Question

Explain in details why crude oil requires to be refined and explain how this process is done with suitable diagram.

Answer 1

Crude oil generally contains a large number and different structures of hydrocarbon molecules. It contains dissolved gases from C1 - C4 as well as asphalt or tar in it with different composition. Different applications requires different type of fuel/materials to work like automobiles require diesel and petrol whereas furnaces in refinery requires furnace oil, for lubrication purpose lubricating oils are required etc., lubricating oil generally requires C30 - C40 carbon chains whereas tar is required for road making and many other things, jet fuel is required for fuel in airplanes. That’s why crude oil is refined to separate different components/compounds/chemistry for different applications.

As you can see in the diagram, firstly the crude oil is passed through a desalting unit where it strips all the salts from crude oil so that it does not corrode the distillation columns. After coming out of the desalting unit, crude oil is pre-heated and transferred to an atmospheric distillation column where depending upon the difference in boiling point, different components separate in different section of distillation column. It can be Cleary seen in the above diagram that depending upon the boiling range of components, they are separating accordingly. Light molecules/fraction travels to the top part of the column whereas, heavy hydrocarbons/fractions deposit in the bottom of the distillation column.

Top Section of an Atmospheric distillation column

The products like LPG (Liquefied Petroleum Gas), Gasoline, LNG (Liquified Natural Gas) rises to the top part of the column where it gets condensed and gets settled.

Middle Section of an Atmospheric distillation column

Medium weight fraction liquids which includes kerosene and diesel, stays at the middle of the distillation column. A heavier liquid like gas oils separates lower down in the distillation column.

Bottom Section of an Atmospheric distillation column

At the bottom of the distillation column, heavier fraction having higher boiling point settles.

Further processing

The bottom of the distillation column is send to vacuum distillation unit where further separation of high boiling components takes place under vacuum. After distillation processes, further purification of the products are done o increase its commercial value like cracking, reforming, or alkylation.

Cracking is done to break large hydrocarbon chains into smaller hydrocarbons with the help of heat, pressure to make into more valuable products. Reforming uses a catalyst and alkylation re-arranges molecules to produce the light products of higher commercial use and value.