Distillation and Separation
Petroleum Refining
The base unit of all fossil fuels, including crude oil, are hydrocarbon molecules composed of hydrogen (H) and carbon (C) atoms.
However, not all hydrocarbons are the same in shape, size and weight - some are short chains such as methane (CH4) as is the case for natural gas, and some form rings such as benzene (C6H6). The gasoline that we use in our vehicles is really a collection of a specific range of hydrocarbon sizes (around C4H10 to C13H28), which are smaller than the hydrocarbons that make up diesel (around C14H30 to C17H36).
Differences in the size, shape and weight of hydrocarbons mean that they have different chemical and physical reaction properties, including the temperature at which they boil. Generally, the larger the hydrocarbon, the heavier it is and the more energy it will take to boil. Using these differences in boiling points and weights, fossil fuels can initially be separated into their various parts within distillation towers