Study On The Process Basis And Reaction Kinetics Of Alkanolamine Solution Decarbonization

CO₂ is a representative greenhouse gas,and chemical absorption is an important means to reduce carbon emissions.The alkanolamine solution can react with CO₂ for its alkalescence and its product will decompose when heated.Therefore,it is widely used in CO₂ capture.Its absorption capacity increases with the increase of alkalescence,however,the concentration and stability of the product are unfavourable for regeneration.It means a single alkanolamine solvent cannot meet the demands of high absorption rate and low regeneration energy consumption simultaneously.Considering that the tertiary amine can generate unstableHCO₃^-which can reduce the regeneration energy consumption,and the activators such as PZ（piperazine）,which has less steric hindrance and is easily to react with CO₂,that is to accelerate the reaction,the mixing solutions can greatly improve the absorption for CO₂ and the regeneration of solutions.Thus,the basic properties,p Ka and viscosity,as well as the characteristics of reaction kinetics of the mixture system,including tertiary amines,primary-or secondary amines,activator,namely AEEA（2-aminoethyl）-ethanolamine),MDEA（N-methyldiethanol-amine）and small quantities of PZ)were studied.Firstly,the COSMO-RS molecular simulation method,based on density functional theory,was used to predict the p Ka values of alkanolamine solvents by classification.The results indicate that the absolute deviations of secondary and tertiary amines are relatively large.It can be explained that the number of active hydrogen atoms on the electron donating,amino groups on secondary and tertiary amines,is less than primary amines and the affinity to protons is relatively weak.In the quantum chemical calculation,the parameters are revised by considering the hydrogen bond interaction.Accordingly,the accuracy is obviously improved,which can provide scientific basis for the rapid screening of alkanolamine solvents in industry.Secondly,the viscosity association was established by the Grunberg-Nissan equation for AEEA/H₂O and MDEA/H₂O binary system alkanolamine solutions with different mass fraction at various temperatures.It shows that the equation can accurately descript the relationship between the viscosity of alkanolamine solution and concentration and temperature.After that,the viscosity of ternary mixed alkanolamine solution system was studied,where the Grunberg-Nissan equation is simplified by combining the characteristic parameters of the system,and compared with the calculated value of logarithmic function.The results show that the accuracy of the simplified Grunberg-Nissan equation is reliable and it can be used for the thermodynamic analysis and computer simulation of CO₂ capture process with ternary mixed alkanolamine solutions.Finally,Gaussian 09 software was used to calculate the reaction path and activation energy of the main degradation products of AEEA generation,HEIA,1-（2-hydroxyethyl）-2-imidazolidinone,and that of AEEA/MDEA/PZ ternary mixing alkanolamine solutions in order to analyze the effect of PZ activator and AEEA degradation on the reaction kinetics.The results show that CO₂ will preferentially react with PZ and then transfer to AEEA or MDEA,where PZ can significantly reduce the activation energy of AEEA and CO₂ reactions.The reaction kinetics model of CO₂capture by AEEA/MDEA/PZ ternary mixed alkanolamine solution was established according to the calculation results.Based on the model,the alkanolamine decarbonization process of the enterprise was simulated and calibrated by Aspen Plus software.The calibration results are close to the enterprise process parameters,which validated the accuracy of the kinetic model.