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Why Do We Use Simple Distillation If The Difference Between The B.p Is Greater Than 25. And Therefore Why Do We Use Fractional Distillation For Crude Oil?

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Rebecca Hunt answered
Fractional distillation is used for crude oil because it allows the oil to be fractioned into useful substances, each of which have hydrocarbons of different boiling points. When processed in large industrial oil refineries, crude oil can be separated cleanly and efficiently. These separations and distillations can create a range of crude oil products including diesel fuel, asphalt, gasoline and kerosene.

  • Diesel fuel.
Diesel fuel is created as a distillate from crude oil. In order to be separated it needs to be kept at atmospheric pressure between 200 and 350 degrees C. This results in a mixture of carbon chains that contain between eight and 21 carbon atoms per molecule.
  • Asphalt.
Fractional distillation separates asphalt from other distillates under vacuum conditions. Further processing of the heavier fractions of the crude oil, within a de-asphalting unit, allow a better separation to occur. This uses propane or butane to dissolve the lighter molecules.
  • Gasoline.
Gasoline is made from the aliphatic hydrocarbons that are distilled from crude oil. These are enhanced with isooctane to increase the octane rating. The virgin or straight run gasoline that comes directly from the distilling process does not meet the necessary requirements for modern engines so it must be included within a blend.
  • Kerosene.
The thin, clear liquid of kerosene is obtained from crude oil through fractional distillation at temperatures between 150 and 275 degrees C. This process creates a carbon mixture that contains six and 16 carbon atoms per molecule.

These are just four of the products that are created through the fractional distillation of crude oil. The reason that fractional distillation is used is that it allows clear separations to be made for a variety of different products. It also allows blends to made to create an even bigger range of end products.

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