Caustic Soda

Caustic soda or sodium hydroxide is a white solid substance with the chemical formula of NaOH and it is resulted from the process of electrolysis of sodium chloride soluble in the electrolytic vessels. 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. Pure Caustic soda is a colorless crystalline solid that melts at 318 °C without decomposition. It is highly soluble in water, with a lower solubility in polar solvents such as ethanol and methanol.

Similar to the hydration of sulfuric acid, dissolution of caustic soda flakes in water is a highly exothermic reaction where a large amount of heat is released, posing a threat to safety through the possibility of splashing. The resulting solution is usually colorless and odorless. As with other alkaline solutions, it feels slippery with skin contact due to the process of saponification that occurs between NaOH and natural skin oils.

Caustic soda is industrially produced as a 50% solution by variations of the electrolytic chloralkali process. Chlorine gas is also produced in this process. Solid sodium hydroxide is obtained from this solution by the evaporation of water. Solid sodium hydroxide is most commonly sold as flakes, pills, and cast blocks.

Properties:

Caustic soda is highly alkaline and strongly hydrophilic. This capacity makes caustic soda extremely corrosive to skin tissue and hazardous to all animal and plant life. All direct, unprotected physical contact with the substance should be avoided. It is moderately toxic; however, the major hazard is its corrosive effects. Caustic soda flakes is not volatile or flammable. We can summarize the properties as;

• 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

General Characteristics

• Caustic soda is the most typical of the strong alkalis. Although there is no danger of it exploding or igniting, it reacts with various acids, such as hydrochloric acid, and is neutralized and generates considerable exothermic heat of neutralization.
• It corrodes metals, such as aluminum, tin, and zinc. During this process, it generates hydrogen, which has the potential to behave as an explosive gas.
• It is highly hygroscopic, and absorbs the moisture, carbon dioxide, or sulfur dioxide in the air. It is also highly deliquescent and absorbs moisture to form an aqueous solution.
• When liquid caustic soda is diluted, it generates a considerable amount of heat of dilution. Since this rapidly generates strong heat and the resulting solution may spatter if the water is carelessly poured into it, care must be taken.
• Caustic soda easily decomposes animal fibers. Although plant fibers are also decomposed, they have a higher resistance than animal fibers. Although materials resistant to corrosion by caustic soda include stainless steel, steel-epoxy resins, and fiber-reinforced plastics, steel and rubber-lined steel are the most frequently used.

Applications

The major users of caustic soda flakes are the aluminum industry, pulp & paper, leather and textile, oil and gas, oil wells, food industry and the chemical industry. The main applications are water treatment and water purification, as cleaning agent, or a wide range of uses in chemical industry like starch production or for the desulphurization in the petrochemical industry.

• Pulp and paper – The largest application for caustic soda worldwide. Uses include in pulping and bleaching processes, the de-inking of waste paper and water treatment.
• Textiles – Used to process cotton and dye synthetic fibers, such as nylon and polyester.
• Soap and detergents – Used in saponification, the chemical process that converts fat, tallow and vegetable oils into soap. It also is used to manufacture anionic surfactants, a crucial component in most detergents and cleaning products.
•  Bleach manufacturing – Used to make bleach, which has industrial and consumer applications such as mold and mildew control around the home.
• Petroleum products – Used to explore, produce and process petroleum and natural gas.
• Aluminum production – Used to dissolve bauxite ore, the raw material for aluminum production.
• Chemical processing – Used as a basic feedstock for a wide range of downstream products, including solvents, plastics, fabrics, adhesives, coatings, herbicides, dyes, inks, pharmaceuticals and more.

Containers

• Solid caustic soda is contained in thin steel drums.
• Flake caustic soda is contained in drums or PVC-lined paper bags as shown in the table.
• Liquid caustic soda is contained in rectangular cans or drums. For the transportation of a large quantity of liquid caustic soda, tank trucks, rail tanks, or tankers are used.
• Reagent-grade caustic soda is contained in glass bottles.