Fractional Distillation

In this video you will learn how fractional distillation separates crude oil into useful fractions crude oil is the term used to describe unprocessed oil that is oil that has been

taken directly out of the ground either on land or under the sea it is an exceptionally valuable resource it provides us with a great number of hydrocarbons some of which are

useful as fuels and others are used in the manufacture of many different chemicals and even plastics however in the raw form as crude oil it can be a viscous dark-colored tar like

consistency and the different fractions of hydrocarbons must be separated by fractional distillation for them to be useful before we understand how fractional distillation works

we should be clear that crude oil is a mixture of hydrocarbons with different chain lengths some being short molecules and some being very long intermolecular forces at

between molecules and the longer the molecule the greater the intermolecular force as you can see here the small molecules have weaker intermolecular forces and so

will require less energy to break them apart and turn them into a gas they have a lower boiling point the longer molecules have greater intermolecular forces more

energy is required a higher temperature will be needed to evaporate these molecules they have a higher boiling point now we understand how chain length is related to the boiling point

of a molecule let us look at how this method works as you can see crude oil is heated up to a high temperature outside of the fractionating column the hot crude oil now mostly in

vapor form is pumped into the column the column as a heat gradient and is very hot at the bottom going cooler as we move up to the top even at the very bottom of the column where the

temperature is still high some long-chain molecules with high boiling points begin to condense back into a liquid these are collected at the bottom of the column the rest

of the molecules start to rise up the column making their way through bubble caps in each tray the bubble caps slow down the rate of the rising vapor and eventually the vapors get

to cool condense and are collected as liquids in the trays small molecules have low boiling points and so condense much higher in the column where the temperature is cooler still

as you can see hydrocarbons with similar boiling points are collected in the same tray and this is why they are known as fractions they are mixtures of hydrocarbons with similar

boiling points each fraction has some important uses some examples of fractions are petrol useful as a fuel for cars naphtha used in the manufacture of chemicals

kerosene as aircraft fuel diesel oil used as fuels for vans cars and lorries and pitchman a mixture of large chain hydrocarbons used to lay roads now at the end of this

video you should understand that crude oil is a mixture of important hydrocarbons and the fractional distillation is the method used to separate crude oil into useful fractions with

similar boiling point you should understand that small chain molecules are collected at the top of the column since they have lower boiling points and larger chain molecules are

collected further down the column as these have higher boiling points

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