Carbon Monoliths by Assembling Carbon Spheres for Gas Adsorption

We report high-surface area, hierarchical pore structured, and robust activated carbon discs (ACDs) prepared via the assembly of micron-sized carbon spheres with mesophase pitch in a low-pressure foaming and carbonization process. The carbon disc ACDCS75 with the largest specific surface area (1338 m2·g–1) was obtained from a blend of 75 wt % carbon spheres and 25 wt % mesophase pitch, and this ACD had a bulk density of 0.62 g·cm–3 and a high compressive strength of 26.3 MPa. A nitrogen-doped ACDCS75 disc was prepared by postcarbonization ammonia treatment to study the effect of nitrogen-containing surface functional groups on the uptake of CO2 on ACDs. The adsorption of pure fluids CO2, CH4, and N2 were measured at temperatures of 298, 308, and 318 K at pressures from 6 to 3496 kPa for CO2, pressures from 9 to 3996 kPa for CH4, and pressures from 7 to 3994 kPa for N2 using a high-pressure gravimetric apparatus (Belsorp-BG). The equilibrium adsorption capacities of ACDCS75 measured at 298 K and pressure close to 1000 kPa were 5.67 mmol·g–1 CO2, 3.60 mmol·g–1 CH4, and 2.09 mmol·g–1 N2, and at 3500 kPa were 6.16 mmol·g–1 CO2, 4.42 mmol·g–1 CH4, and 3.18 mmol·g–1 N2. After ammonia treatment the capacities of N-ACDCS75 at 298 K and 1000 kPa were 6.22 mmol·g–1 CO2, 3.70 mmol·g–1 CH4, and 1.98 mmol·g–1 N2, and at 3500 kPa were 7.16 mmol·g–1 CO2, 4.87 mmol·g–1 CH4, and 3.32 mmol·g–1 N2. The pure gas equilibrium adsorption capacities were regressed to Toth and Langmuir models, and the uptake of components from gas mixtures was predicted using an ideal selectivity to make a preliminary evaluation of the potential to use these ACDs for gas separation. After N-doping the predicted changes in selectivities at 298 K and 100 kPa were from 6.0 to 7.2 for CO2 over N2 and 2.8 to 3.3 for CH4 over N2 on ACDCS75 compared to on N-ACDCS75