Multilayer Diffusion Behavior and the Swelling Effect of 1-Butene and Propylene in Dry AgNO₃-doped Perfluorocarbon Type Ion-Exchange Membranes

Abstract

The transport mechanism of 1-butene and propylene through dry AgNO3-doped perfluorosulfonate ion-exchange membranes was investigated on the basis of the results obtained from sorption and permeation experiments. A derivation of a multilayer diffusion equation was carried out in order to interpret the transport mechanism of gases or vapors through microporous materials, assuming that the BET n-layer adsorption takes place and that the transport of the adsorbed molecules is controlled by the activated diffusion mechanism. The transport mechanism of 1-butene and propylene through dry AgNO3-doped PSM membranes can be explained by multilayer diffusion together with swelling of the surrounding polymer pendant side chains by the sorbed alkene molecules. The diffusion coefficients of the sorbed alkene molecules in the first adsorbed layer, D 1, are always lower than those of the sorbed alkene molecules in the second and higher adsorbed layers, D 2. This indicates that the interaction between the silver salts and the alkene molecules is stronger than that between the alkene molecules themselves, leading to a lower mobility of the sorbed alkene molecules in the first adsorbed layer than those in the second and higher adsorbed layers. The large difference in the permeation flux between 1-butene and propylene is mainly due to the difference in the sorbed concentration between these two alkenes at the same gas pressure in the membrane.

Threshold silver concentration for facilitated olefin transport in polymer/silver salt membranes

“…These include immobilized liquid membranes, solventswollen membranes, and ion exchanged membranes [9][10][11][12][13]. The practical application of liquid-state membranes is limited, however, because such systems are operated with liquid solvent-vapor saturated feed and permeate streams.…”

The structural transitions of π-complexes of poly(styrene-b-butadiene-b-styrene) block copolymers with silver salts and their relation to facilitated olefin transport

“…Previous researches into olefin/paraffin separation have focused on immobilized liquid membranes, solvent-swollen membranes, and ion-exchange membranes [8][9][10][11][12]. However, these types of membranes exhibit critical problems in industrial applications, mainly due to operational instabilities caused by evaporation of the liquid media.…”

π‐complexes of polystyrene with silver salts and their use as facilitated olefin transport membranes

“…Facilitated transport has been receiving tremendous attention as a potential energy‐saving separation technology because it can simultaneously improve both the permeability and selectivity of a membrane 4. The initial development of facilitated transport membranes has been based on immobilized liquid membranes, solvent‐swollen membranes, or ion‐exchange membranes 5–8. However, the commercial application of liquid membranes is limited because they are operated with liquid‐solvent/vapor saturated feed and permeate streams.…”