US1954790A - Fractionation of liquids - Google Patents

Description

AP 17, 1934 E. B. coNKLlN E1' AL 1,954,790

FRACTIONATION 0F LIQUIDS Filed sept. 25, 1930 z sheets-sheet 1 Ap 17, 1934. E. B. coNKLlN Er AL FRACTIONATION OF LIQUIDS Filed sept. 25. 195o 2 Sheets-Sheet 2 Patented Apr. 17, `1934 Nits s'rA'rl-.s

PATENT rOFFICE FRACTIONATION OF LIQUIDS tion of New York Application September 25, 1930, Serial No. 484,288

10 Claims.

This invention relates to a process for fractionating a liquid containing lower and higher boiling compounds into its various constituents in a pure form. More particularly it Vrelates to the fractionation of light oils which are obtained as ley-products in the destructive distillation of coal, or coal tar, and the invention includes correlated improvements and discoveries whereby and wherewith the production of pure products from a mixture is accomplished.

An object of the invention is to provide a process for the fractionation of a liquid mixture in accordance with which the various constituents thereof maybe readily and eiliciently obtained on a commercial scale.

Another object of the invention is to accomplish the separation of a liquid mixture into its various constituents whereby the yield and purity of the separated constituents are improved and the cost of operation lowered.

A further object ofthe invention is to provide a process which may be substantially continuously and automatically operated and in which the amount of material required for treatment is lessened.

More speciiically it is an object of this invention to fractionate a light oil in order to obtain therefrom pure benzol, tuluol and Xylols and in which the toluol and Xylols are obtained in a single distillation step. The term pure, it will be understood, coversV products which conform satisfactorily to the specifications of purity as set up by the usual trade channels into which the products go, thus pure benzol does not mean chemically pure benzol, but a benzol of a quality which satisfactorily meets the requirements of benzol users.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others thereof, which will be exempliiied in the process hereinafter disclosed, and the scope of the invention will be indicated in the claims.

In the practice of the invention a liquid containing lower and higher boiling constituents such as alight oil may be distilled to separate the lower boiling constituents as a single condensate from the higher boiling constituents as a residue. The condensate may then be treated chemically in order to remove undesirable materials therefrom which in the case of a light oil may be unsaturated hydrocarbons, resins. tar-like materials, etc., and the treated condensate distilled to separate the lower boiling compounds, as a distillate containing all the distilled vapors and a residue containing the higher boiling constituents. The condensate thus obtained may then be introduced into a column at an intermediate point thereof and subjected to the action of heated vapors of the higher boiling constituents, thus effecting removal of the lowest boiling members as a distillate and obtaining as a liquid residue the higher boiling compounds free from the lowest boiling compounds. A liquid residue may be withdrawn into a collecting vessel capable of supplying another column, even though the iiow of liquid residue into the vessel or accumulator may be temporarily discontinued, due to an improper temperature gradient within thercolumn, thus allowing a part of the lowest boiling compounds to be present in the liquid residue. When such a condition arises the ilow of liquid residue into the vessel is discontinued and the temperature gradient readjusted in order to again give a residue which shall be free from the lowest boiling constituents. In the meantime the other column is fed continuously from the liquid accumulated in the vessel. The liquid free from the lowest boiling compounds may be introduced into another column at a point intermediate thereof and subjected to the distilling effect of rising heated vapors of the higher boiling compounds, thus eiecting removal of the lowest boiling compound which is condensed and obtaining a liquid residue composed of the higher boiling constituents and free from the lowest boiling constituent. This residue is collected in a vessel and fed to a succeeding column in a manner like unto that hereinbefore described and the operation may be repeated the number of times necessary to effect the separation of the liquid into a desired number of constituents. If such a successive distillation process each Ysucceeding still is normally operated at a reduced feed and in proportion to the amount of product removed in the preceding column. As hereinbefore indicated, these various operations may be carried out as a continuous process.

The practice'of the process of this invention will be exemplified by its application to the fractionation of a light oil. The light oils are those mixtures which are obtained as a by-product in the destructive distillation of coal or by the distillation of coal tar. The light oils are a mixture of higher and lower boiling compounds largely belonging to the aromatic series of organic compounds and containing chiefly benzol, toluol, and xylols with smaller amounts of compounds havsol ing boiling points lower than benzol and of compounds having boiling points higher than the Xylols.

We have found that the principal constituents of light oil, namely benzol, toluol and the Xylols may be obtained in pure form by i'lrst distilling the light oil to eiiect a separation between the lower boiling compounds containing the desired constituents and the higher boiling materials such as resins, tar-like substances, naphthalene, etc. in which all of the distillate is produced as a single condensate, washing the condensate with acid, and subjecting the washed condensate to a further distillation whereby the benzol, toluol, etc. are obtained as a single water-white distillate and the higher boiling compounds remain as a residue. The distillate is then separated into a product containing compounds having boiling points lower than that of benzol, pure benzol, pure toluol and Xylols by a succession of distillations in which the mixture fed to the columns is free from the lower boiling constituent secured as a condensate in the preceding column and in which the pure toluol and the xyloi fractions are withdrawn from a single column.

Thus, when conducting the process for the fractionation of iight oil into first running, benzol, toluol, Xylols and higher' molecular compounds, and a residue containing the compounds having boiling points higher than Xylols, the light oil may be first subjected to a continuous distillation with direct steam to effect a separation of the lower boiling constituents into a condensate containing all of the distilled vapors and a tarry residue containing the higher boiling constituents. This condensate may then be treated with sulfuric acid to remove impurities such as unsaturated hydrocarbons, which treatment may be followed with an alkali wash in order to remove the acid and the treated condensate introduced into a column and again subjected preferably in a continuous manner to the yaction of direct steam, whereby the lower boiling constituents, i. e those which it-is desiredvto recover f in pure form, are separated as `a single distillate from the higher boiling constituents as a residue.

The distillate, which should be water-white, is then introduced into a column at an intermediate point and vapors of the higher boiling constituents admitted to the base of the'column wherein they rise in contact with the descending distillate and remove therefrom the compounds having boiling points lower than that oi benzol. 1n this distillation it may be desirable to permit a portion of the benzol to pass over into the distillate with the lower boiling compounds in order to insure complete removal of the lower boiling compounds. It may also be desirable at this point to permit a larger amount of the benzol to pass into the distillate than is actually required to insure freedom from lower boiling constituents, this being governed by the market conditions at the time, and thus prepare a product which would be suitable for use as a motor fuel in the manner in which benzol is usually so utilized.

The liquid residue from the column, and which is commercially free from compounds having boiling points lower than benzol may be collected in a vessel or accumulator which is capable of serving as the source oi supply for another column in which pure benzol is separated, so that if it is necessary to discontinue collection of the residue from the iirst column due to contamination thereof with lower boiling constituents, this may be effectedV Without discontinuing the feed to the succeeding column. The liquid free from compounds having boiling points lower than benzol is then admitted to a column in which it is contacted with vapors of toluol and higher boiling compounds under vconditions such that all of the benzol is removed and a liquid residue obtained which is free therefrom. This liquid residue is collected in a vessel capable of supplying a succeeding column into which it is introduced at an intermediate point and therein distilled by contact with heated vapors of the higher boiling constituents which may be admitted thereto at the base. From this column toluol may be withdrawn at the top as a distillate of pure toluol, the highest boiling compounds withdrawn from the base as a residue and a fraction containing compounds having boiling points between that of toluol and the highest boiling constituents withdrawn from a point intermediate that at which the benzol-free liquid is introduced and that at which the vapors are admitted to the column. The fraction withdrawn at an intermediate point is Xylol which frequently has a boiling range or" 10 C. and meets commercial specifications for fl0 xylol without further treatment. The distillation is continued until the acid wash color number, preferably is not in excess of 12, Barrett Colorimetric Scale.

' if desired the residue from the still in which the pure toluol is separated, and which may contain'an amount of Xylols, may be introduced into a still and heated therein as by means of indirect steam, and rthe vapors passing off led into a column in which theXylols are separated from the higher boiling compounds. The quality of the xylol obtained by this distillation will depend upon the character of the distillation and the type of column into which the vapors are led. Thus, if the still is a comparatively small one the Xylol fraction will have a nal boiling range which may vary considerably, but if the vapors are led into a larger column, a greater amount of rectification may be accomplished, and the Xylol reiined to a point at which the nal boiling range will not vary from specifications by more than 1 to 10 C.

The foregoing procedure for the fractionation of light oil may be carried out more advantageously if operated in a continuous manner. When so operating the crude light oil, condensates and various liquid residues, free from lower boiling constituents, are continuously, successively and substantially automatically fed through a system consisting of a plurality of reservoirs, .feeding means, columns and accompanying apparatus.

The invention will now be more particularly described with reference to the accompanying drawings which illustrate diagrammatically a procedure and an arrangement of apparatus in which pure benzol, pure toluol and pure Xylols may be obtained from a crude light oil. It will be understood that this described an illustrative embodiment of a manner in accordance with which the invention may be practiced and that the invention is not limited thereto.

Crude light oil from a storage tank 1 is fed by means of a pump 2 through a constant-level reservoir 3 and a U-trapped conduit 4 into a column 5 at an intermediate point. In this col-` umnthe crude light oil is subjected to distillation, preferably by means of direct steam admitted -by a pipe 90 at the base of the column, whereby the crude oi is separated into a condensate of the lower boiling compounds and containing all of the distilled vapors and into a residue containing the higher boiling compounds such as resins, tarry materials, naphthalene, etc. The vapors passing from the column are conducted through a condenser 7 into a separator 3 in which the water and oil are separated, and the oil passes to a storage vessel 9. By means of a pump 10 the distilled light oil is passed to a washer 11 in which it is chemically treated with sulfuric acid introduced through pipe 12. The resulting acid sludge is permitted to settle and may then be withdrawn from the washer into a tank 91.

After the washing treatment with sulfuric acid, the oil is then neutralized with an alkali introduced through pipe 13.

The washed and neutralized condensate, preferably without separation of the aqueous neutralization liquor, is passed through a pipe 14 to a storage holder 15, from whence, by means of a pump 16, a constant-level reservoir 17 and a U-trapped conduit 18, it is fed into a column 19 at an intermediate point, and distilled therein, preferably with direct steam through a pipe 23, to obtain a distillate containing all of the evolved vapors and the constituents which it is desired to recover in pure form, and a residue of the resins, sulfate, naphthalene, etc. The residue is led from the base of the column through a U- shaped pipe 92 to a cooling coil 2e, which may be of the worm type, and then through a U- shaped pipe 93 in which the U is in the reverse direction from that in the pipe 92 to a collecting tank 25. The vapors from the still pass through a condenser 20 into a separator 21 in which the water and oil separate and the oil is then led to a storage tank 22. The distillate in the storage tank 22 contains those constituents of the light oil other than the highest boiling constituents of a tarry or resinous nature, naphthalene, etc. and is primarily a mixture of benzol, toluol and Xylols with a small amount of compounds which have a boiling point lower than that of benzol.

The alkali used for neutralizing the washed oil in washer 11, as described above, may be caustic soda, ammonia, or other suitable neutralizing agent. As disclosed in U. S. Patent 1,779,944 of October 28, 1930, to Joseph J. Lawton, the alkali used is preferably ammonia which has been found to result in improvements in operation as described in said patent of Lawton. The use of ammonia, while possessing certain important advantages over caustic soda as heretofore employed, has been found to result in operating difliculties due to the formation of emulsions in the washed oil which prevented an eincent separation of the aqueous neutralizing solution from the oil being treated. As brought out in the Lawton patent, it has been found that these emulsions are broken down, and the use of ammonia as the neutralizing agent with vattendant advantages, is made possible by subjecting the neutralized oil containing a portion or all of the aqueous neutralization liquor, which may be somewhat alkaline with ammonia, to subsequent distillation with direct steam, as conducted in column 19 described above in connectionV with the present invention. -It has further been found in accordance with the present invention that the formation of emulsions is inhibited to a surprising extent and the difficulty of breaking up emulsions, if formed, is materially reduced, by subjecting the crude light oil to a preliminary distillation with direct steam as conducted in distilling column 5, described above.

The sequence of operations comprising (1) iirst subjecting the crude light oil to a preliminary distillation with direct steam, (2) washing the distillate with sulfuric acid, (3) neutralizing the washed oil with ammonia, vand (4) then distilling the neutralized oil with direct steam, preferably in the presence of a portion or all of the neutralization liquor, has been found to yield a product of exceptional purity and freedom from sulfur compounds, resins and other impurities and to result in lowered operating costs and increased yield of product.

The mixture of benzol, toluol, etc., produced as above described, is introduced into a column 29 at an intermediate point by means of a pump 2S, a constant-level reservoir 27 and a U-trapped conduit 28. In this column the compounds having a boiling point lower than that of benzol are removed by contacting with heated ascending vapors of higher boiling constituents which are admitted at the base Vof the column through a pipe 33 from a still or vaporizer 35. The still or vaporizer 35 has previously been charged with a liquid composed of benzol and higher boiling compounds, but commercially free from compounds having boiling points lower than that of benzol. 1t is desired to mention here that the liquid composed of benzol and high boiling compounds may be obtained at the start of the process by a temporary intermittent operation until a sufficient depth of liquid is reached in the vaporizer which is free from compounds having a boiling point lower than that of benzol. This same general method of obtaining a liquid of a suitable composition in each succeeding vaporizer is used at the start. The operation of the column is such that the lower boiling compounds pass from the top and are accompanied by a portion of the benzolfwhich assures removal of the lower boiling compounds and reduces the volatility of the liquid produced. By means of a condenser 3() the distilled vapors are condensed and pass into a separator 31 from which the oil usually designated as rst runnings, and composed preponderatingly of compounds having a lower boiling point than benzol, is withdrawn and conducted to a receiver 32.

The liquid in the base of the column which, under proper operation, will be free from the lower boiling compounds, is conducted to the vaporizer 35 by means of a U-trapped pipe 34. From the vaporizer it is conducted by means of a Valvcd pipe 36 to a storage tank 37 in which it is held until utilized in the next succeeding column for recovery of pure benzol. The operation of the column, as above indicated, is conducted so that the liquid flowing from the base of the column to the vaporizer will be free from the lower boiling constituents and accordinglyV the liquid flowing from the vaporizer to the storage tank will be free from such compounds. It will be noted also that provision is made for discontinuing the flow of liquid from the vaporizer to the storage tank, and this provision is made and the storage tank is of such a capacity as to be able to continuously supply the next succeeding column even though the flow of liquid from the vaporizer to the storage tank may be ternporarily discontinued in the event that a change in the temperature gradient in the column is of sufficient magnitude as to permit a part of the low boiling constituents to pass into the vaporizer. When this condition arises the valve in the pipe 36 is closed and no liquid is permitted to pass into the storage tank until the temperature gradient in the column has been readjusted and low boiling constituents are no longer passing to the vaporizer. Thus the succeeding column is always fed with a liquid which does not contain any constituent having a boiling point lower than that constituent which it is desired to recover in the pure form in that column.

The liquid in the storage tank 37 which is free from compounds boiling lower than benzol is passed to the column 41 by means of a pump 38, a constant-level reservoir 39and a U-trapped conduit 40 and is therein distilled by means of vapors or" higher boiling constituents admitted at the base of the column through a pipe 44 and arising in a vaporizer 46. The vaporizer is charged at the outset of the operation with a liquid which is free from benzol. The benzol evolved passes from the top of the column through a condenser 42 into a receiver 43, from which it may be conducted to storage, or to drums, or utilized in any desired manner. The operation of this column and of the succeeding toluol and Xylol columns is so carried out that the liquid in the uppermost pan or pans of the column is composed wholly of that constituent which is being distilled over in order that a sharp cut may be made between this constituent and the higher boiling compounds. The benzol-free liquid is Withdrawn from the bottom of the column through a U-trapped pipe 45 and passes to the vaporizer, from whence, by means of the valved pipe 47 it flows to a storage tank 48. The provision of the valved pipe 47 in this instance is for the same purpose as that in connection with the rst runnings column, and thereby the ow to the storage tank may be interrupted in the event that benzol may be found in the liquid flowing from the base of the column. The valve will remain closed until conditions in the column have been readjusted and the liquid in the reservoir is free trom benzol, the storage tank being capable of continuously feeding the benZol-free liquid to the next column during the interruption.

The column 52 in which pure toluol -is separated is fed with the benZol-free liquid from the storage tank 48 by meansof a pump 49,12. constant-level reservoir 50 and a U-trapped conduit 51'. Distillation is effected by vapors of higher boiling constituents evolved ina still or vaporizer 60 and admitted at the base of the column through a pipe 58. The vaporizerf60 is charged with toluol-free liquid prior to initiating operation of the column. The toluol is withdrawn from the top of the column and passes through the condenser 53 to reservoir 54. A residue containing the highest boiling constituents, as naphthalene, etc., is withdrawn from the base of the column through a U-trapped pipe 59 and conducted to the vaporizer 60. A third product or fraction is Withdrawn from the toluol column at a point intermediate that at `which the benzolfree liquid is introduced and that at which the vapors of the higher boiling compounds are admitted to the column, preferably at a point which is adjacent to that at which the vapors are admitted. The withdrawal .of this fraction, which is composed of compounds having a boiling point between that of toluol and the highest boiling compounds in the distillate being fed to the column (more particularly of Xylols which are free from high boiling tarry compounds) and which preferably has an acid wash color which is not in excess of number 12, may be accomplished by a pipe55 by means of which it is led through a condenser 56 and from thence it passes to a receiver 57. The constant- level reservoirs 3, 17, 27, 39 and 50 are provided with overflow pipes 94, 95, 96, 97 and 98 respectively by means of which the excess liquid may be returned to the storage tank from which it was pumped.

The products obtained in the various receivers, namely the iirst runnings,.benzol, toluol and the xylols, are of sufhcient purity not to-require further treatment prior to entry into the usual commercialchannels. The rst runnings product isa highly volatile product and, as previously indicated, may be modified by permitting a larger or smaller amount of benzol to pass over into this distillate, and if a considerable amount of benzol is so permitted to pass over, it may iind use in the preparation of a motor fuel.

Distillation in the column to obtain pure toluol and xylols may be continued until the vapors of the higher boiling constituents in the vaporizer 60 are evolved only with difficulty and until the acid wash color of the Xylol fraction is not in excess of i2, Barrett Colorimetric Scale. When it is no longer possible to conduct the distillation so that the acid wash color of the Xylol fraction is lower than about 12, the liquid in the vaporizer 60 is allowed to pass to a storage tank V61. This liquid is a toluol-free oil containing a certain amount oi solvent naphtha xylols. In order to reduce the xylol content and obtain an added amount thereof, the toluol-free oil is conducted from the tank 6l by means of a pump 62 and pipes 63 and 65 to a storage reservoir 66. From the storage reservoir it flows by a pipe 67 to a washer 68 in which it is treated with sulfuric acid as hereinbefore described with respect to the crude oil condensate iirst obtained. If desired the toluol-free oil may be conducted directly to the washer by means of a pipe 64, thus by-passing the storage vessel 66. The oil flows from the washer to a vaporizer 70 through a pipe 69, wherein it is heated by means of steam coils, and the vapors conducted through pipes 71 and 73 to a column 75 from which a xylol fraction of ordinary commercial purity passes through a pipe 76 to a condenser 77 and thence to a separator 78 in which any water may be separated out, and the oil conducted to a receiver 79. In the production of this Xylol of ordinary commercial purity, a product, suitable for certain purposes, may be obtained in the later stages of the toluol-free oil distillation by eliminating the use of the column 75 and permitting the vapors to by-pass this column through a pipe 74 whereby they are led directly to thecondenser and receiver.

If it is desired to prepare a Xylol from the toluolfree oil of a degree of purity such that the final boiling range will not vary from the specications, more than from 1 to 10 C., the vapors may be passed to a column 81 in which a higher degree of rectication is accomplished. The vapors which pass from the column are led through a condenser 82 into a distillate dividing tting 83 in which the distillate is divided and a portion refiuxed by means of a reflux seal 85 to the top of the column, and another portion conducted to a receiver 84. The higher boiling liquids in the xylol columns 75 and 81 are led back to the vaporizer by means of pipes and 86, respectively.

Further, if a Xylol having other characteristics is desired, the washer 68 may be by-passed as well as the storage vessel 66, and the toluol-free oil introduced directly to the vaporizer 70, through the pipe 99, after which it may be distilled either through column 75 or column 81, depending upon the properties desired in the nished product.

loo

introduced into a further column at an inter- The columns used for theproduction of rst runnings, pure benzol, etc., may be constructed in the usual manner with plates or pans suitably i'ltted with bell-caps, troughs or other eiiective means for causing intimate contact between the rising vapors and the descending liquid, and the tops of these columns may be provided with cooling coils or dephlegmators. The height of the columns will be governed by the separation which it is desired to bring about in a given column, and it should be such that under normal operating conditions the down-flowing stream of liquid is exposed to the upwardly rising hot vapors for a period of time suilicient to cause the complete vaporization of the constituent ofV lowest boiling point and removal thereof from the top of the column without admixture with the next higher boiling constituent, and such that the liquid withdrawn from the base of the column shall be wholly free from the lowest boiling constituent.

Thus, in accordance with the process hereinbefore described, the separation of crude light oil into a water-white preliminary condensate by distillation, chemical treatment and repeated distillation, and the resolution of the condensate into a i'lrst runnings product, benzol, toluol and xylols, may be effected commercially in a satisfactory and efficacious manner. Further, the preliminary distillation and succeeding resolution may be accomplished in a continuous manner. The products obtained are in a condition of purity such that further steps for purification are not required. Further, by the treatment of light oil in accordance with this invention, and in which direct steam is used in the preliminary distillations, products are obtained which have only the characteristic odor of the hydrocarbons and are free from undesirableodors, inasmuch as carrying out the distillation in this particular manner the breaking down of higher boiling sulfur compounds is eliminated. Also, the products are non-corrosive to copper, and the preliminary distillation eifectseconomies, since the high boiling compounds are removed at the outset, thus making it unnecessary to carry themA along into succeeding columns, and the amounts kof acid and steam required are considerably reduced.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that'all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

We claim:

l. A process for fractionating light oil-which comprises subjecting crude [light oil to distillation with steam, condensing the vapors to form a single distillate, treating the condensate with acid, introducing the treated condensate into a column at an intermediate point, distilling with steam, condensing the distillate as a single Yproduct, and then successively separating the condensate into its various constituents by introducing the condensate into a column at an intermediate point, producing a condensate composed preponderatingly of compounds having a lower boiling point than benzol and withdrawing from the column a product free from compounds having a boiling point lower than that of benzol, introducing this product into another column at an intermediate point and distilling benzol therefrom by contact with vapors of the higher boiling compounds, so that all of the benzol is removed, yielding a debenzolized product which is mediate point and subjected to distillation therein in such a manner that pure toluol is withdrawn from thetop of the column, a product composed of the highest boiling-constituents and having an acid wash color number of at least 12 from the bottom of the column, and a fraction containing compounds having boiling points intermediate that of toluol and the highest boiling constituents from an intermediate point.

2. In a process for ractionating light oil, the improvement which comprises separating toluol from higher boiling compounds by introducing a liquid mixture containing toluol and higher boiling compounds and substantially free from lower boiling compounds into a column, subjecting said mixture to the action of heated vapors to distill the toluol, and withdrawing a fraction containing compounds having a higher boiling point than toluol at a point intermediate that at which the mixture to be distilled is introduced and the Vbottom of said column.

3. In a process for fractionating light oil, the improvement which comprises separating toluol from higher boiling compounds by introducing a liquid mixture containing toluol and higher boiling compounds and substantially free from loweriboiling compounds into a column at an intermediate point, subjecting said mixture to the action of heated vapors of the higher boiling compounds to distill the toluol, condensing the distilled toluol, and withdrawing a fraction containing compounds having a boiling point intermediate that of toluene and the highest boiling compounds at a point intermediate that at which the mixture to be distilled is introduced and the bottom of said column.

4. `In a processior fractionating light oil, the

columnto distill toluol, condensing the distilled v toluol, and withdrawing a fraction containing xylols at a point intermediate that at which the mixture to be distilled is introduced and the point of admission of the heated vapors. 5. In a process for fractionating light oil, the improvement which comprises separating toluol from higher boiling compounds by introducing a, liquid mixture containing toluol and higher boiling compounds and substantially free from lower boiling compounds into a column at a` point at which the composition of the liquid in the column is substantially the same as the mixture being introduced, admitting heated vapors of the higher boiling constituents at the base of the column to distill toluol, condensing the distilled toluol, and withdrawing a fraction Acontaining xylols and having an acid wash color number not in excess of 12 at a point adjacent that at which the heated vapors are admitted. 6. In a process for iractionating light oil, the improvement which comprises separating toluol from higher boiling compounds by introducing a liquid mixture containing toluol and higher boiling compounds and substantially free from lower boiling compounds into a column, admitting heated vapors of the higher boiling compounds at the base of the column to distill the toluol, withdrawing a fraction containing compounds having a boiling range Vintermediate that of toluene and the highest boiling compounds at a point intermediate that at which the mixture to be distilled is introduced and the point of admission of the heated vapors, and continuing the distillation until the withdrawn fraction has an acid wash color number of about 12.

7. In a process for fractionating light oil, the improvement which comprises separating toluol from higher boilingY compounds by introducing a liquid mixture containing toluol and higher boiling compounds into a column at an intermediate point, said mixture-being substantially' free from compounds boiling below toluol, heating a mixture of the' higherboiling hydrocarbons in a vaporizer outside the column 'and admitting heated vapors therefrom 'at the base'of the column to distill toluol, condensing the distilled toluol, ywithdrawing a fraction containing xylols and*v having an acid wash color number not in excess of l2 at a point adjacent that at which the heated vapors are admitted, and subjecting the high boiling residue withdrawn from the base of the still to distillation and rectification,

whereby xylols are obtained having a nal boiling point-within a range of 1 to 10 C.

* 8, A process for the continuous fractionation of light loil which vcomprises distilling said light oil with direct steam to separate the lower boiling compounds as ar single distillate and the higher boiling compounds asa residue, treating said condensate with acid, distilling the treated condensate with 4direct steam tov separate the lower boilingcompounds asa singledistillate and the higher boiling compoundsas a residue, in-

troducing the distillate sov produced into a column at an intermediate point and subjecting to the action of vapors of the higher boiling constituents to remove as a condensate -allof the compounds having a boiling point -lower than benzol, withdrawing the residue free from compounds having boiling points lower than Vbenzol into a collecting vessel capable of supplying another column even though flow ofl residue into the vessel maybe temporarily discontinued, discontinuingthe withdrawal of the residue from the column when said residue contains compounds having a boiling point lower than benzol ,Y K and readjusting the conditions in the column to ,50.

again give a residue free from the lower boiling compounds, and then admitting the residue to the collecting vessel, introducing the liquid free from lower boiling compounds into another column at an intermediate point, removing the benzol therefrom by' subjecting the liquid to the action of heated vapors oft'oluol and the higher boiling constituents, withdrawing the benzol-free liquid from the column into a vessel and continuing the process for the separation of toluol and higher boiling constituents in the'manner hereinbefore set forth for benzol.

9. A processv for'the continuous fractionation of light oil which comprises distilling said light oil with direct steam to separate the lower boiling compounds as a single distillate and the higher boiling compounds as a residue, treating said condensate with'acid, distilling the treated oondensate with direct steam to separate the lower boiling compounds as a single distillate and the higher boiling compounds as a residue, introducing the distillate so produced into a column at an intermediate point and subjecting to the action of vapors of thehigher boiling constituents to remove as a condensate all of the compounds having a boiling point lower than benzol, withdrawing the residue free from compounds having' boiling points lower than benzol into a collecting vessel capable of supplying another column even though flow of residue into the vessel may bertemporarily discontinued, discontinuing the Withdrawal of the residuefrorn the column when said `residue containscompounds having a boiling point-lower than benzol and readjusting the conditions in the column to again give' a residue free yfrom the lower boiling` compounds, and then' admitting the residue to the collecting vessel, introducing the liquid free from lower boil'- ingcompounds into another column at an intermediate point, removing' the benzol therefromby subjecting the liquid to the action of heated vapors of toluolrand the higher boiling constituents, withdrawing the benZol-free liquid into aiv collecting vessel capableof supplying another column,as hereinbefore described, feeding the benzol-free liquid into a column at an intermediate point, admitting vapors of the higher boiling compounds at the base of the column whereby the admitted liquid is subjected tothe distilling action of` such vapors; removingandrecovering toluol from the top` ofthe column, withdrawing a residue containing the highest boiling compounds from thebase of the column, and withdrawing a fraction containing compounds having boiling points between that of toluol and the :highest boiling compounds at a point intermediate that' at which' the liquid is introduced into the column and the point of admission of the heated vapors. j

10. In a process for fractionating light oil, the improvement which comprises separating from said light oil vthe constituents having lower boilingl points vthan toluol and a mixture containing toluol and vrhigher boiling compounds, passing saidmixture in contact with heated vapors to vol'atilize therefromtoluol and compounds having a boiling point intermediate that of toluol and the highest boiling compounds of -saidfmixture, and separately and simultaneously condensing the volatilized toluol and said compounds of intermediate boiling point to thereby recover from the vaforesaid mixture toluol, a residue of the highest boiling compounds and a fraction containing said compounds of intermediate boiling point.

EARL BIDDLE CONKLIN. JOSEPH J. LAWTON.

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