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| Titel |
Carbon dioxide intercalation in Na- and Ca-exchanged montmorillonite |
| VerfasserIn |
Paul Giesting, Stephen Guggenheim, Augustus Koster van Groos, Andreas Busch |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049242
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| Zusammenfassung |
| Carbon capture and storage (CCS) is expected to mitigate anthropogenic CO2 emissions from
discrete CO2 sources, such as electric power stations. A widely considered CCS option is
underground geologic storage, and this requires, among other things, a reservoir confined by
an impermeable caprock. Because this caprock is commonly clay-dominated, understanding
the interactions between clay minerals, brines, and CO2 is essential for site selection for
long-term CO2 storage. Two types of high-pressure environmental chambers (HPECs)
developed at UIC were used for X-ray diffraction studies of Na- and Ca-exchanged
montmorillonite (CMS source clay SWy-2): a transmission mode HPEC (THPEC) and a
reflection mode HPEC (RHPEC).
The THPEC experiments used random powder aggregates of Na-exchanged SWy-2. The
clay was grain size sorted by sedimentation to select the fine fraction (< 2 μm), cation
exchanged, dried at 200oC, then stored in a desiccator. This was followed by exposure to
moist air for varying lengths of time to produce samples with different amounts of interlayer
H2O. Samples were then exposed to gaseous or supercritical CO2 and held at a temperature
of 40-45oC. The THPEC results show that the position and shape of the (001) peak
changed for most samples under low CO2 pressures (40-50 bars). This response to
CO2 is strongly related to the initial H2O content. For Na-exchanged SWy-2 with
an initial d(001) = ~10.5 Å, the peak position changes to ~12.25 Å. However,
nearly dry [d(001) = 10.10 Å] samples do not exhibit significant changes to the
(001) peak. Increasing pressure to P = 650 bars (supercritical) does not produce any
further significant changes to the (001) peak compared to the P = 50 bars (gaseous)
results.
The RHPEC experiments used fine fraction, Na- and Ca-exchanged SWy-2 in oriented
aggregates on glass slides, which were either stored in a desiccator or in a vessel above a
saturated salt solution. The RHPEC cannot be used above ~50 bars CO2 due to attenuation of
the X-rays by the pressurizing gas; these experiments were conducted at ambient T (~22oC).
The RHPEC results for NaSWy-2 and CaSWy-2 indicate that both expand under CO2 with a
non-monotonic dependence of CO2-induced expansion on the initial H2O content of the
interlayer. Expansion is minimal for near-dry samples and for samples with an initial d(001)
= ~12.5 Å, i.e., NaSWy-2 or CaSWy-2 having one “plane” of interlayer H2O. For
samples with a significantly different initial d(001), expansion of up to ~10% is
observed.
Financial support from Shell Exploration and Production B.V. and the National Science
Foundation (USA) is gratefully acknowledged. |
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