Blocking phenomenon in permeation of amines through perfluorosulfonate ionomer containing metal(II) ions

The permeation of amines through perfluorosulfonate ionomer containing metal(II) ions was investigated. The feeds were the 1 M aqueous solutions of either ethylenediamine or propylamine. Metal(II) ions, known to complex with amines, used in this study were Fe2+, Mn2+, Zn2+, Cu2+, and Ni2+. In addition, the Na+-form and Ca2+-form membranes were also used to obtain the mass transfer rate through the solution-diffusion mechanism. It was found that incorporation of metal(II) ion into the membrane did not enhance the mass transfer rate through the membrane. In contrast, the complexation resulted in the fluxes lower than those obtained from the solution-diffusion. It was probable that the highly stable complexes forming within the intercluster regions of the membrane led to the blocking phenomenon. An in-depth study on this interesting phenomenon was done by varying the concentration of amine in the feed side. At low feed concentrations, 0.01–0.05 M, an increase in ethylenediamine flux with the increasing amine concentration suggested that the blocking was less than the largest possible extent. The flux then drastically decreased at the concentration of 0.1 M. Further increase in the feed concentration provided a slight increase in the flux, which most likely be attributed to the transport through the solution-diffusion mechanism. Unlike ethylenediamine, propylamine exhibited an increase in flux upon the increase of the feed concentration from 0.05 to 1.5 M.