[0001] This invention relates to an improved lubricant composition for use in internal combustion
engines.
[0002] It is known in the art to use synthetic bases in formulating lubricant compositions
both of single grade and of multigrade type. In this respect, synthetic bases are
able to eliminate or at least alleviate the drawbacks often encountered when using
only mineral bases, these requiring 1) the presence of extremely fluid fractions to
obtain the desired viscosity at low temperature and to limit volatility, 2) the presence
of a high percentage of viscosity index improvers to improve the initial VI, and 3)
other additives for satisfying all the other lubricant performance requirements.
[0003] For use in internal combustion engines, lubricant compositions must possess certain
characteristics, namely thermal stability, oxidation resistance, low volatility and
such viscosity-temperature characteristics as to allow both cold starting and good
lubrication at maximum operating temperature.
[0004] Lubricant compositions which have been proposed for this purpose include those containing
higher dialkyl carbonates in combination with a mineral oil and usual additives. These
compositions, which are described for example in U.S. 2,387,999. U.S. 2,758,975, U.S.
3,642,858 and European patent application 89,709, result in various improvements compared
with compositions based on carboxylic esters, in particular in relation to increased
thermal, hydrolytic and oxidative stability.
[0005] A particular class of higher alkyl carbonates has now been found which results in
a general rheological and engine performance improvement in the lubricant compositions
in which they are incorporated, and thus make them desirable for use as high-performance
lubricant compositions for four-stroke gasoline and diesel engines.
[0006] In accordance therewith the present invention provides a lubricant composition comprising:
a) from 0 to 90% by weight of a mineral base oil;
b) from 0 to 90% by weight of a synthetic base oil;
c) from 5 to 50% by weight of a long-chain dialkyl carbonate;
d) from 6 to 12% by weight of a parcel of usual additives; and
e) from 0 to 15% by weight of viscosity index and pour point improvement additives;
said composition being characterised in that the component c) is the product of transesterification
of a lower dialkyl carbonate with an alcoholic mixture consisting of at least 98%
by weight of aliphatic alcohols with a linear or essentially linear hydrocarbon chain
carrying a -CH
2-OH group on a non-terminal carbon atom, the total number of carbon atoms in the alcohol
varying from 10 to 18 and preferably from 13 to 16.
[0007] In the preferred embodiment, component a) is present in a quantity of between 0 and
60% by weight, component b) from 20 to 60% by weight, component c) from 15 to 30%
by weight, component d) from 8 to 10% by weight and component e) from 5 to 10% by
weight.
[0008] Lubricant oils which can be used as component a) of the composition of the present
invention are oils of mineral origin obtained by petroleum distillation followed by
solvent and/or hydrogen refining generally having a viscosity index of 102-108, a
pour point of between -12 ° C and -6 ° C and a Noack evaporation loss of 12-42%.
[0009] Synthetic base oils which can be used as component b) of the composition of the present
invention are oils of synthetic origin and can be obtained by the polymerization of
terminal or internal olefins followed by purification, or by isomerization and/or
alkylation of petroleum fractions followed by purification.
[0010] Alcohols which can be used for preparing component c) of the composition of the present
invention are mixtures containing at least 98% and preferably at least 99% of aliphatic
alcohols with a linear or essentially linear hydrocarbon chain carrying a -CH
2-OH group on a non-terminal carbon atom, the total number of carbon atoms in the alcohol
varying from 10 to 18 and preferably from 13 to 16. More specifically, alcohols suitable
for the purpose are alcohols definable by the formula:

where m is a whole number and n is zero or a whole number, with the condition that
the total number of carbon atoms in the molecule is between 10 and 18 and preferably
between 13 and 16.
[0011] Preferred mixtures are those in which the -CH
2-OH group is prevalently in position 2 of the chain.
[0012] Mixtures of alcohols (I) suitable for the purpose include the branched fraction of
the oxo-alcohols obtained by hydroformylation, using carbon monoxide and hydrogen,
of linear or essentially linear olefins with a statistical internal or terminal double
bond, operating with cobalt or rhodium catalysts. This branched oxo-alcohol fraction
can be separated from the linear fraction by fractional crystallization operating
in the presence of a hydrocarbon or ether solvent, as described for example in U.S.
patent 4,670,606. According to this patent, a mixture of linear and branched chain
oxo-alcohols is dissolved in a liquid hydrocarbon solvent containing from 3 to 5 carbon
atoms in the molecule, or in methyl tert-butyl ether. The solution is cooled to a
temperature within the range of -20 ° C to -52 ° C to cause separation of a solid
phase consisting of the linear oxo-alcohols, and a liquid phase consisting of a solution
of the branched oxo-alcohols in the chosen solvent. The branched oxo-alcohols can
generally be separated form this solution with a purity of the order of 95%, and be
purified by further crystallization to obtain the mixture of alcohols (I) suitable
for the purposes of the present invention, with a purity exceeding 98% and preferably
exceeding 99%.
[0013] Such a mixture of alcohols (I) is then transesterified with a lower dialkyl carbonate
to give component b) of the composition of the present invention. This reaction can
be effected by bringing the reagents into contact in the presence of a basic catalyst
operating at high temperature and under reduced pressure, and eliminating the lower
aliphatic alcohol evolved as the reaction by-product, as is well known in the art
and described in the examples given in European patent application publication No.
89,709. Preferred lower dialkyl carbonates are dimethyl carbonate and diethyl carbonate.
Active transesterification catalysts useful for the purpose are sodium methylate and
sodium ethylate.
[0014] On termination of the transesterification reaction the long-chain dialkyl carbonate
is recovered to constitute component b) of the composition of the present invention,
its characteristics falling generally within the following value ranges (general and
preferred):

[0015] Such a dialkyl carbonate also has desirable characteristics in relation to low temperature
rheology values, oxidation stability, elastomer compatibility, biodegradability and
toxicity.
[0016] Component d) of the composition of the present invention consists of a parcel of
additives usually used in lubricants and specifically dispersants, antiwear and antirust
additives, metal passivators and copper deactivators, detergent additives (superbasic
and neutral) and antioxidants. These additives are usually chosen from the following
classes of compounds:
alkyl/alkenyl succinimides, succinic esters; alkyl/aryl dithiophosphates of zinc and
olefins; ethoxylates, esters and hemiesters of substituted succinic acids; unsaturated
or carbonyl compounds of chelating action; heterocyclic compounds; metal salts (neutral
and superbasic) of alkyl and aryl sulphonic acids, salicylic acids, phenols and substituted
phenols; sterically hindered amines and phenols; sulphurated compounds.
[0017] Component e) of the composition of the present invention consists of a collection
of additives able to raise the viscosity index and lower the pour point of the resultant
lubricant composition.
[0018] These additives are usually chosen from the following classes of compounds: olefinic
copolymers, methacrylic copolymers, olefinic/methacrylic copolymers. Said additives
can also have other properties such as antioxidant, dispersant and antiwear, together
with the basic properties of viscosity index and pour point improvers.
[0019] Typical lubricant compositions suitable for four-stroke gasoline and diesel engines
contain the aforesaid components in the following weight percentages:

[0020] The long-chain dialkyl carbonate used as component c) in the lubricant compositions
enables lubricant compositions for autotraction to be formulated possessing unexpectedly
good overall rheological and engine performance characteristics. In this respect,
the particular dialkyl carbonate structure enables a high viscosity index, a low pour
point and a low volatility to be obtained simultaneously. In addition the high polarity
of the carbonate group together with its structural characteristics enables high engine
performance to be obtained together with a reduction in the level of addition of component
d). In particular the high polarity results in good dispersing action towards engine
sludge (enabling dispersants to be reduced by about 30% in the lubricant composition),
the greasing of metal surfaces subject to wear (enabling antiwear additives to be
reduced by about 20% in the lubricant composition), and an antirust and electrochemical
protection action on ferrous and non-ferrous metal surfaces (enabling antirust additives,
metal passivators and copper deactivators to be reduced by about 30%). The high thermal
and oxidative stability of component c) enables the antioxidant additives to be reduced
by about 30% in the lubricant composition, and the absence of acid compounds deriving
from decomposition phenomena enables the superbasic detergent additives to be reduced
by about 20%. Finally, component c) of the composition is practically inert towards
the elastomers usually present in the lubrication circuit. As a result, lubricant
compositions can be formulated with a medium-high nitrogen content, avoiding the addition
of specific additives normally introduced to overcome the elastomer compatibility
tests scheduled in the most severe specifications such as CCMC and VW specifications.
[0021] It should be noted that in the known art oxo-alcohols are described as alcohols suitable
for preparing long-chain dialkyl carbonates for lubricant compositions, however without
separation of the linear fraction from the branched fraction. According to the present
invention the use of the mixture of alcohols (I) with the aforesaid characteristics
is critical in order to obtain the required characteristics for the dialkyl carbonates
and for the lubricant compositions which incorporate them, as will be apparent from
the experimental examples which are given hereinafter to better illustrate the present
invention.
EXAMPLE 1
[0022] A mixture of oxo-alcohols of the following characteristics is used:

[0023] This oxo-alcohol mixture is the product of the hydroformylation of substantially
linear olefins with carbon monoxide and hydrogen in the presence of a catalyst.
[0024] The mixture is subjected to fractional crystallization at low temperature in the
presence of a hydrocarbon solvent as described in U.S. patent 4,670,606, to separate
a solid linear alcohol fraction from a liquid fraction containing 95% by weight of
branched alcohols. This liquid fraction is purified by a second fractional crystallization
similar to the first, to separate a liquid fraction with a branched alcohol content
exceeding 99% by weight.
[0025] In this manner a mixture of alcohols of formula (I) is obtained having the following
distribution:

EXAMPLE 2
[0026] The mixture of branched alcohols (I) obtained in Example 1 is transesterified with
dimethyl carbonate operating with sodium ethylate as catalyst, as described in European
patent application No. 89,709, to obtain a dialkyl carbonate (I) with an average molecular
weight of 470 and having the following characteristics:

EXAMPLE 3
[0027] For comparison purposes the linear and branched oxo-alcohol mixture obtained in the
hydroformylation reaction is transesterified (without previous separation) with dimethyl
carbonate using sodium ethylate as catalyst in accordance with Example 2, to obtain
a dialkyl carbonate (II) with an average molecular weight of 470, a viscosity index
of 130, a pour point of + 12 ° C and a Noack volatility of 15%.
EXAMPLE 4
[0028] The lubricant composition (A) of the present invention and the comparison lubricant
composition (B) are prepared in accordance with the following Table I.

[0029] The compositions (A) and (B) are subjected to a series of rheological and laboratory
tests aimed at evaluating the extent to which they satisfy the requirements of the
European Sequence scheduled by constructors for CCMC oil classification and the requirements
of the American sequence scheduled by constructors for API oil classification. The
results are given in the following Table II.

[0030] From the aforegoing data it can be seen that the lubricant composition (A) in accordance
with the present invention satisfies all the requirements of the American API and
European CCMC Sequences. In contrast, the comparison lubricant composition (B) does
not satisfy the requirements of viscosity at -25 ° C, BPT, stable pour point or Noack
volatility. This behaviour is related to the different physico-chemical characteristics
of the dialkyl carbonates (I) and (II) used in the compositions.
[0031] With regard to the engine tests scheduled by the same American API and European CCMC
sequences, both the lubricant compositions satisfy all tests by a wide margin on the
set limits. However only by using the dialkyl carbonates (I) of the present invention
are lubricant compositions obtained which have optimum performance characteristics
from both the engine and rheological aspects.
1. A lubricant composition comprising:
a) from 0 to 90% by weight of a mineral base oil;
b) from 0 to 90% by weight of a synthetic base oil;
c) from 5 to 50% by weight of a long-chain dialkyl carbonate;
d) from 6 to 12% by weight of a parcel of usual additives; and
e) from 0 to 15% by weight of viscosity index and pour point improvement additives;
said composition being characterised in that the component c) is the product of transesterification
of a lower dialkyl carbonate with an alcoholic mixture consisting of at least 98%
by weight of aliphatic alcohols with a linear or essentially linear hydrocarbon chain
carrying a -CH
2-OH group on a non-terminal carbon atom, the total number of carbon atoms in the alcohol
varying from 10 to 18.
2. A composition as claimed in claim 1, characterised in that the total number of
carbon atoms in the alcohol varies from 13 to 16.
3. A composition as claimed in claim 1, characterised in that component a) is present
in a quantity of between 0 and 60% by weight, component b) from 20 to 60% by weight,
component c) from 15 to 30% by weight, component d) from 8 to 10% by weight and component
e) from 5 to 10% by weight.
4. A composition as claimed in claim 1, characterised in that component a) is a lubricating
oil obtained by petroleum distillation followed by refining, and having a viscosity
index of 102-108, a pour point of between -12 ° C and -6 ° C and a Noack evaporation
loss of 12-42%.
5. A composition as claimed in claim 1, characterised in that component b) is the
product of the polymerization of terminal or internal olefins, or of the isomerization
and/or alkylation of petroleum fractions.
6. A composition as claimed in claim 1, characterised in that component c) is the
product of the transesterification of a lower dialkyl carbonate with a mixture containing
at least 98% and preferably at least 99% of aliphatic alcohols definable by the formula:

where m is a whole number and n is zero or a whole number, with the condition that
the total number of carbon atoms in the molecule is between 10 and 18 and preferably
between 13 and 16.
7. A composition as claimed in claim 5, characterised in that said mixture of alcohols
(I) is the branched fraction of the oxo-alcohols obtained by hydroformylation, using
carbon monoxide and hydrogen, of linear or essentially linear olefins with a statistical
internal or terminal double bond, operating with cobalt or rhodium catalysts, said
branched fraction being separated from the linear fraction by fractional crystallization
operating in the presence of a hydrocarbon or ether solvent.
8. A composition as claimed in claim 1, characterised in that said component c) has
the following characteristics:
9. A composition as claimed in claim 1, characterised in that said component d) consists
of a parcel of dispersant, antiwear and antirust additives, metal passivators and
copper deactivators, detergent additives (superbasic and neutral) and antioxidants.
10. A composition as claimed in claim 1, characterised in that said component e) consists
of a collection of additives able to raise the viscosity index and lower the pour
point of the resultant lubricant composition.