CA1103187A - Dewaxing waxy oil by dilution chilling employing static mixing means - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved process for the solvent dewaxing of petroleum oil stocks.
Wax-containing oil is chilled in an elongated chilling zone by introducing cold dewaxing solvent into said zone, at a plurality of points along same, said chilling zone containing or having associated with it a plurality of static means for mixing the solvent and wax-containing oil, thereby avoiding shock chilling without the need for the intense agitation and/or dynamic agitators normally required for such processes.

Description

2 Field of the Invention

3 This invention relates to a process for solvent

4 dewaxing waxy oils. More particularly, this invention re-

5 lates to a process wherein waxy oil is introduced into a

6 cooling zone and the wax is precipitated from the oil by the

7 incremental addition of prechilled dewaxing solvent along the

8 length or height of the cooling zone. Still more particu-

9 larly, this invention relates to a process wherein the mixing

10 of the chilled dewaxing solvent and wax-containing oil in the

11 cooling zone is accomplished by static mixing means, as op-

12 posed to the heretofore employed dynamic mechanical agitators

13 such as impellers, rotating vanes, etc.

14 ~ on of the Prior Art It is well known in the prior art that wax-con-16 taining petroleum oil stocks can be dewaxed by shock chill-17 ing with a cold solvent. It is also known in the prior art 18 that shock chilling, in itself, results in a low filtration 19 rate of the dewaxed oil from a wax/oil mixture. It is now 20 well known that the shock chilling effect can be overcome by 21 introducing the waxy oil or wax/oil mixture into a cooling 2Z zone and incrementally introducing a dewaxing solvent into 23 said zone, along a plurality of points or stages therein, 24 while maintaining a high degree of agitation so as to effect 25 substantially instantaneous mixing of solvent and wax/oil 26 mixture as they progress through the chilling zone. This 27 latter concept is shown in U. S. ~atent No. 3,773,650 and 28 shall hereafter be referred to as Dilution Chilling.
29 A number of improvements have been made to the basic 30 concept of Dilution Chilling. U. S. Patent No. 3~642,609 31 shows that in a vertically staged cooling tower, the velocity 32 of the solvent at the injection points should be at least - 2 - ~ .

~ 3~7 1 5-30 times that of the peripheral velocity of the mixer 2 blades. This results in greater filtration rates and de-3 waxed oil yields than could be obtained without the rela-4 tively high velocity solvent injectionO U. S. 3,681,230 discloses another improvement in Dilution Chilling wherein 6 the waxy oil and solvent are miscible until the temperature 7 approaches the wax-oil separa~ion temperature, which general-8 ly occurs near the last stage of the cooling zone. This re-9 sults in superior dewaxed oil yields and filter rates when the waxy oil stock being fed to the tower is relatively high 11 in viscosity and molecular weight. However~ in all of these 12 processes there must be a plurality of intensely agitated 13 stages so as to effect substantially instantaneous mixing of 14 the waxy oil or wax/oil mixture and solvent.
Agitators normally employed for this purpose are 16 mechanical agitators such as propellers, paddles and disc 17 turbines with disc turbine impellers being the most pre-18 ferred type of agitator. For practical reasons~ this neces-19 sitates the use of large, staged towers employing a single impeller shaft centrally mounted within the tower. The de-21 sign of such towers is complicated, dif~icult to fabricate 22 and install and can be prone to operating difficulties if not 23 done properly. These towers are relatively expensive. Fur-24 ther, there must be a means for sealing the dewaxing solvent in the tower around said shaft and at the same time maintain 26 a strong bearing support for the shaft.
~7 It would be a significant improvement to the art 28 if one could do away with the need for these dynamic mech-Z9 anical agitators.
SUMMARY OF THE INVENTION
31 A procesq has now been found for dewaxing a wax-32 containing oll that has the advantages of Dilution Chilling 1~318~7 with few, if any, of its disadvantages resulting from the dynamic mechanical mixing equipment heretofore required. This process for dewaxing a waxy or wax-containing oil comprises in one aspect: !
(1) introducing a stream of waxy oil into an elongated cooling zone containing static mixing means having a plurality of stationary elements longitudinally disposed within said means to successively divide said stream and to at least partially recombine the divided streams; and (2) introducing cold dewaxing solvent into said cooling zone at a plurality of points along said zone in order to progressively mix said solvent and said waxy oil by said static mixing means as said waxy oil and solvent progress through said cooling zone, thereby precipitating a substantial portion of wax from said waxy oil In another aspect the invention provides, in a continuous solvent dewaxing process for separating solid wax from waxy petroleum distillate oil stock, wherein said waxy oil stock, heated for dissolving all wax therein, is treated with dewaxing solvent in a volume ratio of solvent to oil of about 1.5:1 to 5:1, wherein the oil/solvent mixture is cooled at a rate below about 10 F/min to a temperature for forming a mixture of wax crystals in the oil/
solvent solution, wherein said wax/oil/solvent mixture is separated in a solid-liquid separation zone into a dewaxed oil/solvent solution and wax, the improvement which comprises:
(a) heating a continuously flowing mixture of waxy oil stock and aromatic hydrocarbon dewaxing solvent to a temperature above the melting point of solid wax for forming a waxy oil/aromatic solvent solution;
(b) cooling said heated waxy oil/aromatic solvent solution at a rate below about 10F/min to a dew~xing temperature for crystallizing wax and forming a wax/oil/aromatic solvent mixture;
(c) static mixing of said wax/oil/aromatic solvent mixture with cold ketone dewaxing solvent under conditions of plug flow radial mixing to progressively mix said solvent mixture and said dewaxing solvent and to form a second wax/oil/solvent mixture; and 1~¢3187 (d) flowing said second wax/oil/solvent mixture at said dewaxing temperature to said solid-liquid separation.
It has been discovered that the static mixing can even be under laminar flow condltions without incurring the well known shock chilling effect, which results in relatively small wax crystals with resulting low filtration rates of the dewaxed oil from the wax slurry. Alternatively, the mixing can occur under turbulent flow conditions. Static mixing means may be employed to mix the solvent and wax/oil mixture after each point of solvent injection, or the static mixing means may itself comprise at least a portion of the cooling zone, with cold solvent injected into it at a plurality of points along said zone. Alternatively, it may be advantageous not to employ static mixing means at or after every point of solvent in~ection into the cooling zone.
The process eliminates the need for the intense agitation and dynamic mechanical mixing devices heretofore required. Further, employing static mixing means also eli-- 4a llQ3187 1 minates the need for having a relatively large, staged 2 tower, although such a tower can be adapted for use with 3 static mixing means. Instead of a tower, one can employ one 4 or more vertical or horizontal elongated cooling zones, with 5 static mixing means either associated with said zones or em-6 ployed as an integral part Or the cooling zones. Still fur-7 ther, static mixing means may be employed in conjunction with 8 more conventional dewaxing operations, such as scraped sur-9 face dewaxing, autorefrigerative dewaxing, etc.
By static mixing means is meant mixing means em-11 ploying no moving parts, but which contain therein means or 12 elements for successively dividing or splitting up a stream 13 of fluid into partial streams and then at least partially 14 recombining the divided streams ~efore they are di~ided

15 a~ain. While varlous types of static mixers can be employed,

16 the principle involved in each mixer is basically the same.

17 An incoming flow of unblended or unmixed material is split

18 into a host of substreams which are diverted in various direc-lg tionsJ perhaps rotated and are then brought back together ~ again, at least partially, before being split up once more 21 and so on. The number of substreams increases rapidly as the 22 material passes through the mixer, so that on exiting from 23 the mixer, the material is a fairly homogeneous mixture. In 24 each case, the generation of these substreams ls due to a 25 series of "elements 1l and it is the detailed design of these 26 elements which differentiate on~ type of static mixer from 2~ the ne~t. The~mixing action of the mixers can be more or 2~ less independent of flow rate and the flow therethrough can --29 be either laminar or turbulent.
One type of static mixing device which has been 31 found useful in this invention is a "Static ~ixer" which may 32 be obtained commercially from the Kenic~ Corpor~tlon of 1~3~87 Danvers, Massachusetts. This type of mixer consists of a series of twisted or curved elements enclosed within a tube and is described in U. S. 3,286,992. Each element is a length of twisted sheet metal or plastic sheet cut in 180 twisted sections.
A better understanding of this device can be ob-tained by referring to Figure 1 which is a partial sectional view of a portion of a "Static Mixer" static mixing device comprising tube 1 which encloses mixing elements 2 and 3.
As shown in Figure 1, the right and left-hand twists can be ~uxtaposed and the trailing edge of a mixing element may be at right angles to the leading edge of the next mixing ele-ment. The initial fluid stream consisting, for example, of two or more unmixed components strikes the upstream edge of mixing element 2, which splits it into two partial streams, preferably but not necessarily equal, each stream containing portions of the unmixed components. The twisting configura-tion of the mixing element imparts a double rotational motion on these partial streams while they move forward through the tube 1. As the streams rotate helically in order to follow the configuration of the element, the velocity of the fluid near the wall of the tube is greater than that of the fluid near the tube center. This results in an eddy current motion within each partial stream which causes some mixing of the components. As the fluid meets the upstream edge of the mix-ing element 3, it is forced to split again along a new surface creating two new partial streams, each of them now combining portions of both previous partial streams. The components of these streams are again forced to mix by the aforementioned eddying motion, while the two streams rotate helically follow-ing the configuration of element 3. This process is repeated r~
~ LJ

11~31t37 1 with each element as the fluld travels along tube 1 until 2 the original multicomponent stream has been split and re-3 combined along new surfaces by a number of elements suffi-4 cient for thorough mixing of the original unmixed stream.
5 This is called flow division and results in an exponential 6 increase in stratification defined by S=~n where n is the 7 number o~ elements. It is possible~ therefore, for 20 ele-8 ments to produce over one million splits or substreams or, 9 for a two-component system, over two million layers.
In this type of mixing, there can exist flow divi-11 sion, flow inversion, flow reversal and back mixing, all 12 occurring in a single pass through the mixer. In flow in-13 version, particles migrate from the wall of the mixing means 14 to the center of the stream and back to the wall due to 15 transverse displacement. Flow reversal is caused by the op-16 posite pitch rotation of successive elements reversing the 17 bulk flow at each element ~unction. In addition, a counter 1~ rotation of constituents with respect to element direction

19 occurs in each element which further enhances mixing and con-

20 tacting. Back mixing occurs as a result of the constant

21 change in flow profile of bulk fluid passing through a geo-

22 metric pattern.

23 Other well known static mixers currently commer-

24 clally available are the Ross ISG (Interfacial Surface

25 Generator) and the Sulzer mixer. As with the Static Mixer,

26 each of these mixers comprises an elongated housing or tube

27 containing static elements for successively splitting up a

28 stream into partial streams and then recombining the partial

29 streams. It i5 understood, of course,`that the embodiment

30 contained herein is not limited to the specific examples

31 glven, but applies to any device which employs static elements

32 or means for splitting a fluid stream into partial streams and ~1~3~37 1 then at least partially recombining said partial streams 2 causing mixing thereof.
3 Although static mixing has heretofore been em-4 ployed in the petroleum industry in various blending opera-5 tions such as blending reactor feeds, distillate feed stocks 6 and additives (Process Engineering, April, 1973, page 78), 7 it has not been heretofore suggested that static mixing means could be used in Dilution Chilling operations to mix 9 the waxy oil and solvent and, at the same time, avoid the 10 shock chilling effect without requiring the intense agitation 11 and attendant dynamic mechanical mixers heretofore required.
1~ Dilution Chilling can even be achieved by employing static 13 mixing means at laminar flow rates, thereby greatly reducing .
14 shear of the wax crystals in the wax/oil/solvent slurry.

15 The use of static mixing means can substantially reduce the 16 complexity and cost of Dilution Chilling plant facilities and 17 operations currently employed in the industry.

18 Any waxy petroleum oil stock or distillate fraction l9 thereof may be dewaxed with the process of this invention.

20 In generalJ these oil stocks or distillate fractions will have 2i a boiling range within the broad range of about 500F to about 22 1300F. The preferred oil stocks are the lubrlcating oil and 2~ specialty oil fractions boiling within the range of 550F and 2~ 1200F. These fractions may come from any source, such as the 25 paraffinic crudes obtained from Aramco, Kuwait, the Panhandle 26 North Louisiana, Tia Juana, etc., naphthenic crudes such as 27 Coastal Crudes, etc., as well as the relatively heavy feed 28 stocks such as bright stocks having a boiling range of 1050+~ ;

29 and synthetic feed stocks derived from Athabasca tar sands, 3~ etc.

31 Any solvent useful for dewaxing waxy petroleum oils 32 may be used in the process of this invention. Representative ~ 8 1 examples of such solvents are (a) the aliphatlc ketones 2 having from 3-6 carbon atoms, such as acetone, methyl ethyl 3 ketone (MEK) and methyl isobutyl ketone (MIBK) and (b) the 4 low molecular weight autorefrigerant hydrocarbons, SUCtl as 5 ethane, propane, butane and propylene, as well as mixtures 6 of the foregoing and mixtures of the aforesaid ketones and/
7 or hydrocarbons with aromatic compounds, such as benzene, - 8 xylene and toluene. In addition, halogenated, low molecular g weight hydrocarbons, such as C2-C4 chlorinated hydrocarbons 10 (e.g., dichloromethane, dichloroethane, methylene chloride) 11 and mixtures thereof may be used as solvents either alone or 12 in admixture w1th any of the forementioned solvents. Another 13 solvent that may be used in admixture with any of the other 14 solvents is N-methyl-2-pyrrolidone.
Specific examp]es of suitable solvents are mixtures 16 of MEK and MIBK, MEK and toluene, dichloromethane and dichlo-17 roethane, propylene and acetone. Preferred solvents are 18 ketones. A particularly preferred solvent is a mixture of 19 MEK and MIBK.
The solvent is prechilled to a temperature suffi-21 cient to permit cooling of the waxy oil to the dewaxing tem-22 perature. The exact temperature of the solvent employed will 23 depend upon the amount of oil to be cooled and the amount of -24 solvent to be added to the oil. In many cases, the solvent 25 is prechilled dcwn to at least 0F before being introduced 26 into the cooling zone. The prechilled solvent is added in-27 crementally along the cooling zone so as to maintain an 28 average chilling rate at or below about 10F per minute and 29 preferably between about 1 to about 5F per minute. In gen-30 eral, the amount of solvent added will be sufficient to pro-31 vide a liquid/solid weight ratio between the range of 5:1 32 and 20:1 at the dewaxing temperature and a solvent/oil volume 3~87 1 ratio between 1.5:1 and 5:1.
2 Where the waxy petroleum oil feed stock is to be 3 prediluted with solvent prior to its introduction into the 4 cooling zone, the predilution solvent may be selected from 5 any of the dewaxing solvents known in the prior art including 6 those solvents outlined above.
7 BRIE~ DESCRIPTION OF THE DRAWIN~S
8 Figure 1 is a partial secti,onal view of a type of ., 9 static mixer useful herein. Figure 2 is a flow diagram of a 10 preferred embodiment of the invention.
1i DETAIIED DESCRIPTION
12 Figure 1 has been substantially described under 13 SUMMARY OF THE INVENTION, supra.
1~ Referring to Figure 2, a waxy petroleum oil stock 15 ls introduced into an elongated cooling zone (e.g., the afore-16 described static mixer of Figure 1) via line 4. Cooling zone 17 1 contains static mixing means therein. The waxy oil may or 18 may not have been prediluted with a solvent. Although not I9 shown, heating means may be provided for the waxy petroleum 20 oil stock prior to its introduction into the cooling zone in 21 order to ensure that the feed temperature is above the cloud 22 point of the oil or the depressed cloud point of the oil/
23 solvent mixture prior to introducing same into the cooling 24 zone. Cold dewaxing solvent is introduced into manifold 5 25 which comprises a series o~ paths 6-12 for providing sol~ent 26 to the multiple solvent injection points of cooling zone 1.
27 The rate of flow through each inlet is regulated by flow con-28 trol means (not shown). The rate of solvent flow is regula-29 ted so as to maintain the desired temperature gradient along 3~ the length o~ cooling zone 1. The flrst portion or increment 31 of the cold dewaxing solvent may enter the cooling zone ~ust 32 prior to the ~irst statlc mixing means contained therein, _ 10 -~ 3~7 1 wherein it is contacted with the wax-containing petroleum 2 oil. The waxy oil and solvent progress through the cooling 3 zone to the first series of static mixing elements (or inter~
4 facial surface generators) whereby they are mixed under 5 either turbulent or laminar flow conditions, i. e., at modi-6 fied Reynolds Numbers of from 2 to 150,000. Each additional 7 increment of prechilled solvent is introduced into the cool-ing zone at a point along the length of said zone so as to -9 maintain a controlled cooling rate and at the same time to 10 provide the desired degree of dilution. Downstream of each 11 solvent injection point in the cooling zone is at least one 12 static mixing means containing more than one static mixing 13 element in order to provide mixing of the wax/oil/solvent 14 mixture and the new increment of cold solvent as they pro-15 gress through the cooling zone.
16 It should be noted that any number of solvent in-17 jection points and static mixing means or units may be em-18 ployed, however, it is desirable that at least six points of lg solY~nt injection be used, each point of solvent injection 20 being followed by at least one static mixing means. It will .
21 be apparent to those skilled in the art that the exact sol-22 vent temperature employed will depend on the amount of oil 23 to be cooled, the composition of the solvent, the amount o~
24 solvent to be added to the oil, i. e., the degree of oil di-25 lution which is sought during the filtration step and-the 26 nature or type of waxy petroleum feed stock that is used.
27 The cooling of the waxy oil feed stock continues 28 to a temperature substantially below its cloud point, thereby 29 precipitating at least a portion of the wax therefrom and 30 forming a wax/oil/solvent slurry. The slurry passes from the 31 final mixing æone or the last stage of the cooling zone 32 throu~h ~ine 13 to means for separatlng the wax from the 31~
slurry. Any suitable separation means, such as filtration or centrifugation~ may be employed. Additionally, there may be either substantially bulk miscibility or immiscibility between the solvent and the oil at one or more points within the cooling zone. Before going to the separation means, ad-ditional solvent may be added to the slurry and/or supple-mentary chilling by scraped surface chilling, autorefrigera-tion, etc., may be employed to further cool said slurry.
The cooling zone of the present invention is pre-ferably operated at a pressure sufficient to prevent flash-ing of the solvent. Atmospheric pressure is sufficient when ketones and aromatics are employed as solvents; however, superatmospheric pressures are required when low molecular weight hydrocarbons such as propylene or propylene/acetone and other related autorefrigerative solvents and auto-refrigerative solvent/ketone solvent systems are used. A
process combining both vaporization of the solvent to provide in situ refrigeration and direct cooling from cold dewaxing solvent is disclosed in U. S. 3,658,688, granted on April 25, The recovered lube oil products may, if so desired, be subjected to various finishing operatlons such as clay contacting, hydrofinishing, acid treatment and the like. In addition, various inhibitors and other additive ingredients may be added in order to provide various finished lube oil products.
PREFERRED EMBODIMENT
The invention will be more apparent from the work-in~ examples set forth below.

Laboratory experiments were performed employing a Static Mixer unit purchased from the Kenics Corporation.

. .~
~ 3 11~3~L~37 1 This unit was 21-1/2" long with an I.D. of 0.622" and con-2 talned 21 ~elements." The Static Mixer unit was incorporated 3 into a recycle loop around a single stage Dilution Chilling 4 laboratory batch unit which~ while not completely duplicating 5 continuous multistage operation~ has been found to give re-6 sults approximately equivalent to those obtained with con-7 tinuous, commercial multistage operations. The unit contained 8 a flat bladed impeller and a solvent injection tube. The re-9 cycle loop contained a Moyno pump to provide flow of the wax~
10 oil/solvent slurry through the static mixing device with lit-11 tle or no adverse effect to said slurry. It is well known in 12 the art that Moyno pumps permit pumping of crystal slurries 13 with a minimum of shearing agitation and attendant deleterious 14 effect on the crystal structure of the wax crystals as would 15 occur with more conventional pumpsO
16 Experiments were conducted by filling the unit with 17 the waxy oil to be chilled at just above its cloud point.
18 After the unit was filled with the waxy oilg the impeller and~
19 or Moyno pump were started along with the simultaneous in~ec-20 tion of chilled solvent into the waxy oil at either the im-21 pell~r tip in the mixing section or ~ust upstream of the Sta-22 tic Mixer in the recycle loop, depending upon the variables 23 to be studied.
24 Following the addition of the desired volume of 25 cold dilution solvent, the slurry from the unit was then 26 scrape surface chilled at a rate of 2-3F per minute until 27 the filter temperature was reached. The filter rate and the 28 waxy oil yield were determined by filtration in the well 29 known manner.
The dewaxing solvent used in these experiments was 31 a 45/55 L~ (liquid volume) mixture of MEK/MIBK precooled to 32 -20F. The waxy oil feed used in the experiments was a 11~ 31~37 1 phenol raffinate of a vacuum distillate cut from a West 2 Canadian cru~e (para~finic), with a boiling range of approxi-3 mately 650-1170~, an API gravity of 29, an initial pour 4 point of about 130F, ~n lnitial cloud point of 128F, a dry 5 wax content of about 22% to produce a dewaxed oil having a 6 25F pour point and a viscosity of 575 SUS at 100~, and 60 7 SUS at 210F, which corresponds to a VI of about 90.
8 EXAM.PLE 1 9 The laboratory unit was first run by injecting the 10 cold solvent at the i.mpeller tip with the recycle loop closed 11 off~ thus simulating conventional Dilution Chilling as. hereto-12 fore described. The impeller was run at a speed of 1050 rpm 13 which corresponded to a maximum peripheral Reynolds Number of 14 from 719 at the beginning of the experiment to over 8000 at 15 the end. This resulted in predominantly turbulent conditions 16 at the .impe ler tip for the mixing of the cold solvent and 17 waxy oil. The experiment was then repea-ted, but with the fol-18 lowing changes:
19 (a) the recycle loop was operated to give a flow 20 rate of about 1/2 USG/minute through the Static Mixer, cor-21 respondi.ng to theoretical Reynolds Numbers of from about 16 22 to 194; and 23 (b) cold solvent was added ~ust upstream of the 24 S~atic Mixer instead of at the tip of the impeller, thereby 25 insuring that the solvent and oil were mixed in the static 26 mixing unit.
27 The results of the experiments are given in Table 28 I and show that static mixing at laninar flow rates gave 29 about the same feed filcel r~te as ttle conventional Diluticn 30 Chilling using the more severe dynamlc mechanical agitation 31 and turbulcnt flow heretoiorc required.

14 .

11~3~37 .
4Static Dynamic Mixer Impeller(a) 6 Solvent feed to filter, wt/wt 2.76 2.80 7 Solvent wash/feed, wt/wtØ70 o.88 8 Dewaxed oil yield, wt. % on feed 69 75 9 Feed filter rate, USG/ft2-hr 6.4 6.5 r 10 Note: (a) no recycle.

12 In another experiment, the Static Mixer unit was 13 replaced with an empty (unbaffled) tube of the same length 14 and inside diameter. With the impeller rpm and recycle 15 flow rate the same as for the case where the Static Mixer 16 was employed in Example 1, cold solvent was again injected .
17 into the recycle loop just at the upstream side of the un-18 baffled tube. Severe wax deposition occurred in the unit 19 and the experiment was considered a failure as far as de-20 waxing was concerned.
21 Another run was made with the same impeller speed 22 and the same flow rate through the unbaffled tube, but with 23 the solvent in~ected at the periphery of the impeller. As 24 the data in Table 2 sho~, the effect of operating the con-25 ventional Dilution Chilling laboratory batch unit with recycle 26 was a decrease in the feed filter rate in spite of the fact 27 that considerably more solvent was used.
28 Finally, a third run was made with the unbaffled 29 tube in the recycle loop at the same volumetric flow rate as 30 before, but with the stage agitator running at the negligible 31 speed of 90 rpm. As lndicated in Table 2, no data were 32 available from this run because the apparatus clogged up with

33 wax.

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1~ 3187 1 Compari.ng the results of this example wlth the 2 results obtained in Example 1, both illustrates and proves 3 the beneficial effect of static mixing in Dilution Chilling 4 dewaxing processes.

-6 Another experiment was conducted in order to 7 determine the effect of flow rate and corresponding Reynolds 8 Number through the static mixing unit, while at the same 9 time maintaining a substantially negligible stage impeller 10 speed of 90 rpm. Cold (-20F) dewaxing solvent (45/55LV~
11 MEK/MI~) was added to the waxy ~il just upstream of the 12 Static Mixer.
13 . The results are shown in Table 3 and indicate 14 that the benefits of Dilution Chilling dewaxing can be 15 achieved with static mixing means at turbulent flow rates, 16 ~n addi.tion to laminar flow rates.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A dewaxing process which comprises:
(a) introducing a stream of waxy oil into an elongated cooling zone containing static mixing means having a plurality of stationary elements longitudinally disposed within said means to successively divide said stream and to at least partially recombine the divided streams; and (b) introducing cold dewaxing solvent into said cooling zone at a plurality of points along said zone in order to progressively mix said solvent and said waxy oil by said static mixing means as said waxy oil and solvent pro-gress through said cooling zone, thereby precipitating a substantial portion of wax from said waxy oil.

2. The process of claim 1 wherein said mixing means comprises an elongated conduit containing a plurality of curved, flat strips for mixing fluid flowing therethrough.

3. The process of claim 1 wherein the flow within the static mixing means is maintained between about 2 and 150,000 modified Reynolds Number.

4. The process of claim 1,2 or 3 wherein the flow within said static mixing means is laminar.

5. The process of claim l, 2 or 3 wherein said solvent/
wax/oil mixture is cooled in said cooling zone at a rate of less than 10°F per minute.

6. The process of claim l, 2 or 3 wherein said solvent/
oil/wax mixture is cooled in said cooling zone at a rate of about 1 to 5°F per minute.

7. The process of claim l, 2 or 3 wherein the dewaxing solvent is cooled to at least 0°F before it is introduced into said cooling zone.

8. The process of claim l, 2 or 3 wherein the cold de-waxing solvent is chosen from the group consisting of ketones having 3 to 6 carbon atoms and their mixtures.

9. The process of claim l, 2 or 3 wherein the cold de-waxing solvent is selected from the group consisting of low molecular weight hydrocarbons and ketones having 3 to 6 carbon atoms.

10. The process of claim l, 2 or 3 wherein said solvent comprises a mixture of ketones having 3 to 6 carbon atoms and at least one solvent selected from the group consisting of benzene, toluene and xylene.

11. The process of claim l, 2 or 3 wherein said waxy oil is introduced into said cooling zone at a temperature above its cloud point.

12. The process of claim l, 2 or 3 wherein the waxy oil is prediluted with solvent prior to its introduction into the cooling zone.

13. The process of claim l, 2 or 3 wherein the static mix-ing means comprises at least a portion of said cooling zone.
14. The process of claim l, 2 or 3 wherein said cooling zone contains static mixing means after each point of sol-vent introduction.

15. The process of claim l, 2 or 3 wherein said solvent comprises N-methyl-2-pyrrolidone.

16. A process for dewaxing a waxy petroleum oil stock which comprises:
(a) introducing a stream of said waxy petroleum oil stock into an elongated cooling zone containing static mixing means having a plurality of stationary elements longitudinally disposed within said means to successively divide said stream and to at least partially recombine the divided streams; and (b) introducing cold dewaxing solvent into said cooling zone at a plurality of points along said zone in order to progressively mix said solvent and said waxy oil by said static mixing means after each point of solvent addi-tion as said solvent and oil progress through said cooling zone, thereby precipitating a substantial portion of wax from said oil and recovering petroleum oil having a reduced wax content.

17. The process of claim 16 wherein said waxy petroleum oil stock is a lube oil fraction.
. . .
18. The process of claim 16 wherein the flow within said static mixing means is laminar.

1 19. The process of claims 16, 17 or 18 wherein said waxy petroleum oil stock is introduced into said cooling zone at a temperature above its cloud point.

20. The process of claims 16, 17 or 18 wherein the waxy oil is prediluted with dewaxing solvent prior to its introduction into the cooling zone.

21. The process of claims 16,17 or 18 wherein said solvent/
waxy petroleum oil mixture is cooled at a rate of between 1 and 5°F per minute.

22. The process of claim 16, 17 or 18 wherein the cold dewaxing solvent is chosen from the group consisting of ketones having 3 to 6 carbon atoms in their mixtures.
23. The process of claim 16, 17 or 18 wherein the cold dewaxing solvent is a mixture of methyl ethyl ketone and methyl isobutyl ketone.
24. The process of claim 16, 17 or 18 wherein said solvent comprises a mixture of ketones having 3 to 6 carbon atoms and at least one solvent selected from the group consisting of benzene, toluene and xylene.
25. In a continuous solvent dewaxinq process for separating solid wax from waxy petroleum distillate oil stock, wherein said waxy oil stock, heated for dissolving all wax therein, is treated with dewaxing solvent in a volume ratio of solvent to oil of about 1.5:1 to 5:1, wherein the oil/solvent mixture is cooled at a rate below about 10°F/min to a temperature for forming a mixture of wax crystals in the oil/solvent solution, wherein said wax/oil/
solvent mixture is separated in a solid-liquid separation zone into a dewaxed oil/solvent solution and wax, the improvement which comprises:
(a) heating a continuously flowing mixture of waxy oil stock and aromatic hydrocarbon dewaxing solvent to a temperature above the melting point of solid wax for forming a waxy oil/aromatic solvent solution;
(b) cooling said heated waxy oil/aromatic solvent solution at a rate below about 10°F/min to a dewaxing temperature for crystallizing wax and forming a wax/oil/aromatic solvent mixture;

(c) static mixing of said wax/oil/aromatic solvent mixture with cold ketone dewaxing solvent under conditions of plug flow radial mixing to pro-gressively mix said solvent mixture and said dewaxing solvent and to form a second wax/oil/solvent mixture; and (d) flowing said second wax/oil/solvent mixture at said dewaxing temperature to said solid-liquid separation.

26. The process of claim 25 wherein said aromatic solvent is toluene, and wherein said waxy oil/aromatic solvent mixture is heated to a temperature sufficient for melting said solid wax.