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Production of Ammonia

History of ammonia manufacturing processes

Before the start of World War I, most ammonia was obtained by the dry distillation ofnitrogenous vegetable and animal products; the reduction of nitrous acid and nitrites with

hydrogen; and the decomposition of ammonium salts by alkaline hydroxides or by

quicklime, the salt most generally used being the 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 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.

Industrial Uses

Fertilizers Explosives Food and beverages Industry Metal Treating Mining Industry Refrigerant Rubber Industry

Haber-Bosch process

This process involves the direct reaction between Hydrogen and Nitrogen. Before carrying

out the process, Nitrogen and Hydrogen gas are produced.

Nitrogen

Nitrogen is by far the most abundant gas in the Earth's atmosphere, making up 78.084% of

the air we breathe. Nitrogen is commonly produced industrially by the low-temperaturedistillation of air.

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Hydrogen

Hydrogen can be produced by either of these various processes,

Reforming Methane Reforming Methanol Electrolysis of water

Hydrogen is commonly produced on an industrial large scale by the catalytic reforming of

Methane. Although hydrogen can also be produced by catalytically reforming of methanol

or by the electrolysis of water, neither of those processes are currently practiced on a large

scale.

Reaction

This involves the direct combination of Nitrogen and Hydrogen. The reaction is reversible,meaning that some ammonia will be formed, but not all will react. The reaction is asfollows,

N2(g) + 3H2(g) 2NH3(g) H = -93.6 kJ/mol

Process Flow Diagram

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Modern Ammonia Process Flow Diagram

The first step in the process is to remove sulfur compounds from the feedstock because sulfur

deactivates the catalysts used in subsequent steps. Sulfur removal requires catalytic

hydrogenation to convert sulfur compounds in the feedstocks to gaseous hydrogen sulfide:

H2 + RSH RH + H2S

The gaseous hydrogen sulfide is then absorbed and removed by passing it through beds of zinc

oxide where it is 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 + 3H2

The next step uses catalytic shift conversion to convert the carbon monoxide to carbon dioxideand more hydrogen:

CO + H2O CO2 + H2

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The carbon dioxide is then removed either by absorption in aqueous ethanolamine solutions or

by adsorption inPressure 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 + 3H2 CH4 + H2O

CO2 + 4H2 CH4 + 2H2O

To produce the desired end-product ammonia, the hydrogen is then catalytically reacted withnitrogen (derived from process air) to form anhydrous liquid ammonia. This step is known as the

ammonia synthesis loop.

3H2 + N2 2NH3

The steam reforming, shift conversion, carbon dioxide removal and methanation steps eachoperate 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 on the proprietary design used.