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Патент USA US2412880

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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.
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