Deciphering the transfer mechanisms for CO2 absorption into binary blended solutions

Abstract

A thorough understanding of the mechanisms involved in CO₂ chemical absorption is crucial for the development of efficient CO₂ capture technologies. Due to the insufficient insight into the interaction mechanism of different components in blended solutions, CO₂ absorption reactions were often categorized as unidirectional transfer between absorption products. In this study, the CO₂ absorption performance of binary blended solutions, including piperazine (PZ)/n-methyldiethanolamine (MDEA), ethanolamine (MEA)/MDEA, ammonia (NH₃)/MDEA, PZ/potassium carbonate (K₂CO₃), and NH₃/K₂CO₃, was investigated using a combination of experimental and computational methods. The CO₂ absorption mechanisms of “competitive reaction”, “transfer reaction” and “parallel reaction” in the binary blended solution system were proposed. Kinetic experiments revealed that different blended solutions had varying impacts on the process of CO₂ absorption. Among them, PZ/MDEA and MEA/MDEA solutions reduced the absorption rates by an average of 8% and 25%, respectively, compared to PZ or MEA component solutions. NH₃/MDEA and PZ/K₂CO₃ solutions had absorption rates similar to those of single NH₃/PZ component solutions. NH₃/K₂CO₃ solutions, on the other hand, exhibited an average increase of 17% in absorption rates compared to NH₃ solutions. Quantum mechanical (QM) methods were employed to evaluate of the absorption products and key processes in terms of kinetics and thermodynamics. Quantitative ¹³C NMR analyses were conducted to further investigate the interactions between components and the pathways of mass transport in blended solutions, which demonstrated proton transfer and CO₂/-COO transfer between adsorption products. This study highlights an accurate description of the transfer mechanisms of various blended systems for the enhanced CO₂ capture.