Molecular and Process Design for Sustainable Desalination

Directional Solvent Extraction for Sustainable Desalination

Access to clean, fresh water is an ever-growing concern for modern society: water is critical to ensure human health, to protect threatened ecosystems, and to promote economic growth and prosperity. Modern seawater desalination technologies remain energy intensive: they require three to four times the theoretical minimum energy for separation. This underscores the critical need for energy efficient and renewable energy driven desalination technologies to address these expanding needs for clean water.

Directional solvent extraction (DSE) is a promising new desalination technology. It relies on liquid-liquid extraction with a thermoresponsive solvent that can be regenerated using low-grade heat. This approach has several unique features: (1) water can dissolve in the solvent and the solubility is a function of temperature; (2) the solvent is virtually insoluble in water; (3) the solvent does not dissolve salts and 4) no membrane is required. Previous work includes initial concept demonstration as a batch process, molecular simulation to understand solvent performance, and heat integration for a single-stage continuous process.

We have developed a mathematical optimization framework for the DSE process to explore trade-offs between product quality, energy requirements, and capital costs. This is done using an equation-oriented approach that simultaneously optimizes process operating conditions (such as temperatures, flow rates, compositions), design parameters (such as equipment sizes), and heat recovery opportunities.

Setting Solvent Design Properties with Process Optimization

The developed framework has the ultimate goal of systematically guiding the molecular discovery of new thermoresponsive solvents. Results show that with the use of high-efficiency heat recovery DSE could be a competitive renewable membrane-free desalination technology.

Preliminary sensitivity analysis and costing show an inside on the property target for directional solvents. Results show that the thermoresponsive ability and low solubility of the solvent in water are the most important properties. The thermoresponsive ability decreases the amount of solvent required which decreases recycle ratio needed in the process, decreasing heat and electricity required and reducing equipment size. Lowering solubility of the solvent in water decreases the solvent loss in the system and the costs associated with this. Results also show that by doubling thermoresponsive ability and reducing the solubility of the solvent in water by a factor of ten, can make DSE economically competitive with modern seawater desalination technologies.

Related Presentations

Alejandro Garciadiego*, Tengfei Luo, and Alexander W. Dowling. Mathematical Optimization of Membrane-Free Desalination Systems That Utilize Low-Grade Heat. AIChE Annual Meeting, Orlando, FL, November 14, 2019. Oral Presentation. [link]

Alejandro Garciadiego*, Tengfei Luo, and Alexander W. Dowling. Mathematical Modeling and Optimization of Directional Solvent Extraction for Sustainable Water Desalination. FOCAPD, Copper Mountain Resort, CO, July 14, 2019. Poster.

Alejandro Garciadiego*, Tengfei Luo, and Alexander W. Dowling. Mathematical Optimization of Membrane-free Desalination Systems that Utilize Low-grade Heat. AIChE Midwest Regional Conference, University of Illinois in Chicago, Chicago, IL, March 18, 2019.

Alejandro Garciadiego, Tengfei Luo, and Alexander W. Dowling*. Mathematical Optimization of Sustainable Water Desalination Processes Using Directional Solvent Extraction. AIChE Annual Meeting, Pittsburgh, PA, October 31, 2018. [link]