US20080000806A1

US20080000806A1 - Process to Prepare a Lubricating Base Oil

Info

Publication number: US20080000806A1
Application number: US11/794,005
Authority: US
Inventors: Jacobus Mathias Dirkx
Original assignee: Individual
Current assignee: Shell USA Inc
Priority date: 2004-12-23
Filing date: 2005-12-21
Publication date: 2008-01-03
Also published as: EP1853682A1; JP2008525551A; WO2006067176A1

Abstract

Process to prepare a base oil having an paraffin content of between 75 and 95 wt % by subjecting a mixture of a Fischer-Tropsch derived feed and a gas field condensate derived feed to a catalytic pour point reducing treatment.

Description

The invention is directed to a process to prepare a base oil having an paraffin content of between 75 and 95 wt %.
WO-A-0246333 describes a process to prepare two viscosity grades of base oil, by solvent dewaxing a fraction having a T95% point above 621° C. and catalytically dewaxing a fraction having a T95% point of below 621° C. The two fractions are Fischer-Tropsch derived fractions. Optionally the heavier or the lower boiling fraction may also be a slack wax, a distillate from crude oil or deasphalted residual stocks from crude oil.
NL-C-1015035 describes a process to prepare a base oil from a Fischer-Tropsch derived feed by performing a hydroisomerisation step. The effluent of the hydroisomerisation step is distilled and a residue boiling above 380° C. is obtained. This residue is subjected to a catalytic dewaxing treatment using a catalyst containing platinum and ferrierite.
U.S. Pat. No. 6,294,077 describes a catalytic dewaxing treatment wherein a catalyst is used consisting of ZSM-5 and platinum.
U.S. Pat. No. 6,025,305 discloses a process wherein a Fischer-Tropsch wax feed is first hydroisomerised. The effluent of the hydroisomerisation is then separated into fuels and lubricants. No pour point reducing treatment is disclosed in this publication.
US-A-2002/0146358 describes a process for hydroisomerisation of a Fischer-Tropsch derived wax feed. The effluent of the hydroisomerisation step is distilled and a bottoms fraction comprising compounds having 20 or more carbon atoms is obtained. This bottoms fraction may be subjected to a catalytic dewaxing treatment.
WO-A-0157166 describes the use of a highly paraffinic base oil as obtained from a Fischer-Tropsch wax in a motor engine lubricant formulation. The examples illustrate that such formulations will also consist of an ester, which according to the description of the patent is added to confer additional desired characteristics, such as additive solvency.
The use of ester co-base fluids in lubricant formulations as illustrated in WO-A-0157166 is not desired because such ester co-base fluids are not widely available and thus expensive. Additive solvency may be improved by using a paraffinic base stock, which contains less paraffins. Such base oils may be prepared by hydroisomerisation of petroleum derived waxes, followed by a solvent or catalytic dewaxing step. A disadvantage of such a process is that the starting petroleum derived waxes, such as for example slack wax, are not easily obtainable. Furthermore, such waxes may not always have the desired high paraffin content needed to make the desired base oils as per this invention.
The object of the present invention is to provide a process wherein a base oil with a paraffin content of between 75 and 95 wt % is obtained which does not have the disadvantages of the prior art processes.
This object is achieved by the following process. Process to prepare a base oil having a paraffin content of between 75 and 95 wt %, by subjecting a mixture of a Fischer-Tropsch derived feed and a gas field condensate derived feed to a catalytic pour point reducing treatment.
Applicants found that by using a mixture of a relatively small amount of a gas field condensate derived feed with a Fischer-Tropsch derived feed before performing a catalytic pour point reducing treatment a base oil may be obtained having the desired properties. A further advantage is that the gas field condensate is obtained when natural gas fields are developed. These condensates are the liquid fraction associated with the major compound methane. Fischer-Tropsch processes typically derived their feed from natural gas. Thus it is advantageous to use the gas field condensate in a process to prepare base oils in a Fischer-Tropsch facility based on natural gas because it simplifies logistics.
Preferably from the gas field condensate a fraction is isolated by means of for example distillation, which boils for more than 80 wt % above 340° C., more preferably for more than 80 wt % above 370° C. and even more preferably for more than 80 wt % above 390° C. These fractions may be recovered directly from the gas field condensate as it is separated from the natural gas or may be obtained in dedicated gas field condensate refineries which refineries upgrade the gas field condensate as obtained in a multitude of natural gas wells.
The gas field condensate normally will contain sulphur. If the sulphur content is too high the condensate is preferably treated to reduce the sulphur content to levels below 20 ppm, preferably below 10 ppm in the fraction to be used in the present process. The sulphur level in the combined mixture used in the process of the present invention is preferably below 10 ppm. Treating is advantageously performed by means of hydrotreating or by means of sorption processes. Hydrotreating is a well-known process and may be performed with a supported Co/Mo catalyst. In such hydrotreating the level of aromatics and nitrogen is also preferably reduced. The fraction comprising the gas field condensate preferably has an aromatic compound content of between 0 and 20 wt % and a naphthenic compound content of preferably between 15 and 90 wt %. The composition is analysed using the following technique.
An example of a possible sorbent processes for desulfurizing the gas field condensate is a process wherein the gas field condensate is contacted with a sorbent comprising zinc oxide under conditions sufficient to remove at least a portion of the sulfur from the fluid stream and provide a sulfurized sorbent comprising zinc sulfide. The sulfurized sorbent is thereafter contacted with an oxygen-containing regeneration stream under conditions sufficient to convert at least a portion of the zinc sulfide to zinc oxide, thereby providing a regenerated sorbent. The regenerated sorbent can then be contacted with a reducing stream to provide an activated sorbent. Thereafter, the activated sorbent can, once again, be contacted with the gas field condensate. Examples of such processes are described in WO-A-0016895, U.S. Pat. No. 4,990,318, U.S. Pat. No. 5,077,261, U.S. Pat. No. 5,102,854, U.S. Pat. No. 5,108,975, U.S. Pat. No. 5,130,288, U.S. Pat. No. 5,174,919, U.S. Pat. No. 5,177,050, U.S. Pat. No. 5,219,542, U.S. Pat. No. 5,244,641, U.S. Pat. No. 5,248,481, U.S. Pat. No. 5,281,445 and U.S. Pat. No. 6,544,410.
The cyclo-paraffin (naphthenic compounds) content in this mixture of cyclo-, normal and iso-paraffins is measured by the following method. Any other method resulting in the same results may also be used. The base oil sample is first separated into a polar (aromatic) phase and a non-polar (saturates) phase by making use of a high performance liquid chromatography (HPLC) method IP368/01, wherein as mobile phase pentane is used instead of hexane as the method states. The saturates and aromatic fractions are then quantatively analyzed using a Finnigan MAT90 mass spectrometer equipped with a Field desorption/Field Ionisation (FD/FI) interface, wherein FI (a “soft” ionisation technique) is used for the quantitative determination of hydrocarbon types in terms of carbon number and hydrogen deficiency of this particular base oil fraction. The instrument conditions to achieve such a soft ionization technique are a source temperature of 30° C., an extraction voltage of 5 kV, an emitter current of 5 mA and a probe temperature ramp of 40° C. to 400° C. (20° C./min)
The type classification of compounds in mass spectrometry is determined by the characteristic ions formed and is normally classified by “z number”. This is given by the general formula for all hydrocarbon species: CnH₂n+z. Because the saturates phase is analysed separately from the aromatic phase it is possible to determine the content of the different (cyclo)-paraffins having the same stoichiometry. The results of the mass spectrometer are processed using commercial software (poly 32; available from Sierra Analytics LLC, 3453 Dragoo Park Drive, Modesto, Calif. GA95350 USA) to determine the relative proportions of each hydrocarbon type and the average molecular weight and polydispersity of the saturates and aromatics fractions.
The Fischer-Tropsch derived feed preferably is a hydroisomerized Fischer-Tropsch wax. Such a feed may be obtained by well-known processes, for example the so-called commercial Sasol process, the Shell Middle Distillate Process or by the non-commercial Exxon process. These and other processes are for example described in more detail in EP-A-776959, EP-A-668342, U.S. Pat. No. 4,943,672, U.S. Pat. No. 5,059,299, WO-A-9934917 and WO-A-9920720. The process will generally comprise a Fischer-Tropsch synthesis and a hydroisomerisation step as described in these publications.
In another preferred embodiment of the present invention the, optionally partly desulphirized, gas field condensate comprising at least the fraction boiling in the base oil range as described above is subjected to the hydroisomerisation step together with the Fischer-Tropsch wax. This is advantageous because then sulphided non-noble catalyst as described below can be used in this process step, while at the same time improving the yield to hydrocarbon products from the natural gas well. The fact that the products will contain some sulphur and other non-paraffinic compounds does not have to be a disadvantage if one realises that such products will be blended with mineral oil products comprising sulphur and non-paraffinic compounds anyway.
A preferred process to prepare the hydroisomerised Fischer-Tropsch feed or the blend of a hydroisomerised Fischer-Tropsch feed and the gas field condensate derived feed for use as feed in the present process will comprise the following steps:

(a) hydrocracking/hydroisomerisating a Fischer-Tropsch product or the mixed feed,
(b) separating by means of distillation the product of step (a) into one or more gas oil fractions and a higher boiling Fischer-Tropsch derived feed according to this invention.

Optionally the hydroisomerisation step on the mixed feed can be performed at such a high conversion/isomerisation rate that a separate dewaxing step to obtain the desired base oil grade having the desired pour point can be omitted. In such a situation it is obvious that said hydroisomerisation step is actually the dewaxing step according to the present invention.
Preferably the Fischer-Tropsch product used as feed in step (a) is a product wherein the weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms in the Fischer-Tropsch product is at least 0.2 and wherein at least 30 wt % of compounds in the Fischer-Tropsch product have at least 30 carbon atoms.
Applicants found that by performing the hydro-cracking/hydroisomerisation step with the relatively heavy feedstock a higher yield of gas oils as calculated on the feed to step (a) can be obtained. A further advantage is that both fuels, for example gas oil, and the Fischer-Tropsch derived feed are prepared in one hydrocracking/hydroisomerisation process step. In a preferred embodiment of the present invention a fraction boiling above the Fischer-Tropsch derived feed is isolated in step (b) and recycled to step (a).
A further advantage is that by performing step (a) on the relatively heavy feed a Fischer-Tropsch derived feed is prepared which already has a certain content of cyclo-paraffins.
The relatively heavy Fischer-Tropsch product used in step (a) has more preferably at least 50 wt %, and even more preferably at least 55 wt % of compounds having at least 30 carbon atoms. Furthermore the weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms of the Fischer-Tropsch product is more preferably at least 0.4 and even more preferably at least 0.50. 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 initial boiling point of the Fischer-Tropsch product used in step (a) may range up to 400° C., but is preferably below 200° C. Preferably any compounds having 4 or less 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 step (a). The Fischer-Tropsch product as described in detail above is a Fischer-Tropsch product, which has not been subjected to a hydroconversion step as defined according to the present invention. The content of non-branched compounds in the Fischer-Tropsch product will therefore be above 80 wt %. In addition to the Fischer-Tropsch product and the optional gas field condensate also other fractions may be additionally processed in step (a). Possible other fractions may suitably be the optional higher boiling fraction obtained in step (b) or part of said fraction and/or off-spec base oil fractions as obtained in the pour point reducing treatment of the process of the present invention.
Such a Fischer-Tropsch product can be obtained by any process, which yields a relatively heavy Fischer-Tropsch product as described above. Not all Fischer-Tropsch processes yield such a heavy product. An example of a suitable Fischer-Tropsch process is described in WO-A-9934917 and in AU-A-698392. These processes may yields a Fischer-Tropsch product as described above.
The Fischer-Tropsch product will 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 impurities. Sulphur and nitrogen levels will generally be below the detection limits, which are currently 2 ppm for sulphur and 1 ppm for nitrogen respectively.
The Fischer-Tropsch product may optionally be subjected to a mild hydrotreatment step in order to remove any oxygenates and saturate any olefinic compounds present in the reaction product of the Fischer-Tropsch reaction. Such a hydrotreatment is described in EP-B-668342. The mildness of the hydrotreating step is preferably expressed in that the degree of conversion in this step is less than 20 wt % and more preferably less than 10 wt %. The conversion is here defined as the weight percentage of the feed boiling above 370° C., which reacts to a fraction boiling below 370° C. After such a mild hydrotreatment lower boiling compounds, having four or less carbon atoms and other compounds boiling in that range, will preferably be removed from the effluent before it is used in step (a).
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 of which some will be described in more detail below. The catalyst may in principle be any catalyst known in the art to be suitable for isomerising paraffinic molecules. In general, suitable hydroconversion catalysts are those comprising a hydrogenation component supported on a refractory oxide carrier, such as amorphous silica-alumina, alumina, fluorided alumina, molecular sieves (zeolites) or mixtures of two or more of these. One type of preferred catalysts to be applied in the hydroconversion step in accordance with the present invention are hydroconversion catalysts comprising platinum and/or palladium as the hydrogenation component. A very much preferred hydroconversion catalyst comprises platinum and palladium supported on an amorphous silica-alumina (ASA) carrier. The platinum and/or palladium is suitably present in an amount of from 0.1 to 5.0% by weight, more suitably from 0.2 to 2.0% by weight, calculated as element and based on total weight of catalyst. If both present, the weight ratio of platinum to palladium (calculated as element) may vary within wide limits, but suitably is in the range of from 0.05 to 10, more suitably 0.1 to 5. Examples of suitable noble metal on ASA catalysts are, for instance, disclosed in WO-A-9410264 and EP-A-0582347. Other suitable noble metal-based catalysts, such as platinum on a fluorided alumina carrier, are disclosed in e.g. U.S. Pat. No. 5,059,299 and WO-A-9220759.
A second type of suitable hydroconversion catalysts are those comprising at least one Group VIB metal, preferably tungsten and/or molybdenum, and at least one non-noble Group VIII metal, preferably nickel and/or cobalt, as the hydrogenation component. Usually both metals are present as oxides, sulphides or a combination thereof. The Group VIB metal is suitably present in an amount of from 1 to 35% by weight, more suitably from 5 to 30% by weight, calculated as element and based on total weight of catalyst. The non-noble Group VIII metal is suitably present in an amount of from 1 to 25% wt, preferably 2 to 15% wt, calculated as element and based on total weight of catalyst. A hydroconversion catalyst of this type which has been found particularly suitable is a catalyst comprising nickel and tungsten supported on fluorided alumina.
A preferred catalyst which can be used in a non-sulphided form comprises a non-noble Group VIII metal, e.g., iron, nickel, in conjunction with a Group IB metal, e.g., copper, supported on an acidic support. The catalyst has a surface area in the range of 200-500 m²/gm, preferably 0.35 to 0.80 ml/gm, as determined by water adsorption, and a bulk density of about 0.5-1.0 g/ml. The catalyst support is preferably an amorphous silica-alumina where the alumina is present in amounts of less than about 30 wt %, preferably 5-30 wt %, more preferably 10-20 wt %. Also, the support may contain small amounts , e.g., 20-30 wt %, of a binder, e.g., alumina, silica, Group IVA metal oxides, and various types of clays, magnesia, etc., preferably alumina.
The preparation of amorphous silica-alumina microspheres has been described in Ryland, Lloyd B., Tamele, M. W., and Wilson, J. N., Cracking Catalysts, Catalysis: volume VII, Ed. Paul H. Emmett, Reinhold Publishing Corporation, New York, 1960, pp. 5-9.
The catalyst is prepared by co-impregnating the metals from solutions onto the support, drying at 100-150° C., and calcining in air at 200-550° C. The Group VIII metal is present in amounts of about 15 wt % or less, preferably 1-12 wt %, while the Group IB metal is usually present in lesser amounts, e.g., 1:2 to about 1:20 weight ratio respecting the Group VIII metal.
A typical catalyst is shown below:

Ni, wt % 2.5-3.5

Cu, wt % 0.25-0.35

Al₂O₃—SiO2 wt % 65-75

Al₂O₃(binder) wt % 25-30

Surface Area 290-325 m²/g

Pore Volume (Hg) 0.35-0.45 ml/g

Bulk Density 0.58-0.68 g/ml
Another class of suitable hydroconversion catalysts are those based on zeolitic materials, suitably comprising at least one Group VIII metal component, preferably Pt and/or Pd, as the hydrogenation component. Suitable zeolitic materials, then, include Zeolite beta, Zeolite Y, Ultra Stable Y, ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-35, SSZ-32, ferrierite, mordenite and silica-alumino-phosphates, such as SAPO-11 and SAPO-31. Examples of suitable hydroisomerisation catalysts and processes are, for instance, described in WO-A-9201657, WO-A-0107538 or EP-A-1029029 and US-A-20040065581.
A process wherein step (b) can be omitted is for example described in US-A-20040065581 or in EP-A-1029029. These publications describe the conversion of a narrow boiling Fischer-Tropsch derived wax to a base oil by contacting the feed with a platinum/zeolite beta followed by directly contacting the effluent with a platinum/ZSM-48 or platinum/ZSM-23 dewaxing catalyst. In such a line-up the petroleum derived feed may be advantageously added prior to contacting with the platinum/ZSM-48 or platinum/ZSM-23 catalyst according to the present invention.
In step (a) 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 425° C., preferably higher than 250° C. and more preferably from 280 to 400° C. The hydrogen partial pressure will typically be in the range of from 10 to 250 bar and preferably between 20 and 100 bar. The hydrocarbon feed may be provided at a weight hourly space velocity of from 0.1 to 5 kg/l/hr (mass feed/volume catalyst bed/time), preferably higher than 0.5 kg/l/hr and more preferably lower than 2 kg/l/hr. Hydrogen may be provided at a ratio of hydrogen to hydrocarbon feed from 100 to 5000 Nl/kg and preferably from 250 to 2500 Nl/kg.
The conversion in step (a) as defined as the weight percentage of the feed boiling above 370° C. which reacts per pass to a fraction boiling below 370° C., is at least 20 wt %, preferably at least 25 wt %, but preferably not more than 90 wt %. The feed as used above in the definition is the total hydrocarbon feed fed to step (a), thus also any optional recycle of the higher boiling fraction as obtained in step (b).
In step (b) the product of step (a) is separated into one or more gas oil fractions and a Fischer-Tropsch derived feed having preferably a T10 wt % boiling point of between 200 and 450° C.
The fraction of the gas field condensate in the mixture is preferably higher than 5 wt %, more preferably higher than 10 wt % and preferably lower than 50 wt % and more preferably below 30 wt % and even more preferably below 25 wt %. The actual content of the fraction comprising the gas field condensate in the mixture will of course depend on the paraffin content of said feed. The mixture will preferably contain less than 50 ppm sulphur and/or less that 10 ppm nitrogen.
With the catalytic pour point reducing treatment is understood every process wherein the pour point of the base oil is reduced by more than 10° C., preferably more than 20° C., more preferably more than 25° C.
The catalytic dewaxing or pour point reducing process can be performed by any process wherein in the presence of a catalyst and hydrogen the pour point of the mixture is reduced as specified above. Suitable dewaxing catalysts are heterogeneous catalysts comprising a molecular sieve and optionally in combination with a metal having a hydrogenation function, such as the Group VIII metals. Molecular sieves, and more suitably intermediate pore size zeolites, have shown a good catalytic ability to reduce the pour point of the distillate base oil precursor fraction under catalytic dewaxing conditions. Preferably the intermediate pore size zeolites have a pore diameter of between 0.35 and 0.8 nm. Suitable intermediate pore size zeolites are zeolite beta, mordenite, ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35 and ZSM-48 or combinations of said zeolites. Another preferred group of molecular sieves are the silica-aluminaphosphate (SAPO) materials of which SAPO-11 is most preferred as for example described in U.S. Pat. No. 4,859,311. 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 or mixtures of said metals. Suitable Group VIII metals are nickel, cobalt, platinum and palladium. Examples of possible combinations are Ni/ZSM-5, Pt/ZSM-23, Pd/ZSM-23, Pt/ZSM-48 and Pt/SAPO-11 or stacks of Pt/zeolite beta and Pt/ZSM-22; Pt/zeolite beta and Pt/ZSM-23; and Pt/zeolite beta and Pt/ZSM-48. Further details and examples of suitable molecular sieves and dewaxing conditions are for example described in WO-A-9718278, U.S. Pat. No. 5,053,373, U.S. Pat. No. 5,252,527 and U.S. Pat. No. 4,574,043.
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 metal oxides. 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 are: alumina, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, 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 most preferred binder is silica.
A preferred class of dewaxing catalysts comprise 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 is by contacting an extrudate of the binder and the zeolite with an aqueous solution of a fluorosilicate salt as described in for example U.S. Pat. No. 5,157,191 or WO-A-2000029511. Examples of suitable dewaxing catalysts as described above are silica bound and dealuminated Pt/ZSM-5, silica bound and dealuminated Pt/ZSM-23, silica bound and dealuminated Pt/ZSM-12, silica bound and dealuminated Pt/ZSM-22 as for example described in WO-A-200029511 and EP-B-832171.
Catalytic dewaxing conditions are known in the art and typically involve operating temperatures in the range of from 200 to 500° C., suitably from 250 to 400° C., hydrogen partial pressures in the range of from 10 to 200 bar, preferably from 15 to 100 bar, weight hourly space velocities (WHSV) in the range of from 0.1 to 10 kg of oil per litre of catalyst per hour (kg/l/hr), suitably from 0.2 to 5 kg/l/hr, more suitably from 0.5 to 3 kg/l/hr and hydrogen to oil ratios in the range of from 100 to 2,000 litres of hydrogen per litre of oil. By varying the temperature between 315 and 375° C. at a hydrogen partial pressure of between 15-100 bars, in the catalytic dewaxing step it is possible to prepare base oils having different pour points varying from suitably lower than −60 to −10° C.
Optionally a noble metal guard bed may be positioned just upstream the dewaxing step, for example as a separate catalyst bed in the dewaxing reactor. Such a guard bed is advantageous to remove any remaining sulphur and especially nitrogen compounds present in the feed to the dewaxing process of the present invention.
After performing the pour point reducing treatment lower boiling compounds formed during said treatment are suitably removed, preferably by means of distillation, optionally in combination with an initial flashing step.
The effluent of the pour point reducing treatment may suitably be subjected to a hydrogenation treatment. Hydrogenation may be performed on the entire effluent or on specific base oil grades after the above described fractionation. This may be required in order to reduce the content of aromatic compounds in the reduced pour point product to preferably values of below 1 wt %. Such a hydrogenation is also referred to as a hydrofinishing step. This step is suitably carried out at a temperature between 180 and 380° C., a total pressure of between 10 to 250 bar and preferably above 100 bar and more preferably between 120 and 250 bar. The WHSV (Weight hourly space velocity) ranges from 0.3 to 2 kg of oil per litre of catalyst per hour (kg/l.h). Preferably a hydrogenation is performed in the same reactor as the catalytic dewaxing reactor. In such a reactor the beds of dewaxing catalyst and hydrogenation catalyst will be placed in a stacked bed on top of each other.
The hydrogenation catalyst is suitably a supported catalyst comprising a dispersed Group VIII metal. Possible Group VIII metals are cobalt, nickel, palladium and platinum. Cobalt and nickel containing catalysts may also comprise a Group VIB metal, suitably molybdenum and tungsten. Suitable carrier or support materials are low acidity amorphous refractory oxides. Examples of suitable amorphous refractory oxides include inorganic oxides, such as alumina, silica, titania, zirconia, boria, silica-alumina, fluorided alumina, fluorided silica-alumina and mixtures of two or more of these.
Examples of suitable hydrogenation catalysts are nickel-molybdenum containing catalyst such as KF-847 and KF-8010 (AKZO Nobel) M-8-24 and M-8-25 (BASF), and C-424, DN-190, HDS-3 and HDS-4 (Criterion); nickel-tungsten containing catalysts such as NI-4342 and NI-4352 (Engelhard) and C-454 (Criterion); cobalt-molybdenum containing catalysts such as KF-330 (AKZO-Nobel), HDS-22 (Criterion) and HPC-601 (Engelhard). Preferably platinum containing and more preferably platinum and palladium containing catalysts are used. Preferred supports for these palladium and/or platinum containing catalysts are amorphous silica-alumina. Examples of suitable silica-alumina carriers are disclosed in WO-A-9410263. A preferred catalyst comprises an alloy of palladium and platinum preferably supported on an amorphous silica-alumina carrier of which the commercially available catalyst C-624 of Criterion Catalyst Company (Houston, Tex.) is an example.
After performing the catalytic pour point reducing treatment or after the optional hydrofinishing step hydrogen is suitably separated from the dewaxed/hydrofinished effluent, contacted with a means to remove hydrogen sulphide and recycled to said catalytic pour point reducing treatment. Suitably the hydrogen is contacted with a heterogeneous adsorbent selective for removing hydrogen sulphide. Preferably hydrogen is contacted with zinc oxide to remove hydrogensulphide.
From the effluent of the pour point reducing treatment and the optional hydrogenation treatment one or more base oil grades may be isolated by means of fractionation. Base oil products having kinematic viscosity at 100° C. of between 2 and 10 cSt, having a volatility of between 8 and 11% (according to CEC L40 T87) and a pour point of between −20 and −60° C. (according to ASTM D 97) may advantageously be obtained.
The content of paraffins is more preferably less than 90 wt % and more preferably higher than 80 wt %.
The above-described base oil can suitably find use as base oil for an Automatic Transmission Fluids (ATF), motor engine oils, electrical oils or transformer oils and refrigerator oils. Lubricant formulations such as motor engine oils of the 0W-x and 5W-x specification according to the SAE J-300 viscosity classification, wherein x is 20, 30, 40, 50 or 60 may be advantageously made using this base oil.
It has been found that lubricant formulations can be prepared with the base oils obtainable by the process of the current invention without the need to add high contents of additional ester or aromatic co-base oils. Preferably less than 15 wt % and more preferably less than 10 wt % of such ester or aromatic co-base oil is present in such formulations.

Claims

1. A process to prepare a base oil having a paraffin content of between 75 and 95 wt % comprising subjecting a mixture of a Fischer-Tropsch derived feed and a gas field condensate derived feed to a catalytic pour point reducing treatment, wherein the gas field condensate has an aromatic content of between 0 and 20 wt % and a naphthenic compound content of between 15 and 90 wt %.

2. The process according to claim 1, wherein the content of sulphur in the mixture subjected to the pour point reducing treatment is below 50 ppm and the content of nitrogen in the mixture subjected to the pour point reducing treatment is below 10 ppm.

3. The process according to claim 1, wherein the fraction of gas field condensate in the mixture is higher than 5 wt % and lower than 50 wt %.

4. The process according to claim 1, wherein the base oil is hydrogenated after performing the pour point reducing treatment such that the content of aromatics is below 1 wt %.

5. The process according to claim 1, wherein the catalytic pour point reducing treatment is a catalytic dewaxing process performed in the presence of a catalyst comprising a Group VIII metal and an intermediate pore size zeolite having pore diameter between 0.35 and 0.8 nm, and a binder.

6. The process according to claim 1, wherein after performing the catalytic pour point reducing treatment hydrogen is separated from the dewaxed effluent, contacted with a heterogeneous adsorbent selective for removing hydrogen sulphide and recycled to said catalytic pour point reducing treatment.

7. The process according to claim 6, wherein the heterogeneous adsorbent is zinc oxide.

8. The process according to claim 1, wherein the Fischer-Tropsch derived feed is obtained by hydroisomerisation of a Fischer-Tropsch product.

9. The process according to claim 1, wherein the feed to the catalytic dewaxing step is obtained by hydroisomerisation of a mixture of a Fischer-Tropsch product and a gas field condensate.

10. The process according to claim 8, wherein the hydroisomerised Fischer-Tropsch feed is obtained by means of the following steps:

(a) hydrocracking/hydroisomerisating a Fischer-Tropsch product,

(b) separating by means of distillation the product of step (a) into one or more gas oil fractions and a higher boiling Fischer-Tropsch derived feed.

11. The process according to claim 1, wherein the Fischer-Tropsch product used as feed in step (a) is a product wherein the weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms in the Fischer-Tropsch product is at least 0.4 and wherein at least 30 wt % of compounds in the Fischer-Tropsch product have at least 30 carbon atoms.