EP2864456B1

EP2864456B1 - Lubricating oil compositions comprising heavy fischer-tropsch derived base oils and alkylated aromatic base oil

Info

Publication number: EP2864456B1
Application number: EP13729949.1A
Authority: EP
Inventors: David John Wedlock
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2012-06-21
Filing date: 2013-06-18
Publication date: 2018-10-31
Anticipated expiration: 2033-06-18
Also published as: RU2658914C2; WO2013189953A1; BR112014031227A2; RU2015101730A; CN104508095B; JP6266606B2; CN104508095A; EP2864456A1; BR112014031227A8; JP2015520286A

Description

Field of the Invention

The invention relates to lubricating compositions comprising Fischer-Tropsch extra heavy base oil. In particular, though not exclusively, the invention relates to lubricating compositions comprising a Fischer-Tropsch derived base oil with waxy haze components, which nevertheless have a clear and bright appearance.

Background of the Invention

It is known in the art that waxy hydrocarbon feeds, including those synthesized from gaseous components such as CO and H₂, especially Fischer-Tropsch waxes, are suitable for conversion/treatment into lubricating base oils by subjecting such waxy feeds to hydrodewaxing or hydroisomerization/catalytic (and/or solvent) dewaxing whereby long chain normal-paraffins and slightly branched paraffins are removed and/or rearranged/isomerized into more heavily branched iso-paraffins of reduced pour and cloud point. Lubricating base oils produced by the conversion/treatment of waxy hydrocarbon feeds of the type synthesized from gaseous components (i.e. from Fischer-Tropsch feedstocks), are referred to herein as Fischer-Tropsch derived base oils, or simply FT base oils. US 2008/0300157 A1 relates to lubricating oils of improved low temperature properties, especially viscometrics, and low pour points, and to a method for improving the low temperature properties, especially viscometrics, and reducing the pour points of Gas-to-Liquid (GTL) lubricating oils. The viscosity of FT base oils may vary considerably. They may have a kinematic viscosity at 100°C according to ASTM D445 (VK 100) of at least about 3 mm²/s (cSt), e.g. about 5 mm²/s, or about 7 mm²/s, or about 14 mm²/s. FT residual base oils with a VK 100 of at least 15 mm²/s are often referred to in the art as FT extra heavy base oils. Some FT extra heavy base oils may even have a VK 100 of at least 17 mm²/s, or at least 20 mm²/s or at least 25 mm²/s.
It is known in the art to prepare so-called Fischer-Tropsch residual (or bottoms) derived lubricating base oils, referred to hereinafter as FT residual base oils. Such FT residual base oils are often FT extra heavy base oils and are obtained from a residual (or bottoms) fraction resulting from distillation of an at least partly isomerised Fischer-Tropsch feedstock. The at least partly isomerised Fischer-Tropsch feedstock may itself have been subjected to processing, such as dewaxing, before distillation. The residual base oil may be obtained directly from the residual fraction, or indirectly by processing, such as dewaxing. A residual base oil may be free from distillate, i.e. from side stream product recovered either from an atmospheric fractionation column or from a vacuum column. WO 02/070627 , WO2009/080681 and WO2005/047439 describe exemplary processes for making Fischer-Tropsch derived residual base oils.
FT extra heavy base oils, particularly FT residual extra heavy base oils, have found use in a number of lubricant applications on account of their excellent properties, such as their beneficial viscometric properties and purity. However, such base oils can suffer from an undesirable appearance in the form of a waxy haze at ambient temperature.
Waxy haze may be inferred or measured in a number of ways. The presence of waxy haze may for instance be measured according to ASTM D4176-04 which determines whether or not a fuel or lubricant conforms with a "clear and bright" standard. Whilst ASTM D4176-04 is written for fuels, it functions too for base oils. The presence or extent of waxy haze may also be quantified as turbidity using nephelometric turbidity units (NTU), measured for example as described in US2011/0083995 .
Waxy haze in FT residual base oils, which can also adversely affect the filterability of the oils, results from the presence of long carbon chain length paraffins, which have not been sufficiently isomerised (or cracked).
The content of long carbon chain length paraffins, which stem from the waxy hydrocarbon feed, is particularly high in residual fractions from which residual base oils are derived. Since the presence of long carbon chain length paraffins also causes pour point and cloud point to be relatively high, residual fractions are typically subjected to one or more catalytic and/or solvent dewaxing steps. Such dewaxing steps are highly effective in lowering the pour point and cloud point in the resulting FT residual base oils, and under some conditions can also help to mitigate or eliminate haze, especially when combined with filtering. US 2009/0186786 A1 relates to GTL base stocks and to GTL base stocks of reduced/mitigated haze formation.
However, there remains a need for improved effective and efficient solutions for mitigating haze in FT base oils, especially in extra heavy base oils and residual base oils.
It is hence an object of the invention to address the problems of waxy haze in FT base oils or to solve at least one other problem associated with the prior art.
It has now been recognised by the inventors that eliminating waxy haze in FT extra heavy base oils with the help of conventional catalytic dewaxing steps can be inefficient or, at worst, ineffective. Particular difficulties in eliminating haze by dewaxing have been encountered in FT residual extra heavy base oils made from heavy waxy hydrocarbon feeds. Based on this appreciation, the inventors have developed a new approach to addressing the problem of waxy haze in FT extra heavy base oils.
From a first aspect, the invention resides in a lubricating composition comprising 15 to 35 wt% FT extra heavy base oil and 65 to 85 wt% alkylated aromatic blendstock based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, wherein the FT extra heavy base oil has a kinematic viscosity at 100°C according to ASTM D445 in the range of from 19 to 35 mm2/s and a lower boiling point (T5) of at least 420°C and a higher boiling point (T80) of at least 600°C according to ASTM D-7169..
It has been found that the FT extra heavy base oil and the alkylated aromatic blendstock act in synergy to provide a lubricating composition with good lubricating properties and stability in which waxy haze formation is mitigated. The alkylated aromatic blendstock has been found to solubilise waxy haze in FT extra heavy base oil, including in FT residual extra heavy base oils made from heavy waxy hydrocarbon feeds. The FT extra heavy base oil greatly enhances the lubricating properties of the composition.
From a second aspect, the invention embraces a method of making a lubricating composition, the method comprising blending a FT extra heavy base oil and an alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds.
From a third aspect, the invention resides in the use of an alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds for the purpose of reducing waxy haze in a FT extra heavy base oil, or in a precursor composition comprising a FT extra heavy base oil. The use may comprise blending the alkylated aromatic blendstock with the FT extra heavy base oil or the precursor composition to form a lubricating composition.
From a fourth aspect, the invention resides in a method of reducing waxy haze in a FT extra heavy base oil, or in a precursor composition comprising a FT extra heavy base oil, the method comprising blending an alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds with the FT extra heavy base oil or the precursor composition to form a lubricating composition.
From a fifth aspect, the invention resides in use of a lubricating composition comprising a FT extra heavy base oil and an alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds for lubricating one or more of: an engine, e.g. compression ignition engine, an industrial machine such as a compressor, hydraulic pump, industrial turbine, or a gear box, and a power transmission system.
Further details and preferred features of the invention are set out in the following detailed description.
The term "comprising" is used herein synonymously with the term "including" and is an open, non-limiting term. However, this term also encompasses "consisting of" and may always be limited to such a definition in embodiments of the invention where context permits. For the avoidance of doubt, preferred and optional features of the invention may be applied to each aspect of the invention where context permits.

Detailed Description of the Invention

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 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%, more preferably at least 90 wt%, yet more preferably at least 95 wt%, and most preferably at least 98 wt% of these saturated hydrocarbon molecules are isoparaffinic. 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 iso-paraffins, i.e. iso-paraffins 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 mm²/s. Preferably, its VK 100 may be at least 17 mm²/s, more preferably at least 18 mm²/s, yet more preferably at least 19 mm²/s, again more preferably at least 22 mm²/s, and yet again more preferably at least 24 mm²/s. In embodiments, the VK100 may be at most 100 mm²/s, or even at most 80 mm²/s or at most 50 mm²/s, or even at most 35 mm²/s.
The kinematic viscosity at 40 °C according to ASTM D445 (VK 40) of the alkylated aromatic blendstock may optionally be in the range of from 20 mm²/s to 300 mm²/s, preferably in the range of from 100 mm²/s to 250 mm²/s.
The viscosity index of the FT extra heavy base oil is preferably greater than 140, 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.
The lubricating composition according to the present invention comprises a FT extra heavy base oil having a lower boiling point (T5) of at least 420°C and a higher boiling point (T80) of at least 600°C 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 +10°C, more preferably in the range of from +45°C and +15°C, more preferably in the range of from +40°C and +20°C and most preferably in the range of from +31°C and +20°C.
"Pour point" refers to the temperature at which a sample will begin to flow under carefully controlled conditions. The pour points referred to herein were determined according to ASTM D-97-93. The FT extra heavy base oil may have a pour point of -9°C or lower, preferably of -12°C or -15°C or -21°C or -24°C or -27°C or even -30°C or -36°C or -39°C or -45°C or lower. 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 -30 to -45 °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. 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.
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 ¹³C-NMR, vapour pressure osmometry (VPO) and field ionisation mass spectrometry (FIMS), as described in US 8,152,869 .
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 '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 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 IP 365/97, is suitably from about 700 to 1100 kg/m³, preferably from about 834 to 841 kg/m³.
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 an isomerisation 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 isomerisation 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. The isomerised bottoms product may undergo further downstream processes, for example hydrocracking, hydrotreating and/or hydrofinishing. It is preferably subjected to a dewaxing step, either by solvent or more preferably by catalytic dewaxing, as described below, which serves further to reduce its pour point. However, even after dewaxing, 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.
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 (b) is a heavy bottom fraction obtained from a Fischer-Tropsch derived wax or waxy raffinate feed by: a) hydrocracking/hydroisomerising a Fischer-Tropsch derived feed, 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 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 isomerisation and fractionation, the Fischer-Tropsch derived product fractions may undergo various other operations, such as hydrocracking, 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 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 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 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 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 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 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 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-Il 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 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 and EP-A-1029029 . Another preferred class of molecular sieves comprises those having a relatively low isomerisation selectivity and a high wax conversion selectivity, like ZSM-5 and ferrierite (ZSM-35).
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 intermediate 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 . Examples of suitable dewaxing catalysts as described above are silica bound and dealuminated Pt/ZSM- 5, or silica bound and dealuminated Pt/ZSM-35 as for example described in WO-A--00/29511 and EP-B-0832171 .
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 300 and 330°C. The hydrogen pressures may range from 10 to 200 bar, preferably from 40 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 0.1 to 3 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 composition but this is not essential. Thus other FT extra heavy base oil may be present in the lubricating 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 it fails the 'clear and bright' standard (ASTM D4176-04) at standard conditions, and/or has a measurable turbitidy 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.
The amount of FT extra heavy base oil may be adjusted to achieve a desired waxy haze reduction and viscometric performance. 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 alkylated aromatic blendstock 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 15 to 35 wt%, especially 20 to 25 wt % based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock.
A second essential component of the invention is the alkylated aromatic blendstock. The alkylated aromatic blendstock consists of one or more alkylated aromatic compounds (alkylated aromatics) consistent with achieving desired properties in the lubricating composition.
Alkylated aromatics have an aromatic head group and at least one alkyl chain.
The aromatic head group may be a substituted or unsubstituted mono- or polycyclic ring structure. Aromatic head groups that contain one or more heteroatoms may also be suitable. Preferred aromatic head groups in the context of the invention are benzene and naphthalene, with naphthalene being particularly preferred.
Preferably, the one or more alkyl chains of the alkylated aromatics may each, individually, be a C₁-C₃₀, e.g. C₁-C₂₀ linear alkyl group; or a C₃-C₃₀₀, e.g. C₃-C₁₀₀, or a C₃-C₃₀ branched alkyl group. Longer alkyl chains can help to lower volatility and improve viscometric properties. In some embodiments of the invention, at least one linear or branched alkyl group of the alkylated aromatics may preferably comprise at least ten carbon atoms, more preferably at least 15 carbon atoms e.g. be a C₁₀-C₃₀ or a C₁₀-C₂₀ or a C₁₅-C₃₀ or a C₁₀-C₁₅ linear alkyl group, or a C₁₀-C₃₀₀ or a C₁₀-C₁₀₀, or a C₁₀-C₃₀ or a C_15-300 or a C₁₅-C₁₀₀, or a C₁₅-C₃₀ branched alkyl group.
The number of alkyl chains per aromatic head group may vary. One or more alkyl chains, e.g. one, two, three, four, five or six alkyl chains may be bonded directly to the aromatic system of the aromatic head group. An alkyl chain may be bonded to the aromatic system at every available position on the aromatic head group.
To achieve desired volatility characteristics, the average number of carbon atoms in the alkylated aromatics may be at least 11, preferably at least 15, more preferably at least 25, or even at least 40. The alkylated aromatics may have a number average molecular weight of at least about 150, preferably at least about 180, and more preferably at least about 300 or even at least about 480.
The preparation of alkylated aromatics is well known in the art. Although any method of preparation is suitable in the context of the invention, suitable alkylated aromatics may conveniently be formed by an alkylation reaction between an aromatic compound and an alkylating agent. Olefins are particularly common alkylating agents used in the art. The alkylation reaction is generally performed over acidic catalysts, especially Friedel-Crafts catalysts such as AlCl₃, BF₃, FeCl₃, acidic zeolites, amorphous aluminosilicates, acid clays or acidic metal oxides. Alkylated aromatics obtained by alkylation generally include a mixture of compounds and isomers.
As will be apparent to a person skilled in the art, it is also possible to obtain short chain alkylated aromatics from refining or other petrochemical processes. Conveniently, such alkylated aromatics-containing feeds may be made from aromatisation of a suitable stream available from the FT process. Alkylated aromatics obtained in this manner may be used directly in the invention, or as an alkylation feedstock, depending on desired properties.
Hydrogenated or partially hydrogenated analogues of the alkylated aromatics described herein may optionally also be used in or as the alkylated aromatic blendstock.
Alkylated naphthalenes are particularly preferred alkylated aromatics for use in or as the alkylated aromatic blendstock. Alkylated naphthalenes useful in the context of the invention may have the following general formula (I):
wherein A + B = 1 to 8, preferably 1 to 6, more preferably 1 to 5, and R is C₁-C₃₀, preferably C₁-C₂₀ linear alkyl group, C₃-C₃₀₀, preferably C₃-C₁₀₀, more preferably C₃-C₃₀ branched alkyl group or mixtures of such groups with the total number of carbons in R_A and R_B, preferably being at least 4.
Examples of typical alkyl naphthalenes are mono-, di-, tri-, tetra-, or penta-C₃ alkyl naphthalene, -C₄ alkyl naphthalene, -C₅ alkyl naphthalene, -C₆ alkyl naphthalene, -C₈ alkyl naphthalene, -C₁₀ alkyl naphthalene, -C₁₂ alkyl naphthalene, -C₁₄ alkyl naphthalene, -C₁₆ alkyl naphthalene, -C₁₈ alkyl naphthalene, etc., C₁₀-C₁₄ mixed alkyl naphthalene, C₆-C₈ mixed alkyl naphthalene, or the mono-, di-, tri- , tetra-, or penta C₃, C₄, C₅, C₆, C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈ or mixtures thereof, alkyl monomethyl, dimethyl, ethyl, diethyl, or methylethyl naphthalene, or mixtures thereof. The alkyl group can also be a branched alkyl group with C₁₀ to C₃₀₀, e.g., C₂₄-C₅₆ branched alkyl naphthalene, C₂₄-C₅₆ branched alkyl mono-, di-, tri-, tetra- or penta- C₁-C₄ naphthalene. These branched alkyl group substituted naphthalenes or branched alkyl group substituted mono-, di-, tri-, tetra- or penta C₁-C₄ naphthalene can also be used as mixtures with the previously recited materials. When the branched alkyl group is very large (that is 8 to 300 carbons), usually only one or two of such alkyl groups are attached to the naphthalene head group. The alkyl groups on the naphthalene ring can be mixtures of any of the above alkyl groups.
Typically the alkyl naphthalenes are prepared by alkylation of naphthalene or short chain alkyl naphthalene, such as methyl or di-methyl naphthalene, with olefins, alcohols or alkylchlorides over acidic catalysts inducing typical Friedel Crafts catalysts. Methods for the production of alkyl naphthalenes suitable for use in the present invention are described in US 5,034,563 , US 5,516,954 , and US 6,436,882 , as well as in references cited in those patents and elsewhere in the literature. Because alkylated naphthalene synthesis techniques are well known in the art such techniques will not be further described herein.
Suitable alkylated naphthalenes are available commercially from ExxonMobil Chemical Company (TM) under the tradename Synesstic AN (TM).
Alkylated benzenes are also preferred alkylated aromatics for use in the invention. Alkylated benzenes useful in the context of the invention may have the following general formula (II):
In this structure, C = 1 to 6, preferably 1 to 5, more preferably 1 to 4. When it is monoalkylated benzene, the R can be linear C₁₀-C₃₀ alkyl group or a C₁₀-C₃₀₀ branched alkyl group preferably C₁₀-C₁₀₀ branched alkyl group, more preferably C₁₅-C₅₀ branched alkyl group. When C is 2 or greater than 2, up to C-1 of the alkyl groups can individually be a small alkyl group of C₁ to C₅, preferably a C₁-C₂ alkyl group, with the at least one remaining alkyl group being a linear C₁₀-C₃₀ alkyl group or a C₁₀-C₃₀₀ branched alkyl group preferably C₁₀-C₁₀₀ branched alkyl group, more preferably C₁₅-C₅₀ branched alkyl group. Branched large alkyl radicals can be prepared from the oligomerization or polymerization of C₃ to C₂₀ internal or alpha-olefins or mixture of these olefins.
Alkylated benzenes may be prepared by alkylation of benzene or short chain alkyl benzene, such as methyl or di-methyl benzene, with olefins, alcohols or alkylchlorides over acidic catalysts inducing typical Friedel Crafts catalysts. Preferred alkylated benzene fluids can be prepared according to US 6,071,864 or US 6,491,809 or EP 0,168,534 .
The alkylated aromatic blendstock is defined and described herein as an added component. It may optionally represent the sole source of alkylated aromatics in the lubricating composition but this is not essential. Thus other alkylated aromatics may be present in the lubricating composition and amounts of alkylated aromatics indicated herein must be interpreted accordingly, unless context requires otherwise.
The alkylated aromatic blendstock may consist of or be synonymous with, any of the alkylated aromatics described or defined herein, or any combination thereof, e.g. alkylated naphthalenes and/or alkylated benzenes.
The kinematic viscosity at 100 °C according to ASTM D445 (VK 100) of the alkylated aromatic blendstock may be in the range of from 1 mm²/s to 50 mm²/s, preferably in the range of from 2 mm²/s to 30 mm²/s, more preferably in the range of from 3 mm²/s to 20 mm²/s, most preferably in the range of from 4 mm²/s to 15 mm²/s, e.g. 4 to 7 mm²/s or 11 to 15 mm²/s .
The kinematic viscosity at 40 °C according to ASTM D445 (VK 40) of the alkylated aromatic blendstock may be in the range of from 20 mm²/s to 150 mm²/s, preferably in the range of from 25 mm²/s to 120 mm²/s.
The alkylated aromatic blendstock may preferably have a pour point (ASTM D97) of 0° C or less, preferably -20° C, more preferably -30° C or less; and/or a viscosity index (ASTM D 2270) in the range of from about 0 to 200, preferably about 60 to 200, more preferably about 70 to about 160, e.g. about 75 to about 110; and/or a Noack Volatility (ASTM D5800) of less than 15 wt%, preferably 7 wt%, more preferably 5 wt%.
The amount of alkylated aromatic blendstock may be adjusted to achieve a desired waxy haze reduction. Effective amounts of alkylated aromatic blendstock will depend to an extent on the nature of the blendstock, as well as the nature of the FT residual oil with which it is combined.
The lubricating composition according to the present invention comprises 15 to 35 wt% FT extra heavy base oil and an 65 to 85 wt% alkylated aromatic blendstock based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock.
In embodiments of the invention, the amount of alkylated aromatic blendstock is in the range of from 50 to 95 wt%, preferably 60 to 90 wt%, more preferably 65 to 85 wt%, especially 75 to 80 wt%, based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock.
The lubricating composition has a less hazy appearance than the FT extra heavy base oil used to formulate it. Advantageously, the lubricating composition may pass the 'clear and bright' standard (ASTM D4176-04). 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 composition may conform with one or more of the above haziness measurements at least 14 days after blending.
The lubricating composition according to the present invention comprises a FT extra heavy base oil having a kinematic viscosity at 100°C according to ASTM D445 in the range of from 19 to 35 mm2/s.
The kinematic viscosity at 100 °C according to ASTM D445 (VK 100) of the lubricating composition may preferably be in the range of from 1 mm²/s to 30 mm²/s, preferably in the range of from 2 mm²/s to 25 mm²/s, more preferably in the range of from 3 mm²/s to 20 mm²/s, most preferably in the range of from 4 mm²/s to 18 mm²/s, e.g. 7 to 12 mm²/s or 14 to 17 mm²/s.
The kinematic viscosity at 40 °C according to ASTM D445 (VK 40) of the lubricating composition may preferably be in the range of from 30 mm²/s to 150 mm²/s, preferably in the range of from 35 mm²/s to 140 mm²/s.
The lubricating composition may have a viscosity index (ASTM D-2270) in the range of from 95 to 180, preferably from 110 to 130.
The pour point of the lubricating composition (ASTM D-97-93) may be -10°C or lower, preferably of -15°C or lower, more preferably -20°C or lower, even more preferably -30°C or lower.
The lubricating composition has a surprisingly good oxidative stability and may preferably show the oxidative performance of a Group II base oil.
In some preferred embodiments of the invention, the lubricating composition comprising the FT extra heavy base oil and the alkylated aromatic blendstock may comprise:

5 to 25 wt%, based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, of a FT extra heavy base oil having a VK 100 of at least 15 mm²/s; and
75 to 95 wt%, based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, of an alkylated aromatic blendstock comprising or consisting of alkylated naphthalenes and having a VK 100 in the range of from 4 mm²/s to 15 mm²/s.

In other preferred embodiments of the invention the lubricating composition comprising the FT extra heavy base oil and the alkylated aromatic blendstock may comprise:

5 to 35 wt%, based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, of a FT extra heavy base oil having a VK 100 of at least 15 mm²/s; and
65 to 95 wt%, based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, of an alkylated aromatic blendstock comprising or consisting of alkylated naphthalenes and having a VK 100 in the range of from 11 mm²/s to 15 mm²/s.

The FT extra heavy base oil and the alkylated aromatic blendstock may make up the entirety of the lubricating composition, or preferably 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 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 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 VK100 is required such as in monograde gas engine oils (SAE 40 monogrades) 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.
The lubricating 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 failing the 'clear and bright' standard (ASTM D4176) with an amount of an alkylated aromatic blendstock to provide a lubricating composition that passes the 'clear and bright' standard (ASTM D4176) and/or has any of the other properties defined hereinabove.
The invention also embraces use of the alkylated aromatic blendstock 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 composition comprising FT extra heavy base oil and alkylated aromatic blendstock together with information or advertising relating to a clear and bright appearance or an appearance of absent or low turbidity.
The invention will now be further illustrated by the following non-limiting examples.

Example 1 - Haze

The fluid properties and appearance of lubricating compositions comprising FT extra heavy base oil (XHBO) and alkylated aromatic basestock were compared to those of the unblended components, according to the following standard ASTM methods:

Kinematic viscosity (ASTM 445). Measured at 40 °C and 100 °C in cSt (mm²/s) - VK 40 and VK 100
Viscosity index (ASTM D2270) - VI
Clear and Bright Standard (ASTM D4176) at ambient conditions (20 °C)
Pour Point (ASTM D97)
Cloud Point (ASTM D-5773)

A high pour point (high PPt) XHBO base stock was prepared substantially as described in Example 6 of US 8,152,869 .
A low pour point (low Ppt) XHBO base stock was prepared according to the same process, with the only difference being the temperature at which the dewaxing catalyst was operated. A higher temperature leads to more severe dewaxing and a lower pour point.
The resultant XHBO base stocks had the properties shown in Table 1. Table 1. Properties of the XHBO base stocks

XHBO (low PPt) XHBO (high PPt)

Vk 100 19.00 25.22

Vk 40 132.0 228.9

VI 163 140

Pour Point °C -30 -6

Cloud point °C +31 +31

Clear and Bright No - hazy No - hazy

The boiling range distribution of the XHBO base stocks was analysed according to ASTM D-7169. The carbon number distributions were also determined according to ASTM D-7169. The results are shown in Table 2.

Table 2. Boiling range and carbon number distributions of the XHBO base stocks

XHBO high PPt (-6°C)			XHBO low PPt(-30°C)
Sim dist	Boiling range °C	Carbon numbers	Sim dist	Boiling range °C	Carbon numbers
IBP	417.5	C27	IBP	419.0	C27
5%	473.5	C33	5%	475.5	C33
10%	495.0	C36	10%	497.0	C36
15%	511.0	C38	15%	513.5	C39
20%	525.0	C41	20%	528.0	C41
25%	538.0	C43	25%	541.5	C43
30%	550.0	C45	30%	554.0	C46
35%	562.0	C47	35%	565.5	C48
40%	573.0	C50	40%	577.0	C51
45%	584.0	C52	45%	588.5	C53
50%	595.0	C55	50%	600.0	C56
55%	606.5	C58	55%	612.0	C59
60%	618.5	C61	60%	625.0	C63
65%	631.0	C65	65%	638.0	C67
70%	644.5	C69	70%	652.0	C72
75%	658.5	C74	75%	667.0	C77
80%	675.0	C80	80%	685.0	C84
85%	694.0	C88	85%	703.5	C92
90%	714.0	C97	88.8%	719.5	C100
91.1%	719.5	C100	11.2%	>720	>C100
8.9%	>720	>C100

The alkylated aromatic basestocks were alkylated naphthalenes and were obtained commercially from ExxonMobil Chemical Company under the trade name Synesstic™ AN 5 and Synesstic™ AN 12. They had the measured properties shown in Table 3 and a clear and bright appearance: Table 3. Properties of the alkylated naphthalene fluids

Synesstic™ 5 Synesstic™ 12

Vk 100 4.81 12.75

Vk 40 28.54 111.00

VI 82 108

Pour Point (PPt) -39 -39

Twenty three lubricating composition blends were prepared from the XHBO and alkylated aromatic basestocks. The composition and measured properties of the blends are shown in Tables 4-7.

Table 4. Properties of blends of XHBO (high PPt) and Synesstic™ 5

	Blend 1	Blend 2	Blend 3	Blend 4	Blend 5
Wt% XHBO (high PPt)	25	30	35	40	45
Wt% Synesstic™ 5	75	70	65	60	55
Kinematic viscosity, Vk (40 °C)	50.58	56.75	62.84	68.87	75.48
Kinematic viscosity, Vk (100 °C)	7.76	8.49	9.25	10.08	10.96
Viscosity Index, VI	120	123	126	130	134
Pour Point (PPt)	-45	-42	-42	-45	-42
Clear and Bright	Yes	Yes	Yes	Cloudy	Cloudy

Table 5. Properties of blends of XHBO (low PPt) and Synesstic™ 5

	Blend 6	Blend 7	Blend 8	Blend 9	Blend 10	Blend 11
Wt% of XHBO (low PPt)	25	30	35	40	45	50
Wt% Synesstic™ 5	75	70	65	60	55	50
Kinematic viscosity, Vk (40 °C)	44.65	48.65	52.94	57.82	62.72	68.27
Kinematic viscosity, Vk (100 °C)	7.10	7.63	8.20	8.81	9.44	10.11
Viscosity Index, VI	118	122	126	128	131	132
Pour Point (PPt)	-42	-45	-45	-45	-45	-45
Clear and Bright	Yes	Yes	Yes	Cloudy	Cloudy	Cloudy

Table 6. Properties of blends of XHBO (high PPt) and Synesstic™ 12

	Blend 12	Blend 13	Blend 14	Blend 15	Blend 16	Blend 17
Wt% of XHBO (high PPt)	20	22	24	26	28	30
Wt% Synesstic™ 12	80	78	76	74	72	70
Kinematic viscosity, Vk (40 °C)	130.3	133.0	135.0	137.5	139.0	141.4
Kinematic viscosity, Vk (100 °C)	14.95	15.18	15.41	15.64	15.87	16.11
Viscosity Index, VI	117	117	118	118	120	120
Pour Point (PPt)	-36	-36	-36	-36	-36	-36
Clear and Bright	Yes	Yes	Yes	Cloudy	Cloudy	Cloudy

Table 7. Properties of blends of XHBO (low PPt) and Synesstic™ 12

	Blend 18	Blend 19	Blend 20	Blend 21	Blend 22	Blend 23
Wt% of XHBO (low PPt)	22	24	26	28	30	34
Wt% Synesstic™ 12	78	76	74	72	70	66
Kinematic viscosity, Vk (40 °C)	118.7	119.6	120.3	121.2	120.8	122.3
Kinematic viscosity, Vk (100 °C)	14.07	14.19	14.31	14.44	14.57	14.82
Viscosity Index, VI	118	119	119	120	122	124
Pour Point (PPt)	-36	-36	-36	-36	-36	-36
Clear and Bright	Yes	Yes	Yes	Yes	Cloudy	Cloudy

As is shown, clear and bright blends can be formulated with the alkylated aromatic basestock.
Furthermore it is shown that while the kinematic viscosity of all blends, both at 40 °C and 100 °C, decreases with an increasing proportion of the relatively low-viscosity alkylated aromatic blendstock, the viscosity index, VI, remains largely constant and is comparable to that of an API Group II base oil (VI > 110).
The synergistic behaviour of the blend according to the invention is further demonstrated through improvements in pour point (PPt) over the unblended alkylated aromatic basestock and XHBO base oil components. This indicates that the alkylated aromatic basestock can solubilise waxy haze in the FT extra heavy base oil and the FT extra heavy base oil can lower the pour point of the alkylated aromatic basestock in a blend to below that of either component.

Example 2 - Oxidative Stability

To assess the oxidative stability of the lubricating compositions according to the invention, a comparison was made with two prior art API Group II heavy neutral viscosity grade base oils (Motiva Star 12, commercially available from Motiva Enterprises LLC, and Formosa 500N, commercially available from HS Oil & Chemical International).
As a suitable vehicle to test the oxidative stability characteristics, the base oils/blends were formulated into an industrial turbine oil. This was chosen because of the associated low additive treat rate, but the results would be applicable to other industrial lubricants such as hydraulic fluids or a crankcase lubricant of a passenger car of a heavy duty diesel variety. The additives employed were as follows:

Lubad 1128 is a proprietary industrial turbine oil additive package containing: (1) antioxidants, including N-phenylated naphthylamines, diphenylamines; and (2) corrosion inhibitors, including glycol ether derivatives, ethoxylated carboxylic acids and fatty acids;
Synative AC AMH-2 is a dual function additive; a low silica anti-foaming agent and a demulsifier (both necessary for industrial turbine oils)

Measurements were made according to the standard Rotary Pressure Vessel Oxidation Test (RPVOT), formally the RBOT test (ASTM D2272).

Four formulation were prepared as shown in Table 8, which also shows results of the RPVOT test.

Table 8. Oxidative stability properties of blends of XHBO (low PPt) and Synesstic™ 12

	Formulation 1	Formulation 2	Formulation 3	Formulation 4
Lubad 1128	0.39	0.39	0.39	0.39
XHBO (high PPt)	19.92	23.91	-	-
Synesstic™ 12	79.69	75.7	-	-
Formosa 500N	-	-	99.61	-
Motiva Star 12	-	-	-	99.61
Synative AC AMH-2	75 ppm	75 ppm	75 ppm	75 ppm
Kinematic viscosity, Vk (40 °C)	128.9	133.1	88.25	104.4
Kinematic viscosity, Vk (100 °C)	14.82	15.27	10.43	11.64
Viscosity Index, VI	117	118	100	99
RPVOT (mins.)	1025/1017	1058/1075	1254/1230	897/907

The aromatic head groups present in alkylated naphthalene fluids would be expected to lead to oxidative vulnerability of any blend in which it was incorporated.
As is shown in Table 8, it has been found that the formulation based on blends prepared according to the present invention (formulations 1 and 2), which include the alkylated aromatic blendstock component surprisingly have comparable oxidative stability to that of a typical API Group II base oil (formulations 3 and 4). This provides further evidence of the unexpected beneficial synergistic effect of blending the XHBO with alkylated aromatick blendstock.

Claims

A lubricating composition comprising 15 to 35 wt% FT extra heavy base oil and 65 to 85 wt% alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, wherein the FT extra heavy base oil has a kinematic viscosity at 100°C according to ASTM D445 in the range of from 19 to 35 mm²/s and a lower boiling point (T5) of at least 420°C and a higher boiling point (T80) of at least 600°C according to ASTM D-7169.
The lubricating composition of claim 1, wherein the FT extra heavy base oil contains at least 95 wt% C30+ hydrocarbon molecules and at least 75 wt% of C35+ hydrocarbon molecules.
The lubricating composition of claim 1 or 2, wherein the FT extra heavy base oil has a cloud point in the range of from +60°C to +5°C and a pour point of -6°C or lower.
The lubricating composition of any preceding claim, wherein the FT extra heavy base oil is a residual base oil.
The lubricating composition of claim 4, wherein the FT extra heavy base oil is derived from a Fischer-Tropsch product which has at least 55 wt% of compounds having at least 30 carbon atoms and in which the weight ratio of compounds having at least 60 carbon atoms to those having at least 30 but fewer than 60 carbon atoms is at least 0.4.
The lubricating composition of any preceding claim, wherein the FT extra heavy base oil is hazy in the sense that it fails the 'clear and bright' standard ASTM D4176-04 at standard conditions.
The lubricating composition of any preceding claim, wherein the alkylated aromatic blendstock comprises alkylated aromatic naphthalene and/or alkylated aromatic benzene.
The lubricating composition of any preceding claim, wherein the alkylated aromatic blendstock has a kinematic viscosity at 100° C (ASTM D445) in the range of from 4 mm²/s to 15 mm²/s.
The lubricating composition of any preceding claim meeting 'clear and bright' standard ASTM D4176-04 at standard ambient conditions.
A lubricating composition comprising:
a. 5 to 25 wt%, based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, of a FT extra heavy base oil having a VK 100 of according to ASTM D445 in the range of from 19 to 35 mm²/s; and

b. 75 to 95 wt%, based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, of an alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds comprising or consisting of alkylated naphthalenes and having a VK 100 in the range of from 4 mm²/s to 15 mm²/s.
Use of a lubricating composition according to any preceding claim for lubricating an engine, a compressor, hydraulic pump, industrial turbine, a gear box, or a power transmission system, wherein the lubricating composition comprising 15 to 35 wt% FT extra heavy base oil and 65 to 85 wt% alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock.
A method of making a lubricating composition according to claims 1 to 10, the method comprising, blending a FT extra heavy base oil failing the 'clear and bright' standard ASTM D4176 with an alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds to provide a lubricating composition that passes the 'clear and bright' standard, wherein the FT extra heavy base oil has a kinematic viscosity at 100°C according to ASTM D445 in the range of from 19 to 35 mm²/s and a lower boiling point (T5) of at least 420°C and a higher boiling point (T80) of at least 600°C according to ASTM D-7169.
Use of 65 to 85 wt% alkylated aromatic blendstock consisting of one or more alkylated aromatic compounds for the purpose of reducing waxy haze in 15 to 35 wt% FT extra heavy base oil based on the total weight of FT extra heavy base oil and alkylated aromatic blendstock, or in a precursor composition comprising the FT extra heavy base oil.