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COMPARISON OF EXTRACTION CHARACTERISTICS OF SECONDARY AND TERTIARY AMINES FOR DESALINATION

Abstract

Temperature swing solvent extraction (TSSE) is an effective technique characterized by membrane-less desalination and being a low energy, cost-effective alternative for saline feeds. Evaporative technologies such as distillation consume a great amount of energy and membrane-based technologies are applicable only to sources with low dissolved solids. While the application of TSSE in desalination has been studied, little is known about the effect of different amines on the efficiency of the technology. Therefore, this study focuses on the systematic elucidation of the parameters influencing the TSSE, in particular, the comparison of the affinity of secondary and tertiary amines to water. Diisopropylamine, diisopropylethylamine, N,N-diethyl cyclohexylamine, and other amines were chosen to test the effect of degree of substitution and the types of functional groups on the extraction performance. A cycle of temperature swing extraction was conducted for each type of amine, and Sudan IV dye was employed to visually demonstrate a clear separation between the amine and the aqueous layers. There were noticeable differences in the efficiency of extraction of water from highly concentrated brine for secondary and tertiary amines. A larger volume of water was recovered from the extraction with secondary amines when the same volume of solvents was used, which strongly suggests the differential affinity of solvents to water. Further tests with varying experimental conditions are being conducted, and the conclusive extraction results and analysis of the correlation among parameters will be presented. Future work will include additional set of extraction experiments using asymmetric substituents and the optimization of the extraction temperature for individual amines.

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