(701c) Development of Polymeric Membranes for Pervaporation Application

A critical challenge facing all water desalination, regardless of feedwater type, is management of the produced concentrated waste solutions. Reverse osmosis (RO) is the most commonly used desalination process because it has the lowest energy consumption compared to alternative thermal technologies and operated near its theoretical thermodynamic floor. RO typically achieves 40-90% recovery of the feed water (dependent on concentration and composition), leaving up to 30% of the water as concentrated waste for disposal. For brackish feedwaters (total dissolved solids < 5 g/L) the maximum recovery is typically limited by sparingly soluble salts or minerals (e.g., calcium sulfate or silica, respectively) and, ultimately, depends on the feed water composition. However, for high salinity waters, such as seawater (total dissolved solids ~ 32g/L) or produced waters from hydraulic fracturing (total dissolved solids 30-200 g/L) the maximum recovery is limited when the osmotic pressure of water exceeds the maximum achievable pressure within the system. Pervaporation is a membrane process that operates based on a vapor pressure difference across a dense, selective membrane. Pervaporation is more energy intensive than RO, therefore ultimately it is best suited for applications that exceed the limitations of RO (such as concentrate management or treatment of waters with TDS > 60-80 g/L). However, it shows potential to greatly reduce the volume of concentrate in processes such as RO.

Our team has been working collaborative with researchers from at Rice University and University of Texas El Paso and we have developed a facile solution casting method for freestanding pervaporation membranes. These polymeric membranes show incredible promise for use in pervaporation desalination due to ease of casting and excellent performance parameters, with permeance of 135.5 ± 29 kg m^-2 hr^-1 bar^-1 and salt rejection consistently greater than or equal to 99.5%. This reliably outperforms commercial pervaporation membranes and shows promise for continued desalination and produced water applications.