Chemical Engineering January 2018 - 26

Cover Story
The Dow Chemical Company:
Paraloid™ Edge technology
Urethane coating resins have many desirable
and a few undesirable attributes. Paraloid
Edge urethane coatings are made using a
completely new process that is isocyanate
and formaldehyde free. Paraloid Edge resins
and cross-linkers retain and add to the desirable,
while eliminating some of the most
undesirable attributes of urethane resins. It
is a superior, not a compromised, product.
Paraloid Edge resins:
* are isocyanate and formaldehyde free for
safety
* provide a very fast dry time for improved
productivity
The Dow Chemical Company
Carbamylation
OH
Polyol
O
Hydroformylation
THBA
FIGURE 5. A complete redesign
of the process for
urethane production gives
a product that is superior to
conventional urethanes
O
CHDA
carbamate and a di-aldehyde, forming a
polyurethane without isocyanates. A complete
redesign of the process for urethane
production gives a product that is superior to
conventional urethanes (Figure 5).
Dow Coating Materials developed processes
for cost-effective production of a
two-part, reactive urethane coating system
using polycarbamates and di-aldehydes,
replacing the isocyanates and polyols used
in conventional urethanes. Typical polycarbamate
production uses highly toxic methyl
carbamate. Dow developed processes
based on urea, overcoming process challenges
that hampered development of ureabased
routes in the past.
Polyols polymer and polymerization design.
Paraloid Edge is designed to meet or
exceed the specifications met by conventional
urethane coatings. These properties
(solution viscosity, color, clarity, hardness,
dry-time, UV resistance, chemical resistance)
are essential for the successful application of
the paint and the final performance of the
final cured coating material. The final properties
of the polymeric material are dictated by
the design of its molecular structure, extensive
material science and engineering R&D
established structural-property relationships
26
OH
* have a long pot life, reducing waste
* cure at room temperature for convenience
* are durable and weatherable
* are polyurethanes made with a better process
The final coating forms by reacting a polyO
O
H2N
H2N
O
O
O
Crosslink/
curing
O
NH
O
O
O
NH
OH
used
to design the essential details of the
polymer microstructure.
Once the polymer composition was determined,
the design of the polymerization
reactor system and the process conditions
followed. Among the multiple engineering
challenges were the following:
* Reactor temperature control due to the
high heat of polymerization
* Control of molecular weight and its
distribution
* Control of comonomer composition distribution
Extensive
kinetics and process research
and modeling was carried out to develop
and optimize processes for the production
of acrylic polyols.
Polycarbamates design and reaction.
Polycarbamates are formed through the
functionalization of reactions of polyols with
urea. The carbamates are the cross-link point
across the polymer chain, and therefore, the
extent of the functionalization reaction essentially
dictates the degree of crosslinking of the
final coating material. Extensive material science
and engineering R&D was carried out
to determine the optimum degree of functionalization
for each prototype. The optimum
extent of reaction was proved to be vastly different,
depending on the final application, for
different prototypes, and it varied from 50%
to 80% of the starting polyol hydroxyl functionality,
across different prototypes.
Using urea in the carbamylation reaction
introduces a number of process challenges,
such as byproduct formation, low urea solubility
in reaction media, and formation of
hazy, highly colored product. The process
developed by Dow overcomes these challenges,
resulting in a very high urea conversion
and producing a very clear and lowcolor
acrylic carbamate.
Cross-linker. The di-aldehyde, cyclohexanedicarboxaldehyde
(CHDA), is produced
through hydroformylation of tetrahydrobenzaldehyde
(THBA) with CO and H2 in the presence
of a rhodium catalyst. Two continuously
stirred tank reactors (CSTRs) under pressure,
in the absence of O2, achieve >99% conversion.
Process conditions, the complex operation
of two CSTRs and multiple post-reaction
steps, were optimized through extensive
experimental and process modeling work.
A proprietary process called Non-Aqueous
Phase Separation, which was first commercially
implemented in this technology, recovers
the rhodium catalyst for reuse.
This process was first commercialized in
March 2015 in the U.S.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JANUARY 2018
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Chemical Engineering January 2018

Table of Contents for the Digital Edition of Chemical Engineering January 2018
