15.0 SULPHUR AND ITS COMPOUNDS

Sulphur is a bright yellow, non-metal element found in nature. It is essential for life (in amino acids) and is a key industrial chemical. This chapter explores how sulphur is extracted from underground deposits (the Frasch process), its interesting allotropic forms, the properties of its oxides, and the industrial production of sulphuric acid – the most widely manufactured chemical in the world.

15.1 EXTRACTION OF SULPHUR (FRASCH PROCESS)

Most of the world's sulphur is found underground in salt domes, often associated with natural gas and petroleum. The Frasch process is used to extract this sulphur without mining.

15.1.1 Principle

Sulphur has a relatively low melting point (about 115°C). The Frasch process uses superheated water to melt the sulphur underground, and then compressed air forces the molten sulphur to the surface.

15.1.2 The Process

• A special three-concentric-pipe drill is sunk into the sulphur deposit.
• Superheated water (at about 170°C and high pressure) is pumped down through the outermost pipe. This melts the sulphur underground.
• Hot compressed air is pumped down through the innermost pipe. The air pressure forces the mixture of molten sulphur and water up through the middle pipe.
• The mixture is discharged into large tanks, where the sulphur solidifies (as it is less dense than water and separates). The sulphur obtained is up to 99.5% pure.

15.1.3 W