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Dem 10, 1946. v
Filed June 29, 1944
BY ‘Z97:
Patented Dec. 10,1946
'rnnarmc. s'rrnnnn AND OTHER MONO;
‘ George Goidiinger, Brookline, Mass, assig'nor to
Godfrey L. Cabot, Inc., Boston, Mass., 2. corpo
ration of Massachusetts
Application June 29, 1944, Serial No. 542,728
1 Claim. (Cl. 260-.—689)
This invention consists in anovel process of
uable objects may be achieved, that inhibitor
. freeing styrene, butadiene or other monomeric
may be removed conveniently and completely, and
that the ?rst polymers formed in the system may
vinyl products employed in polymerization proc
esses from inhibitors and for improving the poly
also be removed, by treating inhibited styrene
and the like with commercial carbons, notably
carbon black.v The following illustrative set of
merized product.
_In order to prevent spontaneous or premature
polymerization of styrene and like materials un
der commercial conditions of storage‘ and trans
portation, it is the custom to add. an agent, such
examples will make clearer the e?ect of the treat
ment above outlined when carried out on com
mercial styrene, containing hydroquinone as an
as hydroquinone, which by its presence inhibits
or‘ substantially retards polymerization of the
monomeric material. In some commercial ap
plications, as for example in preparing styrene
molding powders, the presence of small amounts
of inhibitor may be of little consequence. In the 15
‘ manufacture ‘of synthetic rubber or polymers
where the process or product must be more strict
ly controlled, however, it is essential to free the
inhibitor, and employing carbon black sold under
the trade name “Carbolac 1.”
From each of six samples of monomeric styrene
20 cc. were poured into a test tube and heated
to 100° C. At this temperature polymerization
should set in immediately if no inhibitor is pres
cut. The time of the beginning of polymerization
was indicated by pouring a few drops of styrene
from each of the test, tubes at regular intervals.
into an excess of acetone. Since acetone is a
‘ed. Two commercial processes of purifying 20 solvent only for monomeric styrene but not for
the polymer, traces of polymeric styrene imme
styrene and other monomers used for polymeri
diately manifest themselves through cloudiness of .
zation ‘processes have been used heretofore, some
times singly and sometimes in combination. One
the acetone-styrene mixture. Therefore, this is
of these known processes consists in washing the
a satisfactory test for ?nding the time of the
beginning of polymerization through observation
monomer with sodium hydroxide solution, and
of the time the monomeric styrene must be kept
the other is by fractional distillation. Neither,
- monomer from the inhibitor which has‘ been add
at 100° C. before drop'from the heated styrene
induce cloudiness in the acetone solution. The
it is a batch process and the second because in
following table givesthe results of those ‘meas
the distillation low temperatures and low pres
sures must be used for fractionation with the re 30 urements. They show that no polymerization oc
method is entirely satisfactory, the ?rst because
curred in the inhibited styrene after heating for
60 minutes; that polymerization began to take
place in styrene puri?ed by distillation when heat
ed for 20 minutes; that styrene purified by the
quirement of expensive equipment. An object of
the present invention is to provide a process which
may be carried out in a continuous manner with
inexpensive apparatus automatically controlled
in its e?’ect.
The in?uence of an inhibitor in a polymeriza
85 process of my invention began to polymerize after
25 minutes in two cases, after 40 minutes in one
case, and after 50 minutes in the last instance.
tion goes further than merely extending the in
duction period. The removal of inhibitors‘ is of
Styrene polymerization tests-100° C’.
great importance, not only from a standpoint of .
expediting polymerization but also for improving 40
the quality of the polymer. It is well known that
the polymer initially formed in the presence of
inhibitor hasan injurious e?ect on the quality of
the ?nished product. Accordingly, it is very de
' sirable. to treat the monomer so that a small por
tion of the monomer is polymerized, and this ?rst
polymer, along with the inhibitor, is removed.
Thus the quality of the finished product is mate
rially improved.
1. Commercial styrene with inhibitor.
2. Commercial styrene distilled.
3. Commercial styrene with inhibitor shaken
with Carbolac 1, heated to 100° C. for 15 minutes
and ?ltered.
4. Commercial styrene with inhibitor shaken
with Carbolac 1, heated'to 100° C. for 30 minutes
and ?ltered.
5.‘ Commercial styrene with inhibitor shaken
with Carbolac 1, heated to 100° C. for 45 minutes
I have discovered that these important and val 50 and ?ltered.
~ .
jacketed column ll packed with carbon black II,
6. Commercial styrene with inhibitor shaken
with Carbolac 1, heated to 100° C. for 60 minutes
and ?ltered.
a pump l3, and pipe connections between the res
ervoir and the pump. The carbon black packing
20 '
2.-. Cloudy.
Clear _____________ ..
..s__do _ _ _ _ _ . . . _ _ . _ . _
Clear . _ _ _ _ . _ . _
6... _.___do ____________ _.
Cloudy ___________ -. 010 d
3___ Clear..- V. sl' htly cloudy..4...
Clear.-_-...... __
Cloudy.- ---_-_ Cloudy
. Slightly cloudy_ . . __do ........ ..
_ . _ -_
(3-60” and a commercial decolorizing calrbon
.____do ____________ __
Clear ......... ..
The same experiments repeated using a com
mercial adsorpti've carbon known as "Darco
Slightly cloudy.
V. slightly cloudy___
Slightly cloudy.
and the liquid monomer above it are heated to a
temperature approximating the boiling point at
atmospheric pressure of vthe particular monomer
being treated. The rate
in such a manner that
satisfactory ‘removal of the inhibitor and satis
factory reduction of the induction period. The 20 su?icient period of time
column to overcome its
results of these tests indicate that the adsorption
known as “Norite A” also indicate substantial and
of the inhibitor by the carbon or the carbon black
of ?ltration is adjusted
the monomer spends a
in the hot zone of the
entire induction period
' and to polymerize to about 0.25% or 0.5%. Thus
the carbon black is effectivenot only to adsorb
is quite rapid. The inhibitors such, for example,
the inhibitor but also to adsorb the first poly
as hydroquinone, present in the above examples
merized material. The puri?ed and improved
were those commonly used in monomeric vinyl
25 monomer may be drawn from the bottom of the
My invention includes within its scope a simple
column through suitable valve connections l4.
Having thus disclosed my invention, I claim as
commercial process for purifying styrene and
other monomers which are liquid at room temper
new and desire to secure by Letters Patent:
The process of improving .for polymerization
ature. In this application of my invention the
monomeric ‘vinyl products such as styrene and
process may be carried out continuously and re
quire only apparatus of compact arrangement
butadiene, which includes the steps of heating the
and moderate volume. The apparatus is illus
monomer containing an inhibitor such as hydro
quinone to approximately the boiling point while
trated in the accompanying drawing in which
the ?gure is a diagrammatic view in elevation of 35 in contact with carbon black thereby (1) causing
initial polymerization of a small amount of the
the apparatus.‘ The process involves a hot ?ltra
monomer, (2) adsorbing the inhibitor from the
tion of the monomeric material under pressure
through a bed of activated carbon or carbonv
monomer, and (3) also adsorbing the initially
black. .
The apparatus required comprises merely a 40
reservoir ID for the inhibited monomer, a steam
formed polymer.
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