Gas and pervaporation separations using styrenic polymer membranes

Abstract

Poly(DVB/EVB) and sulfonated polystyrenes were investigated for possible use in gas separations. Defect-free ultrathin film composite membranes were synthesized using an electrochemical method using DVB/EVB as the monomer. Ultrathin poly(DVB/EVB) films ([ ca. 2.0 gm thickness) showed identical gas-transport selectivity to those obtained for bulk poly(DVB/EVB) membranes. The effect of various experimental parameters (including monomer concentration, supporting electrolyte concentration, and voltage scan rate) on the thickness of the polymer film were investigated. Gas-transport properties of sulfonated polystyrenes were investigated. The polymers were sulfonated to various sulfonation levels. Permeability coefficients were obtained using the single gas permeation measurement. The time-lag method was applied to obtain the diffusion coefficient. The correlation of the gas-transport properties with the chemical properties of the polymers is discussed. The results suggest that highly-sulfonated Mg2+-forin polystyrene is a promising material for the 02/N2 separation. Water-transport properties were investigated using PSS/AI203 composite membranes. A dew-point device was used to measure the water penneate rate. A mathematical model (used in a previous investigation of water transport in the sulfonated perfluorocarbon polymer Nafion TM) was used to analyze the water transport data for the PSS/AI203 film. In the ethanol/water separation, the results showed that the PSS/ A1203 composite membranes can break up the azeotrope of the ethanol/ water mixtures by pervaporation. Water is the preferred permeate. The highest separation factor (400) was obtained for the 10.5 mole% PSSNa/AI203 composite at the azeotropic feed composition. Ethanol weight fraction in the permeate is always less than 6 wtO/o for this composite membrane and all feed compositions. In the MTBE/MeOH separation, the results showed that the PSS/A1203 composite membranes possess high MEOH transport selectivity, relative to MTBE. MEOH concentrations in the permeate were always greater than 99.5 wtO/o for all membranes and all feed solution compositions studied. Extremely high separation factors (25,000 to 35,000) were observed for the PSS-Mg/AI203 composite membrane of 27.5 mole% sulfonate.