Absorption Of Toluene And Xylene In Imidazolium Ionic Liquids

With the problems of high energy consumption and secondary pollution in theconventional technogy of recovering volatile organic compounds （VOCs） containingtoluene and xylene, the study of new absorbent is necessary. Ionic liquids （ILs） have beendescribed as green solvents. Particularly, the imidazolium-based ILs with anions such as[PF₆]-and [BF₄]-possess several properties that make them attractive alternatives to otherILs. Therefore, the imidazolium-based ILs have been studied to absorb toluene andxylene.In this study, the1-butyl-3-methylimidazole tetrafluoroborate （[Bmim][BF₄]） and1-butyl-3-methylimidazolium hexafluorophosphate （[Bmim][PF₆]） were choosed asabsorbents. The phase equilibria and the physical properties （pH, viscosity, density） of thebinary systems （[Bmim][BF₄] or [Bmim][PF₆]+toluene or xylene） have been measured.The best conditions of absorbing and efficiency were investigated. It was found that theabsorbing effect of [Bmim][PF₆] was better than [Bmim][BF₄]. The reusing of[Bmim][PF₆] and absorbing mechanism have been studied.The results showed that the solubilities of toluene and xylene in the ILs at T=（295.15to356.65） K increased with the increase of temperature under atmospheric pressure. Atthe same conditions, the solubilities of toluene and xylene in the two ILs were in sequence:[Bmim][PF₆]-toluene>[Bmim][BF₄]-toluene>[Bmim][PF₆]-xylene>[Bmim][BF₄]-xylene. The relative ionic affinity was in the order toluene> xylene in the same ILs. ThepH, density, viscosity of the four binary mixtures at T=（293.15to343.15） K decreasedwith the increase of temperature, and decreased with the decrease of the mole fraction ofthe ILs. Comparison showed that the pH, density, viscosity the binary mixtures was insequence:[Bmim][BF₄]<[Bmim][PF₆] at the same temperature and the same molefraction of the ILs. The efficiency was high at the best absorbing conditions, and theabsorbing efficiency of [Bmim][PF₆] was higher than [Bmim][BF₄] significantly. The ILsof [Bmim][PF₆] could be reused many times. The results indicated that hydrogen bondingoccured, and chemical bonding between ILs and toluene （xylene） did not occur by the1HNMR spectra, UV-VIS spectrum and FT-IR spectrum.The study of the phase equilibria and the physical properties （pH, viscosity, density）of the binary systems （[Bmim][BF₄] or [Bmim][PF₆]+toluene or xylene）, has establishedtheoretical foundation for the applications in liquid-liquid extraction and the theoreticalstudy. The efficiency, reusing study and absorbing mechanism of ILs, have offered the theoretical basic for the industrial application.