Competitive sorption of CO2 and H2O in 2:1 layer phyllosilicates

Abstract

Expandable clays such as montmorillonite have interlayer exchange sites whose hydration state can be systematically varied from near anhydrous to almost bulk-like water conditions. This phenomenon has new significance with the simultaneous implementation of geological sequestration and secondary utilization of CO 2 to both mitigate climate warming and enhance extraction of methane from hydrated clay-rich formations. In this study, the partitioning of CO 2 a n d H 2 O between Na-, Ca-, and Mg-exchanged montmorillonite and variably hydrated supercritical CO 2 (scCO 2 ) was investigated using in situ X-ray diffraction (HXRD), infrared (IR) spectroscopic titrations, and quartz crystal microbalance (QCM) measurements. Density functional theory calculations provided mechanistic insights. Structural volumetric changes were correlated to quantified changes in sorbed H 2 O and CO 2 concentrations as a function of percent H 2 O saturation in scCO 2 . Intercalation of CO 2 is inhibited when the clay is fully collapsed (dehydrated interlayer), peaks sharply with the introduction of some H 2 O and partial expansion of the interlayer region, and then decreases systematically with further hydration of the clay. This behavior is discussed in the context of recent theoretical calculations of the montmorillonite H 2 O-CO 2 system.

On sorption and swelling of CO2 in clays

“…In a very recent study Schaef et al (2015) demonstrated, using XRD, IR and quartz crystal microbalance (QCM) on variably hydrated Ca-SWy2, that the swelling depends on the relative amounts of H 2 O and CO 2 in the interlayer. The interlayer space of dry smectite increases sharply upon introduction of some water, and decreases again upon further hydration of the clay.…”

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

“…Adsorption/absorption is reported when the mechanism is not clear. However, recent work suggests that absorption into the interlayer is the dominant process particularly at lower pressures below the critical point (Schaef et al, 2015). Spectra were collected until the CO 2 adsorption/absorption bands no longer changed with time.…”

Supercritical Carbon Dioxide at Smectite Mineral–Water Interfaces: Molecular Dynamics and Adaptive Biasing Force Investigation of CO2/H2O Mixtures Nanoconfined in Na-Montmorillonite

“…[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][52][53][54][55][56] With respect to confinement of hydrophobic species, the 2-dimensional interlayer galleries of expandable clays are known to accommodate CO 2 . 6,[18][19][20][21]23,26,38,[57][58][59][60][61][62][63][64] Owing to their natural abundance, environmental friendliness, large internal surface areas, and tunable affinity and specificity for adsorption of small and complex molecules, 37-45,53-56 the expandable clay minerals continue to serve as ideal models for understanding the behavior of hydrophilic and hydrophobic species in …”

“…[18][19][20][21][22][23][24][25][26][27][28][29]58 For instance, Schaef et. al., 62 estimated the amount of CO 2 in the interlayer of dry sodium montmorillonite (Na-MMT) using quartz crystal microbalance (QCM) measurements while Loring et. al., 20 examined the hydration-dependent variation of the IR-derived integrated absorbance of the asymmetric CO stretching band of the interlayer CO 2 molecules to quantify the amount of CO 2 in the interlayer of Na-MMT at 50 0 C and 90 bar.…”

“…In bulk CO 2 /H 2 O mixtures with low water content, the H 2 O molecules are present as monomers coordinated by CO 2 at temperatures below 373 K at 250 bar pressure. 83 The MD simulations use the CLAYFF 75 force field for the host clay, the SPC 90 model for water, and the parameters for CO 2 developed by Cygan et al 57 The simulations were performed in the NPT ensemble at a temperature of 323 K and a pressure of 89 bar consistent with the experimental conditions 18,20,23,24,26,62,63 using a Langevin thermostat and barostat 91 with a damping coefficient of 5 ps -1 using NAMD 2.9. 92 Periodic boundary conditions were applied.…”