Empirical correlation of electrical conductivity with CO2 absorption and desorption capacity in 10–25 wt% aqueous MDEA solutions during cyclic operation

This study investigates a continuous CO 2 absorption-desorption cycle using 10–25 wt% aqueous methyl-diethanolamine (MDEA) solutions as tertiary-amine solvents for post-combustion CO 2 capture. Absorption is conducted at 25 ℃ and thermal desorption at 80 ℃. Real-time electrical conductivity (EC) measurements are used to correlate EC with CO 2 absorption capacity (CAC) and desorption capacity (CDC). CAC increases nearly linearly with increasing MDEA concentration, reaching only 68.1% of its theoretical value at 25 wt% due to reduced ionic and molecular activity. The highest desorption efficiency occurs at 20 wt%, attributed to weakened MDEA–H⁺ interactions caused by increased concentrations of MDEAH⁺ and HCO 3 - . At 25 wt%, enhanced formation of neutral ion pairs (MDEAH⁺–HCO 3 - ) and van der Waals interactions restrict CO 2 desorption. CO 2 desorption initiates near the bubble point temperature of each solution, which slightly decreases with increasing MDEA concentration due to reduced water content and increased CO 2 loading. During pre-desorption heating, EC increases owing to enhanced ionic activity, reaching a maximum prior to desorption. More than 50% of the total CO 2 is released within the first 10 min after desorption begins, with an average desorption time of approximately 67 min. EC exhibits greater sensitivity to CO 2 capacity changes during desorption than during absorption. Minimum EC sensitivity occurs near 16.9 wt% MDEA, suggesting an optimal balance between ionic association and repulsion. Linear correlations between EC and CAC/CDC enable real-time estimation of CO 2 capacity. ATR-FTIR analysis further confirms that the cyclic EC variations originate from the formation and decomposition of carbonate/bicarbonate species in the MDEA solution. • CO 2 absorption–desorption was evaluated using 10–25 wt% aqueous MDEA. • Real-time electrical conductivity correlated with CO 2 capacity in both phases. • Desorption efficiency peaked at 20 wt% due to weakened ionic binding effects. • Electrical conductivity showed higher sensitivity to CO 2 capacity during desorption. • Linear EC–CO 2 capacity correlations enable real-time process monitoring.