Appraising separation performance of MOF-808-based adsorbents for light olefins and paraffins

The development and design of efficient olefin/paraffin separation processes requires an understanding of the physicochemical properties of the adsorbent for target gas components. This paper presents experimental assessment of the adsorption characteristics of pristine and modified MOF-808s for ethane, ethene, propane and propene gases. The modification of MOF-808s was carried out using a post-synthesis approach, involving the use of two distinct types of ligands and subsequent addition of Cu metal. The pulse inverse gas chromatography technique at infinite dilution was employed to determine adsorption properties, including Henry's adsorption constants, adsorption enthalpies and entropies of the synthesized MOFs. The highest olefin/paraffin selectivity at 1 bar was identified in MOF-808-His-Cu, with selectivity values of 15.7 for ethene/ethane at 30 °C and 26.2 for propene/propane at 50 °C. This notable selectivity is probably attributable to the formation of π complexes between the olefin and Cu atoms present in the adsorbent. This is evidenced by the distinctive asymmetric chromatogram peak with a long tail, which aligns with their adsorption isotherm concavity. Depending on the molecule and the MOF-808 variant, different isotherm shapes and adsorption capacities were obtained.