Exploring the influence of the type of anion in imidazolium ionic liquids on its thermal stability

In this research, three kinds of imidazole ionic liquids were selected as the research objects. Among them, 1-butyl-3-methyl-imidazole bis(trifluoromethylsulfonyl)imine ([BMIM][Tf2N]) was used for gas adsorption, while 1-butyl-3-methyl-imidazole acetate ([BMIM][Ac]) and 1-butyl-3-methyl-imidazole tetrafluoroborate ([BMIM][BF4]) were used as extractants to replace traditional organic extractants. The thermal stability of three selected ionic liquids was studied, and their decomposition pathway and thermal stability were compared to explore the correlation between them. Thermal decomposition characteristic of [BMIM][Ac], [BMIM][BF4], and [BMIM][Tf2N] was analyzed by thermogravimetric analysis. For these three ILs, dynamic thermogravimetric analyses under nitrogen atmosphere were performed using thermal gravimetric analyzer. The TG curve shows that the order of short-term thermal stability of three ionic liquids is [BMIM][Ac] < [BMIM][BF4] < [BMIM][Tf2N]. Both Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods were used to analyze the thermal dynamics of the experimental process. The apparent activation energies calculated by two different kinetic methods of the three ILs also have some slight differences. The possible influence of the decomposition mechanism on thermal stability was analyzed by thermogravimetric coupled with Fourier-transform infrared spectrometry (TG-FTIR). After analyzing the experimental results, it is obvious that as the thermal stability of ionic liquids increases, their decomposition mechanisms become more and more complex.