Length exclusion separation of acetone/butanol using ZIF-302 derivatives with adjustable ellipsoidal cage sizes

Most adsorbents have been developed for the separation of fermentation-derived butanol/acetone mixtures based on a thermodynamic mechanism. Butanol (8.4 Å × 5.5 Å) and acetone (6.4 Å × 5.8 Å) have similar molecular diameters, but different chain lengths. Thus, the objective of this work was to prepare and screen adsorbents for the separation of acetone/butanol mixtures based on a length exclusion mechanism. A number of ZIF-302 derivatives with adjustable cage sizes have been synthesized by adjusting the ratio between the small-sized mIm and large-sized mbIm links. The butanol and acetone separation performance of ZIF-302 derivatives was evaluated using static adsorption and dynamic column adsorption, which showed opposite selectivity. The ZIF-302-S4 adsorbent with large cages (9.6 Å × 6.6 Å) preferentially adsorbed long-chain butanol over short-chain acetone based on thermodynamic separation. By gradually increasing the proportion of the large-sized ligand in the ZIF-302 framework, the long axis size of the ellipsoidal cage was precisely adjusted and the corresponding ZIF-302-S2 adsorbent with small cages (6.5 Å × 6.6 Å) operated in an opposite way and preferentially adsorbed short-chain acetone over long-chain butanol based on length exclusion separation.