Unraveling the influence of dissolved gases on permeate flux in organic solvent nanofiltration – Experimental analysis

Abstract

The first step in quantifying the performance of organic solvent nanofiltration membranes are usually lab-scale experiments with respect to flux and rejection. The necessary pressurization of the feed is either realized mechanically by a high-pressure pump or by means of a pressurized inert gas. While the latter option is most frequently applied, the gas may dissolve in the feed mixture and permeate through the membrane, affecting the transport of the other components. This potential effect is commonly neglected, inherently assuming that the gas solubility is negligible. The current study provides a systematic experimental investigation and analysis of the impact of dissolved gases on solvent flux for a hydrophilic DuraMem membrane, with gas solubilities assessed through PC-SAFT. The results prove that a gas with low solubility has a negligible effect on the solvent flux. In contrast, an increasing gas solubility may result in significant gas flux through the membrane with a considerable effect on the solvent flux. Furthermore, the correlation of the solvent flux with the gas solubility in the feed mixture is strongly non-linear. Therefore, gas solubility is recommended to be critically evaluated when conducting OSN experiments, specifically considering the final application. In that context, the permeation of dissolved gas has to be actively accounted for in OSN experiments for gas–liquid systems.