Al-based Isoreticular Metal-Organic Frameworks with MIL-53 Topology as Effective Adsorbents in Methane Purification

In the present investigation, an isoreticular series of Al-based metal-organic frameworks (MOFs) with MIL-53 topology namely, MIL-53(Al)-FA, MIL-53(Al)-BDC, MIL-53(Al)-NDC and MIL-53(Al)-BPDC formed by organic linkers with different molecular size and correlated porosity were examined for their adsorption capacity for C3H8, C3H6, C2H4, and CH4, and C3H8/CH4, C3H6/CH4, C2H4/CH4 separation selectivity. C3H8 and C3H6 adsorption is found to be sensitive to van der Waals forces and increases with increasing micropore volume of the MOFs. Ideal Adsorption Solution Theory (IAST) has been applied to estimate binary C3H8/CH4, C3H6/CH4 (C-3/C-1), and C2H4/CH4 (C-2/C-1) selectivity. The MOFs investigated have shown high C-3/C-1 selectivity with MIL-53(Al)-FA exhibiting exceptional C3H8/CH4 and C3H6/CH4 selectivity of 330 and 246, respectively, for the 5 : 95 (v/v) mixtures. MIL-53(Al)-FA also exhibited the highest C-2/C-1 selectivity among them. The high affinity of MIL-53 Al-based MOFs for C-3 and C-2 hydrocarbons over C-1 make them suitable as adsorbents for methane purification.