Kinetics,Thermodynamics And Mechanism Of TETA-DMCA For Carbon Dioxide Absorption From Flue Gas

Since the Industrial Revolution,the concentration of CO₂ in atmosphere content is gradually increasing,leading to the exacerbation of greenhouse effect.The anthropogenic CO₂ is mainly the untreated tail gas which exhausted from coal-fired power plants.Benchmark ethanolamine technology is the most mature technology in post-combustion carbon capture,but costs a lot.In recent years,biphasic solvents have attracted wide attention as a potential solvent for CO₂ capture.Upon CO₂ absorption or temperature swing,the CO₂-laden solvent undergoes liquid-liquid or liquid-solid phase transition,and more than 90%of the absorbed CO₂ is concentrated in one phase.After their separation,only the CO₂-rich phase need to be regenerated.As a result,the heat duty,stripper size,and CO₂compression work can be reduced.In this paper,primary,secondary and tertiary amines with different physical properties were selected to prepare aqueous biphasic solvents for CO₂ absorption.Combined with ¹³C NMR and quantum chemical analysis,the following results were obtained:1)The relationship between properties of amines?alkalinity,pKa and hydrophobicity,Log P?and performance of solution,such as absorption capacity,phase separation behavior,mass transfer kinetics and thermodynamics,has been studied.The experimental results show that the alkalinity of tertiary amines is the main factor to determine the absorption capacity of biphasic solvents.Moreover,the hydrophobicity of primary,secondary and tertiary amines affects the phase separation behavior of solvents together.Kinetic analysis exhibits that the total mass transfer resistance decreases with the increase of Log P value of tertiary amines.Thermodynamic analysis shows that the sensible and latent heat decreases and increases due to the increase of Log P value of tertiary amines,respectively.2)According to the above rules of amine properties,a novel biphasic solvent with high efficiency and low heat duty,TETA-DMCA,was developed via screening dozens of different solvents.The optimum component ratio was determined to be 1M:3M.The experimental results show that the absorption capacity of TETA-DMCA is 1.6 times than that of ethanolamine.Kinetic analysis shows that the liquid phase mass transfer resistance in TETA-DMCA solution is dominant except under low temperature?40 ^oC?.Thermodynamic analysis shows that the regeneration heat of TETA-DMCA decreases with the increase of lean solution loading,and the lowest value is only 40%of MEA's regeneration heat.In addition,the reaction mechanism between TETA-DMCA and CO₂is revealed by ¹³C NMR analysis.3)The changes of phase separation behavior and absorption rate in the process of CO₂ absorption into biphasic solvents were studied.Combined with ¹³C NMR and quantum calculation,the two-stage interaction mechanism of biphasic solvents was clarified.At the first stage?the concentration of active amine groups into the solution is high?,proton transfers from zwitterion to tertiary amines via primary/secondary amines.The pathway has lower activation free energy and faster apparent absorption rate,indicating that the reaction is mainly controlled by reaction kinetics;at the second stage?low concentration of active amine groups?,the absorption reaction is controlled by thermodynamics.Due to that the reaction pathway in the first stage was inhibited,combining with the heat released from the absorption reaction,the reaction proceed along the more stable pathway for products?proton transfers from zwitterion to tertiary amines directly?.