Flowchart: The industrial production of fertilisers

1. Key Industrial Processes for Fertiliser Production

The production of fertilisers relies on three main chemical processes:

1. Haber Process → Produces ammonia $(NH₃).$
2. Contact Process → Produces sulphuric acid $(H₂SO₄).$
3. Ostwald Process → Produces nitric acid $(HNO₃).$

2. Overview of Fertiliser Production

Step 1: Production of Ammonia (Haber Process)

• Raw materials: Nitrogen $(N₂)$ from air & hydrogen $(H₂)$ from methane.

• Reaction: $N_2 + 3H_2 \xrightarrow{\text{Fe catalyst}} 2NH_3$

• Ammonia is used to make nitrogen-based fertilisers.

Step 2: Production of Sulphuric Acid (Contact Process)

• Raw materials: $Sulphur (S) + Oxygen$ $(O₂).$
• Reactions:

  • Formation of sulphur dioxide $(SO₂):$ $S + O_2 \rightarrow SO_2$

  • Formation of sulphur trioxide (SO₃): $2SO_2 + O_2 \xrightarrow{\text{V₂O₅ catalyst}} 2SO_3$

  • Conversion to sulphuric acid: $SO_3 + H_2O \rightarrow H_2SO_4$

Step 3: Production of Nitric Acid (Ostwald Process)

• Raw materials: Ammonia (NH₃) + Oxygen $$(O₂).
• Reactions:

  • Oxidation of ammonia to form nitrogen monoxide $(NO):$ $4NH_3 + 5O_2 \xrightarrow{\text{Pt catalyst}} 4NO + 6H_2O$

  • Formation of nitrogen dioxide $(NO₂):$ $2NO + O_2 \rightarrow 2NO_2$

  • Formation of nitric acid (HNO₃): 4NO2+2H2O+O2→4HNO34NO_2 + 2H_2O + O_2 \rightarrow 4HNO_3

3. Production of Common Fertilisers

Fertiliser	Chemical Formula	Industrial Process
Ammonium Sulphate	$(NH_4)_2SO_4$	Haber + Contact Process
Ammonium Nitrate	$NH_4NO_3$	Haber + Ostwald Process
Superphosphates	$Ca(H_2PO_4)_2$	Phosphate Rock + Acid
Urea	$(NH_2)_2CO$	Haber Process

4. Key Takeaways

• The Haber Process produces ammonia, which is the base for many nitrogen fertilisers.
• The Contact Process produces sulphuric acid, needed for phosphate fertilisers.
• The Ostwald Process produces nitric acid, used in ammonium nitrate fertilisers.
• Fertilisers are made from ammonia, phosphoric acid, nitric acid, and potassium salts.