Extraction of 4-nitrophenol from 1-octanol into aqueous solution in a hollow fiber liquid contactor

p-Nitrophenol (PNP) was extracted from 1-octanol into an aqueous buffered s olution using membrane-supported extraction in hollow fiber liquid contacto rs (HFLCs) containing hydrophobic, microporous polypropylene fibers. PNP is a weak acid and in aqueous solution may dissociate to form nitrophenolate ion (PNP-). that has negligible solubility in 1-octanol. The ratio of the t wo species in aqueous solution is governed by pH; therefore, the overall ma ss transfer coefficient based on solvent phase concentrations was determine d as a function of pH. The extraction of PNP is a four-step process. consis ting of diffusion across the solvent boundary layer, diffusion through the solvent-filled membrane, reaction (dissociation) at the solvent/aqueous int erface, and diffusion across the aqueous boundary layer. The reaction step is assumed much faster than the others; a model of the mass transfer capabi lities of the system is presented based on this assumption. The overall mas s transfer coefficients were determined experimentally by recirculating the solvent phase through the shell space of a HFLC and the aqueous phase thro ugh the fibers. The model closely predicts the experimentally measured tren ds of the overall mass transfer coefficient. (C) 2002 Elsevier Science B.V. All rights reserved.