Caustic soda is used to make soaps, rayom, paper, explosives, dyestuffs, and petroleum products. It is also used in processing cotton fabric, laundering and bleaching, metal cleaning and processing, oxide coating, electroplating, and electrolytic extracting. It is commonly present in commercial drain and oven cleaners.Caustic soda is mainly used in textile in the form of caustic soda flakes or pearls. It is also known as sodium hydroxide, has a white solid appearance and a formula of NaOH. It is an inorganic alkali salt, hygroscopic in nature and is soluble in water and polar solvents. It has a slippery feel and also absorbs carbon dioxide in the atmosphere to from sodium carbonate.
Properties of caustic soda:
• Highly soluble in water & dissolution is highyly exothermic.
• Low solubility in ethanol & methanol.
• Insoluble in ether & other non-polar solvents.
• Strong base.
• Readily absorbs water (hygroscopic) and carbon dioxide from the air.
• Strong electrolyte.
• Not volatile, but can rise easily in air as an aerosol.
It is used in many applications, for the production of pulp, aluminum, sugar, soaps and detergents. It is used as catalyst in production of biodiesel. It is used as a cleaning and disinfectant agent.
• Cleaning and disinfectant product : It is used in the production of soaps and different detergents. Chlorine bleach is produced by the combination of chlorine and caustic soda.
• Pharmaceuticals: It is widely used in this industries, especially in production of medicines like aspirin, anticoagulants which helps in preventions of blood clots, and cholesterol reducing medications.
• Energy : Caustic soda is used in fuel cell productin. Fuel cells worl like battries to cleanly and efficiently produce electricity for a wide range of application which includes transport, material handlingand emergency power backup applications. Epoxy resins prepared with caustic soda, which are used in wind turbines.
• Water treatment: Municipal water treatment use caustic soda to regulates the acidity in the water and removes heavy metals. Caustic soda is used in manufacture of sodium hypochlorite, which is a water disinfectant.
• Food Industry : It is used widely in food industry, especially in curing foods like olives which gives characteristic crunch. Caustic soda is used to removes skins of vegetables and fruits. It is also prevents microbial growth in food.
• Castner-Kellener Process – In this process the caustic soda is prepared by the electrolysis of aqueous NaCl. It consist mercury cathode cell which is a rectangular vessel divided into three compartments by a non-porous slate partition which do not touch the bottom of the cell. A layer of mercury divides each compartments at the bottom of the cell. One end of the cell is pivoted and the rest of the part rests on an in centric wheel, which gives the rocking motion to the cell so mercury can circulate from one compartment to other.
• Castner-Kellener cell – It is a rectangular cell made up of steel. The inner walls of the tank is lined wih ‘ebonite’. Anode is titanium and mercury acts as cathode.
• Ionization of NaCl – When the solution is subjected to electric discharge the NaCl disassociates into ions, now the positive and negative charges migrates towards its respective electrodes. The sodium deposited at mercury forms sodium amalgam and the chlorine produces at the anode is removed from the top of the cell.
• Reaction at cathod – 2Na++2e-→2Na | Na+Hg→Na/Hg Reaction at anode – 2Cl-Cl2+2e-
• Metathesis reaction – By reacting sodium carbonate with calcium hydroxide, sodium hydroxide and calcium carbonate is produced. These products can be easily separated by filtration as calcium carbonate is not soluble whereas sodium hydroxide is highly soluble. The solution will then be purified, processed and standardized for industrial consumption.
• Chloralkali process – With the electrolysis of sodium chloride solution, solid sodium hydroxide is manufactured and obtained with the evaporation of water. Chlorine gas is also produced as the main by-product. This is done through three main types of cell, mainly mercury cell, diaphragm cell and the membrane cell.
• Formation of NaOH : Amalgam now passed to the other chamber known as ‘denuder’, where it is treated with water to produce NaOH, it is in liquid state.
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