The Study On The Concentration Distributions Of The Components In The Amine-CO₂-H₂O System

It is very important to improve the existing basic experimental data of the concentration distributions of the components in the amine-CO2-H2O systems for the application of organic amine solvent in the field of thermodynamic/kinetic study and process simulation and practical industry.Therefore,the study focus on the component distributions in the amine-CO2-H2O system detailedly.In addition,to improve the defects of traditional organic amine solvents,the development of blended amine solvents with excellent performance mixed by the existing organic amines is an important development direction of organic amine solvent in the field of CO2 capture,so the research work in this paper mainly focus on the following two aspects.On the one hand,the systems of three selected novel tertiary amines,(1-(2-Hydroxyethyl)piperidine(1-(2-HE)PP),3-(Diethylamino)-1,2-propanediol(DEA-1,2-PD)and N-(2-Hydroxyethyl)pyrolidine(1-(2-HE)PRLD))solutions with with CO2 loadings,at the amine concentration of 1.0 mol/L,were studied by using three methods(pH method,13C NMR method and pH + 13C NMR method)at 298 K.Based on the studies on the pKa values and protonation ratios of these three novel tertiary amine solutions,the absolute changes in the pH value,the CO2 loadings,the concentration distributions of the components(free amine,protonated amine,HCO3-and CO32-)in the amine-CO2-H2O systems,the fitting equations with better fitting effect between pKa value and temperature(T)of these three novel tertiary amines were obtained,the pKa value decreased with the increase of temperature,and the order of pKa values of these tertiary amines was 1-(2-HE)PRLD>DEA-1,2-PD>1-(2-HE)PP>MDEA,the CO2 absorption rate could be ranked as DEA-1,2-PD>1-(2-HE)PP>1-(2-HE)PRLD,the order of CO2 absorption capacity was 1-(2-HE)PRLD>DEA-1,2-PD>1-(2-HE)PP.In addition,the accuracy and the experimental cost of the three methods were compared,both the orders of them were 13C NMR method>pH+13C NMR method>pH method.On the other hand,the systems of MEA-DEA(MEA:DEA = 2.0:0,1.5:0.5,1.0:1.0 and 0:2.0)solutions with CO2 loadings were studied by using 13C NMR method at 301 K.Based on the studies on the 13C NMR spectra and the concentration distributions of the components(MEACOO-,DEACOO-,MEA,DEA,MEAH+,DEAH+,HCO3,CO32-)in these systems,it could be concluded that the reaction process in the blended MEA-DEA-CO2-H2O system could be divided into three stages,and the different competitive and coordinative relationships between MEA and DEA were reflected at different reaction stages.After blended with DEA,both the CO2 loadings corresponding to the highest concentration of MEACOO-and the primary concentration of HCO3-/CO32-were reduced significantly compared with single aqueous MEA solution,which means the blending of DEA to MEA solution is beneficial to the desorption of CO2 from rich amine solution.In addition,based on the comparison of the blended amines with different proportions,it can be concluded that the CO2 absorption and desorption performance of 1.0M MEA-1.0M DEA solution were the best ones,so the blended MEA-DEA solvent with the appropriate proportion was expected to have good absorption and desorption properties.