Investigations on the thermal stability and decomposition mechanism of an amine-functionalized ionic liquid by TGA, NMR, TG-MS experiments and DFT calculations

摘要

Amine-functionalized ionic liquids (ILs) have potential applications for CO2 capture. The CO2 capture process is generally operated at a relatively high temperature for a long term, so determining the thermal stability of amine-functionalized ILs is important. In this study, the thermal stability of an amine-functionalized IL 1,2-dimethyl-(3-aminoethyl) imidazelium tetrafluoroborate [aEMMIM][BF4] was investigated by thermogravimetric analysis (TGA), thermogravimetric mass spectroscopic analysis (TG-MS), H-1 nuclear magnetic resonance (NMR) experiments and density function theory (OFT) calculation. Amine-functionalization was found to reduce the thermal stability of [aEMMIM][BF4] compared to the non-functionalized counterpart. Besides that, we found that [aEMMIM][BF4] favors a unimolecular substitution nudeophilic (SN1) decomposition reaction rather than bimolecular nucleophilic substitution (SN2) reaction. Vaporization and elimination processes are negligible due to amine functionalization. Moreover, an operational temperature, T-oper, is proposed for evaluating the thermal stability of ifs. Results show that T-oper of [aEMMIM][BF4] only reaches 138 degrees C, much less than that of the onset decomposition temperature, T-onset (284 degrees C). Evaluating thermal stability of amine-functionalized Its by T-oper is more practical than by T-onset. (C) 2015 Elsevier B.V. All rights reserved.