离子液体低温吸收合成气中二氧化碳的科学与技术基础

Absorption is an important separation technology in chemical industry, and the selection of suitable separating agent is the core. However, several problems, i.e., high methanol loss and high energy consumption, exist in the current industrial processes (e.g., the Rectisol process) separating CO2 from syngas. Therefore, a new proposal is put forward in this project for the capture of CO2 from syngas with ionic liquids (ILs) at low temperatures. Using single IL or mixed solvents (IL + IL or IL + organic solvent) as separating agent at low temperatures to intensify the absorption process. This project focuses on the scientific and engineering questions during the low-temperature adsorption, including identification of the relationship between IL structures (e.g., the type of cation and anion, the length of alkyl chain on the cation, and the effect of group branch on the cation) and separation performances (solubility and selectivity) for single gas adsorption and gas mixture separation, and the influence of composition of mixed solvents, other gas component (CO, H2, ect), temperature, and pressure on the separation performances. In addition, this project tries to develop effective and efficient predictive thermodynamic models, to investigate the volume expansivity of ILs after the absorption of gases, to explain the separation mechanism at the molecular level, and to quickly screen the suitable ILs at low temperatures. Thus, we can form systemic molecular thermodynamic theory for this system. On this basis, it goes a further step to establish the equilibrium stage (EQ) and nonequilibrium stage (NEQ) mathematical models to simulate the absorption and stripping processes, do the parameter design and performance analysis, and the analysis of the solvent and energy consumptions using process simulation. This project will provide the basic data and theoretic supporting for the actual application of capturing CO2 using ILs/mixed solvents as separating agent at low temperatures.

吸收作为化学工业中重要的分离技术，适宜的分离剂筛选是其关键。本项目针对目前工业脱除合成气中CO2过程（如低温甲醇洗）存在的高物耗、高能耗等问题，提出以离子液体或复合溶剂（离子液体+离子液体、离子液体+有机溶剂）为分离剂在低温条件强化吸收的新思路。重点研究离子液体低温吸收过程中的科学和工程问题，包括低温下离子液体结构（阴阳离子类型、阳离子烷基链长度和烷基链分支效应等）与单一气体吸收及气体混合物分离性能（溶解度及选择性）间的关系，复合溶剂配比、其它气体（CO、H2等）浓度、温度及压力等对分离性能的影响规律；建立适用于该体系的预测型热力学模型，用以考察低温下离子液体吸收气体后的体积溶胀特性、探索其分离机理、筛选合适的分离剂，从而形成系统的分子热力学理论体系。在此基础上建立低温吸收-解吸过程的平衡级和非平衡级数学模型，对工艺流程进行优化设计、能耗物耗分析，为大规模工业化提供基础数据及可行性分析。

吸收作为化学工业中重要的分离技术，适宜的分离剂筛选是其关键。目前工业脱除合成气中CO2过程（如低温甲醇洗）存在的高物耗、高能耗等问题，鉴于此，项目提出以离子液体或复合溶剂（离子液体+离子液体、离子液体+有机溶剂）为分离剂在低温条件强化吸收的新思路，充分发挥离子液体绿色高效的分离特点，且不改变主要工艺路线和生产设备。本项目针对合成气中CO2气体的吸收系统研究了离子液体低温吸收过程中的科学和工程问题，包括低温下单一及离子液体混合物离子液体结构、混合物配比、操作温度等对CO2、CO、H2气体溶解度的影响规律，建立并发展了适用于该体系的预测型热力学模型（UNIFAC-Lei和COSMO-RS模型）用以考察低温下离子液体吸收气体后的体积溶胀特性、探索其分离机理、筛选合适的分离剂；首次考察了CO2、CO和H2气体在长链咪唑阳离子（CnMIM, n=12）基离子液体中的溶解规律；从分子水平考察离子液体吸收气体的相互作用，揭示分离机制；进而在热力学及预测型模型的研究基础上建立了低温吸收-解吸过程的数学模型，对工艺流程进行优化设计、能耗物耗分析，为大规模工业化提供基础数据及可行性分析。