Kinetics of CO2 absorption in aqueous sarcosine salt solutions: influence of concentration, temperature, and CO2 loading

Amino acid salt solutions are a promising alternative to alkanolamines (e.g., MEA) as absorption liquid for CO2 removal due to their ionic nature, their low evaporative losses, and their assumed higher oxidative and thermal stability. Sarcosine is a promising candidate because of its relatively high CO2 loading capacity and reactivity. In this work, CO2 absorption experiments in the so-called pseudo-first-order regime were carried out to determine the reaction rate expression and reaction rate constant of CO2 absorption in aqueous sarcosine salt solutions. Next to the influence of the sarcosine concentration (0.5−3.8 M) and the temperature (298−308 K) on the rate of reaction, the reaction rate constants for partially loaded sarcosinate solutions were investigated. Compared to MEA, very high reaction rate constants for the carbamate formation were obtained for aqueous sarcosine salt solutions. The reaction order in CO2 was found to be equal to 1, which is in accordance with the literature, and for potassium sarcosinate an (apparent) reaction order of 1.66 was found. The activation energy was found to be approximately 26 kJ/mol. The apparent rate of the reaction strongly decreases with increasing partial loading of the solution with CO2 and was found to be directly related to the decrease in free amine concentration in the solution. This observation is especially relevant for cyclic absorption processes such as gas−liquid membrane contactors, where incomplete solvent regeneration occurs.