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DF5

Supply and demand means that there is not enough petrol or diesel. Thus, they have to be produced by cracking of longer chain alkanes.

Cracking

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    Any reaction in which a larger molecule is broken into smaller molecules

\begin{gather*} \text{Alkanes}\rightarrow\text{Branched Alkanes + Branched Alkenes} \\ \text{Alkanes}\rightarrow\text{Smaller Alkanes + Cycloalkanes} \\ \text{Cycloalkanes}\rightarrow\text{Alkenes + Branched Alkenes} \\ \text{Alkenes}\rightarrow\text{Smaller Alkenes} \\ \end{gather*}

Alkenes are unsaturated; they have a triple bond between carbon atoms.

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    Products of cracking must be later separated

Modern Catalytic Cracking

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    Large vessel

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    Zeolite catalyst and vaporised hydrocarbons

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    Mixture force upwards by steam

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    Acts as a fluidised solid bed

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    Coke can form on catalyst, so requires regeneration

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    Coke is burnt off catalyst

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    Energy released from burning coke used to heat and vaporise feedstock