Development of Hybrid Membranes Using Chitosan and Silica Precursors for Pervaporation Separation of Water plus Isopropanol Mixtures

Using a sol-gel technique, organic-inorganic hybrid membranes were prepared using chitosan and mixed silica precursors such as tetraethoxysilane and gamma- glycidoxypropyltrimethoxysilane. The gamma-glycidoxypropyltrimethoxysilane acted as a coupling agent to enhance the compatibility between the organic (chitosan) and the inorganic (tetraethoxysilane) phase. Different techniques such as Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were employed to study the physicochemical changes in the resulting membranes. These membranes were tested for their ability to separate water + isopropanol mixtures by pervaporation in the temperature range of (303 to 323) K. The experimental data demonstrated that both flux and selectivity were increased simultaneously with increasing the amount of gamma-glycidoxypropyltrimethoxysilane. However, this trend no longer remained when the content of gamma-glycidoxypropyltrimethoxysilane was increased beyond 0.25 mass fraction. The membrane containing 0.25 mass fraction of gamma-glycidoxypropyltrimethoxysilane (M-2) exhibited the highest separation selectivity of 18 981 with a thickness-normalized flux of 7.45.10(-7) kg.m(-1).h(-1) at 303 K. The total flux and flux of water were found to be overlapping with up to 0.25 mass fraction of gamma-glycidoxypropyltrimethoxysilane, suggesting that these membranes could be used effectively to break the azeotropic point of water isopropanol mixtures. From the temperature-dependent permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (E-pw) are significantly lower than those of isopropanol permeation (E-pIPA), suggesting that the developed membranes have demonstrated an excellent separation performance for water isopropanol systems.