The adsorption and simulated separation of light hydrocarbons in isoreticular metal-organic frameworks based on dendritic ligands with different aliphatic side chains

Abstract

Three isoreticular metal–organic frameworks, JUC-100, JUC-103 and JUC-106, were synthesized by connecting six-node dendritic ligands to a [Zn₄O(CO₂)₆] cluster. JUC-103 and JUC-106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC-100. The uptake measurements of the three MOFs for CH₄, C₂H₄, C₂H₆ and C₃H₈ were carried out. At 298 K, 1 atm, JUC-103 has relatively high CH₄ uptake, but JUC-100 is the best at 273 K, 1 atm. JUC-100 and JUC-103 have similar C₂H₄ absorption ability. In addition, JUC-100 has the best absorption capacity for C₂H₆ and C₃H₈. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, Ideal Adsorbed Solution Theory (IAST) analyses show that all three MOFs have good C₃H₈/CH₄ and C₂H₆/CH₄ selectivities for an equimolar quaternary CH₄/C₂H₄/C₂H₆/C₃H₈ gas mixture maintained at isothermal conditions at 298 K and JUC-106 has the best C₂H₆/CH₄ selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH₄/C₂H₄/C₂H₆/C₃H₈ mixture into three different fractions of C1, C2 and C3 hydrocarbons.