1-乙胺基-3-甲基咪唑四氟硼酸盐吸收CO_2的理论研究

采用密度泛函理论(DFT)对离子液体1-乙胺基-3-甲基咪唑四氟硼酸盐(NH2e-mim]BF4])吸收CO_2的反应机理进行了研究.在B3LYP/6-311++G(d,p)计算水平下,对离子液体NH2e-mim]BF4]的结构及与CO_2反应的中间体、过渡态和产物进行了全优化,获得了优化结构的构型参数、振动频率和热力学数据.利用自然键轨道(NBO)分析了离子液体NH2e-mim]BF4]和CO_2的自然电荷布居.计算结果表明,通过阳离子NH2e-mim]+自偶解离产生的阳离子NH3e-mim]2+能与阴离子BF4]-结合形成更强的离子键.根据反应吉布斯自由能变(ΔG0—)和焓变(ΔH0—)的计算结果,判断离子液体NH2e-mim]BF4]吸收CO_2按理论摩尔比2∶1分步进行反应,吸收过程中质子的转移需克服52.51 k J/mol的能垒.

Density Functional Theory Studies on the CO2 Absorption by 1-Ethylamine-3-methylimidazolium Tetrafluoroborate

CO2 absorption mechanism by ionic liquids 1-ethylamine-3-methylimidazolium tetrafluoroborate, which was formulated as NH2 e-mim ] BF4 ] , was described via density functional theory ( DFT ) . The structure of ionic liquids NH2 e-mim ] BF4 ] , their reaction intermediates, transition states and products, were optimized using the B3LYP/6-311++G(d, p) basis method, with the optimized configuration parame-ters, vibration frequencies and thermodynamics data obtained. Furthermore, the natural bond orbital atomic charge assignments were also calculated via the natural bond orbital( NBO) method. The computational results demonstrated that the divalent cation NH3 e-mim ] 2+, which was produced by the autoprotolysis of cation NH2 e-mim]+, could be easily combined with anion BF4 ]-, with stronger ionic bond formed. According to the calculation results of standard Gibbs free energy(△G 0—) and enthalpy(△H 0—) , it could be inferred that the absorption of CO2 onto ionic liquids NH2 e-mim] BF4 ] was step by step, in accordance with the theoreti-cal molar ratio of 2︰1. During the absorption process, the energy barrier of 52. 51 kJ/mol should be overcome for proton transfer reaction.