Quantum Chemical Calculation Of CO₂ Absorption By Amino-functionalized Imidazole Ionic Liquids

Global warming and other problems caused by a large amount of CO2 emissions have seriously affected the human economy and environment,and have attracted widespread attention from governments of various countries.This requires the development of efficient,energy-saving,environmentally friendly and economical new methods of carbon capture.The advantages of ionic liquids such as low vapor pressure,wide liquid range,good stability,and simple design provide opportunities for the development of new CO2 absorption methods.In this paper,a COSMO therm screening method based on quantum chemical calculation is used to predict the Henry constant of CO2 in ionic liquids,and then obtains the solubility of CO2 in different ionic liquids.The screening results show that CO2 has good solubility in imidazole ionic liquids.Because amino functionalized ionic liquids have a much better CO2 absorption effect than traditional ionic liquids;therefore,With 1-aminopropyl-3-methylimidazole cation([C3NH2MIm]+)and 1-aminoethyl-3-methylimidazole cation([C2NH2MIm]+)these two cations and tetrafluoroborate[BF4]-anion,hexafluorophosphate[PF6]-anion,bromide[Br]-chloride[Cl]-,and lysine anion[Lys]-the combination of these five anions yields 10 amino-functionalized imidazole ions Liquid,used to study the absorption effect of various ionic liquids on CO2.In studying the effect of cations in ionic liquids on the absorption of CO2,it was found that the absorption effect of 1-aminopropyl-3-methylimidazole ionic liquid on CO2 is higher than that of 1-aminoethyl-3-methylimidazole ionic liquid on CO2 The absorption effect is good,so five amino functionalized imidazole ionic liquids with a cation of 1-aminopropyl-3-methylimidazole,called 1-aminopropyl-3-methylimidazole tetrafluoroborate[C3NH2MIm][BF4]ionic liquid,1-aminopropyl-3-methylimidazole hexafluorophosphate[C3NH2MIm][PF6]ionicliquid,1-aminopropyl-3-methylimidazole bromide[C3NH2MIm][Br]Ionic liquid,1-aminopropyl-3-methylimidazole chloride salt[C3NH2MIm][Cl]ionic liquid and 1-aminopropyl-3-methylimidazole lysine[C3NH2MIm][Lys]CO2 absorbent,Using quantum chemistry theory and Gaussian software under the density functional theory(DFT)calculation method,a 6-311++G(d,p)dispersion basis set was used to perform quantum chemical calculation analysis on the structure and properties of each ionic liquid.Then,the selected several ionic liquids with better absorption of CO2 and the molecular system of CO2 were quantified,and their microstructure and interaction with CO2 molecules were studied.The conclusions are as follows:1.Different anions and cations in ionic liquids also have different effects on the binding energy of molecules.When the anions are the same,the binding energy of[C3NH2MIm]+is greater than that of[C2NH2MIm]+.Ionic liquids are larger than halide salts.Ionic liquids are larger than fluoride salts,in the order of Ebinding([C3NH2MIm][Lys])>Ebindin([C3NH2MIm][Br])>Ebinding([C3NH2MIm][Cl])>Ebinding([C3NH2MIm][PF6])>Ebinding([C3NH2MIm][BF4]),the greater the binding energy,the greater the anion and cation interaction forces in the ionic liquid.2.According to molecular orbital analysis,the HOMO orbits of several amino-functionalized imidazole ionic liquids are mainly occupied by anions,and the CO2 gas molecular orbitals do not substantially overlap with the cation orbitals.This shows that CO2 molecules are more easily absorbed by anions,and Easy to interact with anions.3.The greater the energy difference between HOMO and LUMO,the more energy the electron needs to absorb from the HOMO to LUMO transition,corresponding to the higher its redox stability,the worse the reactivity.The lysine salt ionic liquid is considered to be more likely to react with CO2 than the other four ionic liquids.The order from strong to weak is:[C3NH2MIm][Lys]>[C3NH2MIm][Br]>[C3NH2MIm][Cl]>[C3NH2MIm][PF6]>[C3NH2MIm][BF4].4.The stable configuration of several ionic liquids for absorbing CO2 is obtained by calculation,and the CO2 bond angle in the stable configuration has only a small change./O50-C49-O51 in[C3NH2MIm][Lys]·CO2 is from 180.00 Becomes 179.0480°,[C3NH2MIm][Br]·CO2 changes from 180.00 to 179.0112°,and[C3NH2MIm][PF6]·CO2 changes from 180.0°to 179.0476°,This indicates that several ionic liquids have an adsorption effect on CO2.