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Alkanes: Sources and Relevance

Alkanes: Catalytic Reforming

The transformation of long-chain hydrocarbons with low octane numbers into branched, cyclic or aromatic compounds with high octane ratings is called catalytic reforming. The goal of this process is to produce anti-knocking compounds which can be used as engine fuels.

Fig.1
Catalytic reformer
Fig.2
Distillation installation

Reaction principle

During catalytic reforming, gasoline fractions obtained from the distillation of crude oil are being passed at ca.500 - 550°C over beds of previously chlorinated platinum catalysts on fixed porous aluminum. Therefore, the process is also called plate-reforming. Three processes mainly increase the octane number.

Fig.3
Isomerisation of long-chain to branched alkanes
Fig.4
Dehydrogenation of cycloalkanes to aromatic compounds
Fig.5
Dehydrocyclization of long-chain alkanes to aromatic compounds

Fragmentation into shorter alkanes (cracking) and dehydrogenation to olefins are side reactions observed during catalytic reforming. The formation of olefins, especially of polyolefins, is undesirable because they reduce the stability of fuels towards oxidation and have a tendency to polymerize. The formation of undesirable olefinic compounds is prevented by adding hydrogen to the mixture of alkanes thereby re-hydrogenating the olefins to the corresponding alkanes. The activity of the Pt-catalyst is insufficient for hydrogenation to the desired anti-knocking aromatic compounds.

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