An NMR study of sorption-diffusion properties of MF-4SK-carbon composite membranes in aqueous methanol solutions

Abstract

The distribution of water and methanol and their self-diffusion coefficients (SDCs) in carbon-doped MF-4SK perfluorinated membranes have been studied by NMR. It has been shown that at a concentration of 12–35 wt % in the external solution, the methanol concentration inside the membrane is higher by a factor of 1.4–2 than that in the external solution and increases with increasing the carbon phase content. It has been found that SDC values for water and methanol in the membrane decrease with an increase in the C phase content. In a membrane with 23 wt % C, the SDC of methanol is reduced by a factor of 1.6. It has been shown that the SDC of methanol in these membranes is below that of water by a factor of 1.5. The activation energies of self-diffusion of water and methanol have been determined. It has been found that they remain almost unaffected by the C content and have close values of 19–20 kJ/mol, which are 2–4 kJ/mol above the activation energy of self-diffusion of pure water in these membranes.