Separation of SO₂and NO₂with the Zeolite Membrane: Molecular Simulation Insights into the Advantageous NO₂Dimerization Effect

NO₂and SO₂, as valuable chemical feedstock, are worth being recycled from flue gases. The separation of NO₂and SO₂is a key process step to enable practical deployment. This work proposes SO₂separation from NO₂using chabazite zeolite (SSZ-13) membranes and provides insights into the feasibility and advantages of this process using molecular simulation. Grand canonical ensemble Monte Carlo and equilibrium molecular dynamics methods were respectively adopted to simulate the adsorption equilibria and diffusion of SO₂, NO₂, and N₂O₄on SSZ-13 at varying Si/Al (1, 5, 11, 71, +∞), temperatures (248-348 K), and pressures (0-100 kPa). The adsorption capacity and affinity (SO₂> N₂O₄> NO₂) demonstrated strong competitive adsorption of SO₂based on dual-site interactions and significant reduction in NO₂adsorption due to dimerization in the ternary gas mixture. The simulated order of diffusivity (NO₂> SO₂> N₂O₄) on SSZ-13 demonstrated rapid transport of NO₂, strong temperature dependence of SO₂diffusion, and the impermeability of SSZ-13 to N₂O₄. The membrane permeability of each component was simulated, rendering a SO₂/NO₂membrane separation factor of 26.34 which is much higher than adsorption equilibrium (6.9) and kinetic (2.2) counterparts. The key role of NO₂-N₂O₄dimerization in molecular sieving of SO₂from NO₂was addressed, providing a facile membrane separation strategy at room temperature.