Isomerization of Paraffins 91

Light paraffins are isomerized for two main reasons. The pentane and hexanes (C₅/C₆) are isomerized to increase their octane numbers (ON) in gasoline. Butane is isomerized to make isobutane for feed to alkylation plants. Processes for both purposes are evaluated in this report.

Feedstocks for C₅/C₆, isomerization processes are mixtures of alkanes, cycloalkanes, and other hydrocarbons. Octane improvements by once-through processes are limited by thermodynamic constraints. Two of these processes are evaluated. The use of separation processes and recycle of low-octane components attains further improvements at added costs. Three such processes are evaluated: one recycles normal pentane only, another recycles normal pentane and low-octane hexanes separated by distillation, and a third recycles normal paraffins separated by a molecular sieve process.