Comparison of Bulk, Emulsion, Thin Sheet Supported, and Hollo Fiber Supported Liquid Membranes in Macrocycle-Mediated Cation Separations

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Abstract
The advantages, disadvantages, and possible applications of macrocycle-mediated bulk, emulsion, supported and hollow fiber liquid membranes have been investi-gated. The relative transport rates of the alkali metal cations and of Zn(II), Cd(II) and Hg(II) in sin-gle and competitive cation experiments are studied and compared in the different membrane types. The four membrane types demonstrate similar selectivities but significantly different cation fluxes under comparable conditions using analogous macrocyclic carriers. The degree of distribution of the macrocycle to the organic membrane which is necessary for significant transport varies dramatically among the membrane types, each of which requires unique solvent characteristics. In the experiments, either l8-crown-6, dicyclohexano-l8-crown-6, or 4,1′(5)bis(1-hydroxyheptylcyclohexano)-l8-crown-6 were incorporated into bulk (chloroform, raethylene chloride), emulsion (toluene), supported (phenylhexane) and hollow fiber (phenylhexane or 1-octanol) liquid membranes with the membrane solvents shown in parentheses.