Parametric quantification of sonochemical effect during the high frequency ultrasonic-assisted absorption of bulk CO2

Abstract

Ultrasonic irradiation has been recently applied as a novel technique to the CO2 absorption process. The preliminary studies have proved the ultrasonic-assisted reactor could provide satisfactory performance, in terms of CO2 absorption rate, even by utilizing slow kinetic absorbents. In those studies, the main focus was on the physical effects of ultrasonic irradiation, ignoring the significance of the chemical effect. Elucidating the role of the sonochemical effect, which is linked with the hydroxyl radicals (OḢ), can be a crucial step in further developing this technique. Hence, this study aims to parametrically quantify the sonochemical effect during the CO2 absorption in the high-frequency ultrasonic-assisted reactor using promoter-free methyldiethanolamine (MDEA). The quantification is performed via scavenging of OḢ radicals using terephthalic acid (TA). Subsequently, the high-performance liquid chromatography (HPLC) analytical technique is implemented to analyze the scavenged OḢ radicals, and the findings are presented by calculating the radical scavenging activity (RSA) of TA. The results show that the RSA value increases from 0.14 −2.79 % as CO2 pressure rises from 3 to 11 bar, indicating a rise in the quantity of OḢ radicals formed at high pressure ranges that TA molecules can scavenge. In contrast to the CO2 pressure effect, increasing the temperature, ultrasonic power, and MDEA concentration can suppress the sonochemical effect under the fixed high-frequency condition of 1.7 MHz. Finally, along with the parametric analysis, the CO2 absorption rate is determined, and the significance of the sonochemical effect on the rate enhancement is discussed.