Kinetics And Thermodynamics Of CO₂ Capture Into Dibutylamine Organic-aqueous Solution

In recent years,the one of main environmental problems was global warming which caused by the increase of greenhouse gases.Carbon dioxide?CO₂?as the most main greenhouse gases,in order to cope with the pressure of CO₂ emission reduction,its capture and storage technology?CCS?has been widely concerned by researchers.The methods of CO₂ capture are chemical absorption,membrane absorption,physical absorption,etc.The organic amine aqueous solution has been recognised as one of the most widely used technologies for capturing CO₂ in flue gas.However,the water as a solvent of the traditional organic amine solution was used,it consumes a great quantity of energy resources owing to its higher vaporization enthalpy and heat capacity.Besides,the regeneration efficiency was not ideal.Therefor,in order to resolve these problems,the researchers tried to use organic solvents to replace water,forming a kind of non-aqueous solvents.And it found that non-aqueous absorbents not only can improve the regeneration efficiency and reusability of the absorbent,also reducing the energy consumption of regeneration.However,the absorption loading of the non-aqueous absorbents was lower than the aqueous absorbents.Besides that,the non-aqueous absorbents has some disadvantages such as higher viscosity,which led to the mass transfer efficiency decreased,and forming solids easily when it saturated.In order to reduce the energy consumption and improve the reusability of organic amine absorbents for CO₂ capture,a ternary absorbent composed of organic amine/organic solvent/water was emerged.In this work,the dibutylamine?DBA?was chosen as the CO₂ solvent,the water and ethanol were chosen as the solution.Adjusting the ratio of water/ethanol in DBA solution for CO₂ capture,and the absorption-desorption performance of DBA/water/ethanol ternary absorbent was investigated.Besides,the absorption and desorption mechanisms of DBA/water/ethanol ternary absorbent were analyzed by¹³C NMR.Finally the kinetics and thermodynamics of CO₂ capture were investigated by a closed reactor.The main results of this work are as follows:?1?In the DBA/water/ethanol ternary absorbent for CO₂ capture showed that:when the water/ethanol ratio was 5:5,the absorption loading of DBA/water/ethanol ternary absorbent reached to the maximum value?0.82 mol CO₂·mol^-11 amine?,which was higher than DBA/water(0.66 mol CO₂·mol^-1amine)and DBA/ethanol?0.53 mol CO₂·mol^-11 amine?for absorption loading of CO₂ capture.Its optimum absorption temperature was 313.15 K.The regeneration efficiency could still maintain at about95.5%after five regeneration cycles,which showed that good recycling performance after regeneration ability of DBA/water/ethanol ternary absorbent.?2?The absorption-desorption mechanism of CO₂ capture in DBA/water/ethanol ternary absorbent was investigated:the DBA/water/ethanol ternary absorbent was compared to the DBA/ethanol and DBA/water solutions in the process of CO₂ capture.The results indicated that DBA first reacted with CO₂ to form carbamate?C₂H₅OCO₂^-?,and then it further reacted with water and ethanol to form HCO₃^-and C₂H₅OCO₂^-,respectively.The final products of the reaction were HCO₃^-and C₂H₅OCO₂^-.In addition,the desorption of the saturated DBA/water/ethanol ternary absorbent was the reverse reaction of the CO₂ absorption.The HCO₃^-and C₂H₅OCO₂^-released CO₂ and decomposed to C₂H₅OCO₂^-at 373.15 K for 30 min under atmosphere pressure.The ternary absorbent returns to the initial state,and the absorbent is regenerated and reused.?3?The kinetics and thermodynamics of DBA/water/ethanol ternary absorbent for CO₂ capture indicated that the main reaction was DBA and CO₂,and the mass transfer reaction of absorbing CO₂ was identified as a fast pesudo first order reaction.According to Arrhenius equation,the relationship between k₂ and temperature?T?was calculated to bek₂=5.5305?10 ⁵exp?7?-1568.8 T?8?.The chemical reaction activation energy?Ea?of CO₂ capture into DBA/water/ethanol ternary absorbent was 13.04 kJ mol^-1.According to thermodynamic studies,the regeneration energy consumption of CO₂ capture was 2.75 GJ/ton CO₂,which was lower than the regeneration energy of CO₂ absorbing into 30%MEA solution?3.22 GJ/ton CO₂?.