Selective Extraction of 1-Hexene Against n-Hexane in Ionic Liquids with or without Silver Salt

This paper presents an extensive study on the feasibility of ionic liquids (ILs) for the extractive separation of a 1-hexene/n-hexane mixture. Seventeen ILs were tested at 313 K. The extraction selectivities of 1-hexene to n-hexane were in the range 1.5–3.0. The chemical structures of anion and cation in ILs greatly affected the extraction, and the functional groups, such as carbon–carbon double bond, nitrile, ester, and amide, in the ILs led to higher selectivities. The increase of alkyl chain length in cation led to the increase of extraction capacity of 1-hexene. To increase the distribution of 1-hexene in IL phase, silver salt was added to the ILs. It was found that ILs containing silver salt had a high distribution of 1-hexene, as well as high selectivity of 1-hexene against n-hexane. The extraction efficiency increased with the concentration of silver salt in ILs. When the initial feed concentration of 1-hexene was smaller, the selectivity of 1-hexene to n-hexane was higher. A simple mathematical model has been developed to describe the total 1-hexene content in the reaction media under study, on the basis of the formation of complexes between silver and 1-hexene with different stoichiometry. This work proves that the ILs can act as effective extractants in 1-hexene/n-hexane separation.