(213d) Advanced Membrane Materials for Environmental Liquid Separations

Our group focuses on fundamental understanding of the relationships between formation, structure, material properties, and material performance in advanced membranes for applications in environmentally relevant processes.

Surface and groundwaters have increasing concentrations of salts from agriculture and water softening activities—increasing the need for inland brackish water desalination and concentrate management. During inland brackish groundwater desalination, disposal of the concentrate can often constrain the design and overall feasibility. Reverse osmosis (RO) is typically used to achieve 75 to 85% recovery of the feed water and limited by sparingly soluble salts (e.g., calcium sulfate) or minerals (e.g., silica) and the overall concentration of the feed. Pervaporation is a membrane process that separates mixable liquids by a combination of liquid permeation through and vapor evaporation from a dense semi-permeable membrane. It uses hydrophilic dense nonporous (polymer membranes) or microporous (inorganic membranes), in which the driving forces are vapor pressure of the main permeating species and, indirectly, temperature. In pervaporation there is no limit on the salinity of the feed water. We will discuss our results to incorporate direct solar light to enhance the pervaporation process for desalination as well as our development of new membrane for pervaporation.

Liquid fossil fuels are a significant portion of the annual energy consumption of the United States. Butanol is a second generation biofuel whose production does not compete with food production and butanol is a suitable substitute for liquid fossil fuels. Using a condensation-cure method we have synthesized free-standing polydimethylsiloxane/zeolite-imidazolate framework-71 (PDMS/ZIF-71) mixed-matrix membranes with ZIF-71 loadings of up to 40%. Our membranes have the highest reported selectivity for pervaporation recovery of ethanol and butanol from dilute aqueous solutions (selectivity of 5.64 ± 0.15 for 2 wt% 1-butanol in water and a selectivity of 0.81 ± 0.04 for 2 wt% ethanol in water). Tensile testing indicates that the Young’s modulus of the membranes increased with higher ZIF-71 loadings. We also demonstrate that the organic linkers found in ZIF-71 are incompatible with addition-cured PDMS films.