Vapor-permeation separation of water-ethanol mixtures by asymmetric polyimide hollow-fiber membrane modules.

Abstract

Vapor-permeation separation of water-ethanol mixtures by asymmetric polyimide hollow-fiber membrane modules was carried out in a countercurrent flow pattern and in a both-end-opened pattern to investigate membrane performance and the effects of operating factors on the membrane module responses. The specific permeability coefficient of water vapor for the fibers was about 4 × 10–7 mol/(m2·s·Pa) at 378K, which was about 500 times that of ethanol vapor. The experimental results of membrane module responses for enrichment of ethanol composition at feed outlet, XRE, up to 99.7wt% were in good agreement with the results calculated from a conventional model. The both-end-opened flow pattern was much superior to the countercurrent one, especially for high-level enrichment, because of reduced buildup of permeate pressure inside the hollow fibers. The calculation showed optimum inside diameter and length of the hollow-fibers, depending on XRE and feed-side pressure.