US2462025A

US2462025A - Azeotropic distillation of wide-boiling-range hydrocarbon fractions

Info

Publication number: US2462025A
Application number: US546710A
Authority: US
Inventors: George R Lake; Josephine M Stribley
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1944-07-26
Filing date: 1944-07-26
Publication date: 1949-02-15
Anticipated expiration: 1966-02-15

Description

- G. R. LAKE ETAL. AZEOTROPIC DISTILLATION OF WIDE-BOILING-RANGE HYDROCARBON FRACTIONS Filed July 26, 1944 Feb. l5, 1949,

223cv m2519549?,

INVENTORS.

N oww Q 52.69.91

Patented Feb.. l5, 1949 #narran srares Parent orifice AZEOTROPIC DISTILLATION F WIDE-BOIL- ING-RANGE HYDROCARBON FRACTION S George R. Lake and `losephine M. Stribley, Long Beach, Calif., assignors to Union 0il Company geles, Calif., a corporation of California, Los An of California Application July 26, 1944, Serial No. 546,710

Claims. (Cl. 202 42) fractional distillation or extraction with selective v solvents.

Another object of the invention is to prepare from a given fraction of petroleum such as gasoline or kerosene fractions-these fractions consisting of a mixture of paraffnic, olefinic, naphvthenic, and aromatic hydrocarbons a fraction that consists essentially of parainic, olefinic, naphthenic or aromatic hydrocarbons by distilling the petroleum fraction in the presence of organic solvents hereinafter disclosed.

A further object of this invention is to separate aromatic hydrocarbons from non-aromatic hydrocarbons by distilling the complex hydrocarbon vfraction in the presence of the aforementioned organic solvents. A particular object is to separate benzene and toluene in pure form from wide boiling petroleum fractions containing both aromatic hydrocarbons as well as non-aromatic compounds.

A more specificv object of this invention is to carry out such separation in a more simplified manner than heretofore-employed.

This invention comprises adding to such petroleum fractions from which it is desired to segregate specic compounds or concentrates a mixture of substances hereinafter disclosed having a preferential aifinity for one or more components contained in the fraction, thus causing a disturbance in the vapor pressure equilibrium which formerly existed in the complex mixture, in such a manner that the partial vapor pressure or fugacity of at least one component in the fraction is changed sufficiently to permit separation by controlled fractional distillation. This type of fractional distillation will be referred to hereinafter as azeotropic distillation, and the substances which are added to the fraction to effect the aforementioned change in vapor` pressure equilibrium will be referred to as azeotrope formers.

According to our invention the separation of specific hydrocarbons or hydrocarbon fractions from a mixture of hydrocarbons is accomplished by azeotropic distillation wherein two azeotropic formers are added to the petroleum fraction and the mixture is subjected to a series of controlled distillations.

The addition of azeotrope formers of the type described herein to the petroleum fraction results in the formation of more volatile azeotropes with certain of the hydrocarbon components which may then be distilled from the remaining hydrocarbon components. Thus, by adding to a petroleum fraction containing two or more aromatic hydrocarbons a combination of two azeotrcpe formers and subjecting this mixture to a controlled distillation, we are able to take over-l head the non-aromatic constituents boiling in the range of the lower aromatic hydrocarbons as an azeotropic mixture with the primary azeotrope former. There may or may not be present in this overhead product a small proportion of the secondary azeotrope former present in a ternary azeotrope. In a successive distillation of the bottoms from the initial distillation carried out at a higher temperature it is possible to take overhead the lower aromatic hydrocarbon in conjunction with an azeotropic mixture consisting of the higher boiling non-aromatics and the secondary azeotrope former. The lower boiling aromatic hydrocarbon may or may not form an azeotrope with the secondary azeotrope former, The overhead from this second distillation may then be washed with a suitable solvent to remove the azeotrope former and the lower boiling aromatic is then easily separated from the higher boiling non-aromatics as an overhead product by means of a simple fractional distillation.

The bottomsfrom the second distillation consisting of the higher boiling of the two aromatics and any residual higher boiling non-aromatics which may be present are then distilled to yield an essentially pure aromatic fraction as overhead.

By suitable modication of the above procedure, it is possible to obtain essential pure paraffins, olens or naphthenes from the non-aromatic components of' the fraction employed. This may be accomplished by suitable adjustment of the overhead temperatures in those columns yielding non-aromatic as an overhead product. Also parans, naphthenes, and unsaturated hydrocarbons may be separated from sulfur compounds such as thiophene and thiophene homologs.

Prior to this invention the separation of pure components from petroleum fractions by means of azeotropic distillation has involved close fractionation of the stocks to be processed in order to eliminate any homologous members of a desired hydrocarbon. Thus, in the preparation of pure benzene and pure toluene froma petroleum frac.

` narrow boiling fraction`s each containing only one of these components. The pure benzene and toluene were then obtained by separate azeotropic distillation of each of these fractions. For example, the preparation of benzene from a fraction in which it is contained consists in distilling such a fraction in the presence vof an azeotrope former such as acetone, taking overhead from this fractionation an azeotropic mixture of acetone and non-aromatics leaving as bottoms the benzene, and any high boiling polymer which may remain. In such a process it is necessary i'or the recovery of pure benzene to acid treat this bottoms fraction and subsequently redistill the acid treated material to obtain high quality benzene as an overhead product. In like manner the preparation of pure toluene may be accomplished by similar azeotropic distillation of the second of the aforementioned fractions with an appropriate azeotrope former such as methyl ethyl ketone and water. As in the preceding case to obtain pure toluene as an overhead product, it is necessary to acid treat and redistill the bottoms from this azeotropic distillation.

Several advantages of our invention are, apparent from the foregoing discussion:

By our process of double azeotropic distillation, we have eliminated the necessity of closely fractionating any feed stocks which may be processed to obtain a high grade aromatic fraction.

As another advantage, we are' able by means of our invention to recover pure aromatics or aromatic fractions or concentrates as overhead products, eliminating in all but a few cases, the necessity of acid treatment and redistillation. A still further advantage of this invention is the simplicity of the distillations employed alleviating the necessity for columns of such high eiliciency as are usually necessary. At the same time these advantages have been realized without requiring any more fractionation columns than would be employed in the separate azeotropic distillation of two aromatic containing fractions.

Other objects, features and advantages of our invention will be apparent to those skilled in the art from the following description of the invention which represents a diagrammatic arrangement of apparatus for carrying out our invention. In the following description, the invention will be described as applied to the separation of benzene and toluene from a hydrocarbon fraction using acetone containing about 4% by volume of water as the primary azeotrope former and methyl ethyl ketone containing about by volume of water as the secondary azeotrope former. However, it will be observed that this example is not to be taken as limiting our invention since the process is applicable to separate other components in complex substances employing other primary and secondary azeotrope formers under conditions adapted to effect the desired separations.

In the drawing, the hydrocarbon feed to be resolved into its component parts, such as for example, the hydrocarbon fraction obtained by fractionation of a catalytically reformed gasoline, said fraction having a boiling range of about 150 to about 265 F., and consisting of substantially 15% by volume of benzene, by volume of toluene, 6% by volume of olefins, and the remainder paraln and naphthene hydrocarbons, is taken from tank I0 via line II and is pumped by pump l2 through line I3 controlled by valve I4 into line I5. Primary azeotrope former hereinafter in this example implying acetone-water mixture as described above is taken from tank I6 via line I1 controlled by valve I8 by means of pump 20, pumped into line 2i controlled by valve 22 through line 23, and is mixed with the hydrocarbon feed in line I5. In like manner, th'e secondary azeotrope former hereinafter in this example implying methyl ethyl ketone-water mixture as described above ls taken from tank 24 vla line 25 controlled by valve 25 by means of pump 28 and pumped through line 29 controlled by valve 30 into line 3| entering line I5 and mixed therein with the hydrocarbon feed and the primary azeotrope former. The mixture of hydrocarbon feed, primary and secondary azeotrope formers is then passed from line i5 into fractionating column 34 where the mixture is subjected to fractionation. This distillation is controlled so as to distill overhead an azeotropic mixture consisting of paraffin, olefin and naphthene hydrocarbons boiling below 230 F. together with substantially all of the primary azeotrope former. In the example herein given, this is accomplished at an overhead temperature of approximately 134 F. and at atmospheric pressure. If desired, this and succeeding distillations or extractions may be carried out either at atmospheric or superatmospheric pressure or under vacuum. The above overhead mixture is removed from the fractionating column via line controlled by valve 36 condensed in condenser 31 and passed via line 38 into collecting tank 40. The condensate consisting of the acetone, water and non-aromatic hydrocarbons boiling below 230 F. is withdrawn from the bottom of the collecting tank via line 4I by pump 42, and part thereof may be passed via line 43 controlled by valve 44 into fractlonating column 34 to serve as reflux for the fractionation. The remaining portion of the condensate is passed via line 45 controlled by valve 46 to the acetone-water recovery system as will be described hereinafter.

The bottoms in the fractionating column 34 consisting of the benzene, toluene, non-aromatic boiling in the range of 230 F. to 265 F. and substantially all of the secondary azeotrope former is withdrawn via line 48 controlled by valve 49 and are pumped by pump 50 through line 5i into fractionating column 52. If it is desired. a portion of the secondary azeotrope former may be taken from tank 24 and introduced into line 5I by means of line 53 controlled by valve 54. In fractionating column 52 the bottoms of the initial azeotropic distillation are subjected to controlled distillation giving as an overhead product substantially all of the benzene in the original fraction as an azeotrope with the methyl ethyl ketone and water as well as an azeotropic mixture consisting of parafln, olen, and naphthenic hydrocarbons boiling in the range of 230 F. to 250 F., and the methyl ethyl ketone and water. In this example, this is accomplished at an overhead temperature of approximately F. and at atmospheric pressure. The overhead mixture, consisting of nonaromatic hydrocarbons boiling in the range of 230 F. to 250 F., benzene, methyl ethyl ketone and water is removed from the fractionating column via line 56 controlled by valve 51 concolumn 52 to serve as reux for the fractionation.

The remaining portion of the condensate is passed via line 68 controlled by valve 61 into the methyl ethyl ketone-water extraction systeml which is hereinafter described.

The bottoms from column 52 consisting of substantially all of the toluene in the initial fraction as well as any hydrocarbons boiling above about 250 F. are withdrawn via line 10 controlled by valve 1| and are pumped by pump 12 into distillation column 14, this mixture consisting of toluene and the higher boiling hydrocarbons is subjected to a controlled distillation in column 14 yielding an overhead product consisting of essentially pure toluene. In the example herein described the toluene coming overhead in distillation column 18 is of a purity of better than 99%. This toluene is taken overhead via line controlled by -valve 15 condensed in condenser 11 passed from condenser 11 via line 18 into collecting tank 80. Toluene condensate is withdrawn from collecting tank 80 via line 8|, pumped by pump 82 into line 83 and a part thereof may be returned via line 80 controlled by valve 85 to distillation column 10 to serve as reiiux in the fractionation. The remaining portion is passed vialine 86 controlled by valve 81 into toluene storage tank 90,

The voverhead product from the secondary azeotropic distillation lcolumn 52 consisting of azeotropes of substantially all of the benzene contained in the original feed and of parain, olefin, and naphthene hydrocarbons boiling in the range of 203 F to 250 F. with methyl ethyl ketone and Wateris passed via line 68 controlled by valve 51 into the methyl ethyl ketone-water extraction column |34 provided with suitable packing material for effecting intimate counter-current extraction with water. In extraction column |30 the secondary azeotropic distillate consisting of benzene, non-aromatics boiling below 230 F. and methyl ethyl ketone and water is subjected to a countercurrent extraction giving as the upper phase substantially all of the benzene and the non-aromatics boiling between 230 F and 250 F. This upper phase is taken overhead via line |35 controlled by valve |38 into line |31 and is pumped by pump |38 via line |39 through heater |00 and via line |4| into distillation column |48. In distillation column |48 this mixture consisting of benzene and non-aromatics boiling between 230 i and 250 F., is subjected to a controlled distillacarbons boiling below 230 F. and the acetonewater-azeotrope former is passed through line 45 controlled by valve 46 into the acetone-Water extraction column 9d provided with suitable packing material for eiecting intimate countercurrent extraction with Water. The primary azeotropic distillate is subjected to a countercurrent water extraction giving as the non-aqueous or upper phase water and acetone free non-aromatic hydrocarbons boiling below 230 F. This upper phase consisting of parain, olefin, and naphthene hydrocarbons boiling below 230 F. is drawn via line 95 controlled by valve 95 into line 91 and is pumped by pump 88 via line 09 into storage tank |00. The lower phase in extraction. column 80 consisting of acetone and water is taken from the bottom of extraction column 98 via line |02 controlled by valve |03 and is pumped by pump |00 via line |05 through heater |06 and via line |01 into solvent recovery column |08. In solvent recovery column |08, the waterand acetone mixture are subjected to a distillation controlled so as to give as an overhead product a mixture of acetone containing approximately 4% by volume of water. This overhead product is removed from column |08 via line |09 controlled by valve ||0 condensed in condenser and passed via line ||2 to collecting tank H5. The acetone and water mixture is taken from collecting tank H0 via line ||5 and is pumped by pump .|I6 into line H1, a portion thereoi` may be returnedvia line ||8 controlled by valve ||9 to distillation column |08 to serve as reux for the fractionation. The remaining portion of the condensate `is passed through line |20 controlled by valve |2| into the primary azeotropic former storage tank I8.

The bottoms from columns |08 and 18 consisting of the non-aromatic hydrocarbons boiling in the rst case between 230 and 250 F., and in the second case above 250 F. are passed respectively via lines |60 and |8| controlled by valves |82 and |63 into lines |60 and |85, and are pumped via pumps |88 and |51 via lines |80 and |69 into nonaromatic hydrocarbon storage tanks |10 and lli.

The bottoms product from distillation column |82 consisting in the example herein given, of the waterV employed in the extraction of the methyl ethyl ketone azeotrope former in extraction column |34 is taken via line |96 controlled by valve |91, pumped by pump |98 via line |99 through cooler 200 via line 20|' into solvent storage tank 202. The water is drawn from solvent storage tank 202 via line 203 controlled by valve 204, and is pumped by pump`205 via line 206 into solvent extraction column |34.

While in the above description the primary object was to separate aromatic hydrocarbons in pure form from a petroleum fraction containing paraflln, naphthene and olefin hydrocarbons as well, it is equally as possible by means of the invention to separate aromatics from fractions containing only one other hydrocarbon series as for example parains, oleiins or naphthenes. In such cases Where the hydrocarbon fraction contains more than two components of different chemical characteristics, as described in the above example, and it is desired to separate one or more of these components from the other component or components, the separation may be accomplished by stage fractional distillation to remove first one component and then another component. For example in carrying out my invention as described above it is possible to operate fractionating columns 34 and 52 in such a manner that side cuts may be taken consisting of azeotropic mixtures of the various components with the particular azeotrope formers employed. In this manner We may take overhead in our primary and secondary azeotropic distillations an azeotropic mixture comprising essentially pure parailins and the azeotrope former and as a side cut an azeotropic mixture comprising essentially pure naphthenes and the azeotrope former. In the same manner a separation of olen and parailin hydrocarbons or olefin and naphthene hydrocarbons could be accomplished or if so desired a separation or concentration of parains, olefin or naphthene hydrocarbons could be accomplished in one operation by employing Atwo side cuts from columns 34 and 52 in which the overhead would consist of an azeotrope of parains, a side cut No. 1 would consist of an azeotrope of naphthenes, and a side cut No. 2 would consist of an azeotrope of olens with the azeotrope former employed.

In like manner while the above description of our invention was directed toward the separation of benzene and toluene from a petroleum fraction boiling in the range of 150 to 265 F. it is within the spirit and scope of our invention to employ our process of double azeotroping with other petroleum fractions from which it may be desired to separate essentially pure aromatic, naphthenic, parainic or olefinic hydrocarbons.

VFor example we may wish to obtain toluene and xylen-e from a petroleum fraction such as a hydroformate boiling in the range of about 200 F. to about 300c F. or higher. This may be accomplished in the same manner as above by the choice of suitable primary and secondary azeotrope formers as for example methyl ethyl ketone-water and pyridine, respectively and using suitable solvents for the extraction of the azeo- Lif) trope formers from the hydrocarbon oils such as water, glycols, nitroparailins and the like. In a similar manner xylenes and Co aromatics (cumene, methyl ethyl benzenes or trimethyl benzencs) can be obtained pure by using suitable primary and secondary azeotrope formers such as for example methanol and methyl cellosolve and appropriate solvents for their extraction from the hydrocarbon oil.

In general we may employ any primary azeotrope former which forms a lower boiling azeotrope with the non-aromatics in the range of the lower boiling aromatic than the azeotrope formed between the lower boiling aromatic and the secondary azeotrope former and conversely we may employ any secondary azeotrope former which forms an azeotrope with the lower boiling aromatic boiling above the azeotrope formed by the primary azeotrope former and the non-aromatics boiling in the range of the lower boiling aromatic. It is also preferable to choose azeotrope formers in such a manner that the primary azeotrope former is zeotropic with respect to the lower boiling aromatic and that the secondary azeotrope former is zeotropic with respect to the successive homologous aromatic hydrocarbon. Such a condi-tion while preferable is not essential providing any azeotrope which might form between the primary azeotrope former and the lower boiling aromatic boils above the azeotrope formed with the non-aromatics in the same boiling range and -similarly any azeotrope which is formed by the secondary azeotrope former and the successive homologous aromatic hydrocarbon must boil above the azeotrope formed with the non-aromatics boiling in the same range.

We do not wish to limit our invention by the above description to the separation of any particular aromatic or even to the separation of aromatics. As described hereinbefore we are able by our process to separate or concentrate any particular component from a complex hydrocarbon fraction by employing any primary and secondary azeotrope formers which comply with the general rules stipulated above with respect to the particular type components desired. In like manner our invention is not dependent on or limited by any particular solvents employed in the separation of the azeotrope formers from the azeotropes in which they are found inasmuch as the novelty of this process lies in the principle of double azeotroping as hereinbefore described and not in the methods employed in breaking the azeotropic mixtures which are formed. The following example of the laboratory application of our process will serve to show the advantages inherent in said process but is not meant to imply any limitation to our invention.

Eample A hydrocarbon stock was prepared by adding approximately 15% of benzene to a 15G-260 F. fraction of hydroformate produced by single pass operation on a 200 to 260 F. gasoline fraction. This material contained also approximately 24% by volume of toluene 3% by volume of xylenes and 3.5 per cent by volume of oleiins, the remainder consisting of parailinic and naphthenic hydrocarbons.

Five liters of this stock was charged together with y13.5 liters of acetone containing about 4% by volume of water and 14.2 liters of a mixture of 90% methyl ethyl ketone and 10% water to a 30 plate batch fractionating column. This charge was distilled until a vapor temperature of 135 F. was reached and substantially all of the acetone together with the non-aromatics in the-ben zene boiling range had been taken overhead. At this point the oilcontent of the distillate had decreased to 3%. The-distillation was continued and the temperature of the distillate rose to 165 F. while the oil content of the overhead increased to 33% and then slowly decreased to 2% whereupon the run was discontinued. Three fractions were obtained in this manner consisting of the primary aZeotropic distillate of acetone and the non-aromatics boiling in the benzene range, the secondary azeotropic distillate of methyl ethyl ketone, benzene and the non-aromatics boiling in the toluene range, and the bottoms of toluene and hydrocarbons boiling above the toluene range. Analysis of the primary azeotropic distillate which after the removal of acetone by Water washing constituted 32% by volume of the original hydrocarbon feed showed 4.5% olelns and 1% of benzene and had an A. S. T. M. boiling range of 176 F. initial to 218 F. dry. Similarly the secondary azeotropic distillate which after the removal of the methyl ethyl ketone azeotrope former constituted 40% by volum'e of the original hydrocarbon feed contained 4.6% olens and 41.0% of benzene and had :an A. S. 'I'. M. boiling range of 184 F. initial to 252 F. dry. The bottoms fraction constituting 28% by volume of the original hydrocarbon feed contained 1.0% of olefins and 97% of aromatics and had an A. S.

y 'I'. M. boiling range of 220 F. initial to 275 F. at

the 95% point. I

To obtain the nal products the hydrocarbon oil from the methyl ethyl ketone azeotrope and the non-azeotroped bottoms were separately fractionated in a distillation column of approximately 30 theoretical plates to recover the benzene and toluene respectively therefrom. An overhead fraction was obtained from the secondary azeotroped material of -about 38 volume per cent which consisted of 99+% by volume of benzene and 0.3%by volume of olens and showed a refractive index ND2G of 1.5014. The residue from this distillation constituting 62% of the fraction contained 9.0% by volume of olens and only 3.0% by volume of benzene. The distillation of the non-azeotroped bottoms yielded an overhead fraction of 80 volume per cent which consisted in 99+ volume per cent of toluene and 0.3% by volume of olens and showed a refractive index ND20 of 1.4966. The residue from this distillation constituting 20% of the fraction contained 3.0 per cent olens and 80% aromatics which were substantially all xylenes.

This example proves conclusively that benzene and toluene of better than 99% purity may be produced with yields of 95% or better by our process from a wide boiling hydrocarbon fraction containing higher boiling aromatics as Well as oleinic, naphthenic and parafnichydrocarbons, without the necessity of primarily isolating these aromatics in fractions of comparatively narrow boiling range.

The foregoing description is not tobe taken as in any way limiting but merely as illustrative of our invention for many variations may be made by those skilled in the art without departing from the spirit or scope of the following claims.

We claim:

l. A process for the treatment of a hydrocarbon fraction c-ontaining mixtures of various hydrocarbons to separate said hydrocarbons from each other which comprises distilling said hydrol carbon fraction in the amounts of a primary and a secondary azeotrope former to vaporize certain of the lower boiling hydrocarbons together with said primary azeotrope former as an azeotrope thereby leaving said secondary azeotroper former together with the remaining lower boiling hydrocarbons and all of the higher boiling hydrocarbons contained in said hydrocarbon fraction as distillation residue, separately distilling said distillation residue to vaporize said remaining lower boiling hydrocarbons and ycertain of said higher boiling hydrocarbons together with said secondary azeotrope former thereby leaving the remaining higher boiling hydrocarbons in the residue, said primary azeotrope former being adapted to form azeotropes with certain of the lower boiling hydr ocarbons contained in said hydrocarbon fraction which aZeotropes boil below the boiling point of said remaining lower boiling hydrocarbons and also below the boiling point of any azeotrope formed between said secondary azeotrope former and any hydrocarbons contained in said hydrocarbon fraction and said secondary azeotrope former being adapted to form azeotropes With certain of said higher boiling hydrocarbons which azeotropes boil below the boiling point of any azeotrope formed between said secondary azeotrope former and said remaining higher boiling hydrocarbons.

2. A process for the treatment of a hydrocarbon 'fraction containing a mixture of hydrocarbons to separate said hydrocarbons from each other which comprises distilling said hydrocar bon fraction in the presence of sumcient amounts of a primary and a secondary azeotrope former to vaporize certain of the lower boiling hydro-l carbons together with said primary azeotrope former as an azeotrope thereby leaving said secondary azeotrope former together with the remaining lower boiling hydrocarbons and all of the higher boiling hydrocarbons contained in said hydrocarbon fraction as a distillation residue, extracting said azeotrope with a suitable solvent to separate azeotrope former from the lower boiling hydrocarbons; distilling saidl distillation residue to vaporize said remaining lower boiling hydrocarbons and certain of said higher boiling hydrocarbons together with said secondary azeotrope former thereby leaving the remaining higher boiling hydrocarbons in the residue,

. extracting said last named vaporized mixture with a suitable solvent to remove said secondary azeotrope former and separating said remaining lower boiling hydrocarbons from the higher boiling hydrocarbons by simple distillation; said primary azeotrope former being adapted to form azeotropes with certain of the lower boiling hydrocarbons contained in said hydrocarbon 'fraction which azeotropes boil belowthe boiling point of the remaining lower boiling hydrocarbons and below the boiling point of any azeotrope formed between said secondary azeotrope former and any hydrocarbons contained in said hydrocarbon fraction and said secondary azeotrope former being adapted to form azeotropes with certain of raid higher boiling hydrocarbons which azeotropes boil below the boiling point of any azeotrope formed between said secondary azeotrope former and said remaining higher boiling hydrocarbons.

3. A process for the treatment of a hydrocarbonfraction containing aromatic, olenic and other non-aromatic hydrocarbons in which it is presence of suflicient y 11 desired to separate said aromatic hydrocarbons from said olernic and other non-aromatic hydrocarbons which comprises distilling said hydrocarbon fraction in the presence of surlicient amounts of a primary and a secondary azeotrope former to vaporize the lower boiling olenic and other non-aromatic hydrocarbons together with said primary azeotrope -former as an azeotrope thereby leaving said secondary azeotrope former, low boiling aromatic hydrocarbon and all of the higher boiling hydrocarbons contained in said hydrocarbon fraction as a distillation residue, extracting said azeotrope with a solvent to separate said primary azeotrope former from said lower boiling oleilns and non-aromatic hydrocarbons; distilling said distillation residue to vaporize said lower boiling aromatic hydrocarbon and higher boiling olenic and other nonaromatic hydrocarbons together with said secondary azeotrope former, extracting the resulting distillate with a suitable solvent to separate secondary azeotrope former from said last named vaporized mixture, separating said lower boiling aromatic hydrocarbon from said higher boiling olenic and other non-aromatic. hydrocarbons by simple distillation; distilling the residue from the second azeotropic distillation to vaporize said higher boiling aromatic hydrocarbons thereby leaving still higher boiling hydrocarbons as a distillation residue; said primary azeotrope former being adapted to form azeotropes with the lower boiling olenic and other non-aromatic hydrocarbons which azeotropes boil below the boiling point of said remaining lower boiling aromatic hydrocarbon and also below the boiling point of 4. A process for the treatment of a hydrocarbon fraction containing benzene and toluene and mixtures of non-aromatic hydrocarbons to separate said benzene and toluene in pure form from said non-aromatic hydrocarbons which comprises distilling said hydrocarbon fraction in the presence of sufcient amounts of a primary and a secondary azeotrope former to vaporize the non-aromatic hydrocarbons boiling in the benzene bciling range together with said primary azeotrope former as an azeotrope thereby leaving benzene, toluene and the higher boiling non-aromatic hydrocarbons together with said secondary azeotrope former in the residue; distilling said residue. to vaporize benzene together .with an azeotrope of said secondary azeotrope former and the non-aromatic hydrocarbons boiling in the toluene boiling range, extracting said last named vaporized mixture with a solvent to separate said secdndary azeotrope former from the hydrocarbons contained in the vaporized mixture and distilling the extracted mixture of benzene and nonaromatic hydrocarbons boiling in the toluene boiling range to vaporize benzene in substantially pure V-form thereby leaving the non-aromatic hydrocarbons boiling in the toluene boiling range as a residue; distilling the residue from the secondary azeotropic distillation which residue comprises toluene and any residual higher boiling hydrocarbons originally contained in the hydrocarbon fraction to vaporize toluene in substantially pure form thereby leaving said residual higher boiling hydrocarbons in the residue; said primary azeotrope former being adapted to form .azeotropes with the non-aromatic hydrocarbons boiling in the benzene boiling range, which azeotropes boil below the boiling point ,of benzene, below the boiling point of any azeotrope formed between benzene and said primary azeotrope former and also below the boiling point of any azeotrope formed between said secondary azeotrope former and any hydrocarbons contained in said hydrocarbon fraction and said secondary azeotrope former being adapted to form azeotrope with the non-aromatic hydrocarbons bolling in the toluene boiling range which azeotropes boil below the boiling point of toluene and' below the boiling point of any azeotrope formed between said secondary azeotrope former and toluene.

5. A process for the treatment of a hydrocarbon fractioncontaining .toluene and xylene and mixtures of non-aromatic hydro-carbons to separate said toluene and xylene in pure form from said non-aromatic hydrocarbons which comprises distilling said hydrocarbon fraction iii the presence of sufficient amounts of a primary and a secondary azeotrope former to vaporize '.the nonaromatic "hydrocarbons boiling in the toluene boiling range together with said primary azeotrope former as an azeotrope thereby leaving toluene, xylene and the higher boiling non-aromatic hydrocarbons together with said secondary aromatic hydrocarbons boiling in the xylene boilfing range to vaporize toluene in substantially 4pure form thereby leaving .the non-aromatic hydrocarbons boiling in the xylene boiling range as a residue; distilling the residue from the secondary azeotropic distillation which residue comprises xylene and any residual higher boiling hydrocarbons originally contained in the hydrocarbon fraction to vaporize xylene in substantailly pure form thereby leaving said residual higher boiling hydrocarbons in the residue; said primary azeotrope former being adapted to form azeotropes with the non-aromatic hydrocarbons boiling in the toluene boiling range, which azeotropes boil below the boiling point of toluene, below the boiling point of any azeotrope formed between toluene and said primary azeotrope' former and also below the boiling point of any azeotrope formed between said secondary azeotrope former and any hydrocarbons contained in said hydrocarbon fraction and said secondary azeotrope former being adapted to form azeotropes with the non-aromatic hydrocarbons boiling in the xylene boiling range which azeotropes boil below the boiling point of xylene and below the boiling point of any azeotrope formed between said secondary azeotrope former and xylene.

6. A process as in claim 2, whereby the hydrocarbon fraction to be treated consists of aromatic and non-aromatic constituents and wherein it is. desired to separate said aromatics from said non-aromatics.

7. A process as in claim 3, .whereby the hydrocarbon fraction to be treated consists of aromatic and olefnic hydrocarbons and wherein it is deslred to separate said aromatic hydrocarbons from said olenic hydrocarbons.

8. A process as in claim 4 for the separation of benzene and toluene from a hydrocarbon fraction wherein the primary azeotrope former consists of acetone containing from 0 to 5% by volume of water and the secondary azeotrope former consists of methyl ethyl ketone containing from 0 to 20% by volume of water and the solvent employed in the extraction of said azeot'rope formers from the azeotropes formed in the process is water.

9. A process as in claim 4 wherein the primary azeotrope former consists of acetone containing 4% by volume of Water and the secondary azeotrope former consists of methyl ethyl ketone containing 10% by volume of water and the solvent employed in the extraction of said azeo- REFERENCES @FEED The following references are of record in the le of this patent:

i UNITED STATES PATENTS Number Name Date 2,113,965 Roelfsema Apr. 12, 1938 2,212,810 Field Aug. 27, 1940 2o 2,302,608 Field Nov. 17, 1942 '2,388,040 Clark Oct. 301945