Molecular level insight on thermal stability of ionic liquids

离子液体被认为是一种极具前景的新型溶剂和反应介质。为了对离子液体在高温下大规模应用的潜力进行正确的经济评估，需要了解离子液体的热稳定性。分解动力学以及可能的分解机理和产物是描述热稳定性所必需的信息。现有的离子液体热稳定性的实验研究大多是通过热重技术中的快速扫描进行的。由此产生的“分解温度”、分解速率常数和活化能同时对应于离子液体的汽化和分解。随后对这些不可靠数据的分解动力学、速率和路径的评估变得与描述离子液体的实际热稳定性无关。另一个问题是对可能的分解机制和相关特征的理论评估。大多数理论研究采用密度泛函理论水平来计算0K时气相中的能量差，这种简化的模型远远不能满足离子液体分解的有限温度和相条件。在这个项目中，我们希望开发和改进一套实验装置，以区分和量化分解和汽化过程的动力学数据。此外，我们还希望利用静态和动态理论方法深入了解热引发分解途径的分子水平、其速率常数和活化能。这种理论分析的重要部分是体相和体气界面动力学参数的计算。这些在实验和理论描述方面的改进将使分解动力学的结果相互比较。作为该项目的一个成果，将提出可靠和经过验证的联合实验和理论数据集和协议，以及简单的预测方案。这将使分解和汽化速率的定量描述成为可能，从而为离子液体的热稳定性提供可靠的评估。

Ionic liquids are considered as perspective novel solvents and reaction media. To provide a correct economic assessment of their potential large-scale application at elevated temperatures, the knowledge on thermal stability of ionic liquids is required. The decomposition kinetics, as well as possible decomposition mechanisms and products, are essential information necessary to describe the thermal stability. Most of the available experimental studies of the thermal stability of ionic liquids were carried out by fast scanning in the thermogravimetric technique. The resulting “decomposition temperatures”, decomposition rate constants, and activation energies correspond simultaneously to vaporization and decomposition of an ionic liquid. The subsequent evaluation of the decomposition kinetics, rates, and pathways from such unreliable data become irrelevant to describe the actual thermal stability of ionic liquids. Another problem is the theoretical evaluation of possible decomposition mechanisms and related characteristics. Most theoretical studies employ density functional levels of theory to calculate the difference in the energies in a gas phase at 0 K. Such simplified modeling is far from the finite temperature and phase conditions of ionic liquids decomposition. In this project, we would like to develop and improve the set of experimental setups to distinguishing and quantify the kinetic data of the decomposition and vaporization processes. Also, we would like to provide a deep insight into the molecular level of the thermally initiated decomposition pathways, their rate constants, and activation energies utilizing static and dynamic theoretical methods. The important part of such theoretical analysis is the evaluation of the kinetic parameters in bulk phase and bulk-gas interface. These improvements in experimental and theoretical descriptions will make the results of the decomposition kinetics comparable to each other. As an outcome of the project, the reliable and verified joint experimental and theoretical dataset and protocols will be proposed with simple prediction schemes. These will make possible a quantitative description of decomposition and vaporization rates to provide a reliable assessment of the thermal stability of ionic liquids.