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Quantitative Analysis Of Desalination Efficiency Of Amines For Optimization Of Temperature Swing Solvent Extraction Process**

Abstract

Efficient, low-cost methods of treating saline wastewater are in high demand with an increase in global population and therefore, industrial water consumption. Hypersaline waste brines are of maximum concern due to their negative effects on in-situ ecology, specifically soil fertility. Temperature swing solvent extraction (TSSE) is a high-efficiency, low-energy desalination technique that utilizes low-temperature heat and a low-polarity solvent in combination with temperature-dependent water solubility. This technique differs from conventional desalination in that it is membrane-less, significantly reducing cost. This study primarily focuses on the parameters influencing TSSE using secondary and tertiary amines which are viable solvents for TSSE as they contain hydrophilic moieties within a mainly hydrophobic structure. In particular, the extraction efficiency of each type of amine is to be calculated on mass-, volume- and molar-basis with a view to providing foundations for the optimization of TSSE process. Extraction experiments were conducted for 50 ml of both hypersaline brine and amine solutions across all trials. Secondary amines have been found to extract the largest quantities of product water from 1M hypersaline NaCl solution, yielding 14.02 mL and 8.07 mL with N-methylcyclohexylamine and diisopropylamine, respectively. The recovery for secondary amines appears to be dependent on the concentration of respective amine solutions, as well. Little correlation has been found between the parameters and the recovery rate of tertiary amines. Notably, substituents such as ethyl, diethyl, and triethyl groups led to the lowest water recovery among their corresponding amine-type groups. Future work will include further tests with varying experimental conditions, particularly the product water recovery from increased molarities of 2M and 4M hypersaline brine solutions. Analysis of amine substituents including asymmetry and chain lengths will be observed through extraction experiments. Overall, the viability of TSSE as a practical desalination technology is assessed through comparison of amine-to-water recovery ratios.

Acknowledgements

ACKNOWLEDGEMENT: ​ This Material Is Based upon Work Supported by the National Science Foundation: Grant No. 1826920 (MRI: Acquisition of Total Organic Carbon/Total Nitrogen Analyzer for Interdisciplinary Research and Teaching at Georgia Gwinnett College). Disclaimer: ​ANY OPINIONS, FINDINGS, and CONCLUSIONS or RECOMMENDATIONS EXPRESSED in THIS MATERIAL ARE THOSE of the AUTHORS and DO NOT NECESSARILY REFLECT the VIEWS of the NATIONAL SCIENCE FOUNDATION. ​

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