Patent Grant
6846778
1. Field of the Invention
The invention relates to a synthetic isoparaffinic heavy hydrocarbon useful as a heavy lubricant base stock, produced by isomerizing Fischer-Tropsch wax, and to a heavy lubricant formed from the base stock.
2. Background of the Invention
Heavy lubricants are used for high viscosity applications in which a lubricant based on a lighter oil will not provide sufficient lubrication between moving parts, such as heavy machine oils, gear boxes, deep drawing oils, and manual transmissions. A heavy lubricant is formed by combining a heavy lubricant base stock, which is a heavy oil possessing lubricating oil qualities, with one or more lubricant additives. Most heavy lubricant base stocks are derived from naturally occurring petroleum oil and contain aromatic unsaturates, including polynuclear aromatics, along with sulfur and nitrogen containing compounds. These compounds tend to reduce the viscosity and stability of the oil. Refining the oil to remove these components results in a low yield of the product oil. Heavy paraffins can be refined to low levels of unsaturates and heteroatom compounds, but have unacceptably high pour and cloud points. There is a need for a relatively pure or premium quality, heavy lubricant base stock composition that is a liquid at least at the temperature of use.
The invention relates to a relatively pure, premium quality, synthetic, isoparaffinic, heavy hydrocarbon composition useful as a heavy lubricant base stock, to a heavy lubricant base stock and to a heavy lubricant composition formed from the heavy lubricant base stock. The isoparaffinic, heavy lubricant base stock composition comprises mostly (≧98 wt %) saturated, paraffinic hydrocarbon molecules, is an oily liquid having a kinematic viscosity at 100° C. greater than 8 cSt (centistokes), with initial (5%) and end (95%) boiling points of at least 850° F. (454° C.) and 1,000° F. (538° C.). By isoparaffinic is meant that it comprises at least 90 wt % isoparaffins. It contains hydrocarbon molecules having consecutive numbers of carbon atoms. The extent of branching of the isoparaffinic hydrocarbon molecules, as measured by the percentage of methyl hydrocarbons, hereinafter referred to as the branching index (BI), and the proximity of the branches (or branching proximity), as measured by the percentage of recurring methylene carbons which are four or more carbon atoms removed from an end group or branch (CH2>4), are such that:
BI−0.5(CH2>4)<15; and (a)
BI+0.85(CH2>4)<45; (b)
as measured over the liquid hydrocarbon composition as a whole. The BI is less than 24 and the branching proximity, (CH>4), is greater than 17. In another embodiment, the invention relates to a heavy lubricant composition, formed by combining the heavy lubricant base stock composition of the invention, with one or more lubricant additives. While the hydrocarbon composition of the invention is useful as a heavy lubricant base stock, it will have other uses such as, for example, a heavy white oil, a pharmaceutical oil, as a carrier or base for medicinal formulations, in chemical and pharmaceutical manufacturing, and the like. Thus, in further embodiments the invention comprises one or more of the following, of or in which at least a portion uses or is based on the hydrocarbon composition of the invention; a heavy white oil, a pharmaceutical oil, a carrier or base for medicinal formulations, chemical and pharmaceutical manufacturing processes.
The FIGURE is a graph plotting the BI and % CH2>4 values derived from NMR spectra of the hydrocarbon compositions of the invention, the comparative examples of this application, and the data of U.S. Pat. No. 6,090,989 which includes other hydrocarbon compositions. The disclosure of the '989 patent is incorporated herein in its entirety by reference. The shaded area on the plot defines the NMR parameter space of the compositions of the invention. Only the heavy lube base stocks of this invention which are derived from Fischer-Tropsch synthesized waxy hydrocarbons and PAO base stocks fall in this area of parameter space. The molecular composition of the PAO stocks are different from the compositions of the invention in that (i) they do not contain hydrocarbon molecules having consecutive numbers of carbon atoms, (ii) the % CH3 groups on the molecules is below 15, whereas those for the base stocks of the invention are above 20, (iii) the % CH groups for the PAO stocks is above 3, whereas for the base stocks of the invention it is less than 2.
The hydrocarbon or heavy lubricant base stock composition of the invention is produced from Fischer-Tropsch wax and comprises mostly (≧98 wt %) saturated, paraffinic hydrocarbons, of which at least 90 wt % are non-cyclic hydrocarbons and no more than 10 wt % cyclic hydrocarbons. At least 90 and preferably at least 95 wt % of the paraffinic hydrocarbon molecules are isoparaffins. While paraffinic cyclic hydrocarbons may be present in an amount of up to 5 wt %, more typically they will not exceed 1 wt %, if present. The kinematic viscosity at 100° C. is greater than 8 cSt. The composition of the invention contains molecules having consecutive numbers of carbon atoms and at least 95 wt % C30+ hydrocarbon molecules. The initial boiling point is at least 850° F. (454° C.), preferably 900° F. (482° C.) and the end boiling point is at least 1,000° F. (538° C.). It is a liquid at the temperature and pressure conditions of use and typically, but not always, at ambient conditions of 75° F. (24° C.) and one atmosphere (101 kPa) pressure. The initial and end boiling points values referred to herein are nominal and refer to the T5 and T95 cut points (boiling temperatures) obtained by gas chromatograph simulated distillation (GCD), using the method set forth below.
The extent of branching of the iosoparaffinic hydrocarbon components, as measured by the percentage of methyl hydrocarbons or branching index (BI), and the proximity of the branches (or branching proximity), as measured by the percentage of recurring methylene carbons which are four or more carbon atoms removed from an end group or branch (CH2>4), are such that:
BI−0.5(CH2>4)<15; and (a)
BI+0.85(CH2>4)<45; (b)
as measured over the liquid hydrocarbon composition as a whole. The BI is less than 24 (BI<24) and the branching proximity is greater than 17 ((CH2>4)>17). The composition also preferably contains at least 75 wt % of C35+ hydrocarbon molecules.
The hydrocarbon or heavy lubricant base stock composition of the invention is different from one derived from petroleum oil, slack wax, a PAO oil and the lubricant base stock disclosed by Trewella et al, in U.S. Pat. No. 6,090,989, which was obtained by isomerizing Fischer-Tropsch wax. Sulfur, nitrogen and metals in the form of hydrocarbon compounds containing them are present in amounts of less than 50 wppm. Hydrocarbon compositions of the invention that have been made from Fischer-Tropsch wax contain less than 1 wppm sulfur, nitrogen and metals. These were not detectable by x-ray or Antek Nitrogen tests. While the hydrocarbon or heavy lubricant base stock of the invention is a mixture of various molecular weight paraffinic hydrocarbons, the residual normal paraffin content remaining after hydrodewaxing is less than 5 wt % and more typically less than 1 wt %, with at least 95% of the oil molecules containing at least one branch, at least half of which are methyl branches. At least half, and more preferably at least 75% of the remaining branches are ethyl, with less than 25% and preferably less than 15% of the total number of branches having three or more carbon atoms. The total number of branch carbon atoms is typically less than 25%, preferably less than 20% and more preferably no more than 15% (e.g., 10-15%) of the total number of carbon atoms comprising the hydrocarbon molecules. PAO oils are an oligomerization product of even carbon numbered linear alpha olefins, typically 1-decene. The PAO oil molecules therefore comprise a mixture of even carbon numbered hydrocarbon molecules, differing from each other in the number of carbon atoms, by multiples of the number of carbon atoms in the linear alpha olefin starting monomer. Even if a mixture of linear alpha olefin monomers having even numbers of carbon atoms (e.g., decene and dodecene) were oligomerized to form a heavy lubricant base stock oil, the number of carbon atoms in the resulting hydrocarbon molecules would still have even numbers of carbon atoms. This is different from the mixture of consecutive numbered hydrocarbon molecules of the heavy lubricant base stock of the invention, which comprise hydrocarbon molecules having both even and odd numbers of carbon atoms and which differ from each other by consecutive numbers of carbon atoms (e.g., 1, 2, 3, 4, 5, 6, 7 and more carbon atoms).
That hydrocarbon molecules of the composition of the invention differ from each other by consecutive numbers of carbon atoms, is a consequence of the Fischer-Tropsch hydrocarbon synthesis reaction from which the wax feed, which was isomerized to form the hydrocarbon or heavy lubricant base stock of the invention was produced. In the Fischer-Tropsch hydrocarbon synthesis reaction the source of carbon atoms is CO and the hydrocarbon molecules are built up one carbon atom at a time. In contrast to an oil based on PAO, the molecules of the hydrocarbon or heavy lubricant base stock of the invention have a more linear structure, comprising a relatively long backbone with short branches. The classic textbook description of a PAO is a star-shaped molecule, and in particular tridecane, which is illustrated as three decane molecules attached at a central point. While a star-shaped molecule is theoretical, nevertheless PAO molecules have fewer and longer branches than the hydrocarbon molecules that make up the base stock of the invention. Thus, the molecular make up of a base stock of the invention comprises at least 95 wt % isoparaffins (with no more than 5 wt % saturated cyclics) having a relatively linear molecular structure, with less than half the branches having two or more carbon atoms and less than 25% of the total number of carbon atoms present in the branches. In contrast to the present invention, in the molecular make-up of a PAO oil, more than half the branches contain two or more carbon atoms and more than 25% of the total number of carbon atoms are in the branches.
As those skilled in the art know, a lubricant base stock, sometimes also referred to as a lubricating or lube oil base stock, including a heavy lubricant base stock, is an oil boiling in the lubricating oil range, having a lubricating quality and is useful for preparing various lubricants such as lubricating oils and greases. In the present invention the oil boils in the heavy lubricant oil range. Fully formulated heavy lubricants or heavy lubricating oils are prepared by adding to the heavy lubricant base stock, an effective amount of at least one additive or, more typically, an additive package containing more than one additive. Illustrative, but non-limiting examples of such additives include one or more of a detergent, a dispersant, an antioxidant, an antiwear additive, an extreme pressure additive, a pour point depressant, a VI improver, a friction modifier, a demulsifier, an antioxidant, an antifoamant, a corrosion inhibitor, and a seal swell control additive.
A hydrocarbon or heavy lubricant base stock composition of the invention comprises a dewaxed oil having low temperature properties able to meet target specifications or requirements and will be a clear and bright, oily liquid at the temperature and pressure conditions under which it is used. Typically, but not always, it will be an oily liquid at room temperature and pressure conditions of 75° F. (24° C.) and one atmosphere (101 kPa) pressure and is an oily liquid at this pressure and a temperature of 100° C. In some cases the cloud point may be higher than 75° F. (24° C.). A hydrocarbon or heavy lubricant base stock composition of the invention, having an end boiling point above 1,250° F. (677° C.), with respective cloud and pour points of 1° C. and −31° C., has been made according to the invention. Low temperature property requirements of both a heavy lubricant base stock and a finished lubricant will vary and can depend on both the application for which it is intended and the geographical location in which the lubricant will be used. A lubricant composition, or finished lubricant product (these two terms are used herein synonymously), also referred to as a lubricating oil, is prepared by forming a mixture of a heavy lubricant base stock composition of the invention and an effective amount of at least one additive or, more typically, an additive package containing more than one additive, as mentioned above. The heavy lubricant base stock composition of the invention used in forming the mixture, will typically have been mildly hydrofinished and/or dehazed after hydrodewaxing, to improve its color, appearance and stability.
As is known, haze is cloudiness or a lack of clarity, and is an appearance factor. Dehazing is typically achieved by either catalytic or absorptive methods to remove those constituents that result in haziness. Hydrofinishing is a very mild, relatively cold hydrogenating process, which employs a catalyst, hydrogen and mild reaction conditions to remove trace amounts of heteroatom compounds, aromatics and olefins, to improve oxidation stability and color. Hydrofinishing reaction conditions include a temperature of from 302 to 662° F. (150 to 350° C.) and preferably from 302 to 482° F. (150 to 250° C.), a total pressure of from 400 to 3000 psig (2859 to 20786 kPa), a liquid hourly space velocity ranging from 0.1 to 5 LHSV (hr−1) and preferably 0.5 to 3 hr−1. The hydrogen treat gas rate will range from 2550 to 10000 scf/B (44.5 to 1780 m3/m3). The catalyst will comprise a support component and one or catalytic metal components of metal from Groups VIB (Mo, W, Cr) and/or iron group (Ni, Co) and noble metals (Pt, Pd) of Group VIII. The Groups VIB and VIII referred to herein, refers to Groups VIB and VIII as found in the Sargent-Welch Periodic Table of the Elements copyrighted in 1968 by the Sargent-Welch Scientific Company. The metal or metals may be present from as little as 0.1 wt % for noble metals, to as high as 30 wt % of the catalyst composition for non-noble metals. Preferred support materials are low in acid and include, for example, amorphous or crystalline metal oxides such as alumina, silica, silica alumina and ultra large pore crystalline materials known as mesoporous crystalline materials, of which MCM-41 is a preferred support component. The preparation and use of MCM-41 is disclosed, for example, in U.S. Pat. Nos. 5,098,684, 5,227,353 and 5,573,657.
The waxy feed or Fischer-Tropsch wax comprises the waxy hydrocarbon fraction produced in a Fischer-Tropsch hydrocarbon synthesis reactor, which is liquid at the reaction conditions. It is referred to as wax, because it is solid at 75° F. (24° C.) and one atmosphere (10I kPa) pressure. It must contain sufficient waxy material boiling above 1000° F. (538° C.) to produce the hydrocarbon or heavy lubricant base stock composition of the invention. The waxy feed is typically dewaxed in one or more catalytic dewaxing steps in which the feed is contacted with hydrogen and a dewaxing catalyst under dewaxing conditions. The iso- to normal paraffin ratio is measured by performing GC-FID or adding on product with up to 20 carbon atoms and in combination with 13 C-NMR for products ≧carbon atoms. Aromatics are determined by X-Ray Fluorescence (XRF), as described in ASTM Standard D-2622. Sulfur is measured by XRF as per ASTM standard D-2622 and nitrogen by syringe/inlet oxidative combustion with chemiluminescence detection per ASTM standard D-4629.
The catalyst useful in the hydrodewaxing step comprises a solid acid component, a hydrogenation component and a binder. Illustrative, but nonlimiting examples of suitable catalyst components useful for hydrodewaxing include, for example, ZSM-23, ZSM-35, ZSM-48, ZSM-57, ZSM-22 also known as theta one or TON, and the silica aluminophosphates known as SAPO's (e.g., SAPO-11, 31 and 41), SSZ-32, zeolite beta, mordenite and rare earth ion exchanged ferrierite. Also useful are alumina and amorphous silica aluminas.
As in the case of many other zeolite catalysts, it may be desired to incorporate the solid acid component with a matrix material also known as a binder, which is resistant to the temperatures and other conditions employed in the dewaxing process herein. Such matrix materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays, silica and/or metal oxides e.g., alumina. The latter may be either naturally occurring or in the form of gelatinous precipitates, sols or gels including mixtures of silica and metal oxides. Use of a material in conjunction with the solid acid component, i.e., combined therewith, which is active, may enhance the conversion and/or selectivity of the catalyst herein. Inactive materials suitably serve as diluents to control the amount of conversion in a given process so that products can be obtained economically and orderly without employing other means for controlling the rate or reaction. Frequently, crystalline silicate materials have been incorporated into naturally occurring clays, e.g., bentonite and kaolin. These materials, i.e., clays, oxides, etc., function, in part, as binders for the catalyst. It is desirable to provide a catalyst having good crush strength since in a petroleum refinery the catalyst is often subject to rough handling which tends to break the catalyst down into powder-like materials which cause problems in processing.
Naturally occurring clays which can be composited with the solid acid component include the montmorillonite and kaolin families which include the sub-bentonites, and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays, or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite or anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification.
In addition to the foregoing materials, the solid acid component can be composited with a porous matrix material such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The matrix can be in the form of a cogel. Mixtures of these components can also be used. The relative proportions of finely divided solid acid component and inorganic oxide gel matrix vary widely with the crystalline silicate content ranging from about 1 to about 90 percent by weight, and more usually in the range of about 2 to about 80 percent by weight, of the composite. ZSM-48 is preferably used.
The hydrogenation component will comprise at least one Group VIII metal component and preferably at least one noble Group VIII metal component, as in Pt and Pd. Noble metal concentrations will range from about 0.1-5 wt % of the metal, and more typically from about 0.2-1 wt %, based on the total catalyst weight, including the ZSM-48 zeolite component and any binder used in the catalyst composite. The Group VIII referred to herein refers to Group VIII as found in the Sargent-Welch Periodic Table of the Elements copyrighted in 1968 by the Sargent-Welch Scientific Company.
The preparation of ZSM-48 (ZSM-48 zeolites include EU-2, EU-11 and ZBM-30 which are structurally equivalent) is well known and is disclosed, for example, in U.S. Pat. Nos. 4,397,827; 4,585,747 and 5,075,269, and EP 0 142 317, the disclosures of which are incorporated herein by reference. Other hydrodewaxing catalysts useful in the practice of the invention, include any of the well known catalysts that dewax mostly by isomerization and not by cracking or hydrocracking. Zeolites comprising ten and twelve membered ring structures are useful as dewaxing catalysts, particularly when combined with a catalytic metal hydrogenating component. Hydrodewaxing reaction conditions employed to produce a hydrocarbon or heavy lubricant composition of the invention include a respective temperature, hydrogen partial pressure and space velocity broadly ranging from 450-750° F. (232-399° C.), 10-2,000 psig (69-13790 kPa), and 0.1-5.0 LHSV. These conditions will more generally range from 500-700° F. (260-371° C.), 100-1000 psig (690-6895 kPa) and 0.5-3.0 LHSV, a pressure of from 200-700 psig (1379-4827 kPa) more typical.
In this example, the wax feed comprised the entire 430° F.+ (221° C.) waxy hydrocarbon fraction produced in a slurry Fischer-Tropsch hydrocarbon synthesis reactor, that contained a titania supported, rhenium-promoted, non-shifting cobalt hydrocarbon synthesis catalyst. The wax comprised at least 90 wt % normal paraffinic hydrocarbons and 26.2 wt % of a 1000° F.+ (538° C.) fraction. It was hydrodewaxed with hydrogen in the presence of a ZSM-48 hydrodewaxing catalyst to form an isomerate. The isomerate was fractionated to remove the 700° F.− (371° C.−) hydrocarbons and the remaining 700° F.+ (3716° C.+) fraction then fractionated to remove and recover a 950° F.+ (510° C.+) heavy lubricant isomerate fraction. This heavy isomerate fraction was then further hydrodewaxed with hydrogen, over the same ZSM-48 hydrodewaxing catalyst in a separate reactor, to form heavy hydrocarbon or lubricant base stock compositions of the invention. The hydrodewaxing conditions in the first and second reactors included respective temperatures of 586° F. (308° C.) and 616° F. (324° C.) and a low hydrogen pressure of 250 psi (1724 kPa). These compositions, the properties of which are shown in Tables 1 and 2, had kinematic viscosities of 13 and 15 cSt at 100° C.
The ZSM-48 hydrodewaxing catalyst in both reactors comprised 0.6 wt % Pt as the hydrogenating component, on a composite of the hydrogen form of a ZSM-48 zeolite and an alumina binder. The hydrogen form of the ZSM-48 zeolite was prepared according to the procedure in U.S. Pat. No. 5,075,269, the disclosure of which is incorporated herein by reference. The Pt component was added by impregnation, followed by calcining and reduction, using known procedures.
Gas chromatograph distillations (GCD) were conducted using a high temperature GCD method modification of ASTM D-5307. The column consisted of a single capillary column with a thin liquid phase, less than 0.2 microns. External standards were used, consisting of a boiling point calibrant ranging from 5 to 100 carbons. A temperature programmed injector was used and, prior to injection, the samples were gently warmed using hot water. Boiling ranges were determined using this method and the T5 and T95 GCD results. Cloud point values were measured using ASTM D-5773 for Phase Two Tec Instruments, under the lubricant procedure method. Pour point was measured according to ASTM D-5950 for ISL Auto Pour Point measurement. Cloud and pour points in the Table below are given in ° C. Viscosity and viscosity index were measured according to the ASTM protocols D-445 and D-2270, respectively.
In this example, the wax feed was Paraflint C-80, a commercally available, hydrotreated Fischer-Tropsch wax produced by Sasol in a fixed bed Fischer-Tropsch reactor from a shifting iron catalyst. The untreated raw wax contains relatively high levels of aromatic and aliphatic unsaturates, and heteroatom compounds, which is hydrotreated to produce the Paraflint C-80 wax. This solid wax is a distillate fraction having a viscosity ranging from 6-10 cSt at 100° C. and a nominal T5 boiling point of about 850° F. (454° C.). It was hydrodewaxed with hydrogen in a single reactor, in the presence of a Pt/ZSM-48 catalyst similar to that used above, but which had been sulfided. The hydrodewaxing reaction pressure was 1000 psi (6895 kPa). The hydrodewaxing product was fractionated by distillation to give a hydrocarbon or heavy lubricant base stock composition of the invention with a viscosity of 11 cSt at 100° C. and its properties are also shown in the Table.
This run was similar to that of Example 1, except that the nominally 700-950° F. (371-510° C.) isomerate was then further hydrodewaxed with hydrogen, over the same ZSM-48 hydrodewaxing catalyst in a separate reactor, to form a lubricant base stock not of the invention, which had a viscosity of 4 cSt at 100° C. The hydrodewaxing conditions in the first and second reactors included respective temperatures of 586° F. (308° C.) and 597° F. (314° C.) and a low hydrogen pressure of 250 psi (1724 kPa). This comparative composition is shown in the Table.
This was similar to Example 2 regarding the feed, catalyst and a single hydrodewaxing reactor. Two lubricant base stocks, having viscosities of 6 and 8 cSt at 100° C., were produced by fractionating the hydrodewaxed product by distillation. Neither of these two base stocks are compositions of the invention and are included in the Table below for comparative purposes.
13C NMR
The microstructure of the hydrocarbon or medium and heavy lubricant base stocks in the Table was analyzed by carbon-13 NMR spectroscopy. Samples were prepared at w/w concentration of 20-25% in chloroform d-doped with 7.5 mg/ml Cr(acac)3. Chemical shift referencing was performed with TMS set to 0.0 ppm. Spectra were acquired on a Varian Unity Plus 500, at a carbon Larmor frequency of 125.7 MHz, with 8000 coaveraged transients per spectrum. All spectra were acquired with a 90° excitation pulse on carbon, inverse gated WALTZ-16 decoupling on protons (during the 0.8 second acquisition time), and a recycle delay of 6 seconds. Sample preparation and data acquisition were performed at 50° C. The data acquisition parameters (chromium doping, relaxation decay, inverse gated decoupling) were chosen to insure accurate and quantitative integrals.
Proton NMR analysis of the base stock samples was performed in a 5 mm switchable probe, with approximately 80 mg samples dissolved in 1 gm chloroform-d. Sample preparation and data acquisition were performed at 50° C. on a Varian Unity Plus 500. Free induction decays of 64 coaveraged transients were acquired, employing a 90° excitation pulse, a relaxation decay of 8.4 seconds, and an acquisition time of 3.2 seconds. No relaxation agent was used in the proton NMR.
These data show that the heavy hydrocarbon or lubricant base stock compositions of the invention (those having viscosities of 11, 13 and 15 cSt) have molecules in which the branching index (BI), and the proximity of branching or branching proximity (CH2>4), are such that:
BI−0.5(CH2>4)<15; (a)
BI+0.85(CH2>4)<45; (b)
as measured over the liquid hydrocarbon composition as a whole. In addition, the data show that for compositions of the invention, BI is less than 25, and the branching proximity (CH2>4) is greater than 17.
The FIGURE is a graph plotting the BI and % CH2>4 values derived from NMR spectra of the hydrocarbon compositions of the invention, the comparative examples of this application, and the data of U.S. Pat. No. 6,090,989 which includes other hydrocarbon compositions. The disclosure of the '989 patent is incorporated herein in its entirety by reference. The shaded area on the plot defines the NMR parameter space of the compositions of the invention. Only the heavy lube base stocks of this invention which are derived from Fischer-Tropsch synthesized waxy hydrocarbons and PAO base stocks fall in this area of parameter space. The molecular composition of the PAO stocks are different from the compositions of the invention in that (i) they do not contain hydrocarbon molecules having consecutive numbers of carbon atoms, (ii) the % CH3 groups on the molecules is below 15, whereas those for the base stocks of the invention are above 20, (ii) the % CH groups for the PAO stocks is above 3, whereas for the base stocks of the invention it is less than 2.
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