Research subject: Oxidative degradation of amine solvents represents a major challenge in carbon dioxide absorption processes, leading to the formation of heat-stable salts (HSS) and consequent reductions in CO₂ absorption capacity and kinetics. This study examines the effect of acetic acid, as one of the major degradation products, on the CO₂ absorption performance of aqueous methyldiethanolamine (MDEA) solutions. In addition, the potential remedial role of 1,3-diaminopropane (DAP) as a reactive diamine additive is evaluated.
Research approach: CO₂ absorption experiments were carried out using a volumetric method at 303.15 K and an initial pressure of 620 kPa. First, the effect of acetic acid at three different weight percentages on equilibrium absorption capacity, kinetic behavior, and solution pH of MDEA was investigated. Subsequently, DAP was added to the degraded MDEA solution at concentrations of 2.5, 6, and 10 wt.%, and the resulting changes in absorption capacity, kinetics, and pH were systematically analyzed.
Main results: The results demonstrate that acetic acid significantly deteriorates the CO₂ absorption performance of aqueous MDEA solutions. Specifically, the presence of acetic acid led to a reduction of about 20% in the CO₂ absorption capacity and a significant weakening of the absorption kinetics, accompanied by a noticeable decrease in pH and an increase in equilibrium pressure. These detrimental effects are mainly attributed to the formation of HSS and the reduction of the effective alkalinity of the solution. In contrast, the addition of DAP as a reactive additive successfully compensated for much of the performance loss induced by degradation. Quantitative analysis revealed that at a DAP concentration of 10 wt.%, the CO₂ absorption capacity increased by about 69%, while the equilibrium pressure decreased by 44%. This significant improvement was observed in both thermodynamic and kinetic performance. The underlying mechanism of this enhancement arises from the direct reaction of DAP with CO₂, the recovery of solution alkalinity through interaction with degradation products, and the release of free MDEA molecules. These quantitative and qualitative results confirm the effectiveness of DAP as a promising mitigation strategy against the negative impacts of HSS and highlight its potential for developing more sustainable and cost-effective CO₂ absorption processes.