CA1140067A - Continuous autorefrigerative dewaxing process and apparatus - Google Patents
Continuous autorefrigerative dewaxing process and apparatusInfo
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- CA1140067A CA1140067A CA000348094A CA348094A CA1140067A CA 1140067 A CA1140067 A CA 1140067A CA 000348094 A CA000348094 A CA 000348094A CA 348094 A CA348094 A CA 348094A CA 1140067 A CA1140067 A CA 1140067A
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Abstract
(U.S. 974,070 etc.) ABSTRACT OF THE DISCLOSURE
A continuous solvent dewaxing process wherein a waxy oil is prediluted with a non-autorefrigerative solvent, such as ketone and then passed, at a temperature above its cloud point to the top of a chilling zone (fig. l (26)), which is an autorefrigerant chilling zone operating on a continuous basis, and comprises a vertical, multi-staged tower, operating at constant pressure. In this chilling zone, wax is precipitated from the oil to form a waxy slurry and the so-formed slurry is further chilled down to the wax filtration temperature by stage-wise contact with liquid propylene which is injected into a plurality of said stages and evaporated therein so as to cool the waxy slurry at an average rate of between about 0.1 to 20°F. per minute with an average temperature drop across each stage of between about 2 and 20°F. Some of the propylene remains in the oil which serves to further dilute and reduce the viscosity of the slurry.
The dewaxed oil-containing slurry may then be fed directly to wax filters without having to pass through scraped-surface chillers and filter feed drum.
In a preferred embodiment the non-autorefrigerant solvent is employed cold so as to partially solvent dewax the waxy oil to a temperature within from about 30 to 110°F. of the final wax filtration temperature before being contacted with autorefrigerant in the auto-refrigerant chilling zone to be chilled down to the desired wax filtration temperature.
A continuous solvent dewaxing process wherein a waxy oil is prediluted with a non-autorefrigerative solvent, such as ketone and then passed, at a temperature above its cloud point to the top of a chilling zone (fig. l (26)), which is an autorefrigerant chilling zone operating on a continuous basis, and comprises a vertical, multi-staged tower, operating at constant pressure. In this chilling zone, wax is precipitated from the oil to form a waxy slurry and the so-formed slurry is further chilled down to the wax filtration temperature by stage-wise contact with liquid propylene which is injected into a plurality of said stages and evaporated therein so as to cool the waxy slurry at an average rate of between about 0.1 to 20°F. per minute with an average temperature drop across each stage of between about 2 and 20°F. Some of the propylene remains in the oil which serves to further dilute and reduce the viscosity of the slurry.
The dewaxed oil-containing slurry may then be fed directly to wax filters without having to pass through scraped-surface chillers and filter feed drum.
In a preferred embodiment the non-autorefrigerant solvent is employed cold so as to partially solvent dewax the waxy oil to a temperature within from about 30 to 110°F. of the final wax filtration temperature before being contacted with autorefrigerant in the auto-refrigerant chilling zone to be chilled down to the desired wax filtration temperature.
Description
L40~6~
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 , . ~
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 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 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.
.
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 , . ~
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 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 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.
.
- 5 -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
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$ng process wherein a por-29 tion of the wax is precipitated from the oil in a DI~CHILL
30 dewaxing tower wherein the cooling occurs by the injection 31 o~ cold autorefrigerant into the tower to produce a waxy 32 slurry, foLlowed by autorefrigerative cooling of the slurry 33 in batch chillers. U.S. Patent 2,202,542 suggest a contin-34 uous autorefrigerant dewaxing process wherein a waxy oil above , .... .. _ . . . . .
36 *Registered service mark of Exxon Research and En~ineering Co.
...... ...... ..... ~ ,.......... .
1 its cloud point is premixed with warm, liquid propane. Thi~
2 mixture is introduced into a multi-s.aged cooling tower and 3 li~uid Co2 is injected into each stage out of direct contact 4 with the oil. This patent emphasizes the point that the liquid C02 must be introduced into each stage out of direct 6 cont~ct with the oil in the tower in order to avoid shock 7 chilling. However, this is impractical because the vapor 8 loads on the tower would be far in excess of what could be 9 accommodated in a reasonably sized commercial tower. Also,
14 batch processes are cumbersome, difficuLt to operate and lS energy inefficient.
16 A number of attempts have been made to develop a 17 continuous autorefrigerant process for dewaxing oils, includ-18 i~g combinations of ke~one/autorefrigerant processes. Thus, 19 U.S. Patent No. 3,549,513 discloses an autorefrigeracive batch dewaxing process that is described as continuous but 21 which really ~pera~es via the sequential use of a multiple 22 number of batch chillers or expansion chambers. Waxy oil 23 is diluted with an aromatic/ketone solvent mixture and with 24 liquid autore~rigerant and cooling is achieved by controlled 25 ~vapora~ion of the autorefrigerant by reducing the pressure 26 in each batch chamber in a manner such that ~he au~orefrigerant 27 evaporates at a controlled rate. U.S. Patent 3,658,688 28 discloses an autorefrigeran~ dewax$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.
...... ...... ..... ~ ,.......... .
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~
~ - 8 -.. .. . ... , . .. , ... _ . . .. _ . , ... _ . ........ , ~ _ .... . ~ .. _ .
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 _ 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-
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~
~ - 8 -.. .. . ... , . .. , ... _ . . .. _ . , ... _ . ........ , ~ _ .... . ~ .. _ .
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 _ 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 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~
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, 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 1 +lC~F in order to produce a dewaxed oil having a pour point 2 ranging from between abou, -10F to ~30F.
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~
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 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 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:
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 .. : ' . , - 19 - !
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.
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
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 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~
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, 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 1 +lC~F in order to produce a dewaxed oil having a pour point 2 ranging from between abou, -10F to ~30F.
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~
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 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 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:
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 .. : ' . , - 19 - !
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.
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.
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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.
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Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A continuous autorefrigerant solvent dewaxing process for dewaxing waxy hydrocarbon oils which comprises the steps of:
(a) prediluting the waxy oil with a non-autorefrigerant dewaxing solvent to form a mixture of waxy oil and solvent;
(b) passing said mixture from step (a), at a temperature above its cloud point, into the top of a continuous, autorefrigerative chilling zone which comprises a vertical, elongated, 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 autorefrigerant vapor therefrom;
(c) cooling said mixture as it passes down from stage to stage in said chilling zone to precipitate wax from said oil thereby forming a slurry 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 autorefrig-erant 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 aver-age 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 evapor-ated ranging from between about 2° to 20°F. and wherein the evaporated autorefrigerant is removed from each of said stages into which said liquid autorefrig-erant was injected in a manner such that the autore-frigerant vapor formed in any given stage 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.
(a) prediluting the waxy oil with a non-autorefrigerant dewaxing solvent to form a mixture of waxy oil and solvent;
(b) passing said mixture from step (a), at a temperature above its cloud point, into the top of a continuous, autorefrigerative chilling zone which comprises a vertical, elongated, 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 autorefrigerant vapor therefrom;
(c) cooling said mixture as it passes down from stage to stage in said chilling zone to precipitate wax from said oil thereby forming a slurry 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 autorefrig-erant 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 aver-age 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 evapor-ated ranging from between about 2° to 20°F. and wherein the evaporated autorefrigerant is removed from each of said stages into which said liquid autorefrig-erant was injected in a manner such that the autore-frigerant vapor formed in any given stage 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.
2. The process of claim 1 wherein said autorefrigerative chilling zone of step (b) operates at a constant pressure ranging from about 0 to 50 psig.
3. The process of claim 2 wherein said liquid autorefrig-erant is selected from the group consisting essentially of normal-ly gaseous C2-C4 hydrocarbons, ammonia and normally gaseous fluoro-carbons.
4. The process of claim 3 wherein said prediluted waxy oil is at a temperature at or near its cloud point when it enters said chilling zone.
5. The process of claim 4 wherein said non-autorefrigerant predilution solvent comprises one or more solvents selected from the group consisting essentially of (a) C3-C6 aliphatic ketones, (b) C2-C4 alkyl chlorides and (c) mixtures of C3-C6 aliphatic ke-tones with one or more aromatic compounds including benzene, toluene, xylene and petroleum naphtha.
6. The process of claim 5 wherein said non-autorefrigera-tive solvent comprises one or more C3-C6 aliphatic ketones mixed with one or more aromatic compounds selected from the group con-sisting essentially of benzene, toluene, xylene, petroleum naphtha and mixture thereof.
7. The process of claim 6 wherein no more than 30 LV % of autorefrigerant, based on said waxy oil feed, is present in said first chilling zone.
8. The process of claim 7 wherein no autorefrigerant is present in said predilution solvent.
9. The process of claim 8 wherein said slurry is chilled down to wax filtration temperature in said chilling zone.
10. A continuous autorefrigerant process for solvent dewax-ing waxy petroleum oil fractions which comprises the steps of:
(a) prediluting said waxy petroleum oil fraction with a non-autorefrigerant dewaxing solvent to form a mixture of waxy oil and solvent:
(b) passing said mixture from step (a), at a temperature above its cloud point to the top of a continuous, auto-refrigerative chilling zone which comprises a vertical multi-staged tower operating at a constant pressure ranging between about O to 50 psig wherein each stage contains a liquid space, a vapor space above the liquid space and means for removing autorefrigerant vapor from each vapor space;
(c) cooling said mixture as it progresses down from stage to stage in said chilling zone to precipitate wax from said oil thereby forming a slurry comprising solid particles of wax and a dewaxed oil/solvent solution and further chilling the so-formed slurry by contacting same with a liquid autorefrigerant which is introduced under flow rate control conditions into a plurality of the stages in said chilling zone and allowed to evapor-ate therein at a controlled rate so as to achieve an average cooling rate of the slurry in said chilling zone ranging from between about 0.1° to 20°F./minute with an average temperature drop across each stage into which said liquid autorefrigerant is introduced into and evaporated in ranging from between about 2° to 20°F.
and wherein the evaporated autorefrigerant is removed from each of said stages into which said liquid auto-refrigerant was injected in a manner such that the autorefrigerant vapor formed in any given stage does not pass through all of the stages in said zone above said stage; and (d) filtering the wax from the slurry to obtain wax in a dewaxed oil solution.
(a) prediluting said waxy petroleum oil fraction with a non-autorefrigerant dewaxing solvent to form a mixture of waxy oil and solvent:
(b) passing said mixture from step (a), at a temperature above its cloud point to the top of a continuous, auto-refrigerative chilling zone which comprises a vertical multi-staged tower operating at a constant pressure ranging between about O to 50 psig wherein each stage contains a liquid space, a vapor space above the liquid space and means for removing autorefrigerant vapor from each vapor space;
(c) cooling said mixture as it progresses down from stage to stage in said chilling zone to precipitate wax from said oil thereby forming a slurry comprising solid particles of wax and a dewaxed oil/solvent solution and further chilling the so-formed slurry by contacting same with a liquid autorefrigerant which is introduced under flow rate control conditions into a plurality of the stages in said chilling zone and allowed to evapor-ate therein at a controlled rate so as to achieve an average cooling rate of the slurry in said chilling zone ranging from between about 0.1° to 20°F./minute with an average temperature drop across each stage into which said liquid autorefrigerant is introduced into and evaporated in ranging from between about 2° to 20°F.
and wherein the evaporated autorefrigerant is removed from each of said stages into which said liquid auto-refrigerant was injected in a manner such that the autorefrigerant vapor formed in any given stage does not pass through all of the stages in said zone above said stage; and (d) filtering the wax from the slurry to obtain wax in a dewaxed oil solution.
11. The process of claim 10 wherein the predilution sol-vent comprises a ketone selected from the group consisting of (a) ketones having from 3 to 6 carbon atoms in the molecule and mix-ture thereof and (b) a mixture of 3 to 6 carbon atom ketones and aromatic compounds.
12. The process of claim 11 wherein the liquid autorefrig-erant injected into the chilling zone is selected from the group consisting of from 2 to 4 carbon atom hydrocarbons, ammonia and normally gaseous chlorofluorocarbons.
13. The process of claim 12 wherein the ketone predilution solvent comprises a mixture of MEK/MIBK or MEK/toluene and the autorefrigerant is propylene or propane.
14. A continuous autorefrigerant process for solvent dewax-ing wax-containing heavy petroleum oil fractions which contain at least about 10 wt. % of residual material having an initial boiling point of about 1050°F. which comprises the steps of:
(a) mixing said oil with a predilution solvent;
(b) passing said mixture to the top of a continuous, auto-refrigerative chilling zone which comprises a vertical, multi-staged tower operating at a constant pressure ranging from between about 0 to 50 psig wherein each stage contains a liquid space, a vapor space above the liquid space and means for removing autorefrigerant vapor from each vapor space;
(c) cooling said mixture to precipitate wax therefrom to form a waxy slurry and precipitating additional wax from the so-formed slurry by contacting said mixture and slurry in said chilling zone with a liquid autore-frigerant which is introduced under flow rate control conditions into a plurality of the stages in said second zone and allowed to evaporate therein at a con-trolled rate so as to achieve an average cooling rate of the slurry in said second zone ranging from between about 0.1° to 20°F./minute and wherein the evaporated autorefrigerant is removed from each of said stages into which said liquid autorefrigerant was injected in a manner such that the autorefrigerant vapor found in any given stage does not pass through all of the stages in said zone above said stage; and (d) filtering the wax from the slurry to obtain wax in a dewaxed oil solution.
(a) mixing said oil with a predilution solvent;
(b) passing said mixture to the top of a continuous, auto-refrigerative chilling zone which comprises a vertical, multi-staged tower operating at a constant pressure ranging from between about 0 to 50 psig wherein each stage contains a liquid space, a vapor space above the liquid space and means for removing autorefrigerant vapor from each vapor space;
(c) cooling said mixture to precipitate wax therefrom to form a waxy slurry and precipitating additional wax from the so-formed slurry by contacting said mixture and slurry in said chilling zone with a liquid autore-frigerant which is introduced under flow rate control conditions into a plurality of the stages in said second zone and allowed to evaporate therein at a con-trolled rate so as to achieve an average cooling rate of the slurry in said second zone ranging from between about 0.1° to 20°F./minute and wherein the evaporated autorefrigerant is removed from each of said stages into which said liquid autorefrigerant was injected in a manner such that the autorefrigerant vapor found in any given stage does not pass through all of the stages in said zone above said stage; and (d) filtering the wax from the slurry to obtain wax in a dewaxed oil solution.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000348094A CA1140067A (en) | 1980-03-21 | 1980-03-21 | Continuous autorefrigerative dewaxing process and apparatus |
| CA000399170A CA1144503A (en) | 1980-03-21 | 1982-03-23 | Continuous autorefrigerative dewaxing process and apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000348094A CA1140067A (en) | 1980-03-21 | 1980-03-21 | Continuous autorefrigerative dewaxing process and apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1140067A true CA1140067A (en) | 1983-01-25 |
Family
ID=4116516
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000348094A Expired CA1140067A (en) | 1980-03-21 | 1980-03-21 | Continuous autorefrigerative dewaxing process and apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1140067A (en) |
-
1980
- 1980-03-21 CA CA000348094A patent/CA1140067A/en not_active Expired
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