US2388040A - Process for recovering toluene - Google Patents

Description

. ticable direct Patented Oct. 30, 1945 2,388,040 PROCESS FOB RECCVERING TOLUENE Charles R. Clark, Springiield Township, Mont- Ailiell Che gomerr County, Pa., Dye Corporation, tion of New York- Application December 2 In Canada Jul 17 Claims.

This ing toluene from organic liquids.

Numerous hydrocarbon oils are known which contain toluene in varying proportions. For example, catalytic treatment of a suitable petroleum fraction in the presence of hydrogen, gives an oil consisting chiefly of hydrocarbons of both aromatic and nonaromatic character, and containing about 20% toluene. Gasoline fractions obtained by the distillation of certain types of petroleum frequently contain substantial proportions of toluene, although mainly consisting of other hydrocarbons. Oil of petroleum origin having a considerable content of aromatics, including be treated by well known selectivesolvent processes to produce fractions rich in aromatics; for example, extraction oi suitable fractions o! such petroleum oils with sulfur dioxide may yield fractions of high toluene content. In such cases toluene is accompanied by nonaromatic oils which may be largely paramnic, naphthenic `or cleilnic in character. A considerable portion of these oils cannot be completely separated from the toluene by commercially pracfractional distillation methods because of the closeness of their boiling points to that of toluene or because they form constant boiling mixtures with toluene. Furthermore, while ordinarily toluene is readily separable by direct fractional distillation from light oils produced by the gasification of coal, in some cases the toluene is accompanied by difllcultly separable non-aromatic oils of the same general character as described, owing to carbonization conditions, type of coal used or other'special circumstances. Also synthetic hydrocarbon gas mixtures produced by various catalytic processes may contain toluene which, when recovered. is accompanied by similar diiiicultly separable constituents.

By fractional distillation oi these oils containing tolueneJractions relatively high in toluene content may be obtained. These toluene iractions, however, will still contain large amounts of the other .constituents ci' the oil having boiling points in the neighborhood of the boiling point of toluene or forming mixtures of constant boiling points in the range oi' temperatures at which toluene distills from the oil. For example, by direct fractional distillation oi the above described types oi' oils containing toluene under the most emcient conditions commercially practicable for reotii'ying the vapors, a fraction containing about 32% to 85% toluene appears to mixtures containing it and other invention relates to a process for recover' assigner to New York, N. Y., a corporamical 0, 1941, Serial No. 423,185

' which contains, m addition to toluene,

represent a product of maximum toluene concentration obtainable. Accordingly, recovery oi' toluene of a relatively high purity from these sources presents a difficult problem of great industrial importance.

For many purposes to which toluene is put, it is desirable to use as pure a material as may be economically available. For example, toluene is largely used for the production of TNT, for which purpose aso-called nitration grade" of toluene is now preferred. While toluene products containing substantial proportions of certain hydrocarbon oils other than toluene can be nitrated, the mono-nitro compound made from them must be purified prior to complete nitration. materially increases the cost and complexity of the process for making TNT. Furthermore, even though toluene containing substantial quantities of certain other materials is sometimes used for nitration, this is only because the difculties of preparing a pure toluene have outweighed the disadvantages of using the impure toluene for the production of explosives. Direct fractional distillation, because of the diiiiculties pointed out above, will not effect a recovery of pure toluene from oils such as enumerated and in many cases will not give fractions of suitably high toluene content or iree from materials which even in small concentrations adversely affect the nitration of the toluene or the nitrated product.

It is an object of my invention to provide a process whereby toluene of any desired degree oi purity may be recovered from oils containing it and other hydrocarbons which distill out over the same temperature range as the toluene.

In using my invention for the treatment o1 an oil such as has been described above, containing toluene and other hydrocarbons, particularly when the toluene concentration of the oil is low or the oil is one containing materials of 'wide boiling range. I prefer first to fractionally distill the oil to remove highand low-boiling constituents and to recover an enriched toluene fraction other hydrocarbons which distill at the same temperatures as the toluene. Although toluene fractions having an end boiling point substantially above the boiling point oi toluene (e. g. a' boiling point up to 118 C.) may be azeotropically distilled in the manner hereinafter described, 1' prefer the toluene fraction recovered in the preliminary distillation step be one having a maximum boiling point substantially corresponding to the bolling point of pure toluene; i. e., 111 C. Further, for the reasons which will be more specifically pointed out below, I prefer that the toluene fraction recovered by the preliminary distillation oi' the crude toluene oil be so cut as to exclude therefrom the iorerunnings which do not contain substantial proportions of toluene, for example, to exclude any materials distilling below 100 C.

A toluene fraction such as may be obtained by this preliminary distillation, which may contain paramns, naphthenes, or oleiins, is subjected to a second distillation in the presence of a ketone in which =C=O is directly combined with both an unsubstituted ethyl radical and an unsubstituted alkyl radical containing no more more than 2 carbon atoms, preferably in the presence oi water. These materials may be represented by the formula CxHs in which R is an unsubstituted alkyl radical containing no more than 2 carbon atoms. 'I'he two members of this group are methyl ethyl ketone and diethyl ketone. I have discovered that when one of these ketones is mixed with a toluene fraction, such as is described above, and the mix ture is subjected to fractional distillation with rectification of the vapors in the presence of the ketone and preferably also in the presence of water, non-toluene hydrocarbons present in the toluene fraction are selectively distilled from the mixture in the form of their azeotropes with the azeotropic agent to leave a residue containing toluene of desirable high purity with respect to its content of other hydrocarbons originally present in the toluene fraction and not separable from the toluene by direct fractional distillation in the absence of the azeotropic agent. K

After the distillation has been carried to the Point at which the residue containing toluene has the desired purity with respect to hydrocarbons distillinar from the toluene fraction in the same temperature range as the toluene distills therefrom in the absence of the azeotropic agent. the distillation may be stopped and the residue withdrawn from the still. Usually the toluene fraction subiected to azeotronic distillation in practicing this invention will be one having a top boiling point not above 118 C. and preferably not above 111 C. The toluene fraction, theretore. will contain little, if any, hydrocarbons boiling from the fraction ai temperatures above those at which toluene boils therefrom. Accordingly, the residue withdrawn from the still ordlnarily will contain toluene and other hydrocarbons in the ratio oi 95 or more parts toluene to 5 or less parts of total hydrocarbons other than toluene. It may be puriiled further, as desired, to remove any azeotropic agent it contains and to remove any other impurities present. When the distillation is carried to the point at which all of the azeotropic agent has been distilled out of the residue and the toluene constitutes substantially 99% or more of the total hydrocarbon content of the residue, the residue, which may be given a conventional treatment, for example. treatment with sulfuric acid. neutralization and redistillation, is suitable for marketing as a nitration grade toluene of particularly high purity.

Instead of withdrawing the toluene residue from the still, the distillation may be continued and the toluene distilled over and separately collected from the distillate containing the hydrocarbons from which the toluene residue previously has been separated by azeotropic distillation.

As stated above, ordinarily the toluene fraction treated in accordance with my invention will contain little, if any, hydrocarbons distilling from the hydrocarbon-toluene fraction at temperatures above those at which toluene distills therefrom. On the other hand, it is not necessary that such high boiling hydrocarbons always be excluded from the mixture of azeotropic agent and toluene fraction subjected to distillation in accordance with my invention. For example, one may desire to azeotropically distill a toluene oil from which all high boiling hydrocarbons have not been removed. In that case, the high boiling hydrocarbons may be left with the toluene residue at the conclusion of the azeotropic distillatlon of the toluene fraction under the conditions set forth above to separate the toluene from the hydrocarbons of similar boiling range. After this separation has been effected, one may then separate the toluene from high boiling hydrocarbons present in the residue by fractional distillation in the absence of the azeotropic agent.

My invention will be more particularly illustrated and described in conjunction with the following examples.

The accompanying drawing diagrammatically illustrates an apparatus suitable for carrying out the processes of these examples.

I'he apparatus o! the drawing comprises a still l provided with a heater 2 and connected with a rectification column 3 and a condenser 4 for the vapors leaving the top of the column. By means or valves 5 and 6, condensate ilowing from condenser I is divided in controlled proportions. One part oi the condensate is returned through pipe 1 to the top of column 3 and reiluxed in contact with the vapors rising in the column. The other portion oi the condensate is withdrawn through pipe B. Two receivers 9 and I0 are connected to pipe 8 through valve-controlled branch pipes Il and l2 so that the condensate drawn off through pipe B may be divided and distributed as de scribed below to the two receivers.

Receiver I0 is connected by a pipe I3 controlled by valve i4 with a second still iB. Still i5, like still I, is provided with a heater I8, a rectification column i1, a condenser l! and pipes i8 and 20 controlled by valves 2i and 22 for return oi' determined proportions of condensate from condenser I8 to the top of column I1 and Withdrawal of another portion of the condensate through pipe 20. Pipe 20 leads to a separator 23 into which water may be introduced from a pipe 24. The separator is also provided with a pipe 25 for withdrawal of an upper liquid layer and a pipe 2! for withdrawal of a lower liquid layer which may be i'ormed from the material treated in the separator, Suitable baffles may be provided in separator 23 to facilitate continuous layer separation. Pipe 28 leads to a liquid storage vessel 21. A pipe 28 controlled by valve 29 permits introduction of liquid from storage vessel 21 into still I5. A pipe 30 controlled by valve 3i is also provided for introduction of liquid into pipe 2B and thence into still Il. Pipe 32. controlled by valve 33, permits introducing liquid directly into still IB. A pipe 34 controlled by valve 3l leads from the bottom of still II to a separator 30. Separator 30 is provided with a pipe 31 for withdrawal of an upper liquid layer. with a pipe 38 for withdrawal of a lower liquid layer and a pipe l! for introducing water into aasaoao 3 the separator. Suitable bellies may be provided in separator It to facilitate continuous layer separation.

Example 1.-In carrying out one embodiment of my invention in the apparatus described above, a liquid hydrocarbon mixture containing about 20% toluene, 20% of other aromatic hydrocarbons and the remainder substantially consisting of aliphatic and naphthenic hydrocarbons, with only traces of oletlns, was introduced into still 1. This crude toluene material was produced by catalytic treatment or a petroleum distillate in the presence of hydrogen. It had a speciilc gravity of 0.760 at 15.5 C. `and distilled over a range of from 56 C. to 161 C.

The charge of this hydrocarbon mixture introduced into still l was boiled in the still and the evolved vapors were counter-currently contacted in column 3 with reflux from condenser l, in which the vapors leaving the top of the column were substantially entirely condensed. Most of the condensate from condenser 4 was returned through valve i and pipe l to the top of the column to furnish the reilux for the column, the remaining. small portion oi' the condensate being continuously withdrawn through valve 0 and pipe l and passed into collecting vessel The.

distillation was conducted under substantially atmospheric pressure; i. e., the pressure in condenser l and at the top ol' column 'I was subt stantially atmospheric and the pressure in still l was only enough higher to force the vapor through the rectification column to the condenser.

When the vapor temperature in the top of column I reaches 109.5 C., the condensate passing through pipe I is diverted to vessel l0. The

cut taken in vessel I0 includes the distillate coming over up to and at a temperature of 110.8 C. at the top of the column. After this cut has been taken oi! to vessel I0, the distillation is discontinued and the residue left in the still is withdrawn therefrom. The cut in vessel l contains the low boiling fraction of the original oil. The residue withdrawn from the still contains the high boiling components of that oil. This fraction and residue may be treated or used in any desired manner.

Instead of discontinuing the distillation after ,the desired cut is taken-oi! to vessel il. the distillation may be continued and the condensate passing forward through pipe I collected in a third vessel. not shown in the drawing, while the distillation is continued as long as may be desired.` The cuts in vessel 0 and this third vessel contain low and high boiling fractions of the original oil. 1i' the cut taken oi! to the third vessel is limited to one containing substantial proportions of toluene, e. g. up to 115 C. or 120' C., this cut may be redistilled or introduced to still i with a subsequent batch of oil, and the toluene in this cut recovered.

With edlcient rectification of the vapors in column 8 during the fractional distillation ci the crude toluene oil. the cut collected in vessel Il contains about '16% by weight of toluene, as determined by the gpeciilc dispersion method for analyzing hydrocarbon oils described in Industrial 8: Engineering Chemistry. Analytical Edition. vol. ll, page 614, November 15, 1930.

The toluene fraction collected in vessel Il is 'aibiectec to anisotropic distillation, which repthe second stage of this example. For this purpose a charge con equal proportions by volume of methyl ethyl ketone and the 16% toluene and 25H6 il! volume of water (based on the total charge of ketone and toluenefraction) is introduced into still ll. Distillation of this charge is started and water is fed to the bottom plate of rectification column I1 by an inlet pipe not shown in the drawing as required to maintain at the top of the column a temperature not above 74 C. while permitting the vapors of aceotropes of the hydrocarbons to be removed from the toluene fraction being distilled to pass out oi the rectification column to condenser I0. In distilling the 76% toluene fraction under the foregoing conditions, the temperature at the top of the rectiication column rose to '14 C. from an initial temperature of about 12 C. By continuing the distillation the hydrocarbon residue remaining in the still after wash ing with water will contain 98-99% toluene. The distillate obtained in carrying out the process of this example may be extracted with water to separately recover methyl ethyl ketone from hydrocarbons in the distillate.

The above procedure may be modified as follows:

The hydrocarbon residue left in still I8 by the azcotropic distillation is drawn from the still through pipe 3l to separator 3B in which the residue is washed with water introduced through pipe 39 and then allowed to separate from the water. The bottom water layer is drawn oil through pipe 38. The top layer, drawn oil through pipe 31, will contain Sii-99% toluene.

The distillate drawn oil to separator 28 sepa-' rates into two layers; a top vlayer high in hydrocarbons and low in methyl ethyl ketone and water and a bottom layer high in methyl ethyl ketone and water and low in hydrocarbons. This bottom layer, constituting an aqueous methyl ethyl ketone solution, is drawn oil.' through pipe 2l to storage vessel 21 and in the aaeotropic distillation of a subsequent batch of the toluene iraction, is introduced into the charge to still il for reuse of the methyl ethyl ketone as the azeotropic agent in this distillation.

In distilling a subsequent charge of toluene fraction in still IB with addition thereto oi the aqueous solution of methyl ethyl ketone, no additional water need be added over that contained in the solution returned from vessel 21. Thus, a quantity of water once introduced into the distillation procedure may be largely retained therein and repeatedly be used for extraction of the alcohol from the distillate and its return to the distillation step. Except for any make-up water required to replace incidental losses from the system, no additional water generally is required. Additional water. however, may be introduced into the distillate to increase the efficiency with which the azeotropic agent is extracted for return to the azeotropic distillation step and water may be bled from the system in the toluene residue. from the base of the fractionating column, or otherwise removed from the system. Water may be mixed with the oil decanted through pipe 2l, the mixture allowed to separate into layers, and

added to the aqueous solution in storage vessel 21 to increase the effectiveness with which the methyl ethyl ketone is recovered from the oil distillate for reuse in the aseotropic distillation 75 ume of diethyl ketone and the '10% toluene fraction and 2/2% of water is introduced into still I5 through pipes i3, 30 and 28. Distillation of this charge is started and water is fed to the bottom plate of rectification column Il by an inlet pipe not shown in the drawing, as required to maintain at the top of the column a temperature not above 83 C. while permitting the vapors of azeotropes of non-toluene hydrocarbons to pass out of the rectication column to condenser I8. In distilling the '76% toluene fraction under the foregoing conditions, the temperature at the top oi the recticaticn column rises to about 83 C. from an initial temperature of about 79 C. By continuing the distillation the toluene content of the hydrocarbon residue remaining in the still, after washing with water, will contain 98-99% toluene.

As in the process of Example 1, the distillate drawn off to separator 23 separates into two layers; a top layer high in hydrocarbons and low in diethyl ketone and water and a bottom layer high in diethyl ketone and water and low in hydrocarbons. This bottom layer, constituting an aqueous diethyl ketone solution, is drawn ofi' through pipe 26 to storage vessel 2l and in the azeotropic distillation of a subsequent batch of the toluene fraction, is introduced into the charge to still I5 for reuse of the diethyl ketone as the azeotropie agent in this distillation.

By distilling a toluene fraction in accordance with the process of Example 2 and the similar procedure of the modification o1' Example l described above, the azeotropic agent used in the distillation of the toluene fraction is recovered and returned to the distillation step in a particularly effective, economical manner. 'I'he azeotropic agent is recovered from the distillate by decantation and is reused 1n the distillation of toluene fraction without costly dehydration steps. Only that amount of azeotropic agent required as make-up for any incidental losses oi material need be continuously or periodically supplied to the process. Both methyl ethyl ketone plus water and diethyl ketone plus water appear to form azeotropes with non-aromatic hydrocarbons oi' the toluene distillation range. The ketones plus water have a good selectivity for carrying over the non-aromatic hydrocarbons as distillate and leaving toluene behind in the residue. At the same time, with Water present the ratio o1' hydrocarbons to azeotropic agent (ketone plus water) carried over into the distillate is increased as compared with the anhydrous ketone. Accordingly, both for methyl ethyl ketone and for diethyl ketone, it is preferred to carry out the distillation in the presence of water.

By my procedure substantially pure toluene, for example, a product containing about 99% or more toluene, readily may be recovered commercially from toluene fractions, such as described above, from which pure toluene cannot be recovered practically by fractional distillation in the absence of an azeotropic agent. The products may be given a conventional treatment, for example, treatment with sulfuric acid, neutralization and redistillation, and they are then Suitable for marketing as a nitration grade toluene of particularly high purity.

Example 3.-In fractionally distilling the hydrocarbon mixture containing about toluene described above, the portion distilling between 107.5" C. and 110 C. was separately collected. 100 volumes of this fraction i 68 volume toluene) were charged together with 250 volumes of methyl ethyl ketone and 100 volumes of water into still 15 and fractionally distilled with rectication of the vapors in a column Il of about 36 equivalent theoretical plates. The vapors leaving the top of the column were condensed in condenser I8. Fifteen to 20 parts of the condensate were returned through pipe I9 to the top of column I1 to 1 part o1' the condensate which was withdrawn by pipe 20 to separator 23. The temperature oi' the vapors at the top of the column rose from an initial value of 71.7 C. to '73.4 C. During the course of the distillation an additional 100 volumes of the ketone and 50 volumes of water were added. When the methyl ethyl ketone had been exhausted about oi the toluene available was obtained in the distillation residue as toluene of about 94% (by volume) purity.

Example 1 -The process of this example was used for the treatment of a toluene fraction having a boiling range of approximately 108 C. to 111 C. and containing about '10% by volume toluene.

A charge of this toluene fraction and diethyl ketone in equal proportions by volume was distilled in a still I 5 and the vapors rectied in rectiiication column I1 with condensation o! the vapors in condenser I8, return of redux through pipe i9 and withdrawal of distillate through pipe 20. Most of the non-aromatic hydrocarbons in the oil were selectively distilled over at temperatures up to 107.6'J C., leaving a residue of which the hydrocarbon content was 92% by volume toluene. r

The diethyl ketone employed in the distillation procedure of this example had the particular advantage of carrying over in the distillate' with the non-aromatic hydrocarbons a very small ratio Aof toluene to non-aromatic hydrocarbons. Thus, the initial distillates coming on at temperatures up to 100.5 C. contained no toluene and the succeeding distillate coming over from 100.5 C. to 101.0 C. contained only 4% toluene based on the oil content of the distillate.

Example 5.-A charge of the same toluene fraction as was distilled by the process oi' Example 4 was introduced into still I 5 together with an equal volume o1' diethyl ketone and hall' as much water. Distillation started with the temperature of the vapors at the top oi the rectification column at 80.8 C. When this'vapor temperature had risen to 82.7 C. and the fraction coming over at this temperature contained about 88% by volume toluene based on the oil content of the distillate, the distillation was discontinued. The residue was washed with water to remove diethyl ketone. 'Ihe oil layer which separated from the aqueous extract contained 92% by volume toluene.

Numerous changes and modifications may be made in the above described processes without departing from my invention. While in the rst distillation step of the crude toluene oil it is preferred to take oi a toluene fraction having an end boiling point of substantially 111 C. and fractions with a higher end boiling point, such as 118 C., may be successfully distilled azeotropically to obtain pure toluene, even a larger leeway is permitted in the temperature at which the toluene fraction starts to be taken oi; i. e., in the initial boiling point of the toluene fraction. Nevertheless, it is preferred that the toluene fraction subjected to azeotropic distillation be one boiling in the range of C. to 111 C Such a fraction tropic distillation may be distilled in the azeostep of my process and pure toluene obtained with a relatively small quantity of azeotropic agent present during the distillation. Pure toluene may be obtained by distllling with the azeotropic agent a toluene fraction boiling, for example, from 95 C. to 118 C., but the quantity of azeotropic agent present in the distillatlonof the toluene fraction of wider boiling range must be substantially increased as compared with the quantity which suffices for distilling the fraction of the narrower boiling range.

While I have described my process in conjunction with examples in which the two distillation steps are batch procedures, either or both of these distillations advantageously may be carried out continuously by well known continuous distillation procedures suitable for the fractional distillation of mixtures of two or more liquids.

The minimum ratio of azeotropic agent to the toluene fraction which is suitable for carrying` out my invention will vary with the particular agent used, the amount and nature of the hydrocarbon impurities in the toluene fraction, the purity distillation, the proportion oi toluene in the original toluene fraction which is to be recovered in the residue from the distillation, and the procedure used for the azeotropic distillation. The ratios of the above examples are suitable for a batch process carried out according to the procedures of the examples. However, it is preferred to employ even higher ratios oi azeotropic agent to toluene fraction than in some of the examples, e. g. Example l. In the process of that example the methyl ethyl ketone may be exhausted from the distillation column before in the residue is tls-99% toluene. Although this high toluene content of the residue is obtained in the process of this example by continued distillation with temperatures rising above '14 C'. after the methyl ethyl ketone is exhausted, it is preferred to have present in the distillation suificient methyl ethyl ketone so that when the desired purityl of hydrocarbon in the residue is attained there is still some of the methyl ethyl ketone therein. Irrespective of the particular batch or continuous procedure used, therefore, the quantity of aneotrcpic l tlllation of hydrocarbons from a given quantity of toluene fraction is preferably in excess of that which will forin azeotropic mixtures with the non-toluene hydrocarbons which are to be vaporized and taken over into the distillate. This quantity oi' azeotropio agent includes fresh agent introduced into the material being distilled and also any of the azeotropic agent Vwhich may be separated from the distillate and returned continuously or periodically to the still or rectiflcation column while the distillation of the toluene fraction is pro. Temperature readinsstaken ofthevapor atthetopofthe rectification column provide a particularly good the process with respect to C. Methyl ethyl ketone an Diethyl ketone 102 Methyl ethyl ketone and water Dlethyl ketone and water.-....-

the hydrocarbon desired in the toluene residue from the.

agent used in the dis- By supplying additional azeotropic agent (either ketone or water or both) to prevent this temperature from exceeding the above temperatures, an adequate amount of azeotropic agent will be present during the separation of the nontoluene hydrocarbons from the toluene fraction. It is not necessary that this point oi control temperature be at the top of the column, although this is a satisfactory point for determining this temperature in the equipment used for fractionating the vapors and condensing the fractionated vapors 1n the above examples for effective use of the rectification column. One skilled in the distillation art will recognize suitable points for maintaining this control temperature in any other speciilc apparatus according to well known distillation principles.

It is, of course, obvious that preliminary distillation of a crude toluene oil to obtain a toluene fraction suitable for recovery of toluene therefrom by the azeotroplc distillation need not be carried out in immediate conjunction with the azeotropic distillation. The toluene fraction may be produced in one plant, transported to and treated later in another plant to azeotropically distill it. Nor is my invention limited to any particular procedure for the production of the toluene fraction. My invention contemplates distilling with methyl ethyl ketone or diethyl ketone, preferably with water, any oil containing toluene together with other hydrocarbons which, when the oil is distilled, vaporize therefrom in the same temperature range as the toluene and, therefore, are not separable from the toluene by direct fractional distillation. As used in this specification and the appended claims, the term toluene fraction" refers to all such toluene-containing oils, whether produced by fractional distillation of toluene-containing materials or by any other means.

In this speciiication I have described the azeotropic distillation of toluene fractions as carried out under substantially atmospheric pressure. The temperatures as given in this specification and in the appended claims are corrected temperatures for one atmosphere pressure (760 mm. of Hg). It is, of course, possible to azeotropically distill the toluene fraction under pressures above or below atmospheric. In that case-the temperatures will differ from the temperatures given herein due to the changes in boiling points caused by the change in pressure.

I claim:

1. The process for the recovery of toluene from a toluene fraction containing the same and oontaining non-aromatic hydrocarbons boiling from said fraction in the same temperature range as the toluene boils therefrom which comprises azeotropically distilling said toluene fraction in the presence of a ketone having the formula in which R is an unsubstituted alkyl radical containing no more than 2 carbon atoms, and thereby vaporizing said ketone and non-aromatic hydrocarbons present in said toluene fraction. said ketone being present in amount sulcient to separate selectively from said toluene fraction nonaromatlc hydrocarbons present therein which distill therefrom in the absence of said ketone in the same temperature range as toluene contained therein and to carry over said non-aromatic hydrocarbons with vapors of said ketone, leaving a lwdrocarbon residue of the distillation enriched in toluene.

2. The process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons boiling from said fraction in the same temperature range as the toluene boils therefrom which comprises azeotropically distilling said toluene fraction in the presence of water and a ketone having the formula in which R is an unsubstituted alkyl radical containing no more than 2 carbon atoms, and thereby vaporizing said ketone and non-aromatic hydrocarbons present in said toluene fraction, said ketone being present in amount sufficient to separate selectively from said toluene fraction nonaromatic hydrocarbons present therein which distlll therefrom in the absence of said ketone and water in the same temperature range as toluene contained therein and to carry over said non-aromatic hydrocarbons with vapors oi' said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene.

3. I'he process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom, which comprises distilling said toluene fraction inthe presence of a ketone having the formulaL ClHs in which R is an unsubstltuted alkyl radical containing no more than 2 carbon atoms, thereby vaporlzing said ketone and non-aromatic hydrocarbons present in said toluene fraction, said ketone being present in amount sufiicient to separate selectively from said toluene fraction nonaromatic hydrocarbons present therein which dis-- aqueous solution thus obtained for the azeotropic distillation of a toluene fraction containing nonaromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom.

4. The process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons boiling from said fraction in the same temperature range as the toluene boils therefrom which comprises azeotropically distilling said toluene fraction in the presence of' methyl ethyl ketone and thereby va- Dorizing said ketone and non-aromatic hydrocarbons present in said toluene fraction, said ketone being present in amount sufficient to separate selectively from said toluene fraction non-aromatic hydrocarbons present therein which distill therefrom in the absence of said methyl ethyl ketone ln the same temperature range as toluene contained therein and to carry over said non-aromatic hydrocarbons with vapors of said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene.

5. The process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons boiling from said fraction in the same temperature range as the toluene boils therefrom which comprises azeotropically distilling said toluene fraction in the presence of methyl ethyl ketone and water and thereby vaporizing said ketone and non-aromatic hydrocarbons present in said toluene fraction, said ketone being present in amount suilicient to separate selectively from said toluene fraction non-aromatic hydrocarbons present therein which distill therefrom in the absence of said methyl ethyl ketone and water in the same temperature range as toluene contained therein and to carry over said non-aromatic hydrocarbons with vapors of said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene.

6. The process for the treatment of a toluene fraction to separate the toluene from non-aromatic hydrocarbons contained therein which dis till from the toluene fraction in the same temperature range as the toluene distills therefrom, which comprises distilling said toluene fraction and rectifying the vapors evolved therefrom in the presence of methyl ethyl ketone and water in amount such that at a point in the rectification of the vapors temperatures not substantially above 7 4 C. are maintained while vaporizlng and removing from said toluene fraction hydrocarbons pres- 4 ent therein which distill therefrom, in the absence of said ketone and water, in the same temperature range as toluene contained therein.

7. The process for the treatment of a toluene fraction having an end boiling point not above 118 C. and containing paraiinic hydrocarbons, and which may also contain naphthenic and olefinic hydrocarbons, the aforesaid hydrocarbons distilling from the toluene fraction in the same temperature range as the toluene boils therefrom, which comprises distilling said toluene fraction and rectifying the vapors evolved therefrom in the presence of methyl ethyl ketone and water in amount such that at a point in the rectification of the vapors a temperature not substantially above 74 C. is maintained until the unvaporized residue of the distillation contains at least parts by weight of toluene to every 5 parts by weight of other hydrocarbons, and thereby vaporizing and selectively removingfrom said toluene fraction hydrocarbons present therein which distili therefrom, in the absence of said ketone and water, in the same temperature range as toluene contained therein.

8. The process for the recovery of toluene from a crude toluene oil produced by catalysis of a petroleum fraction in the presence of hydrogen which comprises recovering from said crude oil a toluene fraction having an end boiling point of 111 C. containing paratilnic and naphthenic hydrocarbons, and which may'also contain olefinic hydrocarbons, which hydrocarbons distill from said toluene fraction in the same temperature range as the toluene distills therefrom, distilling said toluene fraction and rectifying the vapors evolved therefrom in the presence of methyl ethyl ketone and water in amount such that at a point in the rectification of the vapors a temperature not above 74 C. is maintained until the unvaporized residue of the distillation contains toluene separated from like-boiling, non-aromatic hydrocarbons which were present in said toluene fraction.

9. The process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons which distill from the toluene fraction in thesame temperature range as the toluene distills therefrom, which comprises distilllng said toluene fraction and rectifying the vapors evolved therefrom in the presence of water and methyl ethyl ketone, thereby vaporizingsaid ketone and non-aromatic hydrocarbons present in said toluene fraction, said ketone being present in amount suillcient to separate selectively from said toluene fraction non-aromatic hydrocarbons present therein which distill therefrom, in the absence of said methyl ethyl ketone and water, in the same temperature range as toluene contained therein and to carry over said non-aromatic hydrocarbons with vapors of said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene, condensing the vapors thus distilled from said toluene fraction to form a liquid distillate, extracting said distillate with water, separating the resulting aqueous layer from the hydrocarbon oil layer, and employing the aqueous layer thus obtained, containing methyl ethyl ketone in solution, for the azeotropic distillation of a toluene fraction containing non-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom.

l0. The process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom, comprises distilling said toluene fraction in the presence of water and methyl ethyl ketone thereby vapcrizing and distilling over a. mixture of vapors of methyl ethyl ketone, water and hydrocarbons present in said toluene fraction which distill therefrom, in the absence of methyl ethyl ketone and water, in the same temperaturerange as toluene contained therein, said ketone being present in amount suilicient to separate selectively said non-aromatic hydrocarbons from said toluene fraction and to carry over the non-aromatic hydrocarbons with the vapors of said ketone and water, leaving a hydrocarbon residue oi the distillation enriched in toluene, cooling said mixture of vapors to condense them and form a liquid containing two phases, an ous phase containing methyl ethyl ketone and a hydrocarbon oil phase, separating the aqueous phase from the hydrocarbon oil, and employing the aqueous solution of methyl ethyl ketone thus obtained for the azeotropic distillation of a toluene fraction containing non-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills Y therefrom.

1l. The process for the recovery or toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons boiling from said fraction in the same temperature range as the toluene boils therefrom, which comprises azeotropically distillins said toluene fraction ln the presence of diethyl ketone and thereby vaporising said ketone and non-aromatic hydrocarbons present in said toluene fraction, said ketone being present in amount suillcient to separate selectively from said toluene fraction non-aromatic hydrocarbons present therein which dlstill therefrom in the absence of said diethyl ketone in the same temperature range as toluene contained therein and to carry over said non-aromatic hydrocarbons with vapors o! said ketone, leavin: a

hydrocarbon residue of the distillation enriched in toluene.

l2. The process for the recovery oi toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons boiling from said fraction inthe same temperature range as the toluene boils therefrom, which comprises azeotroplcally distilling said toluene fraction in the presence of diethyl ketone and water, and thereby vaporizing said ketone and non-aromatic hydro- Carbons present in said toluene fraction, said ketone being present in amount suillcient to separate selectively from said toluene fraction non-aromatic hydrocarbons present therein which distill therefrom in the absence of said diethyl ketone and water in the same temperature range as toluene contained therein and t0 carry over said nonaromatic hydrocarbons with vapors of said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene.

13. The process for the treatment of a toluene fraction to separate the toluene from non-aromatic hydrocarbons contained therein which distill from the toluene fraction in the same temperature range as the toluene distills therefrom, which comprises distilling said toluene fraction evolved therefrom in the presence of diethyl ketone and water in amount such that at a point in the rectification of the vapors temperatures not substantially above 83 C. are maintained while vaporizing and removing from said toluene fraction hydrocarbons present therein which distill therefrom, in the absence of said ketone and water, in the same temperature range as toluene contained therein.

14. The process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom, which comprises distilling said toluene fraction and rectifying the vapors evolved therefrom in the presence of Water and diethyl ketone, thereby vaporizing said ketone and non-aromatic hydrocarbons present in said toluene fraction, said ketone being present in amount sulcient to separate selectively from said toluene fraction non-aromatic hydrocarbons present therein which distill therefrom, in the absence of an azeotropic agent, in the same temperature range as toluene contained therein and to carry over said non-aromatic hydrocarbons with vapors of said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene, condensing the vapors thus distilled from said toluene fraction to form a liquid distillate, extracting said distillate with water, separating the resulting aqueous layer from the hydrocarbon oil layer, and employing the aqueous layer thus obtained, containing diethyl ketone in solution, for the azeotropic distillation of a toluene fraction containing non-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom.

l5. The process for the recovery of toluene from a toluene fraction containing the same and containing non-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom, which comprises distilling said toluene fraction in the presence of water and diethyl ketone, thereby vaporizing and distilling over a mixture of vapors of diethyl ketone, water and non-aromatic hydrocarbons present in said toluene fraction which distill therefrom, in the absence oi the diethyl ketone and water. in the same temperature range as toluene contained therein, said ketone being present in amount sumcient to separate selectively said non-aromatic hydrocarbons from said toluene fraction and to carry over the non-aromatic hydrocarbons with the vapors of said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene, cooling said mixture of vapors to condense them and iorm a liquid containing two phases, an aqueous phase containing diethyl ketone and a hydrocarbon oil phase, separating the aqueous phase from the hydrocarbon oil, and employing the aqueous solution of diethyl ketone thus obtained for the azeotropic distillation of a toluene fraction containing nen-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom.

16. A process for the treatment o! a toluene fraction to separate toluene therefrom from the hydrocarbons contained therein which ordinarily distill from the hydrocarbon fraction in the same temperature range as said toluene distills therefrom which comprises distllling said toluene fraction in the presence of a sumcient amount of methyl ethyl ketone to vaporize hydrocarbons other than said toluene together with methyl ethyl ketone thereby leaving said toluene in the residue substantially completely separated from the hydrocarbons other than said toluene.

17. A process for the treatment of a toluene fraction to separate toluene therefrom from the hydrocarbons contained therein which ordinarily distill from the hydrocarbon fraction in the same temperature range as said toluene distills therefrom which comprises distilllng said toluene iraction in the presence of a sulcient amount o1' methyl ethyl ketone containing water to vaporize hydrocarbons other than said toluene together with methyl ethyl ketone and water thereby leaving said toluene in the residue substantially completely separated from the hydrocarbons other thansaid toluene.

CHARLES R. CLARK CERTIFICATE OF C ORRECTI ON Patent No. 2,588,0iio.

October 50, 19145.

CHARLES R. CLARK.

It is hereby certified that error appears in the printed specification' of the above numbered patent requiring correction as follows: Page 6, second column, line l, strike out the words "and waterm; and that the said letters Patent should be read with this correction therein that the seme may conform to the record of the case in the Patent Office.

signed and `sealed this 29th day of January, A. o. 19Li6.

(Seal) Leslie Frazer First Assistant Commissione:- of Patents.

and water. in the same temperature range as toluene contained therein, said ketone being present in amount sumcient to separate selectively said non-aromatic hydrocarbons from said toluene fraction and to carry over the non-aromatic hydrocarbons with the vapors of said ketone and water, leaving a hydrocarbon residue of the distillation enriched in toluene, cooling said mixture of vapors to condense them and iorm a liquid containing two phases, an aqueous phase containing diethyl ketone and a hydrocarbon oil phase, separating the aqueous phase from the hydrocarbon oil, and employing the aqueous solution of diethyl ketone thus obtained for the azeotropic distillation of a toluene fraction containing nen-aromatic hydrocarbons which distill from the toluene fraction in the same temperature range as the toluene distills therefrom.

16. A process for the treatment o! a toluene fraction to separate toluene therefrom from the hydrocarbons contained therein which ordinarily distill from the hydrocarbon fraction in the same temperature range as said toluene distills therefrom which comprises distllling said toluene fraction in the presence of a sumcient amount of methyl ethyl ketone to vaporize hydrocarbons other than said toluene together with methyl ethyl ketone thereby leaving said toluene in the residue substantially completely separated from the hydrocarbons other than said toluene.

17. A process for the treatment of a toluene fraction to separate toluene therefrom from the hydrocarbons contained therein which ordinarily distill from the hydrocarbon fraction in the same temperature range as said toluene distills therefrom which comprises distilllng said toluene iraction in the presence of a sulcient amount o1' methyl ethyl ketone containing water to vaporize hydrocarbons other than said toluene together with methyl ethyl ketone and water thereby leaving said toluene in the residue substantially completely separated from the hydrocarbons other thansaid toluene.

CHARLES R. CLARK CERTIFICATE OF C ORRECTI ON Patent No. 2,588,0iio.

October 50, 19145.

CHARLES R. CLARK.

It is hereby certified that error appears in the printed specification' of the above numbered patent requiring correction as follows: Page 6, second column, line l, strike out the words "and waterm; and that the said letters Patent should be read with this correction therein that the seme may conform to the record of the case in the Patent Office.

signed and `sealed this 29th day of January, A. o. 19Li6.

(Seal) Leslie Frazer First Assistant Commissione:- of Patents.

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