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Патент USA US2408130

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Sept. 24, 1946.
w. SQUIRES, JR,‘ ET AL
2,408,128
COAGULATION PRVOCES S
Fiied 0012. 24, 1942
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Patented Sept. 24, 1946 ‘I
it
2,408,128
.v _v
UNITED.’ STATES, PATENT", OFFICE
Walter Squires, Jr., and Paul T. Parker, Baton.
Rouge, La., assignors to Standard Oil Develop‘
ment Company, a corporation of Delaware
Application October'24, 1942, Serial No. 463,146
5 Claims. (Cl. 260-96)
2',
,
duce the‘particles of coagulate to such a small
The present invention pertainsto the prepara
tion of synthetic rubber-like materials, and par
size that they do not ?lter readily.
’
'
A suitable apparatus for carrying out our proc
ticularly to a method and apparatus for'coagu
'
I
ess is illustrated diagrammatically in the ac
'
It is an object of this invention to provide the 5 companying drawing.
In the ?gure, I is a coagulating chamber which
art with a method and apparatus whereby latices.
particularly those obtained by the polymerization A is provided with a stirring vdevice 2. As shown,
and as preferred, the stirring device consists of
of diole?ns and in particular the copolymeriza
a series of'flat paddles _3 attached-to a central
tion of diole?ns with other compounds contain
ing a single C=C linkage in aqueous emulsion 10 shaft 4, the paddles and shaft lying in the same
plane. The clearancebetween the paddles and.
may be coagulated continuously.
,
the Walls of the coagulating chamber should be
It is a further object of the present invention
small in order to preventlayers of coagulate from
to provide a method and apparatus whereby
lating lactices continuously.
building up on said walls. The paddles 3. should
latices of synthetic rubber-like materials may be
coagulated continuously under carefully regu 15 be large enough both in width and length to
cover, when thoseon one side of the shaft are ‘
lated pressure without the use of valves, and
staggered with respect to those on the other side,
under controlled conditions of time of contact and
agitation.
\
’
I
more than half the volume of the coagulation
'
chamber. It is preferred that the paddles 3 be
clearly from the detailed" description and claims 20 of such dimensions that the cylinder of slurry
touched by each blade be larger'thanthe'cylin
which follow.
ders between the several paddles and above the
The continuous coagulation of latex‘has con
top paddle and below the bottom paddle. When
s'tituted a major problem in devising a systemsfor
the coagulation chamber and cooperative stir
the continuous production of “Buna S,” off‘Per
These and other objects will appear ‘more
25 ring device are so constructed, and the stirrer
bunan,” and other‘synthetic rubber-like mate
is rotated at about 300-400 R. P. M., it is found
that the agitation is extremely uniform and ef
rials in aqueous emulsion. The latices, themselves
have 'atendency to break and coat the surfaces
of the equipment with which they come into con
fective.
'
'
The shaft 4 is connected to a suitable driving
tion of thelatices are as a general rule extremely 30 means, such as the motor and gear box 5;
A line 6 is provided for supplying latex to the
sticky in character. Because of its sticky char
bottom of the coagulation chamber and a line
acteristics, the coagulate adheres to the equip
tact and the coagulates obtained upon precipita
1 is similarly provided for the supply of brine
or other suitable coagulant. As shown, the lines
tinuous operation lends itself more readily to. 35 6 and ‘l discharge into the coagulating chamber
at the same, or substantially the same level, and
.mass, or quantity, production thanbatch opera?
preferably at the bottom, in order that the
tion, it is obviously desirable, if not essential, to
chamber can be effective for its entire height in
devise a continuous method of operation that
bringing about contact of the latex with the
, will not be subjected toperiodic interruptions for
precipitant to the end that coagulation of the
the cleaning or unplugging of lines, valves and
vment, resulting in the plugging of lines and valves
through which the coagulate passes. Since con
1 other equipment.
'
We have found that latices of synthetic rub
ber-like materials may be coagulated continuous
ly without any danger of plugging lines or other
equipment if separate streams of latex and co-Iv
agulant are introduced at ‘the bottom of a co
agulating chamber at substantially the same level
and at low velocity, and the contents of the co-'
‘
former will be complete.
'
The latex and coagulating medium are sup
plied to the coagulating chamber at a relatively
low linear velocity, for example, at a velocity of
about 1 foot per second. The velocity can be
varied somewhat from this ?gure and generally
may be between 0.5 and about 5'feet per second.
The latex and the coagulant are supplied to the
chamber under pressures which generally are not
'agulation chamber are subjected to a vmoderate 50 more than about 5 lbs/sq. in. greater than the
agitation while maintained under an optimum
pressure maintained in the coagulation chamber.
elevated pressure. By moderate agitation‘we
‘mean an agitation su?icient to prevent coales
The size of the coagulation chamber I is so propor
tioned to the rate at which latex and coagulant
' some of the ‘coagulate particles into lumps which
are supplied that the mixture remains in the
can not be washed but yet ‘not sufficient to re-;_ 55
_ coagulation chamber about 11/2 to about 2 min
{2,408,128
3
utes. From this point of view of capacity it is
desirable to keep the residence time of the latex
in the coagulator to a minimum and it has been
found that residence times of this order are suit
4
vious that the gas vented off may be recycled in
the system and used as part of the charge sup
plied to the polymerization reactor, or it may
be compressed and utilized for repressuring a
able. However, except for the loss in capacity (21 stripped latex. The coagulate is withdrawn from
accumulator 9 through pipe 2 l and sent to ?lters
there would be no objection to the retention of the
and the like for washing and drying the coagulate.
latex for longer periods.
Ifthe quantity of hydrocarbon contained in
The coagulated latex is discharged from the
the
latex is not su?icient to keep the coagulate in
coagulation chamber through pipe 3, which, in
the standpipe agitated, further amounts of hydro
accordance
a variable height
with our
standpipe.
invention,Asisisconstructed
disclosed and
carbon or other gaseous material such as carbon
claimed in application Serial No. 407,476, filed
August 19, 1941, Wendell W. Waterman et al.,
rubber-like polymers or interpol'ymers of the
“Buna”
the presence
type of
area advantageously
small, somewhatcoagulate'd
critical pro»
portion of a low boiling hydrocarbon. The hy
drocarbon may be that portion of the. original.
diole?n which remains in monomeric form after
the polymerization reaction has been carried to
dioxide may be introduced, either in the chamber
1 or directly into the standpipe. The agitation
provided by the release of bubbles of gas in the
the desired point, or it may be added to the latex
after it has been stripped of monomeric materials.
In either case, the presence of the low boiling
hydrocarbon results in a substantial reduction in
the amount of coagulant required and leads to the
formation of a coagulate of a more granular and
less sticky nature than is obtainable in the ab
sence of the hydrocarbon.
Coagulation in the
presence of such hydrocarbons leadsto the forma—
coagulate slurry is highly effective in preventing
the agglomeration of the coagulate into large
lumps or masses‘. Mechanical agitation of the
coagulate, as with rapidly rotating stirrers and
the like, is not satisfactory since the stirrers exert
an attritioning effect so that the coagulate par
ticles are broken down to such a small size that
they cannot be‘?ltered.
Our invention is applicable ‘to the coagulation
of a large variety of emulsion polymerizates such
as “Per'bunan” or “Buna S” type polymers as
well as modi?ed styrene interpolymers such as
are described in application Serial No. 408,814,
?led Aug. 29, 17941, by Anthony H. Gleason, et al.
The particular inethod'of preparing the poly
tion of coagulates of uniform particles and of any 30 merizates is not critical and in general it is noted
that it may be prepared in any of ‘the usual man~
desired size, which are particularly easy to wash
ners. For example, a diole?ne such as butadiene
free from catalyst, emulsifier, coagulant, and any
or its homologues, and a substance capable of co
other water-soluble impurities. Since the hydro
polymer'izing' therewith, such as acrylic acid ni
carbon boils at temperatures below the tempera
trile, methacryllc acid nitrile, styrene and its
ture at which the latex is ordinarily coagulated,
homologues, acrylic and methacrylic acid esters,
the latex must be maintained under pressure in
methyl vinyl ketones and the like, are emulsi?ed
order to prevent the hydrocarbon from ?ashing
in about double the quantity of water, using a
off and becoming ineffective to modify the coagu
suitable emulsi?er such as a soap or other surface
late as described. While batch coagulation under
active material. Polymerization of the resultant
pressure may be carried out without any par
emulsion is effected at about room temperature,
ticular difficulty, continuous coagulation under
or slightly ‘higher, and in the presence of a suit
pressure has given rise to serious problems, since
able oxygen liberating catalyst such as hydrogen
valves provided in lines for maintaining the nec
peroxide or an alkali metal or ammonium perbo
essary pressure in the coagulating zones become
rate or persulfate.
coated with coagulate, eventually becoming com
pletely plugged, thereby necessitating shutting
down the equipment and cleaning the lines and
valves of coagulate. The use of a variable height
The polymerization is continued until approx
imately 75% of the monomeric compounds are
polymerized, The particular percentage conver
sion is a variable, depending upon the nature of
standpipe in accordance with the present inven
the initial materials used and the physical prop
50
tion completely avoids these dif?culties. In the
erties desired in the ?nal .polymer.
?rst place since the height ofthe standpipe is
The resultant latex may then be subjected to
variable the pressure in the coagulation chamber
a
stripping
operation to remove unreacted mono
may be easily and accurately adjusted. Moreover,
meric starting materials, or it may be passed di
the standpipe isfree from obstructions, such as
are present in valves, and, accordingly, there is no 55 rectly through the line 6 to the coagulation cham
point at which a plug of coagulate can be built
up. A further extremely valuable feature of the
variable height standpipe is that as the hydro
ber. If the latex is stripped of such monomeric
materials it is necessary to “repressure” it or add
thereto a suitable low boiling hydrocarbon such
as lbutadiene, before introducing it into the co
coagulate passes up through the standpipe, a point 60 agulation chamber.
The following examples are illustrative of our
is quickly reached at which the hydrocarbon pres
static pressure on the coagulate diminishes as the
invention but it is .to be understood that our in
vention is by no means limited thereto since
numerous modi?cations are possible within the
coagulate to a mild agitation which serves to ‘pre
vent settling or Strati?cation of the coagulate. 65 scope of the present invention and the following
claims.
The size of the standpipe 8 is so proportioned that
Example I
the linear velocity of the coagulate passing there
through is relatively low, generally of the order
The continuous coagulation of a “Perbunan"
of about 1 ft/sec.
The standpipe 3 discharges into the coagulate 70 latex, prepared by the emulsion copolymeriza
tion of butadiene and acrylonitrile to about 75%
accumulator, or ?ash drum 9, wherein the gases
conversion was accomplished by feeding the
freed from the slurry are separated and vented
latex at a temperature of 100° F. to the bottom
through pipe iii to a suitable gas recovery system.
of a closed steel vessel of 1.3 gallons capacity at
Since the gas liberated is usually the diole?n used
originally or added to a stripped latex, it is 0b 75 a rate of 24 gallons per hour. Simultaneously the
ent vaporizes. The bubbles of hydrocarbon gases
thus liberated serve to subject the particles of
2,408,128
5
coagulant, a saturated solution of sodium chlo
ride at a temperature of 85° F. was fed to the bot
tom of the vessel at a rate of 24 gallons per hour.
The mixture was agitated at the rate of 345
R. P. M. with ‘an agitator consisting of seven ?at
paddles mounted on a centrally placed drive
6
4)
shaft connected to a gear box and electric motor.
The nominal holdup time was 1.62 minutes. The
coagulated mixture from the coagulator was
taken oil through a ?exible line elevated to a
the polymerization of a diole?n in aqueous emul
sion, said latex containing some low-boiling un~
polymerized diole?n, into a coagulation zone at a
low linear speed, agitating the latex and coagu
lant in the coagulation zone for a period su?i
cient to cause uniform intermixing of the latex
and coagulant and under a hydrostatic pressure
imposed by a liquid column containing coagulate
which has left said zone, said pressure being suf
?cient to prevent the unpolymerized low-boiling
height suf?cient to give a hydrostatic pressure
in the coagulator of about 12 1b. gauge. Complete
coagulation and trouble-free operation were ob
tained for a period of 31/2 hours.
diole?n from ?ashing off in said zone, and dis
charging the stream of coagulate and aqueous
suspension medium against a gradually dimin
ishing hydrostatic head outside the coagulation
15
Example II .
zone, whereby the unpolymerized low-boiling di~
ole?n is permitted to vaporize and agitate said
A latex prepared by the emulsion copolymeri
liquid column.
zation of styrene and isoprene carried to about
90% conversion was diluted with 50% of its vol
2. The process as de?ned in claim 1, wherein
ume of water and the diluted latex at a tempera 20 the, latex is an emulsion copolymerizate of a di
ture of 100° F. was fed to the coagulator described
ole?n and. a compound containing a single C=C
linkage.
above at a rate of about 181/2 gallons per hour.
An 18% solution of sodium chloride at a tempera
3. The process as defined in claim 1 wherein the
ture of 90% F. was simultaneously pumped to
latex is an emulsion copolymerizate of a buta
the coagulator at a rate of 151/2 gallons per hour.
diene hydrocarbon and a compound containing a
Agitation was (maintained at 345 R. P. M. The 25 single 0:0‘ linkage.
coagulated mixture was taken off through a flex
4. The .process as de?ned in claim 1 wherein
ible line at substantially atmospheric pressure.
The nominal holdup time in the coagulator was
2.3 minutes.
'
the latex is obtained by the polymerization of
butadiene-LB and acrylonitrile in aqueous emul
What we claim and desire to secure by Letters
30 sion.
5. The process as de?ned in claim 1 wherein
Patent, is:
1. The process of preparing synthetic rubber
like materials, which comprises passing a stream
the latex is obtained 1by the polymerization of
butadiene-1,3 and styrene in aqueous emulsion.
of coagulant and a stream of a latex obtained by 35
'
WALTER SQUIRES, JR.
PAUL T. PARKER.
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