Experimental Study On CO₂ Capture From Flue Gas By Two Phase Change Absorption Systems Based On Triethylene Tetramine

Early 19th century to the present,with the rapid development of social industry,the problem of global climate warming has become more and more serious.The key to the solution is to control anthropogenic CO₂ emission,especially to reduce the CO₂ emission from the flue gas of coal-fired power plants.CO₂ capture,storage and utilization technology（CCUS）can reduce CO₂ emission,the development of traditional chemical absorption method is limited due to its high energy consumption and poor absorption performance.Phase change absorbent has become a research hotspot in recent years because of its good energy saving potential.Phase change absorbent can undergo phase separation after absorbing CO₂,and more than 95%of CO₂ will be enriched in the lower liquid phase.Therefore,phase separation can reduce the amount of rich liquid during regeneration,so as to achieve the purpose of reducing energy consumption and equipment cost.This paper aims to study the efficient and low energy consumption phase change absorption system for CO₂ capture.Two phase change systems,TETA-DEEA and TETA-DMCA,which are composed of multistage amines and tertiary amines,are used for experimental research.Determine the best solute ratio and absorption temperature,observe its phase performance,determine the best desorption temperature,explore the reaction mechanism through characterization analysis,and finally estimate its energy consumption.There are main research work and the results in the follow:（1）In TETA-DEEA system,the effects of concentration,molar ratio and temperature on the absorption performance were investigated respectively,and the effect of desorption temperature on the desorption of the system was explored.The experimental results show that1 mol·L^-1 TETA+4 mol·L^-1 DEEA（1T4D）aqueous solution will be separated into two liquid phases after absorbing a certain amount of CO₂,and about 96.15%of CO₂ will be enriched in the lower phase.The corresponding CO₂ adsorption capacity is 4.75 mol·kg^-1,showing a high CO₂ absorption capacity.The absorbent showed the best absorption effect at 30℃and desorption effect at 90℃.Through the analysis of characterization results,the CO₂ absorption product in the lower liquid phase is carbamate,HCO₃^-/CO₃^2-and protonated amine,while the upper liquid phase was mainly DEEA.After AMP was introduced into the system,the CO₂absorption could be improved effectively,and the absorption of 1.5T0.5A3D reached 4.67mol·L^-1,and the phase separation showed a better effect.The circulation capacity of0.5D1.5A3D reaches 4.67 mol·L^-1,1.67 times of that of 1T4D(2.8 mol·L^-1).During the absorption process,TETA reacts with CO₂ to generate amphoteric ion intermediates,which are deprotonated by DEEA to form carbamate.The introduction of AMP in the system will make the generated carbamate unstable and form HCO₃^-,which will reduce the number of hydrogen bonds and thus reduce the viscosity,the phase separation efficiency is improved.（2）In TETA-DMCA system,the effects of concentration,mole ratio and temperature on the absorption properties were investigated,and the effect of desorption temperature on the desorption of the system was investigated.The results show that 1 mol·L^-1 TETA+3mol·L^-1DMCA is more favorable for CO₂ absorption,the volume of CO₂-rich liquid（the liquid phase）is only 59%of the total solution volume.In a certain range,the absorption and desorption performance of TETA-DMCA system increased with the increase of temperature.The absorbent has the best CO₂ absorption effect at 30℃and desorption effect at 90℃.Through the analysis of characterization results,it was found that the TETA-DMCA phase transformation system was mainly enriched in the lower phase after absorbing CO₂,and the absorption products were mainly carbamate,HCO₃^-/CO₃^2-and protonated amines,while the upper phase was mainly DMCA.The introduction of PZ into the system improved the CO₂absorption rate,and the absorption amount of 1T1P2D reached 3.70 mol·L^-1,which was 1.41times that of the optimization without PZ.Moreover,the desorption rate and cyclic load of the system were improved to some extent,and the cyclic capacity of 0.5T1.5P2D reached 2.36mol·L^-1.TETA molecules are constantly consumed during the absorption process,and DMCA as a proton acceptor regenerates TETA to maintain the continuity of the CO₂ absorption reaction process,so that DMCA is constantly transferred from the upper to the lower solution,and the lower solution volume also increases.（3）By estimating the renewable energy consumption,the total energy consumption of TETA-DEEA absorber and TETA-DMCA absorber is 2.45 GJ/t CO₂ and 2.49 GJ/t CO₂,respectively.The energy consumption of the two absorbents is significantly better than that of the traditional MEA absorbent,which is about 35%lower than that of MEA solution.