Mineral oils: processes and products – Products and compositions – Lubricating oils
Reexamination Certificate
2000-06-09
2003-06-17
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Products and compositions
Lubricating oils
C208S028000, C208S299000
Reexamination Certificate
active
06579441
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to a haze free lubricating oil base stock.
BACKGROUND OF THE INVENTION
The present invention relates to a lubricating oil base stock and to a sorption process for dehazing a base oil feed to produce the lubricating oil base stock. Lube base oils are normally prepared from crude oil distillates and residua or synthetic oils using a series of upgrading steps, which may include hydrocracking or solvent extraction to remove heteroatoms and aromatics and to increase the viscosity index of the base oil; dewaxing to remove wax; and a finishing step for stabilizing the product against oxidation and floc and color formation.
API Interchange Guidelines (API Publication 1509) defines a Group II base oil as having ≦300 ppm sulfur, ≧90% saturates and a viscosity index of 80-120. A Group III base oil is defined as having ≦300 ppm sulfur, ≧90% saturates and a viscosity index of ≧120. Group II base oils are typically made using hydroprocessing (hydrocracking or severe hydrotreating) to increase the VI of the crude to the specification value. Hydroprocessing also typically increases the saturate content above 90% and reduces the sulfur below 300 ppm. Approximately 10% of the lube base oil production in the world is in the Group II category. About 30% of U.S. production is Group II. Group III base oils are typically made using wax isomerization technology to make very high VI products. Since the starting feed is waxy VGO or wax which contains mainly saturates and little sulfur, the Group III products have saturate contents above 90% and sulfur contents below 300 ppm. Fischer Tropsch wax is an ideal feed for a wax isomerization process to make Group III lubes. Only a small fraction of the world's lube supply is in the Group III category.
Conventional methods for removing wax from a base oil feed include solvent dewaxing and catalytic dewaxing. The degree of dewaxing during one of these dewaxing processes is generally determined by the desired product pour point, where the pour point is a measurement, expressed as a temperature, at which the sample will begin to flow under carefully controlled conditions. Pour point may be determined by, for example, ASTM D5950-96. The cloud point of a lube base oil is complementary to the pour point, and is expressed as a temperature at which a lube oil sample begins to develop a haze under carefully specified conditions. Cloud point may be determined by, for example, ASTM D5773-95. Generally, both the pour point and the cloud point are decreased during dewaxing.
Typical lube base oils will have pour points below +10° F. (−12° C.) and cloud points below +14° F. (−10° C.). These specifications are satisfactory for the majority of lube base oils used in engine lubrication. For a few small volume applications intended for cold climates, lower pour and/or cloud points may be needed. The pour point, may be reduced by adding chemical pour point depressants, but these chemical additives are expensive.
Solvent dewaxing is the traditional method, but suffers from the need to use expensive solvents which also contribute to air and water emissions. Solvent dewaxing has the additional disadvantage in that it produces slack wax, which generally has low value. Catalytic dewaxing is the more recent technology and eliminates the needs for solvents. In general it is observed that oils produced by solvent dewaxing will have pour and cloud points that are not significantly different. That is, the pour-cloud spread (the absolute value of their differences) will be less than or equal to 5° C. For example, U.S. Pat. No. 4,950,382 shows typical data from solvent dewaxing that does not exceed 5° C. When lube base oils are produced by catalytic dewaxing, however, the pour-cloud spreads can be higher than 5° C. As lube base oils become highly paraffinic, the pour-cloud spread tends to increase. For example U.S. Pat. No. 5,015,361 describes the preparation of a lube base oil by oligomerization of propylene in two stages. The lube base oil has a 50° C. pour-cloud spread.
Some base oil feeds, particularly heavy streams such as bright stock, contain naturally-occurring haze precursors that are more difficult to remove by conventional dewaxing than are the paraffinic waxes which predominate in lower boiling waxy streams. If present in sufficient quantities, the haze precursors form a haze in the base oil at ambient (or lower) temperatures, particularly if the base oil is allowed to stand at the low temperature for some time, e.g. overnight. The base oil may develop a hazy appearance even after being dewaxed to a low pour point, e.g. less than −5° C. Conversely, the haze generally disappears when the base oil is heated slightly, e.g. to a temperature of 80° F. or above. The haze will generally be the color of the base oil in which it forms, and is usually white when present in otherwise colorless oil. Haze precursors which give rise to the hazy appearance have significant paraffinic character, some with cyclic components having a long paraffin-like tail. As such, these haze precursors are expected to have substantially different molecular structures than do the color bodies and heteroatom molecules removed by conventional clay filtering for oil stabilization. The presence or absence of a visual haze may be determined using the clear-and-bright standard of ASTM D-4176-93 (Reapproved 1997). The haze may also be quantified by measure of clarity. Haze and turbidity are less well connected with a functional problem of the lube base oil and more associated with general customer acceptance. Customers prefer to use lube base oils that have no haze or turbidity and are “Bright and Clear” on observation. Haze and turbidity can be present in a lube sample at temperatures in excess of the cloud point. Haze and turbidity is often associated with water, foreign solid material, and/or traces of wax-like hydrocarbons. For the subject of this invention, the cause of the haze is not associated with water or solids as these are assumed to be removed by other processing steps. The subject of this invention relates to haze and turbidity induced by traces of wax-like hydrocarbons.
While haze and turbidity are not functional problems, their importance has been recognized in the prior art. For example U.S. Pat. Nos. 4,702,817 and 4,820,400 describe the removal of haze from a lube base oil solvent mixture by electrophoresis during solvent dewaxing. In U.S. Pat. No. 4,820,400, visual inspection is used to measure the haze in the lube base oil. U.S. Pat. No. 4,627,901 describes a light-scattering turbidity measuring device for control of the electrophoresis de-hazing process.
U.S. Pat. Nos. 4,919,788, 5,110,445 and 5,302,279 mention the formation of haze when a petroleum based catalytically dewaxed oil is stored overnight. This haze is referred to as the Overnight Cloud, and is measured by D2500. These patents also describe how catalytically dewaxed lube base oils typically have higher pour-cloud spreads than solvent dewaxed lube base oils. U.S. Pat. No. 5,614,079 also confirms the higher pour-cloud spreads from catalytically dewaxed lubes and mentions the use of a relative turbidity measuring device as part of D2500.
U.S. Pat. Nos. 4,822,476 and 4,867,862 describe the use of a commercial device for quantifying the turbidity of lube base oils. In these patents, the measurement of the turbidity device is expressed as nephelometric turbidity units (NTU), and a maximum value of 24 is specified. In this test, the oil is dissolved in Methyl-Ethyl-Ketone (MEK), the wax recovered, and then redispersed in MEK where the NTU value is measured by a Hach Model 18900 ratio turbidimeter.
There are several examples in the literature that have lube base oils with satisfactory pour points (below −12° C.) but with unsatisfactory cloud points (above −10° C.). See for example U.S. Pat. Nos. 6,051,129, 5,413,695, 5,376,260, 5,135,638, 5,741,751, and 5,514,362. Use of catalytic dewaxing to remove the last traces of cloud, haze and t
Biscardi Joseph A.
Fong Darren P.
Chevron U.S.A. Inc.
Klaassen Alan W.
Prater Penny L.
Yildirim Bekir L.
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