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There are literally dozens of large-scale '''[[ammonia]] production''' plants worldwide, some of which produce as much as 2,000 to 3,000 tons per day of liquid ammonia. Because of its many uses, ammonia is one of the most highly-produced [[inorganic chemical]]s.  The worldwide production in 2004 was 109,000,000 metric tons.<ref>[http://minerals.usgs.gov/minerals/pubs/commodity/nitrogen/nitromcs05.pdf United States Geological Survey publication]</ref> [[China]] produced 28.4% of the worldwide production followed by [[India]] with 8.6%, [[Russia]] with 8.4%, and the [[United States]] with 8.2%.


==History==
Before the start of [[World War I]], most ammonia was obtained by the dry [[distillation]] of [[nitrogenous]] vegetable and animal products; the reduction of [[nitrous acid]] and [[nitrite]]s with [[hydrogen]]; and the decomposition of [[ammonium salt]]s by [[alkaline hydroxides]] or by [[calcium oxide|quicklime]], the salt most generally used being the [[chloride]] ([[ammonium chloride|sal-ammoniac]]).
The [[Haber process]], which is the production of ammonia by combining hydrogen and [[nitrogen]], was first patented by [[Fritz Haber]] in 1908. In 1910, [[Carl Bosch]], while working for the [[Germany|German]] chemical company BASF, successfully commercialized the process and secured further patents. It was first used on an industrial scale by the Germans during World War I. Since then, the process has often been referred to as the [[Haber-Bosch]] process.
==Modern ammonia-producing plants==
[[Image:Steam-Methane Reformer.png|right|thumb|288px|{{#ifexist:Template:Steam-Methane Reformer.png/credit|{{Steam-Methane Reformer.png/credit}}<br/>|}}Block flow diagram of ammonia production processes]]
A typical modern ammonia-producing plant first converts [[natural gas]] (i.e., [[methane]]) or [[Liquified petroleum gas|LPG]] (liquified petroleum gases such as [[propane]] and [[butane]]) or petroleum [[naphtha]] into gaseous hydrogen. The method for producing hydrogen from [[hydrocarbon]]s is referred to as [[Steam reforming|"steam reforming"]].<ref>{{cite book | author=Twygg, Martyn V. | title=Catalyst Handbook | edition=2nd Edition | publisher=Oxford University Press | year=1989 | id=ISBN 1-874545-36-7}}</ref><ref>{{cite book|author=Samuel Strelzoff|title=Technology and Manufacture of Ammonia|edition=|publisher=Krieger Publishing|year= 1987|id=ISBN 0-89464-250-2}}
</ref> The hydrogen is then combined with nitrogen to produce ammonia. <ref>{{cite book|author=J.R. Jennings (Editor)|title=Catalytic Ammonia Synthesis|edition=First Edition|publisher=Springer|year=1991|id=ISBN 0-306-43628-0}}</ref><ref>{{cite book|author=Sami Matar and Lewis F. Hatch|title=Chemistry of Petrochemical Processes|edition=Second Edition|publisher=Gulf Publishing|year=2001|id=ISBN 0-8841-5315-0}}</ref>
Starting with a natural gas feedstock, the processes used in producing the hydrogen are:
* The first step in the process is to remove [[sulfur]] compounds from the feedstock because sulfur deactivates the [[catalyst]]s used in subsequent steps. Sulfur removal requires catalytic [[hydrogenation]] to convert organic sulfur compounds (RSH) in the feedstocks to gaseous [[hydrogen sulfide]] (H<sub>2</sub>S):
::H<sub>2</sub> + RSH →  RH + H<sub>2</sub>S(gas)
*The gaseous hydrogen sulfide is then absorbed and removed by passing it through beds of [[zinc oxide]] (ZnO) where it is converted to solid [[zinc sulfide]] (ZnS):
::H<sub>2</sub>S + ZnO → ZnS + H<sub>2</sub>O
* [[Catalytic]] steam reforming of the sulfur-free methane (CH<sub>4</sub>) feedstock is then used to form [[carbon monoxide]] (CO) plus hydrogen (H<sub>2</sub>): :
::CH<sub>4</sub> + H<sub>2</sub>O → CO + 3H<sub>2</sub>
* The next step then uses catalytic [[water gas shift reaction|shift conversion]] to convert the carbon monoxide to [[carbon dioxide]] (CO<sub>2</sub>) and more hydrogen:
::CO + H<sub>2</sub>O → CO<sub>2</sub> + H<sub>2</sub>
* The carbon dioxide is then removed either by absorption in aqueous [[ethanolamine]] solutions or by adsorption in [[Pressure swing adsorption|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 by converting them into methane:
::CO + 3H<sub>2</sub> → CH<sub>4</sub> + H<sub>2</sub>O
::CO<sub>2</sub> + 4H<sub>2</sub> → CH<sub>4</sub> +2H<sub>2</sub>O
To produce the desired end-product ammonia, the hydrogen is then catalytically reacted with nitrogen (N<sub>2</sub>) derived from process air to form [[anhydrous]] liquid ammonia (NH<sub>3</sub>). This step is known as the "ammonia synthesis loop" (also referred to as the Haber-Bosch process):
::3H<sub>2</sub> + N<sub>2</sub> → 2NH<sub>3</sub>
The steam reforming, shift conversion, carbon dioxide removal and methanation steps each operate at absolute [[pressure]]s of about 25 to 35 [[Bar (unit)|bar]], and the ammonia synthesis loop operates at absolute pressures ranging from 60 to 180 bar depending upon which proprietary design is used. There are many engineering and construction companies that offer proprietary designs for ammonia synthesis plants.  Haldor Topsoe of [[Denmark]], Technip of [[France]], Uhde GmbH of Germany, and Kellogg Brown & Root of the United States are among the most experienced companies in that field.
==Uses of ammonia==
About 80% or more of the ammonia produced is used for fertilizing agricultural crops in the form of [[aqua ammonia]] (an aqueous solution of ammonia), [[ammonium sulfate]] (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>, [[ammonium phosphate]] (NH<sub>4</sub>)<sub>3</sub>PO<sub>4</sub>, [[ammonium nitrate]]  NH<sub>4</sub>NO<sub>3</sub> and [[urea]]  (NH<sub>2</sub>)<sub>2</sub>CO.
Ammonia is also used for:
* Manufacture of [[nitric acid]] (HNO<sub>3</sub>)
* Manufacture of [[nylon]] and other [[polyamide]]s
* Hydrogen supply for [[petroleum refining processes]]
* Refrigerant in household, commercial and industrial [[refrigeration system]]s
* Manufacture of [[dyes]]
* Manufacture of [[explosives]]
* Cleaning solutions
==References==
{{reflist}}

Revision as of 01:39, 26 February 2008

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