Gas Sorption, Diffusion, and Permeation in Nafion

• Published in: Macromolecules Vol. 49; no. 1; pp. 280 - 286
• Main Authors: Mukaddam, Mohsin, Litwiller, Eric, Pinnau, Ingo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12.01.2016
• Subjects: carbon dioxide; feeds; fluorides; gases; helium; hydrogen; methane; natural gas; nitrogen; oxygen; permeability; sorption; sorption isotherms; vinyl compounds; X-ray diffraction
• ISSN: 0024-9297; 1520-5835; 1520-5835
• DOI: 10.1021/acs.macromol.5b02578

The gas permeability of dry Nafion films was determined at 2 atm and 35 °C for He, H2, N2, O2, CO2, CH4, C2H6, and C3H8. 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/H2 = 5.2, He/CH4 = 445, He/C2H6 = 1275, He/C3H8 = 7400, CO2/CH4 = 28, CO2/C2H6 = 79, CO2/C3H8 = 460, H2/CH4 = 84, H2/C2H6 = 241, and H2/C3H8 = 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.