A mass transfer model based on a concentration boundary layer, as suggested by film theory, is proposed in this study. The mass transfer coefficient for the case of an unstirred batch cell was predicted using an extrapolation technique based on a suitable curve fitted equation. The parabolic partial differential equation resulting from the unsteady state mass balance over the concentration boundary layer was solved by a numerical technique using a second order implicit method. The solution process also couples the osmotic pressure model for the prediction of flux and an equation from irreversible thermodynamics for the prediction of real rejection. All equations were solved simultaneously by the multidimensional Newton-Raphson technique using Broyden's correction factor to enhance the rate of convergence. The final predicted flux and rejection was found to be in good agreement with the experimental data, and the absolute average deviation in both cases was found to be well within 10%.