Mechanism of Gas Permeation Through Polymer Membranes. Part II. Gas Mixtures. Comprehensive Progress Report

摘要

The specific objective of this study is to assess the validity of a free volume model for the permeation of mixtures. This model provides a formalism for the prediction of permeability coefficients for the components of permeating mixtures, as well as of the dependence of these coefficients on pressure and temperature. Steady-state permeability coefficients were measured for equimolar mixtures of CO sub 2 -C sub 2 H sub 4 , CO sub 2 -C sub 3 H sub 8 , and C sub 2 H sub 4 -C sub 3 H sub 8 , as well as for a mixture of 74.9 mole % CO sub 2 -25.1 mole % C sub 2 H sub 4 , in polyethylene membranes. The measurements were made at 20 exp 0 , 35 exp 0 , and 50 exp 0 C and at pressures of up to 18 atm. In all cases, the permeability coefficients for the components of these mixtures were higher, and in some cases considerably higher, than the permeability coefficients for the pure components at comparable partial pressures and temperatures. Each component of the binary mixtures studied had thus the effect of increasing the permeability coefficients for the other components. Furthermore, at equal partial pressures and at the same temperature, the component exhibiting the highest solubility in the polymer had the largest effect in increasing the permeability coefficient of the other component. This behavior is in complete agreement with the predictions of the free-volume model for mixtures. From a quantitative viewpoint, the permeability coefficients for the components of the mixtures agreed, on the average, to better than 25% with the experimental values, the former being usually lower than the latter. The theoretical permeability coefficients can be estimated from the model using parameters determined with the pure components only. The extension of the model to multicomponent mixtures is straightforward. (ERA citation 07:057689)