新型功能化离子液体相变体系的构建及其捕集CO2反应机理

As the most used phase change solvent, alkanolamine still suffered some fatal flaw, such as high viscosity and inferior regenerability of the CO2-rich phase. In this proposal, a novel biphasic solvent based on amino-functionalized ionic liquid-organic alcohol-water mixed solvent was proposed for energy-efficient post-combustion CO2 capture. Quantum chemistry calculations will be used to guide the design of multi-amino-functionalized ionic liquid, which contain multiple amino functionalized groups. In this novel system, amino-functionalized ionic liquid would function as an absorption accelerator and be assured of the high CO2 loading of the absorbent. The mixture of ethanol-water was used as the solvent for the absorbent, in which ethanol would affect the phase change behavior of the solution and water would contribute the low viscosity of the CO2-rich phase. In order to obtain the optimal proportion and CO2 capture performance of the solvent, the absorption rate, the absorption capacity, phase separation, regeneration efficiency and energy penalty will be investigated respectively. The species distribution in the two separated phases will be analyzed, and the chemical reaction mechanism and the phase change mechanism between the new system and CO2 will be clarified. Finally, the volatilization and wastage of the solvent during the reaction separation process would be measured, and the economy of this process will be compared with the benchmark MEA 30wt.% and the traditional biphasic amine solvent. The results of this research proposal will provide a new process for CO2 capture from flue gas.

针对传统醇胺水相吸收剂捕集CO2再生能耗高，现有相变体系吸收CO2后富液粘度大、不易再生的缺陷，本项目创新性地提出构建一种新型功能化离子液体-醇-水三元相变吸收体系，其中，功能化离子液体作为吸收剂，将保证体系高效的CO2捕集性能；醇作为分相试剂，促使CO2吸收产物在混合溶剂中分相；而水作为溶剂，可保证分相富液的低粘度。本项目拟通过量子化学计算辅助设计，筛选并合成高CO2负荷的功能化离子液体，考察吸收剂捕集CO2的吸收-解吸性能，优化体系组成及配比；分析各组分在相层中的分布及中间产物的形态变化规律，构建该三元相变体系的相图，重点阐明其分相调控机制及捕集CO2的反应机理；分析反应和分离过程中的溶剂损失及吸收剂损耗规律，评价该体系循环使用能力及再生能耗。本项目研究结果，将为当前全球关注的碳减排问题提供新思路，为技术的推广和应用提供理论依据。

（1）本项目构建的新型相变吸收剂（[DETAH][Tz]/正丙醇/水），用正丙醇进行调控相分离行为，用于CO2捕集，并从新型离子液体的CO2捕集性能、反应机理、相变机制、动力学特性以及再生能耗等方面展开探索。主要研究工作和结果如下：（1）[DETAH][Tz]/正丙醇/水吸收-解吸CO2性能测试。由50 v/v%正丙醇构成的[DETAH][Tz]/正丙醇/水相变吸收剂具有良好的分相特性（含96%CO2的富相溶液体积仅占总体积44%）、吸收性能（1.71 molCO2·mol-1absorbent）和低富相溶液粘度（2.57 mPa·s）。正丙醇作为再生活化剂时，富相溶液经5次再生循环后其再生效率仍保持90%以上，说明该相变吸收剂具有良好的重复利用性。（2）实验与量子化学理论计算相结合阐明了相分离机制。CO2产物与溶剂分子（水、正丙醇）之间以氢键相互作用为主，分子间氢键长度、和溶剂极性差异会影响CO2产物在溶剂中的分布情况，并促使高密度的CO2产物向下层水溶液中聚集形成CO2富相溶液，而低密度的正丙醇上移为CO2贫相溶液，最终形成液-液相变。（3）借助13C NMR分析体系吸收-解吸CO2过程的产物形态，阐明反应机理。吸收过程中，[DETAH][Tz]中阴、阳离子均可与CO2发生反应生成氨基甲酸酯（RNCOO-），保证吸收剂的吸收性能。[Tz]-质子化后生成的[Tz]-H和正丙醇均可促进了RNCOO-分解，提高了富相溶液再生效率。此外，吸收和解吸互为逆过程。（4）[DETAH][Tz]/正丙醇/水捕集CO2再生能耗评估。[DETAH][Tz]/正丙醇/水的再生能耗（1.99 GJ·ton-1 CO2）比MEA（3.80 GJ·ton-1 CO2）低47.63%，说明该吸收剂具有工业应用潜力。