Influence of polymer concentration in casting solution and solvent-solute-membrane interactions on performance of polyphenylsulfone (PPSU) nanofiltration membrane in alcohol solvents

Abstract

Abstract In this work, the performances of solvent resistant nanofiltration (SRNF) membranes made of polyphenylsulfone (PPSU) were evaluated with respect to alcohol solvent (methanol, ethanol and isopropanol) flux and dye rejection. The experimental results showed that the solvent flux decreased while dye rejection increased with increasing polymer concentration in the casting solution from 17 wt% to 25 wt%. Apart from molecular size of the solute and viscosity of the solvent, the affinity between the solvent and the membrane was also confirmed to play a significant role in affecting the transport rate of the solvent through the membrane. With respect to the effect of solvent properties and solute size on the dye rejection of solvent-dye mixtures, it was found that the variation of dye rejection is governed by solvent-solute-membrane interactions. The solvent-solute interaction causes the same solute to have different solute size in each tested solvents, whereas the solvent-membrane interaction would result in a change in membrane pore size, leading to different separation efficiency. However, it must pointed out that solvent-membrane interaction is more pronounced compared to solvent-solute interaction, as the dye rejection of ethanol solution is reportedly higher than that of methanol, even though the size of solute in ethanol is smaller compared to its size in methanol.