Carbonation of Alkaline Earth Metal Hydroxides: Structure across Nano- to Mesoscales

Hubert King; Ryan Murphy; Avery Baumann; Andrew Allen; Huong Giang T. Nguyen; Lisa DeBeer-Schmitt; Jan Ilavsky

doi:10.1021/acs.energyfuels.4c05924

Carbonation of Alkaline Earth Metal Hydroxides: Structure across Nano- to Mesoscales

Hubert King, Ryan Murphy, Avery Baumann, Andrew Allen, Huong Giang T. Nguyen, Lisa DeBeer-Schmitt, Jan Ilavsky

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Abstract

The conversion of gaseous CO₂ into a solid constitution through mineralization is an active area of carbon capture, and alkaline earth metal hydroxides (M(OH)₂, M = Ca²⁺, Mg²⁺) are frontrunners in this area. As model systems, nanolime samples are excellent templates for the study of this reaction. Here, we have examined these under ambient pressure conditions with controlled humidity and CO₂. Utilizing a broad range of analytical methods, we first established the purity and structures of the selected materials. We then examined the structural changes due to carbonation, using infrared spectroscopy, X-ray scattering, and neutron scattering. The resulting structural changes are resolved from nanoscale to mesoscale and from early-stage to late-stage carbonation. Ca(OH)₂ and Mg(OH)₂ are found to behave quite differently. As expected from prior work, the carbonation of Ca(OH)₂ is kinetically favored. Our structure studies suggest this is due to a facile reaction at the fractal interface of the particles. From early- to late-stage carbonation, there is a consistent increase in the fractal roughness. This is in contrast to Mg(OH)₂ where the same surface evolves into a smooth conformal coating. For this material the major reacting component is at the mesoscale, suggesting globular particle growth or evolving macro-porosity. Because neutron scattering is sensitive to hydrogen content, we expected a significant change as M(OH)₂ evolves to MCO₃. Such a change is found for Ca(OH)₂ but not for Mg(OH)₂, providing evidence for the formation of hydrated carbonates for the later material. The formation of a conformal layer along with water-rich carbonate formation is an impediment to the use of Mg(OH)₂ for carbon capture. For energy-efficient carbon capture, it would be desirable to enhance carbonation rates for Mg(OH)₂, and one possible route would be the use of anhydrous fluids.

Original language	English
Pages (from-to)	4866-4879
Number of pages	14
Journal	Energy and Fuels
Volume	39
Issue number	10
DOIs	https://doi.org/10.1021/acs.energyfuels.4c05924
State	Published - Mar 13 2025

Funding

We thank Dr. George Quinn for optical imaging of Ca(OH)2 and Mg(OH)2. A portion of this research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract No. DE-AC02-06CH11357. A portion of this research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam time was allocated to CG-2 on proposal number IPTS-29592. We thank Dr. George Quinn for optical imaging of Ca(OH) and Mg(OH). A portion of this research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract No. DE-AC02-06CH11357. A portion of this research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam time was allocated to CG-2 on proposal number IPTS-29592. 2 2

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title = "Carbonation of Alkaline Earth Metal Hydroxides: Structure across Nano- to Mesoscales",

abstract = "The conversion of gaseous CO2 into a solid constitution through mineralization is an active area of carbon capture, and alkaline earth metal hydroxides (M(OH)2, M = Ca2+, Mg2+) are frontrunners in this area. As model systems, nanolime samples are excellent templates for the study of this reaction. Here, we have examined these under ambient pressure conditions with controlled humidity and CO2. Utilizing a broad range of analytical methods, we first established the purity and structures of the selected materials. We then examined the structural changes due to carbonation, using infrared spectroscopy, X-ray scattering, and neutron scattering. The resulting structural changes are resolved from nanoscale to mesoscale and from early-stage to late-stage carbonation. Ca(OH)2 and Mg(OH)2 are found to behave quite differently. As expected from prior work, the carbonation of Ca(OH)2 is kinetically favored. Our structure studies suggest this is due to a facile reaction at the fractal interface of the particles. From early- to late-stage carbonation, there is a consistent increase in the fractal roughness. This is in contrast to Mg(OH)2 where the same surface evolves into a smooth conformal coating. For this material the major reacting component is at the mesoscale, suggesting globular particle growth or evolving macro-porosity. Because neutron scattering is sensitive to hydrogen content, we expected a significant change as M(OH)2 evolves to MCO3. Such a change is found for Ca(OH)2 but not for Mg(OH)2, providing evidence for the formation of hydrated carbonates for the later material. The formation of a conformal layer along with water-rich carbonate formation is an impediment to the use of Mg(OH)2 for carbon capture. For energy-efficient carbon capture, it would be desirable to enhance carbonation rates for Mg(OH)2, and one possible route would be the use of anhydrous fluids.",

author = "Hubert King and Ryan Murphy and Avery Baumann and Andrew Allen and Nguyen, \{Huong Giang T.\} and Lisa DeBeer-Schmitt and Jan Ilavsky",

note = "Publisher Copyright: {\textcopyright} 2025 The Authors. Published by American Chemical Society.",

year = "2025",

month = mar,

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doi = "10.1021/acs.energyfuels.4c05924",

language = "English",

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TY - JOUR

T1 - Carbonation of Alkaline Earth Metal Hydroxides

T2 - Structure across Nano- to Mesoscales

AU - King, Hubert

AU - Murphy, Ryan

AU - Baumann, Avery

AU - Allen, Andrew

AU - Nguyen, Huong Giang T.

AU - DeBeer-Schmitt, Lisa

AU - Ilavsky, Jan

PY - 2025/3/13

Y1 - 2025/3/13

N2 - The conversion of gaseous CO2 into a solid constitution through mineralization is an active area of carbon capture, and alkaline earth metal hydroxides (M(OH)2, M = Ca2+, Mg2+) are frontrunners in this area. As model systems, nanolime samples are excellent templates for the study of this reaction. Here, we have examined these under ambient pressure conditions with controlled humidity and CO2. Utilizing a broad range of analytical methods, we first established the purity and structures of the selected materials. We then examined the structural changes due to carbonation, using infrared spectroscopy, X-ray scattering, and neutron scattering. The resulting structural changes are resolved from nanoscale to mesoscale and from early-stage to late-stage carbonation. Ca(OH)2 and Mg(OH)2 are found to behave quite differently. As expected from prior work, the carbonation of Ca(OH)2 is kinetically favored. Our structure studies suggest this is due to a facile reaction at the fractal interface of the particles. From early- to late-stage carbonation, there is a consistent increase in the fractal roughness. This is in contrast to Mg(OH)2 where the same surface evolves into a smooth conformal coating. For this material the major reacting component is at the mesoscale, suggesting globular particle growth or evolving macro-porosity. Because neutron scattering is sensitive to hydrogen content, we expected a significant change as M(OH)2 evolves to MCO3. Such a change is found for Ca(OH)2 but not for Mg(OH)2, providing evidence for the formation of hydrated carbonates for the later material. The formation of a conformal layer along with water-rich carbonate formation is an impediment to the use of Mg(OH)2 for carbon capture. For energy-efficient carbon capture, it would be desirable to enhance carbonation rates for Mg(OH)2, and one possible route would be the use of anhydrous fluids.

AB - The conversion of gaseous CO2 into a solid constitution through mineralization is an active area of carbon capture, and alkaline earth metal hydroxides (M(OH)2, M = Ca2+, Mg2+) are frontrunners in this area. As model systems, nanolime samples are excellent templates for the study of this reaction. Here, we have examined these under ambient pressure conditions with controlled humidity and CO2. Utilizing a broad range of analytical methods, we first established the purity and structures of the selected materials. We then examined the structural changes due to carbonation, using infrared spectroscopy, X-ray scattering, and neutron scattering. The resulting structural changes are resolved from nanoscale to mesoscale and from early-stage to late-stage carbonation. Ca(OH)2 and Mg(OH)2 are found to behave quite differently. As expected from prior work, the carbonation of Ca(OH)2 is kinetically favored. Our structure studies suggest this is due to a facile reaction at the fractal interface of the particles. From early- to late-stage carbonation, there is a consistent increase in the fractal roughness. This is in contrast to Mg(OH)2 where the same surface evolves into a smooth conformal coating. For this material the major reacting component is at the mesoscale, suggesting globular particle growth or evolving macro-porosity. Because neutron scattering is sensitive to hydrogen content, we expected a significant change as M(OH)2 evolves to MCO3. Such a change is found for Ca(OH)2 but not for Mg(OH)2, providing evidence for the formation of hydrated carbonates for the later material. The formation of a conformal layer along with water-rich carbonate formation is an impediment to the use of Mg(OH)2 for carbon capture. For energy-efficient carbon capture, it would be desirable to enhance carbonation rates for Mg(OH)2, and one possible route would be the use of anhydrous fluids.

UR - https://www.scopus.com/pages/publications/86000729211

U2 - 10.1021/acs.energyfuels.4c05924

DO - 10.1021/acs.energyfuels.4c05924

M3 - Article

AN - SCOPUS:86000729211

SN - 0887-0624

VL - 39

SP - 4866

EP - 4879

JO - Energy and Fuels

JF - Energy and Fuels

IS - 10

ER -

Carbonation of Alkaline Earth Metal Hydroxides: Structure across Nano- to Mesoscales

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