Improved propylene/propane separation performance under high temperature and pressures on in-situ ligand-doped ZIF-8 membranes

Metal-organic frameworks (MOFs) used as molecular sieve membranes materials to gas separation has attracted much attention. However, the separation performance was also limited by its intrinsic flexibility of frameworks. Controlling its flexibility is still a big challenge. Herein, the doping of 2-aminobenzimidazole (ambz) into the ZIF-8 framework can obviously improve its original rigidity, which is due to the improved rigidity of the Zn‒N bond. Correspondingly, the high-quality doped ZIF-8 membrane for effective separation of C₃H₆/C₃H₈ mixture were also fabricated. Compared with the permeation results on pure ZIF-8 membranes, the ambz-doped ZIF-8 membrane exhibited two specific transportation performance improvements. The first was that drop extent of C₃H₆/C₃H₈ selectivity on the doped ZIF-8 membrane with the increase in feeding pressure was decreased, and the selectivity was also irreversible as the feeding pressure was released. This phenomenon was attributed to improved rigidity of the framework. The second was that the C₃H₆ permeance was almost independent on the permeating temperature, which was also totally different with that on the pure ZIF-8 membrane, resulting from the significant change of adsorptive heat and diffusion energy of propylene on the ambz-doped ZIF-8 membrane. Therefore, this ambz-doped ZIF-8 membrane is promising in real world C₃H₆/C₃H₈ separation.