相变离子液体水溶液-水合物法捕集分离H2S/CO2/CH4的双效协同作用及热-动力学激励机制

The presence of CO2 and H2S in the low concentration gas extracted from coal seam reduces the CH4 concentration and moreover causes freezing block and corrosion during gas transportation and utilization, which could lead to gas releasing, fire, explosion and even gas poisoning accidents. In order to increase the CH4 concentration and quality, this project proposes to use phase-change ionic liquids (PCILs), based on their tunable structures and phase-change characteristic, to enhance the separation efficiency of H2S/CO2/CH4. A visual high-pressure reaction kettle will be applied to carry out the gas hydrate formation experiments in the presence of PCILs, and gas solubilities in PCIL-H2O solutions and the change of gas hydration kinetics with the cation/anion structures (including the functional groups) and concentrations of PCILs will be analyzed. Thermodynamic parameters of PCIL-H2O-gas will be monitored by a microcalorimeter, and a three-phase thermodynamic equilibrium equation will be built and resolved. Combining with the molecular dynamic simulation, the effect of phase-change thermodynamic properties of PCILs on the formation conditions and thermodynamics transition of each gas hydrate would be revealed. Combining Raman, XRD and XPS technology with Density Function Theory (DFT) and Molecular Dynamic (MD) simulation, the influence of mutual interactions of PCIL-H2O-gas on the PCIL-H2O-gas solution-hydrate transition, gas hydrate formation path and crystal structures could be explained.

CO2与H2S的存在不仅稀释低浓度瓦斯中CH4浓度，还使得瓦斯输送设备面临冻堵和腐蚀，进而引发气体泄漏、火灾、爆炸和中毒事故。为提浓和净化低浓度瓦斯，本项目基于相变离子液体（PCILs）的结构可调与相变特性，提出利用PCILs强化水合物法捕集分离H2S/CO2/CH4。根据PCILs激励下的气体水合物生成过程的可视高压反应釜实验，分析PCILs浓度和阴阳离子结构（包括官能团）对气体在液相中溶解度以及对气体水合物生成动力学影响；利用微型量热仪对各PCIL-H2O-gas水合物体系进行热力学参数监测，建立该三相体系热力学平衡方程，揭示PCILs相变特性参数对气体水合物生成热-动力学过程的影响；采用Raman、XRD和XPS测试技术，结合量子化学DFT计算和MD模拟，阐述PCIL-gas-H2O组分间相互作用对PCIL-gas-H2O水溶液-水合物转换、水合物生成路径及晶体结构的影响机制。

从热力学角度促进水合物生成动力学过程是目前水合物法捕集分离瓦斯气体急需解决的关键问题。本项目探讨了季膦类、季胺类、杂环类室温固态相变离子液体（[N2222]Br、[N2222][NTf2]、[N2222][PF6]、[P2444][PF6]、[P6444][PF6]、[N4444]Br、[P4444]Br、[AMim][PF6]、[EMim][PF6]、[C12Mim][PF6]、[C16Mim][PF6]、[BPy][PF6]、[OPy][PF6]、[PY14][PF6]、[PP14][PF6]）存在下的CO2和CH4水合物生成规律，分析了固态相变离子液体浓度和分子结构对气体水合物形成的相平衡温度、诱导时间、气体消耗量、气体消耗速率、水合物转化率等参数的影响。研究结果显示，阳离子芳香度、杂原子个数、取代链长、阴离子电荷分布等是气体水合物形成的结构性影响因素。阳离子的烷烃取代链越长越有利于CO2水合物成核，六元杂环阳离子比五元杂环阳离子的促进效果更佳；杂原子个数越少越有利于CO2水合物形成和生长；较稳定的不含不饱和键的哌啶结构作为阳离子时，对CO2水合物形成热-动力学过程具有明显的双重促进作用。针对[N2 2 2 2]Br和[N4 4 4 4]Br对CO2水合物影响的差异性，利用密度泛函和分子动力学模拟方法，计算分析了两种离子液体对水合物生成过程的微观影响，阐释了[N2 2 2 2]Br抑制CO2水合物形成而[N4 4 4 4]Br却起促进效果的内在原因，认为两种体系中H2O-Br、H2O-H2O间作用力差异是这两种ILs对CO2水合物形成产生不同影响的主要原因。.此外，本项目还研究了其它促进剂（如氨基酸、木质素磺酸钠、纳米二氧化硅颗粒、微纳米石墨烯颗粒、泡沫金属等）对气体水合物形成热动力学过程的影响。结果显示，虽然微纳米二氧化硅和石墨烯颗粒具有明显的动力学促进效果，但受颗粒表面官能团和粒径影响；泡沫金属是较好的气体水合物合成载体，能够从热动力学两个方面同时改善水合物合成速率和储气量；氨基酸为优良的动力学促进剂，1,3-二氧五环能够明显提高相平衡温度，是较好的热力学促进剂，两者结合可实现气体水合物的热-动力学协同强化作用。