What is isomerization and why is it important in refining?

Isomerization converts straight-chain paraffins to branched isomers for octane improvement. Light naphtha isomerization: C5/C6 fraction over Pt/chlorided alumina or zeolite catalyst at 120-180C, 20-35 bar hydrogen. n-pentane (62 RON) converts to isopentane (92 RON), n-hexane (25 RON) to 2,2-dimethylbutane (92 RON). Process configurations: once-through, recycle of unconverted n-paraffins (DIH, DIP), or integration with molecular sieves for normal paraffin recycle. Butane isomerization converts n-butane to isobutane for alkylation feed. C5/C6 isomerization typically achieves product octane of 82-92 RON depending on configuration. Important because regulations limit benzene in gasoline, so benzene precursors must be hydrogenated and octane recovered via isomerization.