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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, lp, the osmotic permeability, lπ, 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 lπ/lπ 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.
