Tipping Point for Expansion of Layered Aluminosilicates in Weakly Polar Solvents: Supercritical CO₂

Abstract

Layered aluminosilicates play a dominant role in the mechanical and gas storage properties of the subsurface, are used in diverse industrial applications, and serve as model materials for understanding solvent-ion-support systems. Although expansion in the presence of HO is well-known to be systematically correlated with the hydration free energy of the interlayer cation, particularly in environments dominated by nonpolar solvents (i.e., CO), uptake into the interlayer is not well-understood. Using novel high-pressure capabilities, we investigated the interaction of dry supercritical CO with Na-, NH-, and Cs-saturated montmorillonite, comparing results with predictions from molecular dynamics simulations. Despite the known trend in HO and that cation solvation energies in CO suggest a stronger interaction with Na, both the NH- and Cs-clays readily absorbed CO and expanded, while the Na-clay did not. The apparent inertness of the Na-clay was not due to kinetics, as experiments seeking a stable expanded state showed that none exists. Molecular dynamics simulations revealed a large endothermicity to CO intercalation in the Na-clay but little or no energy barrier for the NH- and Cs-clays. Indeed, the combination of experiment and theory clearly demonstrate that CO intercalation of Na-montmorillonite clays is prohibited in the absence of HO. Consequently, we have shown for the first time that in the presence of a low dielectric constant, gas swelling depends more on the strength of the interaction between the interlayer cation and aluminosilicate sheets and less on that with solvent. The finding suggests a distinct regime in layered aluminosilicate swelling behavior triggered by low solvent polarizability, with important implications in geomechanics, storage, and retention of volatile gases, and across industrial uses in gelling, decoloring, heterogeneous catalysis, and semipermeable reactive barriers.

Understanding methane/carbon dioxide partitioning in clay nano- and meso-pores with constant reservoir composition molecular dynamics modeling

“…These results are in good agreement with recent experimental and simulation studies that show that the basal spacing required for CO 2 intercalation in the interlayer galleries of smectite clays is less than for CH 4 due to steric effects. 6,31,32,38,39 At a pore thicknesses of 7.5 Å some CH 4 enters the pore, and the CO 2 /CH 4 ratio decreases rapidly with increasing pore thickness up to 33.0 Å ( Fig. 2a).…”

“…This structuring is consistent with the well-known ability of CO 2 to enter smectite clay interlayers. 6,[20][21][22][23][24][25][26][27][28][31][32][33][34]37,38,40 In contrast, the lack of structuring in the CH 4 peak nearest the surface and the equal distances between the three layers suggest that these molecules are interacting much more weakly with the surfaces and behave like hard spheres with the layers packed on one top of each other. This conclusion is consistent with the incorporation of CH 4 into the interlayer galleries of expandable clays occurring by a passive, space filling mechanism with basal spacings similar to 7.5 Å.…”

“…The results are in good agreement with previous experimental and computational, high T and P studies that show that there can be an energetic driving force for CO 2 incorporation in the interlayer galleries of expandable clay minerals, whereas CH 4 enters these spaces by a passive, space filling mechanism. 6,31,32,38,39,49 The thickness of the surface layer in which the fluid is structured (B15 Å) is similar to that in which H 2 O is structured on oxide and hydroxide surfaces, 72,73 suggesting that computational modeling of geochemically relevant fluids in nano-and mesopores bounded by such materials need only include pores with thicknesses less than a few nm to capture the essential features of their behavior. The results parallel the preference of other inorganic shale components (e.g., calcite and quartz) for CO 2 relative to CH 4 , suggesting that for oxide and oxysalt materials, CH 4 adsorption is relatively weak and its filling of pores bounded by them occurs by a passive, space filling mechanism.…”

“…The interactions among fluid species such as water, carbon dioxide and methane confined in nano-and meso-pores in shales and other rocks is of central concern to understanding the chemical behavior and transport properties of these species in the earth's subsurface and is of special concern to geological C-sequestration and enhanced production of oil and natural gas. [1][2][3][4][5][6] The behavior of water and cations at mineral surfaces and in the interlayer galleries of expandable clays (smectites) has been studied experimentally and computationally for many years, [7][8][9][10][11][12][13][14][15][16][17][18][19] and more recently there has been increased interest in carbon dioxide and hydrocarbons. The mutual interactions between CO 2 and CH 4 in nano-and meso-scale confinement, however, remain poorly understood.…”

Competitive Adsorption of H2O and CO2 in 2-Dimensional Nanoconfinement: GCMD Simulations of Cs- and Ca-Hectorites

“…41,42 We address this gap here by examining the intercalation behavior of H2O and CO2 in hectorite containing a cation with a low hydration energy (Cs + ) and one with a high hydration energy (Ca 2+ ) at 323 K and 90 bar in equilibrium with H2O-saturated scCO2 using GCMD simulations. [40][41][42] Cs + and Ca 2+ are representative of cations with greatly different hydration energies and charge/radius ratios, 48,53,58 and they have greatly different CO2/H2O intercalation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 behavior. 17 The results here are in excellent agreement with experimental data of Bowers et al 17 and provide a basis for their detailed molecular scale structural, dynamic, and energetic interpretation and understanding.…”