Purification of coal mine methane on carbon molecular sieve by vacuum pressure swing adsorption

Data-Driven and Machine Learning to Screen Metal-Organic Frameworks for the Efficient Separation of Methane

With the rapid growth of the economy, people are increasingly reliant on energy sources. However, in recent years, the energy crisis has gradually intensified. As a clean energy source, methane has garnered widespread attention for its development and utilization. This study employed both large-scale computational screening and machine learning to investigate the adsorption and diffusion properties of thousands of metal-organic frameworks (MOFs) in six gas binary mixtures of CH4 (H2/CH4, N2/CH4, O2/CH4, CO2/CH4, H2S/CH4, He/CH4) for methane purification. Firstly, a univariate analysis was conducted to discuss the relationships between the performance indicators of adsorbents and their characteristic descriptors. Subsequently, four machine learning methods were utilized to predict the diffusivity/selectivity of gas, with the light gradient boosting machine (LGBM) algorithm emerging as the optimal one, yielding R2 values of 0.954 for the diffusivity and 0.931 for the selectivity. Furthermore, the LGBM algorithm was combined with the SHapley Additive exPlanation (SHAP) technique to quantitatively analyze the relative importance of each MOF descriptor, revealing that the pore limiting diameter (PLD) was the most critical structural descriptor affecting molecular diffusivity. Finally, for each system of CH4 mixture, three high-performance MOFs were identified, and the commonalities among high-performance MOFs were analyzed, leading to the proposals of three design principles involving changes only to the metal centers, organic linkers, or topological structures. Thus, this work reveals microscopic insights into the separation mechanisms of CH4 from different binary mixtures in MOFs.

Separation and Purification of Hydrocarbons with Porous Materials

This Minireview focuses on the developments of the adsorptive separation of methane/nitrogen, ethene/ethane, propene/propane mixtures as well as on the separation of C8 aromatics (i.e. xylene isomers) with a wide variety of materials, including carbonaceous materials, zeolites, metal-organic frameworks, and porous organic frameworks. Some recent important developments for these adsorptive separations are also highlighted. The advantages and disadvantages of each material category are discussed and guidelines for the design of improved materials are proposed. Furthermore, challenges and future developments of each material type and separation processes are discussed.

Enrichment of Oxygen-Containing Low-Concentration Coalbed Methane with CMS-3KT as the Adsorbent

A type of carbon molecular sieve (CMS-3KT) was used as the adsorbent for the CH₄ enrichment of a methane/oxygen/nitrogen (CH₄/O₂/N₂) mixture using micro-positive pressure vacuum pressure swing adsorption (∼120 kPa). The adsorption isotherms of individual CH₄, O₂, and N₂ on CMS-3KT were studied and fitted. The results indicated the important influence of the adsorbent surface heterogeneity on the adsorption equilibrium process. In addition, the interaction of adsorbent-adsorbate in this process was studied from the measured adsorption heat. The adsorption uptake curves were fitted linearly with a classical micropore model for evaluating the kinetics-based separation possibility of CH₄/O₂/N₂, and the corresponding diffusion time constants of CH₄, O₂, and N₂ were calculated. Based on the results of adsorption equilibrium and kinetics, breakthrough experiments were employed to explore the upper limit value of methane concentration in feed gas such that methane can be enriched feasibly but difficultly. The breakthrough experiments were performed on the CH₄/O₂/N₂ mixture with CH₄ concentration ranging from 1 to 30%. Regarding industrial application, the O₂ removal and CH₄ enrichment performance of ultra-low-concentration methane (CH₄ < 5%) were evaluated according to the results of the breakthrough experiment. The results indicated that the proposed method was promising for enriching O₂-containing ultra-low-concentration CBM.