Nitrogen (N2) is a colorless, odorless and tasteless gas that makes up 78.09% (by volume) of the air we breathe. It is non-flammable and it will not support combustion.
Nitrogen gas is slightly lighter than air and slightly soluble in water. It is commonly thought of and used as an inert gas; but it is not truly inert. It forms nitric oxide and nitrogen dioxide with oxygen, ammonia with hydrogen, and nitrogen sulfide with sulfur. Nitrogen compounds are formed naturally through biological activity. Compounds are also formed at high temperature or at moderate temperature with the aid of catalysts. At high temperatures, nitrogen will combine with active metals, such as lithium, magnesium and titanium to form nitrides. Nitrogen is necessary for various biological processes, and is used as a fertilizer, usually in the form of ammonia or ammonia-based compounds. Compounds formed with halogens and certain organic compounds can be explosive.
Nitrogen condenses at its boiling point, -195.8 0C (-320.4 0F), to a colorless liquid that is lighter than water.
More nitrogen is used by customers than any other industrial gas. It is used in a broad range of industries, including chemicals, pharmaceuticals, petroleum processing, glass and ceramic manufacture, steelmaking and other metals refining and fabrication processes, pulp and paper manufacture, and healthcare. Aside from N2, nitrogen may be referred to as GAN or GN in its gaseous form, and LIN or LN in its liquid form.
Nitrogen is produced in large volumes in both gas and liquid form by cryogenic distillation; smaller volumes may be produced as a gas by pressure swing adsorption (PSA) or diffusion separation processes (permeation through specially designed hollow fibers). Cryogenic processes can produce very pure nitrogen. Adsorption and diffusion processes are typically used to make lower purity product in relatively small amounts. This is attractive to users when purity is not critical and alternatives (purchase of bulk liquid nitrogen, cylinders of high pressure nitrogen, or local cryogenic production) are more expensive or impractical.
Gaseous nitrogen is valued for inertness. It is used to shield potentially reactive materials from contact with oxygen.
Liquid nitrogen is valued for coldness as well as inertness. When liquid nitrogen is vaporized and warmed to ambient temperature, it absorbs a large quantity of heat. The combination of inertness and its intensely cold initial state makes liquid nitrogen an ideal coolant for certain applications such as food freezing. Liquid nitrogen is also used to cool materials which are heat sensitive or normally soft to allow machining or fracturing. Examples are used tires, plastics, certain metals and even pharmaceuticals.
English Units |
Normal Boiling Point (1 atm) | Gas Phase Properties @ 32°F & @1 atm | Liquid Phase Properties @ B P& @ 1 atm | Triple Point | Critical Point | |||||||||
| Temp. | Latent Heat of Vaporization | Specific Gravity | Specific Heat (Cp) | Density | Specific Gravity | Specific Heat (Cp) | Temp. | Pressure | Temp. | Pressure | Density | |||
| Substance | Chemical Symbol | Mol. Weight | ° F | BTU/lb | Air = 1 | BTU/lb °F | lb/cu. ft | Water = 1 | BTU/lb °F | °F | psia | °F | psia | lb/cu ft |
| Nitrogen | N2 | 28.01 | -320.4 | 85.6 | 0.9737 | 0.249 | 0.07807 | 0.808 | 0.4877 | -346.0 | 1.81 | -232.4 | 493 | 19.6 |
Metric Units |
Boiling Point @ 101.325 kPa | Gas Phase Properties @ 0° C & @ 101.325 kPa | Liquid Phase Properties @ B.P., & @ 101.325 kPa | Triple Point | Critical Point | |||||||||
| Temp. | Latent Heat of Vaporization | Specific Gravity | Specific Heat (Cp) | Density | Specific Gravity | Specific Heat (Cp) | Temp. | Pressure | Temp. | Pressure | Density | |||
| Substance | Chemical Symbol | Mol. Weight | °C | kJ/kg | Air = 1 | kJ/kg ° C | kg/m3 | Water = 1 | kJ/kg ° C | °C | kPa abs | ° C | kPa abs | kg/m3 |
| Nitrogen | N2 | 28.01 | -195.8 | 199.1 | 0.9737 | 1.04 | 1.2506 | 0.808 | 2.042 | -210 | 12.5 | -146.9 | 3399 | 314.9 |
The inert properties of nitrogen make it a good blanketing gas in many applications. Nitrogen blanketing is used to protect flammable or explosive solids and liquids from contact with air. Certain chemicals, surfaces of solids, and stored food products have properties that must be protected from degradation by the effects of atmospheric oxygen and moisture. Protection is achieved by keeping these items in (under) a nitrogen atmosphere. "Inerting" or "padding" are other terms used to describe displacement of air and nitrogen blanketing.
"Sparging" with nitrogen is the bubbling of nitrogen gas through a liquid to remove unwanted volatile components, including volatile organic compounds (VOC) which may be necessary to meet pollution reduction regulations.
Certain substances are difficult to pulverize or shred because they are tough or the materials will be degraded by the heat generated by mechanical processes such as grinding. Liquid nitrogen can be used to freeze soft or tough substances prior to their entering a size reduction process. Cold vaporized nitrogen can be used to keep materials cool (and in an inert atmosphere) during grinding. Cryogenic grinding is used in diverse applications, including production of finely ground pharmaceuticals, plastics and pigments; and for shredding tires in recycling plants.
Nitrogen is used to treat the melt in the manufacture of steel and other metals and as a shield gas in the heat treatment of iron, steel and other metals. It is also used as a process gas, together with other gases for reduction of carbonization and nitriding.
“Flash” or “fins” on cast metal can be removed by cooling with liquid nitrogen, making them brittle, allowing then to be broken off by mechanical action.
Shrink fitting is an interesting alternative to traditional expansion fitting. Instead of heating the outer metal part, the inner part is cooled by liquid nitrogen so that the metal shrinks and can be inserted. When the metal returns to its normal temperature, it expands to its original size, giving a very tight fit.
Liquid nitrogen is used to cool concrete, which leads to better cured properties.
When construction operations must be done in soft, water-soaked ground such as tunnel construction underneath waterways, the ground can be frozen effectively with liquid nitrogen. Pipes are driven into the ground, liquid nitrogen is pumped through the pipes under the earth’s surface. When the nitrogen exits into the soil, it vaporizes, removing heat from the soil and freezing it.
Refineries, petrochemical plants and marine tankers use nitrogen to purge equipment, tanks and pipelines of dangerous vapors and gases (for example, after completing a pipeline transfer operation or ending a production run) and to maintain an inert and protective atmosphere in tanks storing flammable liquids.
Cold nitrogen gas is used to cool reactors filled with catalyst during maintenance work. The cooling time can be reduced substantially.
Cooling reactors (and the materials inside) to low temperature allows better control of side-reactions in complex reactions in the pharmaceutical industry. Liquid nitrogen is often used to provide the necessary refrigeration as it can produce rapid temperature reduction and easily maintain the required cold reaction temperatures. Reactor cooling and temperature control systems usually employ a circulating low-temperature heat transfer fluid to transfer refrigeration produced by vaporizing liquid nitrogen to the shell of the reactor vessel. The liquid nitrogen is vaporized in specially-designed heat exchangers that transfer refrigeration to the circulating heat transfer fluid.
Liquid nitrogen is used during well completion to "frac" natural gas bearing rock formations, in particular, tight gas formations, including shale gas and natural gas from coal (coal bed methane) where water based methods should be avoided. Nitrogen is also used to maintain pressure in oil and natural gas producing formations. Unlike carbon dioxide, which is also used for pressurization, nitrogen has little affinity for liquid hydrocarbons, thus it builds up in and remains in the gas cap.
Nitrogen is used an inert gas to push liquids though lines, to clear lines and to propel "pigs" through pipelines to sweep out one material before using the line to transport another material.
Materials become hard and brittle when cooled by to very low temperatures. This property permits the removal of “flash” or “fins” on cast plastics and rubber. The castings are cooled by liquid nitrogen and the flash broken off by mechanical action.
The intense cold in liquid nitrogen allows very rapid freezing of food items, resulting in minimal cell damage from ice crystals and improved appearance, taste and texture. Well-designed cryogenic tunnel and spiral freezers efficiently capture refrigeration from liquid vaporization and from the cold nitrogen gas as it flows through the freezer.
When substances such as vegetable oil and wines are stored, the inert properties of nitrogen can be used to protect against loss of quality by oxidation by expelling any air entrained in the liquid (“sparging”) and protecting liquids in storage tanks by filling the vapor space (“blanketing”).
Nitrogen (and nitrogen mixed with CO2 and oxygen) is used in transport trucks and in Modified Atmosphere Packaging (MAP) to extend the shelf life of packaged foods by preventing oxidation, mold, insect infestation and moisture migration.
Nitrogen is used as a shield gas in the packing of some medicines to prevent degradation by oxidation or moisture adsorption.
Nitrogen is used to freeze blood, as well as viruses for vaccination. It is also used to freeze livestock semen, which can then be stored for years. The quick freezing resulting from the intense cold minimizes cell wall damage. Liquid nitrogen is also used in some MRI (Magnetic Resonance Imaging) devices to pre-cool the low temperature magnets prior to using much more expensive liquid helium for final cooling.
Liquid nitrogen is used in cryo-surgery to destroy diseased tissue.
Nitrogen is used directly as a coolant for severe environmental testing of many items, or as a refrigeration source for chilling circulating dry air.