Chemical Engineering February 2016 - 36

Technology Profile
Acrylic Acid Production via Propylene Oxidation
By Intratec Solutions
A
crylic acid is a moderately
strong carboxylic acid primarily
used as an intermediate
in the production of acrylate
esters. These acrylate esters are
then mainly used to manufacture adhesives,
plastics additives, coatings,
paints and textiles.
The process
Figure 1 depicts a propylene oxidation
process similar to technology for the
production of ester-grade acrylic acid
(EAA) that was developed by Lurgi
GmbH (Frankfurt, Germany; part of Air
Liquide; Paris; www.airliquide.com)
and Nippon Kayaku (Tokyo; www.nipponkayaku.co.jp).
This process is described
in the next paragraphs.
Reaction and quench. Chemicalgrade
(CG) propylene is mixed with
steam and air and fed to a two-step
oxidation reaction system. In the first
step, the propylene is oxidized to acrolein
and, in the second step, the acrolein
is oxidized to acrylic acid. Both
steps are carried out in tubular, fixedbed
reactors. The heat generated by
the exothermic reactions is used to
generate steam. The effluent from the
reaction system is sent to a quench
tower, where the acrylic acid formed is
absorbed in water. Part of the residual
gas obtained by the top of the quench
tower is incinerated, with the balance
being recycled to the first-step reactor.
The aqueous solution is sent to downstream
units for product recovery.
Product recovery. The aqueous solution
from the quench step is fed to an
extractor, where the acrylic acid is sepOff-gas
to
incineration
Air
CW
ST
CG propylene
Steam
5
3
CW
4
ST
10
ST
1
ST
2
6
ST
Wastewater
CW
7
ST
Off-gas
CW
ST
36
CW
11
Heavy
ends
to waste
12
14
13
Figure 1. The diagram shows a process similar to the Lurgi/Nippon Kayaku technology for ester-grade acrylic acid production
ChemiCal engineering www.Chemengonline.Com february 2016
CW Cooling water
ST Steam
8
ST
9
ST
Propylene
Glycerol
Ethylene oxide
Catalytic
oxidation
Dehydration/
oxidation
Carbonylation
n Raw material n Pathway n Main product
Figure 2. Several pathways exist for acrylic acid production
arated by liquid-liquid extraction with a
solvent. The top portion of the extractor,
containing the acrylic acid, is sent
to a solvent-recovery column to recover
a two-phase overheads stream. This
two-phase stream is separated and the
organic phase, containing the solvent,
is recycled to the extractor. The aqueous
phase is mixed with the raffinate
from the extraction step and sent to a
raffinate stripper to minimize the solvent
losses. The bottom stream from the
solvent-recovery column is then fed to
the crude acrylic-acid column, where
a concentrated acrylic acid stream is
obtained as the bottom product. The
column overhead stream, mainly comprised
of acetic acid and light impurities,
is sent to a recovery column. The bottom
stream from the recovery column
is sent to the crude acrylic acid column
and the overhead stream is recycled to
the solvent recovery column.
Purification. In the purification area,
the concentrated acrylic acid stream
from the crude acrylic acid column
is fed to the product column. In this
column, ester-grade acrylic acid is obtained
as the overhead product. The
column bottoms are sent to a dedimerizer
to convert the dimer impurity,
formed in the process, back to acrylic
CW
acid. Finally, the product from the dedimerizer
is sent to the bottoms stripper
column, where the heavy ends are
separated and sent to waste.
Economic performance
The total fixed capital estimated to
construct such a plant producing
150,000 metric tons per year of EAA in
the second quarter of 2015 in the U.S.
is about $350 million. The total fixed
capital estimated includes the insideand
outside-battery limit units (production
units, storage installations, utilities
facilities and auxiliary buildings).
Acrylic acid pathways
Processes based on propylene oxidation
are traditionally most employed in
the production of acrylic acid. Figure
2 illustrates other alternative pathways
for the production of acrylic acid, starting
from different feedstocks.
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 nonconfidential
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.
CW
Estergrade
acrylic
acid
1.
First oxidation reactor
2. Second oxidation reactor
3. Quench tower
4. Liquid-liquid extractor
5. Solvent recovery column
6. Raffinate stripper
7. Crude acrylic acid column
8. Recovery column
9. Product column
10. Dedimerizer
11. Bottoms stripper
12. Incinerator
13. Cooling tower
14. Steam boiler
Acrylic acid
Fermentative
route
Fermentative
route
Reppe
synthesis
Glucose
syrup
Raw sugar
Acetylene

http://www.airliquide.com http://www.nip http://ponkayaku.co.jp http://www.intratec.us http://www.intratec.us/che http://www.Chemengonline.Com

Chemical Engineering February 2016

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