Water scarcity is a topic of growing concern globally. Desalination is one of the few pathways that can meaningfully increase the water supply. Inland desalination will be necessary but can be prohibitively expensive due to the high cost of concentrate management. These concentrates, which are the salty waste streams resulting from the separation of fresh water from the saline feed, are often hypersaline, i.e. exceed the salinity of seawater, and can be toxic if discharged into the environment. Temperature swing solvent extraction (TSSE) offers a promising path forward for hypersaline desalination, which can be used to reduce the volume of the concentrate and thus facilitate its disposal. TSSE is a thermomorphic multiphase system approach that utilizes a low polarity solvent to extract water from the hypersaline brine while rejecting salts. The application of low temperature heat causes the water to then de-mix from the extract, which regenerates the solvent. The need for only a low temperature heat input, which can be supplied by low-grade heat, and the recyclability of the solvent make TSSE a green process for hypersaline desalination. Previous TSSE research has focused on proof-of-concept and exploration of applicable solvents. In this study, we investigate how key performance parameters behave over a range of temperatures in order to gain fundamental insights into the mechanisms driving the process. We demonstrate that both water recovery and solvent loss are less sensitive to process temperature changes than salt rejection, indicating that salt tends to solubilize in water microstructures within the extract. These variations in temperature sensitivity create different optimal operating regimes for different goals, which can include: minimizing specific energy consumption (SEC), maximizing salt rejection, and minimizing solvent loss. In addition, we investigate the degree to which key solvent parameters, such as water solubility and heat capacity, impact the SEC of the TSSE process. These insights will help us to design next-generation solvents that can truly unlock the potential of TSSE.

Solvent extraction desalination: Key insights from temperature dependence analysis

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.