Why do we have fractional distillation

Crude oil is a mixture of hydrocarbons. The crude oil is evaporated and its vapours condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms and a similar range of boiling points. The diagram below summarises the main fractions from crude oil and their uses, and the trends in properties.

Note that the gases leave at the top of the column , the liquids condense in the middle and the solids stay at the bottom. As you go up the fractionating column, the hydrocarbons have:. Crude oil is not the only fossil fuel. Nuclear Fuels. Acid Rain. Climate Change. Climate Feedback. Ocean Acidification. Rising Sea Level. Diagram of a fractional distillation tower, showing where the different fractions will condense. May 25, Crude Oil Distillation Tower [Online].

Kraushaar, R. May 26, Energy and the Environment, 2nd ed. Hoboken, NJ, U. Theoretically, having more beads or plates improves the separation, but adding plates also increases the time and energy required to complete a distillation. Gasoline and many other chemicals are produced from crude oil using fractional distillation. Crude oil is heated until it evaporates.

Different fractions condense at certain temperature ranges. The chemicals in a certain fraction are hydrocarbons with comparable numbers of carbon atoms. From hot to cold largest hydrocarbons to smallest , the fractions might be residue used to make bitumen , fuel oil, diesel, kerosene, naphtha, gasoline, and refinery gas. Fractional distillation cannot completely separate the components of a mixture of ethanol and water despite the different boiling points of the two chemicals. Water boils at degrees Celcius while ethanol boils at If an alcohol-water mixture is boiled, the ethanol will concentrate in the vapor, but only up to a point, because alcohol and water form an azeotrope.

Fractional distillation differs from simple distillation because the fractionating column naturally separates compounds based on their boiling points. It's possible to isolate chemicals using simple distillation, but it requires careful control of the temperature because only one "fraction" can be isolated at a time. How do you know whether to use simple distillation or fractional distillation to separate a mixture?

Simple distillation is faster, simpler, and uses less energy, but it's really only useful when there is a large difference between the boiling points of the desired fractions more than 70 degrees Celcius. If there is only a small temperature difference between the fractions, fractional distillation is your best bet. Here's a breakdown of the differences between simple and fractional distillation:. Actively scan device characteristics for identification.

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