Chemical Engineering October 2020 - 21

Technology Profile
Sodium Chlorate Production
By Intratec Solutions
S
odium chlorate (NaClO3;
also known as chlorate of
soda) is an odorless inorganic
salt with colorless
crystals and a cooling/saline taste.
The compound is soluble in water
and most organic solvents. The main
uses of sodium chlorate derive from
its oxidizing characteristics, and its
main application is as a bleaching
agent in a variety of processes. Because
of its high oxidizing power, sodium
chlorate is generally not found
naturally. Its first uses date to the beginning
of the 20th century, however,
its industrial production only began
at the end of the 1960s.
The commercial-scale synthesis of
sodium chlorate is mainly based on
the electrolysis of a hot sodium chloride
solution - similar to the widely
used
chlor-alkali processes. The
main difference lies in the fact that
there is no need to prevent the reaction
between chlorine and hydroxide
ions. The on-purpose synthesis of
sodium chlorate through chemical
reactions is not commonly employed
on industrial scale.
The process
The present analysis discusses an industrial
process for sodium chlorate
production. The process comprises
two major sections: (1) electrolysis
and (2) sodium chlorate recovery
(Figure 1).
Electrolysis. In a salt dissolver,
a brine solution is prepared from
sodium chloride raw material and
process water. After purification of
the NaCl solution, hydrochloric acid
Hydrogen
CW
ST
3
CHW
Purge
Process water
Sodium chloride
9
1
2
4
5
6
Sodium
Chlorate
1. Salt dissolver
2. Electrolysis
3. Scrubber
4. Crystallizer
5. Dryer
6. Silo
7. Cooling tower
8. Boiler
9. Chiller
CHW Chilled water
CW Cooling water
ST
Steam
FIGURE 1. The diagram shows the production process for sodium chlorate
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8
7
Sodium chloride,
electricity
Electrolysis
Sodium
chlorate
Absorption
Chlorine dioxide,
sodium hydroxide
FIGURE 2. Brine electrolysis is the primary production pathway for sodium chlorate, but others exist
Hydrogen
Sodium chlorite
■ Raw material ■ Process ■ Main product ■ Other product(s)
and sodium dichromate are added
(to increase cell efficiency and to
protect electrodes from corrosion,
respectively). The purified, acidified
solution is then electrolyzed. At the
cathodes, hydrogen gas is generated
and released along with impregnated
chlorine. The released gas is
collected in a column that prevents
chlorine emissions through caustic
scrubbing. At the anodes, chlorine
atoms generated from the electrolysis
combine with water and free
ions to form hypochlorous acid and
sodium hypochlorite. Hypochlorous
acid and sodium hypochlorite then
react to form sodium chlorate. Reaction
tanks downstream from the
electrolytic cells provide a longer
residence time for the chemical reaction
between hypochlorous acid
and sodium hypochlorite to take
place. The liquor from the electrochemical
cell is finally transferred to
the crystallizer in the sodium chlorate
recovery section.
Sodium chlorate recovery. Prior
to crystallization, residual hypochlorites
are eliminated through heating
and addition of chemicals. The cells'
liquor, virtually free of hypochlorites,
is heated, subjected to vacuum
evaporation and finally crystallized
under vacuum. The sodium chlorate
crystals are recovered by centrifugation,
washed and fed to a dryer. Dry
sodium chlorate is conveyed to silos
prior to being packed into bulk bags.
Production pathways
Industrial-scale production of sodium
chlorate is primarily based on
brine electrolysis. Figure 2 presents
different pathways for the production
of sodium chlorate.
Economic performance
The total operating cost (raw materials,
utilities, fixed costs and depreciation
costs) estimated to produce
sodium chlorate was about $440 per
ton of sodium chlorate in the fourth
quarter of 2016. The analysis was
based on a plant constructed in the
U.S. with the capacity to produce
80,000 metric tons per year of sodium
chlorate.
This column is based on " Sodium
Chlorate Production - Cost Analysis, "
a report published by Intratec.
It can be found at: www.intratec.us/
analysis/sodium-chlorate-production-cost.
■
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.

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Chemical Engineering October 2020

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