Manufacture of caustic soda and chlorine using electrolysis process ........... CONTD . http://www.slideshare.net/AnkushGupta40/phase23
MANUFACTURE OF CHLORINE–
SODA USING ELECTROLYSIS
COLLEGE OF ENGINEERING
Introduction to Caustic soda / Chlor
• The Chlor-Alkali industry in India forms an important component of
basic chemicals industry ,comprising around 74% of the basic
chemicals production in India.
• The Chlor-Alkali Industry in the country produces mainly Caustic
Soda, Chlorine and Soda Ash.
• The geographic distribution of Chlor-alkali processes world-wide
differs appreciably (production capacity of chlorine):
-western Europe, predominance of mercury cell process (June
-United States, predominance of diaphragm cell process: 75%
-Japan, predominance of membrane cell process: >90%
PROPERTIES OF CHLORINE-CAUSTIC
Physical State Solid.
Appearance White pellets.
Vapor Pressure 1 mm Hg @ 739 CO
Boiling Point 1390 CO @ 760 mm Hg
Freezing/Melting Point 318 CO
Specific Gravity/Density 2.13 g/cm3.
Molecular Formula NaOH.
Molecular Weight 40.00
PH 14 (5% aq soln).
APPEARANCE AND STATE Colorless gas at normal temperature and
MOLECULAR WEIGHT 2.016
BOILING POINT (1 atm) 423.0 _F (-252.8 _C)
SPECIFIC GRAVITY (Air =1) 0.06960
FREEZING POINT/MELTING POINT -434.5 °F (-259.2 _C)
GAS DENSITY (At 70 F (21.1 C) and 1 atm): 0.00521 lb/ft3(0.08342 kg/m3)
SOLUBILITY IN WATER (Vol/Vol at 60 F (15.6
SPECIFIC VOLUME (At 70 F (21.1 C) and 1 atm 192 ft3/lb (11.99m3/kg)
NAME OF AUTHOR YEAR OF
RESEARCH TOPIC DESCRIPTION
process in environmental
Use of bipolar membrane is
valuable chemicals from
effluents& waste gases
Application of ion exchange
membrane “green” power
source is also discussed
2 yohannes kiros
2008 Low energy consumption
in chlor alkali cells using
Gas diffusion electrode for
use as a cathode to
replace the traditional
electrode in chlor-alkali
associated with ‘flooding’
or‘wetting’ are minimised
by attempt to stablize
RESEARCH TOPIC DESCRIPTION
ms o.ozoute &
2011 Studies on production
of caustic soda using
The research served as an
encouraging inquistive foundation
into possibility of producing
caustic soda directly from solar
powered electrolytic diaphragm
cells in comparison with present
conventional modes of
electrochemical production .
protection in process
•. Protection of environment
through implementation of
effluent treatment productio
integrated process for
minimization of waste and
•Anode destruction of organic
pollutants and new
techniques for purification of
RESEARCH TOPIC DESCRIPTION
5 Subrata Basu,
and Sujata G.
2013 Characteristic Change
of Effluent from a Chlor-alkali
India due to Process
The main focus of this paper
is on the evaluation of waste
minimization at source due to
process modification. The
improvement of the treatment
of effluent is also duly
6 A. Rezaee, J.
Yamini and M.T.
2005 Removal of Mercury
•The removal of mercury ions
by cellulose of Acetobacter
investigated in the synthetic
and chlor-alkali wastewater.
mercury ion removal from
wastewater by aluminum
sulfate and ferric
chloride was also determined.
• There are 3 types of electrolytic
processes used in the production of
(1) The diaphragm cell process
(2) The mercury cell process
(3) The membrane cell process
• A salt solution is electrolyzed by
the action of direct electric
current that converts chloride ions
to elemental chlorine. The overall
process reaction is:
In all 3 methods, the chlorine is
produced at the positive electrode
(anode) and the caustic soda and
hydrogen are produced, directly or
indirectly, at the negative electrode
• In the diaphragm cell process, there are two
compartments separated by a permeable diaphragm.
• Brine is introduced into the anode compartment and
flows into the cathode compartment.
• Similarly to the Membrane Cell, chloride ions am
oxidized at the anode to produce chlorine, and at the
cathode, water is split into caustic soda and hydrogen.
• The diaphragm prevents the reaction of the caustic soda
with the chlorine.
• A diluted caustic brine leaves the cell.
• The caustic soda must usually be concentrated to 50%
and the salt removed. This is done using an evaporative
• Electric current flowing through the cell decomposes the brine passing
through the narrow space between the electrodes, liberating chlorine
gas at the anode and metallic sodium at the cathode
• The chlorine gas is accumulated above the anode assembly and
discharged to the purification process.
• As it is liberated at the surface of the mercury cathode and the sodium
immediately forms an amalgam (a 'mixture' of two metals)
• The liquid amalgam flows from the electrolytic cell to a separate
reactor, called the decomposer, where it reacts with water in the
presence of a graphite catalyst to form caustic soda (sodium hydroxide)
and hydrogen gas.
• The sodium-free mercury is fed back into the electrolyser and reused.
• This technology uses water-impermeable ion-conducting membrane.
• The membrane is made of a special resin which permits cations
(positive ions) to pass through.
• The anode chamber of a membrane electrolytic cell is filled with
brine, and the cathode chamber with water.
• These ions migrate when a current is applied: the positively charged
sodium ions pass through the membrane to the cathode chamber,
while the negatively charged chloride ions are discharged on the
anode surface to form chlorine gas .
• Water in the cathode chamber partly dissociates into hydrogen and
• The hydrogen ions capture electrons on the cathode surface to form
• The hydroxide ions are attracted to the anode, but blocked by the
membrane, and react with the sodium ions from the anode chamber
to form caustic soda (sodium hydroxide, NaOH)
SELECTION OF THE PROCESS
MEMBRANE CELL PROCESS
• The membrane cell process has inherent
ecological advantages over the two older
processes, as it does not use mercury or
• It is the most energy efficient process.
• It is extremely safe to operate it and it produces
a consistently high quality of caustic soda.
• The standard free energy, ΔGº tells us the thermodynamic
feasibility of a reaction. Since the standard electrode
potential of a reaction, E° and ΔG° are intimately linked;
one can use the standard electrode potentials of a reaction
to calculate the thermodynamic feasibility of a reaction.
n= no of electrons transferred
F= Faraday constant = 96630 J/V.mol
Eo = Cell voltage
So, ΔGo = -1*96630*6 -579780 J/mol
ΔGO << 0
SO THIS REACTION IS FEASIBLE
Pressure & Temperature
Combinations for condensing gas
•High pressure (7-10 atms), water cooling
•Medium pressure (2-3 atms), Refrigeration at
•Low pressure (5-10 cm H2O), Refrigeration at
• Basis of Product : 1 ton of Cl2 ; 1.15 tons of NaOH(98%) .
• Plant capacities : 100-1000 tons/day of Cl2 in a series of electrolysis
units each producing 0.5 – 2 tons Cl2 per day
Sulphric Acid (98%) 5-6 kg
Sodium hydroxide 10-15 kg
Steam 11 tons
Electricity 2900 KWH
• DIAPHRAGM CELL TYPE
• Anode : Cl - - e ½ Cl2
• Cathode: Na+ H2O + e Na+ + OH- + ½ H2
• Overall: NaCl + H2O NaOH + ½ H2 + ½ Cl2
• MERCURY CELL PROCESS
• Anode: Cl- - e ½ Cl2
• Cathode: Na+ + e Na
: Na + Hg NaHg(amalgam)
• Denuding: NaHg + H2O NaOH + ½ H2 + Hg
• Overall: NaCl + H2O NaOH + ½ H2 +Cl2
• 2NaCl + 2H2O 2NaOH + H2 +Cl2
Factors affecting Plant location
• Adequate Supply of Raw materials.
• Proximity to the market — Minimum supply time. Relative cost low
(one third of caustic plants are attached to paper and rayon mills).
• Transport Facilities — Good capacity and speedy transportation.
• Supply of Labor — Cheap Labor Supply.
• Power— Regular Power Supply for operation machinery at full
• Supply of Capital — Required for Initial promotion and Expansion.
• Natural Factors — Land, Water, Climate(Agriculture based
• Political Factors — Favorable Development Policies.
• Government Subsidies — Exemptions, Rebates and Subsidies.
• Historical and religious factors.
Need careful analysis of such factors as cheap power and salt sources
coupled with risisng cost of transportation.
Locations of caustic soda plants
NAME PROCESS USED
Durgapur Chemicals Ltd
J.K Chemicals Ltd ,thane
Sirpur Paper mills ,sirpur
Chemfab Alkalies ltd
Rohtas Industries ltd ( bihar) Mercury cell
1 ) Subrata Basu , Swapan Kumar Mukhopadhyay , Amitava
Gangopadhyay and Sujata G. Dastidar “International Research
Journal of Environment Sciences Characteristic Change of Effluent
from a Chlor-alkali Industry of India due to Process Modification”
2) S.Koter.A.Warszawski “Polish Journal of Environmental Studies
Electro- membrane Processes in Environment Protection” (2000)
3) Yohannes Kiros and Martin Bursell “International Journal
Electrochemistry Science Low Energy Consumption in Chlor-alkali
Cells Using Oxygen Reduction Electrodes (2008)”
4) Rezaee, J. Derayat, S.B. Mortazavi,Y. Yamini and M.T. Jafarzadeh
“American Journal of Environmental Sciences Removal of Mercury
from Chlor-alkali Industry Wastewater using Acetobacter xylinum
5) Dryden’s outlines of chemical technology (2012)