August F. Koster van Groos

X-ray Diffraction Study of K- and Ca-Exchanged Montmorillonites in CO2 Atmospheres

Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting with CO(2) at ambient temperatures, depending on their initial hydration state. K-exchanged montmorillonite swells rapidly to a maximum d(001) of ∼12.2 Å. In contrast, Ca-exchanged montmorillonite swells more slowly, but reaches a maximum d(001) of ∼15.1 Å. Reaction kinetics differ significantly between the K- and Ca-exchanged montmorillonite complexes. Expansion of K-exchanged montmorillonite samples was rapid, occurring on time scales of tens of minutes or less. The Ca-exchanged montmorillonite samples continued to expand over periods up to 42 h. Aging of both K- and Ca-exchanged montmorillonite complexes at elevated CO(2) pressure for 1-2 days resulted in greater stability when CO(2) pressure was released. The observed intercalation reactions have important consequences for carbon sequestration: (1) CO(2) absorption by swelling clays may represent a significant pathway for storage of CO(2). (2) The swelling of smectites under CO(2) pressure may have a significant impact on the permeability of caprock formations.

New gas-hydrate phase: Synthesis and stability of clay–methane hydrate intercalate

Intercalated Na-rich montmorillonite-methane hydrate was synthesized for the first time. The upper limit of stability for the intercalate in pressure and temperature is parallel to that of methane hydrate but at temperatures that are ∼0.5-1 °C lower than for methane hydrate. The low-temperature stability of the intercalate is at -11.5 ′ 3 °C at ∼40 bar, where methane and some H 2 O are expelled from the region between the silicate layers (interlayer). In contrast, methane hydrates do not dissociate at these low temperatures. We conclude that at conditions similar to where methane hydrate is stable, smectite may intercalate with methane hydrate and provide additional sinks for methane. The limitation in the stability of smectite-methane hydrate intercalate at low temperatures suggests that, if present in large quantities, it may release at decreasing temperatures sufficient methane to ameliorate a planetary cooling event.

Bond energy of adsorbed and interlayer water; kerolite dehydration at elevated pressures

The dehydration reaction of kerolite was investigated using high-pressure differential thermal analysis at pressures as high as 600 bars. The peak associated with the dehydration is broad, suggesting the presence of a series of overlapping reactions ranging from the release of adsorbed water to interlayer water. The peak temperature is 136°C at 1.8 bars and increases to 516°C at 586 bars. The primary reaction represents loss of adsorbed water having a bond energy of 1.5 ± 1 kJ/mole. A small amount of water may be present as interlayer water and has a bond energy of 7.5 ± 3 kJ/mole.