Alkenes are obtained from crude oil using fractional distillation followed by cracking. Explain how alkenes are produced using fractional distillation followed by cracking.  – 6517

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1. Fractional distillation
   Crude oil is first heated so it boils and turns into vapour. The vapour enters a fractionating column, which is hotter at the bottom and cooler at the top.
   Different fractions in the oil have different boiling points, so they condense at different heights in the column.

   Heavy fractions (with high boiling points) condense near the bottom.

   Light fractions (with low boiling points) condense near the top.

   Cracking
   Large hydrocarbon molecules from fractional distillation can be broken down into smaller ones by cracking.
   This is done by heating them to a high temperature and using a catalyst or steam.
   Cracking produces a mixture of alkanes and alkenes.

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