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

Abstract

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.