements besides those listed may also be present. Furthermore, it should be understood that references to “an embodiment” or “an embodiment” of this disclosure are not intended to be construed as excluding the existence of additional embodiments that also incorporate the described features.

[0013] The inventors have discovered that adding one or more of citric acid and its derivatives to a lubricating oil composition provides unexpected improvements in the air release properties of the lubricating oil composition comprising at least 80% by weight of base oil based on the total weight of the lubricating oil composition, wherein the base oil is selected from Group II base oils, Group III base oils and Fischer-Tropsch derived base oils and mixtures thereof; 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.

[0014] The lubricating oil composition is preferably an industrial lubricating oil composition. Industrial lubricating oil compositions include, but are not limited to, those used as hydraulic oils, gear oils, compressor oils, circulating oils, and turbine oils. In a preferred embodiment of the invention, the lubricating oil is formulated for use with a hydraulic fluid. Hydraulic fluids are used in many different types of hydraulic machinery and are used not only for lubricating machinery but also for transmitting pressure. Air entrainment can be a significant problem in hydraulic systems, causing the hydraulic device to operate loosely or unstably.

[0015] The lubricating oil composition according to the present invention comprises at least one base oil and at least one additive, as well as citric acid or a derivative thereof.

[0016] Industrial lubricating oil compositions contain a lower amount of additives compared to, for example, engine oils. Therefore, the lubricating oil composition comprises at least 80% by weight of base oil. Preferably, the lubricating oil composition comprises at least 85% by weight, more preferably at least 90% by weight, of base oil based on the total weight of the lubricating oil composition. Suitably, the lubricating oil composition comprises no more than 99.5% by weight of base oil based on the total weight of the lubricating oil composition.

[0017] According to the API base oil category, the base oil used in this invention is preferably Group II or Group III, including Fischer-Tropsch derived base oils. Preferably, the base oil includes at least one Fischer-Tropsch derived base oil. Fischer-Tropsch derived base oils are synthesized by, for example, converting natural gas or biomass into liquid fuels. They have very low sulfur and aromatic content compared to mineral oil base oils refined from crude oil, and have a very high alkane content.

[0018] The kinematic viscosity of Fischer-Tropsch derived base oils at 100°C is preferably 2 mm. 2 / s to 20mm 2 / s, more preferably 3mm 2 / s to 15mm 2 / s, and most preferably 3mm 2 / s to 10mm 2 / s. Measure viscosity appropriately using ASTM D445.

[0019] Preferably, based on the total weight of the lubricating oil composition, the total amount of additives in the lubricating oil composition is less than 20% by weight, more preferably less than 10% by weight, and even more preferably less than 5% by weight. Suitably, based on the total weight of the lubricating oil composition, the total amount of additives in the lubricating oil composition is at least 0.5% by weight. Additives may be incorporated into the lubricating oil composition alone or as part of one or more additive packages. Whether added alone or in the form of an additive package, diluent oil may be included together with the additives and form part of the finished lubricating oil composition.

[0020] The lubricating oil composition contains 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. Such additives are known in many types of lubricant compositions. The typical total amount of these one or more additives ranges from 0.001% by weight to 10.0% by weight based on the total weight of the lubricating oil composition.

[0021] Suitable anti-wear additives can be selected from zinc salts such as dialkyl or diaryl dithiophosphate zinc, borates, substituted thiadiazoles, such as polymeric nitrogen / phosphorus compounds prepared by reacting dialkoxyamines with substituted organophosphates, phosphate amines, sulfurized oils of natural or synthetic origin, sulfurized lards, sulfurized esters, sulfurized fatty acid esters and similar sulfurized materials, organophosphates, and triphenyl thiophosphates.

[0022] Rust inhibitors and corrosion suppressants include zinc dithiophosphate, metal phenolates, calcium sulfonates or magnesium sulfonates, and amines.

[0023] Dispersant additives can be reaction products of polyisobutylene succinic anhydride with amines or esters.

[0024] Extreme pressure additives are typically selected from sulfur-based additives, such as DMTD derivatives, sulfurized olefins, sulfurized fats and oils or dithiocarbamates, and molybdenum-based additives, such as dithiocarbamates or dithiophosphates.

[0025] Friction modifiers are typically selected from organic molybdenum compounds, such as molybdenum dithiocarbamate and molybdenum dithiophosphate, or from ashless esters or amides, such as oleamide or glyceryl monooleate.

[0026] Viscosity index improvers include, but are not limited to, olefin polymers such as polyisobutylene, methacrylates, dienes, and alkylated styrene.

[0027] Pour point depressants include alkylated cycloalkanes, polymethacrylates, and phenolic polymers.

[0028] Antioxidant additives can be so-called hindered phenolic or amine antioxidants, such as naphthol, hindered monohydric phenols, dihydric and trihydric phenols, hindered dinucleotides, trinucleotides and polynucleotides, alkylated or stylated diphenylamines, or hindered phenols derived from ionol.

[0029] Preferably, the lubricating oil composition is free of any additives classified as demulsifiers or foam inhibitors, except for citric acid. More preferably, the lubricating oil composition is free of demulsifiers selected from the list of polyalkylene derivatives of alkylphenols, fatty alcohols, fatty acids, fatty amines, fatty amides, and / or polyols (including crosslinked polyols). Even more preferably, the lubricating oil composition is free of foam inhibitors selected from the list of polydimethylsiloxanes, organically modified siloxanes, polyacrylates, and / or nonionic / anionic surfactants.

[0030] 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 is also known by the IUPAC name for 2-hydroxypropane-1,2,3-tricarboxylic acid. Derivatives of citric acid are preferably citrates, including salts and esters of citric acid. Such salts and esters may include monoesters, diesters, and triesters of tricarboxylic acids and / or salts thereof, as well as mixtures thereof. Mixtures of citric acid and its derivatives may be present in the finished lubricating oil composition. However, citric acid is a preferred additive. This is generally available in solid form but is more suitably used in diluted form in non-aqueous carrier fluids. Typically, such diluted forms contain citric acid in the range of 40% to 60% by weight.

[0031] Preferably, citric acid and / or its derivatives are present in or added to the lubricating oil composition in an amount ranging from 0.005% to 0.1% by weight, and more preferably from 0.02% to 0.08% by weight, relative to the total weight of the lubricating oil composition.

[0032] The kinematic viscosity (KV40) of the lubricating oil composition at 40°C is preferably 20 mm. 2 / s to 75mm 2 Within the range of / s, more preferably within 30mm 2 / s to 75mm 2 Within the range of / s, the most preferred value is 40mm. 2 / s to 75mm 2 Within the range of / s.

[0033] The present invention also provides the use of additives selected from one or more of citric acid and its derivatives in a lubricating oil composition for improving the air release properties of said lubricating oil composition, as measured by ASTM D3427, wherein the lubricating oil composition comprises 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 Group II base oils, Group III base oils and Fischer-Tropsch-derived base oils and mixtures thereof; and one or more additives other than citric acid, said one or more additives being 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.

[0034] ASTM D3247 is a standard test method for the air release properties of hydrocarbon-based oils. It measures the time it takes for entrained air in an oil to be released and for the oil's density to return to 99.8% of its initial density.

[0035] The air release properties are improved compared to those achieved using lubricating oil compositions that do not contain one or more of citric acid and its derivatives. Preferably, the air release properties are improved without deterioration of foaming properties, as measured by ASTM D892. More preferably, the air release properties are improved without deterioration of demulsification properties, as measured by ASTM D1401. Most preferably, the air release properties are improved without deterioration of foaming properties, as measured by ASTM D892, and without deterioration of demulsification properties, as measured by ASTM D1401.

[0036] The invention will now be further illustrated with reference to the following non-limiting embodiments.

[0037] Example

[0038] Various hydraulic oil compositions as shown in Table 1 are blended according to standard procedures.

[0039] The base oils used are Fischer-Tropsch Group III base oils. The additive package is a standard hydraulic oil additive package containing detergents, anti-wear agents, antioxidants, corrosion inhibitors, and is free of demulsifiers or citric acid. Acrylic copolymer additives are provided at a concentration of 1%-2% active content. Citric acid additives are provided in liquid form at a concentration of 40%-60% active content.

[0040] Table 1

[0041]

[0042] *Comparative example.

[0043] The demulsification and air release properties of all embodiments were tested, as described in Table 2.

[0044] Table 2

[0045]

[0046] As can be seen from the data reported in Table 2, the addition of citric acid-containing additives increased the air release rate from the tested hydraulic fluid formulations without significantly affecting the foaming or demulsifying properties of the hydraulic fluid. In some embodiments, the foaming properties were even slightly improved.

[0047] As measured by ASTM D3427 at 50°C, the time required to release air from the tested hydraulic oil decreased with the addition of citric acid additive. Hydraulic oils with 25 ppm and 100 ppm of citric acid additive were able to release air in 1.7 minutes and 1.4 minutes, respectively, which is faster than Comparative Example 1 (hydraulic oil without demulsifier) ​​and Comparative Example 2 (hydraulic oil with acrylic copolymer).

Claims

1. 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 Group II base oils, Group III base oils and Fischer-Tropsch-derived base oils and mixtures thereof; one or more additives other than citric acid, said one or more additives being 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 claim 2, wherein the lubricating oil composition comprises at least 85% by weight, more preferably at least 90% by weight and not more than 99.5% by weight 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-derived base oil.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein the one or more additives 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, and the one or more additives are 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.

6. The lubricating oil composition according to any one of claims 1 to 5, wherein one or more of citric acid and its derivatives are present in or added to 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.

7. The lubricating oil composition according to any one of claims 1 to 6, wherein the kinematic viscosity of the lubricating oil composition at 40°C is 20 mmHg. 2 / s to 75mm 2 Within the range of / s, more preferably within 30mm 2 / s to 75mm 2 Within the range of / s, the most preferred value is 40mm. 2 / s to 75mm 2 Within the range of / s.

8. An additive selected from one or more of citric acid and its derivatives in a lubricating oil composition for the purpose of improving the air release properties of the lubricating oil composition as measured by ASTM D3427, wherein the lubricating oil composition comprises 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 Group II base oils, Group III base oils, and Fischer-Tropsch derived base oils, and mixtures thereof; and One or more additives other than citric acid, wherein the one or more additives are 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.

9. The use according to claim 8, wherein the air release properties are improved without deterioration of foaming performance, as measured by ASTM D892.

10. The use according to claim 8 or claim 9, wherein the air release properties are improved without deterioration of demulsification performance, as measured by ASTM D1401.

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