Chemical Engineering August 2015 - 39

Technology Profile
Lactic Acid Production via Glucose Fermentation
By Intratec Solutions
L
actic acid is a naturally occurring
chiral acid most commonly
found in the L(+) form. Driven
by a recent demand for more
sustainable products, the lactic acid
market has expanded beyond the
food, pharmaceutical and cosmetics
industries. Currently, a major growth
application is for the production of
polylactic acid (PLA) polymer. This biodegradable
polymer has the potential
to replace petrochemical-based plastics
in applications such as packaging,
paper coating, fibers, films and a wide
range of molded plastic items.
The process
Figure 1 depicts a process for lactic
acid production via glucose fermentation
similar to that developed by
Purac (now Corbion; Amsterdam, the
Netherlands; www.corbion.com). This
process generates an 88 wt.% lactic
acid solution in water that can be
used as the raw material in polymerization
processes. Rigorous control of
fermentation conditions and additional
purification steps are necessary to ensure
both optically and chemically pure
lactic acid. The quality of the PLA produced
from it depends on the purity.
Fermentation. Glucose solution is
fed to the fermenter. It undergoes a
continuous anaerobic bacterial fermentation,
and is converted to lactic
acid. The fermentation temperature is
controlled by circulating cooling water
through internal coils, and the pH is
controlled by the addition of CaCO3
solution, which reacts with lactic acid
to form calcium lactate.
Sulfuric acid
Glucose
Calcium
carbonate
1
Biomass
CW
2
ST
4
Extractant
solution
3
CW
Calcium
sulfate
ST
5
ST
6
7
ST
Waste stream
12
Figure 1. A lactic-acid production process from glucose, similar to the Purac process
ChemiCal engineering www.Chemengonline.Com august 2015
9
ST
CW
ST
13
14
37
10
11
Waste
stream
Waste stream
CW
Lactic
acid
Recovery. The fermentation broth is
decanted and concentrated solids are
filtered, removing mostly biomass. The
aqueous solutions from the decanter
and from the filter are acidified with
sulfuric acid to convert calcium lactate
into soluble lactic acid and CaSO4,
which precipitates. The slurry outlet
stream from the acidification vessel is
fed to a belt filter for solids removal.
The resulting aqueous filtrate is concentrated
in an evaporator, then fed to
ion-exchange columns for purification.
Purification. Concentrated lactic acid
is sent to a solvent-extraction system.
First, it is contacted with an organic extractant
solution, forming two phases:
a lactic-acid-rich organic phase and
an aqueous phase containing most of
the contaminants. The organic phase
is then washed with water to remove
contaminants. Next, it is contacted
with water at 80ºC to transfer the lactic
acid into the aqueous phase.The resulting
organic phase is washed with
an NaOH solution and then with water
to recover the extractant solution,
while the lactic-acid-rich aqueous solution
is sent to an evaporator.The concentrated
lactic acid stream is fed to a
distillation system where light ends are
removed. Heavy ends are hydrolyzed
and recycled to the process. Lactic
acid is recovered as a side stream.
Economic performance
An economic evaluation for a lacticacid
production plant was conducted,
assuming a facility with a nominal capacity
of 100,000 ton/yr of lactic acid
solution (88 wt.%) constructed on the
Sodium hydroxide solution
Process water
ST
8
17%
13%
13%
11%
n Raw materials
n Calcium sulfate disposal
n Utilities
n Fixed costs
n Depreciation
Figure 2. Production costs breakdown
U.S. Gulf Coast, and including storage
capacity equal to 20 days of operation
for feedstock (no product storage). Estimated
capital expenses to construct
the plant are ~$200 million, while operating
expenses are estimated at
~$1,300/ton of lactic acid solution.
Global perspective
Major production-cost components for
this process are raw material acquisition
(mainly glucose and CaCO3) and
CaSO4 byproduct disposal (Figure 2).
Recent improvement efforts focus on
using less costly cellulosic material
to obtain fermentable sugars, and on
developing low-pH-tolerant bacteria
strains, which would decrease both
CaCO3 use and CaSO4 generation. 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.
1. Fermenter
2. Decanter
3. Acidification vessel
4. Rotary filter
5. Belt filter
6. Evaporator
7. Ion exchange beds
8. Solvent extraction system
9. Evaporator
10. Light end column
11. Heavy end column
12. Hydrolysis reactor
13. Cooling tower
14. Steam boiler
CW Cooling water
ST Steam
46%
http://www.corbion.com http://www.intratec.us http://www.intratec.us/che http://www.Chemengonline.Com
Chemical Engineering August 2015

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