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Title: Role of Cations in CO 2 Adsorption, Dynamics, and Hydration in Smectite Clays under in Situ Supercritical CO 2 Conditions

Abstract

This paper explores the molecular-scale interactions between CO 2 and the representative smectite mineral hectorite under supercritical conditions (90 bar, 50°C) using novel in situ X-ray diffraction (XRD), infrared (IR) spectroscopy, and magic angle spinning (MAS) nuclear magnetic resonance (NMR) techniques. Particular emphasis is placed on understanding the roles of the smectite charge balancing cation (CBC) and H O in these interactions. The data show that supercritical CO 2 (scCO 2) can be adsorbed on external surfaces and in the confined interlayer spaces of hectorite at 50°C and 90 bar, with the uptake of CO 2 into the interlayer favored at low H 2O content and when the basal spacing is similar to a monolayer hydrate of hectorite (1WL, ~12.5 Å). These results are in agreement with published spectroscopic and molecular modeling data for the related smectite Na-montmorillonite.Charge balancing cations with small radii, large hydration energies, and low polarizabilities tend to scavenge H 2O from humid scCO 2 or retain the H 2O they held before scCO 2 exposure, swelling spontaneously to a bilayer hydrate (2WL) dominated state that largely prevents CO 2-ion interactions and influences the extent of CO 2 intercalation into the interlayer. In contrast, ions with largemore » radii, low hydration energies, and large polarizabilities more readily form close associations with CO 2 with the energetics enabling coexistence of CO 2 and H2O in the interlayer over a wide range of scCO 2 humidities. Integrating our results with those from molecular dynamics simulations of wet CO 2-bearing montmorillonites suggest that adsorbed CO 2 in 1WL-type interlayers is oriented with its long axis parallel to the clay sheets and experiences dynamics dominated by anisotropic rotation about the axis perpendicular to the CO 2 long axis at rates of at least ~105 Hz. If appreciable CO 2 is adsorbed in 2WL-type interlayers, it must experience a mean orientation and dynamic averaging affects that mimic the 1WL-type adsorption environment. External surface adsorbed CO 2 is dynamically similar to the 1WL case, but the CO 2 long axis samples a larger range of orientations with respect to the smectite surface and adopts a different mean angle between the long axis and the smectite surface. Our data also suggest that equilibrating hectorite with a largevolume of scCO 2 at 50°C and 90 bar leads to interlayer dehydration, with the extent of dehydration correlating with the hydrophilicity of the CBC.« less

Authors:
ORCiD logo; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Fossil Energy (FE)
OSTI Identifier:
1344031
Report Number(s):
PNNL-SA-122523
Journal ID: ISSN 1932-7447; 48812; KP1704020
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 1; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Environmental Molecular Sciences Laboratory

Citation Formats

Bowers, Geoffrey M., Schaef, H. Todd, Loring, John S., Hoyt, David W., Burton, Sarah D., Walter, Eric D., and Kirkpatrick, R. James. Role of Cations in CO 2 Adsorption, Dynamics, and Hydration in Smectite Clays under in Situ Supercritical CO 2 Conditions. United States: N. p., 2017. Web. doi:10.1021/acs.jpcc.6b11542.
Bowers, Geoffrey M., Schaef, H. Todd, Loring, John S., Hoyt, David W., Burton, Sarah D., Walter, Eric D., & Kirkpatrick, R. James. Role of Cations in CO 2 Adsorption, Dynamics, and Hydration in Smectite Clays under in Situ Supercritical CO 2 Conditions. United States. doi:10.1021/acs.jpcc.6b11542.
Bowers, Geoffrey M., Schaef, H. Todd, Loring, John S., Hoyt, David W., Burton, Sarah D., Walter, Eric D., and Kirkpatrick, R. James. Thu . "Role of Cations in CO 2 Adsorption, Dynamics, and Hydration in Smectite Clays under in Situ Supercritical CO 2 Conditions". United States. doi:10.1021/acs.jpcc.6b11542.
@article{osti_1344031,
title = {Role of Cations in CO 2 Adsorption, Dynamics, and Hydration in Smectite Clays under in Situ Supercritical CO 2 Conditions},
author = {Bowers, Geoffrey M. and Schaef, H. Todd and Loring, John S. and Hoyt, David W. and Burton, Sarah D. and Walter, Eric D. and Kirkpatrick, R. James},
abstractNote = {This paper explores the molecular-scale interactions between CO2 and the representative smectite mineral hectorite under supercritical conditions (90 bar, 50°C) using novel in situ X-ray diffraction (XRD), infrared (IR) spectroscopy, and magic angle spinning (MAS) nuclear magnetic resonance (NMR) techniques. Particular emphasis is placed on understanding the roles of the smectite charge balancing cation (CBC) and H O in these interactions. The data show that supercritical CO2 (scCO2) can be adsorbed on external surfaces and in the confined interlayer spaces of hectorite at 50°C and 90 bar, with the uptake of CO2 into the interlayer favored at low H2O content and when the basal spacing is similar to a monolayer hydrate of hectorite (1WL, ~12.5 Å). These results are in agreement with published spectroscopic and molecular modeling data for the related smectite Na-montmorillonite.Charge balancing cations with small radii, large hydration energies, and low polarizabilities tend to scavenge H2O from humid scCO2 or retain the H2O they held before scCO2 exposure, swelling spontaneously to a bilayer hydrate (2WL) dominated state that largely prevents CO2-ion interactions and influences the extent of CO2 intercalation into the interlayer. In contrast, ions with large radii, low hydration energies, and large polarizabilities more readily form close associations with CO2 with the energetics enabling coexistence of CO2 and H2O in the interlayer over a wide range of scCO2 humidities. Integrating our results with those from molecular dynamics simulations of wet CO2-bearing montmorillonites suggest that adsorbed CO2 in 1WL-type interlayers is oriented with its long axis parallel to the clay sheets and experiences dynamics dominated by anisotropic rotation about the axis perpendicular to the CO2 long axis at rates of at least ~105 Hz. If appreciable CO2 is adsorbed in 2WL-type interlayers, it must experience a mean orientation and dynamic averaging affects that mimic the 1WL-type adsorption environment. External surface adsorbed CO2 is dynamically similar to the 1WL case, but the CO2 long axis samples a larger range of orientations with respect to the smectite surface and adopts a different mean angle between the long axis and the smectite surface. Our data also suggest that equilibrating hectorite with a largevolume of scCO2 at 50°C and 90 bar leads to interlayer dehydration, with the extent of dehydration correlating with the hydrophilicity of the CBC.},
doi = {10.1021/acs.jpcc.6b11542},
journal = {Journal of Physical Chemistry. C},
issn = {1932-7447},
number = 1,
volume = 121,
place = {United States},
year = {2017},
month = {1}
}