Understanding Separation Mechanisms and Recovery of Nitrous Oxide (N ₂ O) from Nitric Acid Plant Tail Gases Using Computational Molecular Modeling

Separation and recovery of nitrous oxide (N2O) from nitric acid tail gases is a pressing environmental challenge due to the dual role of N2O as a potent greenhouse gas and as the leading ozone-depleting substance. While catalytic destruction is the current industrial practice, it often lacks selectivity and generates secondary emissions, overlooking the added value of recovering N2O as a chemical feedstock. In this work, we employ atomistic nonequilibrium Molecular Dynamics (MD) simulations to investigate the selective retention and transport of N2O in zeolitic membranes. Three zeolite types all-silica Linde Type A (LTA), all-silica CDO-type zeolite, and calcium-exchanged Linde Type A (Ca-LTA, Si/Al = 1.0) were examined, and our results show that Ca-LTA exhibits superior recovery performance. Simulations were conducted across a wide range of temperatures (300–600 K) and pressures (100–932 atm) for equimolar binary, ternary, and quaternary mixtures, as well as five cases closely matching industrial gas composition (N2 mole fraction ≈ 0.4–0.8), providing direct insight into realistic operating conditions. Our results demonstrate that Ca-LTA retains N2O through strong interactions with Ca2+, while N2, NO, and NO2 permeate more readily. N2O permeation was negligible under most conditions, but trace breakthrough appeared in equimolar binary mixtures at 500 K, in ternary and quaternary mixtures at 450 K, and under industrial-like feeds with N2 mole fraction = 0.8 at 400 K, where only very few molecules of N2O permeated. In contrast, NO exhibited the highest mobility, while N2 and NO2 showed modest to intermediate permeability, both increasing systematically with temperature. Importantly, our results capture the experimentally observed transport behavior of pure gases in Ca-LTA membranes, and also predict the separation factors (SF), permeability, diffusion coefficients, and adsorption/permeation selectivity. Finally, our results provide the first molecular-level predictions for binary, ternary, quaternary, and industrial-composition mixtures in the absence of experimental data. Together, these findings establish Ca-LTA as a robust recovery medium for N2O, maintaining high selectivity across diverse feed compositions, ranging from simple gases to industrial-like mixtures, and aligning with experimental expectations for zeolitic membranes.