MEMBRANE-MODERATED STRIPPING PROCESS FOR REMOVING VOCS FROM WATER IN A COMPOSITE HOLLOW-FIBER MODULE

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 poly propylene hollow fibers having ka plasma polymerized silicone coating on the fiber outside diameter; a vacuum is maintained on the shell sid e of the fiber. The VOC is stripped into the gas-filled pores of the h ydrophobic substrate, permeates through the nonporous silicone skin an d is recovered by condensation of the shell-side permeate stream. Remo val of trichloroethylene (TCE) present in a concentration range 200-10 40 ppm has been studied at 25 degrees C. Process performance has been obtained over a range of flow rates. The observed TCE permeation and r emoval behavior has been modeled using a resistances-in-series approac h; the two important resistances are the tube-side aqueous boundary la yer resistance and the vapor permeation resistance of TCE through the silicone coating. Employing the known Graetz solution for the tube-sid e flow and the measured vapor permeation resistance of TCE, values of the overall TCE mass-transfer coefficient have been obtained. These va lues compare well with the experimental values. The conventional perva poration 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 b etter than the shell-side based operation. (C) 1998 Elsevier Science B .. All rights reserved.