Chemical Engineering June 2020 - 25

Technology Profile
Production of Orthophthalic Unsaturated Polyester
By Intratec Solutions
U
nsaturated polyester resins
(UPRs) are solutions of unsaturated
polyesters in copolymerizable
monomers,
which
undergo cross-linkage to form
thermosetting plastics. The unsaturated
polyesters are produced by
polycondensation of at least one unsaturated
dicarboxylic acid with diols,
while styrene is usually employed
as a cross-linking agent.
A wide range of UPRs is manufactured
according to the intended processing
and end-use properties. For
example, orthophthalic formulations
are used in marine crafts, marbles,
gel-coat, buttons; isophthalic resins
are used in storage tanks, pipes,
pultruded profile and electrical-grade
laminates; and dicyclopentadiene
formulations are employed in molded
electrical components, bathtub
products and marine applications.
The process
The present analysis covers orthophthalic
UPR production. The process
(Figure 1) comprises three major
sections: (1) esterification; (2) crosslinking;
and (3) glycols recovery.
Esterification. This first step involves
the polycondensation between a
combination of phthalic anhydride
and maleic anhydride, and multiple
glycols. Initially, the glycols - monoethylene
glycol (MEG) and diethylene
glycol (DEG) and propylene glycol
- are charged to the reactor. Subsequently,
maleic anhydride and
phthalic anhydride are added to the
mixture. The esterification reactor is
MAN, PAN, PG,
styrene
MAN, PAN, DEG,
styrene
MAN, isophthalic
acid, PG, styrene
Polycondensation
Polycondensation
Polycondensation
n Raw material n Process n Main product
equipped with stirrers and heating. It
is fed with nitrogen to provide an inert
blanket. The high temperatures in the
reactor cause the evaporation of the
glycols and the water generated in
the reaction.
Cross-linking. Cross-linking is carried
out in a different vessel, where
the polycondensation product is
dissolved in styrene and the reaction
takes place. In this reaction, the
vinyl radical in the styrene monomer
reacts with the unsaturation in
the polyester chains, thus linking
different chains. Also during this
step, promoters are added to initiate
the copolymerization reactions,
and inhibitors are added to moderate
the reaction and keep temperature
within required limits to avoid
product degradation. At last, the
final product is put into drums and
stored in a warehouse.
Glycols recovery. A water separation
column receives the overhead
vaporous glycol-water mixture from
the reactor. The column top temperature
is kept at 100-105°C in such
a way that the column overhead
product contains only water, which
Wastewater
Maleic
anhydride
Propylene glycol
Monoethylene glycol
Diethylene glycol
Phthalic
anhydride
1
Styrene
2
Additives
CW
HO
Orthophthalic Resin
Figure 1. The diagram shows a typical batch process for manufacturing orthophthalic polyester resin
ChemiCal engineering www.Chemengonline.Com June 2020
25
4
5
3
Orthophthalic
resin
Polycondensation
Polycondensation
Polycondensation
MAN maleic anhydride
PAN phthalic anhydride
MEG monoethylene glycol
MAN, PAN, MEG,
styrene
Fumaric acid,
PAN, PG, styrene
MAN,
terephthalic acid,
PG, styrene
PG propylene glycol
DEG diethylene glycol
Figure 2. Shown here are several production pathways for orthophthalic polyester resin
is further routed to a condenser and
discarded. The glycol-rich bottom
product is recycled to the reactor.
Production pathways
Commercial UPR production is
mostly based on batchwise condensation
of dicarboxylic acids or
anhydrides with diols. The specific
acids and diols employed may vary
according to the product properties
need or market price opportunities.
Different feedstock formulation examples
are presented in Figure 2.
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce
orthophthalic resin was about
$1,200 per ton in the second quarter
of 2016. The analysis was based on
a plant constructed in the U.S. with
capacity to produce 70,000 metric
ton per year of orthophthalic resin.
This column is based on " Orthophthalic
Unsaturated Polyester Production
Process - Cost Analysis, " a report
published by Intratec. It can be
found at: www.intratec.us/analysis/
unsaturated-polyester-resin-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. Reactor
2. Dissolution tank
3. Water seperation column
4. Cooling tower
5. Heating oil unit
1. Reactor
2. Dissolution tank
3. Water separation column
4. Cooling tower
5. Heating oil unit
HO Heat-transfer oil
CW Cooling water
HO Heat transfer oil
CW Cooling water

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Chemical Engineering June 2020

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