US2504830A - Recovery of ortho-xylene by chemical treatment and distillation - Google Patents

Description

Aprll 18, 1950 R. B. GREENE RECOVERY OF ORTHO-XYLENE BY CHEMICAL TREATMENT AND DISTILLATION Filed sept. 19, 1945 Patented Apr-` 18,

`I UNI-TED* STATES PATENT ola-loe RECOVERY F ORTHO-XYLENE BY CHEMI- CAL TREATMENT AND`DISTILLATION Richard B. Greene, Melrose Park, Pa., assignmto Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York Application September 19, 1945, Serial No. 617,243

1 Claim. l

This invention relates to a. process for recovering substantially pure ortho-xylene from .oil mixtures containing the same together with other hydrocarbons. Y

Numerous hydrocarbon oils are known which contain xylenes, including ortho-xylene, in various proportions. For example, gasoline fractions obtained by the distillation of certain types of petroleum or gasoline fractions recovered from the products of cracking or aromatizing petroleum oils frequently contain substantial proportions of xylenes, including ortho-xylene, although mainly consisting of other hydrocarbons which may be largely paraflnic or naphthenic or oleflnic in character. A considerable portion of these non-aromatic oils cannot be separated from the xylenes by direct fractional distillation because of the closeness of their boiling points to that of the xylenes or because they form constant boiling mixtures with the xylenes. While ordinarily the xylenes contained in light oils produced by the gasification of coal may be separated from the other hydrocarbons by direct fractional distillation of the light oils, this method of treatment does not lead to the -recovery of substantially pure ortho-xylene. This is particularly true of drip oils and oil fractions recovered therefrom containing ortho-xylene and other like-boiling hydrocarbons, e. g. naphthenes, paraiins and olens. By drip oil I refer to those condensates from carburetted water gas such as the condensates formed in the gas distributing lines or holders or the light oil which may be condensed in cooling carburetted water gas after removal of tar. A common characteristic of drip oils is that in addition to aromatic hydrocarbons they contain a substantial proportion of like-boiling, non-aromatic hydrocarbons including the olens as well as paraflins or naphthenes. Numerous synthetic hydrocarbon mixtures produced from petroleum, particularly those produced by subjecting the petroleum oils to a high temperature thermal cracking, are frequently similarly characterized by containing xylenes and a substantial proportion of like-boiling oleiins as well as large amounts of other nonaromatio hydrocarbons.

By fractional distillation of these oils containing xylenes, fractions of increased ortho-xylene content may be obtained. These fractions, however, will still contain a large amount of other constituents of the oil having boiling points in the neighborhood of the boiling points of ortho- :Lvlene or forming mixtures of constant boiling points in the range of temperatures at which the ortho-xylene dlstills. from the oil. The fact that the oils containing xylene generally have a relatively low content of xylenes of which only a part is ortho-xylene makes it particularly diillcuit to recover therefrom an ortho-xylene product of a high degree of purity. For example, drip oils may contain about 5% ortho-xylene. Distillation of a drip oil with emcient rectification of the vapors may be employed to recover a xylene fraction in which the ortho-xylene is concentrated. However, evenwith efficient rectication a fraction containing more than about to 85% ortho-xylene can rarely be obtained. Oleflns, parailins, metaand para-xylene and usually some naphthenes make up the remaining 15% to 20% of the ortho-xylene fraction. The non-aromatic hydrocarbons individually may have boiling points ranging from considerably below to above the boiling point of orthoxylene, e. g. their boiling points may range from 10 to 155 C., whereas ortho-xylene boils at about 144 C. Nevertheless, these non-aromatics cannot be separated from the ortho-xylene by fractional distillation of their mixtures, e. g. drip oils and cracked petroleum oils, under practical conditions. Apparently in the mixture the various hydrocarbons form azeotropes with each other and this prevents their separation by fractional distillation. Such hydrocarbons, those which cannot be separated by fractional distillation or are diilicultly separable by fractional distillation under practicable conditions for distilling oils, are referred to as like-boiling hydrocarbons. Chemical treatment of oils containing ortho-xylene and like-boiling hydrocarbons may be used to recover pure ortho-xylene therefrom, but such known methods are cumbersome and expensive.

It is, therefore, an object of this invention to provide a process for the separation of orthoxylene from oils containing the same which includes azeotropically distilling an ortho-xylene fraction of the oil in the presence of yan azeo.- tropic agent which is particularly effective for separating from the ortho-xylene like-boiling, non-aromatic compounds contained in the oil.

I have discovered that the methyl ether of ethylene glycol is a particularly effective azeotropic agent for the selective separation from ortho-xylene of other like-boiling hydrocarbons.

I have discovered that by a process in which distillation of an ortho-xylene fraction with rectication of the vapors in the presence of methyl ether of ethylene glycol to selectively separate non-aromatic hydrocarbons from the orthoxylene is combined with a fractional distillation distillation methods, it is adapted to large scale operation for the recovery of a substantially pure ortho-xylene from oils containing the same.

With respect to the treatment of drip oil and oil fractions obtainable therefrom by distillation.) the recovery of pure ortho-xylene from' such oils presents a peculiar problem. While pure toluene and benzene may be obtained from certain drip oil fractions by washing the oil with concentrated sulfuric acid and fractionally distilling the washed material, this is not applicable to the recovery of substantially pure ortho-xylene from drip oil concentrates. Furthermore, distillation in the presence of numerous azeotrpic agents which are eective to recover xylenes from other aromatic oils is not similarly effective for the recovery of theortho-xylene in drip oils. However,.I have discovered that the methyl ether cf ethylene glycol is a particularly effective azeotropic agent for the separation of like-boiling,

non-aromatic hydrocarbons from ortho-xylene in drip oils and drip oil fractions derived therefrom as well as for the separation of these materials in oils from other sources.

The ortho-xylene fraction which is azeotropically distilled in carrying out the process of this invention preferably is one which distills non-azeotropically'within the range 125. to.150 C. Accordingly, when a wide-boiling oil containing ortho-xylene is to be treated in accordance with my invention, it is nrst fractionally distilled with effective rectification of the vapors to producea fraction in which the ortho-xylene is concentrated, preferably one distilling within this range of 125 to 150 C., and this ortho-xylene fraction is then subjected lto the azeotropic distillation step of my process. Better yet, in fractionally distilllng ythe initial oil the cut distilling over at temperatures within the range 136 to 144 C. is separately collected for recovery of the orth'oiulene therein. The ortho-xylene will be largely concentrated in a cut distilling within this relatively narrow temperature range and lower and higher boiling hydrocarbons will be largely excluded. This increases the efilciency with which the ortho-xylene fraction may be treated by the subsequent steps of the process for the recovery of pure ortho-xylene.

I In the treatment of various oils containing ortho-xylene I have found that the presence of large amounts of oleilns in the oil fraction subjected to the azeotropic distillation with the methyl ether of ethylene glycol interfereswith the separation of the ortho-xylene from other hydrocarbons. So long as the oleilns content of the oil azeotropically distilled is low enough for the oil to have a Francis Bromine No. no greater than 0.13 the olens do not prevent pure orthosylene being recovered. This Francis Bromine No. of an oil is a measure of its olen content and is determined by the method described in Industrial and Engineering Chemistry, vol. 18 (1926)., pages 821-822 and 1095.

Many oils containing ortho-xylene have a suitably low concentration of oieilns distilling in the range of temperatures at which ortho-xylene distills therefrom so that the ortho-xylene recovered from such oils has, without any further special treatment. a low enough olefin content 4 y cordance with the process of this invention.

There are, on the other hand. oils containing ortho-xylene and relatively high concentrations of oleilns which. when fractionally distilled, yield ortho-xylene concentrates high in olefins. Such oils or the ortho-xylene concentrates recovered therefrom should be washed with concentrated sulfuric acid in amounts sufficient to decrease the olefin content so that the ortho-xylene concentrate recovered for azeotropic distillation has a Francis Bromine No. not higher than 0.13 specified above. This sulfuric acid wash may be applied to the oils at any point prior to the azeotropic distillation, e. g. the original oil may be acid-washed and neutralized. and the resulting product then fractionally distilled to take oi! an ortho-xylene concentrate sufllciently lpw in olefins for treatment by the azeotropic distillation step. Instead of acid washing the original oil containing ortho-xylene, it may be desirable to ilrst fractionally distill this oil, recovering therefrom an ortho-xylene concentrate which is then acid-washed with sulfuric` acid and neutralized before being azeotropically distilled.

The concentrated ortho-xylene fraction described above isffractionaly distilled in the presence of methyl ether of 4ethylene glycol in the zone where rectification of the oil vapors takes place. The methyl ether of ethylene glycol forms azeotropes with non-aromatic hydrocarbons boil-- ing in the same temperature range as the orthoxylene and carries these hydrocarbons over as distillate leaving a residue inwhich the orthoxylene is concentrated substantially free from ilse-boiling, non-aromatic'hydrocarbo'ns. At the same time any materialsl-Pesent inthe oil sub- Jected to the distillation which, in the absence of an azeotropic agent,jdistill'fiom the oil at temperatures lower than the ortho-,xylene distills therefrom, are taken over'into the distillate of the azeotropic distillation and are removed from the residue containing thegyl'enef In carrying out any aaeotropicfdi'stillation such as is involved in the processof this invention, it is particularly important to be. able to recover the azeotropic agent for reuse. I -have'discovered that this may be done very eil'ectively by a procedure which involves the of twoazeotroplc agents for the distillationofthe xylene concentrate. The -methyl ether 'vofkethylene glycol is employed in the ilrst azeotropic distillation of the ortho-xylene concentrate, where it is particularly effective to accomplish av separation of the likeboiling, non-aromatic hydrocarbons from the ortho-nylene. The former are 4carried over with methyl ether of ethylene glycolas vapors of an azeotropic mixture of the hydrocarbons and methyl ether of ethylene glycol. By fractionating this azeotropic mixture with water, the water forms azeotropes with they non-aromatic hydrocarbons and carries them 'over as distillate while the methyl ether of ethylene glycol, having a higher boiling point than the water-hydrocarbon azeotropes, is left behind as bottoms and may be for the oil to be azeotropically distilled in acwith the vaporsof-themethylether of ethylene vapors in the presence -oi' v Inthus# operating.- the methyl ether-.of ethylene glycol isl condensed and separated from lthe hydrocarbons'` which are carried overas vapor with the water.

A substantially pure ortho-xylene product is recovered from the residue'of the aaeotropic distillation of the ortho-xylene concentrate in the presence of methyl ether'oi ethylene glycol, by fractionally distilllng the residue of this aseotropic distillation in the absence of the methyl ether of ethylene glycol. In this fractional distillation an oil consisting of substantially pure ortho-xylene having a melting point not lower than 27.5 C., preferably not lower than -26' C., is distilled over and collected separate from any forerunnings and higher boiling materials. If desired. the substantially pure ortho-Iene thus obtained may be given a further conventional puriiication, such as washing with concenti-ated sulfuric` acid and redistillation.

The ratio of methyl ether of ethylene glycol to the ortho-xylene fraction which may be employed in carrying out the azeotropic distillation step of this invention depends upon the amount and nature of the hydrocarbon impurities in the ortho-xylene fraction, the proportion of orthoxylene in the xylene fraction which is azeotropically distilled, and the procedure and equipment used for distillation of the mixture of methyl ether of ethylene glycol and ortho-xylene fraction. The quantity of methyl ether of ethylene glycol used in the distillation of hydrocarbons from a given quantity of ortho-xylene fraction preferably is in excess of that which will form azeotropic mixtures with the hydrocarbons which are to be va-porized and taken over with methyl ether of ethylene glycol as distillate. By recovering and returning most or all of the methyl ether of ethylene glycol from the distillate and returning it as reflux liquid to the still or rectifica- "tion column of the apparatus in which this distillation is carried out, the totalamount of methyl ether of ethylene glycol necessary to effect separation of the,y non-xylene constituents'and the xylene will be materially reduced. The methyl ether of ethylene glycol separated from the distillate may be returned continuously or periodically to the still or rectification column while the distillation of the xylene fraction is progressing. Fresh methyl ether of ethylene glycol may be introduced into the ortho-xylene fraction being distilled during the course of the distillation. Suitable conditions with respect to the amount-of methyl ether of ethylene glycol present in the distillation may be maintained by supplying enough methyl ether of ethylene glycol so that the temperature at the top of the fractlonating column (or other suitable control point in the zone where the vapors of hydrocarbons and methyl ether of ethylene glycol are rectified) does not exceed 124-125 C., the boiling point of the methyl ether of ethylene glycol, until the desired separation of like-boiling, non-aromatic hydrocarbons from the ortho-xylene has been effected.

ortho-xylene. Once v water hasv been distilled over.however.` onfcon.-l

tinued Idistillatioi'i themethyl ether of ethylene glycol is thenyaporized and in the fractionation of the vapors serves to selectively separate from the ortho-xylene like-boiling, non-aromaticv hydrocarbons.

Water may, however, separating the azeotropic mixture of methyl ether of ethylene glycol and hydrocarbons with `the former being recovered in a substantially anhydrous condition for reuse in azeotropically distilling the ortho-xylene fraction. This is accomplished' by distilling the mixture of methyl ether of ethylene glycol and hydrocarbons with an amount of water limited to that which carries over into the distillate the hydrocarbons vaporized as azeotropes with the methyl ether of ethylene glycol. The methyl ether of ethylene glycol will then be separated from its azeotropes with the hydrocarbons and be left inthe residue uncontaminated with suiiicient water to materially decrease its effectiveness for separating the ortho-xylene from like-boiling, non-aromatic hydrocarbons. When the ortho-xylene fraction is distilled and the vapors rectified in a rectification column first in the presence of methyl ether of ethylene glycol and then in a higher zone where water is present, by suitably limiting the amount of water introduced into the column, water will be present only in the upper portion of the column and the methyl ether of ethylene glycol which is condensed and flows back into contact with the mixture of vapors of ortho-xylene and non-aromatic hydrocarbons will contain little enough water so that in the lower portion of the column the characteristic effective separation of like-boiling, non-aromatic hydrocarbons from ortho-xylene accomplished by substantially anhydrous methyl ether of ethylene glycol will be obtained.

The following examples are illustrative of the use of my invention for the recovery of a substantially pure ortho-xylene from hydrocarbon oils containing the same and containing other trated is recovered separate from forerunnings I -and higher boiling constituents. `The Xylene 'I'he presence of water inthe methyl ether of ethylene glycol used for the azeotropic distillation of ortho-xylene fractions is not advantageous but-,instead results in lower recoveries of xylene separate v from `non-aromatic hydrocarbons. Thus, when a mixture of aqueous methyl ether of ethylene glycol and ortho-xylene fraction is distilled, the water rst vaporizes and carries over with it hydrocarbons without accomplishing an effective selective separation of non-aromatic fraction is washed with concentrated sulfuric acid, neutralized and fractionated to obtain a close cut ortho-xylene fraction.` This is a conventional procedure for the recovery of concentrated ortho-xylene products from drip oil. concentrate thus obtained had the following characteristics:

Speciiic gravity at 15.5 C., 0.862

Melting point, 31 C.

Francis Bromlne No., 0.119

Distillation range (Barrett boiling range), 92%

distilling at 143-144.1 C.

Ortho-xylene,- ilo-83% by weight This concentrated ortho-xylene oil is introduced into the still of a fractional distillation apparatus together with about 125 volumes of methyl ether of ethylene glycol for every 100 volumes of the oil. The mixture is distilled with the vapors being effectively fractionated in a conventional fractionation column. As the distillation proceeds, by sampling the distillate and determining the melting point of the oil contained therein after removing from vthe distillate the be effectively used for methyl ether of ethylene' glycol by washing the distillate with water, the purity of the distillate with respect to ortho-xylene is determined. When the oilin the distillate has a meltingpoint of 25.5 C., the distillation may be discontinued and the residue-washed .with water to remove any methyl ether of ethylene glycol it contains. The washed residue is then fractionally distilled and that fraction distilling over at about 144-145 C..

with a melting point of v-25.5 C. to 25 C. containing substantially pure ortho-xylene is collected separate from any forerunnings and higher boiling materials. v

Example 2,-The accompanying drawing diagrammatically illustrates suitable apparatus for carrying out the process of this example. This apparatus comprises a series of three stills I, 2 and 3 with communicating rectification columns l, 5 and 6. Each of these columns provides for l rectification of the vapors from the respective The vapor pipes leading from' l accesso y' I6 for separation of the condensate into two liquid phases; the heavier lower phase may be returned4 through pipe I1 as reflux to the top of column 5, and the lighter upper phase may be returned as reflux to the top of the vrectification column through pipe I8 or withdrawn as distillate product through pipe I9. This apparatus and its operation will be described in further detion xylol residue was introduced into still I ofv the apparatus shown in the drawing and fractionally distilled with rectification of the vapors in column 4 by contact with refluxed condensate returned from cooler 1 through pipe III to the top of the column. Distillate was withdrawn through pipe I3 to a storage vessel 2| in the ratio of 1 part withdrawn distillate for every 5 parts of distillate returned as reflux through pipe I0. When -the temperature of the vapors at the top of column l had risen to 147 C. withdrawal oi' distillate to vessel 2l was discontinued. The oil fraction in vessel 2| had the following characteristics:

Francis Bromine No., about 0.08

Distillation range (Barrett boiling range), about Ortho-xylene, about 75% by weight The ortho-xylene concentrate in vessel 2I was introduced into a still 2 together with methyl ether of ethylene glycol in the proportions of 3.6 volumes of the methyl ether of ethylene glycol for every 100 volumes of the ortho-xylene fraction.

Distillation of the mixture of ortho-xylene fracs and their condensation inmoraa. sumcient water was 'introducedlnto the top of column l from a pipe 22 to maintain water in the upper portion of column 5 and the temperature of the vapors at the top of the column at about 94' C., i. e. about the boiling point of the azeotropes of the water and the hydrocarbonsdistilled from the ortho-xylene fraction and carried over as distillate with water. The mixture of'hydroca'rbon and water condensed in cooler 8 passed into separator vI Ii. The water and hydrocarbons formed two layers in this separator. The bottom layer, largely consisting ofwater, was returned through pipe I1 to the top of column 5. The top hydrocarbon layer was withdrawn from separator I l and in part returned through pipe I8 to the top of column 5 as refiuxvand in part drawn 0E as overhead distillate product through pipe I8. A reilux ratio of 15 parts byvolume of combined water and hydrocarbon introduced into the top of column 5 for every l part of hydrocarbon distillate withdrawn through pipe I9 was maintained. Methyl ether of ethylene glycol from a vessel 23 was introduced through a pipe 24 into a mid-portion of column 5 and water was introduced from pipe 22 as needed to maintain methyl Cellosolve present in the lower and greater portion of column 5 and water in the upper portion.

In distilling the ortho-xylene fraction from vessel 2I in the foregoing manner, the methyl Cellosolve in the lower portion of column 5 acted as an azeotropic agent to selectively separate from vthe ortho-xylene the like-boiling and lower boiling non-aromatic hydrocarbons and to carry these hydrocarbons upwardly in rectification column 5 while retaining ortho-xylene in the residue ot this distillation in still 2. In the upper portion of column 5 the water served to separate the hydrocarbons from the methyl ether of ethylene glycol and to carry these hydrocarbons over as distillate of the azeotropes of the water and the hydrocarbons. The methyl Cellosolve was condensed and refluxed back into contact with the hydrocarbon vapors rising through column 5, thus making the methyl Cellosolve again available for the selective separation of the non-aromatic hydrocarbons from the ortho-xylene.

When by analyses of samples of the resid-ue in still 2 the paraffin content of this residue was reduced to 1%, the distillation was discontinued and the residue washed free of methyl Cellosolve with water in a washing and separating vessel 25. The wash water was withdrawn through pipe 26 and the hydrocarbon oil was passedV through a pipe 21 into still 3'. In still 3 the oil was fractionally distilled with rectification of the vapors in column 6 in contact with condensate formed by cooling the vapors in cooler 9 and returned to the top o f column 8 through pipe II. Distillate product was withdrawn through pipe I4 at the rate of 1 volume of product-withdrawn for every 12 volumes of condensate returned through pipeII as reflux to the top of column The foregoing process may be modified to take off in vessel 2I from the nitration xylol residue distilled in still I the cut corresponding to vapor temperatures at the top of column from i to 148 C. Such an ortho-xylene fraction was found to have the following composition:

Per cent Ortho-xylene 78.6 Metaand para-xylenes 13.3 Paraflins 5.5 O l e i'l n s (corresponding to a Francis Bromine No. of .033) 2.6

This ortho-xylene fraction is azeotropically distilled in still 2 and column 5 with rectication of the vapors in the bottom of column 5 in the presence of methyl ether of ethylene glycol and in the top of column 5 in the presence of water. When substantially all of the paraiiins have been removed from the ortho-xylene fraction as distillate taken off through pipe I9, the residue from still 2 is washed with water to remove the methyl ether of ethylene glycol and the water-Washed residue then fractionally distilled in still 3 and rectiiication column 6. Distillate fractional distillation having melting points of substantially 27 C. and higher is separately collected in vessel 28 as a substantially pure orthoxylene product.

The foregoing examples may be modified to recover pure ortho-xylene from fractions containing the same derived from petroleum products. Thus, an oil containing about 84% Xylenes, substantially all of' which was orthoxylene, and the remainder petroleum paraiiins and boiling (Barrettboiling range) from 142.2" C. to 152.3 C. was mixed with an equal volume of methyl Cellosolve and fractionally distilled. When all the parafiins had been removed as distillate, the residue was washed with water to remove methyl ether of ethylene glycol and then i'ractionally distilled. Fractions having melting points within the range 26.75 to -25.3 C. were obtained by this fractional distillation.

In the above examples the azeotropic distillation is carried out as a batch distillation. It is within the scope of my invention to carry out this distillation continuously. For example, a mixture of the ortho-xylene concentrate and methyl ether of ethylene glycol may be fed to a continuously operating fractional distillation column, from the top of which a distillate is taken oi containing the lower boiling hydrocarbons and like-boiling, non-aromatic hydrocarbons, leaving a residue enriched in orthoxylene. This residue may be fed to a second distillation to take off as distillate xylene separated from other hydrocarbons which remain in the residue.

In this specification I have described the distillations as being carried out under substantially atmospheric pressure. The temperatures given herein are corrected temperatures for 1 atmosphere absolute (760 mm. of Hg.). When the distillations are carried out under pressures above or below atmospheric the temperature confrom this ally distilling said drip oil and recovering there-r from a concentrated xylene fraction separate from forerunnings and higher boiling constituents of the drip oil, washing said xylene fraction with concentrated sulfuric acid and neutralizing the acid-washed fraction, fractionally distilling the acid-washed, neutralized xylene fraction and recovering as distillate a concentrated orthoxylene fraction having a distillation range such that about 92% distills at substantially 143-144 C., fractionally distilling said ortho-xylene fraction and rectifying the vapors in the presence of suicient methyl ether of ethylene glycol to carry over as distillate with methyl ether of ethylene glycol the hydrocarbons other than ortho-xylene and leave ortho-xylene in the residue of the distillation substantially completely separated from the other hydrocarbons present in said ortho-xylene fraction, washing said residue with water to remove methyl ether of ethylene glycol therefrom, fractionally distilling the washed residue and in this distillation separately collecting that portion of the distillate distilled over at about 144-l45 C., the hydrocarbon content of which has a melting point in the range RICHARD B. GREENE.

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

UNITED STATES PATENTS Number Name Date 1,919,752 Schmidt et al July 25, 1933 2,162,963 McKittrick June 20, 1939 2,376,870 Engel May 29, 1941 2,358,129 Lake Sept. 12, 1944 2,381,996 Bloomer Aug. 14, 1945 OTHER REFERENCES Rossini, A Decade of Research on the Chemical Constitution of Petroleum, Rener and Natural Gasolene Manufacturer, November 1937. pages 545-561 (pp. 548 through 551 relied on).

Proceedings, American Petroleum Institute, 21st Annual Meeting Section III, Refining, Chicago, Illinois, Nov. 11-15, 1940, pages 43-47. Copy lin Division 25.

Bureau of Standards Journal of Research, vol. 27, pages 39063, July 1941. Copy in Scientific Library.

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