Investigation of CO¿ Mass Transfer in Aqueous MEA Using a Semi-Continuous Lewis Cell

This work investigates the mass transfer of CO2 into aqueous monoethanolamine (MEA) solutions (1 wt%, 5 wt%, 30 wt%) using a Lewis Cell. The experimental setup is a semi-continuous Lewis Cell installed at the Institute of Chemical Engineering and Environmental Technology (CEET) at TU Graz, and further developed in this study. Gas and liquid phases are thermally pre-conditioned. The gas composition is set by mass-flow controllers. All process variables (pressure, temperature, pH, conductivity, density, CO2 signal) are recorded continuously. Experiments were run isothermally at tightly controlled setpoints of 20 °C, 25 °C, and 40 °C. The gas phase used defined CO2/N2 mixtures, typically 30 vol% CO2 and 70 vol% N2 for reference and calibration, and 3 vol% CO2, 4 vol% O2 with balance N2 to simulate post-combustion conditions. System pressure was kept constant and the gas composition was precisely adjusted. Absorption in MEA systems is governed by both physical mass transfer and chemical reaction. Accordingly, data evaluation follows film theory and is performed exclusively with a time-resolved, conductivity-based online method. This approach captures start-up and transition phases reliably and provides continuous estimates of the CO2 loading and the overall volumetric mass transfer coefficient. For context, the obtained values are compared with literature data for the classical batch Lewis Cell (fall-in-pressure method). Within the relevant operating window, the values are in the same range. The conductivity approach offers higher time resolution and is more robust under constant system pressure. From the measurements, key absorption metrics are derived, including the volumetric mass-transfer coefficient, the Hatta number, and the apparent reaction order. The results show the expected trends: higher temperature and a higher CO2 fraction increase the overall mass transfer. With increasing MEA concentration, the physical contribution decreases, and chemical enhancement becomes dominant due to fast reaction in the liquid boundary layer. The series exhibited high reproducibility, and the configuration enabled stable operation. Calibration procedures and analytical limits are documented. Finally, limitations of the approach are discussed (analyzer response time, temperature control, gas conversions) together with guidance for transferring the method to other solvents.