Microstructural response of variably hydrated Ca-rich montmorillonite to supercritical CO2.
First-principles molecular dynamics simulations were carried out to explore the mechanistic and thermodynamic ramifications of the exposure of variably hydrated Ca-rich montmorillonites to supercritical CO2 and CO2-SO2 mixtures under geologic storage conditions. In sub- to single-hydrated systems (≤ 1W), CO2 intercalation causes interlamellar expansion of 8-12%, while systems transitioning to 2W may undergo contraction (∼ 7%) or remain almost unchanged. When compared to ∼2W hydration state, structural analysis of the ≤ 1W systems, reveals more Ca-CO2 contacts and partial transition to vertically confined CO2 molecules. Infrared spectra and projected vibrational frequency analysis imply that intercalated Ca-bound CO2 are vibrationally constrained and contribute to the higher frequencies of the asymmetric stretch band. Reduced diffusion coefficients of intercalated H2O and CO2 (10(-6)-10(-7) cm(2)/s) indicate that Ca-montmorillonites in ∼ 1W hydration states can be more efficient in capturing CO2. Simulations including SO2 imply that ∼ 0.66 mmol SO2/g clay can be intercalated without other significant structural changes. SO2 is likely to divert H2O away from the cations, promoting Ca-CO2 interactions and CO2 capture by further reducing CO2 diffusion (10(-8) cm(2)/s). Vibrational bands at ∼ 1267 or 1155 cm(-1) may be used to identify the chemical state (oxidation states +4 or +6, respectively) and the fate of sulfur contaminants.
Fundamental and Computational Sciences, ‡Energy and Environment, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
Mal-Soon
MS
Lee
B Peter
BP
McGrail
Vassiliki-Alexandra
VA
Glezakou
D000538:Aluminum Silicates / Q000737:chemistry*; D001546:Bentonite / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D000077215:Clay; D004058:Diffusion; D005844:Geology; D013458:Sulfur Dioxide / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D000538:Aluminum Silicates; D014867:Water; D013458:Sulfur Dioxide; D001546:Bentonite; D002245:Carbon Dioxide; D000077215:Clay