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SePf- '24, 1946-
I
J. A. PA1-rERsoN
»
2,407,997
SEPARATION AND PURIFICATION oFiIsoPRENE'
'
3E.it
‘
E» 77
eww/„Ü
J, A. ¿PATTERSON
2,407,991 ^
_’ "SEPARATION AND PURIFIC‘ATION oF IsoPRENE
Filed. Aug. l'7_, 1943
2 sheets-sheet`
PGY-_L4
Buff,
2 `
2,407,997
Patented Sept. 24, 1945
lUNITED STATES PATENT OFFICE
2,407,997
SEPARATION AND PURIFICATION 0F
ISOPRENE
John A. Patterson, Westfield, N. J., assignor to
Standard Oil Development Company, a cor
poration of Delaware
Application August 17, 1943, Serial No. 498,944
2 Claims. (Cl. 202-41)
2
1
This invention relates to the treatment of mix
tures of hydrocarbons of the C3 to Ca range to
fractionally distilling one of the particular dis
tillate fractions from the extractive distillation
effect segregation and purification of paraffins,
operation. Invention was stated to reside not
only in the combination of the fractional dis
mono-oleñns and dioleflns.
The invention re
lates particularly to the separation of dioleñns
containing 5 carbon atoms in the molecule from
their admixture with other hydrocarbons in prod
ucts of the treatment of petroleum fractions; and
also the purification of dioleñns.
The extraction of individual C4 and C5 hydro 10
carbons from easily available sources is beset with
many difficulties because of the low concentra
tions involved and the interrelated properties of
these hydrocarbons in such supplies. Thus, the
hydrocarbons containing 5 carbon atoms in the
molecule have boiling points at 760 mm. and rela
tive volatilities, a as follows:
D
.O
u
ß-methyl butene-i ___________________________________ __
Pentene-l ......... _ _
tillation steps with extractive distillation, but
also in the particular manner of combination in
order to achieve particularly desirable fractions
for the second and third steps in the processing,
namely, for the extractive distillation and the
second fractional distillation steps. It was stated
also in Serial No. 470,426 that in commercial op
eration ít was usual to employ a fourth step,
namely, the recovery of the solvent employed in
the extractive distillation step. Such a step is,
however, incidental rather than an essential fea
ture of the process of the invention.
Thus, according to‘the process disclosed in ap
plication Serial No. 470,426, the concentration of
C5 dioleiins was eifected by supplying the system
20 with a feed stock consisting of a narrow C5 cut
as rich as possible in the desired dioleñn, iso
prene `for example. A debutanized aromatic dis
tillate containing 4% of isoprene was fractional
ly distilled in a 50 plate tower with a reflux ratio '
of from 5 to l0, depending on the nature of the
feed stock, and a product was had containing
from 15% to 25% of isoprene. Such fractional
distillation failed to remove some of the hydro
carbons most difûcult to separate in the subse
Cis~piperylene_ _ _ _
Cyclopentene. _ _ __
Cyclopentane ____________________ _ _
30 quent extractive distillation.
. The boiling points and the relative volatilities
of the various C5 compounds clearly do not fol
low the degree of chemical unsaturation of the
compounds. Even to effect separation upon the .
basis of normal vapor pressure, of a simple from "
a complex mixture would also clearly require ex
tremely expensive equipment. Moreover, if a
In the extractive
distillation with aqueous acetone as the solvent,
trimethylethylene which has a normal volatility
relative to isoprene of 0.88, has a volatility index
a relative to isoprene of 1.23. Thus in both the
fractional and extractive distillation systems iso
prene and trimethylethylene have about the same
spread. The present invention overcomes this
fractional distillation were to be made upon a
deficiency.
plex mixtures is disadvantageous, even in the
extractive distillations either alone or in com
It has now- been found that by substituting in
general mixture of C5 hydrocarbons to separate
close boiling fractions, prolonged heat under high 40 the processing disclosed in application Serial No.
470,426, an azeotropic distillation step for the
reflux ratios would be required and under ,such
ñrst fractional distillation step, concentration of
conditions considerable polymerization of the
the desired dioleíins may be easily effected and
more unsaturated hydrocarbons would occur.
distinction also made between hydrocarbons
Thus, fractional distillation alone as a means of
otherwise
diñicult to separate by fractional and
45
making a separation of hydrocarbon from com
laboratory.
'
bination. By adding a controlled quantity of a
third liquid or solvent to the feed fractionating
y
VIn a co-pending application, Serial No. 470,426,
tower so that the distillate will consist of azeo
filed December 29, 1942, it was disclosed that
complex hydrocarbon mixtures could be advan 50 tropic mixtures, separation can easily be effected
of many different hydrocarbons. Thus, in mix
tageously resolved into their individual constitu
tures containing isoprene and trimethylethylene
ents by a unique combination of at least three
in association with other C4 and Cs hydrocarbons
processing steps. In two of the three steps frac
and employing» aqueous acetone as the solvent,
tional distillation is employed. Between the two
fractional distillation steps is eiiected an extrac 55 there is formed a ternary azeotrope of isoprene,
acetone and water of lower boiling point than
tive distillation. The process of that invention
that of any other Cs hydrocarbon usually pres
is thus the combination of a carefully controlled
ent in such a mixture with the exception of pen
fractional distillation of Va suitable feed stock
tene-l which is otherwise easy to separate from
followed by an extractive distillation rof a par
ticular distillate fraction and then subsequently
60
isoprene. The volatility of trimethylethylene re1
2,407,997
3
4
,
ative to isoprene is depressed, making otherwise
difficult separation: relatively easy. Since pen»
Liquids suitable in extractive distillation are in
general the stable organic liquids of high dielec
tene-1 has a norma1 volatility greater than that
tric constant. The suitable materials are there
of isoprene, the separation of this and lighter hym
drocarbons is easily effected in the subsequent
fore the normally liquid polar organic compounds
containing oxygen, nitrogen, sulfur and related
elements. Suitable liquids also have the follow
ing characteristics:
extractive distillation step disclosed in applica
tion Serial No. 470,426. The following table gives ~
the average relative volatilities of the various
(l) High» solubility for the hydrocarbons;
(2)
Marked effect on the relative volatility;
10
compounds in azeotropic distillation: .
(3') R'eadi‘ly separable from the hydrocarbons by
Relative volatility at 25 lbs/sq. in. gauge
distillation 0r when azeotropes are formed
Component
_
Normal
Azeotropic
Extractivc Y
distillation
distillation '
distillation
Pentene-l ___________ _ _..
Isoprene_-_ ____________ _.
1.06
1.00
1. 12
1.00
Trimethylethylene. _ __ _
. 88
. 78
` by solvent extraction or other means;
_
l; 23'
ness.
In order to furnish a better basis for appreci
ating the invention, analysis of the processing inV
In the case of the" separation of th‘e’Cß hydrocar
bonsA from their admixture withvother hydrocar
each‘ of the essential steps is- presented; In frac
tional' distillation, separation of the constituents~
of a mixture is made upon the basis of differences
bons, acetone, furfural, pyridine, the amines and
their admixtures with waterY have been found' to
' at varying temperatures of the vapor pressures of
. be particularly advantageous.
the“ various compoundsV when in admixture one
with the- other. In extractive distillation andv
azeotropi'c distillation, on the other' hand, sepa
ration of the constituents in the- mixture is based'
In the case of azeotropic distillation' the same
type of liquids are suitable as solvents. In addi
tion, however, the liquids should have‘th’e follow
ing characteristics:
on the differences atV different temperatures of
pounds in the ’presence of' certain types liquids
added to a fractional distillation system.
The presence of suitable liquids in extractive
distillation andV azeotropic‘ distillation effects in
different degrees positive deviations from
Raoult’s law;A that‘is, the volatilities of the var"
ious compounds are greater in the-presence" of the?
added liquid than would be expectedv upon theV
basis of their normal vapor pressures. Thus; in
the ease ofVv a hydrocarbon mixture containing
paraiiins, mono-oleñns and' dioleñns, the added
liquid modiiies in dilîerent degrees the relative
out requiring the use of high temperatures;
<5). Comparative stability when heated in the
presence of hydrocarbons; and
(65 Commercial availability andr non-corrosive
1. 36
l. 00
the vapor pressures of ' selected groups' of' corn
_
(4) Sufficient volatility to permit stripping with..
30
(l)V Ability to form minimum- boiling azeotropes
withth’e desired hydrocarbons;`
(2) `lëteadily separable from the hydrocarbons;
(3) Suiñcient diiiîerence in volatility between the
solvent and the azeotropes;
(e)Y Comparative stability when heated inA the
presence of hydrocarbons; and
<5) Commercial availability and non-corrosive~
ness.
Suitableliquids therefore for azeotropic distilla
tion are the saturated ketones, the amines, the
alcohols and their admixture with water.
l
It will. thus be noted that liquids advantageous
volätiliti‘es of the various type hydrocarbons. In
as` solvents in both extractive and azeotropic disani extractive distillation upon a narrow-boiling
tillation systems have very closely related prop
fraction with a polar type solvent, thep’araiiins’ 45 orties and that, in general, liquids suitable for one
will» be the most‘volatile constituents; the mono
type of distillationl are alsov suitable for the other
oleflns less volatile; and the' diole?lns the least
type or” distillation. The employment of azeo
volatile. Thus, the following table indicates the'
tropic mixtures as a means of4 extractionof the
relative volatility values of four Cs hydrocarbons
desired hydrocarbonsprovides the basis for the
1n the presence andabsence of aqueous acetone: 50 separation of' compounds otherwisedifñcult, and
advantages in'over-all proeessingyespecially when
`
'
No
solvent
Isoprene _ _ _ _ _ _ _ _
_ _ _ _ __
n-Pentane _ _ _ _ _
_ _ _ _ _ _
0.92
1.43
_
0. 92
1.30
Pentene~2 (trans)
Trimethyl'ethylene. _ _
1. 00
With 2'
.volumes of
aqueous
acetone
1.00
__________ _ _
0. 88
1. 26
Cyclopentene ___________________________ __
0. 7l
0. Q5
the same liquid is employed. in the azeotropic.. and
extractive distillation systems. The.` particular.v
processing advantages will be; evident from thev
further description and illustration. of theinven
tion.
Taking the separation of isoprene> as a suitable
example of the process of this invention, the first
step involves the azeotropi’c distillation of anarf
It is. such an elîect. under suitable conditions of 60 row C5 hydrocarbon fraction containing a sub*
stantial amount of isoprene and rejecting as much
pressure. and concentration of the added liquid
as possible of the piperylene, cyclopentadiene, tri
that. contributes to the formation of azeotropic
compositions.
The added liquid inA extractiva distillation is
employed in greater amounts than in azeotropic
distillation in order that the maximum effect of
methylethylene and the pentenes.V A suitable
source for isoprene is the refinery Icy-product dis
tillate from the high temperature cracking of gas'
oil, Virgin' naphtha, kerosene and/or othersuit
the4 solvent may be exercised upon the diiïerent
groups of. compounds; that is, the amount of ex-v
traneous. liquid employed in an extractive distil
lation isz greatly in excess of that which would
able feed stocks. A typical debutanized stock
from'thisV source may contain about 4% isoprene.
A stock’ of this nature is distilled in the pres
ence. of an entrainer so as to separate asa dis-l
form azeotropic mixtures in the system. Thus,
till’ate, essentially all ofthe desired hydrocarbons
the addition vof an extraneous liquid in extractive
distillation is related to, but very distinct from,
the addition of a deñnite amount of the added'v
liquid in an azeotropic distillation system.
as constituents of- azeotropic mixtures and as res
idue, undesirable hydrocarbons of C5 content and
of higher boiling points. Aqueous acetone is usu
ally employed as the entrainer in the separation
2,407,997' 1
6
5
of C5 hydrocarbons containing a high percentage
carefully controlledconditions to obtain as an
overhead product one of the hydrocarbons in sub
stantial purity. In the present case the fractional
distillation is eiîected to obtain substantially` pure
isoprene as the overhead product; and to leave
as distillation residue the piperylenes, and cyclo
pentadiene not previously removed due to the
presence in the system of pentanes, and smaller
of isoprene but any of the lower saturated ke-`
tones,` the amines, the alcohols, either alone or
in admixture with water, may be employed. In
this azeotropic distillation step, a distillate con
taining as high a content of isoprene as is con
sistent with the feed stock is’ usually obtained.
The residue contains a substantial quantity of
such undesirable C5 hydrocarbons as trimethyl
quantities of other impurities.
ethylene and cyclopentadiene and thel higher
boiling C5 hydrocarbons in association with hy
drocarbons of the C54- molecular content.
The distillate material is then subjected to an'
l
Since some polymerization may `occur durin _
the azeotropic and extractive distillation steps,
high-boiling polymeric materials are normally
present in the solvent recycle. Inlorder to main
extractive distillation in the presenceof an added
amount of a solvent liquid which alîects in dif
l tain the polymer content of the solvent at a low
ferent degrees the relative volatilities of the vari
ous type hydrocarbons. For this purpose usually
solvent stock is removed and combined with the,
overhead distillate obtained from the extractive
distillation; and the combined stream is then
value, usually about 3% to 5% of the recycle
the same liquid as in the azeotropic distillation is
employed sincethe liquid is largely selected on
this basis; 'for example, aqueous acetone in the
extraction of isoprene from close-cut C5 hydro
carbon fractions. Other organic liquids such as
acetone itself, furfural, the liquid basic nitrogen
compounds such as pyridine and the amines and
treated for solvent recovery.
»
In order to illustrate the invention more clear
ly, the following detailed description of process
ing is presented. The reference numerals given
in the description refer to \the accompanying
drawings which present a `suitable lay-out `of
mixtures thereof with water, may also be ad
equipment, and indicates a suitable flow of mate
vantageously used. In the case of aqueous ace
rials. for processing according to the invention.
In this illustration, example will be taken of the
tone as the added liquid, the total amount em-`
separation and puriñcation of isoprene as ob
tained from the treatment of a debutanized‘dis
tillate stream from a liquid phase cracking of a
virgin gas oil stock, A specific example of a typi
ployed is usually about twice the volume of the
liquid hydrocarbon mixture ñowing down through l
the distillation tower: in the case of furfural,
the ratio is as high as 7 to 1.
.
When diiîerent added liquids are used in the
cal debutanized distillate stream has the follow- _
azeotropic and extractive distillation operations,
separation of the added liquid from the azeotropic
ing molar percentage composition:
distillate is necessary prior to subjecting the dis
tillate product to extractive distillation. This
may be accomplished by extraction with water
Butenes `_____ _______________ __ ________ __ `
3-"nethyl »butene-l ____________________ __
Pentene-l
0.5
___________________________ __
, 9.4
or other known means. The use of different add
2-methyl butene-l ________ __ ________ ____
2.0
ed liquids has the disadvantage of necessitating
separate recovery systems for each liquid. The
Isoprene ______ _______________________ __
4.1
Trans pentene-2 ______________________ __
1.0A
gain in product purity and saving in heat expen
diture make this method of operation economi
N-pentane ____________________________ __
0.8
Cis pentene-Z` _________________________ __
1.0
cally advantageous in some cases.
2-methyl-butene-2
2.2
Thus, under suitably controlled conditions in
the presence of such quantities of added liquid,
such as aqueous acetone, 'a vapor overhead prod
uct is obtained from the extractive `distillation
system which consists essentially of paraffins and
monooleñns of C5 molecular content.
Cyclopentadiene
Y
Trans
of solvent which is recycled to the proper point
in the tower to maintain as high a solvent to hy
drocarbon ratio as is advantageous for the proc
___________ __ _________ __
1.3
piperylene _____________________ __
l2 9
Cis piperylene _______________________ __
Cyclopentene _________________________ _.
Cyclopentane _____________________ _'____
The res
idue which is usually obtained consists essentially
____________________ __
C6
________________ ___ _______________ __
l
'
2.1
0.1
11.7
Cs aromatics _________________________ __
11.7
C7 ___________________________________ __
18.7
50 '
C8
__________________________________ __
9.8
C9
__________________________________ __
20.2
ess. The most important fraction removed from
The feed stock is supplied to fractionating
the system is the intermediate distillate material 55 equipment l0 (Figure l) through line Il. The
conveniently termed the side-stream product.
fractionating equipment I0 may be any of the
This side-stream product consists mainly of iso
usual types, such as a fracticnating tower con
prene with a lesser amount of piperylene and such
taining
bubble plates. The equipment is usually
traces of liquid polymer products as were formed
operated
at about atmospheric or somewhat
during the distillation operations. Both the over
above _atmospheric pressure. In the diagram,
head and side-stream distillate fractions may 60 equipment l0 is specifically shown as being a
contain substantial quantities of the added liq
tower of multi-plate construction containing bub
uid-that is, aqueous acetone in this case-as
ble cap plates. In normal operation of process
a result of the formation of azeotropic mixtures.
ing according to the invention, about y50 plates
The side-stream product from the extractive 65 are present insuch a tower. _The tower is shown
distillation operation is normally treated to ef
fect the separation of the liquid added in the azeo
tropic and extractive distillation operations.
When aqueous acetone is employed as the added
liquid, the side-stream product is usually counter
currently treated with water to remove the ace
tone, and thus to permit the isoprene and other
hydrocarbons to be separated therefrom. 'The hy
drocarbon material after the separation of the
as being complete with an overhead vapor line
I2, a condenser i3, a reflux drum 14, a reflux line
l5, a bottoms line> i6, a reboiler I8, reboiler vapor
, line IS, and an entrainer supply line ISA.
The
70 distillate product is withdrawn from the distilla
tion system through line 2l` and the bottoms
product from the system through line l'l. The
amount of entrainer liquid supplied to the sys
. tem 4through line 15A is dependent upon the con
added liquid is then fractionally distilled under 75 tent of isoprene in the feed stock so as to form
2,407,997r
8i:
composition. with trimethylethylene„ that is in.
this caseabout one volume of aqueousfacetoneto
I6.v A portionv4 oi the» residue is passed through the
_ ten volumes of the: feed stock.,
Ul
The pressure upon* the. system> for. the treat,
ment of the specific composition is maintained
about 25 lbs. per sq; in. (gauge), in order" to- be
able to employ ordinary water for cooling pur
poses in the condenser I3. The degree of sep
aration in tower I0 is controlledby theheatsup
ply fromthe reboiler I8.' andthe ratio of reiiuvx>
The overhead fraction from- tower I0 as re'
justed‘ so as to take thefmajor. portionî of the
isoprene. in this- fraction. while rejecting' almost
moved’ through-line 2| is pass'edlto- the fraction
ating tower-20; Thetower 20 issimilar in design
to tower Ill and maybe any type of;~ suitable' frac
tionating equipment. The tower 20', however,. is.
of' smaller dimensionsgî than the corresponding>
tower. employed when fractional distillation is.
used in the preparation of thefeed material such
as inthe processing disclosed inthe ,copending
all of the trimethylethylene‘: and. most; of the
piperylene and pentenesv in the residue; In the
example used for illustration,al reflux ratio of'5.
is maintained whiletaking off approximately 6%
to 7% of the feed as distillate product. Under
these conditions, the temperature at the top of
the tower is 140° F., while the temperature at the
applicatiomserial No'. 470,426. TheY reduced` size
of the' tower 20 is» occasioned by the smaller
amount of the>v distillate and the higherl concen
tration therein of the desired hydrocarbons in
the feed supply to the extractive distillation sys
tem'than' when fractional distillation: isfemployed
inthe tower I0. It _is furnished withanoverhead>
'
The overhead product removed through line
I2 contains almost all the aqueous acetone added
through line IEA together with the majority of
the isoprene and some of' the piperylene in the
mixture, some of the pentene-l and traces of
vapor line 22, a condenser 23; a reflux drum24, a
other C5 olefins and parafûns as azeotropic mix- -
tures' formed between the constituents of the
original hydrocarbon mixture.` In this distillate
reboiler I8 where it is vaporized in order to' sup
ply the=heat necessary, to operate thetower, the
vapor being returned; to-` the tower I0 through
line I9?. The remainder of the higher boiling ma
terial is'removed from the system through 1ine.- I'I.
supplied through line I5'. 'I‘heipercentage ofthe
feed takenoff as product through line.. 2|. is? ad
exit of the line I'I is about 275° F.
.
ethylene, the: piperyleneV normal- pentanav some
pentenes, and someisoprene-in addition to-higher
boiling.l hydrocarbons,A is withdrawn through line
therewith the~- azeotropicY composition but ~ insuffi-`
cientv in` amount tol form with anv azeotropic-
reflux li-ne 25,. a bottomsl line 2G,- a reboi-l'er5 28
andI a reboiler vapor return line- 29. The tower
also has a-solvent line- 33, a side streamvapor line
ë! and aside stream return~»line 35. rEh‘efdistil
late product is withdrawn from: the system
the azeotrope containing. isoprene contains 92.0%
isoprene, 7.6% acetone and 0.4% water. Isoprene
through line 4I and the bottoms product through
line 2l. The pressure upon'the system is main
tained at about 25~lbsz per sq. in. (gauge), in order
is thus distilled at a temperature 3° to 4° F. below
to have- aworkab'le condensing temperature sim
its own boiling temperature thereby minimizing
heat eñ‘ects productive of polymer formation.
ilar to that prevailing in- the fractionatingequip’
operating conditions given shows the following
molar percentagecomposition:
stripped of its hydrocarbon: content.
ment I0.
’
The yoverhead distillate'vapor removed through
Moreover, as a resultof the high concentration of
line 22 consists of». azeotropic mixtures'of" C5 ole‘
the isoprene inthe distillate- material, a smaller
quantity of distillate is taken off as compared to 40 iins and parañins when aqueous» acetone is em
ployed as the` solvent material admittedth-rough
straight fractional distillation, thus effecting con
line 39- The'vapors are'condensed in equipment
siderable heat and processing economies. The
23 and passed to‘thetreñux drum-1.24.V A portion
heat` economy involved more than compensates
of the condensatex- is- returned; through linev 25
for the heat input required 'for distillation of theY
45 as reñux, while the remainder is withdrawn
added aqueous acetone.
through line 4|-, cooledl in equipment 42 y(Figure
The entire distillate is condensed in equipment
1A) and conductedïthrough line- ¿t3-to the water
I3 and passed to the drum I4. From the drum
scrubbing equipmentç 5I).
I4, a quantity'of reflux is passed through line I5
The quantity of aqueous acetone admitted
in order to maintain the desired operating condi~
tions. The remainder of the condensed distillate 50 through line 39 l to the. extractive distillation ~ sys'
tem isffor- thevamount and composition of feed
is withdrawn from the drum |4 and passedv
supply in» a volumeratio of solvent to» azeotropic
through line 2| for further‘processing'. The ratiomixtu-re Vof . 2--1y from.u the v point of` introduction> to
of the redux to product is between 4 and 5, de~
the plate upon` which. thefside stream isV with-`
pending upon the feed. In the processing of the
vfeed stock of the specific illustration, the compo 55, drawn.` Below- the plate. from which.> thev side"
stream prod-uct is- withdrawn, the solvent»l is
sition of the distillate material under. the specific
C4
___________________________________ __
B-methyl
butene-l ______________ __ ____ __
P’entene-l ...... __, ____________________ __
2-methyl butene-I ____________________ __
Isoprene ___________________________ __»__
Trans
'
The bottomsw-ithdrawn- throughh line 26I con
sist of relatively pure solvent. A portion of the'
rco bottoms liquid'is passed> through the' reboiler- 28
1.5
where itis vaporized; the vapors being returned
6.0
to~the- tower 20. through the Vvapor line 29, to' supe
3.0
ply the heat‘necessary to operate the tower. The
59.9
remainder of the solvent, except for av small por
pentene-Z ________________ __ ____ __
1.5
65 tion» withdrawn for purification, as to befurther
n-Pentane ______________________ _______._.
Cis `pentene-2 _________________________ __
2’-methy1 butene-Z ____________________ __
.43.0
1.5
3.0
described,.is conducted through line 21 tocooler
y Cyclopentadiene n ______________________ __
1.8
Cis and trans piperylene__ __________ ____
09
Acetone
______________________________ __
8.8
_______________________________ __
1-.3
Water
100.0
38 and then through line 39v to the upper portion
of the tower 20. Thus, the'major part of the
solvent continuously recycles within the extrac
tive distillation system.
Tlíevapor sidev stream removed through line 3|
contains a high concentration of` i'soprene with
small" amounts. of' otherv dioleñns in the presence
of` solvent in- anamount ineequílibrium with a 75
I The residual material containing the tri-methyl' 75 molar' percent" concentration of solvent on th'e
‘ 2,407,997
`10
î 9
plates of the extractive distillation tower 20.
The volume of the solvent is about 50% of the
vapor mixture. This side stream material with
distillation system and to effect the side stream
concentration. In the same way, the condensa
tion needed to produce the required reñux in the
‘ drawn through line 3| is conducted to the base
extractive distillation zone is obtained by sup
plying the heat needed to- concentrate the mono
of the side stream concentrating tower 3|). The
tower 3€) may be any suitable fractionating appa
ratus, such as a tower provided with bubble plates,
as previously employed. The tower is provided
with an overhead vapor line 32, a condenser 33,
. oleñns at the top of the tower 20.
In the operation of the system comprising tow
ers 20 and 33 and their auxiliaries, separation
into the zones indicated above is clearly deñned
a reflux drum 34, a reflux line 35 and a bottoms
by the various temperature Zones. Thus, the va
por leaving the top of the tower 20 is at 140° F.
The temperature rises sharply to 155° F. between
the topl of the tower and the plate on which the
solvent is admitted through line 39, then very
slowly rising to 160° F. at the plate where the side
stream‘is withdrawn through line 3|. Below the
plateirom which the side stream is removed and
line 36, in addition to the vapor inlet line 3|.
The vapor entering the tower 3|] through line 3|
supplies the heat necessary to operate the tower.
’ The overhead distillate removed through line
32 consists essentially of the azeotropic mixture
of isoprene, acetone and water and contains in
addition small quantities of other C5 unsaturates
and higher boiling materials such as polymers
formed during the extractive distillation opera
tion. The vapor is condensed in equipment 33
and conducted to the drum 34. A portion of the
condensate is returned to the tower 30 through
line 35 as reflux, while the remainder is with
drawn through line` 3l to the water scrubbing
as a result of the concentration of the aqueous
acetone, the temperature rises sharply to 208° F.
the temperature prevailing at the bottom of the
tower. The temperature at the top of the side
stream tower 3|) is 145° F. In tower 33, the same
type of temperature, gradient is shown as in the
concentrating section of the tower 20.
equipment 4i).
i 25
The degree of separation of the hydrocarbons
taking place in the extractive distillation system
2B is dependent on two functions, namely, the
The isoprene-acetone-water azeotropic mixture
removed as distillate from the tower 30 through
lline `3l is conducted to the water scrubbing
equipment 4l). Equip-ment 40 may be any suitable
type of a liquid-liquid contacting device, in which
ratio of the solvent to hydrocarbon liquid on the
plates and the ratio of liquid to vapor >íiowing.
» countercurrent `iiow of y,the Lmaterials may be
through the tower. The `ratio of solvent to hy
maintained.' In the‘present‘case, the tower is
drocarbon is ‘controlled by the rate of solvent re
circulation. The ratio of liquid to vapor in the
zone ofA high solvent to hydrocarbon ratio, that
packed with` Raschig ringsfand suflìcient pres
sure is ‘maintained on the tower to prevent vapor
ization of any ofthe materials passing through
is, between the solvent inlet and the side stream
outlet, is controlled by the reflux returned
through line 25 from the reflux drum 2H. Due to
considerable difference in solvent concentration
between the top of the tower and the extractive
- it. The stream removed from the system through
line 3l' is admitted to the bottom of the tower 4U
Y irough‘ a‘distributing device and then allowed
\ toiv now upward countercurrent to a stream of
l water admitted to thetower‘jthrough line 44,
distillation zone and the difference in latent heats`
of the constituents,'the’reflux ratio andfconse
Vquently the ratio of liquid to vapor `at the top of
“In passing through the tower, the acetone is
'removed and the hydrocarbon `is thus completely
. freed >`of the solvent employed in the extractive
the tower must be appreciably higher than the
liquid to vapor Vratio in the extractive distillation
distillation. The quantity of water employed is
determined by the partition of the solvent be
45 tween the hydrocarbon and the water and the
‘ In the case of the specific example, the liquid to
:efñciency‘ of `the extracting equipment 4D.- For
`vapor ratio in the extractive distillation zone is
the specific composition taken, a Volume ratio of
0.80, while the ratio at the top of the -tower is 0.85,
water to distillate'is approximately 1. Passing
the latter being equivalent to a reflux ratio lof
'overhead from the tower 48 is partially purified
5.5. The reñux ratio used in the side stream,
isoprene in a high' concentration.` Impurities
zone.
>
‘
‘
1
tower 3|! is adjusted so asto obtain an overhead
‘ `present in the streamconsist of piperylene, cyclo
product consisting essentially of the azeotropic
' pentadiene, polymers and any-other water in
mixture of isoprene, acetone and‘water» and to
soluble materials contained in the distillate from
supply adequate reflux to the solvent stripping
`thetower 30. `The water extract removed from
section of the tower 2i); whichever requires the,... the tower through line 48 consists of a dilute so
larger amount of reflux determines the refluxV
lution of acetone in water. This extract is com
ratio at the top of the tower30. Inthe case
bined with a similar extract from the tower 5l)
cited in the example, a reflux ratio of 20 is main
tained at the top of the tower 3U, in order to
Tand treated for the recovery of the acetone sol
supply adequate reiiux to the bottoms solventl
vent asto be subsequently described.
The solvent-free diolefln concentrate from the
’tower 40 is conducted through line` 46 to the irac
VThe heat necessary for the extractive distilla
ltionating tower- 13. y This tower may be any suit
tion operation, as well as to concentrate the hy
'
able device for effecting a fractional distillation.
drocarbon fractions and to strip the solvent, is
supplied completely from the single` reboiler '28.,` ` For the speciiic` composition chosen, a tower con
_ taining .50 bubbleLcap plates is employed. The
In this manner, considerable heat economy is
tower 1E! is provided with an overhead vapor line
effected, since the heat to operate the extractive
stripping section of the tower 20.
,
l
distillation zone in tower 20 and the dioleñn con
centrating side stream tower 30 are supplied by
condensation of the solvent mixture at the top
of the solvent stripping section of the tower. If
"
l2, a condenser '13, a reflux drum 14, 1a reflux line
'l5 and a bottoms withdrawal line 16, a reboiler
i3 and a reboiler vapor return line 19. The dis
tillate product is withdrawn through line 8| and -
this were not done, a condenser would have to
the bottoms product through line 71. Pressure
be provided for the solvent stripper to supply the
.reiiux necessary for operation, and additional
heat would be required to operate the extractive
is maintained on the system so as to eiîect satis
factory condensation with ordinary water in the
condenser 13. In the specific example, pressure
2,407,997 l
12
maintained upon the tower ‘l0 is between 12 4and
line 5l, through heat exchangers 52 and line `6| '
15 lbs, per sq. in. (gauge).
tothe solvent recovery tower 60.
»
s
Tower 60 may be any convenient device for
effecting fractional distillation, such asa tower
The distillate withdrawn through line ‘l2 con
sists of highly puriñed isoprene containing traces
of piperylene and pentenes. The distillate is con
densed in equipment T3 and the condensate con
ducted to the reflux drum 14. -A portion of con
containing about 2€! bubble cap plates. It is pro
vided with an overhead vapor line 62, a condenser
t3,> a reiiux dum 64, reflux line E5, a -bottoms
withdrawal line BS and a steam line 68. The dis
densate is returned to the tower 'I0 as reflux
tillate product is withdrawn through line 69
through line 15, while the remainder is withdrawn
as product through line 8|. It is cooled in equip 10 and the bottoms through line 6l. Thedistillate
\ «ment Si! and transferred to Astorage through line
‘ from the tower E@ consists of relatively pure sol
vent. The tower is operated at about atmospheric
82.
pressure. The distillate vapor passes through line
The bottoms consisting of the piperylene and
.52 tothe condenser 63 and the condensate passed
cyclopentadiene, in addition to any polymer or
«high boiling constituents, of the feed to the tower 15 to reflux drum 64. A portion of the condensate
is returned to the tower 60 through line 65, while
and containing “some isoprene, is withdrawn
the remainder is withdrawn and transferred
through line 1S. A portion of the material is
through line 6H to line 39 where it combines with
passed to the reboiler 18 where it is vaporized, the
the solvent admitted to» the tower 28. VHeat is
» «vapors being returned to the tower 'lll through
supplied'to the tower 5% by means of .a steam
line 'H9 to supply the heat necessary to operate the
line G8. through which open steam is `injected
tower. The remainder of the bottoms are re
directly into the bottom of the tower. The bot
moved through the line 11 and recycled to the
toms comprising the major part of the water
feed tower l0 for the'recovery of any isoprene
content of the feed and the condensed steam is
content.
Bynincreasing the number-of-p-lates in tower 10 25 withdrawn through line 66 to the heat exchanger
52. Thefhea't exchanger 52 is utilized to heat
or »increasing the reflux ratio, -essentialh7 all of
the feed Vto the tower Si?. Thus, the sensible heat
`the isoprene may be taken overhead as purified
product. It has been found, however, more elli
Acient tojreject a small amountof isoprene to the
bottomsï and lrecycle same `for recovery as de
scribed. -A reflux ratio vof l2 is vmaintained for
thedesired separation in the tower 10.
’
The distillate fraction from the tower 20 which
of the bottoms is utilized.
The reflux returned to the tower 6B through
line 65 is controlled'at-such a rate that the water
content of the distillate >passing through line 62
and consequently the Vproduct returned to the
tower 30' through lines 59 andr'äß is »the same as
the recycled solvent Vin towerïil. Byy proper ad
is Withdrawn through line 4I, containing the
_azeotropic mixtures of the C5 paraffins and ole 35 justment of the reflux ratio in tower 69, the
water content of the product may be varied to
ñns‘is combined with any recycled solvent from
correct the variations _in the Water `content of
the vbottom of the tower 20 taken .from line 42l
the solvent in the tower 24. Normally a reilux
which fis withdrawn through line 43 to maintain
ratio of about 0.5 is maintained .in the tower 60.
theimpurities in the solvent at a low value. ÍIn
With the foregoing disclosure and illustration
theexample, about 3.5% of the solvent passing 40
ofthe invention .it‘will be obvious to those skilled
through ’line 2l is withdrawn and combined with
in'ïthe art that various combinations and vari
the Ydistillate material removed through line 4|.
ations of the` applications of the principle de
Thefcomposite solution ïis then cooled in equip
scribed and illustrated can be made without de
ment 42 and carried to the water extraction tower
Y 50 by meanszof the line 43. The extraction tower 45 parting from the inventive concept and that the
finvention in, the broad> aspect comprises the
I`5i) is similar to the 4extraction tower 4D. It is
similarly packed with Raschigvrings. Thecom
Dosite solution consisting ofthe Ct -oleiins and
parailins, in addition to acetone and water, is
introduced into the tower 50 near the bottom and 50
passes upward through the tower countercurr ent
ly to a'stream> of'water introduced near the top
through line 4,5.
n
.
In vpassing through the tower, the solvent »is
unique combination «of fractionally' distilling and
I extractively distilling suitable. feed `stock mate
rials for the separation of individual hydrocar
bon compounds.
u
What is claimed is:
.
l. A process for separating isoprene from a
Írefinery cracked stock containing isoprene which
comprises'subjecting said reñnery cracked stock
to distillation in the ,presence of aqueous acetone
to obtain Van azeotropic mixture containing Viso
prene as distillate material, subjecting said dis
portion of the .recycled solvent which was com
tillate material to an extractive distillation in
bined with the distillate from vtower >2i) is ex
the presence of a solvent comprising acetone,-septracted by the hydrocarbons of the distillate ma
terial. The hydrocarbons freed of solvent are 60 arating a distillate fraction containing isoprene
in high concentration and fractionally distilling
removed through line 41 at the top of the tower
the resultant ymaterial to obtain isoprene. 5û Yand discarded. -The water extract consisting
2. vA process according to claim 1 in 4which the
of a dilute solution of acetone in water is with
solvent `employed inthe extractive distillation is
drawn through line 49 at the ybottom of the tower
,
50 and after being combined with a similar ex 65 aqueous acetone. tract -from the tower >4l) is transferred through
"
JOI-IN A.- PATTERSON.
extracted from the hydrocarbon material. Any
Y «polymers »or other high boiling material in the
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