The invention relates to methods for separating mixture components such as reactor effluent components. In particular, the invention relates to the use of an extractive agent such as a hydrocarbon in an extractive distillation process to separate monomers such as a C.sub.4-C.sub.7 isoolefins such as isobutylene from mixtures such as reactor effluents including one or more hydrofluorocarbon(s) (HFC).