Flow Swing Membrane Absorption−Permeation

Abstract

A cyclically-operated membrane permeation technique, flow swing membrane permeation (FSMP), has been studied for effective removal of volatile organic compounds (VOCs) from a gas stream to obtain a highly purified gas stream. Feed gas mixture is supplied to the lumen of hollow fiber membranes for a short period of time; then the feed flow is stopped for a brief period after which the feed gas flow into the fiber lumen is resumed. A vacuum is maintained continuously on the shell side for selective permeation and removal of VOCs from the feed gas mixture. Silicone-coated hollow fibers were employed to bring down the VOC concentration in feed N2 to as low as 1-5 ppmv from feed concentration levels around 200-300 ppmv. The VOCs investigated were methanol, methylene chloride, acetone, and toluene. The purification capacity of the FSMP process has been shown to be considerably higher than that of the conventional steady-state operation of the membrane. To improve the membrane selectivity drastically, a contained liquid membrane concept was employed also using two sets of silicone-coated hollow fibers and silicone oil on the shell side. The permeate in this flow swing membrane absorptionpermeation (FSMABP) process was almost pure VOC. Results of performances for such novel cyclic processes are presented. The potential of such techniques for various gas separations problems has been pointed out.