Self-Assembled Polyelectrolyte Membranes for Dehydration of Isopropanol By Pervaporation

Polyelectrolyte membranes based on chitosanium and poly(acrylic acid) were prepared by layer-by-layer self-assembly on an interfacially polymerized polyamide low-pressure RO membrane for isopropanol/water separation by pervaporation. The charged surface of the polyamide layer facilitates the layer-by-layer deposition of the oppositely charged polyelectrolytes, and its relatively tight surface (compared to the commonly used microporous substrates) helps reduce the number of the polyelectrolyte bilayers needed to achieve a given membrane selectivity.  The membrane selectivity was further enhanced by crosslinking. The resulting composite membranes showed stable performance with good permeation flux and separation factor. For instance, a permeation flux of 0.63 kg/(m².hr) and a separation factor of 215 were obtained at room temperature at 10 wt% feed water concentration using 7.5 double layers. The effects of feed water concentration, number of polyelectrolyte double layers, and operating temperature on the pervaporation performance of the membranes were investigated. In addition, the effects of crosslinking (e.g., concentration of crosslinking agent and crosslinking time) were also considered to determine suitable crosslinking conditions so as enhance the membrane stability and selectivity without considerably reducing the membrane permeability.