Carbon molecular sieves

  When carbon molecular sieves (CMS) are mentioned, most people first associate them with pressure swing adsorption (PSA) for nitrogen production. However, with the upgrading of preparation technologies, the application boundaries of this material are constantly expanding. Endowed with a well-developed pore structure, uniform pore size distribution and excellent thermal stability, carbon molecular sieves are demonstrating irreplaceable value in high-end fields such as CO₂ capture, hydrogen purification, petrochemical separation and catalytic conversion, emerging as a key material driving the upgrading of low-carbon industry and high-end manufacturing.   Driven by the "dual carbon" goals, CO₂ capture and separation have become an important research focus. As a solid adsorbent, carbon molecular sieves exhibit outstanding performance in CO₂ separation. Their microporous structure enables precise molecular sieving of CO₂ from gases such as CH₄ and H₂, making them particularly suitable for natural gas purification and coal bed methane separation. Compared with the traditional amine absorption method, the CMS adsorption method is non-corrosive, free of secondary pollution and lower in energy consumption. It can effectively reduce CO₂ emissions from industrial waste gas and contribute to carbon neutrality. Studies have shown that through modification treatments (e.g., introducing a hierarchical pore structure and adjusting micropore volume), the CO₂ adsorption capacity and separation factor of carbon molecular sieves can be significantly improved, further expanding their application scenarios in the field of carbon capture.   As the core of clean energy, hydrogen energy places extremely high demands on separation materials in its purification process. Relying on its sub-angstrom level pore size regulation capability, carbon molecular sieves can efficiently separate H₂ from impurity gases such as CH₄ and CO₂. New-type carbon molecular sieves have achieved precise pore size control at the 0.1 angstrom level through technologies such as CO₂ concentration gradient activation and double-crosslinked polyimide. Their H₂/CH₄ selectivity can reach 3807-6538 with a markedly improved H₂ permeability, and the separation energy consumption is only 1/3 to 1/5 of that of the traditional distillation method. This greatly reduces the cost of hydrogen purification and provides support for the industrialization of hydrogen energy.   In the petrochemical field, carbon molecular sieves have solved the industry-wide challenge of olefin/paraffin separation. Propylene and propane, as well as ethylene and ethane, have minimal differences in molecular size, resulting in high energy consumption and low efficiency of traditional separation processes. New-type carbon molecular sieves construct a uniform microporous structure through the accurate pyrolysis-rearrangement synergy technology, with a C₃H₆/C₃H₈ adsorption ratio exceeding 100. Some of their performance indicators have broken through the Robeson upper bound, enabling efficient separation of the above-mentioned gas pairs, improving the purity and yield of petrochemical products and reducing production energy consumption.   Carbon molecular sieves also show unique advantages as catalysts or catalyst carriers. In the process of biomass conversion, they can realize the comprehensive conversion of cellulose, hemicellulose and lignin, avoiding the generation of a large amount of acid-containing waste residue and reducing environmental pollution and coking problems. Their abundant microporous structure can provide sufficient catalytic active sites; by loading metal active sites, they can be applied to reactions such as hydrogenation and dehydrogenation, integrating the functions of molecular sieving and catalysis and driving the development of green chemical processes.   Any interestes or questions ,welcome to visit us at www.carbon-cms.com.

I. Adsorption Process: "Oxygen Capture" Under Pressure Adsorption is the stage where carbon molecular sieves "capture" impurity gases and enrich nitrogen, with pressure as the core driving force. Industrial applications usually adopt a double-tower alternating mode to ensure continuous gas production, and the single-tower adsorption process can be divided into three steps:   1. Feed Pretreatment: Purifying the Air "Raw Material" Air is not a pure substance; it contains impurities such as oil, water, and dust, which can clog the micropores of carbon molecular sieves and shorten their service life. Therefore, compressed air first passes through a pretreatment system — an oil remover to eliminate oil stains, a dryer to remove moisture, and a filter to intercept dust — finally obtaining clean and dry compressed air with pressure raised to 6-8 bar, ready for adsorption.   2. Selective Adsorption: Precise "Screening" of Oxygen and Nitrogen After entering the adsorption tower, the clean compressed air, under pressure, allows small molecules such as oxygen, carbon dioxide, and residual water vapor to quickly diffuse into the micropores of the carbon molecular sieve and be firmly adsorbed on the pore walls. In contrast, nitrogen molecules, due to their slow diffusion rate and weak interaction with the micropores, are barely adsorbed. They flow upward along the bed layer and are finally discharged from the top of the tower as product nitrogen with a purity of 99.9%-99.999%, which is collected and stored.   3. Adsorption Saturation: The "Critical State" Before Switching As adsorption proceeds, the micropores of the carbon molecular sieve are gradually filled with impurities such as oxygen molecules, and the adsorption capacity reaches saturation. This process usually takes only about 1 minute. At this time, the pressure inside the tower is maintained at the adsorption pressure, and the system automatically triggers a switching command to prepare for the next desorption and regeneration step.     II. Desorption Process: "Regeneration Ritual" After Depressurization Desorption (also known as desorption) is a key step for carbon molecular sieves to release adsorbed impurities and restore adsorption capacity, with the core logic of "breaking the adsorption equilibrium by depressurization". Similarly, taking a single tower as an example, the desorption process is divided into four steps to ensure thorough regeneration:   1. Pressure Equalization and Depressurization: An Energy-Recycling "Transition Link" The tower saturated with adsorption stops air intake and is briefly connected (for about 10-30 seconds) to another tower at the end of desorption with lower pressure to achieve pressure equalization. This step not only quickly reduces the pressure of the saturated tower but also recovers part of the pressure energy to boost the pressure of the other tower, balancing efficiency and energy conservation.   2. Desorption and Exhaust: The "Release Channel" for Impurities After pressure equalization, the saturated tower is connected to the atmosphere through an exhaust valve, and the pressure drops sharply to near atmospheric pressure. At this point, the adsorption equilibrium inside the micropores of the carbon molecular sieve is broken, and the previously adsorbed impurities such as oxygen, carbon dioxide, and water vapor desorb from the pore walls and are discharged out of the tower with the air flow (the exhaust gas is mainly oxygen and can be directly emitted).   3. Flushing Enhancement: A "Key Step" for Deep Cleaning To thoroughly remove residual impurities in the tower and avoid affecting the next adsorption effect, the system introduces 5%-15% of product nitrogen to backwash the adsorption tower. High-purity nitrogen can displace the residual oxygen-containing exhaust gas in the tower and further activate the adsorption activity of the carbon molecular sieve.   4. Pressure Boosting Preparation: Preparing for the Next Cycle After flushing, the pressure of the desorbed tower is raised back to the adsorption pressure through re-pressure equalization or supplementary compressed air, completing the entire regeneration process. It then waits to switch with the other tower and enters the next adsorption cycle.   Any interestes or questions ,welcome to visit us at www.carbon-cms.com.