Metal Oxides Enhance the Absorption Performance of N-Methyldiethanolamine Solution during the Carbon Dioxide Capture Process

Fly ash from coal-fired power plants can enter chemical absorbents along with flue gas. Silica and metal oxides are the main components of fly ash. To explore the effect of the metal oxides on absorbents, we analyzed the integrated CO2 absorption–desorption process using N-methyldiethanolamine (MDEA) as the standard and an amine absorbent after adding different metal oxides. The effects of each metal oxide on CO2 capture by the MDEA solution, including CO2 reaction heat, absorption rate, cyclic loading, and carbonation rate, were assessed. It was found that supplementation with appropriate calcium oxide and magnesium oxide proportions accelerates the CO2 absorption rate and shortens the saturation time of the MDEA solution by 9%–17%. Magnesium oxide and calcium oxide were precipitated as carbonates during absorption. The CO2 reaction heat of the MDEA solution increased by 95% after adding magnesium oxide, thereby significantly increasing the energy consumption of the desorption process. On the basis of the experimental studies, the increase in CO2 absorption rate by MDEA after adding MgO and CaO may be mediated through two different mechanisms.