Impact of filtration at elevated temperature and solvent pre-treatment on crosslinked polyvinylidene difluoride and polyimide solvent-resistant nanofiltration membranes

Abstract

The high temperature filtration performance of crosslinked polyvinylidene difluoride (XL-PVDF) and polyimide (XL-PI) membranes in solvent-resistant nanofiltration (SRNF) applications was studied. The membranes were tested in four industry-relevant, apolar solvents (toluene, xylene, chloroform, and n-butyl acetate) over a temperature range from 25 °C to 80 °C. The temperature effect on membrane performance was evaluated using a polar probe molecule (5,10,15,20-tetrakis(3,5-di-tert-butyl phenyl)porphyrin (TBPP), 1064 Da), showing that permeance increased with rising temperature due to the anticipating reduced solvent viscosity and enhanced flexibility of the membrane polymer chains. This effect varied clearly between the two polymer systems. After the high-temperature filtration, room-temperature (RT) filtrations demonstrated stable retention in xylene, BuOAc, and toluene, but a decrease in chloroform The membranes exhibited excellent long-term stability, retaining their quasi-intact filtration performance over a full week of operation. To investigate the impact of a pre-filtration solvent treatment, Sudan black (SB)/chloroform filtrations were done before and after exposure to toluene, xylene, BuOAc, and chloroform. Quite surprisingly, such solvent treatment resulted in a polymer-specific impact: an increased permeation for XL-PVDF and a decreased permeation for XL-PI. Retentions were constant for XL-PVDF but slightly increased for XL-PI. Overall, both membrane types showed excellent thermal and solvent stability, but the impact was very different.