US2428467A - Two stage azeotropic distillation of toluene with methanol - Google Patents

Description

vTWO STAGE AZEOTROPIC DISTILLATION 0F TOLENE WITH IETHANOL @@MATTORNEY TQM-'PETRY Erm. 2,428,467

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Patented Oct. 7, 1947 UNITED STAT 2,428,461 orrice F TOLUENE WITH METHAN OL Theodor A. Petry and Russell Lee, Wenonah, and John L. Bles and William V. Betts, Woodbury, N. J., assi'gnors to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corpoy ration of New York Application June 4, 1941, Serial No. 396,532

(Ci. 2oz-42.)

6 Claims.

It has long been known that toluene is present in varying amounts in petroleum fractions of gasoline boiling point and particularly in those gasolines originating from vapor phase vcracking or other high temperature cracking opera- According to a co-pending application, Serial No. 351,716, iled August 7, 1940, any aromatic hydrocarbon present in a petroleum fraction may be substantially wholly recovered, and in relatively high purity, by distilling, in the presence of a suitable azeotrope forming agent, a suitably selected cut of that petroleum fraction, which cut is substantially free of aromatic hydrocarbons of higher boiling point than the sought for aromatic hydrocarbon. A method of determining the cut point to be used in the fractionation forpreparing such selected petroleum fraction is taught therein. It has been found, by examination of numerous types of commercial gasolines, including catalytically cracked, thermally cracked, and straight run gasolines, that a reasonably well fractionated petroleum fraction of about 245 F. end boiling point, (A. S. T. M.), contains substantially all of the toluene originally present, and substantially no higher boiling aromatic hydrocarbons, and that by azeotropic distillation of that 245 F. end boiling point fraction in the presence of methanol, yields of toluene of the order of 90% of the toluene present could be obtained, and the toluene so recovered would beof a relatively high purity, of the order of 90 or 95% to 98%. Reference above to a reasonably well fractionated petroleum fraction of about 245 F. end boiling point (A. S. T. M.) of course, means that-the petroleum fraction had an end boiling point of 245 F. when measured according to testing specifications of the American Society for Testing Materials. Throughout this specication; the abbreviation A. S. T. M.l should be taken to mean the same as the above, that is, that the tests or measurements referred to are taken much simplified.

basic process and Figure 2 of which shows a modification of one portion of the process.

Turning to Figure 1 we find gasoline containing, among other things, toluene, stored in tank 3, which is forwarded by pump 4 through heater 5 `to fractionator 6, where, under reflux introduced at 1 and heat from reboiler 8 it is topped of that portion boiling between the initial boiling point and 200 F. (A. S. T. M.). The overhead distillate is removed by pipe 9 to pipe I0 and storage tank Il. The remaining topped gasoline is forwarded by pump I2 and pipe I3 to a second fractionator I4, where, under reflux introduced at I5 and heat from reboiler I6 a fraction corresponding to that boiling between 200 F. and

245 F. (A. S. T. M.) is removed as an overhead distillate.- The bottoms product, that portion of the gasoline from 245 F. to end point (A. S..T. M.) is removed by pipe l1 andA passes through pipe I0 to tank II. The condensed overhead product of fractionator I4, comprising the 200 F. to 245 F. (A. S. T. M.) fraction nf the gasoline is taken from receiver I8 by pump I9 andpassed -through pipe 20 and heater 2| to fractionator 22, where under reflux introduced at 23 and heat from reboiler 24 and overhead product comprisingl that portion of the gasoline between 200 F. and l215 F. (A. S. T. M.) is removed, to collect in receiver 25 and pass through pipe 26 and pipe I0 to tank Il. The bottoms product of fractionator 22, comprising the 215 F. to 245 F. (A. S. T. M.) cut of the original gasoline, withdrawn by pipe 21 is cooled by passage through heat exchanger 2l and cooler 28 to storage in tank 29 and comprises the toluene-containing feed for the azeotropic distillation step'by the process.

In very many instances the preparation of the hydrocarbon mixture fed to the process may be Non-aromatic hydrocarbons lighter than those normally found in the 215- 245 F. cut will, of course, readily distill therefrom, particularly in the presence of an azeotrope forming substance without carrying away toluene. Benzene, if present, will form with the azeotrope forming substance a constant boiling mixture sufficiently below any formed with toluene that it may be sent away along with the non-aromatic materials. When large amounts of those materials lighter than about 215 F. A. S. T. M. end boiling point arey present, they would preferably be separated as shown to avoid the imposition of their distillation and heat load upon the azeotropic distillation steps. On the other hand, many appropriate starting materials do not contain enough of these lower boiling materials to'render their separate removal prior to the azeotropic distillation economical. In such instances the charge preparation may con' sist only of that step shown still I4 of Figure 1, wherein all of the original gasoline charge of the steps c arried'out i n stills 6 and 22 of Figure l, I which are merely for the purpose of removing.

light ends, being omitted entirely.

The next step for the recovery of toluene inl the "crude" toluene storage tank 68 ,being the same. This modication takesadvantage of the s discovery that water-methanol is an additive for high purity is an azeotropic distillation of 'thev 245 F. end point (A. S. T. M.) cut in the presence of added methanol. This is practiced by 'passing the closely cut gasoline fraction through pipe 30 and heater 3| into fractionator 32 in the presence of an added amount of methanol derived either from tank 33 and introduced by pipe 34 or derived from further process steps'andintroduced by pipe 35, .or both. In fractionator 32, under the iniluence of reflux introduced at 36 and heat from the reboiler 31, the gasoline cut is separated into an overhead product comprising a large portion of the non-aromatic hydrocaroons and all o f the added methanol, which passes through pipe 38 and condenser 39 to receiver 4U, and a bottoms cut containing practically all of the toluene and some of the nony aromatics, which passes through pipe 4|, cooler 42, tank 43, and pipe 44 to a second step of azeotropic distillation. Cooler 42 and tank 43 are,

of course, optional, since in a balanced continuous operation the bottoms cut from 32 may pass directly to the second distillation step. This sec- 'ond azeotropic distillation step is accomplished in fractionator 45 under the innuence of renux introduced at 46 and heat from reboiler 41, in the presence of methanol added by pipe 48. The overhead product from this operation, comprising the non-aromatic hydrocarbons and the methanol passes through pipe 49 and condenser 50 to receiver 5I. From each of the receivers 40 and 5|, a sufcient amount of condensed product is withdrawn and returned as reflux to the respective tower at points 3u and 46, and the remaining overhead product condensate is combined, flowing through pipe 52 to be mixed with water entering through pipe 53,A the whole then passing through mixer 54 into settler 55. 'I'he upper layer in 55 constituting discarded nonaromatic hydrocarbons is withdrawn through pipe '56 and returned through pipe |0 to tank while the lower layer, methanol-water, passes through tank 51 and heater 58 into alcohol recovery still 59 from which a bottom stream of water is taken by pipe 60 to be returned to pipey 53 and to the process and an overhead condensate of methanol is taken by pipe 6| to be returned to process through pipes 62, 48, 35 or to tank 33 by optional use of pipe 03. A portion of this methanolA may be sent, if desired, byv pipe 62 through heater 64 and introduced in vaporphase into the exhausting section of fractionator 45 to act as a stripping medium therein, entering thereinto by pipe 65.

The bottoms product from fractionator 45, withdrawn therefrom by pipe 66, is toluene of a purity of about 98% or even higher, and constitutes about 90% or more of the toluene originally present. Passing through cooler 61 it is sent to tank 68. In case a practically pure toluene is required, as for nitration purposes requiring material of high purity, the 98% toluene may be given an acid treatment with sulphuric acid in treater 69 and the resulting product nished in still 10, yielding a pure toluene in tank 1|.

In Figure II a simpler form of the azeotropic distillation step is shown, all portions prior t-o the placing of the 215-240" F. (A. S. T. M.) cut in tank 29 being the same and all portions beyond azeotropic distillation of better ability for this operation than methanol alone.

'I'he closely cut .gasoline passes from tank 29 `through pipe 12 and heater 13 to fractionator 14 being rst mixed with aqueous methanol from pipe 15. Makeup methanol may be added from 'tank 16 if necessary. In fractionator 14, under the Ainnuence of reflux introduced at 11 and heat from reboiler 18 an overhead lproduct is taken olf through pipe 19 and condenser 90 to receiver 8|. Bottoms product, constituting, as before, all of the toluene and some of the non-aromatic hydrocarbons in the charge is taken through pipe 82, cooler 83, tank 84, and pipe 85 to fractionator 86. In this operation, aqueous methanol having been introduced by pipe 15, water separates within fractionator 14 and is collected on trap tray 81, and removed therefrom through pipe 80 and cooler 89 to accumulator 90. Bottoms product from fractionator 14 proceeding to fractionator 86 through pipe 85 is admixed with aqueous methanol from pipe 9|. In fractionator 86 under the influence of reux introduced at 92 and heatfrom reboiler 93 an overhead product, constituting the methanol and non-aromatic hydrocarbons is formedto pass through pipe 94 and cooler 95 to receiver 96.

As before, the water, from the aqueous methanol charged fractionator 86 is collected by trap i tray 91 and passes through cooler 98 and pipe 99 to accumulator 90'. As before, bottoms product from fractionator 86, constituting about 90% or more of the toluene originally present in the gasoline, andV having a purity of about 98% or higher, tsses through pipe |00 and cooler |0| to tank Of the overhead product collected in receivers 8| and 96, such portion as is not returned for reflux at points 11 and 92 is withdrawn through pipe |02 to mixer |03 where it meets water coming from accumulator 90 through pipe |04, and is delivered into separator |05. The top layer from |05 constituting methanol-free non-aromatic hydrocarbons passes through pipe |06 to disposal with other similar discarded non-aro- The successful operation of this process as a` whole,for the high recovery of toluene of high purity, depends upon carefully effected process steps and controls. Those for the preparation of the gasoline fraction have already been discussed.

Those for the azeotropic distillation step will now be taken up. An increase in the amount of methanol present in such distillations leads to increases in the percent of toluene present in the bottoms, but beyond a certain optimum, simultaneously leads to increasing toluene lost into overhead distillate. It has been found that the optimum amount of methanol to be added for such distillation lies between a minimum of about 86% by volume of the'volume of non-aromatic hydrooarbons present plus 28% by Volume of the volume of toluene, and a maximum of about by volume of the non-aromatics plus 56% by vol-v ume of the toluene.

It has further been found that the amount of reux utilized has a very pertinent bearing.

above will give about 100% recovery of toluene as l' a bottom product of about 70% concentration on initialieeds of around 20%, while with optimum methanol addition and reilux ratios of 8:1 or above it is relatively easy to work such r10% mixtures up to a bottoms product of about 98% or more purity and still reco'ver about 90% or more of the toluene present atreasonable heat loadings, an increase in percent recovered beyond this calling for rises in the reflux ratio and correspondingly increased heat load.

Further, it has been found that because of the inter-relationship oi the optimum amount of. methanol, and the optimum reiiux ratio, that the choice of the most economical scheme of operation, i. e. whether one-stage or two-stage azeotropic distillation, depends upon the amount of toluene present in the starting material. The total amount of material to be sent overhead, and consequently the total heat demand of the process, is greater for a one-stage process than for a two stage process if the concentration of toluene in the initial feed be less than about 40 percent by volume, while above this concentration, the heat demand of a single stage process is less. Consequently, while the process shown in the drawings and described above shows an azeotropic distillation operation consisting of two steps similar except for the toluene concentration of the feed to each, it is to be understood that, depending upon the toluene content of the closely-cut gasoline, a single step may be utilized if desirable.

When toluene content of the 245 F. A. S. T. M. end boiling point petroleum stock is so high as to indicate a single step toluene recovery system, the indicated amount offmethanol will be utilized in this single step recovery. That is, the methanol added will be not less than nor more than M=1.20 (100-T)+ .56T,where T is volume percent of toluene in charge stock and M is percent by volume, based on original charge stock, of methanol added. For example, for 100 bbls. of a charge stock containing 40% toluene, the added methanol would be not less than .86 (100-40) +28 (40) :62.8 barrels, nor more than 1.20 (100-40) +.56 (40) :94.4 barrels.

When the toluene content of the 245 F. A. S. T. M. stock is low enough to indicate a two step toluol recovery system, the calculation of the total added methanol for both steps of the toluene recovery will be the same, but the amount to be added in the first toluene recovery step would be only a fraction, usually about 60'75% of the total. Consequently, the statement of minimum and maximum methanol addition above made applies as well to two-step toluene recovery as to onestep toluene recovery. 1

In its simplest form, then, the process is merely one of two distillation steps, in the rst of which there is prepared a toluene-containing petroleum fraction of about 245 F. (A. S. T. M.) end point, and in the second of which toluene is recovered therefrom in a single distillation step under azeotropic conditions as outlined. Further, as pointed out above, either oi these may be elaborated for economic reasons. Under some circumstances dictated by proportional presence of light ends in the original charging stock it may be advisable to include light ends removal in thepreparation. Also, under certain circumstances of toluene concentration, as outlined herein, lt may be advisable to perform a two stage toluene separation rather than to attempt the accomplishment of this operation in a single step.

Throughout this specification there is made use of the terminology which speaks of a certain petroleum fraction being the 215-245" F. (A. S. T. M.) cu and the like. By this is meant a fraction of the gasoline boiling between the temperatures 215 F. and245 F. as observed in the standard A. S. T. M. distillation of the gasoline.

This application is directed to similar subjectmatter to that disclosed and claimed in applications of Theodor A. Petry, John L. Biles and William V. Betts, Serial No. 351,716, filed Aug. 7, 1940, and Serial No. 400,196, iiled June 28, 1941. The invention disclosed and claimed in those applications is senior to the inventions disclosed and claimed herein.

This application is also directed to subject matter similar to that disclosed in an application of Theodor A. Petry, Henry D. Knoll and Russell R. Lee, led Feb. 5, 1941, which became Patent No. 2,332,493, issued on Oct. 19, 1943. The subjectmatter disclosed and claimed in said patent is senior to the invention disclosed and claimed herein.

We claim:

1. That method of recovering substantially all of the toluene present in a toluene-containing petroleum fraction and recovering said toluene in a high purity of 90% or more, comprising the steps of rst distilling the petroleum fraction to segregate therefrom a charge fraction of approximately 245 F. -end boiling point measured acl cording to the specifications of the American Society for Testing Materials, containing substantially all of the toluene originally present, and then distilling that charge fraction in the presence of an added amount of methanol which is not less than about M=.86(100-T) +.28T where M is the added methanol, expressed as volume percent of the charge fraction and T is the volume percent of toluene in the charge fraction, in which the charge fraction contains less than about 40 percent by volume of toluene, and the charge fraction is first distilled in the presence of a portion of the methanol to yield a first distillation residue containing substantially y all of the toluene and having a toluene concentration substantially more than 40 percent, and that residue is then distilled in thev presence of the remainder of the methanol to yield as a second residue substantially all of the toluene in a condition of relatively high purity.

2. That method of recovering substantially all of the toluene present in a toluene containing petroleum fractionin a high purity of 90% or more which comprises the steps of, iirst distilling the petroleum fraction to segregate therefrom a charge fraction of approximately 245 F. end boiling point measured according to specifications of the American Society ior Testing Materials,

, containing substantially all of the toluene originally present, and then distilling that charge fraction in the presence of an added amount of methanol which is not less than aboutv iii-:.86

(-T) ,-i-.28T where M is the added methanol,

`inne of toluene, and the charge fraction is tlrst distilled in the presence of a portion of the methanol and water to yield a rst distillation residue containing substantially all of the toluene and having a toluene concentration substantially more than 40 percent, and that residue is then distilled in the presence of the remainder of the methanol and water to yield as a second residue substantially all of the toluene in a condition of relatively high purity.

3. In a process for recovering, in a state of high purity of 90% or more, substantially' all oi' all of the toluene originally present, and then dis-y tilling that charge fraction in the presence oi an added amount of methanol vapor which is not less than about M=.86(100T)+.28T where M is the added methanol, expressed as volume percent of the charge fraction and T is the volume the toluene present in a gasoline petroleum fraction, in which, initially such a petroleum fraction is distilled having present in the fraction an amount of toluene less than 40% by volume but containing substantially all vof the toluene originally present and having an end boiling point of about 245 F., secondly, methanol is added to said petroleum fraction, thirdly, the azeotropic mixture is distilled to boil off the methanol with a portion of the non-aromatic compounds and leave a product enriched in toluene, fourthly, additional methanol is added, and fthly, the azeotropie mixture is again distilled to boil off the additional methanol with the remainder of the non-aromatic compounds and leave a substantially pure toluene, the improvement which consists of limiting the amount of methanol added to an amount within a range defined by the lower limit M=.86(100-T) -l-.28T and the upper limit M=1.20(100T +.56T where M is the volume per cent of methanol (based on charge fraction) and T is the volume per cent of the toluene in the charge fraction, and limiting the amounts of methanol added in the iirst stage of azeotropic distillation to a range of .60M to .75M and in the second stage of azeotropic distillation to a range of .25M to .40M.

4. That method of recovering substantially all of thetoluene present in a toluene-containing petroleum fraction and recovering said toluene inI a high purity of 90% or more, comprising the steps of first distilling the petroleum fraction to segregate therefrom a charge fraction of approximately 245 F. end boiling point measured according to specifications of the American Society for Testing Materials, containing substantially all of the toluene originally present, and then distilling that charge fraction in the presence of an added amount of aqueous methanol which is not less than about M=.86(100'T) +.28T Where M is the added methanol, expressed as volume percent of the charge fraction and T is the volurne percent of toluene in the charge fraction, in which the charge fraction contains less than about 40 percent by volume of toluene, and the charge fraction 'is rst distilled in the presence of a portion of the methanol to yield a first distillation residue containing substantially all of the toluene and having a toluene concentration substantially more than 40 percent, and that residue'isV then distilled in the presence of the remainder of the methanol to yield as a second residue'substantially all of the toluene in a condition of relatively high purity.

5. That method of recovering substantially all of the vtoluene present in a toluene-containing petroleum fraction and recovering said toluene in a high purity of 90% or more, comprising the steps Qfrst distilling the petroleum fraction to Y corcling to specifications of the American Society for Testing Materials, containing substantially percent or toluene in the charge fraction, in which the charge fraction contains less than about 40 percent by volume of toluene, and the charge fraction is first distilled in the presence of a portion of the methanol to yield a iirst distillation residue containing substantially all of the toluene and having a tolueneY concentration substantially more than 40 percent, :and that residue is then distilled in the presence of the remainder of the methanol to yield as a second residue substantially all of the toluene in a condition of relatively high purity. V

6. That method of recovering substantially all of the toluene present in a toluene-containing petroleum fraction and recovering said toluene in a high purity of or more, comprising the steps of iirst distilling the petroleum fraction to segregate therefrom a charge fraction of approximately 245 F. A. S. T. M. end boiling point containing substantially all of the toluene originally present, and then distilling that charge fraction in the presence of an added amount of methanol vapor and aqueous methanol which is not less than about M=.86(-T) +.28T where M is the added methanol, .expressed as Volume percent of the charge fraction and T is the volume percent of toluene in the charge fraction, in which the charge fraction contains less than about 40 percent by volume of toluene, and the charge fraction is iirst distilled in the presence of a portion of the methanol to yield a first distillation residue containing substantially all of the toluene and having a toluene concentration substantially more than 40 percent, and that residue is then distilled in the presence of the remainder of the methanol to yield as a second residue substantially all of the toluene in a condition of relatively-high purity.

THEODOR A. PETRY.

RUSSELL LEE.

JOHN L. BILES;

WILLIAM V. BEI'IS. Y

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS OTHER, REFERENCES Journal of Society of Chemical Industry, Japan,

' v01. 35, 1932, page 470B,Artic1e by Mizuta, 2oz-42 misc.

Journal of Society of Chemical Industry of Japan, vol. 35 (1932), pages 1172-1177, vol. 37 (1934), pages 540B, 541B, 542B, 769B, and 770B, V01. 38 (1935), pages 160B, 161B, v01. 39 (1936), pages 258B, 259B, 311B, 312B, 417B, 418.

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