Analysis of the gas transport resistance of CO₂ and CH₄ through ultra-thin DD3R zeolite membrane

Ultra-thin DD3R zeolite membranes exhibit excellent separation properties for CO₂ capture from natural gas, as well as the lower transmembrane resistance. However, the interfacial transport of permeation gas in such systems may dominate the whole separation process. In this work, we employed external force non-equilibrium molecular dynamic (EF-NEMD) simulation to predict the single-component permeabilities of CO₂ and CH₄ through a defect-free DD3R zeolite membrane at different pressured drops. By explicitly including the gas transport from bulk phase to zeolitic channels, the predicted results of EF-NEMD simulation showed good agreements with the reported experimental data. The contribution of interfacial resistance over the total transport resistance (R_inter/R_total) was further evaluated for the membranes with different thicknesses under temperatures between 273 K and 373 K. The results revealed a decrease in R_inter/R_total with increasing membrane thickness, leading to a reduction in CO₂/CH₄ selectivity, and the critical thickness (R_inter/R_total < 0.01) was determined to be approximately 300 nm at pressure of 1.0 MPa and temperature of 298 K. Similarly, the R_inter/R_total decreased with increasing temperature due to the augmentation in molecule kinetic energy. Furthermore, it was confirmed that the gas adsorption effect could expand the effective size of eight membered ring (8-MR) channels in DD3R zeolite membrane, thereby decreasing the CO₂/CH₄ selectivity, despite higher permeation fluxes. The above discoveries essentially benefit the design of the ultra-thin DD3R zeolite membrane through an understanding of CO₂ and CH₄ transport behaviors.