基于DFT和过渡态理论,在B3LYP/6-31+G(d)水平上研究了PZ-MDEA 混合胺溶液吸收CO2 的反应机理,并进行了分子轨道分析.结果表明,在 PZ-MDEA 混合胺溶液吸收 CO2 的过程中,PZ 直接吸收 CO2 生成两性离子(PZH+COO-)的反应最容易发生,是 CO2 捕集的主要反应路径;两性离子可以与PZ、MDEA 或H2O 发生去质子化反应,其中与MDEA反应的能垒相对最低.通过对比分析发现,两性离子与MDEA反应一方面可以大大降低 MDEA 质子化反应活化能,另一方面中间产物 PZCOO-与 PZH+、H2O 的反应可以实现 PZ 的循环,维持CO2 的高效吸收.此外分子轨道分析发现 PZ-MDEA 混合胺的分子轨道能量差值最低(5.95 eV),同样表明 PZ 对MDEA吸收CO2存在活化作用.
Abstract
Based on DFT and transition state theory,the reaction mechanism of CO2 absorption by PZ-MDEA mixed alcohol amine solution was investigated at the B3LYP/6-31+G(d)level,and molecular orbital analysis was performed.The results showed that in the process of CO2 absorption by PZ-MDEA mixed alcohol amine solution,the reaction of PZ directly absorbing CO2 to generate amphipathic ions(PZH+COO-)was the most likely to occur,which was the main reaction pathway for CO2 capture;the amphipathic ions could undergo deprotonation with PZ,MDEA or H2O,with the energy barrier for the reaction with MDEA being the lowest in relative terms.Through comparative analysis,it was found that the reaction of amphoteric ions with MDEA could greatly reduce the activation energy of MDEA protonation reaction on the one hand,and on the other hand the reaction of the intermediate product PZCOO-with PZH+and H2O could realize the recycling of PZ and maintain the efficient ab-sorption of CO2.In addition,molecular orbital analysis revealed that the lowest molecular orbital energy differ-ence(5.95eV)was found for the PZ-MDEA mixed amine,which also indicated that PZ had an activating effect on the CO2 uptake by MDEA.
关键词
CO2/吸收/反应机理/混合胺/量子化学
Key words
CO2 absorption/reaction mechanism/mixed amines/quantum chemistry
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