Thermal stabilities of di-alkylimidazolium chloride ionic liquids

Thermal stability of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl) ionic liquids was investigated using thermogravimetric analysis (TGA). The long-term isothermal TGA studies have revealed that both the ionic liquids exhibit appreciable decomposition at temperatures significantly lower than indicated by the peak or onset decomposition temperature (Tonset) determined from fast scan TGA experiments. The long-term thermogravimetric studies of both the ionic liquids showed linear weight loss as a function of time at each temperature of 10 °C interval in the range 150–170 °C over a period of 15 hours. However, the linear weight loss regime decreased with increasing temperature for the range 180–200 °C. The kinetics of isothermal decomposition of ionic liquids was analyzed using pseudo-zero-order rate expression. Arrhenius activation energy for the decomposition of di-alkylimidazolium chloride ionic liquids in the range 150–200 °C was determined.