Continuous vapor-gas separation with a porous membrane permeation system

In contrast to adsorption processes in which the adsorbent must be regenerated periodically, a thin porous membrane can be used to separate gaseous mixtures in an efficient and continuous manner. It is believed that adsorbed flow and capillary condensation within a porous membrane can greatly increase the vapor permeability and membrane selectivity for a vapor-gas separation.; A Continuous Porous Membrane Permeator (CPMP) was constructed that allowed the condensible vapor in the feed stream to permeate preferentially through the membrane under the driving force of a pressure difference across the membrane. A porous Vycor glass membrane was used to recover acetone and ethanol vapors from nitrogen mixtures. The separation performance, in terms of the apparent solvent permeability, separation factor, and solvent recovery, were evaluated systematically in a parametric study. Operating conditions and system parameters examined in this study were the temperature of the membrane system, total feed pressure, downstream flow rate, flow pattern, and membrane geometry.; A six-mode flow model was applied to correlate the condensible solvent permeability as a function of vapor pressures on both sides of the membrane column. A mathematical model has been developed to describe and predict the CPMP performance under various design and operating conditions. The validity of the model simulation was verified by comparing the model prediction with the experimental results.; Demonstrated by both experimental and theoretical investigations, a large solvent permeability and a high separation factor were obtained simultaneously when the feed solvent vapor pressure approached the capillary condensation vapor pressure. A semipermeable membrane system is also realized when the entire length of the membrane column is saturated with the solvent condensate. The results indicate that the CPMP is a potentially high performance membrane system for industrial application of solvent recovery from waste air emission and Volatile Organic Compounds (VOC) pollution controls.