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Understanding the CO 2 sorption mechanisms of the MgO‐doped Na‐based sorbent at low temperatures
Author(s) -
Xu Zhikang,
Wu Ye,
Cai Tianyi,
Chen Xiaoping,
Ma Jiliang,
Liu Daoyin
Publication year - 2019
Publication title -
greenhouse gases: science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.45
H-Index - 32
ISSN - 2152-3878
DOI - 10.1002/ghg.1896
Subject(s) - sorption , sorbent , thermogravimetric analysis , desorption , materials science , fourier transform infrared spectroscopy , analytical chemistry (journal) , adsorption , doping , chemical engineering , chemistry , organic chemistry , engineering , optoelectronics
Using a solid Na‐based sorbent is one potential option to decrease CO 2 emission in coal‐fired power plants, and the CO 2 sorption reactivity of Na 2 CO 3 /γ‐Al 2 O 3 sorbent was improved by mechanically doping MgO into Na 2 CO 3 /γ‐Al 2 O 3 in our previous study while the mechanism was not clear. In this paper, the CO 2 sorption/desorption mechanisms of the promising MgO‐doped Na‐based sorbent prepared by the two‐step incipient wetness impregnation method were studied using a fixed‐bed reactor, together with characterizations of X‐ray fluorescence, nitrogen adsorption apparatus, field emission scanning electron microscopy, X‐ray diffraction, and thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG‐FTIR). Also, the sorption behaviors were well described with Avrami's fractional‐order kinetic model. Results demonstrated that MgO not only dispersed on γ‐Al 2 O 3 but entered γ‐Al 2 O 3 ’s lattice, leading to the formation of Mg‐Al mixed oxides for CO 2 sorption. In addition, a new phase Mg 6 Al 2 CO 3 (OH) 16 ·4H 2 O was produced during the CO 2 sorption process, which plays a crucial role in facilitating the conversion of Na 2 CO 3 to NaHCO 3 . The CO 2 sorption capacity of MgO‐doped Na‐based sorbents is presumably determined by the trade‐off between microstructure and active component dispersion. The knowledge gained about the promotion mechanism of MgO provides fundamental direction for the synthesis of Mg–Al mixed oxides, supported with the developed microstructure for CO 2 sorption enhancement of Na‐based sorbents. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.