The comparative kinetics study of CO2 absorption into non-aqueous DEEA/MEA and DMEA/MEA blended systems solution by using stopped-flow technique

Abstract

The kinetics of the absorption of CO2 into solutions of (monoethanolamine) MEA-Ethanol, (N, N-diethylethanolamine) DEEA-MEA-Ethanol and (N, N-dimethylethanolamine) DMEA-MEA-Ethanol have been studied by applying a stopped-flow apparatus. In this study, the concentration range of both tertiary amine and MEA were chosen to be 0.2–0.4 kmol/m3 with a temperature range of 293–313 K under non-aqueous conditions. The model based on the termolecular reaction mechanism is proposed to interpret the experimental kinetic data of the reaction occurred in the non-aqueous blended amine systems, and the results indicate that the model is well fitted to the experimental data with an AARD of 5.70% for DEEA-MEA-Ethanol system and 6.53% for DMEA-MEA-Ethanol system. Blended amines show many advantages in kinetics because of the existence of the interaction between the tertiary amine and MEA. The kinetics behaviors of CO2 absorbed in the two non-aqueous blended amine systems are discussed in brief according to the molecular structures of the two tertiary amines. Different from the traditional aqueous systems, this study proved that tertiary amine enhanced the ability of primary amine to absorb CO2 which is due to tertiary amine didn’t react with CO2 directly in a non-aqueous system. The result in the non-aqueous system also shows that DMEA is more easily participate in the termolecular reaction between MEA and CO2 compared with DEEA, which indicate the length of alkyl chain on nitrogen atom also plays an important role in the enhancement effect. Additionally, after comparing the kinetic data of the two blended amine systems under aqueous and non-aqueous conditions, it can be found that tertiary amine can participate in the termolecular reaction between MEA and CO2, and that the protonated MEA can be reconverted to free MEA by the tertiary amine, making it easier for MEA to participate in its own termolecular reactions, so that the overall reaction rate of the blended amine system is accelerated. It can be summarized that there are interactions between the tertiary amine and the primary amine in the non-aqueous blended amine system that positively promote the kinetics.