Synthesis Of Functional Basic Ionic Liquids And Application In CO₂ Absorption

The greenhouse effect has become an increasing problem in the recent years.It is important to curb the emission of the greenhouse gas CO₂ to mitigate the problem.Industrial emissions a large amount of CO₂,at present,Industrial exhausts are usually treated with ethanol amine,however,ethanol is volatile,difficult to recycle and it has corrosive effect on equipment.In turn,ionic liquid is chemically stable with negligible vapor pressure.It is also a benchmark green solvent and has a wide range of applications.CO₂ absorption effects by amino imidazole ionic liquid of different structures had been studied through quantization study.Energy,atomic charge and structural optimization of Bime,Bimpr,Bimb,Bimpe had been analysed with the MM2 method of molecular mechanics and the B₃LYP method of quantum mechanics with 6-31+G and 6-311+G?d,p?as base groups.N atoms on all four ionic liquids were found to be electronegative.Electronegativity of the 11^th N on 1,4-diimidazole propane is the strongest which is-0.331879e;and the 8^th N on 1,5-bismidazole pentane is the weakest which is-0.184167e.The structure of bis?3-aminopropyl-1-imidazole?ethylene bromide,bis?3-aminopropyl-1-imidazole?propylidene bromide,bis?3-aminopropyl-1-imidazole?butylene bromide and bis-?3-aminopropyl-1-imidazole?pentylene bromide had been optimized.There is a stronger interaction between imidazole ring and the bromide ion.With increasing chain length,the N···C bond directly connected to the imidazole ring and the side chain decreased in bond length while bond energy increased.Steric hindrance of C₁₄H₂₆N₆²⁺?C₁₅H₂₈N₆²⁺?C₁₆H₃₀N₆²⁺and C₁₇H₃₂N₆²⁺decreased in turn,while the molecular reactivity increased gradually.Bis?3-aminopropyl-1-imidazole?ethylene bromide and bis?3-aminopropyl-1-imidaz-ole?butylene bromide were synthesized by microwave-assisted methods with a respective yield of 86%and 80%and their existence were confirmed with ¹HNMR,FT-IR and TG.Double imidazole ionic liquids[C₃NH₂-2-C₃NH₂im]Br₂ and[C₃NH₂-4-C₃NH₂im]Br₂were used for repeated trials of CO₂ absorption.Under a total gaseous pressure of 240kPa with CO2/N2=120kPa/120 kPa,best absorption effect was obtained at 308.15K.The optimum absorption concentrations were 54%and 52%.The absorbance selectivity towards CO₂ was 75%and 77%,respectively.With subsequent desorption for 100min at 343.15K,the absorption experiment is repeated again up to 5 times and results were shown to be reproducible.The ionic liquid can thus be said to be a good stable CO2 absorber.