Carbon Monoliths by Assembling Carbon Spheres for Gas Adsorption

Abstract

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 m(2).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 N-2 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 N-2 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) N-2, and at 3500 kPa were 6.16 mmol.g(-1) CO2, 4.42 mmol.g(-1) CH4, and 3.18 mmol.g(-1) N-2. 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) N-2, and at 3500 kPa were 7.16 mmol.g(-1) CO2, 4.87 mmol.g(-1) CH4, and 3.32 mmol.g(-1) N-2. 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 N-2 and 2.8 to 3.3 for CH4 over N-2 on ACDCS75 compared to on N-ACDCS75.