Estimation of the Amount of CO₂ Chemically Absorbed in Real Time by Measuring the Electrical Conductivity Variation of Monoethanol-Amine Aqueous Solutions

CO₂ absorption is carried out using 100–500 mM monoethanol-amine (MEA) aqueous solutions as the solvents at ambient conditions and the real-time (in situ) capacity (amount) both chemically (rCAC_C) and physically (rCAC_P) are separately estimated during the absorption. rCAC_C is calculated using the empirical rate equation derived based on the variations in the measured electrical conductivity (EC_M) of the solutions according to the MEA concentration throughout the absorption time, and rCAC_P is regarded as the balance of the total amount of CO₂ absorbed (CAC_T) in the solutions directly measured in the experiments. The rCAC_P in the initial absorption time of the lower MEA concentration solutions (100 and 200 mM MEA) exceeds the assumed values, and the rCAC_C subsequently remains dominant for a very short time, after which the chemical absorption is completed. Then, physical absorption occurs again to maintain the physical absorption equilibrium at the later time of the absorption. On the other hand, in MEA concentration solutions higher than 300 mM, the physical absorption occurs in a short initial time, and rCAC_C immediately becomes equal to CAC_T, and it is kept for longer than 94% of the total absorption time. Thereafter, the final absorption reaction is completed without additional physical absorption, which is because the relatively higher concentration of HCO₃^– generated from the HCO₃^– generation reaction causes the equilibrium point of HCO₃^– to shift to the left, thus hindering the physical absorption reaction.