Nitrogen is essential to life on Earth. It is a component of all proteins, and it can be found in all living systems. Nitrogen compounds are present in organic materials, foods, fertilizers, explosives, and poisons. Nitrogen is crucial to life, but in excess it can also be harmful to the environment.
Named after the Greek word Nitrogen, for “native soda,” and genes for “forming,” nitrogen is the fifth most abundant element in the universe. Nitrogen gas constitutes 78 percent of Earth’s air, according to the Los Alamos National Laboratory. On the other hand, the atmosphere of Mars is only 2.6 percent nitrogen.
In its gas form, nitrogen is colorless, odorless, and generally considered as inert. In its liquid form, nitrogen is also colorless and odorless, and looks like water, according to Los Alamos [[i]].
Nitrogen is the most abundant uncombined element accessible to man. It comprises 78.1% by volume of the atmosphere (i.e. 78.3 atom% or 75.5 wt.%) and is produced industrially from this source on the multimegaton scale annually. In combined form it is essential to all forms of life, and constitutes, on average, about 15% by weight of proteins. The industrial fixation of nitrogen for agricultural fertilizers and other chemical products is now carried out on a vast scale in many countries, and the number of moles of anhydrous ammonia manufactured exceeds that of any other compound. Indeed, of the top fifteen “high-volume” industrial chemicals produced in the USA, five contain nitrogen [[ii]
Nitrogen is an essential element for all organisms, which composes proteins, nucleic acids, and other important organic compounds. Nitrogen was discovered in 1772 by Daniel Ratherford, and independently by Scheele and Cavendish. The origins of the name “Nitrogen” are the Greek words “Nitron genes” meaning “Nitre” and “forming”. Nitre is a common name for potassium nitrate [[iii]].
Table 1: Nitrogen Atomic Properties
|Atomic Mass||14.0067 g.mol -1|
|Covalent radius||71 pm|
|van der Waals radius||155 pm|
|Oxidation States||−3, −2, −1, +1, +2, +3, +4, +5 (a strongly acidic oxide)|
|Electron configuration||[He] 2s2 2p3|
|Key isotopes||13N, 14N, 15N|
Spectral lines of Nitrogen
At temperatures below nitrogen’s boiling point of -195.79 C (77K), gaseous nitrogen condenses into liquid nitrogen, a fluid that resembles water and remains odorless and colorless. Nitrogen solidifies at a melting point of -210.0 C (63K) into a fluffy solid resembling snow.
Nitrogen forms trivalent bonds in most compounds. In fact, molecular nitrogen exhibits the strongest possible natural triple bond due to the five electrons in the outer shell of the atom. This strong triple bond, along with nitrogen’s high electronegativity (3.04 on the Pauling scale), explains its nonreactivity [[iv]].
Table 2: Nitrogen Physical Properties
|Melting Point||63.15 K (−210.00 °C, −346.00 °F)|
|Boiling Point||77.355 K (−195.795 °C, −320.431 °F)|
|Molar Volume||22.40 L/mol|
|Electron configuration||[He] 2s2 2p3|
|Density (1 atm, 0 °C)||1.2506 g/L at 0 °C, 1013 mbar|
|State at 20°C||Gas|
|Heat of vaporization||5.56 kJ/mol|
|Heat of fusion||0.72 kJ/mol|
|Speed of sound||349 m/s|
|Vapor Pressure||1 Pa (at 37 T(k)), 10 Pa (at 41 T(k)), 100 Pa (at 41 T(k)), 1k Pa (at 53 T(k)), 10k Pa (at 62 T(k)), 100k Pa (at 77 T(k))|
|Critical point||126.21 K, 3.39 MPa|
|Molar heat capacity||29.124 J/(mol·K)|
|Triple point temperature/pressure||63.151 K, 12.52 kPa|
|Speed of sound||353 m/s (gas, at 27 °C)|
|Thermal conductivity||25.83×10−3 W/(m·K)|
|CAS Number||17778-88-0 7727-37-9 (N2)|
Table 3: Main Nitrogen isotopes
Chemical Properties [[v]]
The N element seemed so inert that Lavoisier named it azote, meaning “without life”. Under normal conditions, nitrogen gas does not react with air, water, acid, bases, or halogen. However, its compounds are vital components of organisms, foods, fertilizers, and explosives. The concentration of N in humans is 2.6% by weight. The electronegativity (Pauling) of N is 3.04, in between that of C (2.55) and O (3.44) The stable common oxidation states (valence states) of N are +5, +4, +3, +2, +1, 0, -1, -2, and -3, the largest number among elements. Table 4 shows various N compounds with a wide range of oxidation states. Nitrogen gas (N2; the oxidation state = 0) is colorless, odorless, and generally inert. As a liquid it is also colorless and odorless. The triple bond of dinitrogen (N2) is very stable and the industrial fixation of nitrogen succeeded only in the 20th century. Caro was the first to produce a chemical N fertilizer, lime nitrogen (CaCN2), from calcium carbide (CaC2) and N2 in 1901. Then Harber and Bosh produced ammonia from N2 and H2 under a high temperature (400-600 oC) and high pressure (200- 1000 atm) with iron catalysts in 1912.
The most oxidized form of nitrogen (oxidation state = +5) is nitric acid (HNO3) or nitrate ion (NO3-). Nitrate ion is the most common inorganic nitrogen in soil. Therefore, it is the most important nutrient for higher plants. Nitric acid is a strong acid, and can cause water pollution in groundwater, rivers and ponds. as well as acid rain. N2O4 (+4), NO (+2), and N2O (+1) are gaseous states under normal conditions. N2O has anesthetic properties and is known as “laughing gas”. Recently, N2O has attracted attention because of its role as a global warming gas in addition to CO2 and CH4. Oxides of nitrogen are formed by the action of electronic sparks or high temperature conditions, such as thunder or combustion of gasoline in automobiles. The most reductive state of nitrogen (-3) is ammonia (NH3) or ammonium ion (NH4+). Ammonium ion is released from the decomposition of organic compounds by soil microorganisms and provided to plants as it is or after being oxidized to NO3- in soil.
Technologies for Nitrogen Production [[vi]]
The three main techniques used in the industrial preparation of nitrogen gas are listed below:
- Pressure Swing Adsorption (PSA)
- Membrane nitrogen generation
- Fractional distillation
- Pressure Swing Adsorption (PSA): This method of production of nitrogen gas relies on the ability of adsorbent material to separate a gaseous mixture into its components. The Pressure Swing Adsorption (PSA) separation system is based on the principle of adsorption. Adsorption is processed, in which the gas or liquid molecules adhere on the surface of the adsorbent. This process creates a film of adsorbate on the surface of the adsorbent.
%. In the pressure swing adsorption, Carbon Molecular Sieves (CMS) is used as an adsorption medium to adsorb the gas molecules such as Oxygen, Carbon dioxide, Water vapor and Other gases (except Nitrogen) under high pressure. Because these gases are adsorbed on the surface of the carbon molecular sieves at the faster rate than the nitrogen molecules.
This is the second step in a PSA nitrogen generation process and is essentially a reversal of the adsorption process. Once the saturation point for an adsorptive tower is reached, its function is changed, and oxygen is released from it to regenerate the sieve material to enable another cycle of adsorption.
The PSA systems are convenient for on-site productions lower than 2000 Nm3/h of nitrogen with purities ranging from 95 to 99.9%.
Figure1: Schematic diagram of pressure swing adsorption system
- Membrane Nitrogen Production [[vii]]
Membrane Nitrogen Gas Generators is regarded as an emerging gas separation technique in the industry due to the lower cost in both initial capital and energy consumption, if compared to cryogenic distillation and pressure swing adsorption. The typical design of the membrane gas separation technique is that the air is drawn from the ambient into the membrane module and the targeted gases are separated based on the difference in diffusivity and solubility. In the membrane module, oxygen will be separated from the ambient air and collected at the upstream due to the high diffusivity, whereas nitrogen will be collected at the downstream of the module.
Nitrogen generated using Membrane Generators has the following characteristics:
- Cost-Effective method
- High purity or high volumes at lower purity levels
- High reliability due to simple airflow design
- Utilizes lower operating and delivery pressures
Figure2: Schematic diagram of Membrane Type Nitrogen Generation
The figure shows the simplified schematic of membrane type nitrogen generation. The main components of nitrogen generations are [[viii]]
- Air Compressor
- Dryer Unit
- Inlet Filters
- Air Heater (Optional)
- Nitrogen Storage Reservoir
3-Fractional Distillation Nitrogen Production [[ix]]: Fractional distillation is a highly effective method of generating nitrogen for industrial use. The process involves the supercooling of air to its liquefaction point and then distilling its component gases at their various boiling points. This process will yield nitrogen with a high purity but is generally more costly than PSA or Membrane production.
In this method, Air is filtered to remove dust and other solids, water vapor and carbon dioxide. Water vapor and carbon dioxide are removed because they solidify at low temperatures and this would block the flow of liquid air through the pumps and pipes. As the dry air free of carbon dioxide is compressed to 200 times atmospheric pressure it becomes warm. Heat is removed by a network of pipes carrying liquid nitrogen. The cold, compressed air is then allowed to expand rapidly thus cooling even further to the point where most of the air is liquefied.
The gas mixture is then purified by fractional distillation. Dense oxygen is captured as liquid as it sinks while nitrogen gas escapes from the top and is collected.
Figure 3: Fractional Distillation Nitrogen Production
Nitrogen Applications and Uses:
- Modified Atmosphere Packaging (M.A.P):
To increase the shelf life of fresh products, many manufacturers choose to modify the atmosphere of the packaging to include higher levels of nitrogen. Because it is a safe, inert gas, nitrogen is an excellent replacement for oxygen or supplemental gas in food packaging and manufacturing. Increased nitrogen preserves freshness, protects the nutrients, and prevents aerobic microbial growth. Nitrogen does not support the growth of aerobic microbes, and therefore, inhibits the growth of aerobic spoilage but does not prevent the growth of anaerobic bacteria. The low solubility of N2 in foods can be used to prevent pack collapse by including sufficient N2 in the gas mix to balance the volume decrease due to CO2 going into solution [[x]].
- Nitrogen Uses in the Wine Industry:
Nitrogen is the preferred inert gas for these wine-making processes because of its low solubility in wine as well as for its ability to eliminate the presence of oxygen and to prevent oxygen from coming into contact with the wine throughout the many stages of production.
The problem of prolonged exposure to oxygen is that it causes oxidation, effectively turning wine into a vinegar-like substance over time. The oxygen reacts with a microbe found in wine and starts converting the ethyl alcohol in the wine into acetic acid – the main component of vinegar [[xi]].
- Nitrogen Uses in Beer dispense
Nitrogen has a wide variety of applications, including serving as a more inert replacement for air where oxidation is undesirable as in dispensing beer. Nitrogen is perfect for blending with CO2 and supplying the extra hydraulic push required during dispensing.
Nitrogen is used to nitrogenate some beers, particularly stouts, which make the draft beer smoother with a thicker, tighter knit head (foam) [[xii]].
- Nitrogen in Edible Oil Sparging
The sparging process of vegetable oil with gaseous N2 (or with another inert gas) is one of the most adopted techniques to preserve vegetable oil from spoilage. This technique consists in inject the inert gas directly in the oil stream by means of a porous sparge. Subsequently, the injected gas, during tank filling operation, diffuses trough the free surface on the product, and saturates tank headspace, preventing the contact between oil and atmospheric O2, which is the major spoilage agent. In some cases, sparging is used coupled with blanketing, which consists in saturating the tank inner volume with N2, to create an inert environment. In this case sparging main goal is to separate the O2 dissolved in the product, which could be present in quantity of 36 mg/l. in this case, when gaseous starts to diffuse through product’s free surface, it drags along with itself parts of the dissolved O2 [[xiii]].
- Light bulbs industry:
Bulbs should not be filled with air since hot tungsten wire will combust in presence of oxygen. You cannot maintain vacuum either or external atmospheric pressure will break the glass. So, they must be filled with non-reactive gas like nitrogen. We can use inert gases like argon or helium instead of Nitrogen, but they are more expensive & rarer than nitrogen [[xiv]].
- Nitrogen Injection for Fire Prevention/Explosive Atmospheres:
Nitrogen fire suppression systems utilize pure Nitrogen, which is naturally occurring inert gas present in the atmosphere. It is safe for use in occupied spaces and poses no threat to the environment. Nitrogen operates as a fire suppressant by reducing the oxygen content within a room to a point at which the fire will extinguish, without compromising the safety of individuals present in the room. Nitrogen will not decompose or produce any by-products when exposed to a flame [[xv]].
- Nitrogen in Chemical Industry:
Nitrogen is important to the chemical industry. It is used to make fertilizers, nitric acid, nylon, dyes and explosives. To make these products, nitrogen must first be reacted with hydrogen to produce ammonia. This is done by the Haber process. 150 million tons of ammonia are produced in this way every year [[xvi]].
- Nitrogen for Stainless steel manufacturing:
High-strength austenitic stainless steels can be produced by replacing carbon with Nitrogen. Nitrogen has greater solid-solubility than carbon, is a strong austenite stabilizer, potent interstitial solid-solution strengthener, and improves pitting corrosion resistance. Although the solubility of nitrogen in liquid iron is very low, 0.045 wt.% at 1600 °C and atmospheric pressure, nitrogen levels above 1 wt.% can be obtained through alloying and specialized high-pressure melting techniques. An austenitic stainless steel should be considered “high-nitrogen” if it contains more nitrogen than can be retained in the material by processing at atmospheric pressure; for most alloys, this limit is approximately 0.4 wt.% [[xvii]].
- Nitrogen in Tire Filling Systems
order to increase the fuel efficiency and improve the tire performance, nitrogen, a dry and inert gas, is used to inflate airplane, off-road truck, military vehicle, and race car tires instead of airs recently. Compared to nitrogen, oxygen in compressed air permeates through the wall of the tire much faster, thus reducing the tire inflation pressure. Dry nitrogen can maintain the proper inflation pressure to make tires run cooler, which can decrease the rolling resistance and prevent overload.
Tires degrade over time because oxygen oxidizes the rubber compounds when it migrates through the carcass of the tire, which cause under-inflation and deterioration of the rubber. There is a significant reduction in tire failure. Nitrogen is an inert gas, which will not corrode rims and will help the tire to run cooler.
Because of these characteristics, there are some advantages of using nitrogen in tires.
• Improve Tire Life
• Reduced Operating Cost
• Enhanced Safety for Vehicles [[xviii]].
- Application of Nitrogen in Aircraft fuel systems
In some cases, Nitrogen is used to reduce fire hazard in aircraft fuel systems.
- Pharmaceutical application of Nitrogen
In the pharmaceutical industry, raw materials such as APIs, inactive ingredients, and other chemicals, that may be sensitive to oxygen which will be cause of oxidation.
During storage and transferring of such oxygen-sensitive products through processing, Nitrogen is used as a blanketing gas, purging gas to move the product through pneumatic conveying systems. Nitrogen is often used in the transferring of pharmaceutical products. The use of a safe, inert gas to transfer liquid or powder pharmaceutical materials is necessary, as these materials can be hazardous if improperly handled.
During production of sterile pharmaceutical products, atmospheric contamination needs to be avoided. In such cases, positive pressure is created with Nitrogen. Positive pressure creation prevents ingress of air, thereby eliminating risk of contamination.
Nitrogen is often used in the packaging of medical supplies (Nitrogen helps maintain sterility and cleanliness of the product). Nitrogen is used to purge oxygen from the packaging before it is sealed, creating an environment made of high purity N2 gas, which will also help preserve and protect the product during transport. For drug products which are prone to oxidation (even by oxygen present in air) or hydrolysis (even by moisture present in air), nitrogen is used while packing. During packing process, void space is likely to remain in the pack before sealing. Oxygen or moisture present in the air in this void space of the sealed pack, will likely degrade the drug product. To reduce effect of oxygen or moisture, nitrogen is used to replace the air in the void space and thus increasing the stability/shelf life of the drug product.
Nitrogen is used to keep products dry and sterile, hence improving their durability. Test kits for doctors’ offices, blood supplies, specimen containers and other medical devices are some examples of items frequently packaged with N2 gas [[xix]].
[ii] – James E. House, Kathleen A. House, in Descriptive Inorganic Chemistry (Third Edition), 2016
[iii] – Takuji Ohyama, Kuni Sueyoshi. 2010. Nitrogen as a major essential element of plants. In book: Nitrogen Assimilation in Plants., Publisher: Research Signpost, Edition: 1, Chapter: 1, pp.1-18.
[v] – James E. House, Kathleen A. House, in Descriptive Inorganic Chemistry (Second Edition), 2010, Nitrogen, Descriptive Inorganic Chemistry (Second Edition)
2010, Pages 277-299.
[vi] – MaohongFanHerbert F.M.DaCostaArmistead G.RussellKathryn A.BerchtoldManvendra K.Dubey,2011, Chapter 10 – CO2 Sorptio, Coal Gasification and Its Applications, 2011, Pages 293-339.
[vii] – K. C. CHONG*, S. O. LAI*, H. S. THIAM, H. C. TEOH, S. L. HENG. 2016. Recent Progress OF Oxygen/Nitrogen
Separation Using Membrane Technology, Journal of Engineering Science and Technology Vol. 11, No. 7 (2016) 1016 – 1030
[x] – Michael Mullan and Derek McDowell, 2011, Modified Atmosphere Packaging. Food and Beverage Packaging Technology, Second Edition. Edited by Richard Coles and Mark Kirwan.
[xiii] – Filippo Ferrari(a), Simone Spanu(b), Giuseppe Vignali(c), Modeling and Simulation of Nitrogen Injection in Vegetable Olive Oil..
[xvii] – J.W.Simmons, 1996, Overview: high-nitrogen alloying of stainless steels. Materials Science and Engineering: A
Volume 207, Issue 2, 30 March 1996, Pages 159-169.
[xviii] – Nader Jalili, Ph.D. Prakash Venkataraman, Graduate Student Department of Mechanical Engineering Clemson University, Clemson, South Carolina 29634-0921. TIRE NITROGEN FILLING SYSTEM.