π Electron induced separation of organic compounds using supported ionic liquid membranes

Supported ionic liquid membranes have been tested for fractionation of organic compounds. Imidazolium based ionic liquids; 1-allyl-3-vinylimidazolium bromide, 1-hexyl-3-vinylimidazolium bromide and 1-octyl-3-vinylimidazolium bromide were trapped in the pores of a polypropylene membrane. Fractionation of a feed stream consisting of benzene, naphthalene and phenanthrene in tetradecane and cis- and trans-stilbene in hexane were investigated. The receiving phase was hexane. Differences in the π electron cloud density of the aromatic solutes influence their interactions with the imidazolium cation, which can affect the rates of transport. In the case of the three aromatic solutes, the degree of conjugation and molecular weight increase in order benzene, naphthalene and phenanthrene. These opposing effects result in similar mass transfer coefficients for the three solutes for the three ionic liquids tested. However, for cis-and trans-stilbene, the mass transfer coefficient was larger for all three ionic liquids. It is likely that enhanced aromatic stacking of the trans- isomer led to a higher mass transfer coefficient. In addition, 1-hexyl-3-vinylimidazolium bis(trifluoromethylsulfonyl)imide was used as the liquid membrane phase to fractionate two nucleobases: thymine and cytosine in water. The receiving phase was also water. The membrane mass transfer coefficient for thymine was 5.5 times greater than cytosine indicating the possibility of exploiting multimodal interactions with the imidazolium group to fractionate compounds.