Hybrid ad(b)sorption for CO₂ capture

The rising levels of CO₂ in the atmosphere, leading to climate change, are a major threat to humans in the 21st century. The majority of CO₂ emissions are from the combustion of fossil fuels for energy generation. Capturing CO₂ from the outlet stream of a fossil fuel-based combustion process to mitigate environmental impact is therefore a major part of energy generation processes. The separation of CO₂ from the outlet gas of such processes requires materials with high affinity for CO_2. The current state-of-the-art technology used is amine scrubbing, which uses an absorption processes with a liquid catalyst to capture CO₂. However, this technology is energy-intensive as it requires heating to regenerate the catalyst. Solid materials like Metal-Organic frameworks (MOFs)—a class of nanoporous materials consisting of metal ions coordinated with organic ligands—are considered good candidates for CO₂ separation and require significantly lower heating costs. While MOFs are efficient at capturing CO₂, adsorption on a solid is not favored in continuous processes as solids cannot be pumped. Thus, fluidized catalysts are preferred for such applications. In this project, we consider a slurry, as shown in Figure 1, of glycol and Zeolitic-Imidazolate-Framework-8 (ZIF-8), a MOF, as a medium for a hybrid absorption-adsorption process.¹ While early experimental studies have found this hybrid to be more effective than the individual media, the exact mechanism is not well understood. We use molecular dynamics (MD) simulations to study the mechanism of the diffusion of CO₂ into this mixture as well as to simulate whether glycol molecules enter the framework and identify the sites of CO₂ accumulation. These insights would enable us to design hybrid systems for the separation of CO₂.