Ammonia production

Ammonia production

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Because of its many uses, ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 is one of the most highly-produced inorganic chemicals. There are numerous large-scale ammonia production plants worldwide, producing a total of 131,000,000 metric tons of ammonia in 2010. China produced 32.1% of the worldwide production, followed by India with 8.9%, Russia with 7.9%, and the United States with 6.3%. 80% or more of the ammonia produced is used for fertilizing agricultural crops. Ammonia is also used for the production of plastics, fibers, explosives, and intermediates for dyes and pharmaceuticals.

History


Before the start of World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

, most ammonia was obtained by the dry distillation
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 of nitrogenous vegetable and animal products; by the reduction of nitrous acid
Nitrous acid
Nitrous acid is a weak and monobasic acid known only in solution and in the form of nitrite salts.Nitrous acid is used to make diazides from amines; this occurs by nucleophilic attack of the amine onto the nitrite, reprotonation by the surrounding solvent, and double-elimination of water...

 and nitrite
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...

s with hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

; and also by the decomposition of ammonium salts by alkaline hydroxides or by quicklime
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

, the salt most generally used being the chloride (sal-ammoniac
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...

).

Modern ammonia-producing plants


A typical modern ammonia-producing plant first converts natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 (i.e., methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

) or LPG
Liquified petroleum gas
Liquefied petroleum gas is a flammable mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles. It is increasingly used as an aerosol propellant and a refrigerant, replacing chlorofluorocarbons in an effort to reduce damage to the ozone layer...

 (liquified petroleum gases such as propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...

 and butane
Butane
Butane is a gas with the formula C4H10 that is an alkane with four carbon atoms. The term may refer to any of two structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, butane refers only to the unbranched n-butane isomer; the other one being called "methylpropane" or...

) or petroleum naphtha
Naphtha
Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e., a component of natural gas condensate or a distillation product from petroleum, coal tar or peat boiling in a certain range and containing certain hydrocarbons. It is a broad term covering among the...

 into gaseous hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

. The method for producing hydrogen from hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s is referred to as "Steam Reforming"
Steam reforming
Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to...

. The hydrogen is then combined with nitrogen to produce ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

.

Starting with a natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 feedstock, the processes used in producing the hydrogen are:
  • The first step in the process is to remove sulfur
    Sulfur
    Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

     compounds from the feedstock because sulfur deactivates the catalysts used in subsequent steps. Sulfur removal requires catalytic hydrogenation
    Hydrogenation
    Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...

     to convert sulfur compounds in the feedstocks to gaseous hydrogen sulfide
    Hydrogen sulfide
    Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

    :

H2 + RSH → RH + H2S(gas)

  • The gaseous hydrogen sulfide is then absorbed and removed by passing it through beds of zinc oxide
    Zinc oxide
    Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

     where it is converted to solid zinc sulfide
    Zinc sulfide
    Zinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...

    :

H2S + ZnO → ZnS + H2O

  • Catalytic steam reforming
    Steam reforming
    Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to...

     of the sulfur-free feedstock is then used to form hydrogen plus carbon monoxide
    Carbon monoxide
    Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

    :

CH4 + H2O → CO + 3H2

  • The next step then uses catalytic shift conversion
    Water gas shift reaction
    The water-gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen:The water-gas shift reaction is an important industrial reaction. It is often used in conjunction with steam reforming of methane or other hydrocarbons, which is...

     to convert the carbon monoxide to carbon dioxide
    Carbon dioxide
    Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

     and more hydrogen:

CO + H2O → CO2 + H2

  • The carbon dioxide is then removed either by absorption in aqueous ethanolamine
    Ethanolamine
    Ethanolamine, also called 2-aminoethanol or monoethanolamine , is an organic chemical compound that is both a primary amine and a primary alcohol . Like other amines, monoethanolamine acts as a weak base...

     solutions or by adsorption in pressure swing adsorbers
    Pressure swing adsorption
    Pressure swing adsorption is a technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and so differs from cryogenic distillation...

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


To produce the desired end-product ammonia, the hydrogen is then catalytically reacted with nitrogen (derived from process air) to form anhydrous liquid ammonia. This step is known as the ammonia synthesis loop (also referred to as the Haber-Bosch process):
3H2 + N2 → 2NH3


The steam reforming, shift conversion, carbon dioxide removal and methanation steps each operate at absolute pressures of about 25 to 35 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
Haldor Topsoe
Haldor Topsøe is a Danish catalyst company. The company was founded in 1940 by Dr. Haldor Topsøe. The company also develops process technology for petroleum refining, ammonia production, methanol production, and other industries....

 of Denmark, Uhde GmbH of Germany, Ammonia Casale of Switzerland and Kellogg Brown & Root of the United States are among the most experienced companies in that field.

Sustainable ammonia production



Ammonia production depends on plentiful supplies of natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

, a finite resource
Peak gas
Peak gas is the point in time at which the maximum global natural gas production rate is reached, after which the rate of production enters its terminal decline. Natural gas is a fossil fuel formed from plant matter over the course of millions of years. It is a finite resource and thus considered...

, to provide the hydrogen. Due to ammonia's critical role in intensive agriculture and other processes, sustainable production is desirable. This is possible by using renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

 to generate hydrogen by electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

 of water. This would be straightforward in a hydrogen economy
Hydrogen economy
The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....

 by diverting some hydrogen production from fuel to feedstock use. For example, in 2002, Iceland produced 2,000 tons of hydrogen gas by electrolysis, using excess electricity production from its hydroelectric plants, primarily for the production of ammonia for fertilizer. The Vemork
Vemork
Vemork is the name of a hydroelectric power plant outside Rjukan in Tinn, Norway. The plant was built by Norsk Hydro and opened in 1911, its main purpose being to fix nitrogen for the production of fertilizer. Vemork was later the site of the first plant in the world to mass-produce heavy water...

 hydroelectric plant in Norway used its surplus electricity output to generate renewable ammonia from 1911 to 1971. In practice, natural gas will remain the major source of hydrogen for ammonia production as long as it is cheapest.

Waste water
Sewage treatment
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...

 is often high in ammonia. Because discharging ammonia laden water into the environment can cause problems, nitrification
Simultaneous nitrification-denitrification
Simultaneous nitrification-denitrification is a wastewater treatment process. Microbial simultaneous nitrification-denitrification is the conversion of the ammonium ion to nitrogen gas in a single bioreactor...

 is often necessary to remove the ammonia. This may be a potentially sustainable source of ammonia in the future because of its abundance and the need to remove it from the water anyway
Denitrification
Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen through a series of intermediate gaseous nitrogen oxide products....

.

External links

  • Today's Hydrogen Production Industry
  • Energy Use and Energy Intensity of the U.S. Chemical Industry, Report LBNL-44314, Lawrence Berkeley National Laboratory
    Lawrence Berkeley National Laboratory
    The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...

     (Scroll down to page 39 of 40 PDF pages for a list of the ammonia plants in the USA)
  • Ammonia: The Next Step includes a detailed process flow diagram
    Process Flow diagram
    A process flow diagram is a diagram commonly used in engineering to indicate the general flow of plant processes and equipment.The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations...

    .