US2382473A - Production of butadiene - Google Patents

Description

Aug M 3945- F. E. FREY PRODUCTION OF BUTADIENE Original Filed March 13, 1941 INVENTOR Patented Aug. 14, 1945 PRODUCTION oF BUTADIENE Frederick E. Frey, Bartlesville, okla., assignor to Phillips Petroleum Company, a corporation of Delaware Original application March 13, 1941, Serial No. 383,235. Divided and this application April 23, 1942, lSerial No. 440,213

3 Claims.

This invention relates to the concentration of diolen hydrocarbons. It relates further to the concentration of low boiling diolens, more particularly butadiene, from mixtures containing other hydrocarbons of closely adjacent boiling points. As one modification, it relates to the production of a normal C4 hydrocarbon mixture by the dehydrogenation of normal butane and the separation of a butadiene concentrate therefrom. This application is a division of my copending application Serial No. 383,235, filed March 13, 1941, and also is a continuation-in-part of my copending application Serial No. 354,890, filed August 30, 1940. Y

Diolens are produced in a number of ways which include cracking of heavier oils, pyrolysis of gaseous hydrocarbons. other than methane, the copolymerization of acetylene and ethylene to fol-ln butadiene, catalytic and thermal conversion of alcohols, both of the same number of carbon atoms per molecule as the desired diolefin and of a fewer number of carbonv atoms per molecule, and other more or less involved chemical processes, as well as the dehydrogenation of the corresponding olens which in turn may have been produced by the dehydrogenation of the corresponding parailins. Although this latter procedure is one of the more direct ways of producing diolefins it has not yet found very extensive commercial application, and one'of the obstacles in its commercial developmentl has been the difculty of effecting separation of olens and diolelfins from each other and from mixtures containing the corresponding parains.

In my aforementioned copending vapplication 1 of which this is gt continuation-impart, I have disclosed a process of producing low boiling dioleflns from the corresponding parafins in which a single dehydrogenation step is employed. As discussed therein, this dehydrogenation step apparently does not form the major part of the diolen product by a dehydrogenation of a parain directly to a diolefin with no intermediate reactions, but apparently cooperates with the rest of the process to effect a dehydrogenation of parains other products and are returned to the dehydrogenation along with fresh parain hydrocarbon material.

I have now found that eflicient separation of butadiene from a C4 fraction of the eiiluent of such a dehydrogenation process can be readily carried out, and the butadiene recovered in a state of high purity, by a series of fractional distillation steps, in the first of'which. sulfur dioxide is present in. a limited amount, and in the second of which essentially no sulfur dioxide is presen-t. While my separation step is quite advantageously combined with a step for the dehydrogenation of normal butane to produce butadiene such as is disclosed in my copending application, it is understood that in 'its broadest modification my separation step can operate on any Ci fraction which contains butadiene and other C4 hydrocarbons which are diflicult to remove therefrom.

It has been disclosed in U. S. 2,186,524, of which I am a coinventor, that sulfur dioxide forms minimum-boiling azeotropic mixtures with each of the butanes and butenes. I have .now found that if a C4 fraction containing butadiene together with normal butane and normal butanes is fractionally distilled in the presence of sulfur dioxide, the amount of sulfur dioxide can be so limited that the overhead fraction contains substantially l all the normal butane, l-butene and sulfur dioxide charged to the distillation. the kettle product will thencontain 4,2V-butenes. and substantially all the butadiene charged to the process, and butadiene can be separated in a state of high concentration from this kettle product by subsequent fractional distillation in the absence of sulfur dioxide. In the presence of actinic light and of certain catalysts butenes and butadiene form sulfones and/or heteropolymeric compounds of extremely high molecular weight. Such reactionsy are not desirable in connection with my process, and are to be avoided.

It is an object of my invention to4 produce low boiling diolens in high concentration.

Another object of my invention is to obtain a butadiene fraction of high concentration from the dehydrogenation of normal butane.

Further objects and advantages of my invention will become apparent from the accompanying disclosure and discussion.

`My invention will now be more specifically described in connection with the accompanying drawing which shows diagrammatically by Way of a flow sheet an arrangement of apparatus for practicing one modication of my invention. In

this modification the invention will be described I in connection with a dehydrogenation step for producing butadiene from normal butane.

Referring now to the drawing, a paraffin hydronormal butenes which will be passed to the pipe I through pipes 51 and/or 85. The dehydrogenation is conducted to effect a dehydrogenation both of normal butane and normal butenes to form butenes and butadiene respectively, along with free hydrogen. When a steady state of operation is reached only a limited amount of dehydrogenation per pass will actually take place, since the net reaction will be the dehydrogenation of a small amount of butanevto form butenes` and of butenesto form a corresponding amount of butadiene, and a large substantially adiabatic catalyst chamber may be used with adequate heating of the stream charged to such chamber. The resultant products pass .through pipe I3 and valve I4 to the separating means I5. In separating means I5, lCa and lighter material including free hydrogen is separated from the C4 hydrocarbons and removed through pipe I8 and valve I'I. If any C and heavier material is present in the eluent of the dehydrogenation, this material should also be removed, as 'through pipe I8 'and valveIS." H

A resulting C4 hydrocarbon fraction is passed from separating means I5 through pipe 20 and may be passed through valve 2| to an absorption unit 22. The absorption unit 22 is used to eect a preliminary concentration lof butenes and butadiene, which may be d one by using any suitable absorption-operation, 'but'which is more advantageously accomplished in combination with the present invention by using a liquid sulfur dioxide as a selective absorbent. In such a caseif desired, it may constitute the sole hydrocarbon material charged to the process. If the absorption unit 22 is employed as Just discussed, such a C4 fraction may be passed through pipe 25 and valve 35 to pipe 20. However, if it is not desired to use such an absorption means for concentrating the unsaturated hydrocarbons, the C4 iraction may be passed from pipe 23 through pipe l1 and valve 38 to pipe 3l and on to the fraction 'distillation unit 40. In many instances' when the dehydrogenation unit l2 is used to produce all or part of the butadiene, it will not be necessary 'to use the absorption unit 22 and the C4 fracis removed through pipe 22 and may be discharged from the system through pipe 23 and valve 2li or, ii desired, may be passed through valve 29 to pipe 5l for recycle within the system, as will be discussed hereinafter.

In the absorption unit 22; liquid sulfur dioxide selectively dissolves normal butenes land butadiene and will also take up a certain amountl of normal butane. The rich absorption liquid is passed through pipe lBland valve 32 to a irac-l tional distillation unit &0.

When a normal C4 ractionfis available from any suitable source, such as a fraction obtained from the gases resulting from the cracking of heavier oils or in the cracking o1" light gases to form normally gaseous oleiins, such a material may be charged to the process through pipe 33 and valve 34 and may join a C4 fraction passing from the separating unit I5 through pipe 20 or,

tion from separating means I5 may be passed directly through pipe 20, pipe 35 and pipe 31 to pipe 3l and the fractional distillation unit 40, as

' will be readily appreciated.

In'fractional distillation unit 40, which is illustrated diagrammatically as a single fractionating column. a distillation of the C4 hydrocarbons takes place in the presence of sulfur dioxide, which is added in amount suflicient to form azeotropic mixtures with substantially all of the normal butane and l-butene fraction and in an amount so limited that little if any of the 2- butenes or butadiene are included. Sulfur dioxide for this purpose may either enter the distillation column along with the hydrocarbons through pipe 3| from absorption unit 22, or may be introduced separately at one or more other points along the line of the distillation column through pipe 42 and valve 43 and/or at some other part of the column as through pipe 48 and valve 49. When it is desired to add sulfur dioxide to the material passing through pipe 3i this may be accomplished. by suitable control of valve 4I in pipe 25.

A low boiling mixture containing sulfur dioxide, normal butane and l-butene is passed from the top of the fractionating column 40 through pipe 45, cooling and condensing coil 46 and valve 4l to a suitable separating means such as separator 50. In this separating means a suitable separation may be effected between sulfur dioxide and hydrocarbon constituents passing with it through pipe 45. vThis may be accomplished by suitable condensation and subatmospheric cooling to temperatures within the range of about +20 to 100 F., or by a further azeotropic distillation such as is disclosed rin U. S. Patent 2,186,524, or by other suitable operations. A sulfur dioxide-rich material is passed from separator 50 through pipe 5I and may be discharged from the process entirely or in part through valve 52. Generally, however, a substantial portion thereof will be returned to the fractionating column 60 through pipe 53 and valve 54 as a liquid reflux. If the olen content of this stream tends to build up too high a value, such material may be removed through valve S52 for a further vseparation of more or less pure suliui dioxide which may be reintroduced in the system through pipe Hydrocarbon material separated from 'sulfur dioxide in separator 50 may be removed through pipe 55 and may be passed entirely or in part from the system through valve 56. However, when dehydrogenation unit I2 is va part of the process, it will generally be desirableto recycle all or a part of the hydrocarbons contained in this material to this dehydrogenatiori, and this may be effected by passing any desiredV portion of the stream from pipe 5.5 through pipe 51 and through valve 58 to pipe I Il. If this stream contains an appreciable proportion o! sulfur dioxide, this should be removed 'before the material is passed to the dehydrogenation unit. Such removal may if desired be effected by passing the stream through pipe and valve 6| to a scrubber 62 and passing purified hydrocarbons from the scrubber 62 rthrough pipe 61 and valve 68 back to pipe 51 with valve 58 being closed. A suitable scrubbing agent such as water or an alkali solution such as sodium hydroxide or sodium carbonate may be passed to the scrubber through pipe 63 and valve 64 to effect the removal of sulfur dioxide from the hydrocarbons treated therein and the contaminated scrubbing medium may be removed through pipe and valve 66 for regeneration or such other treatment as may seem desirable. Other suitable means for separating hydrocarbons from -sulfur dioxide may be used, as may seem desirable or expedient.

From the bottom of fractional distillation means 4U a kettle product, which will comprise essentially Z-butenes and butadiene and which should be substantially free of sulfur dioxide, is passed through pipe 10 and valve 1I to a second fractional distillation means 12. If there is sufficient sulfur dioxide in this material to require its removal, this may be accomplished by passing the stream from pipe 10 through pipe 13 and valve 14 for suitable purification as by treatment with a suitable scrubbing medium in'scrubber- 15. A suitable scrubbing medium may be added through pipe and valve 92, and the spent scrubbing medium may be removed from the system through pipe 18 and valve 19. 'I'he purified hydrocarbon material is passed through pipe 16 and valve 11 back to pipe 10 and fractional distillation means 12, valve 1| being closed.

The fractional distillation unit 12 is so operated as to effect a separation of a substantially pure butadiene fraction, which should generally contain more than per cent butadiene and preferably more than per cent butadiene, although a purity greater than about 98 per cent will generally not be necessary. This fraction is removed as an overhead product through pipe 8| and valve B2 for whatever subsequent use may be desired. The kettle product, which will contain substantial quantities of Z-butenes, is removed through pipe 83 and may be discharged from the system through valve 64. In one modification of my process it may be desirable to pass a portion of this kettle 'product back to the fractional distillation unit 46, and this may be accomplished by passing the desired portion through pipe 85,

` pipe 81 and valve 88 to a point in the upper portion of the fractional distillation unit 40, or as may be found more desirable in some particular instance, it may be passed from pipe 81 through pipe 89 and valve 90 to a point in the lower part of this fractional distillation unit. When the dehydrogenation unit I2 is a part of my process and this kettle product does not contain too high a concentration of butadiene, a portion of it may be passed through valve 86 in a continuation of pipe 85 t0 pipe IU.

While fractional distillation units 40 and 12 have been shown as single units, itis to be understood that this is merely diagrammatic and either one or both of them may comprise two or more fractional distillation columns, each with suitable bubble trays or packing not shown, to afford intimate contact by the reflux liquid and ascending vapors with suitable heating means for the kettle, and cooling means for the top, reflux accumulators and refiux lines and the like as will be readily understood by one skilled in the art. It

will be'desrable that the butadiene-containing material, especially when the butadiene is in a somewhat concentrated state, should not be heated to too high a temperature since this material polymerizes somewhat readily. It is well known that sulfur dioxide forms sulfones and high molecular weight heteropolymeric compounds with butenes and butadiene. Such chemical reactions take place in the presence of actinic light and also in the presence of certain catalysts and are to be avoided. In some instances it may be necessary to add materials to inhibit the formation of such compounds, such as phenylbeta-naphthylamine, pyrogallic acid, hydroquinone, catechol, resorcinol, cresols and similar phenolic compounds. Any iso-C4 hydrocarbons presentl in the charge to fractionating means 40 will be removed therefrom in the overhead product, and may be discharged from the system through valves 52`and/or 56. Some or all of any iso-Gis present in the material charged to separating means I5 may be removed, as a part of the Ca and lighter material, through pipe I6.

Although it is desirable that the major part of the 2-butenes be separated along with the butadiene as a kettle product, at times a better separatioi can be effected if la small portion of the Z-butenes, especially the trans-isomer, is permitted to pass from the distillation column 40 through pipe 45 as a part of the overhead product. As an example of my process, a C4 hydrocarbon fraction containing about 7 per cent butadiene, 25

-per cent normal butenes of which. about onefourth is 1butene and three-fourths Z-butenes, and 68 per cent normal butane may be passed as a liquid to a fractional distillation column of plates and in two sections operated under a total column pressure of about pounds per square inch. Sulfur dioxide is introduced to the column in two places, the major part being returned as reflux at a point near the top, with sufficient ,make-up being added along withthe 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 the trans-isomer, is included in the overhead product. A sulfur dioxide-rich fraction is separated from the overhead product and returned to the column as a liquid reflux, thereby controlling the top temperature and furnishing sulfur dioxide for the azeotropic distillation.

A kettle product comprising primarily Z-butenes and butadiene is freed from traces of sulfur dioxide and passed to a second fractional distillation column, containing 120 plates in three sections. This column is operated at a pressure of about 75 pounds per square inch, the overhead fraction contains butadiene of about 98 per cent purity of which a portion is continuously returned as liquid reflux, another being a product of the process. The kettle product contains only a small amount of butadiene and comprises primarily 2- butenes.

I claim:

l. In a process for the production of butadiene from normal butane, which comprises dehydrogenating normal butane together with recycled C4 hydrocarbons in a single dehydrogenation step under conditions effecting dehydrogenation of normal butane to normal butenes including 1- butene and Z-butenes and simultaneous dehydrogenation of normal butenes to butadiene, the improvenient which comprises subjecting eiiiuents of said debydrogenation to selective solvent extraction with liquid sulfur dioxide to eiiect a preliminary concentration of butenes and butadiene, 'passing `the resulting solution of hydrocarbons and sulfur dioxide to a iirst fractional distillation and removing an overhead fraction comprising aseotropes of sulfur dioxide with l-butene and normal butane, removing a liquid kettle product consisting essentially of Z-butenes and butadiene, subjecting said product to a second fractional distillation in the absence of sulfur dioxide, removing therefrom as aA gaseous overhead product a butadiene concentrate as a product of the process, removing also therefrom a. liquid kettle product substantially free of butadiene and comprising essentially 2-butenes and passing same to said dehydrog'cnation as at least apart oi said recycled C4 hydrocarbons. o t

2. In a process for the production of butadiene from normal butane which comprises dehydrozenating normal butane in admixture with recycled normal butane and butenes under conditions effecting conversion'of normal butane to normal butenes including 1butene and 2-butenes and simultaneous conversion of normal butenes to butadiene, the improvement which comprises treating the resulting. eilluent to segregate a fraction consisting essentially of the C4 hydrocarbon content thereof, extracting said C4 hydrocarbon fraction with liquid sulfur dioxide as a selective solvent and thereby effecting selective dissolution of the normal butenes and butadiene content thereof while allowing most of the normal butane to remain undissolved, recycling said undissolved normal butane to the dehydrogenating step, passing the rich solvent from said extracting step to a first fractional distillation zone and there fractionally distilling same in the presence of sulfur dioxide in amount sufiicient to form minimum-boiling azeotropes with all oi the normal butane and l-butene contained therein but insumcient to form an azeotrope with the maior portion of the Z-butenes contained therein, removing as an overhead all of said azeotropes of sulfur dioxide with normal butane and 1bu tene, treating the overhead to effect separation thereof into a sulfur dioxide-rich liquid fraction and. a fraction or normal butane and l-butene. renuxing said distillation zone with at least a part of said sulfur dioxide-rich liquid fraction. recycling said fraction of normal butane and 1- butene to said dehydrogenating step, removing from said distillation zone a kettle product consisting essentially oi' 2butenes and butadiene and substantiallyiree oi sulfur dioxide and passing same to a second fractional distillation zone and there fractionally distilling same in the absence of sulfur dioxide to produce an overhead product consisting essentially of butadiene as the product of the process and a kettle product consisting essentially of 2-but'enes, and recycling said 2bu tenes kettle product to saidv dehydrogenating step.

3. The process for the recovery of substantial ly pure butadiene from a Ci hydrocarbon fraction containing the same in admixture with l-butene, 2-butenes and normal butane which comprises extracting said fraction with liquid sulfur dioxide as a selective solvent and thereby effecting selective dissolution of the normal butenes and butadiene content thereof while allowing most of the normal butane to pass through undissolved, passing 4the resulting rich solvent to a first fractional distillation zone and there fractionally distilling same in the presence of sulfur dioxide in amount suilicient to form minimum-boiling azeotropes with all of the normal butane and l-butene contained therein but insuilicient to form an azeotrope with the major portion of the 2-butenes contained therein, removing as an overhead all of said azeotropes of sulfur dioxide with normal butane and l-butene, treating the overhead 'to effect separation thereof into a sulfur dioxiderich liquid fraction and a fraction of normal butane and l-butene, re'iluxing said distillation zone with at least a part of said sulfur dioxide-rich liquid fraction, removing from said distillation zone a kettle product consisting essentially of 2- butenes and butadiene and substantially free of sulfur dioxide and passing same to a second fractional distillation zone and there fractionally distilling same in the absence of sulfur dioxide to produce an overhead product of substantially pure butadiene and a kettle product consisting essentially of 2-butenes.

FREDERICK E. FREY.

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