Ditetraalkylammonium Amino Acid Ionic Liquids as CO_2 Absorbents of High Capacity

摘要

By grafting butyl or ethyl onto tetramethvlethvlenediamine, quaternary ammonium salts with two positive charge centers were formed at the first step. Metathesis with Ag_2O followed. Through neutralization with gtydne, L-alanine, or valine, a series of new ditetraalkylammonium amino acid ionic liquids (DILs) for CO_2 capture were generated. The structures of DILs, as shown in Figure 1, were verified by using H NMR and EA. These DILs were found to be of quite high viscosity which militated against their industrial application in CO_2 removal. Drawing on the experience of mixed amines' aqueous solutions, these DILt were blended with water or N-methyldiethanol- amine (MDEA) aqueous solutions to act as special absorbents of CO_2. Using a Double-Tank Absorption System, the absorption performance of these DIL solutions was investigated in detail The experimental results indicated that among the three aqueous solutions of DILs (20%, 40%, and 80 wt %), the solution of 40% DIL had a higher absorption rate of CO_2 than die other two, demonstrating the different effects of concentration and viscosity on the absorption. The solution of 40% DIL or the 15% DEL +15% MDEA had much higher capacity for CO_2 than the corresponding monocaaontetraalkvlanunoniumAAlLs, due to the special structure of the dkation which could influence the solubility of CO_2 in the aqueous solution.