Thermal stability and moisture uptake of 1-alkyl-3-methylimidazolium bromide

The thermal stability of the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bromide, [BMIM]Br, and 1-n-octyl-3-methylimidazolium bromide, [OMIM]Br, was evaluated through thermogravimetry (TG). Long-term isothermal TG studies revealed that both of these ILs exhibit appreciable decomposition even at temperatures significantly lower than the onset decomposition temperature, previously determined from fast scan TG experiments. The long-term TG studies of both the ILs showed linear mass loss as a function of time at each temperature of 10 A degrees C interval in the range 533-573 K over a period of 10 h. The kinetics of isothermal decomposition of ILs was analyzed using pseudo-zero-order rate expression. The activation energies for the isothermal decomposition of [BMIM]Br and [OMIM]Br under nitrogen atmosphere are 219.86 and 212.50 kJ mol(-1), respectively. The moisture absorption kinetics of these ILs at 25 A degrees C and 30% relative humidity (RH) and at 85 A degrees C and 85% RH were also studied. Water uptake of ILs exposed at 25 A degrees C/30%RH follows a simple saturation behavior in agreement with Weibull model while that at 85 A degrees C/85%RH fortuitously fit into the Henderson-Pabis model.