Field of the Invention

The present invention relates to a process for preparing a diesel fuel composition.

Background of the Invention

Gasoils prepared by the Fischer-Tropsch process are well known in the art. An example of a Fischer-Tropsch based process is the SMDS (Shell Middle Distillate

Synthesis) described in "The Shell Middle Distillate Synthesis Process", van der Burgt et al (paper delivered at the 5 ^th 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 gasoils 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 Pearl, Qatar, and its products have been blended with petroleum derived gasoils in

commercially available automotive fuels.

By virtue of the Fischer-Tropsch process, a Fischer- Tropsch derived gasoil has essentially no, or

undetectable levels of, sulphur and nitrogen. Further, the Fischer-Tropsch process as usually operated produces no or virtually no aromatic components. An ongoing challenge however with using GTL gasoil as a component in diesel fuel is that it has a low density, typically around 0.78 g/ml, which means that it tends to lower the density of any final fuel blend.

Moreover, because of this the neat GTL fuel is not compliant with the prevailing diesel specifications, such as EN590 and the like.

Naphthenic blending components may be derived from so-called naphthenic crude sources, for example by hydrotreating gasoil from naphthenic high density crude such as West African (WAF) crudes or by hydrogenation of Light Cycle Oil (LCO) as obtained in a catalytic cracking process .

Light Cycle Oil is a challenging feed for

hydrotreating operations, due to its high aromaticity resulting in demanding operating conditions e.g. high hydrogen consumption, high exothermicity and shortened catalyst life. Indeed, hydroprocessing of 100% LCO feedstock is very challenging to carry out in practice. Although hydroprocessing of undiluted light cycle oil

(LCO) to produce gasoil blending components can be done in principle, because deep LCO saturation is extremely exothermal with a very large resulting adiabatic

temperature increase, it requires a dedicated process or major adaptations to an existing unit and is also difficult to manage from a process safety perspective.

Further, naphthenic blending components produced by the hydrogenation of LCOs may result in poor product quality, for example, low cetane index and high product density which may lie outside those required by certain diesel specifications, such as EN590. Maximum density limits of international diesel qualities are currently set in order to meet diesel car emissions requirements and to achieve optimal engine performance. Density limits are to allow fuel energy flow to be controlled. In the EU, the maximum specification for density and cetane number of diesel fuels in EN590 are 845 kg/m ³ and 51 respectively. The consequence of these fuel

requirements is that middle distillate fuels produced from hydrotreatment of LCO feeds predominantly containing LCO may not be suitable to meet the product quality specification requirements being set for diesel, i.e. too high density and too low cetane number. This will result in "off-spec" diesel fuel compositions if such blending components are used in high levels.

Due to these issues with using LCO feed, in order to generate value from LCO streams produced within the refinery, these are usually co-processed in a limited amount (typically up to 15%) with gasoil streams produced at the refinery, often by using harsh operational conditions, or sent to a low value outlet such as fuel oils .

It has now surpisingly been found by the present inventors that if Fischer-Tropsch derived gasoil is combined with LCO feed to the hydrotreater then this can allow the processing of a higher amount of LCO in refinery operations. At the same time this may limit the severity of processing which is necessary in the

hydrotreating step and may also have a positive impact on the hydrotreatment catalyst life cycle. In addition, it has also surprisingly been found that if Fischer-Tropsch derived gasoil is combined with LCO feed to the

hydrotreater then a gasoil product is obtained which has properties that are highly beneficial for differentiated diesel fuels and which meets the requirements of diesel specifications such as EN590. WO2007/071747 teaches a composition having a density at 15°C of between 820 and 845 kg/m ³ and a cetane number of equal or greater than 40, which composition has been obtained by blending the following components:

(a) a cracked gas oil,

(b) a mineral derived gas oil other than (a) , and

(c) a Fischer-Tropsch derived kerosene fraction.

However, there is no disclosure in WO2007/071747 of the addition of Fischer-Tropsch derived gasoil to an LCO feed to the hydrotreater .

EP1350831 relates to a process for hydroprocessing of hydrocarbon feedstock containing sulfur and/or nitrogen contaminants, said process comprising first contacting the hydrocarbon feedstock with hydrogen in the presence of at least one first group VIII metal on a first acidic support catalyst, and thereafter contacting the feedstock with hydrogen in the presence of at least one second group VIII metal catalyst on a less acidic support. It is taught in EP1350831 that the feedstocks to be treated in the process of the present invention are generally petroleum base feedstocks such as solvents, middle distillates, diesel light cycle oil, lube oil, white oil, products from a GTL plant, and mixtures of these feedstocks. However, there is no specific

disclosure in this document of the co-processing in the hydrotreater of a Fischer-Tropsch derived gasoil with an LCO feed.

Summary of the Invention

According to the present invention there is provided a process for preparing an automotive gasoil fraction comprising the steps of :

(i) blending a Fischer-Tropsch derived gasoil with a diesel light cycle oil to produce a blended feedstock, wherein the Fischer-Tropsch derived gasoil has a density of 0.8 g/cm ³ or less; and

(ii) subjecting the blend produced in step (i) to a hydrotreatment step to produce a hydrotreated gasoil fraction preferably having a density of 0.845 g/cm ³ or less, and a cetane index of 46 or greater.

According to another aspect of the present invention there is provided a process for preparing a diesel fuel composition comprising the steps of:

(i) blending a Fischer-Tropsch derived gasoil with a diesel light cycle oil to produce a blended feedstock, wherein the Fischer-Tropsch derived gasoil has a density of 0.8 g/cm ³ or less;

(ii) subjecting the blend produced in step (i) to a hydrotreatment step to produce a hydrotreated gasoil fraction preferably having a density of 0.845 g/cm ³ or less, and a cetane index of 46 or greater, and.

(iii) mixing the the hydrotreated gasoil fraction produced in step (ii) with a diesel base fuel to form a diesel fuel composition, preferably wherein the diesel fuel composition has a density in the range from 0.820 g/cm ³ to 0.845 g/cm ³ .

It has surprisingly been found that the present invention can allow the processing of a higher amount of LCO in refinery operations. In addition, the process may allow a reduced severity of hydrotreatment processing conditions which are necessary and may also have a positive impact on the catalyst life cycle. In addition, the final gasoil product has properties, such as power and fuel economy benefits, that are highly beneficial for differentiated diesel fuels and which meets the

requirements of diesel specifications such as EN590. Detailed Description of the Invention

In order to assist with the understanding of the invention several terms are defined herein.

The term "diesel light cycle oil" as used herein means the light gasoil fraction of the fluid catalytic cracking (FCC) process of heavy hydrocarbons. FCC processes have been around since the 1940s. Typically, an FCC unit or process includes a riser reactor, a catalyst separator and stripper, and a regenerator. A FCC feedstock is introduced into the riser reactor wherein it is contacted with hot FCC catalyst from the regenerator. The mixture of the feedstock and FCC catalyst passes through the riser reactor and into the catalyst separator wherein the cracked product is separated from the FCC catalyst. The separated cracked product passes from the catalyst separator to a

downstream separation system and the separated catalyst passes to the regenerator where the coke deposited on the FCC catalyst during the cracking reaction is burned off the catalyst to provide a regenerated catalyst. The resulting regenerated catalyst is used as the

aforementioned hot FCC catalyst and is mixed with the FCC feedstock that is introduced into the riser reactor. FCC processes and systems are designed so as to provide for a high conversion of the FCC feedstock to products having boiling temperatures in the gasoline boiling range. As a by-product of the FCC process products boiling in the gasoil boiling range are produced, including light cycle oil (LCO) . These typically have a high density and a low cetane number. The quality of these cracked gasoil products is typically not good enough to be used directly in an automotive gas oil fuel product and is thus typically blended with other refinery streams to meet required specifications directed to higher cetane numbers and lower densities.

The light cycle oil (LCO) used herein typically has a density at 15°C of greater than 0.9 g/cm ³ , more preferably in the range from 0.93 to 0.98 g/cm ³ .

Further, the light cycle oil (LCO) used herein typically has a boiling range from 160°C (Initial Boiling Point) to 390°C (Final Boiling Point), more preferably a boiling range from 170 °C (Initial Boiling Point) to 370 °C (Final Boiling Point) .

In a first step of the process a Fischer-Tropsch derived gasoil is blended with a diesel light cycle oil (LCO) to produce a blended feedstock.

The Fischer-Tropsch gasoil may for example be derived from natural gas, natural gas liquids, petroleum or shale oil, petroleum or shale oil processing residues, coal or biomass.

The amount of Fischer-Tropsch derived gasoil fuel blended with the diesel light cycle oil may be from 10% to 80%v of the overall blended feedstock produced in step

(i) , preferably from 20%v to 70%v, more preferably from 20%v to 60%v, even more preferably from 30%v to 60%v, and especially from 40%v to 60%v, based on the overall blended feedstock produced in step (i) . The presence of a large quantity of GTL gasoil in the blended feedstock formed in step (i) means that the gravimetric energy density will be high which is expected to be beneficial for power and fuel economy.

Such a Fischer-Tropsch derived gasoil is any fraction of the middle distillate fuel range boiling in the gasoil range, which can be isolated from the

(optionally hydrocracked) Fischer-Tropsch synthesis product. Examples of Fischer-Tropsch derived gasoils are described in EP-A-0583836, WO-A-97/14768, WO-A-97/14769, WO-A-00/11116, WO-A-00/11117, WO-A-01/83406, WO-A- 01/83648, WO-A-01/83647, WO-A-01/83641, WO-A-00/20535, WO-A-00/20534, EP-A-1101813, US-A-5766274, US-A-5378348, US-A-5888376 and US-A-6204426.

Suitably, the Fischer-Tropsch derived gasoil will consist of at least 90, more preferably at least 95 wt% iso and normal paraffins. The weight ratio of iso- paraffins to normal paraffins will suitably be greater than 0.3. This ratio may be up to 12. Suitably this ratio is between 2 and 6. The actual value for this ratio will be determined, in part, by the hydroconversion process used to prepare the Fischer-Tropsch derived gasoil from the Fischer-Tropsch synthesis product. Some cycloparaffins may be present.

Suitably the Fischer-Tropsch derived gasoil

comprises less than 1 wt% aromatics. The content of sulphur and nitrogen will be very low and normally below the detection limits for such compounds. For this reason the sulphur content of a diesel fuel composition

containing a Fischer-Tropsch product may be very low.

The Fischer-Tropsch gasoil used in the present invention has a density of 0.8 g/cm ³ or less, preferably from 0.76 to 0.79 g/cm ³ at 15°C. The Fischer-Tropsch gasoil preferably has a viscosity at 40°C of from 2.5 to

4.0 mm ² / s .

The blended feedstock which is produced in step (i) preferably has a density of from 0.850 to 0.860 g/cm ³ .

Preferably in step (i) the Fischer-Tropsch derived gasoil is blended with the diesel light cycle oil in such a ratio that the resulting hydrotreated gasoil fraction coming out of hydrotreatment step (ii) has a density of 0.845 g/cm ³ or less and a cetane index of 46 or greater. Further, it is preferred that the Fischer-Tropsch derived gasoil is blended with the diesel light cycle oil in such a ratio that the kinematic viscosity at 40°C of the resulting hydrotreated gasoil emerging from

hydrotreatment step (ii) is at least 2 mm ² /s, preferably at least 3 mm ² /s and at most 4.5 mm ² /s.

Preferably in step (i) the Fischer-Tropsch gasoil is blended with the diesel light cycle oil in a volume ratio of from 1:10 to 10:1, more preferably in a volume ratio of from 1:5 to 5:1, even more preferably in a volume ratio of 1:2 to 2:1.

In the process of the present invention the diesel light cycle oil is preferably present in the blended feedstock formed in step (i) at a level in the range of from 10 wt % to 80 %v, more preferably from 20 %v to 70

%v, even more preferably from 40 %v to 60 %v. In a preferred embodiment, the diesel light cycle oil is present in the blended feedstock formed in step (i) at a level of 45%v or greater, especially from 45 %v to 55 %v, by volume of the blended feedstock formed in step (i) .

It has been found that the present invention enables higher levels of LCO to be blended than hitherto

expected .

Hydrotreatment Step

The blended feedstock produced in step (i) is subjected to a hydrotreatment step. Suitable

hydrotreatment process conditions and catalysts are well known to those skilled in the art and are not discussed in detail herein. Suitable hydrotreatment conditions and suitable catalysts are disclosed for example in Practical

Advances in Petroleum Processing, by C.S. Hsu ad P.R. Robinson, Berlin: Springer, 2006, section 3.4, pages 28- 34, as well as in US2016/0160139. The hydrotreatment process conditions and catalyst are preferably chosen such that the density of the blended feedstock is reduced by an amount of at least 10 kg/m ³ , preferably at least 20 kg/m ³ .

Preferred catalysts for use in the hydrotreatment step include nickel-molybdenum based and cobalt- molybdenum based hydrotreatment catalysts. A preferred catalyst for use herein is nickel-molybdenum based hydrotreatment catalyst having the tradename DN-3636 commercially available from Criterion.

According to the present invention the

hydrotreatment step (ii) is carried out at a pressure from 30 to 90 barg and a weighted average bed temperature of 380 °C or less. Co-processing of the LCO together with GTL gasoil as per the process of the present invention enables production of a gasoil meeting fuel specification requirements, e.g. the EN590 specification, with a high content of processed LCO, in existing hydrotreaters .

Preferably, the gasoil fraction formed in step (ii) has a density at 15°C in the range of from 0.830 g/cm ³ to 0.845 g/cm ³ , more preferably from 0.835 g/cm ³ to 0.845 g/cm ³ , even more preferably from 0.840 g/cm ³ to 0.845 g/cm ³ . The density of the gasoil fraction emerging from hydrotreatment step (ii) is preferably towards the upper end of the density allowed in the EN590 specification, which will be beneficial (or at least not detrimental compared to the market) for power and fuel economy (FE) .

Preferably, the gasoil fraction emerging from the hydrotreatment step (ii) has a kinematic viscosity at

40°C of at least 2 mm ² /s, more preferably at least 3 mm ² /s, more preferably at least 3.5 mm ² /s and even more preferably at least 4 mm ² /s. Preferably the gasoil fraction emerging from hydrotreatment step (ii) has a cetane number of 51 or higher, more preferably 55 or higher, even more

preferably 60 or higher. A high cetane number for the gasoil fraction emerging from step (ii) is likely to be beneficial for fuel economy.

Preferably the gasoil fraction emerging from hydrotreatment step (ii) has a flashpoint as measured according to ISO 2719 of 55°C or greater, more preferably of 58 °C or greater.

In the process of the present invention the gasoil fraction produced in step (ii) is preferably mixed with a diesel base fuel preferably in a weight ratio of from 1:100 to 100:1, more preferably in a weight ratio of from 10:90 to 30:70, to produce a diesel fuel composition.

The diesel fuel composition prepared according to the process of the present invention preferably has a density in the range from 0.820 g/cm ³ to 0.845 g/cm ³ , more preferably in the range from 0.830 g/cm ³ to 0.845 g/cm ³ , even more preferably in the range from 0.835 g/cm ³ to 0.845 g/cm ³ . The diesel fuel composition prepared according to the process of the present invention preferably has a viscosity at 40°C in the range from 2 mm ² /s to 4.5 mm ² /s, more preferably in the range from 3.5 mm ² /s to 4 mm ² / s .

Suitably, the diesel fuel composition herein has a cetane number of 51 or more, 53 or more, 55 or more, or 60 or more.

In accordance with the present invention, the cetane number of a fuel composition or fuel blend may be determined in any known manner, for instance using the standard test procedure ASTM D613 (ISO 5165, IP 41) which provides a so-called "measured" cetane number obtained under engine running conditions . More preferably the cetane number may be determined using the more recent and accurate "ignition quality test" (IQT; ASTM D6890, IP 498), which provides a "derived" cetane number based on the time delay between injection and combustion of a fuel sample introduced into a constant volume combustion chamber. This relatively rapid technique can be used on laboratory scale (ca 100 ml) samples of a range of different fuels.

Alternatively the cetane number or derived ignition quality of a fuel can be tested using a Combustion

Research Unit (CRU) obtained from Fueltech Solutions AS/Norway. Fuels were injected into a constant volume combustion chamber preconditioned as set conditions.

Alternatively, cetane number may be measured by near infrared spectroscopy (NIR) , as for example described in US5349188. This method may be preferred in a refinery environment as it can be less cumbersome than for instance ASTM D613. NIR measurements make use of a correlation between the measured spectrum and the actual cetane number of a sample. An underlying model is prepared by correlating the known cetane numbers of a variety of fuel samples with their near infrared spectral data .

The engine in which the diesel fuel composition herein is used may be any appropriate engine. Thus, where the fuel is a diesel or biodiesel fuel composition, the engine is a diesel or compression ignition engine. Likewise, any type of diesel engine may be used, such as a turbo charged diesel engine. Similarly, the invention is applicable to an engine in any vehicle.

The diesel fuel used as the base fuel herein and which can be used for blending with gasoil oil fraction produced in step (ii) of the process herein includes diesel fuels for use in automotive compression ignition engines, as well as in other types of engine such as for example off road, marine, railroad and stationary engines. The diesel fuel used as the base fuel in the diesel fuel composition herein may conveniently also be referred to as ^x diesel base fuel' .

The diesel base fuel may itself comprise a mixture of two or more different diesel fuel components, and/or be additivated as described below.

Such diesel fuels will contain one or more base fuels which may typically comprise liquid hydrocarbon middle distillate gasoil (s), for instance petroleum derived gasoils other than the petroleum derived gasoil described hereinabove which is derived from naphthenic high density petroleum crude oil. Such fuels will typically have boiling points within the usual diesel range of 150 to 400°C, depending on grade and use. They will typically have a density from 750 to 1000 kg/m ³ , preferably from 780 to 860 kg/m ³ , at 15°C (e.g. ASTM

D4502 or IP 365) and a cetane number (ASTM D613) of from 35 to 120, more preferably from 40 to 85. They will typically have an initial boiling point in the range 150 to 230°C and a final boiling point in the range 290 to 400°C. Their kinematic viscosity at 40°C (ASTM D445) might suitably be from 1.2 to 4.5 mm^/s.

An example of a petroleum derived gasoil is a

Swedish Class 1 base fuel, which will have a density from

800 to 820 kg/m ³ at 15°C (SS-EN ISO 3675, SS-EN ISO 12185), a T95 of 320°C or less (SS-EN ISO 3405) and a kinematic viscosity at 40°C (SS-EN ISO 3104) from 1.4 to

4.0 mm2/s, as defined by the Swedish national specification ECl .

Other diesel fuel components for use herein include the so-called "biofuels" which derive from biological materials. Examples include fatty acid alkyl esters (FAAE) . Examples of such components can be found in

WO2008/135602.

The diesel base fuel may itself be additivated (additive-containing) or unadditivated (additive-free) . If additivated, e.g. at the refinery, it will contain minor amounts of one or more additives selected for example from anti-static agents, pipeline drag reducers, flow improvers (e.g. ethylene/vinyl acetate copolymers or acrylate/maleic anhydride copolymers), lubricity

additives, antioxidants and wax anti-settling agents, and the like. In the diesel base fuel is unadditivated

(additive-free) , additive components or additive

packages, such as those described herein, may still be added to the diesel fuel composition during or after the process for preparing the diesel fuel compositions. In a preferred embodiment, the process of the present

invention comprises an additional step (iii) of adding an additive package or additive component to the diesel fuel composition .

Detergent-containing diesel fuel additives are known and commercially available. Such additives may be added to diesel fuels at levels intended to reduce, remove, or slow the build-up of engine deposits.

Examples of detergents suitable for use as diesel fuel additives for the present purpose include polyolefin substituted succinimides or succinamides of polyamines, for instance polyisobutylene succinimides or

polyisobutylene amine succinamides. Succinimide

dispersant additives are described for example in GB-A- 960493, EP-A-0147240, EP-A-0482253, EP-A-0613938, EP-A- 0557516 and WO-A-98/42808. Particularly preferred are polyolefin substituted succinimides such as

polyisobutylene succinimides .

Other examples of detergents suitable for use in diesel fuel additives for the present purpose include compounds having at least one hydrophobic hydrocarbon radical having a number-average molecular weight (Mn) of from 85 to 20 000 and at least one polar moiety selected from:

(Al) mono- or polyamino groups having up to 6 nitrogen atoms, of which at least one nitrogen atom has basic properties; and/or

(A9) moieties obtained by Mannich reaction of substituted phenols with aldehydes and mono- or

polyamines .

Other detergents suitable for use in diesel fuel additives for the present purpose include quaternary ammonium salts such as those disclosed in US2012/0102826, US2012/0010112, WO2011/149799, WO2011/110860,

WO2011/095819 and WO2006/135881.

The diesel fuel additive mixture may contain other components in addition to the detergent. Examples are lubricity enhancers; dehazers, e.g. alkoxylated phenol formaldehyde polymers; anti-foaming agents (e.g.

polyether-modified polysiloxanes ) ; ignition improvers (cetane improvers) (e.g. 2-ethylhexyl nitrate (EHN) , cyclohexyl nitrate, di-tert-butyl peroxide, those peroxide compounds disclosed in WO96/03397 and W099/32584 and those ignition improvers disclosed in US-A-4208190 at column 2, line 27 to column 3, line 21); anti-rust agents (e.g. a propane-1, 2-diol semi-ester of tetrapropenyl succinic acid, or polyhydric alcohol esters of a succinic acid derivative, the succinic acid derivative having on at least one of its alpha-carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group containing from 20 to 500 carbon atoms, e.g. the pentaerythritol diester of polyisobutylene-substituted succinic acid) ; corrosion inhibitors; reodorants; anti-wear additives; anti-oxidants (e.g. phenolics such as 2,6-di-tert- butylphenol, or phenylenediamines such as N,N'-di-sec- butyl-p-phenylenediamine ) ; metal deactivators; combustion improvers; static dissipator additives; cold flow improvers; organic sunscreen compounds and/or UV filter compounds, and wax anti-settling agents.

The diesel fuel additive mixture may contain a lubricity enhancer, especially when the diesel fuel composition has a low (e.g. 500 ppmw or less) sulphur content. In the additivated diesel fuel composition, the lubricity enhancer is conveniently present at a

concentration of less than 1000 ppmw, preferably between 50 and 1000 ppmw, more preferably between 70 and 1000 ppmw. Suitable commercially available lubricity

enhancers include ester- and acid-based additives. Other lubricity enhancers are described in the patent

literature, in particular in connection with their use in low sulphur content diesel fuels, for example in:

- the paper by Danping Wei and H.A. 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;

- 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 .

It may also be preferred for the diesel fuel composition to contain an anti-foaming agent, more preferably in combination with an anti-rust agent and/or a corrosion inhibitor and/or a lubricity enhancing additive .

Unless otherwise stated, the (active matter) concentration of each such optional additive component in the additivated diesel fuel composition is preferably up to 10000 ppmw, more preferably in the range from 0.1 to 1000 ppmw, advantageously from 0.1 to 300 ppmw, such as from 0.1 to 150 ppmw.

The (active matter) concentration of any dehazer in the diesel fuel composition will preferably be in the range from 0.1 to 20 ppmw, more preferably from 1 to 15 ppmw, still more preferably from 1 to 10 ppmw, and especially from 1 to 5 ppmw. The (active matter) concentration of any ignition improver (e.g. 2-EHN) present will preferably be 2600 ppmw or less, more preferably 2000 ppmw or less, even more preferably 300 to 1500 ppmw. The (active matter) concentration of any detergent in the diesel fuel composition will preferably be in the range from 5 to 1500 ppmw, more preferably from 10 to 750 ppmw, most preferably from 20 to 500 ppmw.

In the case of a diesel fuel composition, for example, the fuel additive mixture will typically contain a detergent, optionally together with other components as described above, and a diesel fuel-compatible diluent, which may be a mineral oil, a solvent such as those sold by Shell companies under the trade mark "SHELLSOL", a polar solvent such as an ester and, in particular, an alcohol, e.g. hexanol, 2-ethylhexanol, decanol, isotridecanol and alcohol mixtures such as those sold by Shell companies under the trade mark "LINEVOL",

especially LINEVOL 79 alcohol which is a mixture of 0 -9 primary alcohols, or a C12-14 alcohol mixture which is commercially available.

The total content of the additives in the diesel fuel composition may be suitably between 0 and 10000 ppmw and preferably below 5000 ppmw.

In the above, amounts (concentrations, % vol, ppmw, % wt) of components are of active matter, i.e. exclusive of volatile solvents/diluent materials.

The present invention will be further understood from the following examples. Unless otherwise stated, all amounts and concentrations disclosed in the examples are based on volume of the fully formulated diesel fuel composition .

Examples

Experiments were carried out to compare the

properties of a hydrotreated gasoil fraction based on a 50/50 (mass basis) LCO/GTL gasoil feedstock (Example 1) and a hydrotreated gasoil fraction based on a 60:40 (mass basis) LCO/GTL gasoil feedstock (Example 2) with a 100% LCO hydrotreated product (Comparative Example 1) . A further comparision was made with a hydrotreated gasoil fraction based on a 50/50 (mass basis) LCO/petroleum based gasoil feedstock (Comparative Example 2) . Table 1 shows the hydrotreatment conditions and the properties of the final hydrotreatment gasoil fraction. The catalyst used in Example 1 and Comparative Examples 1 and 2 was a nickel-molybdenum based hydrotreatment catalyst having the tradename DN3636, commercially available from

Criterion. The catalyst used in Example 2 was a cobalt- molybdenum based hydrotreatment catalyst. The GTL gasoil had the following properties: Density: 0.778 g/cm ³

Cetane index: 85,2

IBP:175,8 °C

FBP: 346,7 °C

Kinematic Viscosity at 40 °C: 2,713 mm ² /s

The LCO had the following properties:

Density: 0.934 g/cm ³

Cetane index: 27,7

IBP: 194,2 °C

FBP: 369,0 °C

Kinematic Viscosity at 40 °C: 3,283 mm ² /s

The petroleum derived gasoil was a straight run oil (SRFO) having a density of 0.869 g/cm ³ .

The following abbreviations are used in Table 1 below :

W(/L)HSV: Weight ( /liquid) hourly space velocity

¾ gas rate: hydrogen gas rate

WABT : weighted average bed temperature

nm: not measured

Table 1

Discussion

The results of the Example 1 in Table 1 above show that when GTL gasoil is introduced into the LCO

hydrotreatment feed at a 50/50 level of LCO/GTL, a gasoil fraction is obtained having a density (834.6 kg/m ³ ) and cetane index (53) falling with the EN590 specification. This is in contrast to the case where the hydrotreatment feedstock is 100% LCO (Comparative Example 1) . In the case of 100% LCO, the density and cetane index lies outside the EN590 specification. It can also be seen from Comparative Example 2 that in the case of a

hydrotreatent feedstock containing 60/40 LCO/petroleum based gasoil, the density and the cetane index of the final gasoil fraction also lie outside those of the EN590 specification .

Although the density of the gasoil fraction produced in Example 2 (60/40 LCO/GTL gasoil) was slightly above that of the EN590 specification, it is still

significantly reduced compared to the gasoil fractions produced in Comparative Examples 1 and 2 and would still fall within other diesel fuel specifications. For example ASTM D975, used as reference in the United States, does not establish limits on density.