功能型离子液体协同吸收NH3和CO_(2)的密度泛函理论研究

Density functional theory investigation on the NH3 and CO_(2) absorption by functional ionic liquids

离子液体(ILs)由于其独特的结构可调性,作为添加剂可有效抑制氨法碳捕集中NH_(3)的逃逸并同时促进CO_(2)的吸收。揭示其吸收NH_(3)和CO_(2)的作用机理对于构建特定的功能型ILs结构具有重要意义。本文采用密度泛函理论(DFT),在B3LYP/6-31'++G(d,p)基组水平下对设计的五种功能型ILs进行了结构优化、频率计算以及原子电荷分析,获得了优化后的结构参数、振动频率以及原子电荷等数据。在此基础上对ILs吸收CO_(2)和NH_(3)进行了相互作用分析。计算结果表明:[HEBim][His]的稳定性最好,经过BSSE校正后的相互作用能为-415.73 kJ·mol^(-1)。通过静电势和电荷分析找到了设计的ILs与气体作用的最佳位点:NH_(3)主要与ILs阳离子的羟基形成O—H…N型氢键,其中,[HEBim][His]吸收NH_(3)的能力最强,形成的氢键结合能为38.52 kJ·mol^(-1),具有较强的氢键作用;CO_(2)主要与阴离子中的氨基形成C—N…C型氢键,[HEBim][Ala]吸收CO_(2)的能力最强,形成的氢键结合能为10.15 kJ·mol^(-1),具有较弱的氢键作用。当ILs同时与NH_(3)和CO_(2)相互作用时,其吸收能力均有不同程度的下降,[HEBim][His]与[HEBim][Ala]的综合吸收效果最佳。

Due to their unique structural tunability,ionic liquids(ILs)can be used as additives to effectively suppress NH_(3) escape and simultaneously promote CO_(2) uptake in ammonia-based carbon capture.Revealing the absorption mechanism of CO_(2) and NH_(3) by ILs plays an important role in reconstructing new functional ILs.In this paper,an analysis of five bifunctional ionic liquids based on structure optimization,frequency calculation and atomic charge has been carried out by using density functional theory(DFT)at B3LYP/6-31'++G(d,p)level,and the data of the optimized structures have been achieved.Then,the interaction among ILs,CO_(2) and NH_(3) has been analyzed.The calculated results demonstrated that[HEBim][His]shows the best stability,of which its interaction energy reaches-415.73 kJ·mol^(-1) after basis function overlap error correction.The best sites for interaction with NH_(3) and CO_(2) were found by analyzing the electrostatic potential and charge of the designed ILs:NH_(3) mainly forms O-H…N hydrogen bond with the hydroxyl groups of ILs cation,and[HEBim][His]has the strongest ability to absorb NH_(3),with a hydrogen bonding energy of 38.52 kJ·mol^(-1),which has a strong hydrogen bonding effect;CO_(2) mainly forms C-N…C hydrogen bonds with the amino group in the anion,and[HEBim][Ala]has the strongest ability of CO_(2) absorption,the formed hydrogen bonding energy of 10.15 kJ·mol^(-1),which is a relatively weak hydrogen bonding.When ILs interact with NH_(3) and CO_(2) at the same time,their absorption capacity decreased to different degrees,and the comprehensive absorption effect of[HEBim][His]and[HEBim][Ala]was the best.