Study On Absorption Performance Of CO₂ In Amino Acid Ionic Liquids-alkanolamine Aqueous Solution

In recent years,a great amount of CO₂ emission from coal-fired boilers and industrial processes has seriously impacted on the environment protection and sustainable development of national economy.Interest increased rapidly in development of CO₂ capture technologies with technical feasibility and affordability.As the most widely applied approach,chemical absorption using alkanolamine as absorbents has the advantages of technological maturity,large absorption capacity and low operation cost.Due to its advantages,chemical absorption has been commercially applied for the removal of CO₂ from refinery gas and natural gas for long years.With its successful demonstration application in Huaneng Beijing power plant,Shanghai Shidongkou No.2 power plant and Chongqing Hechuan Shuanghuai power plant,alkanolamine absorption is promising to occupy a pivotal position in CO₂ capture from thermal power plants.However,high concentrated alkanolamine aqueous solutions take disadvantages like high corrosion to equipments.When applied to CO₂ capture process,its mass fraction must be limited,thus large quantities of superheated steam are needed in the regeneration tower to heat the residual water.To lower the energy cost,it is very necessary to develop new absorbers with higher absorption capacity yet less corrosiveness,e.g.,the blends of amino acid ionic liquids?AAILs?and tertiary alkanolamines may preserve high absorption rate,proper solution viscosity,low corrosion and low energy cost in regeneration,hence it has practical significance to both the improvement of the currently used CO₂ capture technologies and the development of new absorption technologies.In this thesis,new absorbers were developed by blending N-methyldiethanolamine?MDEA?and AAILs including 1-butyl-3-methylimidazolium glycinate?[Bmim][Gly]?,tetramethylammonium glycinate?[N1111][Gly]?and l-butyl-3-methyl-imidazolium lysinate?[Bmim][Lys]?.The time-dependent absorption capacity of CO₂ in AAILs promoted MDEA aqueous solutions was measured under series of temperatures and so lution concentrations,and the saturated absorption capacity and CO₂ loading were determined.The effects of temperature,MDEA concentration and AAILs concentration on the absorption capacity were illustrated.The N2-CO₂ gas mixtures with different CO₂ partial pressures were used to simulate the flue gas.The CO₂ absorption capacity of N2-CO₂ gas mixtures in MDEA-AAILs aqueous solutions was measured,and the effect of CO₂ partial pressure on the absorption capacity was analyzed.To well illustrate the absorption performance of CO₂ in MDEA-AAILs aqueous solution,the viscosities of both CO₂-unloaded and CO₂-loaded MDEA-AAILs aqueous solutions were measured under series of temperatures and solution concentrations,and then correlated by using the Weiland equat ion.The effects of temperature,MDEA concentration,AAILs concentration and CO₂ loading on solution viscosity were demonstrated on the basis of experiments and calculations.The apparent absorption rate of CO₂ in MDEA-AAILs aqueous solution was determined based on the measured time-dependent absorption capacity.The effects of MDEA concentration,AAILs concentration,temperature,CO₂ partial pressure and solution viscosity on absorption capacity and absorption rate were analyzed,and the competition mechanism among solution concentration,CO₂ partial pressure and solution viscosity on the absorption rate was illustrated.A small size tray column was designed to verify the removal efficiency of flue gas CO₂ in AAILs promoted MDEA aqueous solutions.The effects of absorbent concentration,absorbent flow rate,gas flow rate and plate number on the removal efficiency were investigated.The total mass transfer coefficient were determined,and the effects of absorbent concentration,absorbent flow rate,gas flow rate and plate number on the mass transfer coefficient were demonstrated.In summary,new absorbers were developed by blending MDEA and AAILs.Experimental and theoretical studies were carried out for the key issues including mechanism of absorption enhancement,solution viscosity and competition mechanism among solution concentration,CO₂ partial pressure and solution viscosity on the absorption rate.The absorption performance of CO₂ in new absorbers was illustrated,and the CO₂ removal efficiency was verified by using a small size tray column.Compared with traditional amine-based absorbents,the AAILs promoted MDEA aqueous solutions take advantages of high absorption rate,high absorption capacity and low viscosity,thus have good application potential.Our research is of important application value and theoretical significance to energy saving and efficiency improvement in CO₂ capture process.