Chemical Engineering April 2022 - 33

Technology Profile
Production of EPDM Rubber
By Intratec Solutions
E
thylene propylene diene
monomer (EPDM) rubber is a
terpolymer elastomer derived
from ethylene and propylene,
along with small amounts of a nonconjugated
diene as a third monomer
(Figure 1). With a completely saturated
polymer backbone, this random
elastomeric copolymer exhibits interesting
properties, including excellent
weathering stability and heat resistance,
good insulating properties as
well as good resistance to chemicals,
moisture and steam.
EPDM has excellent ozone resistance
compared to natural rubber
and its synthetic substitutes, such
as styrene-butadiene rubber, butadiene
rubber and isoprene rubber.
These features make EPDM a versatile
synthetic rubber, with several applications
in the automotive industry,
in the construction industry and as a
plastic modifier.
Commercial-scale production of
EPDM rubber is mainly based on solution
and suspension polymerization
processes, and the polymerization
conditions determine the structure
of the final product obtained. Different
products vary mainly according
to their ethylene-to-proplyene ratio,
monomer sequence distribution,
molar mass and molar mass distribution,
as well as by the content and
type of the diene used. In this context,
EPDM rubbers are produced in
different grades by each manufacturer
according to the specialty applications
targeted, in such a way that it
is not standardized in the way that
general-purpose rubbers are.
The ethylene percentage of EPDM
products can vary between 15 and
85%. It may be
produced in different
physical forms,
from solid to friable
bales, pellets and
granular forms and
oil blends.
FIGURE 1. EPDM rubber is a random copolymer of ethylene and propylene,
with a diene (norbornene, in this case) added as a third monomer
The process
EPDM rubber production from polymer-grade
(PG) propylene and ethylene
comprises three major sections:
(1) polymerization; (2) purification;
and (3) finishing (Figure 2).
Polymerization. Initially, the monomers
are treated and mixed and the
mixture is continuously supplied to a
stirred, jacketed reactor, as well as
a solution containing the catalysts.
The reaction occurs substantially in
the liquid phase, with an excess of
liquid propylene, which is used as a
diluent. The rate of polymerization is
controlled by the rate of catalyst addition,
while temperature control is
readily accomplished by controlled
evaporation of the propylene. As the
polymer is formed, it precipitates out
of the reaction medium.
Purification. The slurry is pumped
into a vessel, where reaction is terminated
and the slurry is mixed with
small amounts of toluene and water.
The toluene allows the water to
extract the catalyst entrained in the
polymer. Subsequently, unreacted
monomers and solvent are removed
from the catalyst-free polymer slurry
in steam strippers containing water
as dispersing medium, and are recycled
to the polymerization reactor.
Finishing. The rubber polymer, present
in the form of wet crumbs in water,
is fed to a drum with auxiliary
agents, such as an anti-agglomerant,
so as to ensure that copolymer
particles stay suspended and show
a reduced tendency to agglomerate.
The crumb slurry, with moisture
content as high as 90 wt.%, is then
pumped to a rotary screen, where
most of the free water is removed.
The wet polymer is conveyed through
a single screw extruder. While being
conveyed through the extruder, water
is expelled from the polymer. The
extruded dried crumb, containing
less than 0.5 wt.% water, is cooled
down, baled and packed.
Uses and pathways
EPDM is widely used across several
market segments, including automotive
applications, where it can be
found in weather stripping, hoses,
tubing, brake components, isolators,
mounts and grommets. EPDM
is also found in plastics, such as in
impact-modified polypropylene and
thermoplastic olefins, as well as
in construction, such as in roofing
membrane, glass sealers, gaskets
and tapes. Other industrial applications
for EPDM include O-rings,
mounts, cable jacketing, insulation,
cable filler, connectors, footwear,
and carpet underlayment.
n
Editor's note: The content for this column is developed by Intratec
Solutions LLC (Houston; www.intratec.us) and edited by Chemical
Engineering. The analyses and models presented are based on
publicly available and non-confidential information. The content represents
the opinions of Intratec only.
1. Polymerization
2. Finishing reactor
3. Catalyst removal
4. Catalyst recovery
5. Monomers recovery
6. Additives mixing
7. Rotary screen
8. Drying extruder
9. Cooling tower
10. Boiler
CW Cooling water
ST Steam
FIGURE 2. The diagram shows the polymerization process for making EPDM rubber
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APRIL 2022
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Chemical Engineering April 2022

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