Separation of SO₂ and NO₂ with the Zeolite Membrane: Molecular Simulation Insights into the Advantageous NO₂ Dimerization Effect

Abstract

NO2 and SO2, as valuable chemical feedstock, are worth being recycled from flue gases. The separation of NO2 and SO2 is a key process step to enable practical deployment. This work proposes SO2 separation from NO2 using 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 N2O4 on 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 SO2 based on dual-site interactions and significant reduction in NO2 adsorption 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 SO2 diffusion, and the impermeability of SSZ-13 to N2O4. The membrane permeability of each component was simulated, rendering a SO2/NO2 membrane separation factor of 26.34 which is much higher than adsorption equilibrium (6.9) and kinetic (2.2) counterparts. The key role of NO2–N2O4 dimerization in molecular sieving of SO2 from NO2 was addressed, providing a facile membrane separation strategy at room temperature.

Adsorption Mechanism of Benzene Alkylation System Catalyzed by an Acid Catalyst: Effect of Pressure

“…RDFs can be used to identify the probability of the presence of other particles at a distance of r away from a given reference particle. RDFs can be used to map the adsorption sites and help determine the adsorption mechanism. ,, …”

“…RDFs can be used to map the adsorption sites and help determine the adsorption mechanism. 16,19,20 Figure 9a,b shows RDFs of the COM of the adsorbates in an equimolar BEN/PRO system (COM BEN and COM PRO ) around the center of the SCs (Center SC ), denoted as COM BEN -Center SC and COM PRO -Center SC , respectively. At loadings below C-P, the RDFs of BEN and PRO show a single main peak at r = 4.1 and 3.7 Å, which represents the adsorption of adsorbents on the optimal S-site.…”

“…⟨Δ N ij ( r , r + Δ r )⟩ is the ensemble average of the numbers of j around i (from r to r + Δ r ), V is the volume of the simulated system, and N i and N j are the numbers of i and j . The adsorption properties are calculated in the adsorption module of the Material Studio software, which is widely used in competitive adsorption studies . For more details, see refs and .…”

“…The adsorption properties are calculated in the adsorption module of the Material Studio software, which is widely used in competitive adsorption studies . For more details, see refs and .…”