Simulational And Experimental Study On Absorption Of Carbon Dioxide By 1-ethyl-3-methyl Imidazole Fluoride

Energy and environment are two historical concerns all around the world.Besides the famous green-house gas,carbon dioxide(CO2)is also one of the main impurity gases in natural gas pipeline transportation.On the other hand,along the past decades,ionic liquids(ILs)have been attracting more and more attention.Room temperature ionic liquids(RTILs)are widely used in the field of chemistry,especially in green chemistry,due to their good physicochemical properties,such as good solubility and negligible vapor pressure.In the present study,quantum chemical method was used to research the structure of single 1-ethyl-3-methyl imidazole fluoride(EMIMF)ion pair,EMIMF-water complex and EMIMFcarbon dioxide complex.Furthermore,EMIMF ionic liquid was synthesized by "silver-salt method" and carbon dioxide absorption experiments were carried out.The results were compared with the simulation results and the effects of partial pressure and water content on absorption efficiency were studied.The main conclusions were as follows:Ion pair configurations of EMIMF ionic liquids were optimized by GAUSSIAN 09 software at DFT-D3/6-31+G**level.After stable configurations were reached,the relative position relationship between anions and cations and the influence of anions on cationic configurations were analyzed.It showed that there were 5 stable conformers for the structure of EMIMF in gas phase.The anions in three of the configurations are located "outside" the imidazole ring plane and exist in the form of imidazocarbene and hydrogen fluoride.The anions in the other two configurations are located in the "inner" of the imidazole ring plane,and they are isomers and covalent bonds with the C3 position on the ring.The EMIMF-water complex system was optimized at the same level mentioned above.After stable configurations were reached,the relative position relationship between EMIMF ion and water molecule and the effect of water molecule on the structure of the complex were analyzed.The optimized results showed that water content was the main factor affecting the structure of the complex.There is a hydrogen bond structure between the ion pairs and the number of hydrogen bonds at the corresponding sites increases with the number of water molecules,but the average strength of hydrogen bonds decreases.The existence of hydrogen bond structure will lead to the weakening of H-F bonds.However,other changes in configuration are not obvious.The existence mode of the complex in liquid phase was characterized by simulation calculation,which indicates that the complex in liquid phase is unique.The EMIMF(anion,cation and ion pair)-carbon dioxide complex system was optimized at the same level.The optimized results showed that the reaction between cation and carbon dioxide was non-spontaneous,while the reaction between anion and carbon dioxide was spontaneous.The analysis of ion pair-carbon dioxide complex showed that the reaction mechanism was non-spontaneous physical reaction process and the reaction process was dominated by anions.Because of the reaction between ion pair and carbon dioxide,the O=C=O bond angle of carbon dioxide is changed obviously.EMIMF ionic liquid was synthesized by "silver salt method".Carbon dioxide absorption experiments were carried out under different absorption partial pressures and with different content of the samples.The results showed that the absorption capacity increases with the increase of absorption partial pressures and the water content of the samples.EMIMF with more water content would absorb more carbon dioxide.The results showed that the absorption reaction between carbon dioxide and EMIMF ionic liquid was a non-spontaneous physical process.