Foundation 5: Sulphuric Acid

Sulphuric Acid (H₂SO₄) is one of the most widely used chemicals in the world, playing a fundamental role in the fertiliser industry. Its primary use is in the production of phosphate Fertilisers, where it acts as a critical reagent for processing Phosphate Rock into Phosphoric Acid. The efficient production and application of Sulphuric Acid are essential for enhancing agricultural productivity globally.

Production Processes

Sulphuric Acid is primarily produced through the Contact Process, which involves three main stages:

Sulphur Combustion: Elemental Sulphur is burned in the presence of dry air to produce Sulphur Dioxide (SO₂).

Conversion to Sulphur Trioxide (SO₃): The SO₂ is oxidised to Sulphur trioxide (SO₃) using a vanadium pentoxide (V₂O₅) catalyst at high temperatures.

Formation of Sulphuric Acid: The SO₃ is absorbed into existing concentrated Sulphuric Acid to form Oleum (H₂S₂O₇), which is then diluted with water to produce the desired concentration of Sulphuric Acid.

This highly exothermic process allows for energy recovery, making Sulphuric Acid production both efficient and cost-effective.

Transportation and Storage

Due to its highly corrosive nature, Sulphuric Acid requires specialised handling during transportation and storage. It is typically transported in stainless steel or specially lined tankers to prevent leaks and corrosion. Storage facilities must be designed with acid-resistant materials, and strict safety protocols are necessary to minimise environmental and health risks.

Utilisation in Fertiliser Production

Sulphuric Acid is integral to producing key fertilisers by serving as the main input for Phosphoric Acid manufacturing. Phosphoric Acid, in turn, is used to produce phosphate-based Fertilisers:

Ammonium Phosphates: Sulphuric Acid indirectly contributes to producing Monoammonium Phosphate (MAP) and Diammonium Phosphate (DAP), two of the most widely used Fertilisers.

Superphosphates: By reacting directly with Phosphate Rock, Sulphuric Acid is used to produce Single Superphosphate (SSP) and Triple Superphosphate (TSP), which are rich sources of phosphorus for agricultural use.

Fertilisers produced using Sulphuric Acid (H₂SO₄):

Phosphate Fertilisers

Single Superphosphate (SSP)

Produced by reacting Phosphate Rock with Sulphuric Acid. Contains approximately 16-20% Phosphorus (P₂O₅).

Triple Superphosphate (TSP)

Created by using Phosphoric Acid derived from the reaction of Sulphuric Acid and phosphate rock. TSP is highly concentrated, containing about 45% phosphorus (P₂O₅).

Monoammonium Phosphate (MAP)

Derived indirectly, as Sulphuric Acid is used to produce the Phosphoric Acid required for MAP. Contains about 11% nitrogen (N) and 52% phosphorus (P₂O₅).

Diammonium Phosphate (DAP)

Like MAP, DAP production requires Phosphoric Acid made using Sulphuric Acid. It contains 18% Nitrogen (N) and 46% Phosphorus (P₂O₅).

Blended and Compound Fertilisers

NPK Fertilisers (Nitrogen, Phosphorus, and Potassium)

Sulphuric Acid is used to produce the Phosphoric Acid component in NPK blends, providing the phosphorus nutrient.

Phosphorus-Enriched Urea

Urea fortified with phosphorus through Phosphoric Acid produced using Sulphuric Acid.

Sulphur-Enriched Fertilisers

Ammonium Sulphate (AMS)

Often a by-product of industrial processes involving Sulphuric Acid, AMS is a Nitrogen and Sulphur fertiliser containing about 21% Nitrogen and 24% Sulphur.

Miscellaneous Fertilisers

Calcium Phosphate Fertilisers

Includes Fertilisers like Dicalcium Phosphate (DCP), produced indirectly via Sulphuric Acid in the Phosphoric Acid production chain.

Other Applications in Fertiliser Production

Superphosphoric Acid-Based Fertilisers

Sulphuric Acid is used to produce Superphosphoric Acid, which can be applied as a liquid Fertiliser or used to create customised Fertiliser formulations.