CA1111797A - Dilution chilling dewaxing solvent - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improvement in a dilution chilling dewaxing process wherein waxy lubricating oil stocks are solvent dewaxed by contacting them with successive increments of cold dewaxing solvent at a plurality of points along the height of a vertical tower divided into a plurality of stages while agitating the oil-solvent mixture in each stage to provide substan-tially instantaneous mixing of the waxy oil and solvent thereby pre-cipitating wax from the oil while avoiding the well known shock chilling effect. The improvement resides in using as the dewaxing solvent, a mixture selected from the group consisting of (a) methylene chloride and (b) acetone, methylethyl ketone, methanol and mixtures thereof, and wherein the methylene chloride comprises at least about 20 LV% of the dewaxing solvent.

Description

7~ 7 1 BACKGROUND OF T~lE INVENTION

2 Field of the ~nvention _ _

3 'This invention relates to a process for solvent dewaxing

4 waxy hydrocarbon oils. More particularly, this invention relates S to an improved process for dllution chilling dewaxing waxy petrol-6 eum oil stocks in a staged chilling zone wherein cold dewaxing 7 solvent is injected into said zone at a p:Lurality of stages there-8 along and wherein the cold dewaxing solvent and the waxy oil are 9 substantially instantaneously mixed in each stage as the waxy oil-solvent mix~ure passes from stage to stageO
11 Descrlption of the Pr r Art 12 It is well known that wax-containing petroleum oil stocks 13 can be dewaxed by shock chilling with a cold solvent. It is also 14 known that shock chilling, in itself, results in a low filtration rate of the dewaxed oil from the resultant wax/oil-solvent slurry.
16 Be~ause of this, the conventional method of solvent dewaxing wa~-17 containing petroleum oil stoclcs has been by cooling in soraped sur-18 face heat exchangers uslng an incremental solvent addition tech-19 nique. In this technique, the dewaxing solvent is added at sever-20 al points along the chilling apparatus. The waxy oil i9 chilled 21 without solvent until some wax crystalli~ation has occurred and the 22 mixture is thickened considerablyO The first incremen~ of sol~ent 23 is introduced at this point and cooling continues. Each incre-2~ mental portion o solvent is added as necessary to maintain fluid- -ity until the desired filtration temperature is reached at which 26 point the remainder of the solvent required to obtain the proper ~7 viscosity of the m~xture for flltration is added. In using this 28 technique it is well known that the temperature of the in~rernenta~-~9 ly added solvent should be the same as that of the main s~ream of vll at the point of addition ~o a~oid the shock chilling efect.

~ .

1 This process shall be hereinafter referred to as Conventional 2 Incremen~al Dilution Dewaxing for the sake of brevit~
3 It is now well known that the adverse eE~ects of shock 4 chilling can be overcome by introducing the waxy oil into a staged chilling zone and passing the Wc1Xy oil from stage to stage of the 6 zone, w~ile at the same time injecting cold dewaxing so~vent into 7 a plurali~y of the stages and wherein a high degree oE agitation is 8 maintained in the stages so as to effect substantially instantane-9 ous mixing of the waxy oil and solvent. As the waxy oil passes from stage to stage of the coollng zone, it ~s cooled to a temperature ~1 sufficiently low to precipitate wax therefrom without incurring the 12 shock chilling ~ffectO This produces a wax/oil-solvent slurry 13 wherein the wax particles have a unique crystal structure which ~, 14 provides superior fllter~ng characterlstics such as high filtratior rates o~ the dewaxed oil from the wax and high dewaxed oil yields.
16 The basic concept of dilution chilling dewaxing referred to in this 17 invention is disclosed in U.S. Patent No. 3~773,650. This process ', lB shall hereinafter be referred to as ~ILCHILL for the sake of brev~
19 ~ty.
The use of ketones and mixtures thereof as well as mi~-21 tures of ketones and aromatic cmd~or aliphat~c hydrocarbons in sol- ;~
2 2 vent dewaxing is as well known in the art as is the use of autore-~3 frigerant solvents and halogenated solvents. The Di-Me solvent dew 24 waxing and wax deoillng process is a commercially successful solvent 25 dewaxing process employing a binary solvent mixturP of dichloro- ¦
~26 ethane and methylene chloride. Although the use of mixtures of 27 methylene chloride and o~er solvents for solven~ dewa~ing has been 28 suggested many times, such a combination has never met with any com- ¦
29 mercial or practical success other than the Di-Me process using mlx- I
tures o~ dichloroethane and methylene chloride. ;

. .

1 Early disclosures on the use of methylene chloride may be 2 found in U.S. Patent No. 1,978,010 which is directed towards ~he 3 use of methylene chloride alone or in adm:ixture with other wax sol-4 vents such as acetone, butanol, benzol or naphtha ~or solven-t dewax-ing waxy olls and in an article by P.J. Carlisle and A.A. Ievine 6 entitled "Dewaxing Iubricating Oils with Methylene Chloride" in 7 Vol. XXIV, No. 4 of Industrial and Engineering Chemistry (pages 8 384-387, 1932) wherein the use of methylene chloride alone and in 9 admixture with acetone ~s disclosed as a potential dewaxing solventO
However, this did not meet with any commercial success andg on page l7 of. their book e~titled "Petroleum Reining with Chemic21s"
12 (Elsevier, Amsterdam, 1956~, Kalichevsky and Kobe recite, in ~efer-13 ence to the 1932 article by Carlisle and Levine3 that in extracting '~
14 a Pennsy~vania lubricating oil fraction with a mixture containing 40% methylene chlorîde and 60~/o acetone, the filter rates were low.
16 Kalichevsky and Kobe also stated that such solvents (mixtures of 17 methylene chloride and acetone), when used for the liquid phase 18 extraction (precipitation) o~ the wax9 are not practical because 19 of very high oil losses. Thereore, the prior art teaches a com-plete lack o success in solvent dewaxing using a dew~xing solvent 21 comprising methylene chloride alone or in combination with other 22 solvents 9 the one exception being the dichloroethane-methylene 23 chloride mixture of the Di-Me processO Hence, with the exception 24 of Di-Me, the art teaches away from:the use of methylene chloride ~i:
or sol~ent dewaxingD
2~ D~ `V~N~ N
27 Therefore, the i~stant invention was unexpected and oppo-~8 site t~o the teachings of the prior art which is the discovery that 29 the DILCHILL dilution chilling dewaxing processes as herein defined~
supra, c~n be still urther improved b~ employing a dewax-ing solvent . . . - -.
, ., . ~ -.
.

7~

5 - :

1 comprising a mixture o~ at least 20 L~/o methylene chloride vmd a 2 solvent selected from the group consisting of acetone, methyl-3 Pthyl ketone (MEK), methanol and mixtures thereof. That is, in a 4 process for dewaxing a waxy petroleum oil stock comprising intro-S duc~ng sa~d waxy oil stock into an elongated chilling zone divided

6 into a plurality of stages and passing sGLid waxy oil from stage to

7 stage of said zone while injecting cold dewaxing solvent into at least a portion of said stages and maintain:ing a high degree o~
9 agitation in a plurali~y of the solvent-containing stages so as to achieve substantially instantaneous mixing of said waxy oil and 11 said solvent whlle cooling said solvent-waxy oil mixture as it pro~
1~ gresses from stage to stage through said chilling zone, thereby 13 precipitating at least a portion of said wax from said oil under 14 conditions of said high degree of agitation, separating the pre- ~.
cipitated wax from the solvent-oil mixture and recovering a petrol~
16 e~m oil stock o~ reduced wax content from said mixture, the improve-17 ment which comprises using a cold dewaxing solvent selected from the 18 group cons~sting of mixtures of ~a) methylene chloride and (b) ace~
19 ~oneS MEK, methanol and mixtures thereof~ and w~erein the methylene ~0 chlor~de comprises at least about ~0 L~ of said solvent. Using 21 the dewaxing solvent of the instant invention ~n the DILCHILL de-22 waxing process requires less ~otal sol~ent for dewaxing than ketone 23 and ketone/aromatic dewaxing solvents such as mixtures of MEIC/MIBK
Z~ and MEK/toluene, can provide increased dewaxed oil yields~ results 25 in increased filter rate of the dewaxed oil from the w~x based on : I
: 26 he waxy feed entering the chilling zone~ thereby debottlenecking ~` 27 solven~ dewa~ing:operations9 and also reduces the amoun~ of energy ~:~28 subsequently needed to recover the dewaxing solvent from the de- ;
:~; 2:9 waxed oil and wax cake due to ~he lower latent hea~ o~ vaporiza-tion and lower ~oiling point of the methylene chloride. These :
, ,, - - ' -. . .

l advantages arenot achieved if the dewax;ng solvent of this invention 2 is used in Conventional Incremental Dilutlon Dewaxing processes.
3 The methylene chloride content of the dewaxing solvent 4 will range from about 20 to about 85 LV~/o of the solvent compositionO
l~e actual solvent composition used will ~epend on the nature o the 6 oil being dewaxed and dewaxing conditions required. Typîcal solvent 7 compositions are shown in Table 1 for three, widely used lube oil

8 fractions~ The solvent compositions shown in Table 1 have been

9 found to be suitable for miscible solvent/oil dewaxing filtratlons of the respective stocks shown for maintaining minimum wax solubil-11 ity and maximum oil solubility in the dewaxing solvent~
12 Any waxy petroleum oil stock or distillate fraction there-13 of ma~ be dewaxed with the process of this lnvention. In general, 14 these oil stoclcs or distillate fractions will have a boiling range within the broad range of about 500~ to about 1300F. The pre-16 ferred oil stocks are the lubricating oil and specialty oil frac 1~ tions boiling within the range of 550F and 1200F. However, resid-18 ual waxy oil stocks and bright stoclcs having an initial boilingpoint lg o~ above about 800F and containing at least about 10 wt.% of mater-ial boiling above about 1050F may also be used in the process of 21 the instant invention. These fractions may come from ~ny source, 22 such as the paraffinic crudes obtained from Aramco, Kuwait, the Pan 23 Kandle, North Louisiana9 naphthen~c crudes such as Coastal Crudes, 24 Tia Juana, mixed crudes such as Mid~Continentg etc., as well as the relatively heavy feed stocks such as bright stocks having a bolling 26 range of 1050F~ and synthetic feed stocks derived from Athabascar 27 tar sands, ~tco .
~8 2~ Flgure 1 is a flow diagram of a dilutlon chi:Lling dewaxlng - ~0 process employed in the embodlment o~ the instant invention~ ¦

:::
:. , ., .~ : .. . .

: . .:: . . . . . .. : . . . . . -:. .... . : : - .. . : -: . . . . .. :: , -. . . : . . :
: : ; . . .

Fig. 2 is a graph of eed ilter rate vs,. soïvent dllut~on to 2 filter comparing an acetone/methylene chlorlde dewaxing solvent 3 with an MEK/MIBK dewaxing solventO
4 Fig. 3 lllustrates the dewaxed oll filter rate o an acetone/
5 methylene chloride and MEK/methylene chloride dewaxing solvents 6 compared to MEK/MIBK, MEK/toluene and Di-l!Ie ~ewaxing solvents.
7 Fig. 4 illustrates dewaxed oil filter rate as a function of 8 dilution to filter wherein the comparative solvent systems are MEK/
;9 methylene chloride and MEK/MIBK~

10 DET~ILED DESCRIPTION

11 Referring to Fig. 1, the oil stock to be dewaxed is passed into

12 the top of vertical chilling tower 3 via line 2 wherein it enters the first

13 stage of the chiller 4(a). An acetone/methylene chloride dewaxing sol

14 vent is passed through heat exchangers 7 and 8 via line 6 wherein the sol

15 vent temperature is reduced to a level sufficient to cool-the oil to the 3

16 desired dewaxing temperatureO Coolant enters heat exchangers 7 and 8 ~ -

17 through lines 24 and 25~ respectlvely, and leaves through lines 26 and 27.

18 Cold solvent leaves heat exchanger 8 via line 9 and entersEnanifold lû~ l~e

19 manifold comprises a series of parallel 1ines providing solvent inlets 11

20 to the plurality of stages 4 of chilling tower 30 The rate of flow through

21 each inlet is regulated by flow eontrol means ~not shown). '[~e rate of 2~ solvent flow is regulated so as to achieve the desired temperature 23 profile distribution from stage to stage along the height of chill- i 24 ing tower 3. Preferably, the incremental solvent addition is such 25 that the chllling rate of the oil is below about 10F/minu~e and 26 mo~t preferably between about 1 and 5F/miIlute. In general, the 27 arnount of solvent added thereto will be suf~icient to provide a 28 liquidlsolid weight ratio between abollt 5/1 and 100/1 at the dewaxing tem- ;
29 perature and a solvent/oll voluEne ratio bet~ween about l.û/l and 7/1~ `
The first portlon or increment of cold dewa~ing solvent - .-... . .. - .
'~' : ' ' - , - :
.. ~
..
- .
~, . . . .
.
. - . . . . .
. ~ .

.7 l enters first stage 4~a) 9 of chilling tower 3 wherein it is substall-2 tially instantaneously mixed wi-th the oil due to the action oE agi--3 tator l2(a)~ The agita-tor is driven by a variable speed motor 13 4 and the degree of agitation is controlled by a variation of the motor speed with due allowance for the flow rate through the eooling tower.
~ Although only downward flow of the oil solvent mixture through chil]-7 ing tower 3 has been shown, this mixture may also pass upwardly ;
8 through the tower. Additional prechilled solvent is introduced into 9 at least a portlon of the plurality of stages 4, through inlets 11, so as to achieve the desired temperature distribution and total tem-11 perature drop in the tower and at the same kime to provide the de-12 sired degree of dilution. It should be noted that any number of 12 stages, for example 50, may be employed; however, it is desirable 13 that at least six stages be used. ¦-14 The oil-solvent mixture with precipitated wax passes from lS the final stage of the chilling tower through line 1~ to scraped sur 16 faee heat exchanger 30 wherein the oil-solvent mixture is additional-17 ly cooled via indirect heat exchange, thereby precipitating more wax 18 rom the oil-solvent mixture. The oil-solvent mixture wi-th the pre-19 c~pitated wax passes from scraped surface exchang~r 30 via line 32 to means 15 for separating the wax from the solvent-containing dewaxed 21 oil solution. Any suitable means for such separation may be em

22 ployed, such as filtration or centrifuga~ion~ In genera~, rotary

23 vacuu~ or pressure filtra~ion is a preferred means o~ separationO

24 ~he dewaxed oil-solvent mixtures leave wax separation means 15 via line 20 and are sent to further-processing such as solvent recovery 26 to recover the solvent therefrom. ~le wax leaves separation zone 27 15 via line 16 and then passes through to solvent recovery operations 28 and ultimately to additional wax refining operations~
29 An essential eature of ~he DILCHILL dewaxing process ~s the maintenance of a high~degree of a~l~a~ion in at :Least a portlon .

.

7~7 g l of the stages during chillin~ in order to provide substantially 2 instantaneous mixing of the waxy oil and solvent. By substantially 3 instantaneous mixing is meant complete mix:lng of the oil-solvent mix~
4 ture in one second or less. In this way, the deleterious effects of shock chilling are offset, the chilling rate ls more readily con 6 trolled and increased filtration rates are obtained. The degree of 7 agitatîon required in this invention can be achieved by increasing 8 the agitator RPM when all of the mixing variables, elg~, flow rate 9 through the mixer3 vessel and agitator design, viscosity of the in-gredients, etc., are maintained constant. In general, the degree of 11 agitation required ln this invention can be aehieve~ when the modi-12 fied Reynolds Number (Perry, "Chemical Engineers Handbook", 3rd, p.
13 1224, McGraw-Hill New York, 1959), NRe whlch is def:ined by the 14 equation: ,~
N~e = L2n ~Ç~t f 16where L = agitator diameter, ft.
17~ = liquid density, lb/fto3 -18n = ~itator speed, r~p.s.
19~ - liquid viscosity, lb./ft. sec.
is between about 200 and about 150~000.
21The dimensioniess ratio o cooling tower diameter to agi-22 tator di~meter is generally between about l~S/l and about 10/1, and ~3 the ra~io of the impeller blade length to impeller blade width 24 rangefs from about 0.75 to 2 and preerably from about 1 to 1.5.
The ratio of the mixing stage height to the diameter of the stage 26 will generally range from about 0.2/1 to 1/1. A turbine type o~
27 agitator is preferred; howeverg other types of ag~tators such as pro-2~ peller agitators may be used. ~-29 The cooling tower may or may no~ be baffled, bu~ a ba~fle 3~ tower is grea~ly preferred. Each stage will generally ~on~ain from - .. . ~
. - ... .:, . - . .
.. - . ~ .
.. . .. .
", 7 ~ 7 ~ 10 - , 1 about 2 to 8 baffles and preferably from 2 to 4 baffles, located 2 about the outer periphery of each stage. The width of the baffles 3 may vary from about S to 15~/o Of the diameter of the tower. In gen-4 eral, the dimensionless ratio of the cross~section of the restricted flow opening to the cross-section of the tower will ~e between about 6 1~0 and 1/200. Further, the cooling tower will be operated at a 7 pressure sufficient to prevent flashing of the solvent. Atmospheric 8 pressure is sufficient when using the dewaxing solvent of the pres-9 ent invention.
lQ PREFERRED EMBODIMENT
11 The invention will be more apparent from the working exam-12 ples set forth below.

14 In this exampleg experiments were run utilizing a single-stage dilution chilling dewaxing laboratory batch unit which~ while 16 not completely duplicating continuous multistage operation, has been 17 found to give results approximately equîvalent to those obtained 18 with continuous 3 commercial multistage operationsO l~e unit con-19 tained a flat-bladed propeller and a solvent in~jection tube with a recycle loop. Experiments were conducted by filling the unit with 21 the waxy oil to be chilled at just above its cloud point. A~ter 22 the unit was filled with the waxy oil, the impeller was s`tarted 23 along with simultaneous injection of chilled solvent into the waxy 24 oil at the lmpeller tipo The solvent was injected continuously;
but at incrementally increased flow rates for a total of 17 succes-26 si~e incremental increases in flow rate in order to simulate a 17~ ~
; 27 ~age dilu~ion chilling dewaxing tower. Follow7ng the addition o~ 1 -28 the desired volume of cold dewaxing solvent, the slurry ~rom the 29 uni~ was then scrape-surface chilled a~ an average ra~e of about 2F ¦~
~0 per ~inu~e until a filtration temperature of 20F was reached. l~e ; .
~: : .

: ' , ' `7~ ~

1 filter rate and the waxy oll yield as well as the wax cake liquid/
~ solid ratio were determined by ~iltering the cold, dilutecl~a~y 3 slurry through a laboratory filter leaf caLibrated to simulate a 4 rotary filter operation~ followed by washing the wax cake on the filter with additional dewaxing solvent at the filtration tempera-6 ture.
7 Two dewaxing solvents were used in this example. One was ~ a 45/55 LV~/o mixture of MEK/MIBK and the other was a 30~70 L~/o mixture 9 of acetone/methylene chloride, the solvents being precooled to -20F.
; . 10 ~hewaxy oil feed was a phenol raffinate of a vacuum distillate cu~
11 from a paraffinic, Western Canaclian Leduc blend crude oil having an 12 initial pour point of about 130F, a viscosity of 66~7 SUS at 210F

13 with a V~I. of 90. The waxy oil added to the unit was at a tempe~a-14 ture of about 135F. The volumetric ratio of dewaxing solvent to the feed, the volumetric ratio of the wash solvent (wax cake) to the 16 feed, total solvent used, feed filter rate and wax oil content are 17 shown in Table 2. Approximately 21% of the oily feed was removed 18 as wax in each case. These data show that the acetone/me~hylene 19 chlor~de dewaxing solvent resulted in a much greater feed filter rate using significantly less solvent.
21 EX~MPLE 2 22 This example was similar to Example 1 except that the waxy 23 oil ~eed was a phenol raffinate of an Aramco 600 Neutral oil having 2~ a V.I. of 95~ a viscosity at 210F and lQ0F o~ G7.7 and 596 SUS, respectively, a pour point o -15C, an API gravity of 27. The 26~ waxy oil added to the unit was at a temperature of 126F. The de-;
27 waxing solvents used in this example were a 40/60 L~/o ratio ~f 28 MEK/MIBK) a 70/30 L~/o mixture of MEK/tolueney a 20i80 LV~/o Of 29 acetone/methylene ch~orlde~ and 13/87 L~/o and 5/95 L~/o ratios o~ a m~ture o~ methanol/methy~ene chloride, all precooled to 20F. The . ,.. . , . . . . . -. . . .. . . . ..

1 results are shown in Table 3 and illustrate that the acetone/
2 methylene chloride, and methanol/methylene chloride mixtures were 3 superior to both the ~EK/MIBK and MEK/toluene dewaxing solvents in 4 that less solvent was used, the feed filter rate was greater and the S wax had a lower oil content.
6 EX~MPLE 3 7 This experiment was run to compare DILCHILL with Conven-8 tional Incremental Dilution Dewaxing employing the dewaxing solvent 9 o the instant invention and used the same feed and dewaxing method as in Example 2 for the DILCHILL. dewaxing, except that both aceton~/
11 methylene chloride and MEK/methylene chloride clewaxing solvents were 12 compared to an MEK/toluene dewaxing solvent~ For the Conventional 13 Incremental Dilution Dewaxing runs, an elongated, horizontal~ scraped-14 surface chiller was used to chill the waxy oil passing therethrough at a rate of about 6F per minute. The irst increment of solvent 16 was added at 95F, the second at 59~F and the final increment was , 17 added at the filtration temperature of 5F~ -.
18 The data for all of the runs are listed in Table 4 and 19 clearly show that both the acetone/methylene chloride and MEK/
methylene chloride solvents give a 20% increase ln dewaxed oil filter 21 rate ~n DILCHILL dewaxing, but not in Con~entional Incremental Dilu-22 tlon DewaxingO

' ;

, 1 ~`
;

~ .
~. .

7 .

1 T~BLE 1 3 ~ I~S ,~
4 (~ Ac/~ M~K~Me ~ ~ ~ - ~ v/v(C) ~ lS0 Neutral 40/60 70/30 7 600 Neutra~ 25/75 50/50 8 ~500 ~right S~ock 15/85 40/60 1;

" , . I
(a~ Numbers re~er to SUS viscosity at 100F~
~o ~b) AclMe - ace~one/methylene ch~oride.
ll (c) MEK/Me ~ MEK/methy~ene chloride~

.- 1 ,I
': : - `

~ , , : : ' .
: ~: :
~:: ' . ~ '.' ~: :
I

.
:~ :

~ . .

t~ U~P ~, . , .
a) :~ ~
~ t;~ O ~.
~ ~ ~ o Cl~ ~
Q ~ ~ o~ Cits V
~' a,~, ~S

SO ~ I~
~ h h c~
~ 0S--~S 5''1 t~t O ~ .
~ ~ S ~ S ' . .
., ` ' ' ~ P P P ~
. . ~' S

~; ~ ~ t C~
~ ~u~ ~ !
~ ~ ~ ~ ~
J
~ ~ ,~ ~
, .
,,-, -S-t ~q ~
æ E,~

o F~

t g ~ Cl~ trS ~S
O tlS ,~ n t, jS O
~3 ; r~
a) ~ r~ X ' ~ ~rs~ O

:

;~ ' ~ :, .

._ ~ ~ ~ ~ o a~ ~ ~, i ,~ O 0~ r-l r~ JOt) O
~ ~ ~r~
~0 ' I
r~P ~ I
~ ~ ~ c~ O O
00 C~ r~ ~ ~ U~ Ln ~0 1 r~ ~
~ ~ l l l . . .
a) ' ~rl O
O
r~
~ l l l ~, ~9 1 ~ ~ i .
~I) ¦~ ~
~ ~ ~ ~
.~~_~ ~ . '. .
P U~ I ~ O
~o ~ a~
P~ o' .~ ~ c~i ~ ~ n .;
r~ O ~ ~I r~ r~
~ .
t~) O h h ~ P ¢
~1 '~:) oo ~o Or-~ ~ ttf ~ li ~ t~f ~ ~ 1:
C:~ ~: H P~ O -- . .
~ a~ ~ ~ ~ ~ ~ . , :1 ~ o o c~ D f 1 C~) r~
~1 C~l r~
`40 ~ 1~

: : H : : .

,, ,~ ~ ' .

~; ~ ; æ P ~
O ~ P : ~ ~P,~ C
U~ ~ ~ O ~ .
o rr~
~1 ~ rl ~1 0 ~ ~ .!.) ' r~l OC~ i td rd J~ h I
~: r~ X~1:1 , C~ ~ O ~ ~ ~ O ' ~ ~ ~~ F4 3 ~ ;
'~ :: : ' : . I
~ r~ ~I r~l r~l r~ r~ ~1 !, ::.: .: : - : . - :. , , - :: - : :, - - , : . .: . : : . : - : ::

- ,. . - , ~ : ~ - , , .,: . :

16 ~

~0 ~ n ~ s~
~o , . Fl U~ , ~, , . ", c~
~ ~ U~ C~J
' ' ~ ~ ~ oo g ~.
~r) "~ ~
R ~1 :1 1 ~ ~ .
t~ ~ Q
Z; ~ s æ ~ H c~ c~
, ~q ~1 ~ a) o ~0 ~ ~ .~ ` .
H .
E~ ~ ~ .
u i~l Q ,~ ~ P o o a~
e~ 1 ~ ~O
. ~ ~0 0~ ~ P
.,, ~ . ~ .~ ~ O ~

O ~ O H _a~ ~3 0 ~ W

~ o ~ ' ' o ~ ~ O O t~
; O ~ i o o ~: ,~1 O O 0 ~ ~ ~ 1~ 0 ~rl r-1 ~9 ~, ~
! 5-~ o ~ ~ . ~ .
U ~ . .~ ~

O ' o~
': . ' O ~) : ' ?
U ~

rl 0 O r,-l ~ 1) 0 q ~ U .~
~ ~ri ~ ,> ~ ri 3 0 ~ ~1'~ 1 U l ~3 `1.~ ~ , o a~ ~ , .

:~ :
~ : :: : ~ : :
:
:

Claims (9)

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

1. In a process for dewaxing a waxy petroleum oil stock comprising introducing said waxy oil stock into an elongated chill-ing zone divided into a plurality of stages and passing said waxy oil from stage to stage of said zone while injecting cold dewaxing solvent into at least a portion of said stages and maintaining a high degree of agitation in a plurality of solvent-containing stages so as to achieve substantially instantaneous mixing of said waxy oil and said solvent-waxy oil mixture as it progresses from stage to stage through said chilling zone, thereby precipitating at least a portion of said wax from said oil under conditions of said high degree of agitation separating the precipitated wax from the solvent-oil mixture and recovering an oil stock of reduced wax con-tent from said mixture, the improvement which comprises using as said cold dewaxing solvent, a solvent selected from the group con-sisting of mixtures of (a) methylene chloride and (b) acetone, MEK, methanol and mixtures thereof and wherein the amount of methylene chloride in said dewaxing solvent is at least about 20 LV %.

2. The process of claim 1 wherein the amount of methy-lene chloride in said solvent ranges from 20 to 85 LV %.

3. The process of claim 2 wherein said chilling zone is divided into at least six agitated stages.

4. The process of claim 3 wherein said solvent oil mix-ture is cooled in said chilling zone at an average rate of from about 1 to about 5°F per minute.

5. The process of claim 4 wherein said waxy oil stock is a lube oil fraction.

6. The process of claim 5 wherein said waxy lube oil is introduced into said chilling zone at a temperature above its cloud point.

7. The process of claim 6 wherein said solvent is select-ed from the group consisting of a mixture of (a) methylene chloride and (b) acetone or MEK.

8. The process of claim 7 wherein the cold dewaxing sol-vent is a mixture of MEK and methylene chloride and is added to the said chilling zone in an amount such that the dilution ratio of the wax/solvent-dewaxed oil slurry ranges from about 1.75 to about 4 volumes per volume of dewaxed oil.

9. The process of claim 7 wherein the cold dewaxing sol-vent is a mixture of acetone and methylene chloride and is added to the chilling zone in an amount such that the dilution ratio of the wax/solvent-dewaxed oil slurry is at least about 1.75 volumes per volume of dewaxed oil.