CO₂ Absorption Into The Mixed Aqueous Solution Of MDEA And[C₂OHmim][Lys]

Global warming brings severe challenges to human living environment.Among them,it is urgent to control and reduce the emission of greenhouse gas CO2.As a commonly used organic amine absorbent,MDEA has many excellent properties such as good absorption and desorption performance.But the absorption rate of MDEA is low.Therefore,the main idea of industrial application is to develop new absorbents with fast absorption rate as additives to combine with MDEA to strengthen the weakness of MDEA.In this paper,a functional ionic liquid absorbent[C2OHmim][Lys]with high absorption rate which synthesized by our team has been mixed with MDEA to absorb carbon dioxide.The carbon dioxide absorption properties,absorption mechanism and kinetics of MDEA/[C2OHmim][Lys]/H2O mixed system have been also investigated.It is hoped that the advantages of both MDEA and ionic liquids can be combined in the mixed system as well as to increase the absorption rate,absorption capacity and oxidation resistance,so that MDEA can be more suitable for industrial application.In this paper,the following research results are obtained:The absorption rate and absorption capacity of MDEA/[C2OHmim][Lys]mixed aqueous solution at different molar ratios were investigated.It has been found that the higher the molar ratio of[C2OHmim][Lys]in the mixture of MDEA and[C2OHmim][Lys]is,the higher the absorption rate and capacity have.When the molar ratio is 8:2,the initial absorption rate of carbon dioxide in the mixed system is 5.18 times of MDEA,and the average absorption rate is 2.07 times of MDEA.The first regeneration efficiency of 8:2 MDEA/[C2OHmim][Lys]was 97.21%.And the regeneration efficiency was higher than 88.10%after five regeneration cycles which are all higher than the efficiency of MDEA aqueous solution and[C2OHmim][Lys]aqueous solution under the concentration of 1mol/L.Besides,it was found that the antioxidant properties of the mixed system were better than that of MDEA aqueous solution and[C2OHmim][Lys]aqueous solution under different oxygen concentrationsThe absorption mechanism of MDEA/[C2OHmim][Lys]mixed aqueous solution at 8:2 molar ratio was studied by means of NMR and IR spectra.It was found that when the absorption loading was less than 0.29 mol CO2/mol absorbent,two amino groups on[C2OHmim][Lys]will both react with CO2.When the absorption load is greater than 0.29 mol CO2/mol absorbent,MDEA reacts with CO2 and carbaminate which near the carboxylate radical is hydrolyzed.The kinetics of CO2 absorption into the MDEA/[C2OHmim][Lys]mixed aqueous solution was studied in double stirred-cell absorber。It has been found that when the absorption temperature was higher than 40℃ or the absorption load of CO2 was less than 0.45 mol CO2/mol absorbent,the reaction was rapid fast pseudo-1 order reaction reaction.Under other conditions,the reaction is a medium quasi-1 order reaction.When the CO2 absorption load is less than 0.29 mol CO2/mol absorbent,the total mass transfer coefficient kov changes rapidly with the CO2 absorption load.When the absorption load of CO2 is greater than 0.29 mol CO2/mol absorbent,the kov tends to be smooth,which confirms the reaction mechanism.The rate constants of the mixed aqueous solution arefitted as with temperature by the Arrhenius equation as k=4.35×109exp(-4735.4/T).