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

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.