Kinetics of CO2 absorption in N-Methyldiethanolamine solution promoted by potassium sarcosine

Abstract

Potassium sarcosine (KSar) shows promise as an effective co-promoter of N-methyldiethanolamine (MDEA), a tertiary amine known for its high CO2 absorption capacity but relatively slow kinetics. This study investigated the CO2 absorption kinetics in a KSar + MDEA + H2O solution using the pressure-decay technique in a stirred cell reactor. The experiments were performed at temperatures ranging from 303.15 K to 333.15 K, with varying concentrations of KSar (ranging from 3% to 15% by weight), while keeping the MDEA concentration constant at 20% by weight. Furthermore, the study involved assessing the physicochemical and mass transfer properties and comparing them to those of a solution containing MDEA (30 wt%) + H2O solution. Properties like density, viscosity, Henry's constant (HN2O), and the physical mass-transfer coefficient of the liquid phase (kl) were measured and applied to analyze CO2 absorption kinetics. The overall reaction rate constant (kOV) was assessed using both termolecular and zwitterion mechanisms within a pseudo-first-order reaction regime. Additionally, kOV was estimated via correlated Arrhenius power law expression of the individual rate contributions of CO2−MDEA, CO2–H2O, and CO2−KSar. The calculated kOV values were found to closely match the experimental data, with absolute average relative deviations (AARD) of 4.53% and 3.03% for the termolecular and zwitterion models, respectively. The experimental results clearly showed that the rate of CO2 absorption, represented by kOV, can be significantly enhanced by adding a small amount of KSar into the MDEA + H2O solution.