What is the main purpose of fractional distillation in oil refining?

• A. To separate crude oil into fractions with similar boiling points
• B. To remove impurities
• C. To convert all hydrocarbons to methane
• D. To polymerize hydrocarbons

Answer: (A)

Fractional distillation separates a mixture into portions that boil at similar temperatures. Crude oil contains many hydrocarbons with a wide range of boiling points. By heating it in a tall distillation column that gets cooler toward the top, the vapors rise and cool gradually. Substances with lower boiling points rise higher and condense there to form lighter fractions (like petrol), while heavier, higher-boiling components condense lower down to become heavier fractions (like fuel oils). In this way, crude oil is divided into fractions each made of hydrocarbons with similar boiling ranges, making them easier to process into useful products.

Purification or impurity removal isn’t the main goal here, and transforming hydrocarbons into methane or polymerizing them are separate chemical processes, not what this separation step is primarily about.