Study on characterization and pervaporation performance of interfacially polymerized polyamide thin-film composite membranes for dehydrating tetrahydrofuran

Low permeation fluxes with high separation factors were obtained when hydrophilic dense membranes were used for the dehydration of tetrahydrofuran (THF) by pervaporation. To improve the pervaporation performance of a membrane, the polyamide thin-film composite (TFC) membranes were prepared through interfacial polymerization by reacting 1,3-diaminopropane (DAPE), 1,3-cyclohexanediamine (CHDA), or m-phenylenediamine (MPDA) with trimesoyl chloride (TMC) on the surface of a polyacrylonitrile (PAN) membrane (DAPE-TMC/PAN, CHDA-TMC/PAN, and MPDA-TMC/PAN). Pervaporation separation of an aqueous THF solution with polyamide TFC membranes was investigated as functions of diamine structure and operating conditions. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), positron annihilation spectroscopy (PAS), and water contact angle measurements were applied to analyze the chemical structure, surface chemical composition, morphology, surface roughness, free volume, and hydrophilicity of the active polyamide layer of TFC membrane. Varying the diamine structure did affect the physicochemical properties and pervaporation performance of the polyamide TFC membranes. Compared with the CHDA-TMC/PAN and MPDA-TMC/PAN membranes, the DAPE-TMC/PAN membrane showed a lower permeation flux and a higher water concentration in permeate. This was in good agreement with the result of characterization. With an increase in the operating temperature of pervaporation, an increase in the permeation flux and a high water concentration in permeate (>99 wt%) were obtained for the DAPE-TMC/PAN membrane. It was also found that the DAPE-TMC/PAN membrane exhibited a superior performance compared with the several hydrophilic polymers and commercial inorganic membranes discussed in the literature.