Tests of a free‐volume model for the permeation of gas mixtures through polymer membranes. CO2‐C2H4, CO2‐C3H8, and C2H4‐C3H8 mixtures in polyethylene

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Abstract
Steady‐state permeability coefficients have been measured for equimolar mixtures of CO2‐C2H4, CO2‐C3H8, and C2H4‐C3H8, as well as for a mixture of 74.9 mol % CO2 and 25.1 mol % C2H4 in polyethylene membranes. The measurements were made at 20, 35, and 50°C and at pressures of up to 28 atm. Each component of the permeating mixtures studied had the effect of increasing the permeability coefficient for the other component. 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 agreement with the predictions of a free‐volume model for the permeation of gas mixtures proposed by Fang, Stern, and Frisch. From a quantitative viewpoint, the permeability coefficients for the components of the mixtures agreed, on the average, to better than 25% with the predicted values. The theoretical permeability coefficients can be estimated from the model by using parameters determined with the pure components only.