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Dec. 3l, 1946.
H, M_ wElR
2,413,674
MULTISTAGE uETHoD oF PURIFYING s'rYRENE
Filed Feb. 27, 1943
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2,413,674 -
Patented Dec.-3l, 1946 l
UNITED STATES _PATENT omer:
u
2,413,614
i
MULTISTAGE METHOD or
smENE
I G
_
, Pa., assigner to The
Horace M. Weir, Wynnew
United Gas Improvement Company, a comration ‘of Pennsylvania
`
Application February 27, 1943, SerialANnrd'l'lßGä
10 Claims. ` (CL 260-669)
.
'
l
-
This invention pertains generally tothe puri
iication of valuable hydrocarbons _and pertains
particularly to resin-forming unsaturated hydro
carbons.
y
,
.
a light oil fraction. By spe
60% of styrene in very
refined technique, a con
cial measures and
centration of say 80% styrene in a light oil frac
tion is sometimes a possibility. Theoretically,
the production of pure styrene by distillation f
'
The invention _pertains more particularly to
the purification of crude unsaturated hydrocar
bon'fractions derived from 'light oil obtained in
the manufacture of combustible gas, 'such for
example, in a process involving the pyrolysis of
petroleum oil with or without the aid of catalysts.
'I‘he invention pertains still morev particularly
to the purification of> light oil styrene fractions
alone is possible, but is prohibitably expensive
because although the separation of styrene from
meta-xylene and from para-xylene can be more
readily accomplished, the- separation of styrene
from ortho-xylene is extremely difñculty because '
of the very close .proximity of the boiling points
of styrene and ortho-xylene.
-form, including the substantially pure form.
There are various processes for the manufac
-
For resin manufacture and for other purposes,
it is- frequently desirable to have styrene in a
for the recovery of 'styrene in` more concentrated
15 substantially pure or at least a very highly con
-centrated form.
It has hitherto been proposed to concentrate
ture of combustible gas,_ such for example, as -oil _
gas, carburetted water gas, coal gas, etc., which
styrene by fractional distillation to a concentra
yield considerable »quantities of tar as well as
tion of say 50 or 60% or somewhat higher, and
other materials which are readily condensible
then to continue ,the puriñcation by fractional
from the gas. The extent to which such materials 20 crystallization to obtain substantially pure
are removed from the gas is, of course, depend
styrene. Seey copending application Serial Num
ent upon the extent to“ which the gas is treated
ber 319,373, filed February 17, .1940, by Horace
for the removal of condensate therefrom. Var
M. Weir, which has matured into Patent 2,383,
ious tools are available for this purpose, such as
refrigeration, compression, adsorption and ab
sorption and combinations of the foregoing.
The various condensates, including the tar,
comprise sources for numerous resin-forming un
25
174 granted August 21, 1945, and application Se
rial Number 406,142, filed August 9, 1941, by
Gerald L. Eaton.
.
The dii‘ñculty of producing substantially pure
styrene by distillation alone will become apparent
saturated hydrocarbons, such as indene, methyl
styrene, styrene, cyclopentadiene, isoprene, pi 30 from a study of the boiling points of materials
which have been identified as present in light oil
perylene, isobutylene, butadiene, etc. Fractions
styrene fractions.
of these various materials are usually separated
. (l) Styrene boils at approximately 144.9° C.
from the various condensates by fractional dis
` (2) Ortho-xylene boils at approximately
tillation and are then subjected to purification
methods which frequently involve concentration
144.5° C.
to a high state of purity.
_
Due to the fact that many f these materials
are thermally unstable and are present in frac
(3) Meta - xylene
139.1° C.
boils
at
approximately
(4i-Para. »- xylene
boilsI
at approximately
tions containing relatively large quantities of
138.44° C.
'
‘
,
materials of similar boiling point, great difiiculty 40 -(5) Phenyl acetylene boils at approximately
is experienced in attempting to concentrate many
142° C.
.
‘
'
of these materials by‘fractional distillation alone.
In concentrating styrene in a light oil frac
This is particularly true in the caseof styrene
tion by distillation, ortho-xylene concentrates indue to the presence of not only ortho-xylene,
the fraction with respect to the other xylenes
45
meta-'xylene, and para-xylene, but also to nu
merous other similarly boiling materials, such as
phenyl acetylene, and possibly ethyl benzene, iso
since its boiling point is very close to that of ^
styrene. Thus a light oil fraction concentrated
tosay 50 to 60% styrene,'may contain ortho- ,
xylene as the principal constituent other than
Thus by -'ordinary distillation technique, it is
styrene._ At higher concentrations the accom
50
difñcult to exceed a concentration of say 50 to
propyl benzene, etc.
A
2,418,674
3
panying xylene may become entirely ortho
.
The prolonged heating incurred in such dis
tillations results in large losses of styrene due to
polymerization.
>
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.
.
4
'
higher styrene concentration, (3) further contin
ulng the concentration of styrene by another
fractional ~distillation to produce styrene in yet
higher concentration which may be that of sub-
"
stantially pure styrene.
That styrene may be crystallized from a mix
\
For example, `I may concentrate styrene con->
l tained in light oil by fractional .distillation to a
concentration of say from 45 to 80%; then I
may carry the concentration to say 90% by the
ture of styrene and the three isomeric xylenes
commonly foundin light oil styrene fractions pro
vided the concentration of styrene is maintained
~above 33 to 3,5% ¿to avoid the formation of v10
medium of fractional crystallization according to ~
eutectic was an funeXpected eventuality, among
the methods described in the'above copending ap
other reasons. because of the freezing points of
plications or otherwise; and‘then I may concen
the xylenes as compared to that of styrene.
trate the „90% styrene produced by fractional
For example, while the freezoing point ofA
styrene is approximately --31° Cl, the freezing
crystallization to a concentration of styrene of
sibility of commercially separating- styrene from
duced by the preliminary distillation. In fact
it is thotught that there may be a decrease .in the
points --of the isomeric xylenes are respectively 15 95% or higher by .fractional distillation.
I have discovered that in the concentration
as follows:
.
from say 50% styrene to 90% styrene through the
(1) Ortho-xylene, approximately -27°'C.;
medium of fractionalcrystallization, there is not
(2) Meta-xylene, approximately _54° C.; and
an accompanying Aconcentration of ortho-xylene
(3) Para-xylene, approximately +13~2° C.
20 comparative to that which would take place if
From this data, it will be seen that the freez
ing points of two of the xylenes are above the A the concentration from say 50% to 90% styrene
were eiïected through the medium of distillation.
freezing point of'` sty'rene.
`
.
Thus the 90% styrene fraction obtained by crys
Furthermore since the many materials present
tallization frequently contains no greater propor
in light oil fractions are -capable of forming a
tion of ortho-xylene relative tothe other isomeric
very large number of eutectic mixtures, the pos
xylenes than did the 50% styrene fraction pro
a light oil fraction through the medium of
crystallization was ,wholly unexpected. '
From the standpoint ofcrystallization, it is for
tunate that para-xylene which freezes 45° C.
above the freezing point of styrene is reduced in
concentration duringthe preliminary distillation.
From this standpoint, however, it is unfortunate
that meta-xylene which freezes at 22° C. below
the freezing point of styrene and which therefore
is most readily separable by freezing is also re
duced in concentration during the preliminary
distillation, while ortho-xylene which freezes
i proportion of ortho-xylene relative to the other
30
xylenes, in'some cases, due to diiïerence in selec
tive adsorption of the xylenes by the styrene
crystals.
’
.
It will of course be understood that if by some
means a starting styrene-xylenermixture is pro
duced containing styrene in higher concentration
than that of the eutectic composition without any
vinitial concentration, the first concentrating step
may be omitted. Usually, however, `an initial
concentrating step will be necessary.
abov‘e the freezing point of styrene is concen 40
Therefore, the ñnal distillation step, concen
trated with the styrene, due to the extreme close
trating the styrene from say 90% to substantially
ness of the boiling points of the two materials.
pure styrene, may be effected relatively inex
~In such an extremely complicated system, it is
pensively by distillation due to the aforemen
a wholly unforseen circumstance that after a pre
tioned fact. that the 90% concentration was
lìminary concentration of a light oil styrene frac
reached without unduly concentrating the ortho
tion by distillation to a point above 33 to 35%,~ . xylene; which is so diiiîcult to separate by distil
i pure styrene crystals may be made to separatev by
fractional crystallization.
Such fractional crystallization may be carried
to the production of substantially pure styrene.
lation.
.
The provision of a ñnal -distillation step to com
-plete the concentration of the styrene very con
A
siderably reduces the cost ofthe crystallization
'I'he tenacious adherence of the mother liquor 50 step, as it is no longer necessary to wash adsorbed
to the styrene crystals, however, is sometimes
very troublesome, making it more feasible to con
mother liquor from the styrene crystals as com
pletely as otherwise would be required. In fact
duct the crystallization in two stages to reduce
the `final distillation .step usually obviatesv any
the amount of washing required of the styrene
necessity for a second crystallization stage oper
crystals to remove mother liquor. Thus in the 55 ating upon melted crystals from a ñrst crystal
ilrst stage the concentration may be carried to
lization stage, a procedure which- has been found
s_ay 85% to 90% or 95% without excessive wash
necessary, in some cases, in order to eilicie'ntly
ing. The crystals are then melted and subjected
produce substantially. pure styrene when the final
to Irecrystallization for further purification in
purification is by fractional crystallization.
which, however,A substantially greater washing
It will be understood that other methods than
is required. with unavoidable solution of styrene
fractional distillation may be employed in the ini
crystals in wash liquid.
tial concentration of the styrene to a concentra
tion above that of the eutectic composition be
I have discovered that styrene in high concen
tween styrene and the remaining constituents.
tration including substantially pure styrene may
be vseparated from mixtures with xylenes such 65 As an example of such other methods, selective
solvent extraction\as described in Patent 2,295,
as in light oil in economically and in good yields
612, dated Sept. 15, 1942, may be mentioned.
by (1) eiîecting a preliminary concentration of
An alternative method of obtaining styrene of
styrene for example by- fractional distillation or
the desired concentration for the ñnal distilla
_otherwise to produce a fraction having a styrene
tion is that which comprises blending a styrene
concentration above the styrene concentration in
fraction of high concentration, say a concentra
the eutectic mixture capable o'f being formed be
of 95%, such as a styrene fraction obtained
tween styrene and the remaining components, (2) ' tion
by the crystallization of styrene from a liquid
continuing the concentration by fractional crys
material `containing the same, with a styrene
tallization to produce a, fraction containing a. still 75
fraction of low concentration, say 60% such as
-
2,418,674 '
.5
5
a styrene fraction obtained by the distillation of a
crude styrene containing mixture.
`
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Fractional distillation column 5l may be pro
vided with phase contacting means 52 and the
heating coil 53.
~
Further features of the invention reside in the
steps, combination of steps, and sequence of steps,
Column 5| may be operated for example so that
material comprising chiefly xylene is lead oil! as
and the construction, arrangement. , and com-`
bination of parts all of which, together with other ~
features, will become- more apparent to persons
skilled in the art ‘as the specification proceeds
overhead through line 51 to condenser 58.
A part of the resulting condensate may be suD- `
plied by pump 59 through line460 to column 5|
as reflux,‘the remainder being lead away by line
andupon Ireference to the drawing in which
Figure 1 is a now sheet illustrating one form'of 10 El as cgntrolled by valves 82y and 63.
»
my invention, which will be more particularly
From the bottom of fractional distillation
described in connection with the employment of
4column 5|, a styrene fraction may be lead oiI as
an internal refrigerant in the crystallization stage
bottoms containing from say g5 to 80% styrene
of the process and with filtering as the method
depending upon ~the degree of fractionation ef-g
of separating styrene crystals and mother liquor
fected in fractional distillation column 5I. This
in that stage.
material is lead oil.' by way of line 31 and sup
Referring to Figure 1, I indicates a line sup~
plied by pump 68 through valve 69 to the crystal
plying light `oil to the fractional distillation
lizer 10 in admixture with an internal refrigerant,
column 2 which is illustrated as provided with
for example, a liquefied normally gaseous hydro
packing 3. Any desired phase contacting means 20 carbon refrigerant, _such ' as propane, supplied
may be employed in this or other columns in the
through line 1I controlled by valve 12.
'
apparatus, such for example, as conventional
In the operation of the fractional distillation
rings, saddles, balls, jack chain, etc., or columns
columns, it will be understood that suitable reflux
of other types, such 'for example as bubble plate
ratios may be employed, the precise reflux ratios
columns may- be employed instead of packed 25 depending upon other factors as will be readily
understood by those skilled in the art. Also the '
columns. d indicates a heating coil, such as
-steam coil. for example for supplying heat to the
various> fractionationsmay be performed under
any desired pressure. Sub-atmospheric pres~
base of the column.
Column 2 may be operated so that the ligh
sures, produced by means not shown but readily ~
oil is fractionated for example,~ into material oi'>
understood by those skilled in the art, are
especially ladvantageous in minimizing polymeri
predominately six carbon atoms -and lower which
is taken off as overhead through line 5 to con
zation during distillation. Also diluent gases may
denser 6. A part of >the resulting condensate
be employed if desired` to reduce the partial
may be returned to the column 2 by the pump 8
pressures of constituents of the`mixtures being
through line 1 as reñux and a part may be lead :
fractionated.
>Returning to the crystallizer, crystallizer 10 is
off as product through the line 9 as controlled
e
Material of predominately seven carbon atoms
and higher, for example, may be lead off from
maintained at a suitable iluid level illustrated for
convenience at 13.
The crystallizer 10 may be maintained at any
the bottom of the column through line I2 and 40 pressure suitable for the evaporation of suñicient
supplied by pump I3 through line I1 controlled
propane to obtain the desired low temperature in
the fluid mass therein, for'the purpose of crystal
by valve I8 to the fractional distillation column
lizing styrene to form a slurry of styrene crystals.
i9.
Column i9 is illustrated as provided with phase
and mother liquor. Propane vapors are removed
contacting means 20 and heating coil 2|.
through line 11 as controlled by valve 18, through
Column I9 may be operated, for example, in a
which lthe desired pressure in crystallizer 10 may
by the valves l0 and Il.
manner such that material of predominately nine -
be conveniently controlled. Any suitable pressure
regulating mechanism may be employed for this I
carbon atoms and higher is lead oiï as bottoms
from column I9 through line 22 controlled by
purpose. For example, line 18 may lead to the
valve 23.
inlet of a compressor unit not shown.
,
.
Sub-atmospheric pressure is usually employed.v
- Material of predominately eight carbon atoms
and lower may be lead as overhead from column
in order to obtain a copious crop of styrene crys
I9 through line v21 to condenser 28. . A part of the
tals in crystallizer 70, care, however, is exercised
resulting condensate may -be returned to the
column by pump 29 through line 30 and a part
to restrict the cooling sufilciently to avoidsolid/iii
lead by way of line 3| to fractional distillation ‘
The slurry formed in crystallizer 10 is continu
ously removed from the crystallizer byI means of
column 32 as controlled by valves 33 and 31.
The fractional distillation column 32‘ may be
provided with phase contacting means 34 and
heater35.
.
_Column 32 may be operated for example in a
manner such that material -of vpredominately
seven carbon atoms is taken off from column 32
as overhead by way of line 38 to condenser 39.
A partof the resulting condensate may be re
turned by pump 40 andline 4|. to column 32-as
reñux, the remainder of the condensate beingv
lead off as product, ‘through line 42, as controlled
cation of eutectic mixture.
'
line 19 and pump 80, which" circulates the slurry
preferably at a fairly high .rate through lines
60 8| and .82 back to crystallizer 10. This circula-A
tion of slurry assists in maintaining a fairly uni
form temperature in the fluid mixture in the
crystallizer 10 and also provides for agitation of
the slurry in the crystallizer. Agitation of the
slurry in the crystallizer is desirable in order to
avoid or reduce the 'growing of crystal masses on
the walls of the crystallizer.
A part of the circlllating slurry is withdrawn as
ycontrolled by the valves 83 and 81 through line
Material of predominately eight carbon ‘atoms 70 88,' pump 39, line 90 tothe ñlter 9|, having an
by valves 43 and 41.
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l
comprising, for example, approximately 65%
xylene and 35% .styrene may be lead on' as bot
toms from column 32 by way of line 48 and sup
inner revolving cylindrically shaped iilterbed 92.
Filter 9| may, of course, be of any suitable con
I ~ struction and type, the rotating type of filter be
plied by pump49 through valve 50 to fractional
ing particularly convenient, because among other
distillation column 5|.
reasons, its operation is continuous in character. '
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2,413,674
8
7
>There are two general types of rotating filters
95% or higher. If desired however, styrene of a
lower degree- of purity than 95% may be drawn
which may be employed, one receiving the crystals
to be filtered out on the outside surface and the
other receiving said crystals on the inside surface.
on through line H3. '
l
and line 90 has been illustrated as depositing the
The -overhead material taken off from column
||0 through line || 8 is passed to condenser H9.
This material will be relatively rich in xylene
slurry on the inside of the cylindrical ñlter bed 92.
as compared with the bottoms from the col
The filter 9|, as illustrated, is of the latter type
umns. A part of the resulting condensate may
It will, of course, be understood that filter 9|
has a casing which is substantially gas tight, and
be returned by pump |20 by way of line |2| to
10 the column ||0 as reflux. Another portion may
be drawn oir through line |22 as controlled by
'valves |23 and |21. Any reiiux ratio suitable
for the separation desired may be employed. The
particular reflux ratio employed, will depend,
among other things, upon the number of theoreti
cal plates in the column and upon the desired
that the filter and crystallizer, as well as neces
sary accessory apparatus and connections, are
provided with suitable heat insulation in order
to maintain 'the desired low temperatures therein.
The operation of filters of the type particularly
described is well known in the art and further
description may be dispensed with except in so
far as the filter enters into the invention.
l
degree of separation. With a column of 44 the
-
oretical plates and aI desired degree of purity of
\In the operation of ñlter 9|; filtrate is forced
through the iilter bed andis forced off through
line -93 to tank 96.
- 95% or greater in the styrene lead off as bottoms
20 therefrom, and with material of approximately
'
Washing liquid, for example liquid wash pro
90% styrene fed thereto, a reflux ratio of approxi
pane, is introduced through line 91 and is sprayed
mately 20 to 1 has been found convenient.
across the face of the filter cake as itrises out of
` ’I'he relatively xylene rich overhead material
the pool of slurry in the bottom of the rotating
not refluxed to column ||0, may be drawn ofi’ for
filter bed 92.
,
25 any desired disposal through line |28 and valve
Conveniently, this wash liquid may be sprayed
|29, or may be recycled through line |30 to an
‘uniformly through nozzle 98 against the filter
cake.
upstream portion of the purification system. For
example, this material may be recycled to the
Y,
In the filter illustrated,_gas pressure forces the
lines leading to crystallizer 10 by way of line |3|
wash propane as well as the filtrate through the 30 and valve |32, or may berecycledto the line lead»,v
l filter cake and into line 93 previously referred to.
ing to fractional distillation column 5| by way
At the low temperatures at which it is fre
quently preferred to maintain the filtration yzone
of line |33 and valve |31. The particular point
in the system to which the xylene rich material
during the ñltration step, the vapor pressure of
from column | l0 is recycled, will dependI upon the
propane is relatively low. Hence it is frequently 35 proportions of xylene and styrenetherein, which,
desirable when using differential gas pressure for
of course, will depend upon the operation of col
filtration purposes to employ a supplemental gas, '
umn | |0.
which is preferably an inert gas such as nitrogen,
Returning to the crystallizing portion of the
to increase the total pressure during the filtration
system, the gas employed for forcing filtrate and
step and thereby maintain the bulk of the wash 40 wash liquid through the ñlter bed may also pass
' propane in the liquid phase.
through line 93 to tank 96 in which it may be sep
arated from the mother liquor alsopassing there
When the filter cake -has been washed to a de
to, and may be drawn off through line |38, blower
sired extent, it is removed from the vfilter bed
|39 and line |40 to heat exchanger |4| and thence
and is collected in trough 99 by means not shown
but well known in the construction of filters, and 45 through line |42 back to the iilter 9|. The blower
|39 applies a pressure drop across the filter bed
'the cake may be Withdrawn from the filter
through means such as line |00 to heater |0v| in
Q which the cake is melted and in whichany resid
ual propane accompanying the styrene crystals
The manner in which the gas enters the filter
. and is distributed therein is dependent upon the
may be stripped therefrom and lead off through
filter construction and suitable types of equip
line |04 and valve |05.
ment for individual use are well known in the art.
‘
Filtrate is removed from tank 99 through line
|43, pump |41 and line |48 to and through heat
exchanger |4| in which it is brought into heat ex
I ' crystals is carried out in a manner such that the
concentration of the styrene produced therein 55 change relationship with the gas flowing from
blower |39 through' lines |40 and |42 thereby
falls short of substantially pure styrene and,
cooling said gas.
which for example, may be between approxi
_ In the practice of the present invention, the
crystallization step including the washing of the
If desired, additional heat exchangers may be
mately 85%- and 95% and preferably in the
neighborhood of 90%.
ì ~
„
inserted in the >gas iiow to further reduce the
The melted filter cake is passed by way of line 60 temperature of the circulating gas as desired.
After passage of the mother liquor through
|02, pump |03, line |01, Valve |08 and line |09
heat exchanger |4I, this liquid mixture, which is
to the fractional distillation column | I0.
This column may also be provided with anyV de
sìred phase contacting means, such as for ex
rich in xylenebut contains a concentration of
styrene above that of theeutectic mixture, for
ample, packing indicated at |||. The column is 65 example say 40% styrene, is lead off through line
|49 and valve |50 to the propane stripper |54.
provided with heating means, such for example,
Propane is lead ofi' from the stripper through line
,as the heating coil ||2.
>
|55 and Valve |56 and may be reliqueñed for re
' In column ||0, a further concentration of _the
use as’refrigerant or wash liquid. The propane
styrene is effected, the column may be operated
in a manner such that styrene of any desired 70 freed mot-her liquor islead oiî from the stripper
through line |64 by pump |65 and may pass by
degree of purity may be'drawn off as bottoms
through line ||3 provided with valve ||1.‘ For ' line |66 and valve >|61 to any desired disposal,
example, the styrene so drawn off may be the
or may be recycled, if desired, to an upstream
portion of the purification.
substantially pure form which for the purposes of
this invention is considered to be ‘of a purity of .
The precise point to which this material is
’
2,413,674 ’K
9
Either continuous or batch operations may be
recycled will depend among other things upon its
For example, it may be convenient
employed in any of the various stages.
- composition.
to recycle this material as through line L88 and
valve |69 to line I1 leading to fractional distilla
,
, An internal refrigerant may be employed as de
‘ scribed in the above copending applications,
»tion vcolumn I9, inasmuch as this material may `5 Serial Number 319,373 and Serial Number 406,142,
or the crystallization may take place in the ab
contain a small quantity of: material of nine car
sence of an internal refrigerant as described in`
bon atoms and higher which may be separated in
Serial Number 315,631, or otherwise.
The concentrations of styrene given for illus- ‘
If desired, a portion of this material may be
recycled through line |10 and valve I 'II to the >l0 tration at various points in the purification sys
tower I9.
v
crystallizer 10.
As an example of the operation of my inven
tion, the following may be given:
Example
15
tem may be varied Widely except of course as to
the eutectic point. Although possibly the inven
tion finds its most useful employment'invcon
nection with the production of substantially pure »
styrene, it may well have advantages in the pro
s duction of styrene of lower degrees of purity.
A light oil obtained in the manufacture of com
bustible gas may be distilled under reduced pres
sure and under conditions such thatA pot temperatures do not exceed say 110° C. to obtain a light
oil styrene fraction having a styrene concentra 20
tion of say approximately 60%
This 60% materia1 is mixed with say somewhat
more than an 'equal part by Weight of _propane
and introduced intona crystallizer such as that
illustrated at ‘I0 in the accompanyingrdrawing. 25
The crystallizer may be maintained at temper
atures of the order of say about _75° C. or _80°
lëroadly summarizing: this invention rrelates to
the purification of‘hydrocarbons, such as styrene;
and it comprises concentrating, advantageously
by fractional distillation, a liquid material con
taining styrene and other material of similar
boiling point, such as xylene, for example light
oil materia1 containing styrene and xylene, to
partially concentrate the liquid materia1 in re
spect> to styrene, advantageously to such a'con- f
centration that the styrene is present in a con
‘ centration higher than the concentration of sty
rene in the eutectic composition capable of be
C. by the evaporation of a portion of the propane
ing formed between the styrene and the com
content of the mixture.
30
bined
remaining constituents of the partially
In this manner, by the evaporation of propane,
concentrated liquid material, further concentrat- _
a cold slurry containing styrene -crystals is pro
ing the liquid mixture by fractional crystalliza
-vduced. This slurry is introduced into a „ñlter
tion,
advantageously to a styrene concentration
such as 9| and the crystallized styrene removed
of about 90% and thereafter further concentrat
from the slurry. Propane may be introduced into
theñlter for washing the crystalline styrene on 35 ing the thus concentrated liquid material by frac
tional distillation; all as more fully hereinabove
the filter bed.
' The styrene recovered from the filter is intro
duced into a propane recovery system Where pro
set forth and as claimed.
, Therefore, while I have particularly described
certain procedure and equipment and have given
pane, adhering thereto is separated.
The styrene recovered, and depending upon the 40 particular examples. it is tol be understood that
degree of washing, may be of say about 90% ` this is by way of illustration and that changes,
omissions, additions, substitutions and/or modi
purity.
fications may be made within the scope of the
This 90% styrene is placed in a still pot pro
claims without departing from the spirit of the
vided with a packed column having’an efficiency'
'
‘
of sayl 4_5 theoretical plates. A polymerization 45 invention.
I claim:
.
inhibitor such as hydro‘quinone is preferably add
1. A method of purifying styrene contained in
ed. The distillation is carried out at a reflux ratio
of say about 10:1. Upon completion of the dis l - -a mixture with xylenes including ortho xylene,
tillation, styrene of approximately 95% concen ¿o which comprises concentrating styrene in said
mixture by fractionation other than fractional
tration will be obtained.
'
crystallization to produce a fraction richer in `
From the foregoing„it will be understood that
styrene than any eutectic composition capable
the invention may comprise a three stage purifi
cation comprising a fractional distillation (or a
of being formed between styrene and other con
solvent extraction) stage, followed by a fractional 55 stituents of said fraction; subjecting said fraction
crystallization stage, followed by a second frac
to fractional crystallization by cooling to pro
tional distillation stage, and that the fractional
duce a ma'ss comprised ofv styrene crystals and
crystallization stage may be reached by blending
liquid phase materia1, said liquid phase material
material from a first distillation stage with fairly ,
'being richer in xylene than said fraction and
concentrated material from a vprevious crystal
richer in styrene than ‘any said eutectic com
lization stage.
»
position; separating liquid phase material from
It will also be understood that in its broader
said mass to leave a remaining mass containing
aspects, the invention is not limited to the em-xylene but richer in styrene than said fraction;
and fractionally distilling said remaining mass
ployment of any particular method of or means
' for fractional distillation or crystallization in the 65 to further concentrate styrene therein.
respective stages and that, therefore, the specific
means illustrated in the accompanying drawing
.and described above are to be regarded as'illus
trative.
-
'
.
2’. A method of purifying styrene contained @in
a mixture with xylenes including ortho xylene,
whichcomprises fractionally distilling said mix
ture to produce a fraction richer in styrene than
` Such features as the lnumber of -cuts taken in 70- any eutectic composition capable ofv being formed
the fractional distillations, the number of col- - ‘ between styrene‘and ‘other constituents of said
umns employed, the reflux ratios employed, the
general design and'arrangement and operation
of the fractional distillation columns,- may be
varied widely.
fraction; subjecting said fraction to fractional
crystallization by cooling to produce a mass com
prised of styrene crystalsl and liquid phase ma-> `
~76 terial, said liquid phase materia1 being richer in
2,413,674
12
xylene than said fraction` and richer in styrene.
than any said eutectic composition; separating
liquid phase material from said mass to leave a"
combustible gas by a process involving the pyroly
sis of petroleum oil, said light oil containing sty
rene and also containing xylenes including ortho
remaining mass richer in styrene than said frac
tion but containing xylene; and fractionally dis
tilling said remaining mass to further concen
xylene, which comprises fractionally distilling
said light oil material to produce a fraction con
taining between 45 and 80% styrene; subjecting
said fraction to fractional crystallization by cool
trate'styrene therein.
`3. A method of purifying styrene contained in
ing to produce a mass comprised of styrene crys
a mixture with xylenes including ortho xylene,
tals and liquid phase material, said liquid `phase
which comprises fractionally distilling said mix 10 material being richer in xylene than said fraction
ture to produce a fraction richer in styrene than
and richer in styrene than any eutectic compo
any eutectic composition capable of being formed
sition capable of being formed between styrene
between styrene and other constituents of said '
and other constituents of said fraction; separat
fraction; subjecting said fraction to fractional
ing liquid phase material from said mass to leave
crystallization to produce a mass comprised of 15 a remaining mass containing xylene but richer in
styrene crystals and liquid phase material, said
liquid phase material being richer in xylene than
styrene than said fraction; raising the tempera
ture of said remaining mass to melt said'crystals;
and fractionally distilling said remaining mass to
eutectic composition; separating liquid phase ma
further concentrate styrene therein.
terial containing xylene from said mass by filtra 20
7. A method of purifying styrene contained in
tion followed by washing of said crystals to leave
light oil material containing styrene and also
a remaining mass richer in styrene than said
containing xylenes including ortho xylene, which
said fraction and richer'in styrene than any said
fraction but containing xylene; and fractionally
' comprises fractionally distilling said- light oil ma
distilling said remaining _mass to further con
terial to produce a light oi1 fraction containing
centrate styrene therein.
25 between approximately 45 and 80% styrene; sub
4. In a multi-stage method of purifying styrene
jecting said fraction to fractional crystallization
contained in av mixture with xylenes including ` by cooling to produce» a mass comprised of styrene
ortho xylene, which comprises aA stage compris
crystals and liquid/phase material, said liquid
ing fractionally distilling said mixture toproduce
phase material being richer in xylene than said
a fraction richer. in styrene than any eutectic
fraction and richer in styrene than any eutectic
composition capable of being formed between 30 composition capable of being formed between
styrene and other constituents of said fraction;
styrene and other constituents of 4said fraction;
a stage comprising subjecting said fraction to
separating liquid phase material from said mass
to leave a remaining mass containing xylene but
fractional crystallization to produce a mass com
prised of styrene crystals and liquid phase ma 35 containing between 85 and 95% lstyrene, raising
' the temperatureofÀ said remaining mass to melt
terial, said liquid phase material being richer in
said crystals; and fractionally distilling said re
` xylene than said fraction'and richer in styrene
mainingmass to produce a fraction containing
than any said eutectic composition, and separat
ing liquid phase material from said mass to leave ' ~ more than 95% _st ene.
`
a remaining mass richer in styrene than said` 40
8. A method of urifying styrene contained in
light oil material also containing xylenes includ
ing ortho xylene, which comprises fractionally
distilling said light oil material to produce a irac
to produce a fraction in which styrene is fur
tion containing between 45 and >80% styrene;
ther concentrated and a fraction in which xylene
is concentrated; the step of recycling at least a' 45 subjecting said fraction to fractional crystalliza
tion to produce a mass comprised of styrene crys
portion of said last named fraction to said first
tals and liquid phase material, said liquid phase
mentioned fractional distillation stage for ad
material being richer in xylene than said frac
mixture with the material undergoing fractiona
fraction but containing xylene; and a stage com
prising fractionally distilling said remaining mass
tion therein.
’
~
'
‘ 5. In a multi-stage method of purifying sty
rene contained in a mixture with xylenesinclud
tion and richer in styrene than any eutectic com- ‘
50 position capable of being formed between styrene
and other constituents of said fraction; separat
ing ortho xylene, which comprises a stage com
ing liquid phase material from said mass to leave
prising fractionally distilling said mixture to pro
a remaining mass containing xylene but'richer
duce a fraction richer in styrene than any eutec
in styrene than said fraction; melting said crys
tic composition capable of being formed between 55 tals in said remaining mass; and fractionally dis
styrene and other constituents of said fraction;
tilling said remaining mass to concentrate sty
a stage comprising subjecting said fraction to
rene therein to at least 98%.
fractional crystallization to ,produce a mass com
9. A method of purifying styrene contained iny
prised of styrene crystals and liquid phase ma
a light oil material also containing xylenes in
terial,` said liquid phase material being richer 60 cluding ortho xylene, which comprises fraction
in xylene than said fraction and richer in styrene
than any said eutectic composition, and sepa
rating liquid phase material from said mass
to leave a remaining mass' containing xylene
but richer in styrene than said fraction; and 65
a stage comprising fractionally distilling said
remaining mass to produce a fraction in which
ally distilling said light oil material to produce a
fraction richer in styrene than any eutectic com
position capable of being formed between styrene
and other constituents of said fraction; -admixing
said fraction with a liquefied normally gaseous re
frigerant; subjecting said fraction to fractional
crystallization by cooling caused by evaporation
of said refrigerant to produce a mass comprised _of
which xylene is concentrated; the step of recy
.styrene crystals and liquid phase material, said
cling at least a portion of said last named frac 70 liquid phase material being richer in xylene than
tion to said fractional _crystallization stage for ` said fraction and richer in styrene than any said
admixture with the material'undergoing frac
eutectic composition; separating liquid phase
` styrene is further concentrated and a fraction in'
' tionation therein.`
6. A method of purifying styrene contained in
light oil material produced in the manufacture of
'material from said mass to leave a remaining
mass containing xylene but richerv in styrene than
said fraction; and fractionally distilling said re
2,413,674.
13
mainingV mass to further concentratel styrene "
therein.
10. A method of purifying styrene contained in
-a'. light oil material also containing xylenes in
cluding ortho xylene, which comprises fraction
ally distilling said light oil material to produce a
fraction richer in styrene than any eutectic com
position capable of being formed between styrene
and other constituents of said fraction; admixing
~
,
14
ing caused by evaporation of said propane to pro-'
duce a mass comprised of styrene crystals and
liquid phase material, said liquid phase material
being richer in xylene than said fraction and
richer in styrene than any said eutectic composi
tion; separating liquid phase material from said
mass to leave a remaining mass containing xylene y
but richer in styrene than. said fraction; and
fracticnally distilling said remaining mass to fur
10
ther concentrate styrene therein.
said fraction with liqueñed propane; subjecting
HORACE M. WE'IR.4v
said fraction to fractional crystallization by cool
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