Preparation and evaluation of activated carbon from low-rank coal via alkali activation and its fundamental CO2 adsorption capacity at ambient temperature under pure pressurized CO2

Abstract

Mongolian lignite, which has a high ash content, was used as a precursor to prepare activated carbon. A mixture of lignite, melamine, and K₂CO₃ was carbonized to produce activated carbon in a fixed-bed reactor at different mixture ratios (lignite/melamine/K₂CO₃ = 1/0.3/0.3 weight ratio), temperatures (500–900 °C), and holding times (0–3 h) in a He atmosphere. The activated carbon obtained at the lignite/melamine/K₂CO₃ mixing ratio of 1/1/2, 800–900 °C, and holding time of 1 h exhibited the highest specific surface area (1800–2300 m² g⁻¹) and total pore (0.85–1.40 cm³ g⁻¹), micropore (0.75–1.15 cm³ g⁻¹), and mesopore volumes (0.10–0.25 cm³ g⁻¹). The fundamental CO₂ adsorption performance of the prepared activated carbon was examined at 25 °C under pure 0.5–2.0 MPa-CO₂. It was observed that 250–510 mg-CO₂ g⁻¹ was adsorbed by the prepared activated carbon. Pore size distribution analysis revealed that the optimal micropore size for CO₂ adsorption was 0.5–1.2 nm. Thus, this method can be employed to produce activated carbon with an excellent CO₂ adsorption performance.