Alkanes: The Building Blocks of Fuels
Fuels are mixtures of hydrocarbon chains of varying lengths that meet the formula Cn+H2n+2. Molecules that meet this formula are known as ‘alkanes’, and these hydrocarbons are found in all organic matter. They also make up crude oil, and when crude oil is refined through fractional distillation, these alkane mixtures can be separated into many useful products – such as diesel, gas oil, kerosene, marine gas oil and lubricants among others.
Alkanes are not the only hydrocarbon chains found in crude oil – alkenes (hydrocarbons with the formula Cn+H2n) are also present in crude oil, and these are used in chemical processes, not fuels.
When a mixture of alkanes forms a distillate a flashpoint of higher than 42oC they are classified as fuel oils. Learn more about fuel oil here.
If you want to know more about the process of refining crude oil that allows alkanes to create useful fuels and oils, read our guide to crude oil fractional distillation.
Table of alkane hydrocarbons
The below lists the first 20 alkanes, although there are many more. Each type of fuel will have mixtures of different alkane chains, and these mixtures will give the fuel its desired properties.
| Alkane | Molecular Formula | Composition | Carbon atoms in chain | Hydrogen atoms in chain |
| Methane | CH4 | CH4 | 1 | 4 |
| Ethane | C2H6 | CH3-CH3 | 2 | 6 |
| Propane | C3H8 | CH3-CH2-CH3 | 3 | 8 |
| Butane | C4H10 | CH3-2(CH2)-CH3 | 4 | 10 |
| Pentane | C5H12 | CH3-3(CH2)-CH3 | 5 | 12 |
| Hexane | C6H14 | CH3-4(CH2)-CH3 | 6 | 14 |
| Heptane | C7H16 | CH3-5(CH2)-CH3 | 7 | 16 |
| Octane | C8H18 | CH3-6(CH2)-CH3 | 8 | 18 |
| Nonane | C9H20 | CH3-7(CH2)-CH3 | 9 | 20 |
| Decane | C10H22 | CH3-8(CH2)-CH3 | 10 | 22 |
| Undecane | C11H24 | CH3-9(CH2)-CH3 | 11 | 24 |
| Dodecane | C12H26 | CH3-10(CH2)-CH3 | 12 | 26 |
| Tridecane | C13H28 | CH3-11(CH2)-CH3 | 13 | 28 |
| Tetradecane | C14H30 | CH3-12(CH2)-CH3 | 14 | 30 |
| Pentadecane | C15H32 | CH3-13(CH2)-CH3 | 15 | 32 |
| Cetane (Hexadecatane) | C16H34 | CH3-14(CH2)-CH3 | 16 | 34 |
| Heptadecane | C17H36 | CH3-15(CH2)-CH3 | 17 | 36 |
| Octadecane | C18H38 | CH3-16(CH2)-CH3 | 18 | 38 |
| Nonadecane | C19H40 | CH3-17(CH2)-CH3 | 19 | 40 |
| Eicosane | C20H42 | CH3-18(CH2)-CH3 | 20 | 42 |
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