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Factors Affecting the Rate of CO2 Absorption after Partial Desorption in NaNO3-Promoted MgO

Prashar, Atul K., Seo, Hwimin, Choi, Won Choon, Kang, Na Young, Park, Sunyoung, Kim, Kiwoong, Min, Da Young, Kim, Hye Mi, Park, Yong Ki
Energy & Fuels 2016 v.30 no.4 pp. 3298-3305
X-ray diffraction, absorbents, absorption, carbon dioxide, desorption, ions, magnesium carbonate, magnesium oxide, melting point, nitrogen, scanning electron microscopy, sodium nitrate, thermogravimetry, vibration
Sodium nitrate (NaNO₃) and other alkali nitrates are known to accelerate the CO₂ absorption rate of MgO above their melting points. This absorption rate is further enhanced if absorption is performed after partial desorption. Moreover, it does not show any induction period, which is otherwise present if absorption is performed after complete desorption. A thorough study of various factors affecting the rate after partial desorption is performed in this work. We exposed a sample to CO₂ for several different periods before partial desorption and N₂ for several different periods during partial desorption in a thermogravimetric analyzer. Absorbents were also characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM) and studied in an in situ infrared (IR) cell to understand the changes at the molecular scale. The absorbed amount of CO₂ with a fast initial rate after partial desorption is affected by both the amount of CO₂ absorbed before partial desorption as well as the amount of MgO formed during partial desorption. In situ IR studies showed that two phases of bulk MgCO₃ were formed along with the surface carbonate. It can be concluded from the thermogravimetric analysis (TGA) and in situ IR study that defects in MgO, which were introduced from the defect MgCO₃ phase during partial desorption, are responsible for the faster rate after partial desorption. It seems that substitution of nitrate ions in the MgCO₃ phase is responsible for the defect MgCO₃ phase (out-of-plane bending vibration at 876 cm–¹).