A Combined Experimental and Computational Study on the Shuttle Mechanism of Piperazine for the Enhanced CO₂Absorption in Aqueous Piperazine Blends

Piperazine (PZ) blends containing PZ and monoethanolamine (MEA)/N-methyldiethanolamine (MDEA)/2-amino-2-methyl-propanol (AMP) were experimentally and computationally investigated to analyze their potential capabilities for CO2 capture, and the shuttle mechanism of PZ for enhanced CO2 absorption were verified. In experiments, the concentration of both PZ and MEA/MDEA/AMP were varied to show the effect of concentration ratio and the influence of amine components on the CO2 absorption rate and capacity. Experimental results showed that all the PZ blends possessed high absorption rates and large absorption capacities. To further understand the interaction behavior of amines/products and possible reaction pathways, both qualitative and quantitative 13C NMR analyses were conducted. The results indicated the conversion between absorption products, which can release free PZ to capture CO2 and consequently improve the absorption performance. Moreover, the static quantum mechanical calculations and ab initio molecular dynamics (AIMD) simulations combined with metadynamics sampling were conducted to evaluate the thermodynamic stability of absorption products and kinetically favorable key elementary reactions in PZ blends. This study highlights an accurate description of the shuttle effect of PZ for the enhanced CO2 capture by PZ blends.