Sodium hydroxide also known as caustic soda with chemical formula NaOH found in many forms caustic soda lye, flakes, granules and solid. Produced using three different process Mercury Cell, Diaphragm cell, Membrane Cell methods

1. Article written and published
By
www.worldofchemicals.com
3 MODERN SODIUM HYDROXIDE
MANUFACTURING METHODS

2. SODIUM HYDROXIDE HISTORY
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Sodium hydroxide (NaOH) an inorganic compound with
following synonyms
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Caustic soda
Lye
Sodium hydrate
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NaOH widely used inorganic industrial chemical. NaOH is having
certain properties like
Sodium hydroxide's chemical formula is NaOH
NaOH molecular weight of 39.997 g/mol
Sodium hydroxide is contain ph of ~12-14

3. SODIUM HYDROXIDE CHARACTERISTICS
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Sodium hydroxide characteristics can be mentioned as
Raw material for various industrial products
Co-product in chlorine synthesis
Strong base
Highly corrosive
Auxiliary chemical
Odorless material
Caustic soda is available in two forms - Caustic soda lye and Caustic soda
solid. Solid form of caustic soda can be in the form of
Caustic soda flakes
or
Caustic soda granules
Pure form of sodium hydroxide also available as
Sodium hydroxide pellets
Sodium hydroxide flakes
Sodium hydroxide granule
Sodium hydroxide solution

4. INDUSTRIAL APPLICATIONS OF CAUSTIC SODA
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Caustic soda has wide variety of industrial sectors like
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In pulp and paper processing industry caustic soda used at the
stages like bleaching process, in de-inking of waste paper, and in water
treatment.
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Next major industry like textile industry caustic soda is used to process
cotton and synthetic fibers
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Caustic soda is utilized more in the soap and detergent industry.
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Other caustic soda uses include
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In oil and gas industry – to remove pungent smells
In household cleaning products
In beverage bottles
In home soap making
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5. 3 SODIUM HYDROXIDE MANUFACTURING
METHODS
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Sodium Hydroxide solutions are produced by three
different technologies
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Mercury cells
Membrane cells
Diaphragm cells
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Each of above processes utilizes sodium chloride (NaCl)
salt as the primary raw material. Electrolytic splitting of
salt results in products like chlorine and sodium ion (Na+).
In turn Na+ will react with water in the mercury cell to
form Sodium hydroxide and Hydrogen as by product.

6. MERCURY CELL

7. MERCURY CELL CONT ..
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In the Mercury Cell Process saturated brine voyages
down a steel trough roughly 15 meters in length and
one meter wide between a streaming film of mercury
(the cathode) and titanium plates (the anodes). Direct
current is connected between the anode and
cathode. Chlorine freed at the anodes gathers above
the brine and is begun as a hot, wet and corrosive
gas.
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Sodium ions are released at the surface of the
streaming mercury cathode, forming an amalgam of
low concentration with the mercury, which streams
out of the cell without reacting with the water or
chlorine.

8. MERCURY CELL CONT…
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The mercury cell thus has two products
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(i) Hot, wet chlorine
(ii) Sodium amalgam
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The soda cell or decomposer is a cylindrical steel trough
loaded with graphite balls or graphite electrodes. The
sodium amalgam is passed, along with pure water, into
the decomposer, where it reacts to transform Sodium
hydroxide as a controlled 50 per cent aqueous solution
and hydrogen gas, liberating fee mercury, which is reused
again to the electrolytic cell. The graphite provides a
surface that expedites this reaction.

9. MERCURY CELL CONT…
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The following two types of reactions called brine
cell and the soda cell respectively.
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Brine Cell
2Cl = Cl2 + e
Na + e = Na
Na + Hg = Na/Hg
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Soda Cell
2Hg
2 Na/Hg + 2 H2O = 2NaOH + H2 +

10. DIAPHRAGM CELL

11. DIAPHRAGM CELL CONT ..
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This method produces 71 per cent of Sodium hydroxide.
Diaphragm Cell process utilizes asbestos or alternate substitutes
to asbestos, to separate the co-products Sodium Hydroxide
(Caustic Soda) and Chlorine. The production of 50 per cent
NaOH occurs primarily outside of the electrolytic cell.
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The diaphragm cell produces a very weak 'cell liquor,' that
contains 12-14 per cent, by weight, NaOH and the constant
volume of NaCl salt. The cell liquor is subsequently evaporated in
a three or four 'effect' evaporation method to a final nominal
concentration of 50 per cent NaOH by weight. The surplus salt is
precipitated and filtered through the evaporation method for
subsequent reuse/recycle. This method produces the lowest
quality electrochemical NaOH solutions.

12. DIAPHRAGM CELL CONT ..
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he quality considerations with respect to the
diaphragm cell produced Caustic solutions include
comparatively high salt, chlorates, carbonates, and
sulfates. Salt, as NaCl, concentrations are typically
1.0 per cent, with maximums ranging from 1.1 to 1.3
weight per cent, counting on producer.
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The diaphragm cell created Caustic Soda (NaOH) is
usually referred as Diaphragm Cell Grade. It is
conjointly known as Commercial Grade, Technical
Grade, and occasionally Technical Diaphragm or
other similar combinations.

13. DIAPHRAGM CELL CONT ..
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An additional 'grade' of Caustic Soda (NaOH) produced
by the diaphragm cell method is the sublimate grade. The
production of sublimate Grade involves the further
evaporation of the 50 per cent Diaphragm Grade NaOH
solution to cut back the salt concentration. The higher
concentration solution is then re-diluted to the 50%
concentration that is commercially available as sublimate
grade Caustic Soda.
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Common uses include process and sewer water
neutralization, textiles production, soaps and detergents
and aluminum production. These uses and applications
typically can confer with the Caustic Soda as any of the
varied grades.

14. MEMBRANE CELL

15. MEMBRANE CELL CONT ..
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This method produces approximately 13 per cent of Sodium Hydroxide.
The membrane cell method utilizes a selective membrane that
separates the Chlorine and Sodium ions. The membrane permits the
Sodium ion to migrate across the membrane whereas keeping the
Chlorine gas and salt (brine) solution in a compartment on the opposite
facet of the membrane.
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The Sodium ion is reacted with refined water as within the mercury cell
to provide the Caustic Soda (NaOH). Evaporation is employed, as within
the diaphragm method, to lift the concentration up to the nominal 50
weight per cent solution. The salt concentrations are not targeted as
considerably during this evaporation method attributable to the selective
diffusion nature of the membranes as well as the reduced quantity of
evaporation needed during this method opposed to the diaphragm
evaporation.
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The Caustic Soda produced by the membrane cell process is most
typically brought up as Membrane Grade. It conjointly contains a
growing acceptance as a Rayon Grade product in all areas outside of
rayon fiber production.

16. REFERENCE
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Reference
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[1] http://www.essentialchemicalindustry.org/chemicals/sodium-hydroxide.html
[2] http://www.oocities.org/tiger_dil3000/
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Image Reference
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Fig. [1] Mercury cell © From
http://www.essentialchemicalindustry.org/chemicals/chlorine.html#membrane_ce
ll
Fig. [2] Diaphragm cell © From
http://www.essentialchemicalindustry.org/chemicals/chlorine.html#membrane_ce
ll
Fig. [3] Membrane cell © From
http://www.essentialchemicalindustry.org/chemicals/chlorine.html#membrane_ce
ll