离子液体溶解甲烷机理及影响因素研究

The methane(CH4) concentration technology is one of the major bottlenecks for the efficient utilization of CH4 in the low-concentration gas from mine. But the current solvents used to concentrate gas usually are highly volatile, and could mix with CH4 possibly and even release into the air and pollute it. For the low volatility and selectively dissolution for gases of ionic liquids, we propose to use ionic liquids to absorb and dissolve CH4 to concentrate the CH4 gas. Firstly, we will test the CH4 solubility in some ionic liquids with high symmetry cations under different experimental conditions using Quartz Crystal Microbalance. Secondly, based on the Group Contribution theory and the Molecular Dynamics, we will establish solubility prevention model of CH4 dissolving in a variety of ionic liquids, and analyze the general effect laws of temperature, pressure, anions and cations on the dissolution; Thirdly, using the Fourier transform infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) instrument, the chemical structure changes of the ILs before and after reacting with CH4 will be investigated; Moreover, at the molecular and electron levels, using the Quantum Chemical simulation, the chemical reaction pathway and the mechanism of ionic liquid dissolving CH4 will be revealed. Finally, the structure features of the Target-IL, which can efficiently dissolve CH4, will be concluded, as well as the favorable conditions for this ionic liquid dissolving CH4. This investigation will provide a reliable experimental data and theory basis for the application of ionic liquids in the fields of CH4 concentration and the separation of the low-concentration gas from the mines.

甲烷富集技术是目前矿井低浓度瓦斯高效利用的主要瓶颈之一。目前溶剂吸收法回收甲烷所用溶剂多具有高挥发性，易混合于甲烷中，且污染空气。基于离子液体的低挥发性和对气体的选择溶解性，申请人提出利用离子液体溶解甲烷，以达到富集甲烷气体的目的。本项目将通过石英晶体微天平实验测试部分阳离子对称性较高的离子液体对甲烷气体的溶解度；基于基团贡献法和分子动力学模型，建立甲烷在离子液体中溶解的预测模型，以此分析温度、压力、阴阳离子影响该溶解过程的规律；利用红外光谱仪和核磁共振仪测试通入甲烷前后不同离子液体的化学结构变化,结合量子化学计算和分子动力学模拟揭示离子液体溶解甲烷的化学反应路径和反应机理；最后，总结能够高效溶解甲烷的离子液体的结构特征，以及该离子液体溶解甲烷的有利条件。本研究将为离子液体在矿井低浓度瓦斯的富集及瓦斯气体分离技术方面的应用提供理论基础。

高效捕集并利用矿井低浓度瓦斯中的甲烷不仅有助于降低温室气体排放，还有利于增加清洁能源供给。鉴于离子液体低挥发、高稳定性和溶解选择性的特点，本项目利用石英晶体微天平实验系统和量子化学计算软件Material Studio理论模拟计算，分析了CO2、CH4、N2在季胺类离子液体[N4444][NTf2]和季膦类离子液体[P4444][NTf2]中的溶解度。搭建的溶解度实验系统主要由石英晶体微天平、高压反应釜、恒温水浴锅组成。这两种离子液体对三种气体的吸收均符合亨利定律，随压力增加溶解度线性增加。总体来说，CO2的溶解度均高于CH4和N2。溶解度实验结果表明CO2、CH4在[P4444][NTf2]中的吸收量多于在[N4444][NTf2]中的吸收量，而且[P4444][NTf2]对CO2/CH4的理想分离选择性优于[N4444][NTf2]。[P4444][NTf2]的CO2/CH4选择性随压力升高线性增加，3MPa时，[P4444][NTf2]的CO2/CH4选择性达到9；而[N4444][NTf2]的CO2/CH4选择性则较差，随压力变化不明显。这与两种离子液体与气体的作用能有关。 . 利用Material Studio 的Dmol3和Sorption模块对IL-CO2、IL-CH4、IL-N2体系分别进行结合能、前线轨道和分子动力学模拟，结果发现阴离子是离子液体与CO2作用的主要位置，IL-CO2作用能高于IL-CH4和IL-N2体系，这也是CO2溶解度高于CH4和N2的本质原因。由于作用能均低于50 kJ/mol，两种离子液体与CO2、CH4、N2均为物理吸收，这与实验结果一致。[N4444][NTf2]与[P4444][NTf2]在常温时均为呈晶体性状，对气体的吸收以表面吸附为主，高压时部分气体进入离子液体内部，但是与室温离子液体相比，此类非室温离子液体吸收/解吸气体速率较快，解吸能耗较低。固态离子液体吸收气体的研究为离子液体在气体膜分离与气体吸附等方面提供了实验和理论依据。与液态吸收相比，固态离子液体的应用更具经济性和实用性。