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In this study, we investigated the use of ultrasound irradiation to remove CO2 gas from aqueous solutions of monoethanolamine (MEA). The desorption rate of CO2 was measured while MEA solutions were exposed to 28 kHz ultrasound irradiation at 25 °C. The results showed that the rate of CO2 desorption from a low-concentration MEA (0.2 mol/l) solution is significantly increased by ultrasound irradiation as compared with that of desorption by stirring at a low temperature (25 °C). It was also found that decreasing the concentration of MEA solutions increased the rate of CO2 desorption. In addition, we considered the process of desorption of CO2 from MEA solutions according to experimental results.

We developed an effective method for desorbing CO2 from low-concentration (0.2 mol/l) monoethanolamine (MEA) solutions using calcium chloride (CaCl2) and ultrasound irradiation at 25 °C. The proportion of CO2 desorbed from the MEA solution was calculated from the amount of CaCO3 generated and the amount of CO2 emitted. The proportion of CO2 desorbed from the MEA solution was much higher when CaCl2 was added than when CaCl2 was not added. We also characterized the CaCO3 that was generated when the solution was treated with ultrasound irradiation and when the solution was stirred. The CaCO3 particles produced were more homogeneous and smaller when ultrasound irradiation was applied than when the solution was stirred.

This study used three tertiary amine solutions as a CO2 absorbent. Ultrasound can desorb CO2 from CO2(aq) and H2CO3 species at low temperature. Tertiary amine solution with lower pKa created CO2 adsorption equilibrium at lower pH related to a higher CO2 desorption amount using 28 kHz ultrasound because the lower pH environment would increase the existence ratio of CO2(aq). Triethanolamine (TEA) with lowest pKa (7.85) showed the highest CO2 desorption ratio of 48% for 30 min irradiation at 25 °C. The CO2 absorption–desorption capacity of TEA by reuse was evaluated and found to keep the first capacity for three cycles.

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