Improved viscosity control using short-chain zinc dialkyldithiophosphates

Abstract

A method of improving oxidation stability in an internal combustion engine is described. The method includes lubricating the internal combustion engine with a lubricating oil composition. The composition includes a major amount of an oil of lubricating viscosity; and a C3 / C8 zinc dialkyldithiophosphate. The total zinc content of the lubricating oil composition is at least 400ppm.

Description

IMPROVED VISCOSITY CONTROL USING SHORT-CHAIN ZINC DIALKYLDITHIOPHOSPHATESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The This application claims the benefit of U.S. Provisional Application No. 63 / 660,622 filed June 17, 2024, which is hereby incorporated by reference in its entirety.FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to methods of improving performance of a lubricating oil. More particularly, the present disclosure relates to the use of zinc dialkyldithiophosphate to improve oxidation stability of a lubricating oil composition.BACKGROUND

[0003] Over time, lubricants can undergo oxidation leading to sludge, varnish, and oil thickening which detrimentally impacts the lubricant’s performance. Antioxidants such as amines and phenols are widely used to control these decomposition pathways in engine oils. In particular, zinc dithiophosphates are used primarily as anti-wear agents in lubricants but are known to act as a secondary source of antioxidants via peroxide decomposition.SUMMARY OF THE INVENTION

[0004] In one aspect, there is provided a method of improving oxidation stability in an internal combustion engine, the method comprising: lubricating the internal combustion engine with a lubricating oil composition comprising: (a) a major amount of an oil of lubricating viscosity; and (b) a C3 / C8 zinc dialkyldithiophosphate; wherein the total zinc content of the lubricating oil composition is at least 400ppm.

[0005] In another aspect, there is provided a use of a lubricating oil composition to improve oxidation stability in an internal combustion engine, wherein the lubricating oil composition comprises: (a) a major amount of an oil of lubricating viscosity; and (b) a C3 / C8 zinc dialkyldithiophosphate; wherein the total zinc content of the lubricating oil composition is at least 400ppm.BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 compares percent increase in measurement of KV40 values with respect to time for formulations described in the Example section.DETAILED DESCRIPTION

[0007] The following terms will be used throughout the specification and will have the following meanings unless otherwise indicated.

[0008] The term “a major amount” of a base oil refers to where the amount of the base oil is at least 40 wt. % of the lubricating oil composition. In some embodiments, “a major amount” of a base oil refers to an amount of the base oil more than 50 wt. %, more than 60 wt. %, more than 70 wt. %, more than 80 wt. %, or more than 90 wt. % of the lubricating oil composition.

[0009] “HOB” refers to high overbased with a TBN above 250 on an actives basis and “LOB” refers to low overbased with a TBN below 100 on an actives basis.

[0010] The term “Total Base Number” or “TBN” refers to the level of alkalinity in an oil sample, which indicates the ability of the composition to continue to neutralize corrosive acids, in accordance with ASTM Standard No. D2896 or equivalent procedure. The test measures thechange in electrical conductivity, and the results are expressed as mgKOH / g (the equivalent number of milligrams of KOH needed to neutralize 1 gram of a product). Therefore, a high TBN reflects strongly overbased products and, as a result, a higher base reserve for neutralizing acids.

[0011] The present disclosure relates to a method or use of lubricating oil compositions with improved oxidation stability. In one embodiment, the present invention includes a method of reducing oxidation or improving oxidation stability in an internal combustion engine by lubricating the internal combustion engine with a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and a short-chain zinc dialkyldithiophosphate as described herein. It has been surprisingly discovered that the choice of alkyl group(s) on the short-chain zinc dialkyldithiophosphate can have a great impact on antioxidancy (Sequence IIH test results shown later).

[0012] In another embodiment, the present invention includes a use of a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and a short-chain zinc dialkyldithiophosphate in an internal combustion engine to reduce oxidation or improve oxidation stability.Oil of Lubricating Viscosity

[0013] The oil of lubricating viscosity (sometimes referred to as “base stock” or “base oil”) is the primary liquid constituent of a lubricant, into which additives and possibly other oils are blended, for example to produce a final lubricant (or lubricant composition). A base oil is useful for making concentrates as well as for making lubricating compositions therefrom, and may be selected from natural and synthetic lubricating oils and combinations thereof.

[0014] Natural oils include animal and vegetable oils, liquid petroleum oils and hydrorefined, solvent-treated mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic- naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils.

[0015] Synthetic lubricating oils include hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(l -hexenes), poly(l -octenes), poly(l -decenes); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes; polyphenols (e.g., biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulfides and the derivatives, analogues and homologues thereof. Polymerized olefins can also be derived from bio-derived sources such as hydrocarbon terpenes such as myrcene, ocimene and famesene which can also be co-polymerized with other olefins and further isomerized if desired.

[0016] Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., malonic acid, alkyl malonic acids, alkenyl malonic acids, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, fumaric acid, azelaic acid, suberic acid, sebacic acid, adipic acid, linoleic acid dimer, phthalic acid) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid.

[0017] Esters useful as synthetic oils also include those made from C5 to Cl 2 monocarboxylic acids and polyols, and polyol ethers such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol. Esters from bio-derived sources may also be useful as synthetic oils.

[0018] The base oil may be derived from Fischer-Tropsch synthesized hydrocarbons. Fischer- Tropsch synthesized hydrocarbons are made from synthesis gas containing H2 and CO using a Fischer-Tropsch catalyst. Such hydrocarbons typically require further processing in order to be useful as the base oil. For example, the hydrocarbons may be hydroisomerized; hydrocracked and hydroisomerized; dewaxed; or hydroisomerized and dewaxed; using processes known to those skilled in the art.

[0019] The base oil may be a renewable or bio-derived engine oil. Examples of such engine oils are disclosed in W02016061050 and US20190338211, which is incorporated herein by reference. According to some embodiments, the renewable or bio-derived base oil includes a biobased hydrocarbon, such as an isoparaffmic hydrocarbon derived from hydrocarbon terpenes, such as myrcene, ocimene, and farnesene. In some embodiments, the biobased hydrocarbon is produced from fatty acids or fatty esters.

[0020] Unrefined, refined and re-refined oils can be used in the present lubricating composition. Unrefined oils are those obtained directly from a natural or synthetic source without further purification treatment. For example, a shale oil obtained directly from retorting operations, a petroleum oil obtained directly from distillation or ester oil obtained directly from an esterification process and used without further treatment would be unrefined oil. Refined oils are similar to the unrefined oils except they have been further treated in one or more purification steps to improveone or more properties. Many such purification techniques, such as distillation, solvent extraction, acid or base extraction, filtration and percolation are known to those skilled in the art.

[0021] By applying similar refining processes to already-refined oils that have been used in service as those processes that are used to obtain those refined oils in the first place, re-refined oils may be obtained. Such re-refined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques for approval of spent additive and oil breakdown products.

[0022] Hence, the base oil which may be used to make the present lubricating composition may be selected from any of the base oils in Groups I-V as specified in the American Petroleum Institute (API) Base Oil Interchangeability Guidelines (API Publication 1509). Such base oil groups are summarized in Table 1 below:Table 1(a)Determined in accordance with ASTM D2007.(hlDetermined in accordance with ASTM D2622, ASTM D3120, ASTM D4294 or ASTMD4927.Determined in accordance with ASTM D2270.

[0023] Base oils suitable for use herein are any of the variety corresponding to API Group II, Group III, Group IV, and Group V oils and combinations thereof. In one embodiment, the base oil is a Group I base oil or a blend of two or more different Group I base oils. Suitable Group I base oils include any light overhead cuts from a vacuum distillation column, such as, for example, anyLight Neutral, Medium Neutral, and Heavy Neutral base stocks. The base oil may also include residual base stocks or bottoms fractions such as bright stock. Bright stock is a high viscosity base oil which has been conventionally produced from residual stocks or bottoms and has been highly refined and dewaxed.

[0024] In one embodiment, the base oil is a Group II base oil or a blend of two or more different Group II base oils. Suitable Group II base oils include, for example, paraffinic mineral oils obtained by a suitable combination of refining processes such as hydrorefining and dewaxing in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil.Short-Chain Zinc Dialkyldithiophosphates

[0025] The lubricating oil composition of the present disclosure includes a short-chain (C3 / C8) zinc dialkyldithiophosphate (ZDDP). In general, ZDDP is present in the lubricating oil composition in an amount necessary to provide a desirable performance benefit.

[0026] In some embodiments, the lubricating oil composition includes a total of about 400 to about 1000 ppm of Zn, such as about 400 to about 900 ppm, about 400 to about 800 ppm, about 400 to about 700 ppm, about 400 to about 600 ppm, about 400 to about 500 ppm, about 500 to about 1000 ppm, about 500 to about 900 ppm, about 500 to about 800 ppm, about 500 to about 700 ppm, about 500 to about 600 ppm, about 600 to about 1000 ppm, about 600 to about 900 ppm, about 600 to about 800 ppm, about 600 to about 700 ppm, about 650 to about 1000 ppm, about 650 to about 900 ppm, or about 650 to about 800 ppm.

[0027] In some embodiments, the lubricating oil composition includes a total of about 400 to about 850 ppm of Zn, such as about 400 to about 825 ppm of Zn, about 400 to about 800 ppm of Zn, about 400 to about 780 ppm of Zn, such as about 400 to about 760 ppm of Zn, about 450 to 850 ppm of Zn, about 450 to about 825 ppm of Zn, about 450 to about 800 ppm of Zn, about 450 toabout 760 ppm of Zn, about 500 to about 850 ppm of Zn, about 500 to about 825 ppm of Zn, about 500 to about 800 ppm of Zn, about 500 to about 780 ppm of Zn, about 500 to about 760 ppm of Zn, about 550 ppm to about 850 ppm of Zn, about 550 ppm to about 800 ppm of Zn, about 550 ppm to about 780 ppm of Zn, about 550 ppm to about 760 ppm of Zn, about 600 to 850 ppm of Zn, about 600 to about 825 ppm of Zn, about 600 to about 800 ppm of Zn, about 600 ppm to about 800 ppm of Zn, about 600 ppm to about 780 ppm of Zn, or about 400 ppm to about 760 ppm of Zn.

[0028] In some embodiments, the lubricating oil composition includes about 200 to about 850 ppm of Zn from short (C3) chain ZDDP, such as about 200 to about 825 ppm of Zn, about 200 to about 800 ppm of Zn, about 200 to about 780 ppm of Zn, such as about 200 to about 760 ppm of Zn, about 250 to 850 ppm of Zn, about 250 to about 825 ppm of Zn, about 250 to about 800 ppm of Zn, about 250 to about 760 ppm of Zn, about 300 to about 850 ppm of Zn, about 300 to about 825 ppm of Zn, about 300 to about 800 ppm of Zn, about 300 to about 780 ppm of Zn, about 300 to about 760 ppm of Zn, about 350 ppm to about 800 ppm of Zn, about 350 ppm to about 760 ppm of Zn, about 400 to 850 ppm of Zn, about 400 to about 825 ppm of Zn, about 400 to about 800 ppm of Zn, about 400 ppm to about 800 ppm of Zn, or about 400 ppm to about 760 ppm of Zn.

[0029] In some embodiments, the lubricating oil composition includes C4 / C6 ZDDP or C8 ZDDP. Each ZDDP component (e.g., C4 / C6 ZDDP, C8 ZDDP) may contribute about 200 to about 850 ppm of Zn to the lubricating oil composition, such as about 200 to about 825 ppm of Zn, about 200 to about 800 ppm of Zn, about 200 to about 780 ppm of Zn, such as about 200 to about 760 ppm of Zn, about 250 to 850 ppm of Zn, about 250 to about 825 ppm of Zn, about 250 to about 800 ppm of Zn, about 250 to about 760 ppm of Zn, about 300 to about 850 ppm of Zn, about 300 to about 825 ppm of Zn, about 300 to about 800 ppm of Zn, about 300 to about 780 ppm of Zn,about 300 to about 760 ppm of Zn, about 350 ppm to about 800 ppm of Zn, about 350 ppm to about 760 ppm of Zn, about 400 to 850 ppm of Zn, about 400 to about 825 ppm of Zn, about 400 to about 800 ppm of Zn, about 400 ppm to about 800 ppm of Zn, or about 400 ppm to about 760 ppm of Zn.

[0030] In some embodiments, the lubricating oil composition includes total of about 100 to about 1000 ppm of P, such as about 100 to about 900 ppm, about 100 to about 800 ppm, about 100 to about 700 ppm, about 100 to about 600 ppm, about 100 to about 500 ppm, about 100 to about 400 ppm, about 100 to about 300 ppm, about 100 to about 200 ppm, about 200 to about 1000 ppm, about 200 to about 900 ppm, about 200 to about 800 ppm, about 200 to about 700 ppm, about 200 to about 600 ppm, about 200 to about 500 ppm, about 200 to about 400 ppm, about 200 to about 300 ppm, about 300 to about 1000 ppm, about 300 to about 900 ppm, about 300 to about 800 ppm, about 300 to about 700 ppm, about 300 to about 600 ppm, about 300 to about 500 ppm, about 300 to about 400 ppm, about 400 to about 1000 ppm, about 400 to about 900 ppm, about 400 to about 800 ppm, about 400 to about 700 ppm, about 400 to about 600 ppm, about 400 to about 500 ppm, about 500 to about 1000 ppm, about 500 to about 900 ppm, about 500 to about 800 ppm, about 500 to about 700 ppm, about 500 to about 600 ppm, about 600 to about 1000 ppm, about 600 to about 900 ppm, about 600 to about 800 ppm, about 600 to about 700 ppm, about 700 to about 1000 ppm, about 700 to about 900 ppm, about 700 to about 800 ppm, about 800 to about 1000 ppm, about 800 to about 900 ppm, or about 900 to about 1000 ppm.

[0031] In some embodiments, the lubricating oil composition includes a total of about 200 to 725 ppm of P from ZDDP, such as about 200 to 700 ppm of P from ZDDP, 200 to about 690 ppm of P, about 200 to about 680 ppm of P, about 200 to about 670 ppm of P, about 200 to about 660 ppm of P, about 210 to about 725 ppm of P, about 210 to about 700 ppm of P, about 210 to about 690ppm of P, about 210 to about 680 ppm of P, about 210 to about 670 ppm of P, about 210 to about 660 ppm of P, about 220 to about 725 ppm of P, about 220 to about 700 ppm of P, about 220 to about 690 ppm of P, about 220 to about 680 ppm of P, about 220 to about 670 ppm of P, about 220 to about 660 ppm of P, about 230 to about 725 ppm of P, about 230 to about 700 ppm of P, about 230 to about 690 ppm of P, about 230 to about 680 ppm of P, about 230 to about 670 ppm of P, about 230 to about 660 ppm of P, about 240 to about 725 ppm of P, about 240 to about 700 ppm of P, about 240 to about 690 ppm of P, about 240 to about 680 ppm of P, about 240 to about 670 ppm of P, or about 240 to about 660 ppm of P.

[0032] In some embodiments, the lubricating oil composition includes about 200 to about 725 ppm of P from short (C3) chain ZDDP, such as about 200 to 700 ppm of P from ZDDP, 200 to about 690 ppm of P, about 200 to about 680 ppm of P, about 200 to about 670 ppm of P, about 200 to about 660 ppm of P, about 210 to about 725 ppm of P, about 210 to about 700 ppm of P, about 210 to about 690 ppm of P, about 210 to about 680 ppm of P, about 210 to about 670 ppm of P, about 210 to about 660 ppm of P, about 220 to about 725 ppm of P, about 220 to about 700 ppm of P, about 220 to about 690 ppm of P, about 220 to about 680 ppm of P, about 220 to about 670 ppm of P, about 220 to about 660 ppm of P, about 230 to about 725 ppm of P, about 230 to about 700 ppm of P, about 230 to about 690 ppm of P, about 230 to about 680 ppm of P, about 230 to about 670 ppm of P, about 230 to about 660 ppm of P, about 240 to about 725 ppm of P, about 240 to about 700 ppm of P, about 240 to about 690 ppm of P, about 240 to about 680 ppm of P, about 240 to about 670 ppm of P, or about 240 to about 660 ppm of P.

[0033] In some embodiments, P may be contributed by C4 / C6 ZDDP or C8 ZDDP. In such cases, each ZDDP component may each contribute about 200 to about 725 ppm of P, such as about 200 to 700 ppm of P from ZDDP, 200 to about 690 ppm of P, about 200 to about 680 ppm of P, about200 to about 670 ppm of P, about 200 to about 660 ppm of P, about 210 to about 725 ppm of P, about 210 to about 700 ppm of P, about 210 to about 690 ppm of P, about 210 to about 680 ppm of P, about 210 to about 670 ppm of P, about 210 to about 660 ppm of P, about 220 to about 725 ppm of P, about 220 to about 700 ppm of P, about 220 to about 690 ppm of P, about 220 to about 680 ppm of P, about 220 to about 670 ppm of P, about 220 to about 660 ppm of P, about 230 to about 725 ppm of P, about 230 to about 700 ppm of P, about 230 to about 690 ppm of P, about 230 to about 680 ppm of P, about 230 to about 670 ppm of P, about 230 to about 660 ppm of P, about 240 to about 725 ppm of P, about 240 to about 700 ppm of P, about 240 to about 690 ppm of P, about 240 to about 680 ppm of P, about 240 to about 670 ppm of P, or about 240 to about 660 ppm of P.

[0034] Suitable ZDDP can have the following formula:wherein Rl, R2, R3, and R4 are alkyl groups, wherein at least one of Rl, R2, R3, or R4 has 3 carbon atoms and at least one of Rl, R2, R3, or R4 has 8 carbon atoms.

[0035] In some embodiments, at least one of Rl, R2, R3, or R4 is a primary alkyl group. In some embodiments, at least one of Rl, R2, R3, or R4 is a secondary alkyl group.

[0036] Illustrative examples of the alkyl groups include n-propyl (C3), isopropyl (C3), n-octyl (C8), isooctyl (C8), 2-octyl (C8), 3 -octyl (C8), 4-octyl (C8), methylheptyl (C8), 2-ethylhexyl (C8), dimethylhexyl (C8), cyclohexylethyl (C8), ethylcyclohexyl (C8), and vinylhexyl (C8) groups.

[0037] Zinc dithiophosphates are coordination compounds that can be synthesized from phosphorodithioic acids from which metal salts can be prepared. Examples of dihydrocarbylphosphorodithioic acids and zinc salts, and processes for preparing such acids and salts are found in, for example, U.S. Pat. Nos. 4,101,428; 4,215,067; 4,263,150; and 4,495,075. These patents are hereby incorporated by reference for such disclosures.

[0038] Without being limited by theory, it is believed that the specific combination of the alcohols described herein leads to the desirable performance characteristics demonstrated in the Examples. Particularly useful ZDDPs include those derived from a mixture of alcohols. In some embodiments, the mixture of alcohols includes C3 and C8 (C3 / C8) alcohols.

[0039] Phosphorodithioic or dithiophosphoric acids (DTP A) are typically prepared by the reaction of phosphorous pentasulfide with an alcohol or phenol or mixtures of alcohols and / or phenols. The reaction involves at least four moles of the alcohol or phenol per mole of phosphorous pentasulfide, and may be carried out within the temperature range from about 50° C to about 200° C.

[0040] For example, the preparation of O,O-di-(isopropyl / 2-ethylhexyl) phosphorodithioic acid involves the reaction of phosphorous pentasulfide with at least four moles of a mixture of isopropanol and 2-ethylhexanol at about 100° C for up to 5 hours. Hydrogen sulfide is liberated, and the residue is the defined acid. The preparation of the zinc salt of this acid may be by reaction with zinc oxide in the presence of a promoter (for example acetic acid) at elevated reaction temperature and extended reaction period.

[0041] When derived from alkyl alcohols, the zinc dithiophosphate can also be referred to as zinc dialkyldithiophosphate.

[0042] The R groups (i.e., Rl, R2, etc.) derived from a mixture of alcohols having either 3 or 8 carbon atoms may provide performance benefits over other R groups. In some embodiments, the ZDDP comprises a specific ratio of C3 to C8 alcohols. Suitable ratios can range from about 95 / 5 molar ratio of C3 to C8 alcohols down to about 5 / 95 of C3 to C8 alcohols, such as a 90 / 10 ratio ofC3 to C8 alcohols, 85 / 15 ratio of C3 to C8 alcohols, 80 / 20 ratio of C3 to C8 alcohols, 75 / 25 ratio of C3 to C8 alcohols, 70 / 30 ratio of C3 to C8 alcohols, 60 / 40 ratio of C3 to C8 alcohols, 50 / 50 ratio of C3 to C8 alcohols, 40 / 60 ratio of C3 to C8 alcohols, 30 / 70 ratio to C3 to C8 alcohols, 25 / 75 ratio of C3 to C8 alcohols, 20 / 80 ratio of C3 to C8 alcohols, 10 / 90 ratio of C3 to C8 alcohols and so forth.

[0043] In some embodiments, the lubricating oil composition further includes C4 / C6 ZDDP or C8 ZDDPDetergents

[0044] The lubricating oil composition may include a metal detergent. Suitable metal detergents include metal carboxylate detergent, metal salicylate detergent, metal sulfonate detergent, or metal phenate detergent. The metal can be any metal suitable for making carboxylate, salicylate, sulfonate, or phenate detergents. Non-limiting examples of suitable metals include alkali metals, alkaline earth metals and transition metals. In some embodiments, the metal is Ca, Mg, Ba, K, Na, Li or the like.

[0045] Generally, the amount of the detergent is from about 0.001 wt. % to about 20 wt. %, from about 0.05 wt. % to about 3 wt. %, or from about 0.1 wt. % to about 1 wt. %, based on the total weight of the lubricating oil composition.

[0046] The metal detergents may have a wide range of TBN. In some embodiments, the metal detergent is a high-high overbased metal detergent, high overbased metal detergent, medium overbased metal detergent, or low overbased metal detergent.

[0047] Overbased metal detergents are generally produced by carbonating a mixture of hydrocarbons, detergent acid, for example: sulfonic acid, alkylhydroxybenzoate etc., metal oxideor hydroxides (for example calcium oxide or calcium hydroxide) and promoters such as xylene, methanol and water. For example, for preparing an overbased calcium sulfonate, in carbonation, the calcium oxide or hydroxide reacts with the gaseous carbon dioxide to form calcium carbonate. The sulfonic acid is neutralized with an excess of CaO or Ca(0H)2, to form the sulfonate.

[0048] Generally speaking, overbased detergents may be low overbased (LOB), e.g., an overbased salt having a TBN below 100 on an actives basis. In one aspect, the TBN of a low overbased salt may be from about 10 to about 100. In another aspect, the TBN of a low overbased salt may be from about 10 to about 80.

[0049] Overbased detergents may be medium overbased (MOB), e.g., an overbased salt having a TBN from about 100 to about 250 on an actives basis. In one aspect, the TBN of a medium overbased salt may be from about 100 to about 200. In another aspect, the TBN of a medium overbased salt may be from about 125 to about 175.

[0050] Overbased detergents may be high overbased (HOB), e.g., an overbased salt having a TBN above 250 on an actives basis. In one embodiment, the TBN of a high overbased salt may be from about 250 to about 600 on an actives basis.

[0051] Overbased detergents may be high-high overbased (HHOB), e g., an overbased salt having a TBN above 600 on an actives basis. In one embodiment, the TBN of a high-high overbased salt may be from about 600 to about 800 on an actives basis.Dispersant

[0052] The lubricating oil composition may include polyalkenyl succinimide dispersants such as those described herein. In general, the nitrogen content from the polyalkenyl succinimide based on the lubricating oil composition is from about 0.010 wt. % to about 0.30 wt. % such as fromabout 0.050 to about 0.25 wt. %, about 0.050 to about 0.20 wt. %, and about 0.050 to about 0.15 wt. %.

[0053] In one embodiment, a polyalkenyl bis-succinimide can be obtained by reacting a polyalkenyl-substituted succinic anhydride below:R\Owherein R is a polyalkenyl substituent derived from a polyalkene group having a number average molecular weight of from about 500 to about 3000, with a polyamine. In one embodiment, R is a polyalkenyl substituent derived from a polyalkene group having a number average molecular weight of from about 1000 to about 2500. In one embodiment, R is a polyisobutenyl substituent derived from a polyisobutene having a number average molecular weight of from about 500 to about 3000. In another embodiment, R is a polyisobutenyl substituent derived from a polyisobutene having a number average molecular weight of from about 1000 to about 2500.

[0054] Suitable polyamines for use in preparing the bis-succinimide dispersants include polyalkylene polyamines. Such polyalkylene polyamines will typically contain about 2 to about 12 nitrogen atoms and about 2 to 24 carbon atoms. Particularly suitable polyalkylene polyamines are those having the formula: H2N — (R'NH)x — H wherein R' is a straight- or branched-chain alkylene group having 2 or 3 carbon atoms and x is 1 to 9. Representative examples of suitable polyalkylene polyamines include ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylene hexamine, and heavy polyamines (e.g., Ethyleneamine E-100, available from Huntsman Company).

[0055] Generally, the polyalkenyl-substituted succinic anhydride is reacted with the polyamine at a temperature of about 130°C to about 220°C (e.g., 145°C to 175°C). The reaction can be carried out under an inert atmosphere, such as nitrogen or argon. Generally, a suitable molar charge of polyamine to polyalkenyl-substituted succinic anhydride is from about 0.35: 1 to about 0.6: 1 (e.g., 0.4: 1 to 0.5: 1). As used herein, the “molar charge of polyamine to polyalkenyl-substituted succinic anhydride” means the ratio of the number of moles of polyamine to the number of succinic groups in the succinic anhydride reactant.

[0056] One class of suitable polyalkenyl succinimides may be represented by the following:wherein R and R' are as described herein above and y is 1 to 11.

[0057] In some embodiments, the succinimide dispersant may be post-treated by a reactive boron compound (i.e., “borated) or organic carbonate.

[0058] Suitable boron compounds that can be used as a source of boron include, for example, boric acid, a boric acid salt, a boric acid ester, and the like. Representative examples of a boric acid include orthoboric acid, metaboric acid, paraboric acid, and the like. Representative examples of a boric acid salt include ammonium borates, such as ammonium metaborate, ammonium tetraborate, ammonium pentaborate, ammonium octaborate, and the like. Representative examples of a boric acid ester include monomethyl borate, dimethyl borate, trimethyl borate, monoethylborate, diethyl borate, triethyl borate, monopropyl borate, dipropyl borate, tripropyl borate, monobutyl borate, dibutyl borate, tributyl borate, and the like.Other Additives

[0059] Optionally, the lubricating oil composition may further comprise at least an additive or a modifier (hereinafter designated as "additive") that can impart or improve any desirable property of the lubricating oil composition. Any additive known to a person of ordinary skill in the art may be used in the lubricating oil compositions disclosed herein. Some suitable additives have been described in Mortier et al., "Chemistry and Technology of Lubricants," 2nd Edition. London, Springer, (1996); and Leslie R. Rudnick, "Lubricant Additives: Chemistry and Applications," New York, Marcel Dekker (2003), both of which are incorporated herein by reference. In some embodiments, the additive can be selected from the group consisting of antioxidants, antiwear agents, detergents, rust inhibitors, demulsifiers, friction modifiers, multi-functional additives, viscosity index improvers, pour point depressants, foam inhibitors, metal deactivators, dispersants, corrosion inhibitors, lubricity improvers, thermal stability improvers, anti-haze additives, icing inhibitors, dyes, markers, static dissipaters, biocides and combinations thereof.

[0060] In general, the concentration of each of the additives in the lubricating oil composition, when used, may range from about 0.001 wt. % to about 10 wt. %, from about 0.01 wt. % to about 5 wt. %, or from about 0.1 wt. % to about 2.5 wt. %, based on the total weight of the lubricating oil composition. Further, the total amount of the additives in the lubricating oil composition may range from about 0.001 wt. % to about 20 wt. %, from about 0.01 wt. % to about 10 wt. %, or from about 0.1 wt. % to about 5 wt. %, based on the total weight of the lubricating oil composition.

[0061] The following examples are presented to exemplify embodiments but are not intended to limit the application to the specific embodiments set forth. Unless indicated to the contrary, all parts and percentages are by weight. All numerical values are approximate. When numerical ranges are given, it should be understood that embodiments outside the stated ranges may still fall within the scope of the application. Specific details described in each example should not be construed as necessary features.EXAMPLES

[0062] The following examples are intended for illustrative purposes only and do not limit in any way the scope.

[0063] Several formulations (varying amounts of C3 / C8 ZDDP) were tested (Sequence IIH Test) for their impact on KV40. Table 2 summarizes the formulations and results. Each sample contained equal amounts of dispersants, Mg and Ca from detergents, friction modifiers, molybdenum, antioxidant(s), and foam inhibitor(s).Table 2Lower percent change in viscosity (PVIS) values are desirable while greater weighted piston deposit (WPD) values are desirable. Referencing Table 1, direct replacement of C8 ZDDP (Comparative Example 1) with C3 / C8 ZDDP (Example 1) causes a marked increase in the WPD while lowering the PVIS. Furthermore, as shown in Example 2, replacing the C4 / C6 ZDDP with an equivalent amount of C3 / C8 ZDDP, resulted in even greater improvements in PVIS and WPD values. If both C8 and C4 / C6 ZDDP are replaced by the C3 / C8 ZDDP (Example 3), then PVIS and WPD values improve dramatically.Sequence IIH Test

[0064] The objective of the Sequence IIH Test is to measure lubricant thickening and piston deposits under high-temperature conditions. The increase in the kinematic viscosity of the oil indicates the tendency of an oil to thicken because of oxidation. The test conditions are those as reported in ASTM D8111.

[0065] The Sequence IIH results show that upon increasing the amount of C3 / C8 ZDDP in the formulation, better oxidation stability is achieved. This is shown clearly in Figure 1 where an obvious trend is observed with a decrease in percent change of KV40 with an increase in C3 / C8 ZDDP.

[0066] It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of embodiments of the invention. For example, the functions described above and implemented for operating are for illustration purposes only. Other arrangements and methodsmay be implemented by those skilled in the art without departing from the scope and spirit of this application. Moreover, those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

Claims

CLAIMS1. A method of improving oxidation stability in an internal combustion engine, the method comprising: lubricating the internal combustion engine with a lubricating oil composition comprising:(a) a major amount of an oil of lubricating viscosity; and(b) a C3 / C8 zinc dialkyldithiophosphate; wherein the total zinc content of the lubricating oil composition is at least 400ppm.

2. The method of claim 1, wherein the lubricating oil composition includes about 400 to about 1000 ppm of Zn.

3. The method of claim 1, wherein the lubricating oil composition includes about 100 to about 1000 ppm of P.

4. The method of claim 1, wherein the lubricating oil composition further comprises a C4 / C6 zinc dialkyldithiophosphate.

5. The method of claim 4, wherein the C4 / C6 zinc dialkyldithiophosphate provides about 100 to about 1000 ppm of Zn to the lubricating oil composition.

6. The method of claim 1, wherein the lubricating oil composition includes about 200 to about 700 ppm of P.

7. The method of claim 6, wherein the P is provided by short-chain ZDDP comprising C3 group.

8. The method of claim 1, wherein the lubricating oil composition includes about 400 to about 800 ppm of Zn.

9. The method of claim 1, wherein the C3 / C8 ZDDP provides 200 to 760 ppm of Zn.

10. The method of claim 1, wherein the lubricating oil composition further comprises C8 zinc di alkyl dithi ophosphate .

11. The method of claim 1, wherein the lubricating oil composition further comprises a dispersant, detergent, friction modifier, antiwear agent, antioxidant or foam inhibitor.

12. Use of a lubricating oil composition to improve oxidation stability in an internal combustion engine, wherein the lubricating oil composition comprises:(a) a major amount of an oil of lubricating viscosity; and(b) a C3 / C8 zinc dialkyldithiophosphate; wherein the total zinc content of the lubricating oil composition is at least 400ppm.

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