Sorption and transport of methanol and ethanol in H⁺-nafion

Methanol and ethanol sorption and transport in 1100 equivalent weight HNafion were compared to water sorption and transport. Sorption isotherms for methanol and ethanol were fit to a solvation shell model, with four molecules in the first solvation shell. The larger molar volume of alcohols resulted in greater swelling from sorption. Proton conductivity is five times greater for water saturated Nafion than alcohol saturated Nafion. Alcohol pervaporation and alcohol vapor permeation is slower than water pervaporation and water vapor permeation. The Nafion/vapor interfacial transport coefficients for alcohols and water scale with vapor pressure. The diffusivity of water is 3-4 times greater than the diffusivity of methanol and ethanol. The results indicate that alcohols sorb by solvating the sulfonic acid groups, similar to the interaction of water with Nafion. Larger alcohol molecules diffuse slower in the hydrophilic channels of Nafion than the smaller water molecules.