REVERSE OSMOSIS MEMBRANE SEPARATION CHARACTERISTICS OF VARIOUS ORGANICS: PREDICTION OF SEPARATION BY SURFACE FORCE - PORE FLOW MODEL AND SOLUTE SURFACE CONCENTRATION BY FINITE-ELEMENT METHOD

An aromatic polyamide membrane was used to study the separation of selected carboxylic acids, chlorophenols, nitrophenols and sodium chloride. An application for actual treatment of a coal liquefaction wastewater was also performed. Prediction of separation and flux data were obtained using the surface force pore flow (SFPF) model previously reported in the literature. Pore size distribution of polyamide thin film composite membranes and a cellulose acetate ultrafiltration membrane were obtained from vapor adsorption data of CO{dollar}sb{lcub}2{rcub}{dollar} and N{dollar}sb{lcub}2{rcub}{dollar} gases. The prediction of solute concentrations at the membrane wall were obtained from the diffusion-convection equation solved using a finite element method. The pore distribution data and wall concentration data were further used with solute separation data at a particular pressure to obtain the solute-solvent-membrane wall forces parameter involved. The interaction parameters were obtained by simultaneous solution of the ordinary differential equations describing the model, using the software package COLSYS. From the knowledge of the interaction forces, the solute separation and flux data (for nonionized organic solutes and sodium chloride) were predicted over a wide range of pressures and showed excellent agreement with experimental data. The prediction of rejection and flux for carboxylic acids, chlorophenol and nitrophenol systems by the SFPF model were further extended to multicomponent systems. The polyamide membrane used in this study had 97-99% standard NaCl rejections and 24-30 gfd pure water flux at 20.7 {dollar}times{dollar} 10{dollar}sp{lcub}5{rcub}{dollar} N/m{dollar}sp{lcub}2{rcub}{dollar}. For ionizable organics such as phenol, chlorophenol, dichlorophenol dots, the rejection and flux drops were highly dependent on operating pH values. Membrane experimental results showed 99.5-99.8% rejection at pH 11 of phenol, 2-CP and 2,4-DCP. Under no ionization conditions the flux drop observed for nitrophenol and chlorophenol systems was not caused by osmotic pressure effect and was related to physicochemical nature of the solute-solvent-membrane system.