PERMEATION OF CARBON-DIOXIDE THROUGH HOMOGENEOUS DENSE AND ASYMMETRIC CELLULOSE-ACETATE MEMBRANES

Sorption isotherms for carbon dioxide in a homogeneous dense cellulose acetate membrane were measured by the pressure decay method at three temperatures between 20 and 40 degree C and gas pressures up to 1. 7 MPa. Steady-state permeation rates for the same system at three temperatures between 24 and 40 degree C and gas pressures up to 2. 2 MPa were measured by the variable volume method. The equilibrium sorption was described well in terms of the dual-mode sorption model. The pressure dependence of the mean permeability coefficient was interpreted by the total immobilization model, i. e. , a limiting case of the dual-mode mobility model, where the diffusion coefficient for the Henry's law mode is not assumed to be constant but depends upon gas pressure via a modified free-volume theory. The observed pressure dependence of the mean permeability coefficient through an asymmetric cellulose acetate membrane was very similar to that through a homogeneous dense membrane. The thin skin layer in the asymmetric membrane can be simulated by a homogeneous dense membrane from the point of view of gas sorption and diffusion.