Introduction to Nitrogen
Nitrogen is a chemical element with the symbol N and atomic number 7. It is a nonmetal and the lightest member of Group 15 of the periodic table, often called the pnictogens. At standard temperature and pressure, two atoms of the element bond to form dinitrogen (N₂), a colourless and odourless diatomic gas. Dinitrogen is largely unreactive under normal conditions, a property attributed to the strong triple bond between its atoms.
Natural Occurrence of Nitrogen
Nitrogen is one of the most abundant elements on Earth. Its primary natural reservoir is the Earth’s atmosphere, where it constitutes approximately 78% by volume as dinitrogen gas (N₂). Beyond the atmosphere, nitrogen is a crucial component of all living organisms. It is found in organic molecules such as amino acids, proteins, and nucleic acids (DNA and RNA), which are fundamental to life. In the Earth’s crust, nitrogen is present in mineral deposits, though less abundantly, primarily as nitrates and nitrites in soils and certain rocks. The nitrogen cycle describes the continuous movement of nitrogen between the atmosphere, terrestrial, and marine ecosystems through various biological and physical processes.
Industrial Extraction of Nitrogen
Industrially, nitrogen gas is primarily obtained from the air through a process called fractional distillation of liquid air. Air is first cooled to very low temperatures until it liquefies. Since nitrogen, oxygen, and argon have different boiling points (-196°C for nitrogen, -183°C for oxygen, -186°C for argon), they can be separated by carefully warming the liquid air, allowing each component to boil off at its specific temperature. Nitrogen, having the lowest boiling point, vaporizes first and is collected. This method yields high-purity nitrogen.
Another method, less common for large-scale production but used for smaller quantities or specific purities, involves Pressure Swing Adsorption (PSA) or membrane separation. In India, numerous industrial gas plants utilize air separation units to produce nitrogen, oxygen, and argon for various sectors, including steel, chemical, and electronics industries.
Everyday Applications of Nitrogen
1. Food Preservation
Nitrogen gas is widely used in Modified Atmosphere Packaging (MAP) for food products. By flushing food packages, such as those for potato chips, namkeen, or other snack items common in Indian markets, with nitrogen, the oxygen content inside is significantly reduced or eliminated. This inert atmosphere prevents oxidation, which causes rancidity and spoilage, thereby extending the shelf life of perishable foods and maintaining their freshness and crispness.
2. Fertiliser Production
One of the most significant industrial applications of nitrogen is in the production of fertilisers, particularly ammonia (NH₃). The Haber-Bosch process combines atmospheric nitrogen with hydrogen under high temperature and pressure to synthesize ammonia. Ammonia is then used to produce urea, ammonium nitrate, and diammonium phosphate (DAP), which are vital nitrogenous fertilisers. India’s agricultural sector heavily relies on these fertilisers for cultivating staple crops like rice, wheat, and sugarcane, making the country one of the largest producers and consumers of nitrogen-based fertilisers globally. Companies such as IFFCO and National Fertilizers Limited (NFL) are major players in this domain in India.
3. Cryogenics and Refrigeration
Liquid nitrogen, with its extremely low boiling point of -196°C, is an excellent cryogenic agent. It is used for rapid freezing and preserving biological samples, such as blood, tissues, and genetic material, in medical research, hospitals, and IVF (In Vitro Fertilization) centres across India. It is also employed for the cryopreservation of livestock semen and embryos. In the food industry, liquid nitrogen is utilized for flash-freezing food products, which helps maintain their texture and nutritional value.
4. Creating Inert Atmospheres
Nitrogen’s inert nature makes it invaluable for creating oxygen-free or inert atmospheres in various industrial processes. It is used to purge pipelines, tanks, and chemical reactors to prevent explosions or undesirable reactions, for instance, in oil refineries and chemical plants throughout India. In the electronics industry, nitrogen blankets are used during semiconductor manufacturing to prevent oxidation of sensitive components. It is also used in incandescent light bulbs as a filling gas to prevent the filament from burning out prematurely.
5. Tyre Inflation
Nitrogen gas is increasingly used for inflating tyres in specialized vehicles, including aircraft, racing cars, and heavy-duty industrial vehicles. Compared to compressed air, nitrogen provides more stable tyre pressure because it is less prone to temperature-induced pressure fluctuations. Its larger molecule size also means it permeates through rubber more slowly, reducing pressure loss over time. Furthermore, the absence of moisture in nitrogen helps prevent internal corrosion of the wheel rim and valve stem, though this application is less common in standard passenger vehicles in India.