Antioxidant having high monoalkylated diphenylamine content

Abstract

To provide an alkylated diphenylamine antioxidant composition having a high monoalkylated content.SOLUTION: A lubricating oil composition is provided. The composition includes several components including a major amount of a base oil, a mixture of alkylated diphenylamine having a weight ratio of mono-alkylated diphenylamine to di-alkylated diphenylamine ranging from 0.6 to 4.0, and a molybdenum or sulfur additive that provides synergistic enhancement of oxidation stability in combination with the mixture of alkylated diphenylamine.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to antioxidant additive compositions. More specifically, the present disclosure describes alkylated diphenylamine antioxidant compositions having a high monoalkylation content. [Background technology]

[0002] Alkylated diarylamines, such as alkylated diphenylamines, are commonly used as stabilizers or antioxidants in a wide variety of organic materials, including mineral oil-derived and synthetic lubricants. The manufacture of alkylated diphenylamines typically targets a higher ratio of dialkylated diphenylamine to monoalkylated diphenylamine. For example, industrial preparation of alkylated diphenylamines typically results in about 65-75% by weight of dialkylated diphenylamine, 20-30% by weight of monoalkylated diphenylamine, and 5% by weight or less of trialkylated diphenylamine. Conventional wisdom is that dialkylated or trialkylated diphenylamines have superior oxidative stability compared to monoalkylated diphenylamine. Alkylated diphenylamines are commonly made by using relatively light olefin oligomers (e.g., C9 oligomers) as alkylation starting materials. However, these lighter olefin oligomers have safety concerns due to their low flash point and volatility. Summary of the Invention

[0003] The present disclosure relates to antioxidant additive compositions. More particularly, the present disclosure describes alkylated diphenylamine antioxidant compositions having a high monoalkylation content.

[0004] In one embodiment, a lubricating oil composition is provided that includes a major amount of a base oil, a mixture of alkylated diphenylamines having a weight ratio of mono-alkylated diphenylamine to di-alkylated diphenylamine in the range of 0.6 to 4.0, and a minor amount of an antioxidant composition including a molybdenum or sulfur additive that provides a synergistic enhancement of oxidation stability in combination with the mixture of alkylated diphenylamines.

[0005] In a further aspect, there is provided an oxidative stabilizing composition comprising a mixture of alkylated diphenylamines having a weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine in the range of 0.6 to 4.0, and a molybdenum or sulfur additive that provides a synergistic enhancement of oxidative stability in combination with the mixture of alkylated diphenylamines.

[0006] In yet a further aspect, there is provided a method for improving the oxidative stability of a lubricating oil comprising supplying to an engine a lubricating oil composition comprising a major amount of a base oil, a mixture of alkylated diphenylamines having a weight ratio of mono-alkylated diphenylamine to di-alkylated diphenylamine in the range of 0.6 to 4.0, and a molybdenum or sulfur additive that provides a synergistic enhancement of oxidative stability in combination with the mixture of alkylated diphenylamines. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 shows a graphical representation of Pressurized Differential Scanning Calorimetry (PDSC) measurements summarized in Table 1 in the Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] As used herein, the following words and expressions have the meanings given below, if and when used.

[0009] "Antioxidant" or "oxidation inhibitor" or equivalent terms (e.g., "oxidative stabilizer") refer to a composition and its ability to resist harmful attack in an oxidative environment. Antioxidants are often used in organic fluids (e.g., lubricating oils, gear oils, mineral oils, hydraulic fluids, etc.) to improve the oxidative stability of the organic fluid.

[0010] The term "monoalkylated diphenylamine" refers to a diphenylamine that is alkylated at a single site on one of the two aromatic rings. The monoalkylation typically occurs at the para site.

[0011] The term "dialkylated diphenylamine" refers to a diphenylamine that is alkylated at two sites on the aromatic ring(s). The dialkylation typically occurs at the two para sites, or at the para site and the ortho site.

[0012] The term "trialkylated diphenylamine" refers to a diphenylamine that is alkylated at three sites on the aromatic ring(s). The trialkylation typically occurs at two para sites and a single ortho site.

[0013] "Alkyl" or related terms refer to a saturated hydrocarbon group, which may be linear, branched, cyclic, or a combination of cyclic, linear, and / or branched.

[0014] "Minor amount" or related terms means less than 50% by weight of the composition expressed with respect to the listed additive and with respect to the total weight of the composition, calculated as the active ingredient of the additive.

[0015] "Major amount" or related term means an amount greater than 50% by weight based on the total weight of the composition.

[0016] Antioxidants The present invention provides an effective antioxidant composition that can be added to organic fluids (e.g., mineral oils, hydraulic fluids, metal working fluids, gear oils, etc.) to impart stability to the organic fluids in oxidizing environments. It has been unexpectedly discovered that antioxidant compositions including mixtures containing high monoalkylated diphenylamine content can be mixed with organic additives (molybdenum or sulfur compounds) to achieve a synergistic enhancement of oxidative stability.

[0017] More particularly, the antioxidant composition of the present invention comprises (i) a weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine (i.e., 0.6 to 4.0); and (ii) one or more molybdenum or sulfur-based organic compounds that provide a synergistic enhancement of oxidative stability. The present invention advantageously utilizes olefin oligomers such as propylene tetramer, which have a higher flash point (62°C) and are less volatile than the lighter commercial olefin oligomers. Other advantages will become apparent from the disclosure herein.

[0018] Structure 1 shows the chemical structure of diphenylamine which can be used as a starting material in the production of alkylated diphenylamines. [ka]

[0019] The alkylated diphenylamine of the present invention can be formed by alkylating diphenylamine with heavier propylene oligomers such as propylene tetramer.Any alkylation process compatible with the present invention may be used.For example, US6,355,839, which is incorporated herein by reference, describes the preparation of alkylated diphenylamine, in which diphenylamine is alkylated with polyisobutylene.

[0020] The propylene oligomers can be reacted with diphenylamine in the presence of a clay catalyst. The temperature of the reaction can range from 140° C. to 200° C., more typically from 150° C. to 190° C. In some embodiments, the reaction temperature ranges from 160° C. to 180° C. The reaction can be carried out at a single temperature or sequentially at different temperatures. The propylene oligomers are charged with a charge molar ratio (CMR) relative to the diphenylamine charge of 2:1 to 8:1. In some embodiments, the CMR is 3:1 to 7:1, or 4:1 to 6:1. The reaction product can be filtered to remove the catalyst and then distilled to remove unreacted olefin oligomers and diphenylamine.

[0021] The use of clays as catalysts in the alkylation of diphenylamine is disclosed in US Pat. No. 3,452,056, the relevant portions of which are incorporated herein by reference.

[0022] As would be expected by one of ordinary skill in the art, reaction conditions may vary significantly depending on the catalyst used. For example, reactions involving homogeneous acid catalysis may only require temperatures in the range of 75° C. to 100° C.

[0023] In accordance with the present invention, the target content of the antioxidants includes about 40-80% by weight of mono-alkylated diphenylamine and 20-60% by weight of di-alkylated diphenylamine. In some embodiments, the target content is 45-75% by weight of mono-alkylated diphenylamine and 25-55% by weight of di-alkylated diphenylamine. In some embodiments, the target content is 50-70% by weight of mono-alkylated diphenylamine and 30-50% by weight of di-alkylated diphenylamine. In some embodiments, the target content is 55-65% by weight of mono-alkylated diphenylamine and 35-45% by weight of di-alkylated diphenylamine. In some embodiments, the tri-alkylated diphenylamine is present at about 5% by weight or less.

[0024] Since monoalkylated diphenylamines require shorter reaction times compared to dialkylated diphenylamines, it may be economically advantageous to produce antioxidant compositions that target higher monoalkylated diphenylamine content. Typically, the alkylation reaction time is on the order of a few hours. The time required to reach 50% monoalkylated diphenylamine and 50% dialkylated diphenylamine can be three times shorter than the time required to reach >60% dialkylated diphenylamine.

[0025] Propylene Oligomer As mentioned above, alkylated diphenylamines can be prepared by alkylating diphenylamine with propylene oligomers. According to the present invention, the alkylation is carried out with propylene oligomers, such as propylene tetramers, which have a higher flash point than propylene C9 oligomers.

[0026] Propylene tetramers contain carbon chains with a high degree of methyl branching and an average carbon number of 12. In general, propylene tetramers can have a carbon number distribution between 10 and 15 carbon atoms. The tetramers impart oil solubility and compatibility with other oil-soluble lubricant additive components. The tetramers are also cost-effective to produce olefins.

[0027] In one embodiment, the propylene oligomer comprises at least 50 wt.% C 10 ~C 15 In one embodiment, the propylene oligomer contains a distribution of carbon atoms comprising at least 60 wt.% C 10 ~C 15 In one embodiment, the propylene oligomers may contain a distribution of carbon atoms including at least 70 wt.% C 10 ~C 15 In one embodiment, the propylene oligomer contains a distribution of carbon atoms comprising at least 80 wt.% C 10 ~C 15In one embodiment, the propylene oligomer contains a distribution of carbon atoms comprising at least 90 wt.% C 10 ~C 15 It contains a distribution of carbon atoms including carbon atoms.

[0028] As will be apparent to one of skill in the art, propylene oligomer as used herein may also contain lower molecular weight propylene oligomer(s), such as propylene trimer, or higher molecular weight propylene oligomer(s), such as propylene pentamer. In one embodiment, the propylene oligomer is primarily CH at <1 wt.%. 18 , 0 to 5 wt% C 10 H 20 , 0 to 10 wt% C 11 H 22 , 50-90% by weight C 12 H 24 , 10 to 20% by weight C 13 H 26 , 5 to 15 wt% C 14 H 28 and / or 1 to 10% by weight of C 15 H 30 It is a mixture of olefinic hydrocarbons containing

[0029] Alkylation with propylene tetramer generally results in alkylated diphenylamines having an alkyl group(s) falling within these parameters. It should be apparent that for a given di- or trialkylated diphenylamine molecule, the two or more alkylating alkyl groups may be the same or different, in accordance with the present disclosure.

[0030] Propylene oligomers can be prepared by any method known in the art.For example, one suitable process for preparing propylene oligomers is to use liquid phosphoric acid oligomerization catalyst.The description of this liquid phosphoric acid catalyzed propylene oligomerization process is described in U.S. Patent Nos. 2,592,428, 2,814,655 and 3,887,634, the relevant portions of which are incorporated herein by reference.

[0031] The antioxidant compositions of the present invention include mixtures of alkylated diphenylamines having a relatively high weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine. This ratio is about 0.6-4.0, which is higher than conventional alkylated diphenylamine antioxidant mixtures (typically about 0.5 or less). In some embodiments, the weight ratio is 0.7-3, or 0.8-2, or 0.8-1.2, or 0.9-1.1. When mixed with the appropriate additives (molybdenum and / or sulfur-based compositions) according to the present invention, the mixtures provide a synergistic enhancement of oxidative stability.

[0032] Molybdenum Composition The molybdenum compositions for use in the present invention are generally organomolybdenum compounds, including sulfur-free compounds, phosphorus-free compounds, and sulfur-containing compounds. Synthetic methods for organomolybdenum compounds are generally known. Many organomolybdenum compounds are commercially available.

[0033] Examples of sulfur-free and phosphorus-free organo-molybdenum compounds include molybdenum trioxide, ammonium molybdate, sodium molybdate and potassium molybdate. The alcohol group may be a mono-substituted alcohol, a diol, or a bis-alcohol, or a polyalcohol.

[0034] Other suitable organo-molybdenum compounds include, but are not limited to, molybdenum succinimides, molybdenum amino alcohols, etc. The amino group may be a monoamine, diamine, or polyamine.

[0035] Still other suitable molybdenum compositions include those listed in U.S. Pat. No. 8,426,608, which is incorporated herein by reference. Readily available molybdenum compositions include molybdenum di(2-ethylhexyl)phosphorodithioate, available commercially under the tradename Molyvan® L (Vanderbilt Chemicals), molybdenum dialkyldithiocarbamate, available commercially under the tradename Molyvan® 807 (Vanderbilt Chemicals), molybdenum dialkyldithiocarbamate, available commercially under the tradename Molyvan® 822 (Vanderbilt Chemicals), molybdenum ester / amide, available commercially under the tradename Molyvan® 855 (Vanderbilt Chemicals), molybdenum ester / amide, available commercially under the tradename Molyvan® 30 ... molybdenum dithiocarbamate commercially available under the trade name Sakura-Lube® 200 (Adeka); molybdenum dithiocarbamate commercially available under the trade name Sakura-Lube® 165 (Adeka); molybdenum dithiocarbamate commercially available under the trade name Sakura-Lube® 525 (Adeka); molybdenum dithiocarbamate commercially available under the trade name Sakura-Lube® 600 (Adeka); molybdenum dithiocarbamate available commercially under the trade name Sakura-Lube® 300 (Adeka), molybdenum dithiophosphate available commercially under the trade name Sakura-Lube® 310G (Adeka), molybdenum-amine complex available commercially under the trade name Sakura-Lube® 700 (Adeka), and an organo-molybdenum compound available commercially under the trade name Sakura-Lube® 710 (Adeka).

[0036] Sulfur Composition Suitable sulfur compositions are generally organic sulfur compounds including sulfurized olefin esters, sulfurized isobutylene, methylenebisdithiocarbamates, sulfur-containing phenols, thioesters bishydrocinnamic esters, and the like.

[0037] Readily available sulfur compositions include a trisulfide sulfur donor commercially available under the trade name TPS® 20 (Arkema), a pentasulfide sulfur donor commercially available under the trade name TPS® 32 (Arkema), a 4,5-diaminophenyl sulfide sulfur donor commercially available under the trade name Vanlube® 7723 (Vanderbilt Chemicals), and a 5,5-diaminophenyl sulfide sulfur donor commercially available under the trade name Vanlube® 7723 (Vanderbilt Chemicals).4'-methylenebis(dibutyldithiocarbamate), methylenebis(dibutyldithiocarbamate) commercially available under the tradename Vanlube® 996E (Vanderbilt Chemicals), dithiocarbamate commercially available under the tradename NA-Lube® ADTC (King Industries), phosphorus sulfur-containing additive commercially available under the tradename NA-Lube® AW-6330 (King Industries), sulfurized hydrocarbons commercially available under the tradename Elco 213 (Elco Corporation), sulfurized hydrocarbons commercially available under the tradename Elco 226 (Elco Corporation), sulfurized esters commercially available under the tradename Elco 2556 (Elco Corporation), sulfurized esters commercially available under the tradename Elco 2410SE (Elco Corporation), sulfurized esters commercially available under the tradename Elco 2415C (Elco Corporation), sulfurized fatty acids commercially available under the tradename Elco 2418 (Elco Corporation), sulfurized fatty acids commercially available under the tradename Elco 2426C (Elco Corporation), Sulfurized esters available commercially under the trade name Elco 2430C (Elco Corporation), sulfurized vegetable oil available commercially under the trade name Elco 2451 (Elco Corporation), sulfurized vegetable oil available commercially under the trade name Elco 2452 (Elco Corporation), sulfurized vegetable oil available commercially under the trade name Elco 2452D (Elco Corporation), sulfurized esters available commercially under the trade name Elco 2456 (Elco Corporation), sulfurized esters available commercially under the trade name Elco 2456D (Elco Corporation), sulfurized isobutylene available commercially under the trade name C-TEC 321 (Tianhe Chemicals), and sulfur-containing phenols available commercially under the trade name Songnox® 1035 (Songwon).

[0038] Certain compatible additives may contain both molybdenum and sulfur. Examples of these include molybdenum dithiolcarbamate (DTC) and molybdenum dithiophosphate (DTP).

[0039] lubricating oil composition The antioxidant composition of the present disclosure may be used in a lubricating oil to impart oxidative stability to the lubricating oil. When used in this manner, the mixture of alkylated diphenylamines is typically present in the lubricating oil composition at a concentration ranging from 0.05% to 10% by weight (including, but not limited to, 0.1 to 5% by weight, 0.2 to 4% by weight, 0.5 to 3% by weight, 1 to 2% by weight, etc.) based on the total weight of the lubricating oil composition. When other antioxidants are present in the lubricating oil composition, smaller amounts of the antioxidants of the present invention may be used.

[0040] The molybdenum content of the molybdenum composition may vary from about 1-10,000 ppm, 10-9,000 ppm, 100-8,000 ppm, 500-7,000 ppm, 1,000-5,000 ppm, or 2,000-4,000 ppm. The molybdenum composition may be present at about 0.05%-10% by weight, 0.1%-9% by weight, 1%-8% by weight, 2%-6% by weight, or 3%-5% by weight. The concentration of the sulfur composition may range from about 0.05%-40% by weight, 0.5%-30% by weight, 1%-25% by weight, or 5%-20% by weight of the antioxidant composition. Oils used as base oils are selected or blended depending on the desired end use and additives in the finished oil to provide a lubricating oil composition having a desired grade of engine oil, for example, a Society of Automotive Engineers (SAE) viscosity grade of 0W, 0W-8, 0W-16, 0W-20, 0W-30, 0W-40, 0W-50, 0W-60, 5W, 5W-20, 5W-30, 5W-40, 5W-50, 5W-60, 10W, 10W-20, 10W-30, 10W-40, 10W-50, 15W, 15W-20, 15W-30, or 15W-40.

[0041] An oil of lubricating viscosity (sometimes called a "base stock" or "base oil") is the primary liquid component of a lubricant with which additives and possibly other oils are blended to produce, for example, the final lubricant (or lubricant composition). Base oils useful for making concentrates and for making lubricant compositions therefrom may be selected from natural (vegetable, animal, or mineral) and synthetic lubricating oils and mixtures thereof.

[0042] The definitions of base stocks and base oils in this disclosure are the same as those set forth in American Petroleum Institute (API) Publication 1509 Annex E ("API Base Oil Interchangeability Guidelines for Passenger Car Motor Oils and Diesel Engine Oils," December 2016). Group I base stocks contain less than 90% saturates and / or more than 0.03% sulfur and have a viscosity index of 80 or greater and less than 120, using the test methods set forth in Table E-1. Group II base stocks contain 90% or greater saturates and 0.03% or less sulfur and have a viscosity index of 80 or greater and less than 120, using the test methods set forth in Table E-1. Group III base stocks contain 90% or greater saturates and 0.03% or less sulfur and have a viscosity index of 120 or greater, using the test methods set forth in Table E-1. Group IV base stocks are polyalphaolefins (PAOs). Group V base stocks include all other base stocks not included in Group I, Group II, Group III, or Group IV.

[0043] Natural oils include animal oils, vegetable oils (e.g., castor oil and lard oil), and mineral oils. Animal and vegetable oils with favorable thermo-oxidative stability can be used. Of the natural oils, mineral oils are preferred. Mineral oils vary widely with respect to their crude source, for example, whether they are paraffinic, naphthenic, or mixed paraffinic-naphthenic. Oils derived from coal or shale are also useful. Natural oils also vary by the methods used to produce and refine them, for example, their distillation range, and whether they are straight run, cracked, hydrorefined, or solvent extracted.

[0044] Synthetic oils include hydrocarbon oils. Hydrocarbon oils include oils such as polymerized and interpolymerized olefins (e.g., polybutylene, polypropylene, propylene isobutylene copolymers, ethylene-olefin copolymers, and ethylene-alphaolefin copolymers). Polyalphaolefin (PAO) oil base stocks are commonly used for synthetic hydrocarbon oils. Examples include C8-C 14 Olefins, e.g., C8, C 10 , C 12 , C 14 PAOs derived from olefins, or mixtures thereof may also be utilized.

[0045] Other useful fluids for use as base oils include non-conventional or unconventional base stocks, preferably catalytically treated or synthetically processed to provide high performance properties.

[0046] Unconventional or unconventional base stocks / base oils include one or more of a mixture of base stock(s) derived from one or more gas-to-liquids (GTL) materials, as well as isomerized / isodewaxed(s) base stock(s) derived from natural wax or waxy feedstocks, mineral and / or non-mineral oil waxy feedstock stocks such as slack wax, natural wax, and waxy stocks such as gas oil, waxy fuels hydrocracker bottoms, waxy raffinate, hydrocrackate, thermal crackate, or other mineral, mineral oil, as well as waxy materials received from coal liquids or shale oil, as well as mixtures of such base stocks.

[0047] The base oils for use in the lubricating oil compositions of the present disclosure can be any of the 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 the various oils corresponding to Group III through Group V base oils due to their superior volatility, stability, viscometric and cleanliness characteristics.

[0048] Typically, the base oil has a viscosity of 2.5 to 20 mm. 2 / sec (e.g., 3 to 12 mm 2 / sec, 4~10mm 2 / sec, or 4.5-8mm 2 100°C in the range of 1 / sec (ASTM D445).

[0049] The lubricating oil composition may also contain conventional lubricant additives to provide auxiliary functions, resulting in 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, antiwear agents, detergents such as metal detergents, rust inhibitors, deodorizers, demulsifiers, friction modifiers, metal deactivators, pour point inhibitors, viscosity modifiers, antifoam agents, cosolvents, package compatibility agents, 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, may be used in the preparation of the lubricating oil composition of the present invention by conventional blending procedures.

[0050] Each of the foregoing additives, when used, is used in a functionally effective amount to impart the desired properties to the lubricant. Thus, for example, if the additive is an ashless dispersant, a functionally effective amount of the ashless dispersant is an amount sufficient to impart the desired dispersant characteristics to the lubricant. Generally, the concentration of each of these additives may range from about 0.001 to about 20% by weight, for example, from about 0.01 to about 10% by weight, unless otherwise specified.

[0051] The following illustrative examples are intended to be non-limiting.

[0052] Examples 1 to 15 The oxidative stability of the antioxidant compositions was evaluated using Pressurized Differential Scanning Calorimetry (PDSC) according to ASTM D 6186 test protocol. Longer PDSC times indicated improved oxidative stability. The results of Examples 1-15 are summarized in Table 1. Two PDSC runs were performed for each Example. Figure 1 shows this data in graphical form.

[0053] Each sample contained a large amount of base oil and a small amount of an antioxidant composition comprising a mixture of mono- and di-alkylated diphenylamines in a 1:1 weight percent ratio and / or additive, where the alkylating group is propylene tetramer.

[0054] Additives can be categorized into at least three groups: molybdenum-based, sulfur-based, or hindered phenolic. Certain additives can be divided into multiple category groups.

[0055] Example 1 is a PDSC result showing the degree of oxidative stability of Composition A, a mixture of alkylated diphenylamines containing a 1:1 weight percent ratio of monoalkylated (tetrapropenyl)diphenylamine and dialkylated (tetrapropenyl)diphenylamine. The mixture, which serves as the baseline measurement, is the reaction product of propylene oligomers and diphenylamine. Composition A is present at 1 weight percent.

[0056] Example 2 is a PDSC result showing the degree of oxidative stability of Composition B, a molybdenum succinimide. Molybdenum succinimide is a reaction product of an alkyl or alkenyl succinimide of a polyamine with an acidic molybdenum compound. Details of this reaction are described in US 8,476,460, the relevant portions of which are incorporated herein by reference. Antioxidant Composition B is present at 0.44 wt. %. The molybdenum concentration is 200 ppm.

[0057] Example 3 is a PDSC result showing the degree of synergy between compositions A and B. The concentration of A is 1 wt. %. The concentration of B is 0.44 wt. %.

[0058] Example 4 is a PDSC result showing the degree of oxidative stability of antioxidant Composition C. Composition C is a molybdenum amino alcohol commercially available from Vanderbilt Chemicals, LLC (Norwalk, CT) under the tradename Molyvan® 855. The concentration of C is 0.24% by weight. The molybdenum concentration is 200 ppm.

[0059] Example 5 is a PDSC result showing the degree of synergy between compositions A and C. The concentration of A is 1 wt. %. The concentration of B is 0.24 wt. %.

[0060] Example 6 is a PDSC result showing the degree of oxidative stability of Composition D, an ashless alkyldithiol carbamate commercially available from Vanderbilt Chemicals, LLC (Norwalk, CT) under the trade name Vanlube® 7723. The concentration of D is 0.37 wt. %. The sulfur concentration is 2000 ppm.

[0061] Example 7 is a PDSC result showing the degree of synergy between compositions A and D. The concentration of A is 1 wt. %. The concentration of B is 0.37 wt. %.

[0062] Example 8 is a PDSC result showing the degree of oxidative stability of composition E, which is the reaction product butyl-cyclohex-3-enecarboxylate, sulfur, and triphenyl phosphite. This reaction is described in US 3,498,915, which is incorporated herein by reference. The concentration of E is 0.67 wt. %. The sulfur concentration is 2000 ppm.

[0063] Example 9 is a PDSC result showing the degree of synergy between compositions A and E. The concentration of A is 1 wt. %. The concentration of E is 0.67 wt. %.

[0064] Example 10 is a PDSC result showing the degree of oxidative stability of Composition F. Composition F is a sulfur-containing phenolic antioxidant commercially available from Songwon (Friendswood, TX) under the tradename Songnox® 1035. The concentration of F is 1.22% by weight.

[0065] Example 11 is a PDSC result showing the level of synergy between compositions A and F. The concentration of A is 1 wt. %. The concentration of F is 1.22 wt. %.

[0066] Example 12 is a PDSC result showing the degree of oxidative stability of Composition G. Composition G is a non-sulfur containing methylene bisphenol antioxidant commercially available from SI Group, Schenectady, NY under the tradename Ethanox® 4702. The concentration of G is 0.46% by weight.

[0067] Example 13 is a PDSC result showing the level of synergy between compositions A and G. The concentration of A is 1 wt. %. The concentration of G is 0.46 wt. %.

[0068] Example 14 is a PDSC result showing the degree of oxidative stability of Composition H. Composition H is a non-sulfur-containing benzotriazole-substituted phenol antioxidant commercially available from Songwon (Friendswood, TX) under the tradename Songsorb® 3200. The concentration of H is 1% by weight.

[0069] Example 15 is a PDSC result showing the degree of synergy between compositions A and H. The concentration of A is 1 wt. %. The concentration of H is 1 wt. %.

[0070] As shown in Table 1, oxidation stability synergy can be seen between 1:1 mixtures of mono- and dialkylated diphenylamines and several additive compositions. These synergistic compositions include 1:1 mixtures of mono / dialkylated diphenylamines and a molybdenum-containing component (Examples 3 and 5) or a sulfur-containing component (Examples 7 and 9). In general, synergy between 1:1 mixtures of mono / dialkylated diphenylamines and phenolic antioxidants (Examples 13 and 15) was not observed except when a sulfur-containing phenolic antioxidant was used (Example 11). [Table 1]

[0071] Examples 16 to 19 Examples 16-18 include samples containing various weight percent ratios of diphenylamines alkylated with propylene tetramer, including a 50 / 50 mixture of mono- and di-alkylated diphenylamines (Example 16), a 75 / 25 mixture of mono- and di-alkylated diphenylamines (Example 17), and a 30 / 70 mixture of mono- and di-alkylated diphenylamines (Example 18).

[0072] Example 19 is a commercial mixture of mono / dialkylated diphenylamines containing about 70% by weight of dialkylated diphenylamine and about 25% by weight of monoalkylated diphenylamine. The mixture is commercially available from BASF (Florham Park, NJ) under the trade name Irganox® L67.

[0073] These samples were added to conventional lubricating oils containing a major amount of base oil(s) and small amounts of conventional lubricating oil additives (e.g., viscosity improvers, detergents, dispersants, antiwear agents, etc.). The samples were evaluated at equivalent nitrogen levels of 0.74-0.89 wt% using PDSC according to ASTM D6186 protocol. The results are summarized in Table 2 below and show that the high mono-alkylated diphenylamine mixtures are as effective as or more effective than the low mono-alkylated diphenylamine mixtures. Additionally, diphenylamines alkylated with propylene tetramer provide greater oxidation stability compared to diphenylamines alkylated with propylene trimer. [Table 2]

Claims

1. 1. A lubricating oil composition comprising: a major amount of base oil; 1. A small amount of an antioxidant composition comprising: a mixture of alkylated diphenylamines having a weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine ranging from 0.6 to 4; and and a molybdenum or sulfur additive which provides a synergistic enhancement of oxidation stability in combination with the mixture of alkylated diphenylamines.

2. 2. The lubricating oil composition of claim 1, wherein the mixture of alkylated diphenylamines is present at a concentration ranging from 0.01% to 5% by weight of the lubricating oil composition.

3. 2. The lubricating oil composition of claim 1, wherein the molybdenum or sulfur additive is present at a concentration in the range of 0.01% to 5% by weight of the lubricating oil composition.

4. 2. The lubricating oil composition of claim 1, wherein the mixture of alkylated diphenylamines is a mixture of diphenylamines alkylated primarily with propylene tetramer.

5. 2. The lubricating oil composition of claim 1, wherein the additive is a molybdenum succinimide, a molybdenum amino alcohol, a molybdenum dithiol carbamate, a sulfurized olefin ester, a sulfurized isobutylene, a methylene bisdithiocarbamate, a molybdenum dialkyl dithiocarbamate, a molybdenum ester / amide, a molybdenum dithiophosphate, a molybdenum amine complex, methylene bis(dibutyldithiocarbamate), a sulfurized hydrocarbon, a sulfurized ester, a sulfurized fatty acid, a sulfurized vegetable oil, a sulfurized isobutylene, a sulfur-containing phenol, or a thioester bishydrocinnamic ester.

6. 2. The lubricating oil composition of claim 1, wherein the weight ratio of the monoalkylated diphenylamine to the dialkylated diphenylamine ranges from 0.8 to 3.

7. 2. The lubricating oil composition of claim 1, wherein the weight ratio of the monoalkylated diphenylamine to the dialkylated diphenylamine ranges from 0.9 to 1.

1.

8. 10. The lubricating oil of claim 1, further comprising an antioxidant, an ashless dispersant, an antiwear agent, a detergent, a rust inhibitor, a deodorizer, a demulsifier, a friction modifier, a metal deactivator, a pour point inhibitor, a viscosity modifier, an antifoam agent, a co-solvent, a package compatibility agent, a corrosion inhibitor, a pigment, or an extreme pressure agent.

9. 1. An oxidative stabilization composition comprising: a mixture of alkylated diphenylamines having a weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine in the range of 0.6 to 4; and a molybdenum or sulfur additive which provides a synergistic enhancement of oxidative stability in combination with said mixture of alkylated diphenylamines.

10. 10. The oxidatively stabilized composition of claim 9, further comprising a lubricating oil, a mineral oil, a hydraulic fluid, a metal working fluid, or a gear oil.

11. 10. The oxidatively stabilized composition of claim 9, wherein the additive is an organomolybdenum compound, a sulfur-containing organomolybdenum compound, a sulfur-free organomolybdenum compound, or a sulfur-containing organic compound.

12. 10. The oxidatively stabilized composition of claim 9, wherein the additive is a molybdenum succinimide, a molybdenum amino alcohol, a molybdenum dithiolcarbamate, a molybdenum dialkyldithiocarbamate, a molybdenum ester / amide, a molybdenum dithiophosphate, a molybdenum amine complex, a sulfurized olefin ester, a sulfurized isobutylene, a methylene bisdithiocarbamate, a methylene bis(dibutyldithiocarbamate), a sulfurized hydrocarbon, a sulfurized ester, a sulfurized fatty acid, a sulfurized vegetable oil, a sulfurized isobutylene, or a thioester bishydrocinnamic ester.

13. 10. The oxidatively stabilized composition of claim 9, wherein the mixture of alkylated diphenylamines is a mixture of products of diphenylamines alkylated primarily with propylene tetramer.

14. 10. The oxidatively stabilized composition of claim 9, wherein the weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine ranges from 0.8 to 3.

15. 10. The oxidatively stabilized composition of claim 9, wherein the weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine ranges from 0.9 to 1.

1.

16. 10. The oxidatively stabilized composition of claim 9, further comprising an antioxidant, an ashless dispersant, an antiwear agent, a detergent, a rust inhibitor, a deodorizer, a demulsifier, a friction modifier, a metal deactivator, a pour point inhibitor, a viscosity modifier, an antifoam agent, a co-solvent, a package compatibility agent, a corrosion inhibitor, a pigment, or an extreme pressure agent.

17. 1. A method for improving the oxidative stability of a lubricating oil, comprising: a major amount of base oil; a mixture of alkylated diphenylamines having a weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine in the range of 0.6 to 4; and a molybdenum or sulfur additive which in combination with the mixture of alkylated diphenylamines provides a synergistic enhancement of oxidation stability.

18. The lubricating oil composition comprises 20. The method of claim 17, further comprising an antioxidant, an ashless dispersant, an antiwear agent, a detergent, a rust inhibitor, a deodorizer, a demulsifier, a friction modifier, a metal deactivator, a pour point inhibitor, a viscosity modifier, an antifoam agent, a co-solvent, a package compatibility agent, a corrosion inhibitor, a pigment, or an extreme pressure agent.

19. 20. The method of claim 17, wherein the mixture of alkylated diphenylamines is a product mixture of diphenylamines alkylated primarily with propylene tetramer.

20. 18. The method of claim 17, wherein the additive is a molybdenum succinimide, a molybdenum amino alcohol, a molybdenum dithiol carbamate, a sulfurized olefin ester, a sulfurized isobutylene, a methylene bisdithiocarbamate, a molybdenum dialkyl dithiocarbamate, a molybdenum ester / amide, a molybdenum dithiophosphate, a molybdenum amine complex, methylene bis(dibutyldithiocarbamate), a sulfurized hydrocarbon, a sulfurized ester, a sulfurized fatty acid, a sulfurized vegetable oil, a sulfurized isobutylene, or a thioester bishydrocinnamic ester.

21. 1. A lubricating oil composition comprising: a major amount of base oil; and a minor amount of an antioxidant comprising a mixture of alkylated diphenylamines having a weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine in the range of 0.6 to 4, wherein the alkylated diphenylamine is the product of alkylation of diphenylamine and propylene tetramer.

22. 22. The lubricating oil composition of claim 21, wherein the mixture of alkylated diphenylamines is present at a concentration in the range of 0.01% to 5% by weight of the lubricating oil composition.

23. 22. The lubricating oil of claim 21, further comprising an antioxidant, an ashless dispersant, an antiwear agent, a detergent, a rust inhibitor, a deodorizer, a demulsifier, a friction modifier, a metal deactivator, a pour point inhibitor, a viscosity modifier, an antifoam agent, a cosolvent, a package compatibility agent, a corrosion inhibitor, a pigment, or an extreme pressure agent.

24. 22. The lubricating oil of claim 21, wherein the weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine ranges from 0.8 to 3.

25. 22. The lubricating oil of claim 21, wherein the weight ratio of monoalkylated diphenylamine to dialkylated diphenylamine ranges from 0.9 to 1.1.

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