Enhancing microwave heating performance of imidazolium ionic liquids in well stimulation process: the role of magnetic anions and structural modifications

This study investigates the synthesis, characterization, and microwave heating performance of imidazolium-based ionic liquids (ILs) and their magnetic analogs, specifically [BIM][FeCl 4 ] and [OIM][FeCl 4 ]. The ILs were synthesized and characterized using FTIR, NMR, CHN analysis, and VSM, confirming the successful incorporation of Fe 3+ -containing tetrachloroferrate anions in the MILs. Microwave heating experiments were conducted on 0.1 wt% aqueous dispersions of these ILs, and the temperature evolution was measured under 2.45 GHz microwave irradiation at power levels of 200 W and 400 W. Results showed that the presence of ILs significantly enhanced heating compared to pure water, with [BIM][FeCl 4 ] reaching a final temperature of 81 °C and [OIM][FeCl 4 ] reaching 93 °C at 400 W after 60 s. The effect of alkyl chain length on microwave heating was minimal in chloride-based ILs, with only a 2 °C difference between [BIM]Cl and [OIM]Cl. However, a more pronounced effect was observed in MILs, where [OIM][FeCl 4 ] exhibited an 8 °C higher final temperature than [BIM][FeCl 4 ]. Increasing IL concentration from 0.05 to 0.10 wt% led to a 10–15 °C increase in heating efficiency, with [OIM][FeCl 4 ] reaching the highest final temperature at 0.10 wt%. VSM analysis confirmed weak paramagnetism in both MILs, indicating that the enhanced microwave heating was primarily due to increased dielectric loss from ionic conductivity and dipolar polarization, rather than magnetic losses. These findings demonstrate the critical role of ionic liquid structure, anion type, and concentration in optimizing microwave absorption, with significant implications for applications in energy storage and heavy oil upgrading. Future work should focus on improving magnetic responsiveness and exploring the long-term stability of these materials in industrial settings.