Liquid Caustic Soda

Commercially known as Caustic Soda, Sodium Hydroxide is present in different products and applications of our daily lives.

Electrolysis cells are paramount for the chlorine-soda sector. Chlorine and alkali industrial production process by electrolysis can be carried out with three technologies:

  1. Diaphragm cell (Commercial Soda)
  2. Mercury cell (Rayon Soda)
  3. Membrane Cell (Membrane Soda), which also generates Caustic Soda (NaOH), Chlorine (CI2) and Hydrogen (H2)

Regardless of the manufacturing process, it is a viscous, colorless, slightly cloudy liquid free of suspended materials. The product is sold in bulk and transported in a tanker truck.

When sodium chloride goes through temperatures lower than those of the production site, it can precipitate as white crystals. The result is a water sodium hydroxide solution in the declared base (about 50% of sodium hydroxide on its weight).

Manufacture Process: Cubatão and Bahía Blanca Plant

Diaphragm Process – Commercial Liquid Caustic Soda Production

Cubatão Plant

Commercial Caustic Soda is produced in a type of electrolytic cell in which brine flows from one compartment to the other through a porous layer (diaphragm). Caustic Soda produced during electrolysis is found with this brine (cellular liquor). This liquor then goes to an evaporation unit in which it is reduced until obtaining 50% m/m of Caustic Soda and its Sodium Chloride content is reduced to approximately 1% (in weight). 

This is the main difference with the other two processes: Sodas produced by Mercury (Rayon Soda) and Membrane (Membrane Soda) processes are almost Sodium Chloride free (<0.015% NaCl).

Mercury Process – Rayon-Grade Liquid Caustic Soda Production

Cubatão and Bahía Blanca Plant

To produce Rayon Liquid Caustic Soda by Mercury Electrolysis, we use a brine derived from a high-purity evaporated salt. The water used in the production of this Soda comes from a vapor condensation process, also very pure. Rayon Caustic Soda at 50% p/p is almost Sodium Chloride free (<0,015% de NaCl). 

Bahía Blanca Plant

In Bahía Blanca, there are two electrolysis cells units: one with Mercury Cathode Technology (Rayon Liquid Soda) and the other one with the previously mentioned bipolar membrane electrolyzer technology (Membrane Liquid Soda) 

The only difference in this unit is that all volume available to the market is treated as a mixture (Liquid Soda Solution). Due to its design, Bahía Blanca does not perform the membrane evaporation stage. Therefore, the final concentration is produced in 2 types of soda mixture tanks.

Caustic Soda Sold in Argentina has a minimum concentration of 48.5% p/p of NaOH and is almost Sodium Chloride free (<0,015% NaCl).

Membrane Process – Membrane Liquid Caustic Soda Production

Cubatão, Santo André and Bahía Blanca Plants

For this electrolysis, besides deionized water, we use brine treated in two filtration stages and purified by a bed of ion-exchange resin, where we retain the undesirable cations for the process (extremely pure brine). As Rayon-Grade Caustic Soda, membrane Caustic Soda is almost Sodium Chloride free (<0,015% de NaCl).


Technical Information - Physicochemical Features

Chemical formula


Molecular weigh


Melting point

12-15 ºC

Vapor pressure

13 mmHg at 60°C (Information of a 50% of NaOH solution per weight).

Specific weight (density)

1,52 g/cm³- 1,5506 g/cm³ at 15,5°C (range equivalent to a total alkalinity concentration between 49-51% of NaOH)


14.0 (0.5% solution)

*Non-flammable and non-combustible.

*Complete solubility in water.


Due to its alkalinity (chemistry opposed to acidity), it plays an important role in pH neutralization and correction in several segments, including in ion-exchange resins regeneration. Paper and cellulose bleaching is one of its main applications, and it’s also widely used in the chemical and petrochemicals, metallurgical (alumina production for aluminum industry), soap and detergents, textile (mercerization) and food industries.

Technical Information - Download the Liquid Caustic Soda documents

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Sodium Hypochlorite Reactor

 Hypochlorite is produced by a reaction between gaseous Chlorine and a Caustic soda solution being cooled down.


EDC Reactor

EDC (Dichloroethane) is obtained through a reaction between liquid chlorine and ethylene (inserted through a tube) and it is purified by distillation.


Hydrochloric Acid Reaction Furnace

Hydrochloric acid is produced by a controlled combustion reaction of Chlorine and hydrogen, followed by absorption in treated water.



Caustic soda is produced by electrolysis and reduced through the evaporation process.



 Then, the Soda is cooled down and stored in tanks, before being shipped.


(8) Cooling Chlorine

(9) Chlorine Withdrawal

(10) Chlorine Compression

(8) The produced gaseous chlorine is cooled down, (9) dried out and (10) compressed. After being compressed, it turns into a liquid state at low temperature.


(3) Treatment

(4) Filtration

(5) Control

(3) The PICKLE is about eliminating foreign bodies; it is filtered (4) and undergoes a strict control (5) before feeding the ELECTROLYTIC CELLS.


(3) Tratamiento

(4) Filtración

(5) Control

(3) La salmuera se trata para eliminar impurezas, se filtra (4) y pasa por un estricto control (5) para alimentar las CÉLULAS ELECTROLÍTICAS.



If there are salt (sodium chloride) and water in stock, you need to supply our transformers with electricity.


(11) Licuefacción de Cloro

(12) Almacenamiento de Cloro

(11) El cloro en esta forma se almacena en tanques (12) donde se carga en camiones especiales


Sala de Celdas

La ELECTRÓLISIS tiene lugar en la celda. Y así, la energía eléctrica actúa sobre la salmuera y la transforma en SODA CÁUSTICA, CLORO E HIDRÓGENO.

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A Soda Cáustica é produzida na eletrólise e concentrada pelo processo de evaporação.


Cell Room

The ELECTROLYSIS takes place in the cell. This way, electric energy acts on the brine and transforms it into CAUSTIC SODA, CHLORINE AND HYDROGEN.


(3) Tratamento

(4) Filtração

(5) Controle

(3) A SALMOURA é tratada para eliminar impurezas, filtrada (4) e passa sob um rigoroso controle (5) para alimentar as CÉLULAS ELETROLÍTICAS.



Next, prepare the PICKLE obtained from dissolving the salt in the water to use afterwards in the ELECTROLYSIS.