US2119733A - Process for dewaxing oils - Google Patents

Description

June 7, 1938. Au. B. BRAY PROCESS FOR DEWAXING OILS Filed July 2, 1934 Patented June 7, 1938 NETE STE" ears ortica signer to Union (lil Company of California,

Los Angeles, Calif., a corporation of California Application July 2, 1934, Serial No. 733,422

17 Claims.

rlhe present invention relates to a process for separating asphalt and wax from oils containing the same. More specifically, it relates to a process for separting asphalt and wax from oils by means of solvent.

In my co-pending application Ser. No. 466,189, led July 7th, 1930, I disclosed a process for separating asphalt and Wax from oils containing the same. In this process, crude oil, after topping the light oils such as gasoline and kerosene, Was commingled with a liquefied normally gaseous hydrocarbon such as propane, under a superatmospheric pressure suicient to maintain the propane in the liquid state. The mixture was then allowed to settle under pressure to permit settling of asphalt precipitated from solution. The oil solvent solution free from asphalt but containing the Wax Was decanted from the settled asphalt and passed into a chiller Where a portion of the propane was vaporized under reduced pressure which accomplished a reirigerative effect on the remaining oil, Wax and propane and caused the precipitation of the wax. By reducing the pressure to approximately atmospheric, the oil Was chilled to about 40 F. The precipitated Wax was separated from the oil and residual propane by centrifuging and then the Wax-freesolution was heated to vaporize the propane leaving behind a lubricating oil substantially free from both asphalt and wax.

In my co-pending application Ser. No. 659,855, filed March 6th, 1933 which has been issued as Patent No. 2,010,008, I disclosed that the eiliciency of asphalt separation with propane increased as the propane to oil ratio was increased. The higher the propane to oil ratio the more eicient is the separation between the oil and the asphalt. This was evidenced by the fact that greater quantities of asphaltic and semi-asphaltic materials were recovered at the higher propane to oil ratios.

In my application, Serial No. 611,933, now U. S. Patent Number 2,031,095, I have disclosed the use of an asphalt material to promote the crystalli- Zation of the Wax contained in an oil containing the same. The material is added to the Wax bearing oil which does not contain a sufficient amount of the asphalt to promote crystallization of the wax and the mixture is blended with a liquefied normally gaseous hydrocarbon such as propane. The mixture is then chilled to precipitate the Wax and the asphalt and Wax is separated from the diluted oil.

In my application, Serial No. 610,130, now U. S. Patent No. 2,049,046, I disclosed the co-precipitation of asphaltic material and Wax from oils which have been mixed with a liqueiied normally gaseous hydrocarbon. While mixture of oil and diluent is chilled t0 precipitate the Wax in the presence of the asphalt and the precipitated asphalt and wax separated as a mixture from the solution of oil and diluent.

It has also been found that When a considerable amount of high molecular Weight propane insoluble tars or asphalt is carried into the propane solution at, say to 120 F. by virtue of the presence of 20 to 40% of oil in the propane solution, a large portion of the dissolved tars or asphalt precipitates in the devvaxing `stage by cooling to low temperatures so that the wax cake or slurry is badly contaminated with a heavy` resinous impurity which seriously interferes With the handling of the Wax upon the filter or in other operations. The precipitation or a small amount of these propane insoluble materials along With the wax is beneficial as regards filtration and settling characteristics of the wax but an excessive amount is denitely detrimental. On account of the equilibrium involved there appears to be little likelihood, however, of so completely deasphaltizing or de-tarring a stock with propane that the benefit of having some asphaltic material present in dewaxing is completely lost by simple propane extraction with a high ratio of propane.

It is, therefore, apparent that it is desirable to deasphaltize or Ole-tar heavy oil stocks as completely as possible with a relatively high propane to oil ratio before proceeding with the devvaxing of theoil solution.V However, economical considerations have restricted conditions to relatively loW propane ratios in the initial propane solution or extraction of the stock for the purpose of separating the asphaltic material. This is because the initial amount of propane requiredV to chill the oil to precipitate Wax by evaporative refrigeration and to leave an adequate amount of propane at the completion of the chilling op-v eration to provide good settling or filtration characteristics to separate the precipitated wax is rarely over 6 or 'l volumes of propane to one of the oil. For example, if a mixture of 6 volumes of propane to one of oil and Wax ata temperature of 90 F. was chilled adiabatically by vaporization of propane under gradually reducing pressure conditions and at a rate, for example, of 3 F. per minute, the amount of propane vaporized to chill the solution to 40 F. Would comprise about 3 volumes leaving about 3 volumes of propane in the chilled mixture. The latter amount is more than suicient to provide good settling or'ltration of the chilled mixture. However, if a topped crude containing approximately 25% asphaltic materials precipitable at 90 F. with a propane to oil ratio of about 12 to 1, the propane to oil ratio of the mixture upon completion of the' deasphaltizing operation and as the solution enters the chiller would be in the neighborhood of about l5 or 16 to 1. This amount of propane is far in excess of that required to chill the oil down to 40 F. Furthermore, aside from the fact that the cost of handling such a large amount of propane based upon the amount of oil treated is prohibitive for commercial operations, the ltrate would contain an excessive amount of propane which dissolves an appreciable amount of the wax even at 40 F. so that the pour point of the oil is high upon separation of the propane.

It is an object of the present invention to present a process for separating asphalt and Wax in which all of the benefits of a very high propane ratio on heavy oil stocks is obtained without the necessity of standing the cost of such high propane to oil ratios.

It is another object of my invention to separate the asphalt from oils containing the same at a high propane to oil ratio and then separate the wax from the solution at a low propane to oil ratio.

Another object of the invention resides in dissolving the heavy asphalt and wax containing stock at a high propane to oil ratio sufficient to remove substantially all of the asphaltic and dark coloring bodies from the oil, separating the asphaltic material precipitated from solution and then adding a quantity of waxy oil which is substantially free from asphaltic material so as to lower the propane to oil ratio on the resulting mixture and subsequently dewaxing the mixture.

It is a particular object of my invention to separate tarry matter from heavy lubricating oil stocks such as from overhead heavy or viscous distillates containing wax or substantially free from wax with a sufficient amount of a liquefied normally gaseous hydrocarbon diluent as propane and then add a clean waxy stock to the detarred heavy stock and propane, preferably a light or less viscous waxy overhead lubricating oil distillate substantially free from asphaltic, tarry or coloring bodies in an amount sufficient to lower the amount of propane in the resulting mixture to within a range which is merely sufficient to chill the mixture of oils to a dewaxing temperature by vaporization of a portion of the propane and yet to leave a sufcient amount of propane in the chilled mixture to provide good filtration or separation of precipitated wax from solution, then chilling the mixture to a devvaxing temperature and separating precipitated wax from the remaining propane and oils and finally separating the propane from the oils and then, if desired, separating the oils into heavy and light fractions such as by distillation. A particular advantage of treating oils in the above manner resides in the fact that the heavy distillates act in such a manner to alter the character of the Wax in the light distillate so that when precipitated at low temperatures, the wax may be rapidly filtered.

Other objects and advantages of my invention p will be apparent from the following description of the drawing which represents a schematic arrangement of apparatus for carrying out my invention:

Referring to the drawing, an oil containing asphalt and also wax, such as a heavy overhead distillate cylinder stock or a residual stock is drawn from tank I by pump 4 and is passed into line 2 controlled by valve 3 where it meets a stream of asphalt precipitating solvent, preferably a liquefied normally gaseous hydrocarbon which is taken from storage tank 5 via line 6 controlled by valve 1 by means of pump 8 which forces the solution through line 9 into line 2. It will be observed that bythe term asphalt, I intend to inclule such substantially wax-free fractions which will precipitate or separate from oils when such oils are commingled with liquid propane or other solvents. Such fractions include asphalty or bitumen and/or heavy viscous oil fractions, malthas, pseudo asphaltic materials, tars and dark coloring bodies.

The oil solvent solution is passed through turbulence coil or mixing coil l and then into decanter ll where asphalt precipitated from solution by means of the liquefied hydrocarbon is allowed to separate and settle to the bottom of the decanter H.

For the purpose of precipitating the asphalt from solution, I may employ any of the liquefied normally gaseous hydrocarbons comprising methane, ethane, propane, butane, iso-butane or mixtures thereof. Such hydrocarbons are volatile at atmospheric temperatures and pressures. If desired, I may employ the normally gaseous hydrocarbons obtained by rectification of casinghead gasoline by the so-called stabilizing method now conventional in the natural gasoline industry. Such fractions may comprise the overhead fractions of the stabilizing process. 'I'he gaseous fractions may be liquefied by compression and cooling and are drawn oif into pressure chambers where they are maintained in the liquid state until they are used. A fraction of this character may comprise essentially propane which, however, may contain other gaseous hydrocarbons as ethane, iso-butane and butane. Instead of employing a liquefied normally gaseous hydrocarbon for the purpose of precipitating the asphalt, I may also use other solvents which are capable of dissolving the oil and wax from the raw stock but which will precipitate the asphalt. Such solvents may comprise alcohol, mixtures of alcohol and ether, acetone or volatile hydrocarbon solvents such as casinghead gasoline and light naphthas. I find, however, that the process is best carried out by the use of liquefied normally gaseous hydrocarbons, preferably liquid propane, in the ratio of approximately 10 to 20 volumes of propane to one of the oil and in the present discussion of my invention, I shall describe the process employing propane although I do not wish to be specifically limited thereto.

A superatmospheric pressure is maintained in decanter Il sufficient to maintain the propane and oil in the liquid state at the temperature in decanter H. Decanter Il and solvent storage tank are maintained at substantially the same pressure by means of equilibrium line l2 controlled by valve I4. For the solvent given above, i. e. propane, this pressure should be about 125 lbs. per square inch when a temperature of about 75 F. is maintained in decanter Il. At higher temperatures, the pressures Will be correspondingly higher.

The asphalt precipitated from solution by means of propane and settling to the bottom of d-ecanter Il is removed as a slurry of asphalt containing oil and propane. This asphalt slurry is removed via line l5 controlled by' valve I6 by means of pump I1 which forces the slurry via line i8 through heater I9 Where the mixture is heated to a sufficiently high temperature to melt the asphalt and vaporize the residual propane. This mixture is then l'lashed via valve 2l on line 2U into vaporizer 22 which is operated at a lower pressure. Superheated steam is introduced into vaporizer 22 via line 23 to supply additional heat and to reduce the asphalt to proper specication generally only as regards flash and lire points. The overhead from vaporizer 22 is sent through line 24 to cooler 25 where the water and oil vapors are condensed which then pass via line 25 into separator 21. Any condensed light oil in separator 21 is withdrawn through line 28 controlled by valve 29 and condensed water is withdrawn via line 30 controlled by valve 3 l. The uncondensed propane fro-m separator 21 is sent through line 32 controlled by valve 33 to the suction of compressor 34. Also, the propane vaporized in other apparatus in the process, as will be described, will be sent to compressor 34. The propane is compressed in compressor 34 Where the pressure is raised so that in the high pressure system and the compressed propane is passed via line 35 to condenser 36 Where the propane liquees and thence passes via line 31 to propane storage tank 5.

The asphalt is withdrawn from the bottom of vaporizer 22 Via line 38 controlled by valve 39 by means of pump 40 which forces the asphalt through line 4l into asphalt storage tank 42.

The overflow from decanter Il consisting oi substantially asphalt-free oil, wax and propane in a ratio in excess of that introduced into decanter Il due to the separation of a part of theoil as asphalt is Withdrawn via line 43 where it is commingled with l to 3 volumes of waxy oil substantially free from asphalt such as lo-w viscosity distillate or a well chemically treated oil coming from tank 44 via line 45 controlled by valve 46 and pump 41 which forces the oil via line 48 into line 43. This mixture then passes through heater 49 and line 50 controlled by valve 5I into Chiller 52 where the mixture is chilled to a sumciently low temperature to precipitate wax from solution. In heater 49, the mixture is heated to sufficiently high temperature to cause the wax to dissolve in the oil and propane preparatory to dewaxing.

The amount of waxy oil commingled with the decantate from the asphalt separator Il will depend largely upon the propane to oil ratio passing into line 43 and also upon the desired proipane to oil ratio passing into Chiller 52. Ii the original oil in tank l contains approximately 11% of asphalt and is commingled with, say 12 volumes of propane at 90 to 120 F. and approximately 10% of asphalt is removed in decanter H, the propane to oil ratio in line 43 will coniprise about 13 to l. Adding, say 2 volumes oi distillate from tank 44 to the propane and oil in line 43, the propane to waxy oil ratio will be in the neighborhood of 4.3 to l which is in the region commonly accepted as being economical. Add-- ing 3 volumes of the waxy distillate would give a still lower propane ratio in the neighborhood of 3.3.to l, While the addition of only one volume of waxy distillate would give a higher ratio of about 6.5 to 1.

The chilling for dewaxing in chiller 52 is accomplished by vaporizing a portion of the propane under reduced pressure which exerts a refrigerative eiect upon the remaining oil, wax and propane. By gradually reducing the pressure at a rate of, say 2 to 5 per minutedown to substantially atmospheric pressure, a temperature of approximately 40 F. isobtained in chiller 52 which is sulicient to precipitate substantially all of the wax from solution. When other solvents are used, the refrigeration temperature at atmospheric pressure Will vary from 40 F. and in some cases, it may be necessary to operate vthe chiller at sub-atmospheric pressures or to chill the solution by indirect heat exchange with a cold medium such as brine. The propane vaporized in 52 passes via line 53 controlled by pressure reduction valve 54 and passes into line 32 to the suction of compressor 34. The chilling in 52 may be accomplished with or Without make-up propane dependingfupon the propane to waxy oil ratio entering the chiller and the ratio of propane to oil desired at the completion of the chilling operation. If the propane to oil ratio entering the Chiller is insuiiicient so that upon evaporation of pro-pane to vatmospheric pressure, an insufficient amount of propane remains in the chiller to provide for adequate separation of the precipitated wax from the remaining voil and-propane, a further quantity oi propane may bevadded via line 55 controlled by valve 56. This liquid propane may be either precooled or not, depending upon Whether it is desired to obtain further chilling in 52 with the make-up propane. Ii it has been found that the propane to oil ratio was sumcient to obtain the desired low temperature but insufficient to provide for adequate wax separation, it is preferable to add propane cooled to about 40 F. into chiller 52 through line 55, whereas, if the propane was insufficient to produce the desired refrigeration, the propane may be added at a somewhat higher temperature. The chilling may then be continued to 40 F. It is generally desirable to complete the chilling operation with propane to oil ratio of about 2` to 21/2 to 1. This is sufficient to accomplish good separation of the precipitated Wax from the chilled mixture.

The chilled mixture is Withdrawn from the bot-v tom of Chiller 52 via line 51 controlled by valve 58 and pump 59 which forces the mixture under pressure via line 50 through lter 6l Where the precipitated Wax deposits upon the filter leaves and is withdrawn via line 52 controlled by valve 33 from which it may be passed to suitable heaters and separators for removing propane and oil contained in the Wax cake. Instead of separating the precipitated wax by filtration, I may employ other means, such as cold settling or centrifuging. The'ltrate substantially free from wax and asphalt is passed through line B4 through heat exchanger 55 where the low temperature of the solution may be recovered such as by heat exchange as, for example, with solution entering the Chiller' after passing through heater 49. The mixture is then introduced into vaporizer 66 Where the propane is vaporized, aided lby steam circulated through closed coil '61. The vaporized propane passes out of vaporizer 6E via line 33 controlled by valve (i9 and thence passes into line 32 to the suction of compressor 34. The dewaxed oil passes from the bottom of. vaporizer 66 via line 10 controlled by Valve 1| and pump 12 which forces the oil through line 13 into storage tank 14.

After dewaxing and depropanizing,v the mixture' of heavy and light oil stocks may be redistilled and fractionated to give appropriate cuts for further treatment such as Withacid and alkali and clay or by extraction with suitable solvents such as liquid sulphur dioxide, or for use as different viscosity grades of lubricating oils, if

desired. This may be effected in a fractional distillation column supplied from the tank 14 by means of line 16, and having take off lines 11 for the recovery of various fractions as desired.

The following represents an example for carrying out my process on certain stocks. However, this example is not intended to be limiting:

An S. A. E. 70 overhead vacuum distilled stock containing wax was mixed under pressure with about volumes of propane at 90 F. which caused separation of about 12% of heavy greenish-brown tar. After decantation, the propane oil solution was commingled with twice as much of S. A. E. 40 distillate stock based on the original oil giving a propane to oil ratio of about 6.8 to 1. This solution was heated to above the cloud point (about 125 F.) and then chilled adiabatically at a rate of about 21/2 F. per minute to about 40 F. and then was filtered at -40 F. under a pressure of about 10 lbs. per square inch. The volumetric ratio of propane to oil passing to the filter was about 3.3 to 1. The filter rate on a viscous oil basis was 3.9 gallons per square foot per hour. After treating the oil with a selective solvent in the presence of the remaining propane, a raflinate was obtained having a gravity of 60 F. of 27.3 A. P. I., a color of 7 N. P. A., a pour point of 5 F., Saybolt Universal viscosities of 1185 at 100 F., 474 at 130 F., 182 at 170 F. and 92.5 at 210 F., a viscosity index of 88 and a viscosity gravity constant of 0.811.

It will be observed that in addition to obtaining a very thorough de-tarring of the heavy stock Without the expense of propane to oil ratio being charged against the heavy stock by the method shown above, another important advantage is obtained in that the dewaxing characteristics of the added lower viscosity stock are greatly improved by the admixture with the heavy stock.

It will be observed that while I have described the foregoing example in connection with treating an S. A. E. 70 overhead vacuum distilled stock and commingled an S. A. E. 40 distillate with the deasphaltized heavy stock and then dewaxed the mixture, the invention may be applied to the treatment of other oils. Thus, instead of adding an S. A. E. 40 distillate to the heavy stock, I may add a treated waxy distillate such as one which had been rened with acid and alkali or with a selective solvent such as liquid sulphur dioxide or both. Instead of treating a heavy overhead distillate, I may treat a raiiinate produced by selective solvent extraction with liquid sulphur dioxide and obtain an improved color and carbon residue on the rafinate. The treatment with large amounts of propane appears to precipitate color bodies from the raffinate which even selective solvent extraction will not remove.

Thus, there are many variations of the process which may be made within the scope of the following claims by those skilled in the art Without departing from the spirit of the invention; consequently, the foregoing exemplary description is not to be taken as limiting.

I claim:

Y 1; A process for separating asphalt and wax from oils which comprises mixing a heavy oil containing asphalt and wax with a sufficient quantity of liquefied normally gaseous hydrocarbon diluent to elect precipitation of substantially all of the asphalt from said oil, separating precipitated material from the oil and hydrocarbon diluent, commingling said oil and diluent with a Wax containing oil in amount suflicient to reduce the diluent oil ratio to a large extent, chilling said mixture to precipitate wax, separating precipitated wax from said mixture, and subjecting the dewaxed oil to distillation to separate the same into oils of varying viscosities.

2. A process for separating asphalt and wax from oils which comprises commingling an oll containing asphaltic material and wax with a liqueed normally gaseous hydrocarbon diluent in an amount suflicient to separate substantially all of the asphalt and coloring matter from said oil, said hydrocarbon diluent to oil ratio being considerably in excess of a diluent to oil ratio desired during dewaxing of an oil by vaporization of diluent under reduced pressure, separating precipitated asphaltic material from the oil and diluent, commingling said oil and diluent with a suiiicient amount of an asphalt-free waxy oil of lower Viscosity than said first mentioned oil to reduce the diluent to oil ratio within an amount desirable for dewaxing by vaporization of diluent under reduced pressure, chilling said mixture to precipitate wax and separating precipitated wax from said mixture.

3. A process as in claim 2 in which said heavy oil containing asphalt comprises about an S. A. E. 70 oil and said waxy lighter oil comprises one having about an S. A. E. 40.

4. A process for separating Wax from relatively light waxy oils which comprises commingling said relatively light waxy oil with a light hydrocarbon diluent and a raffinate produced by extracting an oil with a selective solvent, said rainate containing color bodies which are not removed by the extraction with the selective solvent but which precipitate when admixed with said light hydrocarbon diluent, chilling said mixture toI precipitate wax and separating the precipitated wax from the mixture.

5. A process for separating wax from waxy oils which comprises commingling a relatively light waxy oil with a light hydrocarbon diluent and a relatively heavier rainate produced by extracting an oil with a selective solvent, said rafnate containing color bodies which are not removed by the extraction with the selective solvent but which precipitate when admixed with said light hydrocarbon diluent, chilling the mixture to precipitate wax and separating precipitated wax from the mixture.

6. A process for separating asphalt and wax from oils which comprises commingling an asphalt and wax containing oil with allarge volume of solvent capable of dissolving the'oil but not the asphalt, separating undissolved asphalt from the oil and solvent, commingling said deasphalted oil and solvent with a second oil containing wax but substantially free from asphalt in amount sufficient to reduce the diluent oil ratio to a large extent, chilling said mixture to precipitate wax and separating precipitated wax from said mixture.

7. A process for separating asphalt and wax from oils which comprises mixing a heavy oil cointaining asphalt and wax with a suicient quantity of liqueed normally gaseous hydrocarbon diluent to effect precipitation of substantially all of the asphalt from said oil, separating said precipitated asphalt from the oil and hydrocarbon diluent, commingling said oil and diluent with a Wax containing oil substantially free from asphalt in amount suiiicient to reduce the diluent oil ratio to a large extent, chilling said mixture to precipitate Wax and separating precipitated wax from said mixture.

8. A process as in claim 7 in which the liquefied normally gaseous hydrocarbon diluent comprises liquid propane.

9. A process for separating wax from waxy lubricating stocks which comprises commingling a relatively heavy rafnate with large quantities of a liqueed normally gaseous hydrocarbon diluent, said rainate being produced by extracting an oil with a selective solvent but containing color bodies which are not removed by the extraction with the selective solvent, adding a quantity of a relativelylighter waxy oil to reduce the oil-diluent ratio, chilling the mixture to precipitate wax and separating the precipitated wax.

10. A process for separating wax from oils which comprises mixing a waxy heavy oil which naturally contains a wax separation aid with a suicient quantity of a diluent which is capable of precipitating said wax separation aid from said oil, and thereby precipitating wax separation aid, separating substantially all of the wax separation aid from the diluted oil, mixing said diluted oil with an oil containing wax in an amount sufcient to reduce the diluent to oil ratio, chilling said mixture to precipitate wax and separating the wax from said mixture.

11. A process for separating wax from a relatively light waxy oil which is substantially free from asphalt which comprises mixing a relatively heavy waxy oil containing asphaltic materials with a light hydrocarbon diluent in an amount sufficient to precipitate a substantial quantity of said asphaltic materials but to leave a small quantity of the asphaltic materials in the oil to serve as a wax-separation aid for the subsequent dewaxing of relatively light waxy oil, mixing said diluted oil with al relatively light waxy oil in an amount su'icient to reduce the diluent to oil ratio to a large extent, chilling the mixture in the presence of the wax separation aid to precipitate the wax and separating the precipitated wax from the mixture.

12. A process as in claim 11 inwhich the light hydrocarbon diluent comprises a liquefied normally gaseous hydrocarbon.

13. A process as in claim 11 in which the light lll. A process for separating wax from a relatively light waxy oil which is substantially free from asphalt which comprises xing a relatively heavy waxy oil containing asphaltic materials with a light hydrocarbon diluent in an amount suflicient to precipitate a substantial quantity of said asphaltic materials but to leave a small quantity of said asphaltic materials in the oil to serve as a wax Yseparation aid for the subsequent dewaxing of the relatively light waxy oil, removing the precipitated asphaltic material from the oil, rdiluent and remaining asphaltic materials, mixing said last mentioned mixture with the relatively light waxy oil in an amount suflicient to reduce materially the diluent to oil ratio, chilling said mixture to precipitate wax and separating the precipitated wax from the mixture. l

15. A process for separating wax from waxy lubricating stocks which comprises commingling a relatively heavy wax bearing raiilnate with large raflinite being produced by extracting an oil with a selective solvent and containing color bodies which are not removed by the extraction with the selective solvent but which precipitate when admixed with said light hydrocarbon diluent, precipitating and separating said color bodies from said rainate and diluent, adding a quantity of a relatively lighter asphalt free waxy oil to reduce the oilediluent ratio, chilling the mixture to precipitate wax and separating the precipitated wax from the solution of diluent and oil.

16. A process as in claim 15 in which the light hydrocarbon diluent comprises a liquefied normally gaseous hydrocarbon.

17. A process as in claim 15 in which the light hydrocarbon diluent comprises liquid propane.

ULRIC B. BRAY.

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