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Transcript of Chlor Akali Industry
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CHLOR-ALKALI
INDUSTRY
Sodium Hydroxide Production
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ELECTROLYSIS
Electrolysis is the means of decomposing
substances by passing an electric current
through them.
Sodium Chloride in solution, called Brine,
during an electrolysis process produces:
Sodium Hydroxide, Chlorine and Hydrogen.
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ELECTROLYSIS OF
BRINE
Brine could be electrolysed by using three
(3) different cells:
Diaphragm Cells
Mercury Cells
Membrane Cells.
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CHLOR-ALKALI
MANUFACTURING PROCESS
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HOW SODIUM HYDROXIDE
IS GENERALLY PRODUCED
When NaOHis dissolved in water, it decomposes/splits into Na+
cations and Cl-
anions. The chloride ions are oxidised at the anode toform chlorine (gaseous form of chloride). Water molecules(H2O) are
reduced at the cathode to form hydrogen gas and hydroxide
anions(OH-). Sodium Hydroxide is formed when the sodium ions in
the solution reacts with the hydroxide produced at the cathode.
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DIAPHRAGM CELLS
A diaphragm cell is a rectangular- shaped box. It
consists of two electrodes, namely: anode and
electrode. The anodes are metallic and are supported
from the bottom with copper base plates. The cathodes
are metal screens or punch plates connected from one
end to the other end of the rectangular tank. Asbestos
is dispersed as a slurry in the bath. It is vacuum
deposited on the cathodes forming a diaphragm.
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DIAPHRAGM CELLS
(ANODE)
Brine, in a saturated form, enters the rectangular
tank from the anode compartment. During
electrolysis, the chloride ions are attracted to the
anode, where it loses electrons. As a result,
chlorine gas is formed and exists from the anode
compartment. The Cl2(aq) is saturated with H2O(aq)
at a partial pressure of water over the anolyte
(electrolyte on the anode).
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DIAPHRAGM CELLS
(CATHODE)
The sodium ions are transported from the anode compartment to
cathode compartment. The sodium ions move by a flow of the
solution and electromigration (the movement of ions under the
influence of p.d). This solution contains the unreacted sodium
chloride, the Na+ ions and water. Hydroxide ions and hydrogen
are generated at the cathode when water molecules are
electrolysed. The diaphragm resists the back migration of OH-
ions, which would otherwise react with Cl2 in the anode
compartment. The sodium ions combine with the hydroxide ions
and forms sodium hydroxide, aka, caustic soda.
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DIAPHRAGM CELLS
(REACTIONS)
2Cl- ==> Cl2 + 2e- anadoic reaction
Na+ + e- ==> Na cathadoic reaction
2H2O + 2e- ==> 2OH- + H2 cathadoic reaction
2Cl- + 2H2O ==> Cl2 + H2 + 2OH- overall ionic
reaction
2NaCl + 2H2O ==> Cl2 +2NaOH + H2
overall reaction
http://electrochem.cwru.edu/ed/dict.htmhttp://electrochem.cwru.edu/ed/dict.htm -
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DIAPHRAGM CELLS
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MERCURY CELLS
A mercury cell consists of steel bottoms with rubber-
coated steel sides. There are end boxes for brineand mercury feed and exit streams with a flexible
rubber or rubber- coated steel cover. The anodes
are made of adjustable metal and they are hung
from the top. Mercury forms the cathode flowing on
the inclined bottom. Current therefore flows from the
steel bottom to the flowing mercury.
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MERCURY CELLS (ANODE)
Saturated brine is fed from the end box
and electrolysed at the anode to
produce chlorine. The chlorine flows
from the top portion of the trough andthen exits.
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MERCURY CELLS
(CATHODE)
The generated sodium ions reacts with the mercury to
form sodium amalgam. The amalgam flows out the end
box vertical, cylindrical tank. The decomposer contains
water and it is packed with graphite particles. The sodium
amalgam reacts with water and produces caustic soda
and hydrogen. H2(g) saturated with H2O(aq) and Hg(g) exitfrom the top. The caustic soda flows out the decomposer.
The unreacted brine flows out the exit end box. The
mercury from the decomposer is pumped back to the cell.
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MERCURY CELLS
(REACTIONS)
2Cl- ==> Cl2 + 2e- anadoic reaction
2Na+
+ 2Hg + 2e-
==> 2Na (in Hg) cathadoic reaction
2Cl- + 2Na+ + 2Hg ==> Cl2 + 2Na (in Hg) overall cell
reaction
2Na (in Hg) + 2H2O ==> H2 +2NaOH + Hg decomposer
reaction
2NaCl + 2H2O ==> Cl2 +2NaOH + H2 overall process
reaction
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MERCURY CELLS
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MEMBRANE CELLS
A membrane cell consists of an anode and
cathode compartments separated by an ion-exchange membrane. The separator is
generally a bi-layer membrane (made of
perfluorocarboxylic and perfluorosulfonic
acid- based films) sandwiched between the
anode and the cathode.
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MEMBRANE CELLS
(ANODE)
Saturated brine is fed to the anode
compartment. After electrolysis at the anode,
chlorine is produced and released. The
sodium ions and some water migrate through
the membrane to the cathode compartment.
The unreacted sodium chloride and other
inert remain in the anolyte.
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MEMBRANE CELLS
(CATHODE)
Hydroxide ions at the cathode are produced
during the course of hydrogen gas evolution fromwater molecules. Sodium ions react with the
hydroxide ions forming caustic soda. H2(g)
saturated with H2O(l) exits from the cathode
compartment. Only part of the caustic soda is
withdrawn from the cathode compartment. The
remaining caustic is diluted and returned to the
cathode compartment.
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MEMBRANE CELLS
(REACTIONS)
2Cl- ==> Cl2 + 2e- anadoic reaction
Na+ + e- ==> Na cathadoic reaction
2H2O + 2e- ==> 2OH- + H2 cathadoic reaction
2Cl- + 2H2O ==> Cl2 + H2 + 2OH- overall ionic
reaction
2NaCl + 2H2O ==> Cl2 +2NaOH + H2
overall reaction
http://electrochem.cwru.edu/ed/dict.htmhttp://electrochem.cwru.edu/ed/dict.htm -
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MEMBRANE CELLS
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SUMMARYAll three basic cell technologies generate chlorine at the anode, and
hydrogen along with sodium hydroxide in the cathode compartment
(or in a separate reactor for mercury cells. The distinguishing
difference between the technologies lies in the manner by which the
anolyte and the catholyte streams are prevented from mixing with
each other, thus to ensure purity of NaOH. Separation is achieved in
a diaphragm cell by a separator, and in a membrane cell by an ion-
exchange membrane. In mercury cells, the cathode itself acts as a
separator by forming an alloy of sodium and mercury (sodium
amalgam) which is subsequently reacted with water to form sodium
hydroxide and hydrogen in a separate reactor.
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ANODES AND CATHODES
The anode in all technologies is titanium
metal coated with an electrocatalytic layer of
mixed oxides.
The cathode is typically steel in diaphragm
cells, nickel in membrane cells, and mercury
in mercury cells.
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1. Pulp and Paper
2. Textiles
3. Bleach
Manufacturing
4. Petroleum Products
5. Aluminium
Production
6. Chemical
Processing
USES OF CAUSTIC SODA
Other small applications for
caustic soda include watertreatment, cleaners for beverage
bottles, cleaning products such
as drain and pipe cleaners, oven
cleaner and other householdcleaning products and home
soap making.
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CAUSTIC AND ITS USES
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Chlorine bleaching
of wood pulp and
dioxin emissions to
the environment.
Ozone layer
depletion.
ENVIRONMENTAL ISSUES
CHLORO-ALKALI INDUSTRY
Polyvinyl chloride
plastic.
Mercury emissions.
Asbestos
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END OF CHLOR-ALKALI
MANUFACTURING
PROCESS
This power point was brought to you by students of Form 5 S
Namely:
Simona Broomes, Kimberly Manbodh, Shenelle Khan, Ryan Patiram