Realizing the impact of the intermediate layer structure on the CO₂/CH₄ separation performance of carbon molecular sieving membranes: Insights from experimental synthesis and molecular simulation

This work is a continuation of our previous study investigating the role of the intermediate layer in carbon molecular sieve membrane (CMSM) formation and its impact on the gas separation performance. Herein, the effect of key preparation variables of CMS/TiO₂ membrane prepared from the polyetherimide (PEI) precursor on the membrane's structure and CO₂/CH₄ separation quality was studied. A set of CMS/TiO₂/Al₂O₃ membranes produced under different conditions (pH of the sol-gel for the intermediate TiO₂ layer preparation, the TiO₂ interlayer thickness and the carbon separation layer thickness) was prepared, characterized by the AFM, FE-SEM and EDXS methods and tested for CO₂/CH₄ separation efficiency. In addition, a molecular simulation was applied to investigate the effect of intermediate TiO₂ layer.All prepared membranes had good separation quality (the separation factor between 37 and 65). The best results for membranes with the thickest TiO₂ interlayer prepared at pH = 5 were identified; notably, membrane samples with the thin defect free carbon separation layer achieved the best balance of permeance vs. selectivity and exceeded the Robeson upper bound. The molecular simulation results support the finding of the intermediate layer plays a vital role for the synthesis of gas separation membranes.