Study of transfer of alcohol (methanol, ethanol, isopropanol) during nanofiltration in water/alcohol mixtures

Abstract This study aimed at studying the impact of alcohol presence in water/alcohol mixtures on the performances of the NF 270 polypiperazine amide nanofiltration membrane (Dow Filmtec). Three alcohols of different physico-chemical characteristics were selected: methanol, ethanol and isopropanol. NF was achieved for several water/alcohol mixtures of different viscosity (up to twice that of water) and dielectric constant, both known to play a role in separation performances. In presence of alcohol (up to 23 vol%, 30 vol% and 21 vol% for methanol, ethanol and isopropanol, respectively) the flux significantly decreased when compared to that of water. This study provides insights in the alcohol transfer mechanisms allowing to select Spiegler & Kedem and reject Solution-Diffusion, both coupled with the film theory. Discussion highlights how surprisingly the membrane swelling can sometimes have no significant impact on the membrane resistance because opposite phenomena can be compensated such as pore radius increase simultaneously with membrane thickness increase.