Impact of realistic vs. Slit models of activated carbon on H2 and H2S Adsorption, and H2/CO2, CH4/H2S separation

We conducted a comparative analysis of the adsorption and separation of H2-CO2 and CH4-H2S systems in simplified slit pore models and realistic atomic models. At 77 K and 4 MPa, cs1000a activated carbon demonstrates excess hydrogen adsorption with gravimetric and volumetric values of 3.2 wt% and 23 kg/m3, respectively. Considering the bulk density of cs1000a, the corresponding values in 0.9 nm slit pores are 7.75 wt% and 56 kg/m3. The adsorption isotherms indicates that the interaction between the walls of the slit pores and the adsorbed fluid molecules is stronger than in the realistic model from Hybrid Reverse Monte Carlo (HRMC) simulation, making adsorption more likely to saturate at low pressures. At 303 K and 4 MPa, cs1000a has the highest CO2 adsorption (7.45 mmol/g) but the lowest selectivity (14.28). In a CH4-H2S mixture, it shows selectivity and adsorption capacity for H2S of 12.1 mmol/g and 7.96, respectively. The slit with a 0.9 nm pore width shows a CO2 selectivity of 127 and an 18.26 mmol/g adsorption capacity, and 14.46 and 15.54 mmol/g for H2S, respectively. The CO2 selectivity within slit pores peaks at 421 (0.65 nm) and 144 (0.95 nm), while H2S selectivity follows a similar trend, reaching 40 (0.65 nm) and 28 (1.0 nm). Optimal widths show both single and double -layer adsorption, aligning with the molecular configurations. The HRMC model, with its non -optimal pores, exhibits reduced adsorption and separation capabilities owing to pronounced geometric and energy heterogeneity. By correlating material density, pore volume, and adsorption behavior, we found that cs1000a_24cooh material, doped with -COOH functional group, achieves an optimal balance in CO2 selectivity and adsorption capacity, reaching 67.3 and 12 mmol/g. This underscores cs1000a's superior decarburization and desulfurization capabilities. In summary, the varying adsorption capacities, heats, and selectivities of fluids on the materials suggest that the simplistic slit pore model is inadequate for characterizing the amorphous nature of activated carbon. This emphasizes the importance of designing materials with low density and a concentrated pore width distribution at optimal values.