Gas Separations with High-Flux Cellulose Acetate Membranes

Abstract

The high-flux cellulose acetate membranes used in desalination by reverse osmosis have been shown to consist of a dense layer, perhaps 0.2 mu m thick, supported on a highly porous substructure. Because they have a very thin diffusion barrier, high-flux cellulose acetate membranes permit a high gas permeation rate through a highly selective amorphous polymer. To examine the trade-off between high flow rates and separating efficiency, the data for cellulose acetate are compared in tabular form with data for other materials previously tabulated by Stern et al. According to Stern, Teflon FEP is available in 25-mu m thickness without pinholes. Such a membrane would give a helium flow rate only one-fiftieth that of the better of the high-flux cellulose acetates if both were operated at 80/sup 0/C. This temperature appears to be satisfactory for Teflon FEP but may be near the upper limit for cellulose acetate. The separation factors obtained with the cellulose acetate samples used were comparable to those reported for Teflon FEP.