Performance And Kinetics Of Carbon Dioxide Capture Into LysK/K₂CO₃ Solution

Global climate change caused by greenhouse gases is one of the most important environmental problems today.As the most important greenhouse gas,carbon dioxide?CO₂?is getting more and more attention,as well as its control and emission reduction.Carbon capture and storage?CCS?is one of promising methods to reduce CO₂ emissions from fossil fuel-fire.Potassium carbonate solution?K₂CO₃?has many advantages such as low absorption heat,no toxicity and high CO₂ loading capacity,which has great potential in the field of carbon capture.However,the slow rate of CO₂ absorption into K₂CO₃ solution limits its application.Therefore,using high-efficiency and environmental activator to enhance the CO₂ capture capacity of K₂CO₃ solution become an important means of this method.In this work,potassium lysine solution?LysK?was chosen as the activator to strengthen the ability of CO₂ capture in K₂CO₃ solution.The absorption and regeneration performance of CO₂ capture in LysK/K₂CO₃ solution were investigated,and the mechanism of absorption-regeneration of CO₂ capture in the mixed solution was explored.Besides,the mass transfer kinetics of CO₂ absorption in the mixed solution was investigated by using the double stirred-cell apparatus.The results are as follows:The results of absorption-regeneration performance of CO₂ capture in LysK/K₂CO₃ solution showed that the absorption rate and CO₂ loading of LysK/K₂CO₃ increased as the concentration of LysK solution increased from 0 to 1mol L-1?M?.The optimum molar ratio of LysK/K₂CO₃ solution was 5:5?the total concentration of absorbent was 1 M?,and the CO₂ loading of the mixed solution was1.24 mol CO₂/mol absorbent,which was 1.68 times larger than that of K₂CO₃ solution.The optimum regeneration temperature and regeneration time of CO₂ saturated Lys K/K₂CO₃ solution were 120 oC and 2 h,respectively.The LysK/K₂CO₃ solvent kept 83.76% of its initial capacity after firstly regeneration,which was slightly lower than that of CO₂ saturated K₂CO₃ solution?92.06%?.In addition,the regeneration efficiency of the mixed solution still kept at 79.19% after fourregeneration cycles,which demonstrated that the mixed solution had a good recycling performance after regenerated.The absorption-regeneration mechanism of CO₂ capture in LysK/K₂CO₃ solution was also investigated,and the results indicated that LysK and K₂CO₃ reacted with CO₂ at the same time in the process of CO₂ absorption.At the beginning of the reaction,as the main component of the mixed solution,K₂CO₃ reacted with CO₂ to form HCO3-.Meanwhile,as an activator,LysK reacted with CO₂ to form carbamate,which was proved according to the zwitterion mechanism.As the reaction carried out,the concentration of LysK and K₂CO₃ solution decreased,while the hydration reaction of CO₂ enhanced and the carbamate was hydrolyzed to produce lysine and HCO3-.In addition,the desorption of the CO₂ saturated mixed solution was the reverse reaction of CO₂ absorption.A part of the HCO3-was decomposed to form CO32-,then the CO32-decomposed and released CO₂ at high temperature,which promoting the lysine to decompose into lysine ion.Another part of the HCO3-reacted with lysine ion to produce carbamate,and then carbamate decomposed and released CO₂ during the regeneration.The mass transfer kinetics of the mixed solution showed that the chemical reaction of LysK/K₂CO₃ solution absorbing CO₂ was a fast pseudo first order reaction.Based on the two-film theory,the mass transfer reaction kinetics model of CO₂ absorption into LysK/K₂CO₃ solution was established,and the important kinetic parameters such as reaction rate constant?k2?and enhancement factor?E?were obtained.The results indicated that the reaction rate constant and the enhancement factor of CO₂ absorption into Lys K/K₂CO₃ solution increased as the concentration of LysK solution increased.The relationship between k2,mix and T was found to be k2=6.3508×1012 exp?-6427.9/T?,and the chemical reaction activation energy of CO₂ absorption into the mixed solution was 53.44 kJ mol-1,which was lower than that of CO₂ absorption into K₂CO₃ solution?63.27 kJ mol-1?.The results further proved that LysK solution had a significant effect on the absorption process of CO₂ into K₂CO₃ solution.