What is Isomerization?

Isomerization with zeolite catalysts covers two distinct industrial applications: hydroisomerization of n-alkanes for dewaxing and cold-flow improvement, and aromatic isomerization (xylenes, ethylbenzene) for petrochemical intermediate production. Each application demands a different zeolite framework, and each converts a lower-value isomer into a higher-value one.

The Two Isomerization Families

n-Alkane hydroisomerization: Linear paraffins are converted to branched isomers to improve cold-flow properties (pour point, cloud point) of diesel and lubricant base oils. This is the chemistry behind catalytic dewaxing. The reference zeolite is SAPO-11, whose AEL framework with elliptical 10-MR channels (~4.0 × 6.5 Å) provides mild acidity and constrained geometry that selectively isomerises linear paraffins with minimal cracking.

Aromatic isomerization: Xylene isomerisation converts a thermodynamic mixture of o-, m-, p-xylene into the p-xylene-enriched stream needed for polyester feedstock, and ethylbenzene conversion produces benzene. The reference zeolite is Beta, whose 12-MR 3D pores accommodate substituted aromatics with strong acidity.

How Bifunctional Catalysts Work

Both families use bifunctional metal/acid catalysts: a noble metal (typically Pt) for dehydrogenation/hydrogenation and the zeolite acid sites for the isomerisation step. The metal function operates at far higher rates than the acid-catalysed rearrangement, so the overall rate is controlled by the acid sites:

1. n-alkane dehydrogenates on Pt → n-olefin
2. n-olefin isomerises on the zeolite acid site → iso-olefin
3. iso-olefin hydrogenates on Pt → iso-alkane

For xylene isomerisation, the metal function also converts ethylbenzene (which does not isomerise over acid sites alone) to benzene and light olefins.

Zeolite Selection Summary

See best zeolite for isomerization for the selection comparison. When requesting a sample, specify your feed type (n-paraffin range or aromatic stream), target isomerization route, and whether you need zeolite powder for catalyst formulation or a pre-formulated bifunctional catalyst.