Permeation of n-butane, 1-butene and 1,3-butadiene through anhydrated Ag+-doped perfluorocarbon-type ion-exchange membranes

The characterization of anhydrated Ag+-doped polyperfluorosulfonate membrane (PSM) was made by using EDS, positron annihilation lifetime measurement and AFM. It was confirmed that the distribution of doped Ag+ in the membrane was homogeneous, the membranes were rather dense ones and the concentration of doped Ag+ was about twice as much as that of charged group SO3- in the membrane. The permeation experiments were also carried out for n-butane, 1-butene and 1,3-butadiene. Anhydrated Ag+-doped PSM exhibited relatively high permeability for 1-butene compared with n-butane and 1,3-butadiene. The ideal separation factor of 1-butene/n-butane, which was the permeability coefficient ratio of 1-butene to n-butane, was about 5400 in the membranes exchanged by AgNO3 aqueous solution at 25 degrees C. Both the permeability of 1-butene and selectivity of 1-butene/n-butane increased with decrease of temperature. On the other hand for 1-butene/1,3-butadiene system, the highest ideal separation factor 11.7 was obtained at 70 degrees C while permeability increased with decrease of temperature. The permeation behaviour of alkenes through anhydrated Ag+-doped PSM could be explained by a swelling model suggested in this paper. Based on such swelling mechanism, the diffusivity and permeability of alkenes were strongly affected by the amount of alkenes absorbed in the membrane. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.