.The Performance of flat sheet polyamide nanofiltration membrane in rejection of binary mixture of heat stable salts (acetate and sulfate) from methyl-diethanolamine (MDEA) solution was investigated. The effects of pressure and concentration of MDEA solution on rejection of acetate and sulfate ions were studied. At MDEA concentration of 20% wt. and pressure of 70 bar, 80% and 98% rejection can be obtained for acetate and sulfate ions, respectively. Membrane performance and transport coefficients investigated using Spiegler-Kedem-Katchalsky (SKK) model, film theory and extended Nernst-Planck (FT-ENP) model. The results of FT-ENP model show accurate agreement with experimental results. This result can be obtained due to the considering the charge repulsion of sulfate ions. For sulfate ions, both models show errors less than 1% with >R2=0.98. In case of acetate, errors less than 3% (>R2=0.75) and 2% (>R2=0.89) were obtained for SKK and FT-ENP models, respectively.
