Chemical Engineering June 2019 - 28

Technology Profile
Polybutadiene Production via a Solution Process
By Intratec Solutions
P
olybutadiene (also known
as butadiene rubber) is produced
from the polymerization
of 1,3-butadiene. In
terms of production volume, polybutadiene
is among the largest synthetic
rubbers produced. This elastomeric
polymer can have a variety of different
properties depending on the ratio of
its microstructural units and its tacticity.
Most polybutadiene is consumed
in the production of vehicle tires. It is
also used to improve the mechanical
properties of plastics.
The process
The production process discussed
here is similar to the CB&I Lummus
Catadiene process, integrated with a
typical solution process. The process
comprises four major sections: (1) nbutane
dehydrogenation; (2) 1,3-butadiene
purification; (3) polymerization;
and (4) rubber molding. Figure
1 presents a simplified flow diagram.
n-butane
dehydrogenation.
Initially,
fresh butane, recovered butane
and mixed butenes are heated to dehydrogenation
temperature. These
components then pass through fixed
beds of chromia-alumina catalysts
in the reactors, where they are converted
into butadiene.
1,3-butadiene
purification.
The
reactor product is quenched for removal
of polymeric compounds. The
quenched gas is compressed and
partially condensed. The liquid condensate,
containing butadiene, is fed
to a series of distillation columns, from
which a butadiene-rich C4 stream is
obtained. This stream is then submitButadiene
n-Butane
Butanes
Polymerization
Dehydrogenation/
extraction/
polymerization
Oxidative
dehyd./
extraction/
polymerization
n Raw material n Pathway n Main product
FIGURE 2. The different polybutadiene production pathways depend on the source of butadiene
ted to extractive distillation in the presence
of N-methylpyrrolidinone (NMP),
used as a solvent. This step yields
high-purity butadiene. Recovered butane
and butenes are recycled to the
dehydrogenation step, while other hydrocarbons
are used as fuel.
Polymerization. High-purity butadiene
is pre-treated for the removal of
polymerization inhibitors, as well as
residual impurities. The treated butadiene
is dissolved in hexane and fed
to a series of two continuously stirred
polymerization reactors, where polymerization
occurs. Polymerization
is interrupted by stopping agents
when the desired molecular-weight
of the polymers is achieved.
Rubber molding. The polymer
slurry from polymerization is passed
through a flasher and subsequently
through a steam stripper for hexane
solvent recovery. Hexane recovered
by flashing is directly recycled, while
hexane recovered via stripping must
be further separated from water before
being recycled. A crumb-water
slurry is obtained and fed to a drying
step. The dried crumbs of polybutadiene
are cooled with air, weighed,
baled and stored.
Production pathways
Different manufacturing routes for
polybutadiene are related to differLight
hydrocarbons
1
3
n-Butane
2
4
5
10
9
Polybutadiene
11
FIGURE 1. This process diagram shows polybutadiene production via solution polymerization
28
RW
CW
ST
12
13
14
6
8
7
ent sources of the butadiene used.
In this context, the most typical production
routes are based on butadiene
produced from isolation of C4
steam-cracker fractions and dehydrogenation
of butane and butenes.
Different pathways for polybutadiene
production are presented in Figure 2.
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce
polybutadiene was about $1,600
per ton of polybutadiene in the second
quarter of 2015. The analysis
was based on a plant constructed
in the U.S. with capacity to produce
120,000 metric tons per year
of polybutadiene.
This column is based on " Polybutadiene
Production via Solution Process
- Cost Analysis, " a report published
by Intratec. It can be found at:
www.intratec.us/analysis/polybutadiene-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.
1. Dehydrogenation Reactors
2. Quench system
3. Compressor
4. Distillation columns
5. Extraction columns
6. Solution preparation
7. Polymerization reactors
8. Flasher
9. Stripper
10. Dryer
11. Baler
12. Refrigeration unit
13. Cooling tower
14. Boiler
CW Cooling water
RF Refrigeration fluid
ST steam
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JUNE 2019
Polybutadiene
Extraction/
polymerization
Dehydrogenation/
extraction/
polymerization
Steam cracking/
extraction/
polymerization
Crude C4s
Butenes
Naphtha

http://www.intratec.us/analysis/polybuta http://www.intratec.us http://www.intratec.us/che http://WWW.CHEMENGONLINE.COM

Chemical Engineering June 2019

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