Characterization of a Macrocycle-Mediated Dual Module Hollow Fiber Membrane Contactor for Making Cation Separations

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Abstract
Separation of metal cations in aqueous solution by a macrocyclemediated Dual Hollow Fiber Membrane Contactor is described. The advantages of this type of supported liquid membrane configuration include easily accessible source, receiving and membrane phases; transport rates competitive with those of other types of membranes; and the potential for continuous operation. The new system was investigated to determine the effect of aqueous solution flow rate and membrane solvent stirring rate on Na+ and K+ transport using dicyclohexano-18-crown-6 as the carrier. The results demonstrated that transport increases with increasing stirring speed, but remains constant with increased aqueous flow rate through the fibers within the range of four to twelve m1/min. The membrane solvents hexane, toluene, octane, 1-octanol, 4-methyl-2-pentanone, octanal, and 2-octanone were tested for their ability to preserve membrane integrity in the presence of aqueous solutions of low pH, and to maximize transport. Of these solvents, 2-octanone was found to be most effective in minimizing acid diffusion across the membrane, while giving the highest facilitated K+ transport rate. Quantitative transport using 18-crown-6 was observed for K+ over Na+ (all solvents studied) and Ba2+ and Sr2+ over Ca2+ (only octanol was studied).