Chemical Engineering April 2021 - 26

Technology Profile
Suspension Polymerization of Polyvinyl Chloride
By Intratec Solutions
P
olyvinyl chloride (PVC) is the
third most commonly produced
synthetic polymer,
after polyethylene and polypropylene.
PVC is a white, brittle solid
and it comes in two basic forms: rigid
(RPVC) and flexible. It can be compounded
for a wide range of properties,
which allows PVC to be used in
a broad range of applications.
This commodity thermoplastic can
be manufactured through different
polymerization processes, however,
most commercial PVC production is
based on a suspension polymerization
processes. To a lesser extent,
PVC is produced at industrial scales
via emulsion polymerization and bulk
(mass) polymerization.
The process
The suspension process for PVC
production comprises three major
sections: (1) polymerization; (2) vinyl
chloride monomer (VCM) recovery;
and (3) drying (Figure 1).
Polymerization. The VCM feed
stream, along with hot demineralized
water and chemicals (polymerization
initiators, dispersing agents and
additives) are supplied to a stirred
reactor. The reaction occurs substantially
in the liquid phase, in VCM
droplets dispersed in water, which
is used as diluent. After the initiation
of VCM polymerization, the heat
from the highly exothermic reaction
is removed by means of a cooling
system, for isothermal temperature
control. The molecular weight of the
polymer produced is defined by the
length of the resulting polymer, which
depends on the polymerization temWaste
gas
Demineralized water
Chemicals
VCM
1
2
3
5
6
PVC
Wastewater
FIGURE 1. The diagram shows polyvinyl chloride production from VCM (suspension polymerization)
26
N2
CW
ST
7
8
9
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4
Off-gas
Vinyl chloride
monomer
Ethylene
dichloride
Ethylene,
ethylene
dichloride
Polymerization
Cracking /
polymerization
Oxychlorination /
polymerization
Polyvinyl
chloride (PVC)
Direct oxychlorination
/ cracking /
polymerization
Direct chlorination /
cracking /
polymerization
Chlorination /
oxychlorination /
polymerization
FIGURE 2. PVC production pathways are based on the sources of the monomer
perature. As the polymer is formed, it
precipitates out of the reaction medium,
floating in the liquid monomer
phase. The polymerization is interrupted
when the conversion of VCM
to PVC reaches about 90%.
VCM recovery. The polymer slurry is
fed to a blowdown vessel, operated
at a lower pressure than the reactor.
Most of the unreacted VCM flashes
off. The polymer slurry is pumped to
a pre-degassing vessel and a sievetray
degassing column, where remaining
VCM is removed from the polymer
suspension. The VCM-rich off-gases
are compressed and condensed in liquid-ring
compressors and fed to a vessel,
in such a way that non-condensed
light contaminants are separated from
the liquid VCM and released as waste
gas. The VCM obtained is recycled to
the polymerization reactor.
Drying. The slurry is passed through a
solid-bowl decantation centrifuge to obtain
a wet PVC cake with residual moisture,
which is conveyed to a drying step.
The drying stage is a combination of a
flash dryer with a cyclone dryer, where
the wet PVC cake is dried until its moisture
content falls within the 0.2-0.3 wt.%
range. The dry PVC powder from the drying
stage is then packed for storage.
Production pathways
PVC production from VCM can proceed
via several different manufacturing
routes,
each related to different
sources of this monomer. In
this context, the most typical PVC
production routes are based on vinyl
chloride produced by reacting ethylene
with chlorine (Figure 2).
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce PVC
was about $850 per ton of PVC in the
second quarter of 2017. The analysis
was based on a plant constructed in
the U.S. with the capacity to produce
400,000 metric tons per year of PVC.
This column is based on " Polyvinyl
Chloride Production from VCM (Suspension
Polymerization) - Cost Analysis, "
a report published by Intratec. It can
be found at: www.intratec.us/analysis/
polyvinyl-chloride-production-cost. 
Edited by Scott Jenkins
Editor's note: The content for this column is supplied by Intratec
Solutions LLC (Houston; www.intratec.us) and edited by Chemical
Engineering. The analyses and models presented are prepared on
the basis of publicly available and non-confidential information. The
content represents the opinions of Intratec only. More information
about the methodology for preparing analysis can be found, along
with terms of use, at www.intratec.us/che.
Ethylene,
chlorine
Ethylene,
chlorine
Ethylene,
chlorine
 Raw material  Process  Main product
1. Polymerization reactor
2. Blowdown vessel
3. Degassing system
4. VCM recovery
5. Dewatering
6. Drying
7. Air separation unit
8. Cooling tower
9. Steam boiler
CW Cooling water
N2
Nitrogen
ST Steam

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Chemical Engineering April 2021

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