Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
2000-11-13
2003-02-11
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S058000, C208S027000, C208S089000, C208S108000, C208S143000, C208S25400R
Reexamination Certificate
active
06517704
ABSTRACT:
FIELD OF THIS INVENTION
This invention relates to the hydrocracking and subsequent catalytic dewaxing of petroleum chargestocks. In particular, it relates to an integrated fuels hydroprocessing scheme which comprises hydrocracking, distillation, catalytic dewaxing and hydrofinishing steps.
BACKGROUND OF THE INVENTION
Mineral oil lubricants are derived from various crude oil stocks by a variety of refining processes directed towards obtaining a lubricant base stock of suitable boiling point, viscosity, pour point, viscosity index (VI), stability, volatility and other characteristics. Generally, the base stock will be produced from the crude oil by distillation of the crude in atmospheric and vacuum distillation towers, followed by the removal of undesirable aromatic components by means of solvent refining and finally, by dewaxing and various finishing steps. Because multi-ring aromatic components lead to poor thermal and light stability, poor color and extremely poor viscosity indices, the use of crudes of low hydrogen content or asphaltic type crudes is not preferred as the yield of acceptable lube stocks will be extremely low after the large quantities of aromatic components contained in the lubestocks from such crudes have been separated out. Paraffinic and naphthenic crude stocks are therefore preferred but aromatic treatment procedures are necessary with feedstocks which contain polynuclear aromatics in order to remove undesirable aromatic components.
In the case of the lubricant distillate fractions, generally referred to as the neutrals, e.g. heavy neutral, light neutral, etc., the aromatics may be extracted by solvent extraction using a solvent such as furfural, n-methyl-2-pyrrolidone, phenol or another chemical which is selective for the extraction of the aromatic components. If the lube stock is a residual lube stock, the asphaltenes will first be removed in a propane deasphalting step followed by solvent extraction of residual aromatics to produce a lube generally referred to as bright stock. In either case, however, a dewaxing step is normally necessary in order for the lubricant to have a satisfactorily low pour point and cloud point, so that it will not solidify or precipitate the less soluble paraffinic components under the influence of low temperatures.
U.S. Pat. No. 5,275,719 (Baker et al, hereinafter “Baker”) disclosed a process for producing a high viscosity index lubricant which possesses a VI of at least 140 from a hydrocarbon feed of mineral oil origin which contains nitrogen compounds and has a wax content of at least 50 wt % wherein the feed is hydrocracked in an initial stage. A preferred feed in Baker is slack wax, which typically possesses a paraffin content as great as 70% as illustrated by Table 1.
TABLE 1
SLACK WAX PROPERTIES IN GENERAL
API
39
Hydrogen, wt. pct.
15.14
Sulfur, wt. pct.
0.18
Nitrogen, ppmw
11
Melting point, ° C. (° F.)
57 (135)
KV at 100 ° C., cSt
5.168
PNA, wt pct:
Paraffins
70.3
Naphthenes
13.6
Aromatics
16.3
Simulated distillation:
%
° C. (° F.)
5
375 (710)
10
413 (775)
30
440 (825)
50
460 (860)
70
482 (900)
90
500 (932)
95
A fuels hydrocracking process with partial liquid recycle is disclosed in U.S. Pat. No. 4,983,273 (Kennedy et al.). In this the feed (usually vacuum gas oil (VGO) or light cycle oil (LCO)) is processed in a hydrotreating reactor, then in a hydrocracking reactor prior to being passed to a fractionator. A portion of the fractionator bottoms is then recycled to the hydrocracker. Yukong Limited has disclosed (International Application PCT/KR94/00046, U.S. Pat. No. 5,580,442) a method for producing feedstocks of high quality lube base oil from unconverted oil (UCO) of a fuels hydrocracker operating in recycle mode.
Catalytic dewaxing processes are becoming favored for the production of lubricating oil stocks. They possess a number of advantages over the conventional solvent dewaxing procedures. The catalytic dewaxing processes operate by selectively cracking the normal and slightly branched waxy paraffins to produce lower molecular weight products which may then be removed by distillation from the higher boiling lube stock. Concurrently with selective catalytic cracking of waxy molecules, hydroisomerization with the same or different catalyst can convert a significant amount of linear molecules to branched hydrocarbon structure having improved cold-flow properties. A subsequent hydrofinishing or hydrotreating step is commonly used to stabilize the product by saturating lube boiling range olefins produced by the selective cracking which takes place during the dewaxing. Reference is made to U.S. Pat. Nos. 3,894,938 (Gorring et al.), U.S. Pat. No. 4,181,598 (Gillespie et al.), U.S. Pat. No. 4,360,419 (Miller), U.S. Pat. No. 5,246,568 (Kyan et al.) and U.S. Pat. No. 5,282,958 (Santilli et al.) for descriptions of such processes.
Hydrocarbon Processing
(Sep. 1986) refers to Mobil Lube Dewaxing Process, which process is also described in Chen et al “Industrial Application of Shape-Selective Catalysis”
Catal. Rev.-Sci. Eng.
28 (283), 185-264 (1986), to which reference is made for a further description of the process. See also, “Lube Dewaxing Technology and Economics”,
Hydrocarbon Asia
4 (8), 54-70 (1994).
In catalytic dewaxing processes of this kind, the catalyst becomes progressively deactivated- as the dewaxing cycle progresses. To compensate for this, the temperature of the dewaxing reactor is progressively raised in order to meet the target pour point for the product. There is a limit, however, to which the temperature can be raised before the properties of the product become unacceptable. For this reason, the catalytic dewaxing process is usually operated in cycles with the temperature being raised in the course of the cycle from a low start-of-cycle (SOC) value, typically in the range of about 450° F. to 525° F. (about 232° C. to 274° C.), to a final, end-of cycle (EOC) value, typically about 670-725° F. (about 354-385° C.), after which the catalyst is reactivated or regenerated for a new cycle. Typically, dewaxing catalysts which employ ZSM-5 as the active ingredient may be reactivated by hot hydrogen. Other dewaxing catalysts may be decoked using air, or oxygen in combination with N
2
or flue gas. Catalysts which contain active ingredients, such as ZSM-23 or SAPO-11, that are less active than ZSM-5 containing catalysts may have start-of-cycle (SOC) and end-of-cycle (EOC) temperatures that are 25 to 50° C. higher than those that contain ZSM-5.
The use of a metal hydrogenation component on the dewaxing catalyst has been described as a highly desirable expedient, both from obtaining extended dewaxing cycle duration and for improving the reactivation procedure. U.S. Pat. No. 4,683,052 discloses the use of noble metal components e.g. Pt or Pd as superior to base metals such as nickel for this purpose. A suitable catalyst for dewaxing and isomerizing or hydro-isomerizing feedstocks may contain 0.1-0.6, wt. % Pt, for instance, as described in U.S. Pat. Nos. 5,282,958; 4,859,311; 4,689,138; 4,710,485; 4,859,312; 4,921,594; 4,943,424; 5,082,986; 5,135,638; 5,149,421; 5,246,566; 4,689,138.
Chemical reactions between liquid and gaseous reactants present difficulties in obtaining intimate contact between phases. Such reactions are further complicated when the desired reaction is catalytic and requires contact of both fluid phases with a solid catalyst. In the operation of conventional concurrent multiphase reactors, the gas and liquid under certain circumstances tend to travel different flow paths. The gas phase can flow in the direction of least pressure resistance; whereas the liquid phase flows by gravity in a trickle path over and around the catalyst particles. Under conditions of low liquid to gas ratios, parallel channel flow and gas frictional drag can make the liquid flow non-uniformly, thus leaving portions of the catalyst bed underutilized due to lack of adequate wetting. Under these circumstances, commercial reactor performance can be much poorer than expected from laboratory studies in which flow conditions
Bixel John C.
Carroll Michael B.
Smith Fritz A.
ExxonMobil Research and Engineering Company
Griffin Walter D.
Hughes Gerard J.
Kliebert Jeremy J.
Nguyen Tam
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