chemical compound, NH₃

Ammonia is a chemical. Its formula is NH3 (not to be confused with Ammonium that has a formula of NH4+). It is made from nitrogen and hydrogen atoms.

Stuctural formula of ammonia. N is nitrogen and H is hydrogen. The lines show that the atoms are joined by chemical bonds.
A picture to show simply how the atoms may fill space. The blue is nitrogen and the white is hydrogen.

Properties change

  • It is a gas at room temperature
  • It is colourless
  • It has a strong, sharp smell
  • It is a base
  • It is an alkali
  • It is harmful when drank or inhaled
  • It dissolves in water to form a solution called household ammonia
  • The liquid boils at −33.3 °C (−27.94 °F).
  • It freezes to white crystals at −77.7 °C (−107.86 °F)[1]

Uses of ammonia change

Ways it can be made change

Many organic nitrogen compounds are in animal waste, including urine and guano. In the 19th century the Distillation (boiling for separation) of nitrogenous vegetable and animal waste was the main source of ammonia. During the 20th century the Haber process using high temperature and pressure with catalysts (things that make reactions faster) became the main source.

Ammonia in fish tanks change

Ammonia is toxic. If a goldfish tank is dirty from their waste, the fish can suffer from ammonia burns which cause black spots or patches on their body. The tank must be large enough and have a filter.

Manufacture of ammonia change

Production trend of ammonia between 1947 and 2007

Because of its many uses, ammonia is one of the most often produced inorganic chemicals. Dozens of chemical plants worldwide produce ammonia. The worldwide ammonia production in 2004 was 109 million metric tonnes.[2] China produced 28.4% of the worldwide production (increasingly from coal as part of urea synthesis)[3] followed by India with 8.6%, Russia with 8.4%, and the United States with 8.2%.[2] About 80% or more of the ammonia produced is used for fertilizing agricultural crops.[2]

Before the start of World War I, most ammonia was obtained by the dry distillation[4] of nitrogenous vegetable and animal waste products, including camel dung, where it was distilled by the reduction of nitrous acid and nitrites with hydrogen; in addition, it was produced by the distillation of coal, and also by the decomposition of ammonium salts by alkaline hydroxides[5] such as quicklime, the salt most generally used being the chloride (sal-ammoniac) thus:

2 NH4Cl + 2 CaO → CaCl2 + Ca(OH)2 + 2 NH3

Today, the typical modern ammonia-producing plant first converts natural gas (i.e., methane) or liquefied petroleum gas (such gases are propane and butane) or petroleum naphtha into gaseous hydrogen. The process used in producing the hydrogen begins with removal of sulfur compounds from the natural gas (because sulfur deactivates the catalysts used in subsequent steps). Catalytic hydrogenation converts organosulfur compounds into gaseous hydrogen sulfide:

H2 + RSH → RH + H2S (g)

The hydrogen sulfide is then removed by passing the gas through beds of zinc oxide where it is adsorbed and converted to solid zinc sulfide:

H2S + ZnO → ZnS + H2O

Catalytic steam reforming of the sulfur-free feedstock is then used to form hydrogen plus carbon monoxide:

CH4 + H2O → CO + 3 H2

In the next step, the water gas shift reaction is used to convert the carbon monoxide into carbon dioxide and more hydrogen:

CO + H2O → CO2 + H2

The carbon dioxide is then removed either by absorption in aqueous ethanolamine solutions or by adsorption in pressure swing adsorbers (PSA) using proprietary solid adsorption media.

The final step in producing the hydrogen is to use catalytic methanation to remove any small residual amounts of carbon monoxide or carbon dioxide from the hydrogen:

CO + 3 H2 → CH4 + H2O
CO2 + 4 H2 → CH4 + 2 H2O

To produce ammonia, the hydrogen then reacts with nitrogen (derived from process air) using a magnetite catalyst under high pressure to form anhydrous liquid ammonia. This step is known as the ammonia synthesis loop (also referred to as the Haber-Bosch process):

3 H2 + N2 → 2 NH3

Hydrogen required for ammonia synthesis could also be produced economically using other sources like coal or coke gasification, less economically from the electrolysis of water into oxygen + hydrogen and other alternatives that are presently impractical for large scale production. At one time, most of Europe's ammonia was produced from the Hydro plant at Vemork, using electrolysis.

Related pages change

References change

  1. Chisholm, Hugh, ed. (1911). "Ammonia" . Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. pp. 861–863.
  2. 2.0 2.1 2.2 "United States Geological Survey publication" (PDF). Retrieved 2009-07-07.
  3. "New coal-based ammonia and urea capacity.(China)". January 2004. Archived from the original on 2013-05-13. Retrieved 2009-07-07.
  4. "Nobel Prize in Chemistry (1918) – Haber-Bosch process". Retrieved 2009-07-07.
  5. "Chemistry of the Group 2 Elements – Be, Mg, Ca, Sr, Ba, Ra". Retrieved 2009-07-07.