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Title:
LUBRICANTS LEADING TO BETTER EQUIPMENT CLEANLINESS
Document Type and Number:
WIPO Patent Application WO/2016/156313
Kind Code:
A1
Abstract:
The present invention relates to the field of lubricants. In particular, the present invention is directed to the use of lubricant compositions comprising a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 11b for the reduction of deposit formation.

Inventors:
ECORMIER MURIEL (DE)
SCHERER MARKUS (DE)
HAYDEN THOMAS (US)
DERY MARY (US)
BACCHI ROBERT (US)
Application Number:
PCT/EP2016/056795
Publication Date:
October 06, 2016
Filing Date:
March 29, 2016
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
BASF SE (DE)
International Classes:
C10M129/68; C10M129/72; C10M129/74
Domestic Patent References:
WO2014005932A12014-01-09
WO2014184068A12014-11-20
WO2015044639A12015-04-02
WO2015078967A12015-06-04
Foreign References:
US20050070450A12005-03-31
US20030186824A12003-10-02
US20120289445A12012-11-15
US20060276354A12006-12-07
US8258326B12012-09-04
US5362378A1994-11-08
US5565086A1996-10-15
US5246566A1993-09-21
US5135638A1992-08-04
EP0710710A21996-05-08
EP0321302A21989-06-21
EP0321304A21989-06-21
US4149178A1979-04-10
US3382291A1968-05-07
US3742082A1973-06-26
US3769363A1973-10-30
US3876720A1975-04-08
US4239930A1980-12-16
US4367352A1983-01-04
US4413156A1983-11-01
US4434408A1984-02-28
US4910355A1990-03-20
US4956122A1990-09-11
US5068487A1991-11-26
US4234435A1980-11-18
US3172892A1965-03-09
US3381022A1968-04-30
Other References:
"Engine Oil Licensing and Certification System", December 1996
Attorney, Agent or Firm:
MAIWALD PATENTANWALTS GMBH (Postfach 33 05 23, München, DE)
Download PDF:
Claims:
Claims

1 . Use of a lubricating composition for reducing the formation of deposits, wherein the composition comprises

(i) at least one lubricating base oil, and

(ii) at least one synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b.

2. Use according to claim 1 , wherein the synthetic ester is selected from

(a) a diester of a dicarboxylic acid,

(b) a polyol ester, or

(d) mixtures thereof.

3. Use according to any one of the claims 1 to 2, wherein the diester of the dicarboxylic acid is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof.

4. Use according to any one of claims 1 to 3, wherein the lubricating base oil is selected from

Group I, Group II, Group III base oils according to the definition of the API, or mixtures thereof.

5. Use according to any one of claims 1 to 4, wherein the composition further comprises one or more other additives selected from the group consisting of viscosity index improvers, polymeric thickeners, antioxidants, corrosion inhibitors, detergents, dispersants, anti-foam agents, dyes, extreme pressure additives, antiwear additives, friction modifiers, metal deactivators, pour point depressants and the like.

6. Use according to any one of claims 1 to 5 wherein

(a) the deposits are determined according to the TEOST MHT D7097 test, or

(b) the deposits are measured according to ASTM D4310.

7. Use according to any one of claims 1 to 6, wherein the oxidation stability measured according to HPDSC test is increased compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof.

8. Use according to any one of claims 1 to 7, wherein the Noack volatility measured according to ASTM D5800 is decreased compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof, and wherein preferably the Noack volatility is below 12% weight loss, or equal or below about 10% weight loss.

9. Use according to any one of claims 1 to 8, wherein the dynamic viscosity determined at -35 °C according to ASTM4684 is at least about 100 mPa*s lower compared to a formulation wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof.

10. A lubricating composition comprising

(i) at least one base oil selected from a Group I oil according to the API classification,

(ii) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b, and

(iii) optional further additives.

1 1 . A lubricating composition comprising

(i) at least one base oil selected from a Group I, Group II oil according to the API classification, or a mixture thereof

(ii) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b ,

(iii) optional further additives.

12. The lubricating composition according to any one of claims 10 and 1 1 , wherein the synthetic ester is a diester of a dicarboxylic acid, and wherein preferably the diester of the dicarboxylic acid is selected from the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, and preferably is di-(isopropylheptyl)-adipate (DPHA).

13. A method for reducing deposit formation in a lubricating composition comprising a base oil comprising at least one Group I, Group II, or Group III base oil or mixtures thereof, comprising adding a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b to said lubricating composition.

14. The method according to claim13, wherein the synthetic ester is added after the lubricating base oil is present in the equipment.

15. The method according to any one of claims 13 to 14, wherein the synthetic ester is a diester of a dicarboxylic acid, and wherein preferably the diester of the dicarboxylic acid is selected from the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, and preferably is di- (isopropylheptyl)-adipate (DPHA).

Description:
Lubricants leading to better equipment cleanliness

Description

The present invention relates to the field of lubricants. In particular, the present invention is di- rected to the use of lubricant compositions comprising a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b for the reduction of deposit formation. Further, the present invention is directed to lubricant compositions comprising a lubricating base oil and a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b.

Technical background

Commercially available lubricant compositions are based on a multitude of different natural or synthetic components. The resulting properties of the various existing lubricant compositions are tailored to the specific technical requirements by the addition of further components and selected combinations thereof. In this way, lubricant compositions are obtained which can fulfill the complex requirements associated with the various special technical applications and equipment such as in the field of motor vehicles, automotive engines and other machinery. Typically, lubricant compositions are needed that provide good cleanliness (i.e. low amounts of deposits), high shear stability, improved low-temperature viscosity, minimum degree of evaporation loss, good fuel efficiency, acceptable seal compatibility and excellent wear protection, among others. In particular, lubricant compositions which are continuously exposed to temperatures of 80 °C or higher tend to form deposits such as sludge. The deposits may be caused by ageing of the components of the lubricant composition. Typically, detergents and dispersants are used to keep the ageing products in solution and thus either reduce or delay the formation of deposits in the lubricant composition. These additives, such as the detergents and dispersants, can only be applied to the composition in certain amounts since on the one hand they exhibit a limited solubility in typical lubricant base stocks such as Group I, Group II, Group III mineral oils or poly-alpha-olefins (PAOs) and on the other hand show in certain concentrations antagonistic effects with other additives or negative effects with respect to certain properties such as low temperature viscosity.

There is a continued need for lubricant compositions which are able to provide improved performance characteristics not found in the already existing ones.

One particular objective of the present invention is to provide improved lubricant compositions which exhibit lower tendencies to form deposits such as sludge. A further objective is to provide improved lubricant compositions which exhibit lower tendencies to form deposits measured according to the TEOST MHT D7097 test and their use in reduction of deposits. A further objective is to provide improved lubricant compositions which exhibit lower tendencies to form deposits measured according to ASTM D4310 and their use in reduction of deposits. One further objec- tive is to provide improved lubricant compositions which reduce the deposit formation (and thus improve the cleanliness) without altering the amount of detergents and dispersants applied in the composition. It is a further objective to provide a method for reducing the deposit formation in lubricant compositions.

Description of the invention

The present invention is directed to the use of a lubricating composition for reducing the formation of deposits, wherein the composition comprises

(i) at least one lubricating base oil, and

(ii) at least one synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b. In one embodiment, the synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b is selected from (a) a diester of a dicarboxylic acid,

(b) a polyol ester, or (c) mixtures thereof.

In another embodiment, the dicarboxylic acid moiety of the diester of the dicarboxylic acid is selected from the group consisting of phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, glutaric acid, diglycolic acid, 1 ,4-cyclohexanedicarboxylic acid, 2,6-decahydronaphthalenedicarboxylic acid, 1 ,3-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid and mixtures thereof.

In a preferred embodiment, the dicarboxylic acid moiety of the diester of the dicarboxylic acid is an aliphatic dicarboxylic acid and is preferably selected from the group consisting of succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, glutaric acid, 1 ,4-cyclohexanedicarboxylic acid, 2,6- decahydronaphthalenedicarboxylic acid, 1 ,3-cyclohexanedicarboxylic acid, 2,5- norbornanedicarboxylic acid and mixtures thereof, and more preferably is adipic acid.

In another preferred embodiment, the ester moiety of the diester of the dicarboxylic acid is in- dependently selected from the structure of formula (I)

whereas q, r and s are defined as follows,

q + r = 4 to 9,

s = 0 to 5,

q = 1 to 8, and

r = 1 to 6.

In another preferred embodiment, the the dicarboxylic acid moiety of the diester of the dicarboxylic acid is selected from the group consisting of succinic acid, maleic acid, fumaric acid, adipic acid, malonic acid, and mixtures thereof, and the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I) above.

In another preferred embodiment, the the dicarboxylic acid moiety of the diester of the dicarboxylic acid is adipic acid, and the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I) above. More preferred selections of the parameters q, r, and s of this embodiment are listed in the table below:

In another preferred embodiment, the diester of the dicarboxylic acid is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof.

In another preferred embodiment, the diester of the dicarboxylic acid is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof. DPHA is preferred. In one embodiment, the amount of diester of the dicarboxylic acid is from about 5 wt.-% to about 50 wt.-%, from about 5 wt.-% to about 40 wt.-%, from about 5 wt.-% to about 30 wt.-%, from about 8 wt.-% to about 28 wt.-%, from about 9 wt.-% to about 25 wt.-%, or from about 17 wt.-% to about 25 wt.-% based on the total weight of the composition.

In one embodiment, the synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b is a polyol ester. The polyol esters are obtainable by reaction polyols with carboxylic acids. Preferably the polyols have 2 to 10 hydroxyl groups per molecule and 3 to 30 carbon atoms, optionally the polyols have one or more ether linkages therein (e.g.dipentaerythritol). The polyols include but are not limited to neopentyl glycol (NPG), trimethylol propane (TMP), pentaerythritol (PE), dipentaerythritol and higher polyether oligomers of pentaerythritol. The carboxylic acid is preferably selected from a C6-C24 carboxylic acids. In one embodiment, the polyol ester of the present invention is trimethylolpropane caprylate (TMTC).

The lubricant compositions according to the present invention further comprise a lubricating base oils (or base stock) selected from the group consisting of mineral oils (Group I, II or III oils), polyalphaolefins (Group IV oils), polymerized and interpolymerized olefins, alkyl naphthalenes, alkylene oxide polymers, silicone oils, phosphate esters and carboxylic acid es- ters (Group V oils).

Preferably, the lubricant base oil is selected from Group I, Group II, Group III base oils according to the definition of the API, or mixtures thereof. Group I and Group II base oils are more preferred.

Definitions for the base oils (base stocks) according to the present invention are the same as those found in the American Petroleum Institute (API) publication "Engine Oil Licensing and Certification System", Industry Services Department, Fourteenth Edition, December 1996, Addendum 1 , December 1998. Said publication categorizes base stocks as follows: a) Group I base oils contain less than 90 percent saturates and/or greater than 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in the following table. b) Group II base oils contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in the following table. c) Group III base oils contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 120 using the test methods specified in the following table Analytical Methods for Base Stock:

d) Group IV base oils contain polyalphaolefins. Synthetic lower viscosity fluids suitable for the present invention include the polyalphaolefins (PAOs) and the synthetic oils from the hydro-cracking or hydro-isomerization of Fischer Tropsch high boiling fractions including waxes. These are both base oils comprised of saturates with low impurity levels con- sistent with their synthetic origin. The hydro-isomerized Fischer Tropsch waxes are highly suitable base oils, comprising saturated components of iso-paraffinic character (resulting from the isomerization of the predominantly n-paraffins of the Fischer Tropsch waxes) which give a good blend of high viscosity index and low pour point. Processes for the hydro-isomerization of Fischer Tropsch waxes are described in U.S. Patents 5,362,378; 5,565,086; 5,246,566 and 5,135,638, as well in EP 710710, EP 321302 and EP 321304.

Polyalphaolefins suitable for the lubricant compositions according to the present invention, include known PAO materials which typically comprise relatively low molecular weight hy- drogenated polymers or oligomers of alphaolefins which include but are not limited to C2 to about C32 alphaolefins with the C& to about C16 alphaolefins, such as 1 -octene, 1 - decene, 1 -dodecene and the like being preferred. The preferred polyalphaolefins are poly- 1 -octene, poly-1 -decene, and poly-1 -dodecene, although the dimers of higher olefins in the range of C14 to Cis provide low viscosity base stocks. Terms like PAO 4, PAO 6 or PAO 8 are commonly used specifications for different classes of polyalphaolefins characterized by their respective viscosity. For instance, PAO 6 refers to the class of polyalphaolefins which typically has viscosity in the range of 6 mm 2 /s at 100 °C. A variety of commercially available compositions are available for these specifications.

Low viscosity PAO fluids suitable for the lubricant compositions according to the present invention, may be conveniently made by the polymerization of an alphaolefin in the presence of a polymerization catalyst such as the Friedel-Crafts catalysts including, for example, aluminum trichloride, boron trifluoride or complexes of boron trifluoride with water, al- cohols such as ethanol, propanol or butanol, carboxylic acids or esters such as ethyl acetate or ethyl propionate. For example, the methods disclosed by U.S. Patents 4,149,178 or 3,382,291 may be conveniently used herein. Other descriptions of PAO synthesis are found in the following U.S. Patents: 3,742,082 (Brennan); 3,769,363 (Brennan); 3,876,720 (Heilman); 4,239,930 (Allphin); 4,367,352 (Watts); 4,413,156 (Watts); 4,434,408 (Larkin);

4,910,355 (Shubkin); 4,956,122 (Watts); and 5,068,487 (Theriot). e) Group V base oils contain any base stocks not described by Groups I to IV. Examples of Group V base oils include alkyl naphthalenes, alkylene oxide polymers, silicone oils, and phosphate esters.

Synthetic base oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(l -hexenes), poly(l -octenes), poly(1 - decenes)); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulfides and derivative, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hy- droxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic base oils. These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-polyiso-propylene glycol ether having a molecular weight of 1000 or diphenyl ether of polyethylene glycol having a molecular weight of 1000 to 1500); and mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C3-C8 fatty acid esters and C13 oxo acid diester of tetraethylene glycol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or polyaryloxysilicone oils and silicate oils comprise another useful class of synthetic base oils; such base oils include tetraethyl silicate, tetraisopropyl silicate, tetra-(2- ethylhexyl)silicate, tetra-(4-methyl- 2-ethylhexyl)silicate, tetra-(p-tert-butyl-phenyl) silicate, hexa-(4-methyl-2- ethylhexyl)disiloxane, oly(methyl)siloxanes and poly(methylphenyl)siloxanes. Other synthetic base oils include liquid esters of phosphorous-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric

tetrahydrofurans.

The lubricant compositions according to the present invention may also comprise a further addi- tive component. The further additive component as used in the present invention may include an additive package and/or performance additives.

The additive package that may be used in the present invention as well as the compounds relat- ing to performance additives are considered mixtures of additives that are typically used in lubricant compositions in limited amounts for mechanically, physically or chemically stabilizing the lubricant compositions while special performance characteristics can be further established or improved by the individual or combined presence of such selected additives. Besides the additive package described in the experimental part of the present application, a variety of such additive packages are known to the person skilled in the art and may commercially be available and typically used in lubricant compositions. One such preferred additive package that is commercially available is marketed under the name lrgalube2030A® by

BASF SE.

However, the individual components contained in the additive packages and/or the compounds further defined in the present invention as so-called performance additives include a larger number of different types of additives including dispersants, metal deactivators, detergents, extreme pressure agents (typically boron- and/or sulfur- and/or phosphorus- containing), anti- wear agents, antioxidants (such as hindered phenols, aminic antioxidants or molybdenum compounds), corrosion inhibitors, anti-foam agents, demulsifiers, pour point depressants, friction modifiers and mixtures thereof.

The lubricating composition of the present invention may further comprise one or more addi- tives selected from the group consisting of viscosity index improvers, polymeric thickeners, antioxidants, corrosion inhibitors, detergents, dispersants, anti-foam agents, dyes, wear protection additives, extreme pressure additives (EP additives), anti-wear additives (AW additives), friction modifiers, metal deactivators, pour point depressants and the like. Viscosity index improvers:

In one embodiment, the lubricant composition according to the present invention may further include at least one viscosity index improver (VII or VI improver). The viscosity index improvers include high molecular weight polymers that increase the relative viscosity of an oil at high tem- peratures more than they do at low temperatures. Viscosity index improvers include

polyacrylates, polymethacrylates, alkylmethacrylates, vinylpyrrolidone/methacrylate copolymers, poly vinylpyrrolidones, polybutenes, olefin copolymers such as an ethylene-propylene copolymer or a styrene-butadiene copolymer or polyalkene such as PIB, styrene/acrylate copolymers and polyethers, and combinations thereof. The most common VI improvers are methacrylate polymers and copolymers, acrylate polymers, olefin polymers and copolymers, and styrenebutadiene copolymers. Other examples of the viscosity index improver include polymethacrylate, polyisobutylene, alpha-olefin polymers, alpha-olefin copolymers (e.g. , an ethylenepropylene copolymer), polyalkylstyrene, phenol condensates, naphthalene conden- sates, a styrenebutadiene copolymer and the like. Of these, polymethacrylate having a number average molecular weight of 10000 to 300000, and alpha-olefin polymers or alpha-olefin copolymers having a number average molecular weight of 1000 to 30000, particularly ethylene- alpha-olefin copolymers having a number average molecular weight of 1000 to 10000 are pre- ferred.

The viscosity index increasing agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from 0.05 to 20.0 % by weight, in relation to the weight of the base stock.

(Polymeric) thickeners:

In one embodiment, the lubricant composition according to the present invention may further include at least one (polymeric) thickener. Suitable (polymeric) thickeners include, but are not limited to, polyisobutenes (PIB), oligomeric co-polymers (OCPs), polymethacrylates (PMAs), copolymers of styrene and butadiene, or high viscosity esters (complex esters).

Antioxidants: In one embodiment, the lubricant composition according to the present invention may further include at least one antioxidant. Antioxidants retard the oxidative degradation of base stocks during service. Such degradation may result in deposits on metal surfaces, such as the presence of sludge, or a viscosity increase in the lubricant. One skilled in the art knows a wide variety of oxidation inhibitors that are useful in lubricating oil compositions.

Antioxidants include phenolic antioxidants such as hindered phenolic antioxidants or non- phenolic oxidation inhibitors.

Useful phenolic antioxidants include hindered phenols. These phenolic antioxidants may be ashless (metal-free) phenolic compounds or neutral or basic metal salts of certain phenolic compounds. Typical phenolic antioxidant compounds are the hindered phenolics which are the ones which contain a sterically hindered hydroxyl group, and these include those derivatives of dihydroxy aryl compounds in which the hydroxyl groups are in the o or p-position to each other. Typical phenolic antioxidants include the hindered phenols substituted with alkyl groups having 6 carbon atoms or more and the alkylene coupled derivatives of these hindered phenols. Examples of phenolic materials of this type 2-t-butyl-4-heptyl phenol; 2-t-butyl-4-octyl phenol; 2-t-butyl-4-dodecyl phenol; 2,6-di-t-butyl-4-heptyl phenol; 2,6-di-t-butyl-4-dodecyl phenol; 2-methyl-6-t-butyl-4-heptyl phenol; and 2-methyl-6-t-butyl-4-dodecyl phenol. Other useful hindered mono-phenolic antioxidants may include for example hindered 2,6-di-alkyl- phenolic propionic ester derivatives. Bis-phenolic antioxidants may also be used in combination with the present invention. Examples of ortho-coupled phenols include: 2,2'-bis(4-heptyl-6-t-butyl- phenol); 2,2'-bis(4- octyl-6-t-butyl-phenol); and 2,2'-bis(4-dodecyl-6-t-butyl-phenol). Para- coupled bisphenols include for example 4,4'-bis(2,6-di-t-butyl phenol) and 4,4'- methylene- bis(2,6-di-t-butyl phenol).

Non-phenolic oxidation inhibitors which may be used include aromatic amine antioxidants and these may be used either as such or in combination with phenolics. Typical examples of non- phenolic antioxidants include: alkylated and non-alkylated aromatic amines such as aromatic monoamines of the formula R 8 R 9 R 10 N, where R 8 is an aliphatic, aromatic or substituted aromatic group, R 9 is an aromatic or a substituted aromatic group, and R 10 is H, alkyl, aryl or R 11 S(0)xR 12 , where R 11 is an alkylene, alkenylene, or aralkylene group, R 12 is a higher alkyl group, or an alkenyl, aryl, or alkaryl group, and x is 0, 1 or 2. The aliphatic group R 8 may contain from 1 to about 20 carbon atoms, and preferably contains from about 6 to 12 carbon atoms. The aliphatic group is a saturated aliphatic group. Preferably, both R 8 and R 9 are aromatic or substituted aromatic groups, and the aromatic group may be a fused ring aromatic group such as naphthyl. Aromatic groups R 8 and R 9 may be joined together with other groups such as S.

Typical aromatic amines antioxidants have alkyl substituent groups of at least about 6 carbon atoms. Examples of aliphatic groups include hexyl, heptyl, octyl, nonyl, and decyl. Generally, the aliphatic groups will not contain more than about 14 carbon atoms. The general types of amine antioxidants useful in the present compositions include diphenylamines, phenyl naphthylamines, phenothiazines, imidodibenzyls and diphenyl phenylene diamines. Mixtures of two or more aromatic amines are also useful. Polymeric amine antioxidants can also be used. Particular examples of aromatic amine antioxidants useful in the present invention include: ρ,ρ'- dioctyldiphenylamine; t-octylphenyl-alpha- naphthylamine; phenyl-alphanaphthylamine; and p- octylphenyl-alpha-naphthylamine. Sulfurized alkyl phenols and alkali or alkaline earth metal salts thereof also are useful antioxidants.

Corrosion inhibitors: In one embodiment, the lubricant composition according to the present invention may further include at least one corrosion inhibitor. Corrosion inhibitors are used to reduce the degradation of metallic parts that are in contact with the lubricant composition. Corrosion inhibitors can be described as any materials (additives, functionalized fluids, etc.) that may form a protective film on a surface that prevents corrosion agents from reacting or attacking that surface with a result- ing loss of surface material. Protective films may be absorbed on the surface or chemically bonded to the surface. Protective films may be constituted from mono-molecular species, oligomeric species, polymeric species, or mixtures thereof. Protective films may derive from the intact corrosion inhibitors, from their combination products, or their degradation products, or mixtures thereof. Surfaces that may benefit from the action of corrosion inhibitors may include metals and their alloys (both ferrous and non-ferrous types) and non-metals.

Corrosion inhibitors may include various oxygen-, nitrogen-, sulfur-, and phosphorus-containing materials, and may include metal-containing compounds (salts, organometallics, etc.) and nonmetal-containing or ashless materials. Corrosion inhibitors may include, but are not limited to, additive types such as, for example, hydrocarbyl-, aryl-, alkyl-, arylalkyl-, and alkylaryl- versions of detergents (neutral, overbased), sulfonates, phenates, salicylates, alcoholates, car- boxylates, salixarates, phosphites, phosphates, thiophosphates, amines, amine salts, amine phosphoric acid salts, amine sulfonic acid salts, alkoxylated amines, etheramines,

polyetheramines, amides, imides, azoles, diazoles, triazoles, benzotriazoles, benzothiadoles, mercaptobenzothiazoles, tolyltriazoles (TTZ-type), heterocyclic amines, heterocyclic sulfides, thiazoles, thiadiazoles, mercaptothiadiazoles, dimercaptothiadiazoles (DMTD-type), imidazoles, benzimidazoles, dithiobenzimidazoles, imidazolines, oxazolines, Mannich reactions products, glycidyl ethers, anhydrides, carbamates, thiocarbamates, dithiocarbamates, polyglycols, etc., or mixtures thereof.

Detergents: In one embodiment, the lubricant composition according to the present invention may further comprise at least one detergent. Detergents include cleaning agents that adhere to dirt particles, preventing them from attaching to critical surfaces. Detergents may also adhere to the metal surface itself to keep it clean and prevent corrosion from occurring. Detergents include calcium alkylsalicylates, calcium alkylphenates and calcium

alkarylsulfonates with alternate metal ions used such as magnesium, barium, or sodium. Examples of the cleaning and dispersing agents which can be used include metal-based detergents such as the neutral and basic alkaline earth metal sulphonates, alkaline earth metal phenates and alkaline earth metal salicylates alkenylsuccinimide and alkenylsuccinimide esters and their borohydrides, phenates, salienius complex detergents and ashless dispersing agents which have been modified with sulphur compounds. These agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from about 0.01 to about 1 .0 % by weight in relation to the weight of the base stock; these can also be high total base number (TBN), low TBN, or mixtures of high/low TBN.

Dispersants:

In one embodiment, the lubricant compositions according to the present invention further comprises at least one dispersant. Dispersants are lubricant additives that help to prevent sludge, varnish and other deposits from forming on critical surfaces. The dispersant may be a succinimide dispersant (for example N-substituted long chain alkenyl succinimides), a Mannich dispersant, an ester-containing dispersant, a condensation product of a fatty hydrocarbyl mon- ocarboxylic acylating agent with an amine or ammonia, an alkyl amino phenol dispersant, a hydrocarbyl-amine dispersant, a polyether dispersant or a polyetheramine dispersant.

In one embodiment the succinimide dispersant includes a polyisobutylene-substituted succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000, or of about 950 to about 1600. Succinimide dispersants and their methods of preparation are more fully described in U.S. Patents 4,234,435 and 3,172,892. Suitable ester-containing dispersants are typically high molecular weight esters. These materials are described in more detail in U.S. Patent 3,381 ,022. In one embodiment the dispersant includes a borated dispersant. Typically the borated disper- sant includes a succinimide dispersant including a polyisobutylene succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000. Borated dispersants are described in more detail above within the extreme pressure agent description.

Anti foam agents:

In one embodiment, the lubricant compositions according to the present invention further comprises at least one anti-foam agent. Anti-foam agents may be selected from silicones, polyacrylates, and the like. The amount of anti-foam agent in the lubricant compositions described herein may range from about 0.001 wt.-% to about 0.1 wt.-% based on the total weight of the formulation. As a further example, an anti-foam agent may be present in an amount from about 0.004 wt.-% to about 0.008 wt.-%.

Extreme pressure additives (EP additives):

In one embodiment, the lubricant compositions according to the present invention further comprises at least one extreme pressure additive. In one embodiment according to the present in- vention, the extreme pressure agent is a sulfur-containing compound. In one embodiment, the sulfur-containing compound may be a sulfurised olefin, a polysulfide, or mixtures thereof. Examples of the sulfurised olefin include a sulfurised olefin derived from propylene, isobutylene, pentene; an organic sulfide and/or polysulfide including benzyldisulfide; bis-(chlorobenzyl) disulfide; dibutyl tetrasulfide; di-tertiary butyl polysulfide; and sulfurised methyl ester of oleic acid, a sulfurised alkylphenol, a sulfurised dipentene, a sulfurised terpene, a sulfurised Diels-Alder adduct, an alkyl sulphenyl N'N- dialkyl dithiocarbamates; or mixtures thereof.

In one embodiment the sulfurised olefin includes a sulfurised olefin derived from propylene, isobutylene, pentene or mixtures thereof.

In one embodiment according to the present invention, the extreme pressure additive sulfur- containing compound includes a dimercaptothiadiazole or derivative, or mixtures thereof. Examples of the dimercaptothiadiazole include compounds such as 2, 5-dimercapto-1 ,3,4- thiadiazole or a hydrocarbyl-substituted 2, 5-dimercapto-1 ,3,4-thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-1 ,3,4-thiadiazole typically form by forming a sulfur-sulfur bond between 2,5-dimercapto-1 ,3,4-thiadiazole units to form derivatives or oligomers of two or more of said thiadiazole units. Suitable 2,5-dimercapto-1 ,3,4-thiadiazole derived compounds include for example 2,5-bis(tert-nonyldithio)-1 ,3,4-thiadiazole or 2-tert- nonyldithio-5-mercapto-1 ,3,4-thiadiazole. The number of carbon atoms on the hydrocarbyl substituents of the hydrocarbyl-substituted 2, 5-dimercapto-1 ,3,4-thiadiazole typically include 1 to 30, or 2 to 20, or 3 to 16. Extreme pressure additives include compounds containing boron and/or sulfur and/or phosphorus. The extreme pressure agent may be present in the lubricant compositions at 0 wt.-% to about 20 wt.-%, or at about 0.05 wt.-% to about 10.0 wt.-%, or at about 0.1 wt.-% to about 8 wt.-% of the lubricant composition. Anti-wear additives (AW additives):

In one embodiment, the lubricant compositions according to the present invention further comprises at least one anti-wear additive. Examples of anti-wear additives include organo borates, organo phosphites such as didodecyl phosphite, organic sulfur-containing compounds such as sulfurized sperm oil or sulfurized terpenes, zinc dialkyl dithiophosphates, zinc diaryl

dithiophosphates, phosphosulfurized hydrocarbons and any combinations thereof.

Friction modifiers: In another embodiment, the lubricant compositions according to the present invention includes at least one friction modifier. A friction modifier is any material or materials that can alter the coefficient of friction of a surface lubricated by any lubricant or fluid containing such material(s). Friction modifiers, also known as friction reducers, or lubricity agents or oiliness agents, and other such agents that change the ability of base oils, formulated lubricant compositions, or functional fluids, to modify the coefficient of friction of a lubricated surface may be effectively used in combination with the base oils or lubricant compositions of the present invention if desired. Friction modifiers may include metal-containing compounds or materials as well as ashless compounds or materials, or mixtures thereof. Metal-containing friction modifiers include metal salts or metal-ligand complexes where the metals may include alkali, alkaline earth, or transition group metals. Such metal-containing friction modifiers may also have low-ash characteristics. Transition metals may include Mo, Sb, Sn, Fe, Cu, Zn, and others. Ligands may include hydrocarbyl derivative of alcohols, polyols, glycerols, partial ester glycerols, thiols, carboxylates, carbamates, thiocarbamates, dithiocarbamates, phosphates, thiophosphates, dithiophosphates, amides, imides, amines, thiazoles, thiadiazoles, dithiazoles, diazoles, triazoles, and other polar molecular functional groups containing effective amounts of O, N, S, or P, individually or in combination. In particular, Mo-containing compounds can be particularly effective such as for example Mo-dithiocarbamates, Mo(DTC), Mo-dithiophosphates, Mo(DTP), Mo-amines, Mo (Am), Mo-alcoholates, Mo- alcohol-amides, and the like. Ashless friction modifiers may also include lubricant materials that contain effective amounts of polar groups, for example, hydroxyl-containing hydrocarbyl base oils, glycerides, partial glycer- ides, glyceride derivatives, and the like. Polar groups in friction modifiers may include hydrocarbyl groups containing effective amounts of O, N, S, or P, individually or in combination. Other friction modifiers that may be particularly effective include, for example, salts (both ash- containing and ashless derivatives) of fatty acids, fatty alcohols, fatty amides, fatty esters, hy- droxyl-containing carboxylates, and comparable synthetic long-chain hydrocarbyl acids, alcohols, amides, esters, hydroxy carboxylates, and the like. In some instances fatty organic acids, fatty amines, and sulfurized fatty acids may be used as suitable friction modifiers.

Examples of friction modifiers include fatty acid esters and amides, organo molybdenum compounds, molybdenum dialkylthiocarbamates and molybdenum dialkyl dithiophosphates. Metal deactivators:

In another embodiment, the lubricant compositions according to the present invention further comprises at least one metal deactivator. In various embodiments, one or more metal deactivators can be included in the composition. Suitable, non-limiting examples of the one or more metal deactivators include benzotriazoles and derivatives thereof, for example 4- or 5- alkylbenzotriazoles (e.g. triazole) and derivatives thereof, 4,5,6,7-tetrahydrobenzotriazole and 5,5'-methylenebisbenzotriazole; Mannich bases of benzotriazole or triazole, e.g. 1 -[bis(2- ethylhexyl) aminomethyl) triazole and 1 -[bis(2- ethylhexyl) aminomethyl)benzotriazole; and alkoxyalkylbenzotriazoles such as 1 -(nonyloxymethyl)benzotriazole, 1 -(1 - butoxyethyl)benzotriazole and 1 -(1 -cyclohexyloxybutyl) triazole, and combinations thereof.

Additional non-limiting examples of the one or more metal deactivators include 1 ,2,4-triazoles and derivatives thereof, for example 3-alkyl(or aryl)-1 , 2,4-triazoles, and Mannich bases of 1 ,2,4-triazoles, such as 1 -[bis(2-ethylhexyl) aminomethyl -1 , 2,4-triazole; alkoxyalky1 -1 , 2,4- triazoles such as 1 -(1 -butoxyethyl)-1 , 2,4-triazole; and acylated 3-amino-1 , 2,4-triazoles, imidazole derivatives, for example 4,4'-methylenebis(2-undecyl-5-methylimidazole) and bis[(N- methyl)imidazol-2-yl]carbinol octyl ether, and combinations thereof.

Further non-limiting examples of the one or more metal deactivators include sulfur-containing heterocyclic compounds, for example 2-mercaptobenzothiazole, 2,5-dimercapto-1 , 3,4- thiadiazole and derivatives thereof; and 3,5-bis[di(2- ethylhexyl) aminomethyl]-1 , 3,4- thiadiazolin-2-one, and combinations thereof. Even further non-limiting examples of the one or more metal deactivators include amino compounds, for example salicylidenepropylenediamine, salicylaminoguanidine and salts thereof, and combinations thereof.

The one or more metal deactivators are not particularly limited in amount in the composition but are typically present in an amount of from about 0.01 to about 0.1 , from about 0.05 to about 0.01 , or from about 0.07 to about 0.1 , wt.-% based on the weight of the composition. Alternatively, the one or more metal deactivators may be present in amounts of less than about 0.1 , of less than about 0.7, or less than about 0.5, wt.-% based on the weight of the composition.

Pour point depressants: In another embodiment, the lubricant compositions according to the present invention further comprises at least one pour point depressant. Pour point depressants (PPD) include polymethacrylates, alkylated naphthalene derivatives, and combinations thereof. Commonly used additives such as alkylaromatic polymers and polymethacrylates are also useful for this purpose. Typically the treat rates range from about 0.001 wt.-% to about 1.0 wt.-%, in relation to the weight of the base stock.

Demulsifiers: In another embodiment, the lubricant compositions according to the present invention further comprises at least one demulsifier. Demulsifiers include trialkyl phosphates, and various polymers and copolymers of ethylene glycol, ethylene oxide, propylene oxide, or mixtures thereof.

It has been found that the application of the synthetic ester having an Iodine value of lower than 10 g I /100 g measured according to DGF c-V 1 1 b in the lubricating composition according to the present invention may be used to reduce deposit formation (i.e. to improve the cleanliness in operation) and the oxidative stability of lubricating formulations in operation such as motor- and turbine oils. The method DGF c-V 1 1 b corresponds to the method according to Kaufmann. In one embodiment the reduction of deposits is determined according to the TEOST MHT

D7097 test. The TEOST MHT D7097 test is designed to predict the deposit forming tendencies of a lubricating composition in the piston ring belt and upper piston crown area. Such deposits formed in the ring belt area can cause problems with equipment operation and longevity. In the TEOST MHT D7097 test deposit are measured on the rods and the filter. The sum of these two deposits at rods and filter is called "total deposits".

In one embodiment, the total deposits are reduced by at least about 5 mg, by at least about 7 mg, by at least about 10 mg, by at least about 15 mg measured according to the TEOST MHT D7097 test compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, group II, Group III base oils or mixtures thereof. For illustrative purposes only, two lubricant composition which may be compared are described below. The illustrative inventive lubricant composition comprises a motor oil formulation (e.g. a 5W-20 motor oil formulation according to SAE classification), to which about 25 wt.-% of a mixture of a synthetic ester having an Iodine value of lower than 10 g I /100 g measured according to DGF c-V 1 1 b (such as DPHA) and an additive package is added. The synthetic ester may be present in an amount of about 90 wt.-%, the additive package in an amount of about 10 wt.-% of the mixture added. The comparative composition comprises said motor oil formulation, to which 25 wt.-% of a mixture of e.g. a Group III mineral oil (replacing the synthetic ester component) and the same additive package is added. The amount of the Group III mineral oil and the additive package in the comparative composition is identical to the ones for the synthetic ester and the additive package in the inventive composition, respectively. In one embodiment, the rod deposits are reduced by at least about 5 mg, by at least about 7 mg, by at least about 10 mg, by at least about 15 mg, by at least about 20 mg measured according to the TEOST MHT D7097 test compared to a composition wherein the synthetic ester component has been replaced by a lubricant base oil selected from Group I, group II, Group III base oils or mixtures thereof.

In one embodiment, the filter deposits are reduced by at least about 0,1 mg, by at least about 0,2 mg, or by at least about 0,5 mg measured according to the TEOST MHT D7097 test compared to a composition wherein the synthetic ester component has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof.

In one embodiment, the total deposits after the TEOST MHT D7097 test has been reduced by about 10%, by about 15%, by about 20%, by about 25%, by about 30% or by about 40% compared to a composition wherein the synthetic ester component has been replaced by a lubricant base oil selected from Group I, group II, Group III base oils or mixtures thereof.

In another embodiment, the deposits are measured according to ASTM D4310. The ASTM method D4310 measures insoluble material or metal corrosion products (or both) that may form in lubricating compositions that are subjected to oxidizing conditions.

In one embodiment, the deposits measured according to ASTM D4310 are less than about 60 mg, less than about 55 mg, or less than about 50 mg.

In one embodiment, the deposits (e.g. sludge) after the test according to ASTM D4310 has been reduced by about 10%, by about 15% or by about 20% compared to a composition wherein the synthetic ester component has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof.

In one embodiment of the present invention, the oxidative stability of the lubricant composition has been increased compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof.

In one embodiment, the oxidation stability is measured by High Pressure Differential Scanning Calorimetry (HPDSC). In one embodiment, the increase in stability is indicated by a higher on- set temperature at which a sample is oxidized at a certain oxygen pressure. In an alternative embodiment, the increase in stability may be indicated by a longer oxidative induction time (OIT) at a given temperature. Again, the increase in stability is measured in comparison to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof, as indicated above. In one embodi- ment, the oxidative induction time (OIT) is measured according to ASTM D6186.

As mentioned above, lubricant composition, which are operated at higher temperatures (e.g. at 80 °C or higher) may show an evaporation loss of the lubricant composition which loss contrib- utes to a consumption of the lubricating composition during operation. This may lead to a change in properties of the lubricating composition. Therefore, it is beneficial that the evaporation loss of a lubricating composition is decreased or kept to a minimum. A method to determine the evaporation loss of a lubricating composition is the so called Noack volatility test. In one embodiment, the Noack volatility test is performed according to ASTM D5800 B.

In one embodiment of the present invention the Noack volatility measured according to ASTM D5800 (such as procedure B of ASTM D5800) is decreased compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof.

In one embodiment, the Noack volatility is below 12% weight loss, equal or below about 10% weight loss, equal or below about 9% weight loss, or equal to or below about 8% weight loss. In one embodiment, the Noack volatility of a composition of the present invention is decreased by about 5%, about 8%, about 10% or about 12% compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, group II, Group III base oils or mixtures thereof. In another embodiment of the present invention the dynamic viscosity determined at -35 °C according to ASTM4684 is at least about 100 mPa * s lower, at least about 200 mPa * s lower, at least about 500 mPa * s lower, at least about 700 mPa * s lower compared to a formulation wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oil or mixtures thereof. In one embodiment, the dynamic viscosity is determined after the TEOST MHT D7097 test has been completed.

In a preferred embodiment, the lubricating composition according to the present invention hibits at least one of the properties described above, i.e. (i) reduced deposit formation measured according to the TEOST MHT D7097 test;

(ii) reduced deposit formation measured according to ASTM D4310;

(iii) an improved oxidative stability indicated by a higher onset temperature in a

HPDSC ramping experiment;

(iv) an improved oxidative stability indicated by a longer oxidation inductive time in a HPDSC oxidation inductive time experiment;

(v) a reduced Noack volatility (measured according to ASTM D5800, e.g. procedure B);

(vi) a lower dynamic viscosity determined at -35 °C according to ASTM 4684.

It is apparent to a person skilled in the art that various combinations (i.e. a composition exhibiting two of the above properties, three of the above properties, four of the above properties, etc) of the properties listed above under items (i) to (vi) are also encompassed in the present invention. In another embodiment, the present invention is also directed to a lubricating composition comprising (i) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b, and

(ii) optional further additives.

In one aspect of this embodiment, the synthetic ester is a diester of a dicarboxylic acid. In a preferred aspect of this embodiment, the diester of the dicarboxylic acid is selected from the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) and mixtures thereof. Di-(isopropylheptyl)- adipate (DPHA) is particularly preferred. In another embodiment, the present invention is also directed to a lubricating composition comprising

(i) at least one base oil selected from a Group I, Group II or Group III oil according to the API classification or a mixture thereof,

(ii) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b, and

(iii) optional further additives.

In another embodiment, the at least one base oil is a Group I base oil. Thus, the present inven- tion is also directed to a lubricating composition comprising

(i) at least one base oil selected from a Group I oil according to the API classification,

(ii) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b, and

(iii) optional further additives.

In another embodiment of this aspect, wherein the synthetic ester is a diester of a dicarboxylic acid, the present invention is also directed to a lubricating composition comprising (i) at least one base oil selected from a Group I oil according to the API classification,

(ii) a diester of a dicarboxylic acid, and

(iii) optional further additives.

In a preferred embodiment, the diester of the dicarboxylic acid of this embodiment is selected from a diester, wherein the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I)

(I) whereas q, r and s are defined as follows,

q + r = 4 to 9,

s = 0 to 5,

q = 1 to 8, and

r = 1 to 6. In another preferred embodiment, the dicarboxylic acid moiety of the diester of the dicarboxylic acid is selected from the group consisting of succinic acid, maleic acid, fumaric acid, adipic acid, malonic acid, and mixtures thereof, and the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I) above. In another preferred embodiment, the dicarboxylic acid moiety of the diester of the dicarboxylic acid is adipic acid, and the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I) above. More preferred selections of the parameters q, r, and s of this embodiment are listed in the table below:

In another embodiment, the diester of the dicarboxylic acid of the lubricating composition of the present invention is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof. In another embodiment, the diester of the dicarboxylic acid of the lubricating composi- tion of the present invention is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof. Di-(isopropylheptyl)-adipate (DPHA) is particularly preferred. Di-(isopropylheptyl)-adipate (DPHA) is commercially available as Synative ES DPHA from BASF SE. In a further preferred embodiment, the lubricating composition comprises

(i) at least one base oil selected from a Group I oil according to the API classification,

(ii) di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof. and

(iii) optional further additives.

In a further embodiment, the lubricating composition comprises

(i) at least one base oil selected from a Group I, Group II or Group III oil according to the API classification or a mixture thereof,

(ii) di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof. and

(iii) optional further additives.

In a further preferred embodiment, the lubricating composition comprises

(ii) at least one base oil selected from a Group I oil according to the API classification, (ii) di-(isopropylheptyl)-adipate (DPHA), and

(iii) optional further additives.

In a further embodiment, the lubricating composition comprises

(ii) at least one base oil selected from a Group I, Group II or Group III oil according to the API classification or a mixture thereof,

(ii) di-(isopropylheptyl)-adipate (DPHA), and

(iii) optional further additives.

In one embodiment, the further additives comprise antioxidants, corrosion inhibitors and metal deactivators. Such an additive package is for example commercially available as Irgalube 2030 A® from BASF SE.

In one embodiment the Group I, Group II, Group III base oil or a mixture thereof may be present in an amount from about 70 wt.-% to about 95 wt.-% based on the total lubricating compo- sition. The diester of the dicarboxylic acid may be present in an amount from about 5 wt.-% to about 15 wt.% based on the total lubricating composition. The further additives, if present, may be present in an amount from about 0.1 wt.-% to about 10.0 wt.-% based on the total lubricating composition. In one embodiment the Group I, Group II, Group III base oil or a mixture thereof may be present in an amount from about 70 wt.-% to about 95 wt.-% based on the total lubricating composition. The diester of the dicarboxylic acid may be present in an amount from about 5 wt.-% to about 15 wt.% based on the total lubricating composition. The further additives, if present, may be present in an amount from about 0.1 wt.-% to about 3.0 wt.-% based on the total lubricating composition.

In one embodiment the Group I base oil may be present in an amount from about 70 wt.-% to about 95 wt.-% based on the total lubricating composition. The diester of the dicarboxylic acid may be present in an amount from about 5 wt.-% to about 15 wt.% based on the total lubricating composition. The further additives, if present, may be present in an amount from about 0.1 wt.-% to about 3.0 wt.-% based on the total lubricating composition. In another embodiment the Group I base oil may be present in an amount from about 80 wt.-% to about 95 wt.-% based on the total lubricating composition. The diester of the dicarboxylic acid may be present in an amount from about 5 wt.-% to about 13 wt.-% based on the total lubricating composition. The further additives, if present, may be present in an amount from about 0.1 wt.-% to about 3.0 wt.-% based on the total lubricating composition.

In another embodiment, the present invention is also directed to a lubricating composition comprising

(i) at least one base oil from a Group I or Group II oil according to the API classification, or a mixture thereof,

(ii) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b, and

(iii) optional further additives. In another embodiment of this aspect, the synthetic ester is a diester of a dicarboxylic acid. Thus, the present invention is also directed to a lubricating composition comprising

(i) at least one base oil from a Group I, Group II oil according to the API classification, or a mixture thereof,

(ii) a diester of a dicarboxylic acid, and

(iii) optional further additives.

In another aspect, the present invention is also directed to a lubricating composition comprising

(i) at least one base oil from a Group I, Group II oil according to the API classification, or a mixture thereof, (ii) a diester of a dicarboxylic acid, wherein the diester of the dicarboxylic acid is selected from the group consisting of Di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA), or mixtures thereof and

(iii) optional further additives.

In another aspect, the present invention is also directed to a lubricating composition comprising

(i) at least one base oil from a Group I, Group II oil according to the API classification, or a mixture thereof,

(ii) a diester of a dicarboxylic acid, wherein the diester of the dicarboxylic acid is Di- (isopropylheptyl)-adipate (DPHA), and

(iii) optional further additives.

In one preferred embodiment, the lubricating composition comprises a motor oil formulation, suchs a a typical 5W-20 motor oil formulation.

In a preferred embodiment, the diester of the dicarboxylic acid on this embodiment is selected from a diester, wherein the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I)

(I) whereas q, r and s are defined as follows,

q + r = 4 to 9,

s = 0 to 5,

q = 1 to 8, and

r = 1 to 6. In another preferred embodiment, the dicarboxylic acid moiety of the diester of the dicarboxylic acid is selected from the group consisting of succinic acid, maleic acid, fumaric acid, adipic acid, malonic acid, and mixtures thereof, and the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I) above. In another preferred embodiment, the dicarboxylic acid moiety of the diester of the dicarboxylic acid is adipic acid, and the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I) above. More preferred selections of the parameters q, r, and s of this embodiment are listed in the table below: Ester moiety

q = 1 r = 3

Ethyl hexyl q + r = 4 s = 1 q = 2 r = 2

q = 3 r = 1

q = 1 r = 5

q = 2 r = 4

Methyloctyl q + r = 6 s = 0 q = 3 r = 3

q = 4 r = 2

q = 5 r = 1

q = 1 r = 4

q = 2 r = 3

Propyl heptyl q + r = 5 s = 2

q = 3 r = 2

q = 4 r = 1

q = 1 r = 5

q = 2 r = 4

Butyloctyl q + r = 6 s = 3 q = 3 r = 3

q = 4 r = 2

q = 5 r = 1

In another embodiment, the diester of the dicarboxylic acid of the lubricating composition of the present invention is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof. In another embodiment, the diester of the dicarboxylic acid of the lubricating composition of the present invention is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof.Di-(isopropylheptyl)-adipate (DPHA) is particularily preferred. Di-(isopropylheptyl)-adipate (DPHA) is commercially available as Synative ES DPHA from BASF SE.

In a further preferred embodiment, the lubricating composition comprises

(i) at least one base oil selected from a Group I, Group II oil according to the API classification, or a mixture thereof,

(ii) di-(isopropylheptyl)-adipate (DPHA), and

(iii) optional further additives.

In one embodiment, the further additives may comprise dispersants, anti-foam agents, diluents, detergents, anti-wear agents, antioxidants, corrosion inhibitors and metal deactivators. In one embodiment the lubricating composition according to the present invention may comprise at least one base oil selected from a Group I, Group II oil according to the API classification, or a mixture thereof in an amount from about 70 wt.-% to about 95 wt.-% based on the total lubricating composition. The diester of the dicarboxylic acid may be present in an amount from about 5 wt.-% to about 30 wt.% based on the total lubricating composition. The further additives, if present, may be present in an amount from about 0.1 wt -% to about 20.0 wt.-% based on the total lubricating composition.

In one embodiment the lubricating composition according to the present invention may com- prise at least one base oil selected from a Group I, Group II oil according to the API classification, or a mixture thereof in an amount from about 75 wt.-% to about 95 wt.-% based on the total lubricating composition. The diester of the dicarboxylic acid may be present in an amount from about 10 wt.-% to about 25 wt.% based on the total lubricating composition. The further additives, if present, may be present in an amount from about 0.1 wt.-% to about 20.0 wt.-% based on the total lubricating composition.

In one embodiment the lubricating composition according to the present invention may comprise at least motor oil in an amount from about 70 wt.-% to about 95 wt.-% based on the total lubricating composition, a diester of the dicarboxylic acid in an amount from about 5 wt.-% to about 30 wt.% based on the total lubricating composition, and further additives, if present, in an amount from about 0.1 wt.-% to about 20.0 wt.-% based on the total lubricating composition.

In a preferred embodiment of the invention the method for reducing deposit formation in a lubricating composition comprising a base oil comprising at least one Group I, Group II or Group III base oil or mixtures thereof, comprising adding a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b to said lubricating composition.

In a preferred embodiment of the invention the method for reducing deposit formation in a lubri- eating base oil comprising at least one Group I, Group II or Group III base oil or mixtures thereof, comprising adding a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b to said lubricating base oil.

In one embodiment, the present invention is directed to a method for reducing deposit for- mation in a lubricating base oil comprising Group I, Group II base oils or mixtures thereof, comprising adding an effective amount of a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b to said lubricating base oil.

In one embodiment, the synthetic ester is added in an amount from about 5 wt.-% to about 50 wt.-%, from about 10 wt.-% to about 40 wt.-%, from about 15 wt.-% to about 35 wt.-% based on the amount of the lubricating base oil.

In one embodiment, the synthetic ester is added after the lubricating base oil is present in the equipment to be lubricated. The equipment can be an engine such as a motor e.g. a vehicle motor. In one embodiment, the synthetic ester is added to the lubricating base oil of an engine (such as a motor oil) when or after the running in phase of said engine is completed. In another embodiment, the synthetic ester is added to the lubricating base oil when or after about 10% or about 20% of the control interval for this engine is reached. In another embodiment, the synthetic ester is a diester from a dicarboxylic acid. Preferabyl the dicarboxylic acid moiety of said diester is selected from the group consisting of succinic acid, maleic acid, fumaric acid, adipic acid, malonic acid, and mixtures thereof, and the ester moiety of the diester of the dicarboxylic acid is independently selected from the structure of formula (I) above. In a more preferred embodiment, the dicarboxylic acid ester is selected from the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, and preferably is di- (isopropylheptyl)-adipate (DPHA).

In one embodiment, the synthetic ester having an Iodine value of lower than 10 g I /100g measured according to DGF C-V 1 1 b can be used as an ester base stock for lubricating applications. In one embodiment the synthetic ester is the major component in the base stock (i.e. it is present in an amount greater than 50.0 wt.-% based on the base stock). In one embodiment the synthetic ester is a minor component of the base stock (i.e. it is present in an amount less than 50.0 wt.-% based on the base stock).

In another embodiment the synthetic ester having an Iodine value of lower than 10 g I /100g measured according to DGF C-V 1 1 b or the lubricating compositions of the present invention are used in engine oils, such as light, medium and heavy duty engine oils, industrial engine oils, marine engine oils, automotive engine oils, crankshaft oils, compressor oils, refrigerator oils, hydrocarbon compressor oils; very low-temperature lubricating oils and fats; high temperature lubricating oils and fats; wire rope lubricants; textile machine oils; refrigerator oils; aviation and aerospace lubricants; aviation turbine oils; hydraulic oils; transmission oils; turbine oils; gas tur- bine oils; spindle oils; spin oils; traction fluids; transmission oils, such as plastic transmission oils; passenger car transmission oils, truck transmission oils, industrial transmission oils; industrial gear oils; axle oils; insulating oils; instrument oils; brake fluids; transmission liquids; shock absorber oils; heat distribution medium oils; transformer oils; fats; chain oils; minimum quantity lubricants for metalworking operations; oil to the warm and cold working; oil for water-based metalworking liquids; oil for neat oil metalworking fluids; oil for semi-synthetic metalworking fluids; oil for synthetic metalworking fluids; drilling detergents for the soil exploration; hydraulic oils; in biodegradable lubricants or lubricating greases or waxes; chain saw oils; release agents; moulding fluids; gun, pistol and rifle lubricants or watch lubricants and food grade approved lubricants. Preferably, the synthetic ester having an Iodine value of lower than 10 g I /100 g measured according to DGF C-V 1 1 b or the lubricating compositions of the present invention are used in engine oils; aviation and aerospace lubricants; aviation turbine oils; hydraulic oils; transmission oils, turbine oils, gas turbine oils or axle oils applications. The method of the present invention leads to reduced deposits and thus to an improved cleanliness of the equipment such as engines, turbines, hydraulic circuits, transmissions and axles.

As used herein, the term "dicarboxylic acid moiety of the diester of the dicarboxylic acid" and "ester moiety of the diester of the dicarboxylic acid" refer to the respective moieties as shown in the figure below illustrated by the non limiting example of the dicarboxylic acid moiety of adipic acid and two ester moieties according to formula (I):

As used herein, the terms "base oil" and "base stock" are used interchangeably.

The determination of the Iodine value according to DGF C-V 1 1 b refers to the method described by the "Deutsche Einheitsmethode zur Untersuchung von Fetten, Fettprodukten, Tensiden und verwandten Stoffen", 2. Edition 2014. The method DGF C-V 1 1 b for the determination of the Iodine value refers to the cyclohexane/glacial acetic acid method according to Kaufmann.

As used herein, the term "about" means that the value following said term may be in the range of ±15% of said value, preferably ±10% of said value, even more preferably ±5% of said value.

Examples

Methods

The various viscosities of the lubricant compositions according to the present invention have been determined following established industry standards:

The kinematic viscosity at 100 °C is determined according to the ASTM D445.

The yield stress and the low temperature viscosity at -35 °C is determined according to ASTM D4684.

HPDSC measurements:

For the HPDSC measurements a small quantity of the lubricant composition sample to be tested is weighted into a sample pan and placed into the test cell. The test cell is adjusted to the desired temperature and then pressurized with oxygen to the desired oxygen pressure.

HPDSC ramping method: A heating rate of 5 °C/min was used for this method.

HPDSC OIT method: The OIT was determined at a temperature of 210 °C at oxygen pressures of 155 psi and 200 psi, respectively. Composition of conventional 5W-20 formulation (Formulation 1) The composition of the 5W-20 formulation applied is shown in Table 1 :

Table 1

The components of the 5W-20 formulation have been combined and blended for 1 hour at 50 °C prior to use.

Composition of the additive package

The composition of the additive package is shown in Table 2:

Table 2

The additive package is obtained by the following procedure: To the blend of Infinuem C9268, the anti-foam agent and the diluent, Infineum C9330 is given and further blended for 1 h at 95 °C. Subsequently Infineum C9417 is added and the mixture is further blended for 1 hour at 70 °C. Irganox L135 and Irganox L57 are added and the resulting mixture is blended for an additional hour at 60 °C. Example 1 : Determination of deposits according to the TEOST MHT D7097 test

To compare the deposit formation of an inventive composition and a comparative composition, conventional 5W-20 motor oil formulations (Formulation 1 ) have been applied. In the comparative composition, to the 5W-20 oil formulation a mixture of a Group III mineral oil and an additive package have been added (resulting in Formulation 2), while in the inventive formulation (Formulation 3), a diester of a dicarboxylic acid (DPHA) and an additive package have been applied. The formulations are listed in Table 3: Table 3

The composition of the additive package used in the present example is provided above. The test procedure is described below:

Test Protocol: Fuel economy testing on the engine dynamometer was conducted using a 5.7L GM crate engine with a high volume oil pan. The engine was run at controlled steady state conditions simulating highway temperatures, speed and load. Fuel consumption was measured constantly with a Coriolis type fuel flow meter. After a specific aging period where oil viscosity and fuel consumption were stabilized, a measured amount of candidate was added to the crankcase. Fuel economy percent benefit was calculated from consumption values before the addition of the additive to the end of test. At end of test, Rocker Covers, Cam baffles, Oil Pan, Oil Screen and Front Cover are removed for visual inspection and photos of deposit formation.

Base Oil - 6 quarts (corresponding to about 5678 ml) of Formulation 1 (5W20 motor oil formulation)

Candidate - 2 quarts (corresponding to about 1893 ml) of a mixture of DPHA and additive package used in Formulation 3 (together 25 wt.-% DPHA and additive package), or 2 quarts (corresponding to about 1893 ml) mixture of Nexbase 3030 and additive package used in Formulation 2 (25wt.-% Nexbase 3030 and additive package)

Oil Sampling has been performed as follows:

- 28.25 hours take 20 ml sample for viscosity measurements

- 28.50 hours Add 2 quarts of Candidate

- 28.75 hours (15 minutes after candidate addition) 1 quart sample

- 90.00 hours End of Test, take 1 quart sample and save all drain oil The following test cycle has been followed: 1 . Run Highway Cycle (2500 rpm, 35 Nm Torque, 125c oil) for 12 to 16 hours overnight till fuel consumption is stable.

2. Run and measure fuel consumption.

3. Follow Oil Sampling procedure above

4. Continue test to 90 hours with fuel consumption measurements.

5. At 90 hours end of test (EOT), take 1 qt. sample, (save drain oil)

6. When engine is cool enough to work on, remove and display RAC's, front cover, cam baffles, oil pump and oil pan for inspection and photos. Notify test engineer.

The results of the various tests of Formulations 1 , 2 and 3 are summarized in Table 4 below:

Table 4

its *** (mg)

* MRV - Mini Rotary Viscosimeter (measurements at -35 °C according to ASTM D4684) * * The Noack volatility is measured according to ASTM D5800 B

*** Deposits are measured according to the TEOST MHT D7097 test. The total deposits are obtained by summing up rod deposits and filter deposits.

#High Pressure Differential Scanning Calorimetry (HPDSC): ramping was performed with 5°C/min.

m HPDSC: oxidation induction time (OIT) measured at 210 °C.

Example 2: Determination of deposits according to ASTM D4310

Furthermore, the synthetic ester of the invention was tested in a turbine oil formulation. To a typical Group I mineral oil formulation has been added DPHA. With this formulation a turbine test according to ASTM D4310 has been performed. The composition of the formulations tested are summarized in Table 5 below:

Table 5

*A mixture of 65 % AP/E CORE 150 and 35% AP/E CORE 600 was used as a Group I mineral oil. AP/E CORE 150 and AP/E CORE 600 are commercially available from Exxon Mobil.

* * Synative ES DPHA from BASF SE

* ** lrgalube 2030A from BASF SE

The kinematic viscosity at 100 °C of formulation 4 was 6.82 mm 2 /s. The kinematic viscosity at 100 °C of formulation 5 was 6.25 mm 2 /s.

The sludge determined according to ASTM D4310 was 65.1 mg for Formulation 4 (comparative) and 46.6 mg for Formulation 5 (inventive). Preferred embodiments of the present invention are described in the following items: Use of a lubricating composition for reducing the formation of deposits, wherein the composition comprises

(i) at least one lubricating base oil, and

(ii) at least one synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b. Use according to item 1 , wherein the synthetic ester is selected from

(a) a diester of a dicarboxylic acid,

(b) a polyol ester, or

(c) mixtures thereof. Use according to items 1 or 2, wherein the dicarboxylic acid moiety of the diester of the dicarboxylic acid is selected from the group consisting of phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, glutaric acid, diglycolic acid, 1 ,4-cyclohexanedicarboxylic acid, 2,6- decahydronaphthalenedicarboxylic acid, 1 ,3-cyclohexanedicarboxylic acid, 2,5- norbornanedicarboxylic acid and mixtures thereof. Use according to any one of the items 1 to 3, wherein the dicarboxylic acid moiety of the diester of the dicarboxylic acid is an aliphatic dicarboxylic acid and is preferably selected from the group consisting of succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, glutaric acid, 1 ,4-cyclohexanedicarboxylic acid, 2,6-decahydronaphthalenedicarboxylic acid, 1 ,3-cyclohexanedicarboxylic acid, 2,5- norbornanedicarboxylic acid and mixtures thereof, and more preferably is adipic acid. Use according to any one of items 1 to 4, wherein the ester moiety of the diester of the dicarboxylic acid is independently s of formula (I)

(I) whereas q, r and s are defined as follows, q + r = 4 to 9,

s = 0 to 5,

q = 1 to 8, and

r = 1 to 6. Use according to any one of the items 1 to 5, wherein the diester of the dicarboxylic acid is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, and preferably is di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof. Use according to any one of the items 1 to 6, wherein the amount of diester of the dicarboxylic acid is from about 5 wt.-% to about 50 wt.-%, from about 5 wt.-% to about 40 wt.-%, from about 5 wt.-% to about 30 wt.-%, from about 8 wt.-% to about 28 wt.-%, from about 9 wt.-% to about 25 wt.-%, or from about 17 wt.-% to about 25 wt.-% based on the weight of the composition. Use according to any one of items 1 to 7, wherein the lubricating base oil is selected from Group I, Group II, Group III base oils according to the definition of the API, or mixtures thereof, and preferably is selected from Group I, Group II base oils, or mixtures thereof. Use according to any one of items 1 to 8, wherein the composition further comprises one or more other additives selected from the group consisting of viscosity index improvers, polymeric thickeners, antioxidants, corrosion inhibitors, detergents, dispersants, anti-foam agents, dyes, extreme pressure additives, antiwear additives, friction modifiers, metal deactivators, pour point depressants and the like. Use according to any one of items 1 to 9 wherein the deposits are determined according to the TEOST MHT D7097 test. Use according to any one of items 1 to 10, wherein the deposits are reduced by at least about 5 mg, by at least about 7 mg, by at least about 10 mg, by at least about 15 mg measured according to the TEOST MHT D7097 test compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof. Use according to any one of items 1 to 9 wherein the deposits are measured according to ASTM D4310. Use according to any one of items 1 to 9 and 12, wherein the deposits measured according to ASTM D4310 are less than about 60 mg, less than about 55 mg, or less than about 50 mg. Use according to any one of items 1 to 13, wherein the oxidation stability measured according to HPDSC test is increased compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof. Use according to any one of items 1 to 14, wherein the Noack volatility measured according to ASTM D5800 is decreased compared to a composition wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof. Use according to any one of items 1 to 15, wherein the Noack volatility is below 12% weight loss, or equal or below about 10% weight loss. Use according to any one of items 1 to 16, wherein the dynamic viscosity determined at -35 °C according to ASTM4684 is at least about 100 mPa * s lower compared to a formulation wherein the synthetic ester has been replaced by a lubricant base oil selected from Group I, Group II, Group III base oils or mixtures thereof A lubricating composition comprising

(i) at least one base oil selected from a Group I oil according to the API classification,

(ii) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b, and

(iii) optional further additives. A lubricating composition comprising

(i) at least one base oil selected from a Group I, Group II oil according to the API classification, or a mixture thereof

(ii) a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b ,

(iii) optional further additives. The lubricating composition according to any one of items 18 and 19, wherein the synthetic ester is a diester of a dicarboxylic acid. The lubricating composition according to any one of items 18 to 20, wherein the diester of the dicarboxylic acid is selected from the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, and preferably is di-(isopropylheptyl)-adipate (DPHA), and preferably is di- (isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof. A method for reducing deposit formation in a lubricating composition comprising a base oil comprising at least one Group I, Group II, or Group III base oil or mixtures thereof, comprising adding a synthetic ester having an Iodine value lower than 10 g I /100 g measured according to DGF C-V 1 1 b to said lubricating composition. The method according to item 22, wherein the synthetic ester is added in an amount from about 5 wt.-% to about 50 wt.-%, from about 10 wt.-% to about 40 wt.-%, from about 15 wt.-% to about 35 wt.-% based on the amount of the lubricating base oil. The method according to item 22 or 23, wherein the synthetic ester is added after the lubricating base oil is present in the equipment. The method according to any one of items 22 to 24, wherein the synthetic ester is a diester of a dicarboxylic acid. The method according to any one of items 22 to 25, wherein the diester of the dicarboxylic acid is selected from the group consisting of di-(isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, and preferably is di-(isopropylheptyl)-adipate (DPHA). A lubricating composition comprising

(i) at least one base oil selected from a Group I oil according to the API classification,

(ii) and a diester of the dicarboxylic acid is selected from the group consisting of di- (isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, wherein the diester of the dicarboxylic acid is preferably di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof and more preferably is di-(isopropylheptyl)-adipate (DPHA), and

(iii) optional further additives. A lubricating composition comprising

(i) at least one base oil selected from a Group I, Group II oil according to the API classification, or a mixture thereof

(ii) and a diester of the dicarboxylic acid is selected from the group consisting of di- (isopropylheptyl)-adipate (DPHA), di-isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, wherein the diester of the dicarboxylic acid is preferably di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof and more preferably is di-(isopropylheptyl)-adipate (DPHA), and

(iii) optional further additives. Use of a lubricating composition for reducing the formation of deposits, wherein the composition comprises

(i) at least one lubricating base oil, and

(ii) at least one synthetic ester, wherein the synthetic ester is a diester of the dicarboxylic acid is selected form the group consisting of di-(isopropylheptyl)-adipate (DPHA), di- isodecyl adipate (DIDA), diisotridecyl adipate (DITA), diisononyladipate (DNA) or mixtures thereof, and preferably is di-(isopropylheptyl)-adipate (DPHA), diisononyladipate (DNA) or mixtures thereof, and more preferably is di-(isopropylheptyl)-adipate (DPHA).