LCST behaviour in aqueous mixtures of 5-phenyltetrazolate ionic liquids
Sanskrita MADHUKAILYA1, Leila MOURA1, John D HOLBREY1
1The QUILL Research Centre, School of Chemistry and Chemical Engineering, Queen's University Belfast, Belfast, United Kingdom
We have previously investigated tetrabutylphosphonium 5-phenyltetrazolate/water ([P4444][Ph-Tet]/H2O) mixtures which exhibit LCST (lower critical solubility temperature) behaviour with a critical point of approximately 40°C1. In line with other tetrabutylphosphonium-based ionic liquids (for example with methyl benzenesulfonate anions2) that have LCST characteristics, there is potential to make use of these materials as draw fluids for low-grade energy desalination or dewatering processes.
Here, we report on an ongoing interest in the investigation of how both the critical temperatures and compositions of the biphase can be controlled by the systematic modifications to the cation or anion of 5-phenyltetrazolate-based ionic liquids/water systems through derivatization of anions and structural modifications in the cations to modify the hydrophobicity of the IL-rich phase and reducing the LCST from 40 to 20 °C or less (see Figure 1). On that note, understanding the chemistry behind the formation of LCST systems in the studied ionic liquid/water systems whilst changing different parameters like composition, and salt concentration, in response to temperature is also investigated.
References
1. Moura, L., Brown, L. C., Blesic, M. & Holbrey, J. D. LCST Phase Behavior and Complexation with Water of an Ionic Liquid Incorporating the 5-Phenyltetrazolate Anion. ChemPhysChem 18, 3384–3389 (2017).
2. Cai, Y. et al. Energy-efficient desalination by forward osmosis using responsive ionic liquid draw solutes. Environ. Sci. Water Res. Technol. 1, 341–347 (2015).