Importance of uniform distribution of impregnated trioctylphosphine oxide in hollow fiber membranes for simultaneous extraction/stripping of phenol

Trioctylphosphine oxide (TOPO) was impregnated in polypropylene hollow fiber membranes. The impregnation process was optimized and a uniform distribution of TOPO was achieved within the membrane walls, when the membranes were treated with a carrier solution containing 600 mg/L TOPO, and air-dried for 30 min at a low air flow rate (Reair = 9.2). The resulting extractant impregnated hollow fiber membranes (EIHFM) were characterized by scanning electron microscopy, water entry pressure, gas permeability and mercury porosimetry analysis, all of which showed significant structural and morphological changes in the EIHFMs; pore size, porosity and tortuosity were estimated to be 0.5 μm, 0.09 and 33, respectively. The EIHFMs exhibited high mass transfer rates and removal efficiency during simultaneous extraction and stripping of phenol. At an initial phenol concentration of 200 mg/L, 99% phenol was extracted from the wastewater within 7 h, whereas more than 91% phenol was recovered in the stripping solution, yielding a concentration factor of 1.79. The performance of the EIHFMs did not change significantly during consequent operations under identical conditions, indicating the stability of impregnation. These results suggest that uniformly impregnated TOPO-based EIHFMs can be promising in the recovery of phenols from wastewater.