Chemical Engineering February 2017 - 34

Technology Profile
Methionine Hydroxy Analog Production
By Intratec Solutions
ethionine
is an essential
amino acid that is widely
used as an animal feed
additive, especially in the
Natural gas/
ammonia
poultry market. Hydroxy-methyl butyric
acid, also known as methionine
hydroxy analog (MHA), is used in
animal nutrition as an equivalent to
methionine, since it is converted into
L-methionine by enzymes inside animals'
bodies.
The process
In the process described here, liquid
MHA is produced from 3-methylmercaptopropionaldehyde
(MMP) and
hydrogen cyanide. In the first step,
MMP is converted to hydroxy-methylthiobutyronitrile
(HMBN), which is then
hydrolyzed to MHA. Finally, MHA is recovered
through solvent extraction.
Figure 1 is a simplified flow diagram of
this process.
HMBN synthesis. Liquid MMP is
continuously fed into the HMBN reactor,
while gaseous hydrogen cyanide
is fed through the reactor bottom.
The reaction of MMP and HCN is
catalyzed by a mixture of pyridine and
acetic acid. MMP is completely converted,
with high selectivity to HMBN,
and a few heavier byproducts. The effluent
from this reactor is conducted
to a nitrogen-stripping column to remove
unconverted hydrogen cyanide,
the HCN-free stream is then directed
to the MHA synthesis.
MHA synthesis. HMBN undergoes hydrolysis
in three steps. At first, HMBN
is introduced into a continuously stirred
tank reactor (CSTR) along with process
water and a sulfuric acid stream.
Catalyst
MMP
HCN
Nitrogen
Process water
Sulfuric acid
7
Extract
3
4
Process water
6
CW
CW
5
CW
FIGURE 1. Methionine hydroxy analog production from MMP and hydrogen cyanide
34
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FEBRUARY 2017
Solvent
Raffinate
CW
ST
10
11
CW Cooling water
ST Steam
1
2
Off gas (to treatment)
ST
9
CW
8
ST
ST
NH4HSO4
solution
MHA @ 88 wt%
Propylene
Hydrogen sulfide/
methanol
Hydrogen cyanide
production
unit
Acrolein
production
unit
Methyl mercaptan
production
unit
FIGURE 2. Integrated process units for the production of methionine hydroxy analog
n Main raw material n Process n Main product
HMBN reacts with water to form an
amide
(2-hydroxy-4-methylthiobutanamide),
with sulfuric acid behaving as a
catalyst. The effluent from this reactor
and additional process water are introduced
into a second CSTR, operated
at higher temperatures. The amide is
hydrolyzed in a reaction with water and
sulfuric acid, forming MHA and ammonium
bisulfate. The effluent from this
second reactor is fed to a plug-flow reactor
to guarantee complete hydrolysis
of the amide formed in the first step.
The resulting aqueous solution is sent
for purification.
Purification. MHA is extracted with
methyl isobutyl ketone (MIBK). The
extract, rich in MHA and solvent, is
steam-stripped. The water and solvent
are recovered from the top product
and a concentrated MHA stream
is recovered from the bottom. The
final product composition is corrected
with process water. The raffinate
from the extraction, mostly water and
ammonium bisulfate, is also steamstripped.
The water is recovered from
the top and an aqueous solution containing
ammonium bisulfate is recovered
from the bottoms and disposed
of as waste.
Economic performance
MHA production cost (including plant
operation, product sales, administration,
R&D activities and depreciation)
is estimated at about $2,400 per ton
of product. The scope of this analysis
assumes a facility with capacity
to produce 160,000 metric tons per
year of MHA (88 wt.% liquid solution)
from HCN and MMP. The production
of these raw materials is usually integrated
to the MHA process (Figure
2). The production cost was estimated
based on data from the second
quarter of 2013 for a plant operating
in the U.S.
This column is based on " Methionine
Hydroxy Analog Production Process
- Cost Analysis, " a report published
by Intratec. It can be found at:
www.intratec.us/analysis/methionineproduction-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. HMBN reactor
2. Nitrogen stripper
3. First hydrolysis reactor
4. Second hydrolysis reactor
5. Finishing reactor
6. Extraction column
7. Extract steam stripper
8. Decanter
9. Raffinate steam stripper
10. Cooling tower
11. Steam boiler
MMP production
unit
MHA production
unit
Methionine
hydroxy analog
M
http://www.intratec.us/analysis/methionine http://www.intratec.us http://www.intratec.us/che http://WWW.CHEMENGONLINE.COM
Chemical Engineering February 2017

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