section_path: Production
section_name: Production
paragraph_text: Production
  
  Nitrogen gas is an industrial gas produced by the fractional distillation of liquid air, or by mechanical means using gaseous air (pressurised reverse osmosis membrane or pressure swing adsorption). Nitrogen gas generators using membranes or pressure swing adsorption (PSA) are typically more cost and energy efficient than bulk-delivered nitrogen. Commercial nitrogen is often a byproduct of air-processing for industrial concentration of oxygen for steelmaking and other purposes. When supplied compressed in cylinders it is often called OFN (oxygen-free nitrogen). Commercial-grade nitrogen already contains at most 20 ppm oxygen, and specially purified grades containing at most 2 ppm oxygen and 10 ppm argon are also available.
  
  In a chemical laboratory, it is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.
  
  Small amounts of the impurities NO and HNO are also formed in this reaction. The impurities can be removed by passing the gas through aqueous sulfuric acid containing potassium dichromate.
  
  It can also be obtained by the thermal decomposition of ammonium dichromate.
  
  Very pure nitrogen can be prepared by the thermal decomposition of barium azide or sodium azide.