Nitric Acid (key component in the manufacture of Fertilizers) Uses, Properties and Manufacture.

 

You might know Nitric Acid since early grades of high school. But have you ever thought about what it is? How is it prepared? Here we will have a brief account of the definition of Nitric Acid, Its industrial manufacture, uses and properties.

 

Definition:-

Nitric acid is colourless, fuming, highly toxic and corrosive liquid. Exposure to it can cause severe burns. It has the boiling point of -83°C and a freezing point of -42°C.It is mostly used in the manufacture of nitrogenous fertilizers.

Manufacture of Nitric Acid:-

Nowadays, Nitric Acid is prepared by three different methods which were developed by time.

Ø  By catalytically oxidation of Ammonia.

Ø  By treating Sodium Nitrate by concentrated Sulfuric Acid(Conc.H₂SO₄)

Ø  By combination of Nitrogen and Oxygen.

So we through each method thoroughly to understand the chemical processing technology.

1.  Oxidation of Ammonia by Catalysts:-

Nitrogen found naturally is in diatomic form and is a very inert gas. It reacts with Oxygen produces Oxides of Nitrogen under certain conditions. An indirect method is followed to produce Nitric Acid by catalytic combustion of Ammonia with Oxygen. To produce Nitric Acid, first, we should have Nitrogen The dioxide will readily react with water to give Nitric Acid.

The reaction of Ammonia and Atmospheric Oxygen (i.e. combustion of Ammonia) is highly economical and has great industrial importance.

Ammonia and Molecular Oxygen will never undergo reaction spontaneously. However, when they are provided with heat in the presence of a specific catalyst they can be caused to react by gaining activation energy. Once the combustion of Ammonia is started, it will continue the evolution of heat. As it is the combustion, so all the reaction will be exothermic.

             4NH₃ + 5O₂ → 4NO + 6H₂O

The Nitric Oxide (NO) produce will react further with atmospheric oxygen to produce Nitrogen Dioxide.

4NO + 2O₂ → 4NO₂

The Nitrogen dioxide formed is made to absorb with water and react with it to give desired Nitric Acid.

             3NO₂ + H₂O → 2HNO₃ + NO

The Nitrogen monoxide formed is reticulated for oxidation of Nitrogen Oxide.

The overall equation for the total process is:

4NO₂ + 2H₂O + O₂ → 4HNO₃

2.  From Sodium nitrate and Sulfuric Acid:-

Chemicals Required:-

·         Sodium Nitrate (NaNO₃)

·         Sulfuric Acid (H₂SO₄)

       Chemical reaction:-

NaNO₃ + H₂SO₄ → HNO₃ + NaHSO₄

Process:-

Nitric acid can be produced on large scale from Sodium Nitrate and Sulfuric Acid. The equal parts of both are added to achieve the desired amount of Nitric Acid. The reactants are directly fired to Cast Iron Retort where these are heated with 150°C-200°C for about 12 hours. During this period Nitric Acid, its Oxides and Water is separated through Distillation Column.

3. Nitric Acid from Instrumental Air:-

Air freed from moisture and CO₂ is passed by a blower through the electric and then subjected to 3000°C. This high temperature is necessary for the combination of nitrogen and Oxygen because both are in diatomic form. They react to produce Nitric Oxide (Nitrogen Monoxide) NO.

            N₂ + O₂ ↔ 2NO

At about 3000°C, only 5% of NO is formed. The temperature of the gases must be dropped suddenly below 1000°C otherwise the equilibrium will shift backwards and only N₂ and O­₂ would be left.

Below 1000°C the decomposition of NO is negligible. The gases are further cooled in the cooling chamber. Now they are brought in contact with fresh air in the oxidizing unit where NO is oxidizes to NO₂.

The brown fumes of No₂ are then absorbed in water in absorption tower; Diluted Solution of Nitric acid is obtained. Diluted solution is simply concentrated by them, again and again, circulation of NO.

             4NO₂ + 2H₂­O → 4HNO₃

Properties:-

1.    Nitric acid is strong monobasic acid with the molecular formula HNO₃.

2.    Pure (100%) anhydrous Nitric Acid is a colourless liquid.

3.    It is a highly corrosive liquid with powerful oxidizing strength.

4.    Due to the presence of Nitric Oxide, its colour can vary from colourless to yellowish-red.

 What are the uses of Nitric Acid?

Ø  Nitric Acid is used in nitrogenous fertilizers more than enough. This is its most important use in the industry; it would not be an exaggeration to say that Nitric Acid is produced to be used in Fertilizers.

Ø  It is an essential compound in the formation of explosives.

Ø  It is used for pickling (cleaning metal surface).

Ø  It is used in the manufacture of Rayon (Artificial Silk).

Ø  It is used in dyes for making Nitro-Compounds which are further reduced to Amino-Compounds.

Ø  Used as solvent e.g. dissolving the insoluble sulphides of Lead, Bismuth, Copper and Carbide.

 

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