Influence of functional groups and pore sizes in porous carbon for methanol acetone adsorptive separation based on molecular simulation

In order to investigate the optimal nitrogen functional group and the most suitable pore size for the efficient adsorptive separation of methanol–acetone mixed vapor, a series of theoretical calculations, including Grand Canonical Monte Carlo (GCMC) simulation and density functional theory (DFT) calculation, were carried out to determine the adsorptive separation properties of AC–Rs (AC = activated carbon, R = Pyridinic, –NH2, Pyrrolic, Quaternary) with different pore sizes (0.6–8.0 nm). The results showed AC–Pyridinic had the highest methanol–acetone adsorption capacities (14.64 mol/kg for acetone and 26.35 mol/kg for methanol at their respective saturation pressures). The high adsorption energies, the hydrogen bonding interaction between the pyridinic nitrogen and hydrogen of methanol’s hydroxyl group, and electrostatic interaction between the pyridinic nitrogen and carbon of acetone’s carbonyl group were crucial factors for that. In the case of methanol–acetone separation, the methanol molecular aggregation resulted in an increase in methanol–acetone selectivities on AC–Rs. Interestingly, AC–Pyridinic still showed the highest methanol–acetone selectivity. Furthermore, the pore with 3.5 nm and 3.0 nm were optimal for methanol and acetone adsorption respectively, in which AC–Pyridinic exhibited superior capture capacities (23.19 mmol/g for methanol at 16 kPa and 11.64 mmol/g for acetone at 30 kPa). And with a 6 nm pore size, AC–Pyridinic had the highest selectivity (~  5.0). The mesopore of 2.5–3 nm is suitable for methanol–acetone adsorptive separation taking both adsorption and selectivity performance into consideration. This investigation predicted the functional group and pore sizes with the best modification effect on AC for methanol–acetone adsorptive separation, which sheds light on ways to design a highly efficient adsorbent for gas adsorption and separation.