The Use of Fractional Distillation to separate components of Crude Oil Refining Crude Oil The Use of Fractional Distillation to separate components of Crude Oil

Fractional Distillation Tower Crude oil is fed into a furnace and heated without the presence of air (oxygen). Most of the oil is converted into a vapour and rises up the tower (column). As the vapour rises up the tower it begins to cool. Heavier ‘fractions’ of crude oil condense first in the lower parts of the tower. The lightest fractions condense at the top of the tower. Some fractions (1 to 4 carbons remain as gases) Each fraction is removed from the tower as it condenses. Fraction = a hydrocarbon with a specific number of carbon atoms Each fraction has its own condensation temperature

Names of commonly used hydrocarbon fractions

A two-step fractionation tower Some fractions never vapourize and sink to the bottom of the tower as bitumen. This solid fraction is used to produce Asphalt

The bubble caps found inside a fractional distillation tower help separate the crude oil vapour into distinct fractions. Heavy fractions that have reached their condensation temperatures will hit the bubble cap, condense and drip down to the pans below. These fractions are then removed from the tower. Lighter fractions remain as vapour will hit the cap but continue to rise up to the next higher layer of bubble caps.

A close-up view of the massive furnaces, fractional distillation towers and pipes found in an oil refinery.

Notice that the cracking unit in this diagram takes large fractions such as lubricating and heavy gas oils and breaks them into shorter more useful compounds such as naphtha, gasoline and kerosene. The coker removes pure carbon (used as coal powder) from the residual or bitumen. Cracking – the process in which long hydrocarbons are broken into shorter (and more useful) hydrocarbon fractions such as gasoline (petrol). Cracking is achieved by adding steam, heat, hydrogen gas, catalysts or viscosity reducing compounds. example: C20H42 + H2 → C12H26 + C8H18 Reforming – the process in which short hydrocarbon fractions are combined to form more useful long hydrocarbon fractions. Catalysts are used to complete this process. example: C3H8 + C5H12 → C8H18 +H2

A flow chart showing the flow of crude oil from the furnace to the fractional distillation tower to cracking and reforming stations and finally to the many storage tanks that store different hydrocarbon fractions

Oil refinery in Sarnia, Ontario Oil refinery in Sarnia, Ontario. Fractional distillation towers and storage tanks are visible.