胆碱类离子液体水溶液分离CH4/CO2过程传递强化研究

By biogas purification, the low-grade energy will be converted into high-grade energy, and the realization of sustainable development with energy saving and emission reduction meet with the strategy of significant demand in China. However, the biogas project needs to rely on government subsidy due to its low economic benefits. So, it is particularly important to reduce the energy consumption of CH4/CO2 separation, but the competition between high-rate and high-effeciency exists in this process . For CO2 removal by liquid absorbents, the selection of absorbents, the enhancement of absorption rate and the reduction of absorption enthalpy is the key to decrease the energy consumption for the biogas purification. The aqueous solution of choline-based ionic liquids (ILs) is chosen as CO2 absorbent, and the selection and the design of absorbent are determined by the calculation of thermodynamic limitation. Based on non-equilibrium thermodynamic model, the reaction and diffusion process of CO2 in the absorbent will be analyzed and regulated. By changing the type of choline-based ILs and interface enhancement, the contribution between absorption rate constant and absorption enthalpy will be regulated. The approach of strengthening the mass transfer process is proposed. Meanwhile, the relationship among absorption, desorption and energy consumption is analyzed by coupling thermodynamic limitation and kinetics. As increasing the rate of CO2 absorption, the efficiency of energy use is improved, and the “profit-free” of bio-methane preparation process is implementated.

沼气脱除CO2制备生物甲烷，将低品位能源转化为高品位能源，实现节能与减排的可持续发展，符合我国战略重大需求。但其经济运行性差，一定程度上需要依赖“政府输血”，因此降低CH4/CO2分离能耗就显得尤为重要。然而CH4/CO2分离过程在本质上存在速率和效率的博弈，对液体吸收剂脱除CO2过程而言，如何选择吸收剂，强化过程吸收速率，降低吸收焓，是解决生物甲烷制备过程能耗降低的关键。本项目选用胆碱类离子液体水溶液作为吸收剂，通过计算热力学极限进行吸收剂筛选和设计，根据非平衡热力学原理，分析CO2在吸收剂中反应与扩散的耦合机制，调控传递阻力构成，选用不同离子液体水溶液和界面强化手段实现最佳吸收剂组成、吸收速率常数与吸收焓最优匹配，提出强化传质过程的新方法。同时，结合热力学极限与动力学过程系统评价吸收、解吸、能耗等因素的影响，在提高过程速率的同时，提高能量的有效利用，实现生物甲烷制备过程的“自身造血”。

沼气脱除CO2制备生物甲烷，实现节能与减排的可持续发展，符合我国战略重大需求，然而，CO2分离过程在本质上存在速率和效率的博弈，亟需新材料与新强化思路的介入。本项目选用胆碱类离子液体水溶液作为吸收剂，运用非平衡热力学原理，分析CO2在吸收剂中的热力学与动力学性质，调控CO2传递过程的推动力与阻力构成，提出强化传质过程的新方法。研究内容包括：（1）设计并制备不同阴离子的胆碱氨基酸离子液体并表征其结构，测定包括其复配体系在内的基础物性数据；（2）采用聚乙二醇（PEG200）和H2O作为共溶剂，测定CO2在离子液体复配体系中的气液平衡关系，获取其热力学性质；（3）测定CO2在离子液体复配体系中的动力学曲线，计算CO2吸收过程的动力学性质，剖析其传质阻力控制因素；（4）引入多孔材料PMMA进行负载，进一步提高离子液体吸收剂的CO2分离性能；（5）耦合CO2在胆碱氨基酸离子液体复配体系中的热力学与动力学性质参数，提出新的性能评价参数。本项目研究发现胆碱氨基酸离子液体具有较好的CO2吸收与解吸性能，解吸焓的数值在-40~-60 kJ/mol，明显低于传统有机胺吸收剂，在离子液体水溶液中引入PEG200，能够有效降低解吸焓和提高复配体系的再生效率；通过共溶剂可以有效实现CO2传质阻力从扩散控制往反应控制的转变；提出了新的吸收度概念对CH4/CO2在胆碱氨基酸离子液体水溶液中分离性能进行评价，胆碱丝氨酸水溶液用于CH4/CO2分离的性能可与商业化的单乙醇胺水溶液相媲美。项目执行期间，共发表11篇SCI论文和1篇中文论文，协助培养博士生2名，培养硕士生8名，其中1人获中瑞双博士学位，此外，相关的科学研究和过程开发的开创性成果也在进一步进行中。