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Файл:Chemistry, technology and properties of synthetic rubber. Tutorial
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2.4 Polymerization of Isoprene
Polymerization of isoprene with titanium catalysts is performed in
isopentane, the viscosity of a polymer solution in which is minimal.
Dried isopentane-isoprene fraction is fed by isoprene to its content of
12-15%, and goes into cooler 1 (Figure 3), cooled by propane
evaporating at -20°C. The modified catalyst complex (up to 1%,
based on isoprene) is fed to the polymerization through the cooler 2
using a special dosing device, automatically regulating the catalyst
feed depending on the viscosity of the polymerizate. Polymerization
of isoprene is carried out in the battery, consisting of two 20 m
connected polymerizers 31 and 32.
Using two-component catalyst complex the polymerization is
carried out in a battery of 4-6 similar devices.
3
Fig.3 Diagram of polymerization, deactivation, cleaning and
stabilization of polymer rubber when obtaining SKI-3:
1, 2 — cooler; 31 З2 — polymerizer, 4, 7, 10, 13 — intensive stirrers;
5 — stirred tank; 6, 9, 12 — pumps; 8, 11 — precipitating tanks.
I — isopentane; II — isoprene; III — catalyst complex, IV —
propane; V — brine; VI — etylene; VII — stopper, VIII — desalted
water, IX — stabilizer suspension; X — polymerizate to degassing,
XI — water to organic compounds steam stripping.
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Polymerizers are stirred tank fitted with blades and scrapers,
providing intense uniform mixing throughout the volume of
polymerizer and continuous cleaning of the surface of heat transfer,
which is necessary to achieve a high heat transfer coefficient.
Removal of heat released during the polymerization of isoprene
(polymerization heat is 1050 kJ/kg) is carried out via the jacket of
polymerizer cooled by brine.
Polymerization temperature increases during the process from
45±5°C in the polymerizer 31 to 55±5°C in the polymerizer 32, which
provides 85-90% conversion of isoprene at a sufficiently low
viscosity polymer. It is also known the method of cooling the
reaction mass by partial evaporation of the solvent and monomer.
The pressure in the polymerizers is 1-1.2 MPa.
2.5 Deactivation of Catalyst Complex
The purpose of this process stage is to break the polymerization
reaction when reaching the preset conversion, and the transformation
of catalyst components into compounds which do not cause
secondary processes (degradation and structuring) during the further
processing of the polymer, which lead to the low quality of isoprene
rubber. There are used compounds for deactivation of the catalyst
that react with the components of a catalyst to form water-soluble
products, - aliphatic alcohols, acids, amines, and others. In the
industry for this purpose there are often used methyl alcohol, which
can be regenerated from washing water, or water. The mixing of the
polymerizate with the deactivator (stopper) is performed in an
intensive mixer 4 (Figure 4). In order to ensure complete conversion
of the active components of the catalyst the stopper is served in a
large excess compared to the stoichiometric amount.
From intensive stirrer 4 the polymerizate enters the stirred
tank 5, where the process of catalyst deactivation completes for 1520 minutes. At the same time the pressure drop in the system is
carried out in this device. The polymerizate is fed from the tank 5 by
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pump 6 into intensive stirrer 7 for mixing with the circulating water
supplied from the precipitating tank 8 by pump 9, and splits in the
precipitating tank 8. Polymerizate partially washed from deactivation
products is sent to the intensive stirrer 10, which is fed with softened
water. The mixture is breaks down in the precipitating tank 11.
Washed polymerizate is applied to intensive stirrer 13 for mixing
with the stabilizer, which is served as hydrocarbon solution or
aqueous suspension, and sent to the degassing. Deactivation products
of the catalyst complex are removed by pumps 9 and 12 for the
chemical refining.
As stabilizers for rubber SKI-3 there are used amine and
phenol compounds: mixture of N-phenyl-β-naphthyl-amine (naphth-
2) and N,N'-diphenyl-n-phenylenediamine (DFFDA) in the ratio of
1:1 with dosage of 0.6-0.8% on the basis of rubber; 2,6-di-tert-butyl4-methyl phenol (ionol) for the light rubber stamps.
In some productions of SKI-3 there are used rotor washing
column having 7 radial-flow impellers on a common shaft and 8
sedimentation zones to provide more complete washing of
polymerizate off the water-soluble products.
According to this scheme, polymerizate enters the intensive
stirrer 1 (Figure 4) for the destruction of the catalyst complex, where
stopper, usually methanol, is supplied too. Polymerizate is
transferred from the intensive mixer 1 to the stirred tank 2, wherein
the mixture of polymerizate with the stopper is held for 15-20
minutes. This device serves as an intermediate tank. The polymer
from the tank 2 by the pump 3 is supplied to the intensive stirrer 4,
where the part of washing water from the bottom of the washing
column 6 is piped to. A mixture of polymerizate and water enters the
precipitating tank 5, where it is separated into two layers. The lower
aqueous layer removes out of the system by the pump 10, and the top
layer, which is partially washed polymerizate, is fed to the washing
column 6, where the polymerizate is completely washed off the
decomposition products of the catalytic complex. For washing, a
mixture of return water from the degassing system and partially
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softened deoxygenated water, acidified with hydrochloric acid up to
pH 3, is used.
Fig.4 Catalyst deactivation and polymerizate washing diagram:
1, 4, 8 — intensive stirrers; 2 — stirred tank; 3, 7, 9, 10 — pumps; 5
— precipitating tank; 6 — washing column.
I — polymerizate; II — solvent; III — stopper; IV — acidified water;
V — polymerizate to degassing; VI — water to organic compounds
steam stripping; VII — stabilizer suspension
Washed polymerizate is removed from the top of the column
6 to the intensive stirrer 8, applied by the pump 9 with water
suspension of stabilizer. Polymerizate, filled with stabilizer, is fed to
the precipiyating tank-averager.
2.6 Degassing of Polymerizate
Water degassing of the polymerizate is carried out in two connected
degassers (Figure 5). Polymerizate from the averager 1 by the pump
2 is consistently served to intensive stirrer 3 and 4, where an aqueous
emulsion of polymerizate is formed. Therefor the circulating water is
supplied to an intensive stirrer 3 in the amount of 20% of the
polymer, with antiagglomerator and 2% solution of potassium
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hydroxide to maintain pH 7-8. The rest of the circulating water
moves to the intensive stirrer 4. The resulting polymerizate emulsion
through the jet blower 5, which receives steam at 1.02 MPa, is
directed to the bottom of the first stage degasser 6, which is a hollow
device. Circulating water from the hub 8 is also served to the bottom
of the degasser 6. The vapours of hydrocarbons and water are
assigned from the top of the degasser 6.
Fig.5 Diagram for water degassing when obtaining SKI-3:
1 – averager; 2, 7, 12, 20, 22 — pumps; 3,4 — intensive stirrers 5, 11
— jet blowers; 6 — first stage degasser; 8 — concentrator; 9 —
pulsator; 10 — second stage degasser; 13 — air condenser; 14 —
separator; 15, 16, 17 — condenser; 18 — precipitating tank; 19, 21
— receiving tank.
I — polymerizate; II — circulating water, antiagglomerator, solution
of potassium hydroxide; III – vapor; IV — nitrogen, V — pulp to the
concentrator; VI — water to polymerizate washing; VII — water to
organic compounds steam stripping; VIII — return products to
alkaline cleaning; IX — fresh solvent; X - brine; XI — air; XII –
softened water.
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The pulp containing 5% rubber are fed from the bottom of the
degasser 6, which is fed by the pump 7 to the concentrator of crumbs
8, which is concentrated up to 10% of rubber content by the water
separation. To prevent sticking of the crumbs on the concentrator
perforators the pulsator 9 introduces nitrogen at the pressure 0.6
MPa. The concentrated pulp is fed to the second stage of degassing –
to the top of the degasser 10, which is partitioned by plates along the
height, the lower part of the device 10 is a separator. The pulp from
the second stage degasser 10 through the external overflow pipe is
throttled down the separator 14, where by reducing the pressure from
0.35 to 0.12 MPa the part of the water evaporates. Water vapor is
removed from the separation section under the bottom of the plate of
the second stage degasser 10 by the jet blower 11, which is fed by
steam under the pressure 1,02-3,00 MPa. The pulp from the
separation section of the degasser 10 is supplied by the pump 12 for
the concentration.
Vapours, selected from the top of of the second stage degasser
10, are sent to the bottom of the first stage degasser 6. Live steam is
fed under the pressure 0.6 MPa to both degassers through the
bubblers. Vapours of first-stage degasser 6 are released into the air
condenser 13, where they are condensed by the air cooling with
blowing fan. Condensate through the separator 14 enters the
condenser 15, cooled by water. Uncondensed vapors from separator
14 go to the water-cooled condenser 16 and then to the condenser 17,
cooled by brine. Condensate from the devices 15, 16, 17 goes into
the precipitating tank 18 for splitting. The lower aqueous layer is
collected in a receiving tank 19, from which is pumped for
polymerizate washing. The receiving tank 19 is served by fresh
softened water. The upper hydrocarbon layer from the precipitating
tank 18 enters the receiving tank 21, where an additional
delamination occurs. The aqueous layer is taken from the bottom of
the unit 21 and sent to the steaming of hydrocarbons, and the
hydrocarbon layer is supplied by pump 22 to the alkaline washing.
The unit 21 is served by fresh solvent from the warehouse.
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2.7 Rubber Separation, Drying and Packing
Aqueous pulp of rubber crumb with 5% concentration is removed in
the concentrator 1 (Figure 6) from the bulk of water. Water is
discharged by gravity from the concentrator to the receiving tank 14,
where it is partially returned from by pump 15 to the concentrator 1,
and is partially withdrawn to the drain system, and the rubber crumb
is fed from the top of the device by screw conveyor into a singlescrew squeez press 2 (expeller), where the water is mechanically
wringed out the rubber and is collected in the receiving tank 14.
Fig.6 Rubber separation, drying and packing diagram:
1 – concentrator; 2 – expeller; 3 – expander; 4 – drier; 5 – spiral lift
vibrator; 6 – horizontal vibrating conveyor; 7 — vibrating feeder; 8
— feed hopper; 9 – briquetting press; 10, 13 — air heaters; 11, 12 –
blower units; 4 — receiving tank; 15 – pump; 16 — screw conveyor.
I – pulp from degassing; II — water to drain system; /// — air; IV —
rubber to packing; V – air to cleaning.
Rubber crumb with humidity from 3 to 10% comes from the
press 2 to the single-screw drying press 3 (expander), where the
rubber is compressed under the pressure of 5.1 MPa and heated to
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180°C due to the heat released from the friction of the rubber against
the screw and frame surface. To reduce heat loss and to warm up
when starting the screw frame is provided with jackets heated by
vapor under the pressure of 1.7 MPa. Rubber containing superheated
water goes through the calibration diaphragm, which has a few holes,
out of the press 3 in the form of tows which are cut into pieces of 1015 mm long by rotating knives. Superheated water contained within
the rubber, evaporates when throttling from 5.1 to 0.1 MPa and
shreds the rubber, which is ejected in the form of crumbs to the
drying oven on a horizontal vibrating conveyor in the dryer 4. The
air heated in air heaters up to 110-140°C supplied with fans to the
chamber and under the bottom of shaking conveyor. The air
saturated with water vapor is sucked by exhaust fan and vented to the
atmosphere.
Dried rubber crumb as with a residual moisture of 0.5% is fed
in the dryer by horizontal shaking conveyor 4 into the cooling area,
cooled to 40-50°C, and sent to the spiral lift vibrator 5. With the lift
vibrator 5, where the water removes from the surface of the rubber,
horizontal vibrating conveyor 6 and vibrating feeder 7 the rubber
crumb is fed into the feed hopper 8 of automatic scales. Rubber from
the hopper enters the briquetting press 9 in portions and then in the
form of briquettes weighting 25-30 kg is applied by belt conveyor to
the packing machine for wraping. Packed briquettes are packaged
into containers and shipped to the warehouse of commodity products.
There are used domestically (LC-4, LC-8, "Neva-8") or
imported produced units ["Crupp" company (Germany), "Andersen"
(USA)] as the extruders.
On some productions the rubber is dried in a hot air in
conveyor dryers of various designs at 100-110°C.
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2.8 Secondary Operations
2.8.1 Preparation of Stabilizer Suspension and Stopper Solution
Aqueous suspension of stabilizer is prepared periodically in unit 3,
which is filled with the required amount of softened and
deoxygenated water, and the appropriate amount of stabilizer is
loaded from the hopper 5 (Figure 7). The mixture is stirred until
dispersion. Continuous circulation of mixture with the pump 4
through the intensive stirrer 7 and colloid mill 6 is carried out in
order the dispersion was finer, maintaining it in suspension. Rreadyto-use suspension is fed by the pump 4 into the measuring tank 1,
wherefrom with the pump 2 is dosed to feeding the polymerizate and
to the measuring tank 8 for preparation of stopper.
Fig.7 Preparation of stabilizer suspension and stopper solution
diagram.
1, 8 — measuring tanks; 2, 4, 10 — pumps; 3 — dispersion
preparation device; 5 — hopper; 6 — colloid mill; 7 — intensive
stirrer, 9 — tank.
I — suspension to polymerizate feeding; II — softened water; III —
stabilizer; IV — stopper; V — to polymerizate feeding.
Stopper from warehouse is supplied to the tank 9 for mixing
with stabilizer suspension in the circulation circuit by the pump 10
and fed to the deactivation of the catalyst complex.
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2.8.2 Preparation of Antiagglomerator
Solution of sodium hydroxide with the concentration 40% is fed
from warehouse to the measuring tank 1, and then by gravity into the
stirred tank 2 for dilution by partially softened water (Figure 8).
Alkaline solution with the concentration 2% after the pump 3 is
divided into two streams: one half of is fed into the line of circulation
water, the half goes to unit 4 for preparing the solution of potassium
stearate. Stearic acid is loaded from hopper 5 to the device 4.
Fig.8 Components for antiagglomerator obtaining preparation
diagram:
1 — measuring tank; 2 – tank for alkali solution preparation; 3, 6, 10
— pumps; 4 — tank for calcium stearate preparation; 5, 9 —
hoppers; 7, 11 — filters; 8 — tank for calcium chloride solution
preparation.
I — softened water; II – potassium hydroxide solution; III —
potassium hydroxide, potassium stearate and calcium chloride
solvents for feeding the polymerizate; IV — stearic acid; V —
calcium chloride; VI — steam.
The resulting potassium stearate is pumped through the filter
7 into the line of circulating water. Devices 2 and 4 are supplied with
coils for steam heating under the pressure 0.6 MPa and fittings for
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