rPatented Dea-17, 1946 ' ¿2,412,880l f. UNITED STATES PATENT ol-‘FlcE AzEoTnoPro ms'rîLLA'rroN or' BUTADIENE AND z-BUTENE Frederick E. Frey, Bartlesville, okle., assigner to _Phillips Petroleum Company, a corporation oi' Delaware Application March 13, 194‘1’4, Serial No. 383,235 ’ ` 7 claims. (crane-42) This invention relates to the concentration of diolefln hydrocarbons. It relates further to the concentration of low boiling vdiolei‘lns, more par ticularly butadiene, from mixtures containing athen hydrocarbons of closely adjacent boiling points. As one modiñcation, it relates to the pro duction of a normal C4 hydrocarbon mixture by the dehydrogenation of normal butane and the 2 I have now found that eñîlcient separation of butadiene from aA C4 fraction of the eilluent of such a dehydrogenation process can be readily carried out, and thebutadiene recovered in a state of high purity, by a series of fractional distilla- ï tion steps, in the ñ'rst of 'which sulfur dioxide is present in a limited amount, and in the second . separation of a butadiene concentrate therefrom. . of which essentially no sulfur dioxide is present. While my separation step is quite advantageous Diolefins are produced in a number of ways l0 1y combined with a step for the dehydrogenation which include cracking of heavier oils, pyrolysis of normal butane to produce butadiene such as is disclosed in my copending application, itis un derstood that in its broadest modiñcation my sep aration _step can operate on any C4 fraction which of gaseous hydrocarbons other than methane, the co-polymerization of acetylene and ethylene to form butadiene, catalytic and thermal conversion of alcohols, both of the same number of carbon atoms per molecule as the desired diole?ln and contains- butadiene and other C4 hydrocarbons' which are difilcult to remove therefrom. of a fewer number of carbon atoms per molecule, and other more or less involved chemical proc esses, as well as the dehydrogenation of the cor-, It has been disclosed in U. S. 2,186,524.. of which I am a coinventor, that sulfur dioxide forms minimum-boiling yazeotropic mixtures with each responding oleilns which in turn may have been 20 of the butanes and butenes. I have now found produced by the dehydrogenation of the corre >that if a C4 fraction containing butadiene to sponding parañìns. Although this latter proce gether with normal butane and normal butenes is . dure is one of the more direct ways of producing fractionally distilled in the presence of sulfur di ’ dioleiìns it has not yet found very extensive com oxide, the amount of sulfur dioxide can be so mercial application, and one of the obstacles in 25 limited that the overhead fraction contains sub its commercial development has been the dini - stantially all the normal butane, l-butene and culty of eiîecting separation of oleilns and diole-` - sulfur dioxide charged to the distillation, the ket , iins from each other and from mixtures contain tle product will then contain Z-butenes and sub ing the corresponding paratiins; stantially all the butadiene charged to the proc "In my copending application Serial No. 354,890, 30 ess, and butadiene can be separated in a state o_f ` high concentration from this kettle product by subsequent fractional distillation in the absence ducing Alow boiling dioleflns from the correspond of sulfur dioxide. In the presence of actinic light ' ing' paramns in which a single dehydrogenation `and _of- certain catalysts butenes and butadiene step is employed. As discussed therein, this de 35 form sulfones and/or heteropolymeric compounds ‘ ^ filed August 30, 1940, now Patent 2,371,817, issued ‘ March 20, 1945, I have disclosed a process of pro ' hydrogenation step apparently does not form the of extremely high molecular weight. Such reac major part of the dioleiìn product by a dehydro genation of a parafl‘ln directly to a dioleiin with ' tions are not desirable in connection with my process, and are to be avoided. ' no intermediate reactions, but apparently coop ' It is any object of my invention to produce low erates with the rest of the process to eiîect a de hydrogenationfof paramns to oleñns and con- , 4.0 boiling dioleflns in high concentration. comitantly a dehydrogenatîon of oleñns to di oleñns, the latter being produced .in substantial Another object of vmy invention is to separate low boiling dioleñns from other hydrocarbons of closely adjacent boiling points. quantities. »In this process the dehydrogenation . ` A further object voi’ my invention is to separate eil‘luentwill contain predominantly free hydrogen, '45 dioleflns in high concentration from other hy and oleñn and dioleiin hydrocarbonscorrespond- ~ " drocarbons without the formation of interme ing to the paraffin hydrocarbon charged to the process, with the oleñns being present in amounts diate chemical compounds. greater than the amounts of dioleflns, as well as from other C4 hydrocarbons. Still another object is to separate butadiene quantities of such paraflin hydrocarbons which 50 Another 'object of my invention is to obtain a. _are unreacted. In this process unreacted par butadiene fraction of high concentration from añins and corresponding oleflns areV separated- the dehydrogenation of normal butane. from the 'other products and are* returned to theFurther objects and advantages of my inven dehydrogenation along with fresh paraiîln hydro tion will become apparent from the accompany carbon material. n ing dìSQIQSLlre and discussion. . . l 2,412,880 3 My invention will now be more speclilcally de scribed in connection with the accompanying drawing which shows diagrammatically by way of a flow sheet an arrangement of apparatus for practicing one modification of my invention. In this modification the invention will be described in connection with a dehydrogenation step for producing butadiene from normal butane. Referring'now to the drawing, a paraffin hy drocarbon material comprising essentially normal butane enters the system through pipe I0 andV valve I I and is passed at a relatively low pressure to dehydrogenation unit I2. The dehydrogena tion unit I2 is comprised of suitable'heating units vor furnaces, catalyst chambers, 'and the like known vto the art for effecting and maintaining catalytic nondestructive dehydrogenation of low heavier oils or in the cracking of light gases to i'orm normally gaseous oleiins, such a material may be charged to the process through pipe 33. and valve 34 and may :loin a C4 fraction passing _from the separating unit I5 through pipe 20 or, ii’ desired.. it may constitute the sole hydrocarbon material charged to the process. If the absorp tion unit 22 is employed as just discussed, such a C4 fraction may be passed through pipe 35 and valve 38 to pipe 20. » However, if it is not desired to use such an absorption means for concentrating the unsaturated hydrocarbons, the Cl- iractionfmay be passed from pipe 33 through pipe `31 and valve 38 to pipe 3| and on to the fraction distillation unit 40. In many instances when the dehydrogenation unit I2’ is used to produce all or part of the butadiene, it will not be necessary to use the absorption unit 22 and the boiling hydrocarbons. The >catalyst chambers C4 fraction from separating means I5 may be maybe so arranged that heat is supplied to the catalyst body or bodies and to the reacting mix 20 .passed directly through pipe 20, pipe 35 and pipe ' ture. The hydrocarbons charged to the process may be joined by recycled normal butane and ncr mal butenes which will‘be passed to the pipe I0 31 to pipe 3| and the fractional distillation unit the net. reactión will be the dehydrogenation of a Z-butenesior butadiene are included. Sulfur di oxide for this purpose may either enter the dis 40, as will be readily appreciated. _ In'fractional distillation unit 40, which is il lustrated diagrammatically as a single fraction through pipes 51 and/or 85. The vdehydrogena tion is conducted to effect adehydrogenation both 25 ating column, a. distillation of the C4 hydro carbons takes place in the presence of sulfur di of normal butane and 'normal butenes to form oxide, which ,is added in amount suilicient to butenes and butadiene respectively, along with form azeotropic mixtures with substantially all free hydrogen. When a steady state of opera of the normal butane and l-butene fraction and tion is reached only a limited‘amount of dehydro- ' genation per pass will actually take place, since 30 in an amount so limited that little if any of the small amount ofl butane to form buteries, and of butenes to form a corresponding amountof buta tillation column along with the hydrocarbons through pipe 3| from absorption unit 22, or may lyst chamber may be used with adequate heating 35 be introduced separately at one or more other " points along the line of the distillation column of the stream charged to such chamber. The re through pipe 42 and valve v43 >and/or at some sultant products- pass through pipe I3 and valve other part of the column as through pipe 48 and I4 to the separatirg means I5. In separating valve 49.` When it is desired toadd sulfur di means I5, Cs and lighter material including free hydrogen is separated from the ‘C4 hydrocarbons 40 oxide to the material passing through pipe 3| this may be accomplished by suitable control of ' and removed-through pipe I6 and valve I1. If valve 4| in pipe 25. any C5 and heavier material is present in the eillu A low boiling mixture containing sulfur dioxide, ent of the- dehydrogenation, this material should normal butane and l-butene is passed from the also be removed, as through pipe I8 and valve I9. .A` resulting C4 .hydrocarbon ,fraction is‘ passed 4‘i5 top of the fractionating column 40 through pipe 45, cooling and condensing coil 46 -and valve'41 from separating means I5 through pipe 20 and to a suitable separating means such as separator may be passed through valve 2| to an absorption 5I). In this separating means a suitable separa unit 22. The absorption unit 22 is used to eiîect tion may be effected between sulfur dioxide and a preliminary concentration of butenes and butadiene, which `may be done by using any 50 hydrocarbon constituents passing with it through pipe 45. This may -be accomplished by suitable suitable absorption operation, but which is more condensation and subatmospherie cooling to tem .advantageously accomplished inl combination peratures within the range of about +20 tov I* with the present invention by using a liquid sulfur _100° F., or by a further azeotropic distillation dioxide as a selective absorbent. In such a case sulfur dioxide is passed through pipe 25 and 55 such as is disclosed in U. S. Patent 2,186,524, or by vother suitable operations. A sulfur dioxide through pipe 26 and valve 21 to a high point rich material is passed from separator 50 through of absorber 22 and therein is passed counter pipe 5I and may be discharged from the process current as a liquid to a hydrocarbon stream, . entirely or in part through valve 52. Generally, introduced through valve 2| as previously de scribed, also. in liquid phase, although it may 30 however,l a substantial portion thereof will be l returned to the fractionating column 40 through ,in some instances be in vapor- phase. Unab sorbed butane is removed through pipe 28 and- ' pipe 53 and valve 54 as a liquid ,.reñux. If the olefin content of this stream tends to build up may be discharged from the system through pipe too high a value, such material may be removed 23 and valve 24 or, if desired, may be passed through valve 29 to pipe 51 for recycle within 65 through valve 52 for a further separation of more or less pure sulfur dioxide which may be the system, as will be ldiscussed hereinafter. reintroduced in the system through pipe 25. In the absorption unit 22 liquid sulfur dioxide >Hydrocarbon material separated from sulfur selectively dissolves normal butenes- and buta- l dioxide in separator 50 may be removed through diene and will also take up a certain amount of normal butane. The rich »absorption liquid 70 pipe 55 and may be passed entirely or in part ‘ from the system through valve 56. However, is lpassed through pipe 3| and valve 32 to a when dehydrogenation unit I2 is a part of the fractional distillation unit 40. process, it will generally be desirable to recycle When a normal C4 fraction is available from all or a part of the hydrocarbons contained in any suitable source, such as a fractionobtained .p from the gases resulting from the cracking of 15 this material to this dehydrogenation, and this ' diene, anda large substantitally adiabatic cata y f` . " 2,412,880 may be effected by passing4 any desired portionl Í timate contact by the reilux liquid and ascending ~of the stream from pipe 55 through pipe 51 and through valve 58 to pipe I0. Ii' this -stream` ' vapors with suitable heating means for the kettle, and cooling -nrieans for the top, reflux accumula-í contains an appreciable proportion» of sulfun J tors and reñux lines and thelike as will be readily dioxide, this should be removed before the ma ‘ understood by'one skilled in the art. It win be e' terial is passed to the dehydrogenation unit.` desirable that the butadiene-containing -mate Such removal may if desired'be effected by pass - rial, especially when the butadiene is int a some ing the stream through pipe 60 and valve 5I to what concentrated state, should notbe heated a scrubber 62eand passing puriñed hydrocarbons to too high a temperature since this material from the scrubber 162 through pipe 61 and valve 10 "polymerizes somewhat readily. `It is well known 68 back to pipe 51 with valve 58 being closed. A that sulfur dioxide forms sulfones and high suitable scrubbing agent such as water or an .molecular weight heteropolymeric compounds ' alkali solution such as >sodium hydroxide orwith butenes and butadiene. Such chemicalfre sodium carbonate may be passed to the scrubber actions take place in the presencev of actinic light ‘ through pipe B13-and valve 64 to effect the re 16 and also in the presence of certain catalysts and moval of sulfur dioxide from the hydrocarbons are to be avoided. In some instances it may be treated therein and t'ne contaminated scrubbing . necessary to add materials to inhibit the forma medium may be removed through pipe 65 and tion of such compounds, such as phenyl-beta e _.valve_„66 for regeneration or such other treat naphthylamine, pyrogallic acid, hydroquinone, ment as may seem desirable. Other -suitable 20 catechol, resorcinol, cresols and similar phenolic means for separating hydrocarbons from sulfur compounds. Any iso-C4 hydrocarbons >present in dioxide may be used, as may seem desirable or’ " the charge to fractionating means 40 will be re expedient. , From the bottom moved therefrom in`the overhead product, and Lmay be discharged from the system through of ' fractional distillation means 40 a. `kettle product,lwhich will comprise valves 52 and/or 56. some or'all of any iso-Cs’s essentially Zf-butenes andbutadiene and which should be substantially free of sulfur dioxide, is passed through pipe 10 and valve 1I to a second fractional distillation means 412. If there is suill clent »sulfur .dioxide in this material to reduire its removal, this may be accomplished by passing the stream from pipe 10 through pipe 13 and valve 14 for suitable puriiication as by treatment with a suitable scrubbing medium in scrubber 15.` A suitable scrubbing medium may be added through pipe 80 and valve 92, and the spent scrubbing medium may be removed from the system through pipe 18 and valve 19. The puri fied hydrocarbon material is passed through pipe 16 and valve 11 back to pipe 10 and fractional distillation means 12, valve 1I being closed. The fractional distillation unit 12 is so oper ated- as to effect a separation of a substantially pure butadiene fraction, which should generally ' contain more than 90 per cent butadiene and preferably more than 95 per cent butadiene, afi though a lpurity greater than about 98 per cent will generally not be necessary. This fraction is removed as an overhead product through pipe 8| and valve 82 for whatever subsequent use may . be desired. The kettle product, which will con tain substantial quantities of Z-butenes, is re moved through pipe 83 and may be discharged from the system through valve 84. In _one modi flcation of my process it may be desirable to pass a portion of this-kettle productv back to the frac tional distillation unit 40, and this may be ac complished by passing the desired portion through present inthe material charged to lseparating means I5 may be removed, as a part of the Ca > and lighter materiaLthrough pipe I6. ` 30` Although it is desirable that the major part_ of the 2-butenes bewseparated along with the .butadiene as a kettle product, at times a better separation can be effected if a small portion of the 2-.-butenes, especially the trans-isomer, is per mitted to pass- from the ldistillation column 40 through pipe 45 as ,a part of the overhead product. As an example of my process, a C4 hydrocarbon fraction containing about 'I per cent butadiene, 25 per cent normal butenes of which about one fourth is 1-butene and three-fourths 2-butenes, and 68 per cent no al butane may be passed as a liquid to a fractionaldistillation column of 100 plates (and in two sections operated under a `total column pressure of about -120 pounds per square inch. Sulfur dioxide is introduced to the column in two places, the major, part being re turned as reilux at a point near the top, with sufficient “make-up” being> addedA along with the C4 stream to give a total amount of sulfur' dioxide introduced equal to about 10 per cent in excess of that required to form azeotropic mixtures with the normal butane and l-butene introduced, under the conditions existing at the top of the column. Under these conditions a small amount of 2-butene, primarily vthe trans-isomer, is in- ‘ cluded in the overhead product. Asulfur dioxide rich fraction is separated from the overhead product and returned vto the column as a liquid pipe :85, pipe 81 and valve 88 to a point in the reilux, thereby controlling the top temperature 3upper portion o-f the fractional distillation unit 60 and furnishing sulfur dioxide for the azeotropic 40, or >as may be found more desirable in some distillation. A kettle product comprising pri particular instance, it may be passed from pipe ’ marily 2-butenes and butadiene is freed from 81 through pipe 89 and valve 90 to a point in traces of sulfur dioxide and passed to a second the lower part of this fractional distillation unit. fractional 4distillation column, containing 120 When the dehydrogenation unit l2 is a part‘of plates in three sections. This column is operated my process and this kettle product does not at a pressure of about 75 pounds per square inch, contain too high a concentration of butadiene, the overhead fraction contains butadiene of a portion of it may be passed through valve 86 about 98 per cent purity of which a portion is ` in a continuation of pipe 85 to pipe I0. continuously returned as liquidfreñux, another While fractional distillation units 40 and 12 being a product of the process. The kettle prod have been shown as single units, it is to be under uct vcontains only a small amount of butadiene stood that this is merely diagrammatic and either and comprises primarily z-butene's. f . one or both of them may comprise two or more fractional distillation columns, each with suitable bubble trays or packing not shown, to afford in I claim: ` _ . 1. A process for separating- butadiene in a highly concentrated state from othernormal C4 _ 2,412,880 1 . ~7 . , oxide to separate butadiene in a highly' concen hydrocarbons, which comprises subjecting a tratedv form from Z-butene. hydrocarbon material comprised essentially of . - _ .4; An improved process for recovering a. buta~ substantial proportions of each of normalbutane, 1-butené,-,2-butene, and butadiene., with the pro. :1 - portion of 2-butene being greater than the pro diene concentrate from an aliphatic' C4 hydrocar bon mixture which comprises >treating an ali phatic C4 hydrocarbon mixture containing sub portion oi butadiene. to fractional distillation in the _presence of sulfur dioxide in amount suflicient to form minimum-boiling azeotropes with all of the normal butane and 1-butene con/tained in stantial proportions of Yeach of normal butane, 1-butene, Z-butene, and butadiene, with the proportion of 2-butene being greater than the pro said material but insufficient to form an azeotrope to selectively absorb and effect' a concentration of butenes and butadiene in said liquid sulfur - dioxide, passing the resulting solution of butenes. and butadiene in said sulfur dioxide to a ñrst portion of butadiene, with liquid sulfur dioxide with the-majór portion of the 2-butene contained in said materialand thereby effecting a sepa ration of Z-butene and butadiene as a kettle product substantially free of other C4 hydrocar bons, removing the' kettle product from said frac tional distillation and subjecting the same in the absence of sulfur dioxide to a `second fractional distillation to separate butadiene in a concen trated'state as a product. y 2. A process for separating butadiene in a I highly concentrated state from other normal C4 hydrocarbons, which comprises subjecting a_ hydrocarbon material comprised essentially of substantial proportions of each of normal butane, 1-butene, 2-butene, and butadiene, with the pro portion of 2-butene being greater than the pro portion of butadiene, to a ñrst fractional distilla tion in the presence of sulfur "dioxide, adding sul fractional distillation and fractionally'distilling< the _same in the presence of sulfur .dioxide in amount sufiicient to form azeotropes with all of the normal butane and 1-butene contained in said. solution but- insufficient to form an azeo trope with the major portion of the 2-butene, ref moving as» an overhead product from said first fractional distillation all of the azeotropes formed with said sulfur dioxide, removing as a kettle product from'said ñrst fractional Adistillation a mixture consisting of a major portion of each of the 2-butene and butadiene present in said origi nai `aliphatic C4 hydrocarbon mixture and free from sulfur dioxide, 1-butene and normal butane, ' and subjecting said kettle product to a second fur dioxide to said first fractional distillation in 30 fractional distillation in the absence of sulfur di oxide to produce a low-boiling overhead fraction / an amount suflicient to form minimum-boiling azeotropes with all of the normal butane and 1 butene contained in said material but insufiicient consisting essentially of butadiene. „Y 5. A process for separating butadiene in a t0 form an azeotrope with the major portion of highly concentrated state from other normal C4 as an overhead product from said first fractional drocarbon' material consisting essentially of sub stantial proportions of- each of normal butane, the 2-butene contained in said material, removing 35 hydrocarbons which comprises subjecting a hy distillation all of the azeotropes formed between said sulfur dioxide and the hydrocarbons con' 1-butene, 2-butene, and butadiene to a first frac tained in said material, separating ‘a sulfur tional distillation in a first distillation zone Ain taining the major portion of said 2-butene and substantially free of sulfur dioxide and passing said kettle product to a second fractional dis tillation. and fractionally distilling said kettle product‘in said second fractional distillation in the absence of sulfur dioxide to produce a ñrst in said material but insufiicient to form an azeo dioxide-rich fraction from said overhead product 40 the presence of sulfur dioxide, adding an addi'- ‘ tional quantity of 2~butene to said distillation as and returning same to said first fractional dis hereinafter recited, adding sulfur dioxide to said tillation as a liquid reflux and as a part of said first fractional distillation in an amount sutil added sulfur dioxide, removing from said frac»cient to form minimum-boiling azeotropes with tional distillation a kettle product consisting, all of the normal butane and 1-butene contained 45 essentially of 2-butene and butadiene and con trope with the major portion of the 2-butene present in said first- distillation zone, removing as an overhead product from said-first fractional distillation all of the azeotropes formed with said sulfur dioxide, separating a sulfur dioxide-rich product consisting essentially of butadiene and a ' ' fraction from said overhead product and return ing same to said ñrst fractional distillation as a liquid reflux and as a part of said added sulfur 3. An improved process for recovering a buta diene concentrate from a C4 hydrocarbon mixture 55 dioxide, removing afkettle product .from said first fractional distillation consisting essentially which comprises `passing a C4 hydrocarbon mix of 2-butene- and butadiene and substantially free ture containing substantial proportions of each of sulfur dioxide and> passing same to a second of 1-butene, 2-butene, and butadiene, with ‘the 'fractional distillation,'fractionally distilling said proportion of 2-butene being greater than the kettle product in said second fractional distilla proportion of butadiene, to a first fractional dis 60 tion in the absence of sulfur dioxide to produce tillation, adding sulfur dioxide to said first frac an overhead product consisting essentially of tional distillation in an amount suiiicient to form butadiene and a kettle product consisting essen azeotropes with all of the hydrocarbons in said tially of '2-butene, and returning a portion of said mixture other than butadiene and Z-butene but 65 last-named kettle product to saidfirst fractional secondproduct consisting essentially of Z-butenez distillation. 6. A process for separating butadiene in a portion of the 2-butene contained in said mix highly concentrated state from other normal C4 ture, _removing from said first fractional distilla hydrocarbons; which comprises subjecting a hy-~ tion as an overhead product all of said azeotropes so formed by said sulfur dioxide, removing also 70 drocarbon material containing about 7 per cent butadiene, about 25 per cent normal butenes of from said first fractional distillation a kettle _ Vinsufficient to form an azeotrope with the major product consisting essentially of said butadiene . which about one-fourth is 1-butene and three- ' and a major portion of said >Z-butene, and frac tionally distilling said kettle product in a second fractional distillation in the absence of sulfur di butane to a ñrst fractional distillation in a ñrst fourths Z-butenes, and about 68 per cent normal distillation column in the presence of sulfur d1 ' -9 - 2,412,880 oxide in an amount' at least suiìîcient and not greater than about 10 per cent- in excess of that suñicient to form- minimum boiling azeotropic mixtures withall of the normal butane and l-bu tene contained in said vi'naterial, under ,the con ditions existing at the top of said column, re covering as aloweboiling fraction from said dis tillation a mixture comprising sulfur dioxide, tenes and normal butane with thel amount of 2-butenes in excess of the amount of‘butadiene to a ñrst fractional distillation in a iirst distilla tion column in the presence of sulfur dioxide in an amountV at least suiìcient and not greater than about 10 per cent in excess of that suliioient to form minimum boiling azeotropic mixtures with al1 of the normal butane and 1-butene contained normal butane and 1-butene and no more than a in said material, under the conditions existing atv minor amount‘of tranS-Z-butene, recovering as a 10 the top ofjsaid column, recovering as a Iow~boilL high~boi1ing fraction a mixture substantially free from sulfur dioxide and comprising said buta diene and the major `portion of said Z-butenes, fractionally distilling said high-boiling mixture in a second distillation column, and recovering as a 1ow-boi1ing fraction butadiene substantially free from other C4 hydrocarbons; Y _ 7. A process for separating butadiene in a highly concentrated state from other normal C4 ing fraction from'said distillation a mixture com prising sulfur dioxide, normal butane and 1-bu'-_ tene and no more than a minor amount of trans 2-butene, recovering as a high-boiling fraction a mixture substantially free from sulfur dioxide and comprising said butadiene and 'the maior portion of said Z-butenes, fractionally distilling ' said high-boiling mixture and in a second distil _lation column, and recovering-as a low-boiling , hydrocarbons, which comprises subjecting a hy 20 fraction butadiene substantially free from other drocarbon material comprising substantial pro portions oi each of butadiene, 1-butene, 2-bu C4 hydrocarbons. l FREDERICK E. FREY.