Pervaporation of methanol from a triglyme solution using a Nafion membrane .1. Transport studies

The feasibility of using pervaporation as a means to recover low concentrations of methanol produced from the catalytic reaction of syngas in triglyme (triethylene glycol dimethyl ether) has been investigated. In this study, Nafion (a perfluorosulfonate ionomer) has been found to be a highly permeable and permselective membrane for methanol separation. Both sorption and diffusion favor methanol, resulting in high permeability and selectivity. A mathematical model for methanol pervaporation through Nafion has been validated by which flux is related to membrane thickness, the equilibrium permeant concentration in the membrane, a diffusion coefficient, and a plasticization term. Using this model to analyze the pervaporization data, the diffusion coefficient for methanol flux through Nafion was determined to be 6.8 x 10(-8) cm(2) s(-1) at 30 degrees C while the Arrhenius activation energy for methanol flux was estimated to be a low 3 kcal mol(-1). By contrast, the diffusion coefficient and activation energy for triglyme are estimated as 1.0 x 10(-8) cm(2) s(-1) and 20 kcal mol(-1), respectively. These values are consistent with the cluster-network model for Nafion whereby methanol would be expected to easily pass through open ionic channels while the larger, less polar triglyme molecule diffuses primarily through the amorphous regions surrounding the clusters.