Reactive CaCO 3 Formation from CO 2 and Methanolic Ca(OH) 2 Dispersions: Transient Methoxide Salts, Carbonate Esters and Sol-Gels
A combination of and characterization techniques was used to determine the mechanism of calcium carbonate (CaCO ) formation from calcium hydroxide (Ca(OH) ) dispersions in methanol/water (CH OH/H O) systems. Mid-infrared (mid-IR) analysis shows that in the absence of carbon dioxide (CO ) Ca(OH) esta...
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Veröffentlicht in: | ACS Physical Chemistry Au 2024-09, Vol.4 (5), p.555-567 |
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Sprache: | eng |
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Zusammenfassung: | A combination of
and
characterization techniques was used to determine the mechanism of calcium carbonate (CaCO
) formation from calcium hydroxide (Ca(OH)
) dispersions in methanol/water (CH
OH/H
O) systems. Mid-infrared (mid-IR) analysis shows that in the absence of carbon dioxide (CO
) Ca(OH)
establishes a reaction equilibrium with CH
OH, forming calcium hydroxide methoxide (Ca(OH)(OCH
)) and calcium methoxide (Ca(OCH
)
). Combined
mid-IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray absorption spectroscopy and scanning electron microscopy examination of the reaction product formed in the presence of CO
reveals the formation of calcium dimethylcarbonate (Ca(OCOOCH
)
). This strongly suggests that carbonation takes place by reaction with the Ca(OCH
)
formed from a Ca(OH)
and CH
OH reaction. Time-resolved XRD indicates that in the presence of H
O the Ca(OCOOCH
)
ester releases CH
OH and CO
, forming ACC, which subsequently transforms into vaterite and then calcite. TGA reveals that thermal decomposition of Ca(OCOOCH
)
in the absence of H
O mainly leads to the reformation of Ca(OCH
)
, but this is accompanied by a significant parallel reaction that releases dimethylether (CH
OCH
) and CO
. CaCO
is the final product in both decomposition pathways. For CH
OH/H
O mixtures containing more than 50 mol % H
O, direct formation of calcite from Ca(OH)
becomes the dominant pathway, although the formation of some Ca(OCOOCH
)
was still evident in the
mid-IR spectra of 20 and 40 mol % CH
OH systems. In the presence of ≤20 mol % H
O, hydrolysis of the ester led to the formation of an ACC sol-gel. In both the 90 and 100 mol % CH
OH systems, diffusion-limited ACC → vaterite → calcite transformations were observed. Traces of aragonite were also detected. We believe that this is the first time that these reaction pathways during the carbonation of Ca(OH)
in a methanolic phase have been systematically and experimentally characterized. |
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ISSN: | 2694-2445 2694-2445 |
DOI: | 10.1021/acsphyschemau.4c00041 |