DE69217907T2 - Lubricating oil compositions - Google Patents

Abstract

This invention relates to a lubricating oil composition which has a major proportion of a biodegradable base fluid which is a blend of (a) at least one ester of isotridecyl alcohol and a mono-, di or polycarboxylic acid, and (b) at least one hydrocarbon oil which has no more than 10%w/w of aromatic hydrocarbons, the rest being aliphatic. The proportion of (a) in the blend is from 25-55%w/w. The biodegradability of the base fluid renders the composition more environmentally friendly.

Description

The present invention relates to environmentally friendly lubricating oil compositions for automotive engines. Lubricating oil compositions for use in automotive engines are known. EP-A-0 259 809 relates to a lubricating oil composition comprising 97 to 60% by weight of mineral oil and 3 to 40% by weight of polyester, the mineral oil having a dynamic viscosity of 2 to 50 centistokes at 100°C, a pour point (determined according to JIS K-2269) of -5 to -30°C, a viscosity index (measured according to JIS K-2283) of not less than 80 and % CA of not more than 3. This lubricating oil composition is suitable for lubricating parts including oil brakes and oil clutches as well as automatic transmissions and tractors. These compositions usually contain a base fluid which may include mineral oils, hydrocarbon oils and/or synthetic fluids and conventional additives such as viscosity index (hereinafter referred to as VI) improvers, antioxidants, corrosion inhibitors, dispersants, antiwear additives and sludge control agents. In recent years there has been a continuing trend in the development of automotive engine oil towards lower viscosity multigrade grades, mainly to improve fuel efficiency. The predominant viscosity grade has moved from generally 20W/50 oil to a 10W/40 or a 5W/40 oil. Automotive engine manufacturers have also tightened the specifications for such oils with regard to oil consumption, bearing protection and shear stability. This means that the engine lubricant must become lower in volatility and more shear stable so that these thinner oils remain within the specified quality range. This means that lubricating oil compositions based solely on conventional solvent-refined mineral oils are no longer sufficient to meet these stringent performance requirements. a growing need has arisen for "special" base oils which have excellent volatility, VI and pour point properties. These special base oils have a VI above 120 and the requirement is met primarily by the use of paraffinic base oils which include, among others, hydrocracked wax distillate based oils. It has also been proposed to use blends of such hydrocracked wax distillates with aliphatic esters to improve the performance of such base oils. These prior art compositions typically contain 80% or more by weight of a hydrocarbon or mineral oil and up to 20% w/w of an aliphatic carboxylic acid ester in the base fluid. However, such compositions, although very efficient and to some extent biodegradable, leave room for improvement.

It has now been found that base oil blends can be formulated that are not only improved in their biodegradability, but also achieve this without loss of performance, while at the same time exhibiting relatively low emissions, lower fuel consumption and lower oil consumption.

Accordingly, the present invention is a lubricating oil composition for automotive engines, which has as a major component a base fluid, the fluid comprising a mixture of:

a) dodecanedioic acid diisotridecyl ester and

b) at least one hydrocarbon oil comprising up to 99.5% w/w aliphatic hydrocarbons and not more than 10% w/w aromatic hydrocarbons, such that aliphatic and aromatics total 100%, the amount of component (a) in the mixture being in the range 25-55% w/w.

As described above, the base fluid comprises a mixture of an ester and a hydrocarbon oil. The ester component (a) is derivable by reacting an aliphatic mono-, di- and/or polycarboxylic acid with isotridecyl alcohol under esterification conditions.

Specific examples of such esters include the isotridecyl esters of octane-1,8-diacid, 2-ethylhexane-1,6-diacid and dodecane-1,12-diacid.

Similarly, the hydrocarbon oil component (b) in the mixture is suitably a hydrocracked wax distillate. In particular, such hydrocarbon oils may contain up to 99.5% w/w, preferably up to 97% w/w, aliphatic hydrocarbons and not more than 10% w/w aromatic hydrocarbons. The term "aliphatic hydrocarbons" as used here and throughout the specification means to include open chain aliphatic hydrocarbons as well as cycloaliphatic hydrocarbons such as naphthenic hydrocarbons. The total polycyclic aromatic hydrocarbons in the hydrocarbon oil is suitably less than 10 ppm, preferably less than 5 ppm and most preferably less than 1 ppm. In general, such a hydrocarbon oil contains 92-97% w/w aliphatic substances and 3-8% w/w aromatic substances.

The hydrocarbon oil component (b) in the mixture is suitably prepared by feeding a wax distillate to a hydrocracking unit at 70-95% conversion under elevated temperature and hydrogen pressure. In the first stage of this hydrocracking unit, sulphur and nitrogen compounds are removed and in the second stage the aromatics are hydrogenated to naphthenes; the hydrogenated products, including naphthenes, are cracked and rearranged to produce a controlled range of paraffins and isoparaffins. Fuel and lubricant products are separated from the resulting hydrocracked products by atmospheric distillation and 5-35% heavy component is then the hydrocarbon fraction which is employed as the hydrocarbon oil component (b) in the mixture. A product prepared by this process is substantially free of any unsaturations. This feedstock may be further refined, if required, by conventional techniques such as additional fractionation, Extraction or dewaxing to the finished product. The hydrocarbon oil obtained has the following physical properties:

Colour (ASTM D 1500) 1.5 Max

Density (ASTM 1298) 0.83

KV(40º)/cSt (ASTM D 445) 17.28

KV(100ºC)/cSt (ASTM D 445) 3.99 - 4.22

VI (ASTM D 2270) 123 - 128

Pour point/ºC (ASTM D 97) -24 - -27

% S (XRF NFM 07053) 0.08 - 0.15

Total N/ppm approx. 12

Aromatics by HPLC/% approx. 7.7

Aliphatics by HPLC/% approx. 92.3

Polycyclic aromatics/ppm 0.1

Of the aliphatic hydrocarbons in this hydrocarbon oil component (b), about 20% w/w comprise isoparaffins having an average carbon number of about 27.

The relative amounts of the ester component (a) and the hydrocarbon oil component (b) in the base fluid within the ranges specified above will depend on the nature of the two components and their relative viscosities. For example, when the hydrocarbon component (b) is within the physical characteristic specification defined above and the ester component (a) is an isotridecyl dodecanedioate, the amount of ester (a) in the mixture may suitably range from 30-50% w/w, preferably 40-50% w/w.

In addition to the above-mentioned blended base fluid, the lubricating oil composition of the invention comprises minor amounts of conventional additives, including, but not limited to, one or more sludge dispersants, one or more VI improvers, one or more antiwear additives, and one or more antioxidants. In general, it is known that the additive bundle comprises components that meet the stringent requirements of an API Performance Classification "SG". These requirements include the successful testing of the following categories: rust test, dispersancy test, piston varnish test, low temperature sludge test and wear test. Such additives are commercially available as additive bundles, sold for example as "SG additive bundles" under the names GBX 2900 and GBX 2905 (both from Adibis Ltd., UK). Such an additive bundle generally constitutes 10-20% w/w, preferably 11-16% w/w of the formulated lubricating oil composition. Examples of compounds which may be present in such a bundle include anti-rust agents such as the overbased calcium or magnesium sulphonates or phenolates; Antiwear agents such as the zinc dithiophosphates, preferably the zinc dialkyldithiophosphates containing 5-15% w/w phosphorus (normally prepared using a mixture of secondary alcohols and representing 0.05%-0.5% w/w phosphorus, generally 0.1-0.14% phosphorus in the finished oil); ashless dispersants such as derivatives of long chain hydrocarbon substituted succinimides, particularly the polyisobutenyl succinimides and sludge dispersants which are oil soluble salts such as amides, imides, oxazolines and esters of mono- or dicarboxylic acids or anhydrides.

The antioxidants generally contain phenolic compounds and a typical antioxidant is commercially available as ADX 545A (ex Adibis Ltd.). The antioxidants are suitably present in an amount of 0.01-5% w/w, preferably 0.1-2.0% w/w of the formulated lubricating oil composition.

The lubricating compositions also contain one or more VI improvers. Examples of such VI improvers include polymethacrylate type dispersants, commercially sold as Plexol 1420 VX (registered trademark of Rohm Gmbh) and hydrotreated polyisoprenes, commercially sold as Shellvis 200 (registered trademark of Shell, Great Britain, Ltd.). In the latter case it can be used as a solution in the hydrocarbon oil component (b) mentioned above. The VI improvers are suitably present in an amount of 2 to 5% w/w. of the formulated lubricating composition. Thus, a typical formulated lubricating oil composition (a) can be represented by the following components in weight/weight %:

SG Additive Bundle (GBX 2905, from Adibis Ltd.) - 15.4

ADX 545A (antioxidant, from Adibis Ltd.) - 1,

Plexol* 1420 (VI improver, from Rohm GmbH) - 3.1

Shellvis * 200 (VI improver, 10% solution, from Shell, GB, Ltd.) - 6,

Dodecanedioic acid diisotridecyl ester - 22.59

and hydrocarbon oil** - 52.71

* Registered trademark

** The hydrocarbon oil is a hydrotreated wax distillate containing 92.3% w/w aliphatic and 7.7% w/w aromatic, substantially free of unsaturation and having a polycyclic aromatic content of about 0.1 ppm. The oil of this type is described above.

Variations of the formulated lubricating oil composition (A) shown above can also be formulated wherein the relative amounts of ester and hydrocarbon oil (B) are 32.28% and 49.32%, respectively, or (C) 39.5%, respectively.

The performance of the lubricating oil compositions formulated in this manner was found to demonstrate relatively low emissions, low fuel consumption, low oil consumption and low nitrogen oxide emissions after engine testing. In addition, the lubricating oil compositions formulated in accordance with the present invention were at least 80% biodegradable as measured by the CEC standard test procedure. The present invention is illustrated with reference to the following examples:

Examples - general

A base fluid was prepared using dodecanedioic acid isotridecyl ester and a hydrocracked wax distillate with the following physical properties:

* Correlated with ASTM D 1401

The hydrocarbon oil was used to prepare formulated lubricating oil composition according to the formulation in (A) in Examples 1-3 below.

example 1

SG Additive Bundle (GBX 2905, from Adibis Ltd.) - 15.4% w/w

ADX 545A (Antioxidant, from Adibis Ltd.) - 1.0% w/w

Plexol* 1420 (VI improver, from Rohm GmbH) - 3.1% w/w

Shellvis* 200 (VI improver, 10% solution, from Shell GB Ltd.) - 6.0% w/w

Dodecanedioic acid diisotridecyl ester - 22.59% w/w

Hydrocarbon oil (as above) - 52.71% w/w

* Registered trademark

The formulation was prepared using standard lubricating oil blending techniques, for example as described in "Lubricants and Related Products" by D Klamann, published by Verlag Chemie, 1984.

The formulated composition had the following properties:

Example 2

SH additive bundle (e.g. OS 99099, from Lubrizol Ltd.) - 15% w/w

Viscoplex* 2540 (VI improver, from Rohm GmbH) - 3.0% w/w

Shellvis* 201 (VI improver, from Shell GB Ltd.) - 3.8% w/w

Dodecanedioic acid diisotridecyl ester - 38.1% w/w

Hydrocarbon oil (as above) - 40.1% w/w

* Registered trademark

The formulated composition had the following properties:

Example 3

SG Additive Bundle (from G8X2905, from Adibis Ltd.) - 16.4% w/w

Plexol* 1420 (VI improver, from Rohm GmbH) - 3.1% w/w

GBX 2715 (VI improver, from Adibis Ltd.) - 5.0% w/w

Dodecanedioic acid diisotridecyl ester - 40.0% w/w

Hydrocarbon oil (as above) - 35.5% w/w

* Registered trademark

The formulated composition had the following properties:

After standard engine testing of each of the formulations described in Examples 1-3 above using the API GS procedure, the following properties were observed:

Biodegradability of the formulated lubricating oil composition of the present invention was tested and compared with commercially available products using the test procedure shown in the table above. The results are tabulated below:

Present invention 91%

Mobile 1 45%

Castrol GTX 63%

Shell Gemini 66%

Castrol Syntron 41%

From the above it is clear that the compositions formulated according to the invention, which contain a mixture of base oil according to the present invention, exhibit excellent properties over those of the prior art, in particular with regard to their biodegradability.

Claims (8)

1. Lubricating oil composition for automotive engines, which has as a major component a base fluid, the fluid comprising a mixture of: a) dodecanedioic acid diisotridecyl ester and b) at least one hydrocarbon oil comprising up to 99.5% w/w aliphatic hydrocarbons and not more than 10% w/w aromatic hydrocarbons, such that aliphatic and aromatics total 100%, the amount of component (a) in the mixture being in the range 25-55% w/w. 2. A lubricating oil composition according to claim 1, wherein the hydrocarbon oil component (b) is a hydrocracked wax distillate. 3. A lubricating oil composition according to claim 1 or claim 2, wherein the hydrocarbon oil component (b) contains less than 10 ppm polycyclic aromatic hydrocarbons, 92-97% w/w aliphatic hydrocarbons and 3-8% w/w aromatic hydrocarbons. 4. A lubricating oil composition according to any one of the preceding claims, wherein the aliphatic hydrocarbons in the hydrocarbon oil component (b) comprise about 20% w/w isoparaffins having an average carbon atom number of about 27. 5. A lubricating oil composition according to any one of the preceding claims, wherein the dodecanedioic acid diisotridecyl ester is present in the mixture in the range 30-50% w/w. 6. Lubricating oil composition according to one of the preceding claims, wherein the composition additionally comprises minor amounts of one or more additives selected from: sludge dispersants, ashless dispersants, VI improvers, anti-wear additives, anti-rust additives and antioxidants. 7. A lubricating oil composition according to claim 6, wherein the antirust agent is an overbased calcium or magnesium sulfonate or phenolate; the antiwear agent is a zinc dithiophosphate; the ashless dispersant is a long chain hydrocarbon substituted succinimide; the sludge dispersant is an oil soluble salt such as amides, imides, oxazolines and esters of mono- or dicarboxylic acids or anhydrides; the antioxidant is a phenolic compound and the VI improver comprises a polymethacrylate dispersant or a hydrotreated polyisoprene. 8. A lubricating oil composition according to any one of the preceding claims, wherein the composition is at least 80% biodegradable as measured by the CEC-L-33-T-82 standard test procedure.