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 (C 2 H 4 ) and propylene (C 3 H 6 ) 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 C 2 H 4 /C 3 H 6 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 C 3 H 6 and C 2 H 4 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 C 3 H 6 and ethane (C 2 H 6 ) over C 2 H 4 under ambient conditions. The adsorption capacities (in cm 3 ·g –1 ) reached 162.4 for C 3 H 6 and 118.5 for C 2 H 6 at 298 K and 100 kPa. The ideal adsorbed solution theory (IAST) selectivity values for C 3 H 6 /C 2 H 4 and C 2 H 6 /C 2 H 4 were 10.1 and 1.8, respectively. Thermodynamic studies and theoretical calculations revealed stronger interactions between C 2 H 6 and C 3 H 6 molecules with the Al-TCPP framework than with C 2 H 4 . Systematic breakthrough experiments demonstrated outstanding separation performance for binary C 2 H 6 /C 2 H 4 and C 3 H 6 /C 2 H 4 mixtures, as well as ternary C 3 H 6 /C 2 H 6 /C 2 H 4 mixtures, achieving record productivities of 150.2 and 86.5 L·kg –1 for polymer-grade C 2 H 4 (≥99.9%) and C 3 H 6 (≥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.