CN115298290A

CN115298290A - Lubricating oil compositions with improved oxidation performance comprising alkylated diphenylamine antioxidants and sulfonate detergents

Info

Publication number: CN115298290A
Application number: CN202180020749.0A
Authority: CN
Inventors: N·A·科特雷尔; C·查姆梅洛克斯
Original assignee: Chevron Oronite Co LLC
Current assignee: Chevron Oronite Co LLC
Priority date: 2020-03-11
Filing date: 2021-03-10
Publication date: 2022-11-04
Also published as: US20230085359A1; EP4118171A1; JP2023517064A; WO2021181286A1; KR20220148849A; CA3173369A1

Abstract

The present invention provides a lubricating oil composition. The composition includes several components, including a base oil; a primary antioxidant comprising an alkylated diphenylamine having alkyl groups derived from propylene tetramer; and sulfonate detergents.

Description

Lubricating oil compositions with improved oxidative properties comprising alkylated diphenylamine antioxidants and sulfonate detergents

Cross Reference to Related Applications

This application is related to U.S. provisional application entitled "IMPROVED OXIDATIVE PERFORMANCE using CARBOXYLATE DETERGENTS (attorney docket No. T-11173), filed on 11.3.2020/2020, the contents of which are incorporated herein by reference.

Technical Field

The present disclosure relates to lubricating oil additives that disrupt oxidation and increase the useful life of the lubricating oil. More specifically, the present disclosure relates to lubricating oil compositions comprising an alkylated diphenylamine antioxidant and a sulfonate detergent.

Background

Oxidation is a problem in lubricating oils because it can lead to thickening of the oil, sludge, varnish, increased acid number and corrosion. These results are generally detrimental to proper operation of the automotive engine and limit the useful life of the lubricating oil. With the ongoing development of engine design, operating conditions, and expectations of engine oil performance, oxidation remains a significant continuing technical challenge.

One approach to slowing engine oxidation is to introduce an antioxidant into the lubricating oil. In addition, antioxidants can extend the drain intervals, maintain viscosity, reduce deposits, reduce foam formation, prevent corrosion, and protect lubricating oils from high temperatures.

There are many antioxidants with varying degrees of effectiveness. Commercial lubricants are typically formulated with one or more antioxidants to protect the fluid under a wide variety of conditions (e.g., temperature, time, air mixture, pressure, etc.).

In particular, alkylated diphenylamines are used as antioxidants. Widely used alkylated diphenylamine antioxidants include nonylated (C9) diphenylamines, which can be added to organic fluids such as engine oils, gear oils, hydraulic oils, compressor oils, turbine oils, and greases.

Disclosure of Invention

The present disclosure relates to lubricating oil additives that disrupt oxidation and increase the useful life of the lubricating oil. More particularly, the present disclosure relates to compositions comprising alkylated diphenylamines and sulfonate detergents.

In one aspect, there is provided a lubricating oil composition comprising: a base oil; a primary antioxidant comprising an alkylated diphenylamine having alkyl groups derived from propylene tetramer; and sulfonate detergents.

In another aspect, a method of improving the oxidation stability of a lubricating oil is provided, the method comprising: supplying to an engine a lubricating oil composition comprising: a base oil; a primary antioxidant comprising an alkylated diphenylamine having alkyl groups derived from propylene tetramer; and sulfonate detergents.

Drawings

FIG. 1 illustrates a comparison of oxidation induction times for formulated oil samples as described in the examples.

Detailed Description

In this specification, the following words and expressions, if and when used, have the meanings assigned below.

The term "antioxidant" or equivalent terms (e.g., "oxidation stabilizer" or "oxidation inhibitor") refers to a composition and its ability to resist harmful attack in an oxidizing environment. Antioxidants are commonly used in organic fluids (e.g., lubricating oils, gear oils, compressor oils, mineral oils, hydraulic oils, etc.) to improve the oxidative stability of the organic fluid.

The term "alkyl" or related terms refers to a saturated hydrocarbon group, which may be linear, branched, cyclic or a combination of cyclic, linear and/or branched.

The term "olefin" refers to a hydrocarbon having at least one carbon-carbon double bond that is not part of an aromatic ring or ring system. Unless otherwise specifically stated, olefins may include aliphatic and aromatic, cyclic and acyclic, and/or straight and branched compounds having at least one carbon-carbon double bond that is not part of an aromatic ring or ring system. Olefins having only one, only two, only three, etc. carbon-carbon double bonds may be identified by using the terms "mono", "di", "tri", etc. in the olefin name. Olefins may also be identified by the position of the carbon-carbon double bond. Depending on the context, the term "olefin" may refer to either "olefin oligomer" or "olefin monomer" or both.

An "olefin oligomer" is an oligomer made by the oligomerization of an "olefin monomer". For example, "propylene oligomers" are made from the oligomerization of propylene monomers. Examples of propylene oligomers include propylene tetramers and propylene pentamers. A "propylene tetramer" is an olefin oligomer product resulting from the oligomerization of nominally 4 propylene monomers. These terms may also be used generically to describe homopolymers, co-oligomers, salts of oligomers, derivatives of oligomers, and the like.

By "minor amount" or related terms is meant less than 50% by weight of the composition, expressed with respect to the additive and with respect to the total weight of the composition, as the active ingredient of the additive.

"substantial amount" or related terms means an amount greater than 50 weight percent based on the total weight of the composition.

Antioxidant composition

The present invention relates to antioxidant compositions that disrupt oxidation and increase the useful life of lubricating oils. More specifically, the present invention describes antioxidant compositions comprising a plurality of lubricant additives. The lubricant additive includes at least one antioxidant and at least one detergent that work together to provide enhanced oxidation performance. The enhanced performance is a result of previously unknown synergy produced in the lubricating oil composition by the lubricant additive components of the present invention. Antioxidants and detergents compatible with the present invention will be described herein.

Primary antioxidant

The antioxidant composition comprises a primary antioxidant and one or more secondary antioxidants. The primary antioxidant of the present invention is an alkylated diphenylamine with one or more relatively long alkyl groups. Conventional alkylated diphenylamine antioxidants typically use relatively short alkyl groups. These include, for example, nonylated diphenylamines nominally having 9 carbons and which can be formed by oligomerization of propylene ("propylene terpolymers").

The alkylated diphenylamines of the present invention have been alkylated by propylene tetramers (nominally having 12 carbons) or by mixtures comprising propylene tetramers, which are the predominant olefin oligomer alkylating agent. Propylene tetramer can be obtained by oligomerization of 4 propylene monomers. Propylene tetramers have several potential advantages over propylene trimers, including but not limited to increased oil solubility, cheaper cost, and superior antioxidant stability.

The alkylated diphenylamines of the present invention may be present in about 0.4 wt.% to about 20 wt.%, for example about 0.5 wt.% to about 15 wt.%, 0.1 wt.% to about 10 wt.%, 0.5 wt.% to about 8 wt.%, or 1 wt.% to about 5 wt.% of the lubricating oil composition.

Propylene oligomers

The propylene oligomers (i.e., propylene tetramers) of the present invention can be prepared by any compatible method known in the art. For example, one process for preparing propylene oligomers uses a liquid phosphoric acid oligomerization catalyst. A description of liquid phosphoric acid catalyzed propylene oligomerization processes can be found in U.S. patent nos. 2,592,428; nos. 2,814,655; and 3,887,634, the relevant portions of which are incorporated herein by reference.

The unrefined product of the oligomerization process typically comprises a mixture of branched olefins having a carbon number distribution. In a commercial environment, olefin oligomers are subjected to extreme conditions during the oligomerization process which result in cracking, reorganization, isomerization, and the like. The refined or processed oligomeric product typically has a higher concentration of the desired product. Thus, the term "propylene tetramer" does not necessarily refer to a pure propylene tetramer product, but rather a mixture of olefin or olefin oligomer products. Thus, the alkylation product involving diphenylamine and propylene tetramer may have a carbon number distribution within the alkylated alkyl group.

Propylene tetramer can be obtained from the oligomerization of 4 propylene monomers. Propylene tetramer is an olefin that is cost effective to produce. As an oligomeric product, it has a highly branched chain of 10 to 15 carbons, has high methyl branching, imparts exceptional oil solubility and compatibility with other oil soluble lubricant additive components. In some embodiments, the average carbon number may range from about 10 to about 15.

The degree of branching of the oligomeric product may vary. For example, the propylene tetramer can exhibit total branching (i.e., the sum of olefinic and aliphatic branching) in the range of 1 to 15. In some embodiments, the average total branching may range from about 1 to about 15.

The propylene tetrapolymers of the invention generally comprise at least 50% by weight of C ₁₀ To C ₁₅ A carbon atom. In one embodiment, the propylene tetrapolymer contains at least 60% by weight of C ₁₀ To C ₁₅ Carbon atom distribution of carbon atoms. In one embodiment, the propylene tetrapolymer contains at least 70% by weight of C ₁₀ To C ₁₅ Carbon atom distribution of carbon atoms. In one embodiment, the propylene oligomers contain C comprising at least 80 wt% ₁₀ To C ₁₅ Carbon atom distribution of carbon atoms. In one embodiment, the propylene oligomer contains at least 90 wt.% C ₁₀ To C ₁₅ Carbon atom distribution of carbon atoms.

As will be apparent to one of ordinary skill in the art, the propylene oligomers used herein may also contain small amounts of lower molecular weight propylene oligomers, such as propylene terpolymers, as well as higher molecular weight propylene oligomers, such as propylene pentamers. For example, the propylene tetrapolymer of the invention may be one containing from 0 to 1% by weight of C ₉ H ₁₈ 0-5 wt% of C ₁₀ H ₂₀ 0-10 wt.% of C ₁₁ H ₂₂ 50-90 wt.% of C ₁₂ H ₂₄ 10-20% by weight of C ₁₃ H ₂₆ 5-15% by weight of C ₁₄ H ₂₈ And/or 1-10 wt% C ₁₅ H ₃₀ Mixtures of olefins of (a).

Alkylation

The alkylated diphenylamines of the present invention may be obtained by any alkylation process compatible with the present invention. For example, US 6,355,839, which is incorporated herein by reference, describes the preparation of alkylated diphenylamines in which the diphenylamine is alkylated with polyisobutylene.

Any suitable catalyst may be used. For example, the alkylation of diphenylamine may be carried out in the presence of a clay catalyst. The temperature of the reaction may range from 140 ℃ to 200 ℃, more typically from 150 ℃ to 190 ℃. In some embodiments, the temperature of the reaction is in the range of 160 ℃ to 180 ℃. The reaction may be carried out at a single temperature, or sequentially at different temperatures. The propylene oligomer may be fed at a feed molar ratio (CMR) of 2 to 8. In some embodiments, the CMR is 3 to 7. The reaction product may be filtered to remove the catalyst and then distilled to remove unreacted olefin oligomer and diphenylamine. The use of clay as a catalyst is disclosed in U.S. Pat. No. 3,452,056, which is incorporated herein by reference.

As would be expected by one of ordinary skill in the art, the reaction conditions may vary significantly depending on the catalyst used. For example, reactions involving homogeneous acid catalysts may require temperatures in the range of 75 ℃ to 100 ℃.

The alkylated diphenylamine product can have various relative amounts of monoalkylated, dialkylated, and/or trialkylated diphenylamine products depending on the reaction conditions. It will be apparent that for a given dialkylated or trialkylated diphenylamine molecule, the two or more alkylated alkyl groups can be the same or different in accordance with the present disclosure.

Secondary antioxidant

The present invention uses one or more secondary antioxidants in combination with a primary antioxidant. The secondary antioxidant may be present at about 0.01 wt.% to about 20 wt.%, such as about 0.05 wt.% to about 15 wt.%, 0.1 wt.% to about 10 wt.%, 0.5 wt.% to about 8 wt.%, or 1 wt.% to about 5 wt.% of the lubricating oil composition.

Many times antioxidants are compatible with the present invention. Examples of secondary antioxidants include molybdenum succinimides, dithiocarbamates, and hindered phenols. These oil-soluble components are generally known.

For example, mono-and polysuccinimides that can be used to prepare the molybdenum complexes described herein are disclosed in a number of references and are well known in the art. Certain basic types of succinimides and related materials encompassed by the term "succinimide" are taught in U.S. Pat. nos. 3,219,666; nos. 3,172,892; and 3,272,746, the disclosures of which are incorporated herein by reference. The term "succinimide" is understood in the art to include many of the amide, imide, and amidine species that may also be formed. However, the predominant product is succinimide, and this term has been generally accepted to mean the product of the reaction of an alkenyl substituted succinic acid or anhydride with a nitrogen containing compound.

Preferred succinimides, because of their commercial availability, are those prepared from a hydrocarbyl succinic anhydride wherein the hydrocarbyl group contains from about 24 to about 350 carbon atoms and an ethylene amine, particularly characterized by ethylene diamine, diethylene triamine, triethylene tetramine, and tetraethylene pentamine. Particularly preferred are those succinimides prepared from polyisobutenyl succinic anhydride of 70 to 128 carbon atoms and tetraethylene pentamine or triethylenetetramine or mixtures thereof.

Also included in the term "succinimide" are cooligomers of hydrocarbyl succinic acids or anhydrides and secondary polyamines which contain at least one tertiary amino nitrogen in addition to two or more secondary amino groups. Typically, the average molecular weight of the composition is from 1,500 to 50,000. Typical compounds are those prepared by reacting polyisobutenyl succinic anhydride with ethylene bipiperazine.

Most preferred are succinimides having an average molecular weight of 1000 or 1300 or 2300 and mixtures thereof. Such succinimides may be post-treated with boron or ethylene carbonate as known in the art.

Suitable dithiocarbamates include, but are not limited to, dithiocarbamates, ashless thiocarbamates, or dithiocarbamates (i.e., substantially metal-free) in which the metal is zinc, copper, or molybdenum, such as methylene bis (dialkyldithiocarbamates), ethylene bis (dialkyldithiocarbamates), and isobutyl disulfide-2, 2' -bis (dialkyldithiocarbamates), in which the alkyl group of the dialkyldithiocarbamate may preferably have 1 to 6 carbon atoms. Examples of preferred ashless dithiocarbamates are methylene bis (dibutyldithiocarbamate), ethylene bis (dibutylthiocarbamate), and isobutyl disulfide-2, 2' -bis (dibutyldithiocarbamate).

The secondary antioxidant used in the lubricating oil of the present invention may be a sterically hindered phenol. Hindered phenolic antioxidants often contain secondary and/or tertiary butyl groups as the hindering group. The phenolic group is also typically substituted with a hydrocarbyl group and/or a bridging group attached to a second aryl group. Suitable hindered phenols include, but are not limited to, 2, 6-di-tert-butylphenol, 4-methyl-2, 6-di-tert-butylphenol, 4-ethyl-2, 6-di-tert-butylphenol, 4-propyl-2, 6-di-tert-butylphenol, or 4-butyl-2, 6-di-tert-butylphenol or 4-dodecyl-2, 6-di-tert-butylphenol.

Detergent composition

The antioxidant compositions of the present invention comprise one or more detergents. The detergent may be present at about 0.01 wt% to about 10 wt%, for example about 0.05 wt% to about 8 wt%, 0.1 wt% to about 5 wt%, 0.5 wt% to about 4 wt%, or 1 wt% to about 3 wt% of the lubricating oil composition.

Detergents are generally salts (e.g., overbased salts) and are single phase, homogeneous newtonian systems characterized by a metal content in excess of that which would be present according to the stoichiometry of the metal and the particular acidic organic compound reacted with the metal.

The detergents of the present invention include sulfonate detergents. Metal detergents, such as sulfonate detergents, typically contain a polar head group and a hydrocarbon tail or lipophilic group. Typically, the length of the hydrocarbon tail can range from about 3 carbons to 50 carbons.

The sulfonate detergents may be natural or synthetic. The detergent may be neutral or overbased. Overbased detergents may be within a range of levels of overbased (as measured by ASTM D2896). Compatible overbased sulfonates include low overbased, medium overbased, high overbased, and high overbased sulfonate detergents. In some embodiments, the detergent may be borated.

Examples of sulfonate detergents include alkyl aryl sulfonates and the like. Specific examples include magnesium alkyltoluene sulfonates as described in US 20110136711. Other examples include calcium alkylaryl sulfonates, calcium alkyltoluene sulfonates, and magnesium alkylbenzene sulfonates.

The metals of the detergent may also include alkali or alkaline earth metals, such as barium, sodium, potassium, lithium, calcium and magnesium. The most commonly used metals are calcium and magnesium, and mixtures of calcium and/or magnesium with sodium, both of which may be present in detergents used in lubricants.

In some embodiments, additional detergents may be used. Additional detergents include phenates, salicylates, phenates, phosphonates, thiophosphonates, ionic surfactants, and the like. In some embodiments, the additional detergent comprises a mixed and/or compounded detergent.

Lubricating oil composition

The antioxidant compositions of the present disclosure can be used in lubricating oils to impart oxidative stability to the lubricating oil. The primary antioxidant, secondary antioxidant, and one or more detergents may be present in any ratio so long as their concentrations are within the guidelines provided herein.

Typically, antioxidant compositions are oil-soluble, meaning that they are, for example, dissolved or stably dispersed in oil to an extent sufficient to exert their intended effect in the environment in which the oil is used. Furthermore, the additional incorporation of other additives may also allow for the incorporation of higher levels of a particular additive, if desired. The term oil-soluble does not necessarily mean that the compound or additive is soluble, miscible or capable of being suspended in all proportions in the oil. If other antioxidants are present in the lubricating oil composition, then lesser amounts of the antioxidants of this invention can be used.

The oil used as the base oil will be selected or blended depending on the desired end use and the additives in the finished oil to provide the desired grade of engine oil, for example, an Society of Automotive Engineers (SAE) viscosity grade lubricating oil composition having a viscosity of 0W, 0W-8, 0W-16, 0W-20, 0W-30, 0W-40, 0W-50, 5W-20, 5W-30, 5W-40, 5W-50, 5W-60, 10W-20, 10W-30, 10W-40, 10W-50, 15W-20, 15W-30, or 15W-40. Pure grades of oils, such as SAE 30, 40, 50 and 60, may also be used.

An oil of lubricating viscosity (sometimes referred to as a "base stock" or "base oil") is the main liquid component of a lubricant into which additives and possibly other oils are blended, for example to produce a final lubricant (or lubricant composition). The base oils which may be used to prepare the concentrates and lubricating oil compositions therefrom may be selected from natural (vegetable, animal or mineral) and synthetic lubricating oils and mixtures thereof.

The definition of Base stocks and Base Oils in this disclosure is the same as that found in appendix E of the American Petroleum Institute (API) publication 1509 ("API Base Oil interchange Guidelines for Passenger Car Motor Oils and Diesel Engine Oils",2016, 12 months). Group I base stocks contain less than 90% saturates and/or greater than 0.03% sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1. Group II basestocks contain greater than or equal to 90% saturates and less than or equal to 0.03% sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1. Group III basestocks contain greater than or equal to 90% saturates and less than or equal to 0.03% sulfur and have a viscosity index greater than or equal to 120 using the test methods specified in Table E-1. Group IV basestocks are Polyalphaolefins (PAOs). Group V base stocks include all other base stocks not included in group I, group II, group III or group IV.

Natural oils include animal oils, vegetable oils (e.g., castor oil and lard oil), and mineral oils. Animal and vegetable oils with good thermo-oxidative stability can be used. Among natural oils, mineral oils are preferred. Mineral oils vary widely in crude oil origin, for example, in whether they are paraffinic, naphthenic or mixed paraffinic-naphthenic. Oils derived from coal or shale are also useful. Natural oils also vary in the methods used for production and purification, such as their distillation range and whether they are straight run or cracked, hydrofinished or solvent extracted.

Synthetic oils include hydrocarbon oils. Hydrocarbon oils include oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene isobutylene copolymers, ethylene-olefin copolymers, and ethylene-alpha olefin copolymers). Polyalphaolefin (PAO) oil basestocks are commonly used synthetic hydrocarbon oils. For example, derivatives derived from C may be used ₈ To C ₁₄ Olefins, e.g. C ₈ 、C ₁₀ 、C ₁₂ 、C ₁₄ PAO of olefins or mixtures thereof.

Other suitable fluids for use as base oils include non-conventional or unconventional base stocks which have been processed (preferably catalytically processed) or synthesized to provide high performance characteristics.

Unconventional or ultra-conventional base stocks/base oils include one or more base stock mixtures derived from one or more gas-to-liquid (GTL) materials, as well as isomerate/isodewaxed base stocks derived from natural wax or waxy feeds, mineral and/or non-mineral oil waxy crude stocks, such as soft waxes, natural waxes and waxy stocks, such as gas oils, waxy fuel hydrocracker bottoms, waxy raffinates, hydrocracked oils, thermal cracked oils or other mineral, mineral oils or even non-petroleum derived waxy materials, such as waxy materials obtained from coal liquefaction or shale oils, and mixtures of such base stocks.

The base oil used in the lubricating oil composition of the present disclosure is any kind of oil corresponding to: API group I, group II, group III, group IV and group V oils and mixtures thereof, preferably API group II, group III, group IV and group V oils and mixtures thereof, more preferably group III to group V base oils because of their excellent volatility, stability, viscosity and cleanliness characteristics.

Typically, the base oil has a kinematic viscosity (ASTM D445) at 100 ℃ of from 2.5 to 20mm ² S (e.g. 3 to 12 mm) ² S, 4 to 10mm ² S, or 4.5 to 8mm ² /s)。

The lubricating oil compositions of the present disclosure may also contain conventional lubricant additives for imparting auxiliary functions to provide a finished lubricating oil composition in which these additives are dispersed or dissolved. For example, the lubricating oil composition may be blended with: antioxidants, ashless dispersants, anti-wear agents, detergents such as metal detergents, rust inhibitors, dehazing agents, demulsifying agents, friction modifiers, metal deactivating agents, pour point depressants, viscosity modifiers, antifoaming agents, co-solvents, package compatibilisers, corrosion-inhibitors, dyes, extreme pressure agents and the like and mixtures thereof. Various additives are known and commercially available. These additives or their analogous compounds can be used to prepare the lubricating oil compositions of the present invention by the usual blending procedures.

Each of the foregoing additives is used in a functionally effective amount at the time of use to impart the desired characteristics to the lubricant. Thus, for example, if the additive is an ashless dispersant, a functionally effective amount of such ashless dispersant will be an amount sufficient to impart the desired dispersion characteristics to the lubricant. Typically, when each of these additives is used, their concentration can range from about 0.001 to about 20 weight percent, for example from about 0.01 to about 10 weight percent, unless otherwise specified.

The following illustrative examples are intended to be non-limiting.

Examples

As shown in fig. 1, the oxidation induction time of the fully formulated engine oil was tested. Fully formulated engine oils include one or more antioxidants and sulfonate detergents as well as common lubricant additives such as dispersants and corrosion inhibitors.

The first engine oil sample ("DPA only") included a sulfonate detergent and an alkylated diphenylamine. The alkylated diphenylamine is nonylated diphenylamine or diphenylamine alkylated with propylene tetramers. The gas chromatographic analysis of the diphenylamine alkylated with the propylene tetramer is summarized in table 1 below. Analysis showed that about half of the sample was monoalkylated diphenylamine. About the other half of the sample was dialkylated diphenylamine. There is a very small amount of diphenylamine having a C3-C8-alkyl group.

TABLE 1

DPA	Dimer	C3-C8 DPA	Total single DPA	Total two DPA
					0.0％	0.0％	0.6	50.8％	48.6％

Other engine oil samples included one or more additional antioxidants (i.e., molybdenum succinimides, hindered phenols, dithiocarbamates). In a mixed engine oil sample with multiple antioxidants, each antioxidant present is present at an equal treat level/weight percent.

Test engine oil samples with two antioxidants included alkylated diphenylamine with molybdenum succinimides ("DPA/molybdenum succinimides"), hindered phenols ("DPA/hindered phenols") or dithiocarbamates ("DPA/dithiocarbamates"). Test engine oil samples with three antioxidants included alkylated diphenylamine with either succinimidyl molybdenum and hindered phenols ("DPA/succinimidyl molybdenum/hindered phenol"), succinimidyl molybdenum and dithiocarbamate ("DPA/succinimidyl molybdenum/dithiocarbamate") or hindered phenols and dithiocarbamate ("DPA/hindered phenol/dithiocarbamate"). Test engine oil samples with four antioxidants included alkylated diphenylamine with molybdenum succinimides, hindered phenols, and dithiocarbamates ("DPA/molybdenum succinimides/hindered phenols/dithiocarbamates").

For each test sample, sulfonate detergents (low and medium overbased sulfonates) were present at 78mM, and the total concentration of antioxidants was 1.5 wt.%.

The data show that the oxidation induction time is consistently higher in the sample with diphenylamine alkylated with propylene tetramer compared to the sample with nonylated diphenylamine.

Oxidative induction times were evaluated using Pressurized Differential Scanning Calorimetry (PDSC) according to ASTM D6186 test protocol. Longer oxidation induction times indicate higher oxidative stability.

Claims

1. A lubricating oil composition comprising:

a base oil;

a primary antioxidant comprising an alkylated diphenylamine having alkyl groups derived from propylene tetramer; and

a sulfonate detergent.

2. The lubricating oil composition of claim 1, further comprising:

a secondary antioxidant comprising a dithiocarbamate, a hindered phenol, or molybdenum succinimide.

3. The lubricating oil composition of claim 1, wherein at least 50% of the alkyl groups of the alkylated diphenylamine has a carbon number of from 10 to 15.

4. The lubricating oil composition of claim 1, wherein the sulfonate detergent is a petroleum-based detergent or a synthetic detergent.

5. The lubricating oil composition of claim 1, wherein the primary antioxidant is present at 0.01 wt.% to 20 wt.% of the lubricating oil composition.

6. The lubricating oil composition of claim 1, wherein the sulfonate detergent is overbased.

7. The lubricating oil composition of claim 1, wherein the secondary antioxidant is present at 0.01 wt.% to 20 wt.% of the lubricating oil composition.

8. The lubricating oil of claim 1, wherein the sulfonate detergent is present at 0.01 wt.% to 10 wt.% of the lubricating oil composition.

9. The lubricating oil composition of claim 1, further comprising:

antioxidants, ashless dispersants, anti-wear agents, detergents, rust inhibitors, dehazing agents, demulsifying agents, friction modifiers, metal deactivating agents, pour point depressants, viscosity modifiers, antifoaming agents, co-solvents, package compatibilisers, corrosion-inhibitors, dyes or extreme pressure agents.

10. The lubricating oil composition of claim 1, wherein the sulfonate detergent comprises an internal olefin sulfonate, an alkyl ether sulfonate, an alcohol ether sulfonate, a linear alkyl aryl sulfonate, or an alkane sulfonate.

11. A method of improving the oxidation stability of a lubricating oil, the method comprising:

supplying to an engine a lubricating oil composition comprising:

a base oil;

a sulfonate detergent.

12. The method of claim 11, wherein the lubricating oil composition further comprises:

13. The method of claim 11, at least 50% of the alkylated diphenylamine having a carbon number of 10-15.

14. The method of claim 11, wherein the sulfonate detergent is a petroleum-based detergent or a synthetic detergent.

15. The method of claim 11, wherein the primary antioxidant is present at 0.01 wt.% to 20 wt.% of the lubricating oil composition.

16. The method of claim 11 wherein the sulfonate detergent is overbased.

17. The method of claim 11, wherein the secondary antioxidant is present at 0.01 wt.% to 20 wt.% of the lubricating oil composition.

18. The method of claim 11, wherein the sulfonate detergent is present at 0.01 wt.% to 10 wt.% of the lubricating oil composition.

19. The method of claim 11, wherein the lubricating oil composition further comprises:

20. The method of claim 11 wherein the sulfonate detergent comprises an internal olefin sulfonate, an alkyl ether sulfonate, an alcohol ether sulfonate, a linear alkyl aryl sulfonate, or an alkane sulfonate.