Brine management is an enormous challenge for implementing nontraditional water sources such as brackish water, seawater, municipal and industrial wastewater (e.g., produced water), especially in inland areas where brine disposal options are limited. Thermal concentrators (e.g., mechanical vapor compression evaporators) are widely used for brine minimization, but these technologies are energy intensive and require high capital investment. Electrodialysis (ED) provides a lower energy alternative to thermal brine concentration and could enable cost-effective treatment of brine concentrations up to 250,000 mg/L TDS. However, conventional ion-exchange membranes (IEMs), originally designed for brackish water desalination, exhibit low permselectivity when contacted by highly concentrated salt solutions, making them unsuitable for this application. While new classes of commercial IEMs for brine treatment via ED have emerged, further improvements in membrane performance are necessary for ED to outcompete conventional technologies in this space. Rational design of better performing IEMs would be facilitated by improved fundamental understanding of the connection between polymer structure and transport properties. Two important membrane structural parameters that influence IEM transport properties are fixed charge density and water uptake. Conventional IEMs for brackish water desalination are highly swollen by water (water mass fractions between 0.4-0.5), while commercial IEMs for treating highly concentrated salt solutions sorb much lower amounts of water (water mass fractions lower than 0.3). The transport properties of the latter class of IEMs (i.e., low water content IEMs) are poorly understood on a fundamental level, which hinders our ability to design new IEMs for treating highly impaired water via ED. In this study, we systematically investigated the influence of membrane water content on IEM transport properties in an effort to better understand the transport phenomena in low water content IEMs. This presentation will discuss our recent findings in this area. A long term goal of this study is to establish structure/property relations for developing high-performance IEMs with properties specifically tailored for high salinity applications such as brine concentration via ED.

Transport properties of ion-exchange membranes for brine concentration via electrodialysis

ACS Fall 2021

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