CO₂ Capture Performance And Reaction Mechanism Of Ionic Liquid Non-aqueous Phase Change Absorption Systems

To achieve carbon peaking and carbon neutrality goals under the new development philosophy,CO2 capture technology based on chemical absorption is an important means of achieving CO2 emission reduction.In consideration of the problems of low absorption loading,poor stability and high heat duty of existing CO2 absorbent,the ionic liquid with high absorption loading,good stability and low reaction heat was selected as the main absorbent,and the organic reagents with low specific heat capacity,high boiling point and low volatility were selected as the solvent and phase change promoter to construct a CO2 phase change system with lower heat duty.This study developed a new type of functional ionic liquid non-aqueous phase change system with high efficiency and low heat duty.Its CO2 capture performance,heat duty,reaction mechanism and kinetics were deeply investigated.First,a novel functionalized ionic liquid tetraethylenepentamine caprolactam salt([TEPAH][CPL])was designed and synthesized.Then,the non-aqueous phase change CO2 absorbent[TEPAH][CPL]/[EG]/[DGDE]was constructed by screening and testing the types of solvents and phase change promoter as well as the solvent ratio.When the volume ratio of ethylene glycol(EG)and diethylene glycol dimethyl ether(DGDE)was 1:1,the CO2 capture performance of the system reached the optimal.The CO2 loading reached 1.88 mol·mol-1,while the rich phase volume was only 40%of the total volume.but the CO2 loading ratio of the rich phase exceeded 98%.The total heat duty was 1.88 GJ·t CO2-1,which was about 51%lower than that of 30 wt%MEA aqueous solution.The reaction mechanism for capturing CO2 by[TEPAH][CPL]/[EG]/[DGDE]was explored by 13C NMR.The results showed that the primary and secondary amines on[TEPAH]+in the system reacted with CO2 to produce carbamate successively.while they protonated with[CPL]-,secondary amine and EG in turn.At the end of the reaction.the absorption product and EG were concentrated in the rich phase,while the poor phase solution was mainly DGDE with a small amount of EG and protonated[CPL].Desorption is the reverse process of absorption,and after desorption,the rich phase can be restored to one phase with the poor phase again.In addition,based on the physical parameters of[TEPAH][CPL]/[EG]/[DGDE]and the mass transfer data of the wet-wall column,the mass transfer-reaction kinetic model of the absorption process was constructed.The results showed that the absorption reaction of the system was a pseudo-first-order reaction with a chemical reaction enhancement factor of 147 at 313.15 K.The reaction rate constant was 58613 s-1:the second-order reaction rate equation was k2=9.85×105exp(-666.36/T),the activation energy of the reaction was 5.54 kJ·mol-1,which was about 80%lower than that of 30 wt%MEA aqueous solution.