US2257283A

US2257283A - Solvent refining process

Info

Publication number: US2257283A
Application number: US169687A
Authority: US
Inventors: Alvah L Snow
Original assignee: Standard Oil Company of California
Current assignee: Standard Oil Company of California
Priority date: 1937-10-18
Filing date: 1937-10-18
Publication date: 1941-09-30
Anticipated expiration: 1958-09-30

Description

sepf`3lof94l- A. L.. sNow *l 2 2,257,283 i SOLVENT REFINING PROCESS Filed 0ST.. 1B., 1937 5 Sheets-Sheet 2 ruw" 'I v1/WMA UVa/7 L. Snow f/ ATTORNEY Patented Sept. 30, 1941 SOLVENT REFDIING PROCESS Alvah L. Snow, San Francisco, Calif., assignor to Standard Oil Company of California, San Francisco, Calif., a corporation of Delaware Application October 18, 1937, Serial No. 169.687

17 claims.

This invention relates to a process and apparatus for treating complex mixtures of carbon compounds with a selective solvent. More particularly, it involves a process of treating such complex mixtures with a liquid phase selective solvent at a temperature above the initial-boiling point, but below the dew point of the mixture being extracted to effect an efficient separation of the carbon compounds into fractions of diierent chemical types.

As is well known, normally liquid petroleum contains a complex mixture of hydrocarbons of different types. For example, certain natural petroleums are known to contain a minor perlcentage of aromatic hydrocarbons and a major proportion of paraflins or naphthenes having 5,`

6 and 7 carbon atoms in the naphthene ring. Because of close similarity in properties it has been very diflicult to separate these hydrocarbons according to their chemical types. Liquid phase extraction of petroleum oils with selective solvents at temperatures substantially below the initial boiling point of the oils constitutes one known method of refining petroleum and separating aromatic and/or naphthenic hydrocarbons from the remaining oil. Although such va process produces an extract containing relatively more aromatic and more naphthenic hydrocarbons and a raffinate relatively more parainic in nature", the separation is only qualitative and yields fractions containing substantial quantities of hydrocarbons which it is desired to eliminate from the particular fraction in question.

It is a. well accepted general rule in the art of selective solvent refining that an increase in the temperature of extraction, although it increases the yield of extract obtained, decreases the selectivity of a given solvent and yields an extract in which the separation between aromatics and/or naphthenes on the one hand and paraflins on the other hand is less sharp than obtained at lower temperatures. That is, as temperature of extraction is increased, the yield of raffinate is lowered and the extract contains more and more of the hydrocarbons which it is desired to keep in the raflinae. When the temperature of extraction is lowered, the yield of raffinate increases but it contains an increased amount of theI type of hydrocarbons (e. g. aromatic and/or naphthenic) which it is desired to retain in the extract. Accordingly it has heretofore been re garded as necessary to adopt a temperature intermediate the above mentioned high and low extremes such that a given solvent will yield a satisfactory quantity of raffinate and yet also give a reasonably eiiicient separation or refinement of the petroleum oils.

In the present process selective solvent extrac tion is carried out under conditions such that the selective solvent is above the initial boiling point but below the dew point of the stock being treated. Remarkable and unpredictable increase in the effectiveness of thel selective solvent extraction process is obtained by this high temperature operation. The process gives three phases in the extraction zone, namely, a vapor phase raffinate, a liquid phase raffinate, and `a liquid phase extract comprising the` selective solvent with its dissolved components. Thus a single stock can be separated into three components by a single extraction step.

Accordingly, an object of thednvention is to provide an improved and effective process and apparatus for treating complex mixtures of carlbon compounds with a selective solvent.

Another object is to' provide a process and apparatus for countercurrently contacting a normally liquid mixture of carbon compounds with a liquid phase selective solvent having a preferential solvent action for one class of the carbon compounds such as aromatics, the temperature of the solvent being above the initial boiling point of the mixture and below the dew point thereof under the conditions of extraction;

A further object is to provide a treating process for continuously separating petroleum into a. plurality of separate'portions comprising an extract fraction, a lower boiling vapor phase raffinate fraction, and a higher boiling liquid phase raffinate fraction.

Another object is to provide a process of selective solvent extraction capable of effecting separation o1 a substantially pure component from a mixture of carbon compounds having overlapping boiling ranges and a relatively Wide range between the boiling point of the lowest boiling compound and that of the highest boiling compound of said mixture.

A further object of the invention is to provide a process capable of separating substantially pure aromatic hydrocarbons from a petroleum fraction containing parainic compounds having boiling points which overlap with those of the arcmatics and also containing paraiinlc compounds having boiling points more than F. higher than the lowest boiling aromatic compound present. y

In the drawings, Figure l is a diagrammatic now sheet illustrating a single stage treating process embodying the principles of this invention. Figure 2 is a diagrammatic illustration of the path ofk flow of the various components through one form of treating column and Figure 3 illustrates the path of the solvent and liquid phase stock through a single plate of such a treating column. Figure 4 is a section on line IV--IV of Figure 3 and shows an arrangement of bubble caps and baille plates for producing the flow of the fluids as illustrated in Figures 2 and 3. Elgure 5 is a perspective view of a baille plate for the apparatus of Figure 4.

Briefly, the specific embodiment of this invention involves intimately contacting a liquid mixture of carbon compounds, such as petroleum hydrocarbons, with a higher boiling selective solvent maintained in liquid phase and at a temperature above the initial boiling point of the mixture being treated. In order that there may be a liquid raiiinate phase the solvent should also be at a temperature below the dew point of the stock in the treating zone. During the intimate contacting of the selective solvent and the stock being treated the solvent preferentially dissolves one type of carbon compounds, for instance aromatics, and this solution is separated to give one of the desired fractions. The more volatile less soluble compounds such as lower boiling parafnic hydrocarbons are converted to vapor phase and separated as such to give a second component from the treating process. The less volatile less soluble types of compounds, such as higher boiling paralinic hydrocarbons having a boiling point more than 60 F. above that of the lowest boiling dissolved aromatics, form a separate liquid Aphase and comprise the third component separated from the treating zone.

In the process as illustrated by the flow sheet of Figure l, the petroleum stock to be treated is passed from storage through valve controlled pipe I and heater 2 to treating column 3. The temperature of the stock is raised by heater 21 to a point above its initial boiling point and preferably below the dew point thereof. Temperatures above the dew point of the stock may be utilized where the temperature of the incoming'solvent is properly controlled so that the mean temperature in the column is below the dew point of the stock. Since the stock is heated to a temperature above its initial boiling point the mixture ladmitted to the treating column will contain both liquids and gases which are to be intimately contacted with the selective solvent admitted to the treating tower through valve controlled line 4. The temperature of the entering solvent is controlled by heater 5 or by cooler 6 in recirculating line 1. The preferred temperature of the solvent is from the boiling point of the stock to the dew point ofthe petroleum stock being treated. The solvent temperature may be higher than the dew point of the stock when it is necessary to compensate for low temperatures of the stock fed to the column. Likewise, the temperature of the solvent may be lower when the temperature of the incoming stock is higher than its dew point. In other words, the temperature of the stock and solvent should be correlated so that the temperature in the column is above the initial boiling point, but below the dew point of the mixture being extracted and at pressures existing in the column. y

Vapor phase compounds pass upwardly through the treating column and are extracted by the down-owing selective solvent. The vapor phase hydrocarbons pass out the top of the column through line 8, condenser 9 and valve controlled conduit III to storage. A portion of the condensed vapors may be returned as reux through pipe I I controlled by valve I2. Liquid phase hydrocarbons may ow either upwardly or downwardly or in both directions through extraction tower 3. If the selective solvent has a specific gravity greater than that of the compounds being extracted, then the liquid phase compounds will tend to oat on the selective solvent and the direction of ow of the solvent will be predominantly downward. This is the normal situation, although in some instances mixtures which have a specific gravity greater than that of the selective solvent being used will be extracted and the direction of flow of the solvent will be predominantly upward. In any event, the liquid phase stock can be separated from the selective solvent and is passed through the column in the proper direction. If the stock comprises the top of the two liquid phase layers then the inlet and outlet ports will have one posittion; if the stock is on the bottom of the two layers than the inlet and outlet ports will have an inverted position. The liquid phase stock which reaches the top of the treating column 3 is removed through conduit I3 to separator I4 where any entrained selective solvent is allowed to separate from the liquid phase stock. The separated solvent is returned to the extraction column through valve controlled line I5 and the separated vstock passed to storage through conduit I 6.

The selective solvent together with its dissolved compounds passes down through the tower and is removed from the bottom of the column through line I1, cooler I8, to separator I9. As previously pointed out, in some instances liquid phase raflinate hydrocarbons may now to the bottom ofth column and be removed through this same path to the separator I9. Such liquid phase compounds as are contained in admixture with the selective solvent and are separable therefrom will be removed in separator I9 and ow through line 20 either by way of valve 2| to the column or by way of valve 22 to storage or both as desired.

In the specific illustration given in this specication the petroleum fraction is lighter than the solvent and the direction of ow of the petroleum stock i`s therefore predominantly upward. However, because the separation between the two liquid phases is not absolutely complete a portion of the petroleum is carried down the column wtih the solvent by entrainment. The stock may therefore be said to flow both upwardly and downwardly in the tower. The amount of flow in each direction depends of course on the amountof entrainment. In order to obtain countercurrent extraction it is preferred to have the solvent flow down the tower and the stock ow up the tower in the oppostie direction. This is accomplished by removing liquid phase ranate from the top of the tower only. Stock which is entrained in the solvent then serves merely as a kind of reflux inasmuch as it in effect is merely recirculated Vdownwardly from an upper plate to a lower plate from which it .ultimately returns as liquid phase ramnate.

Cooler I8 ln line I'I also serves to reduce the temperature of the solvent in order to free some of the less soluble compounds which are actually dissolved in the solvent and thereby enable them to be mechanically separated in separator I9 and returned through line 20 and valve 2| to the treating column as a type of reux. The selective solvent together with the compounds which remain dissolved therein ls removed from the bottom of separator I84 through line 23 to still 2l.

an extracted dissolved compoundsfrom the bottom of treating column 3. The vaporized compounds from heater 26 pass through pipe 21 to the bottom of `treating column 3 `and serve as a source of heat for the treating tower. Solvent from vaporizer 26 is removed through line 28 to still 24 where the remaining dissolved compounds are vaporized and pass to storage in the manner previously described.

To insure intimate contacting in the extraction `column between themixture being treated and the liquid phase selective solvent, various means may be adopted. A tower filled with suitable packing of refractory earthenware, glass, etc., comprises one `effective form of apparatus for this purpose. When such an apparatus is utilized the vapor phase raiiinate istaken off as overhead and the liquid phase rafiinate is removed from the bottom of the tower as is also the selective solvent with its extract when the solvent is heavier than the mixture being treated. Another `form of apparatus which is adapted for treatment, according to the present invention, is a staged counter-flow in which aseries of contacting zones for the vapor phase hydrocarbons and liquid phase selective solvent are provided.

After thorough contacting in each of the zones the extract and rafnate are separated and pass to `succeeding contacting zones. It is apparent that hydrocarbons being extracted should ow in one direction through the series of contacting zones and the selective solvent in an opposite direction through the zones.

A column constructed in amanner analogous to an ordinary fractionating column of the bubble cap type is also an eiicient means of insuring effective contact between the vapor phase mixture, the liquid phase mixture, and the liquid phaseuextraxgting solvent.

and is as follows:

Solvent is admitted to the column at the top by line 4, passed across the rst bubble plate downwardly through an overflow pipe, back across the second bubble plate in the opposite direction from that in the first, through an overflow pipe to the third contacting plate, etc., as shown diagrammatically by the arrows in the solid lines of Figure 2. The stock being treated is admitted through line I as indicated by the dotted line arrows in this figure of the drawings. Since the stock comprises a liquid phase portion and a `vapor phase portion these two fractions follow different paths. The vapor phase portion passes upwardly through the bubble caps in the same manner as in an ordinaryfractionating column and as shown by the dotted line arrows in the center of column of Figure 2. The liquid phase stock `flows horizontally across the plates countercurrently to the selective solvent and vertlcally through the pipes outside of the column from `one plate to the other as shown by the dotted line arrows in Figure 2. Extract is removed from the bottom of the tower through line I1, as shown, and liquid phase raflinate from the top of the tower through line I3. A portion In such a preferred form of 'apparatus the path of owis shown Y' diagrammatically in Figure 2 of the drawings,

- U-shaped as shown in order of the extract is also removed from the bottom of the tower to a vaporizer and the vapors returned to line 21.

being thoroughly extracted with the selective solvent. l

A form of extraction column especially adapted for use in the presentprocess is shown in Figures 3 and 4. The column is provided with a series of bubble caps 30 and a series of down-spouts 3|. Oriices 32 'in down-spouts 3l plate. The upper end of each of the down-spouts is closed to prevent entry of the stock being treated which floats on the solvent layer. Int-he lower end of the down-spout a section is cut out as shown at 33 in order to direct the selective solvent in the general direction desired.

Lift

conduits

34 and 34 are provided for conveying liquid phase ranate from a lower bubble plate to an upper bubble plate. The inlets, that is, the lower ends of the lift conduits, are at the top of the` level at which it is desired to keep the liquid phase railinate layer. 'Ihe outlet ends of the lift conduits are preferably below the selective solvent level so that the liquid phase raflinate will be intimately contacted with `the selective solvent as it rises therethrough.

Two different types of means have been illustrated for causing the liquid phase raiinate to flow upwardly through the lift conduits. The rst is a centrifugal pump 35 and the second a gas lift arrangement 36. When a gas lift is utilized various inert gases may be used. e. g. methane, ethane, propane, a mixture thereof such as obtained in petroleum refinery gases, nitrogen or steam where condensed water does not interfere with the extraction process or render the selective solvent useless by reason of dilution. In those cases where Water is miscible with the solvent and where the selective solvent is relatively non-selective at the high temperatures used in this process, steam will be found particularly desirable since the presence of water or water vvapor decreases the miscibility of the solvent and oil. Phenol is an example of a selective solvent which is relatively non-selective at high temperatures and which can be rendered more selective by the addition of water by this or other methods. Another gas which may be utilized in the gas lift'comprises the raffinate vapors themselves which may be removed from the top of the extraction tower. compressed and introduced into the gas lift device.

Pipe 31 controlled by valve 38 is provided for introducing the lifting gas into the liquid in lift conduit 34. The bottom end of conduit 34 is that the liquid phase raffinate will flow into level above the gas inlet.. The upper end of conduit 34 comprises a goose-neck portion which serves simultaneously as a. gas trap and siphonbreaker. The lifting gas accumulates in the top of the U and is removed through line 40 in order to prevent formation of a gaspocket. Also line 40 acts as a breather to prevent siphoning of fluid from the upper plate through inlet 4| downwardly to the lower plate. l

The level of the solvent and liquid raffinate phase relative to the various inlet and outlet conduits is illustrated at of Figure 4. The lower layer `as represented in this ligure is selective solvent and the upper layer of liquid is the rafllnate being extracted.

Vapor phase rainatepasses from the top` of the tower through line ltiafter serve to admit? selective solvent to the l down-spout throl-Igl'fl` which the solvent passes to the next lower bubble the U and have an upperV the bottom bubble plate Figure 3 shows the arrangement of parts and path of liquid flow on a single bubble plate. Three bubble caps 30 are provided and are separated by a bafiie plate having a cylindrical portion 44 surrounding the center bubble cap and wing portions 45 extending from the cylindrical portion to the sides of the column. Slots 41 (see Figure 5) are provided in the top edge of the baille to direct the upper liquid phase through the desired path of flow. Likewise, slots 48 are placed in the bottom edge of the baffle to cause the selective solvent to flow around the several bubble caps as shown by the solid line arrows of Figure 3. Specifically, the selective solvent fiows from overflow pipe 3Ial around and under the first bubble cap (top of Figure 3) through slot 48 into the cylindrical portion of the baffle around-the center bubble cap and out through the second of slots 48 around and under the third bubble cap to outlet overflow pipe SIb. As indicated by the dotted line arrows the upper layer liquid phase rafnate flows countercurrent- 1y to the selective solvent and passes from inlet pipe 4l over and around the lower' bubble cap through slot 4l across the center bubble cap out second slot 41 and around the third bubble cap to outlet conduit 42. The wings 45 and higher portions 46 'of the baille plate serve to prevent the liquid phase rafiinate from flowing directly across the bubble plate from inlet to outlet. The vapor phase rafnate passing through the bubble caps is extracted by the lower solvent layer and simultaneously the vapors act as an efficient means for agitating the two liquid phases passing across the bubble plate. Thus intimate contact between all three phases is effected in a simple and efficient manner.

The eiiiciency of separation of the two liquid phases on each ofthe bubble plates is subject to control by design of the'size of the column, gas rates through the bubble caps, rate of flow of the liquid phases, etc. However, it should be noted that perfect separation is not absolutely essential since entrainment of either solvent in the stock or stock in the solvent, or both, merely acts as a reflux in that it feeds back a portion of the liquid entrained to the bubble plate from which it came. This entrainment of course decreases the ne't rate of flow through the treating zone, but up to a certain degree may be found to increase the efficiency of extraction as is the case with any reflux.

In its broad aspects the present invention isI applicable to a great number of mixtures of chemical compounds which are difficult to separate because of similarity of boiling points, solu` bility characteristics, or because of formation of constant boiling mixtures. For example, the selective solvent extraction process may be applied to' mixtures of compounds such as phenols, aromatics, sulfur compounds, olefines, naphthenes It will be necessary of course to provide at least one extraction zone for each three components or groups of components to be separated. However, the process at present is regarded as having its greatest utility for the extraction of substantially pure aromatic hydrocarbons from extremely complex mixtures of aromatics, naphthenes or paraffins which occur in natural gasolines of relatively Wide boiling range such as 360 F. end point distillates.

Repeated reference has been made throughout this specification to the use of selective solvents in the process. This generic term is used to define a solvent which has greater solvent power for at least one component of a multi component system than it has for other components of that system. Stated conversely, the term selective solvent designates a solvent which has less tendency to dissolve one compoand paraflins, which commonly occur in petroleum distillates. These mixtures can be passed through a single extraction zone or a series of extraction zones under conditions of temperature and pressure such that the mixture is separated into different components, one component or group of components being removed from the bottom of each extraction zone as an extract phase, the more volatile component or group of components being removed from the top of the extraction zone as a vapor phase overhead and the less volatile less soluble component or group of components being removed from the top of the extraction zone as a liquid phase rainate.

nent of a mixture than other components thereof. The greater the differential in solvent power of a selective solvent for different components of the mixture, the greater is its selectivity and the more efficient it will be in the extraction of the component for which it has the greatest solvent power.

A selective solvent useful for the present process should be highly selective and should have a boiling point well above the dew point of the stock to be treated. The selective solvent must also be of incomplete miscibility with the stock being treated -at the temperature of extraction. In other words, the suitability of a known selective solvent for the process of this invention can be primarily determined by two physical characteristics, namely, boiling point and miscibility temperature. Since the process is operated at temperatures above the initial boiling point of the stock, but below its dew point, the temperature of complete miscibility of solvent and stock must be above the dew point of the stock under the conditions of extraction. This property can be readily ascertained by a simple miscibility test at elevated temperature. It should of course be recognized that by the terms dew point and boiling point used above, one means the dew point or boiling point in the presence of the selective solvents and under the conditions of extraction. For example, vacuum may be utilized on the extraction tower and thereby permit use of a selective solvent which would be miscible with thestock being treated at its ordinary initial boiling point, but which is of incomplete miscibility with the stock at the initial boiling point of the stock and the dew point of the stock under the conditions of extraction, namely, high vacuum. The use of vacuum is therefore contemplated as falling within the broad scope of the present invention.

The following compounds are illustrative of high boiling selective solvents which have high temperatures of miscibility with most petroleum stocks and which are therefore 'operative for separating aromatics such as benzene or toluene from natural petroleum distillates containing the same: triethylene glycol, diethylene glycol, acetamide, monoacetin, diethanolamine, diaminopropanol. In general polar compounds selected from the group consisting of hydroxy benzenes, amides, chlorinated hydrocarbons and esters of polycarboxylic acids which have boiling points and solubility characteristics such as above discussed are contemplated as falling within the broad scope of the invention. The solvents selected from this group preferably should have a `the stock. 'I'he entire `tion with the usual normally liquid petroleum `fractions.

Those selective solvants whicnfare misclble withthe mixture of compounds being extracted `can be utilized in some instances `by adding Vto the solvent a diluent which is miscible with the solvent, but immiscible with` Ithe` stockr being` treated.` For-example, inthe treatment of very,V

volatile stocks, phenol` may have a suitable boil` ing point, but have a miscibility temperature below the dew point of thestock. In such instances `the phenol may be diluted withwater to render it operative in the` process of this invention.

Other diluents which are characteristically im- `miscible with hydrocarbons orpetroleum fractions and which are often miscibflewith the solvents are carbon compounds having a largenumber of hydroxy groups. Glycerol is an example of a poly-hydroxy alcohol having high miscibility l temperatures with petroleum fractions and which is operative as a `diluentin the above suggested combinations.

Obviously, specific conditions of, operation such I as temperature, pressure, relative solvent to stock volumes, and proportion of vaporlphase railinate to liquid phase railinate will vary with the particular mixture being treated and with the selective solvent used. As previously pointed out, a

critical feature of the invention comprises operation oi' the process at a temperature above the initial boiling point, but below the dew point of t process "will usually be carried `out at atmospheric pressures,` although atmospheric desirable in tional jcost pressures will be found sunlclently some instances to justify the addioccasioned by` operation under vac- It will be observed that the present `process is fundamentally diierent from ordinary selective solvent extraction processes in that it operates at temperatures above the boiling point of the l stockbeing treated. Theprocess is also fundamentally different from" ordinary distillation processes in that three phases are present ancil three` components are from the treating zone.

'I'he following principal advantages oi' the invention will be readily apparent. Mixtures of paraliins, aromatica, etc. having much wider boiling `ranges can be separated chemical types by the process o1' this invention. Heretofore it has been 'possible to separate` pure aromatics from parafllns by treatment of relatively narrow fractions in a large number of carei'ully controlled fractionating steps. The present invention avoids such complexmulti-stage operations. By utilizing the present process it is unnecessary `to operate ai; temperatures above the end point of the stock since the high boiling, less soluble components, e. g., paraiiins, are not vaporized as isthe case with ordinary distillation processes carried out in the presence of a solvent. By operating at these lowertemperatures the eftlciency of extraction oi.' the more soluble components, e. g. aromatics, is increased since there is less tendency to distil them outof the solvent.

-The process herein` described effectively separatesthe less soluble paralnic compounds having boiling points nearest those of the arornatics.` Normally-these very similar components are the most dinicult to separate and cause the greatest `super-atmospheric pressures maybe used. Subsaid treating difliculties inf distillation operations. After treatment by the present process any paraflinlc constituents which happen toremain dissolved in the extract with the aromatics are found to have a boiling point; suiii'ciently different from the aromatics (as much as 60 F. or more)` that they can readily be removed by ordinary distillation andfractionation after separation from the solvent.

The actual distillation operation is more eilicient by reason of the fa'ct that the parallins remain in a separate liquid phase than is the case 'Where theparailins are dissolved in a solvent. This is believed to result from the -fact that a,

greater diierentlal in boiling points is produced by the selective `solvent when only one compol nent is dissolved in the solvent than when the entire mixture lsdis'solved therein. I'his greater differential in boiling points in turn increases the eiliciency `of `separation by the fractionation process. Other numerous advantages will be apparent to those skilled in the art.

While the character of this invention has been described in detail this has been done by way of t illustration `only 'and with the intention `that no limitation should be imposed `upon theinvention thereby. Likewise,the drawings are to be regarded as diagrammatical, no attempt having been made to show all the necessary details such as pumps, valves, `pressure control devices and the like. It will be apparent to those skilled in the art that numerous `modincations and variations may be adopted in the apparatus and method of the invention which is of thescope of the appended claims. i

I claim: l. A process oi. separating a multi-component mixture of` carbon compounds into more than two components which comprisespassing said mixture through a treating zone, passing through jzone a selective solvent which remains in liquid phase and is of incomplete miscibility with said mixture, converting a portion only of said multi-component mixture to vapor phase whereby the solvent phase, a vapor phase raiiinate and a liquid phase raiilnate are simulsimultaneously separated taneously present in said zone, passing said vapor phase components through said treating zone, intimately `contacting said three phases while passing said liquid phase raillnate in a direction Xopposite to that of said liquid solvent phase to according to selectively dissolve one type of carbon compound in said solvent, removing the treated vapor phase, and separating the two liquid phases to obtain fractions from said treating zone.

2. A process of separating aromatic hydrocarbcns from mixtures containing aromatic and non-aromatic carboncompounds jof similar boiling range which comprises passingsaid mixture through a treating zone, passing through said `treating zone a liquid phase selective solvent for said aromatic compounds, which solvent is of incomplete miscibility with said mixture, cont verting a portion only of the mixture oi carbon compounds to vapor phase whereby a solvent phase, a vapor phase raillnate and a liquid phase ramnate are simultaneously present in said zone, passing said vapor phase components -through said treating zone.. intimately contacting said three phases and passing said liquid phase railinate countercurrently to said solvent phase to selectively dissolve aromatic compounds in `said solvent. and separately removing the vapor phase,

phase selective solvent which is of incompletef miscibility with said mixtureat the dew point thereof, maintaining the temperature in lthe treating zone abovey the initial boiling .point but belowv the dew point ofthe mixture under the conditionsofextraction whereby a vapor phase raffinate, a liquid phase raffinate and a liquid phase extract are simultaneously presentrin said zone, intimately contacting the said three phases whileflowing said liquid phase rainate through said-treating zone in one direction and flowing said liquid phase extract through said treating zonein the opposite. direction, and separately removing the treatedvapor phase, the liquid raffinate 'phase and the liquid extract phase from thetreating zone. l f

4. A process of separating. aromaticY hydro--Y carbons from petroleum distillates which comprises extracting said distillate withv a liquid phase vselective solvent at a temperature above thev initial boiling point but below the dew point of said distillate and under such conditions of extraction that a vapor phase raffinate, a liquid phase raflinate, and a liquid phase extractare f simultaneously present, said selective solvent being in liquid phase andA of incomplete miscibility with the distillate at the temperature of extraction, passing said liquid phase raiiinate countercurrently with respect to said liquidphase extract; andl separating three different phases comprising-a vaporphaserafiinate, a liquid phase raffinate and a liquid phase extract. Y

5. A process as defined in claim 4, in which the selective solvent is an hydroxyether having a boiling point above approximately 300 F.

'6; A process asin claim 4, in which the selective solvent is a poly-ethylene glycol.

'7. A' process of treating a normally liquid petroleum fraction containing hydrocarbons of dew point thereof into said fractionating vcolumn at av point above that at which said mixture is admitted,v maintaining the'temperature in said columnvabove th'e'initial boilingpoint but belowv the dew point of said mixture and under such conditions that a vapor phase raffinate, a liquid phasefraihnate, and a liquid phase extract are simultaneously present, passing said liquid phase v,raffinate counter/currently to said liquid phase extract, and ycontinuously removing vapor phase raiiinate and liquid phase raiiinate from the top of said column and continuously removing liquid phase extract from the lower portion of said fractionating column.

9. A process as dened'in claim 8, further .characterized in thatentrained railinate is separated from the liquid phase extract and returned to the fractionating column. 10. A process as defined in claim 8, further characterized in that entrained selective solvent is separated from the liquid phase raftiinate and returned to the fractionating column.

l1. A process of treating a multi-phase mixture of carbon compounds having more than one liquid phase which comprises, forming a multiphase system having heavier and lighter liquid phases by only partiallydissolving said mixture in a selective solvent, separating said liquid phases into a lighter and a heavier portion, passing the lighter portion through an extraction system in onedirection', passing the heavier portion through said extraction system in a different direction, partially vaporizing undissolved carbon compounds of said mixture without substantial vaporization of said solvent and contacting the vapors with at least one of said liquid phases different from said partially vaporized undissolved liquid phase.

l2. A process of separating according to chemical type a multi-component mixture of carbon compounds which comprises passing said mixture through a selective solvent extraction zone, forming an undissolved vapor phase fraction and an the aromatic and parainic types and in which the boiling point ofthe highest boiling paraflinic hydrocarbon is more than approximately 60 F. above'the boiling point of the lowest boilingaromatic vhydrocarbon contained therein, which comprisesv passing said `normally -liquid petroleum fraction throughl a treating zone, passing through said treatingzone a liquidphase selectivesolvent which is of incomplete miscibility with theA petroleum fraction-at the'dew point thereof,

maintaining the temperature `in the treating zonev above the initial boiling point but below the dew point'of 'the fraction underthe conditions ,of extraction whereby. a vapor phase raffinate, a liquid phase raffinate and a liquid'phase extract are simultaneously present in the zone, intimately' contacting said three phases,lpassing` said liquid phase rafiinatecountercurrently to said liquid"l phase.l extract,. and separately removing the ducing saidmixture intofa 'frictionating column. ata point intermediate the ends thereof, c'bntinu---A ously introducing a high boiling selective solventk of incomplete miscibility with the mixture at the undissolved liquid phase fraction in said zone, passing said undissolved fractions in-said zone countercurrently to a liquid phase selective solvent having a boiling9 point substantially above the endpoint of said mixture of carbon compounds, contacting said undissolved phases with said selective solvent, withdrawing a liquid phase selective solvent extract from said extraction zone at one point, withdrawing a liquid phase radinate from said extraction zone at a second point remote from said rs't point, maintaining the temperature in said zone at said second point below thedew point but above the initial boiling point of said mixture of carbon compounds, and maintaining said selective solvent incompletely miscible with said mixture of carbon compounds substantially throughout the extraction zone.

y 13. A process of separating according to chemical type a multi-component mixture of carbon compounds which'A comprises passing said mixture through a selective solvent extraction zone, forming an undissolved vapor phase fraction and an undissolved liquid phase rfraction in said zone, passing` said undissolved fractions in said zone countercurr'entlya to a liquid phase selective solvent having a oiling point substantially above the end point of said mixture of. carbon compounds, contacting said undissolved phases with said selective solvent, withdrawing a liquid phase selective solvent extract from said extraction zone at onepoint, withdrawing a liquidphase railinate from said extraction zone lat a second point remotefrom said rst point, maintaining the temperature in said zone at said second point below the dew point but above the initial boiling point of said mixture of carbon compounds, and maintaining said selective solvent incompletely miscible with said mixture of carbon compounds substantially throughout the extraction zone byadding to `said solvent a diluent immiscible with said mixl lective solvent having a boiling point substantially above the end point of said mixture of carbon compounds, contacting `said undissolved phases with said selective solvent, withdrawing a liquid phase selective solvent extract from said extraction zone at one point, withdrawing a liquid phase rainate from said extraction zone at a second point remote from said first point, maintaining 1 the temperature in said zone at said second point low the dew point but above the initial boiling point of said mixture of carbon compounds, and

maintaining said selective solvent incompletely i miscible with said mixture of carbon compounds substantially throughout the extraction zone.

15. A process as defined in claim 14 in which the selective solvent is an hydroxy ether having a boiling point above approximately 300 F.

416. A process f separatingaccording to chemical type a multi-component mixture of carbon compounds which comprises passing said mixture through a selective solvent extraction zone, forming an undissolved vapor phase fraction and an undissolved liquid phase fraction in said zone, passing said undissolved fractions in said zone countercurrently to a liquid phase selective solvent comprising a liquid phase hydroxy benzene having a boiling point substantially above the end point of said mixture of said carbon compounds,

contacting said undissolved phases with said selective solvent, withdrawing the liquid phase hydroxy benzene together with its dissolved carbon compounds from said zone at one point, withdrawing a liquid phase raffinate from said extraction zone at a second point remote from said first point, maintaining the temperature in said zone at said second point below` the dew point but above the initial boiling point of said mixture of carbon compounds, and maintaining said selec-` tive solvent incompletely miscible with said mixture of carbon compounds substantially throughout the extraction zone.

1'?. A process of separating according to chemical type a multi-component mixture of carbon compounds which comprises passing said mixture through a selective solvent extraction zone, forming an undissolved vapor phase fraction and an undissolved liquid phase fraction in said zone, passing said undissolved fractions in said zone vcountercurrently to a liquid phase selective solvent comprising a liquid phase ester of a polycarboxylic acid having a boiling point substantially above the end point of said mixture of said carbon compounds, contacting said undissolved phases with said selective solvent, withdrawing the liquid phase ester of a polycarboxylic acid together `with its dissolved carbon compounds from said zone at one point, withdrawing a liquid phase raiiinate from said extraction zone at a second point remote from said first point, maintaining the temperature in s aid zone at said second point below the dew point butabove the initial boiling point of said mixture of carbon compounds, and maintaining said selective solvent incompletely miscible with said mixture of carbon compounds substantially throughout the extraction zone. ALVAH L. SNOW.