Determining stability of organic solvent nanofiltration membranes by cross-flow aging

Abstract

Organic solvent nanofiltration (OSN) membranes suffer from performance loss over an extended timescale due to aging. Short-term aging tests often conducted in membrane studies may not be representative of the actual behavior of the OSN membranes when used in organic solvents. There is a need to test the performance of OSN membranes in a way that is more relevant to industrial OSN applications. In this work, we conducted a series of aging tests in two different modes to determine the behavior of four commercial OSN membranes (Duramem 200, Puramem 280, GMT-oNF2, and SolSep BV010206) in polar and non-polar organic solvents (i.e., methanol, acetonitrile, and toluene). Firstly, we conducted a 30-day static aging experiment to investigate the stability of four commercial OSN membranes when soaked in the selected solvents. Secondly, we proposed a three-week cross-flow aging protocol with a staged temperature raise to determine the long-term stability of the membranes in real-world scenarios. The operating temperature was controlled between 25 °C and 40 °C in the three-week aging test. The results showed that acetonitrile had the most significant effect on the membranes, and the permeances of the membranes were dependent on the solubility parameters of the polymer and the solvent when the membranes were soaked in the solvents in static operation. The polyimide-based membranes exhibited a noticeable sign of aging with increasing temperature, which could be due to compaction and densification. Our results suggested that the new cross-flow aging protocol can facilitate the rapid screening of OSN membranes for industrial use.