Patent Application
20070170092
The invention relates to a process to prepare a haze free base oil having a kinematic viscosity at 100° C. of greater than 10 cSt from a Fischer-Tropsch wax.
Many publications are known describing processes for the conversion of gaseous hydrocarbonaceous feed stocks, as methane, natural gas and/or associated gas, into liquid products, especially methanol and liquid or solid hydrocarbons, particularly paraffinic hydrocarbons. In this respect often reference is made to remote locations (e.g. in the dessert, tropical rain-forest) and/or offshore locations, where no direct use of the gas is possible, usually due to the absence of large populations and/or the absence of any industry. Transportation of the gas, e.g. through a pipeline or in the form of liquefied natural gas, requires extremely high capital expenditure or is simply not practical.
To make efficient use of such stranded gas reserves on-site Fischer-Tropsch processes are being build. Such processes involve a synthesis gas manufacturing step using the natural gas as feedstock and a Fischer-Tropsch synthesis step to make a heavy wax. WO-A-02070627 describes a process for preparing a base oil having a kinematic viscosity at 100° C. of 22 cSt from a heavy Fischer-Tropsch wax.
A problem of the prior art processes is that especially the base oils having a high viscosity often show a haze. This haze makes the process less suitable for some applications. However not all applications for this family of base oils require that a haze should be absent. The object of the present invention is a process to prepare haze free base oils in an efficient manner.
The following process achieves this object. Process to prepare a haze free base oil having a kinematic viscosity at 100° C. of greater than 10 cSt from a Fischer-Tropsch wax feed by performing the following steps,
The process according the invention is advantageous because step (a) is typically performed at a remote location. Thus any low boiling by-products can be advantageously be blended with lower boiling products of the Fischer-Tropsch process at that remote location. Examples of such products are base oils having a lower viscosity and gas oil. A further advantage of this process is that step (c) can be performed at a location more close to the end users. This allows the user of this process to choose the dewaxing technique most suited for the specific application. Thus if a haze free lubricant is required a solvent dewaxing step according the invention is applied. If on the other hand haze is not a major issue a less selective dewaxing technique can be used. Thus it is not required to have two types of dewaxing technology at the remote location and optimal use can be made of existing dewaxing facilities at the locations more close to the end users. A further advantage is that all of the intermediate product can be efficiently used. Because step (c) is a solvent dewaxing step an oil having the desired viscometric properties and a valuable microcrystalline wax is obtained. Thus all of the intermediate product can be sold as products. In contrast, if a catalytic dewaxing is performed on the intermediate product low boiling by-products would have been obtained which would only have a blending value at the location close to the costumer. This value would be less than the value of these by-products if the dewaxing had been performed at the remote location. A further advantage is that the high quality products such as the haze free base oil as well as the wax as prepared in step (c) do not have to be transported from the remote location to the end users.
A further advantage is that the wax feed used in step (a) may also contain the heaviest molecules as prepared in the Fischer-Tropsch synthesis. This is advantageous because it is now possible to prepare high viscosity grade base oils without having to perform a deep-cut distillation in order to remove possible haze-precursors as for example described in WO-A-03033622.
The Fischer-Tropsch wax as used in step (a) can be obtained by well-known processes, for example the so-called Sasol process, the Shell Middle Distillate Process or by the ExxonMobil “AGC-21” 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.
More preferably the wax used in step (a) is prepared according to the following process. In this process a Fischer-Tropsch product is subjecting to a hydroisomerisation step and a wax containing fraction is isolated from the product of said hydroisomerisation step. More preferably this fraction is a distillation residue comprising the most highly molecular weight compounds still present in the product of the 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 500° C. for certain embodiments of the present invention. In case the feed to step (a) has a 10 wt % recovery boiling point of above 500° C. the wax content will suitably be greater than 50 wt %. The feed to the hydroisomerisation step 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 of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms of the Fischer-Tropsch product is at least 0.2, preferably at least 0.4 and more preferably at least 0.55. 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 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 said hydroisomerisation step.
Such a Fischer-Tropsch product can be obtained by any process, which yields a relatively heavy Fischer-Tropsch product. 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 yield 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 5 ppm for sulphur and 1 ppm for nitrogen.
The hydrocracking/hydroisomerisation reaction of the hydroisomerisation 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 functionality's 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 for use in the process of this invention 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 require special operating conditions and involve environmental problems. Examples of suitable hydrocracking/hydroisomerisation processes and suitable catalysts are described in WO-A-0014179, EP-A-532118, EP-A-666894 and the earlier referred to EP-A-776959.
Preferred hydrogenation/dehydrogenation functionality's are Group VIII metals, for example cobalt, nickel, palladium and platinum and more preferably platinum. In 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 case nickel is used a higher content will be present, optionally 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 between 20 and 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 hydrogen to hydrocarbon feed may range from 100 to 5000 Nl/kg and is preferably from 250 to 2500 Nl/kg.
The conversion in the hydroisomerisation 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 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, thus also any optional recycle to step (a).
One or more distillate separations are performed on the effluent of the hydroisomerisation step to obtain at least one middle distillate fuel fraction and the wax which is to be used in step (a). Preferably the effluent is subjected to an atmospheric distillation. 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. Thus 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. This fraction may be directly used in step (a) or may be subjected to an additional vacuum distillation suitably performed at a pressure of between 0.001 and 0.1 bara. The heavy wax for step (a) is preferably obtained as the bottom product of such a vacuum distillation.
Step (a) may be performed using any hydroconversion process, which is capable of reducing the wax content. to below 50 wt %. 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 %. A minimal amount of wax will is required in order to operate a solvent dewaxing step in an optimal manner. The intermediate product as obtained in step (a) preferably has a congealing point of below 80° C. and more preferably between 20 and 60° 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). The wax content as used in the description is measured according to the following procedure. 1 weight part of the to be measured oil fraction 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. If reference is made to oil content a wt % value is meant which is 100% minus the wax content in wt %.
A possible process is the hydroisomerisation process as described above. It has been found that the wax may be reduced to the desired level using such catalyst. 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 (a), 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 that more of the heavy molecules are retained in the dewaxed oil. Thus a more viscuous base oil can then be obtained.
The dewaxing catalyst which may be applied in step (a) suitably comprises 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 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 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. 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-9718278, U.S. Pat. No. 4,343,692, U.S. Pat. No. 5,053,373, U.S. Pat. No. 5,252,527, US-A-20040065581, U.S. Pat. No. 4,574,043 and EP-A-1029029.
A preferred class of molecular sieves are 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 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-0029511. Examples of suitable dewaxing catalysts as described above are silica bound and dealuminated Pt/ZSM-5, silica bound and dealuminated Pt/ZSM-35 as for example described in WO-A-0029511 and EP-B-832171.
The conditions in step (a) 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 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 0.1 to 5 kg/l/hr, more suitably from 0.1 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.
Transportation in step (b) is preferably performed by means of a ship. The location at which step (a) is performed is preferably a remote location and the location of which step (c) is performed is preferably a location more close to the end users of the base oil. The product is loaded into the ships containers by preferably first purging the empty product containers in the ship with nitrogen in order to lower the oxygen content. Purging is preferably performed for at least 5 minutes and more preferably for at least 10 minutes. After purging the product containers are filled with the intermediate product. Preferably nitrogen is supplied to the loaded containers to achieve a nitrogen atmosphere in the gaseous space above the product in the product containers. More preferably nitrogen is supplied for at least 5 minutes and more preferably for at least 10 minutes to the loaded containers. The duration of the transport in step (b) is typically more than 5 days. The nitrogen used is preferably the nitrogen as obtained when oxygen is isolated from the air in an air separation unit. The oxygen is typically used to prepare synthesis gas, which in turn in used as feedstock for the Fischer-Tropsch reaction to make the F-T wax.
In step (c) the haze free oil is obtained by solvent dewaxing the intermediate product as transported in step (b). Solvent dewaxing is well known to those skilled in the art and involves admixture of one or more solvents and/or wax precipitating agents with the base oil precursor fraction and cooling the mixture to a temperature in the range of from −10° C. to −40° C., preferably in the range of from −20° C. to −35° C., to separate the wax from the oil. The oil containing the wax is usually filtered through a filter cloth which can be made of textile fibres, such as cotton; porous metal cloth; or cloth made of synthetic materials. Examples of solvents which may be employed in the solvent dewaxing process are C3-C6 ketones (e.g. methyl ethyl ketone, methyl isobutyl ketone and mixtures thereof), C6-C10 aromatic hydrocarbons (e.g. toluene), mixtures of ketones and aromatics (e.g. methyl ethyl ketone and toluene), autorefrigerative solvents such as liquefied, normally gaseous C2-C4 hydrocarbons such as propane, propylene, butane, butylene and mixtures thereof. Mixtures of methyl ethyl ketone and toluene or methyl ethyl ketone and methyl isobutyl ketone are generally preferred. Examples of these and other suitable solvent dewaxing processes are described in Lubricant Base Oil and Wax Processing, Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994, Chapter 7.
In step (c) also a wax is obtained. It has been found that such a wax is a relatively soft microcrystalline wax, which may be used for various purposes. An additional advantage of the present invention is that the wax is recovered from the intermediate product at a location near the end-costumer. The soft microcrystalline wax as obtained with the above process has preferably a congealing point as determined by ASTM D 938 of between 85 and 120 and more preferably between 95 and 120° C. and a PEN at 43° C. as determined by IP 376 of more than 0.8 mm and preferably more than 1 mm. The wax is further characterized in that it preferably comprises less than 1 wt % aromatic compounds and less than 10 wt % naphthenic compounds, more preferably less than 5 wt % naphthenic compounds. The mol percentage of branched paraffins in the wax is preferably above 33 and more preferably above 45 and below 80 mol % as determined by C13 NMR. This method determines an average molecular weight for the wax and subsequently determines the mol percentage of molecules having a methyl branch, the mol percentage of molecules having an ethyl branch, the mol percentage of molecules having a C3 branch and the mol percentage having a C4+ branch, under the assumption that each molecule does not have more than one branch. The mol % of branched paraffins is the total of these individual percentages. This method calculated the mol % in the wax of an average molecule having only one branch. In reality paraffin molecules having more than one branch may be present. Thus the content of branched paraffins determined by a different method than above may result in a different value.
The oil content of the wax as determined by ASTM D 721 is typically below 10 wt % and more preferably below 6 wt %. If lower oil contents are desired it may be advantageous to perform an additional de-oiling step. De-oiling processes are well known and are for example described in Lubricant Base Oil and Wax Processing, Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994, pages 162-165. After de-oiling the wax preferably has a oil content of between 0.1 and 2 wt %. The lower limit is not critical. Values of above 0.5 wt % may be expected, but lower values can be achieved depending on the method in which the wax is obtained. Most likely the oil content will be between 1 and 2 wt %. The kinematic viscosity at 150° C. of the wax is preferably higher than 8 cSt and more preferably higher than 12 and lower than 18 cSt.
The haze free base oil will preferably have a kinematic viscosity at 100° C. of above 10 cSt, preferably above 14 cSt which viscosity may range up to 30 cSt and even above. The pour point is preferably below −5° C., more preferably below −18° C. and even more preferably below −21° C. The viscosity index is suitably above 120 and preferably above 130. A haze free base oil is determined by its cloud point. A haze free base oil according to this invention has a cloud point as determined by ASTM D2500 of near the pour point and below 0° C., preferably below −10° C. and more preferably below −15° C.
Because of these properties applicant has found that the base oil may be advantageously be used to prepare a lubricant composition which does not require a viscosity modifier (VM). Applicants further found that such a VISCOSITY MODIFIER-free lubricant may be obtained without having to add a poly-alpha olefin co-base oil as shown in WO-A-0157166. The invention is thus also directed to prepare a VM-free lubricant composition by blending a preferably Fischer-Tropsch derived and low viscosity base oil with the haze free base oil as obtained in step (c) and one or more additives. The low viscosity base oil preferably has a kinematic viscosity at 100° C. of less than 7 cSt. The haze free base oil preferably has a kinematic viscosity at 100° C. of more than 10 cSt, more preferably more than 14 cSt and most preferably more than 18 cSt.
Applicants found that by blending the haze free base oil with the lower viscosity grade base oil it is possible to achieve the properties of a so-called SAE “xW-y” viscosity lubricant formulation without having to add a viscosity modifier. Applicants further found that when a viscosity modifier-free lubricant is used as motor engine lubricant in gasoline direct injection (GDI) engines no build up of residue on the back of the inlet valve tulip occurs, which would happen if a VM is present.
It has further been found that especially SAE “xW-y” viscosity lubricant formulations wherein y minus x is greater or equal than 25 can be prepared without having to add a VM. Based on the teaching of WO-A-0157166 one would have expected that such formulations could only be prepared by having to add a VM.
The low viscosity Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. of less than 7 cSt preferably has a pour point of less than −18° C., more preferably less than −27° C. The kinematic viscosity at 100° C. is preferably greater than 3.5 cSt and more preferably between 3.5 and 6 cSt. The viscosity index (VI) is preferably greater than 120, more preferably greater than 130. The VI will typically be less than 160. The Noack volatility (according to CEC L40 T87) is preferably less than 14 wt %. The low viscosity component may be a typical API Group III base oil and more preferably a Fischer-Tropsch derived base oil as disclosed in for example EP-A-776959, EP-A-668342, WO-A-9721788, WO-A-0015736, WO-A-0014188, WO-A-0014187, WO-A-0014183, WO-A-0014179, WO-A-0008115, WO-A-9941332, EP-A-1029029, WO-A-0118156 and WO-A-0157166.
From a hydroisomerised Fischer-Tropsch wax a distillation residue was isolated having the properties as listed in Table 1. The wax content was 34.1 wt % as determined after solvent dewaxing at a dewaxing temperature of −20° C.
The above residue was contacted with a dewaxing catalyst consisting of 0.7 wt % platinum, 25 wt % ZSM-12 and a silica binder. The dewaxing conditions were 40 bar hydrogen, WHSV=1 kg/l.h, and a hydrogen gas rate of 500 Nl/kg feed. The experiment was carried out at three different reaction temperatures. See results in
wax content as measured after solvent dewaxing at −20° C.
The fraction boiling above 485° C. as obtained in 1a, 1b and 1c was easy to transport. Optionally the fraction to be transported could also comprise the liquid fraction boiling below 485° C. as obtained in the catalytic dewaxing step. The transportable intermediate product was subsequently solvent dewaxed using a mixture of methyl ethyl ketone and toluene (50/50 vol/vol) solvent at a dewaxing temperature of −20° C. The properties and yields of the oils obtained are listed in Table 3.
Based on the above experimental data
From a hydroisomerised Fischer-Tropsch wax a distillation residue was isolated having the properties as listed in Table 4. The wax content was 41 wt % as determined after solvent dewaxing at a dewaxing temperature of −20° C.
The above residue was contacted with a dewaxing catalyst consisting of 0.7 wt % platinum, 25 wt % ZSM-12 and a silica binder. The dewaxing conditions were 40 bar hydrogen, WHSV=1 kg/l.h, and a hydrogen gas rate of 500 Nl/kg feed. The experiment was carried out at 340° C. From the partly dewaxed oil compounds boiling below 500° C. were removed by distillation. The remaining fraction containing 34 wt % wax was a liquid slurry at room temperature and was thus easy to transport. See also the results in Table 5.
*wax content as measured after solvent dewaxing at −20° C.
The liquid slurry fraction boiling above 500° C. was solvent dewaxed using a mixture of methyl ethyl ketone and toluene (50/50 vol/vol) solvent at a dewaxing temperature of −20° C. The properties and yields of the oil as obtained are listed in Table 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03293322.8 | Dec 2003 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/53640 | 12/21/2004 | WO | 6/21/2006 |
