US2389172A - Refining of coke-oven light oil - Google Patents

Description

Nm 20, 3945 B. J. c. VAN DER HoEvEN-ETAI. 2,389,172

Filed Feb. 15, 1941 i Il i1 .i l

1 ii Il i! Il II Il REFINING OF COKE-OVEN LIGHT OIL INVENTORS.

aff/mpv ./.c van vez frane/M Jo/m' WAL/ven 0N/eos.

'Patented Nov. 20, 1945 2,389,172 REFmmG oF COKE-OVEN mehr on.

Bernard J. C. van der Hoeven, Pittsburgh, Pa., and' John Walker Unroe, Steubenville, Ohio, assignors, by mesne assignments, to Hoppers Coma corporation of Delaware ApplicationFebruary 13, 1941, SerllrNo. 378,746

Claims.

particularly, improvements in benzene of so-called nitration taneous recovery of other preferred and useful fractions of crude light oil.

An object of the scribed or claimed.

The presence matics which boil I amounts of intermediate fractions in order to produce benzene of nitration grade which by the Barrett manufacturing specifications for cokef oven light oil distlllates, must solidify at a temperature not lower than 4.85 C.

. According to the invention, crude light o is preferably separated by a continuous fractional' least three fractions having distillation into at distinct and preferred characteristics.

0f these fractions the lowest boiling fraction, namely, the forerunnings, is a relatively small portion of the original crude light oil and isjsubstantially free of benzene and has a high concentration of the sulphur compounds present in the crude light oil. The' lower-boiling constituents are partially condensed and the fixed gases therein are returned for combustion therewith. The forerunnings are employed in part excess thereof y being preferred storage.

Another fraction of intermediate boiling range and low specific gravity, wherein non-'aromatics are highly concentrated and which represents only a small percentage of the total treated iight oil is also continuously removed during this fractional distillation. This product is suiliciently low in sulphur concentration to be utilizable as motor fuel or as a blend with same.

The remainder of the crude l light oil from condensable as reflux, the

which has been removed the two previously de'-` scribed lower bolling fractions, constitutes a, third fraction. From this fraction after acid washing, there can be fractionally distilled to produce benzene of so-called nitration grade not less than substantially per cent of the benzene originally present in the crude light oil. 'lhe-bottoms-prodf uct from this second distillation can be batchdistilled to produce toluene, the xylenes, and light and heavy solvent naphtha.

The present invention thus provides for the production of nitration pure benzene in only two distillation. steps; In the first of these Steps the crude light oil is substantially stripped of those constituents boiling below benzene which heretofore have presented diiliculties in their removal light oil without simultaneous removal of considerable benzene and in' addition the said constituents have 'been segregated into novel fractions having significantly low specific to thecoke-oven-gas stream continuously removed to l 'of this specification and showing for purposes of exempliilcation a preferred apparatus and method in which the invention may be embodied and practiced but without limiting the claimed inventionspecifically to such illustrative instance or instances:

Fig. l is a diagrammatic elevational view of aP- paratus for distillation of crude light oil in accordance with the present invention;

Fig. 2 is a horizontal section on an enlarged scale taken along lines II-II of Fig. l; and

Fig. 3 is a vertical cross section of a fragment of a fractionating column taken along lines III-111 of Fig. 2.

The same characters of reference designate the same parts in each of the views of the drawings.

In Fig. l is shown diagrammatically a distillation system that makes possible the practical realization of the improvement provided by the present invention and which includes fractionating column I0, fractionating column 30, batchstill kettle 90, and batch-still rectifying column |30. The direction of travel of the light oil and of the fractions thereof through the system is indicated by arrows in the drawing.

Crude light oil is pumped continuously through feed line i I into the fractionating column l at a point intermediate the top and bottom of said column. Fractionating column i that is about three feet in diameter and about ninety feet high comprises a shell I3 with a reboiler it and about forty bubble-cap trays i2 which are contained therein. A bubble-cap tray in some detail is shown in the enlarged scale Figures 2 and 3. The trays are disposed horizontally and mutually parallel, and each contains a plurality of vapor ports i6 which are covered by bubble caps I'l. For clarity, the bubble caps in Fig. 3 are shown in slightly larger scale than those in Fig. 2. Adapted for the retention of a preferred depth of liquid on each tray are Weir-plates i8, and adapted for directing the flow of liquid from a tray to the one immediately therebeneath are liquid by-passes i9 which are v apor sealed by liquid retained at their lower ends by seal plates 20. The light oil is received on an intermediate bubble-cap tray l2 of column lli and is therein fractionally distilled by heat from reboiler I4, which is disposed at the bottom of the column, and the said heat of which selectively advances the lighter boiling constituents to the upper plates thereof.

The forerunnings-vapors issuing fro the top of column I0 are conducted through vapor line 2 to condenser 22 wherein the vapors are cooled to approximately C. and wherein a portion of the vapors are thereby condensed. The fixed gases therefrom are returned through vent line 23 to a fuel-gas stream and are eventually burned therein. The issuance of said gases from the system is controlled by an automatic vapor pressure controller 24 which maintains a slight positive pressure on the contents of said column l0. The maintenance of this positive pressure upon the boiling contents of the column by increasing the boiling temperature respectively of each tray advantageously prevents the rise of higher boiling fractions to the top trays of the column and insures the production of purer products than could be otherwise produced.

The condensed forerunnings are continuously withdrawn from condenser 22 and are run through drain line 25 to decanter 26 in which water which may have condensed with the fore- ---1-- an-ha @narrated therefrom. The forcrunnings are thereafter continuously pumped from the decanter through reflux line 21 by pump 28 contained therein, and are continuously returned as reflux through said line to the top of column l0. The volume of the reflux is preferably about double the volume of feed to the column. A previously determined volume of forerunnings can be regulably withdrawn through product line 29 to storage tank 30 by adjustment of valve 3|.

' A sidestream product is withdrawn from one or more of several therefor-adapted adjacentlydisposed bubble-cap trays which are situated intermediate the feed-receiving tray and the top of the column. The volume of sidestream can be adjusted manually by operation of valves 32, and with the ald of flow meter 33 in sidestream product line 34 in which the sidestream is removed. The sidestream is cooled in water-fed indirect cooler 35 and is thereafter owed through a continuation of line 34 to motor-benzol storage tank 36 thatis adapted for the addition of motor-fuel inhibitor by connection with inhibitor storage tank 31.

From the bottom of the column I0 a partially refined light oil that is stripped of its lower boiling fractions is continuously withdrawn through drain line 39 at a rate governed by an automatic liquid-level controller 40 which operates a valve 4i in product line 42. The said partially refined light oil is cooled by indirect contact with-water in cooler 43. This light oil fraction is stored in storage tank whence it is pumped through line 41 to agitator 50 by pump-48 that is included in said line 41. The oil is acid washed in the agitator, is neutralized by an alkali wash in alkali wash tank 5l and, thereafter, the acid-Washed fraction thus neutralized is withdrawn to treated-oil storage tank 52.

This treated product is withdrawn preferably continuously from said storage tank 52 by pump 53, is pumped through feed line 54 to a fractionating column 60 and is received on one bubble-cap tray of a plurality of superposed trays 62 forming the said fractionating column. The so-fed light oil flows downwardly toward a reboiler 64 at the base of the column and is fractionally distilled by the heat of said reboiler in a manner that is similar to that obtaining in column l0 and that is well known to the art.

The vapors leaving column S0 are conducted through vapor line 6.5 to condenser 66 in which they are condensed by indirect contact with cooling water. The condensed overhead fraction is flowed from condenser 63 through pipe line 33 to decanterlli in which water can be separated from the condensed fraction. The pure product is decanted therefrom and flowed through drain line 1| from which a portion of the product is pumped by pump 14 through reflux line 12 to the top of column 60 down through which the said portion is refluxed. The remainder of the product is drained through product line 13 to nitrationbenzene storage tank 15.

From the base of said column 6G a bottomsproduct is withdr^wn through drain line 16 at a rate that is governed by an automatic liquid-level controller 80 which operates a valve 3i in said 70 line. The product is ,flowed through cooler 32 i that is disposed in drain line 16 and into batchfeed storage tank 85. This bottoms-product is pumped therefrom through batch-feed line 31 by pump 88 to batch-still kettle Si) whenever the operation of the batch-still requires a recharging solution to remove any of said kettle. by steam coils distillation is discharged from the kettle through drain line 84.

The vapors flow from the top of column through vapor line |0| to a vapor neutralizer |02 wherein the vapors are washed by a caustic soda thus-condensed product drains through drainline |06 and is separated from therewith-condensed water in decanter |01. Caustic soda solution with entrained light oil is drained from the tion and the water are |01a and |01, respectively, through drain lines |08 and are collected in caustic soda pump-tank |0. The soda solution is returned through caustic soda line ||2 to the vapor neutralizer by soda circulation pump The neutralized and and are cooled therein to about 20 highly volatile compounds that, in comprised about two per cent of the original crude light oil, are returned to the coke-oven-gas to be utilized as added'heat value...

one example,

compounds of the original crude light oil. Undesirable sulphur-bearing constituents are thereby advantageously removed from the oil in relatively The condensed forerunnings selected storage. Pipef trays near the top of column 0 boiling just below 3 cumulate, they are withdrawn throughpipe line 29 to forerunnings-storage tank 30. Certain compounds, such, for example, as carbon bisulphide, which are of advantageously high concentration in the forerunnings, can be obtained therefrom.

From any one or from several of adjacent not more than about 2.5 per cent of the volume of the iniiowin'g light oil is removed as a sidestream having a rather high concentration of non-aromatic constituents. This sidestream is taken from such preferred trays and at a rate such that -it contains: a high concentration of the non-aromatics two per cent of the benzene present in the original crude light oil and a suficiently low concentration of sulphur to make said sidestream product available for, orfor blending with, motor fuel. I'he preferred tray or trays employed are usually characterized by their containing thereon a liquid fraction having a specific gravity lower than that on the superposed trays or on those immediately therebeneath. 'I'he specic gravity of the sidestream product is always below that of pure benzene and has been found to vary from 0.79 to 0.83. These values for specific gravity of the sidestream are low in consequence of the low speciiic gravity of the non-aromaticsthat, as is above mentioned, are present in relatively high concentration therein.

Determinations by standard tests show, for example.. that the paralnic content alone varies from l2 to 26 per cent of the total sidestream and the total sulphur content has been as low as 0.17 per cent and as much as 0.33 per cent of the From the bottom of column |0 is continuously withdrawn a product which contains not less than substantially per cent ofthe benzene originally in the crude light oil, and substantially none of the compounds boiling below benzene. is then acid washed to produce a treated light-oil fraction that can be directly distilled ,tol separate a high yield oi nitration pure benzene; it requires less acid for its washing than boiling lower than and near the boiling temperature'of benzene. After removal of the acid, sludge the acid-treated product is further treated with an alkali to neutralize it. f

In the second fractionating-column 60, this alkali-treated fraction is continuously distilled, and not less than substantially cent of the benzene originally contained in the light oil is volatilized, condensed and thus recovered as nitration pure benzene having a solidication point of at least 4.854

temperatures of, for example, 5.3 C. and higher has been economically produced.

The product benzene, not more than about emuent of the bottom of the colremainder is stored for future that, according to the present invention and by treating evolved VaPOI'S Wi 'benzene comprising not less than 4 as carbon bisulphide, are of such high concent umn 60 contains a small amount of benzene and rality of fractions comprising a low-boiling foresubstantially all of the compounds of the crude runnings fraction that is substantially free of light oil that boil above the boiling point of benbenzene, another fraction containing some benzene; it is continuously withdrawn and stored zene and a relatively high concentration of nonin batch-feed storage tank 85 from which it is aromatic light-oil constituents having boiling intermittently charged to batch-still kettle 90. points lower than but more closely adjacent the The batch still is disposed for operation in comboiling point of benzene than the constituents bination with the two continuous fractionating of the first said fraction, said other fraction havcolumns of the system and adds desirable flexiing a specific gravity of from 0.79 to 0.83, and a. bility to the distillation operation in that large l distillation residuum containing at least substanquantities of the said bottoms-product can be tially ninety-five per cent of the benzene origstored in batch-feed storage tank 85 and in the inally present in the light oil, said residuum being still kettle 90 itself and can thereafter be disfree of fore-runnings and non-aromatic hydrotilled at will. carbon constituents of light oil having boiling The small amount of benzene remaining in the points less than benzene; recovering the plurality said product eflluent to column 60 is distilled in of said fractions; and acid-washing said residuum the batch still and returned through product and fractionally distilling therefrom without subline H6 to the motor-fuel storage tank 36. The stantial Production of lower boiling intermehigher boiling fractions of crude light oil such diates. about ninety per cent of the total origlenes, and light inally contained benzene of said light oil as a as, for example, toluene, the xy and heavy solvent naphtha are successively re- Product having a So 'dlfying point of at least moved-by fractionation from the saidproduct as 4-35" C- overhead vapors w 'ch are thereafter neutralized 2 In a PiooeSS fol' rthe refining of Crude light and condensed, a portion of the liquid products oil that iS obtained from Coke-oven gas. the steps therefrom being employed as reflux whereas the of! Continuously loWing non-Bold Washed crude distribution. light oil aforesaid into a fractionating column; boiling said light oil therein and simultaneously From the above-given description it is apparent th a reflux of forethe use of only two fractionating columns, from runnlngS Constituents of Sn'd light oil having o crude light oilthere can be separated nitration 3o boiling point lower than benzene at a rate. by substantially volume, at least one and one-half the rate, by

volume, at which said crude light oil is flowed benzene, and having a solidiiication point of not into saidirectionating column and thereby 4serioless than 4.85 C. In addition, the highly comrating Said Crude light oil into a plurality of fracplex mixture of constituents of the original crude tions comprising. a -10W-boiling fore-runnings light oil that boil below benzene is separated fraction that is substantially free of benrene, fractions; the another fraction containing some benzene and a one fraction comprising permanent gases an relatively high concentration of non-aromatic very low boiling constituents which are returned light oil constituents having boiling points lower to the gas stream to be burned; another fraof 40 than but more closely adjacent the boiling point on wherein sulphmbeang constituents, Such of benzenethan the constituents of the iirst said re. fraction, said another fraction havinga specific gravity offfrom about 0.79 to 0.83, and a distillation residuum containing at least substantially ninety-five per cent of the benzene originally present in .the light oil, said residuum being subninety per cent of the originally therein present tions that the said fraction-is useful as a raw material from which valuable products are ob- 4 tained; and another fraction of low specific gravity wherein non-aromatica are highly conted and that contains unsetureceds which stantially free of fore-runnings and non-arocentm ehent1 kneek matic hydrocarbon constituents of light oil havare especially valuable for th Properties in motor fuels, the said latter fracin g a boiling lio t less than benzene; and recovtion being s cientLy low in sulphur-bearing conelmg the PlUIollty of Sold fractions.

stituents to make it suitable directly for this pur- 3- In a process for the reiining of crude light Se, That benzene which i5 n1-, recovered as oll that is obtained from coke-oven gas, the steps nitration pure benzene is removed from the crude of: owing non-acid Washed Crude light o il aforelight oil as a product which is suitable for use iaigt ghzrxiartoghllvggga l. Th hi he boilin homologues e as a motor fue e g r g with a reflux of fore-runnings' constituents of of benzene, such as toluene, the xylenes and solvent naphtha are also obtained in extremely Said light oll having o boiling point lower than pure form, benzene at a rate, by volume, at least one and one-half the rate, by volume, at which said crude f r set forth is em- The invention as herembe o e light oil is iiowed into said fractionating column odi d in articula o m nd manner but may be b e p r f r a pe of the claims and thereby segregating in a portion of sald'colgli-tgiges? 122%; d withm the sco umn a liquid lig t-oil fraction containing non- We claim; l aromatic hydrocarbon constituents of said light 1. In a process for the refininl vg of crude light 5 011 um at a hl g her ttempertuguthasd oil that is obtained from coke-oven gas, the steps foiegs cons tuen S an c of: continuously flowing non-acid washed crude adjacent to but below the boiling point of pure light oil aforesaid into a fraotionating column; benzene. Said liquid fraction having a Specic boiling said light oil therein and simultaneoushr ravity of between about 0.79 and 0.83, and recovtreating evolved vapors with a reflux of foreering said hquid fract1on from said fractionatmg runnings constituents of said light oil having a 0 column substantially independently of other fracboiling point lower than benzene at a rate, by tions separated therein from said light oil.

volume, at least about 'one and one-half times the rate, by volume, at which said crude light oil refined benzene from non-acid washed crude is flowed into said fractionating column and coke-oven light oil containing also a non-arothereby separating said crude light oil into a plumatic hydrocarbon of which the boiling point is 4. In a process for the preparation of highlyaromatic hyd n, at s. rate. by volume that boil ow both ne and said non-aroa ut double the rate by volume, of now of crude mastic hy at such 'a rate by volume, t oil into said fractionating apparatus, and 10 langer than the rate by volume, of ow of crude thereby segregating in said fraetionating column ht oil in fraetiona apparatus as to s. qui ure con g soi non-aromatic thereby segnegate in said fractionating column a drocarbon d ha g a spe c gravity of liqui mixture containing said non-aromatic fraction from said i'ractionating column substan- 15 tween 0.79 and 0.83; and recovering ysaid liquid ents of said crude light oil. I tially independently of higher boiling constitu- 5. In a. lprocess for the preparation -of highly` ents of said crude light oil. I refined from non-acid washed crude BERNARD J. C. VAN nlm HOEVEN.

ne coke-oven light oil containing also o non-aro zo JOHN WALKER UNROE.

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