Gas Sorption, Diffusion, and Permeation in Nafion

Abstract

The gas permeability of dry Nafion films was determined at 2 atm and 35 °C for He, H 2, N 2, O 2, CO 2, CH 4, C 2 H 6, and C 3 H 8 . In addition, gas sorption isotherms were determined by gravimetric and barometric techniques as a function of pressure up to 20 atm. Nafion exhibited linear sorption uptake for low-solubility gases, following Henry’s law, and convex behavior for highly sorbing condensable gases, indicating rubber-like behavior at 35 °C. XRD results demonstrated that Nafion contains bimodal amorphous chain domains with average d -spacing values of 2.3 and 5.3 Å. Only helium and hydrogen showed relatively high gas permeability of 37 and 7 barrers, respectively; all other gases exhibited low permeability that decreased significantly as penetrant size increased. Dry Nafion was characterized by extraordinarily high selectivities: He/H 2 = 5.2, He/CH 4 = 445, He/C 2 H 6 = 1275, He/C 3 H 8 = 7400, CO 2 /CH 4 = 28, CO 2 /C 2 H 6 = 79, CO 2 /C 3 H 8 = 460, H 2 /CH 4 = 84, H 2 /C 2 H 6 = 241, and H 2 /C 3 H 8 = 1400. These high selectivities could make Nafion a potential candidate membrane material for dry feeds for helium recovery and carbon dioxide separation from natural gas and removal of higher hydrocarbons from hydrogen-containing refinery gases.