Separation of impurities (CO₂ and N₂) from CH₄ is an important issue for natural gas alternatives (such as coalbed gas, biogas, and landfill gas) upgrading. It is notably challenging to synthesize high N-doped porous carbon with an appropriate porous structure. In this work, high N content (14.48 wt %) porous carbon with micropore size of 0.52 and 1.2 nm and specific surface area of 862 m² g⁻¹ has been synthesized from potassium hydroxide (KOH) activated waste wool upon the urea modification. Pure component adsorption isotherms of CO₂, CH₄, and N₂ are systematically measured on this enhanced N-doped porous carbon at 0 and 25 °C, up to 1 bar, to evaluate the gases adsorption capability, and correlated with the Langmuir model. These data are used to estimate the separation selectivities for binary mixtures of CO₂/CH₄ and CH₄/N₂ at different mixing ratios according to the ideal adsorbed solution theory (IAST) model. At an ambient condition of 25 °C and 1 bar, the predicted selectivities for equimolar CO₂/CH₄ and CH₄/N₂ are 3.19 and 7.62, respectively, and the adsorption capacities for CO₂, CH₄, and N₂ are 2.91, 1.01, and 0.13 mmol g⁻¹, respectively. This report introduces a simple pathway to obtain enhanced N-doped porous carbon with large adsorption capacities for gas separation of CO₂/CH₄ and CH₄/N₂.

Most gas hydrates on the earth are in sediments and permafrost areas, and porous media are often used industrially as additives to improve gas hydrate formation. For further understanding its exploration and exploitation under natural conditions and its application in industry, it is necessary to study the effect of porous media on hydrate formation. The results show that the stacked porous media affects the phase equilibrium of hydrate formation depending on the competition water activity and large specific surface areas, while integrated porous media, such as metal foam, can transfer the hydration heat rapidly and moderate the hydrate phase equilibrium. A supersaturated metal-organic framework is able to significantly improve gas storage performance and can be used as a new material to promote hydrate formation. However, the critical particle size should be studied further for approaching the best promotion effect. In addition, together with the kinetic accelerators, porous media has a synergistic effect on gas hydrate formation. The carboxyl and hydroxyl groups on the surface of porous media can stabilize hydrate crystals through hydrogen bonding. However, the hydroxyl radicals on the silica surface inhibit the combination of CH₄ and free water, making the phase equilibrium conditions more demanding.

Separation of CO₂/CH₄/N₂ is significantly important from the view of environmental protection and energy utilization. In this work, we reported nitrogen (N)-doped porous carbon spheres prepared from sustainable biomass glucose via hydrothermal carbonization, CO₂ activation, and urea treatment. The optimal carbon sample exhibited a high CO₂ and CH₄ capacity, as well as a low N₂ uptake, under ambient conditions. The excellent selectivities toward CO₂/N₂, CO₂/CH₄, and CH₄/N₂ binary mixtures were predicted by ideal adsorbed solution theory (IAST) via correlating pure component adsorption isotherms with the Langmuir−Freundlich model. At 25 °C and 1 bar, the adsorption capacities for CO₂ and CH₄ were 3.03 and 1.3 mmol g⁻¹, respectively, and the IAST predicated selectivities for CO₂/N₂ (15/85), CO₂/CH₄ (10/90), and CH₄/N₂ (30/70) reached 16.48, 7.49, and 3.76, respectively. These results should be attributed to the synergistic effect between suitable microporous structure and desirable N content. This report introduces a simple pathway to obtain N-doped porous carbon spheres to meet the flue gas and energy gas adsorptive separation requirements.

In this work, N-doped hierarchical porous carbon has been successfully fabricated by KOH activation of waste wool. The optimal sample exhibits good CO₂ adsorption capacity under atmospheric pressure (1 bar), as well as excellent CO₂/N₂ selectivity.