Mass transfer and reaction mechanism of CO₂ capture into a novel amino acid ionic liquid phase-change absorbent

In order to overcome high heat duty and poor regeneration efficiency of existing chemical absorbent, a novel aqueous amino acid ionic liquids (AAILs) phase change absorbent with tetraethylenepentamine (TEPA) as cation, L-proline (L-Pro) as anion and N-propanol (NPA) as phase separator was proposed in this study. [TEPAH][Pro]/ NPA/H2O owned the maximum absorption loading of 2.01 mol CO2.mol absorbent-1, and the rich phase viscosity was only 8.06 mPa.s. Moreover, its desorption efficiency was 84.4% while the 5th cyclic loading kept above 1.61 mol CO2.mol absorbent-1. With the presence of NPA, the rich phase only accounted for 41% of the total volume while it contained 99.3% of CO2 products. The heat duty was only 2.39 GJ.t CO2-1, which was 37% lower than that of 30 wt% ethanolamine (MEA) aqueous solution. Meanwhile, the reaction mechanism and product distribution were revealed by 13C NMR and the mass transfer kinetics was investigated using the wetted wall column. The products in the rich phase mainly consisted of carbamate, hydrogen carbonate, propyl carbonate and water while the main component of the lean phase was NPA. The reaction followed a fast pseudo-first order reaction. At 313.15 K, the rate constant of fresh absorbent was 51346 s-1, which showed a decreasing trend with the increase of absorption loading at 313.15 K. The second order reaction rate was calculated by: k2 = 9.88 x 109exp(-3591.2/T), where the reaction activation energy was only 29.86 kJ.mol- 1.