Structural optimization and characterization of fluoro-based protic ionic liquids for high-temperature and high-salinity conditions

Fluorine-based protic ionic liquids (FILs) have unique chemical and structural properties that make them attractive in applications that involve harsh conditions like high temperature and high salinity. In this study, we synthesized the seven FILs with primary amines having varied alkyl chain lengths. The chemical structure was confirmed by NMR, and FTIR spectroscopy. The thermal stability of the FILs was evaluated by the thermogravimetric analyzer (TGA). Additionally, the surface properties and thermodynamic parameters of the three most important FILs were also examined in this study. The long-term thermal and salt tolerance test was performed for three different types of water with having salinity range from 0 to 241,000 ppm. The results showed that the degradation temperature of all synthesized FILs was higher than the reservoir temperature. The surface-activity findings demonstrated that FILs with the alkyl chain range from (C₆-C₁₂) have excellent surface properties. However shorter chain (C₂-C₄) showed very little surface reduction, and the longer chain (C₁₄-C₁₆) faced solubility issues, which hindered the determination of their surface tension. The salt tolerance results provide stable and transparent solutions after one week of ageing at 90 °C. These findings exhibited the importance of the molecular structure of the FILs with their desired properties for the application at high temperature and high salinity conditions.