Simultaneous phase-inversion and crosslinking in organic coagulation bath to prepare organic solvent forward osmosis membranes

Abstract

Organic solvent forward osmosis (OSFO) is an emerging separation process, which can realize simultaneous concentration of pharmaceutical ingredients and solvent recovery. In this work, a time-saving preparation process for solvent-resistant support layers was proposed by a simultaneous phase-inversion and crosslinking (SIM) method. The SIM method combines the formation of porous polyimide (PI) support layer and crosslinking between the PI and hexanediamine (HDA) in the coagulating baths, thus avoiding an extra need of solvent-based synthesis step. Furthermore, isopropanol (IPA) was used as coagulation bath for solvent-resistant PI support layers preparation, which can more effectively retarding the phase-inversion process compared with the DI-water. In addition, the morphologies and properties of these support layers with different synthesis time were prepared and characterized. After interfacial polymerization reaction using the as-prepared solvent-resistant PI support layers, the resultant OSFO membranes exhibited reasonable ethanol fluxes, lower reverse salt fluxes, and excellent pharmaceutical (oxytetracycline, OTC) rejections in both forward and reverse osmosis modes. Moreover, the long-term tests of as-prepared OSFO membranes indicated an excellent stability in 10 h operation with ethanol. After 10 h activation using DMF, the ethanol fluxes of OSFO18h membranes with different thickness of solvent-resistant support layers were significantly improved without sacrificing OTC rejection, which furtherly demonstrated the timeliness of SIM method and potential application of OSFO process in both concentrate the pharmaceutical and solvent recovery.