At the end of the fractional distillation, long hydrocarbon molecules can be transformed into lighter molecules by means of more advanced techniques (cracking). The new molecules can then be combined again into long polymer chains and other synthetic materials to produce increasingly flexible, economic, comfortable, efficient products used in our daily lives.
That process is called thermal cracking and consists in heating hydrocarbons up to a 800°C temperature in special high-pressure chambers (up to 100 atmospheres). As the temperature rises, the bond between carbon atoms break. Besides the lighter hydrocarbon molecules, which can be further refined through catalytic cracking, a large production of coke is achieved. All that remains is used in the production of asphalt and bitumen.
The catalyst used in the catalytic cracking allows to operate at lower temperature and pressure (up to 500°C and from 2 to 4 atmospheres). A process leading to the transformation of light hydrocarbons into even lighter molecules and limiting the production of coke is steam cracking, which envisages operating at low pressure and a temperature of 850°C. The various cracking processes lead to the mutual separation of the various hydrocarbons very effectively, so that 97% pure propylene and almost 100% pure ethylene can be produced. .
A further process is called catalytic reforming: it turns benzene from a saturated into a cyclic hydrocarbon with a higher octane content, thus improving the anti-knock characteristics of petrol and consequently enhancing engine performance.