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sept. l1o, -1946.v` c. R. CLARK 2,407,364 PROCESS FOR THE RECOVERY OF TOLUENE FROM OILS Filed July 1o, 1945 1 ATTORNEY 2,407,364 Patented Sept. 10, 1946. UNITED STATES, PATENT OFFICE PROCESS FOR THE REoovERyr OF TOLUENE » FROM OILS Charles R. Clark, New York, N. Y., assignor to ` Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York Application July.10, 1945, Serial N0. 604,130 Vfron'ims. (ol. 2oz-_42) ' This invention relates to a process for recover ing toluene from mixtures containing it Aand other organic liquids. This application is a continuation-impart of my co-pending application Serial No. 343,499, iiled July 1,1940. 2 1 ` Numerous hydrocarbon oils are known which contain toluene in varying proportions. For eX arnple, catalytic treatment of a suitable petro leum fraction in the presence of hydrogen, gives an oil consisting chiefly of hydrocarbons of both aromatic and non-aromatic character, and con taining about 20% toluene. Gasoline fractions obtained by the distillation of certain types of petroleum frequently contain substantial propor tions of` toluene, although mainly consisting of other hydrocarbons. Oils of petroleum origin fraction containing about 82% to 35% toluene appears to represent a product of maximum tolu ene concentration obtainable by direct fractional distillation. Accordingly, recovery of toluene of a relatively high purity from these sources pre sents a diii‘lcultV problem of great industrial im-Y portance.A _ > » ‘ 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 a so-called “nitration grade” of toluene is now preferred. While toluene products con taining substantial proportions of certain hydro carbon oils other than toluene can be nitrated, the mono-nitro compound vmade from them must be purified prior to complete nitration. This ma terially increases the cost and complexity of the having a considerable content of aromatics, in process for making TNT. Furthermore, even cluding toluene, may be treated by well known selective-solvent processes to produce fractions 20 though toluene containing substantial quantities of certain other materials is sometimes used for rich in aroma-tics;A for example, extraction of nitration, this is only because the difficulties of suitable fractions of such petroleum oils with preparing a pure toluene have outweighed the sulfur dioxide may yield fractions of high toluene disadvantages of using the impure toluene for content. In such cases toluene is accompanied by non-aromatic oils which may be largely par- v 25 the production of explosives. Direct fractional distillation, because of the difliculties pointed out aliinic, naphthenic or olefinic in character. A above, Will not eiT'ect a recovery of pure toluene considerable portion of these oils cannot be comN pletely separated from the toluene by direct-fram from oils such as enumerated and in many cases will not give fractions of suitably high toluene tional distillation because of the closeness of their boiling points to that of toluene or because 30 content or free from materials which even in small concentrations adversely affect the nitra .they form constant boiling mixtures with toluene. tion of the toluene or the nitrated product. Furthermore, while ordinarily toluenevis readily It is an object of my invention to provide a separable by direct fractional distillation from process whereby toluene of any desired degree of light oils produced by the gasification of coal, in some cases the toluene is accompanied by diñl 35 purity may be recovered from Oils containing it and other hydrocarbons which distill out over the cultly separable non-aromatic oils of the same same temperature range as >the toluene, which general character as described, owing to car will be referred to as “like-boiling, non-aromatic bonization conditions, type of coal used or other hydrocarbons.” special circumstances. Also synthetic hydrocar bon gas mixtures produced by various catalytic 40 I have now. discovered a relatively pure tolu ene, accompanied by no more" than 5% of like boiling, non-aromatic hydrocarbons, can be re covered from many -oils containing toluene and arable constituents. ~ , other hydrocarbons by an azeotropic distillation ABy fractional distillation of these oils contain ing toluene, fractions relatively high in toluene` 45 of the oil under the conditions hereinafter de scribed. ' content may be obtained. These toluene frac processes may contain toluene which, when re-> covered, is accompanied by similar ldirliculty sep tions, however, will still contain large amounts In using my invention for the treatment of an Oil such as has been described above, containing of the other constituents. of the oil having boil» toluene and other hydrocarbons, particularly ing points in the neighborhood of the boiling point of toluene or forming mixtures of constant 50> when the toluene concentration of the oil is low boiling points in the range 0f temperatures at ' which toluene distills from the oil. For example, by distillation of the above-described types of oils or the oil is one containing materials of wide boiling range, I prefer first to non-azeotropically fractionally distill the oil (i. e., to fractionally distill the oil in the absence of added azeotropic ditions practicable for rectifying the vapors, a 55 agent) to recover therefromv an enriched tolu» containing toluene under the most eilìcient con 2,407,364 3 4 ene fraction which contains, in addition to tolu ene, other hydrocarbons Which distill at the same temperatures as the toluene. Although toluene fractions having an end boiling point substan tially above the boiling point of toluene (e. g. a in the still and/ or rectification column during the distillation of the toluene fraction to selectively carry over through the rectiñcation treatment the vapors of the hydrocarbons to be removed from the toluene. Some of the toluene may also bc boiling point Urp to 113° C.) may be azeotropically distilled in the manner hereinafter described, I >carried over., ybut so long as the above tempera tures are not exceeded, the undistilled residue will be enriched in toluene and by continuing the distillation, separation of the toluene from the hydrocarbons of similar boiling range will be ac prefer the toluene fraction recovered in the pre liminary non-azeotropic distillation step by one having a maximum boiling point substantially corresponding to the boiling point Vof pure tolu complished. After the distillation has been carried to the ene; i. e., 111° C. Further, for the reasons which point at which the residue containing toluene has the desired purity with respect to hydrocarbons will be more specifically pointed out below, 1I pre fer that the toluene fraction recovered by the preliminary distillation of the crude toluene oil distilling Vfrom the toluene fraction in the same temperature range as the toluene distille there be so cut as to exclude therefrom the forerun from in the absence of the azeotropic agent, the distillation may be stopped and the residue With drawn from the still. Usually the toluene frac tion subjected to azeotropic distillation in prac nìngs which do not contain substantial propor tions of toluene, for example to exclude any ma terials distilling beloW 100° C. A toluene fraction such as may be obtained by ticing this invention will be one having a top this preliminary distillation, which may contain parafñns, naphthenes, or oleñns, is subjected -to boiling point not above 118° C. and preferably not above 111° C. The toluene fraction, therefore, will contain little, if any, hydrocarbons boiling from the fraction at `temperatures above those at which toluene boils therefrom. Accordingly, the residue Withdrawn from the still `ordinarily Will contain toluene and other hydrocarbons in the a second distillation in the presence of the methyl, ethyl or butyl ether of ethylene glycol. TheseV materials act as azeotropic agents during the distillation. I have discovered that when one of these materials is mixed With a toluene frac tion such as described above and the mixture is proportion of 95 or more parts toluene to 5 or tion of the vapors under conditi-ons such vthat a 30 less parts of total hydrocarbons other than toluene. It may be puriñed further, as desired, to temperature not exceeding a Well deñned maxi remove any azeotropic agent it contains and to mum is maintained at a point in the rectiñcation subjected to fractional distillation with rectifica remove any other impurities present. When the of the vapors, non-toluene hydrocarbons present distillation is carried to the point at Which all of in the toluene fraction are distilled from the mix ture in the form of their azeotropes with the 35 the azeotropic agent has been distilled out of the residue and lthe toluene constitutes substantially 99% or more of the »total hydrocarbon content of the residue, the residue, which may be given a azeotropic agen-t to leave a residue containing toluene of a desirable high purity with respect to its content of other hydrocarbons originally pres ent in the toluene fraction and not separable from the toluene by direct fractional distillation of the toluene fraction in the absence of the conventional treatment, for example, treatment With sulfuric acid and redistillation, is suitable for marketing as a nitration grade toluene of particularly high purity. azeotropic agent. My invention comprises azeotropically distilling ’Instead of withdrawing the toluene residue from the still, the distillation may be continued a toluene fraction containing hydrocarbons which have similar boiling points to that of the »toluene` 45 and the toluene distilled over and separately col lected from the distillate containing the hydro With rectification of the evolved vapors in the carbons from which the toluene residue previously presence of the azeotropic Vagent While maintain has been separated by azeotropic distillation. If ing at a point in the rectification of the vapors a azeotropic agent is present during the distillation temperature not -above the boiling point of the azeotrope Vof toluene and the azeotropic agent 50 and collection of the toluene, the azeotrope of toluene may be distilled out. The toluene may be (hereinafter referred to as the “control tempera separated in any suitable manner from the ture”), until the unvaporized residue contains at toluene azeotrope recovered by distillation, for least 95 parts by weight toluene for every 5 parts example by extraction with a liquid which will by weight of said hydrocarbons, which boil from a mixture consisting of toluene and the hydro 55 form separate layers, one containing the toluene and the other containing the azeotropic agent. carbons in the same temperature range as the Water is a suitable liquid for effecting this sepa toluene boils therefrom. This control tempera ration. In the absence of azeotropic agent, in ture will depend upon the azeotropic agent used< distilling out the toluene the temperature in the The following Vtable gives for each material the rectification column may rise to the boiling point control temperature» at or below which the vapors 'of toluene under the conditions prevailing as to should be maintained at some point in their pressure, etc. rectification when using a given material for the As stated above, ordinarily the toluene fraction distillation of a toluene fraction: . U Azeotropic agent . - Control tem treated in accordance With my invention will con 65 tain` little, if any, hydrocarbons distilling from the hydrocarbon-toluene fraction at temperatures perature D above those at which toluene distills therefrom. On the other hand, it is not necessary that such C’. Mono-methyl ether of ethylene glycol ______________ ._ Mono-ethvl other of ethylene glycol ________________ ._ 106 110 Mono-butyl ether of ethylene glycol _______________ . , 110 high boiling hydrocarbons always be excluded 70 from the mixture of aaeotropic 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 Regulation of the temperature in the rectiñca tion of the vapors to meet the conditions set forth above is accomplished by maintaining an adequate quantity of the azeotropic agent present l75 all high boiling hydrocarbons have not been re moved. In that case, the high boiling hydrocar 2,407,364 . . 5 drawn therefrom. The cut in vessel 9 contains the bons may be left with the toluene residue at the conclusion of the azeotropic distillation of the low boiling fraction of the original oil. The resi due Withdrawn from the still contains the high boiling components of that oil. This fraction and residue may be treated or yused in any desired toluene fraction under the conditions set forth . above to separate the toluene from the hydrocar bons of similar boiling range. After this separa tion has been effected, one may then separate the manner. in the residue by fractional distillation in the ab sence of the azeotropic agent. My invention will be more particularly illus trated and described vin conjunction with the fol . Instead of discontinuing the distillation after the desired cutis taken off to vessel I0, the distil toluene from» high Aboiling hydrocarbons present lation may be continued and the condensate pass 10 ing forward through pipe 8 collected in a third vessel, not shown in the drawing, While the distil lation is continued as long as may be desired. The cuts in vessel 9 and this third vessel contain low lowing example. The accompanying drawing diagrammatically and high boiling fractions of the original oil. If the processes of this example. 15 the cut taken ofi” to the third vessel is limited to one containing substantial proportions of toluene, f The apparatus of the drawing comprises a still e. g. up to 115° C. or 120° C., this cut may be redis-` I provided witha heater 2 and ‘connected with a illustrates an apparatus suitable for carrying out Y rectification column 3' and a condenser 4 for the vapors leaving the top of the- column. By means Vof valves 5 and 6, condensate flowing from con denser 4 is returned through pipe 'I to the top of column 3 and refluxed in contact with the vapors rising in the column. The other portion of the condensate is withdrawn through pipe 8. Two receivers 9 and Ill are connected to pipe 8 through valve-controlled branch pipes: II and I2 so that the condensate drawn off through pipe B may be divided and distributed as described below to the vtwo receivers. Receiver IQ is connected by a pipe I3 controlled by valve I4 with a second still I5. Still I5, like still I, is provided with a heaterk I 6, a rectification column I‘I, a condenser I8 and pipes I9 and 29 controlled by valves 2| and 22 for return of de termined proportions o-f condensate from con denser I8 to the top of column I'I and withdrawal of another portion of the condensate through pipe 20. Pipe 2D leads to a separator 23 into which water may be introduced from a pipe 24. In carrying out one embodiment of my inven tilled o-r introduced to still I with a subsequent ~ batch of oil, and the toluene in this cut recovered. 20 With efñcient rectification of the vapors in col umn 3 during the fractional 'distillation of the crude toluene oiljthe cut collected in vessel I0 contains about '74% by Weight of toluene, as de termined by the specific dispersion method for 25 analyzing hydrocarbon oils described in Industrial and Engineering Chemistry, Analytical Edition, vol. l1, page 614, November 15, 1939. The toluene fraction collected in vessel Iß is subjected to azeotropic distillation, which repre 30 sents the second stage of this example. For this purpose the toluene fraction containing '74% tolu ene was introduced into still I5 together with commercial methyl ether of ethylene glycol. The mixture o-f-methyl ether of ethylene glycol and 35 toluene fraction Was distilled with rectiiication of the vapors in column I‘I and condensation of the vapors: leaving the top of the column in con denser I`8. Most of the condensate was returned through pipe I9 to the top of column I‘I while the 40 remainder was withdrawn through pipe 20 to sep tion in the apparatus described above, a liquid arator 23. n , hydrocarbon mixture containing about 20% tol« Toluene and the methyl ether of ethylene gly uene, 20% of other aromatic hydrocarbons and the remainder substantially consisting of paraf iinic and naphthenic hydrocarbons, with only traces of oleñns, was introduced into still I. This crude toluene material was produced by catalytic treatment of a petroleum distillate in the presence col form an azeotrope having a boiling point of 106° C. Azeotropes formed with the methyl ether of hydrogen. f The charge of this hydrocarbon mixture intro- f `duced into still I was boiled in the still and the evolved vapors were counter-currently contacted in column 3 with reñux from condenser 4, in which the vapors leaving the top of the column were substantially entirely condensed. ' of ethylene glycol by the hydrocarbons other than toluene present in the toluene 'fraction in troduced into still I5 have boiling points suffi ciently below that of the toluene azeotrope for them to be preferentially vaporized and by recti fication in column I1 to be largely separated from the toluene and- any toluene-methyl ether of ethylene glycol azeotrope which is vaporized in still I5 and enters column I1 so long as there-is suflicient methyl ether of ethylene glycol pres Most 01"-,y f ent in the vapor and liquid phases in the recti fication column. _ As pointed out above, the req the condensate from condenser 4 was returned through valve 5 and pipe ‘I to the top of the col umn to furnish the reflux for the column, the re uisite quantity of methyl ether of ethylene glycol to be supplied is that which will maintain the maining small portion of the condensate being temperature at apoint in the rectification col continuously withdrawn through valve G and pipe Gi) umn, preferably at the top of the column, not 8 and passed into collecting vessel 9. The distilla above 106° C. In this example the requisite tion was conducted under substantially atmos quantity of methyl ether of ethylene glycol is pheric pressure; i. e., the pressure in condenser d vsupplied in the initial fcharge to the still by in and at the top of column 3 was substantially at troducing about 30 volumes of the methyl ether mospheric and the pressure in still I was only. of ethylene glycol for every 100 volumes of the enough higher to force the vapor through the rec toluene fraction.. Methyl ether of ethylene gly tiñcation column to the condenser. col is vaporized from the still, enters the recti When the vapor temperature in the top of colñcation column as vapor and in part is returned umn 3 reached 109.’7° C., the condensate passing to the column as liquid in the condensate from through pipe 8 was diverted to vessel I0. The cut ~ condenser I8. If insuiñcient methyl ether of eth taken in vessel I0 included the distillaœ coming ylene glycol is initially introduced in the charge over up to and at a temperature of 110.8° C. at to the still, additional methyl ether of ethylene the top` of the column. After this out has ~been glycol, sufficient to maintain the requisite tem taken off to vessel I D, the distillation may be dis perature in the rectification column, may be sup continued and the residue left in the still with- ' plied as the distillation progresses. , This methyl 7 ether of ethylene glycol may be introduced either into the still or into the rectification column it self. The toluene is in large part returned down the rectilication column and retained in the still, 5 the azeotropic agent a toluene fraction boiling, for example, from 95° C. to 118° C., but the quan tity of azeotropic agent present in the distilla tion of the toluene fraction of wider boiling range while the azeotropes of the methyl ether of ethyl- .i must be substantially increased as compared with ene glycol with the other hydrocarbons are dis the quantity which sufñces for distilling the frac tion of the narrower boiling range. tilled out and are collected in separator 23. The loss of toluene from the still to the condensate While I have described my process in conjunc ion with an example in which the two distillation steps are batch procedures, either or both of efficiency with which the vapors are rectiñed. these distillations advantageously may be carried Efficient rectiñcation is employed in order to keep out continuously by well known continuous dis down this loss of toluene. tillation procedures suitable for the fractional in carrying out the process of this example, distillation of mixtures of two or more liquids. as the distillation continued the temperature of The minimum ratio of azeotropic agent to the the vapors at the top of column l'l rose to about toluene fraction which is suitable for carrying out 106C’ C. The toluene content of the oil obtained my invention will vary with the particular agent from the condensate withdrawn through pipe 2l) used, the amount and nature of the hydrocarbon by Washing the condensate with water to free it impurities in the toluene fraction, the purity de of methyl ether of ethylene glycol increased to sired in the toluene residue _from the distillation, about 99 %. At this point the distillation was the proportion oi’ toluene in the original toluene discontinued. The residue left in still I5 may fraction which is to be recovered in the residue be Washed with water to remove methyl ether from the distillation, and theprocedure used for of ethylene glycol. The oil layer which separates the azeotropic distillation. The ratios of the from a water-methyl ether of ethylene glycol 25 above examples are suitable for a batch process layer contains about 99% toluene. carried out according to the procedures of the By agitating the distillate collected in separa example. irrespective of the particular batch or tor 23 with Water and allowing the liquid to re continuous procedure used, the quantity of azeo main quiescent for a short time, it will separate tropic agent used in the distillation of hydro into» two layers. The upper layer is an oil con taining the non-toluene constituents of the tol- u carbons from a given quantity of toluene frac tion should be in excess of that which will form nene fraction originally supplied to still I5 and azeotropic mixtures with the non-toluene hydro the portion of the toluene carried over in the carbons which are to be vaporized and taken over distillation. 'This oil may be treated or used as into the distillate. This quantity of azeotropic desired. By separately recovering and treating agent includes fresh agent introduced into the the distillate in two portions, two oil fractions material being distilled and also any of the azeo may be obtained; one low in toluene, which may tropic agent which may be separated from the be added to toluene oil distilled in still I, and distillate and. returned continuously or periodi a second oil fraction high in toluene, for exam cally to the still or rectiiication column while the ple containing 74% toluene, which may be in troduced into the toluene fraction from vessel I0 40 distillation of the toluene fraction is progressing. rlleinperature readings are taken of the vapor at and redistilled with this fraction in a subsequent the top of the rectification column and, by sup distillation in still i5. By thus reworking the dis- . plying additional azeotropic agent when required tillate the toluene it contains may be recovered. to prevent this temperature from rising above the The aqueous methyl ether of ethylene glycol layer separated in treating the distillate with Water » boiling point of the toluene azeotrope, an ade quate amount of azeotropic agent will be present may be treated in any of the well known man during the separation of the non-toluene hydro ners to recover methyl ether of ethylene glycol carbons from the toluene fraction. It is not therefrom for use in distilling a subsequent batch necessary that this point of control temperature of toluene fraction. l be at the top of the column, although this is a The procedure of this example may be em drawn off through pipe 20 will depend upon the ployed to recover 95% or purer toluene from the starting hydrocarbon mixture using ethyl ether of ethylene glycol or butyl ether of ethylene gly col as the azeotropic agent in place of the methyl ether of ethylene glycol. Numerous changes and modiñcations may be made in the above-described processes without departing from my invention. While in the first distillation step of the crude toluene oil it is pre ferred to take off a toluene fraction having an end boiling point of substantially 111° C. and fractions with a higher end boiling point, such satisfactory point for determining this tempera ture in the equipment used for fractionating the vapors and condensing the fractionated vapors in the above examples for effective use of the recti ñcation column. One skilled in the distillation art will recognize suitable points for maintaining this control temperature in any other specinc appara tus according to well known distillation prin ciples. It is, of course, obvious preliminary distillation of a crude toluene oil to obtain a toluene fraction suitable for recovery of toluene therefrom by the azeotrcpic distillation need not be carried out in immediate conjunction with the azeotropic dis leeway is permitted in the temperature at which 65 tillation. rlille toluene fraction may be produced in one plant, transported to and treated later in the toluene fraction starts to be taken off; i. e., another plant to aueotropically distill it. Nor is in the initial boiling point of the toluene frac my invention limited to any particular procedure tion. Nevertheless, it is preferred the toluene for the production oi’ the toluene fraction. My fraction subjected to azeotropic distillation be one boiling in the range of 100° C. to 111° C. 70 invention contemplates distilling with the methyl, ethyl or butyl ether of ethylene glycol any oil Such a fraction may be distilled in the azeotropic containing toluene together with other hydro distillation step of my process and pure toluene carbons which, when the oil is distilled, vaporize obtained with a relatively small quantity of azeo as 118° C.; may be successfully distilled azeo tropically to obtain pure toluene, even a larger therefrom in the same temperature range as the tropic agent present during the distillation. Pure toluene may be obtained by distilling with 75 toluene and, therefore, are not separable from the 2,407,364 l0 toluene by direct fractional distillation. As used in this speciñcation and the appended claims, the which ordinarily distillV from said hydrocarbon fraction in the same temperature range as toluene containing oils, whether produced by fractional distills therefrom which comprises azeotropically distilling said hydrocarbon fraction in the distillation or toluene-containing materials or by presence of a sufficient amount of a material from any other means. the group consisting of the methyl, ethyl and butyl ethers of ethylene glycol to vaporize the non-aromatic hydrocarbons together With the ether of ethylene glycol thereby leaving toluene term “toluene fraction” refers to all such toluene In this specification I have described the azeo tropic distillation of toluene fractions as carried out under substantially atmospheric pressure. It is, of course, possible to aaeotropicaliy distill the toluene fraction under pressures above or below atmospheric. In that case the particular tem perature used as a control for the amount of azeo tropic agent present in the distillation will corre spond to the change inthe boiling point of the ` toluene azeotrope with change in pressure. The temperatures as given in this specification and in the appended claims are corrected tempera tures for oner atmosphere pressure (760 mm. of Hg). I claim: l ’ - " in the residue substantially completely separated from the hydrocarbons other than the toluene. 3. A process for the treatment of a hydrocar bon fraction containing toluene and non-aromatic hydrocarbons to separate toluene from the non aromatic hydrocarbons contained therein Which ordinarily distill from said hydrocarbon fraction in the same temperature range as toluene distills therefrom which comprises azeotropically dis tilling said hydrocarbon fraction in the presence of a suñicient amount of methyl ether of ethylene f glycol to vaporize the non-aromatic hydrocarbons together With the methyl'ether of ethylene glycol ' 1. A process for the treatment of a hydrocar bon fraction containing toluene and non-aromatic thereby leaving a residue substantially enriched hydrocarbons to separate toluene from the non in toluene. aromatic hydrocarbons contained therein which 25 4. A process for the treatment of a hydrocar ordinarily distill from said hydrocarbon fraction bon fraction containing toluene and non-aromatic in the same temperature range as toluene distills hydrocarbons to separate toluene from the non aromatio hydrocarbons contained therein which therefrom which comprises azeotropically distill ing said hydrocarbon fraction in the presence of a ordinarily distill from said hydrocarbon fraction suñicient amount of a material from the group / in the same temperature range as toluene distills consisting of the methyl, ethyl and butyl ethers of ethylene glycol t0 vaporize the non-aromatic hydrocarbons together with the ether of ethylene glycol thereby leaving a residue substantially en therefrom which comprises azeotropically dis tilling said hydrocarbon fraction in the presence of a sufficient amount of methyl ether of ethylene glycol to vaporize the non-aromatic hydrocarbons together With the methyl ether of ethylene glycol thereby leaving toluene in the residue substan riched in toluene. ' . 2. A process for the treatment of a hydrocar bon fraction having an end boiling point not above 118° C. and containing toluene and non aromatic hydrocarbons to separate toluene from the non-aromatic hydrocarbons contained therein tially completely separated from the hydrocar bons other than the toluene. CHARLES R. CLARK.