CO2/CH4 and CH4/N2 separation on isomeric metal organic frameworks☆

Two isomeric metal–organic frameworks (MOFs) with 2-dimensional (2D) and 3-dimensional (3D) topologies both comprised of Cu(II) and OTf (OTf=trifluoromethanesulfonate) ions were synthesized and characterized. The CO2, CH4 and N2 adsorption properties of the two isomeric MOFs were investigated from 263 K to 298 K at 0.1 MPa. The results showed that the 2D MOF exhibited a higher selectivity for CO2 from CO2/CH4 and CH4 from CH4/N2 compared to the 3D MOF, even though it possessed a lower surface area and pore volume. The higher adsorption heats of gases on the 2D MOF inferred the strong adsorption potential energy in the layered MOFs. Dynamic separation experiments using CO2/CH4 and CH4/N2 mixtures on the two MOFs proved that the 2D MOF had a longer elution time than the 3D MOF as wel as better separation abilities.