The efficient separation of O₂ from N₂ is important for a number of applications. For example, replacing air with oxygen enriched air during combustion serves the dual purpose of eliminating toxic nitrogen oxides and simplifying carbon dioxide capture and recovery. However, separating these gases, typically using cryogenic distillation, has a high energy requirement. Membranes may be able to perform this separation at a greatly reduced energy cost compared to distillation. While polymer membranes are limited by the Robeson upper bound, molecular sieving-based membranes are ineffective for air separation due to similarity in sizes and masses of nitrogen and oxygen gases. In this talk, I will show results employing atomistic modeling to predict the permeation behavior of the two gases through a nanoporous graphene membrane, while artificially tuning the adsorption energy of oxygen onto the membrane while keeping that of nitrogen fixed. We observed increased O₂/N₂ selectivity solely resulting from adsorption energy differences, with oxygen permeability dependent on the oxygen desorption rate. To ensure optimal oxygen permeability at ambient conditions, we explored materials for which oxygen desorption occurs at ambient temperatures. In particular, for two transition metal oxides, Fe₂O₃ and Co₃O₄, density functional theory calculations confirmed that the adsorption energies of O₂ and N₂ on these metal oxides fall in the optimal regime for efficient separation, enabling such materials to function as adsorption-based pore-flow membranes for air separation. Creation of metal oxide-based gas transport membranes with precise pore sizes may therefore be an interesting avenue for future experimentation.

David Bergsman

Appearances