Chemical Engineering April 2020 - 27

Technology Profile
Production Process for Neopentyl Glycol
By Intratec Solutions
N
eopentyl glycol (NPG;
2,2-dimethylpropane-1,3diol)
is an industrially important
and versatile diol,
mainly employed as a building block
for polyesters and polyurethanes.
NPG imparts desirable properties to
its derivatives, including low color,
good weathering and chemical resistance,
and high thermal and hydrolytic
stability.
This glycol is a crystalline solid at
room temperature that is highly reactive
and colorless to white in color. It
has good solubility in water, alcohols,
ethers, ketones and toluene. As a
typical glycol, it can undergo reactions
such as esterification, etherification,
condensation and oxidation.
The process
The process described here is an aldol
reaction followed by hydrogenation
(Figure 1). It comprises three major
sections: (1) aldol condensation;
(2) hydrogenation; and (3) purification.
Aldol condensation. An aldol reactor
is fed with an aqueous solution
of formaldehyde, isobutyraldehyde
and triethylamine. In such a reactor,
an aldol
condensation
reaction
between isobutyraldehyde and
formaldehyde is carried out in the
presence of triethylamine catalysts.
The output from the aldol condensation
reactor, containing crude hydroxypivaldehyde
(3-hydroxy-2,2dimethylpropanal)
intermediate, is
submitted to extraction with octanol
and distillation for the recovery of a
3
Isobutyraldehyde
Formaldehyde
Triethylamine
Octanol
6
4
9
CW Cooling water
ST Steam
5
Hydrogen
FIGURE 1. The diagram shows the production of neopentyl
glycol via aldol addition and catalytic hydrogenation
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8
CW
ST
High boilers
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27
12
13
Wastewater
1
2
Caustic soda
Wastewater
Water
7
Neopentyl
glycol
Isobutyraldehyde,
formaldehyde,
hydrogen
Aldol addition/
Canizzaro reaction
Sodium formate
Neopentyl
glycol
Aldol addition/
catalytic
hydrogenation
Isobutyraldehyde,
formaldehyde,
sodium hydroxide
n Raw material n Process n Main product n Byproduct
FIGURE 2. Two production pathways are available for NPG
purified hydroxypivaldehyde (HPA).
Hydrogenation. The purified intermediate
is fed to a loop-type reactor,
along with hydrogen gas. There, a reaction
between hydroxypivaldehyde
and hydrogen takes place, in the
presence of Raney-nickel catalysts.
This type of hydrogenation reaction
yields a mixture containing crude
NPG, which is then submitted to a
saponification step. In the saponification,
the precursors still present in
the hydrogenation product are converted
to NPG in the presence of a
50 wt.% sodium hydroxide solution.
Purification. In this section of the
process, the product stream rich in
NPG and a stream containing residual
NPG are fed to an extractor,
where water is used as solvent to extract
NPG. The aqueous phase from
the extraction is fed to a distillation
column, which further separates a
mixture of NPG and water from salt
impurities. The NPG-and-water mixture
is fed to the last column, which
further purifies the main product.
High-purity NPG withdrawn from
column bottom is routed to a finishing
step and finally stored.
Production pathways
NPG is commercially produced by
the aldol reaction of formaldehyde
10
11
and isobutyraldehyde, followed by
the reduction of the intermediate
hydroxypivaldehyde, which can be
made with either excess formaldehyde
(crossed Cannizzaro reaction)
or by catalytic hydrogenation of the
aldehyde group (the most common
process). These two possible routes
are shown in Figure 2.
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce
NPG was about $1,380 per ton of
NPG in the second quarter of 2016.
The analysis was based on a plant
constructed in the U.S. with the capacity
to produce 60,000 metric ton
per year of NPG.
This column is based on " Neopentyl
Glycol Production Process -
Cost Analysis, " a report published
by Intratec. It can be found at: www.
intratec.us/analysis/neopentyl-glycol-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. Aldol reactor
2. HPA extraction
3. Isobutyraldehyde recovery
4. HPA column
5. Loop reactor
6. Saponification
7. NPG extraction column
8. Octanol purification column
9. Residual NPG extraction
10. Salt removal column
11. NPG column
12. Cooling tower
13. Boiler
http://www.intratec.us/analysis/neopentyl-gly http://www.intratec.us http://www.intratec.us/che http://WWW.CHEMENGONLINE.COM
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