Chemical Engineering September 2020 - 25

Technology Profile
Polypropylene Carbonate Production
By Intratec Solutions
P
olypropylene carbonate
(PPC) is a thermoplastic
polymer produced from the
catalyzed copolymerization
of carbon dioxide (CO2) and propylene
oxide. The copolymer chain is
composed of alternating segments of
CO2 and propylene oxide, along with
small amounts of propylene oxide
homopolymer. Some of its important
properties include excellent transparency,
good barrier to water and oxygen,
printability and nontoxicity.
PPC offers important environmental
advantages: it acts as a sequester
for CO2, which can help minimize the
impact of global warming, and some
PPC composites are designated as
biodegradable materials.
The process
The present analysis discusses an industrial
process for PPC production
comprising four major sections: (1)
polymerization; (2) phase separation;
(3) monomer separation; and (4) pelletizing
and finishing (Figure 1).
Polymerization. Fresh CO2 feed is
mixed with recycled CO2 from the
monomers separation stage. Propylene
oxide feed is also mixed with
a recovered stream. Both reactants
are treated for moisture removal. Part
of the treated propylene oxide feed
is introduced to the polymerization
reactor outlet to dissolve the polymer
solution obtained in the reactor.
The remainder is mixed with catalyst
and CO2 feed, forming a liquid solution
that is transferred to the prepolymerization
reactor. The prepolymerization
reaction effluent is fed to
Propylene oxide,
CO2
Propylene,
ethylbenzene,
CO2
Propylene,
acetaldehyde,
CO2
Copolymerization
Oxidation/
hydroperoxidation/
copolymerization
Oxidation/
hydroperoxidation/
copolymerization
Polypropylene
carbonate
Epoxidation/
copolymerization
Oxidation/
hydroperoxidation/
copolymerization
Direct oxidation/
copolymerization
Figure 2. Multiple pathways exist for the production of polypropylene carbonate
the polymerization reactor, where the
polymer solution is obtained.
Phase separation. The polymer solution
is contacted with a material
that binds to the catalyst and allows
its removal via filtration. The catalystfree
solution is subjected to gradual
pressure decrease, so that unreacted
monomers can be released. Once
unreacted monomers are removed,
the polymer melt is transferred to the
pelletizing and finishing stage, while
released monomers are routed to the
monomers separation area.
Monomer separation. Unreacted
monomers are fed to two consecutive
distillation columns, from which three
streams are obtained. A high-purity
propylene oxide stream is recycled to
the feed preparation step and mixed
with fresh feed. A carbon-dioxide-rich
stream (also containing propylene
oxide) is also recycled to feed preparation.
Another stream, comprising
heavy ends generated as side-products,
is discharged from the process.
Pelletizing and finishing. The polymer
melt is fed to a pelletizing system,
where it is homogenized and
pelletized. Subsequently, the pellets
are packed in bags before being
stored in warehouses.
6
Carbon dioxide
2
Catalyst
1
3
4
5
7
PPC
1. Feed preparation
2. Prepolymerization
3. Polymerization
4. Catalyst removal
5. Monomers stripping
6. Monomers separation
7. Pelletizing and finishing
8. Cooling tower
9. Boiler
Propylene oxide
Catalyst residue
Figure 1. The diagram shows the production of PPC from propylene oxide and CO2
ChemiCal engineering www.Chemengonline.Com September 2020
25
CW
ST
8
9
CW Cooling water
ST Steam
Production pathways
Commercial production of PPC involves
the catalyzed copolymerization
between carbon dioxide and
propylene oxide, in such a way that
different manufacturing routes are
related to different sources of these
raw materials.
Figure 2 illustrates
PPC production pathways.
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce PPC
was about $1,660 per ton of PPC in
the third quarter of 2016. The analysis
was based on a plant constructed in
the U.S. with the capacity to produce
20,000 metric ton per year of PPC.
This column is based on " Polypropylene
Carbonate Production -
Cost Analysis, " a report published
by Intratec. It can be found at: www.
intratec.us/analysis/polypropylenecarbonate-production-cost.
n
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.
Propylene,
hydrogen peroxide,
CO2
Propylene,
isobutane, CO2
Propylene, oxygen,
CO2
n Raw material n Process n Main product
Hydrocarbons for fuel
http://www.intratec.us/analysis/polypropylene http://www.intratec.us http://www.intratec.us/che http://www.Chemengonline.Com
Chemical Engineering September 2020

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