Separation of Carbon Isotopes in Methane with Nanoporous Materials

Traditional methods for carbon isotope separation are mostly based on macroscopic procedures such as cryogenic distillation and thermal diffusion of various gaseous compounds through porous membranes. Recent development in nanoporous materials renders opportunities for more effective fractionation of carbon isotopes by tailoring the pore size and the local chemical composition at the atomic scale. Herein we report a theoretical analysis of metal-organic frameworks (MOFs) for separation of carbon isotopes in methane over a broad range of conditions. Using the classical density functional theory in combination with the excess-entropy scaling method and the transition-state theory, we predict the adsorption isotherms, gas diffusivities, and isotopic selectivity corresponding to both adsorption- and membrane-based separation processes for a number of MOFs with large methane adsorption capacity. We find that nanoporous materials enable much more efficient separation of isotopic methanes than conventional methods and allow for operation at ambient thermodynamic conditions. MOFs promising for adsorption- and membrane-based separation processes have also been identified according to their theoretical selectivity for different pairs of carbon-isotopic methanes.