hydroisomerization

Hydroisomerization is a catalytic process in hydrocarbon processing that converts straight-chain alkanes into branched isomers in the presence of hydrogen. It is commonly employed in petroleum refining to increase the octane number of low-octane paraffins and to upgrade waxes into branched paraffins suitable for fuels and lubricants.

In a typical system, a bifunctional catalyst provides metal sites for hydrogenation/dehydrogenation and acid sites for skeletal rearrangement. The metal dehydrogenates the alkane, forming an olefin or carbocation that rearranges on the acid sites and is then hydrogenated back to a branched product. This allows isomerization with limited cracking under controlled conditions.

Catalysts combine noble metals (Pt, Pd) or nickel on acidic supports such as zeolites (BEA, Y, MOR) or alumina–silica composites. Zeolites with appropriate pore structures influence iso-paraffin selectivity. Sulfide or other bifunctional hydrocracking catalysts are also used in related hydroisomerization applications.

Industrially, hydroisomerization upgrades straight-chain paraffins in LPG, gasoline components, and waxes, increasing octane and improving cold properties of lubricants.

Typical conditions: moderate temperatures (approximately 150–350°C) and hydrogen pressures from a few to several tens of bar, with higher hydrogen partial pressures promoting selectivity to isomers. Overly severe conditions cause cracking and faster catalyst deactivation from coke.

Hydroisomerization complements hydrocracking and alkylation processes by increasing branching without substantial chain scission, enabling higher-value fuels from relatively inexpensive feedstocks.