ATOMIC-LEVEL IMAGING OF CO2 DISPOSAL AS A CARBONATE MINERAL: OPTIMIZING REACTION PROCESS DESIGN
Fossil fuels, especially coal, can support the energy demands of the world for centuries to come, if the environmental problems associated with CO{sub 2} emissions can be overcome. Permanent and safe methods for CO{sub 2} capture and disposal/storage need to be developed. Mineralization of stationary-source CO{sub 2} emissions as carbonates can provide such safe capture and long-term sequestration. Mg(OH){sub 2} carbonation is a leading process candidate, which generates the stable naturally occurring mineral magnesite (MgCO{sub 3}) and water. Key to process cost and viability are the carbonation reaction rate and its degree of completion. This process, which involves simultaneous dehydroxylation and carbonation is very promising, but far from optimized. In order to optimize the dehydroxylation/carbonation process, an atomic-level understanding of the mechanisms involved is needed. Since Mg(OH){sub 2} dehydroxylation is intimately associated with the carbonation process, its mechanisms are also of direct interest in understanding and optimizing the process. In the first project year, our investigations have focused on developing an atomic-level understanding of the dehydroxylation/carbonation reaction mechanisms that govern the overall carbonation reaction process in well crystallized material. In years two and three, we will also explore the roles of crystalline defects and impurities. Environmental-cell, dynamic high-resolution transmission electron microscopy has been used to directly observe the dehydroxylation process at the atomic-level for the first time. These observations were combined with advanced computational modeling studies to better elucidate the atomic-level process. These studies were combined with direct carbonation studies to better elucidate dehydroxylation/carbonation reaction mechanisms. Dehydroxylation follows a lamellar nucleation and growth process involving oxide layer formation. These layers form lamellar oxyhydroxide regions, which can grow both parallel and perpendicular to the Mg(OH){sub 2} lamella. The number of oxide layers within the regions increases as they grow during dehydroxylation. Selected area diffraction suggests a novel two-dimensional variant of Vegard's law can describe the oxyhydroxide regions, with intralamellar Mg-Mg packing distances observed between those known for Mg(OH){sub 2} and MgO. Intralamellar and interlamellar elastic stress induced during dehydroxylation can contribute to crystallite cracking and MgO surface reconstruction, which may serve to enhance carbonation reactivity. The observed dehydroxylation process indicates a range of candidate materials for carbonation may be present during the carbonation process (i) the hydroxide, (ii) a range of intermediate oxyhydroxides, and (iii) the oxide, potentially in more-reactive, very small particle size form. Partial carbonation of single-crystal Mg(OH){sub 2} fragments over a wide range of reaction conditions (varying CO{sub 2} pressure and temperature) shows a linear or near-linear correlation between carbonation and dehydroxylation, with the extent of dehydroxylation substantially greater than the extent of carbonation. This suggests carbonation primarily occurs via intermediate oxyhydroxide or oxide formation. The range and type of intermediate oxyhydroxides/oxides that can form in advance of carbonation should provide a degree of control over both their formation and the overall reactivity observed for the carbonation process.
- Research Organization:
- Federal Energy Technology Center Morgantown (FETC-MGN), Morgantown, WV (United States); Federal Energy Technology Center Pittsburgh (FETC-PGH), Pittsburgh, PA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- FG26-98FT40112
- OSTI ID:
- 778329
- Report Number(s):
- FG26-98FT40112-01; TRN: US200301%%401
- Resource Relation:
- Other Information: PBD: 1 Sep 1999
- Country of Publication:
- United States
- Language:
- English
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ATOMIC-LEVEL MODELING OF CO2 DISPOSAL AS A CARBONATE MINERAL: A SYNERGETIC APPROACH TO OPTIMIZING REACTION PROCESS DESIGN
ATOMIC-LEVEL IMAGING OF CO2 DISPOSAL AS A CARBONATE MINERAL: OPTIMIZING REACTION PROCESS DESIGN