High performance composite membranes with a polycarbophil calcium transition layer for pervaporation dehydration of ethanol

A new kind of composite membranes, consisting of a polyacrylonitrile (PAN) support layer, a polycarbophil calcium (PCP) transition layer and a glutaraldehyde cross-linked chitosan (CS) active layer, was prepared by sequential casting and spin coating methods. A dense region was formed between the active layer and the transition layer as confirmed by positron annihilation spectroscopy. No distinct boundary between these two layers was observed by field emission scanning electron microscope and the total thickness of these two layers was around 200 nm. The static water contact angle revealed that the PCP layer promoted interfacial compatibility between the PAN layer and the CS layer. T-peel test verified that the interfacial adhesion strength of the composite membrane was enhanced by the incorporation of PCP transition layer. The composite membranes were utilized for pervaporation dehydration of ethanol. Even when the PCP concentration was only 0.05 wt%, the CS/PCP/PAN membrane exhibited a high performance with the separation factor of 1279 and the permeation flux of 1390 g/m2h for 90 wt% ethanol aqueous solution at 353 K with a flow rate of 60 L/h and a pressure of 0.1 kPa at the downstream side of the membrane. Furthermore, the composite membrane displayed desirable stability during the long-term continuous operation.