Experimental Investigation Of CO₂ Absorption Thermodynamic Performance In Conventional Imidazole-based Ionic Liquids

Due to the large amount of greenhouse gas emissions,global warming is a serious threat to human survival and development.CO₂ is the main greenhouse gas.Capturing and fixing CO₂ is an important measure to limit global warming.Ionic liquids?ILs?have elicited considerable attention in the field of gas absorption and separation due to their unique properties.In order to increase the recycle rate of ionic liquids and reduce operating costs,in this paper,we studied the thermodynamic performance of CO₂ absorption by ionic liquids and found an effective method to reduce the regeneration energy consumption.Regeneration energy consumption mainly includes desorption heat,sensible heat and the heat taken away by the gas.This paper focused on the two aspects of desorption heat and sensible heat,and discussed the way to reduce the regeneration energy consumption.Desorption heat is closely related to the CO₂ absorption enthalpy of ionic liquids.First of all,because anions play an important role in ionic liquids capturing CO₂,the quantum chemistry calculation was used to screen out suitable anions.Secondly,based on simulation results,the absorption enthalpy of CO₂ in several kinds of ILs was measured directly.The effects of anions,cationic alkyl chain length,and temperature on absorption properties were discussed.Finally,a variety of ionic liquids and amines were selected,and certain proportioning amine-ionic liquid solution were prepared.The amine-ionic liquid solution which would stratify after capturing CO₂ were screened out.The composition of the upper and lower solutions were measured by nuclear magnetic resonance and the regeneration energy consumption was calculated.The CO₂ absorption enthalpy of the selected anion[AC]^-was-47.569kJ/mol,which was an ideal absorption enthalpy between conventional ionic liquids and amine solutions.1-butyl-3-methylimidazolium acetate presented an ideal CO₂ absorption enthalpy compared with the other investigated ILs with different chain lengths.Because the viscosity of the ionic liquid increased as the length of the cationic alkyl chain increased and the CO₂ absorption enthalpy decreased.Absorption enthalpy was dependent on temperature,and the isosteric absorption enthalpy decreased with an increase in temperature.The effect of temperature on the CO₂ absorption enthalpy was less than that of the anion and cationic alkyl chain length.The desorption heat in the regeneration energy consumption could be effectively reduced by screening out the ionic liquids with idea CO₂ absorption enthalpy.After introducing CO₂ in a certain proportioncompound solven,delamination occured,and the lower solution was put into the absorption tower again as the poor liquid,the upper solution was desorpted by the stripper.Due to the reduction of the quality of the rich liquid,the sensible heat was significant reduced and the regeneration energy consumption reduced by 47%.