Using PSA Simulations for Screening MOFs for Alkene-Alkane Separations

The focus of this communication is on separation of alkene-alkane mixtures using metal-organic frameworks (MOFs) that are selective to alkenes. The desired alkene is recoverable in the desorption cycle of pressure swing adsorption (PSA) schemes. The productivity of purified alkene, with purities meeting the feedstock requirements for polymerization reactors, is highest for MOFs for which the alkane uptake capacities are small. For screening and ranking alkene-selective MOFs, we suggest a simplified two-step PSA scheme, with adsorption followed by counter-current desorption. The suggested methodology involves transient breakthrough simulations of adsorption and counter-desorption for ranking MOFs such as M2(dobdc), M2(m-dobdc), KAUST-7, UTSA-280, ZIF-8, CHA zeolite, and Co-gallate. The productivity of purified alkenes, with desired purities, is highest for KAUST-7, UTSA-280, ZIF-8, CHA zeolite, and Co-gallate; the saturated alkanes are virtually excluded in these MOFs due to strong diffusional influences that affect alkanes more than the alkenes.