Evaluation of CH4/N2 separation performances on ultra-microporous FDCA-based MOFs using experimental and numerical methods

A comprehensive investigation was conducted to explore the adsorption behaviors of CH4 over N2 on ultramicroporous Al/Zr-FDCA frameworks, which were synthesized specifically using the eco-friendly and biosourced 2,5-furandicarboxylic acid (FDCA). Characterization results revealed that both Al-FDCA and Zr-FDCA exhibited similar specific surface area and surface groups, leading to comparable methane uptake per-unit mass at atmospheric pressure. However, the presence of Zr nodes generated ultra-micropores around 0.43 nm in size, leading to a pronounced affinity for CH4. Zr-FDCA demonstrated a higher CH4/N2 selectivity (8.90) calculated from the isotherms compared to Al-FDCA (3.86). Furthermore, breakthrough experiments indicated that under the same dynamic conditions, Zr-FDCA exhibited 1.5 times higher CH4 uptake per unit volume and 2.5 times higher CH4/N2 selectivity when compared to Al-FDCA. Initially, a four-step VPSA process was simulated to investigate the separation of CH4/N2 mixture, in which the effects of feed-gas flow rate, adsorption time, adsorption pressure, and desorption pressure in VPSA cycle were extensively evaluated to enhance the purity and recovery of methane. Subsequently, a six-step process was employed for further optimization, achieving a purity of 95.9 % and a recovery of 99.1 %. The obtained results demonstrated the reliability of the established model and highlighted the significant potential of Zr-FDCA for CH4/N2 separation.