Exploration of Capturing CO2 from Flue Gas by Calcite Slit-Nanopores: A Computational Investigation

Capturing CO2 from flue gas is recognized as a key process to improve the environment, therefore, developing a new cost-effective sorbent is crucial. In this study, the calcite slit-nanopores with various pore sizes ranging from similar to 5 angstrom to similar to 30 angstrom were constructed, the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods were used to examine the microscopic behaviors of CO2 and N-2 in calcite slit-nanopores. Diverse adsorption layer structures for CO2 and N-2 molecules as single component in calcite slit-nanopores are found as the pore size changing, of which the CO2 represents a transformation from single adsorption layer to five adsorption layers, while N-2 represents a variation from single adsorption layer to three adsorption layers. Meantime, different adsorption orientations of CO2 and N-2 molecules adsorbed close onto the calcite pore surface are also found. Moreover, strong competitive adsorption of CO2 over N-2 is found due to the different interactions between CO2 and N-2 molecules with the calcite pore surface, the capacity of competitive adsorption decreases with the pore size increasing. The self-diffusion and isosteric heat of CO2 and N-2 molecules in calcite slit-nanopores are also examined to demonstrate the different adsorption intensities of gases in calcite slit-nanopores. This work demonstrates the detailed microscopic behaviors of CO2 and N-2 molecules in calcite slit-nanopores, which not only enriches the theoretical knowledge about gases adsorption in calcite slit-nanopores, but also gives out the feasibility of capturing CO2 from flue gas by calcite-based substances.