Isomerization
Catalytic reforming has little effect on Light Straight Run gasoline (LSR), which is material in the C5 - 165˚F (74˚C) boiling range. This fraction is removed from reformer feed. Its octane number may be significantly improved by converting normal paraffins into their isomers in the Isomerization Unit.
Isomerization can result in a significant octane increase since n-pentane has a research octane number (RON) of 62 and iso-pentane has a RON of 92. Once through isomerization can increase LSR gasoline octane from 70 to around 82 RON.
Isomerization catalysts contain platinum and, like reforming, must have all sulfur removed. Additionally, some catalysts require continuous additions of small amounts of organic chlorides to maintain activity. Organic chlorides are converted to hydrochloric acid; therefore, Isomerization feed must be free of water to avoid serious corrosion problems. Other catalysts use a molecular sieve base and are reported to tolerate water better. Isomerization uses reaction temperatures of 300-400˚F (150-200˚C) at pressures of 250-400 psi (17-27 bar).
For refineries that do not have hydrocracking facilities to supply iso-butane for alkylation feed, iso-butane can be made from n-butane using isomerization.
