Effect of salt type on mass transfer in reverse osmosis thin film composite membranes

Reverse osmosis separation of inorganic salts in aqueous solutions has been studied using polyamide thin film composite membrane, in spiral wound configuration. Various inorganic salts involving monovalent and divalent ions have been studied. The solute transport through the membrane and the mass transfer coefficient at the high pressure feed side of the spiral wound module were determined for each type of salt. The mass transfer coefficient of each inorganic salt was predicted from the experimental data for the reverse osmosis separation of sodium chloride as reference and the mass transfer empirical correlations. The values obtained were compared with the experimental ones. The free energy parameters for monovalent cations, monovalent anions and divalent cations have been calculated. These parameters were used to predict the reverse osmosis performance of inorganic salts in spiral wound reverse osmosis module. It was observed that the free energy values of the cations are negative while those of the anions are positive, suggesting that the surface of the membrane used is positively charged.

The transport of various inorganic salts in aqueous solutions through polyamide thin film composite membrane in spiral wound -8 DK /δ (10 m/s) from Eq. (14) Monovalent cations Monovalent anions Divalent cations -8 DK /δ (10 m/s) from Eq. (6) Fig. 3. Comparison of the calculated solute transport parameters from Eq. (14) and the ones calculated from Eq. (6).