Elucidation of Operating Parameters Influencing the Ultrasonic-Assisted Absorption of Bulk CO2 Using Unpromoted and Promoted Methyldiethanolamine

Abstract

Various acid gas sweetening processes can be used to separate CO2 from natural gas. As one of the most matured and widely utilized gas sweetening processes, absorption has been continuously improved to meet the stringent separation requirement. Ultrasonic irradiation has recently been introduced as an alternative technique to intensify the absorption process. Nevertheless, further studies are still needed to mature this new technique, particularly using slow kinetic absorbents possessing high inherent CO2 absorption capacity. Moreover, performing experimental studies using blended solvents in the high-frequency ultrasonic-assisted absorption system has also introduced a new idea in this field. This experimental study presents the CO2 absorption into aqueous solutions of methyldiethanolamine (MDEA) and piperazine (PZ)-promoted MDEA in an ultrasonic-assisted batch reactor. The influences of various operating parameters on CO2 absorption performance were evaluated in both promoted and unpromoted conditions. The parameters of the experiments included ultrasonic power at a frequency of 1.7 MHz, absorbent concentration, temperature, and CO2 partial pressure. Based on the results, ultrasonic power was found to be the most critical factor influencing the CO2 absorption rate. Moreover, the potential of the high-frequency ultrasonic-assisted CO2 absorption reactor was further elucidated via comparison with the conventional stirring and silent conditions under identical operating conditions. The highest CO2 absorption rate was achieved at an ultrasonic power of 12.36 W, a temperature of 70 °C, a CO2 partial pressure of 10 bar, an absorbent concentration of 50 wt %, and a promoter concentration of 5 wt %. In addition, the CO2 absorption rate in the high-frequency ultrasonic-assisted reactor using the MDEA absorbent was 28 and 52 times higher compared to stirring and silent conditions, respectively. The CO2 absorption rate enhancement was approximately 17 and 54 times higher for the PZ-MDEA.