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Патент USA US2411025

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Nov. 12,1946. '
c. A. COGHLAN
, 2,411,025
SOLVENT EXTRACTION OF UNSATURATED HYDROCARBON MIXTURES
Filed Feb. 9. 1944
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-
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TETRAETHYLENE GLYCOL.
EQUILIBRILM cuRvE
P
,
.
,‘E U
6E I:h.
u 540
TRIMETHYLENE GLYCOL
5 g‘
-
EQUUBRIUM cuav:
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-
2 °
‘
I- "’
1
3 20
a?
'
0
2'0
54'0
6'0
% summing m RAFFINATE
SOLVENT FREE
- 'a'o
I00 '
2,411,026
3
taining 20% butadiene,v 35% isobutylene, 40%
butylene-2, 3% isobutane, and about 2% normal
butane by volume is‘ charged to the intermediate
portion of the extraction tower maintained at a
temperature of about 100 to 110° F., and under
pressure suiiicient to maintain the hydrocarbons
tower along with the solvent while the more
saturated oie?ns are removed as a distillate from
the upper portion of the extraction tower.
It is also contemplated that the extraction
process may be carried out to obtain an extract
phase containing somewhat lower concentrations
of butadiene, for example, 70 to 80% rather than
in the liquid phase. Tetraethylene glycol is in
‘98%. The extract phase so-obtained may be
troduced to the upper portion of the tower in
passed to another treating zone wherein the
the proportion of about 10 volumes of solvent to 1
volume of hydrocarbon feed. Extract phase is 10 butadiene is recovered by azeotropic distillation
using ammonia or some other suitable compound
continuously withdrawn from the bottom of the
‘ tower and a portion thereof, after removal of
as an azeotrope former. In this way butadiene of
the solvent, continuously returned to the tower
at a point near the point of extract withdrawal.
99% or more purity may be recovered from the
primary extract phase. Advantageously the sol
The amount of solvent-free extract so-recycled 15 vent is stripped from the extract phase prior to
subjecting it to azeotropic distillation.
is about 2.43 volumes per volume of feed hydro
Other glycols which may be used comprise
carbon mixture charged to the tower.
hexaethylene glycol having a molecular weight
The solvent-free extract amounts to about
of about 300, and nonaethylene glycol having a
14.3% by volume of the feed hydrocarbon mixture
and contains about 98% butadiene, the remain 20 molecular weight of about 400. .
Obviously many modi?cations and variations
ing small amount consisting of more saturated
ole?ns.
' of the invention as above set forth may be made
Y
The ra?inate phase after removal of the solvent
will amount to about 85.7% by volume of the
feed hydrocarbon mixture.
- The raf?nate phase as removed from the top
of the tower will contain a relatively small amount
of solvent, about 0.2% and usually not in excess
of about 1% by volume. The solvent may be
without departing from the spirit and scope
thereof, and therefore only such limitations
25 should be,imposed as are indicated in the ap
pended claims.
I claim:
'
.
1. The process for separating butadiene from
hydrocarbon mixtures containing it and C4
removed from the ra?lnate phase by scrubbing 30 mono-ole?ns which comprises subjecting a C74
hydrocarbon mixture of said ole?ns to contact
with water, and the resulting mixtureof water
and'tetraethylene glycol is then subjected to dis
with a polyethylene glycol having a molecular
weight in the range from that for tetraethylene
tillation to strip the solvent from the water after
glycol up to 1000, selectively dissolving butadiene
,
The extract phase which comprises butadiene 35 in said glycol during said contact, withdrawing
said solution from undissolved mono-ole?n hy
and the bulk of the solvent is subjected to frac
drocarbons, and recovering dissolved butadiene
tional distillation to strip the butadiene from the
which the solvent may be used again.
solvent following which the solvent may be re
.used in the extraction tower.
I, from the glycol solvent.
.
2. The process for separating butadiene from
In the foregoing example the butadiene ob 40 a hydrocarbon mixture containing it and C4
mono-ole?ns which comprises subjecting a C4
tained in the extract amounts to about '70%_
hydrocarbon mixture of said olefins to contact
of the total butadiene contained in the feed hy
with tetraethylene glycol, selectively dissolving
drocarbon‘ mixture. By increasing the solvent.
butadiene in said glycol during said' contact,
dosage and the amount of extract recycle, the
butadiene recovery may be increased to about 45 withdrawing said solution from undissolved
mono-olefin hydrocarbons, and recovering dis
95%; for example, the solvent dosage‘may be
solved butadiene from the glycol solvent.
increased to about 30 volumes of solvent per vol- '
3. A process for separating butadiene from a
ume of feed hydrocarbon mixture while the ex
C4 hydrocarbon mixture containing it and mono
tract recycle may be raised to 4 volumes of sol
vent-free extract per volume of feed hydrocar 50 ole?ns which comprises subjecting said C4 mix
ture to counter-current contact with a stream of
bon mixture. It is contemplated that in prac-.»,
tetraethylene glycol, effecting said contact at a
. tice the extraction temperature employed for sep
temperature in the range about 70 to 325° F.,
arating butadiene from a C4 hydrocarbon mixture
forming an extract phase comprising butadiene
may range from about "10° F. to about 325° F.,
the latter temperature being the critical tem 55 dissolved in the bulk of the solvent and a raf
?nate phase’ comprising- C4 mono-ole?ns, sep
perature of butadiene. [Temperatures below ‘70°
arating said phases, and removing butadiene from
F. are not advantageous because the high molecu
the separated extract phase.
lar weight glycols become more viscous so that
4. The method according‘to claim 3 in which
separation between extract and raf?nate phases
is less eiiicient. Moreover, at these low temper 60 the extractive contact is effected at a temporal
ture of about 100° F.
atures the per cent recovery of butadiene is rela
5. The process for separating butadiene from
tively small and the amount of solvent required
a C4 hydrocarbon mixture containing it and
in the system becomes excessive.
mono-olefins which comprises subjecting said
Generally speaking it‘ is desirable to effect
the extraction at a temperature not exceeding 65 mixture to contact with a polyethylene glycol
about 200° F. since at higher temperatures the ' having a molecular weight in the range from that
for tetraethylene glycol up to 400, selectively dis
extract obtained has a higher content of other
ole?ns.
’
.
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'
solving butadiene in said glycol during said con
tact at a. temperature in the range about '70 to
While mention has been made of liquid-liquid
extraction, it is also contemplated that extrac 70 325° F., withdrawing said solution from undis
solved mono-ole?n hydrocarbons, and recovering
tive distillation may be employedcusing the fore
butadiene from the glycol solvent. 1
.
going type of solvent. In such operation the
CHARLES A. COGHLAN.
butadiene is removed from the. bottom of the
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