Research subject: Foaming is one of the major challenges in natural gas sweetening units, as it can lead to reduced absorption efficiency and serious operational problems. Blended amine solutions have emerged as a promising approach to improve the performance of CO₂ absorption systems. Despite extensive studies on single amine solvents, the foaming behavior and CO₂ absorption performance of blended systems containing methyl diethanolamine (MDEA) and 1,3-diaminopropane (DAP) have not yet been comprehensively investigated. In particular, the mutual effects of these two amines on foaming characteristics and absorption capacity remain insufficiently understood.
Research approach: The main objective of this study was to investigate the foaming behavior and CO₂ absorption performance of MDEA–DAP-blended solutions and to determine optimal operating conditions. Blended solutions were prepared at three total amine concentrations (23, 31.5, and 40 wt.%) with three different MDEA-to-DAP ratios. All experiments were conducted at 30 °C. Nitrogen gas was injected into the foaming apparatus at a constant flow rate of 1.5 L/min, and foam volume and foam break time were measured. CO₂ absorption experiments were carried out at a pressure of 620 kPa, and both absorption capacity and absorption kinetics were evaluated for all solvent compositions.
Main results: The results indicated that both foaming behavior and absorption performance are strongly dependent on total amine concentration and the MDEA-to-DAP ratio. Due to its tertiary amine structure, MDEA was identified as the primary contributor to foaming. In contrast, DAP, owing to its two primary amine groups, played a key role in enhancing CO₂ absorption capacity at a total concentration of 31.5 wt.% with 5 wt.% DAP, the best balance between reduced foaming and high absorption capacity was achieved, corresponding to a foam volume of 318.45 mL, a foam break time of 6 s, and an absorption capacity of 0.927 mol CO₂ per mol amine. The optimal condition was identified as a blend containing 26.5 wt.% MDEA and 5 wt.% DAP at a total amine concentration of 31.5 wt%, which is recommended for industrial CO₂ absorption applications.