Enhancement of desorption amount of carbon dioxide gas from monoethanolamine solution using ultrasound and calcium chloride

Abstract

Ultrasound can desorb CO2 from dissolved CO2 gas [CO2(aq)] in a low-concentration monoethanolamine (MEA) solution (0.2 M) at a low temperature (25 °C). However, it is difficult to desorb CO2 using ultrasound at pH >8.2 because CO2 mainly exists as HCO3- and not as CO2(aq). We investigated the increment of the CO2 gas desorption ratio on the synthesis reaction of CaCO3 by the shift in the CO2 equilibrium in the direction of the increase of CO2(aq) by the decrease of pH from 8.2 with an increase in the H+ concentration in the MEA solution. Results indicated that a high Ca recovery ratio of 93.1% was observed by CaCl2 addition and ultrasound irradiation. Compared with the desorption ratio of CO2 gas using ultrasound irradiation without the addition of CaCl2, the CO2 gas desorption ratio increases from 2.2% to 9.8% using ultrasound with a low concentration of CaCl2 (Ca/MEA molar ratio 0.026).