Study On CO₂ Absorption By Phase-change Absorbents In Wetted Wall Column

The greenhouse effect and global warming caused by excessive emissions of CO₂and other greenhouse gases have become a hot topic of concern,which will bring serious environmental problems such as glaciers melting,sea level rising and desertification.In 2015,nearly 200 countries of the United Nations adopted the Paris Agreement,aiming to control the global average temperature to 2 degrees Celsius.Therefore,it is urgent to capture,recycle and utilize CO₂.Carbon capture and sequestration（CCS）is an effective way to achieve CO₂ reduction and control global warming.Generally,CCS can be divided into three components:pre combustion,post combustion and oxygen-rich combustion.Due to its low cost of retrofitting existing equipment and its wide applicability,post combustion has been applied widely in the dustry.MEA（monoethanolamine）has been widely used in industry due to its advantages of fast absorption rate,strong absorption capacity and stable product,but its further development is limited due to its problems of easy foaming,easy degradation and high energy consumption for regeneration.Therefore,the development of new absorbents with fast reaction speed,high absorption capacity,good stability and low energy consumption for regeneration is a hot topic for researchers.Phase change solvent is a novel chemical absorbent with great development prospect,because phase change will occur in the absorption process,resulting in rich and lean phases.Only the rich phase needs to be sent to the stripper during regeneration,which can greatly reduce the energy consumption of regeneration.The biphasic solvents composed of mixed amines have good phase separation behavior and efficient CO₂ regeneration performance.However,the absorption capacity of CO₂ is generally proportional to the volume ratio of rich phase.How to trade-off the relationship between the two is a critical challenge in reducing the energy consumption of regeneration.In this study,we proposed a novel system,DEEA（N,N-diethylethanolamine）-TETA（triethylenetetramine）-sulfolane system,which can reduce the volume ratio of rich phase and increase CO₂loading to achieve the purpose of regulating the phase separation behavior of DEEA-TETA system without sacrificing high CO₂ absorption capacity.In the DEEA-TETA-sulfolane system,sulfolane acted as a physical activator and phase splitter.The replacement of part of water by sulfolane conduced a siginificantly decreased in the volume of rich phase from 83%to 39%.And the CO₂ loading of rich phase increased from 3.1 mol/L to 4.92 mol/L,an increase of1.59 times.On the other hand,the regeneration energy consumption of DEEA-TETA-sulfolane system is reduced to 1.81 GJ/t CO₂,which is 26.4%lower than that of DEEA-TETA system,and 54.6%lower than 5M MEA.In addition,the total mass transfer coefficient of DEEA-TETA system after adding sulfolane is also increased to 1.8 times of the original system,which proves that sulfolane is a physical activator.Next,we also investigated the influence of different temperature,CO₂ loading and flue gas flow rate on the mass transfer coefficient,and did the nuclear magnetic resonance（NMR）analysis of the components of rich and lean phases and the concentration of substances.Finally,the mechanism of the whole reaction process was analyzed.Our research provides a promising strategy for regulating the phase separation behavior of biphasic solvents and improving the efficiency of CO₂ capture and regeneration,and provides a strong theoretical basis for the development of new phase change solvents in the future.