Note: Descriptions are shown in the official language in which they were submitted.
L40~6~
1 BACKGROUND OF THE INVENTION
2 1. Field of the Invention
3 This invention relates to a process for solvent
4 dewaxing waxy oils. More particularly, this invention re-
lates to a continuous, solvent dewaxing process and apparatus
6 wherein a waxy oil is prediluted with a non-autorefrigerative
7 dewaxing solvent, with the prediluted oil, at a temperature
8 above i~s cloud point, then being ed to a chilling zone
9 comprising a vertical, staged tower operating continuously
lC at essentially constant pressure. In the ehilling zone wax
11 is precipitated fro~ the oil to form a waxy slurry and the
12 so-formed slurry is further cooled down to wax filtration
13 temperature by contact with a liquid autorefrigerant injected
14 into a plurality of said stages, said liquid autorefrigerant
evaporating in each of said stages so as to maintain an
16 average slurry cooling rate of from 0.1 to 20F per minute
17 and an average temperature drop per stage of from about 2 to
18 20F, The dewaxed oil-containing slurry is then fed to wax
19 filters. This process is particularly useful for dewaxing
wax-containing lubricating oil fractions and the like.
21 In a preferred embodiment this invention relates to
22 a continuous, combination non-autorerigerant/autorefrigerant
23 solvent dewaxing process employing two chilling zo~es wherein
24 a majority of the wax i~ precipitated in a first chilling
zone in the presence of a non-autorefrigerant dewaxing sol-
26 vent to form a waxy slurry which is then fed directly to a
27 second chilling zone comprising a vertical~ staged tower
28 operating continuously at essentially constant pressure. In
, . ~
67
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1 the second chilling zone the slurry is cooled down to wax
2 filtration temperature and additional wax is precipitated
3 from the oil by contact with a liquid autarefrigerant inj ected
4 into a plurality of said stages, as previously described~
2. Descri~tion or the Prior Art
6 It is well Icnown in the art to dewax wax-containing
7 hydrocarbon oils, particularly the lube oil fractions of
8 petroleum oil, in order to remove at least a portion of the
~ 9 wax therefrom to obtain a dewaxed oil of reduced cloud and
10 pour points. The most common method of removing the wax or
11 waxy constituents from waxy hydrocarbon oils is via the use
12 of various solvent dewaxing processes. In solvent dewaxing
13 processes the temperature of the wax-containing oil is low-
14 ered sufficiently to precipitate the wax therefrom as solid
15 crystals of wax. At the same time, solvents are added to
16 the waxy oil in order ~o improve the fluidity and reduce the
17 viscosity thereof so that various filtration or centrifuga-
18 tion processes can be used to separate the solid particles
19 of the wax from the dewaxed oil. Strong wax antisolvents
(weak oil solvents) such as MEK are often added to decrease
21 wax solubility in the oil/solvent mixture while strong oil
22 solvents (weak wax antisolvents) such as MIBK or toluene are
23 used to modify the solubility characteristics of the solvent
24 so as to allow wax precipitation~ while at the same time
25 avoiding oil immiscibility at wax separation temperatures.
26 Solvent dewaxing processes produce what is known as a pour-
27 filter temperature spread. This is the temperature differ-
28 ential between the wax filtering temperature an~ the pour
29 point of the dewaxed oil. This pour-filter temperature
30 spread is greater when more non-polar hydrocarbon solvents
31 are used than with more polar solvents such as ketones. Thus,
32 an autorefrigerant dewaxing process employing propane can
33 produce a pour-filter spread of 40F, which means that
34 the wax filtration must be done at -40F in order to pro-
35 duce a dewaxed oil having a pour poin~ of 0F. When ketones
36 or mixtures of ketone and aromatic solvents are used, the
.
L4~6'7
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1 pour-filter spread may range from CF to 20F depending
2 on the oil and solvent used.
3 Both ketone and autorefrigerant dewaxing processes
4 have certain advantages and disadvantages. Thus) although
ketone dewaxing processes result in a lower pour-filter
6 spread at the wax filtration temperature and although larger
7 wax crystals can be gro~n in a ketone environment than in an
8 autorefrigerant environment without dewaxing aid, ketones
9 are relatively non-volatile compared to autorefrigerants,
and, therefore, chilling of the solvent/oil mixture must be
11 accomplished by either indirect means or by mixing cold
12 ketone solvent with the oil. In the latter case, practical
13 considera~ions limit the amount and temperature of cold
14 ketone solvent tha~ can be added and ~he temperature to which
the solvent/oil mixture can be cooled. Therefore, some
16 means of indirectly chilling the waxy slurry following the
17 addition of solvent is required in all ketone dewaxing pro-
18 cesses in order to bring the slurry down to the required
19 wax filtration temperature. The most common method of in-
direct chilling is via the use of scraped surface chillers
21 which are expensive and difficult to maintain. Also, the
22 scraped surface chillers tend to damage the wa~ crystals by
23 the shearing action of the scraper blades.
24 Conversely, wax crystals grown in an autorefriger-
ant environment, such as propane or propylene, are generally
26 small which necessitates the use of costly dewaxing aids in
27 order to achieve good filtration rates, although evaporation
28 of the autorefrigeran~ enables one to reach the wax filtra-
29 tion temperature without the necessity of employing scraped-
surface chillers or indirect heat exchangers following the
31 solvent dewaxing operation. Additionally, it has been found
32 necessary to employ batch chilling in autorefrigerant dewax-
33 ing processes in order to allow a gradual reduction in a
34 pressure. This prevents sudden flashing of the autorefrig-
erant a, the point of pressure release, thereby avoidi~g sud-
36 den large temperature drops of the oil slurry ~shock chilling),
4~306
-- 4 --
1 which would result in even smaller wax crystals and concomi-
2 tant slower filter rates of the wax from the dewaxed oil.
3 In some ketone solvent dewaxing processes, the
4 waxy oil and solvent, at a temperature above the cloud point
S of the oil, are mixed before being cooled. This solution is
6 then cooled at a uniform, slow rate under conditions which
7 avoid agitation of the solution as the wax precipitates out.
8 In another method, ketone dewaxing solvent is added to the
9 oil at several points along a chilling apparatus, but the
waxy oil is first chilled without solvent until some wax
11 crystallization has occurred and the mixture has thickened
12 considerably, after which a first increment of solvent, at
13 the temperature of ~he oil, is introduced in order to main~
14 tain fluidity. Cooling continues, more wax is precipitated
out and a second increment of solvent, at the temperature of
16 the mixture, is added to maintai~ fluidity. This process is
17 repeated until a temperature typically ranging from about
18 30~F to 60F is reached, a~ which point an additional amount
19 of solvent at the same temperature as the mixture is added
in order to reduce the viSC05ity of the mixture which is
21 further chilled in scraped-surface chillers to the desired
22 filtration temperature. In these processes, if the solvent
23 is introduced a~ a temperature lower than that of the oil or
24 oil/solvent mixture, shock chilling occurs resulting in the
formation of small and/or acicula shaped wax crystals with
26 attendant poor filter rate.
27 It is now well k wn that the adverse shock chil-
28 ling effect can be overcome by introducing the waxy oil into
29 an elongated, staged cooling zone or tower at a temperature
30 above its cloud point and incrementally introducing cold
31 dewaxing solvent into said zone, along a plurality of points
32 or stages therein, while maintaining a high degree of agita-
33 tion in said stages, so as to efect substantially instantane-
34 ous mixing of the solvent and wax/oil mixture as they pro-
35 gress through said zone. The basic concept of this commer-
36 cially successful process is disclosed in U.S. Patent No.
.
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1 3,773,650, and shall hereina~ter be r~ferred to as
2 DILCHIL~* dewaxing process.
4 Com~ercially success~ul processes employing auto-
rerigerative cooling, wherein the waxy oil is mixed with a
6 liquid au~orefrigerant which is permitted to evaporate there-
7 by cooling the oil by the latent heat of evaporation, are
8 batch or semi batch operations. This mixture of liquid auto-
9 refrigerant and oil are introduced into an expansion chamber
wherein the pressure is slowly reduced to achieve controlled
11 evaporation o the autorefrigerant and controlled cooling o
12 the oil, thus avoiding the shock chilling which would result
13 if the autorefrigerant were allowed to flash of. HoweverJ
14 batch processes are cumbersome, difficuLt to operate and
lS energy inefficient.
16 A number of attempts have been made to develop a
17 continuous autorefrigerant process for dewaxing oils, includ-
18 i~g combinations of ke~one/autorefrigerant processes. Thus,
19 U.S. Patent No. 3,549,513 discloses an autorefrigeracive
batch dewaxing process that is described as continuous but
21 which really ~pera~es via the sequential use of a multiple
22 number of batch chillers or expansion chambers. Waxy oil
23 is diluted with an aromatic/ketone solvent mixture and with
24 liquid autore~rigerant and cooling is achieved by controlled
25 ~vapora~ion of the autorefrigerant by reducing the pressure
26 in each batch chamber in a manner such that ~he au~orefrigerant
27 evaporates at a controlled rate. U.S. Patent 3,658,688
28 discloses an autorefrigeran~ dewax$ng process wherein a por-
29 tion of the wax is precipitated from the oil in a DI~CHILL
30 dewaxing tower wherein the cooling occurs by the injection
31 o~ cold autorefrigerant into the tower to produce a waxy
32 slurry, foLlowed by autorefrigerative cooling of the slurry
33 in batch chillers. U.S. Patent 2,202,542 suggest a contin-
34 uous autorefrigerant dewaxing process wherein a waxy oil above
, .... .. _ . . . . .
36 *Registered service mark of Exxon Research and En~ineering Co.
...... ...... ..... ~ ,.......... .
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1 its cloud point is premixed with warm, liquid propane. Thi~
2 mixture is introduced into a multi-s.aged cooling tower and
3 li~uid Co2 is injected into each stage out of direct contact
4 with the oil. This patent emphasizes the point that the
liquid C02 must be introduced into each stage out of direct
6 cont~ct with the oil in the tower in order to avoid shock
7 chilling. However, this is impractical because the vapor
8 loads on the tower would be far in excess of what could be
9 accommodated in a reasonably sized commercial tower. Also,
10 refrigera,ion requirements are three times those normally
11 needed and conditions for nucleation and growth of wax cry-
12 stals are poor. U.S. Pa~ent 3~720J599 discloses a continuous
13 process for dewaxing a waxy petroleum oil stock wherein the
14 oil is premixed with acetone. This mixture is ~hen introduced
into a horizontal~ elongated chilling vessel containing a
16 plurality of stages operating at different pressures, with
17 the pressure in each stage controlled by a back pressure
18 regulator on each stage. Liquid autorefrigerant is intro-
19 duced into the stages along the length of the chilling vessel
20 while maintaining a high degree of agitation therein to
21 avoid shock chilling. The autorefrigerant is partially evap-
22 orated in each stage, with the amount of evaporation being
23 controlled by the pressure in each stage. Unfortunately,
24 there are problems which currently preclude commercialization
25 of this process, not the leastof which is a practical, effic-
26 ient way of getting the slurry to flow from stage to stage
27 without plu~ging up the entire apparatus with wax or without
28 multiple transfer pumps which would be expensive and would
29 also tend to destroy the wax crystal structure. Another
disadvantage entails the impracticality of providing sep-
31 arately driven agitators for each stage and the mechanical
32 difficulties associated with a common horizontal drive shaft.
33 Additionally, 3,720,599 provides for the nucleation and
34 initial growth of wax to occur in the presence of substantial
amounts ~i.e.,~ 25%) of autorefrigeran~ solvent, which~ in
36 the absence of dewaxin~ aid, has been found to produce wax
~L~4~067
crystals inferior to those produced when nucleation occurs by
chilling in the presence o~ ketones or ketone/aromatic solvents
followed by autorefrigeration. For example, when mixtures of
ketone and high percentages (~ 40%) of propylene were used in
the DILCHILL dewaxing process, a distillate oil/wax slurry was
produced which filtered very poorly.
It would be an improvement to the art if one could com-
bine both ketone and autorefrigerant solvent dewaxing processes `
into a continuous process and in such a manner so as to carefully
form the wax nuclei and begin crystal growth in a substantially
non-autorefri~erant solvent environment such as ketone, to
achieve large, stable, spherical crystals without the use of de-
waxing aid and then further precipitate add~tional wax without
destroying the spheres via direct contact with an evaporating
autorefrigerant, thereby avoiding the need for scraped surface
chillers following the ketone dewaxing step.
SUMMARY OF THE INVENTION
The present invention provides a continuous autorefrig~
erant solvent dewaxing process for dewaxing waxy hydrocarbon oils
which comprises the steps of:
(a) prediluting the waxy oil with a non-autorefriger-
ant dewaxing solvent to form a mixture of waxy oil and solvent;
(b) passing said mixture from step (a), at a tempera-
ture above its cloud point, into the top of a continuous, auto-
re~rigerative chilling zone which comprises a vertical, elon~
gated, multi-staged tower operating at a constant pressure
wherein each stage contains a liquid space and a vapor space above
.-c~ 7 -
6t7
the liquid space, each of s~id vapor spaces also containing means
for removal of autorefrigerant vapor therefrom;
(c) cooling said mixutre as it passes do~n from stage
to stage in said chilling zone to precipitate wax from said oil
thereby forming a slurr~ comprising solid particles of wax and a
dewaxed oil/solvent solution and further chilling the so-formed
slurry by contacting same, in said chilling zone, with a liquid
autorefrigerant which is introduced under flow rate control con-
ditions into a plurality of the stages in said zone and allowed
to evaporate therein so as to achieve an avera~e cooling rate of
the slurry in said zone ranging from between about 0.1 to 20F
per minute with an average temperature drop across each stage
into which said liquid autorefrigerant is introduced and evapor-
ated ranging from between about 2 to 20F. and wherein the eva-
porated autorefrigerant is removed from each of said stages into
which said liquid autorefrigerant was injected in a manner such
that the autorefrigerant vapor formed in any given stages does
not pass through all of the stages in the tower above said stage;
and
(d) separating the wax from the slurry to obtain wax
and a dewaxed oil solution.
In a preferred embodiment of this invention, the pre-
diluted oil will contain a dewaxing aid and will be introduced
into the top of the chilling zone at a temperature at or near its
cloud point and the slurry will be chilled down to the wax filtra-
tion tempera-ture in said chilling zone.
Alternatively, the invention may be practiced employing
cold non-autorefrigerative dewaxing solvent in which case the pro~
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.. .. . ... , . .. , ... _ . . .. _ . , ... _ . ........ , ~ _ .... . ~ .. _ .
4(~067
cess comprises the steps of:
(a) passing the waxy oil, at a temperature above its
cloud point, into a first chilling zone wherein a portion of the
wax is precipitated from the oil by cooling same in the presence
of a non-autorefrigerant dewaxing solvent to form a slurry of oil,
solvent and solid particles of wax;
(b) passing the slurry from the first chilling zone
to a second chilling zone which comprises a vertical, multi-staged
tower operating at a constant pressure wherein each stage contains
a liquid space and a vapor space above the liquid space, each of
said vapor spaces also containing means for removal of autorefrig-
erant vapor therefrom;
(c) cooling said slurry produced in said first chill-
ing zone down to wax filtration temperature and precipitating
additional wax therefrom in said second chilling zone by contact-.'
ing same in said second zone with a li~uid autorefrigerant which
is introduced under flow rate control conditions into a plurality
of the stages in said second zone and allowed to evaporate therein
so as to achieve an average cooling rate of the slurry in said
zone ranging~from between about 0.1 to 20 F per minute with an
average temperature drop across each stage into which said
liquid autorefrigerant is introduced and evaporated ranging from
b~tween a~out 2 to 20F and wherein the evaporated autorefriger-
ant is removed from each of said stages into which said liquid
autorefrigerant was injected in a manner such that the auto~
refrigerant vapor formed in any given stage does not pass through
the slurry on all of the stages in the tower above said stage;
and
(d) separating the wax fro~ the slurry to obtain
wax and a dewa~ed oil solution.
This latter process is claimed in a divisional applica-
tion which was filed March 23, 1982.
The "cloud point" of the oil is defined as a tempera-
ture at which a cloud or haze of wax crystals first appears when
an oil is cooled under prescribed conditions (AsrrM D-2500-66
_ g _
0C967
procedure). "Predilution", as the term is used herein, refer.s
to the mixing of solvent and oil prior to cooling the oil to a
temperature below its depressed cloud point and comprises, in one
embodiment of this invention, prediluting a waxy oil with at least
about 0.1 volume of an autorefrigerative predilution solvent per
volume of oil stock or at least 0.5 volume of a non-autorefriger-
ative predilution solvent per volume of oil stock resulting in
the depression of the cloud point of the oil stock. If predilu-
tion is used, it is preferred to predilute with non-autore-
frigerant solvents, especially ketones. Non-autorefrigerant
solvent, as the term is used herein, refers to dewaxing sol-
vents, pre~erably ketones, that are liquid at normal tempera-
ture and pressure, but may include the presence of as much
as about 30 LV (liquid volume) % of the autorefrigerant
~ 9a -
)067
- lC -
1 used in the second chilling zone, based on the waxy oil feed.
2 The non-autorefrigerative dewaxing solvent
3 employed as predilution and/or first chilling solvent in
4 this invention includes one or more (a) aliphatic ketones
5 having from 3-6 carbon ato~s, such as acetone, methyl-ethyl
6 ketone (~K), methyl-isobutyl ketone (MIBK), methyl-propyl
7 ketone and mixtures thereof, (b) halogenated low molecular
8 weight hydrocarbons such as C2-C4 alkyl chlorides (e.g.,
9 dichloromethane, dichlorethane, methylene chloride) and mix-
10 ture~ thereof, (c) normal or isoparaffins having 5 to 10
11 carbon atoms, (d) aromatics such as benzene, toluene~ xylene,
12 petroleum naphtha and mixtures thereof, and (e) mixtures of
13 any of the foregoing solvents. Non-autorefrigerant solvent
14 as herein defined may include up to 25 LV % of autorefriger-
15 ant solvent, preferably no~ more than lC LV % and still more
16 preferably not more than 5 LV V/o. For example, the ketones are
17 often used in combination with one or more aromatic compounds
18 such as benzene, .oluene, xylene and petroleum naphtha. Pre-
19 ferred solvents comprise ketones. Particularly preferred are
20 mixtures of ~C and MIB~ or MEK and toluene. Autorefrigerants
21 used in this inven.ion include liquid, normally gaseous C2-C4
22 hydrocarbons such as propane, propylene, ethane, ethylene and
23 mixtures thereof as well as ammonia and normally gaseous flour-
24 carbons such as monochlorodifluoromethane (Freon 22). Autore-
25 frigerative solvent as herein defined may contain up to abou~
26 50 LV % of non-autorefrigerative solvent, preferably no more
27 than 10 LV % and preferably no more than 2 LV %.
28 The autorefrigerative chilling zone is a vertical,
29 elongated, multi-staged tower operating at a constant pres -
30 sure and in a manner such that the waxy oil and slurry pass
31 down from stage to stage of the tower by gravity and cold,
32 liquid autorefrigerant is injected into each stage of the
33 tower wherein it contacts the warmer oil or slurry and cools
34 same via autorefrigerative evaporation. At least a por~ion
35 of the cold, liquid autorefrigerant immediately evaporates on
36 contact with the warmer oil or slurry which results in agi-
37 tation in the area of contact sufficient to achieve sub-
~4~67
1 stantially instantaneous mixing (i.e., about one second or
2 less of the oil or slurry with the cold liquid autorefriger-
3 ant~ thus avoiding the shock chilling effect. As herein-
4 before stated, supra, each stage contains Means for re-
5 moving the autorefrigerant vapors therefrom and the slurry
6 flot~7s down from stage to stage in the tower by the action
7 of gravity. The cooled slurry exiting this chilling zone
8 is then passed to means, such as rotary pressure filters,
9 for separating the wax from the dewaxed oil/solvent mixture.
In general, this autorefrigerative chilling zone
11 or tower will operate at a constant pressure within the
12 range of from about C to 5C psig and more preferably from
13 about 2 to 20 psig. The average chilling rate in the tower
14 is the difference between the temperature of the prediluted
15 oil entering the tower and the temperature of the slurry
16 exiting the tower divided by the residence time of the oil
17 or slurry in the tower and will range from about 0.1 to 20F/
18 minute and more preferably from about 0.5 to lCF/minute.
19 Thls is achieved by controlling the autorefrigerant flow
20 rate into~ and oil hold-up in, each stage, rather than by
21 gradually decreasing the pressure in the system as is done
22 in batch chillers. That is, a controlled quantity of autore-
23 frigerant is vaporized in direct contact with controlled
24 quantity of oil or slurry in each stage of the tower. This
25 is accomplished by injecting the liquid autorefrigerant
26 through spray nozzles either submerged in the slurry or above
27 the surface thereof in each stage of the tower under flow
28 rate control conditions, This in turn controls the temp-
29 erature drop for each stage which will range from about ~ to
30 20F. The stagewise chilling rate then depends on the li~uid
31 holdup or residence time for each stage. The autorefrigerant
32 evapora_es and cools the oil primarily by its latent heat of
33 vaporization whieh resul~s in an extremely high heat transfer
34 ra~e. The autorefrigerant vapor is withdrawn from each st~ge
35 in a manner so as to avoid vapor overload in the tower. In
36 a preferred embodiment, this is done by separately removing
.
~ 3~ 461;) ~67
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the vapor from the vapor space of each stage directly through and
outside of -the cooling zone or tower, rather than allowing the
vapor to cumulatively pass up through each upper, successive stage,
as is disclosed in the prior art. However, under certain circum-
stances, it may be advantageous to allow the vapor produced in one
or more given stages to pass up through the tower or cooling zone
through some, but not all, of the stages above said one or more
given stages before removing the cumulative vapor from the cooling
zone or tower. By way of illustration, it may be advantageous to
remove vapor from the zone or tower at every second, third and
fourth successive stage. An amount of autorefrigerant is added per
stage to give a stagewise temperature decrease ranging from 2 to
20F, and more preferably from 3 to 10F. Of course, the ultimate
temperature to which the slurry is cooled in this tower will depend
on the temperature of the predi~uted oil as it enters same, the
liquid hold-up in each stage, the amount, type and temperature of
autorefrigerant injected into each stage as well as the pressure in
the tower and the number of stages in the tower. Therefore, it is
understood, of course, depending on the feed and size of the tower,
that it may not always be necessary to inject liquid autorefrigerant
into each and every stage of the tower. The cooling zone will, in
general, cool and slurry down to a temperature ranging from between
about lO to 40F and, more preferably, 15 to 30 F below the desired
pour point of the dewaxed oil.
When employing cold non-autorefrigerative solvents the
first chilling zone may be any type of chilling zone used in
" 1~4~)06~7 ,
- 12a -
conventional ketone dewaxing processes aescribed under DESCRIPTION
OF THE PRIOR ART, supra, including scraped-surface chilling zones.
However, in a preferred embodiment of this invention, the first
chilling zone will be an incremental DILCHILL zone of the type
disclosed in U.S. Patent 3,773,650 discussed, sup.ra. That is,
a waxy oil at
6~
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1 a temperature above its cloud point is introduced into sn
2 elongated, staged chilling zone or tower and cold, non-
3 autorefrigerant dewaxing solvent, such as ketone, is incre-
4 mentally introduced into said DILCHILL zone along a plurality
5 of stages therein, while maintaining a high degree of agi-
6 tation so as to effect substantially instantaneous mixing of
7 the solven. and wax~oil mixture as they progress through said
8 zone. When employing cold non-autorefrigerative solvent, it
g is also preferred to precipi~ate most of the wax from the oil
lO in this first chilling zone.
11 The slurry from the cold non-autorefrigerative
12 chilling zone is passed directly to the top of a second
13 chilling zone employing autorefrigerative solvent which is
14 the vertical, multi-staged, constant pressure tower wherein
15 the slurry is further cooled down to the wax filtration tem
16 perature and additional wax is precipitated therefrom, as
17 was previously described.
18 Any waxy petroleum oil stock or distilla~e fraction
19 thereof may be dewaxed employing the process of this invention.
20 Illustrative, but non-limiting examples of such stocks are
21 (a) distillate fractions that have a boiling range within
22 the broad range of 500F to about 13C0F~ with preferred
23 stocks including a lubricating oil and specialty oil fractions
24 boiling within the range of between about 56CF and 1200~F,
25 (b) heavy feedstocks containing at least about lO wt.% of
26 residual material boiling above 1050F, examples of which
27 include bright stocks and deasphal~ed resids having an
28 initial boiling point of above about 800F and (c) broad
29 cut feedstocks that are produced by topping or distilling
30 the lightest material or for crude oil leaving a broad cut
31 oil, the major portion of which boils above about SCCF or 650F.
32 Additionally, any of these feeds may be hydrocracked prior to
33 distilling, dewaxing or topping. The distillate fraction
34 may come from any source such as the paraffinic crudes ob-
35 tained from Aramco, Kuwait, the Panhandle, North Louisiana~
36 etc., naphthenic crudes such as Tia Juana, Coastal crudes,
67
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1 etc., as well aC the relatively heavy feedstocks such as
2 bright stocks having a boiling range of lCSC+F and syn-
3 thetic feeds~ocks derived from Athabasca Tar Sands, coal
4 liquids, etc.
When mixtures of MEK and MIBK are used aS the
6 non-autorefrigerant dilution solvent and/or coolant, MEK to
7 MIBK ratios may vary from 9C% MEK/lC% MI~I~ to lC% MEK/90%
8 MIBK and more preferably from 70% MEK/3G% MIBI~ to 70% MI~K/30%
9 MEK. Ketone to oil volume ratios may vary from 0,5/1 to
lO lG/l and more pre~erably from 1.0/1 to 4/1. Predllution
ll volume ratios of either autorefrigerant or non-autorefrigerant
12 solvent may vary from 0/1 to 3/l and ~ore preferably from
13 0/1 to 211 depending on prediluent and feedstock. Chilling
14 ra~es in the first chilling zone may vary from C.1F/min.
15 to 20F/min. and more preferably from 0.5F/min. to 10F/min.
16 Outlet temperatures from the first chilling zone may vary
17 from -20F to +90F and more preferably from 2CF to 80F.
18 Lower outlet temperatures are better for distillate stocks
l9 while higher outlet temperatures are bet~er for residual
20 stocks. When employing cold non-autorefrigerative solvents,
21 it is preferred that most of the wax crystallize out of the
22 oil in the first chilling zone.
23 When propyLene is used as the autorefrigerant in
24 the autorefrigerant chilling zone) from abou~ 0.2 to 2.5
25 volumes of propylene per volume of waxy oil and more pref-
26 erably from about 1.0 to 2.0 volumes per volume are used, to
27 reduce the temperature of the slurry down to the wax fil-
28 tration temperature, and to reduce the viscosity of the
29 slurry sufficiently for wax filtration.- Chilling rates in
30 the autorefrigerative chilling zone will generally range from
31 about 0.1 to 20F/min. and more preferably from about C.5 to
32 10F/min. The temperature of the cold slurry exiting the
33 chilling zone may vary from about -50F to +30F to produce
34 a dewaxed oil having a pour point ranging b~tween about
35 -30F to +80F. In a preferred embodiment, the slurry will
36 exit the chilling zone at a temperature of from -30F to
- 15 -
1 +lC~F in order to produce a dewaxed oil having a pour point
2 ranging from between abou, -10F to ~30F.
3 BRIEF DESCRIPTION OF THE DRAWINGS
4 Figure 1 is a flow diagram of an embodiment of a pro-
5 cess incorporating the instant invention utilizing non-
6 autorefrigerative dilution.
7 Figure 2 is a schematic diagram of a preferred
8 embodiment of a multi-staged, vertical tower comDrising
9 the chilling zone of this invention.
Figure 3 is a schematic diagram of a preferred
11 embodiment of a process incorporating the instant invention
12 utilizing cold non-autorefrigerative chilling.
13 DESCRIPTION OF A P~EFERRED EMBODIMENT
14 Referring to Figure 1, a warm paraffinic lube oil
15 distillate at a temperature of about 160F and having a
16 viscosity of 150 SUS at 100F is mixed with dewaxing aid
17 from line 16 and then prediluted with a solvent comprising
18 a 70/30 volume mixture of MEK/MIBK in an amount of about 1.2
19 volumes of ketone predilution solvent per volume of waxy
20 oil. The prediluted waxy oil/dewaxing aid mixture is then
21 passed from line 10 Lhrough heat exchanger 12 wherein it is
22 cooled ~o a temperature of about 90F or just above its
23 cloud point and from there into multi-staged autorefrigerant
24 chilling tower 26. Liquid propylene at a temperature of -30F.
25 is fed into the various stages of tower 26 via line 28, mani-
26 fold 30 and multiple injection points 32. Multiple injec-
27 tion points 32 are fed to each of the various ctages in tower
28 26 wherein the liquid propylene contacts the slurry in each
29 stage via a sparger located under the surface of the slurry
30 in each stage. About 1.5 volumes of liquid propylene are
31 used in tower 26 per volume of slurry entering therein via
32 line 24. Tower 26 operates at a pressure of about 2 psig.
33 About 1.2 voLumes of the liquid autorefrigerant per volume
34 of fresh feed evaporates upon contact with the slurry, with
35 the autorefrigerant vapors being removed from each stage via
36 multiple tower exit ports 34, manifold 30 and line 38 at
~a~
- 16 -
l an average temperature of ab3ut 24~F. Thus, none of the
2 vapor produced in any stage passes through the slurry on
3 any other stage in the tower. The remaining G.9 volume of
4 propylene per volume of eed go into solution with the MEK/
5 MIBK and dewaxed oil in the wax slurry. Tower 26 contains
6 appro~imately 14 stages in which the average slurry chilling
7 rate is about 3F per minute with an average temperature drop
8 across each stage of about 8.6F. The waxy slurry is further
9 cooled in tower 26 to a temperature of about -30F. The
lO slurry comprising solid wax particles, oil, ketone and
ll liquid propylene is then fed to rotary pressure filter 42
12 via line 40 wherein the wax is filtered from the dewaxed oll
13 solution. The dewaxed oil solution leaves filter 24 via
14 line 44 and from chere is sent to solvent recovery while
15 the wax is removed via line 46 and sent to solvent recovery
16 and further wax processing if desired. The dewaxed oil
17 solution yields a dewaxed oil having a pour point of about
18 -lG~F.
l9 Figure 2 illustrates a preferred embodiment of
20 autorefrigerant chilling tower 26. The diameter of the
21 tower is sized so as to provide a superficial vapor velocity
22 low enough to avoid entrainment of the oil in the vapor. The
23 tower comprises about 14 discrete stages~ 5Ca through 50n.
24 Each stage contains an autorefrigerant vapor coLlector, vapor
25 spaceJ slurry tray~ slurry downcomer, weir and liquid au~ore-
26 frigerant sparger. This is illustrated for stage 5Ca wherein
27 52 is the vapor collectorJ 54 represents the vapor space, 56
28 is the slurry tray, 58 is the slurry, 60 is the downcomer, 62
29 is the weir and 64 is the sparger. The sparger 64 and
30 auturefrigerant vapor collector 52 are detailed in Figures
31 ~-b and 2-c, respectively. Sparger 64 comprises piping
32 containing a plurality of small holes 66. Vapor collector 30
33 is shown as a pipe containing a plurality of rectangular
34 holes 68. In operation, slurry from tower 16 is fed to tower
35 26 via line 24, entering tower 26 through feed inlet 68
36 passing through downcomer 60 wherein it is directed downward
0()67
- 17 -
1 and under the surface of the slurry 58 held up on stage 50a.
2 Liquid ?ropylene is introduced into stage 50 from injection
3 point 32 through sparger 64 and holes 66. The holes are
4 sized so as to provide a level of agitation such that there
is substantially instantaneous mixing (i.e., 1 second or
6 less). The holes are directed downward, opposing slurry
7 flow through the stage. Some of the propylene vaporizes as
8 it enters the warmer slurry and the vapors bubble up
g through the slurry/ with the remainder of the propylene
10 going into solution. Propylene vapors are removed through
ll vapor collector 52 and the cooled slurry flows over weir
12 62 wherein i~ enters downcomer 60 and is directed under the
13 surface of the slurry on the next stage 50b. This process
14 is repeated from stage to stage as the slurry passes down
15 the tower until i~ exits from slurry outlet 70 at wax
16 iltration temperature and fed to wax filter 42.
17 Referring to Figure 3, a warm paraffinic lube oil
18 dis~illate at a temperature of about 160F and having a
19 viscosity of 150 SUS at 100F is passed from line lO
20 through heat exchanger 12 wherein it is cooled to a temp-
21 erature of about 84F or just above its cloud point and
22 from ~here into multi-staged DILCHILL tower 16 via line 14.
23 In tower 16 it is cooled by contact with a cold (-30~F)
24 ketone solvent comprising a mixture of 70V/o MEK/30% MIBK
(volume basis) which is iniected into the various stages of
~6 tower 16 via line 18, manifold 2C and multiple injection
27 points 22. About 1.2 volumes of ~he cold ketone dewaxing
28 solvententers the tower per volume of feed. Each stage
29 (not shown) in tower 16 contains a rotating im~eller so
30 that the cold ketone dewaxing solvent entering therein is
31 substantially instantaneously mixed in the waxy oil. In
32 tower 16 most of the wax is precipitated from the wax~7 oil
33 producing a slurry which leaves the bottom of tower 16 via
34 line 24 at a temperature o about 30~F. The cold, ketone-
35 containing slurry in line 24 is passed directly inco multi-
36 ~taged chilling tower 26. Liquid propylene at a temperature
0
- 18 -
1 of -30~F i~ fed into the variOus s.ages of tower 26 via
2 line 28J manifold 30 and multiple injeccion points 32.
3 Multiple injection points 32 are fed to each of the various
4 stages in tower 26 wherein ~he liquid propylene contacts
5 the slurry in each stage via a sparger located under the
6 surface of the slurry in each stage. About 1.5 volumes of
7 liquid propylene are used in tower ~6 per volume of slurry
8 entering therein via line 24. Tower 26 opera,es at a pressure
9 of about 2 psig. About 0.6 volume of the liquid autore-
10 frigerant per volume of fresh feed evaporates upon contact
11 with the slurryl with the autorefrigerant vapors being
12 removed from each stage via multiple tower exit ports 34,
13 manifold 30 and line 38 at an average temperature of abouc
14 -12F. Thus, none of the vapor produced in any stage passes
15 through the slurry on any other stage in the tower. The
16 remaining 0.9 volume of propylene per volume of feed go
17 into solution with the MEK/MIBK and dewaxed oil in the wax
18 slurry. Tower 26 contains approximately seven stages in
19 which the average slurry chilling rate is about 3F. per
20 minute with an average temperature drop across each stage
21 of about 8.6F. The w~xy slurry is further cooled in tower
22 26 to a temperature of about -30F. The slurry comprising
23 solid wax particles, oil, ketone and liquid propylene is
24 then fed to rotary pressure filter 42 via line 40 wherein
25 the wax is filtered from the dewaxed oil solution. The de-
26 waxed oil solution leaves filter 24 via line 44 and from
27 there is sent to solvent recovery while the wax is removed
28 via line 46 and sent to solvent recovery and further wax
29 processing if desired. The dewaxed oil solution yields a
30 dewaxed oil having a pour po~ t o~ about -10F.
31 The inventi~n will be more readily understood by
32 reference to the following exam~le:
33 EXAMPLF I
34 This examDle provides laboratory data demonstrating
35 the process of this i~vention utilizing non-autorefrigerative
36 solvents as dilution solvents. The feedstock used was a
.. : ' . ,
67
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1 paraffinicJ waxy distillate having a viscosity of 60C SUS
2 a~ lOCF ~600N). A pilot plant autorefrigerant chilling
3 unit was employed which comprised a vessel operating at a
4 constant pressure of about 5 psig. Liquid propylene, at
a Lemperature of about -3GF was`continuously injected into
6 the unit below the surface of the slurry contained therein.
7 Part of the liauid propylene vaporized with the vapors being
8 continuously withdrawn from the constant pressure vapor
9 space above the slurry. A slurry chilling rate of about
lG 5F/min. was maintained by controlling the rate of injection
11 of the liquid propylene into the slurry. Before the feed-
12 stoc~ was placed into the autorefrigerant chilling uni~
13 was mixed with a Paraflow/Acryloid dewaxing aid and pre-
14 dilu~ed with MEK at a temperature above i~ cloud point in
an amount of one volu~e of MEK per volume of feed. The
16 prediluted feed was then prechilled to a temperature o~ 12CF,
17 which was approximately the cloud point o~ the prediluted
18 feed, before being added to the unit. As hereinbefore stated,
19 the prediluted feed was chilledin the autorefrigeration
unIt at a rate of 5~/min. The waxy slurry formed in the
21 unit was chilled down to a temperature of -30F and then
22 filtered at -30F. The amDunt of propane that dissolved
23 in the oil in the unit was 1.5 volume per volume of feed
24 oil.
The results of this experiment are contained in
26 Table A below. These results illustrate the operability of
27 the present invention.
28 TABLE A
29 CONTINUOUS CONST~NT PRESSURE
ATiTOREFRIGERATION D~wTAXING
31 Feedstock 6QGN
32 Dewaxing Aid Type P/~
33 Aid Dose, wt.% on Feed 0.2
34 Predilution Solvent lCO% MEK
35 Predilution Ratio on Feed 1.0
36 Prechilling Start F 150
37 Finish F 12C
38 Rate F/Min. lC.8
39 Autorefrig. Pressure 5 psig
3067~
- ~o -
1 Autorefrig Star~ F 120
2 Finish F -30
3 - Rate F/Min. 5
4 C3 Makeu~ to Chiller Variable
5 Dilution to Filter 2.5
6 Solv. Comp. to Filter 40/60 MEK/Propane
7 Fil.ration TemD. F -30
8 Feed Filter Ra-e GPHPSF 5.0
9 Wax L/S Ra~io 6.3
lG Wax Oil Content~ wt.% 62
11 Mean Crystal Dia., Microns lg
12 Crvstals clO Microns, % 3
13 DWO PourJ F O
14 ~XAMPLE
This example provides laboratory data comparing the
16 combination process of this invention employing cold non-
17 autorefri$erative solvents and autoregrigerative solvent chil-
18 ling with conventional DILCHIL~ ketone dewaxing followed by
19 scraped surface chilling. Three paraffinic lube oil feedstocks
20 were used, a bright stock, and two distillates having viscos-
21 ities of 150 (lSON) and 60C SUS (600N) at lOCF. A pilot plant
22 DILCHILL unit was used for the DILCHILL dewaxing with ketone
23 solvent to produce a ketone-containing slurry comprising solid-
24 particles of wax and a mixture of partially dewaxed oil and
25 ke~one dewaxing solvent. The temperature of the cold keLone
26 solvent fed into the DILCHILL unit was about -30~F. The bright
27 stock was prediluted with 1 volume of warm ketone solvent
28 per volume of feed before being fed into the DILCHILL unit.
29 The waY.y slurry produced in the DILCHILL unit was then fed to
30 either scraped surface chillers or to a simulated continuous,
31 autorefrigerant chilling unit for further chilling down to
32 wax filtration temperature. The cold slurry was then filtered
33 to separate the wax from the dewaxed oil/solvent mixture and
34 both the dewaxed oil and wax were recovered.
The autorefrigerant chilling unit comprised a ves-
36 sel operating at a constant pressure of abou~ 2 psig wherein
37 liquid propylene was continuously injected into the unit,
38 below the surface of -he slurry contained therein. Part of
39 the liquid propylene vaporized with the vapors being continu~
4C ously withdrawn from the constant pressure vapor space above
)67
- 21 - !
1 the slurry. A slurry chilling rate of about 2~F/min. was
2 maintained by controlling the rate of injection of the
3 liquid propylene into -he slurry.
4 The results of these experiments, correlated to
common dewaxed oil pour points, are contained in Table B,
6 belo~. These resul~s illustrate not only the operability of
7 the present invention, but also that superior results can
8 be achieved by i~s use. Thus, using the present inven.ion
9 gave faster feed filter rates, drier wax cakes and wax
10 cakes con~aining less oil than the DILCHILL dewaxing process
11 followed by scraped surface chilling. Further, these results
12 were obtained without. the use of dewaxing aid.
67
- 22 -
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