Efficient One-Step Purification of Methanol-to-Olefin Products Using a Porphyrinyl MOF to Achieve Record C2H4 and C3H6 Productivity

The separation of methanol-to-olefin (MTO) products to obtain high-purity ethylene (C2H4) and propylene (C3H6) is a challenging yet critical task, as these compounds are essential industrial raw materials for polymer synthesis. However, developing adsorbents with high selectivity and productivity for C2H4/C3H6 remains a significant challenge and an urgent necessity. In this study, a porphyrinyl metal-organic framework (MOF), Al-TCPP, was developed for the simultaneous recovery of C3H6 and C2H4 through a one-step adsorption-desorption process. Benefiting from its well-developed microporous structure and abundant N- and O-accessible sites, Al-TCPP demonstrated exceptional adsorption capacities and selectivity for C3H6 and ethane (C2H6) over C2H4 under ambient conditions. The adsorption capacities (in cm3·g-1) reached 162.4 for C3H6 and 118.5 for C2H6 at 298 K and 100 kPa. The ideal adsorbed solution theory (IAST) selectivity values for C3H6/C2H4 and C2H6/C2H4 were 10.1 and 1.8, respectively. Thermodynamic studies and theoretical calculations revealed stronger interactions between C2H6 and C3H6 molecules with the Al-TCPP framework than with C2H4. Systematic breakthrough experiments demonstrated outstanding separation performance for binary C2H6/C2H4 and C3H6/C2H4 mixtures, as well as ternary C3H6/C2H6/C2H4 mixtures, achieving record productivities of 150.2 and 86.5 L·kg-1 for polymer-grade C2H4 (≥99.9%) and C3H6 (≥99.5%), respectively. Notably, the separation performance remained stable under variable flow rates, temperatures, humidities, and multiple adsorption-desorption cycles. Overall, this study highlighted Al-TCPP as a highly competitive adsorbent for addressing the challenges in MTO product separation. Moreover, it offered valuable insights into the design of MOFs with heteroatom-rich accessible sites for efficient separation of low-carbon hydrocarbons.