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

Abstract

SynopsisSteady-state permeability coefficients have been measured for equimolar mixtures of C02-CzH4, C O Z -C~H~, and CzH4-C3H8, as well as for a mixture of 74.9 mol % C02 and 25.1 mol% C2H4 in polyethylene membranes. The measurements were made at 20,35, and 50°C and a t 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 a t 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.

VOC–air separations using gas membranes

“…Although it has been reported that the free-volume model satisfactorily described the behaviour of binary mixtures through polyethylene 8 and styrene-butadiene block copolymer 9 membranes, the predictions for a silicone membrane are less successful. Experimental results and predictions from the free-volume model differ significantly and the deviation increases with increasing molecular weight.…”

Transport Properdines of Gases in Polymers: Bibliographic Review

“…They assigned the differences observed in the case of water to its hydrogen-bonding nature rather than to a failure of the model. The validity of this model (Stern et al, 1983a(Stern et al, , 1986 has been also tested for the permeation of other small molecules (Ar, SF 6 , CF 4 and C 2 H 2 F 2 until 1.5 MPa) in PE from 5°to 50°C and for binary gas mixtures (Stern et al, 1983b;Koros et al, 1981). Vrentas and Duda (1977) used another model also based on free volume, while making use of the thermodynamic theory of Flory as well as on the entanglement theory of Bueche (1962) (friction coefficient idea).…”

Transport Properties of Gases in Polymers: Experimental Methods

“…This technique is very useful in the field of the selective membranes, based mainly on the analysis by gas chromatography. It allows to determine the permeability coefficient of numerous polymers to binary gas mixtures, such as CH 4 -CO 2 [36][37][38][39][40].…”