The invention relates to a lubricating oil

composition comprising Fischer-Tropsch derived extra heavy base oil. Furthermore, the present invention relates to the use of said lubricant composition for lubricating an engine, a gear box, and use as a lubricant in general industrial lubricant applications including as a bearing and circulating oil. In addition, the present invention relates to a method to prepare a lubricating oil composition.

As reserves of easily accessible oil become more scarce there has been an increasing trend to look towards other sources of hydrocarbons in order to meet current needs for petrochemical products. It has been known to utilise GTL technology in order to convert natural gas into heavier hydrocarbons, typically via a Fischer

Tropsch synthesis reaction. Natural gas is abundant in a number of locations around the world that are easily accessible and, as a result, it represents a promising starting point for hydrocarbon conversion to desirable petrochemical products.

High viscosity base oils derived from GTL synthesis often show a hazy appearance that is typically due to the presence of a small quantity of microcrystalline wax particles. There has been a desire in the art to assume that such oils are unsuitable for finished lubricant and process oil applications. In general, there is an overwhelming tendency to favour bright and clear oils due to the perception that these are somehow purer and less likely to include contaminants that will affect the performance characteristics of the oil. Indeed, this conventional view is particularly entrenched with regards to oils with a high viscosity and high cloud point. In particular, there has been a tendency to include

additional dewaxing and distillation steps when refining such base oils in order to obtain substantially haze-free base oils. It is only these haze-free clear and bright base oils that have been considered as suitable for use in a wide range of applications including as process oils and also in finished lubricants.

US2009/203835 describes a process to prepare a blend of a mineral derived residual and de-asphalted oil component, the blend as obtainable, a cylinder oil composition comprising said oil blend, and to the use of the oil blend as a process oil for various processes.

WO2010/125144 describes functional fluid

compositions which are useful as hydraulic fluids and shock absorber fluids and which have improved seal swell properties .

WO2010/094681 describes the use of a lubricating oil composition comprising a Fischer-Tropsch derived base oil and one or more additives for particular use in the crankcase of an internal combustion engine, in particular a diesel engines such as a heavy duty diesel engine.

WO-A-2005/063940 describes a process for the preparation of a Fischer-Tropsch wax derived haze free base oil having a kinematic viscosity at 100°C of greater than lOcSt. WO-A-2005/063940 includes additional

processing intended to reduce the wax content of a

Fischer-Tropsch synthesis product that has been subjected to hydroisomerisation and distillation to remove lighter fuel products by undertaking additional

hydroisomerisation and solvent dewaxing steps. WO-A-03033622 describes a process wherein a haze free base oil is prepared from a Fischer-Tropsch product by removing the heaviest fraction, containing the haze precursors, by a deep-cut distillation performed at a cut-off temperature of between 1150 and 1350 °F

(621-732 °C) . This is not only a technically difficult distillation step it also removes valuable heavy base oil molecules in addition to the haze precursors.

A disadvantage of the processes described in the art is that the processing of Fischer-Tropsch synthesis products is extended considerably in order to produce conventional haze-free clear and bright base oils that are regarded as suitable for use, for example, as lubricants. The cost of production of Fischer-Tropsch derived base oils can be relatively high rendering them less suitable for use as extender oils compared to mineral oil equivalents.

It is an object of the present invention to reduce the overall cost and complexity of production of Fischer- Tropsch derived base oils. In particular, it is an object of the invention to reduce the cost of producing

lubricants that comprise Fischer-Tropsch derived base oils .

It has now surprisingly been found according to the present invention that Fischer-Tropsch derived base oils comprising haze components can be used in lubricant oil compositions without the need to first remove the haze components. In particular, it has been found that lubricants comprising Fischer-Tropsch derived base oils that are not clear and bright at ambient temperatures, are not inferior to lubricating oil compositions

comprising bright stock base oils and in some cases will perform better. To this end the present invention provides a lubricating oil composition comprising a Fischer-Tropsch (FT) derived extra heavy base oil, wherein the FT derived extra heavy base oil has a kinematic viscosity at 100°C in the range of from 19 to 35 mm ² /s and wherein the base oil comprises at least 80 wt . % of compounds having at least 30 carbon atoms.

An advantage of the present invention is that the lubricating oil composition according to the present invention has a high viscosity and a low pour point. Also upon use of the lubricating oil composition according to the present invention in general industrial lubricant applications including as a bearing and circulating oil, and in industrial gear oil, and in monograde heavy duty diesel engine oil, the formulation and the oil have better physical properties, such as a lower pour point, than comparable conventional formulations and oils comprising a mineral bright stock.

Furthermore, upon use of the lubricating oil composition according to the present invention in industrial gear oil formulation, bearing and circulating and oil formulation and in monograde heavy duty diesel engine oil formulation, the performance of said

formulations and oil is comparable to the formulations and oil comprising mineral bright stock and in some cases even better.

A first essential component of the invention is the FT extra heavy base oil component. The "FT extra heavy base oil" is a Fischer-Tropsch derived hydrocarbons base oil product comprising saturated paraffin molecules. On account of being an extra heavy paraffinic oil, it is typically prone to the formation of waxy haze. The FT extra heavy base oil may be characterised by one or more of the features described herein below, with no

additional limiting technical meaning being attributed to the label "extra heavy".

The FT extra heavy base oil may typically comprise at least 95 wt% saturated hydrocarbon molecules.

Preferably, the FT extra heavy base oil is prepared from a Fischer-Tropsch wax and comprises more than 98 wt% of saturated hydrocarbons. Preferably, at least 85 wt% of the saturated, paraffinic hydrocarbons are non-cyclic hydrocarbons. Naphthenic compounds (paraffinic cyclic hydrocarbons) are preferably present in an amount of no more than 15 wt%, more preferably less than 10 wt%.

The FT extra heavy base oil suitably contains hydrocarbon molecules having consecutive numbers of carbon atoms, such that it comprises a continuous series of consecutive saturated hydrocarbons having n, n+1, n+2, n+3 and n+4 carbon atoms. This series is a consequence of the Fischer-Tropsch hydrocarbon synthesis reaction from which the extra heavy base oil derives, following isomerisation of the wax feed. The FT extra heavy base oil is typically a liquid at the temperature and pressure conditions of use and typically, although not always, under standard ambient temperature and pressure.

The inventors have found that the extent of waxy haze in FT extra heavy base oils tends to increase with high viscosity, high boiling points, a high proportion of C30+ molecules, a high cloud point, a high pour point, a relatively low degree of isomerisation, derivation of the oil from residual fractions rather than distillates, derivation of the oil from particularly heavy waxy hydrocarbon feeds, and catalytic dewaxing as opposed to solvent dewaxing. The persistence of haze, particularly in the context of dewaxing, may also be linked to these factors. FT extra heavy base oils in which waxy haze formation is pronounced and/or persistent benefit particularly from the invention and are hence preferred as effective but economical components for use in the invention.

The kinematic viscosity at 100 °C according to ASTM D445 (VK 100) of the FT extra heavy base oil may

typically be at least 15 mm ² /s. Preferably, its VK 100 may be at least 17 mm ² /s, more preferably at least 18 mm ² /s, yet more preferably at least 19 mm ² /s, again more preferably at least 20 mm ² /s, and yet again more

preferably at least 21 mm ² /s. In embodiments, the VK100 may be at most 100 mm ² /s, or even at most 80 mm ² /s or at most 50 mm ² /s, or even at most 35 mm ² /s.

Preferably, the kinematic viscosity at 100 °C according to ASTM D445 (VK 100) of the FT extra heavy base oil is in the range of from 20 to 25 mm ² /s.

The kinematic viscosity at 40 °C according to ASTM D445 (VK 40) of the FT extra heavy base oil may

optionally be in the range of from 20 mm ² /s to 300 mm ² /s, preferably in the range of from 100 mm ² /s to 250 mm ² /s.

The viscosity index of the FT extra heavy base oil is preferably greater than 140, more preferably greater than 150, and preferably below 170.

The FT extra heavy base oil may have a lower boiling point (T5 or 5% off) of at least 420°C. More preferably, its lower boiling point (T5 or 5% off) may be at least 450°C, yet more preferably at least 470°C. An upper boiling point (T80 or 80% off) of the FT extra heavy base oil may be at least 600°C. More preferably, its upper boiling point (T80) may be at least 620 °C, yet more preferably at least 640 °C. The lower and upper boiling point values referred to herein are nominal and refer to the T5 and T80 boiling temperatures obtained by gas chromatograph simulated distillation (GCD) according to ASTM D-7169.

Any boiling range distributions of samples are measured herein according to ASTM D-7169. Since Fischer-

Tropsch derived hydrocarbons comprise a mixture of varying molecular weight components having a wide boiling range, this disclosure refers to recovery points of boiling ranges. For example, a 10 wt% recovery point refers to that temperature at which 10 wt% of the hydrocarbons present within that cut will vaporise at atmospheric pressure, and could thus be recovered.

Similarly, a 90 wt% recovery point refers to the

temperature at which 90 wt% of the hydrocarbons present will vaporise at atmospheric pressure. Unless otherwise specified, when referring to a boiling range

distribution, the boiling range between the 10 wt% and 90 wt% recovery boiling points is referred to in this specification .

The FT extra heavy base oil may preferably contain at least 95 wt% C30+ hydrocarbon molecules. More preferably, the FT extra heavy base oil may contain at least 75 wt% of C35+ hydrocarbon molecules.

"Cloud point" refers to the temperature at which a sample begins to develop a haze, as determined according to ASTM D-5773. The FT extra heavy base oil may have a cloud point in the range of from +60°C to +5°C.

Preferably, the FT extra heavy base oil has a cloud point in the range of from +50°C and -20°C, more preferably in the range of from +30°C and 0°C, more preferably in the range of from +20°C and +10°C and most preferably in the range of from +16°C and +10°C.

"Pour point" refers to the temperature at which a sample will begin to flow under carefully controlled conditions. The pour points were determined according to ASTM D97. The FT extra heavy base oil may have a pour point as measured with ASTM D97 in the range of from 0 to -60°C, preferably in the range of from -10 to -50°C, more preferably in the range of from -15 to -45°C, and most preferably in the range of from -24 to -39°C.

The pour points of FT extra heavy base oil were also determined according to ASTM D5950. The FT extra heavy base oil may have a pour point according to ASTM D5950 in the range of from -9 to -60°C, preferably in the range of from -21 to -60°C, more preferably in the range of from - 30 to -55°C, more preferably in the range of from -40 to -54°C, and most preferably in the range of from -45 to - 54°C.

It may thus be a base oil of the type which has been subjected to relatively severe (i.e. high temperature catalytic) dewaxing, such as can result in a pour point of -30°C or below, for example from -45 to -54 °C. Such base oils may still comprise residual waxy haze and accordingly benefit from the invention. Alternatively, the FT extra heavy base oil may have been subjected to relatively mild dewaxing to result in a pour point higher than -30°C, e.g. at least -15°C, such as in the range of from -12°C to 0°C.

The FT extra heavy base oil can further be

characterised by its content of different carbon species. More particularly, the FT extra heavy base oil can be characterised by the percentage of its epsilon methylene carbon atoms, i.e. the percentage of recurring methylene carbons which are four or more carbons removed from the nearest end group and also from the nearest branch

(further referred to as CH2>4) as compared to the percentage of its isopropyl carbon atoms. Epsilon carbon content is a useful metric in quantifying the amount of linear paraffin functionality in a base oil, thus it is necessary to measure epsilon carbon content of base oils to accurately define their chemical composition and characteristics at the molecular level. In the following text, the ratio of the percentage of epsilon methylene carbon atoms to the percentage of isopropyl carbon atoms (i.e. carbon atoms in isopropyl branches), as measured for the base oil as a whole, is referred to as the epsilon: isopropyl ratio. It has been found that isomerised FT residual base oils as disclosed in US-A- 7053254 differ from Fischer-Tropsch derived paraffinic base oil components obtained at a higher dewaxing severity in that the latter compounds have an epsilon: isopropyl ratio of 8.2 or below. FT extra heavy base oils of both these types are of use in the invention. Mildly dewaxed extra heavy base oils having an isopropyl ratio of above 8.2 may often comprise more pronounced waxy haze. However, it has been found that severely dewaxed extra heavy base oils having an epsilon:

isopropyl ratio of 8.2 or below may also suffer from persistent haze and hence surprisingly benefit from the invention .

Preferably, the FT extra heavy base oil has epsilon carbon atoms according to ¹³ C-NMR in the range of from 0 to 40%, more preferably in the range of from 5 to 30 %, more preferably in the range of 10 to 25% based as a percentage of the total number of carbon atoms in the base oil.

Preferably, the FT extra heavy base oil has methyl carbon atoms according to ¹³ C-NMR in the range of from 0 to 40%, more preferably in the range of from 5 to 35 %, more preferably in the range of 20 to 30% based as a percentage of the total number of carbon atoms in the base oil.

Branching in the FT extra heavy base oil may also be expressed as an average degree of branching. Such an average degree of branching of the FT extra heavy base oil may in some embodiments be in the range of from 6.5 to about 10 alkyl branches per 100 carbon atoms, as disclosed in US 7,053,254. In other embodiments, the average degree of branching in the molecules may be above

10 alkyl branches per 100 carbon atoms, as determined in line with the method disclosed in US-A-7053254.

The branching properties as well as the carbon composition of a Fischer-Tropsch derived base oil blending component can conveniently be determined by analysing a sample of the oil using ¹³ C-NMR, ¹ H-NMR, vapour pressure osmometry (VPO) and field ionisation mass spectrometry (FIMS), as described in US 8,152,869.

Preferably, the carbon composition of a FT derived base oil is determined by analysis a sample of the oil using

¹ H-NMR or ¹³ C-NMR.

The FT extra heavy base oil may typically have a viscosity index (ASTM D-2270) of between 120 and 180. It will preferably contain no or very little sulphur and nitrogen containing compounds. This is typical for a product derived from a Fischer-Tropsch reaction, which uses synthesis gas containing almost no heteroatom impurities . Preferably, the FT extra heavy base oil comprises sulphur, nitrogen and metals in the form of hydrocarbon compounds containing them, in amounts of less than 50 ppmw (parts per million by weight), more

preferably less than 20 ppmw, yet more preferably less than 10 ppmw. Most preferably, it will comprise sulphur and nitrogen at levels generally below the detection limits, which are currently 5 ppmw for sulphur and 1 ppmw for nitrogen, when using, for instance, X-ray or ^x Antek' Nitrogen tests for determination.

The FT extra heavy base oil is preferably a FT residual base oil, i.e. obtained from a residual or high vacuum bottoms fraction from the hydrocarbons produced during a Fischer-Tropsch synthesis reaction.

More preferably, this fraction is a distillation residue comprising the highest molecular weight compounds still present in the product after a

hydrocracking/hydroisomerisation step. The 10 wt% recovery boiling point of said fraction is preferably above 370°C, more preferably above 400°C and most preferably above 480°C for certain embodiments of the present invention.

The density of the FT extra heavy base oil

component, as measured by the standard test method ASTM D4052, is suitably from about 700 to 1100 kg/m ³ ,

preferably from about 800 to 950 and most preferably from about 835 to 838 kg/m ³ .

In its broadest sense, the present invention embraces the use of a paraffinic heavy base oil component having one or more of the above described properties, whether or not the component is Fischer-Tropsch derived.

The FT extra heavy base oil component may contain a mixture of two or more FT extra heavy base oils.

In order to prepare a FT extra heavy base oil for use in the present invention, a Fischer-Tropsch derived residual fraction or bottoms product is suitably

subjected to a hydroisomerisation process. This converts n- to iso-paraffins, thus increasing the degree of branching in the hydrocarbon molecules and improving cold flow properties. Depending on the catalysts and

hydroisomerisation conditions used, it can result in long chain hydrocarbon molecules having relatively highly branched end regions. Such molecules tend to exhibit relatively good cold flow performance. However, even after the hydroisomerisation or dewaxing step, a FT residual extra heavy base oil will still have a residual wax haze due to the extremely high molecular weight molecules which the dewaxing process cannot completely remove . The hydroisomerised bottoms product may undergo further downstream processes, for example hydrotreating and/or hydrofinishing .

In general, a FT extra heavy base oil for use in the present invention may be prepared by any suitable

Fischer-Tropsch process. Preferably, however, the FT extra heavy base oil component is a heavy bottom fraction obtained from a Fischer-Tropsch derived wax or waxy raffinate feed by: a) hydrocracking/hydroisomerising a Fischer-Tropsch derived wax, wherein at least 20 wt% of compounds in the Fischer-Tropsch derived feed have at least 30 carbon atoms, b) separating the product of step (a) into one or more distillate fraction (s) and a residual heavy fraction, preferably comprising at least 10 wt% of compounds boiling above 540°C;

(c) subjecting the residual fraction to a catalytic hydroisomerisation or pour point reducing step; and

(d) isolating from the effluent of step (c) , preferably as a residual heavy fraction, the Fischer-Tropsch derived paraffinic heavy base oil component.

In addition to hydrocracking/hydroisomerisation, hydroisomerisation and fractionation, the Fischer-Tropsch derived product fractions may undergo various other operations, such as hydrotreating and/or hydrofinishing . The feed from step (a) is a Fischer-Tropsch derived product. The initial boiling point of the Fischer- Tropsch product may be up to 400°C. Preferably, any compounds having 4 or fewer carbon atoms and any

compounds having a boiling point in that range are separated from a Fischer-Tropsch synthesis product before the Fischer-Tropsch synthesis product is used in said hydrocracking/hydroisomerisation step .

An example of a suitable Fischer-Tropsch process is described in WO-A-99/34917 and in AU-A-698391. The disclosed processes yield a Fischer-Tropsch product as described above. The Fischer-Tropsch product can be obtained by well-known processes, for example the so- called Sasol process, the Shell Middle Distillate

Synthesis process or the ExxonMobil "AGC-21" process.

These and other processes are for example described in more detail in EP-A-0776959, EP-A-0668342, US-A-4943672, US-A-5059299, WO-A-99/34917 and WO-A-99/20720. The

Fischer-Tropsch process will generally comprise a

Fischer-Tropsch synthesis and a

hydrocracking/hydroisomerisation step, as described in these publications. The Fischer-Tropsch synthesis can be performed on synthesis gas prepared from any sort of hydrocarbonaceous material such as coal, natural gas or biological matter such as wood or hay.

The Fischer-Tropsch product directly obtained from a Fischer-Tropsch process contains a waxy fraction that is normally a solid at room temperature.

The feed to the hydrocracking/hydroisomerisation step (a) is preferably a Fischer-Tropsch product which has at least 30 wt%, preferably at least 50 wt%, and more preferably at least 55 wt% of compounds having at least 30 carbon atoms. Furthermore the weight ratio, in this feed, of compounds having at least 60 carbon atoms to those having at least 30 but fewer than 60 carbon atoms is preferably at least 0.2, more preferably at least 0.4 and most preferably at least 0.55. If the feed has a 10 wt% recovery boiling point of above 500°C, the wax content will suitably be greater than 50 wt%.

Preferably, the Fischer-Tropsch product comprises a C20+ fraction having an ASF-alpha value (Anderson-Schulz- Flory chain growth factor) of at least 0.925, preferably at least 0.935, more preferably at least 0.945, even more preferably at least 0.955.

The hydrocracking/hydroisomerisation reaction of step (a) is preferably performed in the presence of hydrogen and a catalyst, which catalyst can be chosen from those known to one skilled in the art as being suitable for this reaction. Catalysts for use in the hydroisomerisation typically comprise an acidic

functionality and a hydrogenation-dehydrogenation functionality. Preferred acidic functionalities are refractory metal oxide carriers. Suitable carrier materials include silica, alumina, silica-alumina, zirconia, titania and mixtures thereof. Preferred carrier materials for inclusion in the catalyst are silica, alumina and silica-alumina. A particularly preferred catalyst comprises platinum supported on a silica-alumina carrier. Preferably, the catalyst does not contain a halogen compound, such as for example fluorine, because the use of such catalysts can require special operating conditions and can involve

environmental problems . Examples of suitable

hydrocracking/hydroisomerisation processes and catalysts are described in WO-A-00/14179, EP-A-0532118, EP-A- 0666894 and EP-A-0776959. Preferred hydrogenation-dehydrogenation

functionalities are Group VIII metals, for example cobalt, nickel, palladium and platinum, more preferably platinum. In the case of platinum and palladium, the catalyst may comprise the hydrogenation-dehydrogenation active component in an amount of from 0,005 to 5 parts by weight, preferably from 0.02 to 2 parts by weight, per 100 parts by weight of carrier material. In the case that nickel is used, a higher content will typically be present, and optionally the nickel is used in combination with copper. A particularly preferred catalyst for use in the hydroconversion stage comprises platinum in an amount in the range of from 0.05 to 2 parts by weight, more preferably from 0.1 to 1 parts by weight, per 100 parts by weight of carrier material. The catalyst may also comprise a binder to enhance the strength of the catalyst. The binder can be non-acidic. Examples are clays and other binders known to one skilled in the art.

In the hydrocracking/hydroisomerisation the feed is contacted with hydrogen in the presence of the catalyst at elevated temperature and pressure. The temperatures typically will be in the range of from 175 to 380°C, preferably higher than 250°C and more preferably from 300 to 370 °C. The pressure will typically be in the range of from 10 to 250 bar and preferably from 20 to 80 bar.

Hydrogen may be supplied at a gas hourly space velocity of from 100 to 10000 Nl/l/hr, preferably from 500 to 5000 Nl/l/hr. The hydrocarbon feed may be provided at a weight hourly space velocity of from 0.1 to 5 kg/l/hr, preferably higher than 0.5 kg/l/hr and more preferably lower than 2 kg/l/hr. The ratio of the hydrogen to the hydrocarbon feed may range from 100 to 5000 Nl/kg and is preferably from 250 to 2500 Nl/kg. The conversion in the

hydrocracking/hydroisomerisation, defined as the weight percentage of the feed boiling above 370°C which reacts per pass to a fraction boiling below 370°C, is suitably at least 20 wt%, preferably at least 25 wt%, but

preferably not more than 80 wt%, more preferably not more than 70 wt%. The feed as used above in the definition is the total hydrocarbon feed fed to the hydroisomerisation step, thus also any optional recycle to step (a) .

The resulting product of the

hydrocracking/hydroisomerisation process preferably contains at least 50 wt% of iso-paraffins, more

preferably at least 60 wt%, yet more preferably at least 70 wt%, the remainder being composed of n-paraffins naphthenic and aromatic compounds.

In step (b) , the product of step (a) is separated into one or more distillate fraction (s) and a residual heavy fraction, preferably comprising at least 10 wt% of compounds boiling above 540°C. This is conveniently done by performing one or more distillate separations on the effluent of the hydroisomerisation step to obtain at least one middle distillate fuel fraction and a residual fraction which is to be used in step (c) .

Preferably, the effluent from step (a) is first subjected to an atmospheric distillation. The 10 wt% recovery boiling point of the residue may preferably vary between 350 and 550°C. This atmospheric bottom product or residue preferably boils for at least 95 wt% above 370°C. The residue as obtained in such a distillation may in certain preferred embodiments be subjected to a further distillation performed at near vacuum conditions to arrive at a fraction having a higher 10 wt% recovery boiling point . This fraction may be directly used in step (c) or may be subjected to an additional vacuum distillation suitably performed at a pressure of between 0.001 and 0.1 bar. The feed for step (c) is preferably obtained as the bottom product of such a vacuum distillation.

In step (c) , the heavy residual fraction obtained in step (b) is subjected to a catalytic pour point reducing step. Step (c) may be performed using any hydroconversion process, which is capable of reducing the wax content to below 50 wt% of its original value. The wax content in the intermediate product is preferably below 35 wt% and more preferably between 5 and 35 wt%, and even more preferably between 10 and 35 wt%. The product as obtained in step (c) preferably has a congealing point of below 80°C. Preferably, more than 50 wt% and more preferably more than 70 wt% of the intermediate product boils above the 10 wt% recovery point of the wax feed used in step (a) .

Wax contents may be measured according to the following procedure: 1 weight part of the oil fraction under analysis is diluted with 4 parts of a (50/50 vol/vol) mixture of methyl ethyl ketone and toluene, which is subsequently cooled to -20°C in a refrigerator. The mixture is subsequently filtered at -20°C. The wax is thoroughly washed with cold solvent, removed from the filter, dried and weighed. Where reference is made to oil content, a wt% value is meant which is 100 wt% minus the wax content in wt%.

A possible process for step (c) is the

hydrocracking/hydroisomerisation process as described above for step (a) . It has been found that wax levels may be reduced to the desired level using such catalysts. By varying the severity of the process conditions as described above, a skilled person will easily determine the required operating conditions to arrive at the desired wax conversion. However a temperature of between 300 and 330°C and a weight hourly space velocity of between 0.1 and 5, more preferably between 0.1 and 3, kg of oil per litre of catalyst per hour (kg/l/hr) are especially preferred for optimising the oil yield. A more preferred class of catalyst, which may be applied in step (c) , is the class of dewaxing catalysts. The process conditions applied when using such catalysts should be such that a wax content remains in the oil. In contrast typical catalytic dewaxing processes aim at reducing the wax content to almost zero. Using a dewaxing catalyst comprising a molecular sieve will result in more of the heavy molecules being retained in the dewaxed oil. A more viscous base oil can then be obtained .

The dewaxing catalyst which may be applied in step (c) suitably comprises a molecular sieve, optionally in combination with a metal having a hydrogenation function, such as the Group VIII metals. Molecular sieves, and more suitably molecular sieves having a pore diameter of between 0.35 and 0.8 nm, have shown a good catalytic ability to reduce the wax content of the wax feed.

Suitable zeolites are mordenite, beta, ZSM-5, ZSM-12,

ZSM-22, ZSM-23, SSZ-32, ZSM-35, ZSM-48, EU-2 and

combinations of said zeolites, of which ZSM-12, ZSM-48 and EU-2 are most preferred.

In the present invention, the reference to ZSM-48 and EU-2 is used to indicate that all zeolites can be used that belong to the ZSM-48 family of disordered structures also referred to as the *MRE family and described in the Catalog of Disorder in Zeolite Frameworks published in 2000 on behalf of the Structure Commission of the International Zeolite Assocation. Even if EU-2 would be considered to be different from ZSM-48, both ZSM-48 and EU-2 can be used in the present

invention. Zeolites ZBM-30 and EU-11 resemble ZSM-48 closely and also are considered to be members of the zeolites whose structure belongs to the ZSM-48 family. In the present application, any reference to ZSM-48 zeolite also is a reference to ZBM-30 and EU-11 zeolite. Besides ZSM-48 and/or EU-2 zeolite, further zeolites can be present in the catalyst composition especially if it is desired to modify its catalytic properties. It has been found that it can be advantageous to have present zeolite ZSM-12 which zeolite has been defined in the Database of Zeolite Structures published in 2007/2008 on behalf of the Structure Commission of the International Zeolite Assocation.

Another preferred group of molecular sieves are the silica-aluminaphosphate (SAPO) materials of which SAPO-I1 is most preferred as for example described in US-A-

4859311. ZSM-5 may optionally be used in its HZSM-5 form in the absence of any Group VIII metal. The other molecular sieves are preferably used in combination with an added Group VIII metal. Suitable Group VIII metals are nickel, cobalt, platinum and palladium. Examples of possible combinations are Pt/ZSM- 35, Ni/ZSM-5, Pt/ZSM- 23, Pd/ZSM-23, Pt/ZSM-48, Pt/ZSM-12 and Pt/SAPO" 11, or stacked configurations of Pt/zeolite beta and Pt/ZSM-23, Pt/zeolite beta and Pt/ZSM-48 or Pt/zeolite beta and Pt/ZSM-22. Further details and examples of suitable molecular sieves and dewaxing conditions are for example described in WO-A-97/18278, US-A-4343692, US-A-5053373, US-A-5252527, US-A-2004/0065581, US-A-4574043, EP-A- 1029029 and WO2004/007647. Another preferred class of molecular sieves comprises those having a relatively low isomerisation selectivity and a high wax conversion selectivity, like ZSM-12.

The dewaxing catalyst suitably also comprises a binder. The binder can be a synthetic or naturally occurring (inorganic) substance, for example clay, silica and/or a metal oxide. Natural occurring clays are for example of the montmorillonite and kaolin families . The binder is preferably a porous binder material, for example a refractory oxide of which examples include alumina, silica-alumina, silica-magnesia, silica- zirconia, silica-thoria, silica-beryllia and silica- titania as well as ternary compositions, for example silica-alumina-thoria, silica-alumina-zirconia, silica- alumina-magnesia and silica-magnesia-zirconia . More preferably, a low acidity refractory oxide binder material, which is essentially free of alumina, is used. Examples of these binder materials are silica, zirconia, titanium dioxide, germanium dioxide, boria and mixtures of two or more of these, of which examples are listed above. The first preferred binder is silica. The second preferred binder is titania.

A preferred class of dewaxing catalysts comprises zeolite crystallites as described above and a low acidity refractory oxide binder material which is essentially free of alumina as described above, wherein the surface of the aluminosilicate zeolite crystallites has been modified by subjecting the aluminosilicate zeolite crystallites to a surface dealumination treatment. A preferred dealumination treatment involves contacting an extrudate of the binder and the zeolite with an aqueous solution of a fluorosilicate salt as described in for example US-A-5157191 or WO-A-00/29511. An example of suitable dewaxing catalysts as described above is silica bound and dealuminated Pt/ZSM- 12 as for example

described in WO2004/007647.

The conditions in step (c) when using a dewaxing catalyst typically involve operating temperatures in the range of from 200 to 500°C, suitably from 250 to 400°C. Preferably the temperature is between 320 and 330°C. The hydrogen pressures may range from 10 to 200 bar,

preferably from 30 to 70 bar. Weight hourly space velocities (WHSV) may range from 0.1 to 10 kg of oil per litre of catalyst per hour (kg/l/hr), suitably from 0.1 to 5 kg/l/hr, more suitably from 0.5 to 1.0 kg/l/hr.

Hydrogen to oil ratios may range from 100 to 2000 litres of hydrogen per litre of oil.

In step (d) , the product of step (c) is usually sent to a vacuum column where various distillate base oil cuts are collected. These distillate base oil fractions may be used to prepare lubricating base oil blends, or they may be cracked into lower boiling products, such as diesel or naphtha. The residual material collected from the vacuum column comprises a mixture of high boiling hydrocarbons, and can be used to prepare FT extra heavy base oil for use in the present invention.

Furthermore, the product obtained in step (c) may also be further treated, for example in a clay treating process or by contacting with active carbon, as for example described in US-A-4795546 and EP-A-0712922, in order to remove unwanted components. Other suitable processes for the production of heavy and extra heavy

Fischer-Tropsch derived base oils are described in WO-A- 2004/033607, US-A-7053254 , EP-A-1366134, EP-A-1382639, EP-A-1516038 , EP-A-1534801, WO-A-2004 /003113 and WO-A- 2005/063941.

The FT extra heavy base oil is defined and described herein as an added component. It may optionally represent the sole source of FT extra heavy base oil in the lubricating oil composition but this is not essential.

Thus other FT extra heavy base oil may be present in the lubricating oil composition and amounts of FT extra heavy base oil indicated herein must be interpreted

accordingly, unless context requires otherwise.

The FT extra heavy base oil may consist of or be synonymous with, any of the FT extra heavy base oils described or defined herein, or any combination thereof.

The FT extra heavy base oil may be prone to the formation of haze in the sense that the appearance of the FT extra heavy base oil is hazy as determined by ASTM

D4176. In addition, the appearance of the FT extra heavy base oil is hazy as determined by visual inspection at a temperature in a range of from -40 to 40°C, preferably in a range of from 10 to 40°C. Further, the FT extra base oil may have a measurable turbidity of at least 0.5 NTU

(nephilometric turbidity units), preferably at least 1 NTU, more preferably at least 2 NTU, even more preferably at least 3 NTU and most preferably at least 4 NTU.

Turbidity may be measured at 25°C according to the method described in US2011/0083995. The FT exta heavy base oil may be cloudy.

Preferably, the lubricating oil composition

according to the present invention also comprises a mineral bright stock.

The preparation of the mineral bright stock as used in the lubricating oil composition according to the present invention has been described in WO2007/003623.

Preferably, the kinematic viscosity at 100 °C according to ASTM D445 (VK 100) of the mineral bright stock is in the range of from 20 to 40 mm ² /s, preferably 25 and 35 mm ² /s, more preferably in the range of from 30 to 32 mm ² /s .

The kinematic viscosity at 40 °C according to ASTM

D445 (VK 40) of the mineral bright stock may optionally be in the range of from 20 mm ² /s to 500 mm ² /s, preferably in the range of from 400 mm ² /s to 495 mm ² /s.

The viscosity index of the mineral bright stock is preferably greater than 50, more preferably greater than

70, and preferably below 100.

The mineral bright stock may have a pour point in the range of from -5 to -20°C, preferably in the range of from -9 to -15°C.

Preferably, the FT extra heavy base oil has a cloud point in the range of from +20°C and - 20°C, more preferably in the range of from +10°C and -10°C, more preferably in the range of from 0°C and -8°C.

The amount of FT extra heavy base oil may be adjusted to achieve a desired waxy haze reduction and adjust viscometric properties. Effective amounts of FT extra heavy base oil will depend to an extent on the nature of the FT extra heavy base oil, as well as the nature of the mineral bright stock with which it is combined.

In embodiments of the invention, the amount of FT extra heavy base oil is in the range of from 5 to 50 wt%, preferably 10 to 40 wt%, more preferably 10 to 30 wt% based on the total weight of FT extra heavy base oil and mineral bright stock.

The amount of mineral bright stock may be adjusted to achieve a desired waxy haze reduction. Effective amounts of mineral bright stock will depend to an extent on the nature of the bright stock, as well as the nature of the FT residual oil with which it is combined.

In embodiments of the invention, the amount of mineral bright stock is in the range of from 50 to 95 wt%, preferably 60 to 90 wt%, more preferably 65 to 85 wt%, especially 70 to 90 wt%, based on the total weight of FT extra heavy base oil and mineral bright stock.

The lubricating oil composition has a less hazy appearance than the FT extra heavy base oil used to formulate it. Advantageously, the appearance of the lubricating oil composition is clear and bright, as determined by visual inspection or ASTM D4176. It may preferably have a turbidity of at most 2 NTU, preferably at most 1 NTU, more preferably at most 0.5 NTU, even more preferably at most 0.2 NTU and ideally of 0 NTU, as measured according to the method of US2011/0083995 at 25° C. Advantageously the lubricating oil composition may conform with one or more of the above haziness

measurements at least 14 days after blending.

The kinematic viscosity at 100 °C according to ASTM

D445 (VK 100) of the lubricating oil composition may preferably be in the range of from 1 mm ² /s to 30 mm ² /s, preferably in the range of from 2 mm ² /s to 28 mm ² /s, more preferably in the range of from 3 mm ² /s to 25 mm ² /s, most preferably in the range of from 4 mm ² /s to 18 mm ² /s, e.g.

7 to 12 mm ² /s or 14 to 17 mm ² /s.

The kinematic viscosity at 40 °C according to ASTM D445 (VK 40) of the lubricating oil composition may preferably be in the range of from 200 mm ² /s to 400 mm ² /s, preferably in the range of from 250 mm ² /s to 360 mm ² /s, more preferably in the range of from 300 to 350 mm ² /s .

The lubricating oil composition may have a viscosity index (ASTM D-2270) in the range of from 95 to 120, preferably from 95 to 110.

The pour point of the lubricating oil composition (ASTM D-5950) may be -5°C or lower, preferably of -10°C or lower, more preferably -15°C or lower, and most preferably -20°C or lower.

The FT extra heavy base oil and the mineral bright stock may make up the entirety of the lubricating oil composition, or preferably at least 75 wt.%, or at least 80 wt.%, or at least 90 wt.%, or at least 95wt% or at least 98wt%, or at least 99wt% or at least 99.5wt% or at least 99.99wt% of the total composition.

The lubricating oil composition according to the present invention may further comprise one or more additives such as anti-oxidants, anti-wear additives,

(preferably ashless) dispersants, detergents, extreme- pressure additives, friction modifiers, metal

deactivators, corrosion inhibitors, demulsifiers, anti- foam agents, seal compatibility agents and additive diluent base oils, etc. Such additives will typically be present in low quantities.

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.

The lubricating oil composition may be used as a lubricant blendstock, or in any suitable lubricating application. It may be of particular benefit as a base oil blend component where a relatively high kinematic viscosity at 100°C or 40°C is required such as in monograde heavy duty diesel engine oils (SAE 40 monogrades, for example) or industrial lubricants where current low sulphur base oils such as API Group II or Group III are sometimes borderline in VK100 and hence have problems meeting SAE J-300 viscometric

specifications for monogrades.

In a further aspect the present invention provides a method for making a lubricating oil composition by blending a FT derived extra heavy base oil, a mineral bright stock and lubricant performance additives, wherein the base oil has not been subjected to a process for the removal of haze components.

The lubricating oil composition may be formed by simple blending of its components as is known in the art. One preferred method of the invention comprises: blending a FT extra heavy base oil having a hazy appearance as determined by visual inspection or ASTM D4176 with an amount of a mineral bright stock to provide a lubricating oil composition that has an appearance which is 'clear and bright ' as determined by visual inspection or ASTM D4176 and/or has any of the other properties defined hereinabove .

The invention also embraces use of the mineral bright stock for the purpose of reducing waxy haze in a FT extra heavy base oil, or in a precursor composition comprising the FT extra heavy base oil. This use may embrace supplying or offering a lubricating oil

composition comprising FT extra heavy base oil and mineral bright stock together with information or advertising relating to a clear and bright appearance or an appearance of absent or low turbidity.

In another aspect, the present invention provides the use of the lubricating oil composition for

lubricating an engine, an industrial gear box and use as a lubricant in general industrial lubricant applications including as a bearing and circulating oil .

As the person skilled in the art is familiar with the use of lubricating oil compositions comprising a FT base oil and a mineral bright stock for lubricating an engine and a gear box, these are not further discussed here in detail. Specific examples of such use is described in WO 2007/003623, WO 2008/006877 and

WO2007/063125.

Another preferred application is the use of the lubricating oil composition according to the present invention as a lubricant in bearings and circulating oil applications. Bearing and circulating oils are used in a range of industrial systems from fairly heavy load applications such as steel making, where they are an essential lubricant for steel mill operation, to low load, high-speed applications such as textiles and other light manufacturing processes.

Bearing and circulating oils are generally the lubricant of choice in a centralized lubrication system.

In this type of lubrication system, the oil is fed back through the return line into an oil reservoir for reuse (after passing through various points in the system requiring lubrication) . In addition to providing

lubrication, circulating oil lubrication systems perform a range of other functions, including stabilizing the temperature of the various lubrication points, removing and/or filtering out solid contamination or wear

particles from points of contact, preventing rust and corrosion damage, and removing or reducing the effects of water. An effective bearing and circulating oil must be able to handle the challenging conditions just mentioned as well as potentially lubricate many different types of parts, such as bearings, gear sets, and pumps - all often lubricated by one centralized lubrication system. Like gear oils, most bearing and circulation system

applications are lubricated by products that are of ISO 100 viscosity grade and higher.

The invention will now be further illustrated by the following non-limiting examples.

Example

Extra heavy base oil (XHBO) samples 1-6 were produced via Fischer-Tropsch synthesis of n-paraffins followed by hydrocracking/hydroisomerisation, removal of light ends, middle and heavy distillate fractions via a combination of atmospheric and high vacuum distillation, catalytic dewaxing, and finally a second distillation step to remove further light ends. The XHBO samples were obtained using a Fischer-Tropsch process. To this end, total liquid product (C5-75O °C ⁺ fraction) of the Fischer- Tropsch process, as obtained in Example VII using the catalyst of Example III of WO-A-9934917, was continuously fed to a hydrocracking step (a) . The feed contained about

60 wt% C30+ product. The ratio Cgo ⁺ C30+ ^was about 0.55. In the hydrocracking step the fraction was contacted with a hydrocracking catalyst of Example 1 of EP-A-532118. The effluent of step (a) was continuously distilled to give a middle distillate fuel fraction and an atmospheric residue fraction. The atmospheric residue fraction was continuously distilled under vacuum to give a gas oil fraction, a heavy distillates fraction and a residual fraction. 60% of the residual fraction was recycled to step (a) and the remaining part was sent to a catalytic dewaxing step (d) . The conditions in the

hydrocracking/hydroisomerisation step (a) were: a fresh feed Weight Hourly Space Velocity (WHSV) of 0.6 kg/l.h, recycle feed WHSV of 0.17 kg/l.h, hydrogen gas rate = 750 Nl/kg, total pressure = 77 bar, and a reactor temperature of 334 °C.

In the dewaxing step, the residual fraction was contacted with a dealuminated silica bound ZSM-12 catalyst as described in Example 1 of WO2004/007647, however in this example the catalyst comprises 0.70% by weight Pt and 30 wt% ZSM-12. The dewaxing conditions were 40 bar hydrogen, WHSV = 0.4-0.6 kg/l.h and a temperature in the range of from 315°C to 335°C. The properties of the obtained XHBO are given in Table 1.

Table 1

Table 1 displays the percentage of carbon atoms present in methyl groups (%CH ₃ ) determined by ¹ H NMR and the percentage of ethyl groups present in consecutive linear sequences of greater than 4 (%CH ₂ /total CH ₂ ) determined by ¹³ C NMR. Preparation of blend of XHBO sample 6 and Bright stock

XHBO 6 was blended with 20 weight% AC 2500 bright stock at 55 °C for 1 hour. Properties of this blend can be found in Table 2.

Table 2 - Base Oil Properties

AC 2500: A brighstock commercially available as Americas Core 2500 manufactured and sold by ExxonMobil Corporation.

Preparation of blend of Industrial Gear Oil formulations

The Industrial Gear oil formulations were prepared by mixing the components as indicated in Table 3 and followed by stirring at 55°C for 1 hour. Properties of these formulations can be found in Table 3.

Table 3 - Industrial Gear Oil Formulations

¹ AP/E Core 600: A Group I base oil commercially available as AP/E Core 600 manufactured and sold by ExxonMobil

Corporation . AC 2500: A brightstock commercially available as Americas Core 2500 manufactured and sold by ExxonMobil Corporation. ³ HVI 650: A brightstock commercially available as HVI 650 manufactured and sold by Royal Dutch Shell.

Commercially available industrial gear oil additive package. Commercially available pour point depressant.

Commercial available anti-foam additive.

Table 4 - Gear Oil Performance Data

Gear oil samples 2, 3, and 4 showed increased viscosity index (measured by ASTM D2270) compared to gear oil sample 1, demonstrating that the use of "heavy" Fischer-Tropsch derived base oils in gear oil formulations increases viscosity index. An increased viscosity index results in higher kinematic viscosity at temperatures above 40°C compared to a sample with lower viscosity index and equivalent kinematic viscosity @ 40°C, and this increased viscosity at higher temperatures may impart anti-wear performance benefits in gear systems with operating temperatures above 40°C. Gear oil samples 1, 2, 3, and 4 show equivalent anti-foam performance as measured by ASTM D892, equivalent water demulsibility properties as measured by ASTM D1401, and equivalent anti-rust performance as measured by ASTM D665B. Gear oil samples 2, 3, and 4 show improved air release compared to gear oil sample 1 indicated by less minutes required to release a measured amount of absorbed air in the ASTM D3427 test. Gear oil samples 2, 3, and 4 show improved oxidation resistance compared to gear oil sample 1 indicated by lower kinematic viscosity at 100°C after aging in the D2893 test.

Preparation of Bearing and Circulating Oil Formulations

The Bearing and Circulating Oil Formulations as indicated in Table 5 were prepared by mixing the components used to prepare the formulations and followed by stirring at 55°C for 1 hour. Properties of these formulations can be found in Table 5.

Table 5 - Bearing and Circulating Oil Formulations

Concentrations in t%

A B C D

AP/E Core 600 ¹ 23.87 12.93 7.96 -

AC 2500 ² 75.6 10

15/85 Base Oil 86.54

Sample 6/AC 2500 ²

mix

20/80 Base Oil 91.5

Sample 6/AC 2500 ²

mix

30/70 Base Oil 89.53 Sample 6/AC 2500 ²

mix

Bearing and 0.43 0.43 0.43 0.43 circulating oil

additive package ³

Pour point 0.1 0.1 0.1 0.1 depressant ⁴

Demulsifier ⁵ 30 Oppm 30 Oppm 30 Oppm 30 Oppm

Anti-foam 20 Oppm 20 Oppm 20 Oppm 20 Oppm additive ^{6 1} AP/E Core 600: A Group I base oil commercially available a AP/E Core 600 manufactured and sold by ExxonMobil

Corporation .

² AC 2500: A brightstock commercially available as Americas Core 2500 manufactured and sold by ExxonMobil Corporation. Commercially available bearing and circulating oil additive package .

Commercially available pour point depressant.

Commercially available demulsifier.

Commmercially available anti-foam additive.

Table 6 - Bearing and Circulating Oil Performance Data

Property Method A B C D

Kinematic D445 332.1 318.5 322 321 Viscosity,

40°C, cSt

Kinematic D445 24.58 25.56 26.02 26.86 Viscosity,

100°C, cSt

VI D2270 95 104 106 111

Seq I foaming D892 0/0 0/0 0/0 0/0 tendency/stable

foam (ml/ml)

Seq II foaming D892 0/0 0/0 0/0 0/0 tendency/stable

foam (ml/ml)

Seq III foaming D892 0/0 0/0 0/0 0/0 tendency/stable

foam (ml/ml)

Oil / Water / D1401 42/37/1 40/37/3 40/37/3 40/38/2 Emulsion, ml

Separation D1401 15 10 10 10 Time, min

Air Release @ D3428 83.21 68.39 50.72 55.03 50°C, min

Oxidation D2272 550 622 637 679

Stability,

RPVOT (min)

Rust test D665B Pass Pass Pass Pass

Pour Point, °C D5950 -9 -12 -15 -18

Flash Point D93 186 214 218 222

COC, °C

Bearing and circulating oil samples B, C, and D showed increased viscosity index (measured by ASTM D2270) compared to bearing and circulating oil samples A, demonstrating that the use of "heavy" Fischer-Tropsch derived base oils in bearing and circulating oil formulations increases viscosity index. An increased viscosity index results in higher kinematic viscosity at temperatures above 40°C compared to a sample with lower viscosity index and equivalent kinematic viscosity @ 40°C, and this increased viscosity at higher temperatures may impart anti-wear performance benefits in bearing and circulating oil systems with operating

temperatures above 40°C. Bearing and circulating oil samples

A, B, C, and D show equivalent anti-foam performance as measured by ASTM D892 and equivalent anti-rust performance as measured by ASTM D665B. Bearing and circulating oil samples

B, C, and D show improved water demulsibility compared to bearing and circulating oil sample A as indicated by lower separation times measured by ASTM D1401, improved air release compared to bearing and circulating oil sample A indicated by less minutes required to release a measured amount of absorbed air in the ASTM D3427 test, lower pour point compared to bearing and circulating oil sample A as measured by ASTM D5950, and lower flash point as measured by ASTM D93 compared to bearing and circulating oil sample A. Gear oil samples 2, 3, and 4 show improved oxidation resistance compared to bearing and circulating oil sample A indicated by lower kinematic viscosity at 100°C after aging in the D2893 test .

Preparation of Monograde Heavy Duty Diesel Engine Oil

Formulations

The Monograde Heavy Duty Diesel Engine Oil Formulations as indicated in Table 7 were prepared by mixing the

components used to prepare the formulations and followed by stirring at 55°C for 1 hour. Properties of these formulations can be found in Table 7.

Table 7 - Monograde Heavy Duty Diesel Engine Oil Formulations

Commercially available heavy duty diesel engine oil additive package . Table 8 - HDEO Monograde Engine Oil Performance

Monograde heavy duty diesel engine oil samples F and G showed increased viscosity index (measured by ASTM D2270) compared to monograde heavy duty diesel engine oil sample E,

demonstrating that the use of "heavy" Fischer-Tropsch derived base oils in monograde heavy duty diesel engine oil

formulations increases viscosity index. An increased viscosity index results in higher kinematic viscosity at temperatures above 40°C compared to a sample with lower viscosity index and equivalent kinematic viscosity @ 40°C, and this increased viscosity at higher temperatures may impart anti-wear performance benefits in heavy duty diesel engines with operating temperatures above 40°C. Monograde heavy duty diesel engine oil samples F and G show equivalent anti-foam performance as measured by ASTM D892. Monograde heavy duty diesel engine samples F and G show lower pour point as measured by ASTM D5950 than monograde heavy duty diesel engine oil sample E.