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Abstract

Several thin-film composite membrane systems, Poly(ether/amide) and Poly-ether/urea) have been characterized in hyperfiltration and dialysis-osmosis experiments. Using the phenomenological relationships of the thermodynamics of irreversible processes, the hydrodynamic permeability, l^p, the osmotic permeability, l^π, the asymptotic salt rejection, r^∞ , and the reflection coefficient, σ, have been determined as functions of NaCl concentration at 25δC. All membranes yielded large values of r^∞ even at brine concentrations of 0.5 M NaCl and a small variation of salt rejection r, with pressure corresponding to a ratio of l^π/l^π not much larger than r^∞2. The reflection coefficients received from dialysis-osmosis experiments differ substantially from the corresponding values of the asymptotic salt rejection, r^∞. A comparison between the transport coefficients of these thin-film composite membranes and the transport coefficients of some asymmetric cellulose acetate membranes show that the thin-film composite membranes behave much more like a semipermeable membrane.