High performance organic/inorganic hybrid mixed matrix blend membranes of chitosan and hydroxyethyl cellulose for pervaporation separation of ethanol–water mixtures

Ethanol obtained from disposed biomass forms an azeotropic mixture with water. Since, pure ethanol can be replaced for conventional fuel and also it is required as a medium for various organic transformations, its separation from aqueous solution is of industrial importance. Conventional purification methods like distillation are not cost effective and also require an entrainer like benzene. Therefore, pervaporation separation of liquid mixtures by polymeric membranes is a simple, low cost and environmentally benign method. Hence, modification of natural polymers for their efficient application in pervaporation separation of liquid mixture is a vital issue. Composite blend membranes were prepared by solution casting method utilizing two natural polymers viz., chitosan (CS) and hydroxyethylcellulose (HEC) loaded with 2, 4 and 6 wt.% phosphotungstic acid (PWA) nanoparticles. The membranes were characterized by analytical techniques and their (PV) separation performance was investigated for ethanol dehydration that showed higher performance compared to either of the pristine CS/HEC blend membranes. The highest separation factor of 39976 was shown at 2 wt. % loading of PWA nanoparticles compared to 203 that was observed for pristine CS/HEC blend membrane. Increasing the loading of PWA nanoparticles in the matrix beyond 2 wt.% reduced the membrane performance, but on the other side flux increased with increasing PWA concentration, feed water composition and temperature. The changes in driving force, nanoparticle cluster formation and membrane swelling are responsible for such observed trends. The Arrhenius activation energy values evaluated from temperature dependence of diffusion and permeation parameters supported water selective nature of the composite membranes.