Development of novel blocked diisocyanate crosslinked chitosan membranes for pervaporation separation of water–isopropanol mixtures

Using a solution technique, novel polymeric membranes were prepared by incorporating water-soluble blocked diisocyanate into chitosan. The resulting crosslinked membranes were characterized by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD). After measuring the swelling data at different mass% of water, membranes were subjected for the pervaporation separation of water–isopropanol mixtures in a temperature range of 30–60 °C. The experimental results demonstrated that membrane containing 40 mass% of blocked diisocyanate showed the highest separation selectivity of 5918 with a flux of 2.20 × 10−2 kg/m2 h at 30 °C for 5 mass% of water. The total flux and flux of water were found to be overlapping particularly for higher crosslinked membranes, suggesting that the membranes developed with higher amount of blocked diisocyanate could be used effectively to break the azeotropic point of water–isopropanol mixture, so as to remove a small amount of water from isopropanol. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (Epw) were more than three times lower than those of isopropanol permeation (EpIPA), particularly for crosslinked membranes, suggesting that the developed membranes have higher separation efficiency for water–isopropanol system. The activation energy values for total permeation (Ep) and water permeation (Epw) were almost close to each other, signifying that coupled-transport of both water and isopropanol molecules is minimal due to a higher selective nature of membranes. The estimated Ep and ED values ranged between 22.68 and 30.78, and 21.19 and 29.22 kJ/mol, respectively. The positive heat of sorption (ΔHs) observed in all the membranes suggests the Henry's mode of sorption.