Hydrate-Based Desalination Technique Breakthrough Unveiled

Abstract

Hydrate-based desalination (HBD) shows promise as a freshwater production technology for saline water. Liquid-phase hydrate formers, with their ability to facilitate hydrate formation at atmospheric pressure, have gained attention for their high energy efficiency in HBD. This study explored cyclopentane (CP) HBD by experimentally measuring the thermodynamic properties of CP hydrate in saline solutions and developing a theoretical framework to estimate the water yield of CP HBD under various operating conditions. The measured dissociation enthalpy of CP hydrate was found to be 12 % and 22 % lower compared to those of propane and R134a hydrates, respectively. The equilibrium dissociation temperatures of CP hydrate at different NaCl concentrations under atmospheric pressure were experimentally measured and then predicted using the Hu-Lee-Sum correlation. The theoretically achievable maximum salinity and water yield for CP HBD were calculated in the temperature range of 268-280 K and the initial salinity range of 0-8 wt.%. Additionally, the concept of HBD heat efficiency, representing the maximum amount of pure water producible per unit of heat, was introduced to identify an optimal operating condition for the HBD process. Efficiency-maximized temperatures, where the HBD heat efficiency reached its peaks, were determined for various initial salinities in the process, for example, 273.4 K for NaCl 3.5 wt.% solution. This novel approach provides invaluable guidance for determining the most energy-efficient operating conditions in the HBD process and establishes a solid foundation for further advancements in this field.

A research team, led by Professor Yongwon Seo in the Graduate School of Carbon Neutrality at UNIST has unveiled a highly efficient method for desalinating seawater using hydrate-based desalination (HBD) technology. The breakthrough is expected to have far-reaching implications for the application of hydrate-based desalination techniques, with the ability to calculate optimal temperatures for enhanced efficiency.

Hydrate desalination technology, known for its eco-friendly freshwater production capabilities, offers a low-energy solution that can be effectively used in treating high concentrations of brine or contaminated water. By leveraging the phenomenon where impurities, including salts, are expelled during the formation of hydrates from brine or contaminated water, clean water can be obtained.

In this study, the research team experimentally measured the thermodynamic properties of cyclopentane hydrate and evaluated the efficiency of the hydrate desalination technique based on these measurements. They also proposed a novel calculation method for predicting the temperature that maximizes desalination efficiency.

"When specific conditions are met after adding cyclopentane, a colorless volatile liquid, to brine, cyclopentane hydrate, consisting of pure water, is formed," explained Professor Seo. "We experimentally measured the thermodynamic properties of this cyclopentane hydrate to apply it to desalination processes."

Building upon their experiments, the research team calculated the maximum water yield of cyclopentane hydrate under various conditions. The efficiency was determined based on the maximum water yield and the thermal energy required for cooling during the hydrate desalination process. A thermodynamic relational equation was developed to identify the temperature at which maximum efficiency can be achieved for each brine concentration.

For instance, when the hydrate desalination technique is applied to brine with initial salt concentrations of 3.5 wt% and 5 wt%, the relational equation calculates the energy efficiency optimum temperatures as 273.4 K and 271.5 K, respectively. The corresponding maximum water yields are 67% and 61.1%. This research provides a crucial criterion for optimizing the efficiency of real-world desalination processes.

Junghoon Mok, the first author of the study, emphasized the significance of this research, stating, "This study is expected to optimize the energy consumption in high-concentration brine treatment processes using hydrate freshwater techniques." He added, "The proposed approach is not only applicable to hydrate-based desalination but also holds promise for freeze-type desalination technology."

The study was conducted in collaboration with the Korea Institute of Production and Technology and received support from the Ministry of Science and ICT's Korea Research Foundation's basic research project, nuclear research and development project, and the Korea Energy Technology Evaluation Institute.

This research, conducted in collaboration with the Korea Institute of Industrial Technology (KITECH), has received support from the Korea Institute of Energy Technology Evaluation and Planning (KETEP), the Ministry of Trade, Industry and Energy (MOTIE), and the National Research Foundation of Korea (NRF). The paper, detailing this groundbreaking research, was published in the November 2023 issue of Water Research.

Journal Reference

Junghoon Mok, Minseo Park, Wonjung Choi, et al., "Investigation of theoretical maximum water yield and efficiency-optimized temperature for cyclopentane hydrate-based desalination," Water Res., (2023).