(346c) Molecular Simulations of H2 and CO2 Intercalation into Montmorillonite Interlayers in a Geological Gas Storage

CO₂ capture and geological sequestration have been considered important strategies to reduce the greenhouse gas effect. Meanwhile, H₂ produced from water using renewable energy and stored underground will be important components in a H₂ supply chain in a future H₂-based economy. When injected into a reservoir, gas interacts with earth materials that might impact the safety and economic feasibility of a storage. In this talk, we will discuss gas intercalation into smectite that is present in caprock. Intercalation traps CO₂, thus improving CO₂ storage integrity. However, intercalation causes H₂ loss. Using molecular dynamics (MD) simulation, we calculate free energy landscapes of gas intercalation into montmorillonite interlayers as a function of structural charge distributions and interlayer hydration states. Our results reveal that hydrated clay interlayers promote gas uptake into the hydrophobic (e.g., siloxane groups) domain, while inhibiting gas sorption near the hydrophilic sites (e.g., charge sites). On average, the CO₂/water ratio in interlayers is higher than CO₂/water ratio in bulk water. However, H₂/water ratio in interlayers is comparable or less than H₂/water ratio in bulk water. Compared to CO₂, the amount of H₂ intercalated into hydrated interlayers is about one to two orders of magnitude smaller. Our results qualitatively predict that H₂ loss due to intercalation into clay-rich caprock and leak through clay interlayers, if any, is limited.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.