Objective Presently, CO₂ capture technology based on the ethanolamine solutions suffers from drawbacks such as high energy consumption and elevated costs. A primary method to address these challenges is to construct blended amine solutions by synergistically integrating the absorption and desorption advantages of different types of ethanolamines. Hydroxyethyl ethylenediamine (AEEA) and N-methyldiethanolamine (MDEA) represent two major commonly used absorbents, and their blending necessitates an accurate understanding of their CO₂ absorption patterns, including CO₂ loading capacity, the ion-concentration distribution patterns of reaction products, and reaction orders. Currently, their absorption mechanisms remain poorly understood, and there is a lack of relevant reaction parameters, jointly undermining the prediction accuracy of process models.

Methods  By investigating the CO₂ absorption processes of AEEA and MDEA solutions, this study clarified the reaction mechanisms of both solutions. Furthermore, it established ion concentration distribution models of the reaction products based on pH values, determined the reaction orders through regression analysis, and developed the reaction rate models of both solutions.

Results and Conclusions  The results indicate that, under the same concentration, the AEEA solution exhibited higher CO₂ absorption capacity and rates compared to the MDEA solution. The AEEA solution presented a two-stage CO₂ absorption process, with reaction orders approaching 2. Initially, the CO₂ absorption process in the AEEA solution was controlled by the formation of zwitterionic intermediates (R₁R₂NH⁺COO⁻) from AEEA-CO₂ reactions. In the late stage, this process was jointly governed by mass transfer and reactions. In contrast, the CO₂ absorption in the MDEA solution was identified as a base-catalyzed hydration process, with the reaction rate showing a linear correlation with the MDEA concentration and the reaction order determined at 1. The novel insights and models of this study provide theoretical guidance for the optimization of the concentration, retention time, and circulation rate of solvents, along with column design, in carbon capture technique.