The Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen and hydrogen, over an iron substrate, to produce ammonia. Nitrogen fixation is the process by which Nitrogen is taken from its natural relatively inert molecular form (N2 in the atmosphere and converted into Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor ^[1][2][3] The Haber process is important because ammonia is difficult to produce on an industrial scale. Even though 78. 1% of the air we breathe is nitrogen, the gas is relatively unreactive because nitrogen molecules are held together by strong triple bonds. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic It was not until the early 20th century that this method was developed to harness the atmospheric abundance of nitrogen to create ammonia, which can then be oxidized to make the nitrates and nitrites essential for the production of nitrate fertilizer and munitions. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms The nitrite Ion is NO2− The anion is bent being Isoelectronic with O3. In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms Fertilizers ( also spelt fertiliser are chemical compounds given to Plants to promote growth they are usually applied either through the soil for uptake by plant Ammunition, often referred to as ammo, is a generic term derived from the French language la munition which

Contents 1 History 2 The process 2.1 Synthesis gas preparation 2.2 Ammonia synthesis 3 Reaction Rate and Equilibrium 4 Catalysts 5 Economic and environmental aspects 6 See also 7 References 8 External links

History

The process was first patented by German chemist Fritz Haber. This is a list of famous Germans. Actors/Actresses Mario Adorf (born 1930 actor, writer Hans Albers (1891–1960 This is a list of famous chemists: (alphabetical order A Emil Abderhalden, (1877&ndash1950 Swiss chemist Richard Abegg Fritz Haber (9 December 1868 &ndash 29 January 1934 was a German chemist, who received the Nobel Prize in Chemistry in 1918 for his development for In 1910 Carl Bosch, while working for German chemical company BASF, successfully commercialized the process and secured further patents. Year 1910 ( MCMX) was a Common year starting on Saturday (link will display calendar of the Gregorian calendar (or a Common year starting Carl Bosch ( August 27, 1874 &ndash April 26, 1940) was a German Chemist and Engineer who won the BASF SE () is a German chemical company and the largest chemical company in the world Haber and Bosch were later awarded Nobel prizes, in 1918 and 1931 respectively, for their work in overcoming the chemical and engineering problems posed by the use of large-scale high-pressure technology. The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature Ammonia was first manufactured using the Haber process on an industrial scale in Germany during World War I, to meet the high demand for ammonium nitrate (for use in explosives) at a time when supply of Chile saltpetre from Chile could not be guaranteed because this industry was then almost 100% in British hands. World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All Sodium nitrate is the Chemical compound with the formula NaNO3 Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the It has been suggested that without this process, Germany would not have started the war^[4].

The process

The bulk of the chemical technology consists in getting the hydrogen from methane or natural gas using heterogeneous catalysis and then reacting it with the atmospheric nitrogen.

Synthesis gas preparation

First, the methane is cleaned, mainly to remove sulfur impurities that would poison the catalysts. Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 This is done by turning sulfur into hydrogen sulfide:

CH₃SH + H₂ → CH₄ + H₂S

and then reacting with zinc oxide to form zinc sulfide:

H₂S + ZnO → ZnS + H₂O

The clean methane is then reacted with steam over a catalyst of nickel oxide. Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. This is called steam reforming:

CH₄ + H₂O → CO + 3H₂

Secondary reforming then takes place with the addition of air to convert the methane that did not react during steam reforming. Steam reforming (SR hydrogen reforming or catalytic oxidation, is a method of producing Hydrogen from Hydrocarbons. The carbon monoxide formed could also cause catalyst poisoning, which would react with the iron catalyst, forming an iron compound, thus affecting the reaction. The air added during this step also serves as a nitrogen source for ammonia synthesis:

2CH₄ + O₂ → 2CO + 4H₂

CH₄ + 2O₂ → CO₂ + 2H₂O

Then occur two’’shifts’’ which convert CO to CO₂ by reaction with steam, one at high temperature, then one at low temperature:

CO + H₂O → CO₂ + H₂ high temperature

→ the catalyst here is a mixture of iron, chromium and copper

CO + H₂O → CO₂ + H₂ low temperature

→ the catalyst here is a mixture of copper, zinc and aluminium

Then the carbon dioxide is removed by reaction with potassium carbonate. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 WikipediaNaming

K₂CO₃ + H₂O + CO₂→ 2KHCO₃

The gas mixture is now passed into a methanator which converts any remaining CO₂ into methane for recycling:

CO₂ + 4H₂ → CH₄ + 2H₂O

We now have a gas mixture containing nitrogen and hydrogen in the correct ratio of 1:3.

Ammonia synthesis

The final stage is the crucial synthesis of ammonia using promoted magnetite, iron oxide, as the catalyst:

N₂(g) + 3H₂(g) → 2NH₃(g), ΔH^o = -92. Magnetite is not to be confused with Magnesite or Maghemite. Magnetite is a ferrimagnetic Mineral with chemical 4 kJ/mol

This is done at 150 - 250 atmospheres (atm) and between 300 and 550 °C, passing the gases over four beds of catalyst, with cooling between each pass to maintain a reasonable equilibrium constant. The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm For a general Chemical reaction \alpha A +\beta B. \rightleftharpoons \sigma S+\tau T. On each pass only about 15% conversion occurs, but any unreacted gases are recycled, so that eventually an overall conversion of 98% can be achieved.

Reaction Rate and Equilibrium

There are two opposing considerations in this synthesis: the position of the equilibrium and the rate of reaction. The reaction rate or rate of reaction for a Reactant or product in a particular reaction is intuitively defined as how fast a reaction takes At room temperature, the reaction is slow and the obvious solution is to raise the temperature. This may increase the rate of the reaction but, since the reaction is exothermic, it also has the effect, according to Le Chatelier's Principle, of favouring the reverse reaction and thus reducing equilibrium constant, given by:

Variation in K_eq for the Equilibrium
N₂ (g) + 3H₂ (g) ↔ 2NH₃ (g)
as a Function of Temperature^[5]

Temperature (°C)	Keq
300	4. An exothermic reaction is a Chemical reaction that releases Heat. In Chemistry, Le Chatelier's Principle, also called the Le Chatelier-Braun principle, can be used to predict the effect of a change in conditions on a Chemical For a general Chemical reaction \alpha A +\beta B. \rightleftharpoons \sigma S+\tau T. 34 x 10–3
400	1. 64 x 10–4
450	4. 51 x 10–5
500	1. 45 x 10–5
550	5. 38 x 10–6
600	2. 25 x 10–6

As the temperature increases, the equilibrium is shifted and hence, the constant drops dramatically according to the van't Hoff equation. The van 't Hoff equation (also known as the van 't Hoff isochore) in Chemical thermodynamics relates the change in temperature ( T) to the change in the Thus one might suppose that a low temperature is to be used and some other means to increase rate. However, the catalyst itself requires a temperature of at least 400 °C to be efficient.

Pressure is the obvious choice to favour the forward reaction because there are 4 moles of reactant for every 2 moles of product, and the pressure used (around 200 atm) alters the equilibrium concentrations to give a profitable yield. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface

Economically, though, pressure is an expensive commodity. Pipes and reaction vessels need to be strengthened, valves more rigorous, and there are safety considerations of working at 200 atm. In addition, running pumps and compressors takes considerable energy. Thus the compromise used gives a single pass yield of around 15%.

Another way to increase the yield of the reaction would be to remove the product (i. e. ammonia gas) from the system. In practice, gaseous ammonia is not removed from the reactor itself, since the temperature is too high; but it is removed from the equilibrium mixture of gases leaving the reaction vessel. The hot gases are cooled enough, whilst maintaining a high pressure, for the ammonia to condense and be removed as liquid. Unreacted hydrogen and nitrogen gases are then returned to the reaction vessel to undergo further reaction.

Catalysts

The catalyst has no effect on the position of equilibrium, rather, it provides an alternative pathway with lower activation energy and hence increases the reaction rate, while remaining chemically unchanged at the end of the reaction. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined The first Haber–Bosch reaction chambers used osmium and uranium catalysts. Osmium (ˈɒzmiəm is a Chemical element that has the symbol Os and Atomic number 76 Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the However, today a much less expensive iron catalyst is used almost exclusively. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26

In industrial practice, the iron catalyst is prepared by exposing a mass of magnetite, an iron oxide, to the hot hydrogen feedstock. Magnetite is not to be confused with Magnesite or Maghemite. Magnetite is a ferrimagnetic Mineral with chemical This reduces some of the magnetite to metallic iron, removing oxygen in the process. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the However, the catalyst maintains most of its bulk volume during the reduction, and so the result is a highly porous material whose large surface area aids its effectiveness as a catalyst. Other minor components of the catalyst include calcium and aluminium oxides, which support the porous iron catalyst and help it maintain its surface area over time, and potassium, which increases the electron density of the catalyst and so improves its reactivity. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J

The reaction mechanism, involving the heterogeneous catalyst, is believed to be as follows:

1. N₂(g) → N₂(adsorbed)
2. N₂(adsorbed) → 2N(adsorbed)
3. H₂(g) → H₂(adsorbed)
4. H₂(adsorbed) → 2H(adsorbed)
5. N(adsorbed) + 3H(adsorbed)→ NH₃(adsorbed)
6. NH₃(adsorbed) → NH₃(g)

Reaction 5 occurs in three steps, forming NH, NH₂, and then NH₃. Chemistry, a reaction mechanism is the step by step Sequence of Elementary reactions by which overall Chemical change occurs. Experimental evidence points to reaction 2 as being the slow, rate-determining step. The rate-determining step (RDS is a Chemistry term for the slowest step in a Chemical reaction.

A major contributor to the elucidation of this mechanism is Gerhard Ertl. Gerhard Ertl (born 10 October 1936 is a German Physicist and a Professor Emeritus at the Department of Physical Chemistry Fritz-Haber-Institut ^[6][7][8][9]

Economic and environmental aspects

The Haber process now produces 100 million tons of nitrogen fertilizer per year, mostly in the form of anhydrous ammonia, ammonium nitrate, and urea. Fertilizers ( also spelt fertiliser are chemical compounds given to Plants to promote growth they are usually applied either through the soil for uptake by plant Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor The Chemical compound ammonium nitrate, the Nitrate of Ammonia with the chemical formula N[[Hydrogen H]]4 N[[Oxygen O]]3 Urea is an Organic compound with the Chemical formula ( N[[hydrogen H]]22 C[[oxygen O]] 3-5% of world natural gas production is consumed in the Haber process (~1-2% of the world's annual energy supply)^[1],^[10],^[11],^[12]. That fertilizer is responsible for sustaining one-third of the Earth's population, as well as various deleterious environmental consequences. ^[13] Generation of hydrogen using electrolysis of water, using renewable energy, is not currently competitive cost-wise with hydrogen from fossil fuels, such as natural gas, and is responsible for only 4% of current hydrogen production. Notably, the rise of this industrial process led to the "Nitrate Crisis" in Chile, when the British industrials left the country -- since the natural nitrate mines were no longer profitable -- closing the mines and leaving a large unemployed Chilean population behind. Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the

See also

• Chemical kinetics
• Reaction rate
• Rate equation

References

External links

• What is the Haber-Bosch Process?
• Haber-Bosch process
• Fertilizer,agriculture and the production of food
• Britannica guide to Nobel Prizes: Fritz Haber
• Nobel e-Museum - Biography of Fritz Haber
• Uses and Production of Ammonia
• ”CIEC Catalysis”, [2]
• Haber Process for Ammonia Synthesis
• Jim Clark (2002). The Haber Process. Chemguide.

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