Understanding the Positive Role of Ionic Liquids in CO₂ Capture by Poly(ethylenimine)

CO₂ capture technology is one of the most important technical methods for significantly mitigating CO₂ emissions in a low-carbon context. The recent invention of mixed absorbents comprising poly(ethylenimine) (PEI) and ionic liquids (ILs) provides a novel strategy for efficiently capturing CO₂, and this has garnered widespread attention. However, the intermolecular interactions between the IL and other constituents during the CO₂ absorption process remain unclear. In this present work, a series of density functional theory (DFT) calculations and molecular dynamics simulations were conducted to investigate the positive role of IL in CO₂ capture by PEI. The results showed that the formation of hydrogen bonds between the IL anion and the amino groups of PEI primarily drives the addition of IL to PEI. During the CO₂ absorption process, the IL anion not only can absorb CO₂ but also exerts a dehydrogenation effect on the amino group of PEI, facilitating enhanced interaction between PEI and CO₂. Additionally, the IL substantially reduces the viscosity of PEI, promoting the diffusion of CO₂ within the system and enhancing the absorption rate. Based on the information on interaction energy and viscosity, we can easily make theoretical predictions for the optimal proportion of IL to be added. The above results provide fundamental insights to promote the industrial application of the PEI/IL system for CO₂ capture.