Pervaporation of water-alcohol mixtures and acetic acid-water mixtures

In this study, pervaporation experiments were performed with methanol-water mixtures, ethanol-water mixtures, IPA (isopropyl alcohol)-water mixtures, and acetic acid-water mixtures, over the complete concentration range allowed by the membrane (Pervap 2201, Sulzer). The results of the three water-alcohol mixtures are compared to investigate the influence of molecular weight and polarity on the permeation behavior. The results show that ethanol and IPA have a similar permeation behavior, whereas methanol shows a different behavior. This can be explained by the relatively high polarity of methanol, which makes methanol sorption competitive with water sorption. The IPA-water mixtures are compared with the acetic acid-water mixtures. IPA and acetic acid have approximately the same molecular weight, but contain a different functional group. The acetic acid-water mixtures have a higher total flux than the IPA-water mixtures. Moreover, the partial acetic acid flux is higher than the partial IPA flux. Acetic acid contains a carbonyl group, which has a high capacity of forming hydrogen bonds with the alcohol groups of the PVA (polyvinyl alcohol) top layer. Moreover, it is a large molecule, causing high swelling resulting in a high permeation flux and a low separation factor. The behavior of the acetic acid-water mixtures shows more resemblance to the methanol-water mixtures than to the IPA-water mixtures. This suggests that the polarity and functional group of the different feed components is more important than the molecular size.