WO2010069986A1

WO2010069986A1 - Lubricating oil composition

Info

Publication number: WO2010069986A1
Application number: PCT/EP2009/067267
Authority: WO
Inventors: Toru Ikai
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2008-12-19
Filing date: 2009-12-16
Publication date: 2010-06-24
Also published as: JP2010163611A

Abstract

The present invention provides a lubricating oil composition comprising a phenol-based anti-oxidant represented by the following Formula 1 and an amine-based anti-oxidant in a base oil, Wherein R⁵ and R⁶ may be the same or different and independently represent an alkyl group with from 1 to 4 carbons or a cyclic alkyl group with from 3 to 8 carbons, and R⁷ represents an alkylene group with from 1 to 8 carbons.

Description

_ ]_ _

LUBRICATING OIL COMPOSITION

This invention relates to a lubricating oil composition.

In the electricity generation facilities of recent years it has become increasingly common to employ, for example, gas turbines using combustion gases at elevated temperatures, such as liquefied natural gas (LNG) , or combined cycle electricity generation facilities using gas turbines and steam turbines in combination, in order to increase the efficiency of the electricity generation and to utilise energy effectively. In these electricity generation facilities, the thermal load on the turbine oils used has been increasing considerably as the temperatures of the combustion gases rise.

Since turbine oils are used without change for periods as long as possible, and are also used under severe high-temperature conditions, they require superior heat resistance and oxidative stability.

There have hitherto been proposals, for example, for a gas turbine oil in which 2, 6-ditertiary butyl-4-ethyl phenol (DBPC) is blended in a mineral oil or a synthetic oil (Japanese Patent 7-42468 (1995)), and a gas turbine oil in which an alkylated phenyl-α-naphthylamine, a phosphite, an alkylsuccinic acid derivative, and a benzotriazole or a derivative thereof are blended in a mineral oil or a synthetic oil (Japanese Laid-open Patent 7-258677 (1995}) . However, satisfactory results have still not been obtained with these.

This invention is an attempt to offer a superior lubricating oil composition which has oxidative stability such as to present a sufficiently long oxidation life, little increase in viscosity and excellent energy-saving characteristics, even in cases where it is used in turbine bearings when generating electricity with gas turbines or combined-cycle turbines running in severe high-temperature environments.

As the result of repeated and intensive investigations to achieve the aforementioned objectives, the present invention provides a superior lubricating oil composition with high oxidative stability and excellent energy conservation with low viscosity increase, by incorporating a phenol-based anti-oxidant represented by the following Formula 1 and an amine-based anti-oxidant in a base oil of a mineral oil and/or a synthetic oil:

In the aforementioned Formula 1, R⁵ and R⁶ may be the same or different and each independently represents an alkyl group with from 1 to 4 carbons or a cyclic alkyl group with from 3 to 8 carbons, and R⁷ represents an alkylene group with from 1 to 8 carbons.

For the phenol-based anti-oxidant of the aforementioned Formula 1 it is possible in particular to make satisfactory use of such as represented by the following Formula 2:

Also, for the aforementioned amine-based antioxidant it is preferable to use either a diphenylamine compound or a phenylnaphthylamine compound, or a combination thereof. The lubricating oil composition in accordance with this invention, acting as a lubricating oil, presents a sufficiently long oxidation life, little increase in viscosity and excellent energy-saving characteristics, even in cases where it is used in turbine bearings when generating electricity with gas turbines or combined- cycle turbines running in severe high-temperature environments. Consequently, the lubricating oil composition of this invention is extremely useful from the standpoint of extending maintenance intervals of turbine bearing units when generating electricity with gas turbines and combined-cycle turbines.

Appropriate examples of embodiment of the invention are described in detail below. In the following descriptions, in the cases where compounds or functional groups can have linear and branched structures, both linear and branched instances are included in the said compounds, unless specially specified.

For the base oil of the present lubricating oil composition it is possible to use mineral oils describable as highly refined base oils, and synthetic oils, and oil mixtures thereof, and in particular it is possible to use, singly or as mixtures, base oils which belong to Group I, Group II, Group III, Group IV and so on of the API (American Petroleum Institute) base oil categories. The base oils used here preferably have an elemental sulphur content of less than 700 ppm and preferably less than 500 ppm. The density is preferably from 0.8 to 0.9. The aromatic content is preferably not more than 5% and preferably not more than 3%.

Group I base oils include, for example, paraffinic mineral oils obtained by application of a suitable combination of refining processes such as solvent refining, hydrorefining, and dewaxing in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil. The viscosity index is typically from 80 to 120 and preferably from 95 to 110. The kinematic viscosity at 40⁰C is preferably from 2 to 680 mmVs and even more preferably from 8 to 220 mm²/s. Also, the total sulphur content is typically less than 700 ppm and preferably less than 500 ppm. The total nitrogen content is typically less than 50 ppm and preferably less than 25 ppm. In addition, oils with an aniline point of from 80 to 150⁰C, and preferably from 90 to 120⁰C, are typically used.

Group II base oils include, for example, paraffinic mineral oils obtained by application of a suitable combination of refining processes such as hydrorefining and dewaxing in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil. Group II base oils refined by hydrorefining methods such as the Gulf Company method have a total sulphur content of less than 10 ppm and an aromatic content of not more than 5% and so are suitable for this invention. The viscosity of these base oils is not specially limited, but the viscosity index is typically from 80 to 120 and preferably from 100 to 120. The kinematic viscosity at 40⁰C is preferably from 2 to 680 mm²/s and even more preferably from 8 to 220 mmVs. Also, the total sulphur content is typically less than 300 ppm, preferably less than 200 ppm and even more preferably less than 10 ppm. The total nitrogen content is typically less than 10 ppm and preferably less than 1 ppm. In addition, oils with an aniline point of from 80 to 150⁰C, and preferably from 100 to 135°C, are typically used.

Suitable Group III base oils and Group 11+ base oils include paraffinic mineral oils manufactured by a high degree of hydrorefining in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil, base oils refined by the Isodewax process which dewaxes and substitutes the wax produced by the dewaxing process with isoparaffins, and base oils refined by the Mobil wax isomerisation process. They include those that may be designated as "synthetic oils" according to the rulings of the NAD (National Advertising Division) which is responsible for advertising adjudications in America. The viscosity of these base oils is not specially limited, but the viscosity index is typically from 95 to 145 and preferably from 100 to 140. The kinematic viscosity at 40⁰C is preferably from 2 to 680 rnrnVs and even more preferably from 8 to 220 mm²/s. Also, the total sulphur content is typically from 0 to 100 ppm and preferably less than 10 ppm. The total nitrogen content is typically less than 10 ppm and preferably less than 1 ppm. In addition, oils with an aniline point of from 80 to 150⁰C, and preferably from 110 to 135°C, are typically used.

GTLs (gas to liquid oils) synthesised by the Fischer-Tropsch method of converting natural gas to liquid fuel have a very low sulphur content and aromatic content compared with mineral oil base oils refined from crude oil and have a very high paraffin constituent ratio, and so have excellent oxidative stability, and because they also have extremely small evaporation losses, they are suitable as base oils for this invention. The viscosity of GTL base oils is not specially limited, but normally the viscosity index is typically from 130 to 180 and preferably from 140 to 175. Also, the kinematic viscosity at 40⁰C is typically from 2 to 680 mm^z/s and preferably from 5 to 120 mm²/s. Normally the total sulphur content is also less than 10 ppm and the total nitrogen content less than 1 ppm. A commercial example of such a GTL base oil is Shell XHVI (registered trademark) . As examples of synthetic oils mention may be made of polyolefins, alkylbenzenes, alkylnaphthalenes, esters, polyoxyalkylene glycols, polyphenyl ethers, dialkyldiphenyl ethers, fluorine-containing compounds (perfluoropolyethers, fluorinated polyolefins) and silicone oils.

The aforementioned polyolefins include polymers of various olefins or hydrides thereof. Any olefin may be used, and as examples mention may be made of ethylene, propylene, butene (1-butene, 2-butene, isobutene) and ot- olefins with five or more carbons. In the manufacture of polyolefins, one kind of the aforementioned olefins may be used singly or two or more kinds may be used in combination. Particularly suitable are the polyolefins called poly-α-olefins (PAO) . These are base oils of Group IV. The viscosity of these synthetic oils is not specially limited, but the kinematic viscosity at 40⁰C is preferably from 2 to 680 mrti²/s and more preferably from 8 to 220 mmVs. The amount of the aforementioned base oil to be incorporated in the lubricating oil composition of this invention is not specially limited, but, taking as a basis the total amount of the lubricating oil composition, is typically at least 60% by mass, preferably at least 70% by mass, more preferably at least 80% by mass, and yet more preferably at least 90% by mass .

The viscosity of the aforementioned base oils is not specially limited, but the kinematic viscosity at 40⁰C is preferably from 2 to 680 mmVs and more preferably from 8 to 220 mm²/s.

The total sulphur content is typically from 0 to 100 ppm and preferably from 0 to 30 ppm. The total nitrogen content is typically from 0 to

100 ppm and preferably from 0 to 30 ppm.

Further, oils where the aniline point is from 80 to 150⁰C, and preferably from 110 to 135⁰C, are typically used. The lubricating oil composition may be made by incorporating phenol-based anti-oxidants and amine-based anti-oxidants in the aforementioned base oils. For the phenol-based anti-oxidants use is made of those represented by the following Formula 1.

(D

In the aforementioned Formula 1, R⁵ and R⁶ may be the same or different and independently represents an alkyl group with from 1 to 4 carbons or a cyclic alkyl group with from 3 to 8 carbons, and R⁷ represents an alkylene group with from 1 to 8 carbons.

Compounds as represented by the aforementioned Formula 1 are used for the phenol-based anti-oxidant, but among these it is possible to use, for example, as a preferred instance 2, 2' -methylene-bis (4-ethyl, 6-t- butylphenol} as represented by the following Formula 2:

Amine-based anti-oxidants are used in this lubricating oil composition together with the aforementioned phenol-based anti-oxidant . These amine- based anti-oxidants include diphenylamine compounds and phenylnaphthylamine compounds, and these may be used singly or in combination.

As examples of the aforementioned diphenylamine compounds, mention may be made of dialkyldiphenylamine- based compounds, and as examples of phenylnaphthylamine compounds mention may be made of phenyl-ct-naphthylamine- based compounds.

For the aforementioned dialkyldiphenylamine-based compounds it is preferable to use dialkyldiphenylamines as represented by Formula 3 below. _ Q —

In Formula 3, R2 and R3 may be the same or different and each represents an alkyl group of from 1 to 16 carbons.

As specific examples of the alkyl groups represented by these R2 and R3, mention may be made of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undeσyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, and so on (these alkyl groups may be either linear or branched) . Of these, branched alkyl groups with from 3 to 16 carbons are preferred for R2 and R3 from the standpoint of superior solubility, and branched alkyl groups with from 3 to 16 carbons derived from olefins of 3 or 4 carbons or oligomers thereof are preferred. As specific examples of olefins of from 3 to 4 carbons, mention may be made of propylene, 1-butene, 2-butene and isobutylene, but from the standpoint of solubility propylene or isobutylene is preferred.

Also, isopropyl groups derived from propylene, tert- butyl groups derived from isobutylene, branched hexyl groups derived from dimers of propylene, branched octyl groups derived from dimers of isobutylene, branched nonyl groups derived from trimers of propylene, branched dodecyl groups derived from trimers of isobutylene, branched dodecyl groups derived from tetramers of propylene or branched pentadecyl groups derived from pentamers of propylene are further preferred for R2 and R3, again from the standpoint of superior solubility, whilst most preferred are tert-butyl groups derived from isobutylene, branched hexyl groups derived from dimers of propylene, branched octyl groups derived from dimers of isobutylene, branched nonyl groups derived from trimers of propylene, branched dodecyl groups derived from trimers of isobutylene or branched dodecyl groups derived from tetramers of propylene.

If compounds in which one of R2 or R3 or each one is a hydrogen atom are used, there is a risk that sludge will occur owing to oxidation of the compound itself. Also, if the number of carbons in the alkyl group exceeds 16, there is a risk that the proportion of functional groups in the molecules will become too small and the ability to prevent oxidation at high temperatures will be reduced.

The alkyl groups denoted by R2 or R3 can each bond at any position of the phenyl group, but the p-position is preferred for amino groups. That is, the dialkyldiphenyl amines represented by the aforementioned Formula 3 are preferably p,p' -dialkyldiphenyl amines.

Commercial compounds of the dialkyldiphenyl amines represented by the aforementioned Formula 3 may be used, and synthetics may also be used. The synthetics can easily be synthesised by using a Friedel-Crafts catalyst and reacting a diphenyl amine and an alkyl halide compound of from 1 to 16 carbons, or by reacting a diphenyl amine and an olefin of from 2 to 16 carbons or an oligomer thereof. For the Friedel-Crafts catalyst, metal halides as listed in the explanation of the phenyl- α-napthylaraine-based compounds or acidic catalysts may typically be used. Phenyl-α-napthylamines as represented by the following Formula 4 are preferred for use as the aforementioned phenyl-α-napthylamine-based compounds.

In Formula 4, Rl represents a hydrogen atom or a linear or branched alkyl group with from 1 to 16 carbons.

If Rl in the aforementioned Formula 4 is an alkyl group, this alkyl group will be a linear or a branched alkyl group of froml to 16 carbons. As specific examples of such alkyl groups, mention may be made of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl and hexadecyl. If the number of carbons in Rl were to exceed 16, there would be a risk that the proportion of functional groups in the molecules would become too small and this would have a detrimental effect on the ability to prevent oxidation.

If Rl in the aforementioned General Formula 4 is an alkyl group, it is preferable from the standpoint of superior solubility if Rl is a branched alkyl group of from 8 to 16 carbons, and it is further preferable if it is a branched alkyl group of from 8 to 16 carbons derived from an oligomer of an olefin of 3 or 4 carbons. As specific examples of olefins with 3 or 4 carbons, mention may be made of propylene, 1-butene, 2-butene and isobutylene, but from the standpoint of solubility propylene or isobutylene is preferred.

In order to achieve even better solubility, it is further preferable if Rl is a branched octyl group derived from a dimer of isobutylene, a branched nonyl group derived from a trimer of propylene, a branched dodecyl group derived from a trimer of isobutylene, a branched dodecyl group derived from a tetramer of propylene or a branched pentadecyl group derived from a pentamer of propylene. Especially preferred is a branched octyl group derived from a dimer of isobutylene, a branched dodecyl group derived from a trimer of isobutylene or a branched dodecyl group derived from a tetramer of propylene. Also, if Rl is an alkyl group, it can bond to the phenyl group at any position but the p-position is preferred. Further, the amino group can bond to any position on the naphthyl group but the α-position is preferred. Commercial compounds of the phenyl-α-naphthylamines represented by the aforementioned General Formula (4) may be used, and synthetics may also be used. The synthetics can easily be synthesised by using a Friedel-Crafts catalyst and reacting a phenyl-α-naphthylamine and an alkyl halide compound of from 1 to 16 carbons, or by reacting a phenyl-α-naphthylamine and an olefin of from 2 to 16 carbons or an olefin oligomer of from 2 to 16 carbons. For the Friedel-Crafts catalyst, in specific terms, it is possible to use metal halides such as aluminium chloride, zinc chloride and iron chloride; or acidic catalysts such as sulphuric acid, phosphoric acid, phosphorus pentoxide, boron fluoride, acid clays and active clay. The aromatic amine compounds as represented in the aforementioned Formulas (3) and (4) may be used alone as one kind, or may be used as mixtures of two or more kinds with different structures, but, given their ability to maintain the ability to prevent oxidation at high temperatures for longer periods it is preferable to use a 2,2' -alkylenebis (4-alkyl, 6-t-butylphenol) as represented by Formula (1) and a dialkyldiphenylamine as represented by Formula (3) together. The mixing proportion in such case is not limited, but it is preferred if it is in the range of from 1/10 to 10/1 as a mass ratio.

The total amount of phenol-based anti-oxidant in the lubricating oil composition of this invention is not specially limited, but in terms of the total amount of the lubricating oil composition it is preferably from

0.005 to 5% by mass, more preferably from 0.01 to 3% by mass, and even more preferably from 0.02 to 1% by mass. Also, the total amount of amine-based anti-oxidant is not specially limited, but in terms of the total amount of the lubricating oil composition it is preferably from

0.005 to 5% by mass, more preferably from 0.01 to 3% by mass, and even more preferably from 0.02 to 1% by mass.

Further, the phenol-based anti-oxidant : amine-based anti-oxidant mixing ratio is preferably from 1 : 10 to 10 : 1, more preferably from 1 : 10 to 1 : 1, and even more preferably from 1 : 8 to 1 : 2. If the total content is less than 0.01% by mass, there will be a tendency for the oxidative stability or thermal stability to become unsatisfactory. On the other hand, if it exceeds 10% by mass, the oxidative stability effect obtained will not match the amount incorporated, and it may become a cause of an increase in sludge, which is not desirable. As examples of the aforementioned amine-based antioxidants, mention may be made of dialkyl-diphenylamines such as p,p' -dloctyl-diphenylamine (Nonflex OD-3, made by Seiko Chemical Ltd), p, p' -di-oc-πtethylbenzyl-diphenylamine and N-p-butylphenyl-N-p' -octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and monooctyldiphenylamine, bis (dialkylphenyl) amines such as di (2, 4-diethylρhenyl) amine and di (2-ethyl-4- nonylphenyl} amine, alkylphenyl-1-naphthylamines such as octyl-phenyl-1-naphthylamine and N-t-dodecylphenyl-1- naphthylamine, 1-naphthylamine, aryl-naphthylamines such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N- hexylphenyl-2-naphthylamine and N-octylphenyl-2- naphthylainine, phenylenediamines such as N,N'- diisopropyl-p-phenylenediamine and N,N' -diphenyl~p- phenylenediamine, and phenothiazines such as Phenothiazine (made by Hodogaya Chemical Ltd.) and 3,7- dioctylphenothiazine .

Phenol-based anti-oxidants as represented by the aforementioned Formula 1 are used for the phenol-based anti-oxidants, but it is possible to use other phenol- based anti-oxidants together with these.

Such phenol-based anti-oxidants include 2-t- butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5- methylphenol, 2, 4-di-t-butylphenol, 2, 4-dimethyl-6-t- butylphenol, 2, 5-di-t-butylhydroquinone (Antage DBH, made by Kawaguchi Chemical Industry Co. Ltd.), t- butylhydroquinone (TBH, made by Seiko Chemical Ltd. ) , 2, 6-di-t-butylphenol, 2, 6-di-t-butyl-4-alkylphenols such as 2,6-di-t-butyl-4-methylphenol and 2, 6-di-t-butyl-4- butylphenol, 2, 6-di-t-butyl-4-methoxyphenol, 2,6-di-t- butyl-4-methoxyphenol, p-methoxyphenol (Methoquinone, made by Seiko Chemical Ltd.), 2-t~butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, and 2, 6-di-t-butyl-4- alkoxyphenols such as 2, 6-di-t-butyl-4-ethoxyphenol.

Also, there are 3, 5-di-t-butyl-4- hydroxybenzylmercapto-octylacetate, alkyl-3- (3, 5-di-t- butyl-4~hydroxyphenyl) propionates such as n-octadecyl-3™ (3, 5-di-t-butyl-4--hydroxyphenyl) propionate (Yoshinox SS, made by API Corporation), n~dodecyl-3- (3, 5-di-t-butyl-4- hydroxyphenyl} propionate, 2 ' -ethylhexyl-3- (3, 5-di-t- butyl-4-hydroxyphenyl) propionate, and benzenepropanoic acid 3, 5-bis (l,l-dimethyl-ethyl)-4-hydroxy-C7~C9 side- chain alkyl ester (Irganox L135, made by Ciba Specialty Chemicals Ltd.}, 2, 6-di-t-butyl-α-dimethylamino-p-cresol, and so on.

Furthermore, there are bisphenols such as 4,4'- butylidenebis (3-methyl-~6-t-butylphenol) {Antage W-300, made by Kawaguchi Chemical Industry Ltd.}, 4,4'- methylenebis (2, 6-di-t-butylphenol) (Ionox 220AH, made by Shell Japan Ltd.), 2, 2' -methylenebis (4-ethyl, 6-t- butylphenol) {Nonflex EBP, made by Seiko Chemical Ltd.), 2, 2 ' -methylenebis (4-methyl, β-t-butylphenol) (Nonflex HBP, made by Seiko Chemical Ltd.)_/ 2, 2' -methylenebis [6- (1- methylcyclohexyl p-cresol) ] {Nonflex CBP, made by Seiko Chemical Ltd.), 4, 4 ' -bis (2, 6-di-t-butylphenol) , 2,2- (di- p-hydroxyphenyl) propane (Bisphenol A, made by Shell Japan Ltd.), 2, 2-bis (3, 5-di-t-butyl-4-hydroxyphenyl} propane,

4,4' -cyclohexylidenebis ( 2 , 6-t-butylphenol ) , hexamethylene glycol bis [3- (3, 5-di-t-butyl-4~hydroxyphenyl) propionate] (Irganox L109, made by Ciba Specialty Chemicals Ltd.), triethylene glycol bis [3- (3-t-butyl-4-hydroxy-5- methylphenyl) propionate] (Tominox 917, made by API

Corporation) , 2,2' -thio- [diethyl-3- (3, 5-di-t-butyl-4- hydroxyphenyl) propionate (Irganox L115, made by Ciba Specialty Chemicals Ltd.}, 3, 9-bis{ 1, l-dimethyl-2- [3- {3- t-buty1-4-hydroxy-5-methylphenyl) propionyloxy] ethyl}2, 4,8, 10-tetraoxasp±ro [5, 5]undecane (Sumilizer GA80, made by Sumitomo Chemicals), 4,4'- thiobis (3-methyl-6-t-butylphenol) (Antage RC, made by Kawaguchi Chemical Industry Ltd.) and 2, 2 ' -thiobis (4, 6- di-t-butyl-resorcinol) .

Mention may also be made of polyphenols such as tetrakis [methylene-3- (3, 5-di-t-butyl-4-hydroxyphenyl} propionate] methane (Irganox LlOl, made by Ciba Specialty Chemicals Ltd.), 1, 1, 3-tris (2-methyl-4-hydroxy-5-t- butylphenyl) butane (Yoshinox 930, made by API Corporation) , 1,3, 5-trimethyl-2, 4 , 6-tris (3, 5-di-t-butyl- 4-hydroxybenzyl) benzene (Ionox 330, made by Shell Japan Ltd. ) , bis- [3, 3 '-bis- (4 ' -hydroxy-3 ' -t-butylphenyl) butyric acid] glycol ester, 2™ (3 ' , 5 ' -di-t-butyl-4- hydroxyphenyl ) methyl-4- ( 2 ' ' , 4 ' ' -di-t-butyl-3 ' ' - hydroxyphenyl)methyl-6-t~butylphenol and 2, 6, -bis (2 '- hydroxy-3 ' -t-butyl-5 ' -methyl-benzyl ) -4-methylphenol , and phenol-aldehyde condensates such as a condensate of p-t- butylphenol and formaldehyde and a condensate of p-t- butylphenol and acetaldehyde.

Phosphorus compounds may also be incorporated in the lubricating oil composition. Such phosphorus compounds include phosphate esters, phosphite esters and derivatives thereof.

For the aforementioned phosphorus compounds it is possible to use, for example, at least one kind of phosphate esters, phosphite esters, zinc dithiophosphates, dithiophosphate esters or derivatives thereof, or mixtures thereof.

As specific examples of phosphate esters mention may be made of tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trlnoπyl phosphate, tridecyl phosphate, triundecyl phosphate, tridodecyl phosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentadecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate, trioleyl phosphate, triphenyl phosphate, tris (iso-propylphenyl) phosphate, triaryl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyldiphenyl phosphate and xylenyldiphenyl phosphate. As examples of phosphite esters mention may be made of dibutyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, tridodecyl phosphite, trioleyl phosphite, triphenyl phosphite, trialkylphenyl phosphite and tricresyl phosphite.

As examples of zinc dithiophosphates, mention may be made in general of zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates and zinc arylalkyl dithiophosphates . For example, zinc dialkyl dithiophosphates where the alkyl groups of the zinc dialkyl dithiophosphates have primary or secondary alkyl groups of from 3 to 22 carbons or alkylaryl groups substituted with alkyl groups of from 3 to 18 carbons may be used. As specific examples of zinc dialkyl dithiophosphates, mention may be made of zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate, zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zinc diisopeπtyl dithiophosphate, zinc diethylhexyl dithiophosphate, zinc dioctyl dithiophosphate, zinc dinonyl dithiophosphate, zinc didecyl dithiophosphate, zinc didodecyl dithiophosphate, zinc dipropylphenyl dithiophosphate, zinc dipentylphenyl dithiophosphate, zinc dipropylmethylphenyl dithiophosphate, zinc dinonylphenyl dithiophosphate, and zinc didodecylphenyl dithiophosphate .

For dithiophosphate esters or derivatives thereof, mention may be made of the following.

Examples include dithiophosphate monoalkyl esters such as monopropyl dithiophosphate, monobutyl dithiophosphate, monopentyl dithiophosphate, monohexyl dithiophosphate, monoheptyl dithiophosphate, monooctyl dithiophosphate and monolauryl dithiophosphate (the alkyl groups may be linear or branched) ; dithiophosphate ( (alkyl) aryl) esters such as monophenyl dithiophosphate and monocresyl dithiophosphate; dithiophosphate dialkyl esters such as dipropyl dithiophosphate, dibutyl dithiophosphate, dipentyl dithiophosphate, dihexyl dithiophosphate, diheptyl dithiophosphate, dioctyl dithiophosphate and dilauryl dithiophosphate (the alkyl groups may be linear or branched) ; dithiophosphate di ( (alkyl) aryl) esters such as diphenyl dithiophosphate and dicresyl dithiophosphate; dithiophosphate trialkyl esters such as tripropyl dithiophosphate, tributyl dithiophosphate, tripentyl dithiophosphate, trihexyl dithiophosphate, triheptyl dithiophosphate, trioσtyl dithiophosphate and trilauryl dithiophosphate (the alkyl groups may be linear or branched) ; and dithiophosphate tri ( (alkyl) aryl) esters such as triphenyl dithiophosphate and tricresyl dithiophosphate. Among the aforementioned phosphorus compounds, phosphate esters and phosphite esters are more preferred because of their superiority in aspects of performance such as further inhibiting sludge, and trialkylphenyl phosphites, and triaryl phosphites such as tricresyl phosphite, monocresyldiphenyl phosphite and dicresylmonophenyl phosphite, are even more preferred.

The amount of the aforementioned phosphorus compounds is not specially limited, but, in terms of the total amount of the lubricating oil composition, it is preferably from 0.01 to 5% by mass, more preferably from 0.05 to 4.5% by mass, even more preferably from 0.1 to 4% by mass, yet more preferably from 0.5 to 3.5% by mass, and most preferably from 1 to 3% by mass. If the amount of phosphorus compound is less than 0.01% by mass, there is a risk that the improvement in sludge-inhibiting effect according to the amount of phosphorus compound will be unsatisfactory. On the other hand, if it exceeds 5% by mass, there is a risk that thermal and oxidative stability and foaming properties will be reduced.

With the purpose of enhancing performance in various ways, it is possible to use one kind singly or two or more kinds in combination of known lubricating oil additives in the lubricating oil composition of this invention. As examples of such additives, mention may be made of: phenol-based and phenothiazine-based antioxidants; acrylate-based defoaming agents such as polyacrylates or siloxane-based defoaming agents such as alkylpolysiloxanes; metal deactivators such as benzotriazoles or derivatives thereof; and pour-point depressants such as polymethacrylates, polyisobutylenes, olefin copolymers and polystyrenes. The amounts when using these additives is not restricted, but, in terms of the total amount of the composition, it is preferable if, in the case of antioxidants, it is from 0.1 to 5% by mass, in the case of defoaming agents from 0.0005 to 1% by mass, in the case of metal deactivators from 0.005 to 1% by mass, and in the case of other additives from 0.1 to 15% by mass in each case.

The viscosity of the lubricating oil composition is not specially limited, but the range of kinematic viscosity at 40⁰C is preferably not more than 680 mm²/s and more preferably not more than 220 miτι²/s, and also preferably not less than 2 mm²/s and more preferably not less than 8 mm²/s. The range of kinematic viscosity at 100⁰C is preferably not more than 25 mm²/s, more preferably not more than 20 mmVs, yet more preferably not more than 15 mm^£/s and most preferably not more than 10 mm²/s, and also preferably not less than 1.0 mm²/s, more preferably not less than 1.5 mm²/s, yet more preferably not less than 2 itsαVs and most preferably not less than 2.5 mm²/s. Also, the viscosity index of the aforementioned base oil is not specially limited, but is preferably not less than 85, more preferably not less than 100, and yet more preferably not less than 120.

The applications of the lubricating oil composition are not specially limited, but they will be used with special preference as the lubricating oils of compressors and turbine apparatus. Turbine apparatus includes, for example, water turbines, steam turbines and gas turbines, but the lubricating oil composition of this invention exhibits a superior effect when used in combined-cycle turbine apparatus. The outputs of such turbine apparatus are not specially limited.

The lubricating oil composition of this invention, given its superior properties, may be used not only in the aforementioned applications but also preferentially in applications such as hydraulic oils, industrial gear oils, bearing oils and compressor oils. Examples

The invention is explained in specific detail below on the basis of Examples and Comparative Examples, but the invention is in no way limited by the following examples of embodiment. Examples 1 to 3, Comparative Examples 1 to 9

The following base oil and additives were prepared for the manufacture of Examples 1 to 9 and Comparative Examples 1 to 9.

Base oil: Gr II

Paraffinic mineral oil of Group II obtained by application of a suitable combination of refining processes such as hydrorefining and dewaxing in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil. (Properties :- kinematic viscosity at 100⁰C: 10.9 mna²/s; kinematic viscosity at 40⁰C: 91.2 mm²/s; viscosity index: 104; sulphur content (as converted to elemental sulphur) less than 10 ppm. )

Additive Al: 4, 4' -methylene-bis (2, 6-di-tert- butylphenol) (commercial name: Ionox 220AH}

Additive A2: 3, 5-di-tert-butyl-hydroxytoluene (BHT) Additive A3: Octyl-3- (4-hydroxy-3, 5-tert~ butylphenol) propionate (commercial name: Irganox L135, manufactured by Ciba Specialty Chemicals Ltd. ) Additive A4 : Stearyl-3- (4-hydroxy-3, 5-tert- butylphenyl) propionate (commercial name: AIN-100, manufactured by Adeca Ltd.)

Additive A5: 2, 2' -methylene-bis- (4-ethyl-6--tert- butylphenol) (compound of Formula 2) (commercial name: Nonflex EBP, manufactured by Seiko Chemical Ltd.)

Additive B: Phosphorus-based anti-oxidant (commercial name: Irgafos 168, manufactured by Ciba Specialty Chemicals Ltd.) Additive C: Amine-based anti-oxidant (commercial name: Irganox L57, manufactured by Ciba Specialty Chemicals Ltd. )

Additive D: Benzotriazole-based anti-corrosive (commercial name: Irgamet 39, manufactured by Ciba Specialty Chemicals Ltd. }

Additive E: Succinic acid ester (commercial name: LZ859, manufactured by Lubrizol Ltd.)

The lubricating oil compositions of Examples 1 to 10 and Comparative Examples 1 to 9 were prepared using the aforementioned base oil and additives.

Measurement of Properties such as Kinematic Viscosity

The following properties were measured for the lubricating oil compositions of the aforementioned Examples 1 to 10 and Comparative Examples 1 to 9. 1 : Colour (ASTM colour) (on the basis of JIS K2580)

2 : Kinematic viscosity at 40⁰C (on the basis of JlS K2283)

3 : Kinematic viscosity at 100°C (on the basis of JIS K2283) 4 : Acid number (AN) (on the basis of JIS K2501)

The measurement results are shown in Tables 1 to 4. Tests

The following tests were carried out using the lubricating oil compositions of Examples 1 to 10 and Comparative Examples 1 to 9 in order to assess their performance o

Modified RPVOT Test

The test was done by the method stipulated in the gas turbine oil specification GEK 107395a of the turbine manufacturing company GE. First, the RPVOT value of the oil treated under the following test conditions was divided by the RPVOT value of fresh oil, to give the RPVOT residue, by the method standardised in JIS K2514.

* 150 g sample in a TOST test glass container

* N₂ gas inflow: 3 L/hr * Test temperature: 121°C

* Test duration: 48 hr

To the extent that the RPVOT value of the degraded oil is larger, and the RPVOT residue is closer to 100%, the significance is that the anti-oxidant is less volatile, there is less wear, and the stability is better.

RPVOT residue (%) = (treated oil RPVOT value / fresh oil RPVOT value) x 100

Evaluation criterion: an RPVOT residue of 85% or higher is a pass. ISOT Test

As regards the temperature and duration of the tests, measurements were made under the following conditions on the basis of the test method standardised by JIS K2514.

* Test temperature: 175°C

* Test Duration: 72 hr Evaluation criteria: 1 : Percentage change (%) in 40⁰C kinematic viscosity between fresh oil and oil degraded after ISOT test. 9% or less is satisfactory

Percentage change (%) = [(kinematic viscosity of degraded oil) / (kinematic viscosity of fresh oil) ] x 100

2 : Increase in acid number from acid number of fresh oil to degraded oil after ISOT test. 0.6 mgKOH/g or less is satisfactory

Increase in acid number (iugKOH/g) = (acid number of degraded oil) - (acid number of fresh oil) Test Results

The test results are shown in Tables 1 to 4. Evaluation

As is evident from the results in Tables 1 to 4, Examples 1 to 10 are satisfactory in having a modified RPVOT residue of 88 to 99%, and in the ISOT test, too, they are all satisfactory in having a percentage change (%) in 40⁰C kinematic viscosity between fresh oil and the degraded oil after the test of 1 to 4% and an increase in acid number from fresh oil to degraded oil after the test of 0.2 to 0.5 mgKOH/g.

Comparative Example 4 was satisfactory in that the percentage change (%) in 4O⁰C kinematic viscosity between fresh oil and the degraded oil after the ISOT test was 5%, and the increase in acid number from fresh oil to oil degraded after the test was 0.4 mg mgKOH/g, but the modified RPVOT residue was not of pass standard, being 61%.

In the cases of Comparative Examples 1 to 3 and 5 to 9, there was no apparent difference from the Examples in that the modified RPVOT residues were from 91 to 100%, but they were inferior in that in the ISOT test, the percentage change {%) in 40⁰C kinematic viscosity between fresh oil and the degraded oil after the test was from 10 to 112%, and the increase in acid number from fresh oil to degraded oil was from 1.2 to 12.5 mgKOH/g.

The Examples, as mentioned above, all have a high modified RPVOT residue and sufficiently long life, and so can be seen to be suitable as gas turbine oils.

Table 1

Table 2

Table 3

Table 4

Claims

C L A I M S

1. A lubricating oil composition comprising a phenol- based anti-oxidant represented by the following Formula 1 and an amine-based anti-oxidant in a base oil

Wherein R⁵ and R⁶ may be the same or different and independently represent an alkyl group with from 1 to 4 carbons or a cyclic alkyl group with from 3 to 8 carbons, and R⁷ represents an alkylene group with from 1 to 8 carbons .

2. A lubricating oil composition according to Claim 1, wherein the phenol-based anti-oxidant is represented by the following Formula 2:

3. A lubricating oil composition according to Claim 1 or 2, where the amine-based anti-oxidant is either a diphenylamine compound or a phenylnaphthylamine compound or a combination thereof. O _L

4. A lubricating oil composition according to any of Claims 1 to 3, wherein other phenol-based anti-oxidants are used together with the phenol-based anti-oxidant represented by the Formulas 1 or 2.

5. A lubricating oil composition according to any of

Claims 1 to 4 , further comprising a phosphorus compound.

6. A lubricating oil composition according to Claim 5, wherein the phosphorus compound is a phosphate ester, a phosphite ester, or a derivative thereof.

7. Use of the lubricating oil composition according to any of Claims 1 to 6 for improving one or more of: oxidation properties (in particular according to GEK 107395a) ; viscosity properties (in particular according to JIS K2283); and acid number (in particular according to JIS K2501) .