Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and...
Reexamination Certificate
1998-09-04
2002-11-05
Toomer, Cephia D. (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
C585S001000, C585S002000, C208S018000, C208S019000
Reexamination Certificate
active
06475960
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to lubricants based on premium synthetic lubricant base stocks derived from waxy Fischer-Tropsch hydrocarbons, their preparation and use. More particularly the invention relates to fully formulated lubricants comprising an admixture of an effective amount of lubricant additives and a synthetic lubricating oil base stock made by hydroisomerizing waxy, Fischer-Tropsch synthesized hydrocarbons and then dewaxing the hydroisomerate to reduce the pour point.
2. Background of the Invention
Current trends in the design of automotive engines require higher quality crankcase and transmission lubricating oils with high VI's and low pour points. Such lubricating oils are prepared by adding an effective amount of additives, typically in the form of an additive package, to a base stock which is an oil of lubricating quality boiling in the lubricating oil range. Processes for preparing lubricating base stocks from petroleum derived feeds typically include atmospheric and/or vacuum distillation of a crude oil (and often deasphalting the heavy fraction), solvent extraction of the lube fraction to remove aromatic unsaturates and form a raffinate, hydrotreating the raffinate to remove heteroatom compounds and remove aromatics, followed by either solvent or catalytically dewaxing the hydrotreated raffinate to reduce the pour point of the oil. Some synthetic lubricating oils are based on a polymerization product of polyalphaolefins (PAO). These lubricating oils are expensive and can shrink seals. In the search for better lubricating oils, attention has recently been focused on Fischer-Tropsch wax that has been synthesized by reacting H
2
with CO.
Fischer-Tropsch wax is a term used to describe waxy hydrocarbons produced by a Fischer-Tropsch hydrocarbon synthesis processes in which a synthesis gas feed comprising a mixture of H
2
and CO is contacted with a Fischer-Tropsch catalyst, so that the H
2
and CO react under conditions effective to form hydrocarbons. The waxy fraction used to prepare lubricating oil base stocks typically has an initial boiling point in the range of from 650-750° F. U.S. Pat. No. 4,943,672 discloses a process for converting waxy Fischer-Tropsch hydrocarbons to a lube oil base stock having a high (viscosity index) VI and a low pour point, wherein the process comprises sequentially hydrotreating, hydroisomerizing, and solvent dewaxing. A preferred embodiment comprises sequentially (i) severely hydrotreating the wax to remove impurities and partially convert it, (ii) hydroisomerizing the hydrotreated wax with a noble metal on a fluorided alumina catalyst, (iii) hydrorefining the hydroisomerate, (iv) fractionating the hydroisomerate to recover a lube oil fraction, and (v) solvent dewaxing the lube oil fraction to produce the base stock. European patent publication EP 0 668 342 A1 suggests a processes for producing lubricating base oils by hydrogenating or hydrotreating and then hydroisomerizing a Fischer-Tropsch wax or waxy raffinate, followed by dewaxing, while EP 0 776 959 A2 recites hydroconverting Fischer-Tropsch hydrocarbons having a narrow boiling range, fractionating the hydroconversion effluent into heavy and light fractions and then dewaxing the heavy fraction to form a lubricating base oil having a VI of at least 150.
SUMMARY OF THE INVENTION
The invention relates to fully formulated lubricants which comprise an admixture of an effective amount of lubricant additives and a lubricant base stock derived from waxy, Fischer-Tropsch synthesized hydrocarbons. Lubricant additives vary depending on the desired end use. Therefore, the nature and amount of additives added to, blended or admixed with the base stock will depend on the desired use for the lubricant. However, fully formulated lubricating oils such as motor oils, transmission oils, turbine oils and hydraulic oils all typically contain at least one additive selected from the group consisting of a detergent and/or dispersant, antioxidant, antiwear additive, viscosity index (VI) improver and mixture thereof. Such base stocks have been prepared by a process which comprises hydroisomerizing and dewaxing waxy, highly paraffinic, Fischer-Tropsch hydrocarbons boiling in the lubricating oil range, and preferably including waxy hydrocarbons boiling above the lubricating oil range. Base stocks useful in the practice of the invention have been produced by (i) hydroisomerizing waxy, Fischer-Tropsch synthesized hydrocarbons having an initial boiling point in the range of 650-750° F. and an end point of at least 1050° F. (hereinafter “waxy feed”) to form a hydroisomerate having an initial boiling point in said 650-750° F. range, (ii) dewaxing the 650-750° F.+ hydroisomerate to reduce its pour point and form a 650-750° F.+ dewaxate, and (iii) fractionating the 650-750° F.+ dewaxate to form two or more fractions of different viscosity as the base stocks. These base stocks are premium synthetic lubricating oil base stocks of high purity having a high VI, a low pour point and are isoparaffinic, in that they comprise at least 95 wt. % of non-cyclic isoparaffins having a molecular structure in which less than 25% of the total number of carbon atoms are present in the branches, and less than half the branches have two or more carbon atoms. The base stock of the invention and those comprising PAO oil differ from oil derived from petroleum oil or slack wax in an essentially nil heteroatom compound content and in comprising essentially non-cyclic isoparaffins. However, whereas a PAO base stock comprises essentially star-shaped molecules with long branches, the isoparaffins making up the base stock of the invention have mostly methyl branches. This is explained in detail below. Both the base stocks of the invention and fully formulated lubricating oils using them have exhibited properties superior to PAO and conventional mineral oil derived base stocks, and corresponding formulated lubricating oils. Further, while in many cases it will be advantageous to employ only a base stock derived from waxy Fischer-Tropsch hydrocarbons for a particular lubricant, in other cases one or more additional base stocks may be mixed with, added to or blended with one or more of the Fischer-Tropsch derived base stocks. Such additional base stocks may be selected from the group consisting of (i) a hydrocarbonaceous base stock, (ii) a synthetic base stock and mixture thereof. Typical examples include base stocks derived from (a) mineral oil, (b) a mineral oil slack wax hydroisomerate, (c) PAO, and mixture thereof Because the Fischer-Tropsch base stocks of the invention and lubricating oils based on these base stocks are different, and most often superior to, lubricants formed from other base stocks, it will be obvious to the practitioner that a blend of another base stock with at least 20, preferably at least 40 and more preferably at least 60 wt. % of the Fischer-Tropsch derived base stock, will still provide superior properties in many most cases, although to a lesser degree than only if the Fischer-Tropsch derived base stock is used.
The waxy feed used to form the Fischer-Tropsch base stock preferably comprises waxy, highly paraffinic and pure Fischer-Tropsch synthesized hydrocarbons (sometimes referred to as Fischer-Tropsch wax) having an initial boiling point in the range of from 650-7500° F. and continuously boiling up to an end point of at least 1050° F., and preferably above 1050° F. (1050° F.+). It is also preferred that these hydrocarbons have a T
90
−T
10
temperature spread of at least 350° F. The temperature spread refers to the temperature difference in °F. between the 90 wt. % and 10 wt. % boiling points of the waxy feed, and by waxy is meant including material which solidifies at standard conditions of room temperature and pressure. The hydroisomerization is achieved by reacting the waxy feed with hydrogen in the presence of a suitable hydroisomerization catalyst and preferably a dual function catalyst comprising at least one catalytic met
Berlowitz Paul J.
Habeeb Jacob J.
Wittenbrink Robert J.
ExxonMobil Research and Engineering Co.
Marin Mark D.
Scuorzo Linda M
Toomer Cephia D.
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