chlor akali industry

8/2/2019 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)


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)


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

chlor akali industry

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