Study On The Performance Of Functional Ionic Liquids For Fixing CO₂

Carbon dioxide is the major contributor to global greenhouse effect, so theabsorption and separation of carbon dioxide are extremely important. Ionic liquids withlow steam pressure, non-volatile, low melting point and adjustable structure, has attractedmore and more attention on the carbon dioxide absorption and separation. Due to thecharacteristics of ionic liquids’ adjustable structure, many kinds of functional groups canbe introduced into the cation and anion, which can form task-specific ionic liquids（TSILs）. Functional groups, which are in favor of absorbing carbon dioxide, can beintroduced to increase the absorption ability for carbon dioxide.Ionic liquids （[NH₂-emim][Ala] and [NH₂-emim][TfO]） are synthesised, and theirstructure is characterized by Infrared Spectra and Hydrogen Nuclear Magnetic Resonance.Physical properties are also measured through experiments, including solubility, density,viscosity, electrical conductivity and so on. The results show that the density does notchange with temperature; the viscosity decreases with increasing temperature; electricalconductivity goes up with the increase of temperature.The solubility of CO₂in ionic liquids （[NH₂-emim][Gly],[NH₂-emim][Ala],[NH₂-emim][TfO] and [NH₂-emim][CF₃COO]） is determined. The results show that thesolubility of CO₂in ionic liquids increases as the pressure goes up; while decreases withthe increasing temperature. And the sequence is as follows:[NH₂-emim][Gly]>[NH₂-emim][Ala]>[NH₂-emim][TfO]>[NH₂-emim][CF₃COO]. Using the K–K equationassociates on the solubility data about the carbon dioxide in ionic liquids, the henry’sconstants and partial volumes of CO₂in infinite dilution can be achieved. So thesolubility of CO₂in ionic liquids can be calculated. Comparing the experimental datawith the calculated data, the average relative error is less than6%in [NH₂-emim][TfO]and [NH₂-emim][CF₃COO] and5%in [NH₂-emim][Gly] and [NH₂-emim][Ala]. It showsthat the K-K equation can correlate the solubilities of CO₂in these ionic liquids well.