Process to Prepare a Lubricating Base Oil

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 petroleum 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-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 are 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 an paraffin content of between 75 and 95 wt % by subjecting a mixture of a Fischer-Tropsch derived feed and a petroleum derived feed to a catalytic pour point reducing treatment.

Applicants found that by mixing a relatively small amount of a petroleum 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.

The petroleum-derived fraction may in principle be any fraction boiling in the base oil range and containing non-paraffinic compounds. Preferably a petroleum-derived fraction is used which has been subjected to a hydroprocessing step in order to reduce aromatic, sulphur and nitrogen content of such fractions and improve some of the desired properties such viscosity index. The hydroprocessing step may be a hydrotreating optionally followed by a hydrocracking step. Such processes are for example performed when preparing base oils from a petroleum derived vacuum distillate or de-asphalted oils.

A very interesting petroleum derived feed is the bottoms fraction of a fuels hydrocracker. With a fuels hydrocracker in the context of the present invention is meant a hydrocracker process which main products are naphtha, kerosene and gas oil. The conversion, expressed in the weight percentage of the fraction in the feed to the hydrotreater-hydrocracker which boils above 370° C. which are converted to products boiling below 370° C., in the hydrotreater-hydrocracker process is typically above 50 wt %. Examples of possible fuels hydrocracker processes, which may yield a bottoms fraction which can be used in the present process, are described in the above referred to EP-A-699225, EP-A-649896, WO-A-9718278, EP-A-705321, EP-A-994173 and U.S. Pat. No. 4,851,109.

Another interesting petroleum derived feed is the fraction obtained in a dedicated base oil hydrotreater-hydrocracker. In such a hydrotreater-hydrocracker the main products will boil in the base oil range. Typically such processes operate at a feed conversion of below 50 wt % and more typically between 20 and 40 wt %. The petroleum derived feed is thus the high boiling fraction as obtained in such a process prior to dewaxing.

Preferably the fuels hydrocracker is operated in two steps, consisting of a preliminary hydrotreating step followed by a hydrocracking step. In the hydrotreating step nitrogen and sulphur are removed and aromatics are saturated to naphthenes

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.

The mixture of petroleum derived and Fischer-Tropsch derived feeds will suitably have a viscosity corresponding to the desired viscosity of the base oil product. Preferably the kinematic viscosity at 100° C. of the mixture is between 3 and 10 cSt. Suitable distillate fractions obtained in step (a) have a T10 wt % boiling point of between 200 and 450° C. and a T90 wt % boiling point of between 300 and 550° C. The fraction of petroleum derived feed 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 petroleum-derived feed 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 base oil precursor fraction 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 mordenite, ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35 and ZSM-48. 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. 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. 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 pressures in the range of from 10 to 200 bar, preferably from 40 to 70 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 between 40-70 bars, in the catalytic dewaxing step it is possible to prepare base oils having different pour point specifications varying from suitably lower than −60 to −10° C.

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.

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 % the process comprising subjecting a mixture of a hydroisomerized Fischer-Tropsch wax and a petroleum derived feed to a catalytic pour point reducing treatment, wherein the petroleum derived feed has an aromatic content of between 0 and 20 wt % and a naphthenic compound content of between 15 and 90 wt % and wherein the fraction of petroleum derived feed in the mixture is higher than 5 wt % and lower than 50 wt %.

2. The process of claim 1, wherein the petroleum derived feed is a bottoms fraction of a fuels hydrocracker.

3. The process of Process according to claim 2, wherein the content of sulfur in the mixed feed to the pour point reducing treatment is below 50 ppm and the content of nitrogen in the mixed feed to the pour point reducing treatment is below 10 ppm.

4. The process of claim 1, wherein the wax content in the petroleum derived feed is below 30 wt %.

5. The process of claim 4, wherein the pour point of the petroleum derived feed is below −10° C.

6. The process of claim 1, wherein the petroleum derived feed has a saturates content of greater than 98 wt % a viscosity index of between 80 and 150 and a sulfur content of below 0.001 wt %.

7. The process of claim 6, wherein the petroleum derived feed has been obtained in a process comprising a hydrofinishing step performed at a hydrogen pressure of greater than 100 bars.

8. The process of 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 %.

9. The process of 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.

10. The process of 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 sulfide and recycled to said catalytic pour point reducing treatment.

11. The process of claim 10, wherein the heterogeneous adsorbent is zinc oxide.

12. The process of claim 1, wherein the hydroisomerized Fischer-Tropsch wax is obtained by a process comprising:

(a) hydrocracking/hydroisomerizing a Fischer-Tropsch product, and,

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

13. The process of claim 12, 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.

14. The process of claim 2, wherein the content of sulfur in the mixed feed to the pour point reducing treatment is below 50 ppm and the content of nitrogen in the mixed feed to the pour point reducing treatment is below 10 ppm.

15. The process of claim 2, wherein the wax content in the petroleum derived feed is below 30 wt %.

16. The process of claim 15, wherein the pour point of the petroleum derived feed is below −10° C.

17. The process of claim 2, wherein the petroleum derived feed has a saturates content of greater than 98 wt % a viscosity index of between 80 and 150 and a sulfur content of below 0.001 wt %.

18. The process of claim 17, wherein the petroleum derived feed has been obtained in a process comprising a hydrofinishing step performed at a hydrogen pressure of greater than 100 bars.

19. The process of claim 2, wherein the base oil is hydrogenated after performing the pour point reducing treatment such that the content of aromatics is below 1 wt %.

20. The process of claim 2, 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.

21. The process of claim 2, 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 sulfide and recycled to said catalytic pour point reducing treatment.

22. The process of claim 21, wherein the heterogeneous adsorbent is zinc oxide.

23. The process of claim 2, wherein the hydroisomerized Fischer-Tropsch wax is obtained by a process comprising:

(a) hydrocracking/hydroisomerizing a Fischer-Tropsch product, and,

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

24. The process of claim 23, 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.