Fundamental insights into the rejection behavior of polyimide-based OSN membranes

Abstract

Organic solvent nanofiltration (OSN) is still a niche technology in the chemical industry due to time and money consuming process development, as organic solvents cause complex interactions between membrane, solvent, and solute. These interactions are not fully identified, and a fundamental understanding of mass transfer through OSN membranes is not established so far. Accordingly, mathematical models in OSN lack a general predictive capability. To overcome this problem, we aim to extend the current knowledge by a comprehensive experimental investigation of two polyimide membranes in combination with 17 solutes with molecular weights of 114–339 g/mol covering the range from nonpolar to polar, and five solvents with various properties. The results indicate solvent-dependent rejection phenomena that may be explained by a difference in the impact of solute properties on the rejection in dependency of the solvent. Based on these findings, three solvent-dependent solute sensitivity regions are derived similarly to previous results for PDMS membranes. The investigation of membrane–solvent interactions revealed an impact of the spatial distance in the 3D space of the total Hansen solubility parameter between solvent and membrane with a specific impact on membrane–solute sensitivity. These new findings contribute to a better understanding of transport phenomena and can serve as a new basis for predicting the separation performance in OSN.