The adsorption and separation of CH4 from coal-bed methane are both attractive and challenging. Here, we synthesize two nitrogen-containing heterocyclic aluminum-based metal–organic frameworks using a simple aqueous solvent reflux method for the selective separation of CH4 and N2. Adsorption experiments show that Al-PzDC exhibits a higher adsorption capacity and selectivity for CH4 compared to Al-PyDC, achieving an adsorption capacity of 43.99 cm3/g at 273 K and 1 bar. Dynamic breakthrough experiments further confirm the excellent CH4 and N2 separation performance of Al-PzDC under practical conditions. More importantly, Al-PzDC shows good reusability, with no significant change in adsorption capacity after 10 consecutive adsorption–desorption cycles. Grand Canonical Monte Carlo simulations indicate that the nitrogen-rich Al-PzDC has a higher adsorption density and a wider adsorption range for CH4. Density functional theory calculations show that Al-PzDC has a lower adsorption energy for CH4, thus significantly improving its adsorption selectivity.
Zhao et al. (Mon,) studied this question.