Characteristic modification of coal-based activated carbon and its methane adsorption capacity

Methane is an important high-quality clean energy that mainly comes from the decomposition of organic waste, natural gas, fossil fuel extracts, etc. Recycling it from a gaseous mixture is beneficial for environmental protection and energy utilization and development. The new coal-based activated carbon is a widely used storage material for methane because of its economic benefit and practicality; thus, coal-based activated carbon modification is greatly significant. This research aims to further reveal the methane adsorption mechanism of coal-based activated carbon by studying the influence of acidic, basic, and combined modifications on methane adsorption and seek a more efficient means of coal-based activated carbon modification. The coal-based activated carbon made from anthracite coal was processed through acidic, basic, and combined modifications. In addition, the physical and chemical structures of the coal-based activated carbon surface and the adsorption ability of methane were precisely analyzed through low-temperature liquid nitrogen adsorption, Fourier infrared spectroscopy, and high-pressure methane adsorption experiments. The characteristics of adsorption thermodynamics and kinetics were also determined by using the Langmuir adsorption isotherm model and the Freundlich model for data fitting. The results show a significant increase in the specific surface area and pore volume of the coal-based activated carbon after combined modification. The specific surface area and the total pore volume increases by 66.66% and 30.89%, respectively. The methane adsorption capacity of the coal-based activated carbon also significantly improved after combined modification. Methane adsorption increases by 25.686%. In addition, both the pore structure and the contained functional groups on the surface jointly determine the methane adsorption, which is mainly affected by the polarity of the surface functional groups rather than the pore structure.