Porous hydrophobic-hydrophilic Janus membranes for nondispersive membrane solvent extraction

Porous membranes having a particular wetting characteristic, hydrophobic or hydrophilic, are used for nondispersive membrane solvent extraction (MSX) where two immiscible phases flow on two sides of the membrane. The aqueous-organic phase interface across which solvent extraction/back extraction occurs remains immobilized on one surface of the membrane. This process requires the pressure of the phase not present in membrane pores to be either equal to or higher than that of the phase present in membrane pores; the excess phase pressure should not exceed a breakthrough pressure. In countercurrent MSX with significant flow pressure drop in each phase, this often poses a problem. To overcome this problem, flat porous Janus membranes were developed using either a base polypropylene (PP) or polyvinylidene fluoride (PVDF) or polyamide (Nylon) membrane, one side of which is hydrophobic and the other being hydrophilic. Such membranes were characterized using the contact angle, liquid entry pressure (LEP) and the droplet breakthrough pressure from each side of the membrane along with characterizations via scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). Nondispersive solvent extractions were carried out successfully for two systems, octanol-phenol (solute)-water, toluene-acetone (solute)-water, with either flowing phase at a pressure higher than that of the other phase. The phenol extraction system had a high solute distribution coefficient whereas acetone prefers both phases almost identically. The potential practical utility of the MSX technique will be substantially enhanced via Janus MSX membranes.