US2243873A - Method for selective solvent extraction - Google Patents

Description

June 3, 1941.

A. L wwwl METHOD FOR SELECTIVE SOLVENT EXTRACTION Filed Feb.' '7, 1938 "2 sheets-sheet 1 5 QW www @im n, r n @vg wv# ww Aw mi# y ,1 @Sm w SESS ATTORNEY June 3, `1941. A. l. LYVMAN A2,243,873

METHOD FOR SELEGTIVE .SOT-:VENT EXTRACTION Filed Feb. 7, 1938 2 Sheets-Sheet 2 Arf/ufr L yman ay 7 l ATZURNEY Patented June, 3, 1941 i UNITED STATE Amm L. Lm Berkeley.' cam., mimmo Standard il` 'Company ot (lalifornia, San 4 Franc isoo, Calif., a corporation of Delaware lApplication February 7; 19.38, Serial No. 189.162

' uo claims. (ci. ssa-sur This invention relates to a process ofv treating complex mixtures oi chemical compounds with selective solvents to remove one or more of said ly, it involves a process and apparatus for extracting aromatic hydrocarbons from petroleum jhydrocarbon iractions oi relatively wide boiling range.

It is well known that normally liquid petroleum contains a complex mixture oi hydrocarbons oi several diierent chemical types. For example. certain natural petroleum gasolines are known to contain a minor percentage of aromatic hydro-Y carbons and a major proportion oi' pax-omnes and naphthenes. Because of the close similarity in 'compounds i'rom the mixture. More particular` process utilizing both liquid phase' and vapor phase selective solvent extraction. By ilrat ex-A treatingv the complex mixture to be treated in physical properties ci these compounds. it has Y been very diilicult to separate them according to A their chemical types.

Liquid phase extraction oi petroleum oils with selective solvents at temperatures substantially b'elow the temperature oi miscibility of the voil and solvent constitutesone known method oi `separating petroleum into paraillnic and nonparaiilnic fractions. Although such processes will produce an extract containing relatively more aromatic and/orvnaphthenic hydrocarbons and a ramnate otpredomlnantly paramnic character.

the separation is only qualitative in nature. This is illustratedby the i'act that in the art of selective solvent refining it is a well accepted general rule that an increase in the temperature oi extraction decreases the'selectivity oiia given-solvent. Although extraction at high temperatures may remove substantiallyall aromatica from a petroleum fraction, the high temperature del feats its own purposev in this respect because it also causes the solvent to dissolve a greater portion of the parailines and/or naphthenes. When the extraction is carried out at low temperatures with a highly selective solvent. a highly aromatic extract may be obtained (even then, the extract will ordinarily contain substantial proportions or nonaromatic hydrocarbons) but this type of tion of constant boiling mixtures. After a long series oi complicated steps.` substantially pure aromatlcs have been separated from petroleum in the laboratory by distillation and fractionation. Even with'the extreme care possible in the laboratory the yields' have vbeen extremely small because oi losses occasioned by the limitations inherent in ordinary distillation and fractionation p i vzw u' Th p'esent invention involves a combination liquid'plmse. and then iractionating and finally subjecting the fractions to selective solvent; ex' traction in vapor phase, substantially pure compounds can be separated from extremelylcomplex mixtures in a simple and emcient manner.

Accordingly. an object o! the, present invention is to provide an eii'ective and improved process oi v'treating complex mixtures of chemical compounds with selective solvents.

" Another objectl of the invention is' t0 Provide an improved method tor extracting aromatic hvphase selective solvent with petroleum, iirst in process is very ineilicient because a large propori tion of the aromatics are not removed and re- ,..maln in the remonte.

Accordingly, it has heretofore been regarded as necessary to adopt a temperature intermediate the above mentioned highV and low extremos so that a given solvent will yield a `,satlsieatery quantity ol extract or remate and yet also sive a reasonably eclent qualitative separation or refinement of the petroleum fraction.

lt has also been proposed to separate petroleum hydrocarbon mixtures into different types 'of chemical compounds by distillation and fraction-a ation processes. Experience has shown that such separations are extremely diillcult because of the similarity boiling point of the various dierent drocarbons from petroleum fractions.

A further object is the provision oi a combination process for contacting a high boiling liquid liquid phase and then at a temperature above the boiling'point of the petroleum fraction.

' A.lin `additional object oi the invention is to provide a process capable of producing substantially pure aromatic hydrocarbons from petroleum fractions of relatively wideboiling range.'

Figure I is a diagrammatic ow sheet illustrating a method and apparatus embodying the principles of this invention.

Figure lI is a now sheet illustrating an alternative modied species or' method and. apparatus i'or carrying out the selective solvent extraction process of this invention.

Figure III illustrates a simple and eectlve alle paratus for treatment ol less complex m of chemical compounds according to the ples herein disclosed.

Briefly descri the process vlnvlllves tres.

a petroleum fraction such as 360 lll. and point natural gasoline in liquid phase with a selective solvent ha a boiling point suhstauhallyabove lthe enel point oi the gasolineo vapo Y the dissolved carbone from the select-im ksolvent directly into a lractlonating coin, seraboiling selective solvent at a temperature omvethe boiling point ortho hydrooarbonflrootloh.

types ol hydrocarbons and because of the forma to By utilimns this speolo combinations single stage are'separatedv from the selective solvent without substantial vaporization of the solvent and are simultaneously converted to vapor phase for fractionation or for treatment in vapor phase with a selective solvent or for both fractionation and vapor phase extraction.

Furthermore', by extracting the distillate with i a'high boiling selective solvent prior to the fractionation and vapor phase extraction stages, `the separation of pure aromatica is facilitated in that a considerable portion of the paramnes is initially eliminated without undue loss of aromatica. This in turn minimizes formation of constant boiling mixtures and facilitates fractionation without loss of aromatics in rejected fractions.

It should also be noted that there is a considerable saving in heat of vaporization since only the extract is vaporized, thereby eliminating the necessity of vaporizing either the selective solvent which is present in large proportions or theparaflines which were present in the originalhydrocarbon mixture. 'l-'heaprocess also permits the use of solvent to stock ratios which are normally considered excessive in-other types of processes; for example, the ratio oi volume of solvent to volume of-stock can easily be as high as tol,

or even more, without undue-difculties 'or heat losses since the selective solvent remains in the liquid phase throughout the process.

The fact that the liquid phase extraction initially eliminates large quantities of paraillnes and/or naphthenes and permits more elhcient fractionation of the extract in turn enhances the eniciency of the vapor phase solvent extraction stage. This is true because it has been found that for most eicient operation the vapor phase 'ex' traction requires just such a petroleum cut relationating column '8- 'Relatively narrow boiling range sidecuts are removed from the fractionating column through conduits 9, l0 and Il. For examp1e,.a benzene cut having a boiling range of from 75 to 85 C. can be withdrawn through line il, a toluene cut boiling from 105 to 15 C. through line Ill, and a xylene cut boiling from 135 ,to 150 C. through line H. It is to be understood that the process of this invention is applicable to fractions other than these just enumerated vand that the invention in its broad aspects is not limited to extraction lof benzene, toluene and xylene cuts.

The more volatile portion of the extract in fractionatlngcolumn 8 passes from the top of the column through line I2,vcondenser I3 and discharge line Il to storage. Valve controlled reflux line I5 is also provided for returning a portion of the condensate to the top of the fractionating column. The hydrocarbon fraction passing through discharge line i4 will vary in composition with the stock treated and willcomprise predominantly non-aromatic volatile hydrocarbons which are dissolved or entrained in the selective solvent during the liquid phase' "extraction step. 30l

kHigh boiling aromatics, naphthenes and in some cases `unsaturatesare removed from the bottom of extraction towe'r 8 through discharge line It. This fraction may be further treated and reilned for use as a high boiling thinner or solvent.

Each of the side cuts is next subjected to a vapor phase selective solvent extraction treat# ment. l. 'Ihis f type of process is disclosed and claimed per se in a copending application of Cope et al. Serial No. 159,522, iiled August 17, 1937, and assigned to Standard Oil Company of California. Although it is to be understood that the modiiications and variations disclosed' in this that the various stages of the process cooperateVr with each other to produce a new and improved combination method for treating petroleum hydrocarbon mixtures with selective solvents.

The followingV detailed description of the specic features of the apparatus and process of the invention will serve to further clarify the principles involved.

In the form of apparatus shown diagrammatically in Figure 1 distillate to be treated is admitted through inlet line l into the bottom of liquid phase extraction tower and is there treatn1 ed with a suitable high boiling selective solvent. The ratlinate from this extraction ilows: i'rorn the top of tower 2 through conduit 3 to storage. The selective solvent `for extracting the aromatic constituents of the distillate is introduced into the top .of tower 2 from pipe 8 and] ows downwardly through the extraction column countercurrently to the upwardly flowing distillate. 'Ihe preferred procedure is to regulate the height and relative vproportions ot the two iluidsl distillate and selective solvent, lso that the distillate will be the continuous phase through a major portion of the treating-zone. The solvent will -then pass downwardly as a discontinuous phase 'and after extraction will coalesce at the bottom of the tower to again iorm a continuous phase tobe removed through line 5 and heat exchanger 6 to vaporizer 1. Y

Since the selective solvent used is a, high boiling'solvent having an initial boiling point above diate the ends of the column. The fraction may be either in liquid or vaporphase as it enters the extraction zone, but if intliquid phase the temperature should be at approximately the boiling point of the cut.' When the side stream ilowsdirectly from the fractionating column to the extraction column the temperature will be at the proper point.

The aromatic hydrocarbon out is intimately contacted with a high boiling selective solvent in the extraction tower. The solvent is admitted at the top of the tower and flows downwardly through tower il countercurrently to the rising hydrocarbon vapors. To insure intimate contacting in the extraction column between the hydrocarbonsl and selective solvent various means may be adopted. A tower illled with suitable packing of refractory earthenwre. glass. etc.. comprises one eilective iorm of apparatus for this purpose. A column'constructed in the .controlled line 28.

same manner as an ordinary fractionating column of the bubble cap type is also an emcient type of apparatus for intimately contacting the hydrocarbon vapors and selective solvent liquid.

After extraction in tower Il the raffinate vapors pass from the top of the tower through line I8 and condenser I9 to storage. A portion of the condensate can be returned tothe top of the extraction tower as reiiux through valve Downwardly. ilowing solvent, together with the dissolved hydrocarbons, is removed from the extractioncolumn through conduit 2| to still 22 where the dissolved aromatic hydrocarbon, benzene in the particular illustration selected, is distilled from the solvent and passed through pipe 23 and suitable condensers (not shown) to storage.

There are several diiferent ways in which the selective solvent may be manipulated in the vapor phase extraction process. The iirst is to, recirculate solvent in extraction unit Ii independentvdirectly to the top of extractor Il. Only a portion of the selective solvent flows from the bottom of tower I1 through open valve 21 to heater 28. The heavier fractions of the aromatic cut tend to concentrate in the bottom of tower I1 and hence in heater 28 where they may be partially vaporized, together with the more volatile hydrocarbons, returned to thelower portion of the tower through conduit 29 and serve to maintain the temperature in the bottom of the tower at the correct point. The selective solvent from heater 28 then passes through pipe 38 to the top of the extraction tower operating on the next higher' boiling hydrocarbon fraction. This solfrom extraction tower I1 which may have been lly of the other units by passing the selective and that the solvent may also flow by the iollowing route: From vaporizer 1 through line 93 (valves 38 and 40 being closed), valve 34, cooling coil 35. line 32, outlet 2|, still 22, line 24, Valve 25 (valve 24' being closed), cooling coil 3i to extraction tower 38, outlet 4Z, still 43, line 44, valve 45 (valve 46 being closed in this species of operation), and cooling coil 48' to extractor 3l. A portion of the solvent also iiows from the bottom of extraction tower I'I through valve 2l, heater 28, line 30 and cooler 39 to extractor 36.A Likewise; a portion of the solvent passes from the bottom of extractor 38 through conduit 4l, vaporizer 48, line 49 and cooling coil 48 to extraction column 31. As' was the case with extractor II, the more volatile hydrocarbons in the solvent from the bottom of column 36 are returned from vaporizerA 48 to the column through line 59. Similarly, hydrocarbons are vaporized in heater 56 and returned to column Sil through line 59.

Solvent from the last extraction tower 3i flows through line 5I to still 52 (where the extracted hydrocarbons are vaporized and pass through line 55 through suitable condensers to storage), conduit 53, heat exchanger 6, cooler Sil and conduit 4 to the top of liquid phase extraction tower 2. Solvent containing Athe less volatile hydrocarbons flows from the bottom of tower 3l to vaporizer 58, still 51 and line 58 to return conduit 53. The heavy ends are stripped from the solvent in still 51 and pass to storage through vent carries with it the less volatile compounds present in the cut taken from fractionating column 8 through line 9. In some instances the cuts taken from lines 9, I8 and II are each passed through small secondary stills to remove the final traces of heavy ends which may be present.

directly from still 22 through line 24, valve 25 (valve 24' being closed) and cooling coil 3l to the top of the extraction tower operating on the next higher boiling hydrocarbon fraction. When this species of operation is adopted itis often desirable to return the more, volatile overhead from the last mentioned extraction ltower to tower I1 as will be subsequently described in more detail.

Fresh solvent is admitted to tower I1 through inlet pipe 32.l This solvent may be obtained from the liquid phase extraction vaporizer 1 by way of line 33, valve 34 and cooling coil 35. It is usually found desirable to provide an independent solvent supply for each of the extraction towers. 'Ihis may be done by splitting the solvent from vaporizer 1 into-three portions, the rst flowing to extractor I1 as above described, the second to extractor 38 through valve 38 and cooling coil 38, and the third to extractor 31 through valve 48 and cooling coil 4I. However, it should be noted that provision has been made in the apparatus illustrated in Figure I for passing the solvent through the extractors serially 5o traction unit I1 comprises passing the solvent I pipe 83.

When the three vapor phase extraction stages are operated independently and the solvent re circulated in each rather than passed from one to the other serially, solvent in column 3@ ilows through line 44, valve 43 and cooling coil di to the top of column 36. Likewise, in column 3l solvent may be recirculated by passing a portion of the solvent from return line 53 through valve 62 to cooler 4I and the top ofthe column.

If all of the solvent from stills 22 and i3 is recirculated to extracting columns Ill and 36 respectively, it is apparent that solvent from extractor I1 will ow to extractor 36 only by way of heater 28 Vand line 38. Similarly, solvent will flow from extractor 36 to extractor 31 by way of heater 48 and line 49 only.

'I'he overhead from vapor phase extractor 38 passes through condenser 93 where the vapors may be cooled to a temperature above the end point of the aromatics being extracted in column I1. If any of these more volatile aromatics are present in the mixture supplied to extractor 33,

`they, will remain in vapor phase if cooled as just described and can'be separated from the less volatile condensed liquid phase hydrocarbons in separator 84.` The vapor phase hydrocarbons will then flow through valve 65 and line 86 to extractor I1 where they will be recovered together with the other volatile aromatics from fraction` ating column 8. The liquid phase hydrocarbons in separator 64 will flow through line 61 and valve 68.to storage. A por-tion of these condensed hydrocarbons may serve as reflux and pass through line 69 to the top of extracting column 36.

A similar arrangement for partial condensation, separation of liquid and vapor phase hydrocarbons, reiluxing with a partial condensate, and retreatment of the uncondensed fraction in extractor 36 is provided for the overhead from ex tractor 31.

In Figure II of the drawings a simplified form of apparatus has been illustrated and various of omitted; In this species o! apparatus the distillate to be extracted ilows from storage through valve controlled line to liquid phaseextrac- [tion columnv and passes upwardly theretions can be utilized since it is not necessary to vaporize the solvent and by using, for example, a solvent to stock ratio of to 1 a very large proportion of the aromatic hydrocarbons presen-t may be extracted without sacrlclng selectivity as would be necessary if the same proportion of aromatics were removed by extraction with smaller amounts of solvent at higher temperatures. v

Discharge pipe |04 conveys lthe selective solvent together with its dissolved hydrocarbons to vaporizer HB5 where the dissolved hydrocarbons are distilled oil` and pass through conduit lHBS to ractionating column |01. Overhead from the fractionating column ows through outlet |08 and condenser |09 to separator H0. The tempera-ture of the vapors incondens'er i is controlled so that only those hydrocarbons boiling within the range desired, i. e. the boiling range of the aromatics being extracted, remain'ln the vapor phase; For example, if benzene is being removed the vapors may be cooled to 95 F. whereby the benzene will remain in vapor phase and pass from separator ii@ through line H2 to vapor phase extracting column H2. Conthe column to outlet |52 and storage.

densed liquid phase hydrocarbons are returned to column |01 as reux through line lli.

Selective solvent is supplied to extraction tower H3 from vaporizer |05 by way of valve H5, line H5 and cooling coil No. The hydrocarbons entering column ||3 are in vapor phase and are intimately contacted with the hot downwardly owing selective solvent which extracts aromatic hydrocarbons andA allows the ls soluble nonaromatic hydrocarbons -to pass out of the top of the column in vapor phase through pipe il? and condenser H8 to storage. Valve controlled line ||9 is provided for supplying redux to the top of tower H3. The selective solvent, together with the dissolved aromatic hydrocarbons, ows from the bottom of tower M3 to still. l2@ where the solvent and extract are separated by ordinary distillation, the aromatic hydrocarbon through pipe |'2| 'to condensers (not shown d storage. Solvent from still l2@ is cooled and recirculated to inlet line 9b of liquid phase extractor idi.

The bottoms from fractionating column itl pass to vapor phase extraction column |22 by line |23 and solvent is fed to the column from vaporizer |65 through cooler its. Still llh removes extracted aromatics from the selective solvent flowing out of the bottom o! tower |22 in the same manner as described above'with respect to still |20. The vapor phase overhead from extractor |22 is partially condensed by cooling coil. |23 and hydrocarbons which remain in vapor phase within the boilingrange of the hydrocarbons being c the refinements utilized in Figure I have been extracted in column ||3 may be conveyed from separator |2'| through valve |28 and line |29. to the inletline of column ||3. Provision is also made for passing this same fraction ofhydrocarbonsthrough valve. |30 and suitable condensers (not shown) to storage, in the event it is not desired to again treat them in column ||3 as above mentioned. l.

Liquid phase hydrocarbons ow' from the bottom of separator |2`| through lline |32 to storage. A portion of the condensate may be refluxed through line |3| to column |22.v Solvent from still |26 may be cooledV and recirculated to the liquid` phase extractor through. inlet line 99.

Figure III illustrates a very simple method and apparatus which is useful in separating less complex mixtures; such as binary compositions of benzene and cyclohexane or isoprene and pentane, or. for extracting aromatics and unsaturates from very narrow petroleum cuts. In this modification the mixture to be treated enters liquid phase extraction column through valve controlled inlet 85| and flows upwardly through Downwardly ov'ing solvent is admitted through pipe |53 to extraction column |50 and preferentially dissolves certain of the constituents, aromatic hydrocarbons for example, from the upwardly flowing mixture.

The selective solvent together with its extracted constituent flows from the bottom of extractor I through conduit |56 to vaporizer |55. The dissolved hydrocarbons are distilled from the solvent in the vaporizer and pass through pipe |56 to the middle of the vapor phase extraction column |5l. The hot solvent from vaporizer flows through line |58 and cooler |59 to the top of extraction column |51, as shown. The solvent entering the tower should bel at a temperature above the boiling point of the mixture being extracted. This, mixture is in vapor phase and is extracted by the selective `solvent as it ows downwardly through the tower. Final separation of the constituents is effected in this extraction zone. The nal traces of the less soluble constituent, e. g. paramnes or cyclohexan'e, remainin vapor phase and pass out of the top of the column by way of pipe |66 and con-v denser ll to storage. The selective solvent containing its dissolvedl constituent is removed through line Edil to still ISI where the extracted substantially pure material is distilled off and removed as overhead through conduit |62 and condenser les to storage.

A portion of the vapor phase overhead from f tion of the solvent may also bev returned to the vapor phase extraction zone by way of valve it'.

In its broad aspects, the present invention is applicable to a great number of mixtures of chemical compounds which are difcult to separate because of similarity of boiling points, solubility characteristics or beoauseof formation of constant boiling mixtures. For example, a relatively narrow crude petroleum fraction may be extracted in liquid phase with a selective solvent to give an extract fraction containing a mix- 'ture of carbon compounds such as phenols, aromatics, sulfur compounds, olenes, naphthenes and pa 'ies.` This mixture is then passed through a series of' high temperature extraction A eible., v

ooeoeve, Y

zones under conditions or temoeroture und pressure suchthet the mixture ie semroted into ellin ferent components-one comooueut or group oi l componente' being removed fiom the bottom of euch ehtrection zone, oud the vemoinlng coml ponente pessime es overhead to the next extrae oeotflhee which occur@a in noturol geeolinee oi Eeletively wide boiling renee.. euch es 36u F. eno

distilletee.

Etepeeteo reference has been mode throughout l the eoecihcotlon to the use 0 selective solvents in the veoceso, lllhls generic @om le fused todo une eeolveot which has eveeterk eolvehtfpovvee f lo? et-lefeet one eomponent Aor e multioomponent eyetemth'eu it loos for other componente of that eyetem. ototed oonveneelv9 the term selectlve solvent designates o, eolveut which has less tend euoy to dissolve ome component of e mixture then othee oomoouento thereol. The groote? the dif-f ieeeutiol lu solvent power oi e, eelective solvent for fliilevent eomoouents of e, mixture the greater le its selectivity.

Il eelective eolveut useful for' the present :eroe-a eee ehoulol he highly selective ooo ehoulo hove e, boiling ooint Well loloove the eno point of the etoel: to m treated. Heierebly, the oolvent ehould not toom constant boiling :z es with the hmirccericousv but if such constant bollino mint mlztur ore formed the eolubility eherscterietlcs of the solvent should he such that complete recovery by water extraction is pos- 'Zihe following comoounds are illustrative of rating erometics from petroleum mixtures es disclosed herein: l

Resorcinol l ietih Y Tetreethylene glycol Phenol Tnethylene elvccl Te nf Anisidino methylene glycol "oar-bl Aoetomide Trlecetin 'high boiling selective solvents operative Zor sepal j 'ere me communes, ere:

,Tevreeulyrene glycol one methylene @meer have very irish boiling pointe om ere extremely emcieht selective solvente for' vopov' ohoseeutroc tion, y

Tetromihe constitutes on eddltonel exemple of e selective solvent which is ecient in the .procees oi this invention. This compound le ooe of o generic group which moy be represented by the general ormule lllHaCgHc-(Caloltlle-N'Ha or' The first- .iovmulo le on open chulo compound. exempliueo by:

Exemples ol the second generic formule, which can@ 03H6 Dlethylene diamine end y CaHa 4ucterizeci in that they contain more carbon thon nitrogen atoms ln their molecules and` can be formed by the .inter-action ofethylene dichloride with ammonio. followed by liberation oi free amine by treatment with caustic. These compounds which have a. boiling point above 300 F. ere in generell eminently suited` for use as selective solvents in the process of this invention.

Although e. number of specific exemples of suitable selective solvents have been given ano elthough methylene glycol is et present the preferr-ed solvent for the process or this invention, it should be apparent to those skilled in the ort that the broeder aspects of the invention include the use oi e multitude of other selective solvents.

butyl Cerbitol" illustrate operative compounds containing hydroxy. ether and. ester groups.

Emeriments ludlcte that polar compounds selected from the group consisting ol hydroxy benr zeitlos.q lamines,aurolcles, chlorinated hydrocarbons;

estere ot polycerbowllckeclds, and phosphoric acid estere of hydroxy benzenes are'in `eener-ol operative in the procese o! this invention. solvent selected. from this group` preferably should Reeve e boiling point above emroximetely 36W u. in cooler that it oeh be veoolly moihtoiued The.

ysuch as temperature, pressure. relative solventstock volumes. and rei'lux ratio. -wiil vary with the particular mixture being treated and with i the selective solvent used. This is particularly truein the ilrst extraction stage, thatis the liquid phase treatment, where temperature must be adjusted with respect to the particular stock and solvent so as to avoid complete miscibility and at the same time insure extraction of a maior .proportion of the desired component from the mixture. The manner and means of operating such liquid phase extraction systems are known to those skilled in the artand need not be discussed in detail here. However. for purposes oi janatra As an example of the speciilc conditions of operation in the vapor phase extraction stage, the following is given:

Solvent to stock., ratio 5 to l Base of extraction column vF.... 288 Temperature of raillnate vapor F 216 Temperature of still F 490 Temperature oi extract vapor from still F. 249 Temperature of entering solvent 9F..- 254 Temperature of entering stock- F..., 245 Reflux ratio of raillnate 1. 9 l

The particular stock seing treated had s boum range of 200to 300 F. and dew point 5 to 10 illustration the following speciilc examples are given.

A 360 F. end point Kettleman gasoline topped to 158 F. was treated in a 10 foot countercurrent column with 320 volume percentof triethylene glycol at 150 F. Thel original stock contained 6.7% aromatics. The yield of extract was 11.4% containing 41% aromatics. '10% of the total aromatic content of the gasoline having been extracted in this single operation. In another run a refractory gasoline blend (220 to 370 F. boiling range) was extracted in a three-stage countercurrent system with 300 volume percent of triethylene glycol at 80 F. The original stock contained 32% aromatics. The extract yield was 22.2% containing 78% aromatica and amounting to 54.1% of the total aromatic content of the stock. From these two examples it is apparent that at lower temperatures the total aromatic recovery in the liquid phase system is decreased, but that the aromatic content of the extract is higher. Economic considerations will, of course. dictate the particular temperature and solvent ratio selected.

The proper control of the straight fractionation operation is well known and will be obvious to the petroleum renner. Further discussion of this stage of lthe operation is deemed unnecessary.

In operating the vapor phasesolvent extraction systems it is desirable to maintain the temperature of the selective solvent and of the stock above the boiling point of the latter. The temperature of the solvent in the extraction tower must. oi course. be maintained below that at which substantial proportions of theextract hydrocarbons would be vaporized from or .remain undissolved in the solvent while being extracted. It has been found that temperatures from 10 to 'degrees below thetemperature of the entering stock. In this particular run, a stripping column was used on the stilly which'accounts for the large variation between the temperature of the still and the temperature of the extract vapor.

The entire process will usually be carried out at atmospheric pressures although super-atmospheric pressure may be used-particularly in the liquid phase extraction 'stage when volatile stocks are being treated. Sub-atmospheric pressures may be found desirable in instances where the additional cost occasioned by operation under vacuum is iustiiled.

Attention is again directed to the fact that the present invention provides a highly advantageous and economical method and apparatus for producing pure aromatic compounds from complex petroleum mixtures, such as 360 F. end point Separation of pure aromatics from pegasoline. troleum even in the chemical laboratory has heretofore been regarded as extremely dimcult and involved highly complex, time-consuming` the first bubble oi vapor. Dew point refers likedescribed in detail and illustrative examples giv- 20 F. above the dew point of the stock at the pressure of extraction are satisfactory for the solvent. 'I'he stock entering the vapor phase extraction column should be at a temperature not substantially below its boiling point and preferably approximately 5 to 10 F. aboveits dew When no such yliquid seal is provided and a pory tion of the vapors from the still is allowed to flow into the extraction column, the optimum reflux ratio is zero and the optimum solvent to stock ratio is approximately 3 to 1.

enf-this has been done by way of illustration only and with the intention thatv no limitation should be imposed upon the invention thereby. Likewise, the drawings are to be regarded as diagrammatic, 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 modiiications and variations may be adopted in the apparatus and method of the invention which is of the scope of the claims ap 10. In` a method of separating a multi-component mixture o! carbon compounds into at least two fractions of dlerent chemical characteristics, the steps which comprise extracting said mixture in liquid phase with a high boiling selective solvent, separating said selective solvent with its dissolved components from the undissolved carbon` compounds, heating said separated solvent to vaporize said dissolved compounds therefrom, passing saidvaporized compounds through a treating zone, passing said not solvent through said treating #one countercurrentiy to said vaporized compounds, maintaining said sol--4 vent at a temperature above the initial boiling point but no more than approximately 20 F. above the dew point of the hydrocarbon mixture in the treating zone, removing anundissolved .vapor phase from said zone, removing the high 'boiling selective solvent together with redissolved compounds from said vapor phase, and recovering 10 said latter'redissolved compounds.

ARTHUR n LYMAN.

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