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China University of Petroleum (Huadong) has developed crystalline porous composite membranes to achieve efficient separation of hydrogen and carbon dioxide at normal temperature and pressure. May 28, 2024: Injecting \"membrane\" power into the development of the hydrogen energy industry. Gas membrane separation, as an efficient separation technique, has been widely studied. Among them, membrane material is the foundation and core of membrane separation technology, and finding a balance between the membrane’s permeability and its ability to retain impurities has always been a challenge in this industry. Recently, the team led by Professor Sun Daofeng from China University of Petroleum (Huadong) developed a crystalline porous composite membrane that combines rigidity and flexibility, enabling efficient separation of hydrogen and carbon dioxide at normal temperature and pressure. This solution addresses the bottleneck issue in hydrogen purification and contributes to the development of the hydrogen energy industry through the use of such membranes. In gas membrane separation technology, the better the permeability of the membrane, the higher the separation efficiency. However, if the permeability of the membrane is increased, impurities tend to penetrate as well; whereas if the membrane’s ability to block impurities is enhanced, its permeability decreases, and thus the separation efficiency also drops. How to balance permeability and interception while improving efficiency and reducing energy consumption has always been a challenge in the industry. Leveraging the advantages of crystalline porous materials and polymer/graphene oxide materials, Sun Daofeng’s team employed graphene oxide-assisted film-forming techniques, interfacial polymerization methods, and dissolution processing strategies to create a crystalline porous composite membrane that combines rigidity with flexibility. This membrane enables efficient separation of hydrogen and carbon dioxide at normal temperature and pressure, thereby reducing separation energy consumption significantly compared to traditional gas separation methods such as low-temperature distillation. Meanwhile, this series of membrane materials can also overcome the trade-off problem between the permeability coefficient and selectivity that is characteristic of conventional polymer membranes. They enable highly efficient hydrogen purification, maintain good separation stability at 200°C, and offer a cost advantage over commercially available separation membranes. Thus, they are both economical and efficient. “We fully leverage the advantages of crystal engineering in crystalline porous materials to systematically regulate the ligands, metal nodes, and guest molecules of metal-organic frameworks (MOFs) to achieve molecular separation. ”Professor Kang Zixi, a key member of the team, said that just as sand and stones are filtered by mesh screens at construction sites in daily life, larger stones remain on the mesh while smaller sand particles pass through it, thus achieving separation. The crystalline porous composite membrane also functions as a sieve; its pore size can be adjusted at the microscopic level to 0.30 nanometers, which falls between the molecular dynamics diameters of hydrogen (0.28 nanometers) and carbon dioxide (0.33 nanometers). As a result, hydrogen can pass through the membrane while carbon dioxide cannot, enabling precise screening. “The highest separation selectivity for hydrogen and carbon dioxide achieved by our newly developed crystalline porous composite membranes is over 99%; in other words, only 1 carbon dioxide molecule passes through the membrane for every 100 hydrogen molecules that do. The separation selectivity of commercial polymer membranes is generally below 20, and their permeability is much lower than that of the crystalline porous composite membranes we have developed. ”Associate Professor Fan Weidong, a key member of the team, added that this crystalline porous composite membrane is an ideal material for hydrogen decarburization. However, in hydrothermal systems, the coordination bonds between the metal centers and organic ligands break down, causing the framework to disintegrate, which affects its stability under actual hydrogen separation conditions. In light of this, Sun Daofeng’s team proposed a strategy to enhance the hydrothermal stability of crystalline porous materials by strengthening interbonding forces. By taking advantage of the anisotropy of crystals and regulating the orientation of crystal planes, stable crystal planes with lower surface energy and fewer coordination bonds are exposed, thereby improving the stability of MOF materials in hydrothermal environments; the selectivity for hydrogen separation increased by more than 50%. How to achieve large-scale preparation of crystalline porous separation membranes is another challenge commonly encountered by researchers. Crystalline porous materials are brittle as crystals themselves, and are not easy to process and manufacture on a large scale. The research team promptly adjusted their approach and attempted to combine crystalline porous materials with other materials in order to create flexible composite membranes for the efficient and continuous separation of hydrogen. By using graphene oxide (GO) with a two-dimensional structure as the membrane matrix, the research team innovatively leveraged the two-dimensional confinement effect of GO to convert precursors (oxides) in situ into crystalline porous materials (molecular sieves and MOFs) between its layers. This approach enabled the creation of flexible composite membranes consisting of crystalline porous materials and GO, endowing these membranes with a flexibility that is not common in other crystalline porous membranes. As a result, it became possible to manufacture them into efficient membrane modules in roll or tubular forms, thereby solving the issue of flexibility in crystalline porous separation membranes and achieving a highly efficient purification effect of \"1+1>2\". The research findings on crystalline porous composite membranes have attracted attention from many enterprises. Sun Daofeng’s team received an offer from Tianwei Membrane Technology Co., Ltd.; by leveraging major scientific and technological innovation projects in Shandong Province, they aim to carry out large-scale production and industrial development of relevant membrane materials, with the goal of manufacturing crystalline porous materials/GO flexible composite membranes in square decimeter and square meter sizes. “It is hoped that this crystalline porous composite membrane technology will be rapidly adopted, helping to overcome the bottlenecks in the development of the hydrogen energy industry and truly contributing to the transformation of the energy structure and environmental protection through the use of membranes. ”Sun Daofeng said.