abstract
Deep eutectic solvents (DES) have emerged in the past few years as a new class of solvents with promising applications in several fields. In the present work, the application of DES (formed by binary mixtures of cholinium chloride and carboxylic acids or urea) as phase-forming components of aqueous biphasic systems (ABS) is investigated. The mechanisms associated with the phases demixing of ABS composed of DES, as well as the DES stability in aqueous solutions, are investigated to address the critical question whether DES-based ABS are in fact ternary or quaternary mixtures. It is shown that the DES integrity is destroyed in ABS by the disruption of the hydrogen-bonding interactions of the complex (a result of the isolated components preferential solvation by water), and as confirmed by a nonstoichiometric partition of the DES components between the coexisting phases. As a result, there are no "real" DES-based ABS; instead, there is the formation of ABS composed of four components, where the carboxylic acid used as the hydrogen-bond donor species seems to act as an additive. Finally, it is shown that these ABS have an outstanding potential to be used in extraction processes, as it is here demonstrated with the complete separation of two dyes. However, the volatile nature of short chain carboxylic acids and the nonstoichiometric partition of the DES components in ABS make the development of recovery and recycling steps more difficult to accomplish.
keywords
TEMPERATURE MIXTURES LTTMS; IONIC LIQUIDS; PHYSICAL-PROPERTIES; CARBOXYLIC-ACIDS; 2-PHASE SYSTEMS; EXTRACTION; MEDIA; WATER; CATALYSIS; CHLORIDE
subject category
Chemistry; Science & Technology - Other Topics; Engineering
authors
Passos, H; Tavares, DJP; Ferreira, AM; Freire, MG; Coutinho, JAP
our authors
Ana Maria da Conceição Ferreira Takahashi
Junior Researcher
Daniel Pinho Tavares
MSc Student
Helena Isabel Sousa Passos
Junior Researcher
Mara Guadalupe Freire Martins
Coordinating ResearcherGroups
G4 - Renewable Materials and Circular Economy
G5 - Biomimetic, Biological and Living Materials
acknowledgements
This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. The authors also acknowledge FCT for the doctoral grants SFRH/BD/85248/2012 and SFRH/BD/92200/2013 of H.P. and A.M.F., respectively.