Room temperature ionic liquids have potential as novel extractants in the separation of aromatic/aliphatic hydrocarbons. While most of the ionic liquids are viscous and mass transfer rate of hydrocarbons in ionic liquids are noticeably low. Common extraction apparatus may not satisfy the separation process using ionic liquids as extractants. Single stage and four-stage tandem annular space centrifugal extractor were tried to separate ethylbenzene and octane using 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIIM][PF6]) ionic liquid as extractant. The changes of stage efficiency with the rotational speed and total flow rate were explored. Though the ionic liquid is very viscous, high extractive stage efficiency can be effectively achieved using the centrifugal extractor. (c) 2007 Elsevier B.V. All rights reserved.