U.S. patent application number 09/885114 was filed with the patent office on 2001-12-27 for method for recovering a polymer.
This patent application is currently assigned to JSR CORPORATION. Invention is credited to Nakazawa, Kazuyoshi, Takami, Nobuyasu, Uchimura, Kazumi, Yoshioka, Kunio.
Application Number | 20010056176 09/885114 |
Document ID | / |
Family ID | 18687980 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010056176 |
Kind Code |
A1 |
Takami, Nobuyasu ; et
al. |
December 27, 2001 |
Method for recovering a polymer
Abstract
A method for recovering a polymer efficiently from a polymer
solution obtained by a solution polymerization is provided. By
means of a method for recovering a polymer comprising heating a
polymer solution obtained by a solution polymerization indirectly
in a pipe to evaporate a solvent while forming a gas-liquid mixed
phase flow or a gas-liquid-solid mixed phase flow followed by
supplying the mixture to a recovery tank under pressure or under
reduced pressure to separate the polymer from the solvent, the
polymer can efficiently be separated from the solvent without
changing the physical characteristics or the chemical
characteristics of the polymer. When recovering a polymer from a
polymer solution having a high viscosity, an infusion of water or
steam serves to reduce the viscosity of the polymer solution and
also to increase the linear velocity of a gas, whereby preventing
the occlusion of a pipe and facilitating the operation.
Inventors: |
Takami, Nobuyasu; (Tokyo,
JP) ; Uchimura, Kazumi; (Tokyo, JP) ;
Yoshioka, Kunio; (Tokyo, JP) ; Nakazawa,
Kazuyoshi; (Tokyo, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
JSR CORPORATION
2-11-24, Tsukiji Chuo-ku
Chuo-ku
JP
|
Family ID: |
18687980 |
Appl. No.: |
09/885114 |
Filed: |
June 21, 2001 |
Current U.S.
Class: |
528/503 |
Current CPC
Class: |
C08C 2/06 20130101; C08F
6/12 20130101 |
Class at
Publication: |
528/503 |
International
Class: |
C08J 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2000 |
JP |
2000-188136 |
Claims
What is claimed is:
1. A method for recovering a polymer comprising heating a polymer
solution obtained by a solution polymerization indirectly in a pipe
to evaporate a solvent while forming a gas-liquid mixed phase flow
or a gas-liquid-solid mixed phase flow followed by supplying said
gas-liquid mixed phase flow or said gas-liquid-solid mixed phase
flow into a recovery tank to recover said polymer.
2. A method for recovering a polymer according to claim 1, wherein
water or steam is infused into said polymer solution in said
pipe.
3. A method for recovering a polymer according to claim 2, wherein
the amount of said water infused is 0.001 to 20 parts by mass based
on 100 parts by mass as said solvent in said polymer solution.
4. A method for recovering a polymer according to claim 3, wherein
the number-average molecular weight of said polymer in said polymer
solution is 5,000 to 1,000,000.
5. A method for recovering a polymer according to claim 4, wherein
the viscosity of said polymer solution is 0.001 to 300
Pa.multidot.s.
6. A method for recovering a polymer according to claim 5, wherein
the concentration of said polymer in said polymer solution is 0.1
to 80% by mass.
7. A method for recovering a polymer according to claim 6, wherein
said polymer is at least one selected from the group consisting of
butadiene rubber, styrene-butadiene rubber, isoprene rubber,
ethylene-propyrene rubber, butyl rubber, styrene-butadiene
copolymer, styrene-isoprene copolymer, butadiene block polymer,
butadiene resin and acryl resin.
8. A method for recovering a polymer according to claim 7, wherein
the linear velocity of a gas at the outlet of said pipe is 10 m/s
or more.
9. A method for recovering a polymer according to claim 8, wherein
the devolatilizing efficiency is 0.6 or less.
10. A method for recovering a polymer according to claim 2, wherein
the amount of said steam infused is 0.001 to 30 parts by mass based
on 100 parts by mass as said solvent in said polymer solution.
11. A method for recovering a polymer according to claim 10,
wherein the number-average molecular weight of said polymer in said
polymer solution is 5,000 to 1,000,000.
12. A method for recovering a polymer according to claim 11,
wherein the viscosity of said polymer solution is 0.001 to 300
Pa.multidot.s.
13. A method for recovering a polymer according to claim 12,
wherein the concentration of said polymer in said polymer solution
is 0.1 to 80% by mass.
14. A method for recovering a polymer according to claim 13,
wherein said polymer is at least one selected from the group
consisting of butadiene rubber, styrene-butadiene rubber, isoprene
rubber, ethylene-propyrene rubber, butyl rubber, styrene-butadiene
copolymer, styrene-isoprene copolymer, butadiene block polymer,
butadiene resin and acryl resin.
15. A method for recovering a polymer according to claim 14,
wherein the linear velocity of a gas at the outlet of said pipe is
10 m/s or more.
16. A method for recovering a polymer according to claim 15,
wherein the devolatilizing efficiency is 0.6 or less.
17. A method for recovering a polymer according to claim 1, wherein
further removing a residual solvent by supplying said polymer in
said recovery tank to a devolatilizing extruder and molding of the
desolvated polymer.
18. A method for recovering a polymer according to claim 17,
wherein water or steam is infused into said polymer solution in
said pipe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for recovering a
polymer, more particularly, a method for recovering a polymer
efficiently from a polymer solution obtained by a solution
polymerization.
[0003] 2. Description of the Related Art
[0004] Generally in order to recover a polymer from a polymer
solution obtained by a solution polymerization, the polymer
solution after polymerization is washed with water or the like to
decompose and remove the residual catalyst and then devolatilized
to remove the volatiles such as a polymerization solvent, an
unreacted monomer or a small amount of water or the like from the
polymer solution, whereby recovering the polymer. In a conventional
devolatilization process, a polymer solution is concentrated
previously for example by a flash evaporation or the like and then
a steam stripping is performed.
[0005] However, the method described above poses a steam
consumption as problematically large as 70 parts or more by mass
per 100 parts by mass of a solvent in spite of an attempt to
multiple utilization of the steam generally using several
strippers. Accordingly, a devolatilization method employing no
steam stripping, including a method using a devolatilizing extruder
such as a twin-screw extruder and the like or using a thin film
evaporator has been investigated.
[0006] While the steam consumption is reduced substantially by
using a devolatilizing extruder or a thin film evaporator for a
devolatilization, the application to a polymerization solution of
an elastomer such as a butadiene rubber or a styrene-butadiene
rubber or the like was revealed to pose an additional problem which
is described below. Thus, since such elastomer characteristically
causes, unlike to an ordinary thermoplastic resin, a rapid increase
in the solution viscosity at a higher concentration which is not
reduced correspondingly even when the temperature is elevated, a
higher concentration established at a later stage of a
devolatilization process results in a rapid increase in the power
required to be exerted by a devolatilization machine such as an
extruder or the like, which leads to a problematically reduced
devolatilizing efficiency.
[0007] Accordingly, in an attempt to solve this problem, a
twin-screw extruder provided with a vent (for example in Japanese
Patent Publicatin No. 4768/1982, Japanese Laid-Open No. 12949/1979)
or a devolatilization performed using a devolatilization aid such
as water or the like (for example in Japanese Patent Publication
No. 41407/1982, Japanese Patent Publication No. 442/1988, Japanese
Patent Publication No. 91101/1984, Japanese Patent Publication No.
29721/1986, Japanese Patent Publication No. 52163/1986) was
proposed. Nevertheless, such attempt resulted in no sufficient
devolatilizing efficiency.
SUMMARY OF THE INVENTION
[0008] The present invention overcomes the problems experienced
conventionally as described above, and is intended to provide a
method for recovering a polymer with sufficient devolatilizing
efficiency.
[0009] The present invention is based on the findings described
above and can be described as follows.
[0010] 1. A method for recovering a polymer comprising heating a
polymer solution obtained by a solution polymerization indirectly
in a pipe to evaporate a solvent while forming a gas-liquid mixed
phase flow or a gas-liquid-solid mixed phase flow followed by
supplying the gas-liquid mixed phase flow or the gas-liquid-solid
mixed phase flow into a recovery tank to recover the polymer.
[0011] 2. A method for recovering a polymer according to 1 above,
wherein water or steam is infused into the polymer solution in the
pipe.
[0012] 3. A method for recovering a polymer according to 2 above,
wherein the amount of the water infused is 0.001 to 20 parts by
mass based on 100 parts by mass as the solvent in the polymer
solution.
[0013] 4. A method for recovering a polymer according to 3 above,
wherein the number-average molecular weight of the polymer in the
polymer solution is 5,000 to 1,000,000.
[0014] 5. A method for recovering a polymer according to 4 above,
wherein the viscosity of the polymer solution is 0.001 to 300
Pa.multidot.s.
[0015] 6. A method for recovering a polymer according to 5 above,
wherein the concentration of the polymer in the polymer solution is
0.1 to 80% by mass.
[0016] 7. A method for recovering a polymer according to 6 above,
wherein the polymer is at least one selected from the group
consisting of butadiene rubber, styrene-butadiene rubber, isoprene
rubber, ethylene-propyrene rubber, butyl rubber, styrene-butadiene
copolymer, styrene-isoprene copolymer, butadiene block polymer,
butadiene resin and acryl resin.
[0017] 8. A method for recovering a polymer according to 7 above,
wherein the linear velocity of a gas at the outlet of the pipe is
10 m/s or more.
[0018] 9. A method for recovering a polymer according to 8 above,
wherein the devolatilizing efficiency is 0.6 or less.
[0019] 10. A method for recovering a polymer according to 2 above,
wherein the amount of the steam infused is 0.001 to 30 parts by
mass based on 100 parts by mass as the solvent in the polymer
solution.
[0020] 11. A method for recovering a polymer according to 10 above,
wherein the number-average molecular weight of the polymer in the
polymer solution is 5,000 to 1,000,000.
[0021] 12. A method for recovering a polymer according to 11 above,
wherein the viscosity of the polymer solution is 0.001 to 300
Pa.multidot.s.
[0022] 13. A method for recovering a polymer according to 12 above,
wherein the concentration of the polymer in the polymer solution is
0.1 to 80% by mass.
[0023] 14. A method for recovering a polymer according to 13 above,
wherein the polymer is at least one selected from the group
consisting of butadiene rubber, styrene-butadiene rubber, isoprene
rubber, ethylene-propyrene rubber, butyl rubber, styrene-butadiene
copolymer, styrene-isoprene copolymer, butadiene block polymer,
butadiene resin and acryl resin.
[0024] 15. A method for recovering a polymer according to 14 above,
wherein the linear velocity of a gas at the outlet of the pipe is
10 m/s or more.
[0025] 16. A method for recovering a polymer according to 15 above,
wherein the devolatilizing efficiency is 0.6 or less.
[0026] 17. A method for recovering a polymer according to 1 above,
wherein further removing a residual solvent by supplying the
polymer in the recovery tank to a devolatilizing extruder and
molding of the desolvated polymer.
[0027] 18. A method for recovering a polymer according to 17 above,
wherein water or steam is infused into the polymer solution in the
pipe.
[0028] According to the invention, the polymer can efficiently be
recovered without changing the physical characteristics or the
chemical characteristics of the polymer. Especially when recovering
a polymer from a polymer solution having a high viscosity, an
infusion of water or steam serves to reduce the viscosity of the
polymer solution and also to increase the flow rate in the pipe,
whereby ensuring the prevention of the occlusion of a pipe and
facilitating the operation. In addition, a substantial reduction in
the steam consumption allows the operation to be accomplished at a
lower cost.
DETAILED DESCRIPTION OF THE INVENTION
[0029] A method for recovering a polymer of the invention comprises
heating a polymer solution obtained by a solution polymerization
indirectly in a pipe to evaporate a solvent while forming a
gas-liquid mixed phase flow or a gas-liquid-solid mixed phase flow
followed by supplying the mixture to a recovery tank to recover the
polymer.
[0030] Water or steam also may be infused into a polymer solution
in a pipe.
[0031] A polymer to which a method of the invention is applied may
not be limited particularly as long as it is a polymer capable of
being synthesized by a known solution polymerization. With regard
to the preferable physical parameters of a polymer which can
efficiently be recovered, the number-average molecular weight Mn is
preferably 5,000 to 1,000,000, more preferably 20,000 to 800,000
and most preferably 50,000 to 500,000, and the viscosity of the
polymer solution supplied is preferably 0.001 to 300 Pa.multidot.s,
more preferably 0.005 to 200 Pa.multidot.s and most preferably 0.01
to 100 Pa.multidot.s. As a polymer there may be mentioned butadiene
rubber, styrene-butadiene rubber, isoprene rubber,
ethylene-propylene rubber, butyl rubber, styrene-butadiene
copolymer, styrene-isoprene copolymer, butadiene block polymer,
butadiene resin, acrylic resin and the like. For an efficient
operation without any occlusion of the pipe, the concentration of a
polymer supplied is preferably 0.1 to 80% by mass, more preferably
1 to 50% by mass, most preferably 5 to 30% by mass.
[0032] Solvent used in the invention is not particularly restricted
but may be toluene, xylene, n-hexane, cyclohexane, n-pentane,
cyclopentane, iso pentane, n-heptane, cycloheptane, n-octane,
cyclooctane, n-decane, benzene dichloromethane and the like which
is used in solution polymerization.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a schematic view of a system employed in Example
1.
[0034] FIG. 2 is a schematic view of another system according to
the invention.
[0035] FIG. 3 is a schematic view of still another system according
to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] An example of the recovery method of the invention is
discussed with referring to FIG. 1. The system having the structure
shown in FIG. 1 consists of intermediate tank or polymerization
tank 1, volumetric pump 2, long tubular heater 3, recovery tank 4,
first conduit 5, condenser 6, solvent tank 7 and second conduit
8.
[0037] The long tubular heater described above is that jacket is
equipped with a cylindrical pipe and that can heat-exchange with
the fluid in the pipe by flowing a heat medieum such as a steam and
the like. The long tubular heater can be used a double-pipe and
that a long pipe is turned again and again in one shell.
[0038] A polymer solution obtained by a solution polymerization is
pressurized by the volumetric pump 2 to be supplied from the
intermediate tank or the polymerization tank 1 to the long tubular
heater 3. The long tubular heater 3 employs a heat exchange system
consisting of a cylindrical pipe fitted with a jacket which is
heated by a heating medium such as steam or the like, and the
polymer solution entering the long tubular heater 3 receives the
heat from the jacket and is heated to the boiling point of the
solvent. When the boiling of the solution is initiated, the solvent
is evaporated to increase the flow rate in the pipe, resulting in a
turbulent flow in the pipe, which allows the heat to be transmitted
at a high thermoconductivity, whereby evaporating the solvent. In
this manner, a gradual boiling increases the flow rate, which
drives the polymer to enter the recovery tank 4 without plugging in
the pipe. Desolvated polymer which precipitates on the bottom of
the recovery tank 4 is recovered here as a strand, granulated or
powder-like crumb. From the top of the recovery tank 4, the
evaporated solvent vapor comes out and passes through the first
conduit 5 to enter the condenser 6, where it is cooled and
liquefied, stored in the solvent tank 7, enters a purification
system through the second conduit 8, and then is recovered after a
purification.
[0039] A linear velocity of the effluent gas from the long tubular
heater is controlled by inner diameter of the pipe, temperature,
polymer concentration, pressure of the recovery tank or the like,
and is generally 10 m/s or more, preferably 20 m/s or more, more
preferably 100 m/s or more, most preferably 200 m/s or more. Upper
limit is generally 800 m/s. The faster linear velocity of the
effluent gas results in prevention from a polymer degradation or
the like during thermal treatment and an improvement in use of a
steam when compared with a conventional steam stripping method. The
linear velocity of the effluent gas of 10 m/s or less leads to a
problematically reduced effect of occlusion in a pipe.
[0040] The linear velocity of the effluent gas under reduced
pressure is preferably 100 to 200 m/s in condensation of the
polymer solution, preferably 300 to 400 m/s in drying of the
polymer. And the linear velocity of the effluent gas under pressure
is preferably 20 to 100 m/s.
[0041] In addition, a devolatilizing extruder can be combined in
the invention as shown in FIG. 2. The crumb in the recovery tank 4
is supplied directly to the devolatilizing extruder 9, and the
residual solvent is devolatilized and released from the vent, after
that the desolved polymer is molded.
[0042] In the invention, it is essential that a sample solution is
pumped volumetrically into the long tubular heater 3 without
occluding the pipe, and the volumetric pump 2 employed may for
example be a gear pump, a diaphragm pump and a plunger pump, and
the like.
[0043] The inner diameter of the long tubular heater 3 is
preferably 5 to 100 mm, more preferably 6 to 80 mm, and most
preferably 8 to 50 mm. An inner diameter smaller than 5 mm leads to
a problematically larger pressure loss in the heater. An inner
diameter larger than 100 mm leads to less heat transmission to a
polymer solution into the innermost center of the pipe, resulting
in a problematically ineffective devolatilization.
[0044] The length of the long tubular heater 3 may vary to give a
required calories, depending on the calorie exerted upon
evaporation of the solvent of a polymer solution as well as the
calorie given upon heating in the jacket and may for example be 5
to 200 m. The shape of the long tubular heater 3 may be linear,
curved and spiral in order not to ensure the prevention of the
occlusion of a pipe.
[0045] While the recovery tank 4 may be under pressure or under
reduced pressure, it is preferably under reduced pressure. Under
reduced pressure the large volume due to vaporization of the
solvent makes a linear velocity of the effluent gas faster and the
occlusion prevention with polymer deposited in a pipe. On the other
hand, under pressure it is easy to operate a continuous outlet and
handle it.
[0046] In order to ensure the occlusion prevention of a pipe, water
or steam can be infused into a polymer solution into a pipe. By
infusing water, the viscosity of the polymer solution can be
reduced, and, in addition, the flow rate in the pipe can easily be
increased as a result of the increase in the volume upon
vaporization which is attributable to the small molecular weight of
water. Furthermore, the foaming performance of a polymer recovered
can be improved and the devolatilization performance can be
improved. While a non-condensable compressed gas such as nitrogen
or the like instead of water or steam may also be infused, the
presence of a non-condensable gas is disadvantageous in the
subsequent condensation recovery of the solvent vapor. More
preferably, a substance having a lower molecular weight is employed
since a substance having a large molecular weight does not give a
sufficiently increased evaporation volume even if it is a
condensable substance. Therefore, one infused preferably is water
or steam. While the site where the infusion is effected is not
particularly limited, it is preferably the inlet of the long
tubular heater for the purpose of reducing the viscosity of a
polymer solution as soon as possible.
[0047] When water is infused, an infusion of a large amount is
disadvantageous thermally due to a large evaporation latent heat.
The amount of water to be infused is preferably 0.001 to 20 parts
by mass per 100 parts by mass of the solvent in a polymer solution,
more preferably, 0.005 to 15 parts by mass, and most preferably
0.01 to 10 parts by mass. And when steam is infused, the amount of
steam to be infused is preferably 0.001 to 30 parts by mass per 100
parts by mass of the solvent in a polymer solution, more
preferably, 0.01 to 20 parts by mass, and most preferably 0.1 to 15
parts by mass. When steam is infused, it is infused preferably as a
wet vapor in order to prevent a thermal degradation of a
polymer.
[0048] In the invention, a conventional steam stripping method can
be combined with the method of the invention. A polymer solution
heated in a pipe is in a highly foaming condition, and a
combinatory use of a steam stripping results in a substantial
improvement in the solvent recovery per unit steam when compared
with a conventional steam stripping method alone. In the structure
of the system shown in FIG. 3, water is poured onto a polymer
recovered in the recovery tank 4 to form a water slurry, whereby
facilitating the handling for transporting to the subsequent step.
Depending on the type of the polymer, the recovery tank 4 is fitted
further with the stirrer 10 and may also feed a steam.
[0049] When a large amount of a polymer solution is to be
processed, a multi-pipe system can be employed. In such a case, a
sample solution should be pumped into all pipes uniformly, since it
congests in the pipes with undergoing a thermal degradation
together with a possibility of occluding the pipes unless a uniform
pumping to the all pipes is accomplished.
[0050] In the invention, the devolatilizing efficiency, that is the
amount of steam consumption per the amount of solvent, is
preferably 0.6 or less, more preferably 0.5 or less, and most
preferably 0.4 or less.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE 1
[0051] As a sample a 20% by mass solution of a styrene-butadiene
block copolymer whose styrene content was 10% by mass
[number-average molecular weight (Mn); 300,000, melt flow rate
(MFR); 3.0 g/10 minutes (determined at 230.degree. C., loaded with
2.16 kg)] and whose viscosity was 2.0 Pa.multidot.s at 60.degree.
C., polymerized using cyclohexane as a reaction solvent,
n-butyllithium as a polymerization initiator, an experiment was
conducted in a system having the structure shown in FIG. 1. The
abovementioned number-average molecular weight was determined by
gel permeation chromatography, and the viscosity was determined by
Brook-field type viscometer.
[0052] A long tubular heater was of a heat exchange system
consisting of a pipe (made of SUS 304) whose inner diameter and
length were 8 mm and 10 m, respectively, (thermoconductive area of
0.25 m.sup.2) fitted with a jacket, and a steam was introduced to
the jacket to effect a heating so that the jacket was kept at
150.degree. C. Then the sample solution was supplied by a plunger
pump at 60.degree. C., 10 kg/hour. When a vacuum pump was used to
reduce the pressure of the recovery tank to 50 mmHg a white
granulated crumb could be recovered continuously into the recovery
tank. During this operation, the tubular heater was not occluded at
all. The linear velocity of the gas at the outlet of the pipe was
250 m/s.
[0053] The residual solvent was little and the lebel was 500 ppm.
The steam consumption was 30 parts by mass per 100 parts by mass of
the solvent (the devolatilizing efficiency was 0.3), which was
close to 20% by mass which is a required calorie (theoretical
value) in an indirect heating, showing a substantial reduction in
the steam consumption compared with a conventional steam stripping
method.
EXAMPLE 2
[0054] An experiment was performed similarly to Example 1 except
for using as a sample a 20% by mass solution of a butadiene rubber
[number-average molecular weight (Mn); 200,000, Mooney viscosity
ML.sub.1+4(100.degree. C.); 35] whose viscosity was 8 Pa.multidot.s
at 60.degree. C., polymerized using toluene as a reaction solvent
and triethylaluminum as a polymerization initiator, adding 5.0
parts by mass of water via the inlet of the pipe. The Mooney
viscosity was measured in accordance with JIS K6300.
[0055] The linear velocity of the gas at the outlet of the pipe was
290 m/s. During this operation, the tubular heater was not occluded
at all and a string-like crumb could be recovered continuously into
the recovery tank. The residual solvent was little and was 2000
ppm. The steam consumption was 30 parts by mass per 100 parts by
mass of the solvent (the devolatilizing efficiency was 0.3), which
was close to 20% by mass which is a required calorie (theoretical
value) in an indirect heating, showing a substantial reduction in
the steam consumption compared with a conventional steam stripping
method.
EXAMPLE 3
[0056] An experiment was performed similarly to Example 1 except
for using as a sample a 20% by mass solution of a styrene-butadiene
copolymer whose styrene content was 20% by mass [number-average
molecular weight (Mn); 380,000, Mooney viscosity
ML.sub.1+4(100.degree. C.); 70] and whose viscosity was 5
Pa.multidot.s at 60.degree. C., polymerized using cyclohexane as a
reaction solvent and adding 10 parts by mass of steam via the inlet
of the pipe.
[0057] The linear velocity of the gas at the outlet of the pipe was
340 mls. During this operation, the tubular heater was not occluded
at all and a granulated crumb could be recovered continuously into
the recovery tank. The residual solvent was little and was 500 ppm.
The steam consumption was 30 parts by mass per 100 parts by mass of
the solvent (the devolatilizing efficiency was 0.3), which was
close to 20% by mass which is a required calorie (theoretical
value) in an indirect heating, showing a substantial reduction in
the steam consumption compared with a conventional steam stripping
method.
EXAMPLE 4
[0058] An experiment was performed similarly to Example 1 except
for using as a sample a 20% by mass solution of a styrenebutadiene
copolymer whose styrene content was 48% by mass [number-average
molecular weight (Mn); 50,000, MFR; 3.0 g/10 minutes (determined at
230.degree. C., loaded with 2.16 kg)] and whose viscosity was 0.5
Pa.multidot.s at 60.degree. C., polymerized using toluene as a
reaction solvent and adding 2 parts by mass of steam via the inlet
of the pipe.
[0059] The linear velocity of the gas at the outlet of the pipe was
250 m/s. During this operation, the tubular heater was not occluded
at all and a granulated crumb could be recovered continuously into
the recovery tank. The residual solvent was little and was 300 ppm.
The steam consumption was 30 parts by mass per 100 parts by mass of
the solvent (the devolatilizing efficiency was 0.3), which was
close to 20% by mass which is a required calorie (theoretical
value) in an indirect heating, showing a substantial reduction in
the steam consumption compared with a conventional steam stripping
method.
[0060] As result from examples described above, a crumb having a
reduced residual solvent was obtained without occluding the heating
vessel. In addition, the steam consumption was reduced
substantially, enabling an efficient polymer recovery.
* * * * *