Chemical Engineering April 2019 - 33

Technology Profile
Polyacrylonitrile Production
By Intratec Solutions
Acrylonitrile,
methyl acrylate
P
olyacrylonitrile (PAN) is a polymer
resin mainly composed
of acrylonitrile. This important
acrylic resin is used in the
production of a wide range of products,
from ultra-filtration membranes
to high-quality carbon fibers.
The process
The process discussed here comprises
two main phases: first, acrylonitrile
Propane,
methyl
acrylate
Polymerization,
spinning
PAN fiber
precursor
Ammoxidation,
polymerization,
spinning
Dehydration
ammoxidation,
polymer., spinning
FIGURE 2. Multiple production pathways exist for polyacrylonitrile fiber
n Raw material n Process n Main product n Byproducts
is polymerized with methyl
acrylate comonomer and additives
in an aqueous solution of demineralized
water; then the copolymer is
passed through transformation steps
to become a fiber. Figure 1 presents
a simplified flow diagram.
Polymerization. Initially, a mixture
of acrylonitrile, methyl acrylate and
itaconic acid is fed continuously to
a continuous stirred-tank reactor
(CSTR) where the polymerization
takes place. The reaction is initiated
by feeding aqueous solutions of potassium
persulfate (oxidizer), sulfur
dioxide (reducing agent), ferrous iron
(promoter), and sodium bicarbonate
(buffering agent). The heat of polymerization
is removed by water circulated
in a reactor jacket.
Next, an iron-chelating agent is
added to the reactor overflow, where
it acts as a chain stopper for the
polymerization. The reactor overflow,
an aqueous slurry of polymer
particles, is fed to a monomer-separation
column, in which unreacted
monomer is steam-stripped from the
slurry. The monomers recovered are
returned to the reactor.
Pelletizing. The polymer is pelletized,
Demineralized
water
Acrylonitrile
Methyl acrylate
Itaconic acid
1
CW
2
5
Wastewater
3
10
4
FIGURE 1. The diagram shows a production process for polyacrylonitrile (PAN)
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PAN fiber
precursor
9
CW
ST
RW
N2
O2
11
12
13
14
dried, ground and then converted to
fiber through subsequent steps involving
physicochemical transformations,
as briefly described below.
Wet spinning. The polymer is dissolved
in dimethylformamide (DMF),
forming a dope. The dope is pumped
through a spinneret into a precipitating
bath, for the coagulation of the solution
thread line into a highly swollen gel yarn.
Washing, stretching and finish. The
fiber is washed countercurrently by hot
water, for the removal of the solvent.
The fiber is then stretched while passing
over rollers with adjustable speed.
The stretching imparts fiber strength.
Subsequently, silicone is applied as an
aqueous emulsion to the fiber, to act as
lubricant and antistatic agent.
Drying, crimping and relaxation.
The fiber passes through drum dryers
for water removal. Tows are crimped
by means of a stuffer box crimper.
Crimping provides interfilament cohesion
across the tow and facilitates
subsequent handling. Then the fiber
is fed to an autoclave for a relaxation
process that reduces the tendency
for fibrillation and increases the fiber
dimensional stability.
Production pathways
PAN production consists of the copolymerization
of acrylonitrile - the
6
7
8
main component - and other comonomers,
in such a way that different
manufacturing routes are
related to different sources of such
raw materials. In this context, typical
PAN production routes are based on
acrylonitrile manufacturing. Different
pathways for polyacrylonitrile (using
methyl acrylate comonomer) production
are presented in Figure 2.
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce
polyacrylonitrile was about $4,600
per metric ton in the first quarter of
2015. The analysis was based on a
plant constructed in the U.S. with capacity
to produce 9,000 metric ton
per year of polyacrylonitrile.
This column is based on " Polyacrylonitrile
Production - Cost Analysis, " a
report published by Intratec. It can be
found at: www.intratec.us/analysis/
polyacrylonitrile-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. Polymerization reactor
2. Stripping
3. Washing and dewatering
4. Pelletizing
5. Drying and grounding
6. Wet spinning
7. Washing
8. Stretching
9. Finish
10. Crimping and relaxation
11. Cooling tower
12. Steam boiler
13. Chiller
14. Air separation unit
CW cooling water
ST steam
RW refrigerated water
33
Glycerol,
methyl acrylate
Ammoxidation,
polymerization,
spinning
Propane,
methyl acrylate
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