Molecular simulation of swelling and structure for Na-Wyoming montmorillonite in supercritical CO2

Intercalation and retention of carbon dioxide in a smectite clay promoted by interlayer cations

A good material for CO₂ capture should possess some specific properties: (i) a large effective surface area with good adsorption capacity, (ii) selectivity for CO₂, (iii) regeneration capacity with minimum energy input, allowing reutilization of the material for CO₂ adsorption, and (iv) low cost and high environmental friendliness. Smectite clays are layered nanoporous materials that may be good candidates in this context. Here we report experiments which show that gaseous CO₂ intercalates into the interlayer nano-space of smectite clay (synthetic fluorohectorite) at conditions close to ambient. The rate of intercalation, as well as the retention ability of CO₂ was found to be strongly dependent on the type of the interlayer cation, which in the present case is Li⁺, Na⁺ or Ni²⁺. Interestingly, we observe that the smectite Li-fluorohectorite is able to retain CO₂ up to a temperature of 35°C at ambient pressure, and that the captured CO₂ can be released by heating above this temperature. Our estimates indicate that smectite clays, even with the standard cations analyzed here, can capture an amount of CO₂ comparable to other materials studied in this context.

Biotite dissolution in brine at varied temperatures and CO2 pressures: its activation energy and potential CO2 intercalation

For sustainable geologic CO(2) sequestration (GCS), it is important to understand the effects of temperature and CO(2) pressure on mica's dissolution and surface morphological changes under saline hydrothermal conditions. Batch experiments were conducted with biotite (Fe-end member mica) under conditions relevant to GCS sites (35-95 °C and 75-120 atm CO(2)), and 1 M NaCl solution was used to mimic the brine. With increasing temperature, a transition from incongruent to congruent dissolution of biotite was observed. The dissolution activation energy based on Si release was calculated to be 52 ± 5 kJ mol(-1). By comparison with N(2) experiments, we showed that CO(2) injection greatly enhanced biotite's dissolution and its surface morphology evolutions, such as crack formation and detachment of newly formed fibrous illite. For biotite's dissolution and morphological evolutions, the pH effects of CO(2) were differentiated from the effects of bicarbonate complexation and CO(2) intercalation. Bicarbonate complexation effects on ion release from biotite were found to be minor under our experimental conditions. On the other hand, the CO(2) molecules in brine could get into the biotite interlayer and cause enhanced swelling of the biotite interlayer and hence the observed promotion of biotite surface cracking. The cracking created more reactive surface area in contact with brine and thus enhanced the later ion release from biotite. These results provide new information for understanding CO(2)-brine-mica interactions in saline aquifers with varied temperatures and CO(2) pressures, which can be useful for GCS site selection and operations.

In situ molecular spectroscopic evidence for CO2 intercalation into montmorillonite in supercritical carbon dioxide

The interaction of anhydrous supercritical CO(2) (scCO(2)) with both kaolinite and ~1W (i.e., close to but less than one layer of hydration) calcium-saturated montmorillonite was investigated under conditions relevant to geologic carbon sequestration (50 °C and 90 bar). The CO(2) molecular environment was probed in situ using a combination of three novel high-pressure techniques: X-ray diffraction, magic angle spinning nuclear magnetic resonance spectroscopy, and attenuated total reflection infrared spectroscopy. We report the first direct evidence that the expansion of montmorillonite under scCO(2) conditions is due to CO(2) migration into the interlayer. Intercalated CO(2) molecules are rotationally constrained and do not appear to react with waters to form bicarbonate or carbonic acid. In contrast, CO(2) does not intercalate into kaolinite. The findings show that predicting the seal integrity of caprock will have complex dependence on clay mineralogy and hydration state.