Ammonia - znu.ac.ir

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(Applied Chemistry)

Inorganic Industrials Chemistry

Ammonia

R. Pourata

In the Name of God

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Outline Introduction (short history)

Properties

Nitrogen cycle

Ammonia Production

Haber

Bosch process

Effects of parameter

Ammonia Synthesis Reaction

Synthetic Ammonia Manufacture

Uses of Ammonia

Economic Aspects

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Introduction

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Introduction

The name ammonia for the nitrogen - hydrogen compound NH3 is

derived from the oasis Ammon (today Siwa) in Egypt, where

Ammonia salts were already known in ancient times and also the

Arabs were aware of ammonium carbonate.

In the form of sal-ammoniac, ammonia was known to the Arabic

alchemists as early as the 8th century, first mentioned by Geber

(Jabir ibn Hayyan), and to the European alchemists since the 13th

century, being mentioned by Albertus Magnus. It was also used by

dyers in the Middle Ages in the form of fermented urine to alter the

colour of vegetable dyes.

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Introduction In the 15th century, Basilius Valentinus showed that ammonia could

be obtained by the action of alkalis on sal-ammoniac.

Before the start of World War I, most ammonia was obtained by

distillation of nitrogenous vegetable and animal waste products,

including camel dung, hoofs and horns of oxen and neutralizing the

resulting carbonate with hydrochloric acid, the name "spirit of

hartshorn" was applied to ammonia.

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

Distillation of coal

Electric arc process

Cyanamid process

Introduction

In 1913, the first Haber

Bosch plant went on stream, representing

the first commercial synthesis of ammonia from the elements. Today

ammonia is a commodity product of the chemical industry.

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Properties

Properties

Ammonia

IUPAC name Azane

Other names

Ammonia Hydrogen nitride Spirit of Hartshorn Nitro-Sil Vaporole

Properties

Molecular formula NH3

Molar mass 17.0306 g/mol

Appearance Colorless gas with strong pungent odor

Density 0.6942

Melting point -77.73 °C (195.42 K)

Boiling point -33.34 °C (239.81 K)

Solubility in water 89.9 g/100 mL at 0 °C

Basicity (pKb) 4.75 (reaction with H2O)

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Properties

Nitrogen cycle During pre-industrial times, the only way in which molecular N was converted into reactive N was by N precipitation caused by lightning and by biological nitrogen fixation.

N2

2N H0298 = 911 kJ/mol

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Nitrogen cycle

Ammonia and its salts are also byproducts of commercial processing

(gasification, coking) of fuels such as coal, lignite and peat other

sources of nitrogen compounds are exhausts from industrial, power-

generation, and automotive sectors

Ammonia and its oxidation

products, which combine to

form ammonium nitrate and

nitrite, are produced from

nitrogen and water vapor by

electrical discharges in the

atmosphere.

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Ammonia Production

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Ammonia Production

Distillation of coal

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Ammonia Production In principle there are three ways of breaking the bond of the nitrogen

molecule and fixing the element in a compound:

1) To combine the atmospheric elements nitrogen and oxygen directly

to form nitric oxides

2) To use compounds capable of fixing nitrogen in their structure

under certain oxides reaction conditions.

3) To combine nitrogen and hydrogen to give ammonia

A vast amount of research in all three directions led to commercial

processes for each of them: the electric arc process, the Cyanamid process, and ammonia synthesis, which finally displaced the other

two and rendered them obsolete.

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Ammonia Production

http://www.greener-industry.org/pages/ammonia/2AmmoniaMU.htm

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Electric Arc Process The availability of cheap hydroelectric power in Norway and the

United States stimulated the development of the electric arc process.

Air was passed through an electric arc which raised its temperature to

3000 °C, where nitrogen and oxygen combine to give nitric oxide. In

1904 CHRISTIAN BIRKELAND performed successful experiments

and, together with SAM EYDE, an industrial process was developed

and a commercial plant was built, which by 1908 was already

producing 7000 t of fixed nitrogen.

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-industry.org/pages/ammonia/2AmmoniaMU.htm

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Cyanamid process The Cyanamid process, developed by FRANK and CARO in 1898,

was commercially established by 1910.

Calcium carbide, formed from coke and lime in a carbide furnace,

reacts with nitrogen to give calcium cyanamide, which can be

decomposed with water to yield ammonia.

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Cyanamid process

Cyanamide process is a process of manufacturing fertilizer calcium

cyanamide and ammonia. The reaction runs at high temperatures 1000

- 1100 °C often with catalyst in mixture of nitrogen and calcium

carbide, which form calcium cyanamide and carbon:

CaC2 + N2 CaCN2 + C

Further produced calcium cyanamide gives together with water steam

calcium carbonate and ammonia:

CaCN2 + 3 H2O CaCO3 + 2 NH3

The second phase of this process can proceed also in soil. Then the

produced ammonia is oxidized to nitrate and used by plants.

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Cyanamid process

The Haber Process An essential industrial process

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Haber

Bosch process

Around 1900 fritz haber began to investigate

the ammonia equilibrium at atmospheric

pressure and found minimal ammonia

concentrations at around 1000 C (0.012 %).

In 1908 haber approached BASF to seek

support for his work and to discuss the

possibilities for the realization of an industrial

process.

Fritz Haber (1868 1934)

Haber

Bosch process His successful demonstration in April 1909 of a small laboratory

scale ammonia plant having all the features described above

finally convinced the BASF representatives, and the company's

board decided to pursue the technical development of the process

with all available resources.

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Haber

Bosch process

In an unprecedented achievement, carl

bosch, together with a team of dedicated

and highly skilled co-workers, succeeded

in developing a commercial process in

less than five years. The first plant started

production in September 1913 and had a

daily capacity of 30 t of ammonia. Carl Busch

Haber

Bosch process

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The reaction between nitrogen gas and hydrogen gas to produce

ammonia gas is exothermic, releasing 92.4kJ/mol of energy at 298K

(25oC).

N2(g) + 3H2(g) 2NH3 (g) + heat H = -92.4 kJ mol-1

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Increasing the pressure causes the equilibrium position to move to the

right resulting in a higher yield of ammonia since there are more gas

molecules on the left hand side of the equation than there are on the

right hand side of the equation. Increasing the pressure means the

system adjusts to reduce the effect of the change, that is, to reduce the

pressure by having fewer gas molecules.

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Effects of parameter Decreasing the temperature causes the equilibrium position to move to

the right resulting in a higher yield of ammonia since the reaction is

exothermic. Reducing the temperature means the system will adjust to

minimize the effect of the change, that is, it will produce more heat

since energy is a product of the reaction, and will therefore produce

more ammonia gas as well


Effects of parameter As the temperature increases, the equilibrium constant decreases as the yield of ammonia decreases.

Temperature

( oC) Keq

25 6.4 x 102

200 4.4 x 10- 1

300 4.3 x 10- 3

400 1.6 x 10- 4

500 1.5 x 10- 5

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Effects of parameter Rate considerations:

Increased temperature means more reactant molecules have sufficient

energy to overcome the energy barrier to reacting (activation energy)

so the reaction is faster at higher temperatures (but the yield of

ammonia is lower as discussed above).

A temperature range of 400-500oC is a compromise designed to

achieve an acceptable yield of ammonia (10-20%) within an

acceptable time period.

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Effects of parameter Rate considerations:

A catalyst such as an iron catalyst is used to speed up the reaction by

lowering the activation energy so that the N2 bonds and H2 bonds can

be more readily broken.

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Effects of parameter At 200oC and pressures above 750atm there is an almost 100% conversion of reactants to the ammonia product.

Since there are difficulties associated with containing larger amounts of materials at this high pressure, lower pressures of around 200atm are used industrially.

By using a pressure of around 200atm and a temperature of about 500oC, the yield of ammonia is 10-20%, while costs and safety concerns in the building and during operation of the plant are minimized

temperature and pressures


Reaction rate for NH3 synthesis. Dependence on the temperature at various pressures.

Temperature and Pressures

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Reaction rate for NH3 synthesis. Dependence on the ammonia concentration at various pressures.

Ammonia concentration and pressures


Nitrogen reaction rate v in m3 NH3/(m3 catalyst · s) as a function of temperature and ammonia concentration at 20 MPa pressure and 11 vol% inerts in the inlet synthesis gas a) locus of temperatures resulting in maximum reaction rate at a given ammonia concentration

Temperature and Ammonia concentration

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Ammonia conversion as a function of hydrogen/nitrogen ratios in the inlet synthesis gas with space velocity (per hour) as parameter; 9.7 MPa pressure

Hydrogen/Nitrogen Ratios


Performance of a converter as a function of inlet inert gas (CH4 and Ar) content with space velocity (per hour) as parameter, inlet NH3 content is 3.5%; 30 MPa pressure; catalyst particle size is 6 10 mm

Inert gas content

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Ammonia Synthesis Reaction As with every catalytic gas-phase reaction, the course of ammonia

synthesis by the Haber

Bosch process can be divided into the

following steps:

1) Transport of the reactants by diffusion and convection out of the

bulk gas stream, through a laminar boundary layer, to the outer

surface of the catalyst particles, and further through the pore system to

the inner surface (pore walls)

2) Adsorption of the reactants (and catalyst poisons) on the inner

surface

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Ammonia Synthesis Reaction 3) Reaction of the adsorbed species, if need be with participation by

hydrogen from the gas phase, to form activated intermediate

compounds

4) Desorption of the ammonia formed into the gas phase

5) Transport of the ammonia through the pore system and the laminar

boundary layer into the bulk gas stream

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Ammonia Synthesis Reaction Catalyst Catalyst

Ammonia Synthesis Reaction Mechanism of the Reaction

where * denotes a surface atom.

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Process Steps of Ammonia Production

A) Synthesis gas production

1) Feedstock pretreatment and gas generation

2) Carbon monoxide conversion

3) Gas purification

B) Compression

C) Synthesis

D) Ammonia separation

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Synthesis Gas Production

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Manufacture of Mixtures of Hydrogen, Nitrogen and Carbon

Monoxide

Steam Reforming

Partial Oxidation of Heavy Heating Oil

Coal Gasification

Conversion of Carbon Monoxide

Removal of Carbon Dioxide and Hydrogen Sulfide

Final Purification of Synthesis Gases

Synthesis Gas Production

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Raw Materials

Synthesis gas:

N2

- from air or natural gas

H2

- from reaction of natural gas or naphtha with H2O (by

steam reforming)

- from heavy fuel oil and H2O (by partial oxidation)

- from coal and water (by coal gasification)

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Raw Materials Hydrogen Production worldwide:

77% from natural gas/crude oil fractions

18% from coal

4% from water electrolysis

1% from other sources

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Steam Reforming Desulfurization

This is accomplished by contacting the raw materials with CoO- or

NiO- and MoO3-containing catalysts in the presence of hydrogen at

350 to 450°C, whereupon the sulfur-carbon compounds are reduced to

H2S which is adsorbed on ZnO.

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Steam Reforming Primary Reforming

After- desulfurization, steam is added and the mixture heated to 480

to 550°C before it is fed into the primary reformer. The gas leaving

the primary reformer contains between 7 and 10% methane.

CnH2n+2+nH2O nCO+(2n+ 1)H2

methane or naphtha are cracked in a primary reformer at 700 to

830°C under pressure on NiO-Al2O3- or NiO- MgO- Al2O3-catalysts.

Reactions:

CH4 + H2O <==> CO + 3 H2

CH4 + 2 H2O <==> CO2 + 4 H2

CnH(2n+2) + n H2O <==> n CO + (2n+1) H2

CO + H2O <==> CO2 + H2

Steam Reformer

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Steam Reforming Kinetics of Steam Reforming

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Steam Reforming Secondary Reforming

The gas leaving the primary reformer contains between 7 and 10%

methane. This is removed in so-called secondary reformers in

which the gas leaving the primary reformer is partially burnt with air

in nickel catalyst-filled shaft furnaces (autothermal process),

whereupon the temperature increases to ca. 1000°C. Under these

conditions CH4 is converted into H2 and CO at 1000 to 1200°C in the

presence of Cr2O3-containing catalyst.

The quantity of air is adjusted to give the nitrogen to hydrogen ratio

required for the stoichiometry of the ammonia synthesis.

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Partial Oxidation of Heavy Heating Oil In partial oxidation, the raw materials, e.g. heavy heating oil, are

oxidized to hydrogen and carbon monoxide with insufficient oxygen

for total combustion:

2CnH2n+2+ nO2 2nCO+2 (n+1)H2

If oxygen-enriched air is used, its quantity is adjusted to give the

nitrogen to hydrogen ratio required for the stoichiometry of the

ammonia synthesis. The partial oxidation is autothermal and in

contrast to steam reforming does not require a catalyst. It proceeds at

temperatures between 1200 and 1500°C and at a pressure of 30 to 40

bar.

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Partial Oxidation of Heavy Heating Oil The advantage of the partial oxidation process is that sulfur does not

interfere and therefore desulfurization is unnecessary.

Disadvantageous compared with steam reforming is, however, that an

air fractionation plant for oxygen production is necessary.

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Coal Gasification A mixture of hydrogen, carbon monoxide, carbon dioxide, methane

and sometimes nitrogen is formed upon the partial oxidation of coal

with oxygen or air and steam at high temperatures.

C+H2O H2+CO

2C+O2 2CO

Coal Gasification is a autothermal reaction of coal, O2 and H2O-vapor

at high temperature (800 to 1600°C)

30 to 40% of the coal utilized being burnt to attain the required high

reaction temperatures.

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Conversion of Carbon Monoxide

The next step in the manufacture of synthesis gas is the removal of

carbon dioxide by oxidizing it with steam to carbon dioxide, the steam

being reduced to hydrogen:

CO +H2O CO2 +H2

High temperature conversion at 350 to 380°C on iron oxide/chromium

oxide catalysts or on sulfur-insensitive Co/Mo-containing catalysts

Low temperature conversion at 200 to 250°C on very sulfur-sensitive

CuO/ZnO catalysts

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In the next step the carbon dioxide, mostly from the conversion

reaction, and the hydrogen sulfide, if present, are removed from the

gas mixture. This is accomplished either by physical or chemical

absorption in appropriate solvents.

Removal of the acidic gases CO2 and H2S by physical or chemical

absorption

Chemical solvents are best suited to scrubbing gases that have a

relative low CO2 partial pressure, whereas the physical solvents are

more suitable for higher CO2 contents in the raw gas.

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Physical absorption:

with methanol, propylene carbonate, N-methylpyrrolidone,

poly(ethyleneglycol dimethyl ether)

Chemical absorption:

with mono-, di- and triethanolamine, N-methyldiethanoloamine,

diisopropanolaimine, potassium salt of monomethylamino-propionic

acid, solutions of potassium carbonate

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To protect the ammonia synthesis catalysts from premature poisoning

the nitrogen-hydrogen-mixture, after the removal of the acidic

components carbon dioxide and hydrogen sulfide, has to be subjected

to further intensive purification to remove quantitatively any oxygen-

containing impurities present.

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The large quantities of carbon monoxide present after high

temperature conversion (3 to 5% by volume), are removed by liquid

nitrogen scrubbing.

Formerly residual water, carbon dioxide and methane were removed

by adsorption on zeolites to prevent ice formation during liquid

nitrogen

scrubbing and the hydrocarbons removed by condensation.

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Final Purification of Synthesis Gases Nitrogen-hydrogen mixtures resulting from low temperature

conversion contain only 0.1 to 0.3% by volume of carbon monoxide.

In this case the ca. 0.01 to 0.1% by volume of carbon monoxide and

carbon dioxide present after carbon dioxide scrubbing is hydrogenated

to methane (methanation) in the presence of nickel catalysts on a

carrier in an exothermic reaction at 30 bar and 250 to 350°C:

CO + 3 H2 CH4+ H2O (g)

and

CO2 + 4 H2 CH4 + 2 H2O (g)

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Conversion of Synthesis Gas to Ammonia

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Conversion of Synthesis Gas to Ammonia

NH3 synthesis is a cyclic process:

removal of:

NH3

inert gas

reaction heat (utilized for heating up cold synthesis gas)

recycling of unused synthesis gas into the reactor

supply of fresh gas

compensation of pressure losses

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Ammonia Separation

The separation of the ammonia formed from the circulating gas is

mainly carried out by condensation at low temperatures.

The separation of ammonia formed in the synthesis gas is carried out

by absorption in water. Water vapor which thereby enters the cycling

gas is removed by scrubbing with liquid ammonia, to avoid

deterioration of the catalyst by water vapor.

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Ammonia Separation




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Uses of Ammonia

Uses of Ammonia


Main uses of ammonia


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Uses of Ammonia Fertilser

Agricultural industries are the major users of ammonia, representing

nearly 80% of all ammonia produced in the United States. Ammonia

is a very valuable source of nitrogen that is essential for plant

growth. Depending on the particular crop being grown, up to 200

pounds of ammonia per acre may be applied for each growing season.

http://www.rmtech.net/uses_of_ammonia.htm

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Uses of Ammonia Ammonia is used in the production of liquid fertilizer solutions which

consist of ammonia, ammonium nitrate, urea and aqua ammonia. It is

also used by the fertilizer industry to produce ammonium and nitrate

salts.

Ammonia and urea are used as a source of protein in livestock feeds

for ruminating animals such as cattle, sheep and goats. Ammonia can

also be used as a pre-harvest cotton defoliant, an anti-fungal agent on

certain fruits and as preservative for the storage of high-moisture

corn.




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Uses of Ammonia

Fertilser

ammonium sulfate, (NH4)2SO4

ammonium phosphate, (NH4)3PO4

ammonium nitrate, NH4NO3

urea, (NH2)2CO,

CO2 carbon dioxide

+ 2NH3

ammonia

H2NCOONH4 ammonium carbonate

heat, pressure

(NH2)2CO urea

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Uses of Ammonia

Chemicals

nitric acid, HNO3

sodium hydrogen carbonate (sodium bicarbonate), NaHCO3

sodium carbonate, Na2CO3

hydrogen cyanide (hydrocyanic acid), HCN

hydrazine, N2H4 (used in rocket propulsion systems)

chemical intermediates

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Uses of Ammonia Explosives

ammonium nitrate, NH4NO3

2,4,6-trinitrotoluene, TNT

nitroglycerine

Fibers & Plastics

nylon, -[(CH2)4-CO-NH-(CH2)6-NH-CO]-,

Other polyamides

Refrigeration

used for making ice, bulk food storage, large scale refrigeration

plants, air-conditioning units in buildings and plants

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Uses of Ammonia Pharmaceuticals

Used in the manufacture of drugs such as sulfonamide which inhibit

the growth and multiplication of bacteria that require p-aminobenzoic

acid (PABA) for the biosynthesis of folic acids, anti-malarials and

vitamins such as the B vitamins nicotinamide (niacinamide) and

thiamine.

Cleaning

ammonia in solution is used as a cleaning agent such as in 'cloudy

ammonia'

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Uses of Ammonia Pulp & Paper

The pulp and paper industry uses ammonia for pulping wood and as a

casein dispersant in the coating of paper.

Ammonium hydrogen sulfite, NH4HSO3, enables some hardwoods to

be used.

Mining & Metallurgy

used in nitriding (bright annealing) steel,

used in zinc and nickel extraction

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Uses of Ammonia Food industry

The food and beverage industry uses ammonia as a source of nitrogen

needed for yeast and microorganisms

Rubber production

Ammonia is used in the rubber industry for the stabilization of natural

and synthetic latex to prevent premature coagulation.



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Uses of Ammonia Metal plating

Ammonium carbonate used in chrome plating, ammonium formate

and acetate used in other plating processes

Chlorine-Ammonia Treatment

Water purification used to manufacture chloramine (NH2Cl), an anti-

bacterial compound more persistent than chlorine.

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Economic Aspects

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Economic Aspects About 1.6 % of the world consumption of fossil energy (not including

combustion of wood) goes into the production of ammonia. In

developing countries, ammonia is generally one of the first products

of industrialization.

Economic Aspects

Development of ammonia production and world population

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Economic Aspects


Economic Aspects

Development of ammonia prices and DM/$ ratio in North-West Europe

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Economic Aspects

Geographical distribution of ammonia capacity and capacity utilization rate

Economic Aspects



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Economic Aspects Europe and North America, which now together have a 25 % capacity share, lost their leading position (54 % in 1969) to Asia, which now accounts for 38 % (17 % in 1969), as may be seen from Figure

Geographical shift of ammonia world production capacity

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