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

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