Process Technology Quick Reference Cards

Isomerization

Chapter from the Process Technology Quick Reference Cards.

ISOMERIZATION

Process Objective

Convert normal pentane and hexane to their branched isomers to increase octane number of light straight-run naphtha.

Key Operating Variables

Variable	Typical Range	Effect / Notes
Temperature	250-400°F	Lower T → higher equilibrium i-C5/C6 but lower reaction rate
Pressure	200-450 psig	Moderate P, H2 atmosphere for catalyst stability
LHSV	1-3 hr⁻¹	Sufficient contact time for equilibrium approach
H2/HC Ratio	1-4 mol/mol	Prevents coking, maintains catalyst activity
Feed N+2A	<70	Higher naphthenes + 2× aromatics = better feed quality

Process Configurations

Once-through: simplest, lowest octane uplift (78-83 RON)
DIP (deisopentanizer) recycle: recycles n-C5, improves RON (86-88)
DIH (deisohexanizer) recycle: recycles n-C6, highest RON (89-92)
Penex (UOP) / ISOMALK (Axens): common licensed processes

Products & Yields

Isomerate: light naphtha with 82-92 RON (vs. 65-72 LSR feed)
No significant byproducts — very high liquid yield (98-99%+)

Common Troubleshooting

Low octane: check temperature (may be too high — equilibrium shift), feed quality
Catalyst deactivation: water, sulfur, nitrogen poisons — check feed treating
Chloride management: organic chloride addition maintains catalyst acidity

Source: Process_Tech_Quick_Reference_Cards_v1.xlsx · sheet “Isomerization”

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