school energy&environment

Refining

Crude oil includes a large range of hydrocarbons with different quantities of carbon atoms. The ratio of the components varies according to the place of origin. For example, the oil of Venezuela is rich in long molecules making it thicker, whereas the crude oil from the North Sea is more liquid. To subdivide crude oil into its components, while providing its optimum exploitation, a fractioned distillation (or refining or cracking) is necessary. The various hydrocarbons are separated according to their different boiling temperature. Liquid crude oil is heated up to 400° C at the base of the refining tower and turns into a gas mixture rising up. While they rise, the gases cool down and, according to different condensation temperatures, are separated. Heavier hydrocarbons condensate immediately and are deposited at the bottom. The others rise up and liquefy again at different levels, where they are collected. Residues contain over 20 carbon atoms, condensate first and can be further separated by means of vacuum distillation to produce lubricants, paraffin, wax and bitumen.
Gas-oil contains 14/20 carbon atoms and condensates at a temperature of 250/350°C. It is an oil fuel used to propel diesel engines and for household heating purposes.
Kerosene contains 10/15 carbon atoms and condensates at 160/250°C. It is an oil fuel used to propel jet planes and heating systems.
Naphtha contains 8/12 carbon atoms and condensates at 70/160°. It is a yellow liquid used as fuel and processed to manufacture plastic materials, pharmaceuticals, pesticides and fertilisers. It is also a solvent to treat rubber.
Petrol contains 5/10 carbon atoms and condensates at 20/70°. It is used as fuel for cars and planes but also to manufacture plastic materials and detergents. At 20° C only methane, ethane, propane and butane remain gaseous. Most of them are used as energy sources and to produce petrochemical substances and plastic materials. Butane and propane in particular are used in the production of the fuel called liquid natural gas.