Preparation parameters influencing the performance of SRNF membranes cast from polyimide solutions via SEPPI

摘要

Asymmetric nano-sized zeolite-filled polyimide membranes,prepared through the recently reported Solidification of Emulsified Polymer solutions via Phase Inversion(SEPPI)method,were applied in solvent resistant nanofiltration(SRNF).Thanks to the introduction of a short evaporation step prior to coagulation of the cast films,SEPPI allowed the synthesis of highly selective membranes with acceptable solvent fluxes in the separation of rose Bengal(RB)from 2-propanol(IPA).Addition to the casting solution of an organic suspension containing nano-sized silicalite-1 particles had a clear influence on membrane performance as a gradual transition from relatively open towards more dense membranes was observed.This transition coincided with a remarkable morphology change from finger-like to sponge-like membrane structures.An evaporation step of 90 s and an alternative post-treatment,involving solvent exchange coupled to mineral oil impregnation,allowed a significant performance increase of the most promising SEPPI membrane,with IPA permeances around 0.751 m~(-2)h~(-1)bar~(-1)and RB rejections up to 99%.The performance of the optimized SEPPI membrane compared favourably to the best commercial SRNF membranes,not only in the RB/IPA separation but also in other solvent/solute systems,while its specific structure resulted in increased compaction resistances.Molecular weight cut-off(MWCO)measurements in IPA and hexane,using low molecular weight dyes and alkanes,respectively,revealed MWCO values around 380 and 730 g/mol for this membrane.