Researchers developed a durable, bioinspired ZIF-67 MOF membrane that efficiently separates propylene from propane, offering high performance, long-term stability, and industrial scalability.
Polymer-grade propylene (>99.5%) is a vital raw material in the chemical industry. Its production inevitably generates propane as a byproduct in the product stream. A critical step in producing polymer-grade propylene is the separation of propylene from propane—a challenging and energy-intensive process due to the molecules’ nearly identical physical and chemical properties.
Molecular sieve membranes offer an energy-efficient and effective solution for this separation. Metal-organic frameworks (MOFs) are promising materials for these membranes. However, their performance is limited by the “gate-opening” effect of flexible cage windows and non-selective intercrystalline defects, which hinder precise molecular sieving. Additionally, MOF membranes are brittle, and physical impacts or abrasions during use can significantly reduce their separation efficiency.
Innovative Bioinspired ZIF-67 Membrane
In a study published in Nature Communications, a research team led by Prof. Weishen Yang and Assoc. Prof. Yuan Peng from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences developed a wear-resistant MOF membrane, ZIF-67, featuring a tangential-normal interweaving configuration. This membrane enables accurate separation of propylene from propane by utilizing the paralyzed cage windows and addressing intergranular defects.
To survive in harsh natural environments, many plants and animals have evolved concave and convex surface textures that offer exceptional wear and collision resistance. Inspired by these natural, wear-resistant armor textures, researchers grew a precursor layer with an interlacing structure on a porous substrate. This layer was then elegantly transformed into a ZIF-67 membrane with a scale-like, interlacing architecture. This bioinspired ZIF-67 membrane could effectively separate propylene from propane with high performance.
Dual-Section Structure for Optimized Performance
The bioinspired membrane structure consisted of two distinct sections: the tangential (T) section responsible for accurate separation, and the bulgy normal (N) section serving as wear-resistant armor. In the T section, the residual precursor, which was linked to the ZIF-67 grains, inhibited the ligand flipping motions of the six-membered ring sieving windows in the sod cage, effectively eliminating intergranular defects.
Separation performance results revealed that the defect-free membrane achieved excellent separation of propylene and propane, with a separation factor exceeding 220. After 1.5 years of storage in ambient conditions, the paralyzed ZIF-67 framework remained stable, and its molecular sieving capability was well maintained, leading to long-term stability for nearly 1,000 hours. After subjecting the membrane surface to severe sanding three times, the N armor section retained its propylene sieving performance, demonstrating a remarkable wear resistance.
In addition, researchers proposed that this innovative membrane architecture could be “transplanted” onto high curvature capillary ceramic substrates with an outer diameter of just 4 mm. This provided a guideline for the low-cost, large-area production of wear-resistant, high-performance MOF membranes, presenting potential for industrial application.
“MOF membranes are often regarded as an ideal solution for separation challenges. The bioinspired MOF membrane developed by our team addresses key issues in the MOF membrane field and demonstrates the versatility of MOF membranes for highly complex and demanding separation processes,” said Prof. Yang.
Reference: “Metal-organic framework membranes with scale-like structure for efficient propylene/propane separation” by Lun Shu, Yuan Peng, Chenyu Zhu, Kun Li and Weishen Yang, 30 November 2024, Nature Communications.
DOI: 10.1038/s41467-024-54898-4
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