Membrane-moderated stripping process for removing VOCs from water in a composite hollow fiber module

Abstract

The “stripmeation” process for removing volatile organic compounds (VOCs) from water has been introduced and studied. An aqueous solution of the VOC is passed through the bores of hydrophobic microporous polypropylene hollow fibers having a plasma polymerized silicone coating on the fiber outside diameter; a vacuum is maintained on the shell side of the fiber. The VOC is stripped into the gas-filled pores of the hydrophobic substrate, permeates through the nonporous silicone skin and is recovered by condensation of the shell-side permeate stream. Removal of trichloroethylene (TCE) present in a concentration range 200–1040 ppm has been studied at 25°C. Process performance has been obtained over a range of flow rates. The observed TCE permeation and removal behavior has been modeled using a resistances-in-series approach; the two important resistances are the tube-side aqueous boundary layer resistance and the vapor permeation resistance of TCE through the silicone coating. Employing the known Graetz solution for the tube-side flow and the measured vapor permeation resistance of TCE, values of the overall TCE mass-transfer coefficient have been obtained. These values compare well with the experimental values. The conventional pervaporation process where the liquid feed solution is in contact with the nonporous silicone membrane has also been studied by passing the feed on the shell side. The tube-side feed-based operation performs much better than the shell-side based operation.