In Situ Molecular Spectroscopic Evidence for CO₂ Intercalation into Montmorillonite in Supercritical Carbon Dioxide

Abstract

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.

FT-IR study of CO2 interaction with Na+ exchanged montmorillonite

“…Further, they found that CO 2 intercalation into dehydrated smectite results in layer expansion, with d 001 value expanding from 10.0 Å to 12.3 Å for Na + -Mt clay mineral exposed to 700 Torr CO 2 at −48°C. This latter result has been demonstrated at PT conditions relevant to CCUS with direct evidence by Rother et al (2013) based on neutron diffraction analyses and by Loring et al (2012) using XRD, MAS NMR, and in situ high pressure ATR-IR on ion-exchanged versions of Mt STx-1 with less than one monolayer of hydration in the interlayer space. Rother et al (2013) used a sodium-exchanged sample (Na + -STx-1) and Loring et al (2012) used a calcium exchanged sample (Ca ++ -STx-1).…”

“…This latter result has been demonstrated at PT conditions relevant to CCUS with direct evidence by Rother et al (2013) based on neutron diffraction analyses and by Loring et al (2012) using XRD, MAS NMR, and in situ high pressure ATR-IR on ion-exchanged versions of Mt STx-1 with less than one monolayer of hydration in the interlayer space. Rother et al (2013) used a sodium-exchanged sample (Na + -STx-1) and Loring et al (2012) used a calcium exchanged sample (Ca ++ -STx-1). Approximately 70-80% of the layer charge for STx-1 derives from the octahedral sheet, based on analysis of Mg exchange data in Van Olphen and Fripiat (1979) and Jaynes and Bigham (1987).…”

“…The interaction of CO 2 with Na + -STx-1 was investigated at pressures up to 5.9 MPa, a range that lies between CO 2 pressures of b120 Torr (b0.016 MPa) and 9 MPa explored in previous FTIR studies on clay mineral-CO 2 interaction (Fripiat et al, 1974;Loring et al, 2012Loring et al, , 2014. Further, Giesting et al (2012) reported that d 001 value remained unchanged for Na + -Mt (SWy-2) at pressures above 5 MPa PCO 2 , despite working at pressures up to 64 MPa; hence, in this study pressures below 5.9 MPa were targeted.…”

“…Specifically, hydrated and relatively dehydrated Na + -STx-1 were exposed to anhydrous CO 2 and monitored with Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) to discern mechanistic information for CO 2 interaction with the Na + -STx-1 and examine any CO 2 -induced perturbations in vibrational modes associated with interlayer water or the silicate framework. The interaction of CO 2 with Na-STx-1 was investigated at pressures up to 5.9 MPa, a range that lies between CO 2 pressures of b120 Torr (b0.016 MPa) (Fripiat et al, 1974) and 9 MPa (Loring et al, 2012(Loring et al, , 2014 explored in previous FTIR studies on clay mineral-CO 2 interaction.…”

On sorption and swelling of CO2 in clays

“…Permanent trapping of CO 2 in the interlayer of Naexchanged smectite (Na-SWy-2), potentially as carbonates, was also indicated in the work by Hur et al (2013) and Romanov (2013) from Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction data. However, CO 2 trapping in clays was not observed in a number of other studies: Krukowski et al (2015) using FTIR on Na-exchanged (Na-STx-1), and Schaef et al (2012) on Ca-exchanged (Ca-STx-1) Texasmontmorillonite using thermo gravimetric analysis, as well as Loring et al (2012), also on the same Caexchanged samples using a variety of methods, such as magic angle spinning nuclear magnetic resonance spectroscopy and attenuated total reflection infrared spectroscopy. These measurements were performed at 50°C and pressures up to 18 MPa.…”