Effective Adsorption Separation of n‑Hexane/2-Methylpentane in Facilely Synthesized Zeolitic Imidazolate Frameworks ZIF‑8 and ZIF-69

A facile synthesis procedure was built to synthesize zeolitic imidazolate frameworks (ZIFs) ZIF-8 and ZIF-69 under ambient conditions with the prevention of organic solvents. ZIF-69 adsorbent was first introduced in the liquid-phase separation of hexane isomers. A sieving test was carried out using samples of n-hexane (nHEX) or 2-methylpentane (2MP) over two ZIFs and commercial 5A zeolite materials. According to batch adsorption performances and modeling, ZIF-8 exhibits the highest adsorption selectivity and capacity for nHEX, followed by ZIF-69 and 5A zeolite. The equilibrium data at 25 °C show that a significant amount (0.51 g/g) of nHEX and only 0.09 g/g 2MP can be adsorbed in ZIF-8. And the maximum adsorption capacity of nHEX and 2MP on ZIF-69 are 0.34 g/g and 0.10 g/g, respectively. Breakthrough experiments performed at 150 °C with a binary mixture of nHEX/2MP confirm the shape selectivity and adsorption capacities of ZIF-8 toward nHEX at various total pressures from 0.5 to 1.3 MPa and with different feed concentrations, which is attributed to the flexible architecture of ZIF-8 and its excellent shape match with nHEX.