Note: Descriptions are shown in the official language in which they were submitted.
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LUBRICATING OIL COMPOSITION
The present invention relates to lubricating
compositions, more specifically to lubricating
compositions for lubricating rotary air compressors.
The lubrication of compressors, in particular rotary
air compressors, can expose the lubricant to high
temperature conditions.
Lubricating oil compositions for use in such
compressors have to meet a combination of requirements in
order to satisfactorily lubricate each component.
Accordingly, in order that the need for oil changes
can be minimised in such compressors, i.e. in order that
the oil drain interval is favourable, such lubricating
oil compositions must exhibit not only good deposit
control, but also good thermal and oxidative stability.
WO-A-01/64820 describes a lubricating oil
composition comprising a lubricating basestock which
comprises a blend of (A) at least one polyalkylene glycol
(PAG) and (B) at least one alkyl aromatic compound.
It is indicated that said lubricating oil
composition can be used as a positive displacement
compressor lubricant.
WO-A-01/64820 exemplifies lubricating oil
compositions comprising a PAG in combination with an
alkyl naphthalene and various antioxidants.
EP-A-0387979 discloses specific alkyl-substituted
diphenylamines as antioxidants, i.e. p,p'-
dinonyldiphenylamines.
EP-A-0387979 further discloses the use of said
antioxidants in lubricating oil compositions comprising
mineral oil having an aromatic content of 30% by weight
or below and/or synthetic oil containing no aromatic
rings in its structural units.
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That is to say, EP-A-0387979 teaches away from the
use of said antioxidants with aromatic lubricant base
oils.
EP-A-0387979 discloses a composition comprising a
p,p'-dinonyldiphenylamine, N-p-dodecylphenyl-oc-
naphthylamine, and, as base oil, either a purified mineral
oil having an aromatic content of 7% by weight or a poly-
oc-olefin oil. However, there is no disclosure in EP-A-
0387979 of the specific lubricating oil compositions of
the present invention.
Table 2 of EP-A-0387979 discloses a composition
comprising p,p'-branched dinonyldiphenylamine (Ex. 5) and
N-p-branched dodecylphenyl-oc-naphthylamine in said
purified mineral oil which has an oxidation-inhibiting
performance (according to ASTM D2272) of 2154 minutes.
Furthermore, Comparative Example 4 in said Table
describes a composition comprising p,p'-branched
dioctyldiphenylamine and N-p-branched octylphenyl-O(,-
naphthylamine in said purified mineral oil which has an
oxidation-inhibiting performance (according to ASTM D2272)
of 2127 minutes.
US-B1-6180575 describes lubricating oil compositions
which may be used in the lubrication of bearings, gears
and in other industrial applications such as in wet
clutch systems, cooling gear boxes and rotary screw
compressors.
Said lubricating oil compositions comprise a base
fluid which comprises at least 50 wt.% of a hydrocarbon
base fluid; and an additive combination comprising:
(1) an adduct of a substituted triazole and a
hydrocarbon amine phosphate in an amount below about
5 wt. % of the total composition and
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(2) a tri-hydrocarbyl phosphate in an amount up to
wt. % of the total composition,
wherein the ratio of the tri-hydrocarbyl phosphate to the
adduct is between about 2:1 to about 5:1.
5 US-B1-6180575 lists an number of conventional
additives including viscosity index improvers,
antioxidants, anti-wear additives and corrosion
inhibitors which may also be present in said lubricating
oil compositions. It is of note that whilst US-B1-
6180575 lists a number of different kinds of antioxidants
in the description thereof, the antioxidants are not a
critical feature of the Examples in US-B1-6180575 and
they are not described in detail therein.
Thus, Example 3 of US-B1-6180575 is said to be an
ISO grade 32 oil comprising 20.00 %wt. C14 alkyl
naphthalene, 76.78 %wt. of a mixture of PAO and 0.75 %wt.
of an amine antioxidant. Said oil is indicated to have a
RBOT value of 1750 minutes according to ASTM D2272.
However, whilst lubricating oil compositions for use
in compressors are known in the art, there remains the
need to develop lubricating oil compositions having
improved performance in order that the oil drain interval
can be increased still further.
In the present invention, lubricating oil
compositions have been surprisingly found which not only
exhibit good deposit control, but which also exhibit
excellent oxidative and thermal stability.
The lubricating oil composition according to the
present invention comprises one or more hydrocarbyl-
substituted aromatic lubricant base oils in combination
with (a) one or more phenyl-naphthylamines and (b) one or
more diphenylamines, wherein said lubricating oil
composition comprises one or more additional lubricant
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base oils comprising polyalphaolefins and/or Fischer-
Tropsch derived base oils.
The lubricating composition according to the present
invention can comprise a single compound or a mixture of
compounds for each of components (a) and (b).
The one or more phenyl-naphthylamines (a) which are
used in the present invention, can be either substituted
or non-substituted, or a mixture of both. The one or
more phenyl-naphthylamines can be used as such or in the
form of a salt. Examples of such phenyl-naphthylamines
are phenyl-alpha-naphthylamines and phenyl-beta-
naphthylamines. The phenyl-naphthylamine preferably is a
phenyl-alpha-naphthylamine.
A preferred substituted phenyl-naphthylamine is a
mono-alkylated phenyl-alpha-naphthylamine.
Examples of phenyl-naphthylamines that may be
conveniently used include octylphenyl-beta-naphthylamine,
t-octylphenyl-alpha-naphthylamine, phenyl-alpha-
naphthylamine, phenyl-beta-naphthylamine, phenyl-beta-
naphthylamine, p-octylphenyl-alpha-naphthylamine,
4-octylphenyl-l-octyl-beta-naphthylamine,
n-t-dodecylphenyl-l-naphthylamine, N-hexylphenyl-2-
naphthylamine. A particularly preferred phenyl-alpha-
naphthylamine is a monooctylated phenyl alpha-
naphthylamine.
Another preferred phenyl-naphthylamine is a non-
substituted phenyl-alpha-naphthylamine.
Examples of commercially available phenyl-
naphthylamines that may be conveniently used in the
lubricating oil composition of the present invention
include that available from Ciba Specialty Chemicals
under the trade designation "IRGANOX L-06".
The lubricating oil composition according to the
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diphenylamines (b). The one or more diphenylamines can
be substituted or non-substituted. It is preferred to use
a hydrocarbyl-substituted diphenylamine, more preferably
an alkyl-substituted diphenylamine. A preferred
diphenylamine is 4,4'-dialkyl diphenylamine. The alkyl
group preferably contains in the range of from 2 to 15
carbon atoms, more preferably in the range of from 3 to
12 carbon atoms. Preferred diphenylamines include
dialkyldiphenylamines such as p,p'-dioctyl-diphenylamine,
p,p'-di-OC-methylbenzyl-diphenylamine and N-p-butylphenyl-
N-p'-octylphenylamine, monoalkyldiphenylamines such as
mono-t-butyldiphenylamine and mono-octyldiphenylamine,
bis(dialkylphenyl)amines such as di-(2,4-
diethylphenyl)amine and di(2-ethyl-4-nonylphenyl)amine.
Examples of commercially available diphenylamines
that may be conveniently used in the lubricating oil
composition of the present invention include that
available from Ciba Specialty Chemicals under the trade
designation "IRGANOX L-57".
The one or more hydrocarbyl-substituted aromatic
lubricant base oils present in the lubricating oil
composition of the present invention are preferably
alkylated aromatic lubricant base oils, more preferably
alkylated aromatic lubricant base oils selected from one
or more of alkylated naphthalenes, alkylated benzenes,
alkylated diphenyl compounds and alkylated diphenyl
methanes. Such base oils are described in US-B1-6180575
and may be conveniently prepared by the methods described
therein. Different suitable base oils can have different
lubricating viscosity. The one or more hydrocarbyl-
substituted aromatic lubricant base oils essentially
consist of compounds which only contain hydrogen and
carbon. A limited amount of contaminants such as sulphur
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more than 80 %wt of the one or more hydrocarbyl-
substituted aromatic lubricant base oils consists of
compounds consisting of hydrogen and carbon only, more
preferably more than 90 %wt.
Alkylated naphthalenes are preferred hydrocarbyl-
substituted aromatic lubricant base oils for use in the
lubricating oil compositions of the present invention.
Said alkylated naphthalenes may be mono-, di-, tri or
tetra-alkyl substituted naphthalenes such as those
desscribed in US-A-5602086, WO-A-03/048275 and
WO-A-03/048276.
The lubricating oil composition of the present
invention comprises one or more additional lubricant base
oils comprising polyalphaolefins and/or Fischer-Tropsch
derived base oils.
As described in US-B1-6180575 and US-A-5602086,
polyalphaolefins and their manufacture are well known in
the art. Preferred polyalphaolefins that may be used in
lubricating oil compositions of the present invention may
be derived from C2 to C32 alpha olefins. Particularly
preferred feedstocks for said polyalphaolefins are 1-
octene, 1-decene, 1-dodecene and 1-tetradecene.
Preferably, polyalphaolefins that may be conveniently
used in the lubricating oil compositions of the present
invention have a kinematic viscosity at 100 C in the
range of from 3 to 300 mm2/s, more preferably in the
range of from 4 to 100 mm2/s.
Fischer-Tropsch derived base oils which may be
conveniently used as the one or more additional base oils
in the lubricating oil composition of the present
invention include, for example, the Fischer-Tropsch
derived base oils disclosed in EP-A-776959, EP-A-668342,
WO-A-97/21788, WO-A-00/15736, WO-A-00/14188, WO-A-
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00/14187, WO-A-00/14183, WO-A-00/14179, WO-A-00/08115,
WO-A-99/41332, EP-A-1029029, WO-A-01/18156 and WO-A-
01/57166.
In one embodiment of the present invention, said one
or more additional lubricant base oils may further
comprise mineral and/or other synthetic lubricant base
oils.
Such mineral lubricant base oils include liquid
petroleum oils and solvent treated or acid treated
mineral lubricating oils of the paraffinic, naphthenic,
or mixed paraffinic/naphthenic type which may be further
refined by hydrocracking and hydrofinishing processes
and/or dewaxing.
Naphthenic base oils have low viscosity index (VI)
(generally 40-80) and a low pour point. Such base oils
are produced from feedstocks rich in naphthenes and low in
wax content and are used mainly for lubricants in which
colour and colour stability are important, and VI and
oxidation stability are of secondary importance.
Paraffinic base oils have higher VI (generally >95)
and a high pour point. Said base oils are produced from
feedstocks rich in paraffins, and are used for lubricants
in which VI and oxidation stability are important.
Synthetic processes enable molecules to be built from
simpler substances or to have their structures modified
to give the precise properties required.
Other synthetic lubricant base oils which may be
present in the one or more additional lubricant base oils
include hydrocarbon oils such as polyalkylene glycols
(PAGs), polyisobutylenes (PIBs) dibasic acids esters,
polyol esters and other complex esters, and dewaxed waxy
raffinate. Synthetic hydrocarbon base oils sold by the
Shell Group under the designation "XHVI" (trade mark) may
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Optional additional lubricant base oils are
preferably constituted from mineral oils and/or other
synthetic base oils which contain more than 80% wt of
saturates, more preferably more than 90 % wt., as
measured according to ASTM D2007.
It is further preferred that said optional additional
lubricant base oils contain less than 1.0 wt. %, more
preferably less than 0.1 wt. % of sulphur, calculated as
elemental sulphur and measured according to ASTM D2622,
ASTM D4294, ASTM D4927 or ASTM D3120.
Preferably, the viscosity index of said optional
additional lubricant base oils is more than 80, more
preferably more than 120, as measured according to ASTM
D2270.
Preferably, the lubricating oil composition of the
present invention has a kinematic viscosity in the range
of from 32 to 150 mm2/s at 40 C, more preferably in the
range of from 32 to 100 mm2/s, and most preferably in the
range of from 32 to 78 mm2/s.
The amount of the additives (a) and (b) present in
the lubricating oil composition of the present invention,
depends on the specific compounds used therein.
The lubricating oil composition of the present
invention preferably comprises a total amount in the
range of from 0.1 to 5.0 % by weight, more preferably in
the range of from 0.2 to 2.0 % by weight of said one or
more phenyl-naphthylamines, based on the total weight of
the lubricating oil composition.
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The lubricating oil composition of the present
invention preferably comprises a total amount in the
range of from 0.1 to 5.0 % by weight, more preferably in
the range of from 0.2 to 2.0 % by weight, of said one or
more diphenylamines, based on total weight of the
lubricating oil composition.
The hydrocarbyl-substituted aromatic lubricant base
oils are preferably present in the lubricating oil
composition of the present invention in a total amount in
the range of from 0.1 to 30 % by weight, more preferably
in the range of from 1 to 20 % by weight, based on the
total weight of the lubricating oil composition.
The one or more hydrocarbyl-substituted aromatic
lubricant base oils preferably comprise less than
60 wt. % of the total lubricant base oil in the
lubricating oil composition of the present invention,
more preferably less than 25 wt.% of the total lubricant
base oil and most preferably in the range of from 1 to 25
wt.% of the total weight of lubricant base oil, wherein
the total weight of lubricant base oil is the total
weight of the one or more hydrocarbyl-substituted
aromatic lubricant base oils and the one or more
additional lubricant base oils.
In a preferred embodiment of the present invention
the one or more phenyl-naphthylamines (a) and the one or
more diphenylamines (b) are present in the lubricating
oil composition of the present invention in a weight
ratio in the range of from 1:3 to 3:1, more preferably in
the range of from 1:2 to 1:1.
It is preferred that the lubricating oil composition
according to the present invention contains no
substantial amount of phenolic antioxidant. The amount
of phenolic antioxidant present preferably is less than
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even more preferably less than 0.1 % by weight, and most
preferably 0 % by weight, based on total amount of the
lubricating oil composition.
The lubricating oil composition of the present
invention can further comprise additives such as extreme
pressure additives, anti-wear additives, metal
passivators, corrosion inhibitors, foam inhibitors and/or
demulsifiers.
Anti-wear additives that may be conveniently used
include zinc dithiophosphate compounds selected from zinc
dialkyl-, diaryl- and/or alkylaryl- dithiophosphates,
molybdenum-containing compounds, boron-containing
compounds and ashless anti-wear additives such as
substituted or unsubstituted thiophosphoric acids, and
salts thereof. Said anti-wear additives may each be
conveniently added to the lubricating oil composition of
the present invention in an amount in the range of from
0.1 to 3.0 wt. %, based on the total weight of
lubricating oil composition.
Examples of such molybdenum-containing compounds may
conveniently include molybdenum dithiocarbamates,
trinuclear molybdenum compounds, for example as described
in WO-A-98/26030, sulphides of molybdenum and molybdenum
dithiophosphate.
Boron-containing compounds that may be conveniently
used include borate esters, borated fatty amines, borated
epoxides, alkali metal (or mixed alkali metal or alkaline
earth metal) borates and borated overbased metal salts.
Compounds such as alkenyl succinic acid or ester
moieties thereof, benzotriazole-based compounds and
thiodiazole-based compounds may be conveniently used in
the lubricating oil composition of the present invention
as corrosion inhibitors.
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Compounds such as polysiloxanes, dimethyl
polycyclohexane and polyacrylates may be conveniently
used in the lubricating oil composition of the present
invention as foam inhibitors.
The present invention further provides the use of the
lubricating oil composition according to the present
invention for lubricating a rotary air compressor.
The lubricating composition according to the present
invention can be conveniently prepared by blending
together the one or more phenyl-naphthylamines, the one
or more diphenylamines, the one or more hydrocarbyl-
substituted aromatic lubricant base oils and the one or
more additional lubricant base oils comprising
polyalphaolefins and/or Fischer-Tropsch derived base oils
and, optionally, one or more additives as hereinbefore
described.
The present invention is described below with
reference to the following Examples, which are not
intended to limit the scope of the invention in any way.
Examples
Formulations were blended using the base oils and
additives specified in Tables 1 and 2.
The phenyl-naphthylamine (a) used in the formulations
of Tables 1 and 2 was that available from Ciba Specialty
Chemicals under the trade designations "IRGANOX L-06".
The diphenylamine (b) used in the formulations of
Tables 1 and 2 was that available from Ciba Specialty
Chemicals under the trade designation "IRGANOX L-57".
The hydrocarbyl-substituted aromatic lubricant base
oil used in the formulations of Tables 1 and 2 was the
alkyl naphthalene available under the trade designation
"SYNESSTIC 5" from ExxonMobil.
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The PAO 40 base oil used in the formulations of
Tables 1 and 2 was that available from Innovene under the
trade designation "DURASYN 174".
The PAO 8 base oil used in the formulations of
Table 1 was that available from Innovene under the trade
designation "DURASYN 168".
The GTL 8 base oil used in the formulations of
Table 2 was a Fischer-Tropsch derived base oil having a
kinematic viscosity at 100 C of approx. 8 cSt (mm2s-1)
Said base oil may be conveniently manufactured by the
process described in WO-A-02/070631.
Examples 1 and 2 are according to the present
invention whilst the remaining Examples in Tables 1 and 2
are comparative in nature.
The formulations in Tables 1 and 2 were subjected to
the Rotating Pressure Vessel Oxidation Test (RPVOT)
(formerly known as the Rotating Bomb Oxidation Test
(RBOT)) (ASTM D2272) in order to measure the oxidative
stability thereof.
In addition, said formulations were also tested in a
version of the Wolf Strip Test (formerly known as DIN
51392) performed according to the modifications set out
below.
DIN 51392 formerly measured the tendency of engine
oils to produce thermal/oxidative deposits using an
inclined metal plate over which the test engine oils were
pumped. The volume of oil, pumping rate, plate
temperature and test duration specified in said test were
200 ml, 50 ml/hour, 250 C and 12 hours, respectively.
In order to improve the test repeatability and to
more closely simulate the type of thermal/oxidative
stress that a lubricating oil composition would
experience under full hydrodynamic film conditions in a
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compressor, the test conditions used in the Examples of
Tables 1 and 2 were modified to an oil volume of 150 ml,
a pumping rate of 50 ml/hour, a plate temperature of
205 C and a test duration of 24 hours.
It is apparent from Tables 1 and 2 that the
formulations in accordance with the present invention not
only exhibit good deposit control but also display
outstanding performance in the RPVOT.
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