CA1117455A

CA1117455A - Manufacture of lube base stock oil

Info

Publication number: CA1117455A
Application number: CA000317918A
Authority: CA
Inventors: Kenneth W. Smith; Michael S. Sarli; Bernard M. Gillespie
Original assignee: Mobil Oil AS
Current assignee: Mobil Oil AS
Priority date: 1977-12-20
Filing date: 1978-12-14
Publication date: 1982-02-02
Also published as: JPS6115917B2; ES476120A1; FR2412604B1; JPS54116005A; IT7831017A0; DE2854258C2; DE2854258A1; GB2010321A; GB2010321B; AU4269478A; IT1102403B; AU520921B2; ZA787153B; FR2412604A1

Abstract

MANUFACTURE OF LUBE BASE STOCK OIL

ABSTRACT

Lube base stock oil of low pour point and excellent stability is produced from a deasphalted short residium fraction by solvent refining, catalytic dewaxing over a zeolite catalyst such as zeolite ZSM-5 and hydrotreating under specified conditions.

Description

The invention ls concerned with manufacture of high grade viscous oll products from crude petroleum fractions.
It is particularly directed to the manufacture of high quality lube base stock oils from crude stocks of hlgh wax content, commonly classifled as "wax base" as compared with the "naphthenic base" crudes. The latter crudes are relatlvely lean in straight chaln parafflns and yield viscous fractions whlch lnherently possess low pour polnts.

High quality lube base stock olls are conventionally prepared by refining distillate fractions or the reslduum prepared by vacuum dlstllllng a sultable crude oll from which the lighter portion has been removed by distillation ln an atmospherlc tower. Thus, the charge to the vacuum tower is commonly referred to as a "long reslduumt', and the residuum from the vacuum tower is dlstinguished from the starting material by referring to it as the "short residuum".
The vacuum distillate fractions are upgraded by a sequence of unlt operations, the first of which is solvent extraction wlth a ~olvent selective ~or aromatic hydrocarbons.
Thls step serves to remove aromatic hydrocarbons of low viscosity lndex and provides a raffinate of improved viscosity index and quality. Various processes have been used in this extraction stage, and these employ solvents such as furfural, 74~S

phenol, sulfur dioxide, and others. The short residuum, because it contains most of the asphaltenes of the crude o-l, is conventionally treated to remove these asphalt-l~ke constituents prior to solvent extracJion to increase the viscosity index.
The raffinate from the solvent extraction s~ep contains paraffins which ~dversely affect the pour point.
Thus, the waxy raffinate, regardless of whether prepared from a distillate fraction or from the short residuum, mus~
be dewaxed. Various dewaxing procedures have been used, and the art has gone in the direction of treatment with a solvent such as MæK~toluene mixtures to remove the wax and-prepare a dewaxed raffinate. The dewaxed raffinate ~.ay then be ~inished by any of a number of sorption or catalytic processes to improve color and oxidation stability.
The quallty of the lube base stock oil prepared by the sequence of operations outlined above depends on the particular crude chosen as well as the severity of treatment for each of the treatment steps. Additionally, the yield of high quality lube base stock oil also depends on these factors and, as a rule, the higher the quality sought, the less the yie}d. In general, naphthenic crudes are favored because less loss is encountered, particularly in the dewaxin&
step. In many cases~ however, waxy crudes are ~ore readily -, 2;ailable, and it would be desirable to provide a process for preparing high quPlity lube base stock oils in good yields from such waxy crude oils.
, _3_ 1117~
In recent years techniques have become available for catalytic dewaxing of petroleum stocks. A process of that nature developed by British Petroleum is described in The Oil and Gas Journal dated January 6, 1975, at pages 69-73.
See also U.S. Patent 3,668,113.
In reissue patent 28,398 is described a process for catalytic dewaxing with a catalyst comprising zeolite ZSM-5. Such process combined with catalytic hydrofinishing is described in U.S. Patent 3,894,938.
It is an object of this invention to provide a process for preparing a high quality lube base stock oil having a pour point not greater than +30F from a waxy crude oil.
It is a further objeet of this invention to provide a pro-cess for preparing a high quality lube base stock oil having a pour point of about -25F to +30F from a waxy crude oil in high yield and with recovery of valuable paraffin wax. Other objects will be evident to those skilled in the art upon reading the entire contents of this specifieation ineluding the elaims thereof.
Known unit proeesses are applied to short residuum fraetions of waxy erude in partieular sequenee and within limits to prepare lube base stock oils used, for example, in hydraulic fluids, motor oils, turbine oils, marine oils and gear lubrieants. The first step after preparation of a fraetion of suitable boiling range is extraction with a solvent which is selective for aromatie hydroearbons, e.g.
furfural, phenol, or ehlorex, to remove undesirable eom-ponents of the fraetion. With a short residuum fraetion, it is required to propane deasphalt the residuum prior to solvent extraetion. The raffinate from solvent extraction is then eatalytically dewaxed in admixture with hydrogen over a eatalyst of an aluminosilicate zeolite having a r~ ' ~' 4~i silica to alumina ratio greater than 12 and a constraint index of l to 12. Dewaxed oil is hydrotreated to saturate olefins and to reduce product color. The total effluent from the dewaxer, including hydrogen, is cascaded to the hydrotreater and the reaction product thereafter distilled, i.e. topped by distillation, to separate low boiling products of dewaxing in order to meet flash and fire point specifications. Conducting the unit processes at the conditions more fully specified hereinafter results in imparting high quality characteristics to the lube base stock oils and at the same time producing high yields of finished oils.
The present invention in its broadest aspect relates to a process for preparing a high quality lube base stock oil having a pour point of about -25 to +30F from waxy crude oil, which comprises: extracting a deasphalted short residuum fraction of said waxy crude with a solvent selective for aromatic hydrocarbons to yield a raffinate from which undesirable compounds have been removed mixing the raffinate with hydrogen and contacting the mixture at a temperature of 500 to 675F with a dewaxing catalyst com-prising an alumino~ilicate zeolite having a silica/alumina ratio of at least about 12 and a constraint index of about l to about 12, thereby converting wax contained in the raffinate to lower boiling hydrocarbons; cascading the de-waxed raffinate to a hydrotreating zone wherein the dewaxed raffinate is contacted in the presence of hydrogen at a temperature of 425 to 600F with a hydrotreating catalyst comprising a hydrogenation component on a non-acidic support and topping the dewaxed, hydrotreated raffinate to remove therefrom components of a low molecular weight.

45~i DESCRIPTION OF SPECIFIC EMBODIMENTS

The wax base crudes (sometimes called "paraffin base") from which the charge stock is derived by distillation constitute a well recognized class of crude petroleums.
Many scales have been devised for classification of crude, some of which are described in Chapter VII Evaluation of Oil Stocks of "Petroleum Refinery Engineering", W.L. Nelson, McGraw-Hill, 1941. A convenient scale identified by Nelson at page 69 involves determination of the cloud point of the Bureau of Mines "Key Fraction No. 2" which boils between 527 and 572F at 40mm. pressure. If the cloud point of this fraction is above 5F, the crude is considered to be wax base.
In practice of the present invention, a propane deasphalted short residuum fraction is prepared by vacuum distillation of such wax base crude and then solvent refined, preferably by counter current extraction with at least an equal volume tlOO vol.~ of a selective solvent such as furfural. It is preferred to use about 1.5 to about 3.0 volumes of solvent per volume of oil. The furfural raffinate is subjected to catalytic dewaxing by mixing with hydrogen and contacting at 500-675F
wlth a catalyst containing a hydrogenation metal and zeollte ZSM-5 or other aluminosilicate zeolite having a silica/alumina ratio above 12 and a constraint index of 1.12 and a liquid .

X

hourly space velocity (LHSV~ of 0.1 to 2.0 volumes of charge oil per volume of cata~yst per hour. The preferred space velocity is 0.5 to l.0 ~HSV. The effluent of catalytic dewaxing is then cascaded into a hydrotreater containing, as catalyst, a hydrogenation component on a non-acidic support, such as cobalt-molybdate or nickel-molybdate on alumina. The hydrotreater operates in the broad range of 425 to 600F; but the quality results are strongly affected by choice of temperature within this range. Most desirable results with short residuum fractions are obtained in the range of 500 to 575F, and at a space velocity similar to that of the catalytic dewaxing reactor. The reactions are carried out at hydrogen partial pressures of 150-1500psia, at the reactor inlets, and preferably at 250-500 psia, with 500 to 5000 standard cubic feet of hydrogen per barrel of feed (SCF/B), preferably 1500 to 2500 SCF/B.
The catalytic dewaxing reaction produces olefins which would impair properties of the dewaxed oil product if retained. These are saturated by hydrogenation in the hydrotreater. The saturation reaction is evidenced by the temperature rise in the first portion of the hydrotreater~
and confirmed by chemical analysis of the feed and hydro-treated product. By this means lt iq possible to prepare stable good quality lube stock oils having pour points even below -65F.
X

~1117~5 In so~e instances it ~.2y be desirable to partially dewax the charge stock, i.e. solvent-extracted raffinate, b~ conventional sclvent dewa~ing techniques, say to a pour point from 10F to about 50F. The higher meltin~
point waxes so removed are those of higher market value than the waxes removed in conventionally taking the product to a still lower pour point below 10F.
The cracked (and hydrogenated) fragments from crackin~
wax molecules in the catalytic dewaxer will have adverse effects on flash and fire points of the dewaxed raffinate product and are therefore removed by distillation of the product to flash and fire point specifications.
The catalyst employed in the catalytic dewaxing reactor and the temperature in that reactor are important to success in obtaining good yields and very low pour point product. The hydrotreater catalyst may be any of the catalysts commercially available for that purpose but the temperature should be held within narrow limits for best results.
The solvent extraction technique is well understood in the art and needs no detailed review here. The severity of extraction is adjusted to compositlon of the charge stock to meet specifications for the particular lube base stock and the contemplated end-use; this 27 severity will be determined in practice of this inventicn in accordance with well established practices.

S~

The catalytlc dewaxing step is conducted at temperatures of 500 to 675F. At temperatures above about 6~5F, bromine number of the product generally increases slgnificantly and the oxidation stability decreases.
The dewaxing catalyst is a composite of hydrogenation metal, preferably a metal of Group VIII of the Periodic Table, associated with the acid form of a novel class of aluminosilicate zeolite having a silica/alumina ratio of at least about 12 and a constraint index in the range 1 to 12. The term "constraint index" is defined in U.K.
Specification 1,446,522.

X

Constraint Index (CI) values ~or some typical zeolites are:

CAS C.I.
ZSM-5 8.3 ZS~;-ll 8.7 2S~1-12 2 ZS`~ 38 2 ZS~-35 4.5 .IA Offretite 3.7 Beta o.6 ZSM '~ 0,5 H-Zeolon o,4 REY 0,4 Amor~hous Silica-Alumina O.6 Erionite 38 .

ZSM-5, ZSM-ll, ZSM-12, ZSM-35 and ZSM-38 are descrlbed ln U.S.Speci~lcatlons 3,702,886, 3,709,979, 3,832,449, 4,016,245 and 4,046,859 respectlvely.

1~7~5 The specific zeolites described, when prepared in the presence of organic cations, are catalytically inactive, possibly because the intracrystalline free space ls occupled by organic cations from the forming solution. They may be activated by heating in an inert atmosphere at 1000F. for one hour, for example, followed by base exchange wlth ammonium salts followed by calcination at 1000F, in air thus yielding the hydrogen form. ~he presence of organic cations in the forming solution may not be absolutely essential to the formation of this type zeolite;
however, the presence of these cations does appear to favor the formation of this special type of zeolite. More generally, it is desirable to activate this type catalyst by base exchange with ammonium salts followed by calcination in air at about 1000F. for from about 15 minutes to about 24 hours.
Natural zeolites may sometimes be converted to this type catalyst by various activation procedures and other treat-ments such as base exchange, steaming, alumina extraction and calcination, in combinations. Natural minerals _i `

~1~ 174~
which may be so treated include ferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite, and clinop-tilolite.
In a preferred aspect of this invention, the zeo-lites hereof are selected as those having a crystal framework density, in the hydrogen ~orm, of not substantially below about 1.6 grams per cubic centimeter. It has been found that zeolites which satlsfy all three of these criteria are most deslred. Therefore, the preferred zeolites of this invention are those having a constraint index as defined above of about 1 to about 12, a silica to alumina ratio of at least about 12 and a dried crystal density of not less than about 1.6 grams per cubic centimeter. The dry density for known struc-tures may be calculated from the number of silicon plus alu-minum atoms per 1000 cubic Angstroms, as given, e.g., onpage 19 of the article on Zeolite Structure by W.M. Meier.
Crystal framework densities of some typical zeolites are:

Void Framework Zeolite Volume Density 20 Ferrierite 0.28 cc/cc 1.76 g/cc ~Mordenite .28 1.7 ZSM-5, -11 .29 1.79 Dachiardite .32 1.72 L .32 1.61 25 Clinoptilolite .34 1.71 Laumontite .34 1.77 ZSM-4 (Omega) .38 1.65 Heulandite .39 1.69 P .41 1.57 30 Offretite .40 1.55 Levynite .40 1.54 Erionite .35 1.51 Gmelinite .44 1.46 Chabazite .47 1.45 35 A .5 1.3 Y .48 1.27 S

In addltion to the hydrogen ~orm, other forms of the zeolite wherein the original aklall metal has been reduced to less than about l.5 percent by weight may be used. Thus, the original alkali metal of the zeollte may be replaced by ion exchange with other suitable ions of Groups IB to VIII of the Periodic Table, including, by way of example, nickel, copper, zinc palladium, calcium or rare earth metals.

In practicing the desired c~nversion process, it may be desirable to incorporate the above described crystal-line aluminosilicate zeolite in another materi21 resis'ant to the temperature and other conditions employed in the pro-cess. Such matrix materials include synthetic or naturally occurring substances as well as inorgznic ma~eri~ls such 2S
clay, silica and/or metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica znd metal oxides. Nat-urally occurring clays which can be composited with the zeo-lite include those of the mont~orillonite and kzolin families~
which families include the sub-bentonites and the kaolins commonly known as Dixie, McNamee-&eorgia and Florida clays or others in which the main mineral consistuent is halloy-site, kaolinite, dickite, nacrite or anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemic21 modi-fication.
In addition to the foregoing materials, the zeo-lites employed herein may be composited with a porous matrix material, such as aiumina, silica-alumina, silica-magnesiaJ
silica-zirconia, silica-thoria, silica-berylia, silica-titania as well as ternary compositions, s~ch as silica-alumina-tnoria, silica-alumina-zirconia, silica-alumina-mag~esiz and silicz-magnesia-zirconia. The matrix may be in the for~ of a co~el.
The relative proportions of zeolite component and inor~anic oxide gel matrix may vary widely with the zeoli~e content ranging from between about 1 to about 99 percen~ by weight and more usually in the.range of about 5 to zbout 80 ?erCe?.t by weight of the composite.

_14-l-li7~5 In the process of this invention, the total effluent of the catalytic dewaxing step, including the hydrogen, is cascaded into a hydrotreating reactor of the type now generally employed for finishing of lubricating oil stocks. In this "cascade" mode of operation, the hydrotreater ls sized to handle the total dewaxer effluent. Although some modification of the cascade operation is contemplated, such as interstage recovery of gasoline boiling range-by-product, it ls to be understood that such modification contemplates no substantial interruption or substantial delay in passing the dewaxed raffinate to the hydrotreater. Thus, "cascading", as used herein, means passing the dewaxed raffinate plus hydrogen to hydrotreating without storage of the dewaxer effluent.
Any of the ~nown hydrotreating catalysts consisting of a hydrogenation component on a non-acidic support may be employed in the hydrotreating step. Such catalysts include, for example, cobalt-mslybdate or nlc~el-molybdate on an alumina support. Here again, temperature control is required for production of high quality product, the hydro-treater being operated at 425 to 500F with distillate fractions and 500 to 575F for residuum f~actions.
~ he effluent of the hydrotreater is topped by distillation, i.e; the most volatile components are removed, to meet flash and fire point specifications.

; 15 In the examples, all parts glven are by welght unless speci~led o~herwlse.
EXAMPLE l Thls example illustrates the manufacture, without wax recoveryj of premium bright stock frcm short residuum of Arabian Li~ht crude.
The short residuum, commercially prepared ~rom Arabi2n Light crude, was pr~pane deasphalted in a co~merclal unit in such a way as to yleld ~ l.0 to l.5% wt. Conradson -Carbon fiesidue PD raf.inate. Said PD raflinate was then commercially fur~ural extracted to give a product which when dewaxed to 20F pour point had a Viscos.ity Index of 9~.
Two catalytic reactors were assembled so that the total effluent from th_ ~irst reactor was passed.directly to the lnlet Or the second reactor. The first reactor was charged wlth nickel-containln~ HZSM-5 catalyst for catalytlc dewaxing, and the second reactor with a commerc~al cobalt-moly on alumina hydrotreating catalyst (Harshaw HT-400 catalyst, containing 2.8 wt.% CoO and 9.~ wt.~ ~1003).

~.17~S

The above-described commercial bright stock ra~finate was mlxed with hydrogen and passed through the tandem reactors above described to produce a de~axed hydrotreated effluent. Both reactors were run at 1.0 LHSV bzsed on raffinate charge. Reactor pressure was 400 psig H2 with 2500 SCF/3 hydrogen circulation (100% hydrogen once-through).
An initial temperature requirement of 550F was needed ln the flrst reactor to meet pour point specification while the second reactor was held constant at 550F. The temperature in the catalytlc dewaxing reactor was increased 9 to 10F
per day to maintain the pour point of the dewaxed oil at about 20F. The end o~ cycle temperature for the catalytic dewaxer unit was 675~. The effluent from the catalytic reactors was distllled (topped) to a cut point of 800F to meet flash point specificatlons. The bright stock raffinate charge and product properties are summarized in Table I.

'7~

TABLE I

PROPERTIES OF HYDRODEWAXED/HYDROTREATED
PREMIU~ BRIGHT STOCK FURFURAL RAFFINATE

Stream Charge Product Hydrodewaxing Temperature, F - 550-675 Yield on Raffinate, % volumelOO.O 87.8 Product Properties Gravity, API 25.4 24.4 Gravity, Specific at 600F 0.9018 0.9076 Pour Point, F 125 15 Flash Point, F (C.O.C.) - 550 KV at 40c Centistokes - .475 KV at 100C Centistokes - 30.7 KV at 100F Centistokes - 550 KV at 210F Centistokes 29.7 31.8 SUS at 100F Seconds - 2549 SUS at 210F Seconds 141 150 Viscosity Index - 94 Neutralization No. Mg. KOH/gm - 0.09 Carbon Residue, ~ Wt (RCR) O. 55 0.56 Hydrogen, % Wt. 13.29 13.10 Sulfur, % Wt. 1.16 1.06 Nitrogen, ppm 180 180 Refractive Index at 20C - 1.49815 Refractive Index at 70C 1.47701 1.48177 Aniline Point, F 251.5 242. 6 Furfural, ppm - ~l Bromine Number - o 5 Distillation, F D1160-1 5, % vol 859 10, % vol 922 30, % ~ol 1005 50, % vol 1046 70, % vol 1091 5~

The yield, 87.8~ sho~.~ in Table I, is about 13 volume %
higher than obtained w~th conventional comrercial solvent dewaxing to compa~able pour point of the same bri~ht stock raffinate. The catalyt~cally dewaxed and hydrotreated bri~ht stock product passed the required oxidation specification tests.
~t the end of the above-described run the dewaxing catalyst was reactivated with pure hydrogen at 900F for 24 hours with full recovery of initial activity.

-This example is similar to Example 1 except that the bright stock raffinate of Example 1 was first solvent dewaxed to +45F pour point and then catalytically dewaxed and hydrotreated.
Thus, all high grade deoiled wax is recovered in this present example.
The bright stock raffinate described in Example 1 was batch solvent dewaxed in the laboratory at 30F filter temperature using 3.5 to 1 solvent to oil and two 1 to 1 washes. The solvent was a 50/50 mix of methyl ethyl ketone and toluene. The p~rtially dewaxed raffinate had a pour point of +45F, simulating add~tion of foots oll by-product with the solvent dewaxed oll stream prlor to further processlng. A 7.3% volume yield of wax was obtalned which had a satisfactory melting point of 181.5F, oil content of 0.28% wt. and API gravity of 33.7.
The partially dewaxed raffin2te was then treated catalytically as in Example 1 except th2t the start of run temperature of the catalytic de~axer was 530F instead of 550F, and then topped.

Table II summarizes the properties of the catalytically dewaxed, hydrotreated bright stock after 550F hydrotreating and topping. The dewaxed oil yield at 20F pour based on charge to the catalytic dewaxer/hydrotreater was 94.5% by S volume.

7~5 .
TABL~ II

Properties from Comblnatlon Solyent Dewaxing/~Jdrod~waxlng/
Hydrotreating Premlum Bright Stock Furfural Raffinate . . .
Solvent Dewaxed Hydrode-~iaxed Oil and Foots Oil Iube Product .Yield on Raflinate, % Volume 92.7 87.6 . Properties ..
&ra~ity, API ':.24.7............. 24.4 -Gravity,Specific at 60~F 0.9059 . o.go76 . . PouriP.oint, ~F .: ::. ' 45 :;. 15 Flash Point,"F (C.O.C.) - 580 ~V at 40C Centistokes . - 389 482 XV at 100C Centistokes 29.8 31.6 .. -. KV at 100F Centisto~es . 446 558 KV at 210F Centistokes. 30.8 32.7 ... SUS at 100F Seconds 2066 2585 SUS at 210F Seconds 146 155 Viscosity Index 107 96 Color, ASTM 5-3/4 2~
Neutralization No. Mg. KOH/~m C 5 5 ~5rbon Residue, % wt. (RCR)0.52 0.5~
Hydrogen,.% wt. 13.06 . .. 13.01 ..
Sul~ur, % ~. . 1.~4 . 1.00 Nitrogen, ppm 110 62 Refractive Index at 20C 1.49820. 1.49887 Refractive Index at 70~C 1.48095 . 1.48167 Aniline Point, ~ 245.4 243.5 .
~ur~ural, ppm . - < 1 Bromine Number - 0.3 . Oil Content, % wt. - . . - .
Melting Point, ~
.. . ..
Distillation~ Type D 1160 ~-1160 -- . . . ..
IBP, F .
. 9}9 . - . 899 ~50 931 1002 992 ..
50 - . . _ .
- _ . .
. . ' . _ , . . _ -- _ Çompared with conventional commercial sol~en~ de~axed oil of ~-20~ pour point prepared ~ro~ the identical bright stock raffinate,

2 12% increase in volume % yield.is realized ~Jith the process of .
this invention with no chan~e in viscosity index~ and no loss ln deolle~ ~.Jax y~eld.

--~1-- . i

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing a high quality lube base stock oil having a pour point of about -25° to +30°F from waxy crude oil, which comprises:
extracting a deasphalted short residuum fraction of said waxy crude with a solvent selective for aromatic hydrocarbons to yield a raffinate from which undesirable compounds have been removed;
mixing the raffinate with hydrogen and contacting the mixture at a temperature of 500° to 675°F with a dewaxing catalyst comprising an aluminosilicate zeolite having a silica/alumina ratio of at least about 12 and a constraint index of about 1 to about 12, thereby converting wax contained in the raffinate to lower boiling hydrocarbons;
cascading the dewaxed raffinate to a hydrotreating zone wherein the dewaxed raffinate is contacted in the presence of hydrogen at a temperature of 425° to 600 F with a hydrotreating catalyst comprising a hydrogenation component on a non-acidic support; and topping the dewaxed, hydrotreated raffinate to remove therefrom components of a low molecular weight.

2. The process described in claim 1 wherein said raffinate is prepared by extraction of said distillate fraction, the total effluent of said catalytic dewaxing step is cascaded to said hydrotreating zone, and contact with said hydrotreating catalyst is at a temperature of 425° to 500°F.

3. A process according to claim 1 wherein said raffin-ate is prepared by extraction of said deasphalted short residuum fraction, the total effluent of said catalytic dewaxing step is cascaded to said hydrotreating zone, and contact with said hydrotreating catalyst is at a tempera-ture of 500° to 575°F.

4. A process according to claim 1, 2 or 3 wherein said dewaxing catalyst comprises an aluminosilicate zeolite having a crystal framework density of not less than 1.6 grams per cubic centimeter.

5. A process according to claim 1, 2 or 3 wherein said hydrodewaxing catalyst comprises ZSM-5 and a hydrogenation metal.

6. A process according to claim 1, 2 or 3 wherein said raffinate is partially dewaxed by solvent dewaxing before said contact with hydrodewaxing catalyst.

7. A process according to claim 1, 2 or 3 wherein said hydrotreating catalyst is cobalt molybdate on alumina or nickel molybdate on alumina.

8. A process according to claim 1, 2 or 3 wherein said hydrogenation metal is nickel.

9. A process according to claim 1, 2 or 3 wherein the lube base stock oil has a pour point of -10 to +30°F.

10. A process according to claim 1, 2 or 3 including the step of partially solvent dewaxing said waxy raffinate to a pour point of from 10° to about 50°F prior to said catalytic hydrodewaxing step wherein the pour point is further reduced by at least an additional 10°F.

11. A process for preparing a high quality cylinder stock having a pour point not higher than 30°F from a waxy crude, which comprises deasphalting the short residuum from said crude to form a waxy deasphalted residuum, catalytically dewaxing said waxy deasphalted residuum by contact in the presence of hydrogen with a dewaxing catalyst comprising an aluminosilicate zeolite having a silica/alumina ratio of at least about 12, a constraint index of about 1 to about 12, and a crystal framework density of not less than 1.6 grams per cubic centimeter, said contacting being at a temperature up to 675°F and under conditions to reduce the pour point to not higher than +30°F, and cascading the dewaxed raffinate to a hydrotreating zone wherein it is contacted in the presence of hydrogen with a hydrotreating catalyst at a temperature of 425°F to 600°F, said temperature being selected so as to enhance the oxidation stability to the catalytically dewaxed oil.