WO2011110551A1

WO2011110551A1 - Method of reducing the toxicity of used lubricating compositions

Info

Publication number: WO2011110551A1
Application number: PCT/EP2011/053458
Authority: WO
Inventors: Howard Richard Hayes; Janet Marian Smithers; Robert Wilfred Matthews Wardle; David John Wedlock
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2010-03-10
Filing date: 2011-03-08
Publication date: 2011-09-15

Abstract

Method of reducing the toxicity of a used lubricating composition comprising fuelling a diesel engine containing the lubricating composition with a diesel fuel composition which comprises Fischer-Tropsch derived gas oil. The present invention also relates to a used lubricant, the used lubricant having been obtained from a diesel engine fuelled with a fuel composition which comprises Fischer-Tropsch derived gas oil, wherein the used lubricant has a Mutagenicity Index of less than 0.5 as measured by the Modified Ames Test Method.

Description

METHOD OF REDUCING THE TOXICITY OF USED LUBRICATING

COMPOSITIONS

Field of the Invention

The present invention relates to a method of

reducing the toxicity of used lubricating compositions and to a used lubricating composition having reduced toxicity.

Background of the Invention

The primary purpose of lubrication is separation of surfaces moving relative to one another, to minimise friction and wear. The materials most frequently used for this purpose are oils and greases. The choice of lubricant is mostly determined by the particular

application .

The lubricating oils in all engines are at risk of contamination from fuel components, with the

consequential reduction in lubricating properties

exhibited by the lubricating oil. In addition, fuel contamination results in an increase in the toxicity of the lubricant due to accumulation of toxic fuel

components in the lubricant. This is especially the case with gasoline contamination where Platformate {a gasoline blending component) causes significant light poly-cyclic aromatics accumulation in the lubricant. Diesel fuel components are also potentially toxic.

The toxicity increase is a particular issue for the recycling of so-called "used oil". "Used oil" can be defined as any petroleum-based or synthetic oil that, through use or handling, has become unsuitable for its original purpose due to the presence of impurities or loss of original properties. Some examples of types of products that after use can be labeled as used oil are hydraulic oil, transmission oil, brake fluids, motor oil, crankcase oil, gear box oil, synthetic oil, and grades #1, 2, 3, and 4 fuel oil.

Used oil can be used for various purposes including as a fuel in, for example, industrial furnaces or

boilers .

As mentioned above however, one disadvantage of used lubricants from diesel engines is that they contain toxic materials as a result of having been contaminated by diesel fuel components during use. Since it is desirable to recycle these used lubricants for other purposes, it would be useful to find a way to reduce the toxicity of the used lubricants, such that handling and further processing becomes safer and more manageable.

It has now surprisingly been found that by using a Fischer-Tropsch derived paraffinic diesel fuel to fuel a diesel engine containing a lubricating composition, the used lubricating composition has a reduced toxicity.

Summary of the Invention

According to the present invention there is provided a method of reducing the toxicity of a used lubricating composition contained in a diesel engine comprising fuelling the diesel engine with a diesel fuel composition which comprises Fischer-Tropsch derived gas oil.

According to another aspect of the present invention there is provided a used lubricating composition, the used lubricating composition being obtained from a diesel engine which has been fuelled with a diesel fuel

composition comprising Fischer-Tropsch derived gas oil, wherein the used lubricating composition has a

Mutagenicity Index of less than 0.5 as measured by the Modified Ames Test Method (ASTM E 1687). Detailed Description of the Invention

As used herein the term "used lubricating

composition" means a petroleum-based or synthetic-based lubricating composition that, through use, in particular in a diesel engine, has become unsuitable for its

original purpose due to the presence of impurities or loss of original properties. The term "through use" in this context means that the vehicle powered by the diesel engine has preferably done at least 3000 miles.

The method of the present invention involves

fuelling a diesel engine containing the lubricant with a diesel fuel composition comprising Fischer-Tropsch derived gas oil. The method herein results in a used lubricating composition having a reduced toxicity. As used herein the term "reducing the toxicity of the used lubricating composition" means that the used lubricating composition has a significantly reduced Mutagenicity Index, as measured by the Modified Ames Test Method

(according to ASTM E1687), compared to a used lubricating composition obtained from a diesel engine fuelled by a conventional diesel fuel, i.e. not containing Fischer- Tropsch derived gas oil. Preferably the used lubricant also has a significantly reduced Fold Increase (FI) as measured by the Modified Ames Test Method.

The diesel fuel composition for use in the present invention may comprise conventional, petroleum derived, diesel as well as the Fischer-Tropsch derived gas oil.

Typically in a formulation according to the present invention, the concentration of the Fischer-Tropsch derived gas oil (a) may be 0.5%v/v or greater. It may be up to 98%v/v, for example up to 90%v/v such as up to 85%v/v. A suitable concentration may be from 0.5% to 99%v/v or from 0.5% to 90%v/v, for example from 0.5% to 85%v/v.

Where present, conventional diesel is suitably present in a formulation according to the present

invention, at a concentration of 0.5%v/v or greater. It may be up to 85%v/v, for example up to 75%v/v. A

suitable concentration may be from 0.5%v/v to 85%v/v or from 0.5%v/v to 75%v/v, for instance from 0.5%v/v to 50%v/v.

By "Fischer-Tropsch derived" is meant that a fuel is, or derives from, a synthesis product of a Fischer- Tropsch condensation process. A Fischer-Tropsch derived fuel may also be referred to as a GTL (Gas-to-Liquid) fuel. The term "non-Fischer-Tropsch derived" may be construed accordingly.

Fischer-Tropsch derived fuels are known and in use in for instance automotive diesel fuel compositions, and are described in more detail below. They tend to contain low levels of aromatic fuel components and of sulphur and other polar species, and to have relatively high cetane numbers when compared to their mineral derived

counterparts .

The Fischer-Tropsch reaction converts carbon

monoxide and hydrogen into longer chain, usually

paraffinic, hydrocarbons:

in the presence of an appropriate catalyst and typically at elevated temperatures (e.g. 125 to 300°C, preferably 175 to 250°C} and/or pressures (e.g. 5 to 100 bar, preferably 12 to 50 bar}. Hydrogen: carbon monoxide ratios other than 2:1 may be employed if desired.

The carbon monoxide and hydrogen may themselves be derived from organic or inorganic, natural or synthetic sources, typically either from natural gas or from organically derived methane. The gases which are

converted into liquid fuel components using such

processes can in general include natural gas (methane) , LPG (e.g. propane or butane), "condensates" such as ethane, synthesis gas (CO/hydrogen) and gaseous products derived from coal, biomass and other hydrocarbons.

Gas oil products may be obtained directly from the Fischer-Tropsch reaction, or indirectly for instance by fractionation of Fischer-Tropsch synthesis products or from hydrotreated Fischer-Tropsch synthesis products. Hydrotreatment can involve hydrocrackxng to adjust the boiling range (see, e.g. GB-B-2077289 and EP-A-0147873) and/or hydroisomerisation which can improve cold flow properties by increasing the proportion of branched paraffins. EP-A-0583836 describes a two step

hydrotreatment process in which a Fischer-Tropsch

synthesis product is firstly subjected to hydroconversion under conditions such that it undergoes substantially no isomerisation or hydrocrackxng (this hydrogenates the olefinic and oxygen-containing components), and then at least part of the resultant product is hydroconverted under conditions such that hydrocrackxng and

isomerisation occur to yield a substantially paraffinic hydrocarbon fuel. The desired gas oil fraction (s) may subsequently be isolated for instance by distillation.

The gas oil can also be obtained by carrying out the methods described in US 7354508, US 73329072 B2 and EP-A- 0583836. A preferred method of obtaining the gas oil is described in EP-A-1412459. Further information on the method of obtaining the gas oil can also be found in WO2009/080679 and US2009/0200203. Other post-synthesis treatments, such as

polymerisation, alkylation, distillation,

cracking-decarboxylation, isomerisation and

hydroreforming, may be employed to modify the properties of Fischer-Tropsch condensation products, as described for instance in US-A-4125566 and US-A-4478955.

Typical catalysts for the Fischer-Tropsch synthesis of paraffinic hydrocarbons comprise, as the catalytically active component, a metal from Group VIII of the periodic table, in particular ruthenium, iron, cobalt or nickel. Suitable such catalysts are described for instance in EP- A-0583836 (pages 3 and 4) .

An example of a Fischer-Tropsch based process is the SMDS (Shell Middle Distillate Synthesis) described by van der Burgt et al in "The Shell Middle Distillate Synthesis Process", paper delivered at the 5th Synfuels Worldwide Symposium, Washington DC, November 1985 (see also the November 1989 publication of the same title from Shell International Petroleum Company Ltd, London, UK) . This process (also sometimes referred to as the Shell "Gas-To- Liquids" or "GTL" technology) produces middle distillate range products by conversion of a natural gas (primarily methane) derived synthesis gas into a heavy long chain hydrocarbon (paraffin) wax which can then be

hydroconverted and fractionated to produce liquid

transport fuels such as the gas oils useable in diesel fuel compositions. A version of the SMDS process, utilising a fixed bed reactor for the catalytic

conversion step, is currently in use in Bintulu, Malaysia and its gas oil products have been blended with petroleum derived gas oils in commercially available automotive fuels . Gas oils prepared by the SMDS process are

commercially available for instance from Shell companies. Further examples of Fischer-Tropsch derived gas oils are described in EP-A-0583836, EP-A-1101813, WO-A-97 /14768 , WO-A-97/14769, WO-A-00/20534 , WO-A-00/20535 , WO-A-

00/11116, WO-A-00/11117, WO-A-01/83406, WO-A-01/83641, WO-A-01/83647, WO-A-01/83648 and US~~A-6204426.

By virtue of the Fischer-Tropsch process, a Fischer- Tropsch derived fuel has essentially no, or undetectable levels of, sulphur and nitrogen. Compounds containing these heteroatoms tend to act as poisons for Fischer- Tropsch catalysts and are therefore removed from the synthesis gas feed. Fischer-Tropsch derived fuels are known to give rise to reduced levels of. emissions (in particular NOx and particulate matter emissions) compared to their petroleum derived counterparts.

Further, the Fischer-Tropsch process as usually operated produces no or virtually no aromatic components. The aromatics content of a Fischer-Tropsch derived fuel, suitably determined by ASTM D4629, will typically be below l%w/w, preferably below 0.5%w/w and more preferably below 0.2 or 0.1%w/w.

Generally speaking, Fischer-Tropsch derived fuels have relatively low levels of polar components, in particular polar surfactants, for instance compared to petroleum derived fuels. Such polar components may include for example oxygenates, and sulphur- and

nitrogen-containing compounds. A low level of sulphur in a Fischer-Tropsch derived fuel is generally indicative of low levels of both oxygenates and nitrogen-containing compounds, since all are removed by the same treatment processes . A Fischer-Tropsch derived gas oil should be suitable for use as a diesel fuel, ideally as an automotive diesel fuel; its components (or the majority, for instance

95%v/v or greater, thereof) should therefore have boiling points within the typical diesel fuel ("gas oil") range, i.e. from about 150 to 400°C or from 170 to 370°C. It will suitably have a 90%v/v distillation temperature of from 300 to 370°C,

A Fischer-Tropsch derived gas oil will typically have a density from 0.76 to 0.79 g/cm³ at 15°C; a cetane number (ASTM D613) greater than 70, suitably from 74 to 85; a kinematic viscosity (ASTM D445) from 2 to 4.5, preferably from 2.5 to 4.0, more preferably from 2.9 to

3.7, mm²/s at 40°C; and a sulphur content (ASTM D2622) of 5 mg/kg or less, preferably of 2 mg/kg or less.

Preferably a Fischer-Tropsch derived gas oil used in the present invention is a product prepared by a

Fischer-Tropsch methane condensation reaction using a hydrogen/carbon monoxide ratio of less than 2.5,

preferably less than 1.75, more preferably from 0.4 to 1.5, and ideally using a cobalt containing catalyst.

Suitably it will have been obtained from a hydrocracked Fischer-Tropsch synthesis product (for instance as described in GB-B-2077289 and/or EP-A-0147873) , or more preferably a product from a two-stage hydroconversion process such as that described in EP-A-0583836 (see above) . In the latter case, preferred features of the hydroconversion process may be as disclosed at pages 4 to 6, and in the examples, of EP-A-0583836.

Suitably a Fischer-Tropsch derived gas oil used in the present invention is a product prepared by a low temperature Fischer-Tropsch process, by which is meant a process operated at a temperature of 250°C or lower, such as from 125 to 250°C or from 175 to 250°C, as opposed to a high temperature Fischer-Tropsch process which might typically be operated at a temperature of from 300 to 350°C.

Suitably, in accordance with the present invention, a Fischer-Tropsch derived gas oil will consist of at least 70%w/w, preferably at least 80%w/w, more preferably at least 90 or 95 or 98%w/w, most preferably at least 99 or 99.5 or even 99.8%w/w, of paraffinic components, preferably iso- and normal paraffins. The weight ratio of iso-paraffins to normal paraffins will suitably be greater than 0.3 and may be up to 12; suitably it is from 2 to 6. The actual value for this ratio will be

determined, in part, by the hydroconversion process used to prepare the gas oil from the Fischer-Tropsch synthesis product .

The olefin content of the Fischer-Tropsch derived gas oil is suitably 0.5%w/w or lower. Its aromatics content is suitably 0.5%w/w or lower.

According to the present invention, a mixture of two or more Fischer-Tropsch derived gas oils may be used in the fuel formulation.

Where present in the formulation of the present invention, the "conventional diesel" will comprise a diesel base fuel such as an automotive gas oil (AGO) .

Typical diesel fuel components comprise liquid

hydrocarbon middle distillate fuel oils, for instance petroleum derived gas oils. Such base fuel components may be organically or synthetically derived. They will typically have boiling points within the usual diesel range of 125 or 150 to 400 or 550°C, depending on grade and use. They will typically have densities from 0.75 to

1.0 g/cm³, preferably from 0.8 to 0.9 or 0.86 g/cm^, at 15°C (IP 365) and measured cetane numbers (ASTM D613) of from 35 to 80, more preferably from 40 to 75 or 70.

Their initial boiling points will suitably be in the range 150 to 230°C and their final boiling points in the range 290 to 400°C. Their kinematic viscosity at 40°C

(ASTM D445) might suitably be from 1.5 to 4.5 mm²/s.

Such fuels are generally suitable for use in a compression ignition (diesel) internal combustion engine, of either the indirect or direct injection type.

A fuel formulation according to the present

invention may be suitable for use in a compression ignition (diesel) internal combustion engine, of either the indirect or direct injection type.

Such a diesel fuel formulation will suitably comply with applicable current standard specification (s) such as for example EN 590:2004 (for Europe) or ASTM D-975-06 (for the USA) . By way of example, the formulation may have a density (EN ISO 12185) from 0.82 to 0.845 g/cm³ at 15°C a 95% recovered temperature {EN ISO 3405) of 360°C or less; a cetane number (EN ISO 5165) of 51 or greater; a kinematic viscosity (EN ISO 3104) from 2 to 4.5

centistokes at 40°C; a sulphur content (EN ISO 20847) of 50 ppmw or less; and/or a polyaromatics content

{EN 12916) of less than 11 %. Relevant specifications may, however, differ from country to country and from year to year and may depend on the intended use of the fuel composition.

A fuel formulation according to the present

invention may contain other components in addition to the Fischer-Tropsch derived gas oil, and, where present, the conventional diesel oil. It may in particular include one or more diesel fuel additives. Many such additives are known and readily available. The total additive content in the fuel formulation may suitably be from 50 to 10000 mg/kg, preferably below 5000 mg/kg.

Further additives which are often included in diesel fuel formulations are cetane improvers (also known as an ignition improvers) . As a result of carrying out the present invention, however, lower levels of such

additives may be needed as the presence of the Fischer- Tropsch derived gas oil can itself serve to increase the cetane number of the overall formulation, even in the presence of the normally cetane-lowering water. The oxygenate may also contribute to maintaining the cetane number .

The ignition improving additive may be any suitable ignition improver. Many such additives are known and commercially available, and may also be known (in the context of diesel fuels) as "cetane improvers" or "cetane number improvers"; they typically function by increasing the concentration of free radicals in a fuel formulation. The ignition improver may in particular be a diesel fuel ignition improver, i.e. an ignition improving agent suitable for use in a diesel fuel formulation.

An ignition improver may for example be selected from:

a) organic nitrates of the general formula RI-O-NO2 , or nitrites of the general formula RI -O-NO, where is a hydrocarbyl group such as in particular an alkyl,

cycloalkyl, alkenyl or aromatic group, or an ether containing group, preferably having from 1 to 10, more preferably from 1 to 8 or from 1 to 6 or from 1 to 4, carbon atoms;

b) organic peroxides and hydroperoxides, of the general formula R^-O-O-R^, where R^ and R^ are each independently either hydrogen or a hydrocarbyl group such as in particular an alkyl, cycloalkyl, alkenyl or

aromatic group, preferably having from 1 to 10, more preferably from 1 to 8 or from 1 to 6 or from 1 to 4, carbon atoms (provided that R2 and R3 are not both hydrogen) ; and

c) organic peracids and peresters, of the general formula R⁴-C (0) -0-O-R⁵, where R⁴ and R⁵ are each

independently either hydrogen or a hydrocarbyl group such as in particular an alkyl, cycloalkyl, alkenyl or

aromatic group, preferably having from 1 to 10, more preferably from 1 to 8 or from 1 to 6, such as from 1 to 4, carbon atoms.

Examples of ignition improvers of type (a) include (cyclo) alkyl nitrates such as isopropyl nitrate, 2~ ethylhexyl nitrate (2-EHN) and cyclohexyl nitrate, and ethyl nitrates such as methoxyethyl nitrate. Examples of type (b) include di-tert-butyl peroxide.

Other diesel fuel ignition improvers are disclosed in US-A-4208190 at column 2, line 27 to column 3, line 21.

In particular, the ignition improver may be selected from (cyclo) alkyl nitrates such as 2~ethylhexyl nitrate (2-EHN) , dialkyl peroxides such as di-tert-butyl

peroxide, and mixtures thereof. It may in particular be a (cyclo) alkyl nitrate such as 2-EHN.

Diesel fuel ignition improvers are commercially available for instance as HITEC™ 4103 (ex. Afton

Chemical) and as CI-0801 and CI-0806 (ex. Innospec Inc.).

Lubricity enhancing additives used in conventional fuel compositions may be any additive capable of

improving the lubricity of a fuel composition and/or of imparting anti-wear effects when the composition is in use in an engine or other fuel-consuming system.

The lubricity enhancing additive may contain, typically as active constituent (s) , one or more

carboxylic acids. Suitable carboxylic acids include fatty acids and aromatic acids, in particular fatty acids such as those listed below. A lubricity enhancing additive may alternatively be based on non-acid actives such as esters or amides. Preferably the lubricity enhancing additive is ester- or amide-based, more

preferably ester-based.

Suitable esters for use in such additives are carboxylic acid esters, in particular those derived from fatty acids, and mixtures thereof. Such fatty acids may be saturated or unsaturated (which includes

polyunsaturated) . They may for example contain from 1 or 2 to 30 carbon atoms, suitably from 10 to 22 carbon atoms, preferably from 12 to 22 or from 14 to 20 carbon atoms, more preferably from 16 to 18 carbon atoms and most preferably 18 carbon atoms. Examples include oleic acid, linoleic acid, linolenic acid, linolic acid, stearic acid, palmitic acid and myristic acid. Of these, oleic, linoleic and linolenic acids may be preferred, more preferably oleic and linoleic acids. In one

embodiment of the present invention, the lubricity enhancing additive is a derivative (in particular an ester} of tall oil fatty acid, which is derived from tall oil and contains mostly fatty acids (such as oleic and linoleic) with a small proportion of rosin acids.

Lubricity enhancing additives based on ester- functionalised oligomers or polymers (e.g. olefin

oligomers) may also be of use. Such esters may be mono- alcohol esters such as methyl esters, or more suitably may be polyol esters such as glycerol esters. Most preferred is a mono-, di- or tri-glyceride of a fatty acid, or conveniently a mixture of two or more such species .

Suitable amides for use in such additives are fatty acid amides, wherein preferred fatty acids may be as described above, for example fatty acid amides of mono- or in particular di-alkanolamines such as diethanolamine .

Suitable commercially available lubricity enhancing additives include the fatty acid-based R650 (ex.

Infineum) , the fatty acid ester-based R655 {ex.

Infineum} , the amide-based Hitec™ 4848A (ex. Afton) and the fatty acid-based Lz 539 series of products (ex.

Lubrizol) . Of these, fatty acid ester-based additives such as R655 may be preferred.

Other suitable lubricity enhancers are described for example in:

- the paper by Danping Wei and Β.Ά. Spikes, "The Lubricity of Diesel Fuels", Wear, III (1986) 217-235;

- WO-A-95/33805 - cold flow improvers to enhance lubricity of low sulphur fuels;

- WO-A-94/17160 - certain esters of a carboxylic acid and an alcohol wherein the acid has from 2 to 50 carbon atoms and the alcohol has 1 or more carbon atoms, particularly glycerol monooleate and di-isodecyl adipate, as fuel additives for wear reduction in a diesel engine injection system;

- US-A-5490864 - certain dithiophosphoric diester- dialcohols as anti-wear lubricity additives for low sulphur diesel fuels; and

- WO-A-98/01516 - certain alkyl aromatic compounds having at least one carboxyl group attached to their aromatic nuclei, to confer anti-wear lubricity effects particularly in low sulphur diesel fuels.

A lubricity enhancing additive may contain other ingredients in addition to the key lubricity enhancing active (s) , for example a dehazer and/or an anti-rust agent, as well as conventional solvent (s) and/or

excipient (s) . Alternatively, a lubricity enhancing additive may consist essentially or even entirely of alubricity enhancing active, or mixture thereof, of the type described above.

The {active matter} concentration of the lubricity enhancing additive used in a fuel composition according to the present invention may be 1000 ppmw or less, preferably 500 ppmw or less, more preferably 400 or 300 ppmw or less. Its {active matter) concentration will suitably be 100 ppmw or less, preferably 50 or 30 ppmw or less. In the case of any lubricity enhancing additives, these may in fact be reduced to zero as a result of the use of the formulations of the first aspect of the present invention.

There is no particular limitation on the type of lubricating composition which can be used in the present invention, provided it is suitable for use in a diesel engine. WO2007/128740 , which is incorporated herein by reference, discloses suitable lubricating base oils and additives which may be incorporated into a lubricating compositio .

Typically the lubricating composition has a

relatively low phosphorus content such as below 0.12 wt . % (according to AST D 5185) . Preferably, the lubricating composition has a phosphorus content of less than 0.08 wt . % . Preferably, the composition has a phosphorus content of above 0.06 wt.%. Also, it is preferred that the lubricating

composition has a sulphur content of less than 0.6 wt.% (according to ASTM D 5185) .

Further it is preferred that the lubricating

composition has a chlorine content of less than 200 ppm (according to ASTM D 808) .

According to an especially preferred embodiment, the lubricating composition has an ash content of below 2.0 wt.% (according to ASTM D 874).

According to an especially preferred embodiment of the present invention, the lubricating composition comprises a zinc dialkyl dithiophosphate (ZDDP) compound. Typically, if present, the ZDDP compound is present in an amount of 0.01-1.5 wt.%, preferably 0.4-1.0 wt.%. The ZDDP compound may have been made from primary, secondary, tertiary alcohols or mixtures thereof, preferably

containing less than 12 carbon atoms. Preferably, the ZDDP compound has been made from secondary alcohols containing 3 to 8 carbon atoms.

There are no particular limitations regarding the base oil used in the lubricating composition, and various conventional mineral oils, synthetic oils as well as naturally derived esters such as vegetable oils may be conveniently used.

The base oil used may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils; thus, the term "base oil" may refer to a mixture containing more than one base oil. Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing. Suitable base oils for use in the lubricating oil composition are Group I-III mineral base oils, Group IV poly-alpha olefins (PAOs) , Group II-III Fischer-Tropsch derived base oils and mixtures thereof.

By "Group I", "Group II", "Group III" and "Group IV" base oils are meant lubricating oil base oils according to the definitions of American Petroleum Institute {API) for categories I-IV. These API categories are defined in API Publication 1509, 16th Edition, Appendix E, April, 2007.

Fischer-Tropsch derived base oils are known in the art. By the term "Fischer-Tropsch derived" is meant that a. base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To- Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition are those as for example

disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs) , dibasic acid esters, polyol esters, polyalkylene glycols (PAGs) , alkyl naphthalenes and dewaxed waxy isomerates. Synthetic hydrocarbon base oils sold by the Shell Group under the designation "Shell XHVI" (trade mark) may be conveniently used.

Poly-alpha olefin base oils (PAOs) and their manufacture are well known in the art. Preferred poly- alpha olefin base oils that may be used in the

lubricating compositions may be derived from linear C2 to C32, preferably C₆ to C₁₆, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1- octene, 1-decene, 1-dodecene and 1-tetradecene .

A preferred base oil for use in the lubricating composition herein is a Fischer-Tropsch derived base oil, for example GTL 5 {having a kinematic viscosity at 100°C of approximately 5 mm²/s) and GTL 8 (having a kinematic viscosity at 100°C of approximately 8 mm²/s), both of which may be prepared according to the method described in WO02/070631.

The total amount of base oil incorporated in the lubricating composition is preferably present in an amount in the range of from 60 to 99 wt.%, more

preferably in an amount in the range of from 65 to 98 wt.% and most preferably in an amount in the range of from 70' to 95 wt.%, with respect to the total weight of the lubricating composition.

Preferably, the finished lubricating composition has a kinematic viscosity in the range of from 2 to 8Ό mmVs at 100 °C, more preferably in the range of from 3 to 70 mm²/s, most preferably in the range of from 4 to

50 mm²/s.

The lubricating composition may further comprise additional additives such as anti-wear additives, antioxidants, dispersants, detergents, friction modifiers, viscosity index improvers, pour point depressants, corrosion inhibitors, defoaming agents and seal fix or seal compatibility agents.

As the person skilled in the art is familiar with the above and other additives, these are not further discussed here in detail. Specific examples of such additives are described in for example Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526.

Preferably the detergent, if present, is selected from phenate- and sulphonate-type detergents;

accordingly.

The lubricating compositions may be conveniently prepared by admixing the additives that are usually present in lubricating compositions, for example as herein before described, with mineral and/or synthetic base oil.

The used lubricating composition according to the present invention has a reduced toxicity, i.e. it has a Mutagenicity Index of less than 0.5, more preferably less than 0.3, as measured by the Modified Ames Test

(according to ASTM E 1687) . Preferably the used

lubricating composition also has a Fold Increase of less than 1.8, more preferably less than 1.5, as measured by the Modified Ames Test Method (according to ASTM E 1687) .

The used lubricating composition is suitable for a variety of uses, such as a fuel in, for example,

industrial furnaces or boilers.

The present invention will now be described by reference to the following Examples which are not

intended to limit the scope of the invention in any way.

Examples

To determine the effect of various diesel fuels on the mutagenicity of used lubricants, a 2 car trial was carried out. The car used for this trial was a Mercedes- Benz C class light duty diesel. Two lubricants and two fuels were used in the trial. The formulations of the two lubricants were "Lubricant 1" and "Lubricant 2". The formulations of these two lubricants are set out in Table 1 below. The two fuels were a European normal low sulphur diesel fuel ("Fuel A") and a GTL diesel fuel {"Fuel B") . The physical characteristics of the two fuels are set out in Tables 2 and 3 below. Each leg of the trial used one fuel (A or B) and one lubricant (1 or 2) as shown in Table 4 below. The Mutagenicity Index (MI) and Fold Increase (FI) of the lubricants were measured before the vehicle had done any mileage

(designated as "start" of the test in Table 4 below) and were measured again at the 2/3 point of 10,000 mile Oil Drain Interval (designated as "end" of the test in Table 4 below) using the Modified Ames Test (according to ASTM E1687) . The results are shown in Table 4 below, where MPI stands for Mutagenicity Potency- Index.

Table 1

SK Energy, Ulsan, South Korea

2. A Fischer-Tropsch derived Group III base oil with a kinematic viscosity at 100°C of approximately 5 mm²/s which may be conveniently prepared by the process described in WO 02/070631

3. A Fischer-Tropsch derived Group III base oil with a kinematic viscosity at 100°C of approximately 8 mm²/s, which may conveniently be prepared by the process described in WO02/070631 Table 2

Properties of Fuel A (Low Sulphur Diesel Fuel)

Discussion

As can be seen from the results in Table 4, Diesel Fuel B (GTL diesel) gave a much lower increment in mutagenicity index (MI) and Fold Increase (FI) compared to Diesel Fuel A^' (a European normal low sulphur diesel fuel with no GTL diesel), for the used lubricants 1 and 2, relative to their fresh oil counterparts. One can reasonably expect to see a proportion of the benefits in any blend of GTL diesel with conventional diesel.

Claims

C L A I M S

1. Method of reducing the toxicity of a used lubricant from a diesel engine comprising fuelling the diesel engine containing the lubricant with a diesel fuel composition which comprises Fischer-Tropsch derived gas oil .

2. Method according to Claim 1 wherein the lubricant comprises (i) a base oil and (ii) one or more additives.

3. Method according to Claim 2 wherein the base oil comprises mineral oil.

4. Method according to any of Claims 1 to 3 wherein the base oil comprises a Fischer-Tropsch derived paraffinic base oil.

5. Method according to any of Claims 1 to 4 wherein the used lubricant has a Mutagenicity Index of less than 0.5 as measured by the Modified Ames Test Method.

6. Method according to any of Claims 1 to 5 wherein the used lubricant has a Fold Increase of less than 1.8 as measured by the Modified Ames Test Method.

7. A used lubricant obtained from a diesel engine which has been fuelled with a diesel fuel composition

comprising Fischer-Tropsch derived paraffinic gas oil, wherein the used lubricant has a Mutagenicity Index of less than 0.5 as measured by the Modified Ames Test Method.

8. A used lubricant according to Claim 7 wherein the used lubricant has a Fold Increase of less than 1.8 as measured by the Modified Ames Test Method.

9. Use of a diesel fuel composition comprising Fischer- Tropsch derived paraffinic gas oil for reducing the toxicity of a used lubricant obtained from a diesel engine .

10. Use according to Claim 9 wherein the used lubricant comprises a base oil and one or more additives.

11. Use according to Claim 10 wherein the base oil comprises mineral oil.

12. Use according to Claim 10 wherein the base oil comprises Fischer-Tropsch derived paraffinic base oil.