Cracking
Fuels made from oil mixtures containing large A compound that contains hydrogen and carbon only. A collection of two or more atoms held together by chemical bonds. are not efficient as they do not flow easily and are difficult to Set on fire.. Mixture of hydrocarbons, mainly alkanes, formed over millions of years from the remains of ancient dead marine organisms. often contains too many large hydrocarbon molecules and not enough small hydrocarbon molecules to meet demand. This is where cracking comes in.
Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules. In fractional distillation, such as that of crude oil, the different parts of the original mixture are called fractions. The substances in each fraction have similar boiling points to each other. containing large hydrocarbon molecules are heated to To turn from a liquid to a gas or a vapour. them. They are then:
- heated to 600-700掳C
- passed over a A substance that changes the rate of a chemical reaction without being changed by the reaction itself. of silica or alumina
These processes break A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons. in the molecules, causing Type of reaction in which a compound breaks down to form two or more substances when it is heated. reactions. Cracking produces smaller Saturated hydrocarbon. A compound of hydrogen and carbon only, with no C=C bonds. and Unsaturated hydrocarbon with a double bond between the carbon atoms..
Cracking of decane
There is a greater demand for smaller hydrocarbons than larger ones.
decane 鈫 octane + ethene
C10H22 鈫 C8H18 + C2H4
The process is as follows:
Some of the smaller hydrocarbons formed by cracking are used as fuels (eg large chains are often cracked to form octane for petrol, which is in high demand), and the alkenes are used to make A large molecule formed from many identical smaller molecules known as monomers. in the manufacturing of plastics. Sometimes, hydrogen is also produced during cracking.