【Ten Years of Rapid Development in Chemical Processing Equipment】Over the past 10+ years, efforts have been made from 2516 to 2025 to develop silicon-aluminum-based artificial zeolite molecular sieves that enable the conversion of low-concentration gas into valuable resources

In coal mines, at depths of a hundred meters below the surface, the free methane gas in the air acts like an unruly \"wild horse\": it is both the \"number one threat\" to mine safety and a strategic resource for clean energy. How to tame a \"rebellious horse\" into a \"well-behaved steed\"? At a professional seminar organized by institutions such as the Institute of Atmospheric Physics of the Chinese Academy of Sciences at the end of May, Li Jinping, deputy director of the Shanxi Research Institute of the Huairou Laboratory and professor at Taiyuan University of Technology, explained that after more than a decade of research, his team had developed artificial zeolite molecular sieve technology. This technology enables the effective enrichment and concentration of methane, which is easy to escape and difficult to capture, and converts it into clean energy that can be used for power generation. “This technological breakthrough resolves the global challenge of utilizing gas with a concentration of 2%–8% during coal mining, and it holds the potential to provide innovative solutions for the efficient use of low-concentration gas. ”Li Jinping said. Searching for the best “molecular catcher”: Gas is a hydrocarbon gas primarily composed of methane, present in coal seams. When the gas concentration in the air reaches 5%–15%, it can explode at the slightest spark. When dealing with gas, coal mining companies generally face two options: ventilation and extraction, or direct utilization. At present, coalbed methane of different concentrations can be utilized in a stepped manner across most of China. However, low-concentration gas with concentrations between 2% and 8% often has to be released into the air along with coal during mining, as there are no mature technologies available for its direct utilization. The silicon-aluminum-based artificial zeolite adsorbent developed by Li Jinping’s team is designed to target this type of gas. Going back to 2009, Yang Jiangfeng, who was still a doctoral student at that time, learned from Li Jinping during an academic conference that in China, over 10 billion cubic meters of low-concentration gas are released directly into the atmosphere each year. This gas has a greenhouse effect 20 times stronger than that of carbon dioxide, and this methane, which cannot be utilized effectively, represents a valuable source of energy that is being wasted. Once the meeting was over, Li Jinping began to assemble a team and launched research on the improved utilization of low-concentration gas. Preliminary investigations revealed that conventional activated carbon adsorbents, due to their lack of hydrophobicity, in the highly humid environments of mines, cause water-containing gas to adsorb a large amount of water molecules simultaneously, resulting in low methane adsorption efficiency. Therefore, finding materials that serve as better “molecular catchers” became a top priority. Since the 1980s, Taiyuan University of Technology has pioneered a specialized research area in the industry: zeolite materials. Thanks to its excellent properties such as ion-exchange capacity, adsorption and separation capabilities, and reversible dehydration, this material is widely used as a molecular sieve in fields such as gas separation, petroleum purification, and industrial pollution treatment. “Zeolite molecular sieves are crystalline silicoaluminates with a molecular ‘sieving’ function, possessing a unique framework crystal structure. ”Yang Jiangfeng explained that in its lattice, tetrahedral molecules are connected to each other like a stable framework, creating numerous internal pores, which endows it with filtering and adsorption properties. “We faintly sensed that zeolites were precisely the ideal ‘molecular catcher’ material we were looking for. ”Recalls Yang Jiangfeng, who is now a professor at Taiyuan University of Technology.

Creating a dedicated “room” for methane: Once the research direction for the materials was determined, the real challenges had only just begun. Natural zeolites have pores of varying sizes, similar to a fishing net with uneven mesh. Small molecular gases such as hydrogen and helium can pass through easily, while large molecules like methane are also difficult to capture efficiently. “There are millions of pores in 1 cubic micron of zeolite material. The size and shape of these pores and cavities are the key factors that determine their ability to filter molecules. ”Li Jinping’s team attempted to modify the zeolites by precisely controlling their pore size to bring it close to the kinetic diameter of methane molecules, which is 0.5 nanometers, while also enhancing their hydrophobicity to ensure efficient adsorption even in the humid conditions of mines. However, before proceeding with the above steps, the team still faces a challenging task: selecting an appropriate molecular sieve structure from the more than 200 structures listed in the database of the International Molecular Sieves Association, and then making corresponding adjustments and optimizations. Since there were no previous precedents of using artificial zeolites for the upgrading of low-concentration gas, this process was nothing short of searching for a needle in a haystack. The team started with solid fundamental research. They used computer software for simulation, and high-power microscopes to conduct systematic evaluations and calculations of the pore size, geometric configuration, and surface chemical properties of each candidate structure. Through continuous research and extensive screening, the team successfully identified a class of molecular sieve structures in 2016, whose structural units are based on silicon and aluminum elements. At this point, Yang Jiangfeng put forward a new perspective: traditional adsorbents rely on surface electrostatic forces, whereas the key to artificial zeolite molecular sieves lies in creating pore structures that precisely match the geometric shape of methane molecules. The team’s goal is to precisely control the effective pore diameter of the zeolite to around 0.5 nanometers. Furthermore, by optimizing the synthesis formula and increasing the silica-to-aluminum ratio of the framework, the overall hydrophobic properties of the material are significantly enhanced. \"Carving\" the pore size at the sub-nanometer scale is like dancing on a wire, where any minor deviation can determine success or failure. “Silicon atoms and aluminum atoms serve as the ‘cornerstones’ of the molecular sieve framework, and their ratio directly affects the performance of the adsorbent. Just like in cooking, the ratio of ingredients determines the final flavor. ”Yang Jiangfeng used an analogy to explain it. After more than 25,000 trials to optimize the formulation and manufacturing process, the team successfully developed a silico-aluminosilicate-based artificial zeolite molecular sieve with \"superhydrophobic\" properties in 2019.

To create an efficient \"road network\" for gas flow, after the development of silicon-aluminum-based artificial zeolite molecular sieves, the research team discovered in practical applications that their powder form creates resistance to gas diffusion during the adsorption process, thereby affecting their efficiency in real-world use. At a critical moment, Li Jinping came up with a key idea: to prepare the powder as small-grained zeolite, thereby increasing its external specific surface area and enhancing the diffusion rate of gas within the zeolite, thus creating more pathways for gas diffusion. Therefore, the team added artificially synthesized zeolite powder of excellent quality and perfect structure as a \"seed\" to the synthesis solution, in the hope that the seeds would grow into particles within the solution. However, under certain reaction conditions, the seed crystals did not grow; instead, they underwent depolymerization—breaking down into more fundamental building units. Surprisingly, these dispersed units subsequently recrystallized, rapidly growing new particles with a uniform size of about 5 nanometers, which eventually aggregated spontaneously to form erythrocyte-shaped aggregates of about 500 nanometers in size. The team found that this unique structure not only perfectly retains the excellent screening ability of the original molecular sieve for small molecules, but also forms self-connected \"channels\" with sizes ranging from dozens to hundreds of nanometers between the particles within the aggregates. Li Jinping used an analogy: \"It’s like in a building that originally had only small, crowded rooms, ‘corridors’ connecting the different floors and spacious ‘entrance halls’ were created, thus forming a ‘network’ for efficient gas flow. This greatly increased the diffusion rate of gas molecules as well as their adsorption kinetics.\" ” After multiple rounds of iterative optimization, the team finally succeeded in preparing a granular silicon-aluminum-based artificial zeolite with a multi-level pore structure of \"micropores–mesopores–macropores\". This adsorbent has a methane adsorption capacity of up to 80%. In 2023, this achievement was applied to the country’s first demonstration project for a mobile skid-mounted low-concentration coalbed methane concentration unit. “This adsorbent is highly suitable for the concentration and utilization of low-concentration coalbed methane in small and medium-sized coal mining enterprises. ”Liu Youzhi, a professor at North University of China, commented that accelerating the development and utilization of coalbed methane is a key element in driving the revolution in energy production and consumption, and it also serves as an important factor in ensuring **energy security. Li Jinping said that the team has currently filled the global gap in the large-scale utilization of ultra-low-concentration gas at levels of 2%–8%, and established a complete technical framework for the efficient, hierarchical use of coalbed methane across various applications. Looking to the future, Li Jinping said, “We will accelerate the development and utilization of coalbed methane, as well as the promotion of technologies and innovation efforts, in order to provide strong scientific and technological support for ensuring **energy security and promoting the green and low-carbon transformation of coal mines.” ”