Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Nitrogen and heavy metal – or nitrogen and aluminum – in the...
Reexamination Certificate
2001-11-09
2003-08-26
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Nitrogen and heavy metal, or nitrogen and aluminum, in the...
C508S368000, C508S371000, C508S562000
Reexamination Certificate
active
06610636
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to wear resistant lubricants using a premium synthetic base stock derived from waxy Fischer-Tropsch hydrocarbons, their preparation and use. More particularly the invention relates to a wear resistant lubricant, such as a lubricating oil, comprising an admixture of an effective amount of an antiwear additive and a synthetic base stock, wherein the base stock is prepared by hydroisomerizing waxy, Fischer-Tropsch synthesized hydrocarbons and, in the case of a wear resistant lubricating oil, dewaxing the hydroisomerate to reduce the pour point.
2. Background of the Invention
Internal combustion engine lubricating oils require the presence of antiwear additives in order to provide adequate antiwear protection for the engine. Increasing specifications for engine oil performance have exhibited a trend for increasing antiwear properties of the oil. While there are many different types of antiwear additives, for several decades the principal antiwear additive for internal combustion engine crankcase oils has been a metal alkylthiophosphate and more particularly a metal dialkyldithiophosphate in which the primary metal constituent is zinc, or zinc dialkyldithiophosphate (ZDDP). The ZDDP is typically used in amounts of from about 0.7 to 1.4 wt. % of the total lube oil composition. However, it has been found that the phosphorus from these additives has a deleterious effect on the catalyst in catalytic converters and also on oxygen sensors in automobiles. Furthermore, besides being expensive, some antiwear additives add to engine deposits, which causes increased oil consumption and an increase in particulate and regulated gaseous emissions. Therefore, reducing the amount of metal dialkyldithiophosphate such as ZDDP in the oil without compromising its wear performance would be desirable. One solution to this problem is to use expensive supplementary, phosphorus-free antiwear additives as set forth, for example, in U.S. Pat. No. 4,764,294. It would be an improvement to the art if the amount of antiwear additive, such as metal dialkyldithiophosphates or other expensive additives could be reduced without having to resort to the use of the supplementary additives, or if the amount of supplemental additives could be reduced without compromising engine protection. It would also be an improvement to the art if increased wear resistance could be achieved without having to substantially increase the amount of antiwear additives in the oil.
SUMMARY OF THE INVENTION
The invention relates to a wear resistant lubricant comprising an admixture of an effective amount of a lubricant antiwear additive and a lubricant base stock derived from waxy, Fischer-Tropsch synthesized hydrocarbons. The lubricant is obtained by adding to, blending or admixing the antiwear additive with the base stock. The amount of antiwear additive required to achieve a lubricant, such as a fully formulated lubricating oil, of a given level of wear resistance using a lubricant base stock derived from waxy, Fischer-Tropsch synthesized hydrocarbons is less than that required for a similar lubricating oil based on conventional petroleum oil or polyalphaolefin (PAO) oil base stocks. In a preferred embodiment the antiwear additive will comprise a metal dialkyldithiophosphate and preferably one in which the metal comprises zinc. Fully formulated lubricating oils such as motor oils, transmission oils, turbine oils and hydraulic oils all typically contain at least one, and more typically a plurality of additional additives not related to antiwear properties. These additional additives may include a detergent, a dispersant, an antioxidant, a pour point depressant, a VI improver, a friction modifier, a demulsifier, an antifoamant, a corrosion inhibitor, and a seal swell control additive. As a practical matter, a fully formulated lubricating oils of the type referred to above will typically contain at least one additional additive elected from the group consisting essentially of a detergent or dispersant, antioxidant, viscosity index (VI) improver and mixture thereof. Another embodiment of the invention resides in either reducing the amount of antiwear additive required for a given performance level in a fully formulated lubricating oil composition or increasing the wear resistance of a lubricant or fully formulated lubricating oil at a given level of antiwear additive, by using a base stock containing a sufficient amount of a base stock of the invention. Thus, 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. 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. Thus, the base stock of the invention will comprise all or a portion of the total base stock used in achieving the fully formulated lubricating oil. Hereinafter a fully formulated lubricating oil means one containing at least one antiwear additive and will also be referred to as a “lube oil”.
Base stocks useful in the practice of the invention have been prepared by a process which comprises hydroisomerizing and dewaxing waxy, highly paraffinic, Fischer-Tropsch synthesized 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, FischerTropsch 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. This base stock useful for making the wear resistant lubricants in the practice of the invention and those comprising PAO oil, differ from a base stock 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 useful in 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.
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
Berlowitz Paul J.
Habeeb Jacob J.
Wittenbrink Robert J.
ExxonMobil Research and Engineering Company
Foss Norby L.
Howard Jacqueline V.
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