(22f) Novel Solvent-Resistant Hydrophilic Hollow Fiber Membranes for Membrane Solvent Back Extraction

Nondispersive membrane solvent extraction is being extensively used and studied for a number of applications including extraction of metals, pollutants and pharmaceutical products because of its well known advantages over conventional dispersive solvent extraction. Membrane solvent extraction is generally followed by membrane solvent back extraction for regeneration of the organic extraction solvent. The mass transfer rate of solute in membrane-based solvent extraction is controlled by boundary layer resistances and the membrane resistance; the membrane phase resistance can be reduced by preferentially filling the membrane pores with the phase preferred by the solute. In the case of membrane solvent back extraction reactive or otherwise, it is preferable to have the pores of the membrane filled with aqueous phase. Hence there is a need for hydrophilic solvent resistant hollow fiber membranes for efficient back extraction. There are almost no solvent resistant hydrophilic membranes available having the required pore sizes to provide stable aqueous-organic interface at higher organic phase pressures. In the current study, nylon 6 hydrophilic microporous hollow fiber membranes are coated on the inner diameter (ID) to reduce the pore size. The two different coating techniques studied are insolubilization of polyethylenimine(PEI) by crosslinking and interfacial polymerization. The coating provided a stable immobilized organic-aqueous interface over a reasonable range of breakthrough pressures. The fabricated membranes are characterized by performance of membrane solvent extraction as well as by scanning electron microscopy. Back extraction of acetic acid from methyl isobutyl ketone into water is used as a model system for non-reactive extraction and back extraction of phenol from methyl isobutyl ketone into caustic solutions is used as a model system for reactive extraction. Transport rates of phenol and acetic acid are studied and compared with those in hydrophobic microporous polypropylene hollow fiber membranes. The novel solvent-resistant hydrophilic membranes provided better performance for nondispersive membrane solvent back extraction. This study also illustrated the enhancement of mass transfer coefficients in membrane solvent back extraction when the membrane pores are filled with aqueous phase.