US2062266A - Distillation - Google Patents

Description

Patented Nov. 24, 1936 UNITED STATES PATENT OFFICE DISTILLATION Application November 3, 1930, Serial No. 493,037

28 Claims.

This invention relates to the distillation of oil and it is particularly useful in the recovery of high boiling fractions as distillates in continuousv distillation, especially without cracking, and in so recovering such fractions in a state in which each fraction is relatively free of constituents contained in other fractions. use of this invention resides in dividing waxcontaining oil, such as petroleum oil or tar denite or shale, or residues of such petroleumpil or tar, into fractions which contain wax that is in a form well suited to the removal thereof and which taken together contain an unusually large proportion of the lubricating constituents of the petroleum oil or tar.

In my copending application Serial No. 370,852, led June14, 1929, there is described a process for the continuous fractional distillation of oil and especially for the production of fractions of wax-containing oil, which fractions contain wax in a form well suited to the removal thereof. In that process the wax-containing oil is continuously heated, as in a pipe still, to temperatures in 5 the neighborhood of 800 F., and introduced at an intermediate level into a rectifying tower,

such as a bubble tower,'whlle maintaining a ow of reiiux liquid, e. g. condensed exit vapor, into withdrawn from a higher level of the tower, and

successively lower boiling fractions may be with- 40 drawn from successively higher levels of the tower while the lighter constituents, such as,I naphtha, pass from the top of the tower in the form of vapor and are condensed. During the withdrawal of such distillates from the'side of the tower the condensate from the vapors leaving the top of the tower is refiuxed at least in part to the top of the tower and regulated redux is maintained within the tower from the top downward; and steam is usually introduced at at points abovev the bottom. Also sub-atmospheric pressure may be maintained in the tower, in which case lighter constituents cannot becondensed and the oil treated must be preliminarily freed of lighter constituents.

A very important l rived by destructive distillation from coal, ligthe bottom of the tower and may be introduced While the procedure described above i's capable of successful practice and is advantageously employed in the production fromspetroleum or tar of fractions each of which is well freed of con-'- stituents occurring in the other fraction, such as a distillate containing wax that precipitates in such form that it is capable `of continuous centrifugal removal and a distillate that contains wax that is well suited to removal by-.flter pressing, features of this invention render that process more generally applicable and more readily practicable and avoid dilculties and losses that may be encountered in the practice of that process, particularly if that process is not operated with great care.

In the practice of continuous distillation of the type to which that process relates, the heated wax-containing oil, or a major portion of it, vaporizes suddenly when it is introduced into the tower and, due to the. heat required .for such evaporation, the maximum effective temperature in the tower drops from the temperature to which the oil is raised to a lower temperature than is desired, e. g. drops from 800 F. to '715 F. or lower, and radiation still further reduces the temperature in the-tower. The function ofthe highest temperature in the tower is to effect a separation of the most viscous oil from the asphalt in distillation of petroleum and from resins in the distillation of tar. The maximum effective temperature, to which the temperature within the tower is depressed as a result of absorption of heat in the evaporation of that part of the oil which evaporates when the oil is introduced into the tower, is not only insumcient to vapor- 35 ize completely the most viscous oil from the residue, such as asphalt or resin, but, if a reux is flowed downward into the vaporizing zone of the tower for the purpose of separating asphalt .from the highest boiling distillate and causing it to .have a desirable color, the temperature will be further reduced and a quantity of viscous oil additional to that which was not ,vaporized will be thrown down into the asphalt and the .highest boiling distillate will contain even less viscous 45 oil. From the lpoint of view of mere fractiona- 6 tion of oil or tar, this passing of viscous oil into the residue, constitutes a substantial loss, and from the point of View of dewaxing its importance is much greater than the mere value ofthe oil lost into the residue. Thus, I have found that the highest boiling constituents of the oil, other than the residue, include ingredients which when present inthe highest boiling distillate, increase vthe amorphousness ofthe wax precipitated 55 therein\ by chilling and thereby facilitate the continuous centrifugal removal of that wax and permit that distillate to have a greater boiling range while it is still dewaxable by continuous centrifugal dewaxing. Such ingredients may be either highly amorphous wax or impurities other than hard asphalt which are ordinarily removed by extensive acid or clay treatment in the decolorizing of oil, but the exact nature of such constituents is not fully known to me and the expression amorphizing substances is used herein to designate such ingredients.

This deficiency of temperature within the tower cannot be compensated for by heating the oil to a higher temperature before it is introduced into the still, because such higher temperature would cause the oil to decompose to an undesirable extent with consequent loss of viscous constituents and decrease of amorphousness of the wax contained in the most viscous distillate. In this connection, I have found that while it is known generally that cracking converts wax that will precipitate in amorphous form into wax that will precipitate in crystalline form, it is a fact not previously known that cracking that converts amorphous wax to crystalline wax reduces the boiling point of all wax a substantially uniform amount with the result that the cracking of the most amorphous wax produces in the oil crystalline wax having a boiling point that isnot only higher than the boiling point of any crystalline wax naturally occurring in petroleum or tar but sufficiently high to cause such crystalline wax to boil within the boiling range of the distillate that is intended for continuous centrifugal dewaxing, thus impairing the removal of wax from such distillate by such process. And,

this deficiency of temperature cannot be compensated for by increasing the quantity or temperature ofv steam introduced into the column, beyond the quantity or temperature commonly used, because the temperature of such steam must not be so high as to injure the oil and the specific volume of steam is so high that a sufclent quantity cannot be introduced into the tower. This deficiency of temperature exists regardless of the degree of sub-atmosphericpressure maintained within the tower and cannot be compensated for by increasing the degree of subatmospheric pressure.

A feature of this invention is that in continu- .ous fractionation of oil, in which heated oil is introduced to an intermediate level of a rectifying column, an additional quantity of heat is introduced into the rectifying column at or below the point at which the most viscous oil is being separated from the asphalt. Thisadditional heat may be supplied in such quantity and at such maximum temperature as to ensure that without objectionable cracking even the most viscous oil will be separated as a vapor from the residue and to enable such use of liquid reiiux that a relatively sharp separation may be made between the highest boiling distillate and the residue, to the end that the distillate will contain a minimum of the residue, such as asphalt, and the residue will contain a minimum of the highest boiling constituents desired in the highest boiling distillate. A further'feature of this invention is that by so supplying heat to a zone of the tower the temperature of that zone may be brought without occurrence of cracking to any temperature below cracking temperature whereas an attempt to bring a similar quantity of additional heat ineo such zone by increasing thev temperature of the oil passing to the tower for fractionation would cause extensive cracking. A feature of this invention is that the additional heat so supplied is carried into the tower in an auxiliary liquid of which the vapors occupy a relatively small volume as compared with the volume of a similar weight of steam and which is not injured by the temperatures employed and vwhich may in some instances be improved in character by theapplication of such temperatures. A further feature of this invention is that such auxiliary liquid may consist of' a hydrocarbon which is not injured and may be improved by being subjected to the temperature employed and which because of its relatively high molecular weight will carry into the tower a much greater quantity of heat per unit of volume of resultant vapors than will steam. A feature of this invention is that heat may be carried into that zone of the tower within which the highestboiling distillate is being separated from the residue, by withdrawing from a substantially higher level of the tower a distillate of such composition that it is not injured by the temperatures employed, supplying heat to such distillate until its temperature is equal to or exceeds the temperature desired in the above mentioned zone of the tower, and then introducing that heated distillate into thatrzone of the tower. The distillate so heated and returned to thetower will vaporizeand the vapors will rise in the tower and will be condensed and the distillate will be withdrawn from the same level from which it was originally withdrawn if the reheating does not crack-it and from a higher level if it does, but it will supply to the zone at which the highest boiling distillate is being separated from the residue, a sumcient quantity of heat to insure that that highest boiling distillate will be vaporized and to insure that sufficient reflux may be maintained in thatI zone to wash the distillate suilciently free of the residue to avoid impairment of color of the distillate by inclusion of the residue therein.

If a petroleum distillate is utilized as the auxiliary liquid for carrying heat into the tower, and the temperature necessarily employed is equal to or above the cracking temperature of such petroleum distillate, decompositiomwill occur. And, if such distillate be relatively heavy any such decomposition in the tower results in a loss of the most viscous constituents and will` result in a conversion of amorphous wax into crystalline wax which comes out of the tower with the amorphous-wax-containing distillate and impairs the centrifugal removability of wax therefrom. The use, as auxiliary heat-carrying liquids, of substances in which undesirablechanges occur when they are so used, is preferably avoided.

In the practice of this invention the auxiliary liquid employed not only carries into the tower a quantity of heat that compensates for, the latent heat of vaporization of the oil that is being distilled, and thereby prevents undesirable reduction of temperature and permits of raising the temperaturer to the permissible limit, but such added heat is carried in by a substance that is not objectionably aiected by the temperature employed, and is carried in by a substance of which the vapors have a relatively small volume compared to the weight of the liquid and no increase of tower capacity is required, andthe vapors of the auxiliary liquid supplement the steam as a carrier and facilitate stripping of the more viscous constituents from the residue. A maximum proportion of lubricating constituents late that is to be dewaxed by methods suitable to the removal of wax that precipitates amorphous form.

As a feature of this invention the distillate withdrawn from an upper level of the tower and heated and returned to the zone in which thek residue is being stripped, may be distillate which contains wax which precipitates in crystalline form. Such-a distillate, when used as a heatcarrying auxiliary liquid, will meet the requirements and possess the advantages above stated, and any tendency of the temperatures employed to render the wax in such distillate more crystalline is an advantage rather than a disadvantage as removal of such wax by pressing is thereby facilitated.

Moreover, the distillate containing gasoil may be' used advantageously as the auxiliary liquid for carrying heat into the zone of the tower in which the residue is being stripped, because such distillate may be heated to high temperatures,

e. g. temperatures as high as 850 F. or higher,

without injury, and the use thereof insures that none of the lubricating qualities of the crystalline distillate will be lost by decomposition.

This invention may be employed when sub-atmospheric pressure is maintained within the column and in such procedure the oil distilled under sub-atmospheric pressure will be preliminarily freed of lighter constituents such as. naphtha, and the use of this invention in connection with such topped crude petroleum will enable complete and sharp fractionation thereof Without the application of temperatures thatwill produce undesirable cracking.

Other and further features and advantages of this invention will appear from the following description of an illustrative procedure embodying the practice of this invention, but it is to be understood that the invention is not limited to the particular apparatus referred to or to the 50 particular materials or temperatures mentioned in this description.

In the drawing in which like reference characters indicate similar parts,

Fig. 1 is a diagrammatic vertical sectionof apparatus suitable-for the practice of this inven` tion;

Fig. 2 is a view partly in section of a flow-dividing deviceembodied in the construction shown in Fig. 1; and t Fig. 3 is a sectional view on line 3-3 of Fig. 2.

In the construction shown in Fig. 1 the rectifying column I may be of any suitable construc- .tion and `is preferably of the bubble-cap type and includes provision for the withdrawal of liquids and for maintaining a ilow of reflux liquid into the top oi the tower and a regulated flow of reiiuxaliquid downward within the tower. Oil or tar to be fractionated, which in the operation described herein for merely illustrative purposes is freed of lighter constituents which cannot be readily condensed undersub-atmospheric pressure, is supplied through pipe II controlled by valve I2 to heating coils.|3 and I4 to which heat is supplied in any suitable manner as by gas or oil burner I5. 'Ihe oil or tar so heated is supplied at any suitable temperature, e. g. a temperature in the neighborhood of 800 F., through pipe I6 into tower I0 atan intermediate level thereof. immediately below that point of the tower there is located a group of trays IBl each provided with bubble-caps 22 and liquid tubes 23 that extend from such level above each tray as will maintain a suicient depth of liquid thereon to seal the bubble-caps thereof, down into thevliquid on the next tray. Below tray-group I8 is a similar tray-group I'I. Leading from the bottom of the tower is a residue-conduit 24 which extends upwardly within the tower and is provided with a float control valve 25 which maintains a body of residue in the bottom of the tower into which the lowermost tube 23 extends. Pump 26 is provided for withdrawal of residue through pipe 24. Above that level of the tower at which the oil to be fractionated is introduced there is a. tray-group I9, above which is a stripping section 30 which comprises a vapor tube 32 through which vapors rise from the uppermost tray of group I3, bubble trays surrounding tube 32, and a partition 33 which closesl the annular space between vapor tube 32- vand the wall of the tower, to provide a container 34 for the accumulation of liquid. Above stripping section 30 are successively located tray-group 20, stripping section 3l, and tray-group 2I. The .lowermost tray of tray-groups 20 and 2| is not provided with a tube 23 with which all other trays are provided, but is provided instead with tube.35 which extends from such distance above such lowermost trays as will. maintain a seal on the bubble-caps'thereof, down to a fiow-proportionin',r device 36 by 4which the liquid flowing through tubes 35 may be divided into a fraction passing into the stripping sections respectively located below tubes 35 and a fraction passing into funnel 31 and pipe 38 down to the uppermost tray. of the next lower Atray-group. Imdiediately below each tube 35 is a container 39 having an overflow weir 40 which maintains a suiciently high level of liquid is container 39 to seal the lower end of each tube 35 as shown in Fig. 3. Across the edge of Weir 40, dividing plate 4I is movable by means of shaft 42 which is threaded into plate 4I and passes through the wall of tower II), being provided at 'that point with shining boxlla in order that it may be rotated from the exterior of the tower by a hand-wheel 44.' Liquid flowing over Weir 40 and passing plate 4I at one side thereof falls into the stripping section immediately below, but liquid passing over weir 40 at the other side of plate 4I is caught in box 45 and flows `through spout 46 thereof into funnel 31.

Vapors are led from the top of tower I0 through pipe 41 to condenser' 48 from'which liquid ows into receiver 49. Water)is withdrawn from the bottom of receiver `4 9 through valved pipe 50 by pump 5I and hydrocarbon distillate passes from the top of receiver 49 through valved pipe 52 into reflux tank 53 from which the hydrocarbon distillate is withdrawn through n collected in the stripping sections as by valve-v controlled branch lines 59. Liquid collected in the collecting compartment 34 of each stripping section is withdrawn respectively by pipes vSII and 6I. c

In the operation of apparatus embodying the constructional elements so far described, the oil entering through pipe IB will partially vaporize upon entering t'he column and the resulting tem.- perature (e. g. '715 F.) will be materially below the temperaturele. g. 800 F.) to which the oil was heated. The unvaporized liquid drops into the uppermostttray of tray-group I8 and the resulting vapors rise through tray-group I9 and the vapors rising from the uppermost tray of group I9 pass through tube 32 of stripping section 30 into the trays of group 20. The liquid flowing downward through tube 35 of the lowermost tray of group 20 is divided as above described into a fraction that flows through a pipe 38 onto the uppermost tray of group I9 and from there downwardly as a reflux, and a fraction that flows into stripping section 30. The supply of steam to the bottom of each stripping section and the ow of liquid downward therein insures that liquid accumulating in compartment 3d of each stripping section will be Well freed of low boiling constituents which are carried upward in the tower in t'he form of vapor in order that they may be withdrawn from the tower at a higher level. The highest boiling distillate is thus withdrawn through pipe B by means of pump |60.

Drop of temperature in that zone of the tower into which the heated oil to be distilled is introduced, due to the evaporation of the oil in that zone, results in a failureto Vaporize all of the highest boiling distillate from the residue and a part of such distillate passes as liquid down through tray-group I8 and cannot be driven up therefrom as vapor by steam introduced through pipe 58; and diverting of liquid throug'h Pipe 38 on to the uppermost tray of group |9, for the purpose of carrying downwardly in the tower asphalt contained in vapors rising into traygroupv I9, carries an additional quantity of desired high-boiling distillate down into the residue.

Tray-group 2| and stripping section 3| operate in the same manner as tray-group 20 and stripping section 30, and a lower-:boiling distillate will be withdrawn through pipe 6| by means of pump IBI, (for example a distillate containing wax which precipitates in crystalline form may be withdrawn from pipe 6|), and gas oil passing from the top' of the tower asa vapor is used as a reux into the top of the tower while the reflux downward within the tower is regulated by adjustment of the positions of dividing plates 4|.

In the practice of this invention an additional quantity of heat is introduced into a zone of the tower and preferably into the zone in which the heated oil to be fractionated is introduced or into, or below, the zone in which the highest-boiling distillate is being separated from the residue, for the purpose of insuring that an increased proportion of a desired distillate, especially the highest-boiling distillate, will be vaporized, and for the purpose of supplying enough heat to permit a use of a sufficient quantity of reflux to carry one constituent out of another,l and especially to carry residue out of the vapors from which the highest-boiling distillate is condensed. While various liquids meeting the requirements above stated may be employed for this purpose as above set out, in theembodiment shown liquid is withdrawn leither from vthe reux tank 53 through pipe 54 or from the distillate outlet 6| through pipe Gi'i and passed through heating coil y 62, which is heated by valve-controlled burner 63. In coil 62 the temperature of the liquid is raised to a temperature equal to or above the temperature desired in that zone of the tower to which it is introduced, but below a temperature that would undesirably decompose the oil passing through coil 62 or decompose the hydrocarbons with which it is brought into contact. In the construction illustrated such heated oil may be introduced either into the zone of the tower into which the oil to be fractionated is introduced or into a lower zone, such as the zone between tray-groups l1 and I8. 'Ihe heated oil is so introduced by pipe 66 leading from heater 62.

In the practice of this invention the reflux liquid introduced at the top of the tower is introduced in such proportion and at such temperature that the vapors leaving the top of the tower are thoroughly freed, especially in tray-group 2|, of oil-constituents which are to be kept out of the light fraction Withdrawn from reux tank 53 through .pipe 54 and which are to be included in a lower-boiling distillate withdrawn through the side of the tower, such as the distillate withdrawn from stripping section 3| through pipe 6 And, adjustment of the positions of the several plates 4| determines the percentage of the oil introduced through pipe I6 that will be withdrawn from the stripping sections respectively below each ow-proportioning device 36, and

likewise determines the amount of reflux that will be passed from each rectifying section to the rectifying section next below. Thus reflux is regulated throughout the height of the column, and the boiling range of the fractions withdrawn through the side of the column so determined. Also, the amount of reux employed will determine the sharpness of the cut between the fractions into which the oil introduced through pipe I6 is divided. Float valves 61 hold in compartments 34 suihcient liquid to seal tubes 23 extending thereinto.

In the example described it is contemplated that as high a vacuum as is practicable will be maintained within the tower and that the fraction withdrawn through pipe 60 will be a heavy distillate containing Wax which precipitates in amorphous form and is very well suited for remrrval by continuous centrifugal dewaxing, and

-that the fraction withdrawn through pipe 6| will contain the remainder of the lubricating constituents of the oil or tar introduced through pipe |6 and will contain wax which precipitates in crystalline form and is well suited to removal by filter-pressing. Obviously, the rectifying sections such as tray-groups 20 and 2| and stripping sections assrciated therewith may be present in the tower in greater number than shown in the draw ing, particularly when a greater number of fractions are to be withdrawn from the side of the tower. If the oil or tar introduced through pipe I6 is not freed of light constituents and vacuum is not maintained in the tower, a greater number of rectifying sections and stripping sections will usually be employed. Also. if the oil or tar introduced through pipe I6 is of suchnature that the fraction containing crystalline wax and the fraction containing amorphous wax are not adjacent fractions, a rectifying section and a stripping section will be located between stripping section 3| and rectifying section 20 for the purpose of Withdrawing from the side of the tower a cut that contains wax that is too amorphous for lter-pressing and too crystalline for removal by methods suita- `ble to the removal of amorphous wax. In any event the fractionating operation will preferably be so conducted that a sharp cut will be made at the higher-boiling end of the crystalline-wam containing distillate and at the lower-boiling end of the amorphous-wax-containing distillate. Also, every effort is preferably 'to be made to produce a sharp cut at the higher-boiling end of the.

amorphous-waX-containing distillate and the additional heat supplied to the still by auxiliary liquid in accordance with this invention makes it possible to obtain such a sharp cut. If.insu cient heat is supplied to eiect vaprization of all constituents desired to be included in the distillate withdrawn through pipe 60 and to permit sulcient reux -to remove all residue therefrom, it may be necessary to form a non-sharp cut at the ous that the operator will have to adjust in accordance with the general principles stated herein and the specific example set forth herein, the quantity and temperature of auxiliary liquid introduced into the tower through pipe 66. In the practice of this invention a condition to be sought for is that in the zone to which oil is introduced by pipe I6,- the temperature shall be maintained as high as is consistent with the avoidance of cracking, by the introduction of auxiliary liquid, in spite of the tendency for the temperature in that zone to fall below the temperature of oil introduced thereto through pipe I6, which tendency results from the evaporation .of that oil. YOrdinarily the oil introduced through pipe I6 can beheated without cracking to a temperature (e. g. 800 F.) which will result inthe evaporation of '75% to 98% 'of that oil, but such evaporation, in the absencel of auxiliary heat supply, will reduce the temperature in the tower at that point to a temperature (e. g. 715 F.) which is insuilicient to vaporize all of the constituents desired in thedistillate withdrawn through pipe 60 and insufficient to permit complete removal of residue from that distillate. From the foregoing vit is apparent that I have pro vided a method and apparatus whereby, in the continuous fractionation of voil (which term includes oil derived from tar as well as from petroleum) by introducingit in a heated state into a fractionating tower from which fractions having different boiling 'ranges are separately withdrawn,- additional heat may be effectively introduced into any zone of the tower and particularly into the zone in which the highest-boiling distillate is being stripped from the residue; and that such a step is of great value in connection with the production by such distillation of a fraction containing wax well suited to removal by methods suitable for removal of amorphous wax. In the practice of this invention any liquid meeting the requirements above set out may be employed, readily apparent examples of such liquid being naphtha, benzol, kerosene, gas oil, crystalline-wax-containing distillate, amorphous-wax-containing distillate, mercury, low melting alloys, etc.` Instead of valved pipe 68. vWhen the auxiliary liquid conf-A tains crystalline wax the heating thereof prior to introduction to the tower may be carried to a point which effects such cracking as will increase the crystallinity oi' the oilprecipitated by cooling but will not undesirably degrade the oil. In the example above described a distillate containing wax that is amorphous and removable by methods suitable to the removal of such wax as by continuous centrifugal separation is withdrawn from a relatively lower level of the tower, and a distillate containing wax that is well suited to removal by lter-pressing is withdrawn from the next higher outlet through the side of the tower; but in some eases either the nature of the oil to be fractionated or operating conditions may make it necessary to withdraw from the side of the tower at an intermediate level a fraction that contains wax which is too crystalline for centrifugal removal and too amorphous for removal by pressing, in order that the fraction to be dewaxed by pressing will be suiiiciently free of amorphous wax andthe fraction to be dewaxed by methods suitable to the removal of amorphous wax will be suiciently free of crystalline Wax. It is a feature of this invention .that either in a case in which it is necessary to withdraw such a distillate from an intermediate level of the tower or in any other case such a distillate, containing wax that cannot be' removed either by pressing or by centrifuging, may be used `as the auxiliary liquid for carrying heat into the tower and it may be subjected to such cracking in the heating, preliminary to its return to the tower that the wax therein will come out of the side of the tower with that distillate which is intended for dewaxing by lter-pressing. Thus, it is a feature of this invention that the liquid used as an auxiliary liquid may be withdrawn from the side of the tower at a level between the levels at which the amorphous-wax-containing distillate and the crystalline-wax-containing distillate are respectively withdrawn, and such auxiliary liquid may be sufficiently cracked to cause its wax to pass out with the crystalline-wax-containing distillate, in the application of heat to the auxiliary liquid prior to its return to the still, either in cases in which tower with any distillate having substantially 'thel same boiling point, or with the residue, and be separated therefrom by gravity. l K

As a specic example of the operation oi this nvention, to which the invention vis not limited, Mid Continent crude petroleum-was topped to produce a residue having a flash point of 300 F. which was introduced to an intermediate level of the tower after being heated to 800 F. The heaviest distillate withdrawn from the side of the tower had a Universal Saybolt viscosity of about 90 at 210 F. and was very well suited to dewaxing by continuous centrifugal dewaxing. The distillate withdrawn from the side .of the tower at the next higher level had a Universal Saybolt i viscosityof about at 100 F. and was very well suited to dewaxing by pressing. The light fraction leaving the top of the tower as a vapor and being condensed and returned tothe top of the diierence of specific tower as a reflux was mainly gas oil with possibly heavier kerosene constituents.

, tower at a point not above the level thereof at which the highest-boiling distillate is withdrawn an auxiliary liquid of higher molecular weight than water and heated to a temperature above that of said zone and less susceptible to thermal decomposition than the highest-boiling of the resulting fractions which is formed by distillation.

2. In a method for `the fractionation of oil, the steps comprising introducing the oil in a heated state into a zone of a fractionating tower at .an intermediate level thereof, maintaining a flow of reux liquid downwardly in the tower, withdrawing fractions of the oil having different boiling ranges from the tower respectively at dierent levels thereof, and introducing into the tower at a point not above the level thereof at which the highest-boiling distillate is withdrawn an auxiliary liquid of higher molecular weight than water and heated to a temperature above that of said zone and less susceptible to thermal decomposition than the highest-boiling of the resulting fractions which is formed by distillation, said auxiliary liquid having a boiling point lower than that of said last named fraction.

3. In a method for the fractionation of oil, the steps comprising introducing the oil in a heated state into a zone of a fractionating tower at an intermediate level thereof, maintaining a ow of reflux liquid downwardly in the tower, withdrawing fractions of the oil having different boiling ranges from the tower respectively at different levels thereof, and introducing into the tower at a point not above the level thereof at which the highest-boiling distillate is withdrawn a liquid hydrocarbon heated to a temperature above that of said zone and having a boiling point lower than that of the highest-boiling distillate formed from the oil to be fractionated.

4. In a method for the fractionation of oil, the steps comprising introducing the oil in a heated state into a fractionating tower at an intermediate level thereof, maintaining a flow of reflux liquid downwardly in the tower, withdrawing from thetower fractions of the oil respectively having different boiling ranges and comprising a residue withdrawn below said level and a distillate withdrawn above said level in liquid phase, and in- .troducing into the tower at a point not above the level thereof at which the highest-boiling distillate is withdrawn a liquid hydrocarbon having a boiling point lower than that of the highestboiling distillate formed from the oil to be fractionated and introduced in such quantity and at such temperature as to ensure further evaporation of oil from the residue.

5. In a method for the fractionation of oil, the steps comprising introducing the oil in a heated state into a fractionating tower at an intermediate level thereof, maintaining a ow of reflux liquid downwardly in the tower, withdrawing from the tower fractions of the oil lrespectively having different boiling ranges and' comprising a residue withdrawn below said lev'el and a distillate withdrawn above said level in liquid phase.

and introducing additional heat into that zone of the tower wherein the highest boiling constituents of the oil which are contained in a resulting distillate are being separated in vapor form from the liquid residue, by introducing between an upper level of said zone and the bottom of the tower a hydrocarbon heated to a temperature above the temperature existing in said zone and having a higher thermal decomposition temperature than the highest boiling constituents of the oil to be fractionated which are present in said zone in vapor phase.

6. In a method for the fractionation of oil, the steps comprising introducing the oil in a heated state intf'ra zone of a fractionating tower at an intermediate level thereof, maintaining a flow of-reflux liquid downwardlydn the tower, withdrawing fractions of the oil having different boiling ranges from the tower respectively at different levels thereof, and introducing additional heat into said zone of the tower by introducing between an upper level of said zone and the bottom of the tower a hydrocarbon obtained from the same crude oil as is the oil to be fractionated and heated to a temperature above the temperature existing in said zone and having a thermal decomposition temperature higher than the temperature to which said hydrocarbon must be heated in order to carry additional heat into the column.

'7. In a method for the fractionation of oil, the

steps comprising introducing the oil in a heated state into a fractionating tower at an intermediate level thereof, maintaining a ow of reflux liquid downwardly in the tower, withdrawing fractions of the oil having differentboiling ranges from the tower respectively at diiferent levels thereof, and introducing additional heat into that zone of the tower wherein the highest boiling constituents of the oil which are contained in a resulting distillate are being separated in vapor form from the liquid residue, by introducing between an upper level of said zone and the bottom. of the tower a hydrocarbon heated to a temperature above the temperature existing in said zone and having a lower boiling point than those constitutents of the 'oil to be fractionated which predominate in the liquid present in the tower at the zone at which said hydrocarbon is introduced.

8. In a method for the fractionation of oil, the steps comprising introducing the oil in a. heated state into a fractionating tower at an intermediate level thereof, maintaining a flow of reflux liquid downwardly in the tower, withdrawing fractions of the oil having different boiling ranges from the tower respectively at differentlevels thereof, and introducing into the tower at a point between the bottom of the tower and the top of the zone wherein the highest-boiling constituents of the oil which are contained in a resulting distillate are being separated in vapor fo'rm from the liquid residue, a hydrocarbon of lower boiling point than said constituents and heated to a temperature above the temperature of said zone.

9. In a method for the fractionation of oil wherein the oil is introduced in a heated state into a zone of a fractionating tower from which tower fractions of the oil having different boiling ranges are separately withdrawn at different levels thereof, the step comprising introducing into the tower at a point not above the level thereof at which the highest-boiling distillate is withdrawn a liquid hydrocarbon heated to a temperature above that of said zone and obtained from the same crude oil as is the oil to be fractionated and more resistant to thermal decomposition than the highestboiling of the fractions formed by distillation.

10. In a method for the fractionation of oil wherein the oil is introduced in a heated state into a zone of a fractionating tower from which tower fractions of the oil having different boiling ranges are separately withdrawn from successively higher levels of the tower, the step comprising heating a fraction withdrawn from the tower at a level above that at which the highestboiling distillate is withdrawn and returning said fraction to the interior of the tower at a level below that at which it is withdrawn, while said fraction is at a temperature above that within the tower at said last mentioned level.

11. In a method for the fractionation of oil wherein the oil is introduced in a heated state into a zone of a fractionating tower from which tower fractions of the oil having different boiling ranges are separately withdrawn from successively higher levels of the tower, the step comprising heating a fraction withdrawn from the tower at a level above that at which the highest-boiling distillate is withdrawn and returning said fraction to the interior of the tower at a level between the bottom of the tower and the level thereof at which the highest-boiling distillate is separated from the residue, while said fraction is at a temperature above that within the tower at the point at which said fraction is returned thereto.

12. In a method for the fractionation of oil wherein the oil is introduced in a heated state into a Zone of a fractionating tower from which tower fractions of the oil having different boil- `ing ranges are separately withdrawn from successively higher levels of the tower, the steps comprising withdrawing from the tower a fraction containing crystalline wax and a fraction containing amorphous wax, heating a part of said first named fraction and returning it to the interior of the tower at a level below that at which said second named distillate is withdrawn, while the oil so returned is at a temperature above that within the tower at the level at which it is returned thereto.

"13. In a method for the manufacture of dewaxed oil,-the steps comprising introducing the wax-containing oil in a heated state into a rectifying tower at an intermediate level thereof while maintaining a ilow of reflux liquid into the top of the tower and withdrawing from the tower atl an intermediate level an* oil distillate containing amorphous wax and withdrawing a residuefrom the tower at a level below said firstmentioned level;` and introducing into the tower at a level between the bottom thereof and the level thereof at which said last named distillate is withdrawn, a hydrocarbon having a lower boiling point than said last named distillate and heated toa temperature above that existing in the tower at the level at which it is introduced.

14.-In a method for the fractionation of oil, the steps comprising introducing the oil while heated to a temperature high enough to evaporate a substantial proportion thereof into a fractionating tower at an intermediate level of said tower, maintaining a ow of reux liquid downwardly in lthe tower, withdrawing fractions of the oil having different boiling ranges from the tower respectively at different levels thereof, and introducing into that zone of the tower wherein the highest boiling constituents of the oil which are contained in a resulting distillate are being separated in vapor form from the liquid residue, heat additional to that brought into the tower in the oil to be fractionated, by introducing into the tower at a point between the bottom thereof and the top of said zone an auxiliary liquid of higher molecular weight than water and heated to a temperature above that existing in the tower at the point at which it is introduced and substantially as resistant to thermal decomposition as the highest-boiling of the fractions formed by distillation.

l5. In a method for the fractionation of oil wherein it is introduced in a heated state into a fractionating tower from which fractions having different boiling ranges are` separately withdrawn, the step comprising introducing into a zonel of the tower heat additional to that brought into the tower in the oil to b e fractionated, by introducing into the-towerat a' point between the bottom thereof and the top of said zone a crystalline-wax-containingdistillate heated to a temperature causing limited cracking thereof and containing crystalline wax and a fraction con` taining amorphous wax are withdrawn respectively at higher and lower levels of the tower, the step comprising heating at least a part of thel withdrawn distillate containing crystalline wax to a temperature causing limited cracking thereof and returning such heated oil to the interior of the tower at a level below that at which the distillate containing amorphous wax is withdrawn therefrom.

1'7. In a method for the fractionation of oil, the steps comprising introducing the oil in a heated state into a fractionating tower at an intermediate level thereof, maintaining a flow of reflux liquid downwardly in the tower, withdrawing from the tower fractions of the oil respectively having different boiling ranges and comprising a residue withdrawn below said l-evel and a distillate withdrawn above said level in liquid phase, and introducing additional heat into that zone of the tower,l wherein the highest boiling constituents of the oil which are contained in a resulting distillate are being separated in vapor form from the liquid residue, by introducing between an upper level of said/zone and the bottom of the tower a hydrocarbon; heated to a temperature above the temperature existing in said zone and having a higher thermal fdecomposition temperature than those constituents of the oil to be fractionated which are present in said zone in liquid phase.

18. In a method for f'theman'lfacture of dewaxed oil, the steps comprising introducing the wax-containing oil in a heated state into arectifying tower at an intermediate level thereof while withdrawing from the tower at a lower level a residue and from the tower at an intermediate level a liquid distillate containing amorphous wax and maintaining a flow of reflux liquid downwardly in the tower from a level thereof above that at which said distillate is withdrawn, and introducing into the tower at a level between the bottom thereof and the level thereof at which said last named distillate is withdrawn, Iahydrocarbon having a lower boiling point than said last named distillate and heated to a temperature above that existing in the tower at the level at which it is introduced.

fractionating tower from which fractions having- 19. In a method for the fractionation of oil wherein it is introduced in a heated state into a fractionating tower from which'fractions having different boiling ranges are separately withdrawn, the steps comprising introducing wax-containing oil in a heated state into a rectifying tower at an intermediate level thereof .while withdrawing from the sideL of the tower at an intermediate level thereof a distillate containing wax rem'ovable by methods suitable to the removal of amorphous wax and withdrawing from the side of the tower at a level above said last mentioned level a distillate containing Wax that is too crystalline for removal by said last mentioned methods and too amorphous for removal by filter-pressing, heating at least a part of said last mentioned distillate to a temperature causing limited cracking thereof, and returning the heated oil to the interior of the tower at a level thereof at which the temperature is below that 0f theheated oil.

20. In a method for the fractionationv of oil wherein it is introduced in a heated state into a different boiling ranges are separately Withdrawn, the steps comprising introducing wax-containing oil in a heated state into a, rectifying tower at an intermediate level thereof while withdrawing from' the side of the tower at an intermediate level thereof a distillate containing wax removable by methods suitable to the removal of amorphous wax and withdrawing from the side of the tower at a level above said last mentioned level a distillate containing wax'that is too crystalline for removal by said last mentioned methods and too amorphous for removal by filter-pressing, heating at least a part of said last mentioned distillate to a temperature causing limited cracking thereof and returning the heated oil to the interior of the tower at a level below that at which the distillate containing amorphous wax is Withdrawn therefrom.

21. In a method for the fractionation of oil, the steps comprising introducing the oil in a heated state into a fractionating tower at an intermediate level thereof, maintaining a ow of reflux liquid downwardly in the tower, withdrawing from the tower fractions of the oil respectively having different boiling ranges and comprising a residue withdrawn below said level and a distillate withdrawn above `said level, maintaining sub-atmospheric pressure within said tower, and'introducing into the tower at a point not above the level thereof at which the highestboiling distillate is withdrawn a lhydrocarbon which is liquid at ordinary temperatures and is heated to a temperature above that in the tower at its point of introduction thereto said hydrocarbon having a nal boiling-point less than that of the oil introduced in a heated state to the tower.

22. The method of distilling a heavy hydrocarbon oil without any substantial cracking thereof which comprises heating the oil to a temperature below a normal cracking temperature, separately heating a lighter more refractory oil to a materially higher temperature which is above a normal `cracking temperature for the heavy oil, simultaneously flashing the heated oils into a vaporizing zone in such manner that additional heat is imparted from the lighter more refractory oil to the heavier oil to obtain a deeper cut in the heavier oil without subjecting the latter to a cracking temperature for sufficient time to effect any substantial cracking thereof, and fractionating the resultant vapors to separate a substantialaoeaaec ly uncracked heavy oil distillate from the vapors of the lighter more refractory oil.

23. The method of distilling a heavy hydrocarbon oil without any substantial cracking thereof which comprises heating the oil to a temperature below a normal cracking temperature, separately heating in substantially liquid phase a lighter more refractory oilto a materially higher temperature which is above a normal cracking temperature for the heavy oil, si-

multaneously flashing the heated oils into a vareduced crude oil in a confined stream to a temperature below a cracking temperature, separately heating a lighter more refractory voil in a confined stream and in substantially liquid phase to a materially higher temperature which is above a normal cracking temperature for the reduced crude oil, simultaneously ashing the heated oils into a vaporizing zone in such manner that additional heat is imparted from the lighter more refractory oil to the reduced crude oil to obtain a deeper cut of the lubricating fractions of the reduced crude oil without subjecting the latter to a cracking temperature for sufficient time to effect any substantial crackingthereof, fractionatingthe resultant vapors to separate a substantially uncracked lubricating oil distillate from the vapors of the lighter more refractory oil, and removing unvaporized asphaltic residuum from the vaporizing chamber. 25. A process of distilling hydrocarbon oils including heating a wax bearing hydrocarbon oil to distillation temperatures, dashing the heated oil into vapors and unvaporized oil in a fractionating zone, maintaining the fractionating zone under subatmospheric pressure, withdrawing the unvaporized oil from the process, fractionally condensing the vapors in the fractionating zone, withdrawing reflux condensate containing amorphous wax from the fractionating zone, heating a portion of the amorphous waxlbearing condensate to wax cracking and vaporizing temperatures in a stream separate lfrom the charge whereby a portion of the amorphous wax is converted into vapors containing wax which, upon condensation, will form wax I crystals having jipresslng qualities and reintroducing the vapors into the fractionating zone and withdrawing reflux condensate containing pressable wax from said zone.

26. A process as in claim 25 wherein vapors of the heated amorphous wax bearing condensate are introduced into the fractionating zone into contact with the unvaporized oil to strip the same of its more volatile constituents.

27. A process of distilling hydrocarbon oils including heating a wax bearing hydrocarbon oil to distillation temperatures, flashing the heated oil into'vapors and unvaporized oil in a fractionating zone. fractionally condensing the vapors in the fractionating zone, withdrawing reflux condensate containing amorphous wax from the fractionating zone, heating a portion of the amorphous wax bearing condensate to wax' cracking and vaporizing temperatures whereby a portion of .the amorphous wax is converted into vapors containing wax which, upon condensation, will form wax crystals having pressing qualities, separating the thus heated amorphous wax bearing condensate into vapors and unvaporized oil in a second fractionating zone, withdrawing unvaporized oil LEO D. JONES.

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