US20170096614A1

US20170096614A1 - Halogen free ionic liquids as lubricant or lubricant additives and a process for the preparation thereof

Info

Publication number: US20170096614A1
Application number: US15/126,963
Authority: US
Inventors: Om Prakash KHATRI; Rashi GUSAIN
Original assignee: Council of Scientific and Industrial Research CSIR
Current assignee: Council of Scientific and Industrial Research CSIR
Priority date: 2014-03-18
Filing date: 2015-03-17
Publication date: 2017-04-06

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⁻; whereas R may be C⁴to C³⁰straight 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.

Description

FIELD OF THE INVENTION

The present invention relates to halogen free ionic liquids based lubricant or lubricant additives and a process for the preparation thereof Particularly, the present invention provides lubricant or lubricant additives composed of halogen-, phosphorus, and sulphur-free ionic liquids containing fatty acid anions. More particularly, the invention relates to the reduction of friction and wears using these ionic liquids as lubricants or lubricant additives mixed with mineral, synthetic, native lube oils.

BACKGROUND AND PRIOR ART OF THE INVENTION

Need to conserve energy and the environment has catalyzed an interest to develop a new generation green lubricants or lubricant additives, which can improve the efficiency of engineering system, where two or more surfaces are in contact and moving relative to each other. The energy and material loss in such engineering system (pistons, pumps, clutches, bearing, turbines, cutting tools, MEMS and so on) can be reduced by using the appropriate lubricant and/or lubricant additives. The good lubricant should be able to (a) keep surfaces of working parts separate under all loads, temperatures and speed, thus reducing the friction and wear, (b) enhance the energy efficiency of the system, (c) dissipate the heat from the contact surfaces and (d) increase the life of sliding machine tools by protecting their contact surfaces.
Ionic liquids are poorly coordinated salts, composed of bulk organic cations and organic/inorganic anions, which exist in liquid phase at below 100° C. Over the last few years, ionic liquids have attracted significant attention for diversified range of applications owing to combination of their unique and tunable physico-chemical characteristics such as low vapor pressure, good thermal stability, non-flammability, excellent conductivity, high viscosity, favorable miscibility for organic and inorganic compounds etc. These features make ionic liquids as potential candidates for lubricant applications to reduce both friction and wear. High conductivity of ionic liquids dissipate the heat from contact surfaces, which reduced the material loss from contact surfaces. Most of ionic liquids are non-flammable, hence they are more safer in transport and storage perspective compared to the conventional lube oils. Many ionic liquids are non-volatile hence make a significant positive environmental impact.
Reference may be made to (C. Ye, W. Liu, Y. Chen and L. Yu, “Room-temperature ionic liquids: a novel versatile lubricants” Chem. Commun. 2001, 2244-5) wherein the potential of ionic liquids as versatile lubricants was illustrated. They have found that alkylitnidazolium tetraflurophosphate as lubricant reduced the both friction and wear for the contact surfaces of steel, aluminium, copper, silicon dioxide, silicon nitride, aluminium oxide and ceramics. Since then, the interest in ionic liquids as novel lubricants is steadily increasing. The drawbacks are the use of halogenated ionic liquids, which not only corrodes the tribo-surfaces but also pollute the environment.
A large number of studies have been made to explore lubrication capabilities of various ionic liquids having molecular structure flexibility with a diversified range of cations such as imidazolium, pyridinium, ammonium, phosphonium, sulfonium etc., and anions such as tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl) amide, sulphonate etc. It was noted that the inherent polarity of ionic liquids facilitates their strong adsorption to the interacting (contact) surfaces, consequently reductions in friction and wear owing to thin film formation. Reference may be made to (M. Uerdingen, C. Treber, M. Balser, G. Schmitt and C. Werner, “Corrosion behavior of ionic liquids” Green Chem. 2005, 7, 321-25, B. S. Phillips, G. John, and J. S. Zabinski, “Surface chemistry of fluorine containing ionic liquids on steel substrates at elevated temperature using Mossbauer spectroscopy” Tribo. Lett. 2007, 26, 85-91, F. Zhou, Y. Liang and W. Liu, “Ionic liquids lubricants: designed chemistry for engineering applications” Chem. Soc. Rev. 2009, 38, 2590-9 and L. Pisarova, C. Gabler, N. Don, E. Pittenauer and G. Allmaier, “Thermo-oxidative stability and corrosion properties of ammonium based ionic liquids” Tribo. Intl. 2012, 46, 75-83.), wherein the most of ionic liquids studied for lubricant applications, usually contains halogen either in simple or complex form (tetrafl uroboarte, hexafl urophosphate, Trifl uoromethanesulfonate, bis(trifluoromethansulfonyl)amide), which are sensitive to moisture, particularly hydrophilic ionic liquids are more sensitive. Eventually, the interactions of these ionic liquids with metallic surfaces under tribological conditions (high temperature and pressure) cause corrosion, which damages the contact surfaces in the mechanical system. Addition to that halogenated ionic liquids releases toxic and corrosive hydrogen halides to the surrounding environment. Therefore, the use of these ionic liquids as lubricant additives with various lube base stocks is a great challenge owing to their hazardous, toxic and corrosive nature to the environment and engineering surfaces.
Reference may be made to US Patent 2007/0027038 A1 wherein the ionic liquids as base oils or as components are mixed with synthetic base oils in concentration of 1 mol/dm³or more, exhibits low vapor pressure, is non-flammable, exhibits excellent heat resistance, has tribological characteristics equivalent to those of conventional hydrocarbon-based lube oils, and can be used for long time under very severe conditions such as high temperature and vacuum. The drawbacks are (a) no significant improvement in tribological properties and (b) use of halogenated ionic liquids, which pollute the environment by halogen exposure.
Reference may be made to U.S. Pat. No. 7,754,664 B2, that ionic liquids as lubricants or lubricant additives composed of ammonium cations and [F₃C(CF₂)_yS(O)₂]₂N anion are effective for lubrication of many surfaces including aluminum and ceramic surfaces. Herein, all claimed ionic liquids exhibit halogen (fluorine) content, which not only corrodes the contact surfaces of metals but also pollute the environment by halogen exposure.
Reference may be made to US Patent No. 2010/0093577 A 1, a lubrication oil composition comprises a major amount of a base oil and a minor amount of an additive which is a non-halide, non-aromatic ionic liquids with a general formula of C⁺A⁻, where cation C⁺ being a quaternary phosphonium or ammonium ion, and the anion A−, comprising at least one oxygen atom and having an ionic head group attached to at least one alkyl or alicyclic hydrocarbyl group. The ionic liquid may be used as anti-wear and a friction modifier in the lubricating oil composition. The lubricating oil composition may be used in an ignition engine. The addressed ionic liquids contains phosphorus and sulphur elements as main constituents, which are not only hazardous and toxic to environment, but also corrodes the engineering surfaces of metals.
Reference may be made to US Patent No. 2010/0187481 A1, an invention relates to the use of ionic liquids for improving the lubricating effect of synthetic, mineral and native oils, in particular to an improved lubricating composition that is protected from thermal and oxidative attack. The ionic liquids addressed in this invention carries halogen, phosphorus and sulphur elements as main constituents which are not only hazardous and toxic to environment, but also corrodes the engineering surfaces of metals.
Reference may be made to U.S. Pat. No. 8,268,760 B2 that anti-wear and anti-friction properties of a 5W30 lubricating oils can be improved by use of ionic liquids as additives in the range of 0.01 to 5 wt. % based on the total weight of the lubricating oils. The cation in '760 B2 are imidazolium, peridinium, pyrrolidinium, phosphonium and ammonium, while anion are tetrafluroboaite, hexafluorophosphate, bis(trifluoromethylsulfonyl) imides and the like. Theses ionic liquids exhibit no significant reduction in both friction and wear by adding to 5W30 oil as lubricant additives and possesses halogen contents, which not only corrodes the contact surfaces made of metals but also pollute the environment.
Reference may be made to US Patent No. 2012/0202724 A1, a method in which an improved composition containing ionic liquids is used to enable operation of chains, steel ball, wheel bearing, roller bearing, sliding bearing and electric motors by reducing the evaporation loss and the lackification tendency of the lubricant against thernial and oxidative attack. The drawback is that ionic liquids have not been explored for friction and wear reduction. Additionally, the addressed ionic liquids were based on halogen content, which not only corrodes the contact surfaces made of metals but also pollute the environment by halogen exposure.
However, so far no attempt was made on development of halogen-, phosphorus- and sulphur-free ionic liquids composed of fatty acids anions as lubricant or lubricant additives to improve the lubricating properties by reducing friction coefficient and wear between two or more contact surfaces and to minimize the hazardous and corrosive effects to the environment and engineering surfaces, which are emergent call of the hours owing to strict government regulations and policies on environment and energy efficient processes development.

OBJECT OF THE INVENTION

The main object of the present invention is to provide halogen-free ionic liquids based lubricant or lubricant additives and a process for the preparation thereof.
Another object of the present invention is to provide lubricants or lubricant additives composed of halogen-, phosphorus- and sulphur-free ionic liquids containing fatty acids anions, which exhibit superior friction-reducing, anti-wear properties.
Another object of the present invention is 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.
Still another object of the present invention is to provide ionic liquids that exhibits a better combination of friction, wear and heat transfer properties as compared with corresponding lubricant or lubricant additives.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides 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 C4 to C30 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, —C—O—C—; and cations in the ionic liquids are selected from the group consisting of:
wherein R1 to R12 is similar or different from one another, selected from the group consisting of hydrogen, —OH, C1 to C18 alkyl group(s) including straight chain or branched structures, C2 to C12 alkenyl group(s) including straight chain or branched structures, wherein the alkyl or alkenyl group(s) optionally contain heteroatom, C7 to C12 alytalkyl group(s), C7 to C12 alkylaryl group(s).
In an embodiment of the present invention the ionic liquids are substantially or completely free of halogen, phosphorous, and/or sulphur.
In one embodiment of the present invention ionic liquid are selected from Tetrabutylammonium oleate (TBA-OL), 1-Hexylmethylitnidazolium oleate (HMIM-OL) and Tetrabutylammonium linoleate (TBA-LN), Tetrabutylammonium caprylate, Tetrabutylammonium caprate, Tetrabutylammonium laurate, Tetrabutylammonium myrisate, Hexyldimethylcyclohexylammonium oleate and Dioctylmethylpentylammonium oleate.
In another embodiment of the present invention the composition 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.
Still in another embodiment of the present invention the lubricant or lubricant additive composition is having high friction reducing and anti-wearing properties.
Still in another embodiment of the present invention a lubricating oil comprising the lubricant additive composition and a base lubricating oil.
Still in another embodiment of the present invention 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. %.
Still in another embodiment of the present invention the base lubricant oil(s) is selected from synthetic, minerals and native base stock (s) or base oil (s).
Still in another embodiment of the present invention the synthetic oils is selected from the group consisting of polymerized and interpolymerized olefins: polyalphaolefin (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 (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.
Still in another embodiment of the present invention a process for the preparation of lubricant or lubricant additive composition comprising ionic liquid(s), wherein the said process comprises the steps of:

- a) mixing sodium salt of fatty acid in an aqueous solution of tetraalkylainmonium 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.

Still in one embodiment of the present invention, ionic liquids are salts of one or mixtures of fatty acids anions. The suitable cations for the present invention may be imidazoliutn, amtnonium, peridinium, pyrolidinium, pyrrolidinium and the like.
In yet another embodiment of the present invention the contact surfaces are independently composed of metal, ceramic or alloys and more; including the thin film (s) of metallic or ceramic materials on the contact surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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.
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.
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.
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.
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 CO₂emission.
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).
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:
whereas R may be C₄to C₃₀straight 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, —C—O—C— and so on.
The structure of suitable cations for the present invention may be represented as general formula II.
Herein, R¹to R¹²may he the similar or different from one another, represents a group consisting of hydrogen, —OH, C₁to C₁₈alkyl group(s) includes straight chain or branched structure, C₂to C₁₂alkenyl group(s) includes straight chain or branched structure wherein the alkyl or alkenyl group(s) may contain heteroatom, C₇to C₁₂arylalkyl group(s), C₇to C₁₂alkylaryl group(s).
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

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

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

(a) Tetrabutylammonium oleate (TBA-OL)

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 ¹t1 NMR and FTIR spectroscopy. The characterization detail is as follows:
¹H NMR (ppm): 0.88-1.1 (t, 15H_g,kCH₃), 1.2-1.4 (m12H_c,iCH₂), 1.45-1.7 (m, 24H_d,iCH₂), 1.9-2.1 (m, 4H_eCH₂), 2.3-2.4 (in, 2H_bCH₂), 2.45-2.55 (m, 2H₈CH₂), 2.85-3.0(t, 8H_bN—CH₂), 5.3-5.4 (m, 2H_fCH═CH).
FTIR (cm⁻¹): 3010, 2929, 2855, 1764, 1631, 1460, 1375, 1280, 1237, 1105, 993, 721.

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

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 ¹H NMR and FTIR spectroscopy. The characterization detail is as follows:
¹H NMR (ppm): 0.86-0.88 (m, 6H_g,iCH₃), 1.26-1.29 (m, 22H_d,l,k,jCH₂), 1.54-1.55 (m, 4H_cCH₂), 1.81-1.82 (m, 2H_mCH₂), 2.0-2.1 (m, 4H, CH₂), 2.13-2.15 (m, 2H_bCH₂), 2.75-2.8 (t, 2H_a, CH₂COO), 3.94-3.96 (s, 3H_h, N—CH₃), 4.19-4.22 (t, 2H_n, N—CH₂), 5.31-5.34 (q, 2H_fCH═CH), 7.49 8& 7.34 (s, 2H_p,oCH), 9.6 (s, 1H_qCH).
FTIR (cm⁻¹): 3149, 3080, 3006, 2956, 2926, 2852, 1718, 1635, 1569, 1465, 1377, 1277, 1242, 1168, 991, 831, 721.

(c) Tetrabutylammonium linoleate (TBA-LN)

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 ¹H NMR and FTIR spectroscopy. The characterization detail is as follows:
¹H NMR (ppm): 0.86-0.89 (m, 15H_h,1CH₃), 0.98-1.01 (m, 14H_d,kCH₂), 1.26-1.3 (m, 2H_cCH₂), 1.41-1.48 (q, 2H_jCH₂), 1.61-1.67 (m, 4H_eCH₂), 1.95-2.1 (m, 2H_bCH₂), 2.3-2.37 (m, 2H_aCH₂COO), 2.65-2.7 (m, 2H_gCH₂), 3.32-3.35 (m, 8H_i, N—CH₂), 5.3-5.4 (m, 4H_fCH═CH). FTIR (cm⁻¹): 3008, 2960, 2929, 2859, 1727, 1463, 1383, 1178, 1108, 1031, 737.

Example 2

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

Effect of Fatty Acid Ionic Liquid Concentration as Lubricant Additive on their Lubrication Properties
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 μm, 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

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

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 2

WSD and friction coefficient of representative fatty acids
ionic liquids blended (1.5 wt %) with polyol ester.

		Friction
	WSD, μm	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

Friction-reducing and Anti-wear Performance of Representative Fatty Acids Ionic Liquids as Lubricant Additives in 10W40 Lube
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 _atypicalexperiment, 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 3

WSD and friction coefficient of representative fatty acids
ionic liquids blended (1 wt %) with 10W40 lube oil

		Friction
	WSD, μm	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

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

The main advantages of the present invention are:

- 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.
- 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.
- 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.

Claims

We claim:

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 C₄to C₃₀straight 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, —C—O —C—; and cations in the ionic liquids are selected from the group consisting of

wherein R¹to R¹²is similar or different from one another, selected from the group consisting of hydrogen, —OH, C₁to C₁₈alkyl group(s) including straight chain or branched structures, C₂to C₁₂alkenyl group(s) including straight chain or branched structures, wherein the alkyl or alkenyl group(s) optionally contain heteroatom, C₇to C₁₂arylalkyl group(s), C₇to C₁₂alkylaryl 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.