Effect of ring structures on the CO₂ capture performance of piperazine

Piperazine (PZ), as a carbon dioxide (CO 2 ) absorbent with outstanding properties, has been extensively studied on modification and the application as a promoter. However, it is still unclear as to why PZ possesses such excellent properties at present. In this work, we returned to the fundamentals by focusing on PZ and N , N ′-Dimethylethylenediamine (DMEN) as research subjects. Through experimental and computational investigations, we examined the influence of six-membered ring structures on the CO 2 capture performance of PZ. The results of absorption test indicate that the ring structure can reduce the activation energy of the adsorption reaction and increase the cycle capacity, but it also lowers the adsorption rate and reduces the maximum capacity. To further investigate the influence of the ring structure on the absorption process, quantitative 13 C NMR analysis and density functional theory (DFT) calculation were employed. The results indicated that the ring structure enhances steric hindrance effect, thereby promoting bicarbonate formation and improving regeneration performance. This research provides valuable insights for the further development of highly efficient CO 2 capture absorbents based on PZ.