Chemistry of hydrocarbon compounds – Plural serial diverse syntheses
Reexamination Certificate
2000-04-28
2002-07-16
Knode, Marian C. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
C585S001000, C585S734000, C585S737000, C585S738000, C208S018000, C208S019000, C208S024000, C208S028000, C208S049000
Reexamination Certificate
active
06420618
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
FIELD OF THE INVENTION
The invention relates to premium synthetic lubricant base stocks derived from waxy Fischer-Tropsch hydrocarbons, their preparation and use. More particularly the invention relates to a high VI and low pour point synthetic lubricating oil base stock made by reacting H
2
and CO in the presence of a Fischer-Tropsch catalyst to form waxy hydrocarbons boiling in the lubricating oil range, hydroisomerizing the waxy hydrocarbons having an initial boiling point in the range of 650-750° F., dewaxing the hydroisomerate, removing light ends from the dewaxate and fractionating to recover a plurality of base stocks from the dewaxate.
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. Processes for preparing lubricating oils of low pour point 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 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 synthetic 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. 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
Lubricant base stocks are 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. The present invention relates to these base stocks and to a process for making them. Further, while in many cases it will be advantageous to employ only the base stock of the invention for a particular lubricant, in other cases the base stock of the invention may be mixed or blended with one or more base stocks selected from the group consisting of (a) a hydrocarbonaceous base stock, (b) a synthetic base stock, and mixture thereof Typical examples include base stocks derived from (i) PAO, (ii) mineral oil, (iii) a mineral oil slack wax hydroisomerate, and mixture thereof Because the 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 base stock of the invention, will still provide superior properties in many most cases, although to a lesser degree than only if the base stock of the invention is used.
The waxy feed used in the process of the invention 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 650-750° F. and continuously boiling up to an end point of at least 1050° F., and preferably above 1050° F. (105°F+), with 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 which comprises 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. Preferably the hydroisomerization catalyst comprises a catalytic metal component comprising a Group VIB metal component, a Group VIII non-noble metal component and an amorphous alumina-silica component. The hydroisomerate is dewaxed to reduce the pour point of the oil, with the dewaxing achieved either catalytically or with the use of solvents, both of which are well known dewaxing processes, with the catalytic dewaxing achieved using any of the well known shape selective catalysts useful for catalytic dewaxing. Both hydroisomerization and catalytic dewaxing convert a portion of the 650-750° F.+ matenal to lower boiling (650-750° F.−) hydrocarbons. In the practice of the invention, it is preferred that a slurry Fischer-Tropsch hydrocarbon synthesis process be used for synthesizing the waxy feed and particularly one employing a Fischer-Tropsch catalyst comprising a catalytic cobalt component to provide a high alpha for producing the more desirable higher molecular weight paraffins. These processes are also well known to those skilled in the art.
The waxy feed preferably comprises the entire 650-750° F.+ fraction formed by the hydrocarbon synthesis pro
Berlowitz Paul J.
Habeeb Jacob J.
Wittenbrink Robert J.
Dang Thuan D.
ExxonMobil Research and Engineering Company
Knode Marian C.
Scuorzo Linda M.
Simon Jay S.
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