Sodium hydroxide, otherwise called Caustic Soda, is an inorganic compound with chemical formula NaOH. It is called caustic soda because it is highly corrosive in nature. It is available in many forms in the industry, and the most common forms are caustic soda flakes and caustic soda pearls. This product has several industrial applications but it is highly reactive, so it has to be used carefully lest, it can cause skin irritation.
Properties of Caustic Soda:
- White solid
- Highly caustic
- Strong base
- Soluble in water, ethanol and methanol
- Readily absorbs water (hygroscopic) and carbon di oxide from the air
- Strong electrolyte
- Not volatile, but can rise easily in air as an aerosol
- Dissolution of solid caustic soda in water in highly exothermic
Manufacturing Process for Caustic Soda:
Solid caustic soda is manufactured by evaporation of water from liquid caustic soda and then solidification into the required shape. Liquid caustic soda is manufactured by various processes such as the electrolysis of sodium hydroxide - technical grade, the Chloralkali process which is the electrolysis of sodium chloride, or the ammonia-soda process which is the reaction of brine and limestone.
Ammonia-soda process equation:
2 NaCl + CaCO3 → Na2CO3 + CaCl2
Chloralkali electrolyses process equations:
2NaCl + 2H2O → Cl2 + H2 + 2NaOH
2Na+ + 2Cl- + 2Hg → 2Na-Hg + Cl2
2Na-Hg + 2H2O →2NaOH + H2 + 2Hg
Caustic Soda Solid has various applications in different industries. Some of the main applications are:
Caustic Soda is used for the treatment of wood for making paper. Also, both sulphate and sulphite pulps are purified by removing lignin compounds in the caustic extraction stages of the multistage bleach plants. In some paper kraft mills, caustic soda is used as a make-up chemical. It is also used in the initial treatment of deinking secondary fibres.
Caustic soda is used for scouring, bleaching, de-sizing, lustring and mercerizing in textile industry. It is mainly used in processing of cotton and for dyeing synthetic fibres such as nylon and polyester.
Soap and detergents industry
It is used in Saponification process. It saponifies fats into water soluble sodium-based soaps. In detergent industry it is also used in the manufacturing of anionic surfactants.
Caustic soda is used for the refining of petroleum products. It is used as an absorbent for carbon dioxide in light petroleum fractions, for sulphides in the purification of various fractions, and with chlorine, for hypochlorite sweetening, a treatment step which involves the removal of various sulphur compounds.
It is used in the refining of bauxite ores to produce alumina by precipitation, which is the raw material for the production of aluminium metal. It is also used as an etchant in the finishing and chemical milling of aluminium products.
It is used in dyes and also in water treatment. It is even used as a feedstock for downstream products such as solvents, fabrics, adhesives, inks, pharmaceuticals etc.
Caustic Soda is used in the production of renewable fuels, by being used for pH adjustment and formation of in situ sodium methylate in bioethanol and biodiesel processing.