WO2004026997A2

WO2004026997A2 - Lubricating or fuel composition

Info

Publication number: WO2004026997A2
Application number: PCT/EP2003/009640
Authority: WO
Inventors: Dirk Kenbeek; Pietertje Vos Geertrui; Maria Christina Steverink-De-Zoete
Original assignee: Unichema Chemie B.V.
Priority date: 2002-09-20
Filing date: 2003-08-29
Publication date: 2004-04-01
Also published as: WO2004026997A3; AU2003267028A8; TW200413517A; AU2003267028A1

Abstract

The invention relates to lubricant compositions based on a base oil and a frictionreducing additive comprising a polyol ester, having a hydroxyl value of at least 180, the polyol ester being derived from the partial esterification of trimethyolpropane with at least one monocarboxylic acid having a carbon chain length ranging from 10 to 24 carbon atoms. The friction-reducing additives provide enhanced oxidative stability without compromise to their friction-reducing properties, as compared to commercially available friction-reducing additives, in engine oils, fuels and transmission oils. The friction-reducing additives are fully compatible with formulated base oils at the operating temperature of the engine.

Description

Lubricant Composition

The present invention relates to a lubricant composition comprising a frictionreducing additive with enhanced oxidative stability.

Lubricant compositions containing friction-reducing additives have been known for several years. Originally such compositions were used as slip gear oils, automatic transmission fluids, slideway lubricants and multipurpose tractor fluids. Such compositions made use of friction reduction to meet requirements for smooth transition from static to dynamic conditions as well as reduced noise, frictional heat and start-up torque.

Then, when fuel economy became an international issue, initially, to reduce crude oil consumption, friction-reducing additives were introduced into automotive crankcase lubricants to improve fuel efficiency. In the US, additional pressure to improve fuel efficiency was applied to original equipment manufacturers (OEM's) by the Corporate Average Fuel Economy (CAFE) regulation.

Following the introduction of vehicle exhaust emission regulations in various regions around the world, emphasis on friction reduction increased further. This was because it was realised that 20 - 25% of the energy generated in an engine by burning fuel was lost through friction; the majority being lost at the piston liner/piston ring interface with smaller losses occurring in bearings and in the valve train. It has been predicted that, in future engines, the contribution of the piston group to engine friction will increase up to 50%.

One of the ways identified to achieve reduction in fuel consumption and emissions was by suitable choice of the engine lubricant composition. Engine friction originates from several components, which operate at different conditions of load, speed and temperature. Hence, these components may experience various combinations of (elasto) hydrodynamic, mixed and boundary lubrication during engine operation. For each of these regimes, there are a number of factors that govern engine friction.

Investigation of those factors identified basically two main options to reduce friction and fuel economy. The first was to use low viscosity engine oils when fluid lubrication ((elasto) hydrodynamic regime) is the governing factor. Such fluid lubrication is especially prevalent in the bearings. The gradual reduction of engine oil viscosity over the years has already brought significant fuel savings. The second was the addition of friction-reducing agents when boundary and/or mixed lubrication are the governing factors. Those factors are prevalent in the valve train and the piston group. In this instance, additive system design was a crucial element. Emphasis has been on selection of friction-reducing additives and control of additive/additive and additive/base fluid interactions.

Friction-reducing additives that have been used fall into three main chemically- defined categories, which are organic, metal organic and oil insoluble. The organic friction-reducing additives themselves fall within four main categories which are carboxylic acids or their derivatives, which includes some examples of partial esters, nitrogen- containing compounds such as amides, imides, amines and their derivatives, phosphoric or phosphonic acid derivatives and organic polymers. In current commercial practice examples of friction reducing additives are glycerol monooleate and oleylamide.

US 4,208,293 discloses a lubricating oil adapted for use as a crankcase lubricant in internal combustion engines containing 0.05 to 5 wt% of a fatty acid amide or ester of diethanolamine as a friction-reducing additive. The preferred fatty acid is an unsaturated fatty acid, in particular oleic acid.

GB 2,038,356 discloses the addition of 0.25 to 2 wt% of a fatty acid ester of glycerol to a crankcase lubricating oil. The preferred fatty acid esters are glycerol monooleate and glycerol tallowate (beef tallow fat/oil contains between about 40 and 45% unsaturated acids). There is no disclosure of the hydroxyl numbers of the fatty acid ester of glycerol.

GB 2,097,813 discloses the addition of 0.05 to 0.2 wt% of a glycerol partial ester of a C16-18 fatty acid as a fuel economy additive to lubricating oil formulations for both gasoline and diesel engines. There is no disclosure of the hydroxyl numbers of the glycerol partial esters. In the examples the fatty acid from which the ester is derived is glycerol monooleate or a mixture of glycerol monooleate and dioleate.

US 4,304,678 discloses the addition of 1 to 4 wt%, preferably 2 to 4 wt% of a fuel reducing additive, selected from the partial esters glycerol monooleate, glycerol dioleate, sorbitan monooleate, sorbitan monolaurate and the fully esterified diisostearyl malate and diisostearyl tartrate, to a lubricating oil composition for use in an internal combustion engine. For the majority of the selected fuel reducing additives, i.e. the partial unsaturated esters, no reference is made to their individual hydroxyl numbers in the disclosure. Diisostearyl malate and diisostearyltartrate do not have free hydroxyl groups. In the examples glycerol monooleate shows a percentage V-8 engine fuel benefit when present at 2, 3 and 4 wt%. There is no corresponding benefit when the glycerol monooleate is present at 1 wt%.

Whilst initial fuel economy requirements, for which the commercial friction reducing additives described above, were designed, focussed on the fresh oil only, new engine oil specifications have now been developed that will address fuel economy longevity as well. A good example is Sequence Vl-B, an engine test, which has been developed for the ILSAC GF-3 specification. Sequence Vl-B includes ageing stages of 16 and 80 hours in order to determine fuel economy as well as fuel economy longevity. These ageing stages are equivalent to 4000 - 6000 miles of mileage accumulation required prior to the EPA Metro / Highway Fuel economy test. That test is used in determining the CAFE parameter for a vehicle.

- To obtain engine oil formulations that are optimised with regard to fuel economy longevity, demanding targets will be placed on base oil selection and additive system design. Those targets are to minimise the increase of viscosity thereby maintaining a low friction coefficient in the (elasto) hydrodynamic regime and to maintain low friction in the boundary and mixed lubrication regimes.

The increase of viscosity with time in the (elasto)hydrodynamic regime can be reduced or minimised by base oil selection (in terms of volatility, oxidation stability and antioxidant susceptibility) and selection of antioxidants and their treatment level.

To achieve low friction under boundary and mixed lubrication conditions, it is necessary to use effective friction-reducing additives. To maintain low boundary and mixed friction over time, it is necessary to prevent consumption of these additives by processes such as oxidation and thermal breakdown. Therefore, the development of friction-reducing additives with high thermal/oxidative stability is key to meet the new requirement for high fuel economy longevity and hence a successful application in engine oil formulations.

Recent research has indicated that fuel economy can be improved further by addition of friction-reducing additives to the fuel itself. It is believed that the fuel delivers the friction-reducing additives to the piston ring-cylinder wall interface where friction is known to be high and the oil quantity is deliberately kept low. Furthermore it has been found that as the friction-reducing additive in the fuel accumulates in the engine oil friction is also reduced in oil-lubricated parts.

The presence of additives in diesel fuel has been disclosed to address fuel lubricity issues caused by reduction of sulphur compounds and hydrotreating of fuels, in combination with increasing injection pressures in fuel systems in modern engine designs.

For example, US 5,993,498 discloses a polyol ester fuel additive, which enhances fuel lubricity in distillate fuel applications where the distillate is selected from diesel fuel, kerosene, jet fuels and mixtures thereof. The polyol ester has a hydroxyl number from 5 to 180, preferably from 5 to140. The polyol ester is derived from reaction of a polyol with a branched or linear saturated monocarboxylic acid or of a polyol with a polybasic acid and a monoalcohols. When the polyol ester is derived from reaction of a polyol with a monocarboxylic acid, a preferred linear monocarboxylic acid has C2- C10 carbon atoms and a preferred branched monocarboxylic acid has C5-C10 carbon atoms.

Also EP 0680506 A1 discloses the addition of a additive of an ester of a carboxylic acid having 2 to 50 carbon atoms and an alcohol having at least one carbon atom to a diesel fuel to address the fuel lubricity and engine wear problems caused by the reduction in sulphur content in the diesel fuel. It is taught that additive is present at low levels, for example between 10 to 200ppm by weight per weight of fuel. Specific examples of esters are glycerol mono and diesters. There is no specific disclosure about the hydroxyl numbers of the ester additives.

EP 0859040 A1 discloses the addition of a lubricity additive to a diesel fuel containing an anti-foaming additive and an overbased metal detergent to improve the foam behaviour of fuels containing such an anti-foaming additive and overbased metal detergent combination. The lubricity additive is generally in the range 10 to 400ppm, with 20-100ppm being a particularly preferred range. Preferred lubricity additives are carboxylic acids, carboxylic acid amides and carboxylic acid esters. Particularly preferred is glycerol monoricinoleate.

WO 98/111777 A1 discloses the addition of a partially esterified polyol ester fuel additive to a gasoline fuel to enhance control of intake valve and combustion chamber deposits and reduce wear and friction in both the fuel line, combustion chamber and piston/cylinder assembly. The partially esterified polyol ester has a hydroxyl number from 5 to about 180. There is a comparative example to an ester of a mixture of glycerol oleates with a hydroxyl number of 223. The ester of the invention is preferably formed by reacting a polyol with at least one branched or linear saturated acid. For this preferred ester a preferred linear acid has C2-C10 carbon atoms and a preferred branched acid has C5-C10 carbon atoms.

The current range of commercial engine friction-reducing additives was not designed to meet the above-mentioned combination of fuel economy and fuel economy longevity requirements for friction-reducing additives. It is known that both glycerol monooleate and oleylamide are susceptible to oxidative breakdown over time. Furthermore, there is another disadvantage in the use of oleylamide as it has low compatibility with the formulated base oils (base oils plus other additives) currently being used.

Surprisingly, it has been found that specifically chosen polyol esters meet the new demands for friction-reducing additives with respect to oxidative stability without compromise to their friction-reducing properties. Also they are fully compatible with formulated base oils at the operating temperature of the engine.

According to the present invention, a lubricant composition for use in fuel, engine oils and transmission oils comprises a major component comprising fuel or a base oil arid 0.05 to 2.0 weight percent of a friction-reducing additive which comprises a polyol ester, having a hydroxyl value of at least 180, the polyol ester being derived from the partial esterification of trimethyolpropane with at least one monocarboxylic acid having a carbon chain length ranging from 10 to 24 carbon atoms.

The at least one monocarboxylic acid is preferably a fully saturated acid, but it may contain up to 25% of unsaturation, for example coconut oil which has up to 12% unsaturated acids. The at least one monocarboxylic acid has a carbon chain which may be straight chained or branched or comprise an aliphatic ring. Preferably the carbon chain length ranges from 12 to 22 carbon atoms, more preferably 14 to 20 carbon atoms and specifically 18 carbon atoms. Examples of suitable monocarboxylic acids include coconut fatty acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, hydrogenated C18 monomeric acid, C18 monomeric acid, arachidic acid, behenic acid and lignoceric acid and mixtures thereof. Hydrogenated C18 monomeric acid is the C18 monomer by-product resulting from the dimerisation of oleic acid, which is then subsequently hydrogenated. C18 monomeric acid is the C18 monomer by-product itself, which typically is about 20% unsaturated.

The base oil of the lubricant composition may be chosen from mineral oils, poly a olefins, alkylbenzenes, monoesters, diesters, polyol esters, complex esters, polyalkylene glycols and mixtures thereof. Preferably the base oil comprises a mineral oil or a poly a olefin.

The friction-reducing additive according to the invention is present at levels between 0.05 and 2% by weight, more preferably between 0.1 and 1.8%, even more preferably between 0.25 and 1.6% in the lubricant composition.

The kinematic viscosity at 100 °C for the base oil should be chosen such that it allows the formulation of low viscosity, fuel-efficient oils. This ranges from 1 to 20, preferably 3 to 8, and particularly 4 to 6, cSt.

The hydroxyl value is at least 180 and preferably has an upper limit of 250. Particularly preferred ranges are from 190 to 240, especially 200 to 240.

The lubricant composition may also comprise other additives of known functionality at levels between 10 to 20%, more preferably between 12 to 18%, more especially between 14 to 16 % of the total weight of the lubricant composition. Suitable additives include detergents, dispersant, antiwear/extreme pressure additives, viscosity modifiers, anticorrosion additives, antifoam, pour point depressants and the like.

According to a further embodiment of the present invention the use of a lubricant composition which comprises a major component comprising fuel or a base oil and 0.05 to 2.0 weight percent of a friction-reducing additive which comprises a polyol ester, having a hydroxyl value of at least 180, the polyol ester being derived from the partial esterification of trimethyolpropane with at least one monocarboxylic acid having a carbon chain length ranging from 10 to 24 carbon atoms in fuel, engine oils and/or transmission oils.

By fuel it is meant both gasoline and diesel fuel. By engine oils it is meant both gasoline and diesel (including heavy duty diesel) engine oils. By transmission oils it is meant automatic, gear, rear axle and continuously variable transmission oils. The invention will now be described further by way of example only with reference to the following Examples and drawings, in which: Figure 1 is a graphical representation of the results obtained in Example 3 and Figure 2 is a graphical representation of the results obtained in example 5.

Example 1

The oxidative stability of friction-reducing additives in gasoline engine oils was tested as follows:

The induction time in minutes, i.e. the time up to when oxidation of the friction reducing additive starts, was. measured by high pressure differential scanning calorimetry (DSC) of various friction-reducing additives, each with 0.5% by weight antioxidant (Irganox L115 - ex Ciba Speciality Chemicals) present, using a Mettler DSC27HP with a Mettler TC 15 TA controller, under the following test conditions:

Start temperature: 30°C.

Heating rate: 50°C/min till test temperature of 170°C.

Air pressure: 40 bar

Airflow: 50ml/min

Sample quantity: 5 +/- 0.4mg. Crucible: Aluminium type, 40μl.

The results are illustrated in Table 1 below.

Table 1

Trimethyolpropane mono-monomerate is derived from the partial esterification of a molar excess of trimethyolpropane with hydrogenated C18 monomeric acid and has a hydroxyl number of 186. The product is a mixture of esters with about 40% actual trimethyolpropane mono-monomerate content. Trimethyolpropane C12/C14ate is derived from the partial esterification of trimethyolpropane with a 1 :1 molar mixture of lauric acid and myristic acid and has a hydroxyl number of 218.

The data in Table 1 clearly illustrates that friction-reducing additives according to the present invention have significantly enhanced oxidative stability as compared to the commercially available friction-reducing additives specified.

Example 2

The coefficient of friction of a lubricant composition comprising 0.5% by weight of friction-reducing additive was determined over a temperature range of 40 to 140°C using a pin-on-ring tribometer. The ring is a 100Cr6 stainless steel ring of 730mm diameter and the pin is a cylinder of the same material of 8mm diameter, the pin having flexible ends so that each end can bend slightly to allow full alignment with the ring. The load applied was 100N and the speed of rotation was 0.03m/s to ensure that the system operates under boundary lubrication. The results are illustrated in Table 2 where an 0W/30 oil based on hydrogenated oligomers of decene-1 is the formulated baseline oil (engine oil).

Table 2

It is clear from the data in Table 2 that friction-reducing additives of the present invention have similar friction-reducing capabilities to the known friction-reducing additives of glycerol monooleate and oleylamide. Although the friction-reducing additives of the present invention have enhanced oxidative stability as compared to known friction-reducing additives (as illustrated in Example 1 above) there is no corresponding detrimental effect on their friction-reducing properties.

Example 3

Example 2 was repeated for two TMP C12/C14 ate samples having different hydroxyl numbers. The formulated base oil used was CEC RL 179/2, which is a 5W-30 calibration oil for the European fuel economy test. The results are illustrated in Table 3 and Figure 1.

Table 3

In Figure 1 the top line represents no friction reducing additive present, the middle line represents the comparative trimethyolpropane C12/C14 ate sample and the bottom line represents trimethyolpropane C12/C14 ate in accordance with the present invention.

It is clear from Table 3 and Figure 1 that friction reducing additives with a hydroxyl number of at least 180 have improved friction coefficients compared to friction reducing additives that have a lower hydroxyl number. Example 4

The compatibility of trimethyolpropane mono-monomerate as the friction-reducing additive at 0.5% by weight with the OW/30 formulated base oil was determined as follows. The friction-reducing additive was added to the formulated base oil and the mixture cooled to -10°C. The mixture was stored for a maximum of 3 months and periodically checked for compatibility. By compatible it is meant that the fluid is clear and does not show any sign of haziness, turbidity and precipitation.

Trimethyolpropane mono-monomerate was found to be compatible with the formulated base oil for the whole test period whereas for a comparative sample containing oleylamide, crystallisation and sedimentation started to occur on day 3 of the test period.

It is clear from the above data that trimethyolpropane monomonomerate of the present invention is compatible with the formulated base oils.

Example 5

The coefficient of friction of a lubricant composition comprising 1.0% by weight of friction-reducing additive was determined over a temperature range of 40 to 140°C using a Mini Traction Machine. The load applied was 30N and the speed of rotation was 0.06m/s. The results are illustrated in Table 4 and Figure 2 where a 5W/30 oil is the formulated baseline oil (engine oil).

Table 4

Trimethyolpropane monomonomerate (70%) is derived from the reaction of a molar excess of trimethyolpropane with hydrogenated C18 monomeric acid which has then been purified by molecular distillation to achieve the 70% level (as compared to 40% achieved without the additional molecular distillation stage). This product has a hydroxyl value of 212.

It is clear from the data in Table 4 and Figure 2 that friction-reducing additives of the present invention have similar friction-reducing capabilities to the known frictionreducing additive glycerol monooleate. Furthermore the increase in the hydroxyl value of the trimethyolpropane monomonomerate corresponds to an improved friction coefficient.

Although the friction-reducing additives of the present invention have enhanced oxidative stability as compared to known friction-reducing additives (as illustrated in Example 1 above) there is no corresponding detrimental effect on their frictionreducing properties.

Claims

1. A lubricant composition for use in fuel, engine oils and transmission oils which comprises a major component comprising fuel or a base oil and 0.05 to 2.0 weight percent of a friction-reducing additive which comprises a polyol ester, having a hydroxyl value of at least 180, the polyol ester being derived from the partial esterification of trimethyolpropane with at least one monocarboxylic acid having a carbon chain length ranging from 10 to 24 carbon atoms.

2. A lubricant composition as claimed in claim 1 wherein the weight percent of the friction-reducing additive is 0.1 to 1.8.

3. A lubricant composition as claimed in claim 1 wherein the weight percent of the friction-reducing additive is 0.25 to 1.6.

4. A lubricant composition as claimed in any of claims 1 to 3 wherein the hydroxyl value is at least 180 with an upper limit of 250.

5. A lubricant composition as claimed in any one of claims 1 to 3 wherein the hydroxyl value is from 190 to 240.

6. A lubricant composition as claimed in any one of claims 1 to 3 wherein the hydroxyl value is from 200 to 240.

7. A lubricant composition as claimed in any one of claims 1 to 6 wherein the at least one monocarboxylic acid has a chain length ranging from 12 to 22 carbon atoms.

8. A lubricant composition as claimed in any one of claims 1 to 6 wherein the at least one monocarboxylic acid has a chain length ranging from 14 to 20 carbon atoms.

9. Use of a lubricant composition which comprises a major component comprising a fuel and 0.05 to 2.0 weight percent of a friction-reducing additive which comprises a polyol ester, having a hydroxyl value of at least 180, the polyol ester being derived from the partial esterification of trimethyolpropane with at least one monocarboxylic acid having a carbon chain length ranging from 10 to 24 carbon atoms in a fuel.

10. Use of a lubricant composition which comprises a major component comprising a base oil and 0.05 to 2.0 weight percent of a friction-reducing additive which comprises a polyol ester, having a hydroxyl value of at least 180, the polyol ester being derived from the partial esterification of trimethyolpropane with at least one monocarboxylic acid having a carbon chain length ranging from 10 to 24 carbon atoms in an engine oil.

11. Use of a lubricant composition which comprises a major component comprising a base oil and 0.05 to 2.0 weight percent of a friction-reducing additive which comprises a polyol ester, having a hydroxyl value of at least 180, the polyol ester being derived from the partial esterification of trimethyolpropane with at least one monocarboxylic acid having a carbon chain length ranging from 10 to 24 carbon atoms in a transmission oil.

12. A lubricant composition for use in engine oil, fuel and transmission oil comprises as a major component thereof a base oil and as a minor component thereof 0.05 to 1.0 weight percent of trimethyolpropanemonomonomerate having a hydroxyl number of at least 180.