Field of the Invention

This invention relates to a method for extending the life of a lubricant composition. Background of the invention

Lubricant compositions contain a mixture of one or more base oils and one or more additives. Each lubricant composition is formulated to fulfil a specific function in a specific type of device. Much design and innovation has led to the development of lubricant compositions which retain excellent functionality over extended lifetimes. However, even with tailored formulations and ideal operating conditions, lubricant compositions will degrade over time.

At least part of this degradation is due to the depletion of certain additives within the lubricant composition. In particular, antioxidant additives are 'sacrificial' or 'depleting' additives as their mechanism of action involves capture of or reaction with oxidized molecules. Other additives, such as antiwear additives, are also known to deplete or degrade over time.

The extension of a lubricant composition's life is a desirable goal and much research has been focussed on extending the oil drain interval (ODI). This is a measure of how long a machine can function at an efficient level, while lubricated with a certain lubricant composition, before requiring a complete replacement of the lubricant composition .

Not all components in a lubricant composition degrade or deplete at the same rate. Lubricant compositions therefore may require changing when many components within the composition are still in a useable condition. In particular, certain additives become depleted or degraded over time and the thus-depleted lubricant composition becomes unsuitable for use, by failing to meet the mandated standards.

Slow-release additive gels have been suggested as one option for overcoming this problem (for example, in US6843916 and W02010014528). However, the complicated technology to produce such gels has proved challenging and such gels are generally not suitable for a large scale device, such as a turbine.

Filtration systems that remove decomposition products physically and/or chemically, such as those described in US5009799, have also been proposed to extend lubricant life. These systems remove decomposition products, but may also remove useful compounds, especially acidic additives. Filters are also not compatible with all oil types.

Used lubricant compositions are often disposed of, as re-processing and re-use is not yet a standard practice in this area. The drive to extend the life of lubricant compositions and/or oil drain intervals has environmental benefits as well as increasing end-user convenience and reducing cost. Improved methods of extending the life of a lubricant composition will always be desirable.

Summary of the Invention

The present invention provides a method for extending the life of a lubricant composition, said lubricant composition comprising one or more base oils and one or more additives, wherein at least one of the additive is a depleting additive, said method comprising: i. determining the amount of the one or more depleting additives required for a desired extended lifetime of the lubricant composition, wherein said extended lifetime is longer than the standard lifetime of said lubricant composition; ii. providing a first portion of said one or more depleting additives to the fresh lubricant composition; and iii. providing the remainder of the amount of the one or more depleting additives in two or more portions spread over the standard lifetime of the lubricant composition.

Brief Description of the Drawings

Figures 1 to 4 illustrate results from the Examples of the present invention.

Detailed Description of the Invention

The present invention provides a means for extending the lifetime of a lubricant composition. Said lubricant composition comprises one or more base oils and one or more additives.

The lubricant composition may be any lubricant composition suitable for lubricating a device. Said device may be, for example, an internal combustion engine, an electric motor, an automatic transmission, a manual transmission and/or differential, a hydraulic system, a pump, or other mechanical device. The present invention is particularly relevant for lubricant compositions used in turbine oils, for example those suitable for use in steam and gas turbines and turbo compressors, and for lubricant compositions for use in hydraulic systems.

The lubricant composition comprises one or more base oils. There are no particular limitations regarding the base oil used in the present invention, and various conventional known mineral oils and synthetic oils may be conveniently used. The base oil used in the present invention may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils. Mineral 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 hydrofinishing processes and/or dewaxing.

Synthetic oils include hydrocarbon oils such as olefin oligomers (PAOs), dibasic acids esters, polyol esters, and dewaxed waxy raffinate.

Fischer-Tropsch derived base oils (also called GTL base oils) may also be conveniently used as the base oil in the lubricating oil composition of the present invention.

The lubricant composition also comprises one or more additives. Suitable additives may be selected on the basis of the intended use of the lubricant composition, the device to be lubricated and the conditions under which the lubrication is to occur. Typical additives for use in lubricant compositions include, but are not limited to, antioxidants, antifoams, dispersants, viscosity modifiers, friction modifiers, detergents, pour point depressants, corrosion inhibitors, extreme pressure/antiwear additives, demulsifiers and mixtures thereof.

Said one or more additives may be provided to the lubricant composition individually or as part of a preprepared additive package. Additives and/or additive packages may be provided to the lubricant composition in a diluted form wherein the diluent may comprise a further base oil.

At least one of the additives is a depleting additive. Such a depleting additive is one which is consumed over the lifetime of the lubricant composition either by physical or chemical degradation. Depleting additives of particular relevance to the method of the present invention include antioxidant additives, antiwear additives and anti-rust or anti-corrosion additives. More particularly, the depleting additive in the present invention is one or more antioxidant additives.

Antioxidant additives typically used in lubricant compositions and relevant for the method of the present invention are so-called hindered phenolic or amine antioxidants, for example naphthols, sterically hindered monohydric, dihydric and trihydric phenols, sterically hindered dinuclear, trinuclear and polynuclear phenols, alkylated or styrenated diphenylamines or ionol derived hindered phenols. Particularly preferred antioxidant additives for use in the present invention include alkylated diphenylamines, hindered phenols and alkylated phenyl a-naphthylamines.

In the method of the present invention, the amount of the one or more depleting additives required for the desired extended lifetime of the lubricant composition is determined. This is determined by i) identifying the standard (i.e. non-extended) lifetime (X hours) of a lubricant composition containing the same base oils and additives to which the method of the present invention has not been applied; ii) determining the desired extended lifetime (Y hours) of the lubricant composition, wherein Y is greater than X, preferably at least 1% greater than X, more preferably at least 2% greater than X, even more preferably at least 5% greater than X; and iii) determining the amount of the one or more depleting additive required in order to support the lubricating composition for the desired extended lifetime. Determining the standard lifetime (X hours) can be carried out by considering known lubricant composition, equipment, conditions and uses. Determining the desired extended lifetime (Y hours) can be achieved by consideration of the practicalities of the equipment and conditions as well as the lifetime of other components within the lubricant composition. This determination of the amount of the one or more depleting additives required in order to support the lubricating composition for the desired extended lifetime can be done on the basis of known degradation/depletion timescales for the one or more depleting additives in question in the type of oil and for the type of use expected for the lubricating composition.

The overall amount of the one or more depleting additives used in the method of the present invention is suitably no more than lwt% based on the overall mass of the lubricating composition. This is particularly relevant for a mineral oil-based turbine fluid type lubricant composition. Preferably, the overall amount of the one or more depleting additives used in the method of the present invention is suitably no more than 0.80wt%, more preferably no more than 0.75wt%, based on the overall mass of the lubricating composition. Typically, the overall amount of the one or more depleting additives used in the method of the present invention is no less than 0.001wt%, preferably no less than 0.01wt%, more preferably no less than 0.1wt%, based on the overall mass of the lubricating composition .

One potential benefit of the present invention is that the amount of depleting additive needed in order to support the extended lifetime may be no more than required for the standard lifetime.

A first portion of the amount of the one or more depleting additives is added to the fresh lubricant composition. The term fresh, as used herein, refers to a lubricant composition before it has been used in a machine or device. Although elements of the lubricant composition may have been re-used or recycled, the composition itself has not been used previously. The first portion may be added to the lubricant composition during formulation, i.e. while the base oils and any other additives are being blended, or it may be added in situ.

The first portion of the depleting additive may be an amount in the range of from 30 to 70wt%, preferably in the range of from 40 to 60wt%, of the overall amount of the one or more depleting additives.

The first portion may be added as an individual additive or as part of a mixed additive package along with any of the other additives forming the fresh lubricant composition .

The remainder of the amount of the one or more depleting additives is then added in two or more further portions spread over the extended lifetime of the lubricant composition. Suitably, the remainder of the amount is in the range of from 30 to 70wt%, preferably in the range of from 40 to 60wt%, the overall amount of the one or more depleting additives. This remainder is preferably split evenly between the two or more further portions. For example, if two further portions are added, each further portion will preferably contain in the range of from 40 to 60wt%, more preferably about 50wt% of the remainder of the amount of the depleting additive. Or, if three further portions are added, each further portion will preferably contain in the range of from 30 to 35wt%, more preferably about 33wt% of the remainder of the amount of the one or more depleting additives.

The further portions may be provided as the individual additive or may be provided as an additive booster package, containing a mixture of additives and a diluent, such as a base oil. In a preferred embodiment, the further portions are provided as an additive booster package comprising one or more antioxidant additives and one or more base oils.

The further portions are added after periods spaced across the standard lifetime. Preferably, said periods are roughly evenly spaced across the standard lifetime. For example, the periods may be determined by dividing the standard lifetime by the number of portions to be added. „ ,., . standardlifetime(hours)

Period (hours) = - totalnumberofportions

The first portion of the amount of the one or more depleting additives is added to the fresh lubricant composition, i.e. at time = 0 hours. The further portions may then be added in turn at an addition time determined to be within a range of from 30 hours, preferably 20 hours, before each period expires to 30 hours, preferably 20 hours, after each period expires. Thus, the first further portion is added at the first addition time calculated as [0 hours + 1 period] +/- 30 hours. The second further portion is added at a second addition time calculated as [first addition time + period] +/- 30 hours. The third further portion, if present, is added at a third addition time calculated as [second addition time + period] +/- 30 hours, and so forth depending on the number of further portions to be added.

The further portions may be added to the lubricant composition in any suitable manner. Typically the further portions are added through an access point in a device that is being lubricated and allowed to mix through the turbulence generally occurring in a device under lubrication. However, an insert incorporated into the device to be lubricated which allows release of portions over time is also envisaged.

The invention will now be further illustrated by reference to the following non-limiting examples. Examples Examples 1 to 6

In all 6 examples, the fresh lubricant composition contained a Group II mineral base oil and an additive package (overall amount is 360mL). Said additive package contained aminic and phenolic antioxidants and rust inhibitors as well as other additives typical for use in turbine oils.

The typical (non-extended) lifetime of this lubricant composition, under lab-scale aging conditions, was determined to be approximately 800 hours. This is the standard lifetime according to the dry TOST oxidation stability test and is clearly not equivalent to the actual oil drain interval outside the lab.

An antioxidant booster package was blended. The antioxidant booster package contained:

• 30wt% of an alkylated - phenyl alpha naphthylamine;

• 20wt% of a butylated/octylated diphenylamine;

• 20wt% of an alkylated phenol ester; and

• 30wt% of an alkylated naphthalene base oil.

The lubricant compositions of the Examples were maintained under conditions according to ASTM D7873. That is 120°C, oxygen flow rate of 3 litres/hour and in the presence of copper and steel coils. The antioxidant booster package was added to each Example as follows:

• Examples 1 to 3 - the antioxidant booster package was added in 3 portions of 0.55mL at each of 192 hours, 408 hours and 576 hours.

• Example 4 - no antioxidant booster package was added to the fresh lubricant or during the test.

• Examples 5 and 6 - the antioxidant booster package was added as a single portion (1.65mL) to the fresh lubricant at the start of the test (time = 0 hours). During the tests, samples from the Examples were tested according to a variety of tests:

• TOST - Dry Turbine Oxidation Stability Test according to ASTM D7873. Measures insoluble by-products of oxidation process and residual anti-oxidancy.

• RULER - Remaining Useful Live Evaluation Routine according to ASTM D6971. Measures concentration of phenol and amine antioxidants separately (residual anti-oxidancy reserve).

• MPC - Membrane Patch Colorimetry according to ASTM D7843. Measures insoluble oxidation by-products (varnish potential). Oil considered to be at end of life if values exceed 40 DE.

• RPVOT - Rotating Pressure Vessel Oxidation Test according to ASTM D2272. Measures remaining oxidation life relative to fresh oil. Oil considered to be at end of life if retention is less than 25%.

The six examples were tested over time using a variety of tests at different points, as set out in Table 1. The results of the analyses can be seen in Figures 1 to

4.

Table 1

Certain tests used up an entire sample. Therefore, equivalent samples were used to demonstrate the degradation of a sample over time.

In Figure 1, the results of the RULER - amine only tests are plotted for a) the reference oil of Example 4; b) Examples 5 and 6 in which all of the antioxidant booster package was added at 0 hrs; and c) Examples 1, 2 and 3 for which the antioxidant booster package was added portion-wise over time. For cases where more than 1 Example was measured, an average is provided. Examples 1-3 were evaluated before and after addition of the antioxidant booster package. The dotted line on this graph indicates 25% of amine remaining, which is considered to be 'end of life' for lubricant compositions.

In Figure 2, the results of the RULER - phenol only tests are plotted for a) the reference oil of Example 4; b) Examples 5 and 6 in which all of the antioxidant booster package was added at 0 hrs; and c) Examples 1, 2 and 3 for which the antioxidant booster package was added portion-wise over time. For cases where more than 1 Example was measured, an average is provided.

In Figure 3, the results of the MPC DE tests are plotted for a) the reference oil of Example 4; b) Examples 5 and 6 in which all of the antioxidant booster package was added at 0 hrs; and c) Examples 1, 2 and 3 for which the antioxidant booster package was added portion-wise over time. The dotted line on this graph indicates a value of 40 DE, which is considered to be 'end of life' for lubricant compositions.

In Figure 4, the results of the RPVOT tests are plotted for a) the reference oil of Example 4; b) Examples 5 and 6 in which all of the antioxidant booster package was added at 0 hrs; and c) Examples 1, 2 and 3 for which the antioxidant booster package was added portion-wise over time. The dotted line on this graph indicates a value of 25%, which is considered to be 'end of life' for lubricant compositions.

For each test, it is clearly shown that the inventive examples have an extended lifetime over the reference oil of Example 4. In comparison to comparative Examples 5 and 6, it is clearly shown that this is not merely a result of adding extra antioxidant to the lubricant composition, but the method of the invention that results in the extended lifetime of the lubricant compositions.