Caustic soda or caustic lye is sodium hydroxide. It is an inorganic and highly alkaline compound available in the several forms. It is a strong base and is extensively used chemical and has varied applications. The major user of caustic soda are aluminum industry, pulp and paper industry and chemical industry.
Various forms of Caustic Soda
Liquid Caustic Soda : Liquid caustic soda is dangerous compared to its solid form
Caustic Soda Solid
Caustic Soda Flakes
Caustic Soda Pellets
Caustic Soda Pearls
There are two methods for the production of sodium hydroxide: Solvay process and Chloro-alkali process.
The soda ash obtained from the Solvay process is treated with calcium hydroxide in a double displacement reaction, where the carbonate is replaced by the hydroxide ion to produce sodium hydroxide.
Na2CO3 + Ca(OH)2 Ã? 2NaOH + CaCO3
The chloroalkali process replaced the Solvay process and is preferred over it. It is used in the production of chlorine gas and caustic soda is a by-product. In this process, saturated brine is passed over the electrolytic cell, which ionizes the sodium and chlorine ions. At the anode, it oxidizes to chlorine gas. Water at the cathode is reduced to hydrogen and hydroxide ions.
Anode: 2Cl- Ã? Cl2 + 2e-
Cathode: 2H2O + 2e- Ã? H2 + 2OH-
An ion-permeable membrane allows the passage of sodium ions which reacts with hydroxide ions to from sodium hydroxide in solution. Three types of cells are used in this process namely, Mercury cell, diaphragm cell, membrane cell.
Caustic Soda is used to remove grease, oils, fats deposits from production equipment, mainly stainless steel and glass. It is heated with water to perform the cleaning action. It is also present in drain openers for domestic use to unclog drains.
In the food industry, caustic soda is used for washing-off or chemical stripping of fruits, vegetables, chocolates etc. It is also added as a pH balancer in some foods. Sometimes olives are soaked in lye solution to soften them. It is also used in soft drinks processing and ice cream thickening.
The paper industry is one of the major applications of caustic soda. The main use is for the requirement of an alkaline environment during the various stages of the manufacturing process such as delignification, extraction bleaching. It is also used in the Kraft process for separating lignin from cellulose fibers.