The applications of hydrogen
Feedstock for chemical production
- Hydrogen is used to remove sulphur during petroleum refining.
Sulphur compounds present in crude oil form sulphur dioxide when they are burned. Since this gas contributes to acid rain, the sulphur compounds are removed during oil refining. Oil fractions are passed over a catalyst, and reacted with hydrogen under high temperature and pressure to produce hydrogen sulphide. This gas is separated and converted to sulphur for removal.
- Hydrogen is used in the manufacture of ammonia.
Ammonia, used for fertilisers, explosives and dyes, it is produced using the Haber process. In this process, hydrogen and nitrogen react together in the presence of an iron catalyst at around 450 °C and 20 MPa pressure.
Fuel Cells
- Fuel cells produce electricity using liquid or gaseous fuels. When fuelled by hydrogen, the only by-product of a fuel cell is water.
Fuel cells are devices that produce electricity from chemical reactions. Fuel cells powered by hydrogen are very attractive as an environmentally friendly power source, because the only by-product is water. Fuel cells in the International Space Station make electricity and drinking water for the astronauts. Hydrogen fuel cells also power cars, buses and other vehicles.
Glass Making
- Flat "float glass" for windows is made by floating molten glass on molten tin. Hydrogen removes oxygen. This stops the molten tin oxidising or hazy residues forming on the glass.
The flat glass used to make windows and doors is called float glass. Molten glass is floated on molten tin and slowly cooled until it becomes flat and solid. The process needs to take place in a nitrogen atmosphere free of oxygen, because oxygen would react with the molten tin and also leave hazy residues on the glass surface. Hydrogen is included in the atmosphere to react with any oxygen present and so remove it.
Space Exploration
- Liquid hydrogen powered the main engines of the space shuttle. The huge external tank attached to the shuttle at lift-off contained one and half million litres of liquid hydrogen.
- Hydrogen was used to power NASA's Saturn V rockets which took people to the Moon.
Hydrogen is highly flammable. It can be stored as a gas under pressure or as a liquid at -253 °C. Compared to the same mass of petrol, liquid hydrogen stores three times more energy but it occupies ten times the volume. So why use liquid hydrogen for rocket engines instead of petrol? A larger fuel tank may be needed if liquid hydrogen is used, but the mass of the fuel is a third of the mass needed if petrol were to be used. This allows a much heavier payload to be carried into space.
