In order to design better and more efficient MOFs, we are interested in understanding which properties can improve paraffin-olefin separation. Specifically, we systematically studied the effect of adsorbate-metal binding energy in MOFs on the adsorption of paraffins and olefins using the classical grand canonical Monte Carlo simulation techniques on experimentally synthesized MOFs. We performed model studies on a novel MOF, Sal-MOF-2, constructed from salicylic-based ligands and zinc ions. It contains infinite rod-shaped metal-based secondary building units (SBUs) and hexagonal channels. Coordinating solvents on the SBUs were reversibly removed to generate potential unsaturated metal sites, which might interact with pi-bond systems through electron transfer.
The crystal structure of Sal-MOF-2 was obtained by x-ray diffraction techniques which was used for simulations. We artificially varied the zinc-adsorbate binding energy, specifically by varying the interaction strength between the pi-bond of ethylene and zinc and observed how this influenced adsorption. In addition, we explore several other MOF-adsorbate interaction influences and try to find optimal mixed-metal combinations (that can be achieved through post-synthetic metal doping) that achieve the highest selectivity for this separation. We believe that these simulations will aid in narrowing down the possibilities for synthesis of novel MOFs as well as modifications on existing MOFs to make them efficient for paraffin-olefin separations.