HALOGEN FREE IONIC LIQUIDS AS LUBRICANT OR LUBRICANT ADDITIVES AND A PROCESS FOR THE PREPARATION THEREOF

Abstract

A lubricant or lubricant additive composed of halogen-, phosphorus- and sulphur-free ionic liquids containing fatty acid anions exhibit superior friction-reducing and anti-wear properties. Preferably, the lubricant composition comprises a base oil and an ionic liquid or mixed of two or more ionic liquids having concentration of 0.5 wt. % or more. These halogen-, phosphorus- and sulphur-free ionic liquids as lubricant or lubricant additive have minimal hazardous and corrosion effect to the environment and engineering surfaces, respectively. General chemical formula of fatty acid anion is represented as RCOO.sup.; whereas R may be C.sup.4 to C.sup.30 straight chain alkyl, branched alkyl, cycloalkyl, alkyl substituted cycloalkyl, cycloalkyl substituted alkyl, alkenyl (single or more double bonds) includes with or without branched structure and may contain heteroatom.

Claims

1. A lubricant or lubricant additive(s) composition comprising an ionic liquid(s), wherein anions in the ionic liquid(s) are fatty acids of the general formula RCOO , wherein R is selected from C.sub.4 to C.sub.30 straight chain alkyl, branched alkyl, straight or branched alkenyl, cycloalkyl, alkyl substituted cycloalkyl, cycloalkyl substituted alkyl; alkyl or alkenyl group(s) containing heteroatom selected from OH, CN, CO C; and cations in the ionic liquids are selected from the group consisting of ##STR00010## wherein R.sup.1 to R.sup.12 is similar or different from one another, selected from the group consisting of hydrogen, OH, C.sub.1 to C.sub.18 alkyl group(s) including straight chain or branched structures, C.sub.2 to C.sub.12 alkenyl group(s) including straight chain or branched structures, wherein the alkyl or alkenyl group(s) optionally contain heteroatom, C.sub.7 to C.sub.12 arylalkyl group(s), C.sub.7 to C.sub.12 alkylaryl group(s).

2. The composition as claimed in claim 1, wherein the ionic liquids are substatntially or completely free of halogen, phosphorous, and/or sulphur.

3. The composition as claimed in claim 1, wherein ionic liquid are selected from Tetrabutylammonium oleate (TBA-OL), 1-Hexyl-methylimidazolium oleate (HMIM-OL) and Tetrabutylammonium linoleate (TBA-LN), Tetrabutylammonium caprylate, Tetrabutylammonium caprate, Tetrabutylammonium laurate, Tetrabutylammonium myrisate, Hexyldimethylcyclohexylammonium oleate and Dioctylmethylpentylammonium oleate.

4. The composition as claimed in claim 1, further comprising one or more additives selected from dispersants, corrosion inhibitors, detergents, antioxidants, anti-wear and extreme pressure additives, viscosity improvers, fiction improvers, oiliness improver, metal deactivator, demulsifiers, pour point depressants, foam inhibitors, seal-swelling agents, antimicrobial.

5. The lubricant or lubricant additive composition as claimed in claim 1 is having high friction reducing and anti-wearing properties.

6. A lubricating oil comprising the lubricant additive composition as claimed in any of the preceding claims and a base lubricating oil.

7. The lubricating oil as claimed in claim 6, wherein the concentration of ionic liquid (s) as lubricant additive(s) in the base lubricant oil(s) is in the range of 0.5 to 10 wt. %.

8. The lubricating oil as claimed in claim 6 or 7, wherein the base lubricant oil(s) is selected from synthetic, minerals and native base stock (s) or base oil (s).

9. The lubricating oil as claimed in claim 8, wherein the synthetic oils is selected from the group consisting of polymerized and interpolymerized olefins: polyalphaoelefin (PAO) derived from olefins, diol or triol or polyol esters or polyphenyl ether or alkylated di- or triphenyl ether, alkylated naphthalenes, alkylated benzene, polyglycols, polyalkylglycols, silicon oils, perfluoropolyethers; mineral base oil (s) is selected from Group I (solvent refined mineral oils), Group II (hydrocracked mineral oils), Group III (severely hydrocracked oils, also referred to as synthetic or semi oils), Group V (esters, napthenes, and others); native oil(s) as lube base stock (s) is selected from animal and vegetable oils,which are predominantly composed of triglycerides with minor components of mono- and diglycerides.

10. A process for the preparation of lubricant or lubricant additive composition comprising ionic liquid(s) as claimed in claim 1, wherein the said process comprises the steps of: a) mixing sodium salt of fatty acid in an aqueous solution of tetraalkylammonium halide or di-/tri-alklyimidazolium tetrafluoroborate in 1:1 molar ratio with stirring at a temperature ranging between 20-100 C. for a period of time ranging between 4 to 48 hours to get organic layer in reaction mixture; and b) extracting the organic layer as obtained in step (a) using dichloromethane followed by washing with water then removing dichloromethane under reduced pressure subsequently drying under reduced pressure to get lubricant or lubricant additive composed of ionic liquid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 represents a bar graph of the friction coefficient for three representative fatty acid ionic liquids and two conventional lube oils.

[0032] FIG. 2 represents a bar graph of the wear scar diameter (WSD) for three representative fatty acid ionic liquids and two conventional lube oils.

[0033] FIG. 3 represents a composite bar graph of (a) wear scar diameter and (b) friction coefficient of tetrabutylammonium oleate with function of their concentration (wt. %) blended with polyol ester lube base.

DETAILED DESCRIPTION OF THE INVENTION

[0034] Ionic liquids are composed of ions (cations and anions) that are liquids at below 100 C. Ionic liquids exhibit unique physico-chemical characteristics such as higher thermo-oxidative stability, negligible volatility, broad liquid range, non-flammability and excellent heat conductivity, which meet the requirements of high performance lubricants. The flexible molecular structure with diversified range of cations and anions makes ionic liquids as versatile lubricants or lubricant additives for different engineering surfaces. The inherent polarity of ionic liquids found to provide strong adsorption to the matting surfaces and forms thin film of low shearing strength, consequently, reduction in friction and wear.

[0035] The present invention provides halogen-, phosphorus- and sulphur-free ionic liquids composed of diversified cations and fatty acid anions as tube oils for anti-wear and anti-friction performance. The lube oil can be comprised of a base oil and an ionic liquid or mixed of two or more ionic liquids formed of a cation and an anion and having an ion concentration of 0.5 wt. % or more. In this invention, fatty acids in the form of ionic liquids as anions with various types of cations have been developed as anti-wear and friction-reducing agent. Owing to inherent polar nature of these fatty acids anions, they prone to interact with metallic surfaces and forms thin film of low shear strength, which reduces both friction and wear more efficiently compared to that of free fatty acids and fatty acids esters.

[0036] A preferred group of lube oil or lube base stock to which the ionic liquids can be added, use in the present invention may be consist of one or more base stock (s) or base oil (s) selected from synthetic, minerals and native base stock (s) or base oil (s). Natural and synthetic oils (or mixture thereof) can be used unrefined, refined or re-refined.

[0037] The synthetic oils may be selected from polymerized and inteipolymerized olefins including commonly used polyalphaolefin (PAO) derived from olefins. In addition, the synthetic oil may be selected from a diol or triol or polyol esters or polyphenyl ether or alkylated di- or triphenyl ether, alkylated naphthalenes, alkylated benzene, polyglycols, polyalkylglycols, silicon oils, perfluoropolyethers and so on.

[0038] Mineral and synthetic lube base oil (s) or lube base stock (s) may be selected from Group I (solvent refined mineral oils), Group II (hydrocracked mineral oils), Group III (severely hydrocracked oils, also referred to as synthetic or semi-synthetic oils), Group V (esters, napthenes, and others). Animal and vegetable oils (native oils) are predominantly composed of triglycerides with minor components of mono- and diglycerides and other substances. These oils either as it is or in refined or chemically derived form by known methods such as trans-esterifications, hydrogenations, estolide formation and so on, may be selected to which ionic liquids can be added. The use of native oils based on renewable raw materials is important owing to their advantages with regard to biodegradability and reducing or preventing CO.sub.2 emission.

[0039] In the present invention, ionic liquid(s) added lubricants or ionic liquids as lubricants may contain one or more chemicals to provide other desired chemical and physical properties to the lubricating system. Such chemical additives includes dispersants, corrosion inhibitors, detergents, antioxidants, anti-wear and extreme pressure additives, viscosity improvers, friction improvers, oiliness improver, metal deactivator, demulsifiers, pour point depressants, foam inhibitors, seal-swelling agents, antimicrobial additives etc. In the present invention, aforementioned chemical additives are used in the ionic liquid(s) added lubricant in required quantity, to improve the performance characteristics and properties of the base oil(s) or base stock(s).

[0040] In the present invention, halogen-, phosphorus- and sulphur-free ionic liquids are salts of one or mixtures of fatty acids anions. The general chemical structure of fatty acid (carboxylate) anion for the present invention may be represented as formula I:

##STR00002##

whereas R may be C.sub.4 to C.sub.30 straight chain alkyl, branched alkyl, alkenyl (one or more double bonds) includes with or without branched structure, cycloalkyl, alkyl substituted cycloalkyl, cycloalkyl substituted alkyl and so on. Herein, the alkyl or alkenyl group(s) may contain heteroatom comprise groups such as OH, CN, COC and so on.

[0041] The structure of suitable cations for the present invention may be represented as general formula II.

##STR00003##

[0042] Herein, R.sup.1 to R.sup.12 may he the similar or different from one another, represents a group consisting of hydrogen, OH, C.sub.1 to C.sub.18 alkyl group(s) includes straight chain or branched structure, C.sub.2 to C.sub.12 alkenyl group(s) includes straight chain or branched structure wherein the alkyl or alkenyl group(s) may contain heteroatom, C.sub.7 to C.sub.12 arylalkyl group(s), C.sub.7 to C.sub.12 alkylaryl group(s).

[0043] The halogen-, phosphorus- and sulphur-free ionic liquids addressed in the present invention, not only significantly reduces both friction coefficient and wear between two or more contact surfaces but also minimize the hazardous and corrosive effects. Increasing strict regulations and government policies on (a) use of environment friendly lubricants and/or lubricant additives, and (b) improve the fuel efficiency in engineering systems, particularly in automotive industries, have propelled an interest to develop environment-friendly and energy efficient lubricants and lubricant additive. The addressed halogen-, phosphorus- and sulphur-free ionic liquids in the present invention meets all these objectives and has an emergent scope for their practical utilization in lubrication applications.

EXAMPLES

[0044] The following examples serve to provide the best modes of practice for the present invention, and should not be constructed as limiting the scope of the invention:

Example 1

[0045] Preparation of Halogen-, Phosphorus- and Sulphur-Free Ionic Liquids Containing Fatty Acid Anions

(a) Tetrabutylammonium oleate (TBA-OL)

[0046] ##STR00004##

[0047] TBA-OL ionic liquid may be represented by general formula TBA-OL was prepared by mixing sodium salt of oleic acid (0.05 mol) in an aqueous solution of tetrabutylammonium bromide (0.05 mol) at 45 C. for 4 hours under continuous stirring. This led to the formation of an organic layer in the reaction product, which was extracted using dichloromethane This was followed by washing of organic content composed of TBA-OL ionic liquid with pure water until no more bromide ions were detected in the water. Finally, dichloromethane was removed under reduced pressure and the extracted product was dried in a vacuum oven at 80 C. under reduced pressure for 48 hours. The synthesized ionic liquid was characterized by .sup.1t1 NMR and FTIR spectroscopy. The characterization detail is as follows:

##STR00005##

[0048] .sup.1H NMR (ppm): 0.88-1.1 (t, 15H.sub.g,k CH.sub.3), 1.2-1.4 (m12H.sub.c,i CH.sub.2), 1.45-1.7 (m, 24H.sub.d,i CH.sub.2), 1.9-2.1 (m, 4H.sub.e CH.sub.2), 2.3-2.4 (in, 2H.sub.b CH.sub.2), 2.45-2.55 (m, 2H.sub.8 CH.sub.2), 2.85-3.0(t, 8H.sub.b NCH.sub.2), 5.3-5.4 (m, 2H.sub.fCHCH).

[0049] FTIR (cm.sup.1): 3010, 2929, 2855, 1764, 1631, 1460, 1375, 1280, 1237, 1105, 993, 721.

(b) 1-Hexylmethylimidazolium oleate (HMIM-OL)

[0050] ##STR00006##

[0051] HMIM-OL ionic liquid may be represented by general formula IV. HMIM-OL was prepared by mixing an equimolar quantity of sodium salt of oleic acid (0.05 mol) and 1-hexyl-3-methylimidazolium. bromide (0.05 mol) at 45 C. for 4 hours under continuous stirring. The prepared HMIM-OL ionic liquid was extracted using dichloromethane and washed with pure water for couple of times to remove the inorganic slat, until no more of bromide ions were detected in the water. Finally, dichloromethane was removed under reduced pressure and the extracted HMIM-OL ionic liquid was dried in a vacuum oven at 80 C. under reduced pressure for 48 hours. Prior to this, 1-Hexyl-3-methylimidzolium bromide, an ionic liquid precursor was prepared by using an equimolar amount of 1-bromohexane (0.1 mol) and N-methylimidazole (0.1 mol) in a round bottom flask. The reaction mixture was heated at 75 C. for 36 hours under a nitrogen atmosphere with continuous stirring. The prepared 1-hexyl-3-methylimidazolium bromide was purified by washing with ethyl acetate and then used for the synthesis of 1-IMIM-OL ionic liquid. The synthesized ionic liquid was characterized by .sup.1H NMR and FTIR spectroscopy. The characterization detail is as follows:

##STR00007##

[0052] .sup.1H NMR (ppm): 0.86-0.88 (m, 6H.sub.g,i CH.sub.3), 1.26-1.29 (m, 22H.sub.d,l,k,j CH.sub.2), 1.54-1.55 (m, 4H.sub.c CH.sub.2), 1.81-1.82 (m, 2H.sub.m CH.sub.2), 2.0-2.1 (m, 4H, CH.sub.2), 2.13-2.15 (m, 2H.sub.b CH.sub.2), 2.75-2.8 (t, 2H.sub.a, CH.sub.2COO), 3.94-3.96 (s, 3H.sub.h, NCH.sub.3), 4.19-4.22 (t, 2H.sub.n, NCH.sub.2), 5.31-5.34 (q, 2H.sub.f CHCH), 7.49 8& 7.34 (s, 2H.sub.p,o CH), 9.6 (s, 1H.sub.q CH).

[0053] FTIR (cm.sup.1): 3149, 3080, 3006, 2956, 2926, 2852, 1718, 1635, 1569, 1465, 1377, 1277, 1242, 1168, 991, 831, 721.

(c) Tetrabutylammonium linoleate (TBA-LN)

[0054] ##STR00008##

[0055] TBA-LN ionic liquid may be represented by general formula V. TBA-LN was prepared by mixing sodium salt of linoleic acid (0.05 mol) in an aqueous solution of tetrabutylatnmonium bromide (0.05 mol) at 45 C. for 4 hours under continuous stirring. This led to the formation of an organic layer in the reaction product, which was extracted using dichloromethane. This was followed by washing of organic content composed of TBA-LN ionic liquid with pure water until no more bromide ions were detected in the water. Finally, dichloromethane was removed under reduced pressure and the extracted product was dried in a vacuum oven at 80 C. under reduced pressure for 48 hours. The synthesized ionic liquid was characterized by .sup.1H NMR and FTIR spectroscopy. The characterization detail is as follows:

##STR00009##

[0056] .sup.1H NMR (ppm): 0.86-0.89 (m, 15H.sub.h,1 CH.sub.3), 0.98-1.01 (m, 14H.sub.d,k CH.sub.2), 1.26-1.3 (m, 2H.sub.c CH.sub.2), 1.41-1.48 (q, 2H.sub.j CH.sub.2), 1.61-1.67 (m, 4H.sub.e CH.sub.2), 1.95-2.1 (m, 2H.sub.b CH.sub.2), 2.3-2.37 (m, 2H.sub.a CH.sub.2COO), 2.65-2.7 (m, 2H.sub.g CH.sub.2), 3.32-3.35 (m, 8H.sub.i, NCH.sub.2), 5.3-5.4 (m, 4H.sub.f CHCH). FTIR (cm.sup.1): 3008, 2960, 2929, 2859, 1727, 1463, 1383, 1178, 1108, 1031, 737.

Example 2

[0057] Friction-reducing and Anti-Wear Properties of Fatty Acids Ionic liquids as Lubricants

[0058] Lubricating properties in terms of friction coefficient and wear scar diameter (hereon it will be known as WSD) for the fatty acid ionic liquids as lubricants were evaluated on a four-ball test machine as per the ASTM D4172 standard test method For comparison purpose, two conventional lube oils (fully formulated 10W40 lube oil and pentaerythritol tetraoleate, polyol ester) were also evaluated under similar test conditions. In a typical experiment, a 12.7 mm steel ball under the 392 N load is rotated (rotating speed: 1200 rpm) against three stationary steel balls clamped in the holder at temperature of 75 C. for a test duration of 60 minutes. During the experiments, the four balls were fully flooded with a test lube sample, which was used for the friction and WSD evaluation. The friction force was measured during the tribo-test and WSD on the lubricated steel balls was examined by the microscopic measurements. The friction coefficient and WSD for three representative fatty acid ionic liquids and two conventional lubricants are compared in FIGS. 1 and 2. All ionic liquids show very good lubricity with significant reduction in both friction coefficient and WSD compared to that of fully formulated 10W40 lube oil and polyol ester lube base stock. Under tribo-stress, carboxylic anions prepare a thin film of low shearing strength, resulting in large reduction in friction as shown in FIG. 1. The thin film of ionic liquids on metal surfaces avoid the direct contact between steel balls, consequently significant reduction in material loss (WSD) as shown in FIG. 2. It is noted that all these ionic liquids performed better than 10W40 oil and polyol ester lube base stock.

Example 3

[0059] Effect of Fatty Acid Ionic Liquid Concentration as Lubricant Additive on their Lubrication Properties

[0060] In order to improve the lubrication properties, variable concentrations (wt. %) of fatty acid ionic liquid are mixed with the conventional polyol ester (pentaerythrito) tetraoleate) lube base and then evaluated their friction coefficient and WSD on a four-ball test machine as per the ASTM D4172 standard test method. TBA-OL was selected as representative fatty acid ionic liquid for this study. In atypical experiment, a 12.7 mm steel ball under the 392 N load is rotated (rotating speed: 1200 rpm) against three stationary steel balls clamped in the holder at temperature of 75 C. for a test duration of 60 minutes. During the experiments, the four balls were fully flooded with a test lube sample. The friction force was measured during the tribo-test and WSD on the lubricated steel balls was examined by microscopic measurements. FIG. 3 shows the changes in friction coefficient and WSD for different dose (0 to 2 wt. %) of tetrabulammonium oleate in the polyol ester lube base. The friction coefficient and WSD for polyol ester tube oil are found to he about 0.08 and 556 m, respectively. Both friction coefficient and WSD decreases significantly with increasing concentration of tetrabutylammonium oleate. The 2 wt. % of tetrabutylaminonium oleate in polyol ester lube base shows 56% and 22% reduction in friction coefficient and WSD, respectively, compared to that of polyol ester lube base. These results illustrate the ability of fatty acid ionic liquid as an additive to improve the friction-reduction and anti-wear properties of convention tube base oils.

Example 4

[0061] Friction-reducing and Anti-wear Performance of Representative Fatty Acid Ionic Liquids as Lubricant Additives in Polyol Ester Lube Base

[0062] In another set of experiment, eleven representative fatty acid ionic liquids as lubricant additives have been selected for lubrication performance. These fatty acid ionic liquids exhibit structural variations in anions (chain length and degree of unsaturation) and counter cations (ammonium, imidazolium). The structural changes in fatty acid anions influence the physico-chemical properties of ionic liquids. Viscosity is an important physical property of lubricant, which changes with temperature and plays crucial role to monitor lubrication and oil conditioning. Lubricant with high viscosity can bear high contact pressure between moving surfaces, however, it's high internal friction provides larger resistance to the movement of the lubricating parts. In contrast, a lubricant with low viscosity offers low resistance to shear but the lubricant can be squeezed out of the lubricating surfaces, that may lead to high friction and more energy loss. In the present invention, viscosities and viscosity index of 1.5 wt. % fatty acids ionic liquids blended with polyol ester tube base stock are evaluated and shown in Table 1. There is no significant change in both kinematic viscosities at 40 and 100 C., and viscosity index of polyol ester on blending of fatty acid ionic liquids. High viscosity index reveals that all blends of various fatty acid ionic liquids can be even used at high temperature and are suitable for lubrication applications.

TABLE-US-00001 TABLE 1 Kinematic viscosity and viscosity index of polyol ester having 1.5% various fatty acids ionic liquids. Kinematic Viscosity Viscosity Sample Description 40 C. 100 C. Index Reference Oil: Polyol Ester 64.8 12.1 186 (Pentaerythritol tetraoleate) 1.5 wt % of fatty acid ionic liquid in polyol ester Tetrabuytlammonium caprylate 70.7 12.9 175 Tetrabuytlammonium caprate 69.6 12.2 175 Tetrabuytlammonium laurate 70.1 12.8 185 Tetrabutylammonium myristate 69.0 12.7 186 Tetrabutylammonium oleate 67.6 12.5 187 Tetrabutylammonium linoleate 73.4 12.9 178 Hexyldimethycyclohexylammonium oleate 68.4 12.6 187 Dioctylmethylpentylammonium oleate 67.5 12.6 188 1-Hexyl-3-methylimidazolium oleate 68.1 12.6 187

[0063] Lubrication properties in terms of friction coefficient and WSD for 1.5 wt. % fatty acid ionic liquids as lubricants additive blended with polyol ester lube base were evaluated on a four-ball test machine as per the ASTM D4172 standard test method. For comparison purpose, conventional polyol ester lube base was also evaluated under similar test conditions. In a typical experiment, a 12.7 mm steel ball under the 392 N load is rotated (rotating speed: 1200 rpm) against three stationary steel balls clamped in the holder at temperature of 75 C. for a test duration of 60 minutes. During the experiments, the four balls were fully flooded with a test lube sample, which was used for the friction and WSD evaluation. The friction force was measured during the tribo-test and WSD on the lubricated steel balls was examined by the microscopic measurements. The friction coefficient and WSD for representative fatty acid ionic liquids and polyol lube base are compared in Table 2. All fatty acid ionic liquids as additives having wide structural variations shows better lubricating properties by reducing both friction coefficient (upto 54%) and WSD (upto 30%) compared to that of for polyol ester lube base. This is attributed to the formation of tribo thin film on contact surfaces, which provides low resistance to shear and avoid the direct contact between the metallic surfaces, resulting in significant reduction in both friction coefficient and WSD.

TABLE-US-00002 TABLE 2 WSD and friction coefficient of representative fatty acids ionic liquids blended (1.5 wt %) with polyol ester. Friction WSD, m Coefficient Reference Oil: Polyol Ester 556 0.080 1.5 wt % of IL in oil Tetrabutylammonium caprylate 541 0.040 Tetrabutylammonium caprate 524 0.062 Tetrabuytlammonium laurate 507 0.067 Tetrabutylammonium myristate 531 0.036 Tetrabutylammonium palmitate 399 0.049 Tetrabutylammonium oleate 450 0.037 Tetrabuylammonium linoleate 493 0.041 Tetraoctylammonium oleate 446 0.054 Dioctylmethylpentylammonium oleate 403 0.050 Hexyldimethycyclohexylammonium oleate 419 0.055 1-Hexyl-3-methylimidazolium oleate 395 0.049

Example 5

[0064] Friction-reducing and Anti-wear Performance of Representative Fatty Acids Ionic Liquids as Lubricant Additives in 10W40 Lube

[0065] In another set of experiment, seven representative fatty acids ionic liquids as lubricant additives were blended with 10W40 lube oil and then evaluated for lubricity performance. Herein, the 10W40 lube oil is fully formulated commercial oil and contains all required additives in order to provide good lubrication performance. Lubricating properties in terms of friction coefficient and WSD for 1.0 wt. % variable fatty acid ionic liquids as lubricants additive blended with 10W40 lube oil were evaluated on a four-ball test machine as per the ASTM D4172 standard test method. For comparison purpose, 10W40 lube oil was also evaluated under similar test conditions. In .sub.atypical experiment, a 12.7 mm steel ball under the 392 N load is rotated (rotating speed: 1200 rpm) against three stationary steel balls clamped in the holder at temperature of 75 C. for a test duration of 60 minutes. During the experiments, the four balls were fully flooded with a test lube sample, which was used for the friction and WSD evaluation. The friction force was measured during the tribo-test and WSD on the lubricated steel balls was examined by microscopic measurements. The friction coefficient and WSD for representative fatty acid ionic liquids as additives and 10W40 lube oil are compared in Table 3. All fatty acid ionic liquids as additives shows very good lubricating properties by reducing both friction coefficient (17-29%) and wear scar diameter (upto 37%) compared to that for 10W40 lube oil. Though the fully formulated 10W40 tube oil contains all required additives including friction improver and anti-wear additives, but still 1 wt. % dose of these fatty acids ionic liquids in such fully formulated oil, shows significantly improved tribo-characteristics. This is attributed to the formation of tribo thin film of low shearing strength on the contact surfaces.

TABLE-US-00003 TABLE 3 WSD and friction coefficient of representative fatty acids ionic liquids blended (1 wt %) with 10W40 lube oil Friction WSD, m Coefficient Reference Oil: 10w40 465 0.112 1 wt % of IL in oil Tetrabuytlammonium caprylate 413 0.086 Tetrabutylammonium caprate 299 0.089 Tetrabutylammonium laurate 297 0.080 Tetrabutylammonium myristate 312 0.090 Tetrabutylammonium palmitate 307 0.093 Tetrabutylammonium oleate 303 0.088 Tetrabuylammonium linoleate 301 0.081

[0066] In conclusion, the present invention on halogen-, phosphorus- and sulphur-free ionic liquids as lubricants or lubricant additives composed of fatty acids anions exhibit superior anti-wear and anti-friction properties compared to the conventional lubricants.

THE ADVANTAGES OF THE PRESENT INVENTION

[0067] The main advantages of the present invention are: [0068] 1. To provide lubricants or lubricant additives composed of halogen-, phosphorus- and sulphur-free ionic liquids containing fatty acids anions, which exhibit superior friction-reducing and anti-wear properties. [0069] 2. To provide halogen-, phosphorus- and sulphur-free ionic liquids as lubricant or lubricant additive, which minimize hazardous and corrosion effect to the environment and engineering surfaces, respectively. [0070] 3. To provide halogen-, phosphorus- and sulphur-free ionic liquids that exhibits a better combination of friction, wear and heat transfer properties as compared with corresponding lubricant or lubricant additives.