The thermal degradation of ionic liquids 1-octyl-3-methyl imidazolium trifluoromethanesulfonate ([OMIM][TfO]) and 1-octyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([OMIM][Tf2N]) were investigated using spectroscopic and thermal techniques to predict gas chromatographic phase stability.
For differential scanning calorimetry, lowering the heating rate from 10 to 2 °C/min decreased the decomposition temperature of the ionic liquids ∼ 23 °C for [OMIM][TfO] and ∼ 13 °C for [OMIM][Tf2N]. In addition, lowering the heating rate gave better resolution and showed anion thermal decomposition occurred several degrees before cation decomposition for the ionic liquids. Experimental measurements showed that decomposition of the ionic liquids was indicated at lower temperatures when using spectroscopic methods compared to thermal scanning methods. Total synchronous fluorescence spectroscopy was used to monitor the formation of ionic liquid degradation products during thermal stress experiments. Decomposition temperatures determined by differential scanning calorimetry were approximately 140 °C higher compared to measurements by fluorescence spectroscopy. (Publisher abstract provided)
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Journal of Molecular Liquids (2022), Volume 363, Issue 1