Fabrication Of PVA-PES Asymmetric Membranes For Prevaporative Dehydration Of Ethanol

As a kind of renewable energy resource, production and utilization of fuel ethanol has called much attention nowadays. In the process of fuel ethanol production, ethanol dehydration proves a key step. Pervaporation possesses outstanding technical advantages and promising prospects in ethanol dehydration for its low energy cost and unrestraint of vapor-liquid equilibrium.The PVA-PES asymmetric membranes were prepared through phase inversion method by blending polyvinyl alcohol (PVA), a polymer with excellent pervaporation performance, with polyethersulfone (PES) with outstanding mechanical behavior. The PVA chains segregated to membrane surface to form a hydrophilic separation layer. A multi-porous support layer was also formed by controlling the coagulation bath. The X-ray photoelectron spectroscopy (XPS) and Energy dispersive spectrometer (EDS) results confirmed the segregation of PVA. For the PVA(3)/PES(15) membrane which had a PVA content of 16.67%, the coverage density of PVA on the asymmetric membrane surface was 86.79%. The PVA(3)/PES(15) membrane exhibited a flux of 297.6 g/(m2h) and a separation factor of 86.1 for 90 wt.% ethanol solution at 80 OC with a downstream pressure of 0.33 KPa. Asymmetric membranes still showed pervaporation ability even at a high water feed concentration of 60 wt.% with a permeation flux of 654.2 g/(m2h) and a separation factor of 10.7, while the PVA/PES composite membrane in which PVA was cast directly on the PES support swelled severely and lost separation ability.Although asymmetric membranes showed high structural stability, their pervaporation performances need to be enhanced. PVA-PES asymmetric membranes with loose structure were obtained using water as the coagulation bath. Composite membranes GE/PVA-PES were fabricated using PVA-PES asymmetric membranes as the support layers, gelatin (GE) as the active layers and glutaraldehyde as the cross-linking agent. The water contact angle measurement and XPS data confirmed the surface segregation of PVA(the coverage density of PVA on the membrane surface was found to be 79.7%). The FESEM images of membranes cross-section indicated an improved compatibility between the GE layer and the PVA-PES support. T-peel test showed that the maximal force to separate the support layer and the active layer was enhanced by about 3 times compared with the GE/PES membrane. Among the various composite membranes prepared, the GE(2)/PVA(3)-PES(17) membrane exhibited a flux of 1580.6 g/(m2h) and a separation factor of 63.5 for 90 wt.% ethanol solution at 80 oC with a downstream pressure of 0.33 KPa. At a relatively high water feed concentration of 40 wt.%, the GE(2)/PVA(3)-PES(17) membrane still exhibited a permeation flux of 4142.0 g/(m2h) and a separation factor of 48.2, while the GE layer of the GE/PES membrane swelled severely and even dissolved.