When one speaks of crude oil, or petroleum, one may imagine this particular image in mind: a drilling platform or vast dry land with a big black fountain of oil. And from that crude oil, comes different products ranging from the clear petroleum that is used to fuel cars, or to black tires, to plastics, and even crayons. From the crudeness of the oil that gushes out of the earth, oil mining companies refine the oil so that it could be used for different purposes.

To understand the fining process, one must first grasp the multitude of the different hydrocarbons (compounds of carbon and hydrogen which contain a lot of energy) present in crude oil. The most basic of these hydrocarbons is methane, CH4. And the number of carbons in a compound could increase. The compounds may be either straight or branched compounds (such as paraffin: propane, isobutane, hexane) or in a cyclic ring (naphthenes, benzene).

All these hydrocarbons have different boiling points. Therefore it is possible to separate these compounds by the process of distillation – at different temperatures a hydrocarbon of a certain type and length boils and evaporates, and then is condensed separately. Hence, this process wherein the hydrocarbons in the mixture of crude oil are segregated by their boiling points, called fractional distillation, is where it all begins.

Petroleum gas, or known commonly as the compounds methane, ethane, propane and butane have a boiling point less than 40 degrees Celsius (104˚ F). Naptha or ligroin boils at around 60˚to 100˚ C (140˚ to 212˚ F); and these intermediates are further refined into gasoline (a mix of alkanes and cycloalkanes with a boiling range of 40˚ to 205˚C/104˚ to 401˚ F). Kerosene (175˚ to 325˚ C/350˚ to 617˚ F), diesel distillate (250˚ to 350˚ C/482˚ to 662˚ F), lubricating oil (300˚ to 370˚ C/572˚ to 700˚ F) and industrial oil (370˚ to 600˚ C/700˚ to 112˚ F) feature increasing boiling temperature ranges. Finally, residuals such as tar, asphalt, coke and waxes melt at temperatures higher than 600˚ C/1112˚ F.

Fractional distillation starts with heating the crude oil mixture to temperatures around 600˚ C. Most of the substances boil and evaporate. The vapours pass through the fractional distillation column which contains different trays or plates arranged in different levels that correspond to the different boiling points of the hydrocarbons. When a vapour reaches a certain plate which corresponds its boiling temperature, it cools and condenses (those with low boiling points will condense high up in the column where it is cooler and those with high boiling points turn liquid at the lower part of the column). The trays collect the different liquid fractions for further processing and refinement.