A constricted slit pore is constructed and examined as a model nanoporous carbon (NPC) for the adsorption of acidic gases (i.e., CO2 and H2S) as well as for the separation of binary H2S/CH4, CO2/CH4 and H2S/CO2 mixtures and ternary CH4/CO2/H2S mixture using GCMC simulations. The results show that the uptake values and heats of adsorption for pure gases at low pressures in the constricted slit models are larger than those in the simple slit. The obtained adsorption results for pure gases are in line with experimental values reported for NPCs. The adsorptive selectivities of the slit models are calculated for the binary and ternary mixtures. It is observed that the slit pore with the constriction width of about one molecular size of sorbate has the highest selectivity for the acidic gases and its calculated CO2/CH4 selectivity exceeds the experimental values of some activated carbons. The H2S/CH4 selectivities of the constricted slit models are lower than the simulation results of carbon nanotubes with comparable diameter. Our results indicate that the presence of the third component does not reveal any significant effect on the selectivities. Adsorbent performance indicator (API) is also calculated where the constricted slits show greater API values than that of an activated carbon (Takeda 5A). It is expected that the results of this work can be useful to guide the future experimental NPC synthesis efforts for their usage in natural gas purification.
