Mineral oils: processes and products – Products and compositions – Lubricating oils
Reexamination Certificate
1998-09-11
2001-12-25
Myers, Helane (Department: 1764)
Mineral oils: processes and products
Products and compositions
Lubricating oils
C208S027000, C208S086000, C208S087000, C208S122000, C208S121000, C208S950000, C385S046000, C385S046000
Reexamination Certificate
active
06332974
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to a wide-cut, synthetic lubricant base stock synthesized from waxy hydrocarbons produced by a Fischer-Tropsch hydrocarbon synthesis process. More particularly the invention relates to a wide-cut lubricant base stock and formulated lubricating oil having a high VI, low pour point and wide boiling range, produced by hydroisomerizing a waxy Fischer-Tropsch synthesized hydrocarbon fraction, which is then catalytically dewaxed to produce the base stock.
2. Background of the Invention
Internal combustion engine crankcase and transmission oils, as well as some industrial oils, must maintain their lubricating quality over a wide range of temperature without solidifying or volatilizing. The industry is moving toward lighter viscosity grades (e.g., SAE 5W and 10W oils) for fuel economy reasons. However, the oils must also meet volatility specifications. In addition, heavier base stocks, from which fully formulated oils are made, are still utilized in many applications, including industrial oils. With conventional oils, the dewaxed raffinate is typically vacuum fractionated into a plurality of fractions of different viscosities and boiling ranges. The final lubricating oil is made by adding an additive package containing one or more additives such as a VI improver, an antioxidant, a detergent dispersant, antiwear additive, pour point depressant and the like, to the base stock. Lower viscosity base stocks have a higher concentration of lighter and lower boiling hydrocarbons, which tend to volatilize at higher temperatures. Conversely, higher boiling fractions, besides increasing the viscosity, can adversely affect low temperature properties, such as pour point. To use a wide cut derived from a conventional oil, will yield a base stock which will not meet either volatility or pour point requirements. Synthetic base stocks, such as polyalphaolefins (PAO's), are commercially available and have a combination of high viscosity index and low pour point. However, these oils are very expensive, tend to shrink seals and have a narrow boiling range. To be able to use a single, wide-cut oil fraction of lubricating quality as a base stock for a premium lubricating oil, where two or more fractions are now used, would simplify the production, transportation and cost of the oil.
SUMMARY OF THE INVENTION
The invention relates to a wide-cut lubricant base stock having a low pour point and high viscosity index (VI), and to a lubricant formed from the base stock, wherein the base stock is produced from a waxy, paraffinic Fischer-Tropsch synthesized hydrocarbon fraction having an initial boiling point in the range of 650-750° F. (650-750° F.+), by hydroisomerizing the waxy fraction to form a hydroisomerate, which is then catalytically dewaxed to reduce its pour point. Both the hydroisomerization and the catalytic dewaxing convert some of the 650-750° F.+ hydrocarbons into lower boiling hydrocarbons. These light hydrocarbons or lower boiling hydrocarbons, which boil below 650-750° F. (650-750° F.−), are removed from the resulting 650-750° F.+ dewaxate which comprises the base stock. By wide-cut base stock is meant the entire 650-750° F.+ dewaxate. This is in contrast to conventional base stocks, in which the 650-750° F.+ dewaxate is vacuum fractionated into a plurality of fractions of different viscosity and boiling range. By 650-750° F.+ is meant that fraction of the hydrocarbons synthesized by the Fischer-Tropsch process having an initial boiling point in the range of from 650-750° F. and continuously boiling up to an end point of at least, and preferably above, 1050° F. A Fischer-Tropsch synthesized hydrocarbon feed comprising this 650-750° F.+ material, will hereinafter be referred to as a “waxy feed”. By waxy is meant containing hydrocarbons which solidify at standard room temperature conditions of temperature and pressure. The waxy feed has negligible amounts of aromatics, sulfur and nitrogen compound impurities. The waxy feed also preferably has 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. The wide-cut base stock is essentially isoparaffinic, in comprising at least 95 wt. % of non-cyclic isoparaffins, has a VI of at least 120, a pour point no higher than −10° C. and is useful as a base stock for various lubricants, including lubricating oils (lube oils), greases and the like. Lube oils comprise an admixture of the base stock and lubricant additives, and include, for example, multi-grade internal combustion engine crankcase oils, automatic transmission oils, industrial oils and the like.
The lower boiling hydrocarbons, known as light ends, are removed from the 650-750° F.+ dewaxate in order for the wide-cut base stock to meet volatility requirements. These light ends may simply be flashed off, to produce the wide-cut base stock. The use of simple flashing to remove the light ends (650-750° F.−) in the process of the invention is significant, in that it eliminates the need for more costly vacuum distillation commonly used with conventional, petroleum oil raffinates. The superior properties of the base stock of the invention, compared to conventional base stocks derived from petroleum oil or slack wax, results from the combination of the relatively pure and essentially paraffinic Fischer-Tropsch waxy feed, and preferably a waxy feed produced by a slurry Fischer-Tropsch process in the presence of a catalyst having a cobalt catalytic component, the hydroisomerization, catalytic dewaxing and removal of the light ends from the dewaxate.
In the practice of the invention, the hydroisomerization is accomplished by reacting the waxy feed with hydrogen in the presence of a suitable hydroisomerization and preferably a dual function hydroisomerization catalyst comprising at least one catalytic metal component to give the catalyst a hydrogenation/dehydrogenation function and an acidic metal oxide component to give the catalyst an acid hydroisomerization function. The hydroisomerization converts a portion of the waxy feed (650-750° F.+) to lower boiling material (650-750° F.−) which, while useful for fuels, is not useful as base stock material. The hydroisomerate may be dewaxed with or without prior removal of the lower boiling material. Dewaxing is accomplished by reacting the hydroisomerate with hydrogen in the presence of a dewaxing catalyst to form a dewaxate, from which the light ends are removed.
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Berlowitz Paul J.
Habeeb Jacob J.
Ryan Daniel F.
Wittenbrink Robert J.
Exxon Research and Engineering Co.
Myers Helane
Simon Jay
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